Market Survey - TaiyangNewstaiyangnews.info/TaiyangNews_Market Survey Polysilicon CVD Reactors 2017.pdfChemical Vapor Deposition (CVD) process using trichlorosilane (TCS) as feedstock

Authors: Shravan K. Chunduri, Michael Schmela

Market Survey Polysilicon CVD Reactors 2017

2 TaiyangNews | Market Survey Polysilicon CVD Reactors 2017

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Executive Summary

Crystalline silicon is the dominant technology in solar module production with more than 90% of the PV panels being made using polysilicon as feedstock. And that won’t change. What also hasn’t changed in the last few years are overcapacities in the polysilicon production segment, which has kept poly prices at very low levels; at the same time, module cost dramatically dropped. In consequence, polysilicon, despite its low prices today, still contributes over 20% to the cost of the lowest cost solar module producers.

As for silicon production technology, Siemens-type Chemical Vapor Deposition (CVD) reactors remain the state of the art, while the Fluidized Bed Reactor (FBR) is another technology in commercial production, though with a share of only about 10%, much less than experts had anticipated in past forecasts. While some new polysilicon production capacity came online recently, there wasn’t too much activity in capacity expansions because of the overcapacity situation. While there are industry experts expecting oversupply to continue, others are expecting fresh capacity would be needed already in 2017.

Our survey includes the Siemens-reactors from the leading 7 equipment vendors in this field from Asia, Europe and the US (GEC, GT Advanced Technologies, Morimatsu, Schmid Silicon Technology, Silicon Products Bitterfeld, SiTec, VRV). Their products are based on different philosophies, representing various levels of productivity and energy consumption. Reactor size, to be specific, the number of seed rods a CVD reactor can host also has a great influence on the productivity of the tool. Other factors are cycle time and harvest per production cycle.

The products listed in the survey can house between 72 to 12 filaments, silicon output ranges from 3.5 to 10 tons per production cycle. The annual capacity of these CVD reactors varies from 250 to 700 tons. The reactor with the highest nominal output is made by Morimatsu. Power consumption is another important performance characteristic of CVD reactors and ranges between 35 to

45 kWh for the products in our survey. One way to reduce the power needs of the CVD reactor is to recover the heat from cooling water. Nearly all CVD suppliers are offering heat recovery solutions, with recovery efficiency starting from 35 to 95%.

In addition to improving standard features, the CVD reactor suppliers are also working on advanced concepts. One such approach is to coat the inner walls of the bell jar with reflective materials. Such coatings not only help in reducing power consumption by blocking heat energy from going into cooling water, it also improves heat distribution within the process chamber, thereby resulting better quality of the final polysilicon rod. GEC and SPB are mainly focusing on silver-lined bell jars; GTAT developed a low cost alternative, but the company would not reveal the composition. Coating of bell jars is perhaps the latest major technology development within the CVD reactors segment.

Tubular seed rods are yet another innovative approach. GTAT is working on such tubular filaments to replace the typical cylindrical or square in cross-section seed rods. The hollow tube seed rods offer a larger starting surface area, which results in higher initial deposition rates. But the concept is still in the evaluation phase.

We also provide an overview on developments of alternative technologies. A slight deviation from the standard approach is using silane as feed gas instead of TCS in CVD. SST has been offering such a solution with a boasted advantage of reducing power consumption. Start-up Dynatec has made considerable progress with its innovative centrifuge CVD. Finally, we look at Fluidized Bed Reactor (FBR), the only alternative to incumbent high-quality Siemens-based polysilicon production, that so far is being made only based on in-house designed reactors. Now equipment vendor SiTec has developed an FBR reactor. Finally, Gøran Bye, a silicon industry veteran, shares his view on the status of FBR technology.

Enjoy reading our Polysilicon CVD Reactors 2017 Survey

Shravan K. ChunduriHead of Technology, [email protected]+91 996 327 0005Hyderabad, India

Michael SchmelaManaging Director, [email protected]+49 173 15 70 999 Munich, Germany


Contents

01Introduction 7

02Overview 7• Silicon Production Technologies

and Market Shares• Suppliers of CVD Reactors • Polysilicon Market Update

03Basics of Polysilicon Production

11

• Frontend• Backend

04Advanced Concepts 12• CVD with Silver Lining• Silver-free Coatings• Tubular Seeds

05Different reactor design aspects 16• Larger Reactors• Medium-scale Tools• Systems for Tall Filaments

• Small CVDs• Preheating • Filament Production

07Alternative Technologies 23

• Silane based CVD• Centrifuge CVD• Fluidized Bed Reactors

08Interview with Gøran Bye about FBR Technology

31

06Important Performance Charecteristics

20

• Annual Capacity• Power Consumption• Heat Recovery

10Detailed Product Specifications Table

36

09Conclusion 35

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The text, photos and graphs in this report are copyrighted (cover photo credit: GCL Poly). TaiyangNews does not guarantee reliability, accuracy or completeness of this report's content. TaiyangNews does not accept responsibility or liability for any errors in this work.

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1. Introduction

As for the production process used for making polysilicon, the majority of the industry has been relying on the same time-tested Siemens type Chemical Vapor Deposition (CVD) process using trichlorosilane (TCS) as feedstock.

Siemens CVD remains the workhorse of the solar industry, in fact, at this point the technology is enjoying almost a monopoly for producing solar silicon. Nearly every production equipment supplier in the commercial space has designed its products to support CVD process. However, Fluidized Bed Reactor (FBR) technology, used to produce granular

polysilicon, is also contributing a fraction of global solar silicon demand. But FBR technology is owned by few polysilicon makers. Irrespective of the technology, polysilicon suppliers are currently stuck in a whirl of oversupply, often suffering from low prices.

While there are analysts who expect the situation to improve in the coming years, others anticipate the situation to continue. In this chapter, we provide a short overview on the market share of different technologies, suppliers of CVD reactors and a brief update on the polysilicon market.

Crystalline silicon is the dominant technology in solar module production with more than 90% of the PV panels being made using polysilicon as feedstock. And that won’t change. What also hasn’t changed in the last few years are overcapacities in the polysilicon production segment, which has kept poly prices at very low levels; at the same time, module cost dramatically dropped. In consequence, polysilicon, despite its low prices today, still contributes over 20% to the cost of the lowest cost solar module producers.

Acknowledging the importance of silicon, TaiyangNews is starting its series of crystalline silicon production equipment markets surveys from the top of the value chain – polysilicon production. This survey focusses on incumbent Siemens CVD reactor technology (including tables with product details; see p. 36), but we are also taking a look at alternative commercial products – Fluidized Bed Reactors (FBR), as well as new concepts in development.

2. Overview


2.1 Silicon Production Technologies and Market SharesThe 2016 released International Technology Roadmap for Photovoltaic (ITRPV) clearly shows that Siemens-CVD continues to enjoy the lion’s share in the silicon market. According to the 7th edition of the roadmap, about 85% of the polysilicon in 2015 was produced with Siemens reactors, while FBR technology had a market share of 10%. A few years ago, there was a lot of enthusiasm about FBR technology’s promise to lower costs, with MEMC/Samsung entering the fray, and the world’s leading silicon maker GCL announcing to quickly increase the share of FBR. However, as the solar industry has been growing faster than most analysts anticipated, Siemens easily defended its market leading position. ITRPV has been consistently lowering its forecast for the prospects of FBR. Now, a moderate increase of FBR’s share is expected over the next years, supposed to attain 20% by 2020 and 25% in 2026. But the previous 2015 roadmap anticipated that FBR technology would gain a meaningful share of above 20% already in 2019. The 2014 study even assumed that this level would be attained by 2016.

The slowed-down progress is mainly due to the delays of leading polysilicon makers bringing their FBR factories online. There are different reasons – the oversupply situation, the collapse of SunEdison/MEMC, and that FBR technology is a proprietary technology with patent limitations and some technical challenges. In the end, it doesn’t have too much relevance for this survey anyway, FBR silicon manufacturers are usually working with in-house developed processes and custom-designed equipment. This is also the case with Norwegian company Dynatec, which is working on a new centrifuge CVD technology to produce polysilicon.

That’s why our market survey on polysilicon production equipment focuses exclusively on Siemens-type CVD reactors. Still, this survey also includes a chapter on the status and updates about FBR technology (see p. 28), an interview with the former CEO of REC Silicon on FBR technology (see p. 31), and a chapter on Dynatec’s approach (see p. 25).

Dominant: Siemens-type CVD reactors using TCS as feedstock is still the mainstream technology to produce polysilicon.

Source: GEC


2.2 Suppliers of CVD ReactorsOur first market survey on CVD reactors has received a very good response from the companies active in the space. In fact, all suppliers we contacted have sent us back their product information. A total of 7 well-known equipment makers supplying CVD reactors for polysilicon production have provided the data for their products. These are:• GEC GmbH, Germany• GT Advanced Technologies (GTAT), USA• Morimatsu, China• Schmid Silicon Technology GmbH (SST),

Germany• Silicon Products Bitterfeld GmbH & Co. KG (SPB),

Germany• SiTec GmbH, a subsidiary of Centrotherm

Photovoltaics AG , Germany• VRV Group S.p.A, Italy

Thus the survey covers nearly all leading companies in that segment. Among the participants, six CVD reactor suppliers that are building the reactors to support the traditional Siemens-based CVD process employing TCS as feedstock. Schmid is an exception. The German company also uses the same CVD process, but opted to work with monosilane as the precursor.

GTAT is certainly the market leader in the silicon deposition reactor segment with a track record of installing more than 400 CVD reactors. GEC says it has sold more than 150 furnaces so far. VRV, which is in the business of supplying building CVD deposition tools for around 30 years, has not revealed its installation base. SPB is a management buyout of British ingot/wafer manufacturer PV Crystalox. Unlike the others, SPB is actually producing the polysilicon, as it took over Crystalox’ polysilicon factory in Germany. Counting on the fact that the company has built the facility on its own, SPB is now also offering engineering services with its know-how, including CVD reactors.

2.3 Polysilicon Market UpdateAll silicon CVD reactor makers have one thing common – they suffer from low demand for these products today. While the large polysilicon producers actually have more and more to do – with the solar market quickly growing, fact is that silicon prices have continued to be low due to production overcapacities in that upstream-segment for years. So there has been little need for new CVD silicon reactors from equipment suppliers. Daqo from China just completed a 6,000-ton expansion. And Wacker, recently finished its poly factory in Tennessee, USA, but the Germany chemical company used its proprietary in-house developed products.

Without having big order pipelines, most silicon CVD reactor suppliers are working with existing clients, handling small upgrades and helping poly producers to optimize the existing facilities. But there are CVD suppliers that are expecting the situation to change in the near future. Burkhard Wehefritz, Director at SST, expects the oversupply to diminish around 2017 to 2018, leading to stabilized feedstock prices. VRV’s chairman Alessandro Spada also anticipates some improvements this year.

Gøran Bye, the former CEO of silicon maker REC Inc., who is now heading consultancy firm Advanced Materials Management Solutions, LLC (AMMS), thinks the polysilicon industry will soon come out of the oversupply situation as demand grows within the PV-industry. “Demand will exceed supply from 2017,” he told TaiyangNews. In his November 2017 client update, Bye indicated that the polysilicon industry will soon come out of the over-supply situation. Supply/demand will be balanced in 2017, thus the new capacity is needed already in 2017, he believes.


If Bye’s analysis is correct, it could be soon time to invest in new capacities, because it takes at least 2 to 3 years to build a polysilicon production plant and bring it fully up and running. However, additional capacities have been ramped up recently or are on the verge of being taken online. For example, Wacker started its new facility in Tennessee, US in early 2016 and was planning to ramp up to 20,000 ton capacity by end of 2016. Qatar Solar Tech is ready to go online anytime. And besides Daqo, there is East Hope, which plans to bring on several thousand tons this year in China. Then, not only there is intermittent news about expansion plans from polysilicon makers, there are rumors about newcomers aspiring to venture into polysilicon production, especially from China and Middle East. In addition, Jeffery Gum from GTAT expects “one or two players from India getting into polysilicon production. But Albrecht Mozer, former CEO of Centrotherm SiTec and founder of silicon consulting firm Amocon GmbH, says that as long as prices are not getting stable or even without an indication that it is getting better, everyone remains

in preparation mode. “Till then,” he adds, “no one would pull the trigger.”

According to Bye, installed capacity for polysilicon production has increased by 58% from 252,800 tons in 2012 to about 400,000 tons in 2016. In the same period of time, the utilization rate has improved considerably from 71% to 99%. Bye estimates that the gross capacity of above 400,000 tons in 2016 is actually a 16% increase over the 2015 level and expects that 2017 would witness another 11% capacity addition to 445,000 tons.

In contrary, Johannes Bernreuter from Bernreuter Research in his November-published report Polysilicon Market Outlook 2020 estimates, that the polysilicon industry will face “soft demand” in the next three years. He emphasized that reduced annual growth of PV installations and decreasing specific silicon consumption per cell are the reasons for expected lower demand for the feedstock.

Positive outlook: According to silicon expert Gøran Bye, the polysilicon industry will soon come out of the over-supply situation. He believes that supply/demand will be balanced in 2017 – with polysilicon manufacturers adding 11% production capacity this year to the 2016 level of around 400,000 tons.

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AMMS Silicon 5-year Market Outlook

Source: Advanced Materials Management Solutions, LLC (AMMS)—estimate based on industry & company announcements and analyses


3. Basics of CVDThe polysilicon production process has two main parts. Typically, polysilicon makers also manufacture the immediate precursor – trichlorosilane (TCS) – in the frontend. The backend contains the deposition process, in which CVD reactors are employed.

3.1 FrontendTCS can be produced in two ways – using direct chlorination or hydrochlorination. In direct chlorination, powdered metallurgical silicon reacts with hydrogen chloride in a fluidized bed reactor at a temperature of about 300o– 360oC and a pressure of about 6 bar. Hydrochlorination is also accomplished in a fluidized bed reactor, but following a slightly endothermic reaction of metallurgical silicon, hydrogen and silicon tetrachloride at 500 to 550oC and a pressure of 20 to 30 bar. With both technologies, the produced trichlorosilane contains small amounts of contaminants. This mixture of chlorosilanes is separated in a distillation process. The resulting pure TCS is blended with a carrier gas, typically hydrogen, and supplied as a feedstock for the CVD process. Nearly every CVD supplier is also offering TCS production solutions.

3.2 BackendThe TCS produced above is used as the feed gas in the CVD process. A typical Siemens-type CVD reactor has two important parts – a bell jar and a base plate. The base plate has electrical slots to insert the seed rods and ports for feeding the precursor and exhaust gases. The bell jar is fixed on top of the base plat to create an airtight process

chamber. The process is based on a principle that TCS dissociates into elemental silicon as soon as it comes in contact with heated seed rods. The seed rods grow in diameter by adding more and more silicon on the surface. To accomplish this, a pair of seed rods is connected at the top, so they have a U-shape, in order to pass through the electricity to heat them. But the intrinsic nature of the seed rods makes them bad conductors. To overcome this, the seed rods are preheated, which can be accomplished in several ways – using external heaters as well as medium voltage ignition (MVI). Once the seed rods are conductive, they are heated with electrical power to high temperatures of 1,100oC. At such high temperatures the rods radiate heat, which also heats up the bell jar that leads to unwanted silicon deposition on the bell jar’s inner surface. To circumvent the undesired deposition, both the bell jar and the base plate are equipped with a cooling circuit, typically employing water as cooling medium. While at first sight a lot of heat energy is lost for cooling the bell jar, the CVD reactor makers are also offering heat recovery systems that enable reuse of the withdrawn heat for the distillation steps of TCS production. The result of this process are “inverted U” shaped polysilicon rods, which are harvested and crushed into chunks. The number of seed rods processed per production cycle, their height, deposition time, total turn-around time and the final diameter of the fully grown U-rods determines the productivity of a particular CVD reactor. These are the also main differentiating factors among the tools from different vendors.


Every CVD reactor supplier is working on reducing manufacturing costs and reducing power consumption. In addition to optimization of the process, equipment vendors are also working on innovative approaches. Employing tubular filaments developed to improve the initial deposition is one example. The concepts is not commercially ready and major emphasis as of now is on reducing cost and improving quality. Both goals can be attained by coating the inner surface of the bell jar. While GTAT came out with a proprietary coating, CVD suppliers, like GEC and SPB, are promoting silver for this purpose.

4.1 CVD with Silver LiningThe direct effect of applying silver is the reflection of the heat hitting the bell jar’s inner surface back onto the growing rods. This has two benefits. First, it naturally reduces power consumption, which according to GEC’s CEO Heinz Graeber is about 20-30%. Then, as a result of the heat confinement, the better thermal profile within the reaction chamber helps in producing rods with more continuous geometrical shape. According to Graeber, the approach also contributes to a higher quality of the final product by avoiding metal contamination originating from the bell jar. But silver lining of bell jars is not new. German polysilicon maker Wacker has been using silver plated CVD reactors right from the beginning, “since 30 to 40 years,” says Graeber.

Today, there are two silver-based solutions on offer. One is a silver coating of about 250 µm or plating of precious metals resulting in a 2 mm thick layer. Be it coating or plating, the silver lining loses its reflectivity with time. In consequence, it needs to be refurbished approximately every 3 to 4 months, according to Graeber, whose company is also offering specific mobile polishing tools for this purpose.

4. Advanced Concepts

Silver lining: Covering the internal walls of bell jars with silver, as can be seen in the picture of SPB’s reactor, not only reduces power consumption, but also improves the quality of the final product.

Source: Silicon Products Bitterfeld GmbH & Co. KG (SPB)


GEC offers a full package for silver lining of the bell jar. To start with, GEC is proposing a test service. The client sends the bell jar, GEC applies the silver lining and then sends it back. After analyzing the test results, GEC applies that procedure for the remaining bell jars. When it comes to pricing, Graeber chose to provide relative answers. “Silver plating costs are close to the cost of a stainless steel reactor, while coating costs are approximately 1/3 of the plating costs,” he says. But the return of investment (ROI) calculation provided by Graeber indicates that silver plating would cost about €230,000 per reactor. GEC has experience with silver plating so far, the

coating approach yet has to be tested. For a 54 rod reactor configuration, the standard or E-polishing is estimated to consume 45 kWh to produce a kilogram of polysilicon while silver plating would bring it down to 35 kWh – that’s a 15% reduction. The ROI depends on the specific power costs of the polysilicon producer. In a presentation, GEC shows different ROI scenarios based on different power tariffs. The lowest ROI is 1 year for a polysilicon production that has rather high power cost of 8 euro cents per kWh, 1.5 years where power cost are 5 euro cents per kWh, and 2.5 years if electricity cost is 3 euro cents per kWh (see graph).

However, Amoncon’s Mozer shares a different view. He estimates that when power costs are at 7 to 8 US cents, then the silver lining pays off in about 2 years. “If it is below, that may not make sense,” he says. According to Mozer, due to high investment costs, the approach has not entered large-scale production, while a pilot reactor is under testing. VRV’s Spada is also not in favor of the silver lining. He thinks the advantages are only in the initial runs and the benefits would diminish in the long run, let aside it involves high investments.

ROI scenarios: According to GEC, the silver plating has an ROI from 1 to 2.5 years depending on electricity costs.

GEC Calculations on Reactor Silver Plating ROI

Source: GEC


4.2 Non-Silver CoatingWhile GTAT also does not see great benefits with silver lining, especially with thin coating, it is not against a coating approach. In fact, the US company has developed a proprietary material to be applied onto the inner surface of the bell jar instead of the precious metal. It is based on an innovative alloy enhancement process called ‘Gen 2 E-Upgrade’, but GTAT would not disclose the composition. As the process name suggests, the latest solution belongs to the next generation over the previous Gen 1 E-upgrade.

According to Gum, the earlier coating solution was quite successful with about 100 units operating in the field. But it has one limitation – it is primarily applicable to CVD reactors from GTAT alone.

The Gen 2 solution is an open platform, which means that silicon makers having CVD reactors of any brand can use it. In addition, GTAT’s latest solution comes with a new material and a different process that is especially fine-tuned for further high-temperature applications.

Longevity is yet another advantage of the new material, according to GTAT. Gum says that the Gen 2 material has been finalized after careful reviewing the extensive data base of materials, their interaction with chlorosilanes and hydrochlorides, in other words that’s the environment a coating would actually see in a CVD reactor. The coating is also tested for 1,000s of hours. Gum says that the Gen 2 E-Upgrade has an even higher lifespan than Gen 1. “Units in the field out there since 5 years are operating well,” says Gum, adding, “We haven’t seen an end to that.” Since the new material is more robust, Gum expects the life of the coating to be about 10 years. As for the costs of the coating, GTAT would not reveal any information; Gum would only say it is “cost effective.” Gum says that replacing a bell jar with a coated bell jar simply can lower power consumption by 25%. Then, optimizing the process recipe, which is an extra service offered by GTAT, the potential for power savings would go upwards to 40%. Finally, GTAT assures the ROI with its Gen 2 E-Upgrade is at less than 1 year.

4.3 Tubular SeedsGTAT is working on yet another innovative approach called tube filament technology. The concept is all about replacing traditional seed rods with hollow tube filaments. The approach is based on the fact that the growth rate of polysilicon in a CVD reactor is a function of the seed rod’s surface area. The tube seed rods simply offer a larger starting surface area resulting in higher production rates without changing the reactor size, increasing the height of seed rods and their number. The beauty of the technology, according to Gum is, that it can be adapted to any CVD brand. Existing reactors would only need the adaptation or replacement of filament supports to use the new filaments. The filaments are grown from silicon melt by the so-called Edge-defined Film-fed Growth (EFG) method.

GTAT developed the EFG pulling equipment to fabricate the filaments more than a decade ago (German company Schott Solar was producing EFG solar cells before it exited the PV sector). According to Gum, GTAT engineers have spent the last decade in making the tube filament work inside the CVD reactor. End of 2015, GTAT had a breakthrough of successfully running the process with tube filaments in a typical CVD processing environment and at more aggressive temperatures and feed gas flows. The company has also patented the process in the US (US 20070251455 A1), according to which, the tubular filament can have a 40 to 80 mm outer diameter wall with a thickness ranging from 1.75 to 6 mm. The exact measurements depend on several reactor and processing parameters, including power supply specifications. The patent document gives an example that appropriate wall thickness of the tube seed rod with 50 mm outer diameter would be about 1.8 mm or more in order to use the same power supply system as would be used for typical solid filaments of 7 mm in diameter. Without making further major changes at the rector level, shifting to such 50 mm tubular filaments would offer the possibility to boost the productivity of the CVD reactor by 30 to 40%. According to Gum, the recent commercial tests resulted in 140 mm polysilicon rods in about 50 hours with further upward potential.


Now the company has shifted its focus to optimizing the pulling technology in order to make it cost effective. Even though there is a benefit at the deposition process level, this alone might not be enough to push the new technology. It needs to have lower cost in direct comparison with standard filaments. GTAT is evaluating several approaches. One is to decrease the cost of a single puller. “There is lot of opportunities to do that,” says Gum. Alternatively, the company is also exploring various multi-puller designs, so that several tube filaments can be pulled from one tool setup. GTAT is working with key customers with the goal to be either on par or at even lower cost than the standard filaments in costs, says Gum. The company expects to release the tube filament technology in 2017.

According to Gøran Bye, the idea of tube filament is not new but makes a lot of sense. The concept also works as a platform for other innovative approaches. Such tube filaments with hollow cores open up the opportunity to install a heater inside the seed rods, thereby simplifying the pre-heating step. Another idea is to make the filament with a suitable material other than silicon, says Bye, which would facilitate a sort of self-harvesting of fully grown polysilicon rods. This can be attained by creating a contraction between the filament and polysilicon by means of difference in thermal expansion coefficients. The result would be that the silicon rods break by themselves without any external force.

Hollow rods: GTAT is working on a new concept of tubular filaments, which is expected to boost the productivity of any CVD reactor by about 30% to 40%.


5. Different Reactor Design Aspects The above discussed topics are rather advanced concepts, but there are also some developments of standard specifications of silicon CVD reactors that are worth taking note of. The most influential aspects of this CVD process are productivity, preheating and energy consumption. These are also the major differentiating factors among the listed models in the survey. When looking at throughput enhancement alone, there are different philosophies – increasing the number of filament rods processed per production cycle, employing taller seed rods, producing final polysilicon rods with larger diameter, reducing the ideal time between two runs (from stopping deposition to starting deposition in the next production run). At the end, all these factors depend a lot on the reactor design, the number of gas feeding nozzles, their positions, gas flow rate and the distance between the rods so that they do not get in contact with each other during the deposition process. Thus, it is very important to strike the right balance between these parameters in order to attain the best possible productivity per tool. Filaments with heights of 2 m, 2.8 m and even up to 3 m; final rod diameters of 170 mm and 180mm and 220 mm to 225 mm are common in polysilicon production, according to Mozer.

5.1 Large-Size ReactorsIncreasing the number of rods processed per production cycle is an easy way to enhance the throughput of the reactor – and Morimatsu tops in this regard. The SMS-700 CVD reactor of the company comes with the ability to house 74 pairs of seed rods – that’s the highest reported number for this survey. In a production cycle time of 120 hours, out of which the actual deposition takes place for 100 hours, this reactor produces 10 tons of polysilicon. This throughput refers to a final rod diameter of 180 mm (the company has not provided the corresponding filament height).

Large sizes bring also new challenges. The higher the number of filaments, the harder it is to attain process uniformity. The reactor design needs to make sure that all seed rods are exposed to similar temperature profiles and gas flows, which becomes more difficult with larger reactors. A reactor as large as the product from Morimatsu also means that it is more complex regarding handling of big volumes of process gases and a larger power system. According to GEC’s Graeber, such a large production system requires a big power supply system, a larger mix of gas systems and huge valves in order to create uniform deposition conditions. But increasing the number of filaments not only increases the preparation time to install the filaments and unload the fully grown rods, the harvesting step as such also becomes more complex.

Building big: VRV promotes larger CVD reactors to gain in productivity, such as its CVD 96R model, which has the capability to process 48 rod pairs.

Source: VRV Group


VRV is also supplying CVD reactors of different sizes according to the needs of its clientele. According to VRV chairman Spada, the optimum number of rod pairs is between 27 and 48. While the smaller configuration is easy to handle and operate, the degree of complexity is a bit high with the 48 rod pairs configuration, which requires more effort for stable operation. “The effort pays off with the gain in productivity,” says Spada. However, for the current survey VRV has provided the data only for the biggest configuration - CVD 96R. The tool is capable of accommodating 96 filaments, 48 pairs, each with up to a height of 2,700 mm and 7 to 8 mm in diameter. These seed rods are grown to a diameter of 125 to 150 mm in a deposition time of 60 to 70 hours, producing 8 to 8.5 tons of polysilicon per production cycle. The total production cycle lasts 80 hours.

5.2 Medium-Size ReactorsGEC found its optimum at 27 seed rod pairs with its so called 3-ring reactor design, which Graeber believes is the best way in terms of handling, harvesting, power supply and preheating. The bell jar of the CVD-R54 comes with 1,920 mm in height and a base plate of 2,311 mm in diameter, creating a processing environment to process 54 filaments of 2,800 x 220 mm. At a pressure of 6 bars and a temperature of about 1,080oC, the tool produces 6 to 7.5 tons of silicon feedstock in a total production cycle of 120 hours. The actual deposition takes place in about 100 hours, in which the seed rods are grown to a diameter of 150 to 170 mm.

SST has also designed its reactor to process 27 rod pairs. But SST has not provided many specifications of its SST MS CVD2. It did reveal that the system requires about 12 hours of preparation before the actual deposition starts, which needs 152 hours to grow the rods measuring 180 mm in its final diameter. The product yield is 6.8 tons of polysilicon per run.

GTAT introduced a new reactor, CVD-600, in 2016. The important upgrade associated with the new product is the ability to process a higher number of seed rods than the previous tool. GTAT would not reveal the number, it only provided the rod dimensions, 2,400-3,000 mm x 7-8 mm. With an average growth rate of 1.8 mm per hour, the CVD-600 reactor produces about 8 tons of polysilicon per complete production cycle of 90 hours. The actual deposition time is given as 70 hours. GTAT is offering an even larger reactor, called SDR 1K, but the product is not listed in the survey.

Filament count: While the number of filaments processed per run is an important aspect of a CVD reactor, tool makers have found different optimum values – for example, GEC says a 27 pair strikes the right balance.

Source: GEC


5.3 Smaller-Size ReactorsMorimatsu is also supplying smaller CVD reactors, but the company has compressed the data for its 4 models of its SMS series in one column of the survey table. And the given specifications are most likely referring to the top configuration – SEM 700. Thus specific details of the other three models SMS 500, SMS 300 and SMS 150 are missing. Even the number of rod-loading capacity for the first two products is not known, while Morimatsu revealed that its SMS 150 has the ability to process 12 rod pairs.

5.4 Reactors with Tall FilamentsSiTec has been promoting the concept of rather small reactors but growing larger diameter rods by employing taller filaments. Its 24/500/RK-Imp tool comes with a bell jar of 3,925 mm height and 2,580 mm diameter base plate. The system can process 24 pairs of 3,200 mm tall seed rods, the longest in the survey. These rods are grown up to 180 to 200 mm in diameter during the deposition process. The total production cycle of 130 to 145 hours

produces up to 9.4 tons of polysilicon. Consultant Bye emphasizes that the longer rods can create challenges in harvesting, which is usually done manually. “Harvesting silicon rods of above 3 m tall certainly requires some mechanical tools,” says Bye. Moreover, mounting tall and slim rods might also pose a bit of a challenge. But one argument goes in favor of SiTec’s approach - it reduces the number of filaments. Filaments cost may not be the final criterion for selecting a CVD reactor, but they contribute to about 5% of polysilicon manufacturing costs.

SPB, which is exclusively promoting a silver plated bell jar based reactor, designed its reactor to be small, processing only 12 seed rod pairs. The 3,700 mm high bell jar sitting on a1,800 mm base plate, accommodates 3,200 long filaments, similar to SiTec’s tool. These seed rods are grown from about 8 to 9 mm to a final diameter of 180 mm in a total production cycle of 100 hours. Based on an average growth rate of 1.9 mm per hour, the process yields in 3.5 ton of silicon feedstock.

Productivity puzzle: It is difficult to compare the productivity of different CVD reactors as it depends on three different variables – number of filaments, cycle time and harvest per cycle, and it is not easy to say what configuration is best.

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Factors Affecting Productivity of Silicon CVD Reactors

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5.5 PreheatingPreheating of the seed rods is yet another important aspect of polysilicon production. Since the seed rods are made from high-purity silicon, they have very high resistances. Thus it is extremely difficult to heat the filament rods using a standard power supply setup. Employing doped silicon rods instead of intrinsic rods eases the process of preheating, as doping lowers the cold resistivity. However, employing doped filaments is a compromise on the ´final polysilicon quality. “For high quality, such as 12 N, doped filaments are strictly forbidden,” says Graeber. Another method to make them conductive is to heat the filaments externally. Since the resistivity of pure silicon has a strong correlation to temperature, increasing the temperature to about 400oC reduces the electrical resistivity to a level that makes the intrinsic filaments are susceptible for electrical heating. Following this approach, CVD reactors are equipped with drop-in IR heaters to heat the filaments. When the desired temperature is reached, the heaters are removed, the reactor is closed and then the reactor chamber is purged with hydrogen to initiate deposition. This laborious process actually consumes precious time of about 1 to 2 hours. To gain mainly on process time, the industry has been moving to an automated process called medium voltage ignition (MVI). Here, the seed rods are subject to voltages about 8 to 12 kV, while some are also using ever higher voltages of 15 kV, especially when employing taller seed rods. With MVI, everything is automatic. “After switching it on, all the rods will be in operation in less than 10 to 15 minutes,” says Mozer.

The IR based preheating is typically accomplished in nitrogen atmosphere, after which the chamber is purged with hydrogen to evacuate any traces of nitrogen contaminating the silicon. MVI enables filament ignition directly in the hydrogen atmosphere. This automated process also eradicates any possible contamination originating from the IR

heaters. However, the most important benefit of MVI is to reduce the turnaround time, which according to Gum is “about 2 hours of every run.” For these reasons, every CVD reactor supplier is strongly recommending MVI for preheating - and the market is following this advice. But MVI costs about 5 to 10 times of an IR heater and about the same as the reactor’s power control system. However, there are also lower-cost solutions from Asian suppliers that are 25% to 30% cheaper than well-known western brands. Another way to reduce the MVI cost is to share one system with several CVD reactors, but this again requires a special switch-over equipment. But there is no straight forward answer as to how many reactors can be connected to one MVI. GEC follows AEG Power Solutions’ recommendation of connecting 4 to 5 reactors to one MVI, but the number can go up to 10 reactors.

5.6 Filament Production Though not directly involved in the CVD process, the method of producing the seed rods also has a slight influence on polysilicon production. There are two ways – sawing and pulling. Each method has its own set of advantages and limitations. Sawn filaments, due to their rough surface, facilitate quick initial deposition of the polysilicon. But the sawing process may induce some cracks, which may cause serious damage, such as a collapse of silicon rods during the deposition. The pulling process is robust and does not involve any cutting and drilling steps. It also does not have any practical limitation for length of the filament. However, the resultant filaments have smooth surfaces, which requires relatively more time to trigger the initial deposition. Still, the majority of polysilicon makers are relying on pulled seed rods. Among the equipment makers only GEC and GTAT are recommending sawn rods, while the others in this survey are prescribing to use pulled ones. Nevertheless, every CVD reactor can house both types of filaments.


6. Performance Charecteristics Every reactor supplier obviously considers its reactor design the best solution. But there are differences in most important performance characteristics – productivity and power consumption, while heat recovery also contributes to energy consumption equation. As for productivity, it is like putting together a puzzle as there are so many different parameters such as number of filaments, their dimensions, cycle time and harvest per cycle - all of which determine the productivity of the reactor. Though not a precise metric, the annual capacity provided by the manufacturers gives a first consolidated picture of productivity, which, of course, is only one selection criteria.

6.1 Annual CapacityThe highest nominal annual capacity is reached with the SDR 1K from GTAT, which according to the company is 1,000 tons per year. Next is the product from Morimatsu. The SMS 700, as indicated by its model name, has a rated annual capacity of 700 tons. VRV’s top configuration - CVD 96R – produces 600 tons per year. The CVD-600 model from GTAT, as indicated by its name, also has a rated production capacity of 600 tons a year. GEC defines the annual capacity of its CVD-R54 according to the final rod size. The 150 mm rod diameter process results in 400 tons per year, while the annual yield rises to 500 tons when the rod diameter is 170 mm. SiTec’s 24 pair reactor also supports a yearly output of 500 tons. SST’s reactor has a rated capacity of 300 tons and SPB’s product supports 250 tons per year.

Who’s the fastest: Annual capacity of a CVD reactor provides one indication to evaluate the cost performance ratio of a CVD reactor and the graph shows the capacity levels supported by reactors from different vendors

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Annual Capacity Ranges of Silicon CVD ReactorsAnnual Capacity Ranges of Silicon CVD Reactors



6.2 Power ConsumptionIn parallel to increasing the capacity, nearly every CVD supplier is working on reducing power consumption of the reactor. Energy consumption for producing a kilogram polysilicon is one of the most important performance metrics of the CVD reactor as it has a considerable impact on production costs. Among the listed products SST’s system consumes the lowest power, only 30 kWh per kilogram. But it is like comparing apples with oranges, because SST’s product was designed to be fed with monosilane as feedstock, which enables to run the process at rather low temperatures, 900oC, compared to TCS based deposition, which is typically accomplished at close to 1,100oC.

Among TCS based reactors, Morimatsu claims the lowest energy consumption of 35 kWh/kg with its SMS-700. GEC also says it can attain this level, if the product comes with a silver lined bell jar. VRV’s CVD 96R takes the next position in keeping the power consumption low at 40 kWh/kg. The CVD-54model from GEC without silver reflector, GTAT’s SDR-600 and SiTec’s 24/500/RK-Imp all have the same rated energy consumption of 45 kWh/kg. Both, SiTec’s tool as well as Morimatsu’s SMS product range are specified with an upper limit of 60 kWh/kg for energy usage. SPB’s product comes with a silver lining, reaching a specified power consumption of 45 kWh.

Energy efficiency: One of the most important aspects of the CVD process is energy consumption. The majority of the products listed in the survey fall into the range of 35 to 45 kWh/kg, while the most efficient reactor form SST is an exception, as it relies on monosilane as feedstock.

Rated Energy Consumption of Silicon CVD Reactors

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6.3 Heat RecoveryThe majority of the energy put into the CVD process in the form of heat is actually absorbed by the cooling water flowing through the bell jar. The bell jar is actively cooled to keep a prescribed temperature in order to avoid any undesired deposition of silicon on its inner walls. However, there is a possibility to reuse this heat energy by making low pressure steam, which can be used in the distillation process of TCS production.

Nearly every tool maker is offering a heat recovery system as part of a standard system configuration. Like with power consumption, Morimatsu again makes the highest claim in heat recovery efficiency, which it rated with a very broad range from 60% to 95%, whereas the top value seems very high. GTAT says about 80% to 85% of the energy put into its CVD process can be reclaimed as steam, thereby

reducing net power consumption for its reactors SDR 600 and SDR 1K dramatically to 10 kWh/kg from 45 and 40 kWh/kg, respectively. VRV is also offering a heat recovery system as part of its basic engineering package and rates the reclaimed efficiency at 80%. GEC assures about 65% of recovery, which seems very conservative in comparison to its competitors. SPB says about 1/3 of heat put into the CVD process can be reclaimed, which would result in15 kWh/kg. Systems using a silver lining have less recovery potential, as the coating very effectively prevents heat loss to the cooling water.

A heat recovery system is just an option with SST’s tool, that’s mainly because SST uses monosilane-based technology, which already operates at low temperatures. Thus, the investment required for a heat recovery system would not make economic sense.

Making use of waste: A way to reduce the overall power consumption of the CVD process is to recover the heat from the bel jar’s cooling water circuit. Morimatsu makes a very strong claim to recover up to 95% of heat (though the lower number of its range is 65%). While SPB ‘only’ reaches a heat recovery rate of 35%, this is due to the fact that the silver lining in the reactor effectively prevents heat loss to happen.

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7. Alternate TechnologiesLike any other industrial production process, alternate approaches to Siemens CVD are under evaluation for polysilicon deposition. Our survey provides background on some of the interesting alternatives. FBR definitely tops the list, being used in mass production for many years. While FBR has been a proprietary technology, developed by a few silicon producers in-house, production equipment supplier SiTec has attained interesting first results for its product. Then Dynatec has also made progress with its innovative centrifuge CVD concept, while SST is closest to the standard process with only one difference.

7.1 Silane based CVDWhile most of the CVD reactors listed in the survey employ TCS as the feedstock, Schmid Silicon Technology (SST) is the only company that has designed its reactor to work with monosilane. Using monosilane has many benefits. The monosilane based process has been known to produce high-quality end products, for example the silicon rods used for float zone process are usually made with this method. In addition to quality, the approach is also relatively modest in its demand for energy. The technology in principle is very similar to standard polysilicon production. It is an extension of TCS production, while it still relies on Siemens-type CVD reactors in the backend of polysilicon deposition. However, there are several differences in details.

To start with the frontend process of producing feedstock – monosilane – the first step is pretty similar to the standard process. It also begins with hydrochlorination, in which TCS is produced from the reaction of metallurgical silicon, silicon

tetrachloride and hydrogen in a fluidized bed reactor. But according to Burkhard Wehefritz, director of sales at SST, this step is accomplished at lower pressure and high temperature, which is more efficient in conversion rates. “The earlier approach was to employ high pressure in order to avoid conflicts with patents, which are no more valid,” says Wehefritz. But “high pressure is also a bit of a safety issue, though not a big concern,” he adds. In the second step, the catalytic disproportionation, TCS is converted into monosilane and STC. Purification of monosilane is also relatively easy because, it is not an intermediate product and the majority of the impurities have boiling points far away from that of monosilane. According to Wehefritz, all metals are separated in hydrochlorination and other donor and acceptor impurities such as phosphorus and boron are eliminated in the disproportionation. SST says its monosilane production setup is relatively simple. Instead of 8 to 11 high distillation columns employed in typical polysilicon factories, SST’s solution involves having one column for disproportionation and two purification columns. On top, a vent gas recovery is not required as hydrogen is the only byproduct of the deposition process. “We do have a hydrogen blower, but that is not as expensive as vent gas recovery,” says Wehefritz. This hydrogen is pumped back into the hydrochlorination to work as a reactive agent.


Coming to the actual deposition step, as mentioned above, SST also relies on Siemens-type CVD reactors. The CVD reactors are not built in house, but through an exclusive agreement with an unidentified equipment maker. The benefit of this production step is that the deposition takes place in a corrosion free process environment. The only things that can come out of the process is silicon on the rods and hydrogen as the by product. The final deposited rod is very compact and the technology allows running the process at high deposition rates. Even in case of formation of popcorn as a result of high processing rates, etching is not required, says Wehefritz. That is simply because the pockets of the popcorn are not contaminated with chlorine. The absence of corrosive gases in the process is also one of the reasons why SST is not recommending any coating on internal walls of its bell jar. The other reason is - given the low processing temperature 900oC – that the coating would make only little economic sense compared to the gain in the reflected heat. More than eliminating the requirement for coating, the low operating temperature has a great benefit in savings in power consumption. SST says its reactor requires just 30 kWh of electrical energy to produce a kilogram of polysilicon.

While this is the lowest rated power among the CVD reactors listed in the survey, the reactors designed for standard processing come with the option of heat recovery to reduce the overall power consumption. With SST, the low processing temperature would not support a meaningful heat recovery that justifies the investment. As a proof of concept, SST has also built and operates its own polysilicon production facility called Schmid Polysilicon Production.

Regarding cost, SST claims its approach is 20% lower in capital expenditure and reduces the operation costs by about 30%. As to the question of why the technology has not earned any followers, especially when there is such a high costs savings potential, Wehefritz says that the polysilicon segment has not seen a big investment cycle since SST has demonstrated the process at full commercial scale at its facility. Like other polysilicon production solution providers, SST is waiting for the next investment cycle in the segment.

Change of precursor: The major conceptual difference with the polysilicon production process developed by Schmid Silicon Technology is that it employs silane as precursor instead of TCS used in the standard process.

Source: Schmid Silicon Technology


7.2 Centrifuge CVDDynatec AS, a Norway-based start-up, is working on a new technology of adapting the centrifuge principle to the well-established chemical vapor deposition (CVD) method used for polysilicon production. That means, like a washing machine, the reaction chamber of Dynatec’s tool also spins during the process. Dynatec found a new name to its technology, centrifuge CVD - CCVDR. This way, Dynatec says, its approach has two fundamental advantages – an increased precursor utilization rate and reduced power consumption – over the current state of the art Siemens-type CVD principle. Dynatec has already proven the concept with its earlier lab scale reactor. The company now has successfully built and tested the second generation reactor and expects to have a production-scale solution ready around 2018.

The core of the Dynatec’s technology is based on the principle that a centrifuge effectively separates the reactants and products, given the difference in their molecular weight is considerable. This is one of the main reasons why Dynatec’s technology employs monosilane as silicon precursor, unlike the standard Siemens process, which uses TCS as feedstock.

Silane, the only reactant of the process, is 16 times heavier than hydrogen, which is the only gaseous byproduct of the process. “With TCS, chlorine is also formed, which is also heavy, so the benefit is not much,” says Dynatec’s project manager Sverre Sørensen. The fundamental deposition principle is the same as in the standard process - silane is decomposed to silicon and hydrogen at high temperature. However, in CCVDR, the entire reaction chamber rotates, thus forming a centrifuge. During the process, the sidewalls of the reactor are heated, and when silane is introduced into the chamber, it is pushed towards the hot walls and decomposes to form silicon. The byproduct of the reaction is hydrogen, which is lighter and thus forced to the center of the chamber and then vented out easily. The main motive behind tweaking the CVD principle is to increase deposition rates, reduce the fine dust formation and higher precursor utilization rates compared to the standard technology.

Source: Dynatec

Next Generation: After Dynatec proved its concept for a centrifuge CVD technology, it has built a second generation reactor – and is now working on a production-scale product.


How Dynatec’s process works in detailThe decomposition process generally involves various stages – formation of silicon hydrogen complexes to silicon-hydride structures, which gradually desorbs hydrogen to transform into crystalline silicon.

According to a technical paper from Dynatec presented at the 31st EUPVSEC Conference (Low Cost / High Quality Silicon Production by Centrifuge CVD Reactor Upscaled and Hot Harvest; Author: Werner O. Filtvedt), the growth rate depends either on the transport of gaseous species to the surface or the surface chemistry that is responsible for forming crystalline silicon from the silicon complexes. However, with the traditional Siemens-CVD process the transport of gaseous species to the surface mainly depends on gas diffusion and concentration gradients. According to Dynatec’s paper, the growth rate can be increased by two mechanisms. One is actively moving silicon containing species to the growth surface and the other is to create low partial pressure of hydrogen at the growth surface to increase desorption, thereby facilitating incorporation of silicon atoms into the lattice. Dynatec’s approach of turning the entire reactor into a centrifuge

facilitates these two mechanisms to take place. As mentioned earlier, silane and its complexes due to their higher molecular weight are actively forced towards the hot deposition surface. At the same time, the accumulation of silicon containing species at the growth surfaces suppresses the presence of hydrogen. Therefore, hydrogen partial pressure is actively reduced, which in turn increases hydrogen desorption from the growth surface.

All this may sound theoretical, but Dynatec has made considerable progress in the practical world. After proving the concept, the company has moved to the next level with its reactor design. Dyntec has successfully built the second generation of its reactor, called DR2.0, with encouraging results. The reactor accomplishes the process at 600 – 800oC, which is quite low compared to over 1,000oC of the Siemens process. The tool is connected to a mass spectroscopy setup, which analyzes gas composition entering and exiting the machine in real time during operation. The reactor is also equipped with an optical particle monitoring system that helps in checking the type and amount of particles in the exhaust.

How it works: Dynatec’s new technology is based on the principle that the entire reaction chamber rotates forming a centrifuge. When silane is introduced into the chamber, it is pushed towards the hot walls and decomposes to form silicon.

Dynatec’s Centrifuge CVD Process

Source: Dynatec


In order to avoid the formation of dust or fines, the precursor silane is usually diluted with hydrogen. However, the CCVDR principle significantly reduces the chances of dust formation, hydrogen dilution could be less than 5%. “We have run with 100% silane,” emphasizes Sørensen, still, the process generates less dust, keeping the fine formation at less than 0.5%. Even more important is a high precursor conversion rate. According to Sørensen, while the Siemens process has a yield of 40% to 50%, his company’s technology has a silane utilization rate of 90%, with an upward potential to improve it to 95%. The reactor supports a deposition rate of 6 mm/h, which Dynatec claims is 40 times faster than traditional Siemens reactors. However, the majority of the CVD reactors listed in the survey have a nominal growth rate of about 1 mm/ h. The DR2.0 reactor has an annual capacity of 80 tons, which is five times higher than the first generation, and is currently growing 6 mm thick silicon layers per hour.

According to Dynatec, the high deposition rates facilitates a small reactor design that can still compete with traditional CVD systems in productivity. But this also means that harvesting cycles needs to take place at short intervals. In order to save time here, Dynatec is taking advantage of its rotating reactor design and has developed a patented hot harvest method. This method enables initiating the

new production cycle and harvesting the deposited silicon without cooling down the reactor. Before initiating the deposition, a layer of loose, dry and high purity granular silicon is applied onto the reactor’s sidewall. As the reactor is rotating, the silicon powder is kept onto the walls just by means of centripetal force. When silane is introduced during the process, the granular silicon acts as both a seed layer and substrate – on which the silicon is deposited. When the reactor stops, the loose particle layer with the deposited silicon falls out. Dynatec is sourcing the seed silicon granules externally, but eventually plans to integrate that job into the process. According to Sørensen, this silicon powder is a very clean material and has potential to improve in purity even further.

When it comes to the purity of the final product, Dynatec says that the small size of the reactor facilitates a large selection of possible design materials, which makes it much easier to achieve its purity goals. The company has made good progress with its DR2.0, according to a technical paper. While the first Dynatec reactor D1.0 has produced 2nd grade silicon in accordance to SEMI PV17-0611, the DR2.0 has improved the product quality to 1st grade - which is equivalent to “9N,” says Sørensen. Changing the materials used in the reactor design is one among “several improvements” with DR2.0 that have helped in improving the silicon quality, says Sørensen.

It’s different: Not only the technology to produce the silicon is different, even the final product made the Dynatec way is different.

Hot harvest: As show in the schematic, Dynatec applies a layer of granular silicon on the walls of the reactor to work as substrate on which the deposition takes place.

Source: Dynatec

Source: Dynatec


Record-low energy consumptionNext to quality, power consumption is the most important aspect of polysilicon production. Dynatec has a an advantage in this regard. First, as mentioned earlier, the deposition in CCVDR is accomplished at low temperatures. Another important benefit of this approach over Siemens technology is that the entire reactor can be maintained at high temperature and no active cooling is required as it is the case with the standard process. Since no or very little hydrogen is blended into the feed gas, unnecessary hydrogen heating is avoided. All these factors, in addition to silane dissociating in an exothermic reaction, reduces the overall power consumption of Dynatec’s process. According to Sørensen, the power consumption with the DR2.0 is about 3.5 kWh/kg of produced silicon. This is 1/10 of 35 kWh/kg with the best standard CVD tools without taking the heat recovery into consideration.

Dynatec is currently working on a production scale system, tagged DR3.0. The obvious upgrade is scalability with a target of 320 tons/year production capacity. This also involves improvements on materials used and automation in harvesting. “The automation has got to be better than today,” says Sørensen. The Gen 3 production-scale system is expected to be ready by 2018 with a cash cost of “$1.3/kg + silane.” As for the business model, Dynatec is cooperating with polysilicon producers and strives to be a reactor producer, but Sørensen adds, “We are working on it.” That means the business model may change.

In any case, Dynatec’s approach could face one problem from the frontend. Unlike other parts of the value chain, silicon manufacturers typically produce their own direct feedstock - that is TCS. But Dynatec’s technology is based on silane, for which the know-how is not so wide spread. That means Dynatec might need to cooperate with a silane producing solution provider to get support in spreading its technology.

7.3 Fluidized bed reactorFluidized bed reactor (FBR) technology has been the favorite alternative to CVD technology, mainly due to the potential to reduce cost. FBR has two main advantages – low energy consumption and higher utilization of the precursor – compared to the traditional Siemens-CVD process.

In FBR technology a vertical column functions as reactor, which is filled with tiny silicon particles of less than 100 µm in size. A fluidized gas, like hydrogen or nitrogen, is injected at the bottom of the reactor. At certain gas velocity, the drag force exerted on each solid particle equates to their respective weight. At this stage, referred as fluidized bed, the bed of the particle behaves like a liquid and the flow of gas keeps it in contiguous motion. The reactant gas, mixed with fluidizing gas, is introduced into the bed. The particles are heated to a temperature above the decomposition temperature of the reactant gas by means of external heaters. As a result of the decomposition, silicon is deposited on the particles, then grow in size. When the particles are large enough, they are extracted from the reactor and the cycle is repeated by adding fresh seeds to the bed.

Equipment vendors going FBR: The development of FBR reactors for producing granular polysilicon (show here), which has been so far in-house designs of the poly makers, is now also attracting equipment makers, like SiTec.

Source: SiTec


While this is a generic description of the process, every company active in this field has its own way of executing the process. The main differences are how to supply the heat, methods of introducing the gases into the process environment and then how to avoid the seeds hitting the reactor walls. REC Silicon employs submerged beds and relies on nozzle technology to inject the gas into the reactor. The SunEdison FBR technology uses cooled perforated plates. SMP, the joint venture of Samsung and SunEdison in Korea, has been working on high pressure FBR. GCL, which has its own FBR technology, has not revealed any details, but the company recently took over the SunEdison FBR assets.

Like Siemens in its earlier days, FBR is a proprietary technology that has been commercially pursued mainly by silicon suppliers REC and SunEdison (until it went bankrupt), while GCL had announced big plans for its in-house FBR project in the past, but then stayed with Siemens technology. Now FBR is also attracting equipment makers like SiTec GmbH, a division of Centrotherm, which has developed a new FBR technology. The company has already designed a prototypic pilot reactor. SiTec has presented

encouraging first results at the 32rd EUPVSEC conference in Munich in 2016 (New Monosilane Fluid Bed Decomposition Technology for the Production of Solar Quality Silicon Feedstock; Authors: Mark TAIYANGNEWS. Dassel et al). Genesis is the name of SiTec’s technology, which fluidizes the granular reaction bed by mechanically induced vibration. This Vibrationally Fluidized Bed Reaction (V-FBR) is designed to operate at 700oC and high pressure of up to 20 bar using 100% silane (no hydrogen dilution) as the feed gas. According to SiTec’s paper, the approach addresses many challenges associated with the typical FBR processes.

To start with, SiTec avoids the usage of hydrogen, while a typical FBR process uses silane diluted with hydrogen at a 1:5 to 1:20 ratio as feed gas. One of the main reasons for hydrogen dilution is to reduce dust formation. SiTec says its approach keeps the unwanted dust at less than 2%, compared to more than 10% dust formation with the traditional FBR approaches. The dust reduction is attained by keeping the precursor in close contact with the hot granules at all times. The vibrational fluidization also avoids formation of gas bubbles, which is a main phenomenon behind the formation of bubbles.

In short: This schematic provides an overview of SiTec’s Genesis technology based on its newly developed Vibrationally Fluidized Bed Reaction (V-FBR).

SiTec’s FBR Genesis Technology

Source: SiTec


Another reason for dilution is hydrogen supports the fluidization. However, the gas flow rates required for the fluidization process also blows smaller seeds out of the reactor. According to SiTEc’s paper, seed particles of less than 85 µm are typically lost as dust in the off-gas filters. To compensate this loss, the seeds are made off-line. However, seeds formed in the V-FBR reactor stay in the bed, as exit gas velocity is relatively low – only 1/50th to 1/100th – compared to typical FBR technologies. Again, avoiding hydrogen and accomplishing the process at high temperature facilitate dramatic reduction of exit gas velocity. Hydrogen gas has an inherently high heat capacity, thus hydrogen dilution significantly increases heat load and vice versa. Avoiding hydrogen usage also contributes to the reduction in power consumption of SiTec’s process by 35% over the standard FBR process. The actual power consumption is estimated to be 1 kWh/ kg with the commercial scale reactor.

The granular-silicon product withdrawal system of Genesis is also somewhat distinct. Unlike in typical reactors, in which the silicon is harvested from the

bottom as underflow, the silicon granules in V-FBR are withdrawn from the top surface of the reaction bed in an overflow standpipe. This is mainly enabled by the fact that the top surface of the bed, while highly fluidized, is relatively flat and not prone to the surging flow. Adding to that, the product withdrawal system, benefiting from the V-FBR technology, moves the larger particles to the surface and is designed in a way that particles sized smaller than 400 microns stay in the reaction bed, while large particles are preferentially removed.

Finally, counting on all these benefits, SiTec says that its Genesis technology has a potential to reduce the capex by 35% including the monosilane facility over the typical FBR setup and results in costs of $7.25/kg of silicon produced in China. While SiTec has not indicated any time line for the commercialization, a commercial prototype pilot reactor is in the early stages of scale-up testing


8. Interview with Gøran Bye on FBR FBR technology has been a proprietary technology a few companies are producing commercially using their own equipment, that’s why only little know-how has spread to the outer world so far. Long-time seen by many as a challenger to incumbent Siemens-technology, FBR has remained mostly an unfulfilled promises - with big announcements that were not realized, joint ventures, bankruptcy and acquisitions. While it is difficult for an outsider to estimate in which direction the technology is moving, there is one expert in this segment who should know.

TaiyangNews: FBR technology has been a hot topic in the silicon space. What is your take on the technology?

Gøran Bye: The concept of using FBR is inviting people. There are two reasons. One is power usage

in the reactor. That is immediately tantalizing. I

am not entirely convinced that people have clearly

realized that you need more energy for silane

production. In principle OK, you use a little bit more

energy for silane production, which is usually used

for FBR, but if you look at entire FBR, one should

save in cooling water and the off gas and vent gas recovery compared to TCS Siemens. At the end,

it is large energy savings for silane FBR. Then it is

possible to have close to 100% conversion of silane

gas in the reactor in one run, while for TCS we are

looking at 11%, 12% or maybe 16%.

TaiyangNews: Then why it is not really taking off? ITRPV has been consistently lowering its forecast for FBR?

Gøran Bye: One of the main reasons is that using silane as precursor results in the formation of dust,

a fine particulate of silicon. The art of realizing full conversion also involves minimizing dust

generation. This requires a very careful balance of

temperatures and flows. Some people also find it difficult to achieve this balance. Then there are some limitations in terms of freedom to operate FBR; there

are patents that are still valid.

TaiyangNews: What is so complicated about the technology?

Gøran Bye: As a matter fact, FBR itself is not very sophisticated. It is used in a lot of different processes around the world. You have this bed of seeds; you

agitate by gas. When you have to make polysilicon

with this, it has to deal with where do you heat it,

how do you heat it. Because you have a hot wall

technology – and if you heat from outside, there is

a tendency of silane gas adhering to the inside of

the reactor, leading to unwanted deposition on the

wall. This results in higher metal-contamination. So

one challenge is to keeping metals out of reach from

the product. That is not so easy because if there is

a hiccup in the production, the wall scales would fall

down and end up in the product.

Then it is also a matter of how to extract the product

- to suck the beads out or they would fallout at the

bottom? In any case, the beads have to go through

a series of filters, degassers and coolers. Here again, you have a possibility of contaminating the

silicon with metallic impurities, which results in a

large surface area with metallic impurities. The other

challenge is the possibility of porosity in the beads,

attract some oxygen.

So FBR is not as easy as it sounds. It might look

bright from a financial and costs point of view, but there are a lot of things that are not necessarily so

positive with FBR.

Gøran Bye is a former CEO of REC Silicon, a leader in FBR technology, and LDK Silicon & Chemical Technologies, a once promising Chinese newcomer in the field of silicon production, which fell victim to its huge expansion plans. Today Bye is advising businesses and investors on PV and silicon materials industries. At the time of the interview he was interim Chief Project Officer for Qatar Solar Technologies.


TaiyangNews: Are there issues with FBR beyond technology?

Gøran Bye: The last point I want to make is indeed not technical and my personal opinion. The Chinese

industry seems to be very reluctant to use silane

gas. They are somehow afraid of silane gas. True,

silane is highly pyrophoric and we have examples

of its explosion, but TCS and STC are not benign

either. They all need to be treated with care. It

seems like a couple of explosions and accidents

going back quite a few years are still making the

Chinese industry worry of using silane. I think they

are more comfortable to sticking to the technology

they already know. So I think that’s the reason why

many who have been looking at silane FBR, have

decided not to do it. It even might have been difficult in getting financing. However, GCL is in the latter phases of taking over SunEdison’s Solar Material

Division with the IP for SunEdison’s FBR – so let’s

see.

TaiyangNews: What about the limitations on the patents end?

Gøran Bye: I recall the old MEMC patents. One claim was that they had distribution plates with a lot

of holes in it, and they seem to be using hydrogen

in the outer holes in order to create some sort of

hydrogen blanket around the wall to keep the beads

away from hitting it. That is something you are not

allowed to do.

There is also potentially a limitation to have the

distribution plate with a large number of inlet-holes.

REC Silicon also has patents around hydrogen

and silane gas inlets into the FBR. Another area to

maneuver around is putting some sort of liner. If you

keep a liner to prevent beads hitting the walls, you

may have other challenges. The thermal expansion

coefficient of whatever material you are using might

be different from the reactor itself. This might result in some heat stress. Then there is also the challenge

of how to get heat in there and the options are

getting heat from outside to heat through the liner or

install internal heaters in and combinations of these.

This adds to further complexities. For example,

opting for internal heaters leads to the question of

how to prevent silane depositing on these heaters.

Here are also some limitations on what kind of liners you use, because there are some patents out there.

In a nutshell the crucial questions are -How do you get the gas in, what’s the distribution you have

there? And how to keep it away from hitting the wall.

These all have to be handled.

TaiyangNews: So what can you do despite the patent limitations?

Gøran Bye: To have a freedom to operate and proceed further, one must make some compromises

- accept that the beads hit the wall and allow the

gas to pass this film or layer of silicon. It is not the optimum, but in order to be legal, one has to let go

some things.

You need to learn how to operate a FBR reactor.

Even if you have fixed all the issues we talked about and accepted that they are as they are, operation

is the key. How do you balance the velocity, concentrations, dust production, conversion, and not

at least how do you keep the bed relatively stable

when you extract the beads? There is an art to that,

which is both art and science. And it takes time to

learn. That is the big advantage of REC and MEMC.

They had time to learn this. Others like GCL have been trying to catch-up, which could now go faster

after the take-over of the SunEdison IP and technical

resources. It is not unreasonable to think that it

might take 5 to 6 years to learn to master a new

technology.


TaiyanNews: What is your opinion about REC’s latest venture in China?

Gøran Bye: One thing from REC is that they are very open and try to be very good in communication

to the market. They have developed what they call

FBR B, the second generation. It is larger than the

ones they have now; it has some sort of liner in it.

I think that’s the key. In Moses Lake, REC has a product development facility, where they implement

developments in pilot production. It can be done

in pretty large scale in order to test and see how

to operate. And I think FBR B is the technology

that they want to build in China. Before they came

up with the China plans, they announced an

expansion project in Moses Lake that they since have abandoned. It was called reactor 25 and 26,

which was going to be FBR B. Apparently they have

had very good results on what they did on the pilot

scale. Maybe it increases risk a little that they will go

straight to that technology in China without having

been able to test reactor 25 and 26 in Moses Lake on a commercial scale. But I am pretty sure they will

succeed.

TaiyangNews: Do you think REC will finish the China project as announced in their Q3 report, they say that they are on track for startup in 2nd half 2017?

Gøran Bye: They were very open and specific - produce 7,300 tons in 2018, going up to 16,300 tons

in 2019 and culminating it at 19,300 tons in 2020.

They say that they are ready for startup in 2nd half

2017 and would be having half the production output

in 2018. One should count backwards to estimate

the feasibility. There will be a commissioning

period. Wacker in Tennessee announced that their

commissioning period was 8 months, though it

depends how you define commissioning. Considering REC will have 6 months commissioning period, in

order to start up in December 2017, construction

should be finishing in June 2017. It might be a stretch to get there. However, as I said, they were very specific in their projections, so I assume they have a good plan.

TaiyangNews: What is your take on SMP, the joint venture of Samsung and SunEdison?

Gøran Bye: SMP is doing high pressure FBR in Korea. To increase production, you need to increase

the size of the reactor, and/or you can increase the

pressure within certain limits. SunEdison has been

the leader in FBR technology. They have more than

30 years of experience with FBR. When they started

this JV with Samsung, they were building up on a strong knowhow in FBR. I wouldn’t be surprised,

but I don’t know for sure that they already had the

design for this kind of reactor that they have installed

in Korea in their R&D. So they have started with

lot of knowledge, but not so much practical usage

yet. They decided to go with large reactors, and

increased the pressure in order to increase the

capacity of the FBR. According to people who know

a lot about fluidization, they all seem to think that increasing the pressure is not trivial but doable. I

have reason to believe that they have been actually

more successful than what people think on the

outside.


TaiyangNews: Increasing the pressure seems to increase the dust, which is the biggest problem SMP has, right?

Gøran Bye: They report that they have dust and fines. Dust come in different sizes, they produce 12% or less. But look at REC’s reports, they are not

any better. Yes, there have been lots of teething

problems in Korea. But I think the rumors out there

have been more negative than a sober view on

the realities would show. When someone starts

something, we want it to be perfect in a couple of

weeks. FBR simply needs time. Just look at REC, hence my comment to GCL; they are in a learning process.

TaiyangNews: Then why does their US plant have very high cost?

Gøran Bye: Their Pasadena plant is closed. There are two important aspects for FBR or any polysilicon

production. Gas production is at the front-end and CVD

Documents

Market Survey - TaiyangNewstaiyangnews.info/TaiyangNews_Market Survey Polysilicon CVD Reactors 2017.pdfChemical Vapor Deposition (CVD) process using trichlorosilane (TCS) as feedstock