The RTCVD 160Silicon Deposition System

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Fraunhofer Institute for Solar Energy Systems ISEHeidenhofstr. 279110 FreiburgGermanyTel.: +49 (0) 7 61/45 88-0Fax: +49 (0) 7 61/45 88-90 00www.ise.fhg.de

Coordination Crystalline Silicon Thin-Film Solar CellsDr Stefan ReberTel.: +49 (0) 7 61/45 88-52 48Fax: +49 (0) 7 61/45 88-92 48Stefan.Reber@ise.fhg.de

The systemThe RTCVD 160 is a tool for depo-siting silicon layers from the gas phaseusing atmospheric pressure chemicalvapor deposition. We designed it forthe purposes of R&D, especially forcoating rectangular substrates up to125 mm in width. Depending on substrate and process conditions, thesilicon layer either grows epitaxially or polycrystalline. Due to the inno-vative arrangement of the substratesonly little parasitic deposition occurson the quartz parts of the reactor,thus leading to a very high silicon conversion efficiency.

Our RTCVD 160 system is very com-pact and consists of only few, robustparts. A lamp powered cold-wall furnace heats the substrates, whichare fixed in a quartz carrier locatedwithin a quartz tube. Two thyristorunits provide enough power to reachprocess temperatures up to 1300 °C.The main process gas trichlorosilane is stored in a bottle inside the RTCVD160. It gets mixed with hydrogen anddopant gases in a gas mixture panel,which also provides etch gases andpurge gases to the reactor.

Deposition processes as well as safetyloops are being controlled by a pro-grammable logic controller. We havedefined a very convenient control software called MODVIS. It runs on a standard personal computer, and allows the user to create his own recipes for all thinkable layer com-positions.

April 2003

ApplicationsOne of the strengths of the RTCVD160 is its great variability in substrategeometry. Since the substrate carrier isa completely modular, exchangeablepart of the system, substrates of nearly all sizes and shapes can be coated. The only constraints are dia-meter of the reactor tube and lengthof the furnace, which limit the maxi-mum substrate size to about 300 mmin length and 125 mm in width. In thebasic version, we designed the carrierfor coating substrates of 100 mm inwidth and up to 300 mm in length at2 mm thickness at most.

The primary application of the RTCVD160 is silicon epitaxy on crystalline silicon surfaces, with layer thicknessesranging from about 5 to 100 µm.Coating of amorphous surfaces withpolycrystalline silicon of the samethickness range is the second appli-cation we designed the system for.

The large flexibility of the reactormakes the RTCVD 160 the optimumdeposition tool for all R&D applica-tions.

Front view of the RTCVD 160.

Technical Data

Process- process gases: SiHCl3, H2, B2H6,

PH3, purge gas N2, etch gas HCl- process temperature: 850-1300 °C- deposition rate: 1-5 µm/min- silicon conversion efficiency:

up to 50%- layer quality: electronic grade,

efficiency of thin-film solar cell in epitaxial layer up to 17.6% has been demonstrated (RTCVD 100)

Furnace and power supply- 2 vertical lamp fields 400 x 250 mm2

- 15 linear halogen lamps per field, filament length 250 mm, 4.5 kVA at 400 V per lamp

- anodized aluminum, inner side mirrored, water cooled

- 2 thyristor insertions, 6 thyristors each

- each lamp pair individually controllable

Gas mixture panel- H2 bubbling of SiHCl3- pneumatic and manual valves- mass flow controllers or mass

flow meters for each gas- gas stabilization to exhaust- best quality components

The RTCVD 160 Silicon Deposition System

The gas mixture panel plays a crucial role forthe quality of the silicon layer. Therefore weonly use materials and components of highestquality. All gas flows are either controlled ormeasured by mass flow meters or mass flowcontrollers, respectively.

Furnace of the RTCVD 160. 15 linear halogenlamps on each vertical lamp field provideenough light to heat up the substrates to1300 °C. 12 fans keep the temperature of the lamps low, the furnace body itself is water cooled.

Graphical user interface of the MODVIS processcontrol software. Multiple layers deposited atuser-defined process conditions can be pre-defined for reproducible process runs. All massflow data and temperature data are logged andcan be printed in a process protocol.

The substrate carrier is made from quartz and provides space for 2 rows of three 100 x 100 mm2 wafers each. Spacing betweenthe rows can be varied from 6 to 18 mm. A gas pre-heating section combined with agas shower allows optimum gas conditioning.

Process control and safety devices- PLC (Programmable Logic Controller)

controlled by PC software- modular, user defined recipes- data logging during process run - process protocol generator- hydrogen / hydride sensors- thermo switches- reactor over pressure monitoring

Reactor and substrate carrier- all quartz material- reactor tube 160 mm outer

diameter, 1300 mm length- substrate carrier:

- modular setup - for 2 substrate rows of approx.- 100 x 300 mm2 size- gas pre-heating section- optional: gas shower inlet

- quick substrate carrier loading and unloading

Dimensions and supplies- system height x width x depth:

approx. 1900 x 2200 x 900 mm3

- power: 3-phase 400 V, 50 Hz, 70 kVA

- cooling water ~30 l/min at 18 °C- process and standby gases, CDA