PROCESSNEWS 1

We’ve been lucky that distinguished experts in each field have presented at these webinars. They are available to view again, just look inside this newsletter to find out more about them.

www.oxford-instruments.com/plasma-videos

Data storage, Atomic Layer Deposition, MEMS, Graphene and 2D materials have all been presented recently through our series of webinars

Welcome to this issue of PROCESSNEWS 2 Flexible high performance Silicon-

based inorganic electronics

3 Watch again - Fascinating technical webinars – key expert guest speakers

4/5 Exploring Flatlands at Oxford Instruments

6/7 Atomic layer deposition of dielectric materials

8/9 The application of Bosch™ Deep Silicon Etch (DSiE) to the manufacture of X-Ray lenses

10 ICP plasma etching of tapered Via in Silicon for MEMS integration

11 Metallic nanoparticle formation by sputtering and annealing

12 2D plenary sessions attracted enormous interest at recent Beijing Nanotechnology Seminar

13 Nanoparticle and nanosphere mask for etching of ITO nanostructures and their reflection properties

13 University of Science and Technology of China orders an additional plasma etching system for quantum information processing

14/15 Dust management in silane PECVD systems

16 Introducing our new Service agent in Israel

16 Launching new training dates for 2015

IN THIS ISSUE

PROCESSNEWS 1114A Newsletter from Oxford Instruments Plasma Technology

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/oxinst@oxinst

1114Watch again

Taking nano to the next levelFocusing on recent advances in nanoscale etching and in atomic layer deposition (ALD),

from research to manufacturing applications, this webinar was presented by leaders in their

respective fields of research and production.

Two industry-leading speakers discussed their specialities:

• ALD and nanoscale-etch processing techniques and results from recent work carried out

at the LBNL, Deirdre Olynick, Lawrence Berkeley National Laboratory (LBNL):

• Data storage - a technology area that is benefitting from advances in nanoscale

fabrication, Kim Lee, Seagate

Exploring flatlands: fabrication technologiesOne of the key technical challenges when working towards the commercial realization of

graphene and related 2D materials is the development of robust fabrication techniques for

deposition, etching and integration with other processes in a device-fabrication facility. This

webinar focussed on recent advances in research from academic speakers at the forefront of

their fields, as well as from Oxford Instruments.

What you will gain from this webinar:

• Understanding of the use of controlled etching processes for novel 2D heterostructures

– by Dr Andrey V Kretinin (University of Manchester, UK)

• Growth and characterization of graphene and hexagonal boron nitride via CVD and

plasma-enhanced CVD – by Dr Ravi Sundaram (Oxford Instruments, UK)

• Use of ALD in the deposition of low-resistance contacts and high-k dielectrics on

graphene – by Dr A A Bol (Eindhoven University of Technology, Netherlands)

Fascinating technical webinars – key expert guest speakers

PROCESSNEWS 32 PROCESSNEWS

Galo A. Torres Sevilla and Dr. Muhammad Mustafa Hussain / Integrated Nanotechnology Group, King Abdullah University of Science and Technology (KAUST)

Flexible high performance Silicon-based inorganic electronics

Figure 2 shows a comparison between the performance

of released and unreleased samples. It can be seen that no

degradation is introduced to the devices during peel-off process,

hence making our technique suitable for state of the art devices.

In summary, we have developed and presented a practical

way to transform traditional high performance electronics

into flexible ones without the need of expensive substrates or

processes. We expect that in a close future, this technique may

be used to fabricate high performance wearable and ultra-

portable electronics.

Since the introduction of flexible electronics in 1969, many

different approaches have been demonstrated to create high

performance devices on flexible substrates. The most commonly

known is the use of flexible organic substrates to fabricate

devices using microfabrication processes. However, plastic

semiconductors have many disadvantages when compared with

inorganic ones. Plastic thermal instability together with their

inherited low electron mobility hinder their potential for truly

high performance flexible electronics. For this reason, alternate

approaches have been followed to integrate the electrical

advantages of inorganic substrates with the flexibility of organic

semiconductors. These techniques are usually based on transfer

of silicon nano-ribbons released from costly Si (111) substrates

to plastic host substrates. However, the incompatibility between

transfer techniques and industries’ processes along with the

reduced integration density, hinder their potential for very large

scale integration required for high performance electronics.

For these reasons, in recent years, we have demonstrated state

of the art silicon devices on flexible platforms without the need

of transfer processes or expensive substrates. Our process is

based on etch-release-peel-reuse techniques. First, we fabricate

our devices with state of the art industry compatible processes.

Then, with the aid of BOSCH process (Oxford Instruments

PlasmaPro 100) we etch deep trenches in the passive areas

of the wafer. Depending on the etch depth, the final thickness

of the substrate can be controlled. Next, we protect the lateral

walls of the holes using ALD deposition. Finally, using isotropic

etching of silicon (XeF2), we create caves at the bottom of the

trenches, once these caves meet, the top silicon film can be

easily peeled and flexed due to the extremely reduced thickness

(1 to 20 µm). At this point, the remaining substrate can be

polished and reused making our process industry compatible

and cost effective at the same time.

Figure 1 shows a released sample containing the most advanced

transistor architecture (FinFET). The obtained film is only 1

µm thick exhibiting extremely high flexibility (5 mm minimum

bending radius) and semitransparency due to the etch holes

created for the peeling process.

Figure 1: Released sample containing FinFET transistors. Sample is 1µm thick allowing a minimum bending radius of 5 mm and exhibits semitransparency due to the etch holes introduced during the peel-off process.

Figure 2: Transfer characteristics comparing released and unreleased samples showing no performance degradation due to peel-off process. Gate length (L) = 250nm and width (W) = 3.6 µm.

Contact: MuhammadMustafa.Hussain@kaust.edu.sa

Dr Deirdre Olynick, LBNL

Kim Lee, Seagate

Watch either of these webinars at: www.oxford-instruments.com/plasma-videos

Galo A. Torres Sevilla was a guest speaker at our spring seminar at IEMN, Lille, France

Dr Andrey V Kretinin, University of Manchester

Dr Ravi Sundaram, Oxford Instruments

Dr A A Bol, Eindhoven University of Technology

4 PROCESSNEWS PROCESSNEWS 5

Chemical structures are characterized by X-ray photoelectron spectroscopy

(Oxford Instruments-Omicron ESCA+). XPS measurements were performed with

an Al-Kα X-ray source on the samples. Fig. 2 shows the XPS spectrum for the

transferred sample on Nickel, where two peaks at 191.03 eV and 398.4 eV are

identified as the binding energies of the B 1s and N 1s electrons respectively.

These energy values (and integrated intensity analysis) reaffirms the formation

of hexagonal Boron Nitride presented in nearly equal stoichiometric ratio [7].

We have an extensive portfolio of deposition and characterization tools

tailored towards research the field of graphene and 2 dimensional materials.

N 1s

x 103

10

20

30

40

50

60

CP

S

408 404 400 396 392Binding Energy (eV)

B 1s

x 103

4

6

8

10

12

14

16

18

20

22

CP

S

200 196 192 188 184Binding Energy (eV)

References:

[1]. Li, X et al; Science 324, 1312-1314 (2009)

[2] Bae, S. et al; Nat Nanotech. 5, 574 (2010)

[3] Ismach, A. et al; ACS Nano,6, 6378 (2012)

[4] Zhan, Y et al; Small, 8, 966 (2012)

[5] R. Gorbachev et al; Small , 7, 465,(2011)

[6] Reich, S. et al; Phys. Rev. B, 71, 205201, (2005)

[7] Lee, Yi-Hsien et al; RSC Adv., 2, 111(2012)

Fig. 2. (a) Raman spectrum of hBN on Ni showing the characteristic peak ~1368 cm-1 (b)Zoomed in plot of Spectrum shown in (a) to elucidate the absence of non-hBN phase (c) XPS survey scan, (d) N1s(at 398.4 eV) and (e) B1s(at 191.03 eV)

Chemical Vapour Deposition (CVD) has emerged as a

workhorse for the preparation and production of graphene

[1,2] and more recently applied in the synthesis of other

2D materials such as hexagonal Boron Nitride [3] and

Molybdenum Disulphide [4]. We had previously demonstrated

that the Oxford Instruments Nanofab Agile tool with the

capability of both CVD and PECVD processes can be used for

the growth of monolayer graphene and related graphene-like

allotropes. Recently, we have developed a thermal CVD route

to synthesize hexagonal Boron Nitride (hBN) using Nickel foils

as catalyst in this tool.

The processStandard semiconductor process gases, Diborane (B

2H

6) and

Ammonia (NH3) were introduced in the right proportions over

a nickel foil heated (~1000 ºC ) which were pre-treated in

a reducing atmosphere. The reaction of these components

catalysed by nickel resulted in the nucleation and growth of

hBN islands. The load-locked sample transfer enabled quick

sample exchange and also allowed us to precisely arrest the

reaction to observe these growth fronts before the formation

of a continuous film using an SEM and also on an Oxford

Instruments Asylum Research MFP-3D Classic AFM

Dr Ravi Sundaram, Development Scientist, Oxford Instruments

We have been taking a close look at growth and characterisation of 2 dimensional

materials. As the field moves beyond graphene, there is growing interest in

studying atomic planes of other Van der Waals solids and heterostructures

created by stacking layers with complementary characteristics to achieve novel

functionality. One such material that serves as a high quality substrate for

graphene is hexagonal Boron Nitride (hBN).

Fig. 1. (a) SEM image showing a triangular hBN island growing on a Nickel crystal face. (b)AFM topography and (c) AFM lateral force image of a growing edge.

Film characterisationIn order to confirm the deposition of hBN we used Raman spectroscopy and X-Ray Photoelectron Spectroscopy (XPS) (Figure 2).

The presence of a sharp peak at ~1368 cm-1 (excitation at 532 nm) arises from the E2g

phonon and is characteristic of the h-BN

phase. On closer examination of the spectrum we did not see the presence of broad peaks which may arise due to unwanted

co-deposition of the cubic phase, carbon contaminated phase or amorphous BN soot.

1000 1100 1200 1300 1400 1500 1600

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Inte

nsity

(a.u

.)

Raman Shift (cm-1)

Lorentz

Position1367.534 0.11898

FWHM 21.413 0.37

Please contact us for more information on graphene and other 2 dimensional materials:

nanotools@oxinst.com or visit www.oxford-instruments.com/graphene

1114Exploring Flatlands at Oxford Instruments

N1s:398.4 B1s:191.03

0614

PROCESSNEWS 76 PROCESSNEWS

Harm Knoops and Tom Sharp, Oxford Instruments

Atomic layer deposition of dielectric materials

Atomic layer deposition (ALD) is of interest for controlled

deposition of dielectric materials in complex device structures.

To serve the needs of the wide range of devices and applications

fields which can benefit from these dielectric films, there is

a constant drive towards new ALD processes and improved

material properties (e.g., higher dielectric constant). Furthermore

for many applications there is a desire to go towards lower

temperatures, while maintaining high material quality.

To this end, several oxidants can be applied in the ALD cycle

such as water, ozone and oxygen plasma, which differ in

oxidizing strength. Figure 1 shows an overview of common

dielectric materials and whether they have been grown using

Oxford Instrument systems (OpAL and/or FlexAL). The usage

of oxygen plasma allows the deposition of the widest range

of oxides and furthermore has been demonstrated to allow

deposition at room temperature for some (Al2O

3, SiO

2, and

TiO2 have been demonstrated by the Eindhoven University of

Technology). Note that for deposition on sensitive substrates

(such as III-V materials) a low power plasma or weaker oxidant

could be desired.

Besides binary oxides, also the desire to deposit multi-

component oxides using ALD is present. For instance

stoichiometric strontium titanate oxide (STO) can have very

high k values. The cycle wise nature of the ALD process and

the recipe based software of the OpAL and FlexAL allows

easy mixing of materials by alternating ALD cycles of the

binary compounds. Figure 2 for instance shows how the

optical properties of STO deposited on a FlexAL system

can be tuned by varying the [SrO]/[TiO2] ALD cycle ratio. This

example furthermore shows how in situ ellipsometry can be

used to determine the stoichiometry for these materials. Post-

annealing at 600/650 °C for 10 min under N2 gas resulted

in a crystallization into the high-k perovskite phase. The

highest capacitance density has been demonstrated for 15 nm

polycrystalline stoichiometric SrTiO3 films resulting in a capacitor

equivalent thickness (CET) of about 0.7 nm.

One of the main advantages of ALD is its inherent high

conformality, which for instance can be used to deposit

Figure 1 Common dielectric materials and possible oxidants by which they have been deposited. Materials that have been grown at room temperature are also indicated. Processes in blank spaces may have been demonstrated in literature but have not yet been directly demonstrated by Oxford Instruments. Material list is not exhaustive.

dielectric films for trench capacitors. Due to the self-limiting

nature of the ALD surface reactions, complex 3D structures

can be covered with films of equal thickness throughout the

structure, as long as sufficient flux of precursor and oxidant

has reached all surfaces. For thermal ALD processes conformal

coating of extremely high aspect ratio (>1000:1) has been

reported. In this case methods to enclose the precursor in the

reactor chamber, such as the automatic pressure control valve

(APC), are beneficial to limit the precursor usage per cycle

(note that the APC which is standard on the FlexAL system is

now also available as an option for the OpAL system). Due to

recombination of plasma radicals at surfaces, conformality for

plasma processes can be more challenging depending on radical

type and surface material. Nonetheless, conformal coating of

high aspect ratio structures is achievable by plasma deposition.

For instance for plasma ALD of SiO2, conformal coating of 30:1

trenches using an OpAL has been reported. Also for plasma

ALD of HfO2, high conformality can be obtained as shown in

Fig. 3. Here 25:1 trenches are coated by 20 nm HfO2. In general

Oxford Instruments ALD tools are equipped to deposit a wide

range of dielectric materials under demanding conditions, such

as room temperature deposition, stoichiometry control of ultra-

high k materials, and plasma deposition in 3D structures.

Figure 2 (a) Real and imaginary part of the dielectric functions ε1 (a) and ε2 (b), respectively, of as-deposited TiO2, SrO and of STO films.

The corresponding [Sr]/([Sr]+[Ti]) content ratio from RBS and [SrO]/[TiO2] cycle ratio are indicated for the STO films.

Potts et al., Chem. Vap. Deposition, 19, 125 (2013)Aslam et al., Phys. Status Solidi A 211, 389 (2013)Dingemans et al., J. Electrochem. Soc. 159, H277 (2012)Longo et al., ECS Trans. 41, 63 (2011), and ECS J. Solid State Sci. Technol. 2, N15 (2013)

Figure 3 SEM image of Si trenches (AR = 25:1) with conformal coating by plasma ALD of HfO

2 (20 nm) as shown by insets of SEM

images on the right at the trench corner and the trench bottom.

Al2O3 HfO2 SiO2 Ta2O5 TiO2 ZrO2 SrTiO3

Water ✔ ✔ ✗ ✔ ✔ ✔ ✗

Ozone ✔ ✔ ✔

Plasma ✔ ✔ ✔ ✔ ✔ ✔ ✔

Room Temp. ✔ ✔ ✔

8 PROCESSNEWS

1114

PROCESSNEWS 9

Katarzyna Korwin-Mikke a, Mark E McNie a, Lucia Alianelli b

a Oxford Instruments Plasma Technology, Yatton, BS494AP, United Kingdomb STFC Diamond Light Source, Oxfordshire, OX11 0DE, United Kingdom

etched lenses is to tune the process to operate at low pressures

and a low (controllable) DC bias. The other is to reduce the

number of ion impacts on the sidewalls by protecting the lenses

with sacrificial features that can be removed after the process.

In the Oxford Instruments Applications Laboratory, etch

processes for each approach were developed (with and without

compensating features – Fig.2). The results gave close to vertical

lens profiles (89.90°) without compensating features etched to

50µm depth with no mask undercut and controlled scallops to

below 50nm (Fig.3). This process was adapted and extended to

the lenses with compensation features to achieve etch depths in

excess of 70µm with smooth sidewalls (scallops <50nm), no mask

undercut or sidewall damage, vertical profile (89.94°) and clean

surfaces in open silicon areas (Fig.4).

The X-Ray silicon lens etch processes were carried out in a

PlasmaPro 100 Estrelas deep silicon etch tool (Fig.5). This

latest generation deep silicon etch system can trade high rate

performance for increased control to enable a very flexible set

of processes from high etch rate applications (>25µm/min) to

nanoscale etching. The lens processes are being transferred to a

third party commercial supplier for production of the lenses going

forwards.

Adapted from work presented at the International Micro Nano

Engineering (MNE) Conference, Sept. 2014

The trend in X-Ray optical devices, such as refractive lenses, zone plates, curved mirrors, multilayers and multilayer Laue lenses, is towards shrinking dimensions and/or deeper

optics.

Due to excellent properties, such as thermal x-ray absorption, diamond is highly desirable material for use in many optical instruments, however, due to cost of manufacturing, extreme hardness and resistance to chemical attack, diamond is a difficult material to realize structures suitable for x-ray lenses and this is why silicon is the leading material for x-ray lens production. Nanofocusing silicon x-ray lenses require not only high quality material but also high aspect ratio with vertical sidewalls and controlled roughness on the sidewalls to minimize aberrations and parasitic scattering respectively. The focus of this work was to develop the process for etching silicon x-ray lenses with good profile control and smooth sidewalls using the Oxford Instruments PlasmaPro 100 Estrelas etch tool.

To achieve high aspect ratio lenses with vertical profiles and

smooth sidewalls, a short cycle time is used in conjunction

with lower powers for less aggressive process conditions. The

passivation is regularly refreshed to maintain sidewall integrity

through rapid switching with controlled ion energies. Etching

microstructures on the samples with a high silicon exposed area

reduces the etch rate due to loading effects and may cause

undercut of the mask as the result of sidewall plasma attack on

isolated features (Fig.1) even when overpassivated. One of the

solutions to reducing the negative impact of the ions on the

The application of Bosch™ Deep Silicon Etch (DSiE) to the manufacture of x-ray lenses

Figure 1. The negative impact of the ions on etched X-Ray lens structure.

Figure 2. Device mask patterns. Left: Lens with compensation features; Right: Lens without compensation features.

Figure 3. SEM of a lens without compensation features etched to 50µm depth.

Figure 4. SEM of a lens with compensation features etched to 75µm depth. Figure5. PlasmaPro 100 Estrelas.

PROCESSNEWS 11

A proposed method for enhancing the efficiency of silicon solar

cells is to incorporate nanoparticles of gold or aluminium for

improved light capture. In order to develop practical nanoparticle

optimisation criteria, equipment which is suitably scaled for

research, but traceable to volume production is required. To

synthesise nanoparticles, precise and repeatable deposition of thin

metallic films is done using a multiple target magnetron sputtering

tool and post-deposition with an in-situ heater.

Magnetron sputtering is a well established large area technique

for the deposition of metals. In this investigation we have prepared

uniform sputtered films varying in thickness from 200nm to less

than 10nm for nanoparticle seed layers. Deposition rates are

high and result in short sputtering times for the film thickness

required so a cyclical deposition mode is used with short deposition

times and low discharge powers. Resistivity data from multi-

layers formed by successive passes beneath the deposition flux

demonstrates the thickness control that can be met in this mode

which mimics an in-line sputter configuration.

When the substrate is oscillated beneath the target, a shaper is

used to correct the arrival flux such that the sputtered thin films are

uniform and thin. The shaper can be further refined to permit the

use of a range of instantaneous deposition rates which may in turn

influence the morphology of the thin film. When depositing thin

films for short processing times there is a stringent need for process

repeatability. Au film sputtered to date has been 4 nm thick,

determined by measuring the resistivity with a four point probe.

We show examples of nanoparticle formation by post deposition

annealing. These indicate that for successful aluminium

nanoparticle formation, a full in vacuum process is necessary, while

for gold ex-situ annealing may be practical. This is an important

factor in enabling research into the impact of particle size and

distribution to the silicon solar cell efficiency.

Here we demonstrate the formation of aluminium nanoparticles

from a 10nm thick aluminium film. Figure 6 shows SEM images

of film deposited at room temperature and annealed at 600 °C in

the same chamber, using a high temperature substrate table. The

images of before and after annealing clearly show the presence of

nanoparticles.

Figure 1 (a) SEM image of 10nm Al Film deposited at room

temperature; (b) SEM image of Al NPs obtained by annealing Al

film (a) at 600 °C

Au and Al nanoparticles have been formed by sputtering and

annealing. Future work will involve studying the size, shape and

distribution as a function of film thickness and the temperature

of the process and anneal. Other factors such as substrate

orientation may also play a role in nanoparticle formation.

Fabrication of metallic nanoparticles has been demonstrated in a

combined sputtering and anealing tool using a low-cost method.

This work was supported

by FP7 project

246331nanoPV.

ICP plasma etching of tapered vias in silicon for MEMS integration

Metallic nanoparticle formation by sputtering and annealing

Zhong Ren and Mark E McNie, Oxford Instruments Louise R. Bailey, Cigang Xu, Brodie Mackenzie & Gary Proudfoot, Oxford Instruments

This paper reports a technique to achieve variable tapered angle

on an etched TSV profile by means of an ICP etch (PlasmaPro

100 Estrelas), based on a SF6-C4F8 chemistry. Monotonic profile

angles in the range of 60-80º have been achieved on 10-50µm

wide vias through adjustment of the C4F8/SF6 ratio (controlling

F concentration in plasma) [Figure 2]. An etch rate of 10µm/min

was obtained on 60º profile TSV etch, with sidewall roughness of

<1µm. However, the sidewall became significantly rougher (3µm)

when profile was more than 68º. This was due to a reduction

of the isotropic etch in the lateral direction and a lack of ion

bombardment to remove polymer at shadowing area from the

undercutting mask. Profile curvature was dominated by vertical:

lateral etch balance. As a result, a 72º profile via was successfully

realized on 20-50µm wide vias with sidewall roughness of

<300nm and no overhang at the top of via [Figure 3].

Figure 1. Illustration of MEMS 3D integration and wafer-level packaging with TSV technology

Figure 2. Sidewall angle change on TSV profile with increase of C4F8 ratio

Figure 3. Tapered via (72º profile): Roughness of 180nm on sidewall, without any overhang at top

(a) (b)

10 PROCESSNEWS

With extensive applications of CMOS in

smart phone and other portable equipment

there is demand for an increase of integrated

component density to achieve large capacity

memory and high processing speed.

Compared to traditional wire-bonding methods, through silicon

vias (TSVs) provide a short interconnect path with as high as

possible density. Therefore, in recent years conductive TSVs have

become one of the most important components for electrical

connection of stacked devices in the semiconductor industry,

to replace wire bonding. Moreover, usage of TSV techniques is

able to connect and control stacked MEMS modules in order to

save space [Figure 1]. For increased throughput and decreased

fabrication difficulty, silicon wafers can be thinned to 50-100µm

thickness with a handle wafer. This reduces the aspect ratio

required to etch TSVs and subsequent thin film depositing

steps. Therefore, the typical size of TSVs is 10-50µm in diameter

and 50-100µm depth. State-of-the-art wafer-level bonding

techniques are able to integrate heterogeneous materials (e.g.

III-V compounds, ferroelectric, etc) on a silicon base chip with

multiple functions. These pioneering ideas are also creating new

research opportunities for MEMS and opto-electronic integration.

This requires a controllable TSV (60-85º) technique with a wide

material compatibility, in order to fill the via completely with

contact metal.

Using high density plasma technique, the Bosch process based

on cycling deposition and etch steps is usually used to etch TSVs

and provides a vertical profile (88-90º) with a high aspect ratio

(AR). The achievable angular range is too limited to approach to

a tapered profile. Through an isotropic etch, a tapered profile

(<85º) can be achieved, but usually with overhang at top of

via. This would result in void formation in subsequent seeding

and filling steps. To realize a void-free via, this overhang may

be removed by means of a subsequent maskless etch step. But

it results in the loss of a few microns silicon on the surface and

enlarges the critical dimension (CD) of the TSV. The approach may

not be acceptable where there are device areas on the surface.

12 PROCESSNEWS

An additional Oxford Instruments PlasmaPro 100 plasma

etch system was recently ordered by the Center for Micro

and Nanoscale Research and Fabrication at the University of

Science and Technology of China (USTC) Hefei city, Anhui

Province, adding to their already significant installed base of

our leading etch and deposition systems. The systems are

installed in USTC’s newly opened cleanroom and will be used

for fundamental research into the increasingly important field

of quantum information processing.

Multiple Oxford Instruments plasma systems, including a

PlasmaPro 100 ICP380 and PlasmaPro NGP 80 RIE, and

PlasmaPro 100 PECVD deposition tools were already installed

in USTC’s new facility during the past year.

“Our latest Oxford Instruments plasma etching system will

enhance the cutting edge research capabilities in Quantum

Information Processing, currently being undertaken at our

excellent new facility.” Said Prof Zhu, from USTC, “We chose

Oxford Instruments systems as we have found that they offer

extensive process capabilities, and great flexibility, backed by

excellent support and service packages. These tools will allow

our researchers to push the limits in micro- and nanoscale

fundamental research.”

Prof Zhu continued, “USTC has a very strong background in

both nanoscale science and engineering, and this new state-

of-the-art nanofabrication facility aims to drive collaborative,

interdisciplinary, and fundamental research in the micro- and

nano-scale.”

University of Science and Technology of China orders an additional plasma etching system for quantum information processing

2D plenary sessions attracted enormous interest at recent Beijing Nanotechnology Seminar

Nanoparticle and nanosphere mask for etching of ITO nanostructures and their reflection propertiesCigang Xu*1, Ligang Deng1, Adam Holder1, Louise R. Bailey1,

Caspar Leendertz2, Joachim Bergmann3, Gary Proudfoot1,

Owain Thomas1, Robert Gunn1

Au nanoparticles and polystyrene nanospheres were used as

a mask for plasma etching of an indium tin oxide (ITO) layer.

By reactive ion etching (RIE) processes, the morphology of

polystyrene nanospheres can be tuned through chemical or

physical etching, and an Au nanoparticle mask can result in

ITO nanostructures with larger aspect ratio than a nanosphere

mask. During inductively coupled plasma (ICP) processes, Au

nanoparticle mask was not affected by the thermal effect of

plasma, whereas temperature of the substrate was essential to

protect nanospheres from the damaging effect of plasma.

Physical bombardment in the plasma can also modify the

nanospheres. It was observed that under the same process

conditions, the ratio of CH4 and H

2 in the process gas can

affect the etching rate of ITO without completely etching the

nanospheres. The morphology of ITO nanostructures also

depends on process conditions. The resulting ITO nanostructures

show lower reflection in a spectral range of 400–1000nm than

c-Si and conventional antireflection layer of SiNx film.

ITO nanostructures obtained after etching (scale bar = 200 nm)

1 Oxford Instruments Plasma Technology, North End Road, Yatton, Bristol BS49 4AP, UK

2 Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany

3 Leibniz Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany

The full article appeared in PSSA Journal DOI:10.1002/pssa.201431228(2014)

PROCESSNEWS 13

To find out about our forthcoming seminars:

www.oxford-instruments.com

Leading high level international speakers

dominated the Oxford Instruments two day

technical seminar hosted at the prestigious Institute

of Physics in Beijing recently. This event focused

on practical applications, techniques and advances

during a half day ‘2D materials’ plenary session,

and many other applications areas.

Expert speakers from key establishments in China, Europe and

the USA gave talks, as did Oxford Instruments specialists, keeping

participants abreast of the latest technologies and trends in many

current and future industry research topics, including:

• Recent Advancements in 2D Materials at Manchester,

Dr. Aravind Vijayaraghavan, National Graphene Institute in Manchester, UK

• ALD applications for power semi and advanced materials

Prof. Erwin Kessels, Tue Eindhoven, NL

• Nanoscale Terahertz Imaging and Spectroscopy of 2D Materials,

Prof. Yukio Kawano, Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, Japan

• Superconductors and Spin-Based Quantum Processors

Prof. David Cory, University of Waterloo, Canada

• Exchange Induced Interfacial Field from Magnetic Insulators

Prof. Guoxing MIAO, Institute for Quantum Computing, University of Waterloo, Canada

• TEM studies of Nano Core/Shell Hetero structures EDS mapping

at the atomic level

Prof. Robert Klie, University of Illinois Chicago

• Fabrication of dielectric coatings using Optofab3000 Ion Beam

sputtering deposition system

Dr. Xiaodong WANG, Institute of Semiconductors, CAS

• Structure and properties of graphene and graphene-like 2D

materials by STM

Prof. Yeliang WANG, Institute of Physics, CAS

• Nano-structure fabrication by ICP-RIE for optical devices

Dr. Zhe LIU, Institute of Physics, CAS

It was great to host such high calibre speakers and attendance at

the IOP. This event showcased the breadth and diversity of Oxford

Instruments tools and applications, and also it offered a good

opportunity for the wider Nanotechnology research and fabrication

community to meet and share their experiences and vision for the

future of this exciting area.

14 PROCESSNEWS PROCESSNEWS 15

1114Use of atomic layer deposition for MEMS & NEMS applications

Watch again

Webinar hosted by the MEMS Industry Group

Atomic layer deposition (ALD) with its growth control

and unique properties can be used to grow an increasing

variety of films in complex structures. As MEMS and

NEMS applications are becoming more advanced, this

webinar discussed important aspects of ALD and how

they can be applied to MEMS.

Mechanical properties that are important for MEMS, such

as stress, were discussed for thermal and plasma ALD.

Several examples from the literature of how ALD films

can be used in MEMS applications were demonstrated

and discussed.

Presented by Oxford

Instruments’ ALD Technical

Sales Specialist Dr. Harm

Knoops. Before his current

position, Harm investigated the

fundamentals and applications

of atomic layer deposition (ALD)

at the Eindhoven University of

Technology.

Dust management in silane PECVD systems

Dr Mike Cooke, CTO, Oxford Instruments Plasma Technology

Dust creation in plasma enhanced chemical vapour deposition

(PECVD) tools can affect user safety, system reliability, and process

quality. There are two main issues:

- Upstream dust creation, from homogeneous gas reactions in

mixtures of silane and oxidising gases. This can add particles to

wafers, and in the worst case block a gas entry line.

- Downstream dust accumulation of partially reacted silane.

This rarely affects process quality, but can be a serious safety

concern.

Both are made worse the more intensively the tool is used, and the

higher quantity of silane used. We have seen a steady increase in

the total silane flow in PECVD processes, as higher rate processes

are introduced. ICPCVD processes are also becoming more widely

used, and such processes normally use 100% silane.

Regrettably, there have been very serious silane incidents across

the semiconductor industry, almost all involving the silane gas

cylinder or gas delivery. PECVD processes themselves have been in

regular, safe use for decades. This article is not concerned with safe

delivery of silane to the gas box, nor with management of effluent out of

the tool, but only with good practice in managing the PECVD tool.

Upstream powderOxford Instruments assesses the likelihood of upstream powder formation

when a tool is ordered or upgraded. We strongly recommend that

changes to the gases used or increases in maximum flow rates are only

done in consultation with Oxford Instruments. For example, we may

recommend splitting the gas manifold, so that gases mix closer to the

process chamber, or adding upstream pressure monitoring devices to

alert the user to potential line blockages.

Silane reacts far more readily with oxygen than with nitrous oxide, so

we recommend avoiding having oxygen and silane in the same gas box

where possible. We have developed and recommend plasma cleaning

processes using CF4 and N

2O rather than the CF

4/O

2 mixture used

historically.

Good practiceWhere oxygen and silane share some common pipe work, but are

not used together:

• Flush the line, preferably with an inert gas, between silane and

oxygen use

• At least 5 minutes, at least 100 sccm flow

• Pump the line thoroughly before first use of silane and before

first use of oxygen

• At least 20 minutes pumping for a gas box up to 5 metres

from the chamber

• Venting. Use the same procedure before and after venting a

chamber, to prevent air and silane meeting.

The same advice applies to gas delivery lines both to downstream

injection points in ICPCVD (‘gas rings’) and to PECVD showerhead

entry points.

DiagnosticsThe wafer is a good indicator that powder is forming upstream,

because it is often visible to the naked eye. Inspect the wafer under a

bright light for signs of roughness, especially in a pattern matching the

showerhead holes. Such powder might be formed at the showerhead

itself, and eliminated by process changes or by renewing the showerhead.

Issue Worst case fault

Mitigations

Silane – oxidiser reaction up-stream

Worse for silicon dioxide PECVD

Gas line blocks

Mix silane and oxidiser at the lowest possible pressure, close to the process chamber

Use N2O oxidiser not oxygen

Use dilute silane, not 100% silane

Perform regular checks for signs of lines blocking

Investigate if there is an increase in particles on the wafer

Pump and purge lines between gas box and chamber thoroughly before venting

Partially reacted powder downstream, building up in the vacuum line to the pump

Worse for amorphous silicon or silicon nitride PECVD

Dust explosion

Perform regular plasma cleaning

Inspect vacuum line regularly

Run a test wafer and a high flow (>500sccm) of gas and no plasma

to detect if powder is blowing down the line. Irregular mass flow

controller (MFC) behaviour, such as long stabilisation time or

failure to achieve higher flow, could be an indication of powder.

(Inadequate upstream pressure or a faulty MFC should also be

considered).

If a line is contaminated, repeated partial venting with inert gas and

pumping out can sometimes clear powder. Heavy contamination

might need partial disassembly and blowing through to clear

powder, or even renewal of pipe sections.

Downstream powderThis problem is rare, but is also less well known. Type ‘dust explosion’

into a search engine if you are unfamiliar with the issue. White

downstream dust from silicon dioxide PECVD is only a problem to

mechanical components (pumps and valves) and rarely travels back

to the process chamber unless a vacuum joint is opened without first

venting the chamber..

Orange or red dusts in exhaust lines of PECVD tools used for

silicon nitride or amorphous silicon deposition are potentially

hazardous, as well as giving rise to mechanical troubles. If such

powder builds up to more than a millimetre or so, then it can be

dislodged and create a dust cloud in the pipe. If this happens when

pumping down a chamber full of air, the conditions are satisfied for

a dust explosion. A bulletin highlighting this hazard has been written

and is available on request. Contact ptsupport@oxinst.com

Good practicePlasma clean the chamber as recommended by Oxford Instruments.

This will help to oxidise downstream dust, as well as clean the

process chamber. Inspect the vacuum line regularly. Make the first

inspection after 3 months use, then adjust the interval based on the

amount and type of dust seen. Avoid building up more than 1mm

thickness of dust on the pipe wall.

As with all safety matters which depend on how the tool is used, it is

the user’s responsibility to ensure safe operation - Oxford Instruments

are not safety consultants, but will share our own best practice with

our customers.

To view this webinar:

www.oxford-instruments.com/aldformems

16 PROCESSNEWS

We recently signed an agreement with Asher Sonego to provide comprehensive service support to our customers in Israel.

Asher just finished an intensive training course at Oxford Instruments Plasma Technology’s UK manufacturing facility.

“I am extremely impressed by Oxford Instruments leading edge products and commitment to their customers, to provide the very best tools and world-class service and support”, said Asher, “I am excited to be a part of the team and represent the company in Israel.”

Our courses are designed to improve system maintenance and process techniques for engineers and technicians. We ensure our customers get the most from their Oxford Instruments system.

Benefits

• Courses are run by our dedicated training officer supported by our experienced process and system engineers, who know the systems and understand your individual requirements

• We aim to provide the very best training, tailored to meet with your individual needs

• We limit numbers on each course, to ensure best training possible

Book early to ensure your place for 2015 trainingFor more information: www.oxford-instruments.com/trainingEmail: plasmacs@oxinst.com

www.oxford-instruments.com/plasma for more information or scan the code...

This publication is the copyright of Oxford Instruments plc and provides outline information only, which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or regarded as the representation relating to the products or services concerned. Oxford Instruments’ policy is one of continued improvement. The company reserves the right to alter, without notice the specification, design or conditions of supply of any product or service. Oxford Instruments acknowledges all trademarks and registrations. © Oxford Instruments plc, 2014. All rights reserved. Ref: OIPT/ProcessNews/2014/02

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Oxford Instruments Plasma Technology focuses for the future

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Mike Smyth, EMEA BusinessManager, Oxford InstrumentsPlasma Technology and Asher Sonego, shake hands while exchanging the signed Agency agreement