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Apr 7, 2016 - A Newsletter from Oxford Instruments Plasma Technology. Follow us on. ..... Technology 2016 training cours
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PROCESSNEWS

A Newsletter from Oxford Instruments Plasma Technology

Follow us on...

IN THIS ISSUE: Providing leading edge tools and processes to key markets worldwide

2  Two dimensional materials and heterostructures

Optoelectronics Nanotechnology Discrete Devices Sensors

4  Collaboration proves a ‘win-win’ for TU/e and Oxford Instruments

3  Low temperature plasma assisted ALD of conductive films

6  PlasmaPro® systems bought for Chinese LED Manufacture 7  Training: buy one get one half price 8  The Application of Bosch™ Deep Silicon Etch to the Manufacture of X-Ray Lenses 10  Micromachining silicon structures on thin membranes using plasma etching 12  Power device development enabled through University of Glasgow collaboration 13  Energy savings win us a ‘Go Green’ award 13  Record numbers attend 4th BTNT seminar in Chennai, India 14  New etching process for Magnetic RAM developed by Cornell and Oxford Instruments 16  Watch our informative webinars

www.oxford-instruments.com/plasma PROCESSNEWS 1

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Two dimensional materials and heterostructures

Low temperature plasmaassisted ALD of conductive films

Dr Ravi Sundaram, Oxford Instruments Plasma Technology

Harm Knoops, Thomas Sharp, Annika Peter, Owain Thomas, and Robert Gunn, Oxford Instruments

Vapour deposition techniques have gained a lot of interest for growth of two dimensional (2D) materials1-4. The ability to grow large area graphene has spurred research into vapour deposition of a wide variety of atomically thin layered materials.

Many applications have a limited thermal budget for processing, especially when organic materials are involved or diffusion of elements has to be minimized (e.g. dopants in electronic devices).

In the recent past there has been a growing interest in studying atomic planes of these Van der Waals solids and build 2D

The Oxford Instruments Nanofab® is ideal for this field of research as it combines several essential features for high performance 2D material deposition:

• High temperature (1200 ºC) table • Capable of handling up to 200 mm wafers • Shower head technology • Automatic load lock for wafer handling • Plasma enhancement via in chamber (parallel plate ) plasma

Since ALD relies on thermally activated reactions, ALD at low temperatures can be a challenge. A paper presented at the BALD 2015 conference in Tartu, Estonia discussed low temperature plasma-assisted ALD of conductive films where the ALD of TiN and ZnO in the Oxford Instruments FlexAL® remote plasma ALD system serve as case examples.

or remote plasma via ICP

Using a multistep ALD process as shown in Fig. 1, allows deposition of Pt at room

One of the key requirements for developing robust 2D

temperature by O2 plasma and H2 plasma in the cycle [Mackus et al., Chem. Mater.

materials deposition processes is the ability to efficiently

25, 1769 (2013)]. Similarly, this work showed that interleaving H² plasma in an ALD

technologies and processes for large area deposition of these

deliver liquid and solid state precursors in addition to

process for ZnO using ZnEt2 (DEZ) and O2 plasma, allows relatively low resistivity

materials need to be developed.

traditional gases. We offer flexible options for liquid/solid

values, i.e., 5.7 mΩcm for a ~45 nm film at temperatures of 100°C.

heterostructures by stacking layers with complementary characteristics to achieve novel functionality . For successful 5

scaling up of prototypical applications demonstrated to date,

Chemical Vapour Deposition (CVD) has been one of the most successful techniques for the large area fabrication of nanostructured materials such as graphene, carbon nanotubes



precursor delivery. Example:

MoCl5, Mo(CO)6, W(CO)6,

For deposition of metals and metal nitrides that are difficult to reduce from their

DTBSe, DETe etc)

oxide, exposure to oxygen should be avoided. To increase reactivity for ALD of those

• Multiple precursor pod options for depositing a combination

materials plasmas with higher ion energies can be used. Low-resistivity titanium nitride was obtained from the metal-organic precursor Ti(NMe2)4 (TDMAT) and mixed

of 2D materials

and other 1D/2D nanomaterials.

N2/H2 plasma at 200°C. Through precise control of the plasma conditions we were

We have demonstrated growth of monolayer graphene and related graphene-like allotropes using this system. Recently, we Nanofab with precursor delivery system.

have developed a thermal CVD route to synthesize hexagonal Boron Nitride (hBN) and we are currently investigating other 2D materials.

Current library of 2D materials investigated to date5.

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able to achieve a resistivity of 250 µΩ∙cm at 26nm thickness and even 180 µΩ∙cm for Examples of graphene and hBN growth.

a 74 nm film as shown in Fig. 2. TiN from TDMAT therefore offers a viable alternative for devices where chlorine-containing precursors risk device degradation. Control

References

of plasma properties and multistep ALD processes are expected to provide the best

[1]. Li, X et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 324, 1312-1314 (2009) [2] Bae, S. et al. Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nat Nanotech. 5, 574 (2010) [3] Ismach, A. et al. Toward the Controlled Synthesis of Hexagonal Boron Nitride Films. ACS Nano, ,6, 6378 (2012) [4] Zhan, Y et al. Large-Area Vapor-Phase Growth and Characterization of MoS2 Atomic Layers on a SiO2 Substrate. Small, 8, 966 (2012). [5] Geim, A.K and Grigorieva, I.V., Van der Waals heterostructures, Nature, 499,419 (2013)

route to deposition of conductive films by ALD.

For further information on our toolset please email: [email protected]

Figure 1. A schematic representation of the various steps in a multistep process. For low temperature ZnO ALD, B is an O2 plasma and C is an H2 plasma.

Figure 2. The film resistivity as a function of thickness for TiN deposited from TDMAT. Relatively low resistivity values are obtained for thicknesses above 20 nm.

PROCESSNEWS 3

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Collaboration proves a ‘win-win’ for TU/e and Oxford Instruments Sonja Knols, Eindhoven University of Technology

To be able to keep innovating its products, Oxford Instruments invests in close cooperation with academic research groups. One example is the Plasma and Materials Processing group of Eindhoven University and Technology.

low temperatures. “For CVD processes, typically temperatures

He immediately gives an example. “Some time ago, PhD

of over a 1000 degrees Celsius are needed. That is often fatal for

student Harald Profijt developed a method to manipulate the

applications in semiconductors because the high temperature

energy of the deposited atoms by applying an RF voltage on

increases the diffusion of the atoms, which makes it harder to

the substrate. Normally, in plasma assisted ALD, you need

place them at the right spot. We want to have a process that

the incoming ions to have as low an energy as possible. But

yields materials of high quality at lower temperatures. This is

sometimes, the process would improve if you were to increase

especially important for the two-dimensional heterogeneous

that energy a little, thereby increasing the mobility of the

“Our cleanroom facilities are vitally important for our research”

layers I am working on, since at lower temperatures less

atoms at the surface. So now we can offer that option to other

diffusion of atoms between the layers will occur.”

clients too.” Furthermore, Oxford profits from the extensive

says associate professor Ageeth Bol.

Two-way street

Ageeth Bol holds a PhD in physical chemistry and returned to academic research in 2011, after a decade of working in industry. “The presence of the cleanroom facilities here in Eindhoven certainly was a selling point for me in deciding where I wanted to go,” she says. Bol works on the development of new production processes for graphene-like, two-dimensional materials. “To be able to make these very thin layers of materials, you need to have nanometre control over the layer thickness. The Plasma and Materials Processing group I work in has in-depth knowledge of a specific method to produce these layers.” This so-called plasma-assisted atomic layer deposition (ALD) is a technique that makes use of gaseous phases of materials, which are alternately flushed onto a surface. Carefully picked precursor molecules react with specific molecular groups at the surface in a self-limiting way. “That is one of the advantages of ALD over chemical vapour deposition (CVD),” Bol explains. “With ALD, as soon as all the reactive sites are used, the reaction stops. This results in very thin and even layers.”

Replacing scotch tape The group Bol is working in, is interested in optimising these type of ALD processes for a variety of applications, such as thinfilm solar cells and new types of semiconductor devices. “My

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infrastructure in the cleanroom facility, he says. “At Oxford, we have a relatively small ALD lab. The university campus hosts a

Supplier Oxford Instruments is heavily involved in this type of

dedicated cleanroom with all kinds of diagnostic tooling. The

adjustments, she explains. “They help us in customising the

research done there on ALD-processes gives us insight into

machine for our specific needs. In fact, one of their employees

what is happening inside the reactors during the deposition.”

personal focus lies in the usage for two-dimensional layers,

works here in Eindhoven, to make sure the lines are as short

such as graphene. This is important for a new generation

as possible. This employee is technical sales specialist Harm

of nanoelectronics. Even known materials start to behave

Knoops. “For us, this cooperation is a win-win situation,”

differently when you force them into a 2D architecture.”

he says. “Whenever the researchers in Eindhoven publish an

At present, the most sophisticated production method for

article on new results achieved with our machines that helps

these types of structures is the ‘scotch tape method’: you

me to show other potential clients the possibilities of our

stick something to the surface, and rip off a single layer of

equipment.” The cooperation is a genuine two-way street, he

molecules. “Of course, this is not the most reproducible way

emphasises. “When their research requires new options we try

to do it, and more importantly: it is certainly not scalable for

to co-develop them. But also the other way around, when we

industrial purposes.”

have developed some new features they can test them for us.

Bol’s research strongly leans on the cleanroom facilities, in

And their publications act as independent quality markers for

which Oxford Instruments play an important role. “Here in

our products.” For the ALD machines, Oxford Instruments’ main

Eindhoven, we have the equipment to both fabricate and

market lies in research institutes and universities. “Nothing sells

analyse devices. Ranging from lithography and deposition tools

better in that sort of environment than refereed publications in

to a scanning electron microscope and X-ray photoelectron

high impact scientific journals.”

These insights also help Bol in her quest for new production processes. After receiving the prestigious Vici grant in 2014, she was recently awarded an ERC Consolidator Grant as well. With those funds, she will spend the next few years stretching the current limits of the technique: “When we can actually fabricate truly two-dimensional layers, I want to take it to the next level: stack two-dimensional layers made out of different materials. That way we can combine different properties in one device. We will have to do that at low temperatures to prevent the different layers from mixing, since that will deteriorate the quality of the materials. And if we can achieve that, it will open up a whole new field of possibilities for even smaller electronic circuits with totally new properties.” Our thanks to TU Eindhoven for allowing us to publish this article

spectroscopy to characterise the layers we have deposited.” The research group uses advanced commercial tools and ones they have partly constructed themselves. “I am going to work with ALD machines from Oxford Instruments, which have been configured to meet our needs. We want to be able to play around with different parameters of the ALD process,” Bol explains. The researchers are particularly interested in relatively

Image by Mikhail Ponomarev

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PlasmaPro® systems bought for Chinese LED manufacture

Training: buy one get one half price

Ground breaking research into graphene and other 2D materials

Training Offer!

Are you looking for advanced maintenance training or simply training for new users to be safe and competent in the use of your Oxford Instruments tools?

We have developed a range of courses giving our customers the choice to suit you and your users different levels. Book your place on any Oxford Instruments Plasma Technology 2016 training course by 31st May 2016 and your colleagues can book a place on the same course for half

High tech Chinese manufacturer, Enraytek Optoelectronics Co recently purchased several leading edge Oxford Instruments PlasmaPro 800 PECVD systems for the manufacture of their High Brightness LEDs. Enraytek’s key products are High Brightness LEDs for TV

Says Mr.Xu Chunchao. Vice President

backlighting and LED lighting, with manufacturing capability

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‘2D Materials Processing Technology’

7th April 2016, National Graphene Institute, University of Manchester

Book one get one 1/2 price Offer ends 31/05/2016

0316 W FR or EE ks ho p

is taking place at The University of Manchester’s new National Graphene Institute using multiple plasma etch and deposition systems. The workshop includes a wide range of talks presented by the University of Manchester National Graphene Institute, outside guest speakers and Oxford Instruments process and technology experts. It is open to all those people working in industry and academia, with an interest in recent progress plus future trends in research and development, and the application of 2D materials. Talks will include: for 2D materials • ALD Chris Hodson, Oxford Instruments Process Developments • Etch Bob Gunn, Oxford Instruments

Suspended 2D Materials • Truly Jose Luis Sambricio Garcia, Manchester Uni

Materials: Technology Requirements for Potential • 2D Applications in Electronics Prof.Dr.-Ing. Max Lemme, Universität Siegen

Process Technology for 2D Materials • ICP-CVD Michael Stokeley, Oxford Instruments

and Processes for Deposition of 2D • Technology Materials and Heterostructures Dr Ravi Sundaram, Oxford Instruments

Dimensional Contact to a Two Dimensional • One Material Gregory Auton, University of Manchester Developments in Low Temperature • Recent Measurement Tools for Graphene Dr John Burgoyne, Oxford Instruments

• Technical posters • Tour of the National Graphene Institute

demanded by the LED industry.

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The Application of Bosch™ Deep Silicon Etch to the Manufacture of X-Ray Lenses Katarzyna Korwin-Mikkea, Mark E McNiea, Lucia Alianellib, a Oxford Instruments Plasma Technology bSTFC Diamond Light Source, Oxfordshire, UK

The trend in X-Ray optical devices, such as refractive lenses, zone plates, curved mirrors, multilayers and multilayer Laue lenses[1], is towards shrinking dimensions and/or deeper optics.

respectively. The focus of this work was to develop the process

Due to excellent properties, such as thermal resistance, low

passivation is regularly refreshed to maintain sidewall integrity

x-ray absorption, diamond is highly desirable material for

through rapid switching with controlled ion energies. Etching

use in many optical instruments[2], however, due to cost of

microstructures on the samples with a high silicon exposed area

manufacturing, extreme hardness and resistance to chemical

reduces the etch rate due to loading effects and may cause the

attack, diamond is a difficult material to realize structures

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

suitable for x-ray lenses and this is why silicon is the leading

on isolated features (Fig.1) even when over passivated. One of

material for x-ray lens production. Nanofocusing silicon x-ray

the solutions to reducing the negative impact of the ions on the

etch depths in excess of 70µm with smooth sidewalls (scallops

latest generation deep silicon etch system can trade high rate

lenses require not only high quality material but also high

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

25µm/min) to

the sidewalls to minimize aberrations and parasitic scattering

number of ion impacts on the sidewalls by protecting the lenses

for etching silicon x-ray lenses with good profile control and smooth sidewalls in the Bosch process DSiE. 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

with sacrificial features that can be removed after the process. Figure 1. The negative impact of the ions on etched X-Ray lens structure.

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

Figure 2. Device mask patterns. Lens with compensation features

Figure5. PlasmaPro 100 Estrelas

The X-Ray silicon lens etch processes were carried out in a PlasmaPro 100 Estrelas deep silicon etch tool (Fig.5). This

In the Oxford Instruments Applications Laboratory, etch processes for each approach were developed (i.e. with and

Lens without compensation features

Figure 4. SEM of a lens with compensation features etched to 75µm depth

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

[1] L Alianelli, K J S Sawhney, R Barrett, I Pape, A Malik M C Wilson, Optics Express (2011) vol. 19, no.12, 11120-11127 [2] A M Malik, O J L Fox, L Alianelli, A M Korsunsky, R Stevens, I M Loader, M C Wilson, I Pape, K J S Shawhney, P W May, Journal of Micromechanics and Microengineering 23 (2013), 125018 (7pp) Adapted from work presented at the International Micro Nano Engineering (MNE) Conference, Sept. 2014 An article ‘Aberration-free short focal length x-ray lenses’ was published in Optics Letters Lucia Alianelli, 1* Manuel Sánchez del Rio, 2 Oliver J. L. Fox 1,3 and Katarzyna Korwin-Mikke 4 *Corresponding author: [email protected]

nanoscale etching. The lens processes are being transferred to a third party commercial supplier for production of the lenses going forwards. (Article published in Optics Letters (Impact Factor: 3.29). 12/2015; 40(23):5586. DOI: 10.1364/OL.40.005586) Available from: https://www.researchgate.net/publication/284519056_Aberration-free_ short_focal_length_x-ray_lenses 1 Diamond Light Source Ltd., Chilton, Didcot OX11 0DE, UK 2 European Synchrotron Radiation Facility, BP 220 38043 Grenoble Cedex, France 3 School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK 4 Oxford Instruments Plasma Technology, Yatton, BS49 4AP, UK

Inventory Sale Now On! Up to 75% off list price from our new online catalogue We’re selling some quality items of surplus stock, previously purchased for our leading edge process tools. Take a look at the variety of spares available from pumps and chillers to

showerheads and clamps, panels and heater mats to spacers and cables.

• Unused stock • Up to 75% off list price • Efficient worldwide delivery

We have a variety of stock at discount prices, so have a browse and see what you find! 8 PROCESSNEWS

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Micromachining silicon structures on thin membranes using plasma etching Zhong Ren, Mark E McNie, Colin C Welch, Mike Cooke Oxford Instruments

Micromachining detailed silicon structures on thin membranes is regarded as one of the primary MEMS fabrication techniques, but also one of the more difficult processes.

This tool can operate successfully over more than an order of

There is a very sharp transition in chemical loading effect, as

removing polymer which enables a full cycle of deposition,

the silicon clears from the membrane layer whilst the lateral

break through and etch to be as low as 1 s.

heat dissipation from etching structures on a membrane

Results given here used cycle times up to 2.5s. Whilst an

decreases significantly as the membrane is approached. The

electrostatic chuck (ESC) clamps over the whole wafer surface

exothermic etch reaction can even cause the resist pattern

in contact and to conductive layers on the membrane, where

and etch passivation to degrade when the associated heat is

membranes are proud of the clamping plane the gap is large

focused in a small area.

and so heat removal efficiency via Helium back side cooling is

There is a need for very high etch rates to remove bulk material

dramatically reduced. Thus in order to be able to etch structures

to expose the membrane, but also a need for very precise

on membranes without overheating and maintaining profile

profile control in fabricating micro- or nano-scale features. The

control, a low power process capability is also required.

bulk etch can use an anisotropic wet etch that is selective to the

Three devices have been realized using this combination of

crystallographic planes, such as KOH or TMAH. The wet

high rate and precision processing: a micro-resonator high-Q

chemistry is only suitable for low aspect ratio (AR) features and

cavity with a vertical profile (90º) and uniform scallop size

results in a characteristic slope at a 54.74º for silicon

(Fig 1&2); a fine periodic deep grating with 50:1 high AR

wafers that limits geometric freedom and packing density[1].

(Fig 3&4); and a large length-width ratio cantilever on a

A Bosch (or gas-chopping) deep silicon etching (DSiE) process

photoresist (PR) membrane where avoiding mask overheating

with alternating deposition and etch steps can realize a vertical

and not damaging the polymer film underneath the cantilever

profile at high aspect-ratio (AR) with etch rates of up to 30µm/

was key (Fig 5&6). Moreover, high quality and smooth sidewalls

min, and can etch arbitrary shapes as defined by the mask

were also achieved on these etched structures.

magnitude of inductively coupled plasma (ICP) source power, from 5 kW, opening the possibility of both high rate and precision, low rate processes in the same chamber. The minimum time of a single process step is 100-300 ms for

Figure 2. Micro-resonator structure: (a) side view with vertical profile and a 60 µm etch depth; (b) sidewall roughness (scallop size) of 78nm

Figure 5. Challenges on Si membrane etch: (a) grass and striations in corners; (b) optimised etch gives striation-free and smooth sidewall; (c) PR mask burnt out during Bosch etch; (d) optimised etch avoids overheating on PR mask.

Figure 3. Schematic section of gratings in a SOI wafer: the back cavity defined by a high rate Bosch etch and fine period optical gratings realised in the device layer using a precision Bosch etch.

pattern[2, 3] with high packing density. This paper presented at MNE 2015 reports a technique which addresses these problems, and gives example results on three typical structures, using a DSiE tool (PlasmaPro 100 Estrelas)

Figure 6. Si cantilever: (a) Illustration of cantilever fabrication in Si membrane by means wet-etching and Bosch process; (b) 5 mm length × 200 µm width × 50 µm thickness cantilever; (c) and (d) Enlarged view of the cantilever after polymer removal.

in the Bosch process (SF6-C4F8 chemistry). Most DSiE process tools are optimised for high rate anisotropic etch but may be limited in their ability to perform precision, lower rate processes. Such fast switching etch processes often need a significant minimum power to maintain the plasma during the transition between etching and deposition steps.

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Figure 1. Schematic section of a micro-resonator on a Si3N4 membrane: back cavity by KOH etching and the top pattern defined in a silicon membrane using the Bosch process

Figure 4. High aspect-ratio (50:1) fine period (200nm) gratings etched by a Bosch process: (a) Etch depth 5µm; (b) minimal bow at top of trenches

[1] H. Seidel, L. Csepregi, A. Heuberger, H. Baumgartel, J. Electrochem. Soc. 137 (11) (1990) 3614–3626 [2] F. Laermer, A. Schilp, German Patent DE-4241045, 1994 [3] Z.Ren, M.E.McNie, Microelec. Eng. 141 (2015) 261-266 The authors would like to thank Dr. S Vollmeke (CiS Forschungsinstitut fur Mikrosensoik GmbH, Erfurt) for providing cantilever samples for etching at Oxford Instruments and permission to use the SEM images.

PROCESSNEWS 11

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Power device development enabled through University of Glasgow collaboration

500 attendees 2 days 24 talks 30 posters

Oxford Instruments and the University of Glasgow (GU) have entered into a collaboration as part of a project to develop next generation GaN-on-Si power devices. The project will use an Oxford Instruments four chamber cluster

potential in realising smaller, cheaper, better performing and

system combined in a unique configuration. Under vacuum the

more efficient power devices, with the ensuing commercial

cluster will allow device manufacturing and characterisation

rewards.”

measurements to be performed on device interfaces and surfaces without exposure to atmosphere. System installation is currently underway in the James Watt Nanofabrication Centre at Glasgow University and development work is due to commence in March 2015.

“Using Oxford instruments state-of-the-art equipment, the ultimate aims of this project are to produce smaller GaN-on-Si based power devices that offer better performance and levels of efficiency than those currently available.” says Dr David Haynes, Sales & Marketing Director at Oxford Instruments

The cluster system combines a FlexAL® Atomic Layer Deposition

Plasma Technology, “This will result in commercial benefits

tool used for depositing very thin films of metals, oxides and

for various applications, from electronic component power

nitrides using both thermal and inductively coupled plasma

supplies in laptops to aerospace and automotive applications,

(ICP) ALD processes, a PlasmaPro System100 ICP for etching

in particular electric vehicles. Additionally, Glasgow University

of compound semiconductor materials and a PlasmaPro

will run a second project on the cluster focussing on scalable

System100 ICP for High-Density PECVD deposition system

solar thermoelectrics and photovoltaics.”

providing for low damage, low temperature thin films; plus the Omicron Nanoscience NanoSAM LAB, for surface sensitive chemical analysis and high resolution imaging of small (micro

Bringing the Nanoworld Together

Oxford Instruments will continue to support GU throughout the collaboration period, assisting with process development, and sponsoring a PhD student as part of the project, who will

Energy savings win us a ‘Go Green’ award Joining Go Green has inspired and challenged us to make further sustainable improvements to our business.

wide band gap semiconductors and latest advances in sensor

but implementing this in a large organisation takes

fabrication. There followed talks from Nanoanalysis, Asylum

considerable planning and effort. We did just that, and

Research, Nanoscience, and Andor all part of the Oxford

our initiatives have just resulted in our company winning

Instruments group.

Bristol’s ‘Go Green’ Energy & Efficiency Best Newcomer award. We’re also working hard to implement more ‘Green’ initiatives.

This EPSRC funded project bridges the gap between

www.oxinst.com/GoGreen16

manufacture.

fundamental research and commercial manufacture. Funding

Instruments provides an opportunity to be in the vanguard as the power semiconductor market looks to move towards GaNon-Si.”, Comments Prof Iain Thayne, of Glasgow University, “Successful development of GaN-on-Si enables the use of low cost, large diameter substrates and easier routes to high volume manufacture of power devices. This offers significant

12 PROCESSNEWS

Walther-Meissner-Institute, Technical University of Munich. On Day 2, Thin Film Processing sessions covered fabrication of

unique capability for analysis of each stage of prototype device

“This flagship project for both Glasgow University and Oxford

Nanosciences’, with keynote Professor Dr Rudolf Gross from

way of being more sustainable and saving costs,

See how we did it:

Scanning Electron Microscopy (SEM). Installed, this provides a

Plenary sessions on Day 1 were themed ‘Convergence of the

Reducing energy consumption may seem an obvious

work on the newly installed cluster tool.

and nano) structures by Scanning Auger Microscopy (SAM) and

Record numbers attend 4th ‘BTNT’ seminar in Chennai, India

These educational seminars are aimed to enhance our customers’ knowledge and keep them informed of the latest technological advances our systems have to offer.

IISc Bangalore is the venue for 2016: watch out for further details on our website

was granted to GU as part of a consortium of UK Universities (Bristol,

Cambridge,

Glasgow,

Liverpool,

Manchester,

Nottingham and Sheffield) and industrial partners. This five year project will connect the very capable but currently fragmented, world-class UK GaN academic materials and device community, align them with key players in the UK academic power electronics sector, and directly link with the significant UK power semiconductor industry.

PROCESSNEWS 13

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New etching process for Magnetic RAM developed by Cornell and Oxford Instruments Vince Genova, Cornell University Colin Welch, Oxford Instruments

The Cornell Nanoscale Science and Technology Facility (CNF), a leading university research facility located at Cornell University, Ithaca, NY, and Oxford Instruments Plasma Technology (OIPT), UK have collaborated...

suffers from low etch rates, low selectivity, undesirable sidewall

...to develop a novel etching process targeted specifically

CNF/OIPT process is a result of a Design of Experiment (DOE)

redeposition especially for nanoscale features, and damage to the device structure itself. Recently, several research groups have shown that chemical etching of Co, Fe, and Ni based alloys can be achieved using plasmas formed from methanol (CH3OH) and argon. The new

at magnetic random-access memory MRAM based device

in which the level of CH3OH in Ar varied, along with variations

fabrication. These results, obtained at CNF, add a significant

in the ICP power, bias power, and pressure. Methanol, as the

contribution to OIPT’s large portfolio of etching processes.

principal plasma reactant, forms volatile carbonyl compounds

MRAM is a high performance, low power, low degradation,

(e.g. Ni(CO)4, Fe (CO)5, and Co2(CO)8) at room temperature.

non-volatile data storage technology that some suggest gives it the potential to become a “universal memory”, able to replace SRAM, DRAM, EEPROM and flash. Etching of magnetic based materials for the development and scaling of MRAM and spintronic devices is therefore of keen interest to several leading research groups using the CNF.

This chemistry-based process avoids the disadvantages of purely physical milling. The antiferromagnet IrMn also etches in a methanol plasma. In addition, the selectivity over common mask materials such as Al2O3, Ta, Ti, TaN, and TiN is high, while leaving no residue on the etched devices. We demonstrated successful etching of a 41nm thick magnetic tunnel junction

coupled plasma (ICP) based reactive ion etch platform is configured for state of the art nanoscale etching vital to the research work of CNF. The system includes many extras that make for a highly flexible and powerful etch research tool. These include a wide range temperature (-150°C to +400°C) electrode, which greatly enhances the spectrum of materials that can be etched with volatile chemistries, low frequency electrode biasing and a vapour delivery system for methanol

stack stopping on the tantalum under layer (see figure). High

(CH3OH).

Vincent J. Genova, a Research Staff Member at CNF, explains

selectivity (>10:1) over both the Ta mask and under layer is

the technology and the new process, “An element of

This advanced methanol-based etch capability for magnetic

achieved through the formation of tantalum carbide in the

MRAM consists of a magnetic tunnel junction (MTJ) and

materials is an enabling process that is now available to

methanol process.

the researchers at CNF and to the newly formed National

a CMOS transistor.

One of the most challenging steps in

MRAM fabrication is the etching of the MTJ stack. The stack typically contains a non-magnetic seed layer to promote proper crystalline growth (e.g. Ta), an

Nanotechnology Coordinated Infrastructure Network (NNCI). This research work at CNF adds a significant contribution to Oxford Instruments Plasma Technology’s extensive portfolio of etching processes, enabled through the use of our state of the art PlasmaPro 100 Cobra ICP etch system. We are delighted that our technology is assisting such a prestigious research centre achieve its fundamental research goals. For further technical information, please contact Vincent Genova at [email protected] or Colin Welch at [email protected]

CNF was pleased to announce the full facilitation of the new PlasmaPro 100 Cobra ICP etch system from Oxford Instruments Plasma Technology (OIPT) in 2015. This inductively

antiferromagnet such as PtMn or IrMn, a stack of alloy pinned layers (CoFeB), a tunnelling barrier such as MgO, metals such as Ru and/or Pt, and a suitable hard mask such as TiN or Ta. The problem is that magnetic materials have

difficulty

reacting

with

most

chemically active plasma species to form volatile etch products, so users often have to resort to purely physical ion milling processes. However, ion milling

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Scanning electron micrograph of the 41nm thick MTJ

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