Plasma Quest Limited

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1 Plasma Quest Limited A Remote Plasma Sputter Process for High Rate Web Coating of Low Temperature Plastic Film with High Quality Thin Film Metals and Insulators Dr. Peter Hockley and Prof. Mike Thwaites, PQL October 2005 Tel: +44(0) sales@plasmaquest.co.uk

2 Introduction PQL is a small R&D company with 7 years experience of developing, using - and promoting - Remote Plasma Sputtering as a solution to a wide range of materials and applications, providing unique solutions and benefits in most cases. - high rate, low temperature deposition of low stress thin film coatings with near ideal physical properties -significantly increased process scope enabling technology - deposition of metals, alloys, insulators and ferromagnetics* - stable reactive sputter deposition for dielectric thin films - deposition of high quality transparent conducting oxides (TCO) - deposition of DLC with high optical transmission - deposition of polycrystalline silicon for electronic devices - new waveguide materials and system options for opto-electronics [*remote plasma allows thick (6mm+) target use]

3 Outline Objective is to disclose a new means of using the Remote Plasma Sputtering Process that has particular application to high volume, high quality thin film coating applications most obviously in the Large Panel Display, flexible electronics arenas. Structure Review of the Basics of Remote Plasma Sputtering Implementation of the Technique Scale Up Issues and Solution New Linear Source System Basics of Linear Source Operation Results Achieved Current Large Area System Development Work

4 Plasma Density Amplification through Magnetic Confinement Diode Sputtering (no magnetic field) Target : -ve bias Gnd Low ionisation efficiency = low sputter rates, high pressure Target current density ma/cm 2

5 Plasma Density Amplification through Magnetic Confinement Diode Sputtering (no magnetic field) Target : -ve bias Magnetron - confinement at target Target : -ve bias Gnd High local ionisation efficiency = high local sputter rates ( racetrack ) Target current density up to 100 ma/cm 2 locally Gnd Low ionisation efficiency = low sputter rates, high pressure Target current density ma/cm 2

6 Plasma Density Amplification through Magnetic Confinement Diode Sputtering (no magnetic field) Target : -ve bias Magnetron - confinement at target Target : -ve bias Gnd High local ionisation efficiency = high local sputter rates ( racetrack ) Target current density up to 100 ma/cm 2 locally Gnd Low ionisation efficiency = low sputter rates, high pressure Target current density ma/cm 2 Remote Plasma Target : -ve bias Gnd High remote ionisation efficiency = high sputter rates over full target Target current density up to 100 ma/cm 2 over full target

7 Standard System Schematic SIDE ARM PLASMA SOURCE DEPOSITION CHAMBER Plasma Path in Chamber Substrate Holder Assembly, Shutter, etc. Source Electromagnet Target Electromagnet Multiple Indexable Target System

8 Plasma Source Basics External RF antenna (13.56, 40MHz) produces initial low density plasma. Combined RF and DC electromagnetic fields accelerate electrons; magnetic field constrains electron paths and increases average path length. A significant proportion of electrons are accelerated to c. 50eV (probe measurements) optimum for ionisation of argon gas. Combination of long path and high ionisation efficiency results in plasma density amplification towards plasma source exit visible by OES. Plasma densities in excess of cm -3 may be achieved at source exit, limited by ambient gas pressure (90% ionised by OES). Measurements show high ion densities, but low ion energies (~10eV) no sputtering of unbiassed components. Electrodeless system, highly robust and tolerant of reactive gases.

9 Remote Plasma Sputtering Basics DC magnetic field produced by the Source and Target electromagnets continues to constrain electron paths, essentially directing the plasma to the target a cascade generation process. Despite magnetic field variations (30-300G range) and increasing distance from the source, high ionisation efficiencies are maintained producing a high density plasma in front of the target surface. In the absence of target bias no sputtering occurs. Increasing (negative) target bias up to ~100V draws increasing ion current from the plasma. Sputtering begins during this time for most materials. Above -100V bias, the ion current limits at a value dependent on process conditions (Source Power, magnetic field strength, gas pressure). Sputter rate therefore depends on bias voltage from hereon (approx. linearly to 2kV) The plasma itself is unaffected by target bias giving an inherently stable basis for the sputtering process. Independent Source and Target operation allows stable coating over 5 orders of magnitude of deposition rate.

10 Example of Plasma Beam inside the Chamber

11 Production Systems Scale Up Issues The standard HiTUS technology requires a source of similar (c.75%) diameter to the target diameter to be used. Typically 7.5cm to 20cm diameter targets are used in our systems (application dependent) We have successfully demonstrated Plasma Source operation to 20cm diameter potentially allowing use with 30cm targets. The Plasma Source requires an RF supply of similar rating to the target supply a cost disadvantage. Substrate size and deposition rate trade off = bigger targets or multiple targets are required for large throughput applications. Remote Plasma systems are disadvantaged due to multiple plasma source cost implications.

12 Scale Up Development Linear System Trials passing the plasma beam along a rectangular target show improved area coating as expected, but...we also discovered that a cylindrical target can be placed within the plasma beam without compromising the beam in any way. Substantial in-house R&D over the last year has shown that this configuration has many benefits: More efficient use of plasma source one tenth the power required Eliminates need to scale source with target Greatly increased coating area Greatly increased coating rates Retains all HiTUS advantages improves reactive stability.

13 Linear System Schematic Plasma Source Substrate Carrier Or Web Feed (1) Cylindrical Target Launch Electromagnet Substrate Carrier Or Web Feed (2) Target Electromagnet (Note: system shown rotated 90 degrees for clarity)

14 Fundamentals of Linear Source Operation Critical understanding: the plasma beam from our Plasma Source essentially comprises two regions: A tubular cross section generation region A more extensive cylindrical cross section plasma region The former is the main glow discharge that visually defines the apparent plasma beam this must not be obstructed. The latter (may be invisible) can be obstructed. Thus a target may be placed within the plasma generation tube and thereby surrounded by plasma without detriment to the plasma itself. In addition, the generation tube appears to act as a conduit for the RF energy plasma generation efficiency is maintained, providing a uniform plasma density for sputtering from the whole target surface.

15 Linear System - Target Size Comparison Linear Source 35cm 20cm 10cm

16 50cm x 7.5cm dia. Linear Target System (in development)

17 Linear System - High Rate Deposition onto Thin Plastic Sheet for Flexible Electronics A wide range of thin films, from metals to dielectrics, have been successfully deposited onto 50µm Kapton and 25µm PET Films are low stress, controllable from tensile through to compressive Film properties are near ideal and unchanged from those achieved on e.g. glass, and silicon wafers Examples of thin film depositions onto plastics (35cm linear target): Stainless steel 80 nm/min at 30cm separation Titanium 100 nm/min at 26cm separation Iron 45 nm/min at 30cm separation Aluminium 100 nm/min at 22cm separation Alumina 115 nm/min at 22cm separation System limited extrapolated potential rates are 2-3 times this. Target wall thickness ~ 1.5cm for all targets including magnetics.

18 Stress control 800nm Permalloy (Ni/Fe) on 25µm Kapton sheet

19 Linear System - High Rate Deposition of Ferromagnetic Materials onto thin plastic film M-H Loop Data 15mm wall thickness low purity iron (mild steel) 35cm linear target Target - substrate separation 30cm Substrate : 50µm Kapton sheet Deposition rate : 45nm/min; Total film thickness : 120nm; Deposition area : 0.2m 2 Zero stress film sample KAP4 M (kilogauss) H (Oe)

20 Linear System - High Rate Dielectric Deposition Linear System uses the same reactive sputtering technique as standard HiTUS inherently stable process without feedback control Uses metallic sputtering target, e.g. Al for alumina, Si for silica. This allows high rate sputtering and cheaper DC supplies for metallics. Introduce appropriate flow (and distribution) of reactive gas during the sputter process, e.g. O 2 for oxides, N 2 for nitrides or appropriate mixture for oxy-nitrides. High density plasma assists reaction (gas phase or surface) resulting in deposition of high quality, densified dielectrics at room temperature. Fully reacted coatings for optimised process no free metal inclusion. Coatings are generally amorphous (low light scatter).

21 Linear System - High Rate Deposition of Alumina onto thin plastic film Transmission Data Reactive deposition from aluminium 35cm linear target Target - substrate separation 22cm Substrate : 25µm PET sheet Deposition rate : 115nm/min; Total film thickness : 1000nm; Deposition area : 0.2m 2 Very low stress film. RI = Transmission (%) Wavelength (nm)

22 Linear System 50cm Target Development Preliminary Results - tbc Prototype system in test, driven by 15cm diameter Plasma Source. Target diameter is 7cm this has proven undersize for the Plasma Source as expected. Estimated maximum is 12cm. System power limited at present (60kW target supply requirement). (RF requirement is 5kW). Achieving full utilisation of target length i.e. plasma propagates over 0.5m. Scaling data according to prior target dependencies indicates that target rates of 400nm/min will be exceeded potentially 900nm/min. Data shows expected scaling of rate with target size increase a 10cm target could therefore further raise this rate to 1400nm/min or more. (Separation = 25cm)

23 Development In-Line Linear Source Coating System Schematic Multiple substrate carriers Plasma Sources Linear Sputter Targets (50cm) Load/lock chamber Load/lock chamber Vacuum Pumping Gate Valve Two layer sequential or alternating multi-layer coating. Coating rate: ~ 500 nm/min onto 2 off 30x50cm area (aperture) per target (Batch and multi-component target systems also in development)

24 Contacts: Professor Michael Thwaites (CEO) Tel: +44 (0) Barry Holton (MD) Tel: +44 (0) Website:

25 Optical Emission Spectra for Remote Plasma Source n i ~ cm nm Ar Emission Intensity (arb units) nm Ar Wavelength (nm) Optical emission at antenna Optical emission at source exit

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