- Количество слайдов: 37
Plasma Quest Limited Magnetic Data Storage Materials Plasma Quest Perspective Barry Holton Managing Director January 16 th 2006 Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
Objectives: v To tell you who we are! v To present what PQL sees as the challenges for deposition technologies v To indicate where PQL is directing its materials deposition developments v To indicate where PQL sees the potential v To listen
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 (6 mm+) target use]
Hard Disc Developments Already well established with large companies and their R&D operations investing heavily. PQL will not look DIRECTLY at developing in this area, but it will look to promote its technologies where appropriate Currently working with Universities of York and Manchester in a LINK ISD programme to: “demonstrate the potential of Hi. TUS technology for the production of thin films of magnetic materials and other films suitable for application in the field of magnetic information storage” (a number of papers have been generated from this project)
What will PQL develop? PQL seeks to concentrate on “specialist” activities, where the key characteristics of its technology offer new opportunities, for example: v v High target utilisation Sputtering from thick ferromagnetic targets Thin film properties close to bulk Ability readily to control grain size PLUS v v v Readily controllable stress High rate deposition at low temperature Stoichiometric deposition from compound targets Very smooth films High rate, stable reactive sputtering
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 0. 1 – 2. 0 m. A/cm 2
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 m. A/cm 2 locally Gnd Low ionisation efficiency = low sputter rates, high pressure Target current density 0. 1 – 2. 0 m. A/cm 2
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 m. A/cm 2 locally Remote Plasma Gnd Low ionisation efficiency = low sputter rates, high pressure Target current density 0. 1 – 2. 0 m. A/cm 2 Target : -ve bias Gnd High remote ionisation efficiency = high sputter rates over full target Target current density up to 100 m. A/cm 2 over full target
Standard System Schematic
Plasma Source Basics • External RF antenna (13. 56, 40 MHz) 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. 50 e. V (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 1013 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 bias (tens of V) – no sputtering of unbiassed components. • Electrodeless system, highly robust and tolerant of reactive gases.
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 -300 G 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 ~100 V draws increasing ion current from the plasma. Sputtering begins during this time for most materials. • Above -100 V 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 2 k. V) • 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.
Some Indicative Deposition Rates § Reactive Al 2 O 3 § Reactive Ta 2 O 5 § Reactive Si. O 2 § Reactive Ti. O 2 § Fe/Co 240 nm/min 125 nm/min 100 nm/min 200 mm Ø target 100 mm Ø target 120 nm/min 6 mm x 100 mm Ø target
Plasma Quest’s Base Technology High Density Plasma Launch System (Some Benefits) • Plasma Densities 1010 to 1013 cm-3 • Plasma Assisted High Rate Reactive Deposition • High Target Utilisation • Control of Grain Size • Sputter from thick ferromagnetic targets • Exceptional Film Properties eg • Low Stress Films • Refractive Index near bulk • Low absorption • Very Smooth • Stoichiometry of compound targets maintained • Control of Properties • System retrofittable to existing vacuum processes • Deposition onto Organic Substrates • Plasma Clean Facility AN ENABLING TECHNOLOGY
Some Magnetic Materials Information University of York - 2005 PQL/Uo. Y 2005 120 nm Fe deposited onto 25µm Kapton
Si /Cr /Fe. Co-2. 5 nm Cr with different voltage levels for seed Cr seed shows good MS AND lower HC ~ 11 Oe Sample Bias -V 200 250 300 400 Volume (cm 3) 2. 2 x 10 -5 2. 1 x 10 -5 2. 0 x 10 -5 2. 2 x 10 -5 Ms EMU 4. 1 x 10 -2 3. 68 x 10 -2 3. 71 x 10 -2 3. 7 x 10 -2 Ms EMU/cm 3 1865 1754 1858 1685 Ms k. G 23. 4 22 23. 3 21. 2 Hc Oe 21 41 11 33 04050502 8. 5 e-6 500 1. 5 x 10 -5 2. 63 x 10 -2 1744 21. 9 60 04050503 8. 0 e-6 600 2. 0 x 10 -5 3. 481 x 10 -2 1744 21. 9 64 29050501 29050502 03050501 04050501 BP mbar 5. 0 e-6 1. 6 e-6 7. 5 e-6 1. 0 e-6
Production Systems ‘Scale Up’ Issues • The ‘standard’ Hi. TUS technology requires a source of similar diameter to the target diameter to be used. Typically 7. 5 cm to 20 cm diameter targets are used in our systems (application dependent) • We have successfully demonstrated Plasma Source operation to 20 cm diameter – potentially allowing use with 30 cm 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.
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 Hi. TUS advantages – improves reactive stability.
Linear System Schematic Substrate Carrier Or Web Feed (1) Cylindrical Target Plasma Source Launch Electromagnet Substrate Carrier Or Web Feed (2) (Note: system shown rotated 90 degrees for clarity) Target Electromagnet
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.
Linear System - Target Size Comparison Linear Source 35 cm 20 cm 10 cm
50 cm x 7. 5 cm dia. Linear Target System
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 (35 cm linear target): • Stainless steel – 80 nm/min at 30 cm separation • Titanium – 100 nm/min at 26 cm separation • Iron – 45 nm/min at 30 cm separation • Aluminium – 100 nm/min at 22 cm separation • Alumina – 115 nm/min at 22 cm separation • System limited – extrapolated potential rates are 2 -3 times this. • Target wall thickness ~ 1. 5 cm for all targets – including magnetics.
Stress control 800 nm Permalloy (Ni. Fe) on 25µm Kapton sheet
Linear System - High Rate Deposition of Ferromagnetic Materials onto thin plastic film – M-H Loop Data • 15 mm wall thickness low purity iron (mild steel) 35 cm linear target • Target - substrate separation 30 cm • Substrate : 25µm Kapton sheet • Deposition rate : 45 nm/min; Total film thickness : 120 nm; Deposition area : 0. 2 m 2 • Zero stress film
Linear System - High Rate Dielectric Deposition • Linear System uses the same ‘reactive sputtering’ technique as standard Hi. TUS – 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).
Linear System - High Rate Deposition of Alumina onto thin plastic film – Transmission Data • Reactive deposition from aluminium 35 cm linear target • Target - substrate separation 22 cm • Substrate : 25µm PET sheet • Deposition rate : 115 nm/min; Total film thickness : 1000 nm; Deposition area : 0. 2 m 2 • Very low stress film. RI = 1. 7 110 Transmission (%) 105 100 95 90 85 80 200 400 600 800 Wavelength (nm) 1000 1200
Linear System – 50 cm Target Development Preliminary Results - tbc • Prototype system in test, driven by 15 cm diameter Plasma Source. • Target diameter is 7 cm – this has proven undersize for the Plasma Source as expected. Estimated maximum is 12 cm. • System power limited at present (60 k. W target supply requirement). (RF requirement is 5 k. W). • Achieving full utilisation of target length – i. e. plasma propagates over 0. 5 m. • Scaling data according to prior target dependencies indicates that target rates of 400 nm/min will be exceeded – potentially 900 nm/min. • Data shows expected scaling of rate with target size increase – a 10 cm target could therefore further raise this rate to 1400 nm/min or more. (Separation = 25 cm)
Concept In-Linear Source Coating System Schematic Plasma Sources Carrier Plate 9 off 4” dia substrates Load Lock Deposition Chambers Dynamic Deposition Rate > 1000 nm m/min (Continuous feed, Web or carrier plates (Batch and multi-component target systems also in development) Load Lock
Contacts: Professor Michael Thwaites (CEO) Tel: +44 (0) 1256 740682 e-mail: mike. [email protected] co. uk Barry Holton (MD) Tel: +44 (0) 1256 740680 e-mail: barry. [email protected] co. uk Website: www. plasmaquest. co. uk Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
LINK Programme Materials v Rigid Disc Materials §Cr, Co. Pt, Fe. Pt v Soft Magnetic Films and Interlayers §Co. Fe v Antiferromagnetic Materials §Fe. Mn, Ir. Mn, Pt. Mn v Tunnel Junctions §Al 2 O 3, Mg. O Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
No Racetrack Magnetron Racetrack Hi. TUS Full surface erosion >90% UTILISATION Copper Tel: +44(0) 1256 740680 6 mm Cobalt www. plasmaquest. co. uk e-mail: [email protected] co. uk
“Driving” the Hi. TUS Target current (A) Target current/voltage relationship Applied target voltage (V) Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
Range of the Hi. TUS Only 0 n+ tro gne Ma US Hi. T 0 Minimum magnetron plasma striking voltage and current (Not applicable to Hi. TUS) Hi. TUS + Magnetron Hi. TUS Only BUT: Hi. TUS INDEPENDENT of gas pressure !! Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
Comparison of theoretical and actual transmittance vs wavelength for a 14 -layer diagnostic filter Theoretical Actual Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
Waveguide action in Ta 2 O 5 Tel: +44(0) 1256 740680 www. plasmaquest. co. uk e-mail: [email protected] co. uk
Optical Emission Spectra for Remote Plasma Source 434. 8 nm Ar+ 25000 ni ~ 1013 cm-3 20000 15000 Emission Intensity (arb units) 420. 0 nm Ar 10000 Wavelength (nm) Optical emission at antenna Optical emission at source exit 438. 8 437. 3 435. 8 434. 4 432. 9 431. 4 429. 9 428. 4 426. 9 425. 5 424. 0 422. 5 421. 0 419. 5 418. 0 415. 0 0 416. 5 5000