amorphous silicon coatings for control of corrosion and ... 2017 silcotek... · • superalloys are...
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Amorphous Silicon Coatings for Control of Corrosion and Metal Ion ContaminationJames B. Mattzela,D.A. Smith, M. Yuan, J. Bischof, & L. PattersonSilcoTek Corporation · Bellefonte, PA USA
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Motivation
• Purity increasing in importance
• Pushing physical limits• Devices become smaller• Metal ion contamination more important
• Etch (and cleaning) chemistries• Number of removal steps increasing• Gas chemistries more aggressive
• Corrosion limits productivity
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Image from Li, Y. and Quader, K.N. NAND Flash Memory: Challenges and Opportunities. Computer 2013, 46 (8), 23-29.
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Silicon Coatings Technology
• Gas Chromatography• Robust alternative to glass columns
• Oil and Gas• Accurate ppm-to-ppb detection
• Environmental Sampling• Accurate ppm-to-ppb detection
• Corrosion Resistance• Affordable alternative to superalloys
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Industrial CVD
• Commercialized process• 3-D deposition allows coating of all surfaces
• High aspect ratio• Complex geometries
• Bonded to substrate material• Wide range of substrate materials
• Stainless steel, glass, ceramics, aluminum, superalloys
• Scalable process• Fittings to chambers
• Thin coating: ~100 nm up to nearly 2 μm• Does not impact drawing dimensions or
tolerances
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Advantages
• Thermally stable• Wide operating temperature range
• Reasonable cost• Superalloys are much more expensive
• Environmentally known• Silicon is a primary material
• Amorphous• Conformal over edges• Allows for mechanical flexing
• Low outgassing• Vacuum compatible• Barrier to substrate effects (moisture or outgassing)
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Coatings Composition
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Auger Electron Spectroscopy (AES)
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Improved Vacuum Pumpdown
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• Evacuation test on fixed volume chamber
• Corrected for background outgassing
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Coatings Composition
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No metal (Fe, Cr, Ni) signal detected
Oxygen Carbon Silicon
X-Ray Photoelectron Spectroscopy (XPS)
Focused Ion Beam (FIB)Field-Emission Secondary Electron Microscopy (FESEM)
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Corrosion Testing
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• Follow ASTM G31-72(2004) “Standard Practice for Laboratory Immersion Corrosion Testing of Metals”
• Measure Mass Loss During Immersion• Calculate Corrosion Rate in mils per year (mpy)
StandardCoupon
CorrosiveImmersion
Corrosion Rate
Weight loss (g) • K-factor
Density (g/cm3) • Area (A) • Time (hr)=
Calculate
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HCl Corrosion Testing
• Test Conditions• 6 M HCl• Room temperature solution• 24 hrs of exposure
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Uncoated316L S.S.
a-Si:H coated316L S.S.
30x more materiallost on uncoated
coupon
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Elevated Temperature HCl Corrosion Testing
• Test Conditions• 6 M HCl• 50° C solution• 7 hrs of exposure
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Uncoated316L S.S.
a-Si:H coated316L S.S.
30x more materiallost on uncoated
coupon
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HBr Corrosion Testing
• Test Conditions• 6 M HBr (gas dissolved in DI Water)• Room temperature solution• 72 hrs of exposure
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Uncoated316L S.S.
a-Si:H coated316L S.S.
7x more materiallost on uncoated
coupon
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Data Extrapolation
• How long will the coating last in service?
Typical Maintenance Cycle – 3,000 RF Hours
Improvement of coated vs uncoated is ~7.21x(using exposure to 6 M HBr for 72 hrs at r.t.)
Possible Lifetime Extension – 23,000+ RF Hours
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Plasma Exposure
• 50 W SF6 remote plasma exposure (3 min exposure)• Stainless steel appears to begin to pit• Some etching of silicon
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Bare 316L a-Si:H coated 316L
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Conclusions
• Amorphous, hydrogenated silicon can be used as a barrier coatingfor gas delivery in both etch and deposition environments.
• CVD deposition of a-Si:H offers unique benefits including non-line-of-sight deposition on existing components and good adhesion toa wide variety of commonly used materials.
• Additional benefits from a-Si:H deposition may be seen in lowoutgassing of surfaces in vacuum and low particulate creationfrom gas-surface interactions.
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Future Directions
• Develop method for characterizing gas corrosion
• Develop method for characterizing coating lifetime in direct plasma environment
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