Silicon-Based Surface Treatments for Improved Vacuum System - PowerPoint PPT Presentation

Silicon-Based Surface Treatments for Improved Vacuum System Throughput, Inertness, and Corrosion Resistance David A. Smith Bruce R.F. Kendall SilcoTek Corporation Elvac Associates 112 Benner Circle 100 Rolling Ridge Drive Bellefonte, PA 16823 Bellefonte, PA 16823 www.SilcoTek.com

Research Focus: Surface Modification • Surface treatments to improve performance of ordinary materials – Stainless steels / carbon steels – Glass – High performance alloys • Focus on silicon / functionalized silicon – Inert – Corrosion resistant – Diffusion barrier – Tailor properties (i.e. surface energy) 2

New Technology? • Kipping – silicon materials in 1920’s – Reductive coupling of silicon chlorides – Functional polysilanes – [SiR 2 ] n – Functional polysilynes – [SiR] n – Solubility issues • Semiconductor industry (1960’s) – High purity silicon depositions – Controlled doping, etching, implanting 3

Focus: Bulk surface modification • Regardless of – Configuration • 3D • Coiled tubing – Part count – Size (within reason…) • Engineering surface performance beyond original design 4

Why bother? Powerful Example… • Silver texture on copper with heptadecafluoro -1- decanethiol coating • Air layer between water and metal coupon • Critical viewing angle = 48.6 ° (same as water/air reflection boundary); <1% water in contact with surface (CA = 173 ° ) Larmour, I.A.; Bell, S.E.J; Saunders, G.C. Angew. Chem. Int. Ed. 2007, 46 , 1710-1712. 5

Thermal CVD Process H H H H Si Si Si Si Si Si Si H a-silicon hydride 1. vac, heat stainless steel stainless steel 2. SinH2n+2 • Diffusion in to stainless lattice • Native oxide formation on surface upon atmospheric exposure 6

AES Depth Profile Diffusion Zone 100 Silicon 90 80 70 Atomic Concentration (%) 60 Iron 50 40 30 Cr 20 Oxygen Ni 10 Mo 0 500 1000 1500 2000 2500 3000 7 Sputter Depth (Å )

In-Situ Surface Chemistry • Functionalize via thermal hydrosilylation CH 2 R CH 2 R CH 2 R CH 2 H H CH 2 H H CH 2 H Si Si Si Si Si Si Si Si Si Si Si Si Si Si H H CH2=CH-R a-silicon hydride a-silicon hydride steel, glass,ceramic steel, glass,ceramic H CH 2 CH R H Si Si CH 2 CH R + 8 US Pat. #6,444,326

DRIFTS Illustration of Func. Raw 5um Silica a-Si deposition on Silica Hydrocarbon functionalization on a-Si / silica 9

Surface Energy Measurements Force vs Position 3.5 3 2.5 Bare 316ss 37.2 ° advancing 2 0 ° receding 1.5 Force [mN] a-Silicon coated 1 53.6 ° advancing 0.5 19.6 ° receding 0 Functionalized a-Si -0.5 87.3 ° advancing -1 51.5 ° receding -1.5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 Position [mm] 10

Tubing Drydown Example Conditions: 100’, ¼” tubing, 0.35 slpm, 22C 1ppm Equilibration Time: Func. a-Si • Commercial seamless: 180 min. (96% DD) • E-polished seamless: 60 min. (98% DD) • Func. a-Si, e-polished seamless: 30 min. (98% DD) Data courtesy of O’Brien Corporation, St. Louis, MO 11

Anti-Corrosion Benefits Example Untreated 316 SS a-SiH coated 316 SS ASTM G48 Method B: Pitting and Crevice Corrosion 6% Ferric Chloride solution, 72hrs, 20ºC, Gasket wrap ~10X Improvement (weight loss) 12

Tubing Inertness Example Sulfur Flow- Func. a-Si Through Data: • 100’ 1/8” x .020” 316 SS tubing • 0.5ppmv methyl EP Tubing mercaptan in He • SCD detection Data courtesy of Shell Research Technology Centre, Amsterdam • What does this mean? – Activity at metallic interfaces can be 13 minimized or avoided

Vacuum System Issues • Long evacuation times / poor base vacuum – Leaks – Volatile Contamination • Water vapor – Atmospheric – Gas lines • Organic • Metallic / non-volatile contamination • Chamber material • Prior process remnants • Root cause: Surface Interactions

Seasoning • Systems require time / dummy runs / process exposure before steady state is achieved • Time and cost intensive • Root cause: Surface Interactions 15

Heat-Induced Outgassing • How to measure a potential benefit? • Outgassing rate (F) in monolayers per sec: F = [exp (-E/RT)] / t’ t’ = period of oscillation of molecule perp. surface, ca. 10 -13 sec E = energy of desorption (Kcal/g mol) R = gas constant source: Roth, A. Vacuum Technology, Elsevier Science Publishers, Amsterdam, 2 nd ed., p. 177. • Slight elevation of sample temperature accelerates outgassing rate exponentially 16

Experimental Design: Heated Samples • Turbo pump for base pressures to 10 -8 Torr – pumping rate between gauge and pump: 12.5 l/sec (pump alone: 360 l/sec) – system vent with dry N 2 between thermal cycles • Ion pump for 10 -10 Torr (thermal cycles) • Comparative evaluation parts – equally treated controls without deposition 17

Outgassing Data – Heated Samples at HV Pressure increase with heat 25 20 a-Si CVD 1 st gen. 15 Control 10 As received 5 0 • Turbopump, 1 x 10 -7 Torr base pressure 18 • 10hr under vacuum

Outgassing Data – HV Heated Samples Pressure increase with heat 5 4.5 4 ∆ P units of 10 -7 Torr 3.5 a–Si CVD 1 st gen. 3 2.5 Control As received 2 1.5 1 0.5 0 Min. (Temp 0.5 (112) 1 (145) 1.5 (167) 2 (186) 2.5 (195) 3 (201) ºC) • 7.5 fold improvement at 112ºC 19

Outgassing Data – HV Realistic Evacuation Times Pressure increase with heat – 1 hour evacuation 25 20 15 a-Si Coated Control 10 5 0 Seconds 15 (61) 30 (105) 45 (137) 60 (161) (Temp ºC) • Turbopump, 4.6 x 10 -7 Torr base pressure 20 • 1hr under vacuum ( ∆ P1)

Outgassing Data – HV Realistic Evacuation Times Pressure increase with heat – 10 hour evacuation 5 4.5 4 3.5 3 a-Si Coated 2.5 Control 2 1.5 1 0.5 0 Seconds 15 (61) 30 (105) 45 (137) 60 (161) (Temp ºC) • Turbopump, 7.5 x 10 -8 Torr base pressure 21 • 10hr under vacuum ( ∆ P2)

Outgassing Calculations • For the system (P A ), sample area = 125cm 2 , conductance = 12.5 l/sec; therefore, ∆ Q = ∆ P(12.5/125) = ∆ P/10 • At 1 hour, 61ºC: ∆ Q 1 (control) = 5.4 x 10 -8 Torr l sec -1 cm -2 ; ∆ Q 1 (a-silicon) = 0.2 x 10 -8 Torr l sec -1 cm -2 27x improvement • At 10 hours, 61ºC: ∆ Q 10 (control) = 0.14 x 10 -8 Torr l sec -1 cm -2 ; ∆ Q 10 (a-silicon) = 0.01 x 10 -8 Torr l sec -1 cm -2 14x improvement 22

UHV comparison – B/A ion gauge housings Pressure increase with heat 30 25 units of 10-10 Torr 20 control 15 a-Si coated 10 5 0 Sec. (Temp 15 (61) 30 (105) 45 (137) 60 (161) 75 (180) 90 (201) ºC) Ion pump, 1.2 x 10 -10 Torr base pressure • • 156 days under vacuum (5th baking cycle) • 3.3-fold improvement at 105ºC 23 (no measurable Δ P for a-Si at 61ºC, 7.0 x 10 -12 Torr Δ P at 105ºC)

Chamber Comparison; No Heat roughing pump • Common pumping V 3 line G • Valve isolation • Alternating chamber V 2 V 1 measurements • Roughing pump for first 44 min. a-Si Untreated V 4 24 Turbo pump

Chamber Comparisons; No Heat • System conductance: 7.4 l/sec • 360 l/sec turbomolecular pump 25 • Cold cathode gauge

Chamber Comparisons; No Heat Comparative Evacuation Rates 80 70 System Pressure (10 -7 Torr) 60 50 Untreated Chamber 40 a-Si Chamber 30 20 10 0 56 64 72 80 88 96 104 112 Minutes • Alternate-pumpdown system pressures • 80-84 minute range: 2.4-fold improvement 26

Corrected Comparison Corrected Evacuation Rates 60 50 Pressure Drop (10 -7 Torr) 40 Untreated Chamber 30 a-Si Chamber 20 10 0 4 2 6 4 2 0 8 6 s e 5 6 7 8 8 9 0 1 1 1 t u n i M • Alternate pressure drop system measurements (true outgassing of isolated chambers) 27 • 80-84 minute range: 9.1-fold improvement

Current Research: Carbosilane Materials • C, Si, H in CVD-deposited matrix • Excellent inertness • Improved corrosion resistance • High hydrophobicity • Si-H functionality for additional chemistry 28

Carbosilane FT-IR 135 SilcoTek Carbosilane on Si 130 125 120 2891.71 2951.86 115 110 105 %T 100 2102.38 95 1253.44 90 85 745.10 1002.97 80 75 823.52 70 3500 3000 2500 2000 1500 1000 500 Wavenumbers (cm-1) 29

AES Depth Profile 100 Diffusion 90 Zone 80 Fe 70 Atomic Concentration (%) 60 C 50 Si 40 30 20 Cr 10 Ni O 0 0 20 40 60 80 100 120 140 160 180 200 Sputter Depth (nm) 30

Acid / Base Resistance • ASTM G31 screening: – 6M HCl, 24 hrs, 316 SS coupons, 22 ° C Surface mpy Enhancement 316 SS control 91.90 ---- a-Si corr. res. 18.43 5.0 X carbosilane 3.29 27.9 X • High pH Inertness – 18% KOH, 19 hrs, 316 SS sample cylinder, 22 ° C – No weight loss – need further assessment – Inert to 10ppmv H 2 S static storage over 48 hrs. 31

Hydrophobicity / Appearance Surface Advancing / Receding a-Silicon 53.6 / 19.6 Funct. a-Silicon (HC) 87.3 / 51.5 carbosilane 100.5 / 63.5 Funct. Carbosilane (HC) 104.7 / 90.1 Funct. Carbosilane (F) 110.5 / 94.8 -narrowing the hysteresis gap to Cassie-Baxter state 32

Contact Angle Illustration • DI water CA: 127 ° • On 304 stainless corrosion Close to Release… coupon; no topography modification 33