ALUMINUM OXIDE AND SILICON NITRIDE THIN FILMS AS ANTI-CORROSION LAYERS

C. Qu1, P. Li1, J. Fan1, D. Edwards1, W. Schulze1, G. Wynick1, R. E. Miller1, L. Lin1, Q. Fang2, K. Bryson3,

H. Rubin4, and X. W. Wang1*

• Alfred University, Alfred, NY 14802, USA• Oxford Instruments Plasma Technology, Yatton, Bristol BS49 4AP, UK• Duke University, Durham, NC27708, USA• Plasma-Therm, St. Petersburg, FL 33716, USA

• Acknowledgment: DOE USCar Program

• Background InformationNew Automotive Engine & Other Parts:Magnesium-Aluminum Alloy Materials

Fasteners: Carbon Steel

Potential Problems:Galvanic Corrosion

Thin Films

Aluminum oxideE-beam Evaporation Technique

Silicon nitridePlasma Enhanced Chemical Vapor Deposition

(PECVD)

Cerium OxideUV Curable Layer

E-beam Evaporation Technique

– Target: Aluminum oxide

3.Power: 8 KV, 0.1 APressure: 2 x 10-4 torr

– Post deposition heat treatment in ambient environment @ 350 °C for 40 min.

– UV curable materialCe(OCH2CH2OCH3)3

Cured with a UV lamp with the wavelength of 184-400 nm

E-beam Evaporation

• VPT

Plasma Enhanced Chemical Vapor Deposition (PECVD)

• Precursor: Silane, ammonia, nitrogen

– Pressure: 0.1 torr– Substrate holder temperature : 275 oC– Shower head temperature: 100 oC

Plasma Enhanced Chemical Vapor Deposition (PECVD)

• Trikon

SiH4

NH3

N2

RF

Vacuum

Shower head

Shower head

Substrate holder (Bottom electrode)

Top electrode

Issue

• Coverage of steel substrates – Macro-- Defects / Scratches– Micro– Cluster sizes / shapes

Control

Defect

Impedance of Control

Single-layer Aluminum Oxide Thin Film

• 150 nm

Impedance

• 200 nm, 700 nm

Post Deposition

• Post-deposition heat treatment– Aluminum oxide thin films were heat treated at

350 °C for 40 min.– Second deposition of aluminum oxide after the

heat treatment

• UV-curable material as the top layer

Comparison

• UV Curable Coating, Al2O3, UV Curable Coating on Al2O3

Single-layer Silicon Nitride Thin Film

• 60 nm

Increasing Thickness

• 300 nm

Thicker

• 600 nm

Thickest

• 850 nm

Impedance

• Silicon Nitride

Impedance Modulus Comparison

• Single Layer Silicon Nitride vs. 3-layer Aluminum Oxide

Progress• Increasing impedance

Control

Single-layer Aluminum Oxide

Single-layer Aluminum Oxide w/ Heat Treatment

Double-layer Aluminum Oxide w/ Heat Treatment

Double-layer Aluminum Oxide w/ Heat Treatment and UV-curable material on the top

Silicon Nitride via PECVD

Density of Aluminum Oxide Film

– Density: Estimated via ellipsometry

• Single-layer aluminum oxide thin films with different thickness:

83%• Double-layer aluminum oxide thin films with

heat:92%

Conclusion

• For the two-layer aluminum oxide film fabricated with three-steps, the highest impedance modulus value at 0.01 Hz is approximately 4.6x105 Ohm-cm2

• With an additional UV curable cerium oxide layer, the impedance modulus value is increased to approximately 2.1x106 Ohm-cm2

• For 850 nm silicon nitride film fabricated with one-step, the impedance modulus value is 1.4 X 106 Ohm-cm2

• Coverage of the defect areas: related to impedance