Thermal Annealing Effect of taC Film Deposited by
Thermal Annealing Effect of ta-C Film Deposited by Filtered Vacuum Arc Youngkwang Lee *†, Tae-Young Kim*†, Kyu Hwan Oh†, Kwang-Ryeol Lee* *Future Technology Research Division, Korea Institute of Science and Technology †School of Materials Science & Engineering, Seoul National University
ta-C (Tetrahedral Amorphous Carbon) n High ratio of sp 3 hybridized carbon bonds Advantages • High hardness • Smooth surface • Chemical inertness Disadvantages • High compressive residual stress (up to 10 GPa) ta-C deposition
Stress Reduction of ta-C n n n Si incorporation in ta-C Multilayer of ta-C and ta-C: Si Thermal annealing n at 600°C, Vacuum Monterio et al. JAP 88 (2000) p. 2395
Purpose of Present Work ta-C High stress High hardness Thermal annealing Why stress changes?
Experimental Procedure Film deposition Thermal annealing Buffer layer deposition n n Carbon target High frequency bias voltage : 600 V Ar environment (10 -4 Torr) Film thickness : ~5 nm ta-C deposition n n Carbon target High frequency bias voltage : 0 V~650 V Vacuum (10 -5 Torr) Film thickenss : 90~120 nm Rapid thermal annealing n n n Vacuum : below 8 m. Torr Temperature : 600 ºC Time : 7 min
Mechanical Properties of ta-C n As deposited ta-C
Annealing Effect of ta-C
Raman Spectroscopy Intensity(a. u. ) D-peak n Relatively simple and non-destructive structure analysis technique Powerful tool for the structural characterization of diamond or amorphous carbon materials. ü Origin of D-peak ü Origin of G-peak n Breathing modes of sp 2 site in sixfold rings IG GFWHM DFWHM Raman shift(cm-1) ID Bond stretching of all sp 2 site
Raman Spectra of ta-C Annealed D-peak G-peak Intensity (a. u. ) As-deposited
Change of D-peak after Annealing Bias voltage : 200 V Intensity (a. u. ) Bias voltage : 0 V
G-Peak Position of ta-C
Summary of Stress and Raman Result As deposited Bias voltage Stress Hardness sp 2 sites Annealed Sixfold ring 0 V~50 V 200 V~500 V
Annealing Effect Model on Residual Stress n n ta-C of higher residual stress Increase of sp 2 sites by thermal annealing ü Model 1 J. P. Sullivan et al. J. Electron. Mater. 26, 1021 (1997) Ø sp 2 bonding length is shorter than sp 3 bonding length Ø Compressive residual stress is relieved with increase of sp 2 site
Annealing Effect Model on Residual Stress n n ta-C of lower residual stress Increase of sp 2 sites and sixfold rings by thermal annealing ü Model 2 Ø Increase of sixfold rings with increase of sp 2 sites Ø Sixfold rings is distorted in skeleton of sp 3 rich matrix JAP Vol 88. No. 5 (2000) p 2395 O. R. Monterio et al. Ø Compressive residual stress increases by increasing of distorted sixfold rings
Conclusions n n After annealing, sp 2 bond increased in all bias range After annealing, stress of ta-C showed two different behavior n For ta-C of lower sp 2 fraction, stress decreased n n Compressive residual stress is relieved with increase of sp 2 sites For ta-C of higher sp 2 fraction, stress increased n Compressive residual stress is increases by increasing of distorted sixfold rings
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