Filtered vacuum arc taC TaeYoung Kim Churl Seung

Filtered vacuum arc 공정에 있어서 아르곤 가스에 의한 ta-C 박막의 구조 조절 Tae-Young Kim, Churl Seung Lee, Kwang-Ryeol Lee*, Jun Hee Han, Kyu Hwan Oh Future Technology research center in Korea Institute of Science and Technology School of Material Science and Engineering in Seoul National University

Tetrahedral Amorphous Carbon – A class of diamond-like carbons – High ratio of sp 3 hybridized carbon bonds – High hardness, smooth surface, thermal stability, chemical inertness…. sp 3 ta-C: H DAC PAC GAC sp 2 No film H

Compressive Residual Stress – A class of diamond-like carbons – High ratio of sp 3 hybridized carbon bonds – High hardness, smooth surface, thermal stability, chemical inertness…. – High compressive residual stress – Delimitation of film M. W. Moon, Acta Mater. , 50 (2002) 1219. [FP-1 -36]

Atomic Structure of ta-C • Hardness – 3 -D interlink of the atomic bond network • Compressive residual stress – Distortion of bond angle and length – Disordering of atomic structure

Hardness vs Residual Stress

Purpose of This Work • The synthesis of low stress but high hardness ta-C films • Easier process development for low stress and high hardness ta-C films • Method development for effective atomic structure modification of ta-C

Motivation During ta-C deposition process, just introducing Ar gas into the chamber affects the ta-C mechanical properties!!! Systemical investigation of Ar background gas effect

Experimental • Film deposition ØBuffer layer deposition • Ar 8 sccm ( with gun 1 valve), -750 Vb Øta-C deposition at GND substrate bias • Variables : Ar flow (with gun 2 valve)-Just introducing Ar gas into the chamber • Analysis –Compressive residual stress –Hardness – nano-indentor –Composition – RBS –Atomic structure – Raman, ESR

Residual Compressive Stress

Hardness and Strain Modulus

Question Why didn't the hardness change? Why did the residual stress decrease?

RBS Ar 6 sccm treated ta-C film No Ar in the films

Raman Spectra 4 sccm 2 sccm 1 sccm 0. 5 sccm 0 sccm

Raman G-peak Position 4. 1 cm-1/GPa J. K. Shin et al. , Appl. Phys. Lett. , 78 (2001) 631. sp 3 fraction of films was not changed as Ar flow

ESR Reference sample Mg. OMn 2+

Residual Stress vs Defect density

Defects in ta-C ESR detects the paramagnetic components σ π π* σ* A A state diamagnetic • disordering between sp 2 clusters B A B state paramagnetic • • • sp 3 dangling bond Isolated sp 2 clusters Ordered sp 2 clusters Disordered sp 2 clusters

Defects in ta-C Dangling sp 3 Isolated sp 2 Ordered sp 2 cluster Disordered sp 2 cluster

Decrease of Defect Density Defect density decreased with condition of same sp 2/sp 3 fraction Dangling sp 3 Isolated sp 2 Structure rearrangement Ordered sp 2 cluster Disordered sp 2 cluster

Conclusions ü Simple deposition process was developed for low stress ta-C. It just used Ar background gas in FVA for atomic structure modification of ta. C films. ü As the Ar gas flow increased, residual stress of ta-C film decreased without significant deterioration of hardness. ü We could suggest that decrease of residual stress was caused by atomic structure rearrangement.