금속이 혼입된 DLC 박막의 응력감소 거동 ; 제일원리계산 17, Feb., 2006 광운대학교 제 30회 학술발표회 반도체 및 박막 T-13 금속이 혼입된 DLC 박막의 응력감소 거동 ; 제일원리계산 한국과학기술연구원 미래기술연구본부 최정혜, 안효신, 이승철, 이광렬

Diamond-like carbon (DLC) films High hardness High wear resistance Low friction coefficient Optical transparency Chemical inertness Smooth surface Bio-compatibility Protective coating Bio materials Video Head Drum Coronary Artery Stent Hard disk Hip Joint

Disadvantages of DLC films High residual compressive stress (6~20 GPa) poor adhesion Hard disk Before deposition After deposition Substrate bending Delamination M. W. Moon, Acta Mater., 50 219 (2002).

Stress and sp3 bond fraction Hardness

To reduce residual scomp in DLC films Substrate biasing Post-annealing ; T-11 이영광 발표 Metal atom incorporation ; Ti, W, Mo, Cr, Al….

W-incorporated DLC films Ion beam deposition & Magnetron sputtering 1.9 at % W Mechanism ? Not fully understood yet !!! A.-Y. Wang APL 86 111902 (2005).

Purpose of this work ; First Principles Calculation DLC Diamond ; ideal sp3 bonding 109.5o ≠109.5o DLC ; distorted sp3 + sp2, sp bonding Known as a primary cause of the residual stress in DLC structure dependency of total energy of the system on the bond angle & the electron density distribution and its effects on the stress reduction behavior of DLC films ; First Principles Calculation

First principles calculation Quantum modeling “first principle” or “ab-initio” calculation Without any empirical parameters For a given atomic number, coordination  Schroedinger eq. HY = EY Theoretically accurate Cohesive energy Charge density Electronic structure (band, DOS) Nature of bonding STM image simulation……. femtosec picosec nanosec microsec sec 1 nm 0.1 nm 1 mm 1 cm 1 m Quantum modeling Atomistic min Continuum

Tetrahedron bond model C 109.5o Me tetrahedral bonding of carbon(or Me)-carbon structure relaxation total energy calculation ; reference state DEC-C DEMe-C 90o~ 130o C 90o~ 130o Me Bond angle distortion bond distance relaxation total energy calculation

Calculation condition Code; DMOL3 ; Density Functional Calculation Exchange-correlation potential; Generalized Gradient Approximation (GGA-PBE) Atomic orbital; double-zeta polarization basis set Cutoff radius of atomic orbitals; 9 Å All electron calculation Spin consideration

Total energy change by the bond angle distortion

Formation energy of Me-C tetrahedron DEfM-C = (EtotM-C + EatomC) - (EtotC-C + EatomM) Me DEfM-C Me

Isosurface of electron density; C-C-tetrahedron 0.5 1.5 1.0 90o C 1.5 1.0 0.5 Inset values are the electron density [Å-3] of the isosurface

Isosurface of electron density right before it is separated V 0.63 Ti 0.64 Ni 0.67 Si 0.72 Mn 0.70 W 0.70 Cr 0.72 Mo 0.72 Co 0.76 Fe 0.82 C 1.50 109.5o

Isosurface of electron density right before it is separated Ag 0.40 Ar 0.01 Cd 0.36 Au 0.40 Al 0.45 Zn 0.45 Cu 0.53 Pd 0.58 C 1.50 109.5o

Electron density right before its isosurface is separated (res) Weaker bonding Lower angular dependency of total energy  stress reduction Lower res Lower shape anisotropy of electron density

W-incorporated DLC films

Conclusion C 1.50 Mn 0.70 Au 0.40 Al 0.45