1. Residual Compressive Stress of Diamond-like Carbon Films : Control and Usage 2007. 4. 12. 이 광 렬 한국과학기술연구원 미래융합기술연구소 krlee@kist.re.kr 제이엔엘테크 세미나, 2007. 4. 13.

2. Outline 다이아몬드상 카본필름과 잔류응력 잔류응력의 제어 –Ar background 효과 –Si addition 효과 –W addition 효과 –Perspective 잔류응력의 활용 –Buckling –Interfacial Toughness 측정 –Elastic Property 측정

3. Applications of DLC VCR Head Drum CD/DVD Mold Spacer Tool Form Die Hard Disk & Slider Digital VCR Tape Razor Blade Wrist Pin

4. What is DLC ? Amorphous Solid Carbon Film Mixture of sp 1, sp 2 and sp 3 Hybridized Bonds High Content of Hydrogen (20-60%) Synonyms –Diamond-like Carbon –(Hydrogenated) amorphous carbon (a-C:H) –i-Carbon –Tetrahedral Amorphous Carbon Heart valve Hard disk

5. Bond Structure of Carbon 1S 2 2S 2 2P 2

6. a-C:Hta-C 2-D Analogy of Structure

7. Properties of Solid Carbon PropertyDiamondDLCGraphite Density (g/cm 3 )3.511.8 – 3.62.26 Atomic Number Density (Mole/cm 3 ) 0.30.2 – 0.30.2 Hardness (Kgf/mm 2 )100002000 - 8000500 Friction Coeff.0.050.03 – 0.20.1 Refractive Index2.421.8 – 2.62.15 – 1.8 TransparencyUV-VIS-IRVIS-IROpaque Resistivity (  cm) >10 16 10 10 - 10 13 0.2 – 0.4

8. Deposition Methods Energy Ion Source Cold Substrate Impact Energy (eV) 1 10 100 1000 Amorphous Carbon (sp 2 ) Dense Carbon Source Hydrocarbon Source Dense Hydro- Carbon Polymer Like Carbon Plasma Polymers

9. Example : Filtered Vacuum Arc

10. Residual Compressive Stress of DLC Film Film Deposition

11. Applications of DLC Carbofilm TM by Sorin Biomedica, Inc.

12. Structure and Mechanical Properties Hardness –3-D interlink of the atomic bond network Residual Stress –Distortion of bond angle and length Both are dependent on the degree of 3-D interlinks. 2-D Analogy of the Structure

13. Hardness Hardness and Residual Stress

14. Hardness Hardness and Residual Stress

15. Multilayer (S. Anders et al ) Stress is not an interpolation between the data for high and low bias only, but is considerably reduced for the multilayer in comparison to single layers. S. Anders et al., MRS Proc. 383 (1995) 453.

16. Post Annealing (T. A. Friedman et al ) Annealing at 600 o C for 1-2 min could reduce the residual stress down to 0.2 GPa, without significant structural change. T. A. Friedmann et al., Appl. Phys. Lett. 71 (1997) 3820.

17. B addition (M. Chhowalla et al ) Residual stress of B added ta-C remains within 1 - 3 GPa for all sp 3 fraction. M. Chhowalla et al., Appl. Phys. Lett., 69 (1996) 2344.

18. Outline 다이아몬드상 카본필름의 잔류응력 잔류응력의 제어 –Ar background 효과 –Si addition 효과 –W addition 효과 –Perspective 잔류응력의 활용 –Buckling –Interfacial Toughness 측정 –Elastic Property 측정

19. Experimental Film deposition – Buffer layer deposition Ar 8 sccm ( with gun 1 valve), -750 Vb – ta-C deposition at GND substrate bias In various Ar gas pressures in the chamber Analysis – Compressive residual stress – Hardness – nano-indentor – Film Composition – RBS – Atomic structure – NEXAFS, ESR T.Y.Kim et al., J. Appl. Phys. 101, 023504 (2007).

20. Compressive Residual Stress

21. Hardness & Strain Modulus

22. Experimental Results & Questions –As the Ar background pressure increased, Stress decreased Hardness didn’t changed significantly. –Why did this phenomenon happen? Compositional change? Atomic structural change?

23. RBS – film composition Ar 6sccm treated ta-C film No Ar in the films Pure Carbon system!!!

24. NEXAFS – sp 2 /sp 3 bonding ratio sp 2 /sp 3 bonding ratio was not changed at the different process condition.

25. ESR – Defect Density

26. Stress vs. Defect Density

27. Decrease in Defect Density  Structural relaxation of distorted sp 2 clusters bonding/clusters supports the paramagnetic spin density measurement Distorted sp 2 clusterOrdered sp 2 cluster

28. Energy Distribution with Ar Background

29. Ar ion knock-on Ar Massage

30. Energy Dispersion Energy Population

31. MD Simulation Deposition Method –Brenner potential for carbon atom –Substrate Diamond substrate (6a 0 x5a 0 x6a 0 ) 1512 Atoms –Incident atom Reference energy = 75 eV Dispersion method –Gaussian distribution (σ=0 ~ 10) –Density of a-C structure ~ 3.14 [g/cm 3 ] Fixed LayerDynamics Layer 54.4 A

32. Residual Compressive Stress MD Simulation with Energy Dispersion ta-C film deposited by FVA with Ar background gas

33. Radial Distribution Function 2.02~2.17 Å

34. sp 3 Ratio & Density 3.14±0.03 [g/cm 3 ] 53.7±1.7 [%]

35. Outline 다이아몬드상 카본필름의 잔류응력 잔류응력의 제어 –Ar background 효과 –Si addition 효과 –W addition 효과 –Perspective 잔류응력의 활용 –Buckling –Interfacial Toughness 측정 –Elastic Property 측정

36. Si Incorporated ta-C C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203 S.-H. Lee et al, to be Submitted (2005)

37. Mechanical Properties

38. Lennard-Jones: Inert Gas Embedded Atom Method : Metals Many Body Potential : Si, C Interatomic Potentials Time Evolution of R i and v i i Molecular Dynamics Simulation

39. Brenner force field for C-C bonds Tersoff force field for C-Si and Si-Si bonds Diamond substrate : 6a 0 x 4.75a 0 x 6a 0 –1,368 atoms with 72 atoms per layer Deposition –Total 2,000 atoms –Incident Kinetic Energy : 75 eV for both C and Si –Si concentration : 0.5 % ~ 20 % Fixed Layer Fully Relaxed Layer Deposited atoms created on this plane

40. Snapshots after Deposition 0.0 % 0.5 % 1.0 % 2.0 % 3.0 % 5.0 % 10.0 % 20.0 %

41. Distribution of Si Atom in ta-C Film 0.0 % 0.5 % 1.0 % 2.0 % 3.0 % 5.0 % : Silicon atom: Carbon atom : Substrate

42. Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11, 198 (2002). Residual Compressive Stress

43. Atomic Bond Structure Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203 Raman G-peak Position MD Simulation

44. 2.54 Å 1.54 Å Radial Distribution of Pure a-C and Diamond

45. Radial Distribution Function

46. Carbon for Satellite Peak 93.1° 94.2° 2.184 A 2.185 A

47. 109.5° 120.0° Bond Angle Distribution

48. Outline 다이아몬드상 카본필름의 잔류응력 잔류응력의 제어 –Ar background 효과 –Si addition 효과 –W addition 효과 –Perspective 잔류응력의 활용 –Buckling –Interfacial Toughness 측정 –Elastic Property 측정

49. W-DLC by Hybrid Ion Beam Deposition  Sputter gun: Third elements addition to DLC (W, Ti, Si …);  Ion gun: Easy controlling the ion bombardment energy with high ion flux. W n+ H +, C m+

50. Composition of the Deposted Film C Si in substrate Ar W

51. Stress & Mechanical properties 21±3 GPa 170±15 GPa

52. TEM Microstructures 8.6 4 nm  -W 2 C(102)  -W 2 C(101) 1.9 4 nm W atoms are dissolved in a-C:H matrix. Nano-crystalline  - W 2 C phases evolve. 4 nm 3.6  -W 2 C (101) -W2C-W2C 4 nm 2.8 Amorphous to crystalline WC 1-x transition occurs.

53. Raman & EELS Spectra I  /I  = 0.55  0.1

54. TEM Microstructures 8.6 4 nm  -W 2 C(102)  -W 2 C(101) 1.9 4 nm W atoms are dissolved in a-C:H matrix. Nano-crystalline  - W 2 C phases evolve. 4 nm 3.6  -W 2 C (101) -W2C-W2C 4 nm 2.8 Amorphous to crystalline WC 1-x transition occurs.

55. Role of W atoms- ab initio calculation W atoms dissolved in amorphous carbon matrix played a role of a pivot site where the atomic bond distortion could occur without inducing a significant increase in elastic energy, causing the stress reduction. C C H W C H

56. Other Candidate Elements

57. Summary Residual stress reduction by third element addition –Small amount addition of Si and W is effective. Ab-initio calculation and MD simulation using a hybrid force field of Brenner and Tersoff type force fields –Small amount of Si incorporation in a-C network effectively relaxes the distorted bonds. –W atoms dissolved in a-C matrix play a role of pivot site where the atomic bond distortion can occur without inducing a significant increase in elastic energy. Relax Bond Distortion while Keeping 3-D Interlinks

58. Outline 다이아몬드상 카본필름의 잔류응력 잔류응력의 제어 –Ar background gas 의 효과 –Si addition 효과 –W addition 효과 –Perspective 잔류응력의 활용 –Buckling –Interfacial Toughness 측정 –Elastic Property 측정

59. Telephone Cord Buckling M.W.Moon et al, Acta Mater., 50 (2002) 1219.

60. Buckling Configurations

61. Delamination of Floor Paint Bottom of parking lot of a chinese restaurant in Vancouver (2004)

62. Off-Piste Run in Hoghfügen

63. What can we do with this phenomenon?

64. Quantitative Analysis K.-R. Lee et al, Diam. Rel. Mater., 2 (1993) 218.

65. What can we do with this phenomenon? Can be a useful tool to estimate the mechanical properties of thin films and the fundamental interface toughness (adhesion)

66. What can we do with this phenomenon? For Isotropic Thin Films

67. Measurement of Residual Stress Curvature (R) Ds DfDf

68. What can we do with this phenomenon? For Isotropic Thin Films

69. DLC Bridges by Micro Fabrication DLC film Deposition ( on SiO 2 ) DLC Patterning SiO 2 Isotropic Wet Etching Wet Cleaning Strain Estimation

70. C 6 H 6, 10mTorr, -400V, 0.5  m 150  m Microstructure of DLC Bridges

71. Strain of the Buckled Thin Films Z X 2A 0

72. Effect of Bridge Length  m

73.  V  V  V  V DLC Bridges

74. Biaxial Elastic Modulus Bridge Method

75. DLC film Deposition Cleavage along [011] Direction Si Etching (by KOH Solution) Wet Cleaning Strain Measurement Preparation of Free Overhang

76. Free Overhang Method Biaxial elastic modulus Strain of the free overhang

77. A 0 / λof Free-hang at 546 nm I II III a-C:H, C 6 H 6 -400V

78. 5.6 ㎛ 11.3 ㎛ 2 ㎛ 11 ㎛ Effect of Etching Depth t=546 nm t=55 nm

79. Elastic Modulus for Various Ion Energies Nanoindentation t>1.0 ㎛

80. Advantages of This Method Completely Exclude the Substrate Effect Can Be Used for Very Very Thin Films

81. Nano-indentation The elastic strain field >> the plastic strain field Substrate Effect is Significant. Substrate

82. Substrate Effect on the Measurement

83. Advantages of This Method Completely Exclude the Substrate Effect Can Be Used for Very Thin Films

84. a-C:H, C 6 H 6 -400V J.-W. Chung et al, Diam.Rel. Mater. 10 (2001) 2069. ta-C (Ground) Elastic Modulus of Very Thin Films

85. Biaxial Elastic Modulus 20 233 166 100

86. 233 166 100 20 Structural Evolution of DLC Films Si Substrate J.-W. Chung et al, Diam.Rel. Mater., 11, 1441 (2002).

87. Residual Stress of ta-C film

88. Biaxial Elastic Modulus of ta-C film

89. What can we do with this phenomenon? Can be a useful tool to estimate the mechanical properties of thin films and the fundamental interface toughness (adhesion)

90. Fundamental Adhesion

91. Fundamental Adhesion DLC on Glass

92. Delamination of Patterned Substrate SEM FEM 2b* = 2.573  m 2b 0

93. Conclusions Can be a useful tool to estimate the mechanical properties of thin films and the fundamental interface toughness (adhesion)