다이아몬드상 카본필름의 잔류응력과 기계적 물성 한국기계연구원 2001. 8. 7 한국과학기술연구원 이 광 렬

Outline 다이아몬드상 카본필름의 소개 박막의 잔류응력 다이아몬드상 카본필름의 잔류응력 다이아몬드상 카본필름의 일반적 특성 장단점 및 응용 박막의 잔류응력 잔류응력의 종류 잔류응력의 측정 다이아몬드상 카본필름의 잔류응력 잔류응력의 발생거동 및 영향 제삼원소 첨가에 의한 잔류응력의 제어 잔류응력을 이용한 박막의 탄성계수평가

Carbon Atomic Bond Structure

What is DLC ? Amorphous Solid Carbon Film Mixture of sp1, sp2 and sp3 Hybridized Bonds High Content of Hydrogen (20-60%) Synonyms Diamond-like Carbon (Hydrogenated) amorphous carbon (a-C:H) i-Carbon Tetrahedral Amorphous Carbon

a-C:H ta-C

Properties of Solid Carbon Property Diamond DLC Graphite Density (g/cm3) 3.51 1.8 – 3.6 2.26 Atomic Number Density (Mole/cm3) 0.3 0.2 – 0.3 0.2 Hardness (Kgf/mm2) 7000 - 10000 2000 - 8000 <500 Friction Coeff. 0.05 0.03 – 0.2 Refractive Index 2.42 1.8 – 2.6 2.15 – 1.8 Transparency UV-VIS-IR VIS-IR Opaque Resistivity (Wcm) >1016 1010 - 1013 0.2 – 0.4

Historical Survey 1972 Aisenberg and Chabot : Arc Ion Beam 1979 Holland and Ohja : PACVD 1984 Mori and Namba : Ion Plating 1986 Savvides : Sputtering 1992 Collins et al : Laser Ablation Filtered Vacuum Arc

Deposition Methods Ion Source Energy Cold Substrate Impact Energy (eV) 1 10 100 1000 Amorphous Carbon (sp2) Dense Source Hydrocarbon Hydro- Polymer Like Plasma Polymers Ion Source Energy Cold Substrate

Energy Dependence of DLC

Ion Energy Distribution 이 표는 현재 코팅 공정에서 사용되고 있는 각각의 소스들에서 발생되는 이온의 에너지 분포를 나타낸 것입니다. 일반적으로 CVD나 전자빔 증발법에서 발생되는 이온의 에너지는 거의 열에너지 정도인 0.1eV를 넘지 못합니다. 그리고 이온빔이나 마그네트론 을 이용한 스팟트링에서도 발생되는 이온의 에너지는 수 eV를 넘지 못합니다. 하지만 본 실험에서 사용된 FVAS는 수십 eV 범위의 에너지를 가진 이온들을 생성할 수 있읍니다. 특히 아크 증발법에서 발생되는 증발 물질은 90% 이상의 이온화률을 가지고 있으며, 특히 자장 여과 장치를 이용하면 거의 99%의 이온을 모재까지 수송할 수 있읍니다. PACVD

Examples of Deposition Methods 다음은 Si 함유 DLC 필름을 증착하는데 사용한 장비의 간략한 모식도와 증착조건 입니다. 13.56 MHz를 사용한 R.F PACVD법을 사용하였고 Source Gas로는 벤젠과 수소로 희석된 Silane개스를 혼합하여 사용하였습니다. 증착압력은 10mtorr로 하였고, 바이어스 volatage는 -400V를 가하였습니다. 필름내 Si의 함량을 조절하기 위하여 혼합개스 내의 Silane개스의 함량을 0에서 90%로 변화시켜 가면 증착을 하였습니다. 기판은 Si(100)웨이퍼를 사용하였고, 필름의 두께는 1 micro meter로 증착하였습니다. Si함량에 따른 마찰거동을 조사하기 위하여, Si이 포함되지 않은 순수한 DLC 필름과 Si이 0.5, 2, 9.5 at.% 함유된 DLC 필름을 제작하였습니다.

Examples of Deposition Methods

합성방법의 특징 합성 방법 특징 High Productivity, Very Smooth Film PECVD (DC, HF, RF,ECR, pulsed DC) High Productivity, Very Smooth Film Low Hardness & Thermal Stability Non Uniform in Complicated Shape Sputtering : ion beam Process Compatibility for HDD Low Adhesion, Poor Film Quality Ion Beam Deposition Medium Hardness, Medium Productivity Uniform Coating for Complicated Shape High Residual Stress, Poor Adhesion Complicated Deposition System Laser Ablation High Adhesion & Hardness Low Productivity FVA (Filtered Vacuum Arc) High Hardness & Thermal Stability

Properties of Solid Carbon Property Diamond DLC Graphite Density (g/cm3) 3.51 1.8 – 3.6 2.26 Atomic Number Density (Mole/cm3) 0.3 0.2 – 0.3 0.2 Hardness (Kgf/mm2) 7000 - 10000 2000 - 8000 <500 Friction Coeff. 0.05 0.03 – 0.2 Refractive Index 2.42 1.8 – 2.6 2.15 – 1.8 Transparency UV-VIS-IR VIS-IR Opaque Resistivity (Wcm) >1016 1010 - 1013 0.2 – 0.4

Major Points of DLC Films Low Deposition Temperature (R.T. – 200oC) No limitation of Substrate Materials Smooth Surface Roughness : few nm Wide Range of Physical Properties Tunability of the Properties Uniform Large Area Deposition High Productivity and Low Cost

AFM Image of DLC coated Si

IR Transmittance of DLC Coated Ge Windows

Courtesy of J&L Tech. Ltd

Minor Points of DLC Films Thermal Instability Degradation at High Temperature (400 – 600oC) High Residual Compressive Stress Max. 10 GPa Poor Adhesion Stable Chemical Bonds Especially on Ferrous Materials

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

Failure during Tribotest Self Delamination Failure during Tribotest

DLC 필름의 특성과 응용 2,000 - 8,000Hv 구 분 특 성 응 용 마찰계수 0.05 - 0.2 구 분 특 성 응 용 2,000 - 8,000Hv (cf. Diamond 10,000Hv) 비철금속 가공용 공구, 정밀금형의 표면경화코팅 High hardness 치구, GEAR, SURGICAL BLADE, HARD DISK등의 고체 윤활 코팅 Low friction and high wear resist. 마찰계수 0.05 - 0.2 (cf. Stainless Steel : 0.6 - 0.7) Chemical Inertness 산 또는 알카리와 반응치 않는다 부식 방지막, 인체삽입물의 BIO-COMPATIBLE COATING Optical Transmittance 특히 적외선 영역의 높은 광투과도 IR WINDOW, SCANNER WINDOW의 표면보호 코팅

경질박막의 내마모 윤활특성 DLC WC TiN CrN TiCN 마모도 마찰계수. 2.0 1.6 1.2 0.8 0.4 (상대비교치) 0.2 0.4 0.6 0.8 1.0

DLC 필름의 특성과 응용 2,000 - 8,000Hv 구 분 특 성 응 용 마찰계수 0.05 - 0.2 구 분 특 성 응 용 2,000 - 8,000Hv (cf. Diamond 10,000Hv) 비철금속 가공용 공구, 정밀금형의 표면경화코팅 High hardness 치구, GEAR, SURGICAL BLADE, HARD DISK등의 고체 윤활 코팅 Low friction and high wear resist. 마찰계수 0.05 - 0.2 (cf. Stainless Steel : 0.6 - 0.7) Chemical Inertness 산 또는 알카리와 반응치 않는다 부식 방지막, 인체삽입물의 BIO-COMPATIBLE COATING Optical Transmittance 특히 적외선 영역의 높은 광투과도 IR WINDOW, SCANNER WINDOW의 표면보호 코팅

Applications of DLC Film

Video Cassette Recorder

DLC 코팅 VTR 헤드드럼 Courtesy of Daewoo Electronics Co.

DLC Coated Digital VCR Tape

HDD용 Hard Disk

DLC coated Head Slider

DLC Coated Razor Blade

Schematic of Diesel Engine

Results of Wear Test under Dry Lubrication Conditions

Result of Dynamo Test (900h) Hard Cr Coated Ring DLC coated Ring Before Test Before Test After Test After test

Hard Cr Coated Piston Ring DLC/Cr Coated Piston Ring 6.5mm 100mm Before Test Before Test 5.3mm After Test After Test

Sliding Tools for Electron Gun Grids (2) manipulate the electron beam. Sliding Tools is used to make spacing between the grids (Tolerance is about 4mm) Smooth grid surface and parallel positioning are important.

DLC Coated Sliding Tools Low friction Long life time Electrical insulation No corrosion on the shelves Courtesy of J&L Tech. Co., Ltd.

IC Packaging 반도체 packaging용 EMC mold cavity의 이형성 증진 및 수명연장을 위한 코팅

DLC Coating on Packaging Tools Courtesy of J&L Tech. Co., Ltd.

인공 고관절 및 무릎관절 무릎관절 고관절

Biological Application of DLC DLC Coating for Wear Resistance

인공 심장, 수정체 인공심장 판막 인공수정체

DLC Coated Stents

Schematic of Wear Tester Load  Load : High &Low  Surroundings : Wet Condition Dry Condition Test disk Ruby Ball Saline

Wear Volume Wear Volume DLC on Ti DLC on Ti-Alloy  Condition : 0.026 mm3 0.021mm3  Condition : High Load 3000 cycle 0.002mm3 0.002 mm3 Dry Wet Dry Wet

Life Time of DLC Coatings Fracture Cycle DLC on Ti 92250 cyc DLC on Ti-Alloy  Condition : High Load 10250 cyc 6750 cyc 3172 cyc Dry Wet Dry Wet

IR Windows for Missile and Night Vision System

IR Transmittance of DLC Coated Ge Windows

Sand Blast Type Erosion Rig J. E. Field, Carvendish Lab. Cambridge University

Solid Particle Impact Erosion

Damage Pattern of Multilayer Coated Ge windows 200 sec 1000nm DLC 690nm a-Si 1900nm DLC 510nm a-Si 600 sec Ge Multilayer Structure

DLC Coated CD-R Pressing Die Courtesy of J&L Tech. Co., Ltd.

CD Surface Formed by Using Uncoated Mold RMS roughness = 1.31nm

CD surface formed by using DLC coated mold RMS roughness = 0.95nm

Residual Stress of Thin Films Thin films typically support very high stresses due to the constraint of the substrate to which they are attached Normally at near failure stress! Determines mechanical behaviors of the coating and devices (elastic distortion, plastic deformation, fracture, adhesion) Substrate Interaction Stresses Intrinsic Stresses Relative Dimensional Change after Growth Thermal Stress Epitaxial Stress Interfacial Stress Structure Evolution During Growth

Relative Dimensional Changes Condition : Adhesion between film and substrate Any process that changes the in-plane dimension of the film relative to that of the substrate

Thermal Stress Condition : Difference in thermal expansion coeff. Difference in temperature

Condition : Coherency with different lattice parameters Epitaxial Strains Condition : Coherency with different lattice parameters

Interfacial Stresses Condition : Inherent but significant in very thin film or multilayer

Intrinsic Stress (Growth Stress)

Residual Stress of Thin Films

Measurement of Residual Stress Assumption 1-D Treatment of Elastic Equilibrium Sufficient Adhesion df << ds ds << R ds df Curvature (R)

Stress of Multilayer Ko f1 K1 f2 f1 K2

Measurement of Curvature

X-ray Strain Measurement : sin2Y Method dY Y : Angle between normal vector and scattering vector sin2Y

Typical Behavior of Residual Stress of DLC Films ta-C by FVA a-C:H by rf-PACVD

Instability of Coating and Device High Residual Stress However, high residual compressive stress of ta-C films results in poor adhesion and the limitation of thickness. For example, like the left figure, the flat wafer strip was considerably bended after the deposition of ta-C film. As shown in the right figure, this high residual compressive stress makes ta-C film delaminate from the Si substrate and resulted in poor adhesion. It greatly limits the usefulness of ta-films for many applications. Many attempts have been reported to reduce the stress of the ta-C films without changing the other mechanical properties. In the present work, we attempt the study on the addition of silicon into ta-C to overcome the drawback of pure ta-C films. Instability of Coating and Device

The Effect of Stress on Raman G-peak Position Stressed Stress-relieved 4.1cm-1/GPa This is our previous work about the effect of the stress on G-peak position. In the left figure, upper Raman spectrum is that of ta-C films with 7GPa stress. After stress was fully relieved by the substrate etching technique, G-peak position was shifted to lower wavenumber like this figure. As a result, we observed that the residual compressive stress shifted the G-peak to higher wavenumber by 4.1 kaiser per GPa. J.K.Shin et al., Appl. Phys. Lett., 78 (2001) 631

Fundamental Adhesion T : Elastic energy U : Bending strain energy Δγ : Surface energy =(- gfs+ gfv+ gsv)

Energy Dependence of DLC

Synthesis of ta-C:Si Bias: Ground Control parameter Ar gas flow 10 ~ 20 SCCM Pressure B.P.= low 10-6 torr W.P.= mid 10-4 torr We synthesized silicon incorporated ta-C films by using filtered vacuum arc process with simultaneous silicon sputtering. This is the schematic of the deposition system used in the present work. Si concentration could be controlled by changing the flow rate of the Ar sputtering gas. Ar sputtering gas was supplied via gas feedthrough placed near the sputter gun. In order to minimize the Ar sputtering of films, the substrate was grounded. One hundred nanometer thick films were deposited on silicon wafer and thin silicon strip was also used for the stress measurement. Si was incorporated in the ta-C film by simultaneous magnetron sputtering of Si during the FVA deposition.

Si Incorporation C Si in substrate Si in the film This figure is the RBS spectrum of one of the Si incorporated ta-C films. As can be shown in this figure, we confirmed that silicon was uniformly incorporated in ta-C films. By this way, we analyzed the composition of films. Si in the film

Composition This result is the composition of the deposited films measured by RBS. The silicon concentration in the film could be controlled in a systematic way by changing the flow rate of the Ar sputtering gas. As shown in this figure, silicon concentration was strongly dependent on the Ar flow rate. When the Ar flow rate was less than 9 sccm, we could not obtain the Si incorporated ta-C film due to unstable ignition of the magnetron sputter source. However, as the Ar flow rate increased from 9 to 12 sccm, the Si concentration increased from 0.5 to 2.5 at.%. When the Ar flow rate was higher than 12 sccm, the significant increase in Si concentration was observed with increasing the Ar flow rate. When Ar flow rate was 18 sccm, the Si concentration of the film was 85 at.%. In all samples, small amount of oxygen was also incorporated with Si, which seems to be due to the surface oxide layer of the sputter target. However, the ratio of oxygen to silicon was less than 0.1 in most cases. The effect of oxygen on the structure of the film was assumed to be negligible in the present work.

Mechanical Properties These results are the changes in stress and mechanical properties with various silicon concentrations measured by nanoindentation. The Si incorporation significantly reduced the residual compressive stress. As shown in left figure, the stress sharply decreased from 6.0 to 3.3 GPa by adding only 1 at.% of silicon to the ta-C films. However, beyond 1 at.% of silicon, the stress gradually decreased to 0.8 GPa with the Si concentration. Hardness and plane strain modulus were summarized in the right figure. In contrast to the residual compressive stress, the mechanical properties did not sharply decrease with the Si addition. In the range of the Si concentration from 0 to 8.5 at.%, the hardness was reduced from 41 to 22 GPa, and the plane strain modulus from 354 to 200 GPa. The further increase of the Si concentration resulted in saturated values of the hardness and the plane strain modulus, which are comparable to those of nanocrystalline silicon carbide films.

Reduction of Hardness and Residual Stress II III This figure clearly shows the different behavior between the reduction in stress and hardness. We can divide the variation of mechanical properties into three regions. The first region is where the Si concentration was lower than 1 at.%.(with pointing the figure) In the case of the stress, 52 % of the total reduction occurs in this region. But,in the case of the hardness, there is 20 % reduction in this region. In this second region, there are linearly decrease in the both stress and hardness. When the Si concentration was higher than 10 at.%, there are the continuous decrease in the stress, while the hardness show the saturated values.

Raman Spectra & G-peak III II I Region I These open circles were the corrected G peak positions where the stress effect was excluded by previous stress data. Hence, the data of open circles reflect only the structural change due to the silicon incorporation. Now I will discuss the changes in the atomic bond structure in the previously mentioned region 1. That is, there is a significant reduction of the stress while the hardness gradually decrease by addition of a small amount of silicon. In this region, the shape and intensity of the Raman spectra were essentially same as those of pure ta-C films. Furthermore, as can be seen in the right figure, G-peak position did not vary significantly with silicon concentration. These results show that the ratio of sp3 over sp2 in the film was kept almost constant in this region. This implies that silicon atoms preferentially substituted the carbon atoms of sp3 bonds. Region I No significant changes in atomic bond structure. The stress effect on G-peak position

Atomic Bond Structure I II III Therefore, the behavior of the mechanical properties can be explained by the following model. When the silicon concentration is lower than 1 at.%, this silicon atom will form Si-C bonds like this figure, if silicon atoms preferentially substitute the carbon atoms of sp3 bonds This silicon incorporated site can play a role to compensate the distortion of the nearby C-C bonds. The relaxation of the residual stress would occur with large strains in the weaker Si-C bonds compared with C-C bonds. On the other hand, the hardness of the film is proportional to the degree of three dimensional interlinks of the atomic bond structure, which would be enhanced by sp3 bond. Because the incorporated silicon atoms substitutes the carbon of sp3 bond, the degree of three dimensional interlinks would not be reduced by the incorporated silicon atoms. Thus the decrease in the hardness is due to the weaker Si-C bonds rather than the decrease in the three dimensional interlinks. It caused the gradual change of the hardness in this concentration range.

Raman Spectra & G-peak III II I Region II When the silicon concentration was higher than 2.5 at.%, the shape of Raman spectra become different from those of pure ta-C films. With increasing silicon concentration, the intensity of Raman peak increase and the position shifted to lower wavenumber. At 22%, single large Raman peak was observed at about 1450 kaiser. Some researchers reported that this Raman peak is related with the nanocrystalline silicon carbide. Then, when the Si concentration is higher than 22 at.%, the intensity of the Raman peak decreased and eventually disappeared at the silicon concentration of about 50 at.%. These result means that structural changes occurred in the different way from that of region I. In addition, the G-peak position was abruptly shifted to lower wavenumber. These changes can be understood in the following way. It was well known that the increase in the Raman intensity was related with the symmetry breaking of the aromatic sp2 cluster. From the increase in the Raman intensity in this region(with pointing), it can be judged that the incorporated silicon start to substitute the carbon atoms in sp2 clusters. Region II The initial stage of SiC phase appearance Nanocrystalline SiC related peak at 1450 cm-1

The Changes of the Structure I II III FTIR Si-Si C-Si This is the result of FTIR spectra. Until the silicon concentration was 4 at.%, there was no change in the FTIR spectra. When Si concentration was higher than 8.5 at.%, the Silicon Carbon stretching absorption band started to appear around 750 cm-1. It can be thus said that the increase in the content of silicon carbide phase is the dominant structural change. Furthermore, from the result of XPS(pointing the XPS), we can see that silicon silicon bonds increased when the silicon concentration was higher than 22 at.%. Therefore, the changes of structure and properties in this region were mainly due to the increase of both the silicon carbon bonds and silicon silicon bonds. Consequently, the saturated behavior of the mechanical properties of which value are comparable to those of SiC, was the result of a large amount of silicon carbide phase formation in the region III. XPS Si 2p Region III SiC phase was dominant Si-Si bonding increased

Conclusions ta-C:Si films prepared by hybrid FVA Si concentration can be controlled by Ar gas flow The significant stress reduction by Si addition Hardness was reduced by 23 % ,while stress was reduced by 48 % in low Si concentration. Weaker Si-C bond sites relieved the stress without breaking the three dimensional interlink. When the Si concentration was higher than 22 at.%, the SiC phase strongly influenced on the structure and mechanical properties. Finally, I’d like to summarize our conclusion. Silicon incorporated tetrahedral amorphous carbon films were synthesized by using filtered vacuum arc process with simultaneous silicon sputtering. Si concentration can be controlled by Ar gas flow. The most important result in the present work is that. When the silicon concentration was lower than 2.5 at.%, the addition of silicon to the ta-C significantly reduced the stress, while the hardness gradually decreased. Hardness was reduced by 23 % ,while stress was reduced by 48 % in low Si concentration. Weaker Si-C bond sites relieved the stress without breaking the three dimensional interlink. When the silicon concentration was higher than 22 at.%, the silicon phase strongly influenced on the structure and mechanical properties.

압축 잔류 응력을 이용한 박막의 탄성계수 평가 Mechanical properties of thin films are not the same as those of materials having the sample composition in bulk form High quench rate in deposition process High defect densities and textures Non-equilibrium compositions Confinement of dislocations, craction, etc. in small dimensions

Nano-Indentation Initial unloading is pure elastic. Sneddon’s elastic contact theory

Nano-indentation Results

Laser-Acoustic Technique Sonic Vibration and Laser-Acoustic Technique Sonic Vibration Laser-Acoustic

Bulge Test For Isotropic Film

Key Idea of the Present Method Recently, we suggested a simple method to measure the elastic modulus of a DLC film which has a compressive residual stress This is a simple stress-strain relation for elastically isotropic thin films. In this equation, If one can measure the strain and the residual stress of the film, The biaxial elastic modulus would be obtained For Isotropic Thin Films

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

Strain From DLC Bridge by Micro Fabrication SiO2 Isotropic Wet Etching Wet Cleaning DLC film Deposition ( on SiO2 ) DLC Patterning Strain Estimation

Microstructure of DLC Bridges 150mm C6H6, 10mTorr, -400V, 0.5mm

Strain of the Buckled Thin Films (I) Z X 2A0

Stain of the Buckled Thin Films (II)

Elastic Modulus for Various Ion Energies Nanoindentation t>1.0 ㎛ 그래서 본 실험에서는 버클링 현상과 필름의 탄성특성을 이용하여 fundamental adhesion 에너지를 정량적으로 평가 하려고 합니다. 또한 이렇게 평가된 정량적인 값이 얼마나 타당하여 이 방법이 얼마나 타당한지에 대해 확인해 보려고 합니다.

Advantages of This Method Simple Method Completely Exclude the Substrate Effect Can Be Used for Very Thin Films The possibility of elastic modulus measurement in very thin film In contrast to the other measurements method, the present technique has many advantages. The most important advantage is that the elastic property of thin film can be measured without the substrate effect, because we can completely exclude the substrate effect by etching process. So we can accurately measure the elastic modulus very thin films, using this method.

Elastic Modulus of Very Thin Films The free overhang method was successfully employed to measure the biaxial elastic modulus of very thin DLC film. The left figure is the elastic modulus of a-C:H film made by rf-PACVD, and the Right figure is that of ta-C film made by Filtered Vacuum Arc. Here, the a-C:H film is polymeric, but the ta-C film is very hard. Using this method, we could successfully measure the elastic modulus of the film about 33nm thickness. The more important observation is that , in contrast to ta-C films, the elastic modulus of the film decreased when the film thickness was very small, in a-C:H film. In our previous work, we showed that the decrease in elastic modulus of very thin film is not due to the interfacial layer but due to the structural evolution during the initial stage of the film growth. These results show that the mechanical property measured in thick film cannot be always used for very thin film. Therefore, the mechanical properties of the film and the structural evolution during the initial stage of the film growth should be carefully investigated for a specific deposition condition. a-C:H, C6H6 -400V ta-C (Ground) J.-W. Chung et al, Diam.Rel. Mater. in press (2001)

Residual Compressive Stress & G-peak Position of Raman The left figure is measured residual stress and the right figure is G-peak positions of the Raman spectra of the thick DLC film. The residual stress of the film shows a maximum of 2.3 Gpa at the value of v over square root p of 100. This behavior agrees with the previous work in the precursor gas effect in rf-PACVD. In the previous work, EELS and electrical conductivity shows that the character of the film changed from polymeric to dense carbon and then to graphitic one as the value of V over square root P increased from 20 to 220. The structure change can be also observed by Raman spectrum analysis. The Raman spectrum analysis of DLC film includes deconvolution of the spectrum with two Gaussian peaks, G and D-peak. It is empirically known that the G-peak position illustrates the changes in atomic bond structure of the film. For example, graphitization of the film during high temperature annealing is correlated with the g-peak position shift to higher wave number. In the present work, G-peak position of the Raman spectra shifted to higher wave number as the value of V over square root P increased. We know that black point’s film has more polymeric component than the red point, the red point has dense and hard carbon bonding and the green and blue points have more graphitic component than red. From the data of this figure, it can be said that the G-peak position shifts to high wavenumber when the graphitic component increased and shifts to lower wave number when the polymeric component increased

Biaxial Elastic Modulus 100 166 233 20 This Figure shows the dependence of the biaxial elastic modulus on the film thickness A fixed elastic modulus was observed only at red point, hard and dense carbon film deposited In both case of higher or lower value of V / root P, decreasing the elastic modulus was observed in very thin films. The observed elastic modulus shows that the structural evolution during the initial stage of the film deposition is significant in the films of high content of polymeric or graphitic component.

G-peak Position of Raman 233 166 100 20 This figure shows the G-peak position of Raman spectra as a function of film thickness. The red point was deposited at optimum ion energy, and had maximum residual stress. It exhibits almost fixed G-peak position regardless to the film thickness It means that there are no structural changes during the growth in red point. But in the black point of the polymeric film, the G-peak position shifts to lower wave number with decreasing film thickness. Previously, we mentioned that, as the film became more polymeric, the G-peak position shifted to lower wave number. Hence, this result shows that the structure of the film is more polymeric, when the film is very thin. On the other hand, in green and blue points of the graphitic films, The G-peak positions shift to higher wavenumber. Because the G-peak position shifted to higher wavenumber, as the film became more graphitic This result shows that the structure of the film is more graphitic, when the film is very thin.

Schematic Film Structure Si Substrate 233 166 100 20 Si Substrate In polymeric and graphitic films, the elastic behavior of very thin film is similar. The biaxial elastic modulus decreased with decreasing film thickness. But the reason for the decrease of elastic modulus is not the same. In polymeric film, more polymeric film reduced the elastic modulus In graphitic film, more graphitic film reduced the elastic modulus Si Substrate

Conclusions Using the free overhang method, we could accurately measure the biaxial elastic modulus of very thin DLC film. (down to 50nm). The structural evolution in the initial stage of the film growth depended on the deposition conditions. - At the optimum ion energy, the film exhibited a fixed elastic modulus and G-peak position regardless to the film thickness. - On the other hand, the structural evolution during the initial stage of the film deposition was significant in the films of high content of polymeric or graphitic component. Now, I’d like to summarize my results Using the free overhang method, we can measure the biaxial elastic modulus of very thin DLC film accurately (up to 50nm). The structural evolution in the initial stage of the film growth depend on the deposition conditions It means that, At an optimum ion energy, the film exhibited a fixed elastic modulus and G-peak position regardless to the film thickness. On the other hand, the biaxial elastic modulus of the graphitic film and the polymeric film decrease with decreasing the film thickness. It shows that structural evolution during the initial stage of the film deposition is significant in the films of high content of polymeric or graphitic component.

Acknowledgement Financial Support Researchers 과기부 한러협력기술개발사업 (91-94) 과기부 선도기술개발사업 (94-01) 과기부 중소기업지원사업 (97) 산자부 산업기반기술개발사업 (99-01) KIST 기관고유사업 (92-00) 산업체 : 대우전자, 대우중공업, 제이엔엘테크 Researchers Postdoc : 오제욱, 최준엽, 신진국 위촉연구원 : 김성화, 김종국, 김명근 학생연구원 : 조성진, 이철승, 박세준, 정진원