Jin-Won Chung *+, Kwang-Ryeol Lee *, Dae-Hong Ko +, Kwang Yong Eun * * Thin Film Technology Research Center, Korea Institute of Science and Technology. +Department of Ceramic Engineering, Yonsei University. Elastic Modulus of Very Thin Diamond-like Carbon (DLC) Films

Measurement of Mechanical Properties of Very Thin Films Various industrial applications need very thin film. The reliability for applications. For Example –Protective layer for a hard disk Thickness of the protective layer has been reduced to less than 5nm.

Measurement of Elastic Properties of Thin Films Nano-indentation –From Analysis of Unloading Curve –Significant Substrate Effect Sonic Vibration Method –Using Sonic Vibration Resonance –Need Thick Films for High S/N Ratio Other Acoustic Method –Using Laser, SAW –Difficult to Separate Acoustic Signal Bulge Test –From Strain of Pressurized Membrane –Difficult Micro-fabrication Technique

Nano-indentation Measure the Elastic Modulus - Initial unloading is pure elastic. Substrate Effect -The elastic strain field is much wider than the plastic strain field.

Key Idea of the Present Method For Isotropic Thin Films

Measurement of Residual Stress Curvature (R) dsds dfdf

Si Substrate Etching by KOH Solution Preparation of Free overhang

Strain From DLC Free overhang Biaxial elastic modulus Strain of the films 2A 0

Free overhang Method E/(1- ) (GPa) Negative Bias Voltage (V) S.J.Cho et al, Diam. Rel. Mater. 8 (1999) S.J.Cho et al, Thin Solid Films 341 (1999)

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

Previous Work a-C:H, C 6 H V J.-W. Chung et al, Diam.Rel. Mater. in press (2001) ta-C

Purpose of the Present Work Evaluate the biaxial elastic modulus of very thin film in wide rage of deposition conditions in RF-PACVD Investigate the structural evolutions by the Raman spectroscopy

Synthesis of DLC Films RF PACVD (13.56MHz) Gas : CH 4 V b / P 1/2 : 20 ~ 233 V b /mTorr 1/2 Substrate : P type (100) Si Thin Si wafer for Stress Measurement Raman spectroscopy Film Thickness : ~ 50nm

Residual Compressive Stress & G-peak Position of Raman

Biaxial Elastic Modulus

G-peak Position of Raman

Schematic Film Structure 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.