Contents Introduction to Residual Stress of Thin Films

Contents • Introduction to Residual Stress of Thin Films • Industrial Application and Residual Stress of DLC Films • Elastic Modulus Measurement by a Simple Micro-Fabrication

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! – Affects the mechanical behaviors of the coating and devices (elastic distortion, plastic deformation, fracture, adhesion) • Origin of the Residual Stress – Any process that changes the in-plane dimension of the film relative to that of the substrate

Relative Dimensional Changes Substrate Interaction Stresses Intrinsic Stresses Due to Property Misfit Thermal Stress Epitaxial Stress Structure Evolution During Growth Stress

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

Epitaxial Strains Condition : Coherency with different lattice parameters

Intrinsic Stress (Growth Stress)

Relative Dimensional Changes Substrate Interaction Stresses Intrinsic Stresses Due to Property Misfit Thermal Stress Epitaxial Stress Structure Evolution During Growth Stress

Bending due to Residual Stress DLC Films Deposited by Filtered Vacuum Arc.

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

Stress Measurement

Properties of Solid Carbon Property Diamond DLC Graphite Density (g/cm 3) 3. 51 1. 8 – 3. 6 2. 26 Atomic Number Density (Mole/cm 3) 0. 3 0. 2 – 0. 3 0. 2 Hardness (Kgf/mm 2) 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 Opaque Resistivity (Wcm) >1016 1010 - 1013 0. 2 – 0. 4

Applications of DLC Film

Residual Stress DLC Films Deposited by Filtered Vacuum Arc.

Deposition Method for DLC Films 1000 Energy Cold Substrate Impact Energy (e. V) Ion Source 100 Dense Carbon Polymer Like Carbon 10 1 Dense Hydro. Carbon Amorphous Carbon (sp 2) Carbon Source Plasma Polymers Hydrocarbon Source

Intrinsic Stress (Growth Stress)

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

Self Delamination of DLC Films • K. -R. Lee et al. , Diam. Rel. Mater. 2 (1993) 208. • M. -W. Moon et al. , Acta Mater. , 50 (2002) 1219.

Failure Due to Residual Stress Constant Temperature and Humidifier Motor Fn Ft At 90% R. H.

Stress Effect on MEMS Structure 0. 45 mm thick DLC coating Courtesy of SAIT

Key Idea of the Present Method For Isotropic Thin Films

Relative Dimensional Changes Substrate Interaction Stresses Intrinsic Stresses Due to Property Misfit Thermal Stress Epitaxial Stress Structure Evolution During Growth Stress

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

Preparation of DLC Bridges by Micro Fabrication DLC film Deposition ( on Si. O 2 ) DLC Patterning Si. O 2 Isotropic Wet Etching Wet Cleaning Strain Estimation

Microstructure of DLC Bridges 150 mm C 6 H 6, 10 m. Torr, -400 V, 0. 5 mm

Strain of the Buckled Thin Films (I) Z X 2 A 0

Stain of the Buckled Thin Films (II)

Elastic Modulus for Various Ion Energies Nanoindentation t>1. 0 ㎛

Elastic Modulus of Thin Films • 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 of Thin Film Substrate

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

Bulge Test For Isotropic Film

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

Freehang and Micro Bridge

Advantages of This Method – Simple Method – Completely Exclude the Substrate Effect – Can Be Used for Very Thin Films ü The possibility of elastic modulus measurement in very thin film

Nano-Indentation of Thin Film Substrate

Nano-indentation Results

Elastic Modulus for Various Ion Energies Nanoindentation t>1. 0 ㎛

HDD용 Hard Disk

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

Residual Compressive Stress & G-peak Position of Raman

Biaxial Elastic Modulus 100 166 233 20

G-peak Position of Raman 233 166 100 20

Schematic Film Structure Si Substrate 233 166 Si Substrate 100 20 Si Substrate J. -W. Chung et al, Diam. Rel. Mater. , 11, 1441 (2002).