Microwave plasma enhanced chemical vapour deposition (MWPCVD) of polycrystalline diamond coatings and their characterisations for thermal applications Awadesh Kumar Mallik, Someswar Datta, Sumana Ghosh, Vamsi Krishna Balla CSIR - Central Glass & Ceramic Research Institute, Kolkata – 700032, India INTRODUCTION Figure 3. Chemical Mechanical Planarization (CMP) CMP is a process of removing topography of the surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching and free abrasive polishing. However, the removal and planarization mechanism is much more complicated in case of MPCVD diamond considering extreme nature of the material. Figure 1. CVD Diamond for Thermal Management developed at CSIR-CGCRI Figure 8. Cross-sectional microscopy of one large area PCD coating – samples taken from different surface points Material Thermal Conductivity (W /cm-K) Thermal Diffusivity (cm2/s) Pure Mo, Pure W ~160 0.54 Pure Cu 393 1.11 Pure Al 238 0.84 Cu-W, Cu-Mo alloys 220 - AlN ceramics 285 1.47 Al-SiC, Cu-Al-SiC, Si-SiC ceramic metal composites 200 Single Crystal Diamond 2000 3-11 CVD Diamond >1000 1-11 Diamond-Cu composite 550 Figure 9. XRD micrographs and Raman signals taken from table 2 samples, showing good crystallinity and quite high quality Poly- crystalline Diamond sample Diameter of circular plate (mm) Weight in Carat Thickness -from mass (µm) Thermal diffusivity (D) (cm2/s) Thermal Conductivity (k) (W/m-K) Black, Opaque 12,5 0.347 161 3.5 6.3 White, Transluscent 40 1.73 78 3.7 6.6 Figure 4. CSIR-CGCRI stationed STR 500 Raman Spectrometer (Cornes Technologies) Table 1. Comparison of CVD Diamond with other known thermal manager materials RESULTS & DISCUSSIONS APPLICATION AREAS Microwave power devices High power switches Modern laser diodes GaN LEDs Slab coupled Optical waveguide amplifier (SCOWA) Optically pumped semiconductor laser, OPS lasers Vertical External cavity surface emitting lasers, VECSELs (a) (b) (c) (d) Table 3. Thermal properties of CSIR-CGCRI developed diamond samples MATERIALS & METHODS CONCLUSIONS (a) (b) Figure 5. Perfect octahedrals indicating α parameter = 3 (√3[V100/V111]) Figure 2. (a) CSIR-CGCRI located DT1800 – one MPCVD 915 MHz diamond reactor (Lambda Technologies Inc. USA), (b) Detonation nanodiamond (ITC, USA) seeded Si wafer, (c) Microwave plasma during diamond synthesis, (d) Polycrystalline diamond coated Si wafer after CVD run SEM image of DND seeded Si substrate Figure 10. Freestanding PCD plates and discs CSIR-CGCRI has successfully grown PCD over large area with ± 10% thickness uniformity CMP produces large flattened regions with 2 nm roughness but do not decrease overall surface roughness WET ETCHING of Si substrate produced freestanding Diamond Plates LASER MICROMACHINING cut Diamond Plates into different geometrical shapes CSIR-CGCRI produced PCD foils and plates have high enough thermal conductivity to be used in many thermal management engineering applications (d) (c) Figure 6. FESEM micrograph of (a) Chemo-Mechanically Polished MPCVD diamond, (b) and (c) are magnified image of (a), (d) and (e) are the magnified view of the circled flat region of (c). Table 2. Diamond CVD processing conditions Sample Time (hr) H2 flow rate (sccm) CH4 flow rate (sccm) Pressure (torr) MW power (kW) Probe (cm) Short Stage Substrate Centre temperature (oC) W1 12.5 850 25.5 118 9.3 8.7 58.6 0.9 1000-1080 21.5 500 15 1 920-1140 W2 66 9 920-1060 W3 96 900-1140 W4 140 900-1110 ACKNOWLEDGEMENTS This work is being carried out with full financial support from CSIR, India. DST International Travel Support, India provided AKM, the presenter, necessary return air fare with visa fees for attending this diamond conference at Riva del Garda, Italy, 2-5 Sept. 2013. Dr. V. Ralchenko kindly extended his support for thermal property evaluation of the CSIR-CGCRI grown PCD coatings in his GPI-RAS, Diamond Laboratory. Lambda Technologies Inc. USA helped in CVD experiments. Figure 7. AFM line scan on the (a) as-grown and (b) polished surface of MPCVD diamond coating, 3D AFM images of the (c) as-grown and (d) polished surface of MPCVD diamond coatings, AFM image of a single grain on the (e) as-grown and (d) polished surface of MPCVD diamond coatings.