1. 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 – , 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
21.5
500 15 1 W2 66 9 W3 96 W4
140
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
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.