Property mapping of polycrystalline diamond coatings over large area

Abstract

Large-area polycrystalline diamond (PCD) coatings are important for fields such as thermal management, optical windows, tribological moving mechanical assemblies, harsh chemical environments, biological sensors, etc. Microwave plasma chemical vapor deposition (MPCVD) is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall. However, the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings. In the present work, a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor; the temperature gradient resulted in a non-uniform diamond coating. An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating. It was found that there was large instability inside the system, in terms of substrate temperature (as high as ΔT = 212 ℃), that resulted in a large dispersion of the diamond coating's final properties: residual stress (15.8 GPa to +6.2 GPa), surface morphology (octahedral pyramids with (111) planes to cubo-octahedrals with (100) flat top surfaces), thickness (190 µm to 245 µm), columnar growth of diamond (with appearance of variety of nanostructures), nucleation side hardness (17 GPa to 48 GPa), quality (Raman peak FWHM varying from 5.1 cm 1 to 12.4 cm 1 with occasional splitting). This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.

Characterizations of microwave plasma CVD grown polycrystalline diamond coatings for advanced technological applications

“…In our earlier published results [44], it has been shown that how the substrate temperature varies widely across the 100 mm diameter silicon substrate surface, and it was also observed that efficient tuning of the reactor parameters helped in achieving better thermal management for CVD diamond growth. In the present case, citing earlier work report [53], it can be inferred that cubic morphology and abnormality in substrate temperature was responsible for such anomaly in results for as-grown region of study for the sample W3.…”

Some Aspects of Diamonds in Scientific Research and High Technology

“…The diamond peak positions of both the white and black annealed PCD samples are at 1328.45 cm −1 which is a downshift from the theoretical peak position for single crystal diamond as shown in Figure 6. Down shift of spectra is due to the tensile stress inside the lattice (thermal stress due to expansion mismatch with the Si substrate does not exist as the PCDs are freestanding) [129]. Now on the other hand, a-C (amorphous carbon) hump centre is around 1486 cm −1 for white annealed PCD but such diamond like carbon (DLC) phase centre shifts to 1560 cm −1 for the black annealed PCD sample.…”

Microwave Plasma CVD Grown Single Crystal Diamonds - A Review

“…Such high energy transmission necessitates large diameter diamond window for efficient thermal management and also low loss transmission [164]. So far large diameter polycrystalline diamond windows [165][166][167] have been used but they have grain boundaries which affect the transmission loss. So the best window material would have been large area single crystal diamond but synthesis of inch size SCD is still a technological challenge.…”