The Influence Of Methane Content On The Growth Of Single Crystal Diamonds And The Study Of Etch-pit On The Diamond

Microwave plasma chemical vapor deposition is the main method to preparehigh quality diamond with high growth rate and methane content plays a decisive roleon the growth and quality of diamond during the deposition. On the basis of the highspeed growth, increasing methane content may cause several effects including:(1) It can change the precursors of diamond phase and non-diamond phase, theconcentration of H atom ratio in plasma. Compared with other reactive groups, theprecursors of non-diamond phase C2increased significantly with the increasing ofmethane content. Plasma etching effect shows a trend of decrease after the firstincrease in the chamber. It makes the quality of diamond improve, while whenmethane content is much higher, the quality will fall. As the total concentration ofcarbon source continues to increase, the growth rate keeps increasing.(2) It can cause the increasing of nucleation rate and change the growth mode ofthin film. Because the growth rate under this mode is high, the density of stepsincreases and the surface morphology changes.(3) It can reduce the spread of nitrogen. N atom spread into the crystals bydiffusion. With the deposition rate increasing, diffusion rate of N reduce relatively. Asa result, the N content in the epitaxial layer will reduce.The plasma with a mixture of hydrogen and oxygen gases could etch non-diamond phase firstly, and then diamond phase. It can eliminate the mechanicalpolishing defects on diamond surface. In this paper, we will study the influence ofH2/O2plasma etching on the surface topography of diamond. We get someconclusions by comparing four different diamond etching conditions.(1) Plasma etching mainly begins at non-diamond phase and grain boundary, sothe density of etching pits is higher around those places.(2) It is well known that the quality of HTHP diamond is poor than that of CVDdiamond. So in the same conditions, the density of etching pits on HTHP diamondsurface is higher. On the other hand, we can determine the quality of diamond bycomparing the surface etching pits density.(3) The etching pits on HTHP diamond surface is platform shaped, while it isirregular on CVD diamond that is something like inverted cone shape.(4) With the increasing of etching time, etching pits caused by mechanical polishing defects are gradually disappeared. But if they are caused by crystal defects,they will not disappear.