Analysis of improving the edge quality and growth rate of single-crystal diamond growth using a substrate holder
During single-crystal diamond growth by microwave plasma chemical vapor deposition (MPCVD), polycrystalline diamonds are prone to growing at the edge regions. This substantially reduces the usable area of the grown diamond. In recent years, a series of experimental studies have been carried out to solve this, and some achievements have been obtained. However, to understand the diamond growth mechanism more deeply, the relationship between growth quality and various influencing factors still needs to be studied quantitatively through simulations. The plasma density and substrate temperature are important factors that affect the quality of diamond crystallization. In this paper, the growth conditions of the diamond were simulated and compared with the experiments. The results showed that the temperature distribution on the substrate surface was uniform in the axial direction, while the CH3, H, and electron number density decreased significantly at the edge regions. When the substrate holder mentioned in the literature was used for growth, it was found that the number density uniformity of CH3, H, and electrons on the substrate surface improved significantly, without changing the temperature uniformity, and so did the edge quality of the grown diamond. However, the average growth rate decreased significantly and, combined with the approximate growth rate formula, it was found that the number density of CH3 and H on the substrate surface decreased significantly. The main reason for this was that the substrate holder was too high, which led to the substrate reaching the growth temperature at lower deposition conditions. Therefore, a substrate holder with a 6 mm height reduction was designed for simulation and experiment. The edge quality of the grown diamond with this substrate holder was better than that found using the previous substrate holder, and the growth rate was significantly improved. However, there was still a gap in the growth rate compared with results without the substrate holder. Finally, a substrate ring was proposed, to achieve the goal of high quality and high growth rate at the same time.