Study on diamond temperature stability during long-duration growth via MPCVD under the influence of thermal contact resistance

Abstract

During the process of growing diamond crystals via microwave plasma chemical vapor deposition (MPCVD), the substrate temperature will gradually increase with increasing growth time. At present, the commonly used method to compensate for the temperature increase is to reduce the deposition parameters (gas pressure and input power) or adjust the height of the susceptor. However, according to previous studies, reducing the substrate parameters will reduce the growth rate. In addition, adjusting the height of the susceptor may cause secondary plasma, which could damage the equipment. Therefore, it is necessary to find the reason for the substrate temperature increase with the growth time and eliminate it. Firstly, the effect of substrate size change on the substrate temperature was simulated dynamically, which indicated that the substrate size change was not the main reason for the continuous increase of the substrate temperature. Subsequent analysis showed that non-diamond carbon formed at the bottom of the grown diamond, which may cause a change of the thermal contact resistance. Therefore, a thermal contact resistance component was introduced into the existing model of diamond growth, and it was found that the substrate temperature increased with the roughness of the bottom of the substrate. In order to eliminate the influence of thermal contact resistance, a welding growth method was proposed with the aim of avoiding the accumulation of the non-diamond carbon at the bottom of the substrate. The growth with different welding materials showed that the grown diamond's internal stress distribution after welding growth was similar to that without welding growth, but the non-diamond carbon at the bottom was obviously restrained. However, the selection of welding materials needs to be further optimized with respect to the welding stability and growth rate.