A Novel Approach of Utilizing Mechanically Flexible SiC Substrate to Grow Crack-Free AlN Bulk Crystal by Thermal Strain Relaxation Functionality

Abstract

The fabrication of novel semiconductor seed crystals using hetero-epitaxial growth on substrates such as Si, sapphire, and SiC, which have been successfully grown to large diameter and high quality, is very attractive as a breakthrough technology. However, a critical issue in heteroepitaxial growth is the formation of cracks due to thermal stress caused by the difference in the thermal expansion coefficient between the substrate and the growth layer during the cooling process after growth. In this study, we propose a method to reduce thermal stress by using a "Flexible substrate," which is a substrate with mechanical flexibility enhanced by removing more than 80% of its volume with periodic through holes. Using this method, we obtained an AlN hetero-epitaxial growth layer with absolutely no cracks observed. This method is applicable not only for AlN on SiC but also for the fabrication of various new semiconductor materials.