ROLE OF OXYGEN IN THE FORMATION OF VOIDS AT THE SIC-SI INTERFACE

The purpose of this letter is to observe voids at the SiC-Si interface beneath the SiC layers grown by chemical vapor deposition at high tem perature. It is shown in this letter that the volume of the voids per unit area is proportional to the oxygen concentration in the Si substr ate over seven orders of magnitude. In situ dynamical reflectivity mea surements show that the voids are formed during the carbonization step and especially when the carbon, which has diffused deeply into the Si substrate, diffuses back toward the SiC layer just completed at the s ubstrate surface. This back diffusion is due to the inversion of the c arbon concentration gradient sign at that moment. It is accompanied by the formation of CO, resulting either from the reduction of SiO SiO2 dissolved in the Si substrate. Diffusion of carbon in silicon might im prove the methods of purification for the removal of oxygen which rema ins the main impurity of the purest silicon material. (C) 1997 America n Institute of Physics.