SOME CONSIDERATIONS RELATING TO GROWTH CHEMISTRY OF AMORPHOUS SI AND (SI,GE) FILMS AND DEVICES

摘要

Recent experiments suggest that the chemistry responsible for the growth of amorphous and microcrystalline Si and (Si,Ge) alloys is more complicated than suggested by the standard model of growth. In particular, unexpected phenomena related to the density of ion flux, magnitude of ion energy and the presence of inert gas ions in the discharge suggest that both inert and reactive ion flux profoundly influence the growth of amorphous and microcrystalline films and devices. The influence of the ion flux is particularly important in understanding the growth of high quality a-(Si,Ge):H films. By carefully controlling this flux, we can change significantly the H bonding environment in a-(Si,Ge):H and produce high quality materials and devices. These observations suggest that the standard model of growth, which postulates that the growth is primarily limited by surface diffusion of radicals, and that H is eliminated by spontaneous bond breaking between neighboring Si-H bonds and formation of H2 molecule, does not describe the actual growth chemistry very well. Rather, the growth is limited by both surface diffusion of radicals and more fundamentally, by how rapidly H desorbs from surface and subsurface bonds. Ion induced desorption of excess H is shown to be very important in controlling the growth of both a-Si and a-(Si,Ge):H.