Breakdown physics of low-temperature silicon epitaxy

We describe new insights into the mechanisms that affect low-temperature silicon epitaxy growth (T$<$630\r{ }C) by chemical vapor deposition (CVD). Experiments using hot-wire CVD show that below 500\r{ }C epitaxial growth is limited to relatively small thicknesses ($\sim $0.5$\mu $m), after which an amorphous nucleates and takes over film growth. Above $\sim $600\r{ }C, however, epitaxy is possible to very large thicknesses (at least 11 $\mu $m) and no breakdown is observed. We present an isotropic model for growth that explains the morphologies observed after breakdown to a-Si:H at low temperatures. The cause of breakdown, however, is still not well understood. However, our hot-wire CVD experiments over a large range of temperatures (200-700\r{ }C) provide important insights into the roles of roughness (that is implicated in the failure of low-T molecular beam silicon epitaxy) and hydrogen in epitaxy failure.