Interface-layer formation mechanism in a-Si:H thin-film growth studied by real-time spectroscopic ellipsometry and infrared spectroscopy

Real-time spectroscopic ellipsometry (SE) and infrared attenuated total reflection spectroscopy (ATR) have been applied to investigate interface layer formation mechanisms in an a-SI:H film on a c-Si substrate covered with native oxide (similar to 30 Angstrom) in a conventional rf plasma-enhanced chemical vapor deposition. These real-time monitoring techniques allow us to determine a depth profile of hydrogen content for the SIH and SiH2 bonding states, together with the microscopic structural evolution during the a-Si:H deposition. The analyses of these real-time measurements show the formation of a 35-Angstrom-thick H-rich layer having an average hydrogen content of similar to 17 at.% at the a-Si:H/substrate interface. A deuterium diffusion experiment performed after a 130-Angstrom-thick a-Si:H deposition supports the H-rich layer formation at the interface. This interface layer formation is primarily caused by the H-rich three-dimensional island growth on the substrate in the early a-Si:H deposition stage. In a following coalescence process, we found a significant reduction in the hydrogen content in a-Si:H bulk layer, accompanied by a clear surface smoothening of the a-Si:H layer. The above results indicate that surface diffusion of precursors promotes a dense a-Si:H network formation during the coalescence and confines H-rich a-Si:H islands at the film/substrate interface region. [S0163-1829(99)01944-X].