IN-SITU SPECTROSCOPIC ELLIPSOMETRY STUDIES OF INTERFACES OF THIN-FILMS DEPOSITED BY PECVD

The formation of a-Si:H-a-SiN(x) and p-doped a-Si:H (p)-intrinsic (i) interfaces has been investigated in situ by spectroscopic phase modula ted ellipsometry (PME) from UV to IR. The thin films are deposited by plasma enhanced chemical vapor deposition (PECVD). In both cases, the nature of the interface is found to be influenced by the deposition se quence affecting the corresponding devices' behaviour. The a-SiN(x)/a- Si:H and p/i interfaces are found to be atomically sharp. A different behaviour is observed when p-doped a-Si:H or a-SiN(x) is deposited fir st. In the latter case, the ellipsometric measurements clearly reveal a nitrogen incorporation in the first monolayers of a-Si:H together wi th an increase of intensity of the SiH bonds at the interface. Likewis e, a hydrogen accumulation, at a level of a few monolayers, is observe d at the i/p interface. More generally, the monolayer sensitivity of I RPME to vibrational absorption is emphasized.