In situ investigation of the amorphous silicon/silicon nitride interfaces by spectroellipsometry

We present an in situ study, by spectroellipsometry, of interfaces between amorphous silicon (a-Si:H) and silicon nitride (a-SiN_x). The nature of the interface between amorphous silicon and silicon nitride depends on the order of deposition. A behavior compatible with an atomically abrupt interface is observed when a-SiN_x is deposited on top of a-Si:H. On the contrary, a graded transition with a width estimated at ≊15 Å is observed when a-SiN_x is deposited first. An NH₃ plasma treatment has little influence on the interface properties. These different behaviors are attributed to the plasma process.