DEPTH PROFILES OF THE OPTICAL-PROPERTIES OF BURIED OXIDES (SIMOX) BY ELLIPSOMETRY

The optical properties of the buried oxide in silicon-on-insulator films synthesized by oxygen implantation are investigated by ellipsometry performed during progressive etching of the structure. Both thin and thick buried oxides are considered as well as the system thermal oxide/buried oxide formed by oxidation of the silicon overlay. The experiment suggests that the in-depth profile of the refractive index is flat around 1. 45 and reveals the presence of an intermediate layer (10-30 nm thick with higher and variable refractive index) at the interface between the buried oxide and the bulk silicon substrate. As this transition layer causes the standard ellipsometry abacus to become inappropriate, a consistent four-region model is constructed and shown to give a realistic description of the SIMOX structure.