Investigations on high-temperature thermal oxidation process at top and bottom interfaces of top silicon of SIMOX wafers

The structure of separation by implanted oxygen (SIMOX) wafers oxidized at temperatures from 1000 to 1350°C has been investigated using cross-sectional transmission electron micorscopy and spectroscopic ellipsometry. By high-temperature oxidation at 1350°C, a 43 nm thick internal thermal oxide (ITOX) layer is grown between the top Si layer and the buried oxide layer formed by oxygen implantation and subsequent annealing. The resulting buried-oxide thickness is one and one-half times the original. The thickness of ITOX increases with increasing oxidation temperature. In addition, the superficial thermal oxide layer formed on the SIMOX wafers during the oxidation is somewhat thinner than that on the bulk Si wafers. A mechanism to account for both superficial thermal oxidation and internal thermal oxidation is proposed. The top Si-buried oxide interface, where some oxygen atoms react with Si during high-temperature oxidation, acts as a sink for them and causes them to diffuse more easily through the thin top Si layer to the interface.