Optical Thickness Evaluation of Separation by Implanted Oxygen (simox) Wafers

In low-dose SIMOX (Separation by IMplanted OXygen) of SOI (silicon on insulator) structures, the thickness of the surface-Si and buried-oxide layers was evaluated using ellipsometry, reflection and XTEM (cross-sectional transmission electron microscope). Due to the simplicity of the low-dose SIMOX structure, layer thickness could be successfully determined by single-wavelength ellipsometry once the thermal-oxide layer had been etched off. Dislocation density in the surface-Si layer was low, and no Si-islands or Si-pipes were observed in the buried-oxide layer by XTEM. Total errors of measurement and calculation were ≤±1 nm for the surface-Si layer and ≤±2 nm for the buried-oxide layer. These error values were acceptable to guarantee the ≤±5 nm thickness uniformity necessary for VLSI applications.