Issues involved with the use of optical reflectance systems for measurements of SIMOX silicon-on-insulator thickness

Current visible light reflectance spectrometers in nearly all wafer fabs have the capability to measure thin film (<5000 Å) Silicon-On-Insulator (SOI) layer thicknesses. Additionally, variable spot sizes and pattern recognition with precise stage movement make these systems highly desirable for routine monitoring of SOI thickness in production environments. Unfortunately not all users of this equipment are aware of the capabilities and shortcomings of their systems when applied to measurements of SIMOX produced SOI. Sensitivity analysis should be used to aid in setup of recipe parameters before release to production. In this work, various SIMOX wafers were measured using a Prometrix FT-600 system which was upgraded to include the spectral analysis software which is normally resident on newer systems. Mean Square Error (MSE) is used to evaluate the `goodness of fit´ between measured reflectance curves and the theoretical curve for a solution