High speed whole wafer film thickness mapper

An instrument for rapidly generating a thickness map of the silicon overlayer in SOI wafers has recently been developed. This instrument can view entire wafers up to 200 mm in diameter by using a high-resolution wide-field optical system and CCD camera. The output from the camera comprises a set of digitized multispectral images of the SOI wafer; these images are used to generate reflectance maps of the bonded wafer at a discrete number of wavelengths and are then used to compute the silicon thickness over the entire wafer by comparing measured spectral patterns with a pre-computed library. Pattern matching algorithms are used in conjunction with a parallel processor, yielding measurement speeds orders of magnitude faster than conventional instruments (e.g. one minute for a 64×64 array of locations). The technique simultaneously measures the buried oxide thickness, an important capability in SOI wafer fabrication. Measurement accuracy is better than ±2 nm with excellent repeatability