Method of determining a wafer characteristic using a film thickness monitor

A method for determining a wafer characteristic, such as the surface quality of a film formed on the wafer, using a film thickness monitor is described. In one embodiment, the method comprises the following steps. A measured spectrum for a processed wafer is generated. A set of parameters is chosen and then used to generate a calculated spectrum. The measured spectrum is compared to the calculated spectrum to determine if the two spectra match. If the two spectra do not match or the degree of nonconformity between the two spectra is greater than an acceptable error value, then there is probably a defect with the processed wafer. For example, the film formed on the wafer may have a nonuniform or hazy surface quality.