Size determination of microscratches on silicon oxide wafer surface using scattered light

Scattered light intensity distributions from microscratches on a silicon oxide wafer surface are simulated and analyzed for the purpose of microscratch sizing using a boundary element method (BEM)-based electromagnetic scattering simulator. At normal incidence, the characteristic scattered light resulting from microscratches appears in two symmetric regions of scattering angles, namely, at high and low angles. The scattered light intensities at high and low angles show characteristic fluctuation according to the depth and width variations of microscratches. It is found that the size of a microscratch can be obtained from the scattered light intensities at these characteristic angles. We propose microscratch sizing map which uses the detected light intensities to size the microscratches. Once the map is created, quick and easy categorization of microscratch size can be realized by collating the detected intensities with the map. The major advantage of using the map is the ability to measure simultaneously not only microscratch width but also depth. Generally, the depth cannot be obtained from an imaging system. Several experiments demonstrate the feasibility of our scheme and their results are in very good agreement with the simulation results.