Fine Particle Inspection Down to 38 nm on Bare Wafer with Micro Roughness by Side-Scattering Light Detection

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Abstract
A system for detecting fine particles on LSI wafers is proposed. This system illuminates the wafer with a laser at a large angle of incidence, and uses a detector with a small pixel size. In this way, optical noise from the bare wafer is reduced, enabling the detection of standard 38-nm particles. Optical noise from a wafer surface is analyzed and shown to be caused by diffracted light. Simulation with a diffraction model indicates that the optical noise level is related to the wafer roughness. To detect fine particles with a high probability of 95%, a high illumination energy of 180 J is needed. With small pixels, a low illumination energy of 1.2 J will also detect small 50-nm particles, but with a low probability of 10%. This technique will be useful in monitoring the cleanliness of submicron LSI production.

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