Spot-scanning laser scattering system for defects detection of wafer surface

Abstract

As semiconductors' critical dimension decreases, higher precision inspection instruments are needed to detect defects in the manufacturing process. Optical inspection methods based on light and dark field microscopy can detect defects on large wafer areas well without damaging the wafer, but the minimum detectable defect size is limited because the defect scattering signal is easily buried by the scattering background noise from the wafer's rough surface. To detect submicron defects on wafer surfaces, a spot-scanning laser scattering scheme is developed based on the dark-field scattering technique. Using the Finite Difference Time Domain (FDTD) method and the inspection scheme, an electromagnetic scattering model of the defect on the wafer surface is established, and the defect characteristics and electromagnetic field distribution are simulated. Moreover, the effects of the collecting aperture angle on the signal intensity of defects and the discrimination of defects of different sizes, as well as the effects of the incident angle on the scattered signal intensity of submicron defects, are examined. A spot-scanning laser scattering experimental platform was built, and 200 nm, 1 μm, and 5 μm diameter polystyrene latex (PSL) spheres were deposited on the wafer surface to verify the validity of the proposed method. Signals of the three sizes of spheres were detected in the stitched images with good discrimination of signal intensity, and the signal of the 200 nm PSL sphere displayed a peak signal-to-noise ratio of 32.07 dB. This method provides a reference for further industrialized defect detection systems on wafer surfaces.