Surface Inspection of Silicon-on-lnsulator Wafers with Ultrathin Top-Si Layer by Laser Scattering: Numerical Analysis of Light Scattering by Voids

摘要

The dependences of the scattering of laser light on the size and shape of voids, which are known as "killer" defects of silicon-on-insulator (SOI) wafers in the fabrication of transistors, were investigated. Forward scattering dominated in the higher reflectance films at a wavelength of 488 nm and in all cases of a wavelength of 355 nm. Side scattering dominated in the lower reflectance films at a wavelength of 488 nm. These results indicated that the scattering properties of voids in the SOI wafers with various reflectance values depending on the thicknesses must change using an inspection tool with a laser wavelength of 488 nm. This characteristic is unsuitable in the detection of voids. The dependence of light scattering at a wavelength of 355 nm was not observed with void sizes of 240 or 500 nm. Circular and square-shaped voids showed similar scattering patterns. Therefore, an inspection tool with a wavelength of 355 nm is superior for detecting not only particles but also voids.