Inspection of ultra fine particles on the Si wafer surface using a laser light scattering method

We have been developed a surface inspection system for ultra fine particles on a bare silicon wafer. The system combines scanning laser beam illumination technique with a cooled CCD detector and ultramicroscopic technique in a single instrument. In this system, the wafer is illuminated by blue-green light from an argon ion laser source (wave length: 488nm, power: 1.5W) at oblique incidence 76 degree. The scattering light from the particles on the wafer is detected with a 12-bit cooled CCD camera at the upper side of the wafer. Lower limit of detection is about 30 nm in particle diameter. The limit is determined by comparing the light scattering from particle and micro-roughness on the surface. The scattering light from particle and surface is brighter with p-polarization illumination than that with s-polarization illumination. The light scattering intensity of ultra fine particle is strongly dependent on the particle size, and it is proportional to the sixth power of the particle diameter.