Measurement of Ultra Fine Defects on the Si Wafer Surface Using a Laser Light Scattering Method

We have been developed a laser light scattering detector system for the observation of a fine defect on a bare silicon wafer surface. The argon ion laser beam with a single wavelength of 488 nm is turned into a scanning beam through a x-y deflection mechanism, and focused to a small spot by a long focus lens onto the wafer surface at oblique incidence angle of 76 degrees. The system combines a cooled CCD detector and ultramicroscopic technique. The light scattering by the defects on the wafer surface is detected by the high power optical microscope equipped with a 12-bit cooled CCD camera at the surface-normal direction of the wafer. The long exposure and high dynamic range capability of the system allows images with both high sensitivity and high signal to noise ratio to be produced. The light scattering intensity from Si wafer surface depends on the Si wafer samples supplied by corporation. The entire surface of mirror-polished wafer contains micro-roughness and micro-scratches. Micro-roughness constructs a speckle pattern, and the average intensity depends on the magnitude of micro-roughness. The image of the micro-scratch strongly changes with the angle between the incident laser beam and the micro-scratch. The most sharp image is constructed at the angle of 90 degrees. The theoretical estimation of averaged width and depth of the micro-scratches are the order of nanometer, respectively.