Apparatus and method for surface inspection by specular interferometric

Abstract

A simple yet versatile noncontact optical inspection instrument and method are described for the inspection of magnetic disk surfaces for surface defects. This instrument is capable of inspecting the disk surface at any point in the disk manufacturing process. Surface defects such as bumps, pits and scratches can be measured. Surface contaminants such as particles and stains can also be measured. The instrument is also capable of discriminating between surface defects and surface contaminants. The instrument is comprised of two identical optical sensors which are located on opposite sides of the disk. A carriage supports and translates these sensors along the disk radius while a spindle rotates the disk. Both surfaces of the disk are therefore simultaneously scanned in a spiral fashion. The sensor's illumination optics produce a monochromatic focused spot of light which is normally incident upon the disk surface. The sensor uses two collection optics channels which simultaneously detect both the specular reflected light and the diffuse scattered light produced by the disk surface. Both the angle and power of the specular reflected light are measured, while just the power of the diffuse scattered light is measured. The output signals from the sensors are processed to estimate the size of the defects and to determine the type of defect.