磁気ディスクサブストレート表面欠陥検査装置の開発

Abstract

A laser multi-sensing technique for detection and determination of various kinds of microdefects on diamond turned surfaces of magnetic disk substrates has been designed and implemented on a fully automatic surface inspection system. The technique includes the following three sensing methods : (1) a laser diffraction pattern method using a wedge-ring detector array (WRD), which identifies steep-sloped defects such as pits, scratches, and periodical machine marks ; (2) a laser beam deflection method using a position sensitive detector (PSD), which identifies smooth-sloped defects ; (3) a reflectivity method using a pair of photodiodes corresponding to the detection of the incident and the reflected beam intensities, which identifies reflectivity-changing defects such as stains and erosions. The automatic inspection system consists of laser optics and signal processors for multi-sensing, a disk handling and scanning mechanism, and a host computer. Using a multi-sensing technique, the host computer determines the surface quality and controls the mechanism. Experimental results for a number of disks confirmed that the system can detect and determine defects at a high rate of up to 25 s/ side for 5.25'' disks with a reliability equal to or better than that of specially trained visual inspectors.