Topographical evaluation of optical disks with polycarbonate substrates in the manufacturing process

An optical contour mapping with a laser-interference method was carried out to evaluate the topographical deformation of optical memory disks. The dynamics of the deformation in a manufacturing process was studied. Reflective films and a protective resin coating increased the dishing, irrespective of the original shape of a substrate. A bonding process decreased the dishing and contributed to mechanical stability that lasted for a long period in daily use. In the case of a 0.6-mm-thick substrate, as with a DVD disk, the large dishing of the single substrate was suppressed by the bonding to less than 100 microm. In addition, it was shown that distortions arising from the molding process remained in the final product and that the initial process should be carefully controlled.