Effect of insulation layer on transcribability and birefringence distribution in optical disk substrate

As the need for information storage media with high storage density increases, digital video disks (DVDs) with smaller recording marks and thinner optical disk substrates than those of conventional DVDs are being required. Therefore, improving the replication quality of land-groove or pit structure and reducing the birefringence distribution are emerging as important criteria in the fabrication of high-density opticai disk substrates. We control the transcribability and distribution of birefringence by inserting an insulation layer under the stamper during injection-compression molding of DVD RAM substrates. The effects of the insulation layer on the geometrical and optical properties, such as transcribability and birefringence distribution, are examined experimentally. The inserted insulation layer is found to be very effective in improving the quality of replication and leveling out the first peak of the gapwise birefringence distribution near the mold wall and reducing the average birefringence value, because the insulation layer retarded the growth of the solidified layer.