A design methodology to replicate the sub-micron land-groove structure in DVD-RAM substrates by injection-compression molding

Recently, the sub-micron structured substrates of 0.74 μm track pitch and 800 Å groove depth are required for DVD-RAM, and the track pitch is expected to be narrower as the storage density for optical disk is getting higher. For the accurate replication of the land-groove structure in the stamper to the plastic substrates, it is important to control the injection-compression molding process such that the integrity of the replication for the land-groove structure is maximized. However, the determination of the processing conditions has been relied on experience or trial-and-error. In the present study, polycarbonate substrates were fabricated by injection compression molding and the land-groove structure regarded as one of the most important geometrical properties for DVD-RAM substrates was measured. The effects of the mold temperature and the compression pressure on the integrity of the replication were examined experimentally. An efficient design methodology using the response surface method (RSM) and the central composite design (CCD) technique was developed to obtain the optimum processing conditions which maximize the integrity of the replication with a limited number of experiments. The model used in this study was verified using the analysis-of-variance (ANOVA), and it was found to be adequate within the confidence limit.