Fabrication of optical disk mastering using electron beam and embossing process

For the requirement of higher storage capacity of an optical disk, it is a good choice to shorten pit length and linewidth. However, the conventional laser beam mastering is difficult to fabricate smaller pit length and linewidth because of the optical diffraction limit. In order to solve this problem, optical disk mastering using electron beam lithography is presented. The process parameters of the electron beam mastering such as beam current, constant linear stage velocity, developing time, and focus distance are discussed in this research. In the experiments, it was found that the focus distance is an important parameter to fabricate nano-linewidth. The experimental results reveal that the 10 μm variance in focus distance causes about 12% variation in linewidth. The photoresist with nano-pattern defined by eletron beam was transferred into metal Ni–Co (Nickel–Cobalt) mold by electroplating process. The Ni–Co mold with hardness larger than Vicker Hardness (Hv) 650 was developed. Then, with the Ni–Co mold, LIGA (German: Lithographie GaVanoformung Abformung) process was applied to replicate high-density optical disk. The Ni–Co mold is served as a master for hot embossing process to transfer the nano-pattern onto PMMA sheet. Since the feature size is in nano-meter range, the study presents an innovative demolding mechanism to demold the master from the PMMA sheet without damaging the nano-meter structure. A spiral nano-groove with 112 nm in linewidth and 80 nm in depth has been successfully fabricated about 50 Gbytes storage capacity.