A high-density optical disk fabricated using electron beam mastering exhibited excellent performance. Read-only disks with the recording capacity of 25 to 30 GB were fabricated by electron beam mastering and their jitter values were evaluated by a blue laser read out system. As a result, very low jitter values of 5.4, 6.2 and 7.7% were obtained for the disks whose capacity was 25, 27.5 and 30 GB, respectively. Characteristics of the disks such as track pitch variation, track roundness and recording stability are also shown. The electron beam recorder used in the experiments is described. In particular, details of the electron beam column, properties of the beam, how to adjust and evaluate the beam and a beam blanker are presented. Finally, several problems are addressed.

Cold development of positive-tone resist ZEP520A (Nippon Zean) in electron-beam lithography needs quantitative analysis for further improvement in resolution. Contrast curves and groove widths in cold development of ZEP520A were analyzed using models, and resolution enhancement was confirmed experimentally. Although the contrast improved at the expense of sensitivity in cold development, the improvement of contrast became smaller when the development temperature became colder. The dependence of contrast curve on developing temperature can be explained assuming resist dissolution rates that have an activation energy. For resolution evaluation, circumferentially aligned line-and-space patterns were exposed using an electron-beam recorder with a rotary stage. The resolved groove widths were explained by using the resist dissolution model and an incident electron distribution that consists of three Gaussians. Using these models, groove widths after development can be easily calculated at arbitrary development and exposure conditions. The resolution improved in lower temperature, and dense line-and-space patterns of 35 nm pitch were resolved in −10 °C.

A mastering system for the next-generation digital versatile disk (DVD) is required to have a higher resolution compared with the conventional mastering systems. We have developed an electron beam mastering machine which features a thermal field emitter and a vacuum sealed air spindle motor. Beam displacement caused by magnetic fluctuation with spindle rotation was about 60 nm(p-p) in both the radial and tangential directions. Considering the servo gain of a read-out system, it has little influence on the read-out signal in terms of tracking errors and jitters. The disk performance was evaluated by recording either the 8/16 modulation signal or a groove on the disk. The electron beam recording showed better jitter values from the disk playback than those from a laser beam recorder. The deviation of track pitch was 44 nm(p-p). We also confirmed the high density recording with a capacity reaching 30 GB.

We had developed an electron beam recorder for high-density mastering. The electron beam recorder has a capability to record high-density patterning beyond 200 Gbit/in2 density because it has characteristic of fine beam convergence. The behavior of electron scattering is important to realizing high-density patterning. Scattered electrons degrade patterning resolution and high-density patterning can not be realized. Thus, we adopted a new substrate made of a material that reduces the influence of the electron backscattering and attempted to record high density patterning beyond 200 Gbit/in2 density. As experimental result, 300 Gbit/in2 density patterning could be realized.

We have developed an electron beam recorder and utilized it in high-density disk mastering. We discussed an electron scattering in disk mastering that degrades the reproduction performance of disks. In order to improve the reproduction performance, we applied a dry etching process to the disk mastering process, and confirmed its efficacy in reducing the scattering effect and improving disk noise by calculation and experiments. We fabricated `Blu-ray Disc'-type read-only memory disks with and without the dry etching process, and noticed the advantage of the dry etching process from the jitter comparison. Finally, a 4.7% jitter was achieved in a 25 GB capacity disk, while a 5.7% jitter was obtained in a 27 GB capacity disk with additional recording compensation.