Masahiro Katsumura

High-Density Recording Using an Electron Beam Recorder

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.

High Density Mastering Using Electron Beam

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.

Enhanced resolution and groove-width simulation in cold development of ZEP520A

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 .

Electron Beam Recorder for Patterned Media Mastering

Patterned media are promising technologies to realize the next-generation hard disk drives (HDD) with an areal density beyond 1 Tbit/in.2. Two types of patterned media have been proposed: one is the discrete track medium (DTM) and the other is the bit-patterned medium (BPM). Both DTM and BPM require very small feature sizes and extremely tight tolerances. The mastering process is a key technology for production of patterned media, and electron beam mastering is the only means to carry out the process. We developed a new electron beam recorder (EBR) for patterned media mastering. In this paper, we introduce the technologies and the recording performance of the EBR. The EBR has four primary technical features: a 100 kV EB column, a high-precision r–θ stage system, a stage error correction system, and an EBR formatter for patterned media. In experimentals, the EBR demonstrated the following recording performance. The EBR achieved sufficient recording accuracy for the requirements of DTM with 1 Tbit/in.2 areal density. The EBR succeeded in high-density recording of a DTM pattern with 35-nm track pitch for over 1.5 Tbit/in.2 areal density. The EBR showed high throughput and good recording stability by recording a 1.8-in. DTM master. In this experiment, the EBR achieved a line width uniformity of less than 1 nm and a short exposure time of about 50 h for whole-area recording. We proved the practicality of the EBR for patterned media production.

Practical electron beam recorder for high-density optical and magnetic disk mastering

Electron beam mastering is a promising technique to realize next-generation disk media. We have been developing electron beam recorders since 1993 and have proved their effectiveness for high-density disk fabrication. To introduce electron beam mastering technology into practical application in next-generation disk mastering, we developed a new electron beam recorder as a commercial prototype. The electron beam recorder was improved in terms of recording resolution, beam-blanking characteristic and recording stability. For production use, a load-lock system was adopted to improve throughput, and the recording and substrate exchange operations were automated through computer control. The recording stability was proved experimentally by fabricating 100-GB-capacity stampers recorded on the whole recording area of 22 to 58 mm radius with a good pattern size uniformity. A superhigh-density patterning of 350 Gbit/in.2 density (510 GB capacity/layer) was realized for the next-generation optical disk, and a 35 nm line and space pattern could be fabricated for the next-generation magnetic disk.

Electron Beam Recording beyond 200 Gbit/in2 Density for Next Generation Optical Disk Mastering

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.

High-Density Groove Mastering Using an Electron Beam Recorder and Plasma Etching Process

An electron beam recorder (EBR) has been confirmed to have high-resolution performance and we think it is a promising recorder to produce a master stamper for the next-generation high-density optical disks. Because the high-density groove recording disk requires a narrower track pitch, the improvement of the recording resolution of the mastering recorder is necessary. However, owing to electron scattering, fabricating a groove structure was difficult even when we use a finely controlled conventional EB mastering process. A plasma etching process is an expected process as one of the solutions. Consequently, we adopted the plasma etching process for high-density groove disk mastering. A data bit length of 112 nm/bit was successfully recorded on the groove disk at a wavelength of 405 nm and an objective lens of 0.85 numerical aperture.

Nanopattern Profile Control Technology Using Reactive Ion Etching for 100 GB Optical Disc Mastering

We had developed an electron beam recorder (EBR) and studied a process technology for high-density optical disc mastering. In this study, we aimed at controlling a nanopattern profile by adopting inductively coupled plasma reactive ion etching (ICP-RIE) under simple conditions. To control a pattern inclination angle, we introduced an etching power ratio of antenna to bias and investigated the relationship. From the results of our investigation, we confirmed that inclination angle depended on etching power ratio linearly. Furthermore, in the case of a 100 GB read-only memory (ROM) equivalent pattern, we formed two kinds of inclined pattern by adopting ICP-RIE. We evaluated line edge roughness (LER) to determine the difference in pit profile accurately. As the result, we confirmed that LER was improved at a steep inclination angle. In addition, we applied ICP-RIE to a 300 GB ROM pattern.

Study of Chemically Amplified Resist Using an Electron Beam Recorder

We have been developing an electron beam recorder for next-generation optical disk mastering. Using a ZEP-520 resist that had high resolution, we fabricated read-only memory disks and obtained sufficient reproduction performance. But the recording velocity was 0.7 m/s to obtain sufficient jitter of the disk. We could not expect such low recording velocity to be used in mass production. Therefore we decided to use a chemically amplified resist, which had high sensitivity. To reduce the recording time, we adopted the resist to the optical disk mastering and investigated the process conditions. We examined the effect of development power and post-exposure banking (PEB) temperature on the jitter of the reproduced signals and obtained 6.4% jitter at a 2.5 m/s recording velocity.

Application of Retarding Technology to Electron Beam Recorder

The paper reports the outline of the developed electron beam recorder (EBR) for the purpose of developing future optical disk storage media. A rotation stage is developed and is installed to the EBR. The EBR using the retarding field can vary the beam energy only by adjusting the high voltage for the substrate (10 keV to 50 keV)