Yoshiaki Kojima

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.

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.

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)

Study of chemically amplified resist using an electron beam recorder

A user data capacity of more than 23 Gbytes (GB) is required for the next-generation optical disks to store HDTV signals for over 2 hours. To achieve such recording capacity, mastering recorders must have higher resolution performance than present ones. Therefore we have been developing an electron beam recorder (EBR) (Y. Kojima et al, Joint MORIS/ISOM 1997 Tech. Dig., Th-L-06, 1997). Previously we reported the high-resolution performance of the EBR using an electron beam (EB) resist (ZEP-520). At the same time we confirmed the performance of read-only memory (ROM) disks (M. Katsumura et al, ISOM 2000 Tech. Dig., We-C-02, 2000; Y. Wada et al, Jpn. J. Appl. Phys. vol. 40, pp. 1653-1660, 2001). We acquired sufficient process quality for next generation optical disks, but the recording speed in this process is not sufficient for mass production. Accordingly it is necessary to raise the recording speed in EB mastering. Although there are several proposals for high-speed recording, we propose a chemically amplified resist (CAR) method for the improvement of mass production. In this paper, we report the application of the CAR to high-speed EB recording and the reproduction performance of the 25 GB CAR disks.

Development of Practical Electron Beam Recorder for High-Density Optical and Magnetic Disc Mastering

We developed a practical electron beam recorder, which was improved recording stability, resolution and throughput. The stable recording performance for the whole recording area and the capability for high-density recording beyond 200 Gbit/in2 were realized.

Development of electron beam recorder with a /spl theta/-stage

In this paper, outline of EBR and the results of circle patterning were reported. Electron beam recorder with the /spl theta/-stage had a promising ability for high accuracy recording.

Improvement of recording positional accuracy in an electron beam recorder

A next generation optical disk is required to have over 23 Gbyte recording capacity for over 2 hour storage of digital high-definition television (HDTV) data. Since track pitch becomes narrower for such a large capacity disk, a high resolution and high accuracy mastering system is required. To realize this objective, we have developed an electron beam recorder (EBR) and have been studying fabrication of master stampers for next generation optical disks and for future optical disks (Y. Kojima et al, Jpn. J. Appl. Phys. vol. 37, p. 2137, 1998; Y. Wada et al, ibid., vol. 40, p. 1653, 2001). In this paper, we report an investigation of recording accuracy in the EBR and a trial for improvement.