Kazumi Kuriyama

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.

Bd-type write-once disk with pollutant-free material and starch substrate

We realized an inorganic write-once disk for an optical recording system of the Blu-ray disk format. We developed a new Al alloy for the reflective layer and a Nb-compound oxide nitride material for the dielectric layer. By adopting these materials for the reflective layer and the dielectric layer of our write-once disk, we achieved complete exclusion of toxic substances specified in the pollutant release and transfer register (PRTR) law. That is, this disk did not contain any substances specified in the PRTR law. We confirmed this disk to be compatible with 1× to 2× recording at the user capacity of 25.0 GB. The bottom jitter values of both 1× and 2× were less than 6.0%. In addition, we developed another kind of substrate, which was made of a natural polymer derived from corn starch. The bottom jitter value was 6.0% at the user capacity of 25.0 GB with the limit equalizer.

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.

Modeling of Polarization Effects in Au Nanodots Excited With InAs Quantum Dot Emitters for Use as a HAMR Heat Source

We present modeling of a novel device structure with possible application as a heat assisted magnetic recording source. The structure consists of a mesa of GaAs containing InAs quantum dots (QDs), on a GaAs substrate. An Au dot atop the MESA is in proximity to a HAMR medium. The Au dot acts as a resonant absorber of the QD emission and also provides coupling between the optical transducer and recording medium. The device is illuminated through the substrate, with light that is absorbed by the QDs and re-emitted at a longer wavelength, characteristic of the dots. For varied polarization of the QD light emission, finite element modeling was used to compute the electromagnetic field structure of the device, along with the resultant temperature field in the recording medium and the device. We show that certain polarization emission are preferable for attaining more intense excitation of resonance in the Au dot atop the mesa. Temperature ratios (medium versus the Au dots) greater than 60 times were seen, due to the good heat sinking of the Au dot provided by the GaAs mesa and substrate. Coupling efficiencies between the device and medium were low, with typically less than 0.3% of the power emitted by all radiators coupling into the full-width half-maximum of the medium hot spot. While improvements may be possible, even at low efficiency this device shows promise in keeping the near field transducer cool relative to the medium.

A Process for Transferring and Patterning InAs Quantum Dot Optical Gain Media for HAMR Near Field Optical Sources

We report a process by which a 270 nm layer of optical gain medium is transferred to a dielectric substrate via a flip chip process and patterned into disk structures suitable for microcavity lasers. This process is anticipated to have application to near field transducers for heat assisted magnetic recording (HAMR). Specifically, the gain medium consists of 5 layers of InAs quantum dots embedded in GaAs. The transfer process was accomplished by depositing a series of etch stop layers on the GaAs substrate before the QD gain layers, and then using these etch stop layers in a polishing and etching process to remove the substrate of the gain medium. To support the gain medium during this removal, the GaAs wafer was flipped onto an epoxy layer that had been applied to a glass wafer, where the gain medium layer was eventually left in place and separated from the substrate. This gain medium layer on epoxy was then patterned using photolithography and ion milling. Photoluminescence studies show little effect on the optical properties resulting from the transfer and the patterned devices show optical mode structures consistent with an approach to lasing. However, the epoxy substrate is revealed to be too poor a thermal conductor for optical pumping to reach the lasing threshold. Detailed analysis of the temperature rise upon illumination combined with literature values for the lasing threshold pump levels suggests that substrates with thermal conductivities of around 10 W/m-K are required for the process to yield working lasers.

Nano-Pattern Profile Control Technology Using Reactive Ion Etching for 100 GB Optical Disc Mastering

For high-density patterning, we tried to control the nano-pattern profile using a reactive ion etching technology. Line edge roughness could be improved and the line width fluctuation 7 nm could be realized.

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.