Yoshiyuki Matsumura

Tilt Compensation Method of Two-Beam Angle Multiplexing Holographic Memory

In a two-beam angle multiplexing holographic memory, there is a problem that the tilt margin is small. Therefore, we propose a radial tilt compensation method (radial tilt is a tilt in the vertical direction to a surface that is made by reference and signal beams). When the radial tilt occurred during the reading, we brought the relative angles of interference fringes and the reference beam near the state at the time of recording. Concretely speaking, we shifted the disc to the circumferential direction slightly to obtain the optimum signal-to-noise ratio (SNR) and then recovered the hologram. In our experiments, we recorded 1 hologram (no multiplexing) and 51 multiplexing holograms, and recovered them using this compensation method. As a result, we confirmed that our method improved the tilt margin markedly in both cases. This compensation method is thus effective for interchangeability without the need for an additional mechanism and making for smaller drives.

Dvd/cd/cd-r Compatible Pick-up With Two-wavelength Two-beam Laser

The CD-ROM and CD-R (recordable CD) playback compatibility is in great demand for DVD-ROM disc drive devices. The authors developed a new optical mechanism that utilizes a holographic optical element with wavelength selectivity, and two-wavelength two-beam laser in order to produce a DVD/CD/CD-R playback compatible pick-up with one objective lens.

Digital Video Disc/Compact Disc Compatible Pick-up With Liquid Crystal Shutter

We have developed an optical pick-up with a liquid crystal shutter that can read both digital video discs (DVDs) and compact discs (CDs). An objective lens which is designed for reading DVDs with a numerical aperture (NA) of 0.6 is used in this optical pick-up. The pick-up can be used to read CDs by changing the diameter of the laser beam which enters the objective lens, using the liquid crystal shutter. The wavelength of the laser diode is 635 nm. When a CD is read, the NA of the objective lens is 0.35. For focus error detection when reading CDs , an astigma method was used, and for tracking error detection, a 3-beam method was used. We have confirmed that both DVDs and CDs can be successfully read by changing the NA of the objective lens according to thee thickness of the disc substrate.

Evaluation of Mercaptobenzothiazole Anticorrosive Layer on Cu Surface by Spectroscopic Ellipsometry

Mercaptobenzothiazole (MBT) anticorrosive layer on copper surface prepared in MBT solutions was analyzed by spectroscopic ellipsometry (SE). The results showed that MBT anticorrosive layer was formed on Cu2O layer in the MBT solution at temperatures higher than 50 °C. Additionally, it was confirmed that MBT anticorrosive layer was formed in the MBT solution at room temperature by adding about 20 wt % acetone to the solution. From polishing experiments of MBT anticorrosive layer and benzotriazole (BTA) layer, it was revealed that MBT anticorrosive layer was physically stronger than BTA layer. It is considered that dishing amount in Cu chemical-mechanical polishing (CMP) can be reduced by using MBT. However, MBT anticorrosive layer was not formed in the MBT solution including Hydrogen peroxide (H2O2) suggesting that slurry should be composed without H2O2 in order to use MBT for Cu CMP.

Evaluation of Cu Ion Concentration Effects on Cu Etching Rate in Chemical-Mechanical Polishing Slurry

The effects of Cu ion concentration of the different solutions on Cu etching rate were investigated. From the dipping experiment of Cu substrates in different solutions of malic acid, hydrogen peroxide (H2O2), benzotriazole (BTA), and Cu ions, it was revealed that Cu etching rate is increased if the concentration of Cu(II) ions added in the solution is high. This is considered to be caused by the effect of Cu(II) ions on H2O2 molecules. In the solution of pH 7, the Cu etching rate increased markedly between 1.7×10-4 and 3.4×10-4 M Cu(II) ion concentrations. The maximum increase in the etching rate was from 990 to 2200 nm/min at a H2O2 concentration of 2 wt %. In the solution of pH 3, a marked change in the etching rate was not observed. Our results show that the concentration of Cu ions on the polishing pad in chemical-mechanical polishing (CMP) process is very important.