Masayuki Takeda

Improvements of lubricant performance in hard-disk media by vacuum ultraviolet irradiation

In order to increase the reliability of hard disk media especially for corrosion-resistant property, we have tried lowering the surface energy of a media with high coverage and high bonded ratio of lubricant. In this study for the UV treatment of a media we examined the wavelength of 172 nm that is shorter than that of the low-pressure mercury lamp normally used, which irradiates at wavelengths of 185 nm and 254 nm. We found a drastic improvement in corrosion-resistant property in the case of 172-nm irradiation. In this paper improved corrosion-resistant property and its mechanisms are discussed.

Effects of vacuum ultraviolet irradiation to lubricant layer on hard-disk media

Summary form only given. Adhesion between a lubricant and DLC (diamond-like carbon) used as a protective layer in magnetic recording media improves HDI (head disk interface) characteristics. Therefore, magnetic recording media coated with lubricant are treated with heat or ultraviolet (UV) to increase the thickness of the bonded layer on the DLC and to optimize friction, durability, and other characteristics of the media. Because there are many different photoreactions and photo-induced reactions are known, we believe that this UV treatment is an attractive technique to improve the characteristics of the media. Usually, UV treatment is carried out by using a low-pressure mercury lamp, which irradiates at a wavelength of 185 and 254 nm with an intensity ratio of one to five. Our research interest includes investigating applications of short-wavelength irradiation because it can produce more photoelectrons increasing the thickness of the bonded lubricant layer. To examine and determine the potential of ultraviolet treatment, we investigated the effects of 172 nm irradiation in the vacuum ultraviolet region.

ETCHING RESIDUES OF SPUTTERED TA FILM USING CHLORINE-BASED PLASMA

Ta films are used as X-ray mask absorbers. Spindly etching residues of the Ta film are generated on a polished SiC film when using chlorine-based plasma. We found that etching residues were generated because of microholes which exist on the polished SiC film surface, and that etching residues generally originated from the steep slope of the substrate. For the Ta film on the Si slope, a broad peak of β-Ta(410) was observed in addition to that of β-Ta(002), which is found on the Si plane. An orientation different from β-Ta(002) appears to reduce the dry etching rate. We attempted Ar sputtering of the SiC surface to smooth the slopes in the SiC microholes. Etching residues did not originate in the case of the Ta film deposition on the polished SiC film after Ar sputtering. Therefore, Ar sputtering of polished SiC is very useful for avoiding the formation of etching residues.

Effect of SiC x-ray masks on alignment accuracy of heterodyne alignment

This paper describes the results of a study to investigate the applicability of silicon carbide (SiC) x-ray masks to an optical-heterodyne alignment technique. SiC was deposited at a thickness of 2 micrometer on a 4 inch silicon (Si) wafer. Its surface roughness was improved from 15 nm Ra (geometrical average) to 0.2 nm Ra using a polishing method. Using this SiC material, x-ray masks with Ta absorber patterns for alignment marks and overlay measurement were fabricated. To obtain a high overlay repeatability, we have deposited an anti- reflection coating (ARC) on both sides of the x-ray mask, which increased an optical transmission at a wavelength of 785 nm from 37% to 73%. We have also deposited an opaque coating (OPC) on the mask alignment mark. Using the x-ray mask, the overlay repeatability by mix-and-match method was evaluated. The overlay repeatability near the X, Y and (theta) alignment marks was 21 nm, 21 nm, and 49 nm (3 sigma) for the corresponding axes. The overlay repeatability of the X and Y directions was 61 nm and 54 nm (3 sigma) in a wafer. These results are equivalent to the results obtained using SiN x-ray masks. From these results, we consider that SiC x-ray masks are applicable to optical heterodyne alignment, and can also be used in practical x-ray lithography.