Toshihiko Ushiro

Fine gold grating fabrication on glass plate by imprint lithography

In this paper, fabrication of a fine gold grating on glass substrate is demonstrated using imprint lithography for optical elements. A Si mold with fine grating patterns is prepared using conventional IC’s process. The line widths of the gratings are varied from 1.0μm to 200nm. About 20nm thick Si3N4 film is coated on the mold surface by LP-CVD to improve hardness of the mold. The Si mold is pressed to a gold film on a glass substrate at room temperature. To eliminate fatal fracture of the sample in pressing, the form of the sample is just aligned to the mold to avoid stress concentration at the mold edges. The gold film is plastically deformed and fine gold grating with 200nm in line width and 300nm in height is successfully fabricated on the glass plate. The cross sectional profile of the gold pattern is fine rectangular shape. Using room temperature direct imprint lithography, metal gratings are successfully fabricated on a glass plate. This method is a promising way to fabricate fine micro optical elements by low cost.

Design and performance of multilevel phase fan-out diffractive optical elements for laser materials processing

A multilevel phase fan-out diffractive optical element (DOE) has been developed and introduced into various kinds of laser materials processing such as drilling, cutting, welding, and soldering. The larger the number of arrayed spots the DOE generates on the surface of the workpiece, the more sensitive the intensity uniformity of the spots becomes to fabrication errors, which are deviations between designed and fabricated surface microstructures. Errors in etch depth have, in particular, a significant effect on the intensity uniformity. A new design method has been developed for increasing the tolerance to the etch depth error, and applied to the design of a 16-level phase 7×7 fan-out element. The result indicates a uniformity less sensitive to etch depth error. The effect of a linewidth error due to the side etch introduced during a plasma etching process is also evaluated by computing high-resolution graphics data representing the phase of the DOE with the line width errors. Mask alignment errors, the s...

Beam-splitting ZnSe diffractive optical element

ZnSe Diffractive Optical Element (DOE) is one of the advanced optics which utilizes the optical diffraction phenomena by fabricating a micron order pattern on polished mirror-like surface of ZnSe polycrystal substrate. Various applications for a carbon dioxide (CO 2 ) laser material processing such as beam-splitting, beam-shaping and beam-homogenizing are available. The micro pattern of ZnSe DOE is fabricated by the photolithography and reactive ion etching (RIE) technique. Its optical property is highly dependent on the depth precision of microfabricated pattern. In RIE by using BCl3 as the etchant gas we have achieved an etching technique to maintain the smooth surface of the ZnSe polycrystal with minimal etching rate dependency on the crystal orientation of each crystal grain. The surface roughness is 2nm Ra before etching and 5 nm Ra after about 4 microns depth etching. This good roughness brings better depth precision. With these etching technique beam-splitting ZnSe DOE with less than 10% intensity uniformity of splitted beams is successfully obtained and it can be put to use for practical CO 2 laser hole drilling.