The hot embossing of glass with a size on the submicron or micron level is a target of interest for the industrial production of products such as microdevices. For fluidic micro chip applications, polymer materials have been used with the advantage of a relatively low cost of fabrication. However, glass is suitable for high-temperature applications such as in microreactors.Although glass is also a good candidate material for optical devices because of its enhanced optical properties, the development of mold materials has not been established for the hot embossing of glass. In this study, we used Ni-W as a mold material for the hot embossing of glass. A plated Ni-W film has a high heat resistance and a linear expansion coefficient, properties that are similar to those of glass materials. Focused ion beam (FIB) machining was employed for the micron and submicron structurings of a Ni-W mold material. Borosilicate glass, D263, was used as glass material. Glass patterns of 0.4 mm width were obtained by hot embossing with the Ni-W mold.

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We fabricated microlenses and the logo of the National Institute of Advanced Industrial Science and Technology (AIST) on Pyrex glass by employing thermal nanoimprint technology. The mold material used for imprinting on Pyrex glass was an amorphous Ni-P alloy that was deposited on Inconel-600 by electroless plating technology. The complete fabrication technique consisted of highly accurate processing by focused-ion-beam (FIB) on material that involved a high-temperature thermal treatment that has the advantage of improving the hardness of the mold. An amorphous Ni-P alloy layer on an Inconel-600 substrate was characterized by measuring its X-ray diffraction spectrum. Using this technique we successfully developed a low-cost mold for imprinting on Pyrex glass instead of using a more expensive glass-like carbon mold that is commonly used for this purpose. Microlenses with concave curvatures having radii of 12 and 20 mm were created on the mold by a FIB system equipped with three-dimensional computer-aided-design (CAD) software. This mold was used for thermal imprinting on Pyrex glass substrates to fabricate microlenses and the AIST logo. When polished Inconel-600 was used as a substrate for molds, the accuracy of the Ni-P mold proved to be of higher quality than a mold made of unpolished Inconel-600. The microlenses made using Ni-P/ polished-Inconel-600 molds showed lubricious surfaces that were not possible to achieve using Ni-P/unpolished-Inconel-600 molds. Moreover, some of the parameters in Ni-P electroless plating were changed in order to make three kinds of molds with P content ratios of 4, 8, and 16 wt %. The micro-vickers hardness caused by thermal treatment and the differences among the transcript values on Pyrex glass were also evaluated experimentally.

Glass is a good candidate material for optical devices because of its enhanced optical properties, the technique of die machining has not been established for the hot embossing of glass. In this study, we used the glassy carbon (GC) mold for the hot embossing of glass. An inductively coupled plasma reactive ion etching (ICP-RIE) using oxygen plasma was employed for the submicron structuring of the GC mold. Hydrogen silsesquioxane (HSQ) is a negative-type electron beam (EB) resist used to be resistant to oxygen plasma. HSQ patterns drawn by electron beam lithography (EBL) were used as the O 2 dry etching mask. The etching selectivity between HSQ and GC was 35. The average of the extent of side etching was 40 nm at a depth of 300 nm. The side etching functioning as the draft angle was caused mainly by oxygen radicals, because HSQ patterns remained even after GC patterns were side-etched. We confirmed that the GC mold fabricated by O 2 dry etching can be used for glass hot embossing. Since the mold lubricant was not rubbed on the mold surface, GC is the appropriate mold material for Pyrex glass.

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