Bi/In as patterning and masking layers for alkaline-base Si anisotropic etching

Abstract

A new resist for alkaline-based silicon anisotropic etching process has been developed. Bismuth over Indium films, 30 nm to 90 nm thick for each layer, were DC-sputtered on silicon substrates, and were used as a thermally activated photoresist on which patterns were generated using focused Argon laser beam. Both physical and chemical properties of the bimetallic film changed after the laser exposure. Unlike normal organic photoresist, Bi/In is laser wavelength invariant as it is a thermal processes. The laser exposed patterns were developed in diluted RCA2 solution that selectively removed the unexposed area and retained the exposed. The developed Bi/In patterns acted as an etching mask for the subsequent alkaline-based silicon anisotropic etch at 85°C. It was found that the developed Bi/In has a lower etch rate than that of SiO₂ in the etching solutions, making it a potential masking material for silicon bulk micromachining process. Solar cells with V-groove surface textures were manufactured to show the compatibility of Bi/In with conventional processes.