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We have used reactive sputter etching to texture the surface of Si wafers. The texturing was in the form of pillars whose diameters and spacing were small compared with the useful solar wavelengths and whose heights were comparable with or larger than these wavelengths. The normal and hemispherical reflectances of textured wafers were measured. The solar absorptance was found to be 0.99 for wavelengths below 1.0 μm. Because of the sharp drop in absorptance for photon energies less than the energy gap, the overall solar absorptance was about 0.85. The calculated thermal emittance was about 0.25 and was primarily due to multiphoton absorption processes normally observed in thick Si crystals. Much smaller values of thermal emittance would be obtained from thin textured films.

Reactive sputter etching in fluorocarbon gases (i.e. CF4, CHF3) not only results in a large increase of the etch rates, but it can also be used for a high fidelity pattern transfer from patterns delineated in positive photoresist into underlaying substrates (i.e. Si, SiO2, Si3N4). Square wave gratings with micron and submicron periodicities and etch depths of up to 3 μm have been etched. A relatively large etch selectivity of SiO2 over Si has been observed (etch rate ratio=15:1). Reactive sputter etching is primarily a chemical process due to highly reactive species produced on the substrate surface by an ion–molecule reaction between ions from the plasma and neutral gas molecules impinging onto the substrate surface.

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