Abstract

Electron beam lithography can be used to pattern arbitrary geometries with high resolution, limited mainly by the size of the electron beam and proximity exposure by backscattered electrons in the resist. We have optimized the exposure conditions for the fabrication of the etch mask which we use to create a photonic crystal in the optical wavelength range. This polymethylmethacrylate (PMMA) electron beam resist mask is then transferred into a silicon dioxide etch mask by reactive ion etching with a C₂F₆ rf plasma. Once the mask is made, apertures are created by mask-aligning an optical lithography pattern on this micro-fabricated array of holes. The aperture pattern consists of thick photoresist covering the photonic bandgap mask, which then is used to lift off an optically opaque metal mask. In this way, we create micro-fabricated apertures with 50 μm openings, which facilitate the light transmission through only the patterned photonic crystals. The thickness of the mask has to be sufficient to withstand the angle etching process, and consists of a gold layer followed by sputter-deposited silicon dioxide. The processing sequence is schematically illustrated in Figure 1.

© 1995 IEEE