Direct fabrication of two-dimensional photonic crystal structures in silicon using positive and negative Hydrogen Silsesquioxane (HSQ) patterns

The use of Hydrogen Silsesquioxane (HSQ) as a negative-tone electron-beam resist and a hard etching mask to directly fabricate two-dimensional Si-based photonic crystals (PhC) was investigated. We demonstrate a protocol using the HSQ resist, including spin coating processes, low-energy electron-beam exposures, development, post-development treatments, and dry-etching, to achieve sub-micron two-dimensional photonic crystal structures in silicon. An electron-beam area dose of 315 μC/cm2 at 30 kV was sufficient to produce anisotropic 267-nm deep HSQ-based PhC features upon development. Subsequent oxygen plasma treatment and dry etching processes were done to transfer the final patterns to the underlying silicon with a 1:1.23 etch selectivity (Si:HSQ) using a CF4/O2 plasma. These results demonstrate the use of HSQ to simplify the fabrication processes for photonic crystals and their integration with other optical-based on-chip components.

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