Dry etching of horizontal distributed Bragg reflector mirrors for waveguide lasers

Abstract
Distributed Bragg reflector mirrors were etched in InP and GaAs. The mirrors were patterned using electron-beam lithography and etched with an electron cyclotron resonance source. This fabrication technique has the advantage that no regrowth step is required and the length of the passive mirror region is confined to a few micrometers. The structure requires etching vertical profiles with smooth surface morphology and high selectivity to the masking material. The effects of rf power, Cl2 percentage in Ar, chamber pressure, and stage temperature were studied. Increasing the rf power from 100 to 250 W caused the InP selectivity to Ni to decrease from 147 to 55. A similar effect was observed for etching GaAs. For both InP and GaAs, a vertical profile can be obtained by reducing the Cl2 percentage in Ar and by using low chamber pressure of 1 mTorr. Increasing the Cl2 percentage, however, improves selectivity to the Ni mask. With 20% Cl2 in Ar, vertical profiles and high selectivities are obtained for both InP and GaAs. Using high temperature increases the volatility of InClx etch products and improves the selectivity of InP to Ni. For InGaAsP/InP waveguide lasers, 122 nm wide mirrors were etched in InP to a depth of 2.0 μm for maximum reflectivity at 1.55 μm. For AlGaAs/GaAs waveguide lasers, 59 nm wide mirrors were etched in GaAs to a depth of 1.5 μm. Etching of nλ/4 mirrors, where λ is the emission wavelength, was studied and the dependence of gap spacing on etch depth was measured. The variations in etch depth for different gaps were minimized by reducing the pressure.

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