Self-aligned Etching of Subwavelength Longwave Infrared Type-Ii Superlattice Pixels

Due to the demand for increasingly large format focal plane arrays, smaller and smaller pixels are required for high resolution imaging. A promising technique for backside illuminated devices is self-aligned etching of the mesas, or using the metal contact pad as the etch mask. In this work, we report on the self-aligned etching of two Type-II superlattice materials and some of their constituent material components to create pixels with subwavelength dimensions in a longwave infrared detector. Palladium was used as the primary mask material to prevent the exposure of the gold contacts to the etch plasma. The inductively coupled plasma conditions were varied, including varying the etch gas composition through different ratios of BCl3 and Cl-2, and the etch rate and sidewall angle were measured. Using a mixture of BCl3 and Cl-2 produced higher etch rates at room temperature than previously reported results at high temperatures with similar sidewall angles, thus reducing undesired diffusion of the device stack layers.