ICP Dry Etching of Type Ⅱ InAs/GaSb Superlattice Long-wavelength Focal Plane Arrays

Dielectrical layer SiO₂/SiN is used as a mask in studying inductively coupled plasma (ICP) etching conditions of InAs/GaSbⅡsuperlattice infrared materials for improving the electrical performance of the device. In this article, ICP etching parameters of InAs/GaSb type-Ⅱ superlattice with SiO₂/SiN were investigated. Two common phenomena observed in the ICP etching process, mesa lateral undercutting and under mesa undercutting, were analyzed in detail. The mesa lateral undercutting was efficiently improved by increasing the thickness of the SiO₂ film and reducing the Ar gas flow rate. The table undercut was effectively eradicated by reducing the radio frequency (RF) power of the bottom electrode. A bright and flat etching surface with a surface roughness of 0.193 nm was obtained by using an appropriate thickness of SiO₂/SiN mask and optimized ICP etching parameters. The etching mesa angle was greater than 80°, and the etching selection ratio was greater than 8.5:1. The dark current density of a long-wavelength 640×512 focal plane array manufactured using improved ICP etching conditions was lower by an order of magnitude, reaching 3×10^-4A/cm². Other parameters, such as response non-uniformity, signal-to-noise ratio, and effective pixel rate were also improved, and a clear image was obtained.