Multi-step plasma etching process for development of highly photosensitive InSb mid-IR FPAs

Abstract

Reactive ion beam etching (RIBE) with CH4/H2/Ar or Cl2/Ar and ion beam etching (IBE) with Ar has been widely used for indium-contained compound semiconductors such as InAs, InP and InSb. To improve the performance of InSb FPAs, reduction of the ion-induced defects and the surface roughness is one of the key issues. To find the optimized plasma etching method for the fabrication of InSb devices, conventional plasma etching processes were comparatively investigated. RIBE of InSb was observed to generate residual by-products such as carbide and chloride causing the degradation of devices. On the other hand, very smooth surface was obtained by etching with N2. However, the etch rate of the N2 etching was too slow for the application to the device fabrication. As an alternative way to solve these problems, a multi-step plasma etching process, a combination of the Ar etching and the N2 etching, for InSb was developed. As gradually increasing the amount of N2 gas flow during the etching process, the plasma damage causing the surface roughen decreased and consequently smoother surface close to that of N2 RIE could be obtained. Furthermore, Raman analysis of the InSb surface after the plasma etching indicated clearly that the multi-step etching process was an effective approach in reducing the ion-induced damages on the surface.