Successful MWIR FPA fabrication using gas cluster ion-beam InSb surface finishing

Abstract

As the demand for mid wavelength infrared (MWIR) focal plane arrays (FPAs) continues to increase, the quality of InSb surfaces becomes more stringent. State-of-the art InSb contains <20 etch pits/cm² (EPD), and provides a surface suitable for rapid oxide desorption and high quality MBE growth. In order to satisfy resolution and sensitivity requirements for advanced MWIR FPA imaging systems ( 1 to 5.4 &#956;m region @77°K), the surface and sub-surface of the material must be of excellent quality. CMP has proven to be a qualified finishing process for InSb surfaces in the fabrication of IRFPAs. However, a time consuming surface etch is universally required in the IRFPA manufacturing process. Gas cluster ion beam processing (GCIB) has been shown to significantly enhance the surface oxide desorption of both GaSb and InSb substrates for MBE growth and provides an alternate surface finish for IRFPA manufacturing. The use of GCIB may preclude the need for surface etching, thus reducing IRFPA processing time and chemical cleanup. This study examines the comparison of CMP and GCIB finishes on InSb surfaces and the effect on final IRFPA device pass rates. NF₃/O₂ dual energy GCIB surface processing was used in this study. Atomic force microscopy (AFM), cross-section transmission electron microscopy (XTEM), and rocking curve x-ray diffraction (XRD) examine the surface and subsurface InSb integrity. A comparison of pass-rates for completed IRFPAs with the CMP and GCIB surface shows the pass-rate to be the same, opening the possibility for etch step elimination.