A new MIS Interface Control Technology for Fabrication of High Spatial Resolution InGaAs Change Coupled Devices for Imaging

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For advanced image technologies including HDTVs, solid state imaging devices whose spatial resolution is much higher than today's standard is required. The spatial resolution of conventional Si CCDs is limited not by lithography, but by its indirect bandgap nature which makes the optical absorption layer inevitably thick, causing smearing of images due to carrier diffusion. This difficulty can be overcome by using a direct energy gap materials like InGaAs. However, compound semiconductor MIS interfaces generally possess high density of gap states which makes realization of MIS devices difficult.The purpose of the present research was to establish a new practical MIS interface control technology for fabrication of InGaAs MIS CCDs. The main achievements are listed below :(1) The new technology uses a ultrathin Si interface control layer (Si ICL). The basic sequence consists of MBE growth of InGaAs, MBE growth of Si ICL on InGaAs, partial oxidation of Si ICL and deposition of photo-CVD Si … More O_2 layer using ArF excimer laser. In this structure, the Si ICL terminates surface bonds of InGaAs by a pseudomorphic array of Si atoms which make in turn a smooth transition to a outer thick SiO_2 layer. The necessary conditions for Si ICL are (a) maintenance of its pseudomorphic matching to InGaAs, (b)its capability of prevention of direct oxidation of InGaAs and (c) formation of a good SiO_2/Si interface with minimal suboxide components.(2) Using in-situ XPS monitoring, an optimized process involving a repeated deposition-oxidation-annealing cycle has been established which simultaneously achieves the above three conditions, and reduces N_<ss>.(3) By changing the surface stoichiometry towards As-rich condition by HF treatment and subsequently reducing As-rich oxide by Si ICL, the present Si ICL technology has been made compatible with the conventional device processing technology where exposure of sample surface to air is inevitable.(4) The new Si ICL technology has been successfully applied to fabrication of recessed gate depletion mode MISFETs and MIS CCD structures with the maximum channel mobility of 3850 cm^2/V.s. and a very small current drift.(5) The new Si ICL technology has also been applied to passivation of InGaAs wire structures, control of GaAs Schottky barrier heights over 400 meV and control of heterojunction band line-up. Less