Advanced thin film-based optoelectronic/rf mixed-signal systems.

摘要

The work outlined in this thesis aims to deposit thin silicon films on a variety of substrates, pattern them into very small islands to make individual devices, then anneal the islands to turn them into quasi-single crystals. An important consideration is keeping the anneal temperature low, since many substrates and metals do not tolerate high temperatures. Another key issue is developing non-destructive characterization methods to test the islands for crystalline quality, a task rendered difficult by the 100nm size of the islands. The initial characterization was based on AFM, SEM, TEM and FIB methods. These approaches are shown to be useful in calibrating the islands' properties, but most of them are destructive, so a new x-ray-based methodology is proposed and explored. The x-ray measurements were found to work best using EXAFS, giving a good picture of the islands' internal structure. To get statistically significant results, 1000 x 1000 island arrays were fabricated, with island dimensions varying from 1μm down to 0.1μm. These islands were annealed at temperatures ranging from 590°C to 710°C, taking EXAFS spectra after each new anneal. It was found that as the temperature increased, the local ordering of the atoms also increased and that the islands became crystalline at approximately 650°C. Numerical analysis then brought out the additional information that island size affected the crystallization rate, with the 0.1μm islands reaching crystallinity before the larger islands. This data supports our theory that the smallest islands crystallize into single crystallites, as evidenced also by our previous TEM studies.; Another process element studied was metallization. As the ultimate goal of this research is to build thin-film detectors and transistors, the metallization is crucial, and new uses have been found for it. This thesis describes a way to use the films for wavelength filtering in the optical domain. Specifically, a judiciously chosen set of sub-wavelength holes in the metal film, can be used to make color photo-sensors without the use of color dyes or external filters. Finally, the thesis describes a full system including a thin-film sensor, customized metallization and underlying support CMOS circuitry.