Exploratory Development of Thin-Film Polycrystalline Silicon Photovoltaic Devices. Report No. 3. Electron Beam Ribbon-to-Ribbon (EB RTR) Recrystallization of Microcrystalline Silicon Ribbons

摘要

The electron beam has been applied as the energy source for ribbon-to-ribbon (RTR) recrystallization of thin-film silicon with very small (approx. 1 mu m) grains into sheets with very large grains (> 1 cm). The system described uses two e-guns, one for producing a thin molten region across the microcrystalline ribbon (except for the edges), the other for establishing desirable thermal profiles in the cool-down (and heat-up) regions. In this way, no furnace, heat shield, or cooling structures are present, in contrast to all the other ribbon growing techniques. This simple arrangement is gained at the (reasonable) expense of having to work in a vacuum. A CCTV camera observes the temperature distribution and melt shape during growth; its output is coupled to a real-time image analyzer system and a computer. When there is a need to alter the temperature or melt shape in a region, the deflection/modulation circuitry is appropriately instructed, and (closing the loop) the change is made. The vacuum chamber with cassette feed for ribbons, electron guns, and camera, was completed and placed in operation. The overall system was run with a fined temperature profile for small RTR samples; resulting thin-film silicon ribbon quality was comparable to that obtained with laser beam RTR. The entire electronic system was not finished, however, so potential utility of the system for improving silicon ribbon quality and economics could not be ascertained. (ERA citation 08:009527)