Ultra-low mass delivery system for anti-sag brakes and sidewall heater diffusion furnaces

Abstract

Multi-zone, solar cell diffusion furnaces having a plurality of radiant element (SiC) or / and high intensity IR lamp heated process zones, including baffle, ramp-up, firing, soaking and cooling zone(s). The transport of solar cell wafers, e.g., silicon, selenium, germanium or gallium-based solar cell wafers, through the furnace is implemented by use of an ultra low-mass, wafer transport system comprising laterally spaced shielded, synchronously driven, metal bands or chains carrying non-rotating alumina tubes suspended on wires between them. The wafers rest on raised circumferential standoffs spaced laterally along the alumina tubes, which reduces contamination. The high intensity IR flux rapidly photo-radiation conditions the wafers so that diffusion occurs>3 faster than conventional high-mass thermal furnaces. Longitudinal side wall heaters comprising coil heaters in Inconel sheaths inserted in carrier tubes are employed to insure even heating of wafer edges adjacent the side walls.

Description

technical field [0001] The present invention relates to a continuous conveyor, multi-lane diffusion furnace for processing solar cell wafers by heating with radiant resistance or / and IR lamps in the range of 700-1100° C. to make P and / or The or B dopant composition diffuses or / and co-diffuses into the silicon (or other advanced material) in the wafer, thereby forming a p-n junction surface layer or / and a back surface electric field layer. Specifically, the present invention relates to a solar cell diffusion furnace having one or more heating zones and an ultra-low mass, low friction, lateral wire-hanging alumina tube delivery system, plus longitudinal sidewall radiant heaters and Anti-sag brake assembly. Background technique [0002] Manufacturing silicon-based solar cells requires a "wire saw" to cut thin slices of silicon laterally from an ingot to form rough solar cell wafers. These wafers, whether formed from single crystals or polycrystals bonded together, are then pr...

AI Technical Summary

Problems solved by technology

The defects are traps where electron-hole pairs can recombine, reducing cell efficiency or power output

Also, it is not currently possible to increase the power of the lamps, as higher outputs can lead to overheating of the lamp elements, caused by the thermal mass of the furnace (mainly in high quality solid ceramic roller conveyor systems)

To prevent overheating, thermocouples are used to reduce the power density, but this results in a substantial change in the spectral output emitted by the IR lamp (lower luminous flux and energy output)

Reduced luminous flux results in the need to reduce the speed of the conveyor belt or extend the length of the furnace (while maintaining the original belt speed), thus slowing down the process

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