Plasma implantation of silicon solar cells for emitter and localized BSF formation

It has been estimated that 1 MWp cell production requires almost 10 million liters of de-ionized water, not including chemicals such as HF, HCl, and NaOH. Consideration of the current industry trends, including use of thinner Si wafers and growing incompatibility screen-printed Al-alloyed back surface filed (BSF) formation on increasingly thinner wafers due to wafer warpage and increasing Al costs, also reinforce the need to develop alternate, low-cost manufacturing processes. Dry processing approaches are well-placed to addressing these issues. For example, plasma texturing can be modified to remove saw damage as well as texture the surface in one step. Similarly, plasma implantation of textured surfaces offers an alternate, low-cost approach to form front and back surface doped layers. We report on design and fabrication of a simple, low-cost plasma immersion implantation system. This system is capable of implanting upto 6″-diameter wafers. We have demonstrated of implantation in few minutes with implant activation using long furnace anneals. The junction depths in 0.1–0.4-μm range have been achieved. By optimizing dose, implant energy, and activation profile, we expect to fabricate high efficiency solar cells.