Yield enhancement using source/drain BF2+ implant process optimization

This investigation employs an optimized method to alleviate defects occurring at BF₂⁺ implanted source/drain areas, some white spots defects found at scribes lines after BPSG (boron and phosphorus doped silicon glass) anneal. The results of physical failure analysis indicate the white spot defects are relative to outgassed fluorine that can´t be released out during BPSG thermal annealing. Various approaches which includes changing the stress of post cap layer, lowering down the BF₂⁺ implant doping concentration, and optimizing the ramp-up speed of post-annealing are all able to alleviate the generation of white spot defects. The optimized process with an additional RTP (rapid thermal annealing) right after BF₂⁺ implantation delivers 7% yield improvement.