Fig X shows the epi plug from each of the recipes. R1 has very low temperature and very high PH3 flow. This results in very high doping but the epi height has taken a hit as it could only reach ~ 10 nm of epi height. R2 allows us to sacrifice some of the crystallinity in favor of improved epi height. This recipe contains higher temperature (~ 15 C compared to R1), while maintaining the same PH3 flow. This results in a non-selective epi dep (including the side walls). The side wall deposits are removed by using an etch back made of only HCl. The HCl etch back selectively etches away the non-crystalline deposits on the sidewalls and other polycrystalline regions. But the etch rate of the monocrystalline epi plug is very low. Therefore, the epi plug is not etched as much as the side walls, giving us a nonvoided epitaxial plug. R3 decreases the PH3 significantly compared to R2, while maintaining the same high temperature. This decrease in PH3 serves two purpose 1) Lowers the overall doping 2) Makes the epi deposition more selective. Hence, by simply lowering the PH3, we have lowered the doping and increased the selectivity of the epi deposition. Therefore, we can remove the etch back that we did in R2.