Boron diffused emitter etch back and passivation

In this study, a well-controlled etch-back technique was developed using HF and HNO3 mixture solution to remove the boron depletion layer caused by post-oxidation step. The etching rate can be manipulated by changing HF proportion; meanwhile the sheet resistance variation can be maintained smaller than 10% after etching back. Nitric acid oxidation of Si technique was used to passivate the boron emitter before and after etch back. The presence of the surface boron depletion layer makes the surface boron concentration lower, which is better for low Dit at the surface after passivation, while it can also introduce extra recombination by making the electron and hole concentration closer at the surface. PC1D was used to simulate the results for further understanding the recombination in the whole emitter region.