Method for improving metal Ni mask selection ratio in back hole process

The invention discloses a method for improving the metal Ni mask selection ratio in a back hole process. The method includes adopting a Cl-based plasma to conduct surface passivation on the back of a substrate with formed back hole graphs to enable NiCl3 to be formed on the contact surface of a metal Ni mask and the Cl-based plasma. By conducting passivation on the surface of the metal Ni mask, the metal etching rate in the SiC back hole etching process can be reduced, and the selection ratio of SiC to metal Ni is effectively improved. The selection ratio is improved from 30:1 to 90:1. By means of the method, the thickness of the metal mask required by SiC back hole etching can be reduced, and process difficulty is reduced accordingly.