SEM images of the passivation layer. a is the top view. The hexagons are SiNx patterns, with a center-to-center distance of 100 μm and a spacing of 22 μm. b represents SiNx film with a good etching result and uniform coverage, without residual photoresist and symptom of overetching. The inset shows the pores as a result of HF horizontal etching.