Deep GaN through-substrate via etching using Cl2/BCl3 inductively coupled plasma

Abstract

In this study, the etching characteristics for fabricating deep GaN through-substrate vias at a high etching rate exceeding 1 μm/min using high density Cl2/BCl3 inductively coupled plasma were investigated. The etching rate decreased almost linearly with increasing BCl3 content up to a 25% gas mixture ratio; however, an etching rate of more than 1 μm/min was achieved. The highest GaN/Ni metal mask etching selectivity was obtained at the gas mixture ratio of 10%. However, large pillars were formed in almost all the via holes, which was attributed to the wafer temperature during etching. By optimizing the etching conditions, GaN via holes with depths of 91 μm and diameters of 80 μm without pillars were successfully formed at an etching rate as high as 1.5 μm/min and with an etching selectivity as high as 35. Furthermore, it was clarified that the etch-back of the Ni metal mask produced sidewalls with two different slopes in these via holes.