New Variable Selective Etching Technology for Thick SOI Devices

In this paper, a new variable selective etching (VSE) technology is proposed for thick silicon-on-insulator (SOI) devices. The VSE is realized by introducing a 5-layer composite hard-mask to realize the silicon etching with a selectivity ratio of 35: 1 and the buried oxide layer (BOX) with a ratio of 100: 1. The VSE technology provides a core process engineering for advanced deep trench isolation (DTI) technology with trench electrode connected to the substrate. The VSE technology is demonstrated by experiments of a SOI with 7 µm silicon and 1.5 µm BOX layer, which revealed that the VSE technology can realize a steep and continuous etching for both silicon and oxide layer and the wafer bow is also be reduced by the stress compensation of the hard-mask.