Gas-phase etching of TEOS and PSG sacrifice layers using anhydrous HF and CH3OH

Abstract

One of the key processes in silicon surface micromachining is the selective etching of a sacrificial layer to release silicon microstructures. The newly developed anhydrous HF/CH3OH gas-phase etching (GPE) of TEOS (tetraethylorthosilicate) and PSG (phosphosilicate glass) sacrificial layers on silicon nitride and polgcrystalline silicon (polysilicon) substrates has been employed to release polysilicon microstructures. However, a residual product has been observed on the surface after etching of the TEOS on the nitride substrate because a SiOxNy layer is formed at the TEOS/nitride interface. Also, a residual product has been observed after the etching of PSG on the nitride and the polysilicon substrates because this process generates H3PO4(H2O). The polysilicon microstructures are stuck to the underlying substrate because neither the SiOxNy nor the H3PO4(H2O) layer vaporizes. We found that the only sacrificial etching without any residual product and stiction is the etching of TEOS on a polysilicon substrate.