Characterization of Residues on Anhydrous HF Gas-Phase Etching of Sacrificial Oxides for Surface Micromachining

We employed a newly developed anhydrous HF gas-phase etching (GPE) process for the removal of sacrificial oxides. The structural layers are P-doped multi-stacked polysilicon and silicon-on-insulator (SOI) substrates and sacrificial layers are chemical vapor deposition (CVD) tetraethylorthosilicate (TEOS) oxide, low-temperature oxide (LTO), phosphosilicate glass (PSG), and thermal oxides on silicon nitride or polysilicon substrates. The characteristics of residues on polysilicon or silicon nitride were scrutinized by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). After the GPE of CVD TEOS oxide, LTO, and PSG on the silicon nitride substrate, the polysilicon microstructures adhere to the underlying substrate because neither the SiO x N y layers nor the H 3 PO 4 (H 2 O) layer vaporize. We found that the etching of CVD TEOS oxide, LTO, and thermal oxide on a polysilicon substrate shows no residue and no stiction. Finally, the fabricated microstructures, symmetrically stacked to 6 µm thickness, operated at DC 4 V and AC 0.1 V in a vacuum chamber at 100 mTorr.