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 mu lti-stacked polysilicon and silicon-on-insulator (SOI) substrates and sacri ficial 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 characteri stics of residues on polysilicon or silicon nitride were scrutinized by sca nning electron microscopy (SEM) and Auger electron spectroscopy (AES). Afte r the GPE of CVD TEOS oxide, LTO, and PSG on the silicon nitride substrate, the polysilicon microstructures adhere to the underlying substrate: becaus e neither the SiOxNy layers nor the H3PO3(H2O) layer vaporize. We found tha t the etching of CVD TEOS oxide, LTO, and thermal oxide on a polysilicon su bstrate shows no residue and no stiction. Finally, the fabricated microstru ctures, symmetrically stacked to 6 mu m thickness, operated at DC 4 V and A C 0.1 V in a vacuum chamber at 100 mTorr.