THE EFFECTS OF HF CLEANING PRIOR TO SILICON-WAFER BONDING

The effects of preparation of silicon surfaces in hydrofluoric acid (HF) solutions, prior to direct wafer bonding, is investigated. Surface analysis with atomic force microscopy, electron spectroscopy for chemical analysis, and estimation of the surface particle density is made. This is related to results from room temperature bonding experiments. A diluted (1-10%) HF solution is most favorable for hydrophobic silicon wafer bonding. The subsequent water rinse should be omitted, or performed in a careful way, to avoid particle contamination. HF:NH4F solutions generally are not favorable for bonding. The initial room temperature bonding is attributed to the relatively weak van der Waals forces, which makes the bonding sensitive to the surface roughness and particle density. The surface chemistry appears to have a second order influence in hydrophobic bonding.