Modification of silicon surfaces with H2SO4:H2O2:HF and HNO3:HF for wafer bonding applications

Paper in proceeding, 1995

Two combinations of oxidizing and etching agents, H2SO4:H2O2:HF and HNO3:HF, have been used to modify silicon surfaces for wafer bonding. By tuning the HF-content of the mixtures, the chemical oxide thickness can be controlled between 0 and 10 Å. Using X-ray photoelectron spectroscopy it is found, that the chemical composition of the surfaces can also be controlled. Terminating species, which can be obtained by the described procedures, are OH, F, and H. Both the described cleaning procedures permit hydrophilic bonding, giving a high room temperature bond strength, with a minimum of interfacial oxide. Different bonded combinations of terminated surfaces were investigated, and it was found that bonding a mainly F-terminated, or a mainly OH-terminated, surface to an H-terminated surface, does not yield any higher bond strength than bonding two H-terminated surfaces