Two combinations of oxidizing and etching agents, H2SO4:H2O2:HF and HNO3:HF, have been used to modify silicon surfaces prior to wafer bonding. The chemical oxide thickness can be adjusted between 0 and 10 Angstrom by tuning the HF content of the mixtures. Using x-ray photoelectron spectroscopy it was found that the chemical composition of the surfaces can also be affected. Hydroxyl groups, fluorine, and hydrogen are terminating species that can be obtained by the described procedures. Both the described cleaning procedures permit hydrophilic bonding, giving a high room temperature bond strength with a minimum of interfacial oxide. The bond between a mainly fluorine-terminated or a mainly OH terminated surface and a hydrogen-terminated surface is no stronger than the bond between two hydrogen-terminated surfaces.