Polished Cu surfaces were silylated with trimethylmethoxysilane or trimethylchlorosilane and washed in water to determine the stability of the silane layers. The surfaces were analyzed using X-ray photoelectron spectroscopy (XPS). Methoxysilane was found to remain stably bound during washing, whereas chlorosilane was completely washed away. This confirmed that methoxysilanes were probably bound to surface oxides as hydrogen-bonded Si-O-R species or metal siloxanes, whereas chlorosilanes could only physisorb because they had removed surface oxides and hydroxyl groups. The silane layers were cured at high temperature in vacuum to promote the formation of metal siloxanes from hydrogen-bonded Si-O-R groups. For both silanes, the cured layers were almost completely washed away. The Si-O-R groups in methoxysilane layers were probably converted to less stably bound siloxane dimers during curing. The polished Cu samples were pre-oxidized in an attempt to increase the amount of oxides on the surface and thereby retain chlorosilane. Pre-oxidation converted Cu2O to CuO. This did not change the behavior of chlorosilane and reduced the uptake of methoxysilane. Solution and surface reactions are suggested for both silanes. For methoxysilane, silanes or silanols directly hydrogen-bonded to surface oxide or hydroxyl groups are proposed to be the primary species that lead to metal siloxanes.