METAL-BONDING DURING SPUTTER FILM DEPOSITION

We studied the bonding between two flat Si substrates with thin metal films. The bonding was accomplished during thin film sputter depositio n on contamination free surfaces of metal films. In this work we used Ti and Pt. Successful bonding of these metal films (each having a thic kness of 10-20 nm) occurred at room temperature over the entire bonded area (12 mm x 12 mm). Self-diffusion, particularly at grain boundarie s and film surface, was the mechanism for bonding. Suitable metal bond ing only occurred if the film surface roughness is sufficiently smalle r than the self-diffusion length of metals. Particularly in the bondin g of Ti to Ti films, transmission electron microscope observation reve aled that complete crystalline grains had been formed across the forme r interface between the single thin Ti films. The interfaceless bondin g can be explained by recrystallization of the Ti lattice due to the h igh self-diffusion coefficient of Ti. This technique would be applied to bonding of wafers to fabricate thin film devices or microsystems. M oreover, this bonding technology can be used with many different thin film materials and various semiconductor substrates. (C) 1998 American Vacuum Society. [S0734-2101(98)05004-0].