Determination of wafer bonding mechanisms for plasma activated SiN films with x-ray reflectivity

Abstract

Specular and diffuse x-ray reflectivity measurements were employed for wafer bonding studies of surface and interfacial reactions in ∼800 Å thick SiN films deposited on III–V substrates. CuKα1 radiation was employed for these measurements. The as-deposited films show very low surface roughness and uniform, high density SiN. Reflectivity measurements show that an oxygen plasma treatment converts the nitride surface to a somewhat porous SiOx layer (67 Å thick, at 80% of SiO2 density), with confirmation of the oxide formation from x-ray photoelectron spectroscopy. Reactions at the bonded interface of two oxygen plasma treated SiN layers were examined using a bonded structure from which one of the III–V wafers is removed. Reflectivity measurements of bonded structures annealed at 150°C and 300°C show an increase in the SiOx layer density and thickness and even a density gradient across this interface. The increase in density is correlated with an increase in bond strength, where after the 300°C anneal, a high interfacial bond strength, exceeding the bulk strength, was achieved.