A model of low-temperature wafer bonding and its applications

Si-OH groups can polymerize to form strong covalent Si-O-Si bonds at low temperatures. Based on this behavior a model for hydrophilic Si wafer bonding is suggested which allows significant increase of bonding strength by low-temperature annealing. A possible extension of this model to materials other than Si is discussed. Methods to prevent generation of interface bubbles during the low-temperature annealing are presented. The low-temperature bonding approach has been employed in layer transfer applications such as an ultrathin silicon-on-insulator layers by an implanted carbon etch stop, single-crystal Si layer on quartz, glass, or sapphire. Analysis of thermal peeling stresses in bonded pairs of dis-similar materials led to the development of bonding and heating-cooling schedules as well as a low vacuum bonding method to avoid peeling during annealing and subsequent thinning (etching).