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 dissimilar 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).