A method to maintain wafer alignment precision during adhesive wafer bonding

In this paper, a novel method is presented that prevents aligned wafers from shifting relative to each other during adhesive bonding. The attainable pre-bond wafer alignment accuracy on commercially available bonding equipment is typically 2-5 mum. However, in adhesive wafer bonding, the intermediate adhesive material must exist in a liquid-like state to wet the wafer surfaces and thereby achieve bonding. When pressing the wafers together with the bond chucks during the bonding process it is practically inevitable that shear forces occur, which act in parallel to the bond line. The intermediate liquid adhesive material cannot counteract the shear forces, thus, the wafers move relative to each other. Consequently, the achievable alignment accuracy in adhesive wafer bonding is typically less than 15 mum using commercial bonding equipment. A novel method has been developed that utilises structures at the wafer surfaces to provide areas with solid-state material contact between the two wafers during the bonding process. The resulting frictional forces prevent the wafers from shifting relative to each other during the time the intermediate adhesive material is in a liquid state. Thus, the pre-bond alignment accuracy of 2-5 mum can be maintained during adhesive wafer bonding using standard wafer bonding equipment as compared to a wafer alignment accuracy of 15-50 mum when no frictional structures are used. (C) 2003 Elsevier B.V. All rights reserved.