Influence of surface treatment on adhesion of iCVD PGMA thin films for wafer-level bonding

Abstract

ABSTRACTThis work demonstrates wafer bonding using initiated chemical vapor deposition (iCVD) poly(glycidylmethacrylate) (PGMA) thin films, and studies the impact of surface treatment to manipulate adhesion energy between polymer film and silicon substrate. Substrates were modified with organosilanes or nitrogen plasma prior to iCVD and bonding. Adhesion was characterized by measuring critical energy release rate (Gc) using a 4-point bend technique. Results demonstrate a correlation between substrate surface energy and polymer-substrate adhesion energy where, depending on the functional group, close to an order of magnitude variation in adhesion energy was observed. These results point to minimal covalent interaction between polymer and substrate for these samples. Exposing the bonded wafers to a thermal anneal step led to an improved grafting of PGMA to substrate. For grafted films, the sample failure mode shifted from adhesive to cohesive, with drastic increase in Gc. These findings demonstrate that the adhesion energy and failure mode of iCVD-PGMA bonded wafers can be manipulated through surface functionalization and thermal treatment, which enable both temporary and permanent chip-bonding applications using iCVD polymer films as adhesives.