Influence of surface treatment on adhesion of iCVD PGMA thin films for wafer-level bonding
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Influence of surface treatment on adhesion of iCVD PGMA thin films for wafer-level bonding Vijay Jain Bharamaiah Jeevendrakumar1, Bruce A. Altemus2, Adam J. Gildea2, Magnus Bergkvist1 1 College of Nanoscale Science and Engineering, University at Albany, SUNY, Albany, NY 12203, U.S.A. 2 U.S.Technology Development Center, Tokyo Electron U.S Holdings Inc., 2400 Groove Blvd, Austin, TX 78741, U.S.A. ABSTRACT This 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. INTRODUCTION Manipulating adhesion between polymer thin film and substrate is of critical importance for applications in semiconductors, sensor technology, tissue engineering and aerospace industry [1– 6]. Self-assembled monolayers are commonly used as intermediate layers in such applications owing to their strong chemical bonding to substrates and varied end-group functionality [7–9]. We are interested in utilizing organosilanes as intermediate layers to manipulate adhesion between silicon and polymer thin film adhesives in wafer bonding applications. Traditionally polymer adhesives are deposited by solvent based techniques such as spin casting and spray coating [10]. However, the use of solvents poses challenges with substrate compatibility, film dewetting and conformality [11]. Gas phase deposition techniques can alleviate such drawbacks forming thin, conformal films on a variety of materials and structures [12]. Initiated chemical vapor deposition (iCVD) is one such technique with several advantages compared to traditional vapor-phase polymerization techniques like plasma-enhanced chemical vapor deposition (PECVD), or hot-wire chemical vapor deposition (HWCVD). It is a low-energy technique resulting in higher retention of polymer functional groups compared to high-energy PECVD and HWCVD processes [13]. Furthermore, iCVD preserve the substrate chemistry, unlike PECVD which involves
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