Improvement in Adhesion for the Epoxy-SiC System via Plasma and Silane Surface Modification Techniques

The adhesion durability of coatings and encapsulant materials utilized in electronic packaging is vital for device reliability in the microelectronics industry. Due to adverse operating conditions such as high moisture and high temperature environments, the adhesion between an adhesive and its substrate is typically compromised. This thesis addresses the advantages of employing plasma pretreatments and surface derivatization using silane coupling agents as surface modification techniques in an effort to enhance the adhesive bonding of epoxy to SiC coated Si wafers (SiC/Si). Durability was evaluated by immersing coated-Si samples in aqueous solutions at elevated temperature (60°C) to simulate prolonged severe operating conditions.

Three surface modification approaches for the SiC/Si substrate to be discussed include: 1) a silane coupling agent treatment, which involves a reaction of either 3-aminopropyltriethoxysilane (APS) or 3-glycidoxypropyltrimethoxysilane (GPS) with the substrate, 2) an oxygen plasma pretreatment followed by a silane treatment, and 3) a water/oxygen plasma pretreatment followed by a silane treatment. Samples were immersed in aqueous solutions at various pH at 60°C for extended periods of time. Adhesion durability of treated epoxy/SiC/Si systems was qualitatively evaluated by visual inspection for debonding, and quantitatively evaluated using a probe test to evaluate the critical strain energy release rate G_c. Additionally, X-ray photoelectron spectroscopy (XPS) surface characterization was carried out following the surface treatments and again after complete failure in the durability tests.

The durability tests illustrated that surface treatments involving an oxygen plasma pretreatment prior to silane derivatization resulted in significant improvement in adhesive performance. Furthermore, the results of XPS analysis suggested that the improved bonding was due to cleaning of the substrate surface, promotion of silane adsorption and the formation of a thicker oxide layer. The effectiveness of the surface modification methods in relationship to surface chemistry and adhesion for the epoxy/SiC/Si system is reported and discussed in this work.