Distinct Molecular Structures of Edge and Middle Positions of Plasma Treated Covered Polymer Film Surfaces Relevant in the Microelectronics Industry

Plasma treatment processing is a ubiquitous and necessary processing step in the manufacturing of electronic components. In the semiconductor industry, this processing step is utilized to clean the polymer substrates prior to soldering and applying epoxy underfill resins in flip-chip technology. In this paper, two polymers, polystyrene and polyimide, were protected with a cover and exposed to various plasmas, to simulate the plasma processing steps found within the microelectronics industry. The industrial step that is modeled is when the silicon die and polymer substrate are connected via solder bumps (flip-chip) and the region in between is exposed to plasma prior to the underfill dispensing step, during the assembly process. Two optical techniques, sum-frequency generation (SFG) vibrational spectroscopy and Fourier transform infrared (FT-IR) spectroscopy, were utilized to investigate the polymer surface and bulk structures, respectively. It was demonstrated that the middle and edge regions of the covered polymer surface behaved differently when exposed to various plasmas. Specifically, the polymer surface, as measured by SFG spectroscopy, changes drastically at the edge, and negligible or much smaller changes are detected at the middle position after the plasma treatment. The FT-IR spectroscopic measurements showed that both the edge and the middle positions of the bulk polymer film are generally unaffected by the plasma treatment, which demonstrates that the changes detected by SFG spectroscopy only occur on the polymer surface. The surface structural changes induced by the plasma treatment include the changes of surface functional group orientation and ordering (or orientation distribution). A better understanding of how plasma processing affects polymer surfaces while covered is of utmost importance to the microelectronics industry and is paramount to improved adhesion and quality in semiconductor devices.