Removal of Photoresist by Large-Area Atmospheric Pressure Plasmas
Branden Bodner, Jacob Fuss, and Arthur Mazzeo
Abstract: Since the beginning of the integrated circuit era, photoresist has played an integral role in the development and manufacturing of advanced circuits. Historically, removal of photoresist from silicon wafers has been conducted using solvents such as acetone and isopropyl alcohol, which are environmentally undesirable. Dry etching methods such as low-pressure plasma treatments have been employed; however, the necessity of vacuum systems for these methods pose significant economic and technological costs. An attractive alternative to both low pressure plasma photoresist cleaning and wet etching is the use of atmospheric pressure plasmas (APP). Our senior design project focused on experimentally and economically validating the feasibility of using a large-area APP device from Comet Group in large-scale semiconductor manufacturing. Experimental trials of APP wafer cleaning yielded total removal of 1.3 µm thick photoresist at a non-optimized etch rate of 7.1 nm/min. FTIR spectroscopy confirmed complete removal of photoresist by observing the emergence of the Si-O-Si stretching peak and disappearance of the C-H bending peak throughout the APP removal process. SRIM simulations and surface profilometry demonstrated the negligible impact of ion bombardment upon wafer surface quality through minimal variation in surface roughness comparable to wet chemical etching. Economic analysis concluded the total cost of removing photoresist per wafer to be significantly less than that of chemical removal methods: $0.367 and $5.27, respectively.
Decommissioning High-Temperature Gas-Cooled Micro Reactors
Justin Hearne, Ryan Wais, and Joseph Wunschel
Abstract: High-temperature gas-cooled (HTG) micro reactors are small modular reactors that operate at hot temperatures and use helium as a coolant. These reactors also employ a new type of fuel, called TRI-structural ISOtropic (TRISO) particle fuel, which is a uranium oxide pellet with carbide layers. HTG micro reactors have several advantages over conventional reactors, such as increased efficiency, better safety, and reduced costs. However, decommissioning HTG micro reactors poses a significant challenge because of their complex design and new technology. Therefore, there is a need for developing and evaluating a novel method for dismantling and disposing of HTG micro reactors safely and efficiently. The objective of this study was to propose and test a new process for decommissioning HTG micro reactors that would reduce the radiation exposure to workers, minimize the generation of secondary wastes, and comply with the regulatory requirements. The sequence of this process begins with a dormancy period of 2 to 10 years (SAFSTOR), followed by decontaminating the reactor, then cutting the reactor into segments using a diamond wire cutter, encapsulating the segments in concrete containers, and transporting them to a low-level radioactive waste disposal facility. The diamond wire cutter was chosen because it could cut through the thick stainless steel reactor pressure vessel without producing many sparks or dust. The results showed that the proposed method was feasible and effective for decommissioning HTG micro reactors. The specific segmentation design met acceptance criteria for low-level radioactive waste disposal facilities, such as the radionuclide inventory, the surface dose rate, and the mechanical stability. The method also complied with the international standards and guidelines for decommissioning nuclear facilities. To conclude, the proposed process was proven to be a viable option for decommissioning HTG micro reactors. The method offered several benefits over existing options, such as reduced risk, increased efficiency, and reduced cost. This process was created to be applied to all similarly designed HTG micro reactors, such as the Micro-Modular Reactor demonstration project at the University of Illinois at Urbana-Champaign. It is the hope of this project to contribute to enhancing the sustainability and safety of nuclear energy.
