Negative-tone development of photoresists in environmentally friendly silicone fluids

The large amount of organic solvents and chemicals that are used in today's microelectronic fabrication process can lead to environmental, health and safety hazards. It is therefore necessary to design new materials and new processes to reduce the environmental impact of the lithographic process. In addition, as the feature sizes decrease, other issues such as pattern collapse, which is related to the undesirable high surface tension of the developers and rinse liquids, can occur and limit the resolution. In order to solve these issues, silicone fluids are chosen as alternative developing solvents in this paper. Silicone fluids, also known as linear methyl siloxanes, are a class of mild, non-polar solvents that are non-toxic, not ozone-depleting, and contribute little to global warming. They are considered as promising developers because of their environmental-friendliness and their unique physical properties such as low viscosity and low surface tension. Recently, there have been emerging interests in negative-tone development (NTD) due to its better ability in printing contact holes and trenches. It is also found that the performance of negative-tone development is closely related to the developing solvents. Silicone fluids are thus promising developers for NTD because of their non-polar nature and high contrast negative-tone images are expected with chemical amplification photoresists due to the high chemical contrast of chemical amplification. We have previously shown some successful NTD with conventional photoresists such as ESCAP in silicone fluids. In this paper, another commercially available TOK resist was utilized to study the NTD process in silicone fluids. Because small and non-polar molecules are intrinsically soluble in silicone fluids, we have designed a molecular glass resist for silicone fluids. Due to the low surface tension of silicone fluids, we are able achieve high aspect-ratio, high-resolution patterns without pattern collapse.