14 May 2004 Resolution limitations in chemically amplified photoresist systems
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Abstract
A variety of experimental evidence suggests that positive-tone chemically amplified photoresists have an intrinsic bias that might limit resolution during high-volume lithographic processing. If this is true, the implications for the semiconductor industry require careful consideration. The design concept of chemical amplification is based on generation of a chemically stable catalytic species in exposed regions of the photoresist film. The catalytic action of the photoproducts on the photoresist polymer causes a change in the dissolution rate in the irradiated regions of the film. Formation of a stable catalyst species is required for chemical amplification, but it has long been recognized that catalyst migration can produce a difference between the initial distribution of exposure energy and the final distribution of photoproducts. This difference, known as diffusion bias, depends on the photoresist chemistry and processing conditions. Diffusion bias is insensitive to exposure conditions, but it is possible to reduce catalyst migration through changes to resist formulation such as increasing the size of the catalyst molecule or processing conditions such as reducing the post exposure bake temperature. Another common approach to limiting diffusion bias is to incorporate base additives into the photoresist formulation to scavenge diffusing acid catalyst. All of these approaches to reducing catalyst migration generally reduce the catalytic efficiency of each photoproduct and therefore increase the total exposure dose required to pattern the film. Increases in required exposure dosage reduce the throughput of the exposure tools and can reduce the profitability of the manufacturing process. In this paper we present experimental results that are suggestive of an intrinsic photoresist bias. This diffusion bias sets a minimum resolution limit for chemically amplified resist systems that can be improved at the cost of reduced throughput and productivity.
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Gerard M. Schmid, Gerard M. Schmid, Michael D. Stewart, Michael D. Stewart, Chia-Ying Wang, Chia-Ying Wang, Bryan D. Vogt, Bryan D. Vogt, Vivek M. Prabhu, Vivek M. Prabhu, Eric K. Lin, Eric K. Lin, C. Grant Willson, C. Grant Willson, } "Resolution limitations in chemically amplified photoresist systems", Proc. SPIE 5376, Advances in Resist Technology and Processing XXI, (14 May 2004); doi: 10.1117/12.536656; https://doi.org/10.1117/12.536656
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