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9 June 1995 Nonconstant diffusion coefficients: short description of modeling and comparison to experimental results
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Chemical changes within a resist material (for example, resulting from the exposure and subsequent chemical reactions during post exposure bake) will in general, result in a change in diffusivity of components within that material. In the case of positive chemically amplified resists, the diffusivity of the photo-generated acid changes as a function of the extent of polymer deprotection. The deprotection reaction leads to the generation of small reaction product molecules, some of which are volatile. The liberation of these reaction products causes an increase in the free volume and changes in the chemical behavior in the exposed area. These changes, primarily the increase in free volume, results in an increase in the diffusivity of the acid. Low exposure areas have lower acid diffusivity, leading to a lower efficiency of reaction. This results in a contrast enhancement of the latent image due to the concentration dependent diffusivity of the acid. In this paper, a concentration dependent diffusivity expression is incorporated into a lithography simulator to explore these effects on lithographic performance. Using the assumption of free volume, suitable expressions for the diffusivity are examined and compared to experimentally measured values. The experimental work consists of XP-9402 positive acting, chemically amplified resist that was imaged using different thermal doses.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
John S. Petersen, Chris A. Mack, John L. Sturtevant, Jeff D. Byers, and Daniel A. Miller "Nonconstant diffusion coefficients: short description of modeling and comparison to experimental results", Proc. SPIE 2438, Advances in Resist Technology and Processing XII, (9 June 1995);

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