Postexposure bake models

To account for the effect of postexposure bake in reducing standing waves through thermally driven diffusion of the photoacid, lithographic simulators employ models 

Hornberger, P.S. Hauge, and J.M. Shaw, Characterization of positive photoresists, IEEE Trans. Electron Dev. ED-22(7), 445 452 (1975). 

Diamond and J.R. Sheats, Simple algebraic description of photoresist and contrast enhance ment, IEEE Electron Device Lett. EDL-7(6), 383 386 (1986). 

Using the initial distribution of A as the boundary condition, the solution to Eq. (12.69) is the Gaussian distribution function 

In reality, impulse sources do not exist under PEB conditions. An impulse source can be approximated as having a concentration Cq over some small distance Ax centered at Xq, with zero concentrations outside this range. Using this modified impulse source as a boundary condition, the solution of Eq. (12.69) can be approximated as 

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Lithographic modeling simulates several key steps in the lithographic process comprising image formation, resist exposure, postexposure bake diffusion,... 

The effects of thermally driven diffusion of active chemical species within the resist during the postexposure bake are modeled with appropriate diffusion... 

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