Lithography Materials - Kinetic Modeling of Image Blur in Chemically Amplified Photoresists
The figure below illustrates how image blur limits the resolution of CA resists. This figure depicts the outcome of the post-exposure bake step for a hypothetical case where a line, one nanometer in width, was generated by exposure. The prediction is made using our physically-based, validated reaction diffusion model for TBOC resist. The profile of deprotected polymer does not resemble the initial 1 nm profile of acid, but has broadened 50-fold (Case A [red line] ). Image broadening has been experimentally measured on a related CA photoresist, with results consistent with these predictions.
In-depth examination by kinetic modeling demonstrates that a key metric controlling spatial resolution in CA resists is the ratio of the average rate of deprotection to the average rate of diffusion. If this ratio can be increased, then image blur due to diffusion during post-expose bake will be decreased. The potential improvement is illustrated in as Case B (green line) where the rate ratio is increased by a factor of ten. The prediction is that the spatial resolution can be improved by a more than a factor of three by such change.