Resist Sensitivity and Contrast

Resist contrasts are defined as the slopes of the linear portion of the sensitivity curves (Fig. 3) and depend on process conditions. Thus, the sensitivity (contrast) curves are constructed to semi-optimize process conditions for a given formulation. However, final optimization of a resist formulation and process conditions requires lithographic imaging of target features. A plot of a dissolution rate as a function of exposure dose (cf. Fig. 172) is very useful in assessing the developer selectivity (development contrast) as mentioned earlier. 

Another useful contrast values are related to the resist chemistry in the film, which will subsequently affect the lithographic contrast. Sensitivity (contrast) curves similar to Fig. 3 can be generated by following the degree of reaction (deprotection, for example) with IR or by measuring thinning (in deprotection, for example) as the function of exposure dose. Comparison of a chemical contrast curve with a development contrast curve provides useful information on resist behavior, such as a degree of deprotection at E0. 

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Optimization of both resist sensitivity and contrast requires a fundamental appreciation of the radiation chemistry in addition to appreciation how polymer molecular parameters affect the lithographic behavior of the resist. The intent of this chapter is to further the readers understanding of the polymer and radiation chemistry that is associated with a large part of the microelectronics industry, and provide some of the necessary background to effect future developments. 

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