Optical Density And Contrast Of Positive Photoresists

We derive a general relation that exhibits the interdependence of the exposure and development processes in determining the contrast and the sensitivity curve of any photo-resist. We show,that for several limiting cases, the contrast is given by the reciprocal of the (pre-or post-expose) optical density of the resist, in agreement with the measured contrasts for PR102, AZ2400 and Dupont 2041 Elvacite PMMA resists. We also calculate the dependence of the threshold exposure energy D/35, and the dose Dp required to completely develop the resist, and hence, the contrast, on development time for a hypothetical solvent and simulate the results obtained using MF314 developer.