Chemically amplified photoresist characterization using interdigitated electrodes: an improved method for determining the Dill C parameter

We have recently developed a technique that utilizes capacitance data from resist coated interdigitated electrodes to measure the kinetic rate constant of photoacid generation (commonly referred to as the Dill C parameter) for photoacid generators in chemically amplified resists. The work presented in this paper focuses on a recently improved version of the IDE Dill C measurement technique. The original version of the technique required coating several IDEs with resist films containing different loadings of photoacid generator and then using the capacitance data from these IDEs to calculate linear mixing relationships between IDE capacitance and the content of PAG or photoproducts within the resist film. The improved version of the technique reported here totally eliminates the need for this “calibration process” through the use of normalized capacitance data. Elimination of the need to measure linear mixing relationships independently for each PAG and polymer combination gives the improved technique many advantages over the prior version. These include improved curve fitting and accuracy of Dill C calculations; fewer raw materials, IDEs, and experimental time; and most importantly, the potential to measure the Dill C for a resist from a single IDE with no prior knowledge of the resist’s photoacid generator type or loading. A detailed derivation of the normalization scheme is presented in this paper, along with evidence of the dramatic improvement in model curve fit that can be achieved using this technique. In addition, Dill C parameters measured for five different photoacid generators with both the original and normalized version of the IDE technique are presented to demonstrate that both techniques measure the same Dill C parameter and hence are describing the same physical phenomena.