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

Abstract

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.

Advances in Patterning Materials for 193 nm Immersion Lithography

“…The water uptake of a resist per unit thickness is roughly constant and increases with exposure and increased resist hydrophilicity . In particular, the water uptake fraction of the fast diffusion process in Figure was observed to be roughly equivalent of the molar fraction of polar hydroxyl- and lactone-containing monomers in the resist polymer. , In addition to having a lower water diffusion coefficient than phenolic-based 248 nm resists, , typical 193 nm methacrylate resists were found to absorb less water (∼1.5−4 wt %) than hexafluoroisopropanol-functionalized norbornene addition polymers (5−8 wt %), poly(hydroxystyrene) (9−10 wt %), and novolac (2−5 wt %). , Polymeric topcoats (whether alkali soluble or organic-developable) have been shown to be permeable to water by reflectance , and quartz crystal microbalance ,,, measurements. Even though highly fluorinated organic-developable topcoats absorb very little water themselves (<0.1 wt %), , water still permeates through them (albeit less than through more hydrophilic alkali-soluble topcoats) and is taken up into the underlying resist .…”

“…All resists studied show measurable increases in mass and thickness when placed in contact with water. ,,− The kinetics of water diffusion into the resist material as derived by Crank is described by eq . , M ( t ) M ∞ = 1 − 8 π 2 ∑ n = 0 ∞ 1 false( 2 n + 1 false) 2 .25em exp [ − false( 2 n + 1 false) 2 normalπ 2 D t L 2 ] wherein M ( t ) is the mass uptake at time t , M ∞ is the mass uptake at infinite time, D is the diffusion coefficient, and L is the film thickness. For short water-contact times, the solution is given by eq M ( t ) M ∞ = 2 D t L 2 true( 1 π 1 / 2 + 2 ∑ ...…”

“…For short water-contact times, the solution is given by eq M ( t ) M ∞ = 2 D t L 2 true( 1 π 1 / 2 + 2 ∑ n = 1 ∞ ( − 1 ) n .25em ierfc [ n L D t ] true) wherein ierfc is the integrated complementary error function. , The majority of water uptake occurs in the first few seconds of water contact (as seen in Figure ). ,, For example, finite element modeling indicated a resist film is over 50% saturated in 5 s and 93% saturated in 15 s . For short contact times ( M (t)/ M ∞ < 0.6), modeling the water uptake using a single diffusion coefficient provides a good fit to the experimental data. , For longer contact times, water uptake has been described using time-dependent diffusion processes or multiple diffusion processes. , …”