Previously, a method which utilizes interdigitated electrode (IDE) sensors to collect capacitance versus exposure dose data for thin films containing a photoacid generator (PAG) and polymer and subsequently calculate the Dill C photoreaction rate constant for the photoacid generator has been presented. This paper discusses a method for extending such IDE methods to calculate the Dill C rate constant for a photoacid generator in a film containing a polymer, photoacid generator, and base quencher. This three component formulation more closely resembles the composition of commercial chemically amplified photoresists. It is shown that by using a data normalization approach, the IDE data can be successfully analyzed to compute accurate Dill C values for a PAG in the presence of base quencher and to estimate the concentration of base quencher in the film. The technique also thus allows for measurement of the impact of the presence of base quencher on the photoreaction rate constant of the photoacid generator.
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.
The ability of interdigitated electrodes to serve as novel chemically amplified resist characterization tools has recently been demonstrated through their ability to measure the Dill C kinetic rate constant for photoacid generation. The work presented in this paper attempts to further extend the capabilities of the interdigitated electrode (IDE) sensors by investigating their potential use as a measurement tool for photoacid diffusion coefficients. Impedance spectroscopy of chemically amplified photoresist coated interdigitated electrodes is used to calculate the bulk ionic conductivity of the resist film. The ionic conductivity is subsequently utilized in the Nernst-Einstein equation to calculate the diffusion coefficient of the photoacid, assuming that it is the major charge carrying species in the film. A detailed description of the measurement and data analysis processes required to calculate the diffusion coefficient of triphenylsulfonium triflate in poly(p-hydroxystyrene) is provided. In addition, the effect of varying the relative humidity of the measurement environment upon the impedance data collected has been examined. It has been observed that the presence of water within the resist film, typically as a result of absorption of water from the humid ambient environment, dramatically changes the conductivity of the resist coated IDE. This change is apparently the result of changes in the proton conduction mechanism within the resist as a function of film water content. A discussion of several possible causes of this phenomena and its impact on the interpretation of the electrical data and the calculation and meaning of an acid diffusion coefficient are presented.
Alicyclic polymers, such as substituted polynorbornenes, are one potential material solution for providing photoresist polymer resins with high transparency backbones for photolithography at 193 nm and 157 nm wavelengths. In addition, the bis-trifluoromethyl carbinol functional group has been identified as a highly transparent base soluble group that can be used for producing photoresist resins from polynorbornene materials for 157 nm lithography. In this work, the interactions between commercial photoacid generators (PAGs) and bis-trifluoromethyl carbinol substituted polynorbornene (HFAPNB) are examined. It was found that photoacid generators can act as strong dissolution inhibitors for bis-trifluoromethyl carbinol substituted polynorbornene homopolymers. More importantly, it was found that a variety of photoacid generators can act as photoswitchable dissolution inhibitors for these materials, with exposure of the photoacid generator resulting in a reduction in the dissolution inhibition (i.e. increased dissolution rate) of the functionalized polynorbornene. The complete inhibition of unexposed HFAPNB polymers by iodonium photoacid generators allows for the formulation of photodefinable materials using a simple two component system consisting only of PAG and the HFAPNB polymer.
A novel technique for determining the Dill C rate constant for photoacid generation has been investigated. This technique involves using capacitance measurements of interdigitated electrodes (IDE) coated with chemically amplified resist to monitor the generation of photoacid within the resist polymer matrix. It is shown that a linear relationship exists between measured capacitance of the IDE and photoacid or PAG concentration within the polymer matrix. Based on this linear relationship, a method is developed for calculating the Dill C parameter for chemically amplified resists based on interdigitated electrode capacitance data. This approach is demonstrated by measuring the Dill C parameter for acid generation using 248 nm exposure of triphenylsulfonium triflate photoacid generator in a poly(p-hydroxystyrene) matrix. A Dill C parameter value of 0.0445 was calculated using this capacitance method which is in good agreement with other literature reported values for this PAG.
The equilibrium resist film water content at various water partial pressures and the rate of diffusion of water into photoresist thin films was investigated fro three model resist polymers: (1) a traditional novolac matrix, (2) poly(p-hydroxystyrene), and (3) bis-trifluoromethyl carbinol substituted polynorbornene. A quartz crystal microbalance (QCM) was used to measure the mass of water added to resist films exposed to environments of differing relative humidity. All three polymer systems absorbed significant quantities of water at 100% relative humidity with PHOST absorbing the most (9.8wt.%) followed by the polynorbornenes (5-8 wt%) and the novolacs (2-3 wt%). The diffusion of water into the polymer films was observed to follow Fickian diffusion behavior initially (Mt/Ms<0.6) followed by behavior indicative of concentration dependent diffusion at large water uptake values. Finally, interdigitated electrodes were utilized to estimate the impact of varying humidity upon the net dielectric constant of the resist films. A linear relationship was observed for measured capacitance versus water uptake for all polymers measured and a power law dielectric mixing rule was found to properly describe the effective dielectric constant of the water/polymer mixtures.
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