As 193 nm immersion lithography continues to evolve, the need to understand the effect of the immersing liquid on the resulting photoresist properties continues to grow. With this in mind, the sorption of water (using both liquid and vapor environments) in two model photoresist polymer resins based on functionalized poly norbornene) was examined using quartz crystal microbalance techniques. Similar to the results presented by Berger and coworkers, it was found that the water uptake in bis-trifluoromethyl carbinol substituted polynorbornene (HFAPNB) increases as the polymer molecular weight increases, while the diffusion coefficient of water in these materials remains relatively constant over the same range in molecular weight. In contrast, trifluorosulphonamide-substituted polynorbornene displays a relatively constant level of water uptake as a function of polymer molecular weight, while the diffusion coefficient decreases by more than an order of magnitude over the same molecular weight range. Sorption experiments performed as a function of temperature have shown that the water diffusion in these polynorbornene polymers can be described using an Arrhenius relationship. The activation energy of water diffusion was compared in both HFAPNB and poly(hydroxystyrene). The activation energy for diffusion of water in HFAPNB is substantially larger than in the case of poly(hydroxystyrene). This is consistent with the view that polynorbornenes possess relatively stiff and rigid backbones as compared to more flexible polymers such as poly(hydroxystyrene). The activation energy for water diffusion in HFAPNB was found to be a strong function of polymer molecular weight, with the activation energy decreasing with increasing molecular weight.
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.
As features shrink below 100 nm, new exposure technologies such as 157 nm lithography are being developed. One of the critical challenges in developing these new lithographic tools and processes is the development of appropriate resist materials that can be used at these lower exposure wavelengths. Creating organic resist polymer resins for 157 nm exposure is a particularly challenging issue since many organic functional groups absorb at this wavelength. It has been previously shown that fluorinated polymers may offer the required low optical absorbance needed to serve as resist resins for 157 nm lithography. In particular, there has been interest in bis-trifluoromethyl carbinol substituted polynorbornenes (HFAPNB) and similar materials for use in photoresists. The bis-trifluoromethyl carbinol group offers a base soluble group that is sufficiently transparent to be used at 157 nm. This work has focused on the dissolution behavior and other characteristics of bis-trifluoromethyl carbinol substituted polynorbornenes. In particular, it was found that the dissolution behavior of the HFAPNB homopolymer is strongly controlled by its ability to hydrogen bond with both neighboring chains and also other small molecule additives such as dissolution inhibitors and photoacid generators. A detailed molecular level explanation for these effects is presented. The interaction of a series of commercial photoacid generators with HFAPNB polymers are presented. The use of such information for the rational design of advanced resist materials using these polymers will be discussed.