No abstract

Neutron reflectivity and Fourier transform infrared spectroscopy measurements are used to profile the deprotection reaction-diffusion front with nanometer resolution in a model photoresist polymer using three perfluoroalkane-based photoacid generators (PAG) with varying chain lengths. As expected, the spatial extent of the deprotection reaction front increases with decreasing PAG size. Although the total extent of deprotection increases with increasing postexposure bake time for each PAG, the reaction-diffusion of deprotection does not propagate continuously into the photoresist polymer. The form of the deprotection reaction front changes because the diffusion process is affected by the changing polymer composition. The data are well described by a reactiondiffusion model that includes a simple acid-trapping term and does not require a varying PAG diffusivity. This high-resolution profiling, together with modeling, illustrates details of the coupled diffusion and deprotection reaction processes that affect lithographic performance.

The effects of amine base quencher on the photoacid catalyzed deprotection reaction-diffusion front in model photoresists were measured by combination of neutron reflectivity and Fourier transform infrared spectroscopy. Modulation in the location of the base with respect to the diffusing photoacid catalyst changes the spatial reaction extent and illuminates the complex role of the base on the shape of the reaction-diffusion front. Despite similar total extents of reaction, a comparison between uniform base and model photodegradable base distributions demonstrates distinct reaction time and base concentration effects on the deprotection profile shape. These differences arise from the modification of the initial deprotection extent due to both the neutralization of the photoacid and the influence of the changing photoresist composition on the reaction-diffusion process. The use of the model photodegradable base results in a sharper front due to these effects. Lastly, aqueous hydroxide development of these latent images demonstrates a limit to the improvement in feature quality obtained from sharpening of the deprotection profile with base additives.

We demonstrate a general approach to characterize compositional heterogeneity in polymer thin films using Fourier transform infrared (FTIR) spectroscopy. Polymer films with varying degrees of heterogeneity were prepared using a model chemically amplified photoresist where a photoacid catalyzed reaction-diffusion process results in the formation of methacrylic acid (MAA) rich domains. Within these domains, the carboxylic acid groups dimerize through hydrogen bonding. FTIR measurements of the relative fraction of hydrogen-bonded vs free carboxylic groups are used to quantify the degree of compositional heterogeneity. The FTIR data from compositionally homogeneous systems, statistical copolymers, and polymer blends follow the expected linear dependence of the relative hydrogen-bonded fraction with composition. For the chemically amplified photoresist system, the FTIR data deviate substantially from that of the homogeneous distribution. Furthermore, parameters describing the size of the heterogeneity can be determined from a solid sphere model of the deprotected regions catalyzed by the diffusing photoacid. The degree of the spatial heterogeneity varies with changes in the photoacid concentration, reaction conditions, and initial copolymer composition. Increased nonreactive comonomer content decreases the degree of heterogeneity by reducing the hydrogen-bonding efficiency, which is consistent with the dilution of MAA groups.