A general approach to characterize compositional heterogeneity in polymer thin films using Fourier transform
infrared (FTIR) spectroscopy has been demonstrated 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 versus free carboxylic
groups are used to quantify the degree of compositional heterogeneity. It was shown that the degree of the spatial
heterogeneity varies with changes in the deprotection level and initial copolymer composition. The degree of
heterogeneity is small at very low and very high deprotection level and maximize when the deprotection level is around
0.25. Increased non-reactive comonomer content decreases the degree of heterogeneity by reducing the hydrogen
The spatial distribution of polymer photoresist and deuterium labeled developer highlights a fraction of material at a
model line edge that swells, but does not dissolve. This residual swelling fraction remains swollen during both the in
situ development and rinse steps uncovering that the final lithographic feature is resolved by a collapse mechanism
during the drying step. We demonstrate that contrast variant neutron reflectivity provides a general method to probe the
nanometer resolved in situ development and rinse process step.
The dissolution of partially deprotected chemically amplified photoresists is the final step in printing lithographic features. Since this process step can be tuned independently from the design of the photoresist chemistry, measurements of the dissolution behavior may provide needed insights towards improving line-edge roughness. We have studied the dissolution behavior of a model 193-nm photoresist, poly (methyladamantyl methacrylate), as a function of deprotection extent and developer strength. The kinetics of the dissolution process is followed using the quartz crystal microbalance technique. These photoresist films exhibit strong swelling without dissolution over a significant range of deprotection levels. At larger extents of deprotection, we observe a combination of swelling with dissolution. Additionally, we find that the degree of film swelling decreases with tetramethylammonium hydroxide developer concentration. These studies provide the insight needed to better understand the fundamentals of the dissolution of the photoresist - a key step in lithographic process.
An understanding of acid diffusion-reaction in chemically amplified photoresists during the post-exposure bake (PEB) is critical for both critical dimension (CD) and line edge roughness (LER) control. Despite its importance, there remains insufficient understanding of the diffusion-reaction process. This is due in part to the complex interplay between diffusion and reaction where the deprotection of the resin modifies the local acid diffusivity which in turn changes the rate of deprotection. Here, we report the direct measurement of the reaction diffusion front at a model line edge from neutron reflectivity and Fourier transform infrared spectroscopy measurements. The photoacid generator size influences the reaction extent and breath of the deprotection profile. A larger photoacid results in a sharper deprotection profile and a shorter reaction length. Under the same post-exposure bake time and temperature, the smaller photoacid leads to a much broader deprotection profile. These measurements illustrate the complexity of the reaction-diffusion process.