Karen Turnquest

Influence of base additives on the reaction-diffusion front of model chemically amplified photoresists

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 l...

The deprotection reaction front profile in model 193 nm methacrylate-based chemically amplified photoresists

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.

Direct measurement of the in-situ developed latent image: the residual swelling fraction

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.

Dissolution fundamentals of 193-nm methacrylate based photoresists

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.

Copolymer fraction effect on acid catalyzed deprotection reaction kinetics in model 193 nm photoresists

A correlation between polymer molecular structure and acid catalyzed reaction kinetics is demonstrated by a photoresist copolymer with an acid-labile and a non-reactive monomer. The acid catalyzed deprotection kinetics depend significantly on the composition of the non-reactive comonomer in the polymer chain. The apparent reaction rate constant decreases monotonically with increasing non-reactive comonomer composition. The phenomena are interpreted as the reduction of diffusivity of photoacid in the polymer matrix from a hydrogen-bonding interaction with the polar group in the inert comonomer. In addition, hydrogen-bonding interactions between the photoacid and the reaction product, primarily methacrylic acid, can account for the acid loss or trapping effect observed by various researchers.

Evaluation of the 3D compositional heterogeneity effect on line-edge-roughness

The controlling factors in the formation of the compositional heterogeneity at the deprotection front were investigated using 3D computer simulation. The results illustrate that the chemical composition fluctuation (CCF) formed by the photoresist deprotection reaction is an important factor contributing to the line-edge-roughness (LER) in addition to the deprotection gradient (DG) of the reaction front. The magnitude of the chemical composition fluctuation and the deprotection gradient are found to depend on the ratio of the deprotection reaction rate constant to diffusion coefficient (kP/D) and the number of hoping step (n) With this new finding, the influence on LER from various process/material parameters such as dose/contrast, diffusivity, and reactivity can all be understood through their effects on kP/D and n.

FTIR measurements of compositional heterogeneities (

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 bonding efficiency.

Performance of a dry 193nm resist under wet conditions

193 nm immersion lithography is rapidly moving towards industrial application, and an increasing number of tools are being installed worldwide, all of which will require immersion-capable photoresists to be available. At the same time, existing 193 nm processes are being ramped up using dry lithography. In this situation, it would be highly advantageous to have a single 193 nm resist that can be used under both dry and wet conditions, at least in the initial stages of 45nm node process development. It has been shown by a number of studies that the dominant (meth)acrylate platform of 193 nm dry lithography is in principle capable of being ported to immersion lithography, however, it has been an open question whether a single resist formulation can be optimized for dry and wet exposures simultaneously. For such a dry/wet crossover resist to be successful, it will need to make very few compromises in terms of performance. In particular, the resist should have similar LER/LWR, acceptable process window and controlled defects under wet and dry exposure conditions. Additionally, leaching should be at or below specifications, preferably without but at very least with the use of a top protective coat. In this paper, we will present the performance of resists under wet and dry conditions and report on the feasibility of such crossover resists. Available results so far indicate that it is possible to design such resists at least for L/S applications. Detailed data on lithographic performance under wet and dry conditions will be presented for a prototype dry/wet crossover L/S resist.