Accelerated Diffusion Following Deprotection in Chemically Amplified Resists

Abstract

Polymeric chemically amplified resists (CARs) are critical materials for high-throughput lithographic processes. A photoactivated acid-anion catalyst changes the polymer’s solubility via a deprotection reaction, which enables pattern development through selective dissolution. To capture observed reaction kinetics, reaction-diffusion models employ a catalyst diffusivity that is accelerated by reaction. However, the microscopic origin and factors contributing to this phenomena remain unclear. Herein, we employ detailed atomistic molecular dynamics simulations to examine the impact of protecting group removal and material relaxation on catalyst mobility. We report data on polymer density, catalyst dispersion, excess free volume, and segmental dynamics with increasing time/extent of deprotection. We then propose simple kinetic Monte Carlo algorithms that can describe both molecular dynamics simulations of deprotection reactions and experimental data.

Role of counter-anion chemistry, free volume, and reaction byproducts in chemically amplified resists

“…Software and Algorithms. Following our past studies, 4,5 atomistic molecular dynamics simulations were conducted using GROMACS 2018.1. 19 Integration was performed using the leap-frog algorithm with a timestep of 1.5 fs.…”

“…kinetic Monte Carlo Method with Accelerated Diffusivities. A kMC model, described in detail in our prior work, 5 was used herein to model reaction kinetics for both TPS-TFL or TPS-PFBS in the resist. The model assumes that locals regions (1 nm 3 ) of the resist progress through two states of elevated catalyst diffusivities after being reacted, before transitioning to catalyst diffusivities, D 0 , in the absence of reaction.…”

“…In our prior work, this model was found sufficient to model deprotection kinetics for H + TFLin both experiments and simulations with volume relaxation. 5…”

“…Past literature demonstrates that deprotection is influenced by both catalyst and resist chemistry, with recent atomistic simulations suggesting that the generation of excess free volume and catalyst clustering each play a key role in controlling deprotection. 4,5 A prior study that compared photoacid generators (PAGs) of triphenylsulfonium triflate (TPS-TFL) and triphenylsulfonium perflurobutanesulfonate (TPS-PFBS), which produce acid-triflate (H + TFL -) and the larger acid-perfluorobutanesulfonate (H + PFBS -), respectively, measured a decrease in reaction rates with increasing counter-anion size. 6 This result suggested that the increased counter-anion size of PFBScompared to TFLdecreased the diffusivity of the H + catalyst.…”

“…10,11 In our recent work, a kMC (kinetic Monte Carlo) model of transient local diffusivities was implemented to probe aspects of the CAR system that are difficult to quantify experimentally. 5 The model serves as a bridge between measurements of bulk reaction kinetics and atomistic simulations investigating the physical processes that are controlling catalyst diffusion. In this work, we use the KMC model to fit bulk reaction kinetics data as a function of temperature, catalyst concentration, and catalyst chemistry to examine their impact on catalyst diffusion and reaction.…”