Lumped parameter model for chemically amplified resists

Abstract

Recently the Lumped Parameter Model (LPM) has been extended to three dimensions enabling fast calculations of full resist profiles. This resist model incorporates most of the lithographically significant physical phenomenon of resist systems. This model works well to match isolated and semi-isolated line resist systems. However, it is not very successful at matching contact hole or isolated trench resist systems. The reason for this mismatch can be traced to the influence of base quencher present in chemically amplified (CA) resists yet absent from the original LPM. The quencher effectively splits the aerial image into two complementary images. These two images (acid and base) simultaneously diffuse and react with each other. A single aerial image diffusion model cannot approximate the resulting coupled quenching-diffusion system.An improved LPM that incorporates quencher and its diffusion is presented. Successful implementation of this model requires solving the coupled quenching-diffusion system in a fast and accurate manner. Several solution methods are discussed. The agreement between the Lumped Parameter Model and a full CA resist model is greatly improved. This improvement will enable fast and more accurate calculations of resist affects on threedimensional imaging bias.

Universal approach for process optimization of chemically amplified photoresists in electron beam lithography

“…How to identify and choose the correct parameters can be illustrated using the development kinetics of the lumped parameter model (LPM). 19 The LPM describes the photoresist solubility as a function of the exposure dose. If this dosedependent development rate and the energy distribution in the resist layer are known, the resulting photoresist structures can be calculated in respect to the development duration.…”

“…For chemically amplified resists, it must be noted that existing TRACER fit routines merge all specific effects into one effective process blur fit parameter, simplifying PEB kinetics, not taking base quencher into account, and thus resembling the original LPM. 19 To explain the overall procedure in more detail, the applied approach is described stepwise. First, the GenISys TRACER software is used to simulate the electron scattering PSF via Monte Carlo (MC) simulations in the layer stack.…”

“…As resist mask properties may vastly fluctuate at unstable operation points, selecting appropriate development conditions is essential here. How to identify and choose the correct parameters can be illustrated using the development kinetics of the lumped parameter model (LPM) 19 …”

“…This implemented model-based approach resolves the complex parameter dependency of the base dose, resist contrast, resist thickness, and PSF, while considering the substrate type, layer stack, and acceleration voltage. For chemically amplified resists, it must be noted that existing TRACER fit routines merge all specific effects into one effective process blur fit parameter, simplifying PEB kinetics, not taking base quencher into account, and thus resembling the original LPM 19 …”

Predicting the critical features of the chemically-amplified resist profile based on machine learning

“…There are many photoresist models, some of them are rigorous models describing the physical and chemical processes in lithography, while some of them are empirical models fitting data by observation and experiment. For example, the reaction-diffusion model is a rigorous model introduced in simulating the reactant distribution in photoresist during the post exposure bake 1,2 (PEB), and the lumped parameter model is an empirical model introduced in simulating the photoresist profile 3,4,5 . However, the tradeoff between accuracy and efficiency of these models holds back their development in other fields, like optical proximity correction 6 (OPC) and source mask optimization 7 (SMO).…”