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For many years, lithographic resolution has been the main obstacle in allowing the pace of transistor densification to
meet Moore's Law. For the 32 nm node and beyond, new lithography techniques will be used, including immersion ArF
(iArF) lithography and extreme ultraviolet lithography (EUVL). As in the past, these techniques will use new types of
photoresists with the capability to print smaller feature widths and pitches. These smaller feature sizes will also require
the use of thinner layers of photoresists, such as under 100 nm.
In previous papers, we focused on ArF and iArF photoresist shrinkage. We evaluated the magnitude of
shrinkage for both R&D and mature resists as a function of chemical formulation, lithographic sensitivity, scanning
electron microscope (SEM) beam condition, and feature size. Shrinkage results were determined by the well accepted
methodology described in SEMATECH's CD-SEM Unified Specification. In other associated works, we first
developed a 1-D model for resist shrinkage for the bottom linewidth and then a 2-D profile model that accounted for
shrinkage of all aspects of a trapezoidal profile along a given linescan. A fundamental understanding of the
phenomenology of the shrinkage trends was achieved, including how the shrinkage behaves differently for different
sized and shaped features. In the 1-D case, calibration of the parameters to describe the photoresist material and the
electron beam was all that was required to fit the models to real shrinkage data, as long as the photoresist was thick
enough that the beam could not penetrate the entire layer of resist. The later 2-D model included improvements for
solving the CD shrinkage in thin photoresists, which is now of great interest for upcoming realistic lithographic
processing to explore the change in resist profile with electron dose and to predict the influence of initial resist profile on
shrinkage characteristics. The 2-D model also included shrinkage due to both the primary electron beam directly
impacting the profile and backscattered electrons from the electron beam impacting the surrounding substrate. This dose
from backscattering was shown to be an important component in the resist shrinkage process, such that at lower beam
energies, it dominates linewidth shrinkage. In this work, results from a previous paper will be further explored with
numerically simulated results and compared to experimental results to validate the model.
With these findings, we can demonstrate the state of readiness of these models for predicting the shrinkage
characteristics of photoresist measurements and estimating the errors in calculating the original CD from the shrinkage
trend.
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