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Proceedings Paper

Experimental validation of 2D profile photoresist shrinkage model
Author(s): Benjamin Bunday; Aaron Cordes; Andy Self; Lorena Ferry; Alex Danilevsky
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Paper Abstract

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.

Paper Details

Date Published: 20 April 2011
PDF: 21 pages
Proc. SPIE 7971, Metrology, Inspection, and Process Control for Microlithography XXV, 79710W (20 April 2011); doi: 10.1117/12.881406
Show Author Affiliations
Benjamin Bunday, SEMATECH (United States)
Aaron Cordes, SEMATECH (United States)
Andy Self, Hitachi High Technologies America, Inc. (United States)
Lorena Ferry, Hitachi High Technologies America, Inc. (United States)
Alex Danilevsky, Hitachi High Technologies America, Inc. (United States)

Published in SPIE Proceedings Vol. 7971:
Metrology, Inspection, and Process Control for Microlithography XXV
Christopher J. Raymond, Editor(s)

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