A Novel Wafer-plane Dosimeter for EUV Lithography

Published

November 1, 2009

Author(s)

Steven E. Grantham, Charles S. Tarrio

Abstract

Extreme Ultraviolet Lithography (EUVL) incorporates 13.5 nm light for patterning wafers and requires in-situ wafer-plane dosimetry that can be tailored to the requirements of an EUVL stepper’s environment. There are several types of detectors that are sensitive to EUV radiation including photodiodes, CCDs, and pyroelectrics to name a few. All of these require electrical connections and can be intrusive in a stepper’s projection optics box and will deteriorate with time causing changes to their calibration. The community has settled on using photoresist as a dosimeter in the wafer-plane because it is a convenient non-intrusive way to measure the dose in the wafer plane an it has very little overhead in the fab environment. However, recent experiments have found that the accepted values for the dose-to-clear for resists may not be accurate. In addition, dosimetry using a photoresist can be dependent on fab conditions and cause uncertainty due to varying process conditions. NIST has recently begun working on a wafer plane dosimeter, based on storage phosphor technology, which can pass through a stepper as wafer surrogates. Storage phosphors act as passive detectors that store latent images until they are read out using a visible light laser-based scanner. They are sensitive to 13.5 nm and are linear over at least 4 orders of magnitude. A dosimeter based on storage phosphor can be constructed in a configuration such that it mimics a wafer and can be passed through a stepper just like a wafer. In addition, storage phosphors are reusable and can be recalibrated as needed. EUV-sensitive storage phosphors are extremely sensitive and tend to saturate at levels of order a few mJ/cm2, however we have developed attenuating polymer layers that can be deposited on the front surfaces. In this paper we will present the dosimeter along with the results of several experiments that characterize the performance of the dosimeter at 13.5 nm, such as in the attached figure

Proceedings Title

2009 International Conference on Frontiers of Characterization and Metrology for Nanoelectronics

Volume

1173

Conference Dates

May 11-15, 2009

Conference Location

Albany, NY

Pub Type

Conferences

Keywords

Extreme ultraviolet, dosimetry, radiometry, lithography, wafer plane

Citation

Grantham, S. and Tarrio, C. (2009), A Novel Wafer-plane Dosimeter for EUV Lithography, 2009 International Conference on Frontiers of Characterization and Metrology for Nanoelectronics, Albany, NY (Accessed December 13, 2024)