This paper presents analysis, modeling, and test results of a 193 nm systems designed to minimize the dose effects due to the transient absorption (TA) in fused silica at 193 nm exposure. Fused silica is a material widely used to build optical systems for DUV lithography. Different types of fused silica have been subjected to thorough theoretical examination and testing in the leading laboratories of the world -- IBM Almaden Research Center, MIT Lincoln Labs, Laser-Laboratorium Gottingen and others. One of the most important effects discovered in some types of fused silica, was the TA demonstrated at 193 nm. Pulsed laser illumination may cause a substantial temporary decrease of the sample transmission. After the laser is shut off, the transmission recovers approximately to the initial value. Research results published over the last decade demonstrated that not only the magnitude of TA but also the time constant are functions of fluence. These transients can cause substantial dose variations, making the exposure process unstable and reducing the process yield. SVG manufactures high precision tools for critical-layers lithography where dose stability is crucial. Therefore, the TA was modeled and tested at the system level (laser illuminator and projection optics) to predict behavior of the optical elements in different exposure regimes. This paper presents the theoretical description of the behavior, results of computer simulation and testing for a multi-element system. Criteria of the systems engineering decisions allowing minimization of the TA impact on the dose control are discussed in the conclusion.
The semiconductor industry is investigating metrology methods and tools to ensure the high accuracy and stability required for chip making. Lithography equipment manufacturers are under constant pressure to provide in situ measurements that prevent wafer processing form slipping from the established parameters. This is especially true for DUV exposure tools utilizing excimer lasers with high repetition rates. Dose metrology is one of the key parameters for linewidth control in photolithography. This paper discusses current developments in dose metrology for 248, 193, and 157 nm wavelengths. Particular emphasis is placed on the methodology to support dose stability over the lifetime of the tool. Aspects of tool-to-self and tool-to- tool matching are examined in detail, as well as the implications of the mix-and-match use of lithography equipment. To ensure the long-term accuracy of present tools, strong cooperation is needed within the semiconductor industry from suppliers and end users; and beyond, from standards organizations and international consortia. This paper describes the tasks that have to be accomplished to sustain the dose metrology during the transition from the existing tools to future generations of optical micro lithographic tools.
In the semiconductor equipment business, self-metrology calls for in-situ measurements and diagnostics of the process parameters. For exposure tools, self-diagnostics and self-tuning are the core features. The present paper discusses a dose control system that allows for monitoring, correction and periodic self-calibration of the litho tool. Creation of such a system becomes a task even more complex in view of the aggressive illumination environment - 193 and 157 nm - that makes most traditional optical materials inapplicable; and causes many that are applicable to have time-varying performance.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.