Share Email Print

Proceedings Paper

Factors that determine the optimum reduction factor for wafer steppers
Author(s): Harry J. Levinson; Paul W. Ackmann; Moshe E. Preil; William T. Rericha
Format Member Price Non-Member Price
PDF $17.00 $21.00
cover GOOD NEWS! Your organization subscribes to the SPIE Digital Library. You may be able to download this paper for free. Check Access

Paper Abstract

The optimum reduction factor for stepper lenses is determined by trade-offs among several competing constraints and practical limitations. Lens reduction factor were chosen initially on the basis of several factors, including maximum lens element size, usable reticle field, stepper throughput and reticle glass size. These considerations led to the choice of 5x for the reduction factor initially and 4x for the most recent generation of step-and-scan systems. A large reduction factor is beneficial because it reduces the negative impacts of reticle linewidth variations, reticle registration errors, and reticle defects. This is particularly important for optical lithography processes that operate near the diffraction limit, where the mask error factor can be large. For this reason, as well travel down the roadmap, the 4x reduction factor for critical stepper lenses needs to be reconsidered. Before a decision is made, all consequences of a large reduction factor must be taken in to account. For fixed field sizes, reduction factors have been limited to 4x in order to achieve compatibility between 26 mm X 33 mm field sizes and 6 inch reticles, and the assumption of large die size. The reduction factor of 4x can be reconsidered if prior predictions of large die size are not realized of capability for making 230 mm reticles becomes available. The economics of 230 mm reticles changes favorably when the reduction factor is increased. Large reduction factors have relatively neutral effects on lens cost, but will make fast scanning more difficult. A proposal for a possible new optimum reduction is given from the analysis of these critical factors.

Paper Details

Date Published: 14 June 1999
PDF: 11 pages
Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350834
Show Author Affiliations
Harry J. Levinson, Advanced Micro Devices, Inc. (United States)
Paul W. Ackmann, Advanced Micro Devices, Inc. (United States)
Moshe E. Preil, KLA-Tencor Corp. (United States)
William T. Rericha, Micron Technology, Inc. (United States)

Published in SPIE Proceedings Vol. 3677:
Metrology, Inspection, and Process Control for Microlithography XIII
Bhanwar Singh, Editor(s)

© SPIE. Terms of Use
Back to Top