Copyright 2002 Society of Photo-Optical Instrumentation Engineers. This paper was (will be) published in and is made available as an electronic reprint [preprint] with permission of SPIE. Single print or electronic copies for personal use only are allowed. Systematic or multiple reproduction, distribution to multiple locations through an electronic listserver or other electronic means, duplication of any material in this paper for a fee or for commericial purposes, or modification of the content of the pater are all prohibited. By choosing to view or print this document, you agree to all the provisions of the copyright law protecting it.
Femtosecond pulsed lasers offer fundamental advantages over other techniques for repairing lithographic masks. Since the femtosecond ablation process is non-thermal, the spatial resolution is not degraded by thermal diffusion and is therefore limited only by optical diffraction. In addition, metal splatter, gallium staining, reduced optical transmission, beam induced charging, quartz damage, and phase errors inherent in other repair methods are eliminated. A second generation femtosecond laser repair tool is described. The tool utilizes DUV optics which allow ~100nm mask features to be imaged. The laser beam is focused to a round, gaussian spot. This gaussian spot is scanned over the defect, thus allowing arbitrarily shaped repairs to be performed with a spatial resolution of ~100nm. Since the mask is not degraded in any way during the repair process, repairs can be performed iteratively by ablating small slices of the defect. Mask features can be trimmed to an RMS precision of ~5nm. The system is also highly automated: masks are loaded into the tool from a SMIF pod via a robot and the tool is controlled from a single screen operator interface. This new tool has been operating successfully in the IBM Burlington mask house since late 2001, and is currently IBM's primary repair tool for 248 and 193nm chrome on glass and phase shift masks.
By: Alfred Wagner, Richard Haight, Peter Longo
Published in: SPIE Proceedings, volume 4889, (no 1), pages 457-68 in 2002
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