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22 January 2001 Innovations in lithography metrology for characterization of phase-shift mask materials
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One of the difficult challenges faced by the semiconductor manufacturingindustry is the pressure to create ever more powerful, complex chips with smaller geometries. Currently, the demands for smaller feature sizes are being met by utilizing exposure wavelengths in the deep-UV range (248 nm and 193 nm). To further reduce feature size and squeeze the very last potential out of optical lithography, the technology has moved towards the incorporation of phase-shift materials. For such materials, rapid and accurate measurement is imperative to produce and maintain the correct phase-shift. The complete and accurate characterization of phase-shift materials requires that the measuring instrument provide phase-shift information plus thickness of the phase-shift material and values oin (the index of refraction and k (the extinction coefficient) at the specified wavelength. Furthermore, transmittance through both the phase-shift material and substrate must be measured at that specified wavelength. Specifically, the characterization data must indicate whether the ideal phase-shift of 180°, in addition to pre-specified transmittance in the 5-10% range, has been achieved. In this article we present a method of data collection and analysis that allows the phase-shift, film thickness and values of n and k to be determined simultaneously from the concurrent measurements of transmittance and reflectance, allowing the detection of non-uniformities in phase-shift in either patterned or un-pattemed films, with close correlation to direct-measured values. This technique offers the advantage of high throughput (entire masks can be characterized in minutes) and can be applied equally well to patterned or unpattemed masks.
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Dale A. Harrison, John C. Lam, and A. Rahim Forouhi "Innovations in lithography metrology for characterization of phase-shift mask materials", Proc. SPIE 4186, 20th Annual BACUS Symposium on Photomask Technology, (22 January 2001);

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