28 July 1997 Effect of phase error on 180-nm and 250-nm grouped-line KrF lithography using an alternating phase-shift mask
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Extension of optical resolution using technologies such as alternating phase-shifting mask, chromeless PSM, or attenuated PSM combined with off-axis illumination is necessary for manufacturing 180 nm devices. Strong shifters, like alternating and the chromeless type PSM, hold the most promise for optical extension to k1's less than 0.5. However, it is difficult to produce error free masks of these types using today's technologies. Focus-exposure data for 180 nm and 250 nm grouped lines produced with an alternating PSM and a KrF stepper show an asymmetric response about the center of focus (CoF) and an exposure dependent shift in CoF. The CoF changes with changes in phase for varying aerial image critical dimensions (CD), and thus explains that deviations from 180 degree phase cause the observed changes in CoF. Phase error also induces change in image placement. Modeling predicts that the observed CoF is the result of phase greater than or less than 180 degrees, the shape of the entire focus-exposure CD response curve can elucidate which error is observed as can image placement deviation. Monitoring shifts in image placement lends itself to measuring phase error using aerial image analysis. In this paper modeling using the vector analysis package of PROLITH/2 (FINLE Technologies) suggested that the experimentally observed CoF could be explained by a 10 degree error to either side of 180 degrees. Aerial image shifts measured with a MSM-100 AIMS tool (Zeiss) indicated that the error was above 180 degrees. Then combining simulation and aerial image data, the effective phase of the mask was estimated to be 190 degrees.
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John S. Petersen, John S. Petersen, Alvina M. Williams, Alvina M. Williams, Georgia K. Rich, Georgia K. Rich, Daniel A. Miller, Daniel A. Miller, Arturo M. Martinez, Arturo M. Martinez, "Effect of phase error on 180-nm and 250-nm grouped-line KrF lithography using an alternating phase-shift mask", Proc. SPIE 3096, Photomask and X-Ray Mask Technology IV, (28 July 1997); doi: 10.1117/12.277282; https://doi.org/10.1117/12.277282


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