28 July 1997 Large assist feature phase-shift mask for sub-quarter-micrometer window pattern formation
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Proceedings Volume 3096, Photomask and X-Ray Mask Technology IV; (1997); doi: 10.1117/12.277278
Event: Photomask Japan '97, 1997, Kawasaki City, Japan
Abstract
To improve the depth of focus of isolated windows, large assist feather technique has been proposed. This large assist method uses the assist features having almost the same size as main patterns, and the quartz substrate was vertically etched at the assist features. These large assist features were not printed on a wafer by mask topography effect; that is, the light intensity at large assist feature was decreased by the scattering effect of the vertical quartz edges. In this large assist feature masks, the phase shift angle of an assist feature has large effect on focus latitude. We chose two phase shift angles: 180 degrees for small sigma illumination and 360 degrees for annular illumination. The performances of two large assist feature masks were evaluated by using a 0.55 NA, valuable sigma, and KrF excimer laser stepper. Moreover, we applied surface insoluble layer to the assist feature method. Large assist features having the same size as main patterns were not printed on resist surface for 0.16 - 0.2 micrometer windows. Wide DOF (0.8 micrometer) of 0.16 micrometer window was obtained by using this method.
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Shinji Ishida, Tadao Yasuzato, Hiroyoshi Tanabe, Kunihiko Kasama, "Large assist feature phase-shift mask for sub-quarter-micrometer window pattern formation", Proc. SPIE 3096, Photomask and X-Ray Mask Technology IV, (28 July 1997); doi: 10.1117/12.277278; https://doi.org/10.1117/12.277278
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KEYWORDS
Photomasks

Phase shifts

Quartz

Excimer lasers

Lithographic illumination

Semiconducting wafers

Etching

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