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26 July 1999 Depth of focus enhancement for 193-nm window lithography with subresolution assist features
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The properties of sub-resolution assist features for 193nm wavelength contact window lithography have been investigated. A test mask consisting of a variety of window and assist feature sizes and pattern density environments was fabricated and printed. Windows, 160nm in diameter, where exposed in conventional and quadrupole off-axis illumination. Results show a substantial increase in depth- of-focus when quadruple illumination and assist features were employed, when compared to conventional illumination and standard contacts. The improved process latitude is especially apparent in thicker resist formulations, which are required for etching. By employing improved resists with assist features and quadrupole illumination, isolated 160 nm contacts have been fabricated in 510 nm thick resist on 1000 nm SiO2, without anti-reflective coatings. The depth-of- focus is approximately 0.5 microns. BY lowering the numerical aperture of the projection optics, the measured depth-of-focus is unchanged, but assist feature printing can be significantly reduced. Preliminary results of 160 nm windows etched into oxide show that resist loss may be unacceptable with conventional pattern transfer processes.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Pat G. Watson, Armen Kroyan, Raymond A. Cirelli, H. L. Maynard, James R. Sweeney, Fred P. Klemens, G. L. Timp, and Omkaram Nalamasu "Depth of focus enhancement for 193-nm window lithography with subresolution assist features", Proc. SPIE 3679, Optical Microlithography XII, (26 July 1999);

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