Experimental demonstration of dark field illumination using contact hole features

The use of off-axis illumination in present lithography processes has enabled patterning to push below k1<0.40. This continual drive toward printing smaller feature sizes at the 193nm wavelength has led to the investigation and successful implementation of a number of new resolution enhancement technique (RET) approaches. In this work, the application of dark field imaging as a RET for low-k1 contact hole features was examined using both simulation and experiment on a standard lithography tool set. Here dark field imaging is defined as imaging where a portion of the illumination source is placed outside of the projection optics. This approach is similar to standard off-axis illumination approaches using the familiar two-beam imaging but at greater incident angle where the zeroth diffraction order is not captured and image modulation is created by higher diffraction orders. This approach creates a number of “unexpected” effects and the authors show these for contact hole patterns using ASML Twinscan lithog...