For projection printing imaging systems with fixed or restricted illumination modes, pupil filters may enhance imaging
for select features by blocking rays of light that negatively contribute to imaging. A method to design pupil filters for
the optimum printing of a select feature type and size is presented. With this method, a series of pupil filters have been developed and are being tested to enhance the resolution of the Albany Alpha Demo Tool (ADT, 0.25NA) in order to enable resist and process development at feature sizes relevant to the 10 and 7nm nodes. By only allowing light to
propagate to the wafer that positively contributes to imaging, six filters have been custom designed to optimize printing of the following sub-resolution feature types and sizes: 22 and 19 nm HP lines, 24 and 21 nm HP contacts, and 27×22 nm HP rectangular contacts. Development and installation of enabling hardware on the scanner is complete, six filters have been manufactured and imaging in resist has validated the concept. Over 20% improvement in tool resolution has been achieved for 22nm HP lines, allowing resist process development for NXE3300 conditions on the ADT. This paper discusses the theory behind the filter designs, the experimental in-resist evaluations, and other aspects of the development, to include challenges caused by the filters with slit uniformity, stray light, and reticle alignment.