This paper reveals a methodology for substantially eliminating footing on native TiN substrates. The first generation DUV resists, such as APEX-E, reported a foot size of $GRT 100 nm. The large foot size severely limited the capability of these resists. This paper introduces a superior resist for TiN substrate footing, TitaN$+TM$/ photoresist, with a foot size of only 13 nm at 250 nm feature sizes. This resist also has high resolution and fast photospeed, and good process windows for isolated and dense structures. The key design concept was to reduce the surface inhibition at the resist/TiN interface. The key chemistry to accomplish this reduction in surface inhibition is to generate stronger acids at the resist/TiN interface. We also considered high and low acrylate polymers. There was little difference in footing for the high and low acrylate polymers, however, the low acrylate polymer shows superior etch resistance necessary for metal levels.
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