Defects on high-resolution negative-tone resist: "The revenge of the blobs"

Resist materials rely on solubility differences between the exposed and unexposed areas to create the desired image. Most negative-tone resists achieve the solubility difference by crosslinking the exposed area causing it to be insoluble in developer. The negative tone resist studied here is a high sensitivity negativetone resist that relies on polarity switching, similar to a positive-tone mechanism, but where the exposed area is insoluble in aqueous developer resulting in a negative-tone image. During mask evaluation for 14nm optical technology applications of the studied non-cross linking (polarity switching) resist, 1 - 5 μm size blob-like defects were found in large numbers under certain exposure conditions. This paper will describe the process and methodologies used to investigate these blob defects.