Super-resolution critical dimension limits of positive tone i-line photoresists

Applying a technique borrowed from super-resolution microscopy to photolithography, we achieve critical dimensions well below the diffraction limit. Exposing photoresist in the far-field, over a broad area, we can demonstrate dimensions as small as λ/7. In this paper, we show that conventional i-line photoresists exposed with this technique, along with modified processing, are capable of supporting features as small as 50 nm, and possibly smaller. We consider the necessary requirements to achieve sub-diffraction dimensions, detail a simple model for photoresist development, and show its use in predicting the minimum attainable feature size. Finally, we characterize two commercial photoresists, and compare the resulting features to those of the model.