Roughness and variability in EUV lithography: Who is to blame? (part 1)

Process variability in today’s EUV lithography might be a showstopper for features below 27nm dimensions. At these feature sizes, electrical devices are influenced by quantum effects and thus have to face the discrete behavior of light and matter. More in general, lithography uncertainties arise from each lithographic element: the source, the photomask, the optical system, and the photoresist. In order to individually assess all the different contributions to the final resist roughness, a EUV mask with known absorber pattern variability was used to expose different resists at different process conditions. CD-SEM analyses were performed on both mask absorber and resist pattern and then used to build a stochastic resist model. In this first paper, we present a complete characterization of the root causes which are responsible of the CD nonuniformity for 27nm half-pitch dense contact-holes exposed with the ASML NXE:3100 scanner installed at imec. Using the same stochastic model, a simulated evaluation to quantify the possible impact of the different elements composing the lithographic process is performed at higher numerical aperture.