Impact of pupil plane filtering on mask roughness transfer

Abstract

Line edge roughness (LER) is a common problem to all lithography techniques and is seen as an increasingly important challenge for advanced technology nodes. Contributions to LER can come from the aerial image itself or the resist related processes. Mask roughness belongs to the former group, which can contribute to the low frequency roughness. This paper investigates the mitigating effect of pupil plane filtering on the mask roughness transfer. Experiments were performed using a mask with edge roughness programmed at different periods on 128 nm pitch vertical line/space patterns. A target phase filter was optimized for ArF illumination source and the roughness period of 200 nm. The filter introduces an orientation dependent defocus; hence, reducing the image fidelity in the direction of roughness features without significantly impacting the fidelity of vertical line and space features. Experimental results showed significant reduction in mask roughness transfer for the target roughness period.