Ryota Aburada

Source and mask optimization to mitigate hotspots in etch process

A new optical metric, termed resist deformation factor (RDF), to represent deformation of three-dimensional (3D) resist profile has been introduced into a source and mask optimization (SMO) flow to mitigate defects caused by a reactive ion etching (RIE) process at the lithography stage. Under the low-k1 lithography conditions with both a highly-coherent source and a complicated mask, the 3D resist profile is subject to top-loss or bottom footing, resulting in hotspots and/or defects after the RIE process. In order to represent the 3D resist profile on a fast lithography simulation, a sliced latent image along resist depth direction is used to define RDF as the ratio of integrated optical intensities within the resist pattern to those around its surrounding area. Then the SMO flow incorporating the RDF into its cost function is implemented to determine both a source and a mask as the 3D resist profile is less likely to deform. The result of new SMO flow with RDF shows 30% improvement of resist top-loss.

Configurable hot spot fixing system

Hot spot fixing (HSF) method has been used to fix many hot spots automatically. However, conventional HSF based on a biasing based modification is difficult to fix many hot spots under a low-k1 lithography condition. In this paper we proposed a new HSF, called configurable hotspot fixing system. The HSF has two major concepts. One is a new function to utilize vacant space around a hot spot by adding new patterns or extending line end edges around the hot spot. The other is to evaluate many candidates at a time generated by the new functions. We confirmed the proposed HSF improves 73% on the number of fixing hot spots and reduces total fixing time by 50% on a device layout equivalent to 28nm-node. The result shows the proposed HSF is effective for layouts under the low-k1 lithography condition.