Test pattern extraction for lithography modeling under design rule revisions

Abstract

While technology is being developed, design rules undergo a number of revisions. An initial lithography model built with test patterns before the revisions inherently become inaccurate for the revised patterns. Preparing a new test layout and updating a lithography model every time design rules are revised is not practical, and cannot be a solution. We prepare some synthetic patterns in addition to initial test patterns. Synthetic patterns originate from popular test pattern generator (TPG), while projected design rule changes are taken into account. A challenge is to sort out the synthetic patterns which are really necessary in building a generic lithography model when they are used together with test patterns. Each pattern, either synthetic or test, is identified in image parameter set (IPS) space. For each test pattern in IPS space, two concentric spheres are drawn; outer one indicating the region where revised versions of test pattern may exist, and inner one indicating the region which is well covered by test pattern alone. Synthetic patterns that reside in the region bounded by the two spheres are kept, while the others are dropped. Clustering is now performed on test patterns and synthetic patterns separately, and representative pattern is drawn from each cluster. When a set of representative patterns are used to build a lithography model in 10nm memory devices, it achieves 43.5% lower CD root mean square error (RMSE) for revised design layout compared with only using a set of initial test patterns.