2D measurement using CD SEM for arbitrarily shaped patterns

Abstract

As the design rule of lithography becomes smaller, accuracy and precision in Critical Dimension (CD) and controllability of pattern-shape are required in semiconductor production. Critical Dimension Scanning Electron Microscope (CD SEM) is an essential tool to confirm the quality of the mask such as CD control, CD uniformity and CD mean to target (MTT). Unfortunately, in the case of extremely rounded region of arbitrary enclosed patterns, CD fluctuation depending on Region of Interest (ROI) is very serious problem in Mask CD control, so that it decreases the yield. In order to overcome this situation, we have been developing 2-dimensonal (2D) method with system makers and comparing CD performance between mask and wafer using enclosed arbitrary patterns. In this paper, we summarized the results of our evaluation that compare error budget between 1-dimensonal (1D) and 2D data using CD SEM and other optical metrology systems.Key word: CD SEM, 2D, AREA MEASUREMENT, MTT, UNIFORMITY INRODUCTIONBasically, the quality of a mask is determined by the degree of equality with design data, i.e. pattern shape and CD target of the mask should be the same as those of its design. Various proposals of Resolution Enhancement Technology (RET), however, were made and applied to the recent mask technology. With the RET know-how being developed, the mask pattern shape is getting complicated due to the deformed, shrunk and rounded patterns.In case of extremely narrow region of arbitrarily shaped patterns, the measured CD can easily be fluctuated depending on setting of Region of Interest (ROI) in a rounded area. It is very difficult to define real error budget and MTT of masks using the conventional CD SEM systems which are based on 1D measurement algorithm. To overcome these difficulties, it is needed to analyze the CD with a 2D method and interpret 2D data as 1D format.The conventional CD SEM systems supply area measurement function only for simple contact and dot patterns, but cannot support 2D function for complex and arbitrarily shaped patterns. In order to get 2D data of arbitrarily shaped patterns, we have shared ideas and concepts with system manufacturers. As a result, we construct a system that can measure the area of arbitrarily shaped patterns, and evaluate a method to analyze 2D data from the 1D point of view.This paper summarizes the evaluation results that compare error budget between 1D and 2D data using CD SEM and other optical metrology systems.

Two-dimensional mask effects at the 14 nm logic node

“…Area of the feature was calculated by assessing the edge of the feature and numerically integrating the contour to calculate contact area. 5 Corner rounding radius was evaluated at each corner by assessing the region of interest around the corner as half the length of designed dimension and finding the bisecting line (see Figure 6). The contact pullback and subsequently corner rounding radius were calculated geometrically using the bisector length measurement.…”