Three-Dimensional Shape Estimation for Bottom Footing of Gate Patterns by CD-SEM

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  • 測長SEMによるゲートパターン裾引きの三次元形状推定

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In the semiconductor manufacturing, a critical dimension scanning electron microscope (CD-SEM) is widely used as a process monitoring tool. As design rules become finer and denser in recent years, needs for controlling three-dimensional (3D) shape in addition to one- and two-dimensional size of the pattern, such as the CD value, have risen for the process monitoring. In this paper, we propose a novel approach for estimating 3D bottom footing shape of gate patterns from two SEM images, with 5 and 10 degree tilt. Bottom footing shape can provide valuable clues for inspecting and analyzing electrical properties of semiconductor devices. The proposed method realizes a highly precise estimation by combination of existing inverse stereo matching (ISM) method with a bottom footing index, which is the width of the range where the bottom footing exists. The measured shape of ISM method is represented with a cubic spline curve and is then corrected by transformation of the curve on the basis of the pre-learning relationship between bottom footing index and curve parameters. The proposed algorithm was verified with 12 samples of gate pattern. As the results of the evaluation, the average and deviation (three sigma) of the measurement error in the part of bottom footing were 1.3nm±1.0nm. The proposed method can effectively provide an accurate 3D shape and is expected to be applied to the process monitoring in actual production lines.

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