CAD-based line/space mix-up prevention for reticle metrology

This paper describes a method to automatically distinguish between line and space for 1:1 line space patterns in mask metrology. As the number of measurements typically performed on a reticle is significantly higher than on a wafer, automated CAD based CD-SEM recipe creation is essential. Such recipes typically use synthetic pattern recognition targets instead of SEM based pattern recognition targets. Therefore, a possible different contrast between lines and spaces on a mask cannot be utilized for distinguishing lines from spaces. We demonstrate an algorithm solution based on the analysis of the SEM waveform profiles to identify potential L/S mix-ups and correct them automatically. The solution allows fully automated CAD based offline recipe creation with a high success rate of distinction between lines and spaces for 1:1 pitch cases without the necessity of editing recipes on the tool in advance of performing the measurements.