CD-SEM-based critical shape metrology of integrated circuits

Abstract

With critical dimensions (CD) of integrated circuits shrinking to tens of nanometers, accurate metrology of threedimensional feature shapes at different stages of the lithographic process becomes crucial to circuit performance. We propose Critical Shape Metrology (CSM), a CD-SEM-based technique that extracts accurate feature shape information from images obtained during routine in-line wafer inspection. Intensity profiles from CD-SEM images of known materials are compared in real time to profiles in an off-line generated Monte-Carlo SEM simulation library for the same materials with various model shapes. When the best match is found, metrics like bottom CD, top CD, sidewall angle, foot size and angle, and corner rounding can be obtained with high accuracy.The proposed technique takes advantage of the high resolution and throughput of low-voltage CD-SEMs, and does not require any additional tool calibration beyond the standard calibrations performed for conventional top-down CD metrology. While similar to optical scatterometry in concept, this technique allows for measurement of both isolated targets and dense arrays. Examples of performance on etched polysilicon and resist lines of different shapes are included and compared to SEM cross-sections and CD-AFM data.

The application of critical shape metrology toward CD-SEM measurement accuracy on sub-60nm features

“…Most of them are based on Monte-Carlo modelling of beam interaction with the sample. Our method is also Monte-Carlo based 3,5 , but is executed in real time and performs in tandem with the CD-SEM (Soluris Yosemite SP-1000 CD-SEM) to produce simultaneously CD measurements and 3-D profile information. The CSM technique begins by generating a wide range of feature geometries and pre-computes a library of secondary electron (SE) intensity profiles associated with the shapes and stores the information in a database server.…”