3D-AFM enhancement for CD metrology dedicated to lithography sub-28-nm node requirements

Abstract

With the continuous shrinkage of feature dimensions on IC in the semiconductor industry, the measurement uncertainty is becoming one of the major components that have to be controlled in order to guarantee sufficient production yield. Already at the R&D level, we have to cope up with the accurate measurements of sub-40nm dense trenches and contact holes coming from 193 immersion lithography or E-Beam lithography. By using top-down CD-SEM it is currently impossible to extract profile information. Moreover, electron proximity effect leads to non-negligible CD bias in the final measurements. To enable measurement of challenging dimensions with better measurement and reduced measurement uncertainty we have explored and fine tuned an alternative 3D-AFM mode (so-called DT mode) for CD measurements purpose. Theoretically, this mode is supposed to be dedicated only for height measurement but for certain applications it could be extended to reach the nanometer scale accuracy of CD-measurements employing certain optimized scan parameters. In this paper, we will present and discuss results obtained related to the use of this particular mode for CD measurement purpose versus conventional 3D-AFM CD Mode that shows important limitations for aggressive trenches dimensions measurements. We will also present some results related to the use of advanced 3D-AFM tips (typically of 28nm diameter) that have been used with the enhanced DT mode parameters. Example of applications will be shown with typical sub-45nm trenches measurements dedicated to advanced lithography process development that will demonstrate that we have succeed to push ahead the limit of the 3D-AFM technology in measuring the tight dimensions that would allow to continue its use for current and upcoming technology nodes. Finally, we introduce the concept of hybrid metrology in order to smartly use the benefit of reference metrology (i.e 3D-AFM) through the optimization of CD-SEM algorithm that could be used for example for OPC model optimization. © 2010 Copyright SPIE - The International Society for Optical Engineering.