Critical Dimension AFM (CD-AFM) is a widely used reference metrology. To characterize modern semiconductor devices, very small and flexible probes, often 15 nm to 20 nm in diameter, are now frequently used. Several recent publications have reported on uncontrolled and significant probe-to-probe bias variation during linewidth and sidewall angle measurements [ , ]. Results obtained in this work suggest that probe bending can be on the order of several nanometers and thus potentially can explain much of the observed CD-AFM probe-to-probe bias variation. We have developed and experimentally tested one-dimensional (1D) and two-dimensional (2D) models to describe the bending of cylindrical probes. An earlier 1D bending model reported by Watanabe et al. [ ] was refined. Contributions from several new phenomena were considered, including: probe misalignment, diameter variation near the CNT apex, probe bending before snapping, distributed van der Waals-London force, etc. The methodology for extraction of the Hamaker probe-surface interaction energy from experimental probe bending data was developed. To overcome limitations of the 1D model a new 2D distributed force (DF) model was developed. Comparison of the new model with the 1D single point force (SPF) model revealed about 27 % difference in probe bending bias between the two. A simple linear relation between biases predicted by the 1D SPF and 2D DF models was found. This finding simplifies use of the advanced 2D DF model of probe bending in various CD-AFM applications. New 2D and three-dimensional (3D) CD-AFM data analysis software is needed to take full advantage of the new bias correction modeling capabilities.
Proceedings Title: Metrology, Inspection, and Process Control for Microlithography XXVI, Proceedings of SPIE Volume: 8324
Conference Dates: February 13-16, 2012
Conference Location: San Jose, CA
Conference Title: Metrology, Inspection, and Process Control for Microlithography XXVI
Pub Type: Conferences
CD-AFM, tip bending, linewidth, distributed force, CNT