Minimizim CD measurement bias through realtime acquisition of 3D feature shapes

CD measurement bias has long been reported as an inherent artifact of CD-SEM measurements. However, as feature dimensions decrease and line-to-space ratios increase, the magnitude of previously acceptable levels of measurement bias requires re-examination. Traditional attempts at correcting the bias has entailed slow, destructive or laborious techniques, such as comparisons of top-down CD-SEM measurements using standard algorithms with cross-section information, or correlating top-down data with complex tilted images. In this paper we expand the application of Critical Shape Metrology - a physics-based metrology technique for 3-D profile acquisition based on CD-SEM, to minimizing CD bias in real-time for a variety of feature dimensions and profiles. Samples used for the experiments were fabricated through E-Beam lithography and 193 lithography with a wide variation of sidewall angles and CDs, so that the measurement bias could be assessed over a sufficiently large range of patterned shapes. Reference measurements were performed using a CD-AFM and FIB-SEM.