The extraction of nanoscale dimensions and feature geometry of grating targets using signature-based optical techniques is an area of continued interest in semiconductor manufacturing. In the current work, we have performed angle-resolved scatterometry measurements on grating targets of 180 nm pitch fabricated by elec-tron beam lithography and anisotropic wet etching of (110)-oriented silicon. The use of oriented silicon results in grating lines with nominally vertical sidewalls, with linewidths estimated by scanning electron microscopy (SEM) to be in the sub-50 nm range. The targets were designed to be suitable for both optical scatterometry and small-angle x-ray scattering (SAXS) measurement. As a consequence of the lattice-plane selective etch used for fabrication, the target trenches are not flat-bottomed, but rather have a wide vee shape. We demonstrate extraction of linewidth, line height, and trench profile using scatterometry, with an emphasis on modeling the trench angle, which is well decoupled from other grating parameters in the scatterometry model and is driven by the crystalline orientation of the Si lattice planes. Issues such as the cross-correlation of grating height and linewidth in the scatterometry model, the limits of resolution for angle-resolved scatterometry at the wavelength used in this study (532 nm), and prospects for improving the height and linewidth resolution obtained from scatterometry of the targets, are discussed.
Proceedings Title: Proceedings of the SPIE Conference on Optics and Photonics | 2008 |
Conference Dates: August 10-14, 2008
Conference Location: San Diego, CA
Conference Title: NanoScience + Engineering
Pub Type: Conferences
ellipsometry, gratings, optical critical dimension metrology, oriented silicon, reflectometry, rigorous coupled-wave, scatterometry