| Scatterometry1 is one optical measurement technique that has been explored extensively for semiconductor sub-micrometer dimensional metrology. The technique refers to the measurements of reflected power upon the interaction of an incident beam with some periodic surface (grating). The characteristics of the diffractive surface affect directly the acquired measurements. Therefore it is possible to resolve some information about the grating line profile and dimensions from the measurements, which is referred to as the inverse scatterometry problem. As technology is continuously pushing lithographic processes to sub-nanometer precision2, aspects of the inverse scatterometry problem related to the accurate estimation and modeling of errors and the enhancement of the optimization methods become of great importance. For this purpose the effects of measurement errors on the estimated grating profile are analyzed in this dissertation and optimization methods are proposed to improve the accuracies in the estimated geometrical parameters for various grating profiles in real experimental conditions. A technique based on the information content analysis of the measurement data is further suggested to reduce the number of measurements required without the loss in the solution accuracies resulting in lower cost and more suitable real time implementation. Theoretical and experimental results are presented to validate these studies where the solutions to the profile parameters are accomplished by implementing a linear regression technique3.; In addition a new scheme is proposed to address resolving more difficult profile parameters with sub-wavelength dimensions (sub-100 nm) that are until now subject to ongoing investigation with inconclusive results. The proposed approach consists of using a large number of angular reflectance measurements with linearly polarized TM incidence. In the case where the profile dimensions are many times smaller than the light wavelength, the parameter solutions in the inverse scatterometry problem are resolved with most accuracy using such a measurement scheme. The proposed technique allows resolving the sub-100 nm profile dimensions with lower cost of instrumentation using visible sources and is ideal for nanotechnology research in small research lab environments.; 1S. S. H. Naqvi, J.R. McNeil, R.H. Krukar, and K.P. Bishop, "Scatterometry and the simulation of diffraction-based metrology," Microlith. World 2(3), pp. 5-16, 1993. 22004 International Technology Roadmap for Semiconductors, "Metrology 2004 Update", ITRS Web Resources, http://www.itrs.net/Common/2004Update/2004_13_Metrology.pdf . 3E. M. Drege, R. M. Al-Assaad, and D. M. Byrne, "Mathematical Analyses of Inverse Scatterometry," Proc. of SPIE 4689, pp. 151-162, 2002. |
