2 September 1997 New aspects of optical scatterometry applied to microtechnology
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Abstract
During the last years, optical scatterometry (OS) has become a competitive technique in micrometrology. Not only is it a very rapid and non-destructive method, but it also meets the accuracy needs imposed by nowaday technology. Relative rms- values of one percent and below have been reported for the multi-parametric characterization of submicron profiles. Although being basically a far field approach, the resolution and accuracy limits of imaging optical methods may be overcome to a certain degree. The goal of this paper is to discuss some new aspects of this technique. Particularly, there are two main topics--the improvement of the 2(theta) -principle for the characterization of sublambda gratings and the extension of the optical scatterometry to the measurement of real scene features instead of periodic ones. As for 2(theta) -scatterometry, first the ability of this method for quantitative measurements is shown with a 0.8 micron pitch grating etched in silicon oxide. Second, the polarization sensitivity is investigated with a 512 nm chromium grating on quartz. While the TE polarization is useful for the coarse characterization of the basic profile in terms of linewidth and height, TM polarized light might be the better choice for sensing sidewall variations and other profile subtleties. And third, a new scatterometer design is presented, which enables a simultaneous 2(theta) - measurement providing for an increased measuring throughput. Here, the application as a resist development monitor is outlined. The second main topic is the extension of the OS to single features in a more common sense, i.e., comprising also small groups of lines or spaces. In a former paper, the authors presented the basic principle and first modeling results. Here, further investigations are discussed aiming at the light scatter dependence on the sidewall angle and the characterization of double lines. The simulations confirm the enhanced sensitivity of TM polarized light to variations in the sidewall steepness. Besides, some nearfield calculations reveal how the light interacts with the scatterer.
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Joerg Bischoff, Lutz Hutschenreuther, Horst Truckenbrodt, "New aspects of optical scatterometry applied to microtechnology", Proc. SPIE 3215, In-Line Characterization Techniques for Performance and Yield Enhancement in Microelectronic Manufacturing, (2 September 1997); doi: 10.1117/12.284680; https://doi.org/10.1117/12.284680
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