Measuring overlay and profile asymmetry using symmetric and anti-symmetric scatterometry signals
First Claim
1. An ellipsometry method for estimating overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, the method comprising:
- providing a plurality of cells that each include a portion of the first and second structures, wherein each cell is designed to have an offset between its first and second structures portions;
illuminating the cells with electromagnetic radiation using a rotating polarizer;
obtaining measurements with an analyzer set at a plurality of polarization angles, wherein the measurements include reflected radiation intensities with the analyzer set at the plurality of polarization angles;
combining the measurements into combinational signals for each of the cells so that the combinational signals are even or odd functions of a total shift between the first and second structures; and
estimating and storing any overlay error between the first structures and the second structures based on the combinational signals.
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Abstract
Systems and methods are disclosed for using ellipsometer configurations to measure the partial Mueller matrix and the complete Jones matrix of a system that may be isotropic or anisotropic. In one embodiment two or more signals, which do not necessarily satisfy any symmetry assumptions individually, are combined into a composite signal which satisfies a symmetry assumption. The individual signals are collected at two or more analyzer angles. Symmetry properties of the composite signals allow easy extraction of overlay information for any relative orientation of the incident light beam with respect to a 1D grating target, as well as for targets comprising general 2D gratings. Signals of a certain symmetry property also allow measurement of profile asymmetry in a very efficient manner. In another embodiment a measurement methodology is defined to measure only signals which satisfy a symmetry assumption. An optional embodiment comprises a single polarization element serving as polarizer and analyzer. Another optional embodiment uses an analyzing prism to simultaneously collect two polarization components of reflected light.
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Citations
27 Claims
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1. An ellipsometry method for estimating overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, the method comprising:
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providing a plurality of cells that each include a portion of the first and second structures, wherein each cell is designed to have an offset between its first and second structures portions; illuminating the cells with electromagnetic radiation using a rotating polarizer; obtaining measurements with an analyzer set at a plurality of polarization angles, wherein the measurements include reflected radiation intensities with the analyzer set at the plurality of polarization angles; combining the measurements into combinational signals for each of the cells so that the combinational signals are even or odd functions of a total shift between the first and second structures; and estimating and storing any overlay error between the first structures and the second structures based on the combinational signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A system for estimating overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, comprising:
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an ellipsometry module for; illuminating the cells with electromagnetic radiation using a rotating polarizer; obtaining measurements with an analyzer set at a plurality of polarization angles, wherein the measurements include reflected radiation intensities with the analyzer set at the plurality of polarization angles; and combining the measurements into combinational signals for each of the cells so that the combinational signals are even or odd functions of a total shift between the first and second structures; and a processor operable for estimating any overlay error between the first structures and the second structures based on the combinational signals. - View Dependent Claims (20, 21, 22, 23, 24)
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25. An ellipsometry method for measuring profile asymmetry of a structure of a sample, the method comprising:
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(a) illuminating a structure with electromagnetic radiation using a rotating polarizer; (b) obtaining a plurality of measurements with an analyzer set at a plurality of polarization angles, wherein the measurements include reflected radiation intensities with the analyzer set at the plurality of polarization angles; (c) combining the measurements into a combinational signal so that the combinational signals is an odd functions; and (d) determining a degree of profile asymmetry of the structure based on the combinational signal. - View Dependent Claims (26, 27)
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Specification