| US 7,525,672 B1 | ||
| Efficient characterization of symmetrically illuminated symmetric 2-D gratings | ||
| Shuqiang Chen, Sunnyvale, Calif. (US); and Guoguang Li, Fremont, Calif. (US) | ||
| Assigned to n&k Technology, Inc., San Jose, Calif. (US) | ||
| Filed on Dec. 16, 2005, as Appl. No. 11/305,449. | ||
| Int. Cl. G01B 11/24 (2006.01) | ||
| U.S. Cl. 356—625 [356/636; 250/559.22] | 42 Claims |
| 1. A system for optically determining one or more parameters of a 2-D grating having substantial reflection symmetry in a
grating reflection plane, the system comprising:
a) an optical source providing optical radiation at a variable wavelength and illuminating said 2-D grating, wherein said
radiation has a wave vector in said reflection plane;
b) an optical detector receiving radiation from said 2-D grating and providing a measured spectral response; and
c) a processor receiving said measured spectral response and providing a modeled spectral response of said 2-D grating having
said parameters as variables, wherein said processor determines said one or more parameters by adjusting said variables to
fit said modeled spectral response to said measured spectral response;
wherein said modeled spectral response is provided by a symmetry-simplified rigorous coupled wave analysis (RCWA);
wherein said grating is in an x-y plane, wherein said reflection plane is an x-z plane, wherein said RCWA accounts for Nx positive diffraction orders and Nx negative diffraction orders in the x direction, and wherein said RCWA accounts for Ny positive diffraction orders and Ny negative diffraction orders in the y direction;
wherein said grating reflection plane is perpendicular to a plane in which said 2-D grating is disposed.
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