U.S. Patent No. 7,884,947, issued on February 8, 2011 to Zygo Corp. of Middlefield, CT, discloses an optical interferometer for characterizing a surface.
According to the ’947 patent, scanning white light interferometry (SWLI) scans white light, having a limited coherence length, over a surface and combines the reflected light with reference light to produce a scanning interferometry signal indicative of the surface being analyzed (e.g., its surface topography). Ellipsometry measures the complex reflectivity of a surface illuminated by light at a variable oblique angle using multiple wavelengths. The complex reflectivity is dependent on the intrinsic properties of the surface being analyzed, as well as on the properties (i.e., wavelength, incident angle, and polarization state) of the incident light, so information regarding the surface can be obtained by measuring variations of the reflectivity produced by varying these light parameters. The ’947 patent discloses an optical system that produces angle-resolved interference signals over a range of wavelengths. The interference signals corresponding to light with different incident angles are detected by different elements of a multi-element detector, and the system can provide concurrent angle-resolved measurements of the complex reflectivity and surface topology measurements.
According to its website, Zygo “designs, manufactures, and distributes high-end optical systems and components for metrology and end-user applications.” The company markets its NewView™ optical surface profilers which utilize “Zygo’s patented scanning white-light interferometry (SWLI) technology,” but none of the descriptions of the existing models mention the concurrent interferometry/ellipsometry capability disclosed by the ’947 patent. This feature may be in the works for a future model.
Zygo was issued 11 U.S. patents in 2010, about half as many as the company received in either 2009 (23 U.S. patents) or 2008 (25 U.S. patents). So far, in 2011, Zygo has obtained 5 U.S. patents, putting the company on a pace to match or exceed its yearly average (about 25 U.S. patents/year) over the previous seven years.
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