Patents by Inventor Shankar Krishnan

Shankar Krishnan has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Publication number: 20060274310
    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 ID 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.
    Type: Application
    Filed: January 4, 2006
    Publication date: December 7, 2006
    Inventors: Daniel Kandel, Kenneth Gross, Michael Friedmann, Jiyou Fu, Shankar Krishnan, Boris Golovanevsky
  • Patent number: 7050160
    Abstract: A process for measuring both the reflectance and sheet resistance of a thin film, such as a metal film or a doped semiconductor, in a common apparatus comprises: directing a beam of radiation from a radiation source on the common apparatus onto a portion of the surface of the thin film, sensing the amount of radiation reflected from the surface of the thin film, and contacting the surface of the thin film with a sheet resistance measurement apparatus on the apparatus at a portion of the surface of the thin film coincident with or adjacent to the portion of the thin film contacted by the radiation beam to measure the sheet resistance of the thin film. The sheet resistance measurement apparatus may, by way of example, comprise a 4 point probe or an eddy current measurement apparatus. The respective measurements may be carried out either simultaneously or sequentially.
    Type: Grant
    Filed: April 3, 2003
    Date of Patent: May 23, 2006
    Assignee: KLA-Tencor Technologies Corporation
    Inventors: Walter H. Johnson, Jagadish Kalyanam, Shankar Krishnan, Murali K. Narasimhan
  • Patent number: 7006222
    Abstract: A system for performing single wavelength ellipsometry (SWE) on a thin film on a multi-layer substrate such as silicon-on-insulator (SOI) applies a measurement beam having an absorption distance less than the thickness of the superficial layer of the multi-layer substrate. For example, for an SOI substrate, the measurement beam is selected to have a wavelength that results in an absorption distance that is less than the superficial silicon layer thickness. The system can include a cleaning laser to provide concurrent cleaning to enhance measurement accuracy without negatively impacting throughput. The measurement beam source can be configured to provide a measurement beam at one wavelength and a cleaning beam at a longer wavelength, so that the absorption depth of the measurement beam is less than the superficial layer thickness while the absorption depth of the cleaning beam is greater than the superficial layer thickness.
    Type: Grant
    Filed: January 8, 2003
    Date of Patent: February 28, 2006
    Assignee: KLA-Tencor Technologies Corporation
    Inventor: Shankar Krishnan
  • Publication number: 20050018189
    Abstract: In a device for measuring the complete polarization state of light over a spectral bandwidth, an optical input signal (41) with wavelengths of light within a spectral band is incident on two or more diffraction gratings (42, 44, 46, 48), or incident from at least two directions on one or more diffraction gratings (72, 74), and the intensity is measured as a function of wavelength for at least four of the diffraction spectra produced by the grating(s). The polarization state of light is then calculated as a function of wavelength over the spectral bandwidth from the intensity measurements.
    Type: Application
    Filed: February 13, 2003
    Publication date: January 27, 2005
    Inventors: D. Hampton, Shankar Krishnan, James Rix
  • Patent number: 6812925
    Abstract: A map simplification system performs dynamic view dependent simplification of relatively large geographic maps.
    Type: Grant
    Filed: October 30, 2001
    Date of Patent: November 2, 2004
    Assignee: AT&T Corp.
    Inventors: Shankar Krishnan, Suresh Venkatasubramanian, Nabil Mustafa
  • Publication number: 20040130718
    Abstract: A system for performing single wavelength ellipsometry (SWE) on a thin film on a multi-layer substrate such as silicon-on-insulator (SOI) applies a measurement beam having an absorption distance less than the thickness of the superficial layer of the multi-layer substrate. For example, for an SOI substrate, the measurement beam is selected to have a wavelength that results in an absorption distance that is less than the superficial silicon layer thickness. The system can include a cleaning laser to provide concurrent cleaning to enhance measurement accuracy without negatively impacting throughput. The measurement beam source can be configured to provide a measurement beam at one wavelength and a cleaning beam at a longer wavelength, so that the absorption depth of the measurement beam is less than the superficial layer thickness while the absorption depth of the cleaning beam is greater than the superficial layer thickness.
    Type: Application
    Filed: January 8, 2003
    Publication date: July 8, 2004
    Applicant: KLA-Tencor Technologies Corporation
    Inventor: Shankar Krishnan
  • Patent number: 6710890
    Abstract: An apparatus for measuring a thickness of a substrate having an upper surface, without contacting the upper surface of the substrate. A platen having a base surface receives the substrate, and a reference surface is disposed at a known first height from the platen surface. A non contact sensor senses the known first height of the reference surface without making physical contact with the reference surface. The non contact sensor further senses a relative difference between the known first height of the reference surface and a second height of the upper surface of the substrate without making physical contact with the upper surface of the substrate. A controller controls the sensor and determines the thickness of the substrate based at least in part on the known first height of the reference surface and the relative difference between the known first height of the reference surface and the second height of the upper surface of the substrate.
    Type: Grant
    Filed: February 26, 2003
    Date of Patent: March 23, 2004
    Assignee: KLA-Tencor Technologies Corporation
    Inventors: Shankar Krishnan, Christopher M. Pohlhammer, Michael P. Green
  • Patent number: 6052187
    Abstract: A device to provide hyperspectral reflection spectrum, hyperspectral depolarization, and hyperspectral fluorescence spectrum data in a portable, remote sensing instrument. The device can provide a large range of remotely-sensed optical property data, presently only obtainable in laboratories, in a low-cost field instrument. Among its many uses, the present invention can be used by farmers as a tool for determining the nitrogen content of crops to optimize fertilizer laydown.
    Type: Grant
    Filed: August 31, 1998
    Date of Patent: April 18, 2000
    Assignee: Containerless Research, Inc.
    Inventors: Shankar Krishnan, Daniel Scott Hampton, Paul C. Nordine
  • Patent number: 5011295
    Abstract: Method and apparatus for accurately and instantaneously determining the thermodynamic temperature of remote objects by continuous determination of the emissivity, the reflectivity, and optical constants, as well as the apparent or brightness temperature of the sample with a single instrument. The emissivity measurement is preferably made by a complex polarimeter including a laser that generates polarized light, which is reflected from the sample into a detector system. The detector system includes a beamsplitter, polarization analyzers, and four detectors to measure independently the four Stokes vectors of the reflected radiation. The same detectors, or a separate detector in the same instrument, is used to measure brightness temperature. Thus, the instrument is capable of measuring both the change in polarization upon reflection as well as the degree of depolarization and hence diffuseness.
    Type: Grant
    Filed: October 17, 1989
    Date of Patent: April 30, 1991
    Assignee: Houston Advanced Research Center
    Inventors: Shankar Krishnan, George P. Hansen, Robert H. Hauge, John L. Margrave, Charles A. Rey