Shankar Krishnan

US Patent:

6710890, Mar 23, 2004

Filed:

Feb 26, 2003

Appl. No.:

10/375554

Inventors:

Shankar Krishnan - Santa Clara CA
Christopher M. Pohlhammer - San Ramon CA
Michael P. Green - Palo Alto CA

Assignee:

KLA-Tencor Technologies Corporation - Milpitas CA

International Classification:

G01B 1106

US Classification:

356630, 25055928

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.

US Patent:

6812925, Nov 2, 2004

Filed:

Oct 30, 2001

Appl. No.:

10/021645

Inventors:

Shankar Krishnan - Chatham NJ
Suresh Venkatasubramanian - Morristown NJ
Nabil Mustafa - Durham NC

Assignee:

ATT Corp. - New York NY

International Classification:

G06T 1530

US Classification:

345423, 345428

Abstract:

A map simplification system performs dynamic view dependent simplification of relatively large geographic maps.

US Patent:

7006222, Feb 28, 2006

Filed:

Jan 8, 2003

Appl. No.:

10/339518

Inventors:

Shankar Krishnan - Santa Clara CA, US

Assignee:

KLA-Tencor Technologies Corporation - Milpitas CA

International Classification:

G01J 4/00

US Classification:

356369, 356445

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.

US Patent:

7050160, May 23, 2006

Filed:

Apr 3, 2003

Appl. No.:

10/407669

Inventors:

Walter H. Johnson - San Jose CA, US
Jagadish Kalyanam - San Jose CA, US
Shankar Krishnan - Santa Clara CA, US
Murali K. Narasimhan - San Jose CA, US

Assignee:

KLA-Tencor Technologies Corporation - Milpitas CA

International Classification:

G01N 21/00

US Classification:

356 73, 356630

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. By deriving the resistivity of the thin film from the measured reflectance at any particular region of the thin film surface, the thickness of the thin film, at that region of the film, may be obtained by dividing the derived resistivity by the measured sheet resistance for that same region.

US Patent:

7274440, Sep 25, 2007

Filed:

Sep 8, 2004

Appl. No.:

10/936019

Inventors:

Gary Janik - Palo Alto CA, US
Shankar Krishnan - Santa Clara CA, US

Assignee:

KLA-Tencor Technologies Corp. - Milpitas CA

International Classification:

G01B 11/16
G01J 4/00

US Classification:

356 34, 356 33, 356365

Abstract:

Systems and methods for measuring stress in a specimen are provided. One system includes an optical subsystem configured to measure stress-induced birefringence in patterned structures formed on the specimen. In some embodiments, the optical subsystem may be configured as a spectroscopic ellipsometer, a multi-angle laser ellipsometer, a polarimeter, a polarized reflectometer, or some combination thereof. The system also includes a processor coupled to the optical subsystem. The processor is configured to determine stress in a material of the patterned structures using the stress-induced birefringence measurements. One method includes measuring stress-induced birefringence in patterned structures formed on the specimen using an optical technique. The method also includes determining stress in a material of the patterned structures using the stress-induced birefringence measurements.

US Patent:

7408641, Aug 5, 2008

Filed:

Feb 14, 2005

Appl. No.:

11/058153

Inventors:

Hidong Kwak - San Jose CA, US
Shankar Krishnan - Santa Clara CA, US
Shing Lee - Fremont CA, US
Haixing Zou - Sunnyvale CA, US

Assignee:

KLA-Tencor Technologies Corp. - Milpitas CA

International Classification:

G01J 4/00

US Classification:

356369

Abstract:

An illumination subsystem configured to provide illumination for a measurement system includes first and second light sources configured to generate light for measurements in different wavelength regimes. The illumination subsystem also includes a TIR prism configured to be moved into and out of an optical path from the first and second light sources to the measurement system. If the TIR prism is positioned out of the optical path, light from only the first light source is directed along the optical path. If the TIR prism is positioned in the optical path, light from only the second light source is directed along the optical path. Various measurement systems are also provided. One measurement system includes an optical subsystem configured to perform measurements of a specimen using light in different wavelength regimes directed along a common optical path. The different wavelength regimes include vacuum ultraviolet, ultraviolet, visible, and near infrared wavelength regimes.

US Patent:

7453562, Nov 18, 2008

Filed:

Sep 28, 2007

Appl. No.:

11/863334

Inventors:

Torsten R. Kaack - Los Altos CA, US
Shankar Krishnan - Santa Clara CA, US
Fabio A. Faccini - San Jose CA, US

Assignee:

KLA-Tencor Corporation - San Jose CA

International Classification:

G01N 21/00

US Classification:

3562372

Abstract:

A method of performing a measurement of properties of a sample, by directing a first beam of light at the sample, where a combination of the wavelength, energy, and length of time is sufficient to cause temporary damage to the sample. The first beam is reflected from the sample. The properties of the reflected beam are sensed to create a signal. A length of time is waited, sufficient for the damage to substantially heal, before a second beam of light is directed at the sample, where a combination of the wavelength, energy, and length of time is sufficient to cause temporary damage to the sample. The second beam is reflected from the sample. The properties of the reflected beam are sensed to create a signal. The first and second electrical signals are analyzed to determine the properties of the sample.

US Patent:

7755764, Jul 13, 2010

Filed:

Jan 24, 2008

Appl. No.:

12/019592

Inventors:

Hidong Kwak - San Jose CA, US
Shankar Krishnan - Santa Clara CA, US

Assignee:

KLA-Tencor Corporation - San Jose CA

International Classification:

G01N 21/55

US Classification:

356445, 356630, 356600, 356369, 250372, 250373, 25055932

Abstract:

An optical method and system for measuring characteristics of a sample using a broadband metrology tool in a purge gas flow environment are disclosed. In the method a beam path for the metrology tool is purged with purge gas at a first flow rate. A surface of the sample is illuminated by a beam of source radiation having at least one wavelength component in a vacuum ultraviolet (VUV) range and/or at least one wavelength component in an ultraviolet-visible (UV-Vis) range. A flow rate of a purge gas is adjusted between the first flow rate for metrology measurements made when the source radiation is in the VUV spectral region and a second flow rate for metrology measurements made when the source radiation is in the UV-Vis spectral region. The system includes a light source, illumination optics, collection optics, detector, a purge gas source and a controller. The purge gas source is configured to supply a flow of purge gas to a beam path in the light source and/or illumination optics and/or sample and/or collection optics and/or detector.