Chandra Sek Saravanan

US Patent:

20090296075, Dec 3, 2009

Filed:

May 29, 2008

Appl. No.:

12/129448

Inventors:

Jiangtao Hu - Sunnyvale CA, US
Chandra Saru Saravanan - Fremont CA, US
Silvio J. Rabello - Palo Alto CA, US
Zhuan Liu - Fremont CA, US
Nigel P. Smith - Hsinchu, TW

Assignee:

Nanometrics Incorporated - Milpitas CA

International Classification:

G01N 21/00

US Classification:

356 73

Abstract:

An overlay error is determined using a diffraction based overlay target by generating a number of narrow band illumination beams that illuminate the overlay target. Each beam has a different range of wavelengths. Images of the overlay target are produced for each different range of wavelengths. An intensity value is then determined for each range of wavelengths. In an embodiment in which the overlay target includes a plurality of measurement pads, which may be illuminated and imaged simultaneously, an intensity value for each measurement pad in each image is determined. The intensity value may be determined statistically, such as by summing, finding the mean or median of the intensity values of pixels in the image. Spectra is then constructed using the determined intensity value, e.g., for each measurement pad. Using the constructed spectra, the overlay error may then be determined.

US Patent:

7362448, Apr 22, 2008

Filed:

Sep 8, 2004

Appl. No.:

10/937248

Inventors:

Zhuan Liu - Fremont CA, US
Sangbong Lee - San Leandro CA, US
Jiangtao Hu - Alameda CA, US
Chandra Saravanan - Fremont CA, US

Assignee:

Nanometrics Incorporated - Milpitas CA

International Classification:

G01B 11/02

US Classification:

356504

Abstract:

A residue detection system collects at least one of the spectrum and image from a measurement region on a sample. Spectral analysis is performed on the collected spectrum to determine whether residue is present and if so the thickness of the residue. The spectral analysis uses a calibration metric that correlates a monitoring parameter to the thickness of the residue. The monitoring parameter is at least one of the reflectance value at one or more of the local minima and maxima in the spectrum, the shape of one or more of the local minima and maxima in the spectrum, and the difference in reflectance values between at least two of the local minima and maxima in the spectrum. In one embodiment, imaging analysis is performed on the collected image of the measurement region if no residue is detected by the spectral analysis.