Onto Innovation Inc.

Nanometrics Inc.

Nigel P Smith

George Andrew Antonelli

Jie Li

Zhuan Liu

Silvio J Rabello

Nicholas James Keller

Kevin Eduard Heidrich

Holly M Edmundson

Francis Scott Hoover

Michael A Gilmore

Overlay is determined for a device using signals measured from the device and a signal response to overlay determined from a plurality of calibration targets. Each calibration target has the same design as the device, but includes a known overlay shift. The calibration targets may be located in a scribe line, within a product area on the wafer, or on a separate calibration wafer. Each calibration target may have a different overlay shift, including zero overlay shift. The device may serve as a calibration target with zero overlay shift. The overlay shift may be in two orthogonal directions. The signal response to overlay may be determined based on a set of signals obtained from the calibration targets. A second set of signals may then be obtained from the device and the overlay determined based on the second set of signals and the determined signal response to overlay.

Multi-layer calibration for empirical overlay measurement

Defects are detected using data acquired from an interference channel and a polarization modification channel in an interferometer. The interference objective splits a polarized illumination beam into a reference illumination that is reflected by a reference surface without modification to the polarization, and a sample beam that is reflected by a sample surface, that may modify the polarization. Light from the sample beam with no change in polarization is combined with the reference illumination and directed to the interference channel, which may measure the reflectivity and/or topography of the sample. Light from the sample beam with modified polarization is directed to the polarization modification channel. The intensity of the light detected at the polarization modification channel may be used, along with the reflectivity and topography data to identify defects or other characteristics of the sample.

Sample surface polarization modification in interferometric defect inspection

Defects are detected using surface topography data. The defects may be detected by determining topography characteristics within a region of interest on a sample, and the same topography characteristics of at least one reference surface. By comparing the topography characteristics in the region of interest for the sample and reference surface, common pattern structures may be removed, leaving only variations, which may be used to identify the presence of defects. For example, thresholds may be used to identify variations in the topography characteristics as defect candidates. Defects may be identified based on, e.g., size, height, shape, texture, etc. of candidate defects. In some implementations, rather than using a reference surface, the topography characteristic of the surface within the region of interest may be inspected based on prior knowledge of a required surface topography for the region of interest to determine if a defect is present.

Sample inspection using topography

An optical metrology device, such as an interferometer, detects sub-resolution defects on a sample, i.e., defects that are smaller than a pixel in the detector array of the interferometer. The optical metrology device obtains optical metrology data at each pixel in at least one detector array and determines parameter values of a signal model for a pixel of interest using the optical metrology data received by a plurality of pixels neighboring a pixel of interest. A residual for the pixel of interest is determined using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest. A defect, which may be smaller than the pixel of interest can then be detected based on the residual for the pixel of interest.

Sub-resolution defect detection

An interferometer uses a phase shift mask that includes an array of pixels that are aligned with a corresponding array of pixels of a detector. Each pixel in the phase shift mask is adapted to produce one of a number of predetermined phase shifts between a test beam and a reference beam. For example, the pixels may be linear polarizers or phase delay elements having one of the number of polarizer orientations or phase delays to produce the predetermined phase shifts between the test beam and the reference beam. The pixels in the phase shift mask are arranged in the array to include each of the predetermined phase shifts in repeating pixel groups in rows that are one column wide, columns that are one row high, or blocks of multiple rows and columns.

Interferometer with pixelated phase shift mask

A white light interferometric metrology device operates in the image plane and objective pupil plane. The interferometric metrology device extracts the electric field with complex parameters and that is a function of azimuth angle, angle of incidence and wavelength from interferometric data obtained from the pupil plane. Characteristics of the sample are determined using the electric field based on an electric field model of the azimuth angle, the angle of incidence and the wavelength that is specific for a zero diffraction order. A center of the pupil in the pupil plane may be determined based on a Fourier transform of the interferometric data at each new measurement and used to convert each pixel from the camera imaging the objective pupil plane into a unique set of angle of incidence and azimuth angle of light incident on the sample.

Scanning white-light interferometry system for characterization of patterned semiconductor features

An image based overlay measurement is performed using an overlay target that includes shifted overlying gratings. The overlay target is imaged and an asymmetry is measured in the image of the overlaid gratings. The asymmetry is used to determine the overlay error. For each measurement direction, the overlay target may include two or more overlay measurement pads with different offsets between the top and bottom gratings. The measured asymmetries and offsets in the overlay measurement pads may be used to determine the overlay error, e.g., using self-calibration. The pitch and critical dimensions of the overlay target may be optimized to produce a greatest change of symmetry with overlay error for a numerical aperture and wavelength of light used by the image based metrology device.

Image based overlay measurement with finite gratings

An empirical diffraction based overlay (eDBO) measurement of an overlay error is produced using diffraction signals from a plurality of diffraction based alignment pads from an alignment target. The linearity of the overlay error is tested using the same diffraction signals or a different set of diffraction signals from diffraction based alignment pads. Wavelengths that do not have a linear response to overlay error may be excluded from the measurement error.

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Beaverton, OR, United States of America

Nigel P Smith