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Patent for License:

Feature-based defect detection    

Detection of defects in patterned substrates, such as semiconductor wafers, particularly based on features in voltage-contrast images.

Overview

Methods and apparatus are provided for inspecting a patterned substrate, comprising: preparing a reference image and a test image, extracting features from the reference image and extracting features from the test image, matching features of the reference image and features of the test image; and comparing features of the reference image and of the test image to identify defects. Embodiments include apparatus for inspecting patterned substrates, computer-readable media containing instructions for controlling a system having a processor for inspecting patterned substrates, and computer program products comprising a computer usable media having computer-readable program code embodied therein for controlling a system for inspecting patterned substrates. The images can be electron-beam voltage-contrast images.


Summary of Technology
Methods and apparatus consistent with the technology employ feature-based image processing to detect, quantify and analyze defects in inspection of patterned substrates, such as semiconductor wafers, from voltage contrast e-beam images. A method of inspecting a patterned substrate comprises: preparing a reference image and a test image, extracting features from the reference image and extracting features from the test image, matching features of the reference image and features of the test image, and comparing features of the reference image and of the test image to identify defects. The images can be aligned before matching features. The reference image can be a voltage-contrast image of a first patterned substrate and the test image a voltage-contrast image of a second substrate, or the reference image can be a voltage-contrast image of a first region of a patterned substrate and the test image a voltage-contrast image of a second region of the same patterned substrate, or the reference image can be an image of repeating cells of a patterned substrate and the test image a duplicate of the reference image shifted by one cell relative to the reference image. The images can be pre-processed to reduce noise and/or artifacts such as by spatial smoothing, and/or normalizing. Comparing features of the images to identify defects can comprise computing feature properties (such as size, shape, average pixel intensity, center of gravity, diameter, area, standard deviation, etc.), comparing computed feature properties, and determining comparison results which meet predetermined defect criteria. Extracting features from an image can comprise enhancing the features (such as by computing an average background level of the image and removing the average background level from the image) to produce a first modified image, thresholding the first modified image to produce a second modified image, and identifying features in the second modified image. Alternatively, extracting features from an image can comprise matching a feature template in the image and identifying features in the image that match the feature-template.

The technolgy include apparatus for inspecting patterned substrates, computer-readable media containing instructions for controlling a system having a processor for inspecting patterned substrates, and computer program products comprising a computer usable media having computer-readable program code embodied therein for controlling a system for inspecting patterned substrates.

Patent Summary

U.S. Patent Classes & Classifications Covered in this Patent:

Class 382: Image Analysis

This is the generic class for apparatus and corresponding methods for the automated analysis of an image or recognition of a pattern. Included herein are systems that transform an image for the purpose of (a) enhancing its visual quality prior to recognition, (b) locating and registering the image relative to a sensor or stored prototype, or reducing the amount of image data by discarding irrelevant data, and (c) measuring significant characteristics of the image.

Subclass 149: Fault or defect detection
Subclass 286: Measuring image properties (e.g., length, width, or area)

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