Automated direct patterned wafer inspection
AssigneeThe Board of Trustees of the Leland Stanford Junior University
InventorsBabak H. Khalaj, Hamid K. Aghajan, Thomas Kailath
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Abstract
Disclosed is a new self-reference signal processing technique for detecting the location of any nonregularities and defects in a periodic two-dimensional signal or image. Using high-resolution spectral estimation algorithms, the proposed technique first extracts the period and structure of repeated patterns from the image to sub-pixel resolution in both directions, and then produces a defect-free reference image for making comparison with the actual image. Since the technique acquires all its needed information from a single image, on the contrary to the existing methods, there is no need for a database image, a scaling procedure, or any apriori knowledge about the repetition period of the patterns.
Claims4
A method of inspecting a two dimensional periodic image of a semiconductor device and a photomask as used in semiconductor device fabrication for irregularities and defects comprising the steps of
- a) estimating repetition periods of patterns in horizontal and vertical directions in said image,
- b) extracting a building block of said image based on said repetition periods including obtaining a sub-pixel weighted sum of repeated patterns throughout said image, and
- c) subtracting shifted versions of said building block from said image to locate defects and irregularities.
A method of inspecting a two dimensional periodic image of a semiconductor device and a photomask as used in semiconductor device fabrication for irregularities and defects comprising the steps of
- a) estimating repetition periods of patterns in horizontal and vertical directions in said image,
- b) extracting a building block of said image based on said repetition periods including obtaining a sub-pixel weighted sum of repeated patterns throughout said image, and
- c) locating defects and irregularities in said image based on said building block.
Dependencies are inferred from the claim text.