Method for facilitating automatic analysis of defect printability

• US 8,111,898 B2
• Filed: 12/06/2002
• Issued: 02/07/2012
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Synopsys Incorporated
• Original Assignee: Synopsys Incorporated
• Inventors: Pang, Linyong
• Primary Examiner(s): Liew, Alex
• Application Number:
  US10/313,706
• Publication Number:
  US 20040109601A1
• Time in Patent Office: 3,350 Days
• Field of Search: 382115-124, 382141-152
• US Class Current: 382/141
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

Defect printability analysis in a mask or wafer requires the accurate identification of defect images and reference (i.e. defect-free) images, in particular for a die-to-die inspection mode. A method of automatically distinguishing a reference image from a defect image is provided. In this method, multiple images can be accessed and aligned. Then, a common area of the multiple images can be defined. At this point, a complexity of each of the images, as defined by the common area, can be computed. Advantageously, by comparing the complexity of the multiple images, the reference and defect images can be quickly and accurately designated. Specifically, the most complex image is designated the defect image because the defect image must describe the defect. Complexity can be computed using various techniques.

Claims

1. A method of automatically distinguishing a reference image from a defect image, the method comprising:

using a mask defect printability system,

accessing multiple images, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a Fourier transform (FFT); and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein higher frequencies or larger values of high frequencies appear on an FFT representation of the defect image compared to an FFT representation of the reference image, wherein subtracting FFT representations of the multiple images from each other results in difference images, and wherein a difference image having more positive values in a high frequency domain identifies a defect image.

2. A method of automatically distinguishing a reference image from a defect image, the method comprising:

using a mask defect printability system,

accessing multiple images, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each image, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a JPEG file; and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein generating the JPEG file includes grouping pixels of each image into blocks, each block of pixels being transformed into another domain to generate a set of transform coefficients, which indicate unique blocks and instances of blocks, and

wherein a defect image has one or more additional unique blocks compared to a reference image.

3. A method of automatically distinguishing a reference image from a defect image, the method comprising:

using a mask defect printability system,

accessing multiple images, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each image, as defined by the common area, by performing a set of steps for partitioning; and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein partitioning includes dividing each image into blocks, the blocks being equal-sized, wherein duplicated blocks are exempt from further partitioning, wherein each unduplicated block is further partitioned into smaller blocks, the smaller blocks being equal-sized, wherein duplicated smaller blocks are exempt from further partitioning, wherein the partitioning continues until the reference image and the defect image are distinguished, each further partitioning having yet smaller blocks,

wherein a defect image has a greater total number of all size blocks than a reference image.

4. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by said machine to perform method steps to analyze a lithographic medium, the method steps comprising:

accessing multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a Fourier transform (FFT); and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein higher frequencies or larger values of high frequencies appear on an FFT representation of the defect image compared to an FFT representation of the reference image, wherein subtracting FFT representations of the multiple images from each other results in difference images, and wherein a difference image having more positive values in a high frequency domain identifies a defect image.

5. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by said machine to perform method steps to analyze a lithographic medium, the method steps comprising:

accessing multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a JPEG file; and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein generating the JPEG file includes grouping pixels of each image into blocks, each block of pixels being transformed into another domain to generate a set of transform coefficients, which indicate unique blocks and instances of blocks, and

wherein a defect image has one or more additional unique blocks compared to a reference image.

6. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by said machine to perform method steps to analyze a lithographic medium, the method steps comprising:

accessing multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

aligning the multiple images;

defining a common area of the multiple images;

computing a complexity of each of the images, as defined by the common area, by performing a set of steps for partitioning; and

designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein partitioning includes dividing each image into blocks, the blocks being equal-sized, wherein duplicated blocks are exempt from further partitioning, wherein each unduplicated block is further partitioned into smaller blocks, the smaller blocks being equal-sized, wherein duplicated smaller blocks are exempt from further partitioning, wherein the partitioning continues until the reference image and the defect image are distinguished, each further partitioning having yet smaller blocks,

wherein a defect image has a greater total number of all size blocks than a reference image.

7. A computer program product comprising:

a non-transitory computer usable storage device having a computer readable program code embodied therein for causing a computer to analyze a lithographic medium for defects, the computer readable program code comprising;

computer readable program code that accesses multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

computer readable program code that aligns the multiple images;

computer readable program code that defines a common area of the multiple images;

computer readable program code that computes a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a Fourier transform (FFT); and

computer readable program code that automatically designates reference and defect images by comparing the complexity of each of the multiple images,

wherein higher frequencies or larger values of high frequencies appear on an FFT representation of the defect image compared to an FFT representation of the reference image, wherein subtracting FFT representations of the multiple images from each other results in difference images, and wherein a difference image having more positive values in a high frequency domain identifies a defect image.

8. A computer program product comprising:

a non-transitory computer usable storage device having a computer readable program code embodied therein for causing a computer to analyze a lithographic medium for defects, the computer readable program code comprising;

computer readable program code that accesses multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

computer readable program code that aligns the multiple images;

computer readable program code that defines a common area of the multiple images;

computer readable program code that computes a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a JPEG file; and

computer readable program code that automatically designates reference and defect images by comparing the complexity of each of the multiple images,

wherein generating the JPEG file includes grouping pixels of each image into blocks, each block of pixels being transformed into another domain to generate a set of transform coefficients, which indicate unique blocks and instances of blocks, and

wherein a defect image has one or more additional unique blocks compared to a reference image.

9. A computer program product comprising:

a non-transitory computer usable storage device having a computer readable program code embodied therein for causing a computer to analyze a lithographic medium for defects, the computer readable program code comprising;

computer readable program code that accesses multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

computer readable program code that aligns the multiple images;

computer readable program code that defines a common area of the multiple images;

computer readable program code that computes a complexity of each of the images, as defined by the common area, by performing a set of steps for partitioning; and

computer readable program code that automatically designates reference and defect images by comparing the complexity of each of the multiple images,

wherein partitioning includes dividing each image into blocks, the blocks being equal-sized, wherein duplicated blocks are exempt from further partitioning, wherein each unduplicated block is further partitioned into smaller blocks, the smaller blocks being equal-sized, wherein duplicated smaller blocks are exempt from further partitioning, wherein the partitioning continues until the reference image and the defect image are distinguished, each further partitioning having yet smaller blocks,

wherein a defect image has a greater total number of all size blocks than a reference image.

10. A system for analyzing a lithographic medium for defects, the system comprising:

means for accessing multiple images of the lithographic medium, the multiple images being undesignated as reference or defect images;

means for aligning the multiple images;

means for defining a common area of the multiple images;

means for computing a complexity of each of the images, as defined by the common area, by performing at least a portion of a spatial frequency transform, the spatial frequency transform including generating a Fourier transform (FFT); and

means for designating the reference and defect images by comparing the complexity of each of the multiple images,

wherein higher frequencies or larger values of high frequencies appear on an FFT representation of the defect image compared to an FFT representation of the reference image, wherein subtracting FFT representations of the multiple images from each other results in difference images, and wherein a difference image having more positive values in a high frequency domain identifies a defect image.

11. The system of claim 10, wherein the lithographic medium is a mask.

12. The system of claim 10, wherein the lithographic medium is a wafer.