Method and apparatus for removing dummy features from a data structure

• US 8,219,940 B2
• Filed: 07/06/2005
• Issued: 07/10/2012
• Est. Priority Date: 07/06/2005
• Status: Active Grant

• Current Assignee: TechInsights, Inc. (M3, Inc.)
• Original Assignee: Semiconductor Insights Incorporated (Informa PLC)
• Inventors: Ouali, Mohammed, Abt, Jason, Keyes, Edward, Zavadsky, Vyacheslav
• Primary Examiner(s): LEVIN, NAUM B
• Application Number:
  US11/174,732
• Publication Number:
  US 20070011628A1
• Time in Patent Office: 2,561 Days
• Field of Search: 716/51, 716/55, 716/118, 382/144, 382/145, 382/218
• US Class Current: 716/51
• CPC Class Codes: G06F 18/2113 by ranking or filtering the set of features, e.g. using a measure of variance or of feature cross-correlation
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347

Abstract

A method and apparatus to reduce occurrences of electrically non-functional elements, known as dummy features, from a source data structure is described. The source data structure may be image data, a vector based data structure or some other data format. Dummy features in the source data structure are detected and then deleted. Dummy features may be detected by selecting a representative dummy feature, using it as a reference pattern or polygon and comparing it to features in the source data structure. The step of comparing the selected reference to the comprises selecting a cut-off correlation threshold value, and computing the correlation coefficients between the reference and the feature. Features are selectively removed based on a comparison between their correlation coefficients and the selected cut-off correlation threshold value. This threshold value may require updating to remove all dummy features in the source data structure. When different shaped dummy features in the same data structure are encountered, a further reference feature may be selected and the process repeated.

Claims

1. A method of processing a source data structure representation of an IC layout comprising dummy features, which are electrically non-functional elements that ensure the planarity of subsequent dielectric and conductive layers where there is no circuitry, comprising the steps of:

(a) selecting a pre-determined dummy feature from a portion of the source data structure to be used as a reference pattern in a computerized processing system, and comparing the selected reference pattern to feature patterns in the source data structure to detect previously unidentified dummy features in the source data structure; and

(b) removing the detected previously unidentified dummy features from the source data structure, thereby producing a processed source data structure representation of the IC layout with reduced occurrences of dummy.

2. A method as claimed in claim 1 wherein the source data structure is in the form of image data.

3. A method as claimed in claim 1 wherein step (a)(1) comprises:

(a)(1)(i) framing the dummy feature reference pattern by a pixel matrix of m×

n pixels; and

(a)(1)(ii) selecting a cut-off correlation threshold value.

4. A method as claimed in claim 3 wherein step (a)(2) comprises:

(a)(2)(i) computing correlation coefficients between feature patterns in the source data structure and the selected reference pattern; and

(a)(2)(ii) comparing computed correlation coefficients to the selected cut-off correlation threshold value.

5. A method as claimed in claim 4 wherein the computed correlation coefficients are based on gray scale values.

6. A method as claimed in claim 4 wherein the correlation coefficients are, calculated using a sum of squared differences equation:

7. A method as claimed in claim 3 further comprising, the steps of:

(c) examining the source data structure with the removed dummy features; and

(d) selecting anew cut-off correlation threshold value; and

(e) repeating steps a. and b. if necessary.

8. A method as claimed in claim 7 wherein step c comprises examining the source data structure with the removed dummy features to determine if further dummy features remain.

9. A method as claimed in claim 7 wherein step c comprises examining the source data structure with the removed dummy features to determine if non-dummy features have been removed.

10. A method as claimed in claim 7 further comprising, the steps of:

(f) repeating steps c., d. an e. if necessary.

11. A method as claimed in claim 10 further comprising, the steps of:

(g) storing the source data structure with the removed dummy features in a memory;

(h) storing the dummy feature reference pattern in a memory; and

(j) storing the last selected cut-off correlation threshold value in a memory.

12. A method as claimed in claim 3 further comprising, the steps of:

(k) examining the source data structure with the removed dummy features to determine if a significant number of dummy features have been removed; and

(l) selecting another dummy feature pattern as a reference pattern if a significant number of dummy features have not been removed.

13. A method as claimed in claim 1 wherein the source data structure is in the form of a vector based data structure.

14. A method as claimed in claim 13 wherein step (a) comprises:

(a)(1) selecting a dummy feature as a reference polygon; and

(a)(2) comparing the selected reference polygon to feature polygons in the source data structure.

15. A method as claimed in claim 14 wherein the dummy feature reference polygon is selected from a portion of the source data structure.

16. A method as claimed in claim 14 wherein step (a)(1) comprises:

(a)(1)(i) forming the dummy feature reference polygon by extracting points of interest from the dummy feature; and

(a)(1)(i) selecting a cut-off correlation threshold value.

17. A method as claimed in claim 14 wherein step (a)(2) comprises computing correlation coefficients between points of interest in feature polygons in the source data structure and the reference polygon.

18. A method as claimed in claim 17 further comprising, the steps of:

(c) examining the source data structure with the removed dummy features to determine if further dummy features remain; and

(d) selecting a new cut-off correlation threshold value; and

(e) repeating steps (a) and (b) if necessary.

19. A method as claimed in claim 18 wherein step (c) comprises examining the source data structure with the removed dummy features to determine if further dummy features remain.

20. A method as claimed in claim 18 wherein step (c) comprises examining the source data structure with the removed dummy features to determine if non-dummy features have been removed.

21. A method as claimed in claim 18 further comprising, the steps of:

(f) repeating steps (c), (d), and (e) if necessary.

22. A method as claimed in claim 21 further comprising, the steps of:

(g) storing the source data structure with the removed dummy features in a memory;

(h) storing the dummy feature reference polygon in a memory; and

(j) storing the last selected cut-off correlation threshold value in a memory.

23. A method as claimed in claim 17 further comprising, the steps of:

(c) examining the source data structure with the removed dummy features to determine if a significant number of dummy features have been removed; and

(d) re-selecting another dummy feature polygon if a significant number of dummy features have not been removed.

24. An apparatus for processing a source data structure representation of an IC layout comprising dummy features, which are electrically non-functional elements that ensure the planarity of subsequent dielectric and conductive layers where there is no circuitry, comprising:

a memory for storing the source data structure;

a data processor comprising;

means for selecting a pre-determined dummy feature from a portion of the stored source data structure to be used as a reference pattern in a computerized processing system, and for comparing the selected reference pattern to feature patterns in the source data structure to detect previously unidentified dummy features in the source data structure; and

means for removing the detected previously unidentified dummy features from the source data structure, thereby producing a processed source data structure representation of the IC layout with reduced occurrences of dummy features; and

a memory for storing the processed source data structure.

25. An apparatus as claimed in claim 24 wherein the source data structure is in the form of image data.

26. An apparatus as claimed in claim 24 wherein the source data structure is in the form of a vector based data structure.

27. An apparatus as claimed in claim 24 wherein the comparing means comprises:

means for selecting a cut-off correlation threshold value; and

means for computing correlation coefficients between feature patterns in the source data structure and the reference pattern.

28. An apparatus as claimed in claim 27 wherein the computed correlation coefficients are based on gray scale values.

29. An apparatus as claimed in claim 27 wherein the cut-off correlation threshold value selection means comprises:

means for framing the dummy feature reference pattern by a pixel matrix of m×

n pixels; and

means for selecting the cut-off correlation threshold value.

30. An apparatus as claimed in claim 27 wherein the correlation coefficient computing means includes means for calculating using a sum of squared differences equation:

31. An apparatus as claimed in claim 27 further comprising means for selecting anew cut-off correlation threshold value.

32. An apparatus as claimed in claim 31 further comprising:

a memory for storing the dummy feature reference pattern; and

a memory for storing the last updated cut-off correlation threshold.