Method and system for subnet defect diagnostics through fault compositing

• US 8,402,421 B2
• Filed: 10/12/2010
• Issued: 03/19/2013
• Est. Priority Date: 10/12/2010
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Bartenstein, Thomas Webster, Swenton, Joseph Michael
• Primary Examiner(s): Thompson, A. M.
• Application Number:
  US12/903,035
• Publication Number:
  US 20120089872A1
• Time in Patent Office: 889 Days
• Field of Search: None
• US Class Current: 716/136
• CPC Class Codes: G06F 11/2205 using arrangements specific to the hardware being tested

Abstract

A method and system for subnet defect diagnostics through fault compositing is disclosed. A testing apparatus generates callout data for an integrated circuit device under test. A computer received the callout data, which includes a list of faults. Each fault of the list of faults has associated with it one or more failures and/or conflicts. In order to explain the failures, two or more faults are selected and composited, yielding a composite fault having a composite conflict count. The composite fault is assigned a score based on the composite conflict count, which score determines a candidate composite that best explains the faults of the list of faults. This procedure may be repeated to explain all the failures.

Claims

1. A computer-implemented method of diagnosing subnet defects, comprising:

(i) receiving, at a computer, callout data comprising a list of faults, each fault of the list of faults comprising failure data and conflict count, the failure data containing miscomparing measures that each fault models, and a conflict indicating that each fault predicts a failure that was not measured;

(ii) selecting a first fault on a fan-out sink of a fan-out net, the first fault explaining a first failure of the plurality of failures;

(iii) selecting a second fault on a different sink of the fan-out net, the second fault explaining a second failure that the first fault does not explain;

(iv) compositing the first fault and the second fault to yield a composite fault, wherein the composite fault comprises a combination of the failure data and conflict count of the first fault and the failure data and conflict count of the second fault;

(v) generating a composite conflict count by combining the conflict count of the first fault and the conflict count of the second fault;

(vi) assigning a score to the composite fault based on the composite conflict count; and

(vii) determining a best candidate composite fault explaining the first fault and the second fault based on the score.

2. The computer-implemented method of diagnosing subnet defects of claim 1, further comprising repeating (ii) through (vii) until the composite fault explains all of the plurality of failures.

3. The computer-implemented method of diagnosing subnet defects of claim 1, wherein the fault data includes a first count of test-failed (TF) faults, a second count of test-failed, simulation-detected (TFSD) faults, a third count of test-passed, simulation-detected (TPSD) faults.

4. The computer-implemented method of diagnosing subnet defects of claim 1, wherein the score is calculated by TFSD/(TF+TPSD/a), where a is a numerical weighting factor greater than zero, TF is a count of test-failed faults, TFSD is a count of test-failed, simulation-detected faults, and TPSD is a count of test-passed, simulation-detected faults.

5. The computer-implemented method of diagnosing subnet defects of claim 1, further comprising assigning a minimum conflict count to the composite fault.

6. The computer-implemented method of diagnosing subnet defects of claim 5, wherein the score is given a higher value when the composite conflict count is smaller than the minimum conflict count.

7. The computer-implemented method of diagnosing subnet defects of claim 1, wherein the plurality of failures comprises a defect caused by an inverting fault.

8. The computer-implemented method of diagnosing subnet defects of claim 7, wherein the inverting fault is caused by a shorted net.

9. The computer-implemented method of diagnosing subnet defects of claim 1, wherein the plurality of failures comprises a timing defect.

10. The computer-implemented method of diagnosing subnet defects of claim 1, wherein the first fault and the second fault are logically unrelated.

11. A computer-readable storage medium having stored thereon a plurality of instructions, said plurality of instructions when executed by a computer, cause said computer to perform:

(i) receiving callout data comprising a list of faults, each fault of the list of faults comprising failure data and conflict count, the failure data containing miscomparing measures that each fault models, and a conflict indicating that each fault predicts a failure that was not measured;

(ii) selecting a first fault on a fan-out sink of a fan-out net, the first fault explaining a first failure of the plurality of failures;

(iii) selecting a second fault on a different sink of the fan-out net, the second fault explaining a second failure that the first fault does not explain;

(iv) compositing the first fault and the second fault to yield a composite fault, wherein the composite fault comprises a combination of the failure data and conflict count of the first fault and the failure data and conflict count of the second fault;

(v) generating a composite conflict count by combining the conflict count of the first fault and the conflict count of the second fault;

(vi) assigning a score to the composite fault based on the composite conflict count; and

(vii) determining a best candidate composite fault explaining the first fault and the second fault based on the score.

12. The computer-readable storage medium of claim 11, having stored thereon a plurality of instructions, said plurality of instructions when executed by a computer, cause said computer to further perform repeating (ii) through (vii) until the composite fault explains all of the plurality of failures.

13. The computer-readable storage medium of claim 11, wherein the fault data includes a first count of test-failed (TF) faults, a second count of test-failed, simulation-detected (TFSD) faults, a third count of test-passed, simulation-detected (TPSD) faults.

14. The computer-readable storage medium of claim 11, wherein the score is calculated by TFSD/(TF+TPSD/a), where a is a numerical weighting factor greater than zero, TF is a count of test-failed faults, TFSD is a count of test-failed, simulation-detected faults, and TPSD is a count of test-passed, simulation-detected faults.

15. The computer-readable storage medium of claim 11, having stored thereon a plurality of instructions, said plurality of instructions when executed by a computer, cause said computer to further perform assigning a minimum conflict count to the composite fault.

16. The computer-readable storage medium of claim 15, wherein the score is given a higher value when the composite conflict count is smaller than the minimum conflict count.

17. The computer-readable storage medium of claim 11, wherein the plurality of failures comprises a defect caused by an inverting fault.

18. The computer-readable storage medium of claim 17, wherein the inverting fault is caused by a shorted net.

19. The computer-readable storage medium of claim 11, wherein the plurality of failures comprises a timing defect.

20. The computer-readable storage medium of claim 11, wherein the first fault and the second fault are logically unrelated.

21. A diagnostic system for fault compositing, the diagnostic system comprising:

(i) an input for receiving callout data from a tester, the callout data comprising a list of faults, and each fault of the list of faults comprising failure data and conflict count, wherein the failure data contains miscomparing measures that each fault models, and a conflict indicates that each fault predicts a failure that was not measured;

(ii) means for compositing a first fault and a second fault to yield a composite fault, wherein the first fault is selected on a fan-out sink of a fan-out net, the first fault explaining a first failure of the plurality of failures, the second fault is selected on a different sink of the fan-out net, the second fault explaining a second failure that the first fault does not explain, and the composite fault comprises a combination of the failure data and conflict count of the first fault and the failure data and conflict count of the second fault;

(iii) means for generating a composite conflict count by combining the conflict count of the first fault and the conflict count of the second fault;

(iv) means for assigning a score to the composite fault based on the composite conflict count; and

(v) means for determining a best candidate composite fault explaining the first fault and the second fault based on the score.