1. VTS 2012: Zhao-Agrawal1 Net Diagnosis using Stuck-at and Transition Fault Models Lixing Zhao* Vishwani D. Agrawal Department of Electrical and Computer Engineering Auburn University, AL 36849 USA * Presently with FutureWei Technologies, Inc., Santa Clara, CA 95054 USA April 25, 2012

2. 2 Outline  Motivation  Background  Problem Statement  Diagnosis Method  Fault Filtering  Fault Ranking  Net Ranking  Conclusion  References VTS 2012: Zhao-AgrawalApril 25, 2012

3. VTS 2012: Zhao-Agrawal3 Motivation  Fault diagnosis can bring the yield up in manufacturing rounds by identifying the possible causes of defects in earlier tape-outs.  Net fault diagnosis is an important area of fault diagnosis. Because of the large routing area of modern VLSI devices, the routing interconnection nets are more vulnerable to certain defects. April 25, 2012

4. Background Net defects sometimes have certain complicated characteristics. Simply using traditional fault models cannot solve the net fault diagnosis problem well. Using complicated fault models to match the behavior of a net fault is time consuming, not supported by tools, and not suitable for practical use. VTS 2012: Zhao-Agrawal4April 25, 2012

5. Problem Statement Find an effective method for solving the net-fault-diagnosis problem using available software tools. VTS 2012: Zhao-Agrawal5April 25, 2012

6. VTS 2012: Zhao-Agrawal62012 VTS6 Diagnostic Test Patterns We use test patterns, which have high diagnostic coverage for single stuck-at faults and single transition faults. 1.Y. Zhang and V. D. Agrawal, “A Dianostic Test Generation System,” Proc. International Test Conf., 2010, Paper No. 12.3. 2.Y. Zhang and V. D. Agrawal, “Reduced Complexity Test Generation Algorithms for Transition Fault Diagnosis,” Proc. International Conf. on Computer Design, 2011, pp. 96-101. April 25, 2012

7. Diagnostic Procedure Start with collapsed set of faults. First Filter (Simple): Test pattern matching. Second Filter: Primary output (PO) matching. Discard faults below count thresholds. Rank order remaining faults. Map top suspects onto nets. April 25, 2012VTS 2012: Zhao-Agrawal7 A: patterns detecting fault F B: patterns failing CUT on ATE C Count (F) = |C|/|A|

8. Count for Second Threshold Set a high threshold for first count; few faults left. Compute a second PO-specific count April 25, 2012VTS 2012: Zhao-Agrawal8 D: C ×PO pairs for fault F C ×PO pairs for CUT on ATE E: Hit patterns Count (F) = |E|/|D|

9. Training for Count Thresholds Set a high threshold for the first filter. Generate sample circuits by injecting some (e.g., four) randomly chosen faults. Select second threshold so 90% injected faults survive the two filters. If necessary, lower the first threshold. April 25, 2012VTS 2012: Zhao-Agrawal9

10. 10 Filtering Results Circuit# of Total Faults Reduction Rate Survival Rate C4325240.770.975 C8809420.970.96 C135515740.750.97 C190818790.850.95 C267027470.9250.97 C354034280.950.965 C628877440.9330.96 C755274190.9920.96 April 25, 2012

11. VTS 2012: Zhao-Agrawal11 Ranking Suspects  Rank filtered fault candidates in a list of key suspects.  Only patterns failing on ATE are simulated.  A structure called erroneous PO-tree (EPO-tree) is constructed for all failing patterns.  Faults are ranked at each PO separately by their total number of appearances in EPO-trees. April 25, 2012 Failing pattern 1

12. Diagnostic Experiments ISCAS’85 circuits. 200 faulty circuit samples: 1-4 randomly selected faults injected. Diagnosis: –Diagnosability (Dia): fraction of injected faults found –First hit rank (FHR): Position of an injected fault in the ranked suspect list –Resolution (Res): Ratio of number of diagnosed faults to injected faults April 25, 2012VTS 2012: Zhao-Agrawal12

13. Experimental Results VTS 2012: Zhao-Agrawal13 CiruitOur Work (1 Stuck-at)Wang et al. (1 stuck-at) DiaFHRRESCPU sDiaFHRResCPU s c26701.0 6.41.01.271.30.01 c35401.0 0.51.01.21.50.01 c62881.0 0.61.01.11.30.01 c75521.0 1.51.01.151.60.01 Z. Wang, M. Marek-Sadowska and J. Rajski, "Analysis and Methodology for Multiple-Fault Diagnosis,” IEEE Tran on CAD of Integrated Circuits and Systems, March 2006, vol. 25, pp. 558- 576. Circui t Our Work (2 Stuck-at)Wang et al. (2 stuck-at) DiaFHRRESCPU sDiaFHRResCPU s c26700.971.02.080.971.352.00.05 c35400.951.0 0.60.951.21.70.06 c62880.991.02.010.971.282.00.2 c75520.931.02.01.70.9251.252.00.2 April 25, 2012

14. VTS 2012: Zhao-Agrawal14 CircuitOur Work (3 Stuck-at)Wang et al. (3 stuck-at) DiaFHRRESCPU sDiaFHRResCPU s c26700.941.02.0130.9251.352.60.1 c35400.941.02.00.70.921.152.40.1 c62880.951.02.02.70.931.152.50.5 c75520.901.042.02.90.921.22.30.25 CircuitOur Work (4 stuck-at)Wang et al. (4 stuck-at) DiaFHRRESCPU sDiaFHRResCPU s c26700.891.062.0170.921.32.60.2 c35400.911.02.01.80.891.252.50.2 c62880.921.022.05.70.821.152.80.8 c75520.881.12.03.20.911.22.40.5 April 25, 2012

15. Net Ranking Each ranked fault is uncollapsed and all equivalent faults are given the same rank as the parent fault. Count for a net is the highest rank of any fault on it. Nets are ranked in order of descending count. April 25, 2012VTS 2012: Zhao-Agrawal15

16. VTS 2012: Zhao-Agrawal16 CircuitOne Net Fault (Stuck-at)Two Net Faults (Stuck-at) DiaFHRResCPU sDiaFHRResCPU s c4321.01.12.00.10.981.23.00.2 c8801.01.12.00.11.01.13.00.1 c13550.982.03.01.00.752.65.016 c19080.921.43.07.50.861.33.013 c26700.981.43.07.40.951.144.012 c35400.981.043.00.50.961.13.00.7 c62880.981.13.030.91.063.04 c75520.961.13.030.91.23.011 Experimental Results April 25, 2012

17. VTS 2012: Zhao-Agrawal17 CircuitOne Net Fault (Transition)Two Net Faults (Transition) DiaFHRResCPU sDiaFHRResCPU s c4321.01.052.00.480.91.23.00.7 c8800.91.22.00.8 1.33.02.3 c13551.0 0.90.861.33.013 c19080.961.22.07.20.931.43.035 c26701.01.162.00.90.971.062.04.6 c35400.981.22.01.70.951.12.02.3 c62881.01.082.02.80.921.32.02.8 c75520.981.32.07.50.961.082.013.1 April 25, 2012

18. VTS 2012: Zhao-Agrawal18 Conclusion  Net diagnosis is a practical way of identifying possible sites of defects.  Use of fault models facilitates test generation, fault grading and diagnostic analysis.  Using a variety of fault models may have benefits in diagnosis.  Tests with higher diagnostic coverage may be beneficial.  Basic idea is to gradually narrow down the list of suspects using single fault analysis tools:  Initial filtering only uses collapsed fault list and all test patterns.  Next filtering uses failing PO information, filtered faults and failed patterns.  Suspect ranking uses failed patterns, filtered fault list and PO matching.  Suspected net ranking is based upon the ranked faults and their equivalent fault sets. April 25, 2012

19. VTS 2012: Zhao-Agrawal19 References 1.Y. Zhang and V. D. Agrawal, “A Dianostic Test Generation System,” Proc. International Test Conf., 2010, Paper No. 12.3. 2.Y. Zhang and V. D. Agrawal, “Reduced Complexity Test Generation Algorithms for Transition Fault Diagnosis,” Proc. International Conf. on Computer Design, 2011, pp. 96-101. 3.N. Sridhar and M. S. Hsiao, “On Efficient Error Diagnosis of Digital Circuits,” Proc. International Test Conference, 2001, pp. 678-687. 4.S. M. Reddy, H. Tang, I. Pomeranz, S. Kajihara and K. Kinoshita, “On Testing of Interconnect Open Defects in Combinational Logic Circuits with Stems of Large Fanout,” Proc. International Test Conf., 2002, pp. 83-87. 5.Z. Wang, M. Sadowska, and J. Rajski, “Analysis and Methodology for Multiple-fault Diagnosis,” IEEE Tran on CAD of Integrated Circuits and Systems, vol. 25, pp. 558- 576, Mar. 2006 6.S. Venkataraman and S. B. Drummonds, “Poirot: Applications of a Logic Fault Diagnosis Tool,” IEEE Design and Test of Computers, Jan. 2001, pp. 19-29. 7.J. Segura and C. F. Hawkins, CMOS Electronics: How It Works, How It Fails,”Wiley- IEEE, Apr. 2004. April 25, 2012

20. VTS 2012: Zhao-Agrawal20 Thank You... April 25, 2012

21. VTS 2012: Zhao-Agrawal21 Questions April 25, 2012