What Does VLV Testing Detect?

Transcription

1 Center for RC eliable omputing What Defect Does L Testing Detect? Stanford University Nov. 1, 1999 Outline Introduction Physics of Tunneling Proposal of Tunneling Defect Theoretical Calculation Experiment Evidence Future Work Summary 1 Introduction L effectiveness table [Chang 96] Failure Mode IDDQ L Transmission gate opens NO YES Threshold voltage shifts NO YES Diminished-drive gates NO YES Gate oxide shorts YES YES Metal shorts YES YES Defective interconnect buffers YES YES High resistance interconnects NO NO Tunneling open NO NO Introduction 9 L-only CUTs in Murphy 5 CUT can not be explained by the table Goal of this talk 3 4 Physics of Tunneling Put Them ll Together 5 6 Page 1 Nov.1, 1999

2 Proposal of Tunneling Defect L-only CUT behavior Previous study Possible explanations Proposal of a tunneling defect formation of a tunneling defect qualitative description of the circuit behavior at nominal voltage at very low voltage L-only CUT Behavior Long time IDDQ leakage phenomena IDDQ in u time (second) 8 Maly Previous Study Possible Explanations location C R Logic 1fF 1T 1pF 1G I/O 1pF 1G 9 1 Formation of a Tunneling Defect Qualitative Description I DDQ (t) very long leakage Metal X SiO SiO Poly very thin in out 11 1 Page Nov.1, 1999

3 @ Nominal ery Low oltage fast ckt response log I very slow I DDQ leakage log I very slow response very slow I DDQ leakage Theoretical Calculation electrical model analytical equations simulation results nominal voltage L IDDQ leakage J tunnel Electrical model d, = defect oxide thickness, area E ox = ox /d ox C d metal C gate poly nalytical equations Tunneling effect (FN+Dir) [Schuegraf 9] tunnel Eox J ( t) = e correction _ fector = (1 ( / Eox ) b b ox ) e B( b ox ) b / E ox Simulation: 5,C gate = 4fF, d=1 =1 m m p_tunnel p_couple J poly( t) = C Coupling Effect tunnel gate ( t) dt voltage 3 = ox d Cd poly = metal Cd + C Cd gate time (ns) 18 Page 3 Nov.1, 1999

4 I DDQ Leakage Simulation: 1.7 nalytical equation voltage m p_tunnel p_couple time (ns) 19 T leakage = C J gate L_tunnel ssumptions (@ nominal voltage) = (th -t) =.5 -.7=1.8 C gate = 4fF T leakage = 1ms ~ 1S = 1 m Calculation result J L_tunnel = 7 ~ 7. /cm Experimental Evidence Boolean Test - Expected Behavior Boolean Test Evidence expected behavior experimental results IDDQ Test Evidence expected behavior experimental results Failure nalysis Evidence If not tunneling [Chang 96] Delay Ratio = T_bad / T_good either fail or less than 1 x slower Defect Max Delay Weak driven gate 41.7 Tran. gate open Fail t shift.98 Diminished drive gate Boolean Test - Expected Behavior Boolean Test - Expected Behavior If Tunneling extremely long L eventually work minimum functional voltage same as good Expected shmoo plot N Good not tunneling tunneling L min 3 ns s ms delay 4 Page 4 Nov.1, 1999

5 Boolean Test - Experiment Results Table of delay different voltage I DDQ Test - Expected Behavior Table of expected IDDQ behavior cut id Good 3nS 6nS 1ns 47nS sq 38nS 114nS N 6nS sq 3nS 86nS N Fail 35.8.m1 36nS N Fail Fail sq 36nS N Fail Fail 1.3.m1 34nS 3ns 5 S 3mS sq 37nS 148nS 4nS 1 S m1 35nS ns 3 S ms sq 37nS 9nS 6 S 3 S m1 35nS 7nS 9 S 4 S defect high IDDQ () IDDQ leakge GOS Y N - - t shift N N - - WD gate Y N - - Tr. gate open Y N - - RC Y Y S No D/S junction leakage Y Y ms ~ S decrease decrease Tunneling Y Y ms ~ S No 5 6 IDDQ in u I DDQ Test - Experiment Results I DDQ different voltage (from sq) Time (second) I DDQ Test - Experiment Results Table of experimental I DDQ behavior cut id max decrease leakage IDDQ decrease sq N sq N m1 18 N sq 38 N m1 88 Y 14~56mS N sq 5 Y 56~7mS N m1 14 Y 8~69mS N sq 35 Y 4~57mS N m1 1 Y 4~55mS N 8 Failure nalysis Sematech data [Nigh 98] dd=5 dd=3.3 dd=1.8 m d t ns m d t ns m d t ns Page 5 Nov.1, 1999

6 Q: Why sequence L? ll tunneling defect CUTs are seq. tunneling effect has polarity rise time different than fall time Q3: Is it process error or defect? Defect 5 CUTs from 3 lots, different wafer Q4: What is the best test condition? L transition pattern maybe low temperature 31 Q5: Will it cause reliability problem? Yes low quality oxide, break down easily No Sematch data [Nigh 98] IDDQ did not change much after burn-in after break down, becomes high impedance 3 Q6: Will it cause more trouble in the future technology? No Cg smaller, coupling effect dominates dd decreases, FN tunneling decrease Yes metal intensive direct tunneling is field depdent 33 Summary 5/9 L CUT can be explained by FN tunneling CUT ID high IDDQ slow IDDQ possible defect sq N N N t shift? sq N N N t shift? 35.8.m1 Y N N shorts? sq Y N N shorts? 1.3.m1 Y Y Y Tunneling sq Y Y Y Tunneling m1 Y Y Y Tunneling sq Y Y Y Tunneling m1 Y Y Y Tunneling 34 Reference ppendix 35 Page 6 Nov.1, 1999

7 Direct Tunneling Oxide thinner than 4~5nm Fowler-Nordheim Tunneling Strongly depends on electric field Trap ssisted Tunneling Depends on oxide quality I DDQ Test - Experiment Result Definition of I DDQ I(t) = I leak exp (-t/ ) + I final I leak I fianl 39 time 4 Page 7 Nov.1, 1999