Defect Localization Using Modulated-Thermal Laser Stimulation and Phase-Shift Imaging Method

Transcription

1 Defect Localization Using Modulated-Thermal Laser Stimulation and Phase-Shift Imaging Method A. Reverdy a, P. Perdu c, M. de la Bardonnie a, H. Murray b, P. Poirier a a NXP Semiconductors, b LaMIPS, c CNES 1

2 Purpose Defect localization : last step before destructive analysis (Physical characterization) Additional informations on the defect localization could improve the localization efficiency Experimental studies show that TLS spots can be difficult to interpret Could M-TLS be a solution to improve TLS signature interpretation? Case study: Could M-TLS be a solution to distinguish artifacts from real signatures? 2

3 Outline M-TLS acquisitions and phase-shift imaging A solution to access additional information: Application on a 65nm non defective test structure A solution for a better interpretation of TLS signature: Application on a 45nm defective structure Conclusions 3

4 Modulated-TLS principle Requirement: modulated laser source Study of the M-TLS signal time dependence Thermal Time Constant (TTC) ΔR( t) = ρ. L 0 S. αtcr. ΔT ( t) Magnitude (A. U.) 1 0 TLS signal Laser stimulation Time (µs) 50 4

5 Practical access to the Time Requirements: dependency Compatible with TLS configuration (laser scan) Access to magnitude and phase-shift shift ( ( time dependency) information Magnitude (A. U.) 1 Transposition in the Frequency domain τ struct Time domain Laser modulation TLS signal τ env Time (µs) Magnitude (A. U.) Phase (deg.) Frequency domain Frequency (khz) Frequency(kHz) 5

6 M-TLS acquisition flow Scanner Laser modulation Treatment flow & Image reconstruction (R, φ) External acquisition Magnitude (A. U.) 0.8 Phase-shift (deg.) -35 V ΔI(t) X, Y: In-phase & out-ofphase components Acquisition of both magnitude and phase-shift shift information during a single scan 6

7 Outline M-TLS acquisitions and phase-shift imaging A solution to access additional information: Application on a 65nm non defective test structure A solution for a better interpretation of TLS signature: Application on a 45nm defective structure Conclusions 7

8 Application: structure description Study of a matrix of embedded copper lines, 65 nm technology: Metal layers: M5 => M1 Widths: 1100nm 740 nm 480 nm Min width (110 or 90 nm) Studied line Objective: apply phase-shift detection analysis to discriminate each test structure 8

9 Metal layer influence (LDE) Layer n 5 Layer n 4 Layer n 3 Layer n 2 1 st harmonic phase-shift (deg.) Good discrimination level between 2 consecutive metal layers Deeper the line, quicker the TLS response Resistance of the thermal path through the silicon substrate TTC Phase-shift 9

10 Line width influence (LDE) 110 nm* 480 nm 740 nm 1100 nm 3 rd harmonic phaseshift (deg.) Line width information available: Wider the line, slower the TLS response Line width heat capacity TTC phase-shift 10

11 Outline M-TLS acquisitions and phase-shift imaging A solution to access additional information: Application on a 65nm non defective test structure A solution for a better interpretation of TLS signature: Application on a 45nm defective structure Conclusions 11

12 Electromigration case study Structure description EM test structure, CMOS 45nm, V2M3 copper line Specific design for copper migration detection: Extrusion lines Measurement lines Line width: 70nm Line pitch: 70nm EM test: 10mA/² at 300 C Stop criteria 1% of resistance increase 70 Extrusion lines 10 Studied line Measuremen t Lines 12

13 Standard TLS approach Classical OBIRCH analysis OBIRCH spot located at center Same result on several dies No defect found Conclusion: This specific signature results from surrounding changes Reflected image OBIRCH image, 150mV, 50x obj. TLS ARTEFACT SEM image along the line (X-section) 13

14 M-TLS study (artifact area) Magnitude image Same artifact is present (as expected) Shape and value variation M-TLS, magnitude image 1 2 Mag. A.U. Phase-shift shift image Shape variation BUT same value along the line Convincing quantitative values M-TLS, phase-shift image Regular value (1) Spot value (2) Mag Phase Phase (deg.)

15 Phase-shift analysis interest The artefact (magnitude image) is not visible on the phase-shift image M-TLS phase-shift analysis appears as a relevant and unique method to identify this kind of artifact resulting from surrounding interaction What is the phase shift signature on a real defective area? 15

16 M-TLS study (defective area) Magnitude Resistance increase voiding formation Via areas are preferential e locations for voiding - Comparison of M-TLS M magnitude acquisitions Anode signature Center signature Mag. A.U. The two M-TLS signatures are similar Do they come from the same interaction? 16

17 M-TLS study (defective area) Phase-shift Specific phase-shift signature in the via location (shape & value) Small variation but visible in image mode with an appropriate treatment More significant mean values extraction Mag. Phase Regular value (2) M-TLS, magnitude image 1 Spot value (1) M-TLS, phase-shift image 17 Mag. A.U. Phase (deg.)

18 Physical Characterization SEM image of the anode side 18

19 Conclusions Phase-shift detection associated with M-TLS acquisition allows to: Access additional information on the excited structure, like depth and structure dimensions Improve the TLS signature interpretation Design + Additional information => Indirect improvement of the localization accuracy More information on the defect More confidence on the defect localization step Better interpretation of complex TLS signature (ARTEFACT) 19

20 Physical interpretation 2 possible explanations: Multiple reflection on copper surroundings Heat conduction in copper surroundings then heat transfer to the studied line 2 consequences: Increase of energy transferred to the copper line Indirect heating => Spatial expansion 1 result: 1 result: Deeper and larger OBIRCH spot signature in the measurement lines implementation area 20