Characterization and Failure Analysis Characterization and Failure Analysis of Silicon Devicesof Silicon DevicesCurrent and FutureCurrent and Future

Dieter K. SchroderDieter K. SchroderDept. of Electrical EngineeringDept. of Electrical Engineering

Arizona State UniversityArizona State UniversityTempe, AZTempe, AZ

IntroductionIntroductionBackgroundFailure site location

IDDQ testingLiquid crystalEmission microscopyPicosecond imaging circuit analysisVoltage contrastOptical beam induced resistance change

Physical AnalysisHigh resolution TEMMicroprobing

Failure AnalysisFailure AnalysisPhysical analysis difficult

Small feature sizeComplex device structureNew materials

Failure site location IC ⇒ circuit block ⇒ circuit element

⇒ contact/gate Failure site location difficult

Device complexityReduced accessibility

Flip-chipIncreasing metal layersDummy metal for chemical/ mechanical polishing

Solution: back side localization

Where is the defect?

Once the defect is found, how to

analyze it?Lgate = 60 nm

I’m trying to digup a defect

Defect Density TrendsDefect Density Trends

Courtesy of IC Knowledge, www.icknowledge.com

One defectin 20 cm2!

Def

ect D

ensi

ty (c

m-2

)

Year

Failure Site LocationFailure Site LocationIDDQ testingLiquid crystalEmission microscopyPicosecond imaging circuit analysisVoltage contrastOptical beam induced resistance changeMicroprobing

IIDDQDDQ TestingTestingIDDQ

Quiescent drain current flowing from power supply to groundDevice in quiescent state10-9 A range in quiescent stateIncreases due to defectsMainly detects physical defects,is supplemental to logic testing

R. Rajsuman, Iddq Testing for CMOS VLSI, Proc. IEEE 88, 544-566, April 2000;L.C. Wagner, Failure Analysis of Integrated Circuits, Kluwer, Boston, 1999

VDD

Gate OxideShort

MetalBridgingShort

Source-DrainShort

IIDDQDDQ TestingTestingBridging shorts and gate oxide shorts are detectable with IDDQ

Opens are more difficult or impossible to detect

Gate oxide short⇒360 µA IDDQ

Micrographs courtesy of IBM

Poly-poly short⇒5 mA IDDQ

Metal bridging defect⇒5 µA IDDQ

Large area defect(28 transistors)⇒620 µA IDDQ

Liquid Crystal MicroscopyLiquid Crystal MicroscopyChip heated slightly below liquid crystal (LC) clearing temperature Tc

LC is transparent below Tc , black above Tc

For ROCE 1510 (Hoffmann La Roche): Tc = 48°CChip voltage is pulsed for easier detection

L.C. Wagner, Failure Analysis of Integrated Circuits, Kluwer, Boston, 1999

Lamp

Observer

LiquidCrystalIC

Heater

Hot Spot

NematicPhase

IsotropicPhase

PolarizerAnalyzer

Liquid Crystal MicroscopyLiquid Crystal Microscopy

Poly-Si bridge causes hot spotCourtesy of C.G.C. De Kort, Philips Research Laboratories

Bipolar Junction Transistor

Hot spot due to 2.2 mW power dissipation

3.5 mW 2.65 mW 2.2 mW 1.75 mW

Courtesy of N. Nenadovic, DIMES, Delft University

Emission Microscopy (EMMI)Emission Microscopy (EMMI)

Image of circuit is taken in ordinary lightImage of circuit is taken in the dark with circuit powered up; defects appear as bright spotsThe two images are superimposed, showing defect locations on the circuit

C.G.C. de Kort, “Integrated Circuit Diagnostic Tools: UnderlyingPhysics and Applications,” Philips J. Res. 44, 295-327, 1989.

Emission MicroscopyEmission MicroscopyProblem: latch-up of CMOS circuitFrontside emission microscopy gave light spots at the metal edge; actual latch-up spot likely somewhere under the metalDevice was thinned to 50-100 µm; light emission was measured from the back of the wafer ⇒ latch-up initiation site

I = 30 mA (no latch-up) 50 mA (no latch-up)

T. Kessler, F.W. Wulfert, and T. Adams, Diagnosing Latch-upwith Backside Emission Microscopy,” Semicond. Int. July 2000.

70 mA (latch-up)

PicosecondPicosecond Imaging Circuit AnalysisImaging Circuit AnalysisPICA utilizes light emission to analyze device/circuit performance

Can measure thousands of gates simultaneously or observe one gateNon invasive, contactlessNo external excitation

Hot electron light emission is coincident with MOSFET switchingDuring CMOS switching, transient current flows on time scale of ps

Photos: www.research.ibm.com/topics/popups/serious/chip/html/pica.html

Each snapshot in this shift register lasts 34 ps !

9.6 10.0 10.4 10.8Time (ns)

Inte

nsity

Inverters#1 #9

508 ps

PicosecondPicosecond Imaging Circuit AnalysisImaging Circuit Analysis

Problem: incorrect timing at one particular output pin; switched too slowWas it transistor 25, gate 1, gate 3 or interconnect short or open ?

Time-integrated emission and optical waveform from problem T25Time-integrated emission and optical waveform from good transistor

Localized the defect to T25

T. Lundquist and M. McManus, “Characterize Gate-Level Transistor Performance with PICA,” Semicond. Int. 8, 249-254, July 2001.

Voltage ContrastVoltage ContrastThe electron beam is the probe

Small, can contact very narrow linesNo damage to lines; no capacitive loadingFast, can be programmed to probe entire chipChip can be at wafer level or packaged (cover removed)Can measure through insulator by capacitive couplingCan be used for visual inspection - SEM mode

Can measureNode voltages - mV rangeVoltage waveforms - subnanosecond time resolutionVoltage contrast - can look at a portion of the chip and by using stroboscopic techniques, can watch circuit operation

Voltage ContrastVoltage ContrastVoltage contrast: modulation of secondary electron yield by voltages on conductorsSE yield is influenced by:

Local electric fieldTopography - SE yield ~ 1/cos(θ)Material density Material work function

M. Vallet and P. Sardin, “Electrical Testing for Failure Analysis:E-Beam Testing”, Microelectron. Eng. 49, 157-167, 1999.

0 V 0 V 0 V

Detector

Retarding Grid

Primary Beam

SecondaryElectrons

0 V +5 V 0 V

Courtesy Siemens Corp.

E-beamθ

Voltage ContrastVoltage Contrast

Courtesy of T.D. McConnell, Intel Corp.

x

y

x

t1 ns

Open via in contact chainB. Fiordalice and D.W. Price, KLA-Tencor

x-y Defect location

Circuit timinginformation

Optical Beam Induced Resistance ChangeOptical Beam Induced Resistance Change

IR Laser

TV Display

I ± ∆ II

Current I flows through lineScanned laser irradiates the lineHeat leads to resistance ± ∆RCurrent changes by ∆I = (∆R/R)I∆I is detected and displayed in synchronism with laser scan

Increased R

Shorts

TRIRRI ∆∆∆=∆ ~;)/(

Leakage current path

Metal line defects

http://usa.hamamatsu.com/sys-failureanalysis/microamos/default.htm

OBIRCHOBIRCHDRAM, VDD to ground leakage path failure“Leakage” line is dark lineShort circuit is bright spot

5 µm

Micrographs courtesy of Hamamatsu Photonics

Probe DiameterProbe Diameter

1 10 100 1,000Å 1 10 100µm 1mm 1cm

Analytical Diameter

Electrons

Ions

X-Rays

Light

Probes

Physical Failure Analysis ChallengesPhysical Failure Analysis ChallengesReduced feature sizeSmaller defects

Field - emission SEMTransmission electron microscopyConfocal microscopyScanning probe microscopy

New materials – new failure mechanisms?Al ⇒ CuSiO2 ⇒ low KSiO2 ⇒ high K

Single dislocation

NaImages courtesy of T.J. Shaffner, NIST

GateDrain

Depletion region Substrate

Source

Imaging of Single Bi Atoms in SiImaging of Single Bi Atoms in Si

EELS Spectrometer

EELS Spectrometer

E BeamE BeamScanning Scanning

ProbeProbe

The best TEM has resolution of 0.8 ÅCan see individual impurity atoms

Courtesy of G. Duscher, North Carolina State University

Bi

Z=31 Z=33

Conductive Atomic Force MicroscopyConductive Atomic Force Microscopy

Image courtesy A. Olbrich, Infineon

AFM Topograph Tunnel current image, 1 µm scan, 0.5 pA

current scale

Field GateOxides

C-AFM measures sample topography and currentAllows current-voltage measurements

Scanning Probe MicroscopyScanning Probe MicroscopyScanning probes can have atomic resolutionConductive atomic force microscopy (C-AFM)

Sample flatnessCurrent-voltage

Scanning capacitance probeDoping profiles

Micro spreading resistanceDoping profiles

J.C. Lee and J.H. Chuang, Microelectr. Rel. 43, 1687 (2003)

AFM Topograph

AFM Current

Contact B

0.13 µm Technology

I ≠ 0

I = 0

High resistancelayer

Failure analysis made difficult by today’s ICs6 - 8 metal layersSmall feature size: < 0.1x0.1 µm2 gates, viasThin insulators: 10 - 20 Å

New materialsLow K dielectrics; Cu metallizationSilicon-on-insulator: tSi = 200 - 500 ÅStrained Si: composition, stress

Push existing characterization tools to the limitDevelop new tools

High resolution TEMProbe microscopy Picosecond emission microscopy

SummarySummary