lab manual by dr lo

8/7/2019 lab manual by Dr Lo

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LaboratoryManual

bv Dr V.C.Lo


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Tableof ContentsA. Wire bond strengh testingB. Investigationof drifting of parametersusing curve tracerC. Investigationof ionic coDtaminationin MOSFET usingCV plotD. Eiectromigrationfailures*

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fi Wire Bond Strength Tester

Objective: to performth e wire bond strensthtestinsApparatus:1. TUI uire bondstrengthtester(9101-00),s'ilh differentpull-gauges,packageopener.2 . Var iousmetalcanpacka-eebipolar junct iontransis tors3. Optical microscopeand a glassmagnifier.

Int roduct ion:

The Wire BondStrengthtestercanperformsthe standardmeasurementin accordancervithMIL-STD-45662.lt consistsofa pull gauge,anactualor,a stoPscrewanda dashpotProcedure:l. open thecovefof the metalcanpackageof thetestsample.For bestresult,youshould

nor applyroo much forcein the blade,so that the can rotatealongthe blade.Slightlyincreasetheforce,untilthe can-coveris separatefromthebasemetalheader'2. Investigatethervire-bondconfigurationusingan opticalmicroscope.Make surethatthewiresarenotbroken.

3. Mountthetestsampleon thetop ofthe accessorychuck'4. Mountthepullgauge,startingfromthelowest$eight5. Adjustthepullingarm by thescrew',sotharit ishorizontal'6. Insenrhepullingkook rorhervirebeingtesledusinga microscopeanda forceps.7. For besrperformance,therensionof thervireshouldbe increasedgradually.Adjustthe

pulling speedusingrhe adjusrablescrervof the dashpotal the bonom of the tester.


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Clockwiseadjustmentis fo r slowerpulling speed,andcounter-clockwiseadjustmentisfor fasterspeed.

8. To stad the testing,turntheactualorknobclockrvise.It shouldbe fastenoughsothat thedashpotdeterminesthetruetestingspeed.

9. If the wire still anachesro the bond, the pulling force is still belowthe wire bondstrength.Replacea gaugewith a largerscale.

10.Repeat8 until thebondis broken,Ricordthe readingat thegauge.I l- Investigatethe rvirebeingtesredusingtheopticalmicroscope.Makesurethatit is indeed

broken.12 .Calculatethe tensilestrengthof thealuminumwire,thediamereris 3gm.

Questions:1. \Vhatis the failuresite(fractureposition)?2. Supposeyou want to ensurethat the fracturepositionis at the wire bond-metallization

interface,what mustbetherequirement(s)on the wire?3. \Yhatarethe potentialcausesthatdeterioratethe rvirebondstrenglh?


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B Investigation of Drifting of Parametersusing the Curve TracerObjective:I . to study the operadonofthe curveEacet and2. to investigatethe drifu of parametersof elecrroniccomponelts due to various ambientconditionsApparatus:1. Teltronic Curve Tracer 577-177-Dl *.ith 013-0lll-00. 013-0098-01and 178 testfi;cures.2- Variouselecfonic componentsurder test:6 x lk ohms resistors.6 x diodes,6 x Zenerdiodes5 x npnplastic packageBIT6x p-A.74i linar OP Alv{PThey are divided into tlree groups, eachgroup has trvo identical compone s for resistors,drodes,tansistors and OPAMP. Thete$ conditionsare:a. Under200oC24 hoursheatingin vacuurn:ff'V)b. Under100%RH in saltchamberfor 24 hours(RS) L S ? ot?c. As-receivedwithout any additional lrearnents.

Notesto the investigators:Reliabilityproblems in eleclronic componentsare of stafittical narure. Verydtfierent resuhsmay beobtained even with identical treatmentsand measuremenlt.Similar results might alsobe obtainedeven under difierent conditions.A conclusioncan only be drawn by testing abalch of samples,and evaluate their statisfical values,For the limit of time, this experimentonly serveslo demonstratethemelhodologt andprinciple-Procedure:Priliminary Settings:l. Mountthe test fi>.tue 0i3-0l l l-00 intothe right handside ofthe accessoryconDecrorsof577-177 Dl curvetracer.2. Mounta 1 kohms resistor at the adaptorclips.3. Adjust the INTENSITY, FOCUS, aad BRIGHTNESS settings so thar the be:m spo!

visibility is sharp and clear.4. Setthe following settiags:STORE(upper): "out"positionflower): "out"positiotrERASE(upper): either posirion(lorver): eitler positionSTEPFAMILY: (REP) pushedinSTEPRATE: Q'IORM) PushedinSTEP/OFFSETPOLARITY: CNORM) pushediaOFFSETZERO pushedinSEtl ,]a. l PUSneOrn

STEP/OFFSETAMPL I nA/DIVNUI\{BER OF STEPS I (counter-clock$ise)


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MAXPEAKVOLTS 25\4AXPEAK POWER'*'ATTS O.i5SEzuESRESISTOR 2KCOLLECTORSI.]PPLYPOLARIry ACVARIABLECOLLECTOR% OX l0 HORIZ N{AGPLIL pushedinHORZVOLTS,DTV 2OOCOLLECTORVOLTSDISPLAYIN\,ERT QtlORM): pushediaDISPLAYFILTER(NORM): pushedin\IERTICAI SENSITMry I nA/DIVXlO\ERT NLA.GPULL pushedinEMITIER GROI.N{DEDBASETERM STEPGENLEFT-RIGI{ITOGGLESWTICH "of' (centerposition)5. Centerthebeamspotat thecenrerof thegratitude.Tesring th: re


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Testjngthe Breakdor'"nvoltage of a Zenerdiodei. Replace the diodesith aZener diode.2. Center the beam spot at the ceffer of rhe gratitude. Set the COLLECTOR POLARITY to3. Tum the LEFT-RIGHT SWITCH to RIGHT position, and slo*'ly increasethe collecrorvoitage, until the follo*ing curve is observed. This is the tvpical [V cha.racteristic curve of

a Zener diode.4. Compare *re Zenerbreakdosl voltages undervarious conditicns.Testingth e orrtJrutcharactetiqticnln tri lolarjuiaion transisofr1. Remove the drodeadaptor(013-0il l-00) uith the tansistor test fixture (013-0098-01),

sel the system in the follorlintg settings:LEFT-RIGFIT CenterOFFSET MIILT 0 (ccw)OFFSET (zero) pushedinOFFSETHORIZ VOLTS/DW ]V/DIV COLLECTORVOLTSCOLLECTORSUPPLYPOLARITY: '+ 'VARIABLECOLLECTOR% 0(ccx)\TERTIC{ SENSITMry imA./DIV\IAXPEAKVOLTS 25I\[AX PEAK?OWER -I5NUN{NBER OF STEPS I (ccw)STEP/OFFSETAMPL 0.5 AJDN2. lvlount a npn transistor i o oneofthe right uaasistor sockets.3. Turn the LEFT-RIGHI SWITCH to RIGHT position, and slowly increasethe collectorvoltage to up to l0 volts. Turn the STEP/OFFSETAMPL clockwise, until a slep appearson the ouput characteristiccurve.4. Turn the NIIMBER OF STEPSto 10.

5. Calcr:latethe forward currentgain F=AIc /dle oftle transistor.6. Set the terrniaal selestorswitch to EMITTER GROIJNDED BASE TERM OPEN (OREXT).7. Measurethe breakdorvncollector to emitter voltage(with base open circuit).8. Set the terminal selectors*itch to EMITTER GROTINDEDBASE TERM SHORT.9. Measurethe breakdorvncollectorto emittervoltage(with baseground).10. Comparethe forn'ard currentg'i"s and breakdonn voluges under different conditioDs.F -d"eaz1u11r3ljc.q)1. Removethe 177StandardTestFixture,andreplaceby l7ELinear IC Test fi.xure.2. Centerthe beamspotby pressing'ZERO" button on the fourt paaelof the test fixture,

and adjustthe horizontalandverticalpositionloobs.3. Setthe followirg settings:VARIABLE COLLECTOR% OCOLLECTORSTJPPLYPOLARITY ACMAXPEAKVOLTS 25N,[AXPEAK POWER O.I5+ SUPPLY 15-SUPPLY TRACK+SLJPPLY(cw)SOURCERESISTANCE 50OHMSLOAD RESIST.ANCE 50KOFANSDLTTSLIPPLY offpositionSWEEPFREQUENCY 0.01Hz, (ccw)HORIZVOLTS/DIV 5 COLLECTORVOLTS


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SWEEP AMPLITUDE firlly crvSTORE(upper): "in" position(lower): in" positionERASE(upper): "in" position(lower): "in" positionNIMBER OF STEPS: I (ccu)4. Selectthe FUNCTION srvitch to GAIN: it displays the dift'erential inpur volragesas x-axis, and output voltage as x axis. Measure the input differential vohage range that rheouput volr"ge remaim hnear.Mean sure also the output saturation voftage.5. From 4, determine the slopein the linear region, thus determinethe gain of the OP AMP.6. Comparettre pararnetersunder differcnt conditions.Q,'estions,l. Your answerlab repon shouldinclude tlregraphs for all componensunderall conditions,irrespeaive that thev aredifferent or nol.


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C Investigationof Ionic Contaminationin MOSFET usingCV PlotterObjective: to measurethe drift of tireshold voltagedue to the field inducedionicmigration of the MOS transistorsand henceto determinethe surfacedensityofthe ionic contamination.Apparafus: IBI\4,PC computer,PCL71I S ADC interfacingcard,SrandfordResearchSR720RLC meter,RS232Ccable.Samples:n-channelMOSFETiRF830,one as-received,two bum-inat 200'C for 24hours underconstant(t5V) DC bias at the gate,an d thensubjectro I00% RH3o/osaltspray for 24 hours.

Srudentsare requiredto bring a 1.441u1/3.5"floppyro storedata.Introduction:

MOSFET is an importaat elecrroniccomponentboth for analogand digitaiapplication.The t}reshold voltageV, at the gate electrodedeterminesthe conductingstateof the underlying channel,which in tum, determinesthe logic level.(Readersareadvisedto refer to "Physics o1[SemiconductorDevices",S M Sze,or "ModernMOSTechnolod' D G Ong" ) . The altemation of logic levels comprisesinformationerrors(soft or hard errors).There are many factorsthat have detrimentaleffecc on the tlresholdvoltage,such as radiation, packagedegradation,and ionic contaminatio!.In this experimEnt,we concenEateonly on the effect of ionic contamination.Its exisrenceis mainlyattributedto the following causes:

(a) The environment:watervaporanddustparticles;(b) Humal contact: sweat, saliv4 o! even a minute skin particles containscontaminationl(c) Processingmaterials:etchants,scribes,filrnaces,all introduceconlaminants;(d) Packaging materials: adhesives,and lead fiame comprisea major source ofcontamination;The commontypes of contaminationsare alkali ions such as Na=aadK', or halogenions suchas Cf. Na- is consideredto play the dominanteffectsTheremight be no immediate effectson the theshold voltageevenif the samplesurfaceis contaminated, if the ions are located onto the Al/SiO, interface.Thesubsequentheatingdue to theapplicationof current causestheseionsto migrate,fromone side to the other, underthe influence of the gatebias.The schematicdiagrambelorvshorvsthe typical sansarioinsideaa oxide layer:In orderto reduce the failure due the shift of threshold,the componentsshouldhave


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been passedthrough the screeningprocessbeforegoing out to the consumers/ciients-The screening involves acceleratingthe ionic migration '*.hich results in the changeof threshold voltage. The concentration of rhe contaminaars are estimated by thefollo'*'ing ways,

trC- l.aob't. n.utrol

a\ a\ r'\v, =-Ysq-a6.-YL-$*v* (1)' ( - ' ( - ( ' vo r vo rwhere Q.. is the space chargeon the depletion layer of the semiconductorsurface, Q, the fixed odde chargeinducedby the interfacewtaps, 0r theswface potential, Vvs the work function difference between metal andsemiconducotr,Co,the oxide capacitanceper unit area.In the plesenceofioniccontaminationN. (perunit area),locatingat the Si/SiO,interface,the thresholdvoltageis then modifiedby

nnn .Nvr'=-)ss-a6,-i .- i*Y*-s= Q)!o . uo r Lo . uo xThe presencebf the ionic contaminationis manifestedin the drift of thethresholdvoltageAVt, the differencebetweenone was as-receivedand the onethat has been contaminated.The total contamination canthen be evaluatedbv

Nc=-co,avr=-c",(v+- vr) (3)The values of Vr, Vrr and Co. cal be determinedfrom thehigh frequencyCVplot. The capacitanceC is expressedas

2c'?",lv- vFBlQNaE,

c(v,f)=

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i .Procedure

The layout of IM830 is as follow:

Insen the gateelectrodeto thepositiveterminalof the fixture of the RLC meter,u'hile the drain andsourceelectrodeare twisted together and insertedinto thenegativeterminal.In this coruection,the gatevoltage (Vp0) is positive2. Switch on the RLC meter,and the computer,inserta L.44W3.5" floppy intothe B drive of the PC.3. On the front panelof theRLC meter,switchthe PARAMETER settingin "C+R'.All othersettingsareautomaticallyselectedby the computerprogram:They are: Extemal biasing, Trigger Mode, Excitation frequency : l0OkHa Drivevoltage: 0.15,Ralge Hold is disabled,Display the Averagedvalue,the samplesize for the averagiagis 5, samplingrate is MED, the equivalentcircuit is series.

Qnterestedreadersale welcometo exploredthe detailedprogramcommandsandthe prograrnsourcecodein TURBO PASCAL).

3. At theDOS PromptC:>,activatethe ADC card by issuing the commandADCONJ

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ThesystemacrivatestheADC cardandat thesamerimegoesto thepathC:\ TP\TPU4. At this path, issuethe command

CvJ6. The systemnor,r'asksyou ro inpur the file namefor storingthe CV data-Pleaseinput the file nameincludingtheDrive a:rdpathnames.The filenameshouldalsodistinguishesthe forwardbiasto the reversedbias.For example,ifI want to savethe datain the flopp1'diskin B: drive,I uould input

B:FORWARDl.TXTJfor the forward bias data,and

B:REVERSEl.TXTJfor the reversebias. Thedatafile is in thefollowing format:

(Biasvoltagein [V]), (Capacitancein ([pF])

The biasing volta,eewill be automatically increasedby the program via theADC card in stepof 0.05Vfrom 0V to +5V.Press key to start the measurement.The systemthen prompts you torevert the polarity of the biasingvoltage,DO NOT REVERT THE POLARITYOF THE BIASING VOLTAGEAT THE REAR TERMILAS, it *ill damagetheinstrument. Instead,put the Gate electrodeat the negative fixture, and theDrain and Source at rhe positive Fixture. Press and repeat themeasuremeDt.

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Questions

For better noise reduction,it is desirabletotimes. You can use another filenamesREVERSE2.TXT, FORWARD3.TXT...etc.Repeatthe measurementfor all threesamples.After the CV measurement,you can import the datafile using Microsoft Excel,or other spreadsheetsoftwares.For a given biasingvoltage,take the averagevaluefrom theseveralfiles.Plot the CV curvesof the threesampleson the sanregraph.Determine AV, ,Co,from the graph-

repeal the measurementseveralsuch as FORWARD2.TXT.

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l Determine C"..,andN. of thestressedsamples.Are there ary restrictionson the drivevoltage, excitationfrequency?\\rhat arethey?Does our instrumentmeetall the requirements?

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D Investigation of Electromigration Failures in a Thin Conducting Film

Objective:to investigatethecracksandhiliocksin aa aluminumcondrrctorwhich hasbeenstressunderelectromigration.

Apparatus:Optical microscopewith 35 mm camera.Samples:aluminumconductingfilmson siliconsubstrate.Theory:

Electromigrationcomprisesone of the imporrant reliabiliry issues inmodem microelectronics.As the feature length is shrinking, thismechanism becomesvery pronounced. The failure is causedby thedraggingof positiveionsby the flowingelectronsundertheinfluenceofanexternal bias.The influenceis called electronicforce. The electromierationinducedflow of the ionscanthenbe expressedas:Jev= NPZ'E ( l )

There are two driving forces, namely, the field ion force as a positivechargeis drivenby an electricfield, and the "electron windforce" q'hjch isopposedto the electricfield. The analogy of the secondforce is like themovementof a floating ball underthe inJluenceof a flo*ing stream.Forcotnmon thin metallic films used in microelectronic componentssuch asgold and aluminum,the seconddriving force, electron windforce, bas ahigher influenceon the ions, so that Z' is negative.Tbis movementof ionsby the electron wind force comprises the failure mecbanism inelecuomigration.Thereareseveralfluxesofions insidethe conductor,J", = Jo,,r+ JE!{+Jr +J5,where the J's represents, respectively, the diffrrsion flux, theelectromigrationflux, the thermomigrationflux, and tle back flux causedby stressgradient.In usualcase,only the first two termsare dominant.Theactualtemporalevolutionofions at everypoint in the conductoris govenedby the drift-diffusionequationasA N d l d ( ; N ) av : r - - - J ! o ' = " l 5 " t ' l - i ( v , . ' , x ) ( 3 )a ax ^\ 'ax) a\ .D" ' ,

whereVo = prZ-Ethe drift velocityof ions.For an reliability engineering,or as an failure analysisprocedure,it is

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required firstly to document(or to identifl') the failure mode, whichmarifestsin undesirableelectricalcharacterisrics.ln the presentof a fluxdivergence,which may be arisenfrom one of the following causes:(i)tbmperatureor current density inhomoseneities,(ii) bimodal granularsturctules,(iii) the interfacecomecting the rransponfrom oneconductortothe other,and(iv) neckingat the oxide srepu'herethe crosssectionalareaabruptlydecreases.The failuremodesinc.ludethe opencircuitfailurewherethe discontinuitvultimarelyleadsto 1.hedeplerionof hosratoms,or a sbortcircuit whereaccumulationoccurs.The fai lure modecaabe obsen'ableorverified by locating the presenceof failure defects.The depletion ofcracking can be identified by the voids, or continuouscrack acrosstheconductorwidth. On the otherhand,the accumularionmanifestsas hillocksandextrusion.Thepresenceof defectscanalu'a1'sby locatedby microscope.in general, in a failure analysis,one has to identify the failure rnode, tolocateor to obseryethe faiiuredefectsu'hich is relatedto thefailuremode.Then, one has to hypothesizethe causeof failure by suggestinga failuremechanism, which involves the knowledge ard materialsscience andphysicalbackground.Ifthis pictureis consistence,thenonemightsuggestamethodto improve or to avoid the failure.

depletion

accumulation-ai dummy

Becausefailure processis a dme-consumingprocess,it takesseveral daysto have a conductorfailed, evenat high currentdensity.in this experiment,we only observedthe failure defects, instead of simulating the failureprocess.You are askedto idendfy the defects.Observethemwith respecttotheir positions in a conductor. The sample is the aluminurn tbin filmconductor depositedonto a silicon substrate(as in the abovemask pattem).The conductorpanernswere developedusing conventionphotolithographicmethod.There is one dunmy neighboringto the suessedsample.They areidentical in all preparation proceduresand heat ueatrnent.The stressedsampiewas undera constantDC currentat the order of I lv!d/cm?at abouti 00 to I 50"C.The stressing\\'asDerformedin a vacuurnoven.

Procedure1. Mountthe sampleontothe opticalmicroscopestage.Locatethe dummy on thefield of v iew, using a lo*' magnification(X I 00). Increasethe magnificationI 0

abourX400. Take a picture in this magnification at the contactpad/conductorinterface.

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Locate the cathode side of the stressed conductor using low magnification.Identify the defectscaused by depletion. Then rum to high magnification (aboutX400), and take a picture. Characterizethe defect size by moving the samplestage-Move along the conductor until to the anode end. Describe what you observedin your own word. Take a picture in high magnification showing the importantfeature.

4- At the anodeend,locatethe defectcausedby accumulation.Take a pictureusinga highmagnification(X400).5. Recordthe date,names,positionof the picrure(anode,carhode,dummy, midd.leof the conductoretc) in the recordsheetprovidedby the rechnician.The pictureswill be availableto you oncerhe film has beendeveloped.You shouldtake arleastfour, but not rnorethaasix picnres.Sincethereare twc participantsin every

group.You aresuggestedto userhe scannerin CD620 !o capturethe picturesinTiF , BMP , GIF or JPG files.Embeddedthe pictures(in picnuefiles) in your labqu"rtioo*1. Describein your orvnwordswhatdid you observein eachpicrure?2. Voids or cracks canbe generatedby other causessuch as evaporationinto thevacuun. How cal you concludethat the presentdefects causedby depletionarereallythe resultof electomigration?3. Explain the causeofthe flux divergencein thesamples.4. Insteadof using themicroscope,$'hatother methodscan be usedto characterizelhe in-situ electromierationeffect?

lab manual by dr lo

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