An Analysis of Contact Resistance between Probe Tip and ...

1 An Analysis of Contact Resistance between Probe Tip and Gold PadChang Hoon. HyunSamsung Semiconductor Institute of TechnologyCompanyLogoContents Model of Probe Tip Contamination by Al Oxide Introduction to Gold Pad Structure Relationship of Fine Pitch and Resistance Contact Resistance of Gold Pad Work Function of Tip and Pad Materials Contact Resistance Measurement of Gold Pad (Rhenium Tungsten vs Platinum Tip) Summary1 Key Points Modeling of Ti Oxide Creation Probing Result of Fine Pitch Bump The Surface Analysis of Gold Pad Ohmic Heating by Work Function Difference Contact Resistance Measurement by ATE2 Model of Probe Tip Contamination by Al Oxide3 Conducting Metal to Metal a SpotsLocalized Joule Heating in a Spot Area during TestAl Oxide Film growth on Pad.

2 Probe Tip Contamination a Spot : Real Inter Metallic Contact AreaU : Voltage drop( U = Forcing Current Cres)Tbulk: Ambient Temperature : Temperature Coefficient of Resistivity : Resistivity at the Bulk Temperature : Thermal ConductivitySource : Jerry J. Broz, Probe Contact Resistance Variations during Elevated Temperature Wafer Test Test Conference,19994 Improve oxide films: Oxide film resistanceAcontact: Contact areaOxide Resistance ReductionOxide Film RestraintContact Area Expansion Al2O3 Removal (FAB Control) Storage in an Inert Mood Tip Surface Cleaning Probe materials Over drive ( Contact pressure ) Probe tip shapeResistance of Contact AreaModel of Probe Tip Contamination by Al Oxide5 Introduction to Gold Pad StructureWaferPad MetalGoldPassivationUBM Pad Material Aluminum UBM (Under Barrier Metal) For Adhesion ( between Pad Metal and Gold) Materials are Ti and W Gold Material Purity.

3 (20kV, X50k)Scope Image (X100)6 Relationship of Fine Pitch and ResistancePitch size or Width(um) Resistance ( )[um]PitchWidthWidth Tip Diameter3012~10259~10207~8155~6 : Diameter of Contact spotn: Number of Contact spotA. Relationship of a Spot Reduction and Cres What is Fine Pitch Gold Bump Pad? Pad Pitch : Under 30um Pad Width : Under 20um7 Relationship of Fine Pitch and ResistanceB. Experiment of Fine Pitch Probing 15um11umWidth:15umWidth:11um We made another Bump Width on Wafer Tip Diameter : 6um Yield Monitoring by using ATEP robing Direction25um10um(Pad to Pad)8 Relationship of Fine Pitch and ResistanceC. Experiment Result Number of Total Chips : Etch 1000 die Z Height : Electrical First Pass + 10um Needle Polish Paper : 3M AlO3 Lapping Film Cleaning T/D : 20 up downMeasurePad Width11um15umOpen Fail Ratio(Non Cleaning)93%87%Open Fail Ratio(Interval 50 Chip) Fail (SEC Standard)Bump BrokenStick Out9 Contact Resistance of Gold PadTiW Etching (by H2O2) Ti+TiO2 ( )TiW + 2H2O2 (TiO2 )+2H2O Step 1 : Reaction of between Ti and H2O2 Step 2.

4 Reabsorption of TiO2on Bump SurfaceWO52 (aq)Wafer Electrical TestProbe TipAu BumpClassificationTiTiO2 Resistivity ( cm) Constant Model of Probe Tip Contamination by Ti Oxide 10 Before ContactProbe TipBumpAfter ContactPad to Tip Touch CountResistance( )Oxide Film Absorption After Surface Cleaning(Same Situation to Aluminum) B. Resistance vs. Contact Count Contact Resistance of Gold Pad11 TiO2 TiC. ToF SIMS Analysis Finding of Insulation Ingredient TiO TiW + 2H2O2 (TiO2 )+2H2O Sputter Time (sec) Contact Resistance of Gold Pad12 Work Function of Tip & Pad MaterialsA. Relationship of Material s Work Function ClassificationWork Function ( ) [eV] ~ ~ (ReW) ~ ~ We had to needle cleaning on Gold bump pad when used ReW Tip Cleaning Interval : Average 35 Chip Card Life Time Reduction Wafer Moving Time Increase : 30~40 min/Wafer Production Loss Tip Material Change Cleaning Interval : 1 Time a Wafer Assumption : If Same Work Function of Function of Tip & Pad MaterialsB.

5 ReW or Pt Tip to Gold Pad Contact Fermi level (Pt) = (W) = level An Ohmic Contact is a junction between a metal anda smaller work function metal Joule heating, also known as ohmic heating and resistive heating If eVincrease, Ohmic heating will increase AuWRhenium TungstenPlatinumFermi level ElectronsPt (Au) = (Au) (W) = (Au) (W)AuAu (Au) (Pt) = (Au) (Pt)ElectronsElectrons14A. Tip Material Resistivity Measurement Contact Resistance Measurementof Gold Pad(ReW vs. Pt Tip)Tip MaterialResistance( )Resistivity(u cm)Rhenium sIssssIVVVVssIVssIV 212112121212;2112322332 cmIVs 2 VASource : D. K. Schroder, Semiconductor Material and Device Characterization , 3rd edition, 2006S = 50mmKEITHLEY 2750 / Cmpl V : / I = 100mA15B.

6 General Method Using DMM Prober Wafer Handler Pad to Tip Automatic Contact & Probing P 8 (TOKYO Electronics Ltd.) Source : Keithley 2750 Multimeter/Switch/Data Acquisition systemUp DownContact Resistance Measurementof Gold Pad(ReW vs Pt Tip)Deposited Gold(5um)Bare 10 50 100 Contact Resistance [ ]Number of Contacts [X1000]Sample 01 Sample 02 Sample 03 Sample 10 50 100 Contact Resistance [ ]Number of Contacts [X1000]Sample 01 Sample 02 Sample 03 Sample 0416C. Measurement Result (DMM)ReW TipPt TipContact Resistance Measurementof Gold Pad(ReW vs Pt Tip) Measurement Condition Sample : 5um Gold Deposition on 8 Bare Wafer Touch down : 100,000 Cmpl = 1V, I = 10mA, Over Drive = 30um 17 ATE (Electrical Tester) For Testing DC & Function Source Chip GO NOGO Judge(Good or Fail) TS6700 (YOGOGAWA Co.)

7 The General Tester For Testing of Display Drive IC(DDI) Wafer Prober Wafer Handler Pad to Tip Automatic Contact & Probing UF200 (TOKYO SEIMITSU Co.) D. Automatic Tester Equipment (ATE) used for the Fist Resistance Measurementof Gold Pad(ReW vs Pt Tip)18E. Measurement Using ATE Contact Test This Item is more important than others Good Contact Good Signal Conduction Using Protection Diode This test method is so general When using the under diode, negative current was pulled from tester DC source It is principle of ISVM(Current Source Voltage Measure) Current Voltage V IR Ohm s Law I = 2mA (I1= 3mA, I2=5mA) Contact Resistance Measurementof Gold Pad(ReW vs Pt Tip)19F. Measurement Result (ATE)01020304050012345 Contact Resistance [ ]Number of Contacts [X100]Sample 01 Sample 02 Sample 03 Sample 0401020304050012345 Contact Resistance [ ]Number of Contacts [X100]Sample 01 Sample 02 Sample 03 Sample 04 ReW TipPt TipContact Resistance Measurementof Gold Pad(ReW vs Pt Tip) Cresincreases linearly This Situation is same as Al pad The cause is Ti oxide Cresis Stable Platinum and Gold are similar characteristics Why is Ti Oxide not affected ?

8 20 Variation of Contact Resistance with number of prior contacts for constant of 30umand copper specimen60um01020304050012345 Contact Resistance [ ]Number of Contacts [X100]Sample 01 Sample 02 Sample 03 Sample 04 Using ATE (Circuit Resistance include) The result is resemblanceSource : D. S. Liu, Measurement and Analysis of Contact Resistance in wafer Probe testing , 3rd edition, Microelectronics Reliability 2006 Comparing of Other Results30umContinuous Probing Result (ReW vs Pt)2101020304050607080110120130140150160 170180190110011101120113011401 PIN_01 PIN_02 PIN_03 PIN_040102030405060708011012013014015016 0170180190110011101120113011401 PIN_01 PIN_02 PIN_03 PIN_04 ChipPIN_01 PIN_03 PIN_02 PIN_04 Platinum TipRhenium Tungsten TipThe Method of Reduced Cres TiO2 Removal (FAB Control) Storage in an Inert mood Tip Surface Cleaning ( Card Loss)

9 Need with the same aProbe tip material22 Summary We discovered a Ti oxide film as studied in Al oxide has similar characteristics by ToF SIMS Analysis The Contact Resistance tendency of Gold pad resembles Al pad There is advantage that the measurement using ATE get function & Resistance data together Platinum Probe card showed a good result in Gold pad When Probe card material is chosen, The work function must be carefully investigatedNext Steps Need to a method to remove the Ti oxide film As a solder bump business increases, we will study solder bump pad deeply23 Acknowledgements Samsung Bump Process Engineering Team> Yong Ho. Kim (Senior engineer) Teaching Professor in SSIT> Jeong Taek. Kong (General Director)> Hyun Ho. Park Ph. D. Will Technology Engineering Team24 Thank You.