Cu CMP Cleaning - Avsusergroups.org

Cu CMP CleaningAqueous, Alkaline ChemistryMarch 2002

Outline• Introduction• ESC Chemical Formulation Overview• Cleaning Requirements• SummaryFebruary 20022

Introduction• Focus is on developing a robust Cu CMP cleaningprocess that achieves the cleaning objectives with awide range of polishing processes• A two-step cleaning process has been studied tomeet these requirements.– Good results were observed initially– Since the writing of the paper issues appeared with a 2-step, high pH/low pH clean• Single-step cleaning process is desiredFebruary 20023

Versatility in Cu Processing• ESC has developed alkalinechemical formulations that areversatile enough to be used formany Cu integration applications– Post-CMP cleaning– Post-Etch Cleaning– Miscellaneous cleans• In Cu processing applications,the main concern is particle andresidue removal withoutcorrosion of the bulk Cu andother exposed films• Base formula can be customizedbased on requirementsPost-CMPCleanMiscellaneousCleansPost-EtchCleanApplication region that is addressedby the “base chemistry”February 20024

ESC Chemical Formulations• Base Formulation- ESC 784– High pH (>10) with buffering agent– Oxygen scavenger– Provides some chelating effect– Aqueous solution (>80% water) that is easily diluted• Customization using optional additives– Surfactants– Fluorides– Solvents– Chelating agents– Additional corrosion inhibitors• Process Flexibility– Time, Temperature, Tool and ConcentrationFebruary 20025

Particle Removal• Defect counts afterblanket Cu CMP toTEOS.• 25-wafer lot testedLPD's >0.2µm (Tencor 6420)10080604020ESC 784 (average = 15.1)0135791113151719212325Wafer IDFebruary 20027

Cu CompatibilityESC Products include proprietary Cu inhibitors thatare effective in preventing Cu corrosionUntreated showing CMP contaminationTreated w/ ESC 784 solution(ambient, 30 sec, 20:1)February 20028

Cu Etch Rate for Post-CMP10Cu Etch Rate vs. Concentration4-Point Probe DataEtch Rate (Å/min)8642784 @ 22˚C784 @ 50˚C00% 20% 40% 60% 80% 100%Concentration (wt. %)February 20029

2-Step Clean• A 2-step clean, high pHfollowed by low pH,shows good Cucontamination removal• Evidence from leakagecurrent data• However, damage tofront-end devicesreported compared toone-step, high pH clean• Also, unique corrosiondefect observedCumulative Probability100908070605040302010010.90.80.70.6Normalized DataESC 784 + MR10ESC 784 onlyESC 784 + ElectracleanESC 784 + DHF0.5February 200210

Corrosion Defect• Cu corrosion defectseen with 2-stepcleaning process• Observed at severalcustomers withdifferent chemistries• High pH, followed bylow pH in each case• High pH-only and lowpH-only do not createthis defectFebruary 200211

1-Step, High pH Clean• Several customers have qualified ESC 784 as asingle-chemistry clean• Cu contamination level has been demonstrated to bewithin spec without additional cleaning steps• Development of improved chelating efficacy toaddress future needs for Cu contamination levelsand to increase the CMP process windowFebruary 200212

ESC 784 vs. TMAHDefects on Patterned Cu/Oxide Waferafter CMP Process300Cu Concentration on DielectricSurface Following Cu CMP Processon Patterned Wafers1,000Average # ofdefects250200150100Processed in SprayToolProcessed inDouble-sided ScrubberAtoms/cm 2 x E 10TOF-SIMS100500TMAH ESC 784 DIW TMAH ESC 78410DIW TMAH ESC 784• ESC 784 shows better particle removal performance without mechanicalassistance• ESC 784 shows slightly better particle removal performance in scrubberprocess• ESC 784 shows significantly better Cu contamination removal performanceFebruary 200213

Applied MIRRA MESA Data• Customer SPCdata154-Week Patterned WaferProcess Data for ESC 784• Patterned wafertested daily forparticle defects• One-chemicalclean with 784only on brushesin Mesa cleanerDefects (KLA)1050032 21420 021210120 020 0 01 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28212031DaysFebruary 200214

Preliminary Data on Modified Formulation• TEOS wafercontaminated withCuCl solution• 782 is 784 withchelating agent added• Encouragingpreliminary results• Further testing ofproduct wafersscheduledAtoms/cm 2 x E 101.E+161.E+151.E+141.E+131.E+121.E+111.E+101.E+09PrePostMR-10 / 784 782-A 782-B 782-CFebruary 200215

BTA Removal• BTA is typically used between the polish processand the cleaning step.• Removal is desired to prevent defects and increaseelectrical resistance.• High pH cleaning chemistries can remove BTA morereadily than low pH chemistries• XPS data demonstrates thisFebruary 200216

CMP Equipment Performance• Contact Cleaning– Double-sided scrubbers– “Disk-type” scrubbers• Non-Contact Cleaning– Single wafer megasonics– Batch megasonics• Single-pass chemistry is typical• Ambient temperature operation• No particle brush loading in scrubbers• Megasonic performance enhancement for particle removalFebruary 200217

CMP Equipment Supplier Experience• AMAT Mirra Mesa• Lam TERES• IPEC/Speed-Fam 776• Ebara• Verteq Goldfinger• Verteq Cobra VcS• DNS AS2000• Ontrak DSS/Synergy• FSI Mercury• SSEC ScrubberFebruary 200218

Megasonic Cleaning EnhancementStatic Cleaning Angle TestVerteq Goldfinger Megasonic SystemContaminated WaferMeasured Static Cleaning Angle120100806040200Solution A(pH 8)Oxalic Acid(pH 5.3)100:1 NH4OH(pH 11)Slurry ASlurry BSlurry CSolution B(pH 5)ESC 774(pH >11.0)GoldfingerMegasonicTransducerArea cleaned bychemical andmegasonic energyWafer is cleaned with megasonics andchemistry without wafer rotationArea not cleaned bychemical andmegasonic energyStatic AngleFebruary 200219

Cost of Ownership• 20:1 to 40:1 dilution– 10 - 30 ml of concentrate per wafer• No particle loading in brushes• Easily rinsed with DI water• 30-45 sec chemical process time can be performedin a single station with excellent results• Reduced waste treatment cost compared tofluorinated chemistriesFebruary 200220

CMP Cleaning Summary• Cleaning performance and cleaning processdependent on polish process and cleaning tool• Excellent particle removal performance• Good Cu contamination removal with excellent Cucompatibility• 1-step process is possible to replace 2-step processand its defect and yield issues• Successfully used with variety of process equipment• Low cost of ownershipFebruary 200221