WET工藝介紹

1、WETWET工藝介紹工藝介紹 LNLN234Wet Cleaning (Pre-treatment)Wet Cleaning (Post-treatment)Resist RemovalDiffusionCVDPVDLithographyEtchingDopingWafer InWafer OutIC Processing5Wet Process1.FEOL post-ash clean35%- typical SPM.- trend is to integrate resist striping and cleaning.2.Pre-diffusion clean30%- RCA clean

2、- trend is to use dilute chemistries to reduce cost, improve equipment reliability and process performance.3.BEOL post-etch clean20%- issues with technical, cost, environment- trend is to use single wafer dry clean4.Others (Post CMP and special cleaning)15%- SC1 based cleaning6 ChemicalName H2O (DI)

3、De-Ionized water H2SO4Sulfuric Acid H2O2Hydrogen Peroxide H2O Water HF Hydrofluoric Acid NH4OH Ammonium Hydroxide HCl Hydrochloric Acid IPAIsopropyl alcohol O3Ozone H3PO4Phosphoric AcidChemicals Involved7Wet bench 89 Purpose of Pre-clean is to remove the last unwanted oxide layer and prepare surface

4、 free of metallic contaminants and good PC for next oxidation.Pre-diffusion clean - RCA cleanH2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinseH2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC10SiO2( s ) + 6HF( l ) H2SiF6( l ) + 2H2O( l ) The etch rate (or reaction rate of

5、HF with oxide) can be slowed by adding more water and lowers the concentration of HF. HF will etch BPSG Oxide Nit Si H2O:HF 100:1 (50: 1, 49%) Function : Remove Oxide(SiO2) Mechanism: Reacts with Oxide and form a solvable byproduct.Oxide Etch HFH2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinse

6、H2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC11Etching off native oxide leaving hydrophobic Si surface, repels H2O, that is prone to H2O markAs a method to passivate surface, H2O2/SC1/SC2 last is used.After cleaning HF on Si, the Si wafer has H2SiF6= it is charged up with Si

7、F6 2- ions = this has high affinity to attract defects, due to strong polarity.12 What is H2O mark?It is some H2O stain which oxidises the Si surface. It can also be a concentration of H2O contaminants.H2O attracted area easy to create H2O markoxoxSi wafer13What is the impact of water mark?Water mar

8、k can cause problems with adhesion of films, contact resistance, non-uniformity between conducting layers, block etch, gate oxide defects.How to prevent it?Treat the wafer surface with eg.H2O2, SC1,SC2 (some oxidation effects) to ensure hydrophilic surface throughout.Ensure dryers performanceVapor J

9、et dryerLow pressure DryerSpin DryerMicro Mist Dryer14 DI water is De-ionized water. Tap waterNa+Cl-Na+K+K+Cl- F- F-Water Rinse: DI WaterDe-ionized waterH2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinseH2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC15DIW tank is for rins

10、ing wafer as clean as possible before going into the next chemical tank to prevent cross-contamination or before leaving the hood.DIW can overflow or quick dump rinse (QDR). Overflow is very stable flow of DIW and gives good PC control. It makes use of diffusion and dilution. QDR, on the other hand

11、makes use of extra drag force when DIW dump & it is fast at removing acid trace, but since there is more agitation in the tank, it may result in higher PC. Control of the DIW tank and surrounding cleanliness is important.DIW tank overflows at all times with by-pass flow to prevent bacteria. Bact

12、eria will result in PC & metallic contamination.DIW Tank16DIW can be hot or cold - depends on previous and next tanks.Hot Chemical will be followed by Hot DIW/Cold DIW; this is to prevent thermal shock. For high viscosity chemical, HDIW rinse will improve solubility of the chemical, thus improve

13、 the diffusion of chemical to bulk of DIW, this improves the rinse efficiency.There is also the DIW Megasonic Tank (overflow or with quick dump rinse). The extra Megasonic power helps particle reduction and improves rinsing efficiency especially for viscous chemical.DIW Tank17nDIW flow-rate.nProcess

14、 Time.nDump Cycle & Process Time for each sequence.nMegasonic On Sequence.Critical Parameters18 30C, NH4OH: H2O2:H2O (1:2:50) Function: Particle removal, Light polymer removal Mechanism: oxidation and electrical repulsion OxidationDissolutionSurface etchingElectrical repulsionOxidation mechanism

15、Electrical repulsion mechanismParticle clean SC1 (Standard clean 1)H2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinseH2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC19 SC1 with MegasonicTransducerTransducerTransducerPartial wettingSolvent diffusing at interfaceTotal wettin

16、gFloating free Benefit: enhance the particle remove rate. Drawback: H2O2 will be reduced during operation, which cause surface roughness!20 The mechanism producing the rough surface is the NH4OH acts as the etchant of the oxide while H2O2 acts as the oxidant: Surface Micro-roughness Si H2SiO42- (H3S

17、iO4-, HSiO43- etc)V1V2HO2-OH -Path-1Path-2OH -V3V1 = k1HO2-3 k1=1.2x1014 (65C)V2 = k2OH- k2=5970 (65C)V3= k3OH-2 k3=2.0 x109 (65C)Path-1Path-2Si Substrate21Methods of reducing the microroughness can be summarized as:nReduce the proportion of NH4OH ( the etchant)nReduce the temperature of the bathnRe

18、duce the cleaning timevConventional SC1: (1:1:5), 7080C22NH4OH evaporate & H2O2 decomposes with usage and timeNH4OH lost in one hour: 32% at 50; 44% at 70H2O2 decomposition is a strong function of metal ion contentSC1 Bath Life Problems:23Heater Burnt - Inline heater is made of Quartz and SC1 et

19、ches Si, thus inline heater has lifetime. If burnt and leaking, there can be metal contaminations like AL and Fe.NH4OH and H2O2 will degrade and cause bubbling, may result in streak defects on the waferCommon Issues with SC124To get rid of bubbles :Tilt wafer to face back m/c.Slight agitation of waf

20、ers to release bubble from wafer surface m/c.Bubble collapser/degaser.PFBubble DegasserfilterPumpinOuter weir filtered liquidBubble DegaserCommon Issues with SC125 30C, HCl: H2O2:H2O Function: Ionic and Metallic Contamination Removal Metallic clean SC2 (Standard clean 2) Mechanism: HCL reacts with m

21、etal to form a soluble salt which is removed from wafer surface by dissolving in H2O. As far as H2O2, it passivity the active surface.H2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinseH2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC26 HCl & H2O2 are not easy to be prod

22、uced to be ultraclean and as such, the chemical itself have some metallic. When diluted SC2 is used, metallic from wafer can still be removed and the chemical also has less metallic to deposit on the wafer. This is the best scenario. - Cleanup is not always removing defects/contaminants; it depends

23、on who is dirtier - Diffusion principle : movement of solutes from higher concentration to lower concentration until equilibrium.Problem with SC227Dryer Isopropyl Alcohol (IPA) Function : removes water from wafers Mechanism: Alcohol vapors displace water from surfaceIPA VaporsDrop ofwaterIPA displac

24、es waterIPA evaporates The alcohol evaporates more easily than water. It leaves a dry surfaceCleaningH2O: H2O2 : NH4OH(50:2:1)30oCH2O RinseRoom TempH2ORinseH2O: H2O2 : HCl(50:1:1)30oCH2O RinseRoom TempDryerH2O : HF(100: 1)23oC28HF + H3PO4 (Phosphoric Acid)Function: AA nitride strip after growing iso

25、lation oxideNitride Remove29E tc h ra tec o n c e n tra tio n8 7 %b o ilin g1 6 00C c o n sta n tE tc h ra tec o n c e n tra tio n8 7 %b o ilin g1 6 00C c o n sta n tNitride etch rate in H3PO4 At 1600C, H3PO4 is 87% at boiling point. Original chemical concentration = 86% As the chemical heats up, DI

26、W spikes in to maintain chemical % - boils at 1600C - optimal etch rate30SMSDIW spikeSESBest Process Control NISSO System.DIW spikeDIW spikeOld DNSMay result in wafer cross slot due to water super boil.DIW spiking position and control are critical for optimal process.Nitride Remove31Mechanism: Si3N4

27、 + 6H2O - 3SiO2 + 4NH3 (H3PO4 as catalyst)0.11101000100200104105106107ER A/minSi Conc. (ppm)Particle (#/ml,0.2um)SiNSiO2ParticleNitride Remove32When the Silicon content is very high, oxide etch rate decreases. Silicon may even re-deposit on wafer and trap some H3PO4. If this Phos is implanted/driven

28、 into the wafer, it will give extra “n type which may lead to leaky Field Oxide and poor GOI.In order to stabilize the etch loss of oxide, for the 2 H3PO4 tank process time, Tank 1 time is set to remove all the Nitride while Tank 2 takes care of the overetch.As a result, the Tank 2 oxide etchrate is

29、 more stable which leads to better oxide remains control.33Oxynitride/oxidePad Oxide RemainPad Oxide Remain7070757580808585909095951001001 18 815152222292936364343505057576464Run No.Run No.Thickness (A)Thickness (A)AA SiN100A Pad OxideHF dipAA SiN100A Pad OxideHPO 1100A Pad OxideHPO 2 AA SiN Strip P

30、rocess for CM71DRAM Pad Oxide RemainedHPO lifetime dependent!(Recipe NLH240AHPO2550ASC1M)34SPM(Sulfuric Peroxide Mixture) 98%H2SO4 : 30% H2O2 = 5 : 1, 125C Caros acid / SPM / Piranha Function: Photo-resist stripping Organic contamination removal Mechanism: H2SO4 + H2O2 HO-(SO2)-O-OH + H2O HO-(SO2)-O

31、-OH + -(CH2)n CO2 + H2O Use hot QDR (Quick Dump Rinse) with mega-sonic to rinse off viscous H2SO4 on wafers 35STAGESEQSTEP DESCRIPTIONWORK AREARECIPEAA-PHOTO260AA PHOTOPHOTODS7000CIH3A003700.120AAAA-PHOTO270AA CD-PHPHOTOP003700_120APAA-PHOTO280AA ADIPHOTOP003700_120A1AA-PHOTO290AA PHOTO KLA DEFECT I

32、NSPECTIONPHOTO0037A_AA_PHAA-ET300AA SIN ETCHETCHPDR20-AA02AA-ET310AA ASHETCHPAFB1S0AA-ET320AA WET RESIST STRIPDIFFNDH10APRRMMAA-ET330AA cleanDIFFNSC1MAA-ET340AA CD-ETETCH0037A_120AEAA-ET350AA AEIETCHAE01AA-ET360AA ETCH KLA DEFECT INSPECTIONPHOTO0037A_AA_ET Recipe for PR Strip NDH10APRRMM: DHF(100:1)

33、 15 + SPM 5+SPM5+HQDR(with Mega)STAGESEQSTEP DESCRIPTIONAREARECIPENLDD2-PHOTO11200NLDD-2 PHOTOPHOTO$RPHNLHNLDD2-PHOTO11210NLDD-2 ADIPHOTO$RPHNLHNLDD2-IMP11220NLDD-2 IMPIMPP075K35E3T45R400NLDD2-STRIP11230PLASMA PR STRIPETCHPAFB1S0-HINLDD2-STRIP11240PR STRIPDIFFNPRRMNLDD2-STRIP11250NLDD-2 ASIETCHAE01

34、NPRRM: SPM 5+SPM5+HQDR(w/o Mega)36BOE (Buffered Oxide Etch) 23C,Mixture of 40%NH4F and 49%HF SMIC define MB:BOE(10:1), LB:BOE(130:1:7), DB:BOE(200:1) Surfactants are often added to improve wetting Benefit compared to DHF: 1) Low selectivity oxide etch for DRAM contact pre-clean 2) Prevent photo resi

35、st liftoff for KV, Dual gate process For BOE etch with PR on wafers, S/D or Marangoni is used for drying37SiO2 / BPSG etching mechanism SiO2 is mainly etched by HF2- SiO2 + 2HF2- + 2H3O+ SiF4 + 4H2OSiF4 + 2HF H2SiF6 (in HF solution)SiF4 + 2NH4F (NH4)2SiF6 (in BOE solution)BPSG is mainly etched by HF

36、 B2O3 + 6HF 2BF3 + 3H2O38BPSG /SiO2 etching selectivity controlNH4F , BPSG/SiO2 NH4F NH4+ + F-HF H+ + F- K1=H+F-/HF=0.00068 HF + F- HF2- K2=HFF-/HF2-=0.193NH4F concentration (mol/Kg)Etch rate at 25C (A/min)39DHF pre-clean for Poly depOxide AOxide BOxide CFilmE/R(A/min)Sel.E/R(A/min)Sel.E/R(A/min)Sel

37、.E/R(A/min)Sel.Thermal Ox28.71.0056.51.0048.51.00201.11.00PETEOS82.72.89170.93.0275.51.56427.22.12B36P65, 800flow 20min304.210.62557.19.8588.81.83314.41.56HDP + 1100Annl. 30min31.61.1060.11.0650.91.05217.91.08F-poly0.60.0211.00.01821.50.4415.40.077Doped A-Si (1.15E21)2.40.0832.20.04017.90.3716.90.08

38、4SiN4.011.80.044.10.02HF(100:1)HF(50:1)BOE(200:1)FilmE/R(A/min)Sel.E/R(A/min)Sel.E/R(A/min)Sel.E/R(A/min)Sel.Thermal Ox28.71.0056.51.0048.51.00201.11.00PETEOS82.72.89170.93.0275.51.56427.22.12B36P65, 800flow 20min304.210.62557.19.8588.81.83314.41.56HDP + 1100Annl. 30min31.61.1060.11.0650.9

39、1.05217.91.08F-poly0.60.0211.00.01821.50.4415.40.077Doped A-Si (1.15E21)2.40.0832.20.04017.90.3716.90.084SiN4.011.80.044.10.02HF(100:1)HF(50:1)BOE(200:1)40ACT940 is used to remove Plasma cured photoresist Hard crest of side-wall polymer Cl- ions trapped in the side-wall polymer/photoresist

40、O3/plasma Ashing PRS + PRS(photo resist strip) PSR(Post stripper rinse) DIW (dryer) Plasma Ashing: remove hard-cured photoresist (95-99%) PRS: remove side-wall polymer by reductive etch with NH2OH (HDA-Hydroxyl Amine)* PRS = ACT-690C; ACT-940; EKC-265; EKC-270, etc. PSR: neutralize amines; minimize

41、OH induced corrosion causing by uneven micro-etch in DI water rinse* PSR = NMP, IPA, etc.(PRS) ACT940 Solvent (1)41Metal etch post clean42VIA Etch post clean43Other Wet Etch Chemicals in SMIC 44Dryer IntroductionDryer is used to ensure that the DIW on the wafer is not evaporated but either displaced

42、 or physically removed.Presently there are following types of dryers in Fab7Spin dryer (S/D)VJD(Vapor Jet Dryer)LPD(Low pressure dryer)MMD (Micro Mist Dryer)45Spin DryerOn-Centre Type Off-Centre TypeCritical Parameters : Transfer Time (On-centre faster)Ramp up speedMax speedProcess TimeExhaustIonize

43、r46Standard Vapour DryerEither made of Quartz or Stainless Steel. IPA CondensateDrain PlateHeat Transfer AdhesiveHeater BlockIPACritical Parameters :Wafer transfer time from F/R to base of dryer 13sIPA recovery time 78oC after 30 sec.IPA DIW %B (Meniscus Geometry)IPA Decreases Surface TensionSurface

44、 Tension ABMARANGONI Force Liquid Flow from A to BWithdraw Wafer out of WaterResults in Dry and Clean Wafer Surface48Marangoni Dryer (1)49Marangoni Dryer (2)50Marangoni VaporEvaluation at Bare WaferSiSiO2H2OIPA Evaluation at Device ProcessororororBehavior of IPA on Wafer surface51LPD: low pressure d

45、ryer52Process Sequence of FL-820L(1)53Process Sequence of FL-820L(2)54Process Sequence of FL-820L(3)55Process Sequence of FL-820L(4)56FED2IPA grain： ：smallCarried N2： ：ManyIPA grain： ：bigCarried N2： ：fewIPA grain： ：smallCarried N2： ：fewIPAN2DIWCondensedIPA+N2 Supplyafter pick-upIPA+N2 Supplyafter pick-upIPA+N2 Supplyafter pick-upN2IPAIPA nonuniformityN2 doesnt enterIPA is hardlysupplied newlyN2 doesnt enterIPA is hardlysupplied newlyN2 enters.IPA is