2022年WET工艺介绍

1、WET Process IntroductionPurpose of Wet Cleaning ProcessThrough to a series of processes to make the wafers free from particles, organic contaminations, metal contamination, surface microroughness and native oxide using some kinds of chemicals including DIW.Purpose of Wet Cleaning ProcessFor Etching

2、process Oxide remove. Nitride remove. Photoresist & polymer remove. For Cleaning process Free of particles. Free of metal ion. Free of organic. Free of micro-roughness. Free of native oxide.Wet Cleaning (Pre-treatment)Wet Cleaning (Post-treatment)Resist RemovalDiffusionCVDPVDLithographyEtchingDoping

3、Wafer InWafer OutIC ProcessingWet Process1.FEOL post-ash clean35%- typical SPM.- trend is to integrate resist striping and cleaning.2.Pre-diffusion clean30%- RCA clean- trend is to use dilute chemistries to reduce cost, improve equipment reliability and process performance.3.BEOL post-etch clean20%-

4、 issues with technical, cost, environment- trend is to use single wafer dry clean4.Others (Post CMP and special cleaning)15%- SC1 based cleaningChemicals InvolvedWet bench Purpose of Pre-clean is to remove the last unwanted oxide layer and prepare surface free of metallic contaminants and good PC fo

5、r next oxidation.Pre-diffusion clean - RCA cleanSiO2( s ) + 6HF( l ) H2SiF6( l ) + 2H2O( l )The etch rate (or reaction rate of HF with oxide) can be slowed by adding more water and lowers the concentration of HF.HF will etch BPSG Oxide Nit SiH2O:HF 100:1 (50: 1, 49%)Function : Remove Oxide(SiO2)Mech

6、anism: Reacts with Oxide and form a solvable byproduct.Oxide Etch HFEtching 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 SiF6 2

7、- ions = this has high affinity to attract defects, due to strong polarity. 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 waferWhat is the impact of water mark?Water mark can ca

8、use 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 Jet dryer

9、Low pressure DryerSpin DryerMicro Mist DryerDI water is De-ionized water. Water Rinse: DI WaterDIW tank is for rinsing 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

10、 very stable flow of DIW and gives good PC control. It makes use of diffusion and dilution. QDR, on the other hand 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 s

11、urrounding cleanliness is important.DIW tank overflows at all times with by-pass flow to prevent bacteria. Bacteria will result in PC & metallic contamination.DIW TankDIW 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 the

12、rmal shock. For high viscosity chemical, HDIW rinse will improve solubility of the chemical, thus improve 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 re

13、duction and improves rinsing efficiency especially for viscous chemical.DIW TankDIW flow-rate.Process Time.Dump Cycle & Process Time for each sequence.Megasonic On Sequence.Critical Parameters30C, NH4OH: H2O2:H2O (1:2:50)Function: Particle removal, Light polymer removal Mechanism: oxidation and elec

14、trical repulsion OxidationDissolutionSurface etchingElectrical repulsionOxidation mechanismElectrical repulsion mechanismParticle clean SC1 (Standard clean 1)SC1 with MegasonicTransducerTransducerTransducerPartial wettingSolvent diffusing at interfaceTotal wettingFloating free Benefit: enhance the p

15、article remove rate. Drawback: H2O2 will be reduced during operation, which cause surface roughness! 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- (H3SiO4-, HSiO43- etc)V1V2HO2-OH -Path-1Pat

16、h-2OH -V3V1 = k1HO2-3 k1=1.2x1014 (65C)V2 = k2OH- k2=5970 (65C)V3= k3OH-2 k3=2.0 x109 (65C)Path-1Path-2Si SubstrateMethods of reducing the microroughness can be summarized as:Reduce the proportion of NH4OH ( the etchant)Reduce the temperature of the bathReduce the cleaning timeConventional SC1: (1:1

17、:5), 7080CNH4OH 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:Heater Burnt - Inline heater is made of Quartz and SC1 etches Si, thus inline heater has lifetime. If burnt an

18、d 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 SC1To get rid of bubbles :Tilt wafer to face back m/c.Slight agitation of wafers to release bubble from wafer surface m/c.Bubble col

19、lapser/degaser.PFBubble DegasserfilterPumpinOuter weir filtered liquidBubble DegaserCommon Issues with SC130C, HCl: H2O2:H2OFunction: Ionic and Metallic Contamination Removal Metallic clean SC2 (Standard clean 2)Mechanism: HCL reacts with metal to form a soluble salt which is removed from wafer surf

20、ace by dissolving in H2O. As far as H2O2, it passivity the active surface.HCl & H2O2 are not easy to be produced 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

21、 on the wafer. This is the best scenario.Note - Cleanup is not always removing defects/contaminants; it depends on who is dirtier - Diffusion principle : movement of solutes from higher concentration to lower concentration until equilibrium.Problem with SC2DryerIsopropyl Alcohol (IPA)Function : remo

22、ves water from wafersMechanism: Alcohol vapors displace water from surface The alcohol evaporates more easily than water. It leaves a dry surfaceCleaningHF + H3PO4 (Phosphoric Acid)Function: AA nitride strip after growing isolation oxideNitride RemoveNitride etch rate in H3PO4 At 1600C, H3PO4 is 87%

23、 at boiling point. Original chemical concentration = 86%As the chemical heats up, DIW spikes in to maintain chemical % - boils at 1600C - optimal etch rateSMSDIW spikeSESBest Process Control NISSO System.DIW spikeDIW spikeOld DNSMay result in wafer cross slot due to water super boil.DIW spiking posi

24、tion and control are critical for optimal process.Nitride RemoveMechanism: Si3N4 + 6H2O - 3SiO2 + 4NH3 (H3PO4 as catalyst)ER A/minSi Conc. (ppm)Particle (#/ml,0.2um)SiNSiO2ParticleNitride RemoveWhen the Silicon content is very high, oxide etch rate decreases. Silicon may even re-deposit on wafer and

25、 trap some H3PO4. If this Phos is implanted/driven 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

26、 overetch.As a result, the Tank 2 oxide etchrate is more stable which leads to better oxide remains control.Oxynitride/oxideAA SiN100A Pad OxideHF dipAA SiN100A Pad OxideHPO 1100A Pad OxideHPO 2 AA SiN Strip Process for CM71DRAM Pad Oxide RemainedHPO lifetime dependent!(Recipe NLH240AHPO2550ASC1M)SP

27、M(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-OH + -(CH2)n CO2 + H2OUse hot QDR (Quick Dump Rinse) with mega-sonic to rinse off viscous H2

28、SO4 on wafers Recipe for PR Strip NDH10APRRMM: DHF(100:1) 15” + SPM 5+SPM5+HQDR(with Mega) NPRRM: SPM 5+SPM5+HQDR(w/o Mega)BOE (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 compar

29、ed to DHF: 1) Low selectivity oxide etch for DRAM contact pre-clean 2) Prevent photo resist liftoff for KV, Dual gate process For BOE etch with PR on wafers, S/D or Marangoni is used for dryingSiO2 / BPSG etching mechanism SiO2 is mainly etched by HF2- SiO2 + 2HF2- + 2H3O+ SiF4 + 4H2OSiF4 + 2HF H2Si

30、F6 (in HF solution)SiF4 + 2NH4F (NH4)2SiF6 (in BOE solution)BPSG is mainly etched by HF B2O3 + 6HF 2BF3 + 3H2OBPSG /SiO2 etching selectivity controlNH4F , BPSG/SiO2NH4F 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)DHF pre-cl

31、ean for Poly depOxide AOxide BOxide CACT940 is used to remove Plasma cured photoresist Hard crest of side-wall polymer Cl- ions trapped in the side-wall polymer/photoresistO3/plasma Ashing PRS + PRS(photo resist strip) PSR(Post stripper rinse) DIW (dryer) Plasma Ashing: remove hard-cured photoresist

32、 (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 OH induced corrosion causing by uneven micro-etch in DI water rinse* PSR = NMP, IPA, etc.(PRS) ACT940 Solvent (1)Metal etch post

33、 cleanVIA Etch post cleanOther Wet Etch Chemicals in SMIC SC1(NH4OH:H2O2:H2O=1:1:1)/24C 3040min : Ti Selective EtchSC1(NH4OH:H2O2:H2O=1:1:5)/50C 5min + : Co selective etch M2(H3PO4:HNO3:CH3COOH70:2:12)/75C 20 min49%HF , HF(20:1) : Oxide reclaimPoly etch(HNO3:HF=6:1)/23C : Poly reclaimSC1(NH4OH:H2O2:

34、H2O=1:1:5)/50C : W Metal reclaimSPM(H2SO4:H2O2)=5:1/125C : Al/Cu, Ti, TiN Metal reclaim Dryer IntroductionDryer is used to ensure that the DIW on the wafer is not evaporated but either displaced or physically removed.Presently there are following types of dryers in Fab7Spin dryer (S/D)VJD(Vapor Jet

35、Dryer)LPD(Low pressure dryer)MMD (Micro Mist Dryer)Spin DryerOn-Centre Type Off-Centre TypeCritical Parameters : Transfer Time (On-centre faster)Ramp up speedMax speedProcess TimeExhaustIonizerStandard Vapour DryerEither made of Quartz or Stainless Steel. IPA CondensateDrain PlateHeat Transfer Adhes

36、iveHeater 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 Tension ABMARANGONI Force Liquid Flow from A to BWithdraw Wafer out of WaterResults in Dry and Clean Wafer SurfaceMarangoni Dryer (1)Marangoni Dryer (2)Marangoni VaporEvaluation at Bare WaferSiSiO2H2OIPA Evaluation at Device ProcessororororBehavior of IPA on Wafer surfaceLPD: low pressure dryerProcess Sequence of FL-820L(1)Process Sequ