PLASMA RIE ETCHING FUNDAMENTALS AND .
Nanotechnology CenterPLASMA RIE BirckETCHINGFUNDAMENTALS AND APPLICATIONS1
O tliOutline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmas4 Anisotropy4.A i tMechanismsM h ig of Si and its Compoundsp5. The Etching6. The Etching of Other Materials2
DEFINITIONS¾ Electron ((e-)¾ Positive ion (Ar , Cl , SiF4 , CF3 )Positive ion mass in RIEs mass of electron¾ Radical (F, Cl, O, CF3)Uncharged atoms with unsatisfied chemicalbonding3
DEFINITIONS (continued)( ti d)¾ Mean free ppath5λ ((cmcm) P (mT )averageg distance a pparticle travels before collisions((Dependentpon the species)p)¾ Pressure1atmosphere 760 Torr 1*105 Pascals¾ Pumping speed (S) [liters/sec]¾ Gas flow rate (Q) [Torr-liters/sec] or [sccm]4
PlPlasmaVacuumVSSystemtGas linesvalveMixed gas [Q]MFC boxChamberVRFMatchingnetworkdP(t)( ) (Q - S P(t))( )) dtVIn Steady state : Q S P5APC & gatevalveVacuum pump [S]He backsidecoolingV chamber volume
M h i l PumpsMechanicalPWet and Dry PumpsPumping speed: 20-500 m3/hUltimate pressure: 1-10 mTorr[BOC Edwards Dry Pump][Kurt J. Lesker]6
T b PumpsTurboPRotation speed 20000-9000020000 90000 rpmPumping speed: 50-3000 l/sUltimate pressure: 10-5-10-8 Torr[Wiki][BOC Edwards Turbo Pump][TP controller]7
M FlowMassFl ControllerC t ll (MFC)Thermal-based flow meterHeaterQ [sccm]T1T2T2 – T1 Cp QCp is specific heat.[HORIBASTEC]8
MFC or GGas BBoxMixed gaslineGasGlinesPanasonic MFC Box9
A tAutomaticti PressurePControllerC t ll (APC)& Gate ValvePendulum valveButterfly valveQ S P10[VAT]
ClClampor ElectrostaticEl t t ti ChuckCh kClampElectrostatic Chuck (ESC)Si waferDielectric------ ------Base Plate V -He11-V
RF GGeneratort & MatchingM t hi NetworkN tkRF GeneratorMatchingNetworkPFPLChamber ZLZInPRZS 50ΩPL PF- PRIn general: ZL ZSPurpose of Matching Network: Zin ZS tomaximize power delivery from source.ZSManual or AutomaticMatching NetworkC1C2ZIn12LZL[Gambetti]
O tliOutline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmas4 Anisotropy4.Anisotrop Mechanisms5. The Etching of Si and its Compounds6. The Etching of Other Materials13[Plasmas.org]
Wh t isWhati Plasma?Pl? Plasma is the fourth state of matter. It is an ionized ggas, a ggasinto which sufficient energy is provided to free electrons fromatoms or molecules and to allow both species, ions andelectrons to coexist.electrons,coexist[Plasmas org][Plasmas.org]14
H tto MakeHowM k PlPlasma?Plasma¾ CapacitivepRIE- Low density plasmane 109 [electron/cm3]Ionization efficiency 10-7¾ Inductive RIEMagnetic field- High density plasmaWaferne 1013 [electron/cm3]Ionization efficiency 10-315[Oxford Instruments]
DC Glow Discharge¾Only used for sputtering system not for etching.etchingVc -100Vc 0nRed: niBlack: neXV( )V(x)V(x)VpXVp-100vVp a few volts16X
RF Glow Discharge¾Used for any materials (insulating and conductive) .VRF(t)VRFVp (t) Vp(t)AE AG ZG ZEVp (t) VRF (t)VRF(t)ZEV(x)VRF17XZGVRF (t)ZG ZEZG
RF Glow DischargeZGVp (t) VRF (t)ZG ZEActual RIEVRF(t) ZEE AG ZG ZAA AZEGEGVpV(t) VRF0(t)p(t)¾Ion transit time (Tion) is the time it takes the ionto traverse the sheath.q Tion !¾1/Freq18Freq q 13.56 MHz
P h ’ LPaschen’sLawDescribes how the breakdown voltage depends on electrodeseparation and the pressure based on ideal gas law.a (p(p.d))V l n(p.d) bV: Voltagep: Pressured: gap distancea & b: constantsV80060040010-119100101Pd [Torr cm]
I d ti CoupledInductiveCl d PlasmaPlRIESTS ASE and AOE systems20
Wh High DensitWhyDensity Plasmas?¾ Lower ion bombardment energies improve selectivity and reduce ionbombardment-induced physical damage of the wafer surface.g , however,, result in the lower etch rates and reduced¾ Lower ion energies,anisotropy!¾ HoweverHowever, the etch rate can be increased by using much higher ion fluxesdue to high density plasmas.¾ The anisotropy can also be restored by operating at low pressure.pressure21
O tliOutline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmas4 Anisotropy4.Anisotrop Mechanisms5. The Etching of Si and its Compounds6. The Etching of Other Materials22
Electron Molec le CollisionsElectron-Molecule¾ An energetic electron colliding with a neutral etch gas molecule cancreate any of the following processes:9 Dissociation AB e-A B e-CF4 e-CF3 F e-9 IonizationAB 2e-Ar e-Ar 2e-AB e-Often dissociation and ionizationOccur in one collision:CF4 e-23CF3 F 2e-
R di l andd IonsRadicalsIini PlasmasPl24¾Positive ions are veryy importantpfor etchingg pprocesses.¾Radicals are more numerous than ions in gas glowdischarges because:1.The electron energy required in order to break chemical bonds in themolecules is usually less than the energy required to ionize thesemolecules.2.Radicals have a longer lifetime in the plasma compared to ions becausean ion is almost always neutralized during a collision with a surfacewhile radicals often do not react with a surface and are reflected backinto the plasma.
Wh t iis PlWhatPlasma Etching?Et hi ?CF4CF4 eSi 4FCF3 F 2eSiF4 (gas)valveChamberGate valve ,CF3 FSi WafersVacuum pumpSiF41- Need an etching gas2- Establish a glow discharge3- Choose chemistry so that the reactive species react with the substrateto form a volatile by-product4- Pump away the volatile by-product25
Wh PlWhyPlasma EtEtching?hi ?¾¾¾¾Clean processCompatible with automationAnisotropic etchingP i patternPrecisetttransfertf especiallyi ll forf Nano-scaleNl featuresf tMaskSubstrateIsotropic etch26Directional etchVertical etch
Gas Solid SystemsGas-SolidSolidSiliconEtch GasEtch ProductCF4,Cl2, SF6SiF4, SiCl4, SiCl2CF4, C4F8,CHF3, SF6SiF4, CO, O2, N2,FCNAlBCl3/Cl2Al2Cl6, AlCl3Ti, TiNCl2, CF4TiCl4, TiF4Organic SolidsO2, O2/CF4CO, CO2,GaAs & III-VCl2/Ar, BCl3Ga2Cl6, AsCl3Cl2/O2CrO2Cl2SiO2, SiNxCrDifficult materials to etch:Fe, Ni, Co, Au, Ag, Pthalides not volatileCuCu3Cl3 is volatile above 200C27
Halogen SiSizee Effect[Handbook of Advanced Plasma Processing Techniques by Pearton]28
O tliOutline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmas4 Anisotropy Mechanisms4.5. The Etching of Si and its Compounds6. The Etching of Other Materials29
D fi itiDefinition Etch rateMaskG ldGold Mask (Photoresist, Metal, SiO2, )Substrate Selectivity Anisotropy degreeLAf 1 H30LH
Reactive etching¾R¾Reactiveti etchingt hi isi an isotropici ti process!¾Has very high selectivity!Si 4FMaskSiF4FSubstrateIsotropic etch31SiF4 (gas)
Ion etching¾Ion etching or mechanical etching is an anisotropicprocess!¾Has lower selectivityy and etch rate!Si Ar SSi Ar SSiAr MaskSubstrateDirectional etch32Vertical etch
Reactive ion etching¾Reactive ion etching is an anisotropic process!¾Has better selectivity and much higher etch rate![J. Appl. Phys. 50, 3189 (1979)]33Effect of Ions:Breaks bonds, raises temperature locallyon the surface and provides activation energy
Side all PassivationSidewallPassi ation¾Deposition of carbon polymer material on the sidewallswhere:(a) Either the carbon is provided by the feed gas through the chambersuch as CHF3, C4F8.(b) Or the carbon is provided by the erosion of the photoresist etchmask.34
Side all PassivationSidewallPassi ation¾Oxidation of the sidewall by adding O2 gas.35
B hPBoschProcessSwitching SF6 and C4F8500um Silicon Etched by T.Maleki using STS ASE(8um/min etch rate)Th sidewallTheidll filfilm thicknesshi kddependsd to theh ddepositioni i or passivationi i time.i36
TTemperatureteffectsff t ini plasmaletchingt hi¾Wafer surface temp. depends on:- Chuck temperature- Ion’sI ’ energy anddddensityit¾Reaction probabilityy of radicals depends on substratetemperature.¾Helium backside cooling helps anisotropic etch by preventingor reducing reaction of F and Cl species with sidewalls.37
Notch Effect¾ Notching effect due to chargingoxide by ions¾ Can be reduced by using lowfrequency (LF) 380kHz bias generatorin pulsed modee- RF biasonRF biasoff[J. Vac. Sci. Technol. B 19.5., Sep/Oct 2001]STS ASE has LF pulsed generator!!38
Other EffectsGrass or micromaskingg issue mainlyybecause of metal mask sputtered onthe waferAspectt RatioAR ti DependentDd t EffEffectt (ARDE)Typically large open areas etch faster thansmaller features!39
Other EffectsMicroloading effect:Feature of the same size etch more slowly in dense patternsThan in wide open areas!EtchingEt hiSpeciesDensityx40
O tlineOutline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmaspy Mechanisms4. Anisotropy5. The Etching of Si and its Compounds6. The Etching of Other Materials41
STS ASE DRIEIt’s a 6” ICP Bosch pprocess dedicatedfor silicon etching!Gases:42SF6C4F8O2Ar
STS ASE DRIEHighg etch-rate recipe:pEtchhPassivationSwitchingtimePressureRF coil powerRF biaspowerGas flow[sccm]8 5 sec8.540 T40mTorr2200W40W450 SF63 sec14mTorr1500W20W200 C4F8Etch rate 8µm/min for 500 µm featuresize with 20% exposed areaHigh selectivity to PR 75-10043
STS ASE DRIELow etch-rate recipe:pSwitchingtimePressureRF coil powerRF biaspowerGas flow[sccm]Etchh13 sec5 T5mTorr800W25W160 SF6Passivation7 sec1mTorr600W20W85 C4F8Etch rate 2µm/min for 500 µm featuresize with 20% exposed areaHigh selectivity to PR 50Smooth side wall44
STS AOE DRIEIt’s a 4” ICP tool dedicated for etchinggof oxide, nitrite, and polymers!Gases:Oxide EtchSF6C4F8CF4O2ArHePressureRF coil powerRF biaspowerGas flow[sccm]2mTorr600W50W13 CF4Etch rate 0.3µm/min0 3µm/minSelectivity to PR 1-245
Panasonic RIEIt’s a 6” ICP tool for etching of silicon,oxide, nitrite, III-V, polymers, and somemetals!GGases:46SF6CHF3Cl2O2CF4ArBCl3N2
Panasonic RIESiEtchPPressureRF coililpowerRF biasbipowerSF6 flowfl[sccm]O2 flowfl[sccm]11Pa900W75W3030Etch rate 1µm/minSiEtchPressureRF coilpowerRF biaspowerCl2flow[sccm]O2 flow[sccm]0.8Pa350W50W631.2Etch rate 200nm/min47[Panasonic][Panasonic]
Panasonic RIEOxideEtchPressureRF coilpowerRF biaspowerCHF3 flow[sccm]0.16 Pa450W50W40SiO2Etch rate 60 nm/minSiN3EtchPressureRF coilpower2 Pa400WEtch rate 100 nm/min48RF bias CF4 flowpower[sccm]30W48CHF3 flow[sccm]50SiN3[Panasonic]
Panasonic RIESiC EtchPressureRF coilpowerRF biaspowerSF6 flow[sccm]4 Pa700W280W50Etch rate 0.46 µm/min[Panasonic]SiCEtchPressureRF coilpowerRF biaspowerCl2 flow[sccm]O2 flow[sccm]1.5 Pa500W150W3020Etch rate 0.19 µm/min49[Panasonic]
Plasma Tech RIE9 It’s a simple RIE.9 It can be used for etching silicon, oxide,nitrite, SiC, and polymers.Gases:SF650O2Ar
Outline1 Introductory Concepts1.2. Plasma Fundamentals3. The Physics and Chemistry of Plasmaspy Mechanisms4. Anisotropy5. The Etching of Si and its Compounds6. The Etching of Other Materials51
Panasonic RIETiEtchPressureRF coilpowerRF biaspowerCl2 flow[sccm]Ar flow[sccm]2 Pa400W100W1005Etch rate 3 µm/min52
Panasonic RIEGaAsEtchPressureRF coilpowerRF biaspowerBCl3 flow[sccm]Cl2 flow[sccm]Ar flow[sccm]3 Pa900W75W5015020Etch rate 5.3µm/minSelectivity to PR 553[Panasonic]
Panasonic RIEGaAsEtchPressureRF coilpowerRF biaspowerBCl3 flow[sccm]Ar flow[sccm]0.6 Pa500W50W1560Etch rate 120 nm/minSelectivity to PR 4[Panasonic]54
Panasonic RIEGaNEtchPressureRF coilpowerRF biaspowerCl2 flow[sccm]4 Pa900W90W50Etch rate 500 nm/minSelectivity to PR 00.55Selectivity to SiO2 5[P[Panasonic]i ]55
General Process TrendsHow to Increase Etch Rate?¾ Increasing Main Coil Power¾ Increasing Platen or Bias Power¾ Increasing Process pressure¾ Increasing etching flow¾ Increasing Etch cycle time (for Bosch process)How to Reduce Sidewall Roughness/Scallops?¾ Keep etch and deposition cycle times to minimum, (for Bosch process)¾ Reduce process pressure¾ Reduce etch gas flow¾ Increase deposition componentcomponent, time,time power,power or flow (for Bosch process)How to Increase Selectivity?¾ Increasing the pressure¾ Reducing platen power56
General Process TrendsHow to Straighten the Profile?¾ Using low pressure¾ Decreasing etch cycle time or increasing deposition cycle time (for Bosch process)¾ Optimizing platen power57
General Process Trends58Trends forControllingprocess resultsEtchrateEtch gas increaseProfileSelectivitySidewallRoughness Pressure increase Etch Coil Powerincrease Platen Powerincrease
Ackno ledgmentAcknowledgment¾We would like to thank faculty members, staff, andstudents for their support.Questions?59
Plasma Fundamentals Plasma Fundamentals 3. The Physics and Chemistry of Plasmas 4. Anisotrop MechanismsAnisotropy Mechanisms 5. The Etching of Si and its Compounds 6. The Etching of Other Materials 13 [Plasmas.org] Wh t i Pl ?What is Plasma? Plasmais
Plasma Etching Page 2 OUTLINE Introduction Plasma Etching Metrics – Isotropic, Anisotropic, Selectivity, Aspect Ratio, Etch Bias Plasma and Wet Etch Summary The Plasma State - Plasma composition, DC & RF Plasma Plasma Etching Processes - The principle of plasma etching, Etching Si and SiO2 with CF4
Parylene etching has been demonstrated in multiple modes including plasma etching [19, 25, 26], reactive ion beam etching (RIBE) [27], reactive ion etching (RIE) [28, 29] and high-density plasma etching [30]. However, no attempt has been made to optimize anisotropy or employ sidewall passivation to produce high aspect ratio structures. Yeh
Etching is a process of removing material from the substrate’s surface. In general, there are two categories that etching can be divided into dry etching, and wet etching. The focus of this section will be solely on dry etching. Wet etching, a process where the substrate is submerged
Dry plasma etching has become the dominant patterning technique for the group-III nitrides, due to the shortcom-ings in wet chemical etching. Plasma etching proceeds by either physical sputtering, chemical reaction, or a combination of the two often referred to as ion-assisted plasma etching, Physical sputtering is dominated by the
Plasma Etching Plasma etching involves physical bombardment of the substrate by an ion which is nominally inert. – Ar is the most common gas used for this. The impact (momentum transfer) from accelerated Ar ions knocks loose substrate ions, called sputter etching or simply plasma etching.
- Ion milling or Ion etching. - Plasma sputtering. Plasma Etching. It is a Plasma assisted chemical reactive on the substrate which erodes. Reactive Ion Etching (RIE). Occur due to chemical reaction over bombarding ions on the material. Advantages: Capable for small feature definition 1nm. High quality etch.
etching is usually faster than the rates for many dry etching processes and can easily be changed by varying temperature or the concentration of active species. Wet Etch Synonyms: chemical etching, liquid etching Definition: Wet etching is a material removal process that uses liquid chemicals or etchants to remove materials from a wafer.
Weight of pile above scour level Wp1 220.893 kN Weight of pile below scour level Wp2 301.548 kN Tota l ultimate resistance of pile Qsf Qb – Wp2 8717.452 kN Allowable load (8717.452 / F.S.) – Wp1 3266 kN. From above calculations, Required depth 26.03m below design seabed level E.G.L. ( ) 1.15 m CD . International Journal of Engineering Trends and Technology (IJETT) – Volume .
