WAVES, FLUXES AND POLYMERS: PLASMA EQUIPMENT AND PROCESS MODELING FOR MICROELECTRONICS FABRICATION

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1 WAVES, FLUXES AND POLYMERS: PLASMA EQUIPMENT AND PROCESS MODELING FOR MICROELECTRONICS FABRICATION Mark J. Kushner Unversty of Illnos Department of Electrcal and Computer Engneerng Urbana, IL November 1999 MSU9901

2 AGENDA Introducton to plasma processes of mcroelectroncs Needs and requrements for plasma equpment modelng Descrpton of the Hybrd Plasma Equpment Model Desgnng Plasma Tools and Processes from Frst Prncples: Waves, fluxes and polymers Concludng Remarks MSU9903 Unversty of Illnos Optcal and Dscharge Physcs

3 MOORE'S LAW IN MICROELECTRONICS FABRICATION In the early 1980s Gordon Moore (Intel) observed that the complexty and performance of mcrelectroncs chps doubles every 18 months. The ndustry has obeyed Moore s Law through > 12 generatons of devces. MSU9904 Unversty of Illnos Optcal and Dscharge Physcs

4 INCREASED COMPLEXITY REQUIRES NEW SOLUTIONS: INTERCONNECT WIRING The levels of nterconnect wrng wll ncrease to 8-9 over the next decade producng unacceptable sgnal propogaton delays. Innovatve solutons such as copper wrng and low-k delectrcs are beng mplemented. AFOSR9905 Ref: IBM Mcroelectroncs Unversty of Illnos

5 EVEN SMALLER DEVICES CAN BE BUILT... BUT THEY ALSO MUST BE MANUFACTURABLE The technology to fabrcate 0.06 mcron devces currently exsts. The addtonal challenge s to devse MANUFACTURABLE processes whereby 1012 devces per month can be successfully fabrcated. IBM demonstraton of a 0.06 mcron CMOS transstor usng e-beam mask exposure. UMINN9803 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

6 PLASMA PROCESSING FOR MICROELECTRONICS In plasma processng of semconductors, electron mpact on feedstock gases produces neutral radcals and ons whch drft or dffuse to the wafer where they remove or depost materals. ELECTRODE NON-REACTIVE GAS FLOW CF4 PLASMA REACTOR e + CF4 CF F + 2e CF 2 + 2F + e F CF3 + SF2 S WAFER PRODUCT REMOVAL SF4 Ths process s often called cold combuston snce the feedstock gases are cool compared to the electrons. CECAM98M15 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

7 PLASMAS ARE ESSENTIAL FOR ECONOMICALLY FABRICATING FINE FEATURES IN MICROELECTRONICS In plasma processng, ons are accelerated nearly vertcally nto the wafer, thereby actvatng etch processes whch produce straght walled, ansotropc features ION + SHEATH IONS NEUTRAL RADICALS MASK SO2 WAFER S POSITION Ion Asssted Etchng Neutral Domnated Etchng CECAM98M21 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

8 TEGAL CORP.

9 APPLIED MATERIALS DECOUPLED PLASMA SOURCE (DPS) CECAM9825 Unversty of Illnos Optcal and Dscharge Physcs

10 APPLIED MATERIALS DECOUPLED PLASMA SOURCE (DPS) CECAM9826 Unversty of Illnos Optcal and Dscharge Physcs

11 COST OF FABRICATION FACILITIES The cost of a major (> 20,000 wafers/month) fabrcaton faclty exceeds $1 Bllon wth an ncreasng fracton of the cost beng the processngequpment. AFOSR9904 Unversty of Illnos Optcal and Dscharge Physcs

12 THE VIRTUAL FACTORY: A DESIGN PARADIGM The vrtual factory s a computer representaton of a fabrcaton faclty, modeled ether heurstcally or from basc prncples. Ref: SIA Semconductor Industry Assocaton Roadmap, AFOSR9907 Unversty of Illnos Optcal and Dscharge Physcs

13 SPATIAL SCALES IN PLASMA PROCESSING SPAN MANY ORDERS OF MAGNITUDE e + CF4 > CF3 + + F + 2e PLASMA WAFER IONS PLASMA EQUIPMENT SCALE (cm - 10s cm) Gas Flow Heat Transfer Plasma Transport Chemcal Knetcs 10 s - 100s µm SHEATH WAFER SUBSTRATE IONS µm SHEATH TRANSITION SCALE (10s -100s µm) Electron and Ion Transport Sparse Collsons Electrodynamcs WAFER FEATURE SCALE (10s nm - µm) Electron, Ion, Radcal Transport Plasma Surface Interacton Surface chemstry ICRP97M12 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

14 SCHEMATIC OF THE HYBRID PLASMA EQUIPMENT MODEL Es(r,θ,z,φ) v(r,θ,z) S(r,θ,z) PLASMA CHEMISTRY MONTE CARLO SIMULATION FLUXES ETCH PROFILE MODULE = 2-D ONLY = 2-D and 3-D I,V (cols) MAGNETO- STATICS MODULE CIRCUIT MODULE E ELECTRO- MAGNETICS MODULE FDTD MICROWAVE MODULE Bs(r,θ,z) E(r,θ,z,φ), B(r,θ,z,φ) ELECTRON MONTE CARLO SIMULATION ELECTRON BEAM MODULE ELECTRON ENERGY EQN./ BOLTZMANN MODULE NON- COLLISIONAL HEATING Es(r,θ,z,φ) N(r,θ,z) S(r,θ,z), Te(r,θ,z) µ(r,θ,z) FLUID- KINETICS SIMULATION HYDRO- DYNAMICS MODULE ENERGY EQUATIONS SHEATH MODULE LONG MEAN FREE PATH (SPUTTER) SIMPLE CIRCUIT Φ(r,θ,z,φ) V(rf), V(dc) Φ(r,θ,z) R(r,θ,z) Φ(r,θ,z) R(r,θ,z) EXTERNAL CIRCUIT MODULE MESO- SCALE MODULE SURFACE CHEMISTRY MODULE J(r,θ,z,φ) I(cols), σ(r,θ,z) VPEM: SENSORS, CONTROLLER, ACTUATORS PEUG9904 Unversty of Illnos Optcal and Dscharge Physcs

15 ELECTROMAGNETICS-CIRCUIT MODULES Unversty of Illnos Optcal and Dscharge Physcs AFOSR9909 In the Electromagnetcs-Module, the wave equaton s solved n the frequency doman ( ) ( ) = µ ε σ v r r r E E t E J t o, σ ν ω ν = q n m j j j j j 2 1 r r r r r E r t E r t r (, ) ( )exp( ( ( ))) = + ω ϕ Wth statc appled magnetc felds, conductvtes are tensor quanttes: ( ) m e 2 o m 2 z 2 z r z r z r 2 2 r z z r r z 2 r m o m n q, m q / E j B B B B B B B B B B B B B B B B B B B B B B 1 q m ν σ ν ω α σ α α α α α α α α α α α ν σ σ θ θ θ θ θ θ θ = + = = = r &&& v r &&&

16 ELECTROMAGNETICS-CIRCUIT MODULES Col currents Jo are obtaned from an equvalent crcut model for the antenna. Each dscrete element of the transmsson lne has mpedance: Z = ωl + ωc + R + Z c T L = Physcal nductance C = Capactve couplng Rc = Ohmc resstance of col ZT = Transformed mpedance of the plasma The drvng voltage from the generator s obtaned by specfyng a total power deposton by the electrc feld. Match condtons are obtaned by varyng the matchbox crcut elements to mnmze the reflected power. The complex ampltudes of the components of the wave are obtaned usng ether successve-over-relaxaton or conjugate-gradent-sparse matrx technques. AFOSR9909 Unversty of Illnos Optcal and Dscharge Physcs

17 ELECTRON ENERGY TRANSPORT Electron transport coeffcents and electron mpact source functons are obtaned by solvng the electron energy equaton. 3 2 nekte 5 = S( Te ) L( Te ) kte ( Te ) T Φ κ e + SEB t 2 where S(Te) = Power deposton (from EEM and FKS) L(Te) = Electron power loss due to collsons Φ = Electron flux (obtaned from FKS) κ(te) = Electron thermal conductvty S EB = Electron source from beam electrons (MCS) Transport coeffcents are obtaned as a functon of average energy (ε = (2/3) Te) from soluton of Boltzmann' Equaton for the electron energy dstrbuton. The energy equaton s mplcty solved usng Successve-over-Relaxaton. Secondary electron emtted from surfaces are addressed usng a Monte Carlo smulaton. AFOSR9910 Unversty of Illnos Optcal and Dscharge Physcs

18 PLASMA CHEMISTRY KINETICS SIMULATION Unversty of Illnos Optcal and Dscharge Physcs AFOSR9911 In the plasma chemstry module we solve separate contnuty, momentum and energy equatons for ons and neturals, and the electron contnuty equaton. S ) v (N t N + = r ( ) ( ) ( ) ( ) B v E m N q v v N kn T m 1 t v N µ + + = r r r r r r ( ) j j j j m j m j v v N N m ν r r + ( ) E ) ( m N q ) U (N U P Q t N ω ν ν ε ε + = ± j j B j j j j B j j j j 2 s 2 T k R N 3N ) T (T k R N N m m m 3 E m N q ν,

19 PLASMA CHEMISTRY KINETICS SIMULATION Slp boundary condtons are used for neutral transport for momentum and energy to address temperature jump condtons. Gas flow (nput nozzle, pumpng) s ncluded by specfyng nflux/outflux boundary condtons. Pressure s specfed and the pump-speed s throttled to mantan constant pressure and mass flux. Important aspects of ths formulaton are: Includng "reflux" of speces from surfaces Momentum trransfer between speces leadng to on drag, jettng of nput gases and entranment. All equatons are dscretzed usng flux-conservatve fnte-volume technques. Tensor transport coeffecents are used wth statc magnetc felds. PDEs are ntegrated n tme usng Runge-Kutta technqes. AFOSR9911 Unversty of Illnos Optcal and Dscharge Physcs

20 PLASMA CHEMISTRY KINETICS SIMULATION Posson's equaton s solved usng a sem-mplct formulaton whch ncludes a predcton of denstes for the tme at whch the felds wll be used. Surface charges are ncluded here. where ε Φ ( t + t) = - ρ q N - t ( q φ ) s + φ r e = qeµ e Φ De ne r φ r ION = ( from momentum equatons) Boundary condtons are obtaned from a crcut model of the reactor and drvng electroncs whch specfy voltage harmoncs (ampltude and phase) on metal surfaces. AFOSR9911 Unversty of Illnos Optcal and Dscharge Physcs

21 MONTE CARLO FEATURE PROFILE MODEL (MCFP) Cl + Cl + Ar + 2 Resst Cl "Passvaton" The MCFP model predcts tme and spatally dependent etch profles usng neutral and on fluxes from the PCMCS. Any chemcal mechansm may be mplemented n the MCFP usng a "plasma chemstry" nput herarchy. Sde-wall Passvaton p-s Cl 2 SCl x Ar SO 2 e.g., Cl+ + SCl2(s) > SCl2(g) All pertnent processes can be ncluded: thermal etch, on asssted etch, sputter, redeposton, passvaton. Energy dependent etch processes may be mplemented usng parametrc forms. The MCFP may utlze ALL flux statstcs from the PCMCS Ion energy and angular dstrbutons Neutral energy and angular dstrbutons Poston dependent fluxes CECAM98M16 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

22 HOW DO YOU FILL LARGE REACTORS WITH PLASMA TO PROCESS LARGE WAFERS? CREATE WAVES MSU9911 Unversty of Illnos Optcal and Dscharge Physcs

23 TRANSFORMER COUPLED PLASMA ETCHING TOOL Low gas pressure, hgh plasma densty etchng tools often use wave exctaton to produce the plasma. Typcal Operatng Condtons: RF 5-20 mtorr sccm 17.0 SPIRAL COIL (TYPICAL) B W (ICP) W bas [e] = /cm3 Te = 3-5 ev 8.5 NOZZLE PUMP SUBSTRATE PORT TI = ev RADIUS (cm) E WINDOW (QUARTZ E RF WAFE CECAM98M17 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

24 300 mm ETCH TOOL: ELECTRIC FIELD, POWER, ION DENSITIES ELECTRIC FIELD [11.5 V/cm, 2 dec] 26 POWER DEPOSITION [0.48 W/cm 3, 2 dec] RADIUS (cm) Cl + [max = 8.5(10)] Cl + 2 [max = 4.2(10)] SRC96M RADIUS (cm) Ar/Cl2/BCl3 = 1/1/1, 10 mtorr, 600 W ICP, 100 V bas, 150 sccm UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

25 300 mm ETCH TOOL: PRECURSORS, ETCH PRODUCTS Cl [max = 1.3(14)] SCl, SCl 2 [max = 4.8(13)] RADIUS (cm) BCl + 3, BCl + 2 [max = 8.7(10)] SCl + 2, SCl + [max = 1.1(10)] SRC96M RADIUS (cm) Ar/Cl2/BCl3 = 1/1/1, 10 mtorr, 600 W ICP, 100 V bas, 150 sccm UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

26 WAVE PROPAGATION IN ICP PLASMAS: HELICONS It s often desrable to produce plasmas n the "volume" large reactors. Ths s dffcult to accomplsh usng ICPs due to ther fnte skn depth. Wth a solenodal magnetc feld, electromagnetc waves can be made to propagate nto the volume of the plasma. One such wave s a helcon. B-FIELD E&M WAVE ANTENNA SOLENOID PLASMA SUBSTRATE Example Geometry MSU9910 Unversty of Illnos Optcal and Dscharge Physcs

27 40 HELICON TRANSITION - AZIMUTHAL ELECTRIC FIELD (E θ ) Eθ B = 10 G Phase B = 20 G B = 40 G B = 80 G B = 150 G Eθ Phase Eθ Phase Eθ Phase Eθ Phase Glass Cols Solenod 10 Substrate 0 10 RADIUS (cm) 15 (V / cm) Radans 0 Ar, 10 mtorr, 1 kw, 50 sccm At a crtcally low magnetc feld, the azmuthal electrc feld remans nductvely coupled and a radally propagatng wave domnates. As magnetc felds are ncreased, standng wave patterns arse n radal drecton and the electrc feld begns to propagate n the axal drecton. AVS99_6 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

28 HELICON TRANSITION - RADIAL ELECTRIC FIELD (E r ) Er B = 10 G Phase B = 20 G B = 40 G B = 80 G B = 150 G Er Phase Er Phase Er Phase Er Phase (V / cm) Radans 0 Ar, 10 mtorr, 1 kw, 50 sccm The propagaton of radal electrc feld Er s smlar to azmuthal electrc feld Eθ. Intally propagaton s domnantly n the the radal drecton, wth a hghly damped wave. AVS99_7 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

29 HELICON TRANSITION - POWER AND ELECTRON DENSITY Power B = 10 G Electron Densty Power B = 20 G Electron Densty Power B = 40 G B = 80 G B = 150 G Electron Densty Power Electron Densty Power Electron Densty 6 (W / cm 3 ) E+12 (cm -3 ) 7E+10 Ar, 10 mtorr, 1 kw, 50 sccm At low magnetc felds power deposton s nductvely coupled and occurs near the cols As nodal structure develops n the azmuthal and radal felds, the skn depth of the power deposton s ncreased to wthn the volume of the plasma. AVS99_8 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

30 TRIKON MORI TM 200 HELICON PLASMA SOURCE A commercal Trkon Technologes, Inc., Pnnacle 8000 helcon source plasma system wll be used to valdate smulaton models. Antenna Permanent Magnets Electromagnet Wafer Process Chamber PRELIM99_32 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

31 50 cm APPLICATION OF HPEM TO HELICON TOOL DESIGN At low felds, the electromagnetc propagaton s manly radal, producng standng wave pattern n the radal drecton. However as the feld ncreases, propagaton domnates n the axal drecton, shftng standng wave patterns n the drecton of propagaton. B = 20 G B = 100 G B = 300G Eθ Phase Eθ Phase Eθ Phase 0 20 cm 0 20 cm Ar, 10 mtorr, 1kW, 50 sccm PRELIM99_34 15 (V / cm) Radans 0 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

32 APPLICATION OF HPEM TO HELICON TOOL DESIGN Axal electrc feld propagaton and wave pattern resembles radal electrc felds. As magnetc felds are ncreased, overall electrc feld propagaton n the axal drecton domnates. B = 20 G B = 100 G B = 300G 50 cm Ez Phase Ez Phase Ez Phase 0 20 cm 0 20 cm PRELIM99_36 Ar, 10 mtorr, 1kW, 50 sccm 5 (V / cm) Radans 0 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

33 ANALYSIS OF TRIKON HELICON TOOL : VALIDATION As statc magnetc feld ncreases, on saturaton current peaks further downstream. Smulatons show a smlar trend for the on saturaton profle. For smulatons at constant power, downstream peak decreases wth ncreasng statc magnetc felds snce plasma peaks at larger radus (.e. larger plasma volume). Expermental Axal Ion Saturaton Profle 50 0 G 200 G G Bell Jar Regon Downstream Regon Axal Poston (cm) G -10 Theoretcal Axal Ion Densty Bell Jar Regon 300 G Downstream Regon 100 G Axal Poston (cm) Ar, 2.3 mtorr, 1kW (Trkon Technologes, Inc.) Ar, 10 mtorr, 1kW, 50 sccm AVS99_14 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

34 50 cm ANALYSIS OF TRIKON HELICON TOOL : POWER AND ELECTRON DENSITY As the magnetc felds ncrease, axal propagaton domnates depostng power n the downstream regon. An ncrease n on current to the substrate comes at the loss of flux unformty. Power e- Densty Power e- Densty Power e- Densty B = 20 G B = 100 G B = 300 G AVS99_ cm 0 20 cm Ar, 10 mtorr, 1kW, 50 sccm 1 (W / cm 3 ) E+12 (cm -3 ) 4E+10 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

35 HOW DO YOU FILL EXTREMELY SMALL FEATURES WITH METAL FOR INTERCONNECT WIRING? CONTROL FLUXES MSU9912 Unversty of Illnos Optcal and Dscharge Physcs

36 PHYSICAL VAPOR DEPOSITION OF METALS Physcal-vapor-deposton (PVD) s a sputterng process n whch metal (and other) layers are deposted for barrer coatngs and nterconnect wrng. MAGNETS TARGET (Cathode) ANODE SHIELDS Typcal Condtons: < few mtorr Ar buffer 100s V bas 100s W - a few kw PLASMA ION NEUTRAL SPUTTERED TARGET ATOMS WAFER SUBSTRATE CACEM98M01 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

37 PVD DEPOSITION PROFILES In PVD, the atoms arrvng at the substrate are mostly neutral wth broad angular dstrbutons. The corners of the trench see a larger sold angle of the metal atom flux, and so have a hgher deposton rate. METAL ATOMS The end result s a nonunform deposton and vod formaton. Columnators are often used to flter out large angle flux; at the cost of deposton rate and partcle formaton. METAL SO2 CACEM98M02 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

38 IONIZED METAL PHYSICAL VAPOR DEPOSITION (IMPVD) In IMPVD, a second plasma source s used to onze a large fracton of the the sputtered metal atoms pror to reachng the substrate. MAGNETS ANODE SHIELDS TARGET (Cathode) PLASMA ION NEUTRAL TARGET ATOMS INDUCTIVELY COUPLED COILS SECONDARY PLASMA + e + M > M+ + 2e WAFER Typcal Condtons: CACEM98M mtorr Ar buffer 100s V bas on target 100s W - a few kw ICP 10s V bas on substrate SUBSTRATE BIAS UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

39 IMPVD DEPOSITION PROFILES METAL IONS In IMPVD, a large fracton of the atoms arrvng at the substrate are onzed. METAL ATOMS Applyng a bas to the substrate narrows the angular dstrbuton of the metal ons. The ansotropc deposton flux enables deep vas and trenches to be unformly flled. METAL SO2 CACEM98M04 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

40 PVD/IMPVD OF Cu: REACTOR LAYOUT PVD/IMPVD reactor wth Cu Target mtorr Ar (constant pressure), 150 sccm Annular magnetc feld (200 G below target Target: -200 V dc (2.4 kw) Substate: 40 V, 10 MHz, 350 W Cols: 2 MHz, 1250 W wth Faraday sheld Physcs ncluded: Gas heatng by sputtered target atoms Ion energy dependent sputter yeld Neutral and on momentum and energy Bulk electron energy equaton Monte Carlo secondary electrons Cross feld Lorentz forces AFOSR9912 Unversty of Illnos Optcal and Dscharge Physcs

41 MAGNETRON SPUTTER TOOL: Ar/Cu Secondary electron emsson from the target, and electron heatng n the sheath, produces a torrodal electron source. Peak on denstes are md-1012 cm-3. e-source Ar+ Cu+ CECAM98M05 Ar, 3.5 mtorr -200 V Target, 200 G UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

42 FLUXES IN THE Ar/Cu PVD TOOL Ion sputterng of the target produces a neutral Cu flux nto the plasma. Ion Flux The low gas pressure and long mean free math of Cu atoms results n the flux to the substrate beng drect neutrals. CECAM98M06 Ar, 3.5 mtorr -200 V Target, 200 G UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

43 IMPVD TOOL: FIELDS AND TEMPERATURES The added nductvely coupled electrc feld from the rf cols heats electrons n the bulk plasma producng a peak n temperature away from the target. Electrc feld Electron Temperature CECAM98M07 Ar, 20 mtorr -200 V Target, 200 G 1.25 kw ICP, 2 MHz UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

44 IMPVD TOOL: ELECTRON SOURCE AND DENSITY The combnaton of the magnetron felds and heatng from the rf cols produces a more extended electron source and electron densty. The on densty s 75% argon. Electron Source Electron Densty Ar+ CECAM98M08 Ar, 20 mtorr -200 V Target, 200 G 1.25 kw ICP, 2 MHz UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

45 IMPVD TOOL: ION FLUX AND SPUTTER SOURCE The magnetron focus the on flux to the target, producng a sputter source of Cu atoms. Due to the hgh gas pressure, the Cu atoms are thermalzed n the vcnty of the target. Ion Flux Cu Source CECAM98M09 Ar, 20 mtorr -200 V Target, 200 G 1.25 kw ICP, 2 MHz UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

46 IMPVD TOOL: Cu DENSITIES Due to the longer resdence tme of Cu n the chamber and the hgher electron temperature produced by the rf heatng, the Cu nventory s largely converted to ons and metastables [Cu(2D)]. Cu(2S) Cu(2D) Cu+ CECAM98M10 Ar, 20 mtorr -200 V Target, 200 G 1.25 kw ICP, 2 MHz UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

47 IMPVD TOOL: Cu FLUXES TO SUBSTRATE The flux of Cu to the substrate s 85-90% onzed. The neutral flux s largely metastable Cu(2D). Ar, 20 mtorr -200 V Target, 200 G 1.25 kw ICP, 2 MHz CECAM98M11 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

48 HOW DO YOU SELECTIVELY ETCH MATERIALS? MAKE POLYMERS MSU9913 Unversty of Illnos Optcal and Dscharge Physcs

49 PLASMA PROPERTIES: ICP S/SO 2 ETCHING USING C 2 F 6 Inductvely Coupled Plasma (ICP) reactors havng a based substrate are common plasma etchng tools for S and SO 2. The ICP power produces radcals and ons. The bas accelerates the ons nto the substrate. Gas mxtures contanng fluorocarbons (eg., C 2 F 6 ) are used as a source of both F atoms and polymer precursors (e.g, CF 2 ). ELECTRIC FIELD (1.5 V/cm) POWER DEPOSITION (1.7 W/cm 3 ) ANTENNA SHOWERHEAD BIASED SUBSTRATE PUMP PORT Ar/C 2 F 6 = 50/50, 10 mtorr, 600 W, 125 V MSU9908 Unversty of Illnos Optcal and Dscharge Physcs

50 PLASMA PROPERTIES: ICP S/SO 2 ETCHING USING C 2 F 6 ELECTRON DENSITY (4.5 x cm -3 ) CF2 DENSITY (1.7 x cm -3 ) Plasma denstes > cm-3 are typcal. Ar / C2F6 = 50/50 Pressure = 10 mtorr 650 W, 200 sccm Vo = 125 V F DENSITY (2.3 x cm -3 ) Feedstock dssocaton fracton s» 50% Ar/C 2 F 6 = 50/50, 10 mtorr, 600 W, 125 V MSU9909 Unversty of Illnos Optcal and Dscharge Physcs

51 S ETCH MODEL FOR FLUOROCARBON PLASMAS The S etch model n fluorocarbon plasmas s based on dffuson of F atoms through the polymer layer, passvaton of S stes and on actvated desorpton of the etch product. CFn F I + FI F FI SILICON Ss S Ss POLYMER CF4 CFn Ft SFn F CFn F I + F S SFn LAM9955 Unversty of Illnos Optcal and Dscharge Physcs

52 REACTIVE FLUXES AND ETCH CHARACTERISTICS For the test condtons and derved rate coeffcents, polymer eroson s domnated by F atom etchng, whose flux s farly unform. The polymer thckness s therefore domnated by the CF 2 flux, whch s center-hgh. The etch rate s therefore center-low. C 2 F 6, 10 mtorr, 200 sccm, 600 W, 100 V bas F, CF2 FLUXES (cm -2 s -1 ) CF2 (10 16 ) F (10 17 ) CF3 + (10 16 ) CF3 + FLUX (cm -2 s -1 ) ETCH RATE (A/mn) ETCH RATE POLYMER POLYMER LAYERS RADIUS (cm) RADIUS (cm) LAM9961 Unversty of Illnos Optcal and Dscharge Physcs

53 SPUTTERING PROBABILITY Wth ncreasng bas, the sputter rate of the polymer ncreases, polymer thckness decreases and etch rate ncreases. The sputter probablty was parameterzed to determne the senstvty of the model to ts value. Even at zero sputterng, etchng occurs due to the eroson of the polymer by F atom etchng. C 2 F 6, 10 mtorr, 200 sccm, 600 W ETCH RATE (A/mn) POLYMER ETCH RATE POLYMER LAYERS ETCH RATE (A/mn) ETCH RATE POLYMER POLYMER LAYERS SHEATH POTENTIAL (V) POLYMER SPUTTER PROBABILITY (po) LAM9964 Unversty of Illnos Optcal and Dscharge Physcs

54 REACTIVE FLUXES AND ETCH RATES vs WALL CONDITIONS Experments by Oehrlen and Cook have demonstrated that etch propertes can be propertes of wall condtons, partcularly wall temperature. The hypothess s that the CF 2 stckng coeffcent decreases wth ncreasng wall temperature, leadng to larger CF 2 fluxes, thcker polymer and lower etch rates. C 2 F 6, 10 mtorr, 200 sccm, 600 W, 100 V bas CF2 EMISSION MODEL (vs STICK) T(Wall) 1/ EXPERIMENT (vs T(wall) 1/2 ) CF2 STICKING COEFFICIENT 17 ETCH RATE (A/mn) ETCH RATE POLYMER CF2 FLUX CF2 STICKING COEFFICIENT POLYMER LAYERS CF2 FLUX (10 16 /cm 2 -s) LAM9962 Unversty of Illnos Optcal and Dscharge Physcs

55 Ar DILUTION It s dffcult to change the rato of neutral to on reactve fluxes by power or small changes n pressure. Ths rato can be changed by dlutng wth a non-fluorocarbon such as argon. Ar dluton ncreases the (on flux)/(cf2 flux) rato, decreasng the polymer thckness and ncreasng etch rate untl the F atom flux s nsuffcent to saturate stes. Ar/C 2 F 6, 10 mtorr, 200 sccm, 600 W FLUXES (cm -2 s -1 ) CF2 (10 16 ) F (2 x ) 1 ION/CF FRACTION Ar IN Ar/C2F6 ETCH RATE (A/mn) POLYMER ETCH RATE FRACTION Ar IN Ar/C2F POLYMER LAYERS LAM9967 Unversty of Illnos Optcal and Dscharge Physcs

56 REACTION MECHANISM FOR C 2 F 6 ETCHING OF SO 2 The reacton mechansm for SO 2 etchng s based on: Growth of C x F y Passvaton layer (balance of deposton and consumpton). Formaton of complex at the nterface between oxde and passvaton layer resultng from chemsorpton of CF x. Ion actvated (through passvaton layer) etchng of complex. Rate of actvaton scales nversely wth passvaton layer thckness. Dffuson of etch precursor and etch product. AVS99-14 Plasma C x F y Passvaton Layer SO 2 CF x CF x Flm Growth F F CF 4 Flm Etchng SO 2 Ι + CF x CF 4 Sputterng F CO 2 Energy Transfer SF 4 Dffuson F SF x Etch CF x Ι+ CO 2 Ι +, F SO 2 SF x CO 2 SF x SF 4 Etch UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

57 SURFACE COVERAGE The wafer surface stes are occuped by several surface speces. The surface coverages at steady state depend on the relatve rates of - complex formaton - Ion actvaton - F atom etchng - Sputterng 0.5 Fractonal Coverage SF 3 SO 2 SF 2 SF 2 CO 2 C 2 F 6, 10 mtorr 100 sccm 650 W ICP 100 V bas Radus (cm) AVS99-15 UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS

58 SUBSTRATE BIAS Wth ncreasng substrate bas, the passvaton layer thckness decreases and the etch rate ncreases. Smulatons and experments obtaned smlar trends. Passvaton Layers AVS C 2 F 6, 10 mtorr Rate Smulaton Passvaton Substrate Bas (V) Etch Rate (nm/mn) Passvaton Thckness (nm) CHF 3, 10 mtorr * Substrate Bas (V) Rate Experment Passvaton *N.R. Rueger, G.S. Oehrlen et al, J. Vac. Sc. Technol. A 15, 1881 (1997) UNIVERSITY OF ILLINOIS OPTICAL AND DISCHARGE PHYSICS Etch Rate (nm/mn)

59 SELECTIVITY IN S/SO 2 ETCHING: MODERATE BIAS Selectvty (and ansotropy) n S/SO 2 etchng s obtaned wth chemstres whch preferentally polymerze on the SO 2 sde walls and on S surfaces. "Break-through" to the underlyng S layer results n rapd polymer formaton and a commensurate decrease n etch rate. PHOTORESIST SO2 S 12.5 s 62.5 s s s Vo = 125 V Ar / C2F6 = 50/50 Pressure = 10 mtorr s s 650 W, 200 sccm MSU9905 Unversty of Illnos Optcal and Dscharge Physcs

60 SELECTIVITY IN S/SO 2 ETCHING: HIGH BIAS At hgher bas voltage, the commensurately hgher on energes produce a hgher etch rate, but also sputter the polymer faster. As a result, the polymer passvaton layer on the S s thnner and the process s less selectve (etch rate of S s hgher). PHOTORESIST SO2 S 12.5 s 62.5 s s s Vo = 190 V Ar / C2F6 = 50/50 Pressure = 10 mtorr s 650 W, 200 sccm MSU9906 Unversty of Illnos Optcal and Dscharge Physcs

61 SELECTIVITY IN S/SO 2 ETCHING: LOW BIAS At lower bas voltage, the lower on energes etch the SO 2 slower and produce thcker polymer layers whch mproves selectvty. The resultng buldup of polymer on the S must be cleaned out later, typcally by usng another plasma processng step (O 2 /H 2 O plasma). PHOTORESIST SO2 S 12.5 s 62.5 s s s Vo = 94 V Ar / C2F6 = 50/50 Pressure = 10 mtorr s s s 650 W, 200 sccm MSU9907 Unversty of Illnos Optcal and Dscharge Physcs

62 CONCLUDING REMARKS Modelng and smulaton of plasma equpment and plasma processes has developed to the pont that reactors are now frst desgned on the computer. Sgnfcant mprovements are, however, requred n our databases of fundamental parameters (e.g., cross sectons) so that more ntrcate plasma chemstres can be addressed. As the complexty (and cost) of new generatons of mcroelectroncs devces ncreases the ndustry wll, by necessty, ncreasngly rely on the vrtual factory to ad n ther development. MSU9914 Unversty of Illnos Optcal and Dscharge Physcs

63 ACKNOWLEDGEMENTS Past and Present Graduate Students and Post-Docs Fundng Agences Ron Knder June Lu Peter Xu Da Zhang Rob Hoekstra Mchael Grapperhaus Shahd Rauf Peter Ventzek Natonal Scence Foundaton Semconductor Research Corp. DARPA/Ar Force Offce of Scentfc Research Lam Research Corp. Motorola Appled Materals Tokyo Electron-Arzona MSU9902 Unversty of Illnos Optcal and Dscharge Physcs