Consequences of Long Term Transients in Large Area High Density Plasma Processing: A 3-Dimensional Computational Investigation*

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1 ISPC 2003 June 22-27, 2003 Consequences of Long Tem Tansents n Lage Aea Hgh Densty Plasma Pocessng: A 3-Dmensonal Computatonal Investgaton* Pamod Subamonum** and Mak J Kushne*** **Dept of Chemcal and Bomolecula Engneeng ***Dept of Electcal and Compute Engneeng Unvesty of Illnos Ubana, IL 61801, USA emal: subamon@uuc.edu mjk@uuc.edu *Wok suppoted by SRC and NSF

2 AGENDA Intoducton Descpton of 3-dmensonal paallel hybd model Consequences of asymmetc pumpng Pulsed opeaton of ICPs Summay Pamod_spc_02 Unvesty of Illnos Optcal and Dschage Physcs

3 300MM WAFER PROCESSING: CHALLENGES Sde-to-sde asymmetes n plasma popetes become moe ctcal as wafe sze nceases. Sde pumpng and sde gas njecton ae common n ndustal eactos and can lead to asymmetes n speces denstes, fluxes and tempeatues. Flow asymmetes become ponounced when feedback though plasma conductvty make the nductve felds and powe deposton non-unfom. In ths wok, we nvestgate the effect of long tem tansents such as dung pulsed opeaton of ICPs on flow nduced asymmetes. Pamod_spc_03 Unvesty of Illnos Optcal and Dschage Physcs

4 HYBRID PLASMA EQUIPMENT MODEL (HPEM-3D) Hybd Plasma Equpment Model (HPEM-3D) s a modula smulato to addess low tempeatue plasmas. ELECTRO-MAGNETIC MODULE (EMM) E,B ELECTRON ENERGY TRANSPORT MODULE (EETM) V, N S, Te, µ FLUID KINETICS MODULE (FKM) Pamod_spc_04 Unvesty of Illnos Optcal and Dschage Physcs

5 GOVERNING EQUATIONS IN HPEM-3D Unvesty of Illnos Optcal and Dschage Physcs Contnuty (heavy speces) : Momentum (heavy speces) : Enegy (heavy speces) : Dft-dffuson (electon) : ( ) ( ) ( ) ( ) + + = j j j j s s v v N N k τ N v v P m 1 B v E N m q t v N ( ) S N v t N + = ( ) e e e s e e e S n D E µ n t n + + = E 2 ω 2 ) 2 (ν m 2 ν q N 2 s E ν m 2 q N ) ε (φ v P T κ t T v c N = Pamod_spc_05

6 GOVERNING EQUATIONS IN HPEM-3D Electon enegy tanspot s addessed by solvng the electon enegy equaton coupled wth a soluton of Boltzmann s equaton fo tanspot coeffcents. Electon enegy: k T e + ( ΓT ) e = Pheatng Ploss Posson s equaton : ε Φ(t + t) = ρ(t) + Wave equaton : E = µ dρ(t) dt ( ε E) ( σe + J ) t t = ρ(t) + q t[. ϕ + S ] Pamod_spc_06 Unvesty of Illnos Optcal and Dschage Physcs

7 REACTOR GEOMETRY AND SIMULATION CONDITIONS 2-tun symmetc col, showehead and an asymmetc pump pot SHOWER HEAD Heght-B 2-TURN COIL Base case condtons: Powe: 600 W, 10 MHz Heght-A ELECTRODE PUMP PORT Flow ate: 160 sccm Pessue: 5 mto A, C 2 F 6 /CF 4 Top Vew: Heght-A Heght-A: Denstes, Tempeatues, Fluxes Heght-B: ICP powe, Conductvty, Souces Pamod_spc_07 Unvesty of Illnos Optcal and Dschage Physcs

8 SYMMETRIC CASE: PLASMA PROPERTIES [Cl] ICP POWER [E] T e Powe s deposted beneath the cols wthn the skn depth. T e peaks n the skn depth due to postve powe deposton fom nductve felds. Electon densty peaks off-cente n the bulk of the plasma. C 2 F 6 /CF 4 (40/60), 600 W, 5 mto, 160 sccm Pamod_spc_08 Unvesty of Illnos Optcal and Dschage Physcs

9 CONTINUOUS WAVE (CW) OPERATION OF ICPS Flow nduced non-unfomtes n eacton souces make on densty non-unfom. Non-unfom plasma conductvty make the nductve felds and powe deposton non-unfom even wth symmetc cols. Non-unfom powe deposton enfoces the asymmetes n eacton souces. Ths feedback loop dung CW opeaton stengthens flow nduced asymmetes. Pamod_spc_09 Asymmetc Flow Neutal densty Reacton souces Electon, Ion densty CW Opeaton ICP Powe Plasma Conductvty Unvesty of Illnos Optcal and Dschage Physcs

10 PLASMA CONDUCTIVITY AND POWER DEPOSITION As a esult of asymmetc pumpng, the plasma conductvty s azmuthally asymmetc even at the plane below the showehead. Reacton souces ae non-unfom wth a maxmum away fom the pump pot. Pamod_spc_10 Unvesty of Illnos Optcal and Dschage Physcs

11 ASYMMETRIC ELECTRON AND RADICAL DENSITIES [F] Lage eacton souces esult n lage on and adcal denstes opposte to the pump pot. Wall ecombnaton esults n a vtual asymmetc souce of CF 2. Pamod_spc_11 Unvesty of Illnos Optcal and Dschage Physcs

12 PULSED OPERATION OF ICPS CW Opeaton of ICP Pulsed Opeaton of ICP Can pulsed opeaton of ICP mpove azmuthal unfomty? Pum p 1.5 Pot 1.0 Contnuous f bas ICP Powe Powe RF Bas Tme (µs) Pamod_spc_12 Unvesty of Illnos Optcal and Dschage Physcs

13 PULSED INDUCTIVELY COUPLED PLASMAS Pulsed plasmas Plasma etchng wth bette unfomty and ansotopy Impoved etch selectvty by modfyng the ato of chemcal speces Reduce chage buldup on wafes and suppess notchng Cuent models fo nvestgatng pulsed opeaton ae typcally global o 1-dmensonal. Dffcult to esolve long-tem tansents n mult-dmensonal plasma equpment models. Modeately paallel algothms fo 2-D and 3-D hybd models wee developed to nvestgate long tem tansents. Pamod_spc_13 Unvesty of Illnos Optcal and Dschage Physcs

14 DESCRIPTION OF PARALLEL HYBRID MODEL The HPEM, a modula smulato, was paallelzed by employng a shaed memoy pogammng paadgm on a Symmetc Mult- Pocesso (SMP) machne. σ E,B S EMM EETM FKS N E,N,σ The Electomagnetcs, Electon Monte Calo and Flud-knetcs Modules ae smultaneously executed on thee pocessos. E,B σ SHARED MEMORY S E,B,N E,N,σ S Pamod_spc_14 The vaables updated n dffeent modules ae mmedately made avalable though shaed memoy fo use by othe modules. EMM EETM FKS Unvesty of Illnos Optcal and Dschage Physcs

15 PULSED OPERATION OF ICPS Pulsed plasma s a f dschage n whch the ICP powe s pulsesquae wave modulated. Asymmetc Flow Pulsed Opeaton ON: Actveglow OFF: Afteglow Flow asymmetes also become ponounced when feedback though plasma conductvty make powe deposton nonunfom. Neutal densty Reacton souces ON OFF ICP Powe Pulsed opeaton of ICPs may ad n educng these asymmetes. Pamod_spc_15 Electon, Ion densty Dffuson smoothens densty n afteglow Plasma Conductvty Unvesty of Illnos Optcal and Dschage Physcs

16 TEMPORAL DYNAMICS OF PULSED PLASMAS Electon Densty (x cm -3 ) % 50% 70% Tme (µs) 20 khz Tme (µs) As the duty cycle nceases, the eacto aveage electon densty n the actveglow nceases. Electon densty n the actveglow nceases wth decease n 5 KHz as the ICP powe s ON fo longe duaton. Electon Densty (x cm -3 ) A, 600 W, 5 mto, 160 sccm, PRF: 10 khz, 50% Pamod_spc_16 Unvesty of Illnos Optcal and Dschage Physcs

17 PULSED ICPS: SYMMETRIC PUMPING [A + ] S-A + POWER cm -3 5 X X X cm -3 s -1 3 X Wcm Utlzng the plane of symmety, the smulatons need to be pefomed only fo 180 o. Wth symmetc pumpng, the plasma popetes ae azmuthally symmetc. A + densty peaks n the cente of the dschage. The powe deposton s also symmetc. Pamod_spc_17 Anmaton slde Unvesty of Illnos Optcal and Dschage Physcs

18 PULSED ICPS: ASYMMETRIC PUMPING At the wafe plane, densty and souce functon of A + ons ae asymmetc dung CW opeaton. By pulsng, asymmetes at the wafe plane ae educed. Dung the afteglow, dffuson smoothens the plasma densty pofle. In pulsed ICPs, feedback between non-unfom denstes and powe deposton s educed. [A + ] Pump Pot [S-A + ] Pump Pot Anmaton slde Pamod_spc_18 5 X 10 9 cm -3 5 X X cm -3 s -1 3 X Unvesty of Illnos Optcal and Dschage Physcs

19 PULSED ICPS: ASYMMETRIC PUMPING Dung CW opeaton, though the cols ae symmetc, ICP powe deposton s non unfom. ICP powe peaks at egons of lage plasma conductvty owng to a lage electon densty. Wth 50% duty cycle, ICP powe s off dung 50% of the pulse peod. In the absence of non-unfom souces, the plasma becomes moe unfom n the afteglow. ICP POWER Pump Pot [A + ] Pump Pot Anmaton slde Pamod_spc_19 3 X 10 9 cm -3 3 X Wcm Unvesty of Illnos Optcal and Dschage Physcs

20 EFFECT OF DUTYCYCLE: A + DENSITY 30% cm -3 70% 6 X X Pump Pot Pump Pot As the duty cycle deceases, the ICP powe s OFF fo longe duaton. Hence the educed feedback and nceased dffuson make the tme aveaged on densty moe unfom. Radal plasma unfomty s bette at a duty cycle of 70% compaed to 30%. Pamod_spc_21 Unvesty of Illnos Optcal and Dschage Physcs

21 TIME AVERAGED PLASMA PROPERTIES The pulsed opeaton of ICP makes the powe deposton moe unfom compaed to CW. On a tme aveage bass, the on densty s moe unfom. The flux of ons mpngng the wafe wll be moe symmetc CW Pulsed ICP POWER Pump Pot W/cm 3 [A + ] 0.95 Hence the etch o deposton pofles wll be moe unfom at dffeent azmuths on the wafe. Pamod_spc_22 1 x 10 9 cm x x x Unvesty of Illnos Optcal and Dschage Physcs

22 SUMMARY A new 3-D paallel hybd model was developed to addess tansents based on modeate computatonal paallelsm. Reacto scale asymmetes can esult n non-unfom tench evoluton dung fluoocabon etchng at dffeent azmuthal locatons. Dung pulsed opeaton, dffuson smoothens the plasma densty pofle n the afteglow, povdng a moe unfom set of ntal condtons fo the next powe pulse. The feedback between non-unfom denstes and powe deposton s also educed. The flux of ons mpngng the wafe wll be moe symmetc dung pulsed opeaton. Pamod_spc_23 Unvesty of Illnos Optcal and Dschage Physcs