Chamber Wall Effects on Polycrystalline-Si Reactive Ion ...web.eecs.umich.edu/~fredty/My Talks/NCAVS 2005/NCAVS Plasma Us… · Fred L. Terry, Jr., NCAVS Plasma Etch Users Meeting

Fred L. Terry, Jr., NCAVS Plasma Etch Users Meeting Sept 8, 20051

Chamber Wall Effects on Polycrystalline-Si Reactive Ion Etching in Cl2: A Multiple Real-

Time Sensors StudyFred L. Terry, Jr.

Dept of EECSUniversity of Michigan

+1-734-763-9764+1- 734-763-9324 (fax)

[email protected]://www.eecs.umich.edu/~fredty


Acknowledgements

Dr. Pete Klimecky (now with Intel)Dr. Craig Garvin (now with Inficon)

Prof. Jessy Grizzle (UofM)Dr. Jay Jefferies (Stanford)


Outline

• Multi-sensor Study of Cl2 Etching of Poly-Si in Lam 9400 TCP / Variations with F-cleans

– OES/Actinometry for Cl– Broadband RF for Plasma Density– RTSE for Poly Si Etch Rate

• Wall Recombination Affects Both Neutral Species and Ion Concentrations

• Ion Density Measurement Control of Cl2 etch of Si• Interpretation of Actinometry Results Requires Careful

Consideration of Gas Dilution Effects on ActinometerConcentration

• HBr-Cl2 Mixtures


Motivation• Chamber wall state as source of

transient variations• Loss rates at walls dependent on

wall buildup• Wall condition dynamically alters

chemical and plasma densities• Solutions for process drift: PMs,

additional clean steps, test wafers

Control of plasma density will improve process tolerance limits & OEE!

gas inlet

TCP coil

Plasmageneration

(energetic e-)

ion transport& l o sse s

upper electrode

lower electrode

wallbuildup

losseslosses


Previous Wall State Work• Sawin: 1st reported Etch Rate changes in Cl2 due to

O2 ( ) & CF4 ( ) chamber exposure. (JECS 1992)

• Donnelly: Increasing Cl neutral conc. with time in a quartz tube helical resonator. (JVSTA 1996)

• Aydil: Atomic Cl drifts due to SiO2 wall conditioning & SF6 wall cleans. (JVSTA 2002)


This Work

• 1st experimental evidence of Cl2 plasma density variation with F-cleans/wall prep.

• 1st direct correlation of real-time plasma density & real-time etch rate variations

• 1st direct real-time feedback control of plasma density to stabilize poly-Si etch rate in Cl2

• Improved Understanding of Wall Effects and Actinometry Results


Real-Time Monitorsa) RTSE – wafer stateb) BroadBand RF – plasma statec) FTIR – exhaust chem; SiCl4, SiF4

d) Diode Laser Absorption – chem statee) OES – [F], [Cl] intensity in chamber

Time Stamped Sensor System

CCDfor real time ER

1.79 m diode laserw/ alignment laser

µ

Detector

LAM 9400SE TCP

Broad band

RTSE

EMACS Real-Time DataAcq. & Control Computer

EMACS I/O Hardware

EMACS Real-Time System

Plasma Tool

Relay/Routing Box

Tool Signals

Actuator Signals

Digital I/O

Digital I/O

External Sensors (OES, lasers, etc.)

Inputs

Outputs

Inputs

Outputs

OEM Tool Controller

GPIB TCP/IP

Sensor Computers

Lock-ins

laser


RTSE

• Real-Time Spectroscopic Ellipsometer (RTSE)– Can optically model film etch depth, CD, sidewall slope– Use for real-time etch rate monitoring & transients


BroadBand RF

Quartz Tube

ProcessChamber Wall

Antenna

Wafer4 "

Network Analyzer

Remarks• High frequency (GHz), low power (mW) sweep of plasma• Plasma impedance spectroscopy• Must analyze broad spectrum of data (Broadband RF Probe)• Yields plasma density metric


BroadBand RF Circuit Analogy

• Loss paths give many resonance peaks in |Γ| for single ωp

• Model peaks as RLC circuit resonances w/

LCni1

=ω

Quartz Tube

ProcessChamber Wall

Antenna

Wafer4 "

Network Analyzer ZA

Zp2

Zp1

Zp3

Wall

Elec. Stat. ChuckCchuck

Ccoil

Cw

BB probe

ε(ω)

TCP Coil

Zp

Lp(ω) Rp(ω)C


BroadBand Signature

Frequency

Ref

lect

Coe

ff.

Electron Density

Condition 1

Condition 2

Signal sensitive to several important plasma outputsPlasma densityDelivered plasma powerChamber wall stateWafer surface chemistry


BB Peak Shifts & Density

• Two prominent resonance modes, ωn1 & ωn2, for these chamber conditions

• Peak frequencies shift right for increasing density

1 1.5 2 2.510

−2

10−1

100

LOG

| Γ

|

frequency in GHz

Seasoning etch rate recovery: BB response

run1run2run3run4run5

ωn1

ωn2


FTIR Effluent Measurements

• Fourier Transform InfraRed (FTIR) spectroscopy measures volatile etch products in foreline exhaust

• Yields dynamic chemical state changes in SiCl4 & SiF4

• Used commercial INDUCTtm FTIR from On-line Tech.

MovingMirror

StationaryMirror

Source

Beamsplitter

Interferometer

Sample

Detector

Computer


Etch Conditions

• Lam 9400 TCP SE• 10 mTorr• 100 sccm Cl2 flow

– 100 sccm total etch gas flow for Cl2/HBr experiments• 5 sccm Ar flow• 250 W TCP Power

– Varied for Plasma Density Control (Closed Loop) Runs• 100 W Bias Power

– Bias Voltage Measurement Not Available• Unpatterned 150 mm Poly-Si/30nm SiO2/Si

Test Wafers


Experimental Definition 1

• First project; 3 experiments• Compensate for ion density losses due to F-

cleaning of chamber walls1) Nominal Etch: Run plasma chamber at steady state chlorine

condition to establish real-time etch rate, BB peak position, and SiCl4 effluent level

2) Open loop recovery: Prep chamber walls using C2F6 clean to strip Silicon Oxychloride buildup, then run identical Cl2recipe.

3) Closed loop compensation: Run identically as uncontrolled open loop etch, only now use TCP power to maintain BroadBand setpoint.


(OL) Open Loop Drift Recovery

• Nominal etch rate flat, OL rate increasing (upper plot)• Nominal BroadBand ωn2 flat, OL ωn2 increasing (lower)• OL signals do not recover in 60sec

0 10 20 30 40 50 600

1

2

3

4

5

rate

(nm

/s)

Cl2 etch from F−prep chamber walls

nominalopen loop

0 10 20 30 40 50 601.2

1.4

1.6

time (s)

ω n2 (G

Hz)


(CL) Closed Loop Recovery

• Both nominal & CL etch rate flat (upper plot)• Both nominal & CL BroadBand ωn2 flat (lower plot)• CL signals recover in ~5sec

0 10 20 30 40 50 600

1

2

3

4

5

rate

(nm

/s)


nominalclosed loop

0 10 20 30 40 50 601.2

1.4

1.6

time (s)

ω n2 (G

Hz)


SiCl4 Effluent from FTIR

• Nominal SiCl4 is flat with no disturbance (black)• OL SiCl4 effluent is suppressed = lower ER (green)• CL SiCl4 is mostly compensated by controller (blue)

0 10 20 30 40 50 600

1000

2000

3000

4000

5000

time (s)

SiC

l 4 (uns

cale

d)

SiCl4 etch product from FTIR

nominalclosed loopopen loop


TCP Power OL vs. CL

• TCP power compensation in CL is very high at the start to make up for lost Cl+ ions to the walls

0 10 20 30 40 50 600

50

100

150

200

250

300

350

400T

CP

Pw

r (W

)


time (s)

open loopclosed loop


Experimental Definition 2

• Second project; 2 experiments, OL vs. CL• 1st wafer effect elimination with plasma

density compensation– Prep chamber walls using C2F6 clean– Follow with 3 open loop etches for 30s each in Cl2 and

measure etch depth– Prep chamber with C2F6 clean again– Follow with 3 closed loop etches for 30s each and

compare etch depth variation with that in OL case


1st Wafer Effect Reduction

• Open loop etch depth• Etch rate increases, both in

situ (RTSE) & ex situ(Reflectometer)

• Etch depth variation ~150Å

Closed loop etch depth with density correctionEtch depth variation reduced to ~50Å

1st wafer effect, open loopSP max-min: 156.2 Å, RTSE max-min: 146.7 Å

950

1000

1050

1100

1150

1200

1 2 3

run #

etch

ed m

ater

ial (

Å)

SPRTSE

1st wafer effect reduced, closed loopSP max-min: 49.2 Å, RTSE max-min: 56.7 Å

1150

1200

1250

1300

1350

1400

1 2 3

run #

etch

ed m

ater

ial (

Å)

SPRTSE

Three 30s Cl2 etches after single F-prep of chamber


TCP Compensation R2R

• Closed loop TCP power compensation reduces with each successive run as chamber begins to season

0 5 10 15 20 25 300

50

100

150

200

250

300

350

400

time (s)

TC

P p

ower

(W

)sequential closed loop control action

run1run2run3

(nominal)


Summary• 1st evidence of real-time Poly-Si etch rate variation in

Cl2 due to F-exposure.• 1st demonstration of ion density control in Cl2 to

compensate for Poly-Si real-time etch rate transients.• Effluent SiCl4 chemistry verifies both real-time

performance drifts and feedback correction.• Significant 1st wafer effect reduction after chamber

cleans with density feedback control. • Question: How Do We Explain the Results of Earlier

Researchers?– Actinometry Results & Interpretations– Key Point Is That Even For Qualitative Conclusions,

Actinometry/OES Results Must Be Carefully Analyzed Considering All Gasses Present In Chamber


Intensity Ratio ICl/IAr

λAr: 750.4nmλCl: 822.2nm

• After F-disturbance, both controlled & uncontrolled cases show similar Cl-neutral suppression and recovery.

• Simple Conclusion is that Ions (not neutrals) control etch rate for this process.0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 10 20 30 40 50 60

ICl

/IAr

Nominal

ICl

/IAr

OL

ICl

/IAr

CL

I Cl/I Ar

Nom

inal

time(s)


Cl Intensity

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60

ICl

Nominal

ICl

Open Loop

ICl

Closed Loop

I Cl N

omin

al

time(s)

• Cl Intensity is Flat in Nominal/Seasoned-wall case & varies in Open Loop and Closed Loop Cases


Ar Intensity

2

2.5

3

3.5

4

4.5

5

0 10 20 30 40 50 60 70

IAr

Nominal

IAr

Open Loop

IAr

Closed Loop

I Ar N

omin

al

time(s)

• Intensity of Ar Being Nearly Flat Was Previously Taken By Some Researchers To Show that the Plasma Density Was Constant

• This led to the conclusion that neutral Cl loss was responsible for Si etch rate variations

• We have shown that neither of these conclusions can be correct


OES Setup Equations

• Mass balance: Cl2 2dCl + (1-d)Cl2• Raw optical intensity signals:

• Intensity ratio:

d = Cl2 dissociation fractionfAr = mole fraction of Ar in feed gas (5%)

12Cl Cl Ar

Ar Ar Ar

I K fdI K f⎡ ⎤ ⎛ ⎞ ⎛ ⎞−

= ∝⎜ ⎟ ⎜ ⎟⎢ ⎥⎣ ⎦ ⎝ ⎠ ⎝ ⎠ 1

'

11 2

Cl

if d

Ar

Cl Ar

n

fdfα

→

⎛ ⎞ ⎛ ⎞−= ⎜ ⎟ ⎜ ⎟

⎝ ⎠⎝ ⎠

2( )Ar Ar e n ArI K T nω=2( )Cl Cl e n ClI K T nω=

coupledsimply byd, fAr(ne∝ωn

2)


Detailed Look at Dissociation Diluation Effect on Ar

( )

( ) ( ) ( ) ( ) ( )( )

2 2

2 2

2 1 Chlorine Dissociation

Now including the Ar actinometer concentration1 2 1 1 1

input gasmixture gascompositionin plasma

Ar Ar Ar Ar Ar

input gasmixture g

Cl dCl d Cl

f Ar f Cl f Ar d f Cl d f Cl

→ + −

+ − → + − + − −

( ) ( )( )

2The concentration of Ar is diluted by dissociationSo in the plasma, assuming all molecules, atoms, ions at the same temperature:

2 1 1 1

ascompositionin plasma

ArAr

Ar Ar Ar

Cl

fnf d f d f

=+ − + − − ( )

( )( ) ( )( )

( )( )

( ) ( )

1 1

2 1 2 12 1 1 1 1 1

Thus

2 1 12

Artot tot

Ar

Ar ArCl tot tot

Ar Ar Ar Ar

Ar ArCl

Ar Ar Ar

fn nd f

d f d fn n n

f d f d f d f

d f fn dn f f

⎡ ⎤ ⎡ ⎤=⎢ ⎥ ⎢ ⎥

+ −⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦⎡ ⎤ ⎡ ⎤− −

= =⎢ ⎥ ⎢ ⎥+ − + − − + −⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦

⎡ ⎤ ⎡ ⎤− −= =⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦


OES Fits

• Clean Chamber / High Recombination Case Yields Actinometry Data with Enough Structure to Extract αCl’ & KAr’ by Nonlinear Regression

• Dissociation Fractions for Other Runs Estimated by Assuming αCl’ is the same as the Clean Chamber Result

– Possible Te variations Errors– Possible Window Variations


Fitting of OES Data

( )( )( )

2 21

2 22

2

( )1 1

2 1( )

1 1

1 122 1

cl

ArAr Ar e n Ar n tot

Ar

ArCl Cl e n Cl n tot

Ar

Cl Cl ClAr Ar Ar

Ar Ar Ar Cl Ar Ar meas

Ar Ar tot n

fI K T n K nd f

d fI K T n K n

d f

I K If K fd dI K f K f I

I K n

α

ω ω

ω ω

ω

⎡ ⎤= = ⎢ ⎥+ −⎣ ⎦

⎡ ⎤−= = ⎢ ⎥+ −⎣ ⎦

⎛ ⎞⎡ ⎤ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎡ ⎤−= → = ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥−⎣ ⎦ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ ⎣ ⎦⎝ ⎠

=

( )2 2

2 22

1 1 11 1 1 12 1 2 2

( )

Ar Ar ArAr tot n Ar n

Cl Cl ClArcl Ar cl Ar cl Ar

Ar Ar Ar Armeas meas meas

Clcl Ar

Cl e n Cl Cl tot n

f f fK n KI I If f f f

f I I I

IfI K T n K n

ω ωα α α

αω ω

⎡ ⎤ ⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥′= =⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎛ ⎞ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤+ − + +⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎢ ⎥ ⎢ ⎥ ⎢ ⎥−⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦⎣ ⎦ ⎣ ⎦ ⎣ ⎦

= = 2 2

1 1 11 1 12 2 2

Cl Clcl Ar Ar

Ar Ar Armeas meas measCl n Ar n

Cl Cl Clcl Ar cl Ar cl Ar

Ar Ar Armeas meas meas

I If fI I I

K KI I If f fI I I

αω ω

α α α

⎡ ⎤ ⎡ ⎤ ⎡ ⎤⎡ ⎤ ⎡ ⎤ ⎡ ⎤⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥

⎣ ⎦ ⎣ ⎦ ⎣ ⎦⎢ ⎥ ⎢ ⎥ ⎢ ⎥′ ′= =⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎡ ⎤ ⎡ ⎤ ⎡ ⎤+ + +⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎢ ⎥

⎢ ⎥ ⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦ ⎣ ⎦⎣ ⎦ ⎣ ⎦ ⎣ ⎦

Fitting 2 constants allows quantitative extraction of d from OESdata


Ar OES Signal & Fit: SiCl4Ignored

0 10 20 30 40 50 60-0.5

0

0.5

1

1.5

2

2.5

3

3.5WNpoly11c_ol.txt Fitted Ar Signal K'Ar = 3.8284 +/- 0.114 α 'Cl = 15.8952 +/- 1.4055 (95.4% confidence limits)

Ar I

nten

sity

(arb

itrar

y un

its)

Time (s)

Measured IArFitted IArIAr-IAr,f it


Cl OES Signal & Fit: SiCl4Ignored

0 10 20 30 40 50 60-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5WNpoly11c_ol.txt Fitted Cl Signal K'Ar = 3.8284 +/- 0.114 α 'Cl = 15.8952 +/- 1.4055 (95.4% confidence limits)

Cl I

nten

sity

(arb

itrar

y un

its)

Time (s)

Measured IClFitted IClICl-ICl,f it


Cl2 Net Dissociation: SiCl4Ignored

0 10 20 30 40 50 600.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75WNpoly11c_ol.txt Dissociation Fraction d and nCl/ng K'Ar = 3.8284 +/- 0.114 α 'Cl = 15.8952 +/- 1.4055 (95.4% confidence limits)

Frac

tion

out o

f 1

Time (s)

dissociation fraction (d)ncl/ng


Ar Fraction: SiCl4 Ignored

0 10 20 30 40 50 60

2.5

3

3.5

4

Time (s)

Ar P

rece

ntag

e

nAr/ngScaled ωBB

2 (ne)

Minimum Possible Ar Precentage

IAr(t) ~const. due to opposing effects of dilution (↓) & ne (↑)


Dissociation Fractions: SiCl4Ignored

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Dissociation Fractions

Dis

soci

atio

n Fr

actio

n

time (s)

WNpoly11c_ol.txt WNpoly10c_CL.txt WNpolygold_nom.txt


Intensity Ratio ICl/IAr λAr: 750.4nmλCl: 822.2nm

Why is feedback controlled ICl/IArstill low? – Our Next AVS Paper : GENERATION of Cl Is Increased but COMSUMPTION by Si Etching & Dilution by SiCl4Offset Generation0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 10 20 30 40 50 60

ICl

/IAr

Nominal

ICl

/IAr

OL

ICl

/IAr

CL

I Cl/I Ar

Nom

inal

time(s)


Key Reactions2

2

4

4 2 2

4 2 3 2

2 Dissociation2 Recombination (wall & bulk gas phase)

2 Ionization & Bulk Deionization4 Etch

Deposition Reactiox y

v z x y

Cl ClCl Cl

Cl e Cl eSi Cl SiClSiCl SiO SiO Cl Cl Cl

SiCl Al O Al Si O Cl Cl Cl

− + −

→→

+ ++ →

+ → + + ⎫⎪⎬+ → + + ⎪⎭

ns (unbalanced)


Simplified Reaction Set

2 2 2

molecules in

Assuming Cl ionization and Si-species depositionReactions have small effects on gas species concentrations,the other remaining reactions yield:

Cl Ar Si SiF Cl F Ar F Si xCl yCl F Si+ + → + +

( ){ }

2

2

4

chamber gas phase molecules

2

2

1 2 for mass balance2

1 where Net Dissociation Fraction of

atoms/s consumed by etching known from measured etch rate & f

Ar

Si Cl

Cl

Si

Cl f Ar

x y F F Cl

y d F d Cl

F Si

+

+ + =

= − =

=

2

lowsSo

2 4Cl Six dF F⎡ ⎤= −⎣ ⎦


Result of Simplified Reaction Set

( )( )

( )

( )

2 2

2

2

2

2

2 4 1

1 3

2 41 3

1 3

g Si Ar

g Cl Si Cl Si Ar

g Cl Ar Si

Cl SiCl g g

Si Ar Cl Ar Si

Ar ArAr g g

Si Ar Cl Ar Si

Cl Cl Cl e Ar Ar

n x y F F

n dF F d F F F

n d F F F

dF Fxn n nx y F F d F F F

F Fn n nx y F F d F F F

I K n n I K

∝ + + +

∝ − + − + +

∝ + + −

⎡ ⎤−⎡ ⎤= = ⎢ ⎥⎢ ⎥+ + + + + −⎢ ⎥⎣ ⎦ ⎣ ⎦

⎡ ⎤⎡ ⎤= = ⎢ ⎥⎢ ⎥+ + + + + −⎢ ⎥⎣ ⎦ ⎣ ⎦= =

2

'

Measured Actinometry Ratio:2 41

Ar e

Cl SiCl Cl Cl Cl em

Ar Ar Ar Ar e Cl Arm

n n

dF FI K S n nAI K S n n Fα

−⎡ ⎤⎡ ⎤≡ = = ⎢ ⎥⎢ ⎥

⎣ ⎦ ⎣ ⎦

ClActinometry Signal Suppressed by Etch/Loading


2

2

2

' '2

'

'2

'

'2

'

112

112

112

Cl Cl m ArCl BB

Cl Cl m Ar Si

Ar m ArBB

Cl Cl m Ar Si

Ar ArAr BB

Cl Cl m Ar Si

K A FI PF A F F

K A FPF A F F

K FI PF A F F

αωα

ωα

ωα

⎡ ⎤⎢ ⎥⎢ ⎥=

⎛ ⎞⎢ ⎥+ + −⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦⎡ ⎤⎢ ⎥⎢ ⎥=

⎛ ⎞⎢ ⎥+ + −⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦⎡ ⎤⎢ ⎥⎢ ⎥=

⎛ ⎞⎢ ⎥+ + −⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

2eAssume is constant & n =C where C is a portionality constant fixed during the etch run.

g g gg

g BB

PVPV n RT nRT

T ω

= → =

' '& are the only unknownsThey can be extracted if there is sufficientvariation in ( ) & ( )

Ar Cl

Cl Ar

K

I t I t

α


Ar OES Intensity & Fit: SiCl4Included from RTSE

0 10 20 30 40 50 60-0.5

0

0.5

1

1.5

2

2.5

3

3.5WNpoly11c_ol.txt Fitted Ar Signal K'Ar = 3.7347 +/- 0.10994 α 'Cl = 17.1368 +/- 1.3555 (95.4% confidence limits)

Ar I

nten

sity

(arb

itrar

y un

its)

Time (s)

Measured IArFitted IArIAr-IAr,f it


Cl OES Intensity & Fit: SiCl4Included from RTSE

0 10 20 30 40 50 60-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5WNpoly11c_ol.txt Fitted Cl Signal K'Ar = 3.7347 +/- 0.10994 α 'Cl = 17.1368 +/- 1.3555 (95.4% confidence limits)

Cl I

nten

sity

(arb

itrar

y un

its)

Time (s)

Measured IClFitted IClICl-ICl,fit


Ar Fraction : SiCl4 Included from RTSE

0 10 20 30 40 50 60

2.5

3

3.5

4

Time (s)

Ar P

rece

ntag

e

nAr/ngScaled ωBB

2 (ne)

Minimum Possible Ar Precentage


Dissociation Fraction : SiCl4Included from RTSE

0 10 20 30 40 50 600.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

WNpoly11c_ol.txt Dissociation Fraction d and nCl/ng K'Ar = 3.7347 +/- 0.10994 α 'Cl = 17.1368 +/- 1.3555 (95.4% confidence limits)

Frac

tion

out o

f 1

Time (s)

dissociation fraction (d)ncl/ng


Dissociation Fractions: SiCl4Included from RTSE

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Dissociation Fractions

Dis

soci

atio

n Fr

actio

n

time (s)

WNpoly11c_ol.txt WNpoly10c_CL.txt WNpolygold_nom.txt

• Net Dissociation Fraction (d) Is Increased by Higher TCP Power in Closed Loop Run

• Net d is higher than estimated from procedure ignoring SiCl4

• Wall Recombination Still Suppresses Cl, d


( )4n

eCl

f T onlyIω⎡ ⎤

=⎢ ⎥⎣ ⎦

-1

0

1

2

3

4

5

6

0 10 20 30 40 50 60

Intensity Cl WNpoly 10c Closed Loop

ω4BB

/1.57 WNpoly10c Closed Loop

Intensity Cl WNpoly11c

ω4BB

/1.3882 WNpoly11c Open Loop

Arb

Uni

ts

Time

With some assumptions which we believe are justified:

Te for open loop case appears ~constant

Te is increased initially for closed loop case (constant αCl’ assumption may not be accurate)

Te (EEDF) Issue


Wall-State Effects Model• nCl reduced due to recombination on F-cleaned walls.

• nCl+ reduced due to lower availability of nClprecursor. ER decreases due to lower ion bombardment.

• Real-time feedback control corrects for ne≈nCl+losses by increasing Te, but does not fully recover nCl.

• Model supports ion dominated etch of Si w/ Cl2; nCl+ ER ≠ nCl. High nCl keeps surface Cl-saturated. ∴ion bombardment is rate limiting step.

• Extracted d varies significantly, causing constant IAr.


HBr/Cl2 Etches• HCl Is Formed In Mixing Manifold By HBr/Cl2 Reaction• Collaboration With Stanford Group Shows Similar Plasma/Gas

Chemistry Trends To Cl2 Only Cases– HCl absolute concentration was measured by laser diode absorption– HCl Dissociation follows BB-RF/plasma density trends– Chamber cleaning suppresses dissociation of HCl & increases plasma

density variation

• Open Loop Etch Rates Become More Constant With Increasing HBr & Show Less Sensitivity to Chamber Wall Condition

• Closed Loop Plasma Density Control Causes More Time Variation In Etch Rate for High HBr Concentration Cases

• HBr/Cl2 Etch Rates Are Not Directly Ion Limited & Future Work is Needed

– Wafer Surface Temperature?


HBr/Cl2 Etch (80/20)

Open Loop Closed Loop

0

1

2

3

4

5

40 60 80 100 120 140 160 180 200

wnpoly19c

ER (nm/s)

ER (n

m/s

)

time (s)

0

1

2

3

4

5

40 60 80 100 120 140 160 180 200

wnpoly1c

ER (nm/s)

ER (n

m/s

)

time (s)


Future Work• Modeling of BB Signals to extract more from the

shape of the data – collision parameters– Possible Te/EEDF Information

• Improved antenna designs for BB System• Lower-cost electronics for BB reflectometry• Apply density control to topography & profile variations.• Expand to other ion-dominated etches besides Cl2 etching of

Poly-Si.• Larger scale, multi-wafer tests to verify control improvements.• Ion density control most effective when etch is ion dominated.

Chemically dominated etches do not show same effects.• Combine ion density control with ion energy control.


Funding Acknowledgements• Initial Work Funded by SRC Center of Excellence for

Automated Semiconductor Manufacturing– Project Ended August, 1999

• Research funded in part by: AFOSR/DARPA MURI Center for Intelligent Electronics Manufacturing (AFOSR F49620-95-1-0524)

– Projected Ended August, 2001

• Research funded in part by: NIST Intelligent Control of the Semiconductor Patterning Process (70NANB8H4067)

– Project Ended June, 2002

Documents

Chamber Wall Effects on Polycrystalline-Si Reactive Ion ...web.eecs.umich.edu/~fredty/My Talks/NCAVS 2005/NCAVS Plasma Us… · Fred L. Terry, Jr., NCAVS Plasma Etch Users Meeting