Plasma etch control by means of physical plasma parameter measurement with HERCULES

Andreas Steinbach, Stefan Wurm, Christian Koelbl Ferdinand Bell, Daniel Koehler, Dirk KnoblochSematech AEC/APC Symposium X - 1 -

Plasma etch control by HERCULES

Plasma etch control by means of physical plasma parameter

measurement with HERCULES

A. Steinbach S. WurmF. Bell Ch. KoelblD. Knobloch D. Köhler



Contents

- Introduction - Motivation

- Plasma monitoring tool HERCULES

- Al etch on LAM TCP 9600 SE

- Contact etch on Applied Materials Centura MxP+

- Summary



Our way of plasma processing today – an effective way ?

- Experience and statistical methods in process development- “Process Monitoring” and Tool control by test wafers

Process parameters

powerpressure

B fieldgas flow

......

„Black Box“ called plasma

processing

Process resultsetch rateuniformityselectivityparticles

.......



Measuring Techniques for real time Plasma Monitoring

Hercules ne, e, PBulk

OES k*i( )

rf proberf voltagerf current

power

Ion flux probej+ (wall)

InterferometryReflectence spectroscopylayer thickness

We begin to

measure ! ProcessResultsexternal

measuredetch rateuniformityselectivityparticles

Species in the volume

ion densityion temperatureneutral densitiesneutral temp.excitations

Wafer Surface

ion energyion currentradiationneutral flows (radicals)surface temp.layer thickness

Plasma excitation

Power balance and potential distribution

electron collision rate, electron energy distributionelectron densityplasma potentialbulk power

Chamber parameters

surface temp.polymer e.g. gas ad / desorption depending on ion current

Process parameter

rf voltage (wafer)rf currentbias voltageeffective powerProcess

parametersexternal

powerpressureB fieldgas flowbody temp.



High Frequency Electron Resonance Current Low Pressure Spectroscopy

Basic HERCULES Model



Principle and experimental setup

- Passive electrical method,no influence on the plasma

- Integral measurement

Algorithm

rf currentrf voltage

F F T

ModelSEERS

Electron collision rate Electron densityBulk powerDC bias voltage



SEERS provides reciprocally averaged parameters

Self Excited Electron Resonance Spectroscopy



TCP: Al etch - trend analysis main etch

3640 3710 3780 3850 3920 3990 4060Lot No.

3.2.109

4.109

4.8.109

5.6.109

6.4.109

7.2.109

8.109ele

ctron

dens

ity [1

/cm3 ]

5.106

107

1.5.107

2.107

2.5.107

3.107

3.5.107

colls

ion ra

te [1

/s]op

tical

emiss

ion (E

P) *3

000

40

60

80

100

120

140

etch

time [

s] quick cleanquick clean

Cl2-MFC drift/errorCl2-MFC drift/error

Cl2-MFC errorCl2-MFC error

main cleanmain clean

Al etching - trend analysis main etch - LAM TCP 9600

Joint project Siemens - ASI - Lam

- Cl2 - MFC failure - Cleans



TCP: Al etch in Cl2 - first wafer effect

First wafer effect in main etch

0 40 80 120 160process time [s]

3.109

4.109

5.109

6.109

7.109

8.109

elec

tron

dens

ity [1

/cm

3 ]

first waferfirst wafer

third waferthird wafer

secondsecond

Al etching in Cl2 - first wafer effect - LAM TCP 9600Product wafer - resist mask on Al (appr. 50%)

main etchmain etch



TCP: Al etch - with / without barrier (TiN,Ti)Ti layer detected

0 20 40 60 80 100 120process time [s]

0

107

2.107

3.107

4.107

5.107co

llision

rate

[1/s]

with TiN (100 nm), Ti (15 nm)with TiN (100 nm), Ti (15 nm)

Ti layerTi layer

Al etching - with/without barrier (TiN, Ti) - LAM TCP 9600each curve averaged from five testwafers

Joint project Siemens - ASI - Lam

800 nm AlSiCu800 nm AlSiCu

break through (Al2O3)break through (Al2O3)

SiO2SiO2



MxP+: CT etch: Plasma parameters dependíng on process parameters

Electron Collision Rate vs. Pressure

5

7

9

11

120 140 160 180 200

Pressure [mTorr]

Col

l. R

ate

[10 7 s

-1]

BPSGStructure

Bulk Power vs. rf Power

10

15

20

25

30

600 700 800 900 1000RF Power [W]

B. P

ower

[mW

/ cm

²]

BPSGStructure

Change of process chemistry strong nonlinear correlation

Electron Collision Rate vs. CF4 flow

6.8

7.2

7.6

0 10 20 30 40CF4 flow [sccm]

Col

l. R

ate

[107 s

-1]

9.4

9.6

9.8BPSGStructure



MxP+: CT etch - Etch rate BPSG (blanket) depending on plasma parameters

Etch Rate and Uniformity BPSG vs. Bulk Power

400

500

600

12 14 16 18 20

Bulk Power [mW / cm ²]

Etch

Rat

e [n

m /

min

]

2

3

4

Uni

form

ity

[%]

RF Power increasing

Etch Rate BPSG vs. Electron Collision Rate

620

640

660

680

6 7 8 9

Electron Collision Rate [10 7 s -1]

Etch

Rat

e [n

m /

min

]

Pressure increasing

Etch Rate vs. Electron Density

610

630

650

670

10.2 10.7 11.2Electron Density [10 8 / cm ³]

Etch

Rat

e [n

m /

min

]

CF4 flow decreasing

Obvious correlations between etch rate and

electron collision rateelectron densitybulk power



MxP+: CT etch - Contact angle depending on plasma parameters

Contact Angle vs.Electron Collision Rate

86

87

88

89

90

8 9 10 11 12


Ang

le [°

]

Pressure increasing

Cont. Angle vs. Electron Density

84

86

88

90

10.2 10.4 10.6 10.8 11.0 11.2

Electron Density [10 8 / cm ³]

Ang

le [°

] CF4 flow decreasing

Cont. Angle vs. Electron Density

86

87

88

89

10.5 10.6 10.7 10.8

Electron Density [10 8 / cm ³]

Ang

le[°

]

CHF3 flow decreasing

Change of process chemistry no obvious correlation between electron density and contact angle



MxP+: Chamber monitoring of contact etch processes on product wafers

Process mix in Applied Materials Centura MxP+ chamber:Oxide and Nitride etch with CF4 / CHF3 / Ar / O2 chemistry

Process 1 Process 2 Process 3

Descum --- N2 / O2 ---

Step 1 BPSG BPSG OxideStep 2 --- Nitride ---



MxP+: CT etch - Chamber monitoring of product wafers: electron collision rate

Electron collision rate

- decreases with rf hours

- very sensitive to etch chemistry Pr1 Pr2 !

One point - one wafer

Electron Collision Rate vs. RF Hour

8,0

9,0

10,0

11,0

12,0

0 20 40 60 80 100 120RF Hour [h]

Colli

sion

Rat

e [1

0 7 s

-1]

Pr1 BPSGPr2 BPSGPr2 NitridePr3 Oxide



MxP+: CT etch - Chamber monitoring on product wafers: electron density

Electron density

- decreases with rf hours slightly

- sensitive to etch chemistry

Electron Density vs. RF Hour

7,5

8,5

9,5

10,5

11,5

12,5

0 20 40 60 80 100 120RF Hour [h]

Elec

tron

Dens

ity [1

0 8 cm

-3] Pr1 BPSG

Pr2 BPSGPr2 NitridePr3 Oxide




MxP+: CT etch - Chamber monitoring on product wafers: bulk power

Bulk power

- decreases with

rf hours- very sensitive

to power input- nearly not

sensitive to etch chemistry

Bulk Power vs. RF Hour

23

25

27

29

31

33

35

37

0 20 40 60 80 100 120RF Hour [h]

Bulk

Pow

er [m

W/c

m2 ]

Pr1 BPSGPr2 BPSGPr2 NitridePr3 Oxide




MxP+: CT etch - Chamber monitoring on blanket BPSG wafers

- Electron collision rate correlates with uniformity.

- Electron density and bulk power too

Electron Collision Rate vs. RF Hours

5

6

7

8

9

0 20 40 60 80 100 120RF Hour [h]

Col

lisio

n R

ate

[10

7 s -1

]

ER BPSGKondPARPL

Uniformity vs. Electron Collision Rate

3

4

5

6

7

8

9

5.2 5.7 6.2 6.7


Unifo

rmity

[%]

Uniformity vs. rf hours

3

4

5

6

7

8

9

0 20 40 60 80 100 120

rf hours [h]

Uni

form

ity [°

]



MxP+: Conditioning after wet clean

Wetclean

Stable chamber conditions after about 10 wafers.

Electron Collision Rate vs. rf hours

6

7

8

9

110 111 112rf hours [h]

Col

l. R

ate

[10

7 s -1

]

ResistREM SS5

Bulk Power vs. rf hours

16

18

20

22

24

110 111 112

rf hours [h]

B. P

ower

[mW

/cm

2 ]

Resist

REM SS5

Electron Density vs. rf hours

8.5

9.5

10.5

110 111 112rf hours [h]

Den

sity

[10

8 / cm

³]

ResistER BPSG



MxP+: CT etch - short term chamber drift depending on idle time

- Collision rate shows dependence on chamber idle time.- Constant chamber conditions after about 40 min.- Change in electron collision rate corresponds to change in electrical

failure counts.

Bad chamber

Electrical failure counts at Contact etch

Electron Collision Rate vs. Wafer Number

9,5

9,7

9,9

10,1

0 4 8 12 16 20 24Wafer

Colli

sion

Rat

e [1

0 7 s

-1] 0 min

45 min 5 h

Idle time

Wafer



Electron collision rate (mean)

2.0

2.2

2.4

2.6

2.8

3.0

0 2 4 6 8 10 12

wafer

colli

sion

rat

e [1

07 s-1

]eMxP+: Arcing detection

Electron collision rate vs. time

0

5

10

15

20

25

30

0 20 40 60 80 100 120 140

time [s]

colli

sion

rat

e [1

06 s-1

]

Wafer 9

Arcing between e - chuck and wafer



Summary

- Al etch in LAM TCP 9600 SE, oxide and nitride etch in Applied Materials Centura MxP+ have been monitored with HERCULES.

- The measured parameters depend significantly on chamber conditions and etch results.

- The masured parameters are absolute values.

- No difficult modeling by the user is necessary, results are immediate.



- Development and optimizing processes yes- Long and short term tool stability yes- Tool matching yes- Control of chamber cleaning yes- Control of power coupling into plasma yes - Endpoint detection possible - Layer resolution possible- Spatial resolution no- Reduction of test- and monitor wafers yes- Detection of tool failureyes- Arcing detection yes

Applications of the tool

Plasma etch control by means of physical plasma parameter measurement with HERCULES

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