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12.12.2000Page 1
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Tool Comparison at GC Stack Etch in LAM TCPUsing Plasma Parameters (SEERS)
Christoph Steuerdiploma thesis
Institut für Oberflächen- und Mikrostrukturphysik, TU Dresdenin cooperation with Infineon Technologies GmbH & Co. OHG
Center for Development and Innovation
Das diesem Bericht zugrundeliegende Vorhaben wurde mit Miitteln des SächsischenStaatsministeriums für Wirtschaft und Arbeit (Förderkennzeichen 5706) gefördert.
Die Verantwortung für den Inhalt dieser Veröffentlichung liegt beim Autor.
12.12.2000Page 2
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Motivation
! Comparison of two plasma etch chambers LAM TCP 9400 SE atGate Conductor Stack Etch
! Critical etching of gate oxid found at finished products depending onchamber " find reason
! Investigate impacts of process parameter variations on in-situplasma parameters electron collision rate and electron density
! Find correlations between plasma parameters and measurementsas etch rate, uniformity
! Monitoring of high volume production
12.12.2000Page 3
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Principle plasma etch (LAM TCP)
! LAM TCP 9400 SE:! 1 - wafer - plane - chamber! low pressure at chamber! inductive RF power coupling (= Top
Power)! additional power capacitively coupled
(Bottom Power)! reactive gases flow as mixture into
chamber
! plasma:# low pressure# high density# asymmetric RF discharge
123
107
854
69
12.12.2000Page 4
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
GC Stack - Principle
Si3N4
WSix
poly - Si
SiO2
wafer
+ +
-- +
+ condensor
gate
gate connection (gate conductor GC)
wafer surface
gate oxide ( GOX insulator)
channel
12.12.2000Page 5
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
SEERS - electrical model of RF discharge
12.12.2000Page 6
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Principle of HERCULES measurement system
12.12.2000Page 7
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Plan of experiments
parameter from to step width Test Etchduration (s)
pressure 5 mTorr 30 mTorr 1; 2; 5 mTorr 30
top power 50 W 400 W 50 W 20
bottom power 0 W 300 W 25 W 20
Cl2-flow 0 sccm 80 sccm 5 sccm 25
HCl- flow 0 sccm 160 sccm 10 sccm 25
O2- flow 0 sccm 50 sccm 1; 5 sccm 25
NF3- flow 0 sccm 50 sccm 1; 2; 5 sccm 25
! parameter variations:# changing one gas flow while leaving all
others constant# pressure variation# power grid, remaining sizes under
process conditions
! process characteristics:# process chemistry at main etch dominated by
chlorine# competition between chlorine and fluorine
species# competition between deposition and erosion
depending on process conditions
! measured values:# electron collision rate# electron density# etch rate, uniformity at
several tests
! wafer types:# mono Si wafer, raw# poly Si wafer for etch
rate & uniformity
12.12.2000Page 8
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of parameter variations:Electron collision rate depending on pressure
! Pressure variation: collision rate shows nonlinear behaviour! Distinction of domination by ohmic heating / stochastic heating possible
(= different modi of power conversion into plasma)! Saturation / maximum at even higher pressures estimated
Mean electron collision rate vs. pressure, chamber 1
2,0E+07
4,0E+07
6,0E+07
8,0E+07
1,0E+08
1,2E+08
1,4E+08
0 10 20 30 40
pressure [mTorr]
Elec
tron
collis
ion
rate
[1/s
]
12.12.2000Page 9
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of parameter variations: Correlationbetween uniformity and electron collision rate
! Nonlinear behaviour of uniformity depending on meanelectron collision rate
! No explicit function at whole parameter range
uniformity vs. mean electroncollision rate; pressure variation,
Chamber 1
0,0
2,0
4,0
6,0
8,0
10,0
12,0
0,0E+00 5,0E+07 1,0E+08 1,5E+08
Electron collision rate [1/s]
unifo
rmity
[%]
12.12.2000Page 10
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of parameter variations: Correlationbetween electron collision rate and NF3 flow
! Using chamber several hours with chlorine chemistry exclusively! after that input of NF3
! Competition between chlorine and fluorine species (atoms, ions, radicals)! Explanation for shown behaviour ?
Mean electron collision rate vs.NF3-flow, chamber 1 & 2
0,0E+00
5,0E+07
1,0E+08
1,5E+08
0 10 20 30 40 50NF3-flow [sccm]
elec
tron
collis
ion
rate
[1/s
]
Ch.1 Ch.2
Mean electron density vs. NF3-flow, chamber 1 & 2
7,50E+09
1,00E+10
1,25E+10
1,50E+10
1,75E+10
2,00E+10
2,25E+10
2,50E+10
0 10 20 30 40 50NF3-flow [sccm]
elec
tron
dens
ity [1
/cm
³]
Ch.1 Ch.2
12.12.2000Page 11
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of parameter variations: Etch rate andplasma parameters depending on pressure
! Partly correlationbetween in-situ and in-line measurementspossible (right part)
! Example: mean etchrate (blue) and quotientelectron density /electron collision rate(purple) at pressurevariation
! some more sizes seemto influence etch rate
ER & f(CR, ED) vs. pressurechamber 2
160
170
180
190
200
0 10 20 30 40pressure [mTorr]
Etch
rate
[nm
/min
]
10,00
20,00
30,00
40,00
50,00
60,00
f(CR
, ED
) [ar
b.u.
]
Mean_Etch Rate ED/CR
12.12.2000Page 12
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of chamber comparison:Long term drift of chamber conditions
Control tests during whole experimental time:
mean collision rate[107 s-1]
mean electron density[1010 cm-3]
relative standard deviationcollision rate [%]
cham
ber 1
0
4
8
12
1,2
1,6
2,0
2,4
0%
25%
50%
75%
100%
cham
ber 2
0
4
8
12
1,2
1,6
2,0
2,4
0%
25%
50%
75%
100%
test No. test No. test No.
! All values at bothchambers showdrifts about wholetime exceptedmean electrondensity of ch. 2
! Ch.2: deviations ofmean values arehigher withincreasingtendency
! During eachparametervariation just smalldrifts
12.12.2000Page 13
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Chamber comparison by electron collision ratedepending on top power and bottom power
! No significant qualitative differences! Quantitative difference in collision rate! Interesting: local minimum along increasing bottom power
" separating ohmic + stochastic heating
reference chamber striking chamber
Mean Electron Collision Rate vs. VariationTop and Bottom Power, Chamber 1, t = 86 rfh
Mean Electron Collision Rate vs. VariationTop and Bottom Power, Chamber 2, t = 73 rfh
12.12.2000Page 14
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Chamber comparison by electron densitydepending on top power and bottom power
! Significant different shape and quantity at electron density area! Hint for cause of chamber difference: power coupling " hypothesis: top
power
reference chamber striking chamber
Mean Electron Density vs. VariationTop and Bottom Power, Chamber 1, t = 86 rfh
Mean Electron Density vs. VariationTop and Bottom Power, Chamber 2, t = 73 rfh
12.12.2000Page 15
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
electr
on de
nsity
[109 c
m-3
]
chamber 2
top *
botto
m po
w.
(top p
ow.)2
(pres
sure
)2
botto
m po
w.
top po
w.
press
ure
HCl-f
low
(botto
m po
wer)2
NF3-f
low
8
-2
42
6
0
2018
121416
10
-4
electr
on de
nsity
[109 c
m-3]
ow
chamber 1
pres
sure
top po
w.
botto
m po
w. (pre
ssur
e)2
top*b
ottom
pow.
(top p
ow.)2
(bott
om po
w.)2
Cl2-f
low
HCl-fl
ow
86
42
0
-4
-2
12
10
Results of chamber comparison - Pareto
proof by Pareto comparison:! sequence and size of
influences change chamberby chamber
! Top power has biggestinfluence on plasmaparameters at strikingchamber
! Pressure plays second roleafter powers
! Gas flows have just verylittle influence
reference chamber striking chamber
12.12.2000Page 16
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Application of electron density on RF power inputcalibration
! Idea: calibration of powerdissipation by electron densitymeasurement
! Problem:# strong nonlinearity, set point
near local minimum atstriking chamber
# to achieve target value(reference chamber) halvingactual value is necessary
! Strong nonliearity possibly caused by interaction of TCP power matchboxand bottom power matchbox
! Because of this strong nonlinear effect electron density could not be usedfor chamber matching,
! Hardware reason of local maximum must be fixed before chamber tuning
reference chamber
striking chamber
12.12.2000Page 17
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results of production monitoring - main etch! More than 25 000 product
wafer were monitored! Good results and high yields at
all time
! Main etch step! Means and relative standard
deviations of wafers! Two logic products! Products clearly
distinguishable " recipe andwafer impact
! Chamber drift during wet cleancycle visible " influence ofchamber
electron collision rate vs. wafer (mean)
5
10
15
20
25
30
35
40
0 5000 10000 15000 20000 25000
wafer
colli
sion
rate
[107 s
-1]
one point - one wafer
Logic product 1
Logic product 2
electron collision rate vs. wafer (rel. std. dev.)
0,0
0,2
0,4
0,6
0,8
0 5000 10000 15000 20000 25000wafer
rel.
std.
dev.
one point - one wafer
Logic product 2
Logic product 1
12.12.2000Page 18
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Results production monitoring - Over Etch
! Conditioning effectsremarkable after every shortclean
! Memory products causesignificant chamberconditioning effects
! Logic products lessconditioning
! Means of over etch steps(productive)
! Several selected memoryand logic products shown
! Products distinguishableeach by each " influence ofwafer and process
electron collision rate vs. wafer [mean]
0
50
100
150
200
3000 3200 3400 3600 3800 4000wafer
colli
sion
rate
[107 s
-1]
DRAM product 1 DRAM product 2 DRAM Product 3DRAM Product 4 Logic Product 1 Logic Product 2 one point - one wafer
electron density vs. wafer [mean]
5
10
15
20
2530
35
40
45
50
3000 3200 3400 3600 3800 4000wafer
el. d
ensi
ty [1
09 cm
-3]
DRAM Product 1 DRAM Product 2 DRAM Product 3DRAM Product 4 Logic Product 1 Logic Product 2 one point - one wafer
12.12.2000Page 19
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Summary
! Plasma parameter measurement was used sccessfully to identify the mainreason chamber performance difference – the top power coupling# Detection by electron density and electron collision rate# Proofed by Pareto analysis
! " Recommendation for maintenance team:# Check whole RF input parts and connections and power coupling into the
chamber
! Changes in pressure, powers, gas flows have nonlinear effects on electrondensity and electron collision rate
! Competing processes / reactions between chlorine and fluorine species! Distinct between ohmic heating and stochastic heating shown by plasma
parameters " effects on etch rate and uniformity
12.12.2000Page 20
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Summary (cont.)
! Drifting chamber conditions proven at both chambers by means ofelectron density and electron collision rate
! Production monitoring shows:# long time drift during wet clean cycle at main etch step# short time drift during short clean cycle at over etch step# memory products and their processes cause conditioning effects# products and groups of them distinguishable inside plasma parameters
12.12.2000Page 21
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Questions and possibel aims
! Reason is narrowed down - confirmation by maintenance teamnecessary
! Detailed hardware reason not known! Provide plasma parameter measurements including RF bias voltage
(depending on tool supplier)! Sequence inverted gas flow variation might confirm chamber chemistry
influence on plasma parameter (for example: saturation behaviour ofchamber wall)
12.12.2000Page 22
APCAPC
Christoph SteuerTU DresdenInstitut fürOberflächen- undMikrostrukturphysik
ProjectPULSAR
2nd Workshop on Self Excited Electron Plasma ResonanceSpectroscopy, 11th-12th December 2000, Dresden, Germany
Tool Comparison at GC Stack Etch at LAMTCP Using Plasma Parameters (SEERS)
Acknowledgement
! Acknowledge for all help, support and stimulating discussions to:# Profes. C. Laubschat (IOMP) and J.W. Bartha (IHM) - TU Dresden# A. Steinbach, S. Bernhardt, L. Christoph
Center for Development and Innovation# L. Dittmar, F. Zschorlich, J. Bullmann - ETCH# M. Klick et al. - ASI GmbH Berlin# U. Nehring - Product Engineering# M. Pierschel, T. Werner, H. Wendel, S. Mothes
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