Transcript No Slide Title

AVS 2002
Nov 3 - Nov 8, 2002
Denver, Colorado
INTEGRATED MODELING OF ETCHING, CLEANING
AND BARRIER COATING PVD FOR POROUS AND
CONVENTIONAL SIO2 IN FLUOROCARBON BASED
CHEMISTRIES*
Arvind Sankaran1 and Mark J. Kushner2
1Department of Chemical Engineering
2Department of Electrical and Computer Engineering
University of Illinois, Urbana,
IL 61801, USA
email: [email protected]
[email protected]
http://uigelz.ece.uiuc.edu
*Work supported by SRC, NSF and SEMATECH
AGENDA
 Low dielectric constant materials
 Surface reaction mechanism and validation
 Fluorocarbon etching of SiO2/Si
 Ar/O2 etching of organic polymer
 High aspect ratio etching of porous and non porous SiO2
 Integrated Modeling: Ar/O2 strip of polymer and IMPVD
 Concluding Remarks
AVS03_AS_02
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LOW DIELECTRIC CONSTANT MATERIALS
 The increase in the signal propagation times due to RC delay has
brought the focus onto low dielectric constant (low-k) materials
(inorganic and organic)
 Inorganics such as porous silica (PS) are etched using
fluorocarbon chemistries; organics are etched using oxygen
chemistries.
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GOAL FOR INTEGRATED MODELING
 Plasma processing involves an integrated sequence of steps,
each of which depends on the quality of the previous steps.
CFDRC_0503_05
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SURFACE REACTION MECHANISM - ETCH
 CFx and CxFy radicals are the precursors to the passivation layer
which regulates delivery of precursors and activation energy.
 Chemisorption of CFx produces a complex at the oxide-polymer
interface. 2-step ion activated (through polymer layer) etching of
the complex consumes the polymer.
I*, CF 2
Plasma
CxFy
Passi vation
Layer
CFx
Ion +
Ion +
CxFy
CO 2
SiO 2CxFy
SiOCFy
Ion +,F
F
CxFy
Passi vation
Layer
Si
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CO 2
Ion +,F
SiF 3
Polymer
SiO2
Plasma
Ion +
SiF 3
 Activation scales as  1/L and
the L scales as  1/bias.
 In Si etching, CFx is not
consumed, resulting in thicker
polymer layers.
CFx
SiF 3
 Si reacts with F to release SiFx.
Polymer
SiF
SiF 2
SiF 3
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SURFACE REACTION MECHANISMS - STRIP
 Ar/O2 is typically used for polymer stripping after fluorocarbon
etching and resist removal.
 Little polymer removal is observed in absence of ion
bombardment suggesting ion activation.
P (s )  O(g )  P * (s )
P * (s )  I (g )  COFx (g )
 For SiO2 etching in mixtures such C4F8/O2, the fluorocarbon
polymer is treated as an organic. Resists are treated similarly.
AVS03_AS_06
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MONTE CARLO FEATURE PROFILE MODEL (MCFPM)
 The MCFPM predicts time and spatially
dependent profiles using energy and
angularly resolved neutral and ion fluxes
obtained from equipment scale models.
 Arbitrary chemical reaction mechanisms may
be implemented, including thermal and ion
assisted, sputtering, deposition and surface
diffusion.
 Energy and angular dependent processes are
implemented using parametric forms.
 Mesh centered identity of
materials allows “burial”,
overlayers and transmission of
energy through materials.
INTELTALK_AS_17
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MODELING OF POROUS SILICA
 MCFPM may include “two phase” materials characterized by
porosity and average pore radius.
 Pores are incorporated at random locations with a Gaussian pore
size distribution. Pores are placed until the desired porosity is
achieved with/without interconnects.

( r r0 )2
( r )2
P (r )  e
r0 : average pore radius
r : standard deviation
 Interconnected structures can be addressed.
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TYPICAL PROCESS CONDITIONS
Coils
Height (cm)
15
10 Feed ring
5
Substrate
Pump
port
8
Neutral Fluxes (cm-2 s-1)
F (1017)
6
4
CF (1017)
2
CF2 (1017)
H (1018)
0
6
Ion Fluxes (cm-2 s-1)
0
Wafer
5
F+ (1017)
4
3
2
CF2+ (1017)
1
0
CF3+ (1016)
0
1
2
3
4
5
6
Radius (cm)
10
5
0
Radius (cm)
5
10
 Process conditions
 Power: 600 W
 Pressure: 20 mTorr
 rf self-bias: 0-150 V
 C4F8 flow rate: 40 sccm
 The fluxes and energy distributions
are obtained using the HPEM.
AVS03_AS_08
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BASE CASE ION AND NEUTRAL FLUXES
CF (1016 )
6
5
6
F (1015 )
Ion Fluxes (cm-2s-1)
Neutral Fluxes (cm-2s-1)
7
CF2 (1017)
4
C2F4 (10 17)
3
2
C2F3 (10 16)
1
0
0
1
2
3
4
Radius (cm)
5
6
 Ions have a narrow energy and
angular distribution, in
contrast to neutrals.
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CF+ (10 14)
5
CF3+ (1014)
4
3
C2F4+ (1015 )
2
1
0
CF2+ (1015)
0
1
2
3
4
Radius (cm)
5
6
 Self-bias = - 120 V. Decrease
in neutral and ion fluxes
along the radius have
compensating effects.
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VALIDATION OF REACTION MECHANISM: C4F8
Model - M
Experiment - E
Etch Rate (nm/min)
600
500
SiO2 - M
400
SiO2 - E
300
 The mechanism was validated with
experiments by Oehrlein et al using
C4F8, C4F8/Ar and C4F8/O2.1
 Threshold for SiO2 etching was well
captured at self-bias  -40 V.
Polymer formation is dominant until
the threshold bias
200
100
0
C4 F 8
0
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50
100
150
Self Bias (-V)
 As polymer thins at higher biases,
the etching proceeds.
200
1
Li et al, J. Vac. Sci. Technol. A 20, 2052,
2002.
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Optical and Discharge Physics
VALIDATION: C4F8/Ar and
C4F8/O2
Etch Rate (nm/min)
500
400 SiO2 - M
 Larger ionization rates result in
larger ion fluxes in Ar/C4F8
mixtures. This increases etch rates.
SiO2 - E
300
200
100
C4F8/Ar
0
0
20
40
60
80
100
Ar Content (%)
 With high Ar, the polymer layers
thins to submonolayers due to less
deposition and more sputtering and
so lowers etch rates.
Etch Rate (nm/min)
300
SiO2 - M
 O2 etches polymer and reduces its
thickness. Etch rate has a maximum
with O2, similar to Ar addition.
SiO2 - E
200
100
C4F8/O2
0
0
20
40
60
O2 Content (%)
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80
100
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PROFILE COMPARISON: MERIE REACTOR
MERIE Reactor
Experiment
Model
CF2
Density
V. Bakshi, Sematech
 Process conditions
 Power: 1500 W CCP
 Pressure: 40 mTorr
 Ar/O2/C4F8: 200/5/10 sccm
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Etch Rate (nm/min)
600
PS = Porous
SS = Solid SiO2
E = Experiment
M = Model
2 nm, 30%
CHF3
E-PS
400
VALIDATION OF POROUS
SiO2 ETCH MODEL
500
M-PS
300
E-SS
M-SS
200
 Two porous substrates
 2 nm pore radius, 30% porosity
 10 nm pore radius, 58% porosity
100
Etch Rate (nm/min)
0
600
10 nm, 58%
500
CHF3
M-PS
E-PS
400
300
E-SS
M-SS
200
100
0
0
20
40
60
80
 Process conditions
 Power: 1400 W (13.56 MHz)
 Pressure: 10 mTorr
 rf self-bias: 0-150 V
 40 sccm CHF3
 Etch rates of P-SiO2 are higher than
for NP-SiO2 due to lower mass
densities of P-SiO2.
100 120 140
Self Bias (-V)
Exp: Oehrlein et al, J. Vac. Sci.Technol. A 18, 2742 (2000)
AVS03_AS_13
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WHAT CHANGES WITH POROUS SiO2?
 The “opening” of pores during etching of P-SiO2 results in the
filling of the voids with polymer, creating thicker layers.
 Ions which would have otherwise hit at grazing or normal angle
now intersect with more optimum angle.
 An important parameter is
L/a (polymer thickness / pore
radius).
 Adapted: Standaert, JVSTA 18, 2742 (2000)
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EFFECT OF PORE RADIUS ON HAR TRENCHES
50%
Etch Depth (nm)
500
CHF3
ER - PS
400
300
CER - PS
200
ER - SS
0
4 nm
10 nm
16 nm
4
6
8
10
12
14
16
Pore Radius (nm)
 With increase in pore radius, L/a decreases causing a decrease
in etch rates.
 Thicker polymer layers eventually lead to mass corrected etch
rates falling below NP-SiO2. There is little variation in the taper.
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HAR PROFILES: INTERCONNECTED PORES
0%
60%
Interconnectivity
INTELTALK_AS_40
100%
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Optical and Discharge Physics
EFFECT OF PORE RADIUS ON CLEANING
Fraction of Residual Polymer
1.0
0.8
0.6
16
13
0.4
10
7
0.2
4 nm
0.0
0.0
0.2
0.4
0.6
Time (Arb Units)
0.8
1.0
 Larger pores are harder to clean
due to the view angle of ion
fluxes.
 Unfavorable view angles lead to a
smaller delivery of activation
energy, hence lower activated
polymer sites.
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ANIMATION SLIDE
4 nm
16 nm
 Ar/O2=99/1, 40 sccm,
600 W, 4 mTorr
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Optical and Discharge Physics
CLEANING INTERCONNECTED PORES
 Cleaning is
inefficient with
interconnected
pores.
 Higher
interconnectivity
leads to larger
shadowing of
ions.
0%
60%
Interconnectivity
CHEME_AS_19
ANIMATION SLIDE
100%
 Ar/O2=99/1, 40 sccm,
600 W, 4 mTorr
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Optical and Discharge Physics
EFFECT OF ASPECT RATIO ON STRIPPING
 Cleaning decreases
with increasing
aspect ratios.
 Pores at the top of
the trench are
stripped better due
to direct ions (view
angle).
1
3
Aspect
Ratio
5
 Ar/O2=99/1, 40 sccm,
600 W, 4 mTorr
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ANIMATION SLIDE
 Pores near the
bottom see ions
reflected from the
bottom of the
trench and are
cleaned better.
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EFFECT OF PORE RADIUS ON Cu DEPOSITION
 Larger pores
require longer
deposition times
for conformal
coverage.
 This produces
thicker bottom
and open field
films.
NP
4 nm
10 nm
16 nm
 Surrogate study for seed layer
deposition and barrier coating.
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 Voids are created
or initiated by
larger pores.
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EFFECT OF INTERCONNECTIVITY ON Cu IMPVD
 Interconnected
pores need to be
sealed to avoid pinhole formation.
 Pore sealing by Cu
IMPVD ineffective
at larger
interconnectivities.
0%
30%
60%
Interconnectivity
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100%
 Thicker layers to
seal pores
produces trench
narrowing, which
can lead to pinch
off.
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CONCLUSIONS
 Etching of PS obeys scaling laws as that of SS. Etch rate
increases for smaller pores and slows for larger pores (at high
porosities).
 L/a determines etch rate variation of P-SiO2. Polymer filling
increases the net thickness.
 Stripping is inefficient for interconnected pore networks and for
larger pores due to the unfavorable view angles for the ion fluxes.
Low aspect ratio pores are better cleaned.
 Cu IMPVD is non-conformal for closed pore networks with larger
pores. Pin-hole formation and trench narrowing is seen for
interconnected networks.
AVS03_AS_22
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Optical and Discharge Physics