impact mechanisms of plasma-induced 193 nm photoresist...
TRANSCRIPT
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IMPACT
Mechanisms of Plasma-Induced 193 nm Photoresist Roughening
David B. GravesUniversity of California, Berkeley
IMPACT – UC DiscoveryDecember 2, 2009
UC Berkeley
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IMPACT
AcknowledgementsNanotechnological Manufacturing: Nanostructured Polymers Designed for Plasma/Energetic Beam Templating of Materials 2005-2009; NSF NIRT (DMR-0506988)G. Oehrlein (UMd), R. Phaneuf
(U Md); A. Alizadeh
(GE); G. Willson (UT); D. Graves (UCB) B. Long, R. Bruce, T. Kwon, D. Nest, J. Végh, G. Choudhary, H. Kan, F. Weilnboeck, T. Lin
Interaction of Plasma/Energetic Beams with Organic Masking Materials2005-present; NSF GOALI (DMR-0406120; -
0705953)G. Oehrlein (UMd), D. Graves (UCB), E. Hudson (Lam Research), C. Andes/D. Wang (Rohm & Haas; Dow)D. Nest, T. Chung, J. Végh, M. Titus, F. Weilnboeck, S. Engelmann, R. Bruce
Plasma-Surface Interactions in Nanoscale Feature Shape Evolution 2008-present; IMPACT: UC DiscoveryJ. Chang (UCLA), M. Lieberman (UCB), D. Graves (UCB)M. Titus, M. Morimoto
(Hitachi
visitor)
Plasma Etching and Surface Modification of Dielectrics2008-present; SRC (1862)J. Kelber (UNT), D. Graves (UCB)S. Behera, J. Lee
John Coburn (UCB)Dave Fraser (UCB)Harold Winters (UCB)
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IMPACT
Recent Focus on 193 nm PR
Pattern Transfer and Etching Complications
CH2 C
CH3
C O
CH2 C
CH3
C O
OO
CH2 C
CH3
C O
O
RO
O
x
y z
MAMA RAMAα-GBLMA
193 nm Photoresist (Dow Chemical)
Roughening•
Line-Edge (LER)•
Line-Width (LWR)•
Contact-Edge (CER)
Negishi, N. et al. J. Vac. Sci. and Technol. 23(1). 2005.
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IMPACT
Plasma-Induced Roughness in 193 nm Photoresists
29th International Symposium on Dry ProcessNovember 13-14 2007
Tokyo, Japan
Dense Features
Isolated Features
DARC Etch
Oxide Etch 1
Oxide Etch 2
MSL Etch Ash
Sidewall striations post-etch
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IMPACT
Additional Examples
After Development
ARC (Plasma)
Oxide (Plasma)
Ash (Plasma)
Final Feature
Spansion (unpublished)
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IMPACT PR Roughness: Device Performance Implications
What role can/does plasma play in improving or worsening this?
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IMPACT
PR Roughness: Exposure and Development
Namatsu et al., J. Vac. Sci. Technol. B 16, 3315 (1998).
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IMPACT
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IMPACT
Plasma-Polymer Interactions: Ions and Radicals
1.
Ion-surface interactions –
ion impact profoundly alters the near-surface polymer region.
-
dramatic example of ion-neutral synergy
2.
Key concept in ‘radiation’
effects in polymers: cross- linking vs. scissioning.
3.
How do these effects manifest themselves in plasma- polymer interactions?
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IMPACT Classic Ion-Neutral Synergy for INORGANIC Materials
JOURNAL OF APPLIED PHYSICS 50 (5): 3189-3196 1979
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IMPACT
Can There be Other Important Plasma-Induced Effects?
Well known that polymers are susceptible to scissioning and/or cross-linking by electrons and photons
- Electron beam and optical lithography are based on this!
Even well known that plasma-generated UV/VUV can strongly alter polymers….
- Earliest paper: may be from Martin Hudis, 1972
Look for photon and electron synergies in plasma-organic material interactions
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IMPACT 193 nm PR Roughness Observed: Ar-only plasma
»
ICP system: 10 mtorr; Vdc
~ -150 V; 100% ArG.S. Oehrlein
et al., UMd
800 W / 20 s Argon plasma-exposed 193 nm PR
0.5 m 0.5 m
0 nm
10 nm
5.10
What explains this extreme roughness??
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IMPACT Strategy to Identify Plasma-Surface Alteration Mechanisms
Ion G
un
Faraday Cup
Substrate
Turbo Pump
UV/VUV Source
Beam Experiments
Plasma Experiments
To NeutralMass Spec.
To IonMass Spec.
VUVSpec. Load-Lock
Port
To RoughingPump
OES
Ion CurrentProbe
Sample
To NeutralMass Spec.
To IonMass Spec.
VUVSpec. Load-Lock
Port
To RoughingPump
OES
Ion CurrentProbe
Sample
MD Simulations
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IMPACT
Molecular Dynamics (MD) Simulation
Interatomic Potential Interatomic Forces
r ij rik
rjk
typical MD time step:
Ions assumed toneutralize beforeimpact: fast neutralinteracting withsurface
initialconfiguration
update velocities
evaluateforces
update positions
Fi = -grad() = mi d2r/dt2
is assumed to model all reactive and non-reactive interactions(r
t
tt
(r
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IMPACT
Interatomic
Potentials
-
Tersoff-Brenner style, many body REBO potential for short range covalent bonds like Si-C-F-O-H systems*
-
Repulsive pair potential (Molière) for Ar
‘ion’ interactions
-
No van der
Waals
forces *C.F. Abrams and D.B. Graves, J. Appl. Phys., 86, 5938, (1999); J. Tanaka, C.F. Abrams and D.B. Graves, JVST A 18(3), 938 , (2000);D. Humbird
and D.B. Graves, J. Chemical Physics, 120 (5), 2405-2412, 2004
I. K. Jang, S. B. Sinnott, J. Phys. Chem. B. 108, 18993 (2004).
. B. Ni, H.K. Lee and S.B. Sinnott, J. Phys. Condens Matter, 16 7261-75
(2004)H/C
H/C/O
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IMPACT
MD Setup for MD Setup for PolymersPolymers•
C-H-O REBO Potential*
•
Ar+
at 100 eV
(normal incidence) from top•
Sample polymer simulation cell (~20 Å
in x and y)
–
9 chains of 20 monomers each–
Bottom two fixed
•
Periodic boundary conditions in X and Y•
Additional material added to the bottom
•
Minimum # of atoms maintained•
Cell cooled back to 300K
••
Polymers simulated (C/H/O)Polymers simulated (C/H/O)1.1. PS, PMMA, PVN, PBN, P4MS, PMAMAPS, PMMA, PVN, PBN, P4MS, PMAMA2.2. HDPE, TeflonHDPE, Teflon
* Ni B, Lee H K and Sinnott B S 2004
Top View
Side View
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IMPACT
Periodic boundary conditionsPeriodic boundary conditions
•
Mimics an infinite surface
17
Top View
Side View
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IMPACT
PMMA (CPMMA (C55
HH88
OO22
) simulation) simulation
•
C (red); O (green); H (black)
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IMPACT
Sputter yield v. Sputter yield v. fluencefluence
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IMPACT
Depth Profile: Steady StateDepth Profile: Steady State
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IMPACT
MD vs. experimentMD vs. experiment
•
Ion beam data•
Initial sputter yield matches well.
•
Sharp drop observed•
Initial sputter yield–
MD ~14 C/Ar
–
Experiment ~ 12 C/Ar D. Nest
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IMPACT
Propose 3 Effects to Generate PR Roughening in Ar
Plasma
•
Ion bombardment (Ar+)
Compare plasma (Ar) and vacuum beam exposures
•
VUV photons
•
Substrate temperature (50°C -100°C)
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IMPACT
Vacuum Beam Setup
To Turbo Pump
VUV Spec.
VUV Source
Ion SourceFaraday Cup
Sample
H2O InH2O Out
To Turbo Pump
VUV Spec.
VUV Source
Ion SourceFaraday Cup
Sample
H2O InH2O Out
To Turbo Pump
VUV Spec.
VUV Source
Ion SourceFaraday Cup
Sample
H2O InH2O Out
Vacuum Beam (VB) System: Side View
Base Pressure: 5 x 10-8
TorrSample Temperature: 20 –
100°CIon Source: 150 eV
Ar+
(Commonwealth)VUV Source: Xe
& Ar
VUV Source
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IMPACT
»
150 eV
Ar+, 4.0 x 1017
ions•cm-2
Ion bombardment only: Not enough roughening
0 nm
2.5 nm
50°C 60°C 75°C 100°C
1 m
193
nm P
R 0.86 nm 2.62 nm
10 nm
0.88 nm0.95 nm
200 nm
200 nm
248
nm P
R 0.78 nm0.64 nm0.34 nm0.45 nm
1 m
(D. Nest et al, 2007)
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IMPACT
»
Minimal surface roughness forms with remote UV/VUV exposure.
Only VUV: surface observation»
Surface roughness quantified with 1x1 m2
AFM images.
0.34
193
nm P
R 0.34 0.52 0.75
0.26 0.34 0.33 0.63
248
nm P
R
0 nm
2.5 nm
5 min 20 min 2.5 hr 11.5 hr
200 nm
(D. Nest et al, 2007)
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IMPACT
Simultaneous Ions and Photons: agreement!
1.17 nm
5.10 nm
2.03 nm
11.82 nm
Argon plasma“floating”75°C 100°C
9.80 nm5.19 nm
1.59 nm2.30 nm
193
nm P
R24
8 nm
PR
Ar+ & VUV (Ar) Beam
0 nm
25 nm
0 nm
10 nm
(D. Nest et al, 2007)
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IMPACT
Ar
104.8 and 106.7 nmTotal VUV Flux
To NeutralMass Spec.
To IonMass Spec.
VUVSpec.
Load-LockPort
To RoughingPump
OES
Ion CurrentProbe
H2
O In
H2
O Out
RF BiasPlasma StabilityPlasma Chemistry
Ion Composition ~ Products
Ion Energy
Ion Flux
Langmuir Probe:ne
, Te
, Φp
250 nm thick PR Sample
1 cm2
Ar
ICP ComparisonICP Chamber: Top-Down View10 mT
Ar, J+
~ 1 mA.cm-2
H. Singh, (UC Berkeley, 2000)
(M. Titus et al, 2009)
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IMPACT Elevated Temperature Necessary for Enhanced Roughening
Conditions:•
Vacuum Beam System•
150 eV
Ar+, Ar
VUV•
40 min Exposures•
4 x 1017
ions/cm2
Results:•
Monotonic increase in roughening
•
No variation in C = O and CH2
/CH3
loss i.e. bulk modification is independent of temperature.
20 40 60 80 1000
2
4
6
8
10
12 Plasma (120 eV Ar+) Beam (150 eV Ar+)
RM
S R
ough
ness
(nm
)
Temperature (°C)
(M. Titus et al, 2009)
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IMPACT
0 50 100 150 200 250 3000
1
2
3
4
5
6
7
8
Ion Energy (eV)
Vacuum BeamExperiment
(a)
No Crosslinking Little Crosslinking Crosslinked
RM
S R
ough
ness
(nm
)‘Damaged’
Layer Necessary for Enhanced
Roughening: Energetic Ions + VUV + Televated
(M. Titus et al, 2009)
J+ .t ~1017 cm-2
Jh
.t ~ 1017 cm-2
T~ 60°C
Beam vs. plasma: remarkable agreement overall
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IMPACT
Heat Only Ion Only VUV Only Simultaneous
Isol
ated
Den
se
Unprocessed
100nm 65degC 65degC 65degC 65degC
1.0E18 (ions/cm2) 4.8E17 (photons/cm2)4.8E17 (photons/cm2)
1.0E18 (ions/cm2)
Patterned Sample: Beam Measurements M. Morimoto (Hitachi visitor); C. Gabriel (Spansion 193 nm immersion samples)
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IMPACT
PMS vs. P4MS
P4MS PMS
CH2 CH CH2 CCH2
CH CH2
C
4.8x1017 147 nm photons·cm-2
1018 0.15 keV Ar+·cm-2
‘Cross-linking’
‘Scissioning’
Beam exposure
Deep scissioning necessary for enhanced roughness with Ar+
(D. Nest et al., accepted J. Phys. D, 2009)
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IMPACT Electrons: Scissioning Amplifies Roughening; Cross-Linking Suppresses Roughening
0
1
2
3
4
5
6
7
8
0
2
4
6
8
0 1 2 3 4 5 6 7 8 90
1
2
3
4
5
6
7
8
0 2 4 6 80
2
4
6
8
0 2 4 6 80
2
4
6
8
0 2 4 6 80
1
2
3
4
5
6
7
8 Ion+VUV 65oC
RMS
Roug
hnes
s (n
m)
Electron Fluence (mC/cm2)
Ion 65oC VUV 65oC
Ion 25oC Ion+VUV 25oC
VUV 25oC
•
Low fluence electrons (1mC/cm2) enhance surface roughness.
•
Electron-induced cross-linking changes surface morphology.
•
High fluence electrons (8mC/cm2) reduce surface roughness
•
Elevated substrate temperature increases surface roughness.
(T. Chung et al, 2009)
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IMPACT
PMMA-Based 193 nm PR Roughening Mechanism?
•Ion bombardment alters near-surface (1-2 nm), creating a heavilyH-, O-depleted, C-rich region
- probably compressively stressed
•There is a 1-to-1 correspondence between ion-induced C-rich surface layer and enhanced roughening
•VUV photon penetrate ~ 50-100 nm, breaking C-O bonds;this is known to increase polymer mobility or relaxation dynamics (cf. E. Pargon, LETI)
•Heating increases polymer mobility or relaxation dynamics
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IMPACT
PMMA-Based 193 nm PR Roughening Mechanism?
Pristine PR
Scissioned
(C-O depleted)
Cross-linked Layer (Carbon-rich)
Si
~100 nm
2 nm
R. Huang. Kinetic Wrinkling of an elastic film on a viscoelastic substrate. J. Mech. Phys. Solids. 53 (2005).
Huang model: wrinkling Compressively stressed
Our model of PR in plasma
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IMPACT
Conclusions
•Ion bombardment, VUV photons, (and substrate heating) act synergistically to give observed roughening
•Comparisons of beam and plasma exposure experiments show similar roughening when ion fluence and energy, VUV fluenceand wavelength and surface temperature are the same – even though fluxes and therefore experiment duration differ by ~ 102!
•Similar results for patterned 193 nm PR: ion/VUV/heating synergyin enhanced roughening
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IMPACT
Conclusions, continued
•1 keV electron beams on 193 nm PR act like VUV photons in enhanced roughening synergy if they remain in low fluencescissioning mode; cross-linking electrons suppress roughening
• P
methyl styrene vs. P4 methyl styrene experiments showed same pattern for these homopolymers: deep scissioning + ion bombardment and elevated T results in enhanced roughening