IMPACT

Mechanisms of Plasma-Induced 193 nm Photoresist Roughening

David B. GravesUniversity of California, Berkeley

IMPACT – UC DiscoveryDecember 2, 2009

UC Berkeley

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)

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.

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

IMPACT

Additional Examples

After Development

ARC (Plasma)

Oxide (Plasma)

Ash (Plasma)

Final Feature

Spansion (unpublished)

IMPACT PR Roughness: Device Performance Implications

What role can/does plasma play in improving or worsening this?

IMPACT

PR Roughness: Exposure and Development

Namatsu et al., J. Vac. Sci. Technol. B 16, 3315 (1998).

IMPACT

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?

IMPACT Classic Ion-Neutral Synergy for INORGANIC Materials

JOURNAL OF APPLIED PHYSICS 50 (5): 3189-3196 1979

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

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??

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

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

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

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

IMPACT

Periodic boundary conditionsPeriodic boundary conditions

•

Mimics an infinite surface

17

Top View

Side View

IMPACT

PMMA (CPMMA (C55

HH88

OO22

) simulation) simulation

•

C (red); O (green); H (black)

IMPACT

Sputter yield v. Sputter yield v. fluencefluence

IMPACT

Depth Profile: Steady StateDepth Profile: Steady State

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

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)

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

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)

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)

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)

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)

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)

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

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)

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)

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)

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

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

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

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