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Electrodeposition of nanomaterials W. Schwarzacher H. H. Wills Physics Laboratory, University of Bristol Form Approved Report Documentation Page OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to

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SLIDE 1

Electrodeposition of nanomaterials

  • W. Schwarzacher
  • H. H. Wills Physics Laboratory,

University of Bristol

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SLIDE 2

Report Documentation Page

Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

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Electrodeposition of Nanomaterials

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Physics Laboratory,University of Bristol

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See also ADM001697, ARO-44924.1-EG-CF, International Conference on Intelligent Materials (5th) (Smart Systems & Nanotechnology)., The original document contains color images.

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Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std Z39-18

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SLIDE 3

Introduction:

Electrodeposition

  • has long history
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Miniature mask from Loma Negra, Moche culture, northern Peru: 100 B.C. – 800 A.D. Au applied to Cu by displacement plating.

From: ‘Pre-Columbian Surface Metallurgy’, H. Lechtman, Sci. Am. (1984).

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SLIDE 5

Introduction:

Electrodeposition

  • has long history
  • is an important current technology
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SLIDE 6

Metal interconnects in ultra large scale integrated circuits

  • electrodeposited Cu has

replaced Al in ULSI

  • higher conductivity –

better electromigration resistance

  • P. C. Andricacos, Interface,

8(1) (1999). Cu interconnects on IBM chip

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SLIDE 7

Introduction:

Electrodeposition

  • has long history
  • is an important current technology
  • will play pivotal role in nanofabrication
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SLIDE 8

Topics:

  • Controlling morphology
  • The dual-damascene method
  • Electroless deposition
  • Multilayer electrodeposition
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SLIDE 9

Topics:

  • Controlling morphology
  • The dual-damascene method
  • Electroless deposition
  • Multilayer electrodeposition
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SLIDE 10

Why do electrodeposited thin films become rough?

100 300 5000 nm 200 400 1000 nm

AFM image of film electrodeposited from 0.3M CuSO4 / 1.2M H2SO4, 4 mA cm-2, t=6 mins

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SLIDE 11
  • Surface tension leads to smoothening
  • Random fluctuations noise

m eq

v κ µ µ Γ + = ) , ( ) , ( / ) , (

4

t t h c t t h x x x η + ∇ − = ∂ ∂

  • Can incorporate these ideas in equation of motion for

surface e.g.

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SLIDE 12
  • Mass transport is by diffusion Laplacian instability

Peaks grow faster than valleys

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SLIDE 13

z (distance from electrode) C (Cu2+) C bulk

δ

Further consequences of diffusion:

  • Diffusion limited current
  • depends on convection

δ

bulk

C D − ∝ δ

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SLIDE 14

Complex non-linear system but simple power law behaviour (scaling)

10 100 1000 10000 1 10 100 1000

wsat (nm) deposition time t (s)

  • Local roughness scales as
  • Large-scale roughness ( ) scales as

sat

w

loc

t β

loc

t

β β +

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SLIDE 15
  • Can change current density, electrolyte concentration,

temperature

  • Only βloc changes.
  • βloc depends on ratio of current to diffusion-limited

current – Laplacian instability

  • S. Huo and W. Schwarzacher, Phys. Rev. Lett. 86, 256 (2001)
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SLIDE 16

This is a useful result:

  • Only 5 numbers (scaling exponents and pre-

factors) needed to describe roughness on any length-scale of film of any thickness

  • 2 are invariant, 2 can be determined from a single

film.

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SLIDE 17

Example: deposition on patterned electrodes

Resist

  • selective method
  • widely used in microfabrication (‘through-mask plating’)
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SLIDE 18

Example: deposition on patterned electrodes

200 nm

Electrodeposited Co-Ni alloy pillars for patterned media

  • studies. Patterning used interference lithography.

(Collaboration with C. A. Ross et al., M.I.T.)

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SLIDE 19

Example: deposition on patterned electrodes

Resist

  • edge greater current density
  • what happens to roughness?
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  • Edge significantly rougher than centre:

1E-5 1E-4 10 100

Centre Edge

wsat (nm) total charge deposited (C)

  • but same scaling exponent β+βloc
  • R. Cecchini, J. J. Mallett and W. Schwarzacher

(Electrochem. Sol. State Lett., in press)

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Tools for controlling morphology:

  • Pulse electrodeposition
  • High current density for ‘on’-pulse high

nucleation density

  • Complexing agents and additives

Current density time ton toff

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Influence of additives

  • When textured substrate used, Cl- has major effect

13.5 min

Cu-on-Si substrate No Cl-

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Influence of additives

  • When textured substrate used, Cl- has major effect

13.5 min

Cu-on-Si substrate 0.25mM Cl

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SLIDE 24

Topics:

  • Controlling morphology
  • The dual-damascene method
  • Electroless deposition
  • Multilayer electrodeposition
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SLIDE 25

Metal interconnects in ultra large scale integrated circuits

  • electrodeposited Cu has

replaced Al in ULSI

  • higher conductivity –

better electromigration resistance

  • P. C. Andricacos, Interface,

8(1) (1999). Cu interconnects on IBM chip

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SLIDE 26

Damascene plating Through-mask plating

seed layer resist seed layer resist

1 patterning 1 patterning

plated metal plated metal

2 electrodeposition 2 electrodeposition 3 planarization 3 seed layer etching

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SLIDE 27

PVD CVD plating

‘Superfilling’ needed to avoid defects

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Requires appropriate additives

  • D. Josell, B. Baker, D. Wheeler, C. Witt

and T.P. Moffat,

  • J. Electrochem. Soc. 149, C637 (2002).
  • 1.8 M H2SO4
  • 0.25 M CuSO4
  • 1 mM NaCl
  • 88 µM PEG (Mw=3,400) n=77
  • ~ 5 µM SPS/MPSA
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SLIDE 29

Simple model:

  • Additives act to block deposition
  • Additive diffusion to recesses slow

additive molecules

Unfortunately this model is wrong!

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SLIDE 30

Curvature Enhanced Accelerator Coverage Mechanism

Curvature enhanced accelerator coverage

  • Metal deposition rate increases with catalyst coverage
  • Local catalyst coverage increases

coverage increases as local area decreases area decreases - converse also true.

T.P. Moffat, D. Wheeler, W.H. Huber and D. Josell, Electrochemical and Solid-State Letters 4, C26 (2001).

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Curvature Enhanced Accelerator Coverage Mechanism

  • Initial condition - catalyst

coverage θ = 0

  • Catalyst accumulates from

reaction with precursors in electrolyte

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Curvature Enhanced Accelerator Coverage Mechanism

  • Catalyst coverage increases
  • n bottom, concave surface,

may decrease on top, convex corners.

  • Deposition rate highest at

bottom of feature.

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SLIDE 33

Curvature Enhanced Accelerator Coverage Mechanism

  • Catalyst coverage

maximized on bottom surface

  • Metal deposition rate at

bottom is accelerated.

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SLIDE 34

Curvature Enhanced Accelerator Coverage Mechanism

  • Catalyst coverage

maximized on bottom surface.

  • Metal deposition is highest
  • n bottom
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SLIDE 35

Curvature Enhanced Accelerator Coverage Mechanism

  • Inversion of curvature

‘Bottom’ is above trench. ‘Momentum plating’

  • Catalyst coverage θ

decreases as bump area increases

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SLIDE 36

Topics:

  • Controlling morphology
  • The dual-damascene method
  • Electroless deposition
  • Multilayer electrodeposition
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SLIDE 37

No need for electrical contact to substrate!

  • Conventional electrodeposition:

electrons that reduce metal ions in solution supplied from external circuit

  • Electroless deposition:

electrons generated at substrate by chemical reducing agent

  • Need catalytically active surface
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SLIDE 38

Example: electroless Cu

Typical electrolyte: 0.04 M CuSO4, 0.08 M EDTA (ethylenediaminetetraacetic acid - complexing agent), 0.24M HCHO (formaldehyde - reducing agent), 0.4 mM 2,2’-bipyridyl (stabilizer) 2 HCHO + 4 OH- 2 HCOO- + 2 H2O + H2 + 2 e- CuEDTA2- + 2 e- Cu0 +EDTA4-

ADS

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SLIDE 39

Mixed potential theory

Mz+ + ze

  • Mlattice

Resolution

  • Oxsolution + ne

Potential log i

catalytic surface catalytic surface

Oxidation Reduction

metal deposition metal dissolution electron generation electron consumption

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SLIDE 40
  • Electroless deposition can deposit single metals e.g.

Cu, Ni, Au or alloys e.g. CoFeB

  • Despite versatility, under-exploited in nanotechnology

T.Osaka, N.Takano, S.Komaba; Chem. Lett., 7 657 (1998)

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SLIDE 41

Topics:

  • Controlling morphology
  • The dual-damascene method
  • Electroless deposition
  • Multilayer electrodeposition
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SLIDE 42

Multilayer electrodeposition

  • Use electrolyte containing ions of more than one metal:

pulse deposition multilayer

  • Typical example: 0.05M Cu2+; 2.3M Ni2+; 0.4M Co2+
  • 0.2V pure Cu
  • 1.6V ferromagnetic Co-Ni-Cu alloy

Co-Ni-Cu Cu

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SLIDE 43

Multilayer electrodeposition

  • For 1-2 nm layers, electrodeposited multilayers show

Giant Magnetoresistance

  • Even greater effect with multilayer nanowires prepared

by template deposition:

Electrodeposition Research Group

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SLIDE 44
  • 8000
  • 4000

4000 8000 20 40 60 80 100 120 77K 295K %MR H (Oe)

Multilayer electrodeposition

  • Over 110% GMR at 77K, over 55% at room temperature

250Å

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SLIDE 45

Multilayer electrodeposition

  • What happens as layer thickness further reduced?
  • Multilayer heterogeneous alloy

Cu Ni Electrodeposition Research Group

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Multilayer electrodeposition

  • Can control Cu-Ni alloy composition through lengths of Cu

and Ni pulses

Ni-rich Cu-rich Cu-rich Ni-rich

Electrodeposition Research Group

2 .4 2 .8 3 .2 3 .6 4 .0

  • 4 0 0
  • 3 0 0
  • 2 0 0
  • 1 0 0

1 0 0 2 0 0

Current (mA) T im e ( s)

Current (mA)

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Application: alloy/alloy superlattice

40 42 44 46 48 3 4 5 6

log (intensity)

2 θ

100×(Cu0.19Ni0.81 6nm/ Cu0.79 Ni0.21 2nm) alloy/alloy multilayer

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SLIDE 48

Acknowledgments:

  • S. Huo, J. J. Mallet, R.Cecchini and P. Evans

(Bristol)

  • T. P. Moffat (NIST)

Disclaimer: the information in this presentation is provided in good faith, but no warranty is made as to its accuracy.