Transcript PRODUCTION OF NANOWIRES WITH NANO

SYNTHESIS OF COPPER
NANOWIRES WITH NANOTWIN SUBSTRUCTURES
1Joon-Bok
Lee
2Dr. Bongyoung I. Yoo
2Dr. Nosang V. Myung
1Department
of Chemical Engineering, A-217 Engineering Quadrangle,
Princeton University, Princeton, NJ 08544-5263, USA
2Department of Chemical Engineering, University of California, Riverside, CA
92521, USA
Outline
Purpose of Research
– Usage of copper nanowires in VLSI (verylarge scale integration)
Objective of Research
Experimental Procedures
– Copper thin film electrodeposition
– Template-based copper nanowire fabrication
Results and Discussions
Introduction
Integrated circuit
– Discovery in 1970-driving force in advent of computer
systems
– Contain transistors and other semiconducting devices
– metal interconnections that serve as interconnections
for each component
– 1997: Electrodeposited Copper replaces sputtered
Aluminum as interconnecting material
Much higher conductivity and lower electromigration
Introduction
Advancements in technology increasing
interconnections in smaller areas
– International Technology Roadmap for
Semiconductors (ITRS) 2005: 100 million
transistors, 100,000 I/O in 30nm2 chips by
2015
Copper wires must also be reduced to the
nanometer scale
– Need high electrical conductivity and tensile
strength
A cross section of a microchip showing copper interconnections.
Introduction
strength of materials increase with decreasing
grain sizes that form the materials
– Smaller grain sizes give greater grain boundaries (GB)
– GBs resist propagation of dislocations
– But GBs also scatter electrons-higher resistance
Twin Boundary (TB) blocks dislocation but
maintains conductivity
Optimum: find methods to make nanowires with
TBs
– No known attempts in literature or otherwise
Grain Boundary
An example of twin
boundaries found
within specially
prepared copper
thin film samples
Objective
Understand effect of electrodeposition
conditions for synthesizing copper nanotwinned nanowires
Investigate meterials properties, including
morphology and microstructures, of
copper nanowires
Investigate electrical properties of copper
nanowires by measuring temperature
dependent electrical resistivity
Procedure
Determination of electrodeposition
conditions
– Form contiguous copper thin films without
powdery deposits
Plated on Brass substrates with 99.9% copper as
anode
Acid copper electrolyte
Direct Current and Pulse-reverse current tested
Selective chemical etching for grain size
observation
Procedure
Electrodeposition of Copper nanowires
Anodization of Al to form alumina
templates
– A) clean and cut Al to appropriate size
– B) Anodization of Al
20V Al anode Platinum coated Titanium
cathode
– C) formation of hexagonally close
packed Alumina
Average pore size 30nm
– D), E) selective chemical etching
D) Aluminum backing
E) Barrier layer etching to open pores
Procedure
Electrodeposition of Copper nanowires
– F) Sputter Au seed layer
To form working conductive electrode
– G) Place templates on glass slide to
form workable electrode
Copper tape and silver paint used to
form electrical connection
– H), I) electrodeposition of nanowires
Same electrolyte solution
– J), K) Isolation of alumina template
with enclosed nanowires
J) removal from glass slide through
acetone
E) mechanical removal of gold seed
layer
– L) Chemical dissolution of alumina
template
Grain Size versus Current Density
Increasing current
1000
900
800
700
Grain Size (nm^2)
Without Agitation
600
With Agitation
500
400
300
200
100
0
0
5
10
15
20
25
Current Density (mA/cm^2)
Grain size decreases as direct current is increased.
Agitation increases grain size.
30
Prelim. Grain Size Tests
Average current:
24mA/cm^2
250
Grain Size (nm^2)
200
150
100
50
0
Direct Current
Forward-Reverse Current
Figure 3. Grain size was similar or slightly decreased in reverse-forward
plating as compared to direct current plating
Prelim. Grain Size Tests
101
Current Efficiency (percent)
100
99
98
97
96
95
0
20
40
60
80
100
120
Current Density (mA/cm^2)
Figure 4. The efficacy was nearly 100% for most of current density conditions.
Prelim. Dep. Rate Tests
50
45
Deposition Rate (nm/second)
40
35
30
25
DC
20
Forward Reverse
Linear (DC)
15
10
5
0
0
20
40
60
80
100
120
Current Density (mA/cm^2)
Figure 5. The deposition rate seems to linearly increase as a function of current density.
Alumina Templates
2 hours
3 hours
4 hours
Figure 8. alumina template cross sections, taken after 2hours, 3hours,
and 4 hours of oxidation. (19, 44, 65 micrometers, respectively)
Alumina Templates
80
Deposition rate (nm/second)
70
60
50
40
30
20
10
0
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
Current Density (mA/cm^2)
Figure 9. The thickness seems to linearly increase as a function of time in oxidation.
Templates with enclosed nanowires
Nanowire deposition in custom alumina
templates.
Processed nanowires from the same
template.
Results-300nm thick nanowires
Copper nanowire, length 8.4
micrometers. Grown under 20mA/cm2
forward 60mA/cm reverse conditions
Copper nanowire, length 12.7
micrometers. Grown under16mA/cm2
conditions.
Nanowire Lengths
Copper nanowire, diameter 30
nanometers. Grown under 20mA/cm2
forward 60mA/cm reverse conditions
Copper nanowire, diameter, 30
nanometers. Higher resolution.
Future Plans
Further nanowires have been made with
custom anodized alumina templates
– sent to TEM for imaging and confirmation of
nanotwin structure growth
If nanotwin structures within the nanowires
are confirmed
– further testing to find out the optimum current
condition and other aspects will be done
Acknowledgement
I would like to thank:
Dr. B.Y. Yoo
Dr. Nosang Myung
UCR NSF REU BRITE program
UCR Nano Electrochemical System
Laboratory (NESL)