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Jaya Parulekar, Illinois Institute of TechnologySathees Selvaraj, University of Illinois at Chicago
Christos Takoudis, University of Illinois at Chicago
NSF REU: UICAugust 1st, 2013
Selective Atomic Layer Deposition of Zirconium Oxide on Copper Patterned Silicon Substrates
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Motivation
Applications in microelectronics and nanoelectronics Semiconductors, transistors, memory and fuel cells
Challenges Need for transistor gates made with high dielectric
constant materials Need to achieve a precise level of thickness for gate
dielectric layers to prevent problems, such as leakage Need to selectively deposit layers on to specific
surfaces
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Atomic Layer Deposition (ALD)
Process by which thin films are deposited on surface of substrates at the Ångström level
Precursors are injected one at a time in a sequential and self-limiting manner
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Schematic of ALD design
Ethanol
Nitrogen
Nitrogen
Metal Precursor
Silicon wafer
Reactor
Activated switching valve
Vacuum pump
LN2 cold trap
Substrate loading port
Quartz tube
Furnace
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ALD Reactor
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Selective atomic layer deposition (SALD)
Selectively depositing films on patterned substrates
Molecular masking and self-assembled monolayers are techniques for SALD, but are inefficient
More efficient and practical method: SALD based on surface physics and chemistry of different materials
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Work from previous studies
Growth of HfO2 was observed on silicon immediately
Not observed on copper after 25 cycles
Growth on copper after 50, but not to the extent of siliconFigure from Q. Tao, C. Takoudis, and G. Jursich, Appl. Phys. Lett. 96, 192105 (2010)
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Work from previous studies
Increased amounts of Hf and O and decreased amounts of Si from 0 to 50 ALD cycles indicate HfO2 film growth
HfO2 deposition for copper is not observed until after more than 25 ALD cyclesTable from Q. Tao, C. Takoudis, and G. Jursich, Appl. Phys. Lett. 96, 192105 (2010)
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Reduction of copper oxide to metallic copper
Method to achieve purely SALDAs the number of cycles increases, the copper
surface undergoes oxidation and deposition is observed.
Challenge: selecting a reducing agent powerful and practical enough to ensure deposition of metal oxide
Reducing Agent selected: Ethanol
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Accomplishments and Open Challenges
Adding a reactant line to supply ethanol to the ALD reactor
E-beam deposition of 200 nm metallic copper on silicon substrate
Chose zirconium precursor, (Tris(dimethylamino)cyclopentadienyl zirconium).
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Accomplishments and Open Challenges
Difficulty in measuring film thickness on copper with ellipsometer Four point probe to
measure sheet resistance
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Accomplishments and Open Challenges
Ran trials on silicon wafers at 10, 15, 20, 25, 50, 75, 100, 150, and 200 cycles
XPS on silicon wafers treated with ethanol and zirconium precursor
Determined H2O oxidant line is unnecessary
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Results Obtained
Linearity is observed, indicating ALD has occurred on silicon substrate
0 50 100 150 200 2500
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2
3
4
5
6
7
8
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f(x) = 0.0402101723413199 xR² = 0.994545735383871
ALD Linearity of Si Substrate
Number of ALD cycles
ZrO
2 t
hic
kn
ess
(n
m)
*Carried out at 200 °C and base pressure of 500 mTorr
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Results Obtained
0 200 400 600 800 1000 1200 14000
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
XPS ZrO2 on Si Wafer at 50 cycles
Binding Energy (eV)
Inte
nsit
y (
co
un
ts/s
ec)
Zr 4p
Zr 3d
Zr 3p
Zr 3s
O 1s
O KVV
C 1s
Si 2p
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Future Work
XPS for copper patterned wafersFour point probe analysisSubmitting for potential publication in
reference journal
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Acknowledgements
The National Science Foundation: REU program EEC-NSF Grant #1062943
Additional National Science Foundation support CBET-NSF Grant #1346282
Air Liquide for supply of precursorProfessor Christos Takoudis and Dr. Gregory
JursichSathees Selvaraj, Graduate StudentThe Advanced Materials Research labFellow REU participants
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References
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