Selective Atomic Layer Deposition
of TiO2 on Silicon/Copperpatterned Substrates
UIC REU 2011
AMReL, University of Illinois at Chicago
Abigail Jablansky
Department of Chemical and Biomolecular Engineering,
University of Pennsylvania
What is ALD?
• Atomic layer deposition
• Method:
–
–
–
–
Precursor (TDEAT)
Purge (N2)
Oxidant (H2O)
Purge (N2)
• Batch adsorption process
• Easily controlled but
time-consuming
• Characterized with ellipsometry,
X-ray photoelectron spectroscopy
(XPS)
• Diverse applicationswww.cambridgenanotech.com/ald
Copper and Silicon
• Conductive substrate
• Small channels of
conduction in
microelectronics
• Need a thin barrier
layer on silicon
• Copper oxidizes more
easily
– Selective ALD (SALD)
– Native oxide
www.electroiq.com
• Prevention
Native Oxides
– Self-assembling
molecules1
• Minimization
– Limited air exposure2
– Few cycles3
• Reduction
– GaAs oxide remains under
HfO2 but converted under
Al2O34
1Chen,
Tao, Q.; Jursich, G.; Takoudis, C.
App. Phys. Lett. 2010, 96, 192105
R.; Kim, H.; McIntyre, P.C.; Bent, S.F. Chem. Mater. 2005, 17, 536.
2Lee, H.D.; Feng, T.; Yu, L.; Mastrogiovanni, D.; Wan, A.; Gustafsson, T.; Garfunkel, E. App. Phys. Lett. 2009, 94,
222108.
3Tao, Q.; Overhage, K.; Jursich, G.; Takoudis, C. Submitted to Journal of Physi Chem. C. 2011.
4Frank, M.M.; Wilk, G.D.; Starodub, D.; Gustafsson, T.; Garfunkel, E.; Chabal, Y.J.; Grazul, J.; Muller, D.A. App.
Phys. Lett. 2005, 86, 152904.
Copper Oxides
• Cu2O (cuprous oxide)
– Linear
– Most stable copper
compounds at high T
– Forms ammine under
NH35
• CuO (cupric oxide)
– Square planar
– Decomposes at high T
to Cu2O + O2
– H2 or CO reduction at
250oC5
• Cu2O forms first, then CuO if stable6
• Reduction methods
5Cotton,
F.A.; Wilkinson, G. Advanced Inorganic Chemistry, 2nd ed. New York: Interscience Publishers, 1966,
pp.894-902.
6Zhu, Y.; Mimura, K.; Lim, J.; Isshiki, M.; Jiang, Q. Metal. and Mineral Trans. A. 2006, 37A, 1231.
Project Description
• ALD of TiO2 onto Si/Cu wafers
– Precursor: tetrakis(diethylamino)titanium (TDEAT)
– Oxidizer: water
• Compare 24-hr Cu (1 nm native oxide) exposure
to 1-hr7
• Minimize exposure from reactor to ellipsometer,
x-ray photoelectron spectroscopy (XPS)
7Tao,
Q. PhD Dissertation, University of Illinois at Chicago, 2011.
Reactor Schematic
Ice bath
Hot wall reactor
Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.
Experimental Setup
Characterization
Ellipsometry
• Reflects light off thin films
• Measures polarization
after reflection
X-ray photoelectron
spectroscopy (XPS)
• X-rays are energy source
• Measures kinetic energy,
number of escaping
electrons
Results
• Verified Tao’s work7
– Constant growth rate = linear growth
Thickness of TiO2 on Si
35
30
Thickness (A)
25
y = 0.8587x
R² = 0.9049
20
15
10
5
0
0
7Tao,
5
10
15
20
Number of cycles
Q. PhD Dissertation, University of Illinois at Chicago, 2011.
25
30
35
Troubleshooting
• Temperature
– Increases along path to reactor
– Keep oxidizer cold
• Pressure
– “Resting pressure” around 0.176 torr
– Cycles during deposition
• N2 tank, H2O level in bubbler
• Check ellipsometer
• Precursor level, clogged pipes
Results (cont.)
The colors could represent a deposition layer
thickness profile or a chemical vapor deposition (CVD).
Summary
• Objective: SALD of TiO2 on Si for microelectronic
applications
• Method: reduce native oxide on Cu
– Minimize air exposure (in progress)
– In situ reduction (future work)
•
•
•
•
Characterization: ellipsometry, XPS
Results to date verify prior research
Not enough data to conclude about TiO2 on copper
Troubleshooting, design setbacks are important
parts of engineering
Acknowledgements
• National Science Foundation, EEC-NSF Grant
# 1062943
• CMMI-NSF Grant # 1134753
• Jorge I. Rossero A.
• Runshen Xu
• Arman Butt
• Dr. Jursich
• Dr. Takoudis
References
• Chen, R.; Kim, H.; McIntyre, P.C.; Bent, S.F. Chem. Mater. 2005, 17, 536.
• Lee, H.D.; Feng, T.; Yu, L.; Mastrogiovanni, D.; Wan, A.; Gustafsson, T.; Garfunkel, E.
App. Phys. Lett. 2009, 94, 222108.
• Tao, Q.; Jursich, G.; Takoudis, C. App. Phys. Lett. 2010, 96, 192105
• Tao, Q.; Overhage, K.; Jursich, G.; Takoudis, C. Submitted to Journal of Phys. Chem.
C. 2011.
• Frank, M.M.; Wilk, G.D.; Starodub, D.; Gustafsson, T.; Garfunkel, E.; Chabal, Y.J.;
Grazul, J.; Muller, D.A. App. Phys. Lett. 2005, 86, 152904.
• Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry, 2nd ed. New York:
Interscience Publishers, 1966, pp.894-902.
• Zhu, Y.; Mimura, K.; Lim, J.; Isshiki, M.; Jiang, Q. Metal. and Mineral Trans. A. 2006,
37A, 1231.
• Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.
• Falkenstein, Z.; Hakovirta, M.; Nastasi, M. Thin Solid Films. 2001, 381, 84.
• Tompkins, H.G.; Allara, D.L. J. Colloid and Interface Science. 1974, 49, 410.
• Sakata, Y.; Domen, K.; Maruya, K.-I.; Onishi, T. Appl. Spec. 1988, 42, 442.