Selective Atomic Layer Deposition of TiO2 on Silicon/Copper-

patterned Substrates

UIC REU 2011

AMReL, University of Illinois at Chicago

Abigail JablanskyDepartment 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

Native Oxides• Prevention

– Self-assemblingmolecules1

• Minimization– Limited air exposure2

– Few cycles3

• Reduction– GaAs oxide remains under

HfO2 but converted under Al2O3

4

Tao, Q.; Jursich, G.; Takoudis, C. App. Phys. Lett. 2010, 96, 192105

1Chen, 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 NH3

5

• 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

0 5 10 15 20 25 30 350

5

10

15

20

25

30

f(x) = 0.858713450292395 xR² = 0.956743860444266

Thickness of TiO2 on Si

Number of cycles

Th

ickn

ess

(A)

7Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.

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.