1. Selective Atomic Layer Deposition of TiO 2 on Silicon/Copper- patterned Substrates UIC REU 2011 AMReL, University of Illinois at Chicago Abigail Jablansky Department of Chemical and Biomolecular Engineering, University of Pennsylvania

2. What is ALD? Atomic layer deposition Method: –Precursor (TDEAT) –Purge (N 2 ) –Oxidant (H 2 O) –Purge (N 2 ) Batch adsorption process Easily controlled but time-consuming Characterized with ellipsometry, X-ray photoelectron spectroscopy (XPS) Diverse applications www.cambridgenanotech.com/ald

3. 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

4. Native Oxides Prevention –Self-assembling molecules 1 Minimization –Limited air exposure 2 –Few cycles 3 Reduction –GaAs oxide remains under HfO 2 but converted under Al 2 O 3 4 Tao, Q.; Jursich, G.; Takoudis, C. App. Phys. Lett. 2010, 96, 192105 1 Chen, R.; Kim, H.; McIntyre, P.C.; Bent, S.F. Chem. Mater. 2005, 17, 536. 2 Lee, H.D.; Feng, T.; Yu, L.; Mastrogiovanni, D.; Wan, A.; Gustafsson, T.; Garfunkel, E. App. Phys. Lett. 2009, 94, 222108. 3 Tao, Q.; Overhage, K.; Jursich, G.; Takoudis, C. Submitted to Journal of Physi Chem. C. 2011. 4 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.

5. Copper Oxides Cu 2 O (cuprous oxide) –Linear –Most stable copper compounds at high T –Forms ammine under NH 3 5 CuO (cupric oxide) –Square planar –Decomposes at high T to Cu 2 O + O 2 –H 2 or CO reduction at 250 o C 5 Cu 2 O forms first, then CuO if stable 6 Reduction methods 5 Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry, 2nd ed. New York: Interscience Publishers, 1966, pp.894-902. 6 Zhu, Y.; Mimura, K.; Lim, J.; Isshiki, M.; Jiang, Q. Metal. and Mineral Trans. A. 2006, 37A, 1231.

6. Project Description ALD of TiO 2 onto Si/Cu wafers –Precursor: tetrakis(diethylamino)titanium (TDEAT) –Oxidizer: water Compare 24-hr Cu (1 nm native oxide) exposure to 1-hr 7 Minimize exposure from reactor to ellipsometer, x-ray photoelectron spectroscopy (XPS) 7 Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.

7. Reactor Schematic Ice bath Hot wall reactor Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.

8. Experimental Setup

9. 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

10. Results Verified Tao’s work 7 –Constant growth rate = linear growth 7 Tao, Q. PhD Dissertation, University of Illinois at Chicago, 2011.

11. Troubleshooting Temperature –Increases along path to reactor –Keep oxidizer cold Pressure –“Resting pressure” around 0.176 torr –Cycles during deposition N 2 tank, H 2 O level in bubbler Check ellipsometer Precursor level, clogged pipes

12. Results (cont.) The colors could represent a deposition layer thickness profile or a chemical vapor deposition (CVD).

13. Summary Objective: SALD of TiO 2 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 TiO 2 on copper Troubleshooting, design setbacks are important parts of engineering

14. Acknowledgements National Science Foundation, EEC-NSF Grant # 1062943 CMMI-NSF Grant # 1134753 Jorge I. Rossero A. Runshen Xu Arman Butt Dr. Jursich Dr. Takoudis

15. 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, 2 nd 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.