1

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

2

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

1

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 th

ickn

ess

(nm

)

*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 (c

ount

s/se

c)

Zr 4p

Zr 3d

Zr 3p

Zr 3s

O 1s

O KVV

C 1sSi 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

[1] O. Engstrom, B. Raeissi, S. Hall, O. Buiu, M.C. Lemme, H.D.B. Gottlob, P.K. Hurley, K. Cherkaoui, Solid State Electron. 51 (2007) 622.

[2] J.W. Long, B. Dunn, D. R. Rolison, and H.S. White, Chem. Rev. 104. 4463 (2004) [3] X. Jiang, H. Huang, F.B. Prinz, and S.F. Bent, Chem. Mater, 20, 3897, (2008) [4] R. Xu, Q. Tao, Y. Yang, C.Takoudis, Thin Solid Films, 520 (2012) 6752–6756 [5] Q. Tao, C. Takoudis, and G. Jursich, Appl. Phys. Lett. 96, 192105 (2010) [6] X.R. Jiang and S.F. Bent, J. Phys Chem. 113 17613 (2009) [7] Elam, J. W.; Zinovev, A.; Han, C. Y.; Wang, H. H.; Welp, U.; Hryn, J. N.; Pellin, M. J. Thin Solid

Films, 515, 1664 (2006) [8] G. Dey, S.D. Elliot. J. Phys. Chem. A, 116 (35), pp 8893–8901 (2012) [9] Z. Li, A. Rathu, R.G. Gordon. Journal of the Electrochemical Society. 153 (11) C787-C794 (2006) [10] B.S. Lim, A. Rathu, R.G. Gordon, Nature Materials: Harvard University, 2, pp 749-754 (2003) [11] P. J. Soininen, K.-E. Elers, V. Saanila, S. Kaipio, T. Sajavaara, and S. Haukka, J. Electrochem.

Soc. 152, (2), G122-G125(2005)

[12] A.P. Premkumar, N.S. Prakash, F. Gaillard, N. Bahlawane, Materials Chemistry and Physics 125 (3) pp 757-762 (2011)

[13] A. Satta, D. Shamiryan, M.R. Baklanov, C.M. Whelan, Q.T. Le, G.P. Beyer, A. Vantomme, K. Maex, J. Electrochem. Soc. 150, 5, G300-G306 (2003)

[14] J. A.T. Norman, M. Perez, S. E. Schulz, T. Waechtler, Microelectron. Eng. 85, 2159-2163 (2008) [15] K. L. Chavez, D. W. Hess, J. Electrochem. Soc. 148. 11. G640-G643 (2001)