Atomic Layer Deposition of Hafnium Oxide at Temperatures below 100ºC

K. C. Kragh

Dept. of Physics and Optical Engineering, Rose-Hulman Institute of TechnologyREU Student in the Advanced Materials Research Laboratory, University of Illinois – ChicagoMentors: Dr. G. Jursich and Dr. C. G. Takoudis

Objectives

• To examine low temperature Atomic Layer Deposition (ALD) growth of HfO2 on Si

• To verify the composition of low temperature HfO2 films

• To deposit HfO2 on polymer fibers for creating nanotubes

Thin film layers compose the structures of micro-scale technology.

• International Nomenclature– MEMS: Micro Electro Mechanical Systems– MST: Micro Systems Technology

• Applications to every scientific field

SiO2

AlTi

Nanoscale thickness of layers requires a separate deposition technique

Oxidizer

One AtomicLayer

Precursor

Atomic Layer Deposition (ALD)

Hf(N(C2H5)2)4 H2O

Process Overview

• Control Parameters• Substrate Preparation & Insertion• Lower the Reactor Pressure• Reaction• Raise the Reactor Pressure• Removal of Substrate• Analysis

ALD Reactor

Analysis of Film Thickness

• Spectral Ellipsometer– Material Model– Calibrated Reflection– Sample Preserved

• Low Temperature Results– Nonuniformity– Variation in values

Average Thickness after 50 cycles for a 5s Pulse Time with various Reactor

Temperatures

0

50

100

150

200

250

20 40 60 80 100 120 140 160

Reactor Temperature (ºC)

Ave

rage

Thi

ckne

ss (Å

)

X-ray Photoelectron Spectroscopy (XPS) identifies elements by binding energy.Source: 1486.6 eV Al KαThe photon (hf) must overcome

– Work Function (φ)

– Binding Energy (B.E.)Resulting Data from:

B.E. = hf – K.E. – φ

Sample DestroyedBy Photoemissive Electrons

Image: Simon Garretthttp://www.cem.msu.edu/~cem924sg/Topic09.pdf

Examine the Complete SurveyXPS Survey across HfO2 deposited on Silicon at 60ºC

02004006008001000Binding Energy (eV)

531 eV O 1s 213 eV and 224 eV Hf 4d5/2 and 4d3/2

381 eV Hf 4p3/2

439 eV Hf 4p1/2 282 eV C 1 s

17eV Hf 4f

Examine the Hf 4f Doublet

062308 Reactor at 60ºC for 5s pulsesXPS Hf 4f scan after sputtering

1416182022

Binding Energy (eV)

Inte

nsity

(a.u

.)

17.6 eV19.3 eV

Confirm HfO2 Films at Low Temperatures

• Peaks are in place• 15.8 eV Bulge is Hf-N

Bonding

1416182022 Binding Energy (eV)

Inte

nsity

(a.u

.)

30ºC 40ºC 60ºC 70ºC 80ºC

Inorganic nanotubes are the focus of increasing research.

• PCL Fibers (Poly-Caprolactone)

• Hafnia tubes by ALD• Applications:

– Electrical– Chemical– Mechanical

Top Image: Berserker79 http://en.wikipedia.org/wiki/Image:Pcl_synthesis.pngRight Image: Dr. Alan W. Nicholls & K. C. Kragh

PCL Fibers from Dr. A. Yarin

Cautions & Considerations for Polymer Fibers

• Temperature Operation• Careful Loading • Rigid Support• Slowly Dropping Pressure• Heating Strip Caution

Problems & Concerns

• Melting Temperature ~ 60ºC – Aldrich Polycaprolactone (PCL) Beads– Worrisome deposition– Drop to sub-60ºC runs

• Time Per Run

• Quality of Fibers

Pressure Variations

• Worried about Blowing out Fibers• Tried Lengthen the Distance

– Tube Temperature Concerns– Deposition Rate Concerns

• Tried Grating Possibilities

• Solution: Steel Envelope

Examination of HfO2 Coated Fibers

Scanning Electron Microscope (SEM)– Scattered Electrons– High Magnification– Composition found by Energy

Dispersive X-ray (EDX) – Back-Scattering for relative Atomic Number

Uncoated and Coated PCL Packets

Hafnium Oxide on PCL Fibers by Back-Scattering

EDX Composition of HfO2 PCL Fibers

Conclusions and Future Work

• ALD growth of HfO2 films will occur down to room temperature of 30ºC on Si & PCL

• ALD could be used to create hafnia nanotubes with polymer heating

Future Work: Heat out the PCL to create the actual nanotubes and evaluate their properties

Photo References• Garrett, Simon J. 2001. Special Topic in Analytical

Chemistry (CEM 924) Resource Page. http://www.cem.msu.edu/~cem924sg/index.html. Accessed 2008 June 16.

• Berserker79 http://en.wikipedia.org/wiki/Image:Pcl_synthesis.png

• All SEM photos captured on the Hitachi S-3000 N Scanning Electron Microscope operated by Dr. Alan W. Nicholls, Director of Research Service Facility and Electron Microcopy for University of Illinois at Chicago

• All other figures and graphs from K. C. Kragh

Acknowledgements

• National Science Foundation (NSF)• Department of Defense (DoD)• Grants: NSF-EEC 0755115 & NSF-CMS 0829903• Professor G. Jursich• Professor C. G. Takoudis• Professor A. Yarin• Dr. Alan W. Nicholls• Adam Kueltzo • Qian Tao • Manish Singh• Suman Sinha Ray • Lin Jiang