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