k. overhage , q. tao, g. m. jursich , c. g. takoudis advanced materials research laboratory...
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K. Overhage , Q. Tao, G. M. Jursich , C. G. Takoudis Advanced Materials Research Laboratory University of Illinois at Chicago. Atomic Layer Deposition of TiO 2 on Silicon and Copper Substrates: Investigation of the Initial Growth. Acknowledgements. - PowerPoint PPT PresentationTRANSCRIPT
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K. Overhage, Q. Tao, G. M. Jursich, C. G. TakoudisAdvanced Materials Research LaboratoryUniversity of Illinois at Chicago
Atomic Layer Deposition of TiO2 on Silicon and Copper Substrates:Investigation of the Initial Growth
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Acknowledgements REU 2010 at UIC, sponsored by the National Science
Foundation and the Department of Defense
EEC-NSF Grant # 0755115
CMMI-NSF Grant # 1016002
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What is ALD?The Atomic Layer Deposition (ALD) process is used to deposit thin films layer by layer until a desired thickness is achieved.
Introduce one precursor, purge, then the other precursor, purge and repeat many times in the gas phase to deposit films on a substrate
Useful because ALD can deposit very thin films with uniform, conformal coverage
The focus of this study is deposition of TiO2
Photo from Barrier Layers Technology by Prof. Yosi Shacham-Diamand, Tel-Aviv University, 2000
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Substrate with active sites
Chemisorption of source A and saturation mechanism.
Purge
Chemical reaction between source A and source B and saturation mechanism
Purge
Source B (H2O)
Source A (TDEAT)ST
EP
1ST
EP
2STEP
3STEP
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Reaction Mechanism of typical ALD cycleALD is a surface-saturation reaction that deposits each monolayer of film, allowing for precise thickness control.
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Example application of ALDAn example application of an ALD process is the construction of the copper barrier layer in a chip.
The copper barrier layer prevents Cu from reacting with other chip materials, particularly silicon
Diagram from http://www.tms.org/pubs/journals/JOM/9903/Frear-9903.fig.5.lg.gif
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Objectives
Study TiO2 deposition on silicon and copper with different surface chemistries, with the goal of achieving selective deposition
Temperature-independent window Early growth / nucleation period Late growth / constant growth region
Findings can be used in future work to further promote selective deposition of TiO2 on Silicon
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SubstratesDeposition was performed on substrates with different surface chemistries.
Silicon with native oxide (approximately 1.5 nm-thick)
Silicon with reduced oxide (less than 1 nm-thick, 2% HF etching treatment)
Copper with native oxide (approximately 2 nm-thick)
ALD is surface reaction driven – therefore, the surface chemistry of the substrate is critical. Careful preparation steps were taken to properly prepare the substrates.
Optical test, measures film thickness
Light source shines on film, detector measures reflected light
Computer models calculate thickness based on reflective index of material
SE TheorySpectral Ellipsometry – measures film thickness
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Temperature-independent window
TiO2 deposition on silicon is independent of temperature between 150 and 200 °C.
Silicon with native oxide:Slope 1.2 A / cycle
100 125 150 175 200 225 25055
60
65
70
75
TiO2 on Si - Temperature Study
Temperature (oC)
Thic
knes
s (A
ngst
rom
s)
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Late GrowthDeposition from 50 to 150 cycles on silicon with native oxide
Once the early growth phase is complete, TiO2 deposition proceeds at 1.3 Å / cycle. This is in agreement with current literature values.
0 50 100 150 2000
50
100
150
200
250
TiO2 on Silicon with Native Oxide
Number of Cycles
Thic
knes
s (A
ngst
rom
s)
Slope = 1.3 Å / cycle
0 10 20 30 40 50 600
10203040506070
TiO2 Growth on Si(100)
Number of Cycles
Thic
knes
s (A
ngst
rom
s)
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Early GrowthDeposition from 0 to 50 cycles on the two kinds of silicon surfaces
Here we see a negligible nucleation time on both substrate surfaces. Growth rates are equal to the slope of the best fit line.
Silicon with native oxide:Growth rate 1.2 Å / cycle
Silicon with reduced oxide: Growth rate 1.0 Å / cycle
Silicon with < 1 nm oxide
Silicon with 1.5 nm native oxide
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X-rays penetrate sample surface, knocking out core electrons of the film atoms
Detector records energy signal from electrons emitted
Each element has signature peak pattern
Inte
nsity
(Cou
nts)
Binding Energy (eV)
Sample Spectrum
Stronger signal = XPS detects more
atoms
XPS TheoryX-ray Photoelectron Spectroscopy – used to analyze film composition
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Early GrowthXPS results – TiO2 signal on silicon substrate
The TiO2 signal gets stronger as the number of cycles increases, indicating growth of the TiO2 film on the silicon substrate.
445 450 455 460 465 470 4750
500
1000
1500
2000
2500
3000
3500
XPS of Ti 2p, TiO2 on Si (with native oxide less than 1 nm)
30 cycles TiO
15 cycles TiO
10 cycles TiO
5 cycles TiO
Binding Energy (eV)
Inte
nsity
(Cou
nts)
4.2 nm
2.5 nm
2.3 nm
0.8 nm
452 454 456 458 460 462 464 466 468 4700
500
1000
1500
2000
2500
3000
3500
XPS of Ti 2p on Copper, 175oC
30 cycles on Si30 cycles on cu
25 cycles on cu
Binding Energy (eV)
Inte
nsity
(Cou
nts)
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The TiO2 signal is weak, but present after 15 cycles and it does not increase by 20 cycles. The effective nucleation time of TiO2 on copper is about 15 cycles.
0.3 nm
Thickness can’t be determined by SE, should be less than 2 monolayers (<0.3 nm)
4.2 nm (Si)
CopperXPS results – TiO2 signal on copper substrate
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Discussion No nucleation period on silicon
Considerably delayed formation of TiO2 on copper
Selective deposition is achieved at the conditions used in this study
Nucleation period enables selective growth, for thicknesses up to 2.5 nm - could satisfy the requirement for copper barrier application1
1International Technology Roadmap for Semiconductors (Semiconductor Industry Association, San Jose, CA, 2001).
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Future Work
Before I leave … SEM (scanning electron microscopy) will be applied to
probe the early TiO2 film nucleation on both silicon and copper substrates from 5 to 30 cycles of ALD
Later work … Other surface treatments are still in progress to promote
the growing selectivity, such as complete removal of native oxide without immediate reoxidation
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Conclusions
TiO2 nucleation time on silicon substrate is negligible, and the initial growth rate is 1.0 to 1.2 Å / cycle, depending on surface chemistry
Temperature-independent window for TiO2 deposition on silicon is 150 to 200 °C
Nucleation time on copper substrate is found to be ~ 15 - 20 cycles
The potential to achieve greater selective deposition of TiO2 with further research appears to be high
Questions?