1 K. Overhage, Q. Tao, G. M. Jursich, C. G. Takoudis Advanced
Materials Research Laboratory University of Illinois at Chicago
Slide 2 2 Acknowledgements REU 2010 at UIC, sponsored by the
National Science Foundation and the Department of Defense EEC-NSF
Grant # 0755115 CMMI-NSF Grant # 1016002 Slide 3 3 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 TiO 2 P hoto from
Barrier Layers Technology by Prof. Yosi Shacham-Diamand, Tel-Aviv
University, 2000 Slide 4 4 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) STEP 1 STEP 2 STEP 3 STEP 4
Reaction Mechanism of typical ALD cycle ALD is a surface-saturation
reaction that deposits each monolayer of film, allowing for precise
thickness control. Slide 5 5 Example application of ALD An 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
Slide 6 6 Objectives Study TiO 2 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
TiO 2 on Silicon Slide 7 7 Substrates Deposition 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. Slide 8 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
Theory Spectral Ellipsometry measures film thickness Slide 9 9
Temperature-independent window TiO 2 deposition on silicon is
independent of temperature between 150 and 200 C. Silicon with
native oxide: Slope 1.2 A / cycle Slide 10 10 Late Growth
Deposition from 50 to 150 cycles on silicon with native oxide Once
the early growth phase is complete, TiO 2 deposition proceeds at
1.3 / cycle. This is in agreement with current literature values.
Slide 11 11 Early Growth Deposition 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 /
cycle Silicon with reduced oxide: Growth rate 1.0 / cycle Silicon
with < 1 nm oxide Silicon with 1.5 nm native oxide Slide 12 12
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 Intensity (Counts) Binding
Energy (eV) Sample Spectrum Stronger signal = XPS detects more
atoms XPS Theory X-ray Photoelectron Spectroscopy used to analyze
film composition Slide 13 13 Early Growth XPS results TiO 2 signal
on silicon substrate The TiO 2 signal gets stronger as the number
of cycles increases, indicating growth of the TiO 2 film on the
silicon substrate. 4.2 nm 2.5 nm 2.3 nm 0.8 nm Slide 14 14 The TiO
2 signal is weak, but present after 15 cycles and it does not
increase by 20 cycles. The effective nucleation time of TiO 2 on
copper is about 15 cycles. 0.3 nm Thickness cant be determined by
SE, should be less than 2 monolayers (
