DOI: 10.1002/adem.201300132
High Temperature Thermal Conductivity of Amorphous
Al
2
O
3
Thin Films Grown by Low Temperature ALD
By Andrea Cappella, Jean-Luc Battaglia,* Vincent Schick, Andrzej Kusiak, Alessio Lamperti,
Claudia Wiemer and Bruno Hay
Al
2
O
3
grown by atomic layer deposition could be proposed as a nonactive layer for back end processes in
view of the integration of scaled phase change memory devices. In this paper we report on thermal
characterization from 50 to 600 °C of amorphous Al
2
O
3
thin films grown on thermally oxidized silicon
substrate at a temperature of 100 °C and capped with a 30 nm thick Pt layer. The effects of low
temperature deposition and of a post-deposition rapid thermal annealing process (RTP) on the thermal
properties of the films are investigated using a modulated photo-thermal radiometry technique coupled
with post-annealing morphological characterizations. Degassing process occurring at high temperature
greatly affects the film surface quality, though measurements of the films after RTP show that the
thermal conductivity of amorphous Al
2
O
3
increases as a function of temperature from 1.8 W K
1
m
1
at
50 °C to 3.3 W K
1
m
1
at 600 °C. At the same time, the value of the thermal boundary resistance at the
Pt-Al
2
O
3
interface decreases from 1.02 10
7
Km
2
W
1
at 50°C to 4.8 10
8
Km
2
W
1
at 600 °C.
1. Introduction
Thin amorphous Al
2
O
3
(a-Al
2
O
3
) films are relatively good
thermal insulators which can be deposited at very low
temperature,
[1,2]
becoming potentially attractive for novel
electronic devices based on temperature-sensible materials like
polymers
[3]
or phase change chalcogenides.
[4]
For the heat-based
phase change memory (PCM), an engineered spacer increases
the heating efficiency of each cell by increasing the thermal
insulation, and therefore allowing the reduction of the cell size.
a-Al
2
O
3
grown by atomic layer deposition (ALD-dep a-Al
2
O
3
)
is proposed as a nonactive layer for back end processes in view
of the integration of scaled PCM devices due to the capacity of
ALD to grow films at low temperature.
[2]
Thermal conductivity
of amorphous alumina thin films has been largely studied
[5–11]
in the range of temperature from cryogenic to 100–200 °C.
Nevertheless, temperature required to achieve the crystalline-
amorphous phase change in PCM can be as high as 600–700 °C.
In addition, the thermal boundary resistance
[11–14]
(TBR) at the
interfaces between ALD-dep a-Al
2
O
3
and a dielectric layer or a
metallic electrode is of high interest for the implementation of
such a material in PCM devices.
In this work, we present the evaluation of ALD-dep a-Al
2
O
3
thermal conductivity and of the TBR at the a-Al
2
O
3
/SiO
2
and
a-Al
2
O
3
/Pt interfaces in the 50–600 °C temperature range.
2. Sample Preparation
a-Al
2
O
3
thin films in the 150–400 nm thickness range were
grown by ALD in a Savannah-200 reactor (Cambridge Nanotech
Inc.) at a growth temperature of 100 °C on top of a silicon wafer
covered with 50 nm of thermal SiO
2
. The Al(CH
3
)
3
precursor was
used as Al source, while H
2
O was used as oxygen source. The
precursor pulse to N
2
purge time was1:200. Such high ratio
should assure low OH contamination of the growing Al
2
O
3
amorphous layer. a-Al
2
O
3
samples are capped with a 30 nm thick
Pt layer deposited by RF-magnetron sputtering. This capping
layer serves as optical transducer for the incident laser beam
during the photo-thermal radiometry experiment. The film
[*] Prof. J.-L. Battaglia, Dr. A. Cappella, Dr. V. Schick,
Dr. A. Kusiak
Universit e de Bordeaux, Institut de M ecanique et d’Ing enierie
de Bordeaux I, UMR CNRS 5426, 351 cours de la lib eration,
33405 Talence, France
E-mail: jl.battaglia@i2m.u-bordeaux1.fr
Dr. A. Cappella, Dr. B. Hay
Laboratoire National de M etrologie et d’Essais, LNE, 29 rue
Roger Hennequin, 78197 Trappes, France
Dr. A. Lamperti, Dr. C. Wiemer
Laboratorio MDM, IMM-CNR, via C. Olivetti 2, 20864 Agrate
Brianza (MB), Italy
[**] This research receives funding from the “Laboratoire National de
M etrologie at d’Essais”, from the European Union on the basis of
Decision No. 912/2009/EC, and was partially supported by
“MONADS” Project (code No. 2009–2715) of the Cariplo
Foundation. The authors thank Dr. Luca Lamagna from MDM
for depositing the Al
2
O
3
layers and Dr. Yannick Anguy from
I2M for the ESEM measurements.
ADVANCED ENGINEERING MATERIALS 2013, 15, No. 9999 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1
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