One of the most important reasons why Silicon (Si), in
place of Germanium (Ge), was propelled to the front of the class in the semiconductor
industry from the very beginning, is the fact that Si forms a very stable
oxide-semiconductor interface with SiO2. A high-quality oxide
interface is a key to making field-effect transistors (MOSFETs). Germanium
oxide is water-soluble which rendered it useless for MOSFET fabrication in the
early days (now the industry is advanced enough to possibly solve that).
Thermal oxidation of Si at temperatures >
800 °C yields SiO2. To avoid such high temperatures and long
processing times and tune the material properties, (wet) chemical oxidation,
(plasma-enhanced) chemical vapor deposition or sputtering and electron beam
evaporation are also preferred methods to grow SiO2. The advantages
of precise thickness control, optimal large-area uniformity, and the
conformality over demanding substrate topologies of atomic layer deposition
(ALD) based SiO2 films, all led to an expansion of target applications
such as; spacer based self-aligned double/quadruple patterning (SADP or SAQP)
in fabricating DRAM and logic chips (Link), interface engineering between Si and
high-k materials (Link), moisture barrier
or protective or insulator coatings (Link), nanolaminate structures with
tailored optical and electronic properties (Link) and double layer
surface passivation in Si photovoltaics (Link), etc. to name but a few.
Link for the image
Bis(diethylamino)silane
(BDEAS) [SiH2[N(CH2CH3)2]2, also known as SAM-24, is one of the most preferred Si precursors for ALD of
SiO2 and other Si-containing films. It’s an air-sensitive, moisture-sensitive,
flammable, colorless, and odorless liquid precursor (boiling point 70 °C
(30mm), density 0.804), which exhibits a high vapor pressure, i.e. ~100 Torr at
100 °C.
The research group of Prof. W. M. M. Kessels,
Department of Applied Physics, Eindhoven University of Technology, has reported
that BDEAS is suited for low-temperature synthesis of high-quality
SiO2 by ALD with the SiO2 properties being relatively
insensitive to the substrate temperature for the temperature range of 100 – 300
°C; for temperatures reaching 400 °C thermal stability issues of the precursor
and its ligands start to play a role. The process is also relatively fast as it
combines a high growth-per-cycle (0.8 – 1.7 Å/cycle) with relatively short
dosing and purge times. The ALD SiO2 processes with BDEAS precursors are therefore of interest for high-volume
manufacturing applications, for instance, using ALD batch processes or inline
(plasma) ALD equipment.
Link for the image
Strem Chemicals, Inc., a high
purity specialty chemicals manufacturer and supplier, headquartered in
Newburyport, Massachusetts, USA, boasts a vast variety of ALD/CVD precursors, including
BDEAS for depositing Si-based films in different
applications.
Since 1964, Strem Chemicals, Inc. has been serving its
clients from academic, industrial, and government research and development
laboratories as well as commercial scale businesses in the pharmaceutical,
microelectronic, and chemical/petrochemical industries. Strem also provides
custom synthesis (including high-pressure synthesis) and current good
manufacturing practice (cGMP) services. With ISO 9001 certification for the Quality
Management System (QMS) standard and documentation, Strem products are high purity
materials, typically 99%, with some at 99.9999% metals purity. Strem utilizes a
comprehensive range of analytical techniques tailored to each product to ensure
quality because researchers typically
rely on the supplier's quality procedures and documentation, which if poorly
conducted may kill a great research idea. All of Strem's catalogs,
since inception, have listed “Color and Form” for every product as primary
indicators of quality.
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Promotional blog written and researched by Abhishekkumar Thakur and Jonas Sundqvist, BALD Engineering AB