50
MATERIALS
More than just
a precious jewel
Thin, smooth
diamond is
emerging as an
with a source of energy such as a plasma or
enabler for
filaments held at around 2000 °C. The energy
semiconductor
F
or decades, designers and engineers
have sought to harness the
unsurpassed properties of diamond from the plasma/filaments breaks apart the source
for electronic devices. But diamond has been gases into many different radicals, but the main
manufacturing.
notoriously difficult to work with, prohibitively ones involved in diamond growth are CHx
Diane Hickey,
expensive for mainstream applications and without (x=0,1,2,3) and atomic hydrogen (H). Making
a reliable supply. Now, thanks to the development thin film diamond over large areas nets down to
Ph.D. and
of new synthesis chemistries and deposition generating these constituents over large areas with
John Carlisle,
techniques, thin film diamond is rapidly maturing the same relative proportional stability over time
as an engineering and electronic material. Thin and space. The pressures at which diamond is
Ph.D. from
film diamond captures the hardness, modulus and grown is typically in the convective regime, so like
Advanced
other extreme properties of natural diamond in a other CVD (chemical vapour deposition)
CMOS compatible process on wafers up to 300 techniques dynamic effects such as gas flow and
Diamond
mm in diameter. thermal profiles have a profound effect on a
Technologies
number of film properties.
Introduction Previous work focused on making “perfect” single
explain the
Diamond is nature’s extreme material. In just crystal diamond, and in fact there is work ongoing
increasing
about every major property category diamond is at today growing single crystal diamond in the
the top of the list: hardness, refractive index, laboratory (homo epitaxial growth) [Hemley]. But
importance of
breakdown voltage, thermal conductivity, and making homo epitaxial diamond requires that one
thin film
electron hole mobility, to name a few. A great deal start with “seed” substrates that are single crystal
of basic research has been devoted to the diamond to start with, and the growth conditions
diamonds.
development of synthetic pathways to make needed are difficult to produce over large areas.
diamond [ICHIRO ]. Bulk diamond particles Current technologies only can do this over a few
millimetres to nanometres in size have been made millimetres square. The situation improved greatly
on a large scale for over half a century using high in the early 1990s with work on nanocrystalline
pressure, high temperature (HPHT) processing. diamond films at Argonne National Laboratory
But thin film diamond, such as would be [Gruen]. Advances in the manipulation of the
integrated with the myriad other thin films growth chemistry that favoured continuous re-
commonly used to make semiconductor devices of nucleation during growth produced ultra nano
various types, is nowhere to be found. Neither a crystalline diamond, a phase pure nanocrystalline
single semiconductor production line nor even a diamond film, without any amorphous or
minor MEMS foundry offers the material. There diamond-like carbon material between grain
are many reasons that thin film diamond is not boundaries. An image of the nanoscale structure
offered in a foundry, but one main cause is it’s of ultra nano crystalline diamond is shown in
very challenging to scale the techniques developed Figure 1.
in research labs to deposit films that meet even the The results capture the hardness, modulus, and
minimum standards for thickness and property other extreme properties of natural diamond in a
uniformity on wafers even as small as 50 mm in smooth, thin film with very low internal stresses.
diameter. That is until now. This was a major advance over
previous.approaches that could only produce large
Making diamond easy to work grained polycrystalline diamond coatings that, due
with: Synthetic thin film diamond to the changes in film structure during growth,
processing had to be thick, had to be removed from the
Fig 1: Structure of nano Making thin film diamond typically involves substrate, and had to be heavily polished in order
crystalline diamond mixing hydrogen and methane gas in a reactor to be useful.
www.euroasiasemiconductor.com December 2008 / January 2009
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