80
75
70
65
60
55
50
0 5000 10,000 15,000 20,000
Transmission (%)
Wavelength (nm)
b)
a)
ne ws world
NOVEL MATERIALS
Synthetic diamond offers much
more than heat sinking
In heat-sinking applications for optoelectronic components, synthetic diamond
dissipates heat much better than conventional materials such as copper and silicon
carbide, enabling semiconductor-device
manufacturers to produce smaller, faster,
and higher-power optoelectronic devices
such as laser diodes with longer lifespans
and improved reliability. In fact, Element
Six (Santa Clara, CA) fabricates materials with thermal conductivity ranging
from 1000 to 2000 W/mK—as much as
a factor of five better than copper.
But diamond is much more than a heat
spreader: tightly controlled growth condi-
tions are enabling the use of diamond as
a high-power optical window, a broad-
band optical prism for spectroscopy, and
even in detection of the Higgs boson, or
the so-called “God particle.”
“Element Six grows both single-crys-
tal and polycrystalline synthetic diamond
material from a hydrocarbon-gas mixture
using a propriety microwave chemical-
vapor-deposition [CVD] process,” says
Henk de Wit, optical business manager
for Element Six. “We eliminate chemical
impurities and engineer various proper-
ties into the diamond material for pre-
dictable behavior tailored to meet the
needs of a specific application. Heating
a gas mixture to > 2000°C within the
microwave CVD process means that
high-quality polycrystalline and single-
crystal materials can be produced.”
In February 2013, Element Six
expanded its Silicon Valley facility to
increase volume production of syn-
thetic diamond optical windows—a
critical component of laser-produced-
plasma (LPP) extreme ultraviolet (EUV)
lithography systems—by 50%. The
process allows fabrication of high-purity
diamond wafers in diameters up to 135
mm (see figure).
Diamond windows
The unrivaled room-temperature thermal
conductivity of synthetic diamond makes
it the perfect optical window material for
high-power carbon-dioxide (CO2) lasers
above 6 k W; in fact, synthetic diamond
is the only material that can withstand
power levels beyond 8 k W (and up to
more than 35 k W). The minimal wave-front distortion of λ/20 at 633 nm enables
diamond window use for EUV lithography systems. Compared to zinc selenide
(ZnSe), heat generated through the
absorption of light is instantly dispersed
by diamond’s high conductivity into the
environment to prevent the appearance
of hot spots, meaning there is no need to
compensate for thermal lensing.
High-purity chemical vapor deposition
(CVD) growth processes developed by
Element Six result in diamond windows
up to 135 mm in diameter (a) for use as
high-power optical windows, broadband-spectroscopy prisms, and particle-detection
sensors. Synthetic diamond has the widest
transmission spectrum for any optical
material: 220 nm to greater than 50 µm (b).
