8-16 News v2 10/9/09 13:24 Page 10
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Next generation materials
IMPORTANT developments by the implantation-induced crystal damage interatomic
ATOMICS team were made in modelling the through the application of very high distance. This
activation or deactivation of dopants in temperatures. The earliest annealing can be
silicon. Dopants are impurities added in procedures were at temperatures of 900°C achieved by
small quantities to modify semiconductors’ and above for hundreds of minutes. putting the
electrical conductivity. Semiconductors such Miniaturisation required a continuous layer of silicon
as silicon or germanium are crystalline reduction of the “thermal budget”, which over a substrate of
lattices in which each atom shares electrons originally referred to the product of silicon germanium. As
with four neighbours. annealing time and temperature. the atoms in the silicon
layer align with the atoms of the
Replacing some atoms with atoms of other Annealing in today’s production processes underlying SiGe layer, the links
elements, such as phosphorus or arsenic usually means a rapid increase to the peak between the silicon atoms become
that have five bonding electrons, makes temperature of around 1050°C followed by stretched – or strained. Moving the atoms
extra electrons available. Because of the immediate cooling. New techniques such as apart reduces the atomic forces that
additional negative charges, these are called “flash annealing” or non-melt laser annealing interfere with the movement of electrons
n-type (for negative). Doping with acceptor will reduce the annealing process from through the transistor. They can move 70%
atoms such as boron, which have only three seconds to milliseconds. faster through a strained silicon transistor
electrons available, creates “holes” that are and switch 35% faster, resulting in better
positively charged (p-type for positive). The work undertaken by ATOMICS has also chip performance and lower energy
The performance of microprocessors helped to define the research route to consumption.The models created by the
depends on extremely precise methods of computer modelling of processes such as ATOMICS team have been validated by
ion implantation for almost all doping in flash annealing, according to Pichler. STMicroelectronics, a globally acting
silicon integrated circuits. (Ion implantation For many years, silicon dioxide has been the manufacturer of very advanced integrated
is more precise, reliable and repeatable than material of choice in field-effect transistors circuits. And the lessons learnt in ATOMICS
the older thermal diffusion of deposited because of its uniformity and high interface are already being applied by industry. The
dopants used previously.) To dope a quality. But with the 32nm process, silicon models have been integrated into
semiconductor wafer, a stream of ions is dioxide and related materials, such as ‘Sentaurus Process’, the industry-leading
fired into the substrate so that the ions nitrided oxides, are reaching their limits and process simulation software from Synopsys.
come to rest around a defined depth new materials need to be introduced. That The ATOMICS project received funding
beneath the silicon surface. adds complexity to the manufacturing from the ICT strand of the EU’s Sixth
process. Framework Programme for research.
“As long as ion implantation remains the Media note: This feature can be republished
standard technique for doping, especially in The ATOMICS team established quantitative without charge provided ICT Results is
this context, you will need very high doping models for new materials. Most important is acknowledged as the source at the top or
concentrations, requiring very high dose ion probably “strained” silicon. But also silicon- the bottom of the story. You must request
implantations,” says Pichler. “However, ion germanium alloys and advanced point- permission before you use any of the
implantation does a lot of damage to the defect engineering methods were photographs on the site. If you do
crystal and a damaged crystal does not give investigated. republish, we would be grateful if you
you good performance in devices.” Silicon is strained when the silicon atoms could link back to the ICT Results site
Therefore “annealing” is used to repair are stretched beyond their normal http://cordis.europa.eu/ictresults
GaN design win
For the third consecutive year, an amplifier the model in precisely predicting the University of Technology, Sweden, and
using the Cree, Inc. CGH40010 GaN required impedance conditions for high- Junghwan Moon and Jungjoon Kim from
HEMT transistor won the best power efficiency operation was instrumental in Pohang University of Science and
amplifier competition at the 2009 achieving first-pass design success. The Technology (POSTECH), Korea.
IEEE/MTT-S International Microwave winning 3.27 GHz amplifier produced 7.1
Symposium. David Yu-Ting Wu, watts of RF output power at a power added “This is a hat trick, of sorts, for Cree,” said
representing the University of Waterloo, efficiency (PAE) of 71%. Jim Milligan, Cree director of RF and
received the award for best performance Microwave products. “It’s exciting for us to
amplifier designed and demonstrated as The second- and third-place student teams see the next generation of engineers
judged on efficiency, power and frequency also used the CGH40010 in Inverse Class- creating innovative designs based on our
of operation. Wu’s Inverse Class-F amplifier F circuit architectures. They were, industry-leading technology. Cree
was designed using Cree’s proprietary non- respectively, Paul Saad, Hossein Mashad congratulates the students for their efforts
linear GaN HEMT model. The accuracy of Nemati and Mattias Thorsell from Chalmers and wishes them continued success.”
10 www.compoundsemiconductor.net September 2009
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