Power Semiconductors
Precise control of carrier lifetime
is an essential factor in meeting the ever-increasing market
demands for efficient power semiconductor device performance.
The market is dominated by inverter and converter
topologies, requiring high performance thyristors, IGBTs and very
fast diodes. Mounting requirements for reduced on-state
losses, short turn-off times and soft recovery promote the use of
sophisticated techniques to improve the design and performance of
modern devices. Excellent soft switching characteristics can
be achieved by irradiation, reducing or eliminating the use of
undesirable heavy metals in fabrication clean rooms and offering an
exact process by which to realise different lifetime profiles.
Applied Sterilisation Technologies
(AST) is the only fast-turnaround provider of both Electron
and Ion beam treatments for semiconductors. They are used in
combination to optimise switching characteristics.
Treatment with a high energy
electron beam provides bulk control of minority carrier lifetime
throughout the entire volume of the die, giving a very even and
consistent performance across different production
batches. 
Products can be treated in trays or boxes, preserving
the clean conditions in which they were
packed. Electron Beam treatment provides effective
and uniform tailoring of the softness of reverse recovery, while
avoiding the increased leakage current associated with other
techniques, such as gold or platinum diffusion.
Ion beam treatment, using protons
or helium ions, targets the lifetime killing centres to the precise
region required, ensuring that localised control is provided.
The primary interaction of these ions with the
silicon structure has a relatively sharp depth profile, allowing
the region for treatment to be defined to a few microns. This
enables, for example, the drift region near the PN junction of a
diode to be treated to reduce the reverse recovery parameters for
soft switching, while leaving the forward voltage drop unchanged.
Ion beam treatment is a vacuum process and so wafers are handled
individually in our ISO Class 7 cleanroom in order to control
particulates. A range of ion species is available, the most
commonly used of which are protons and helium ions (alpha
particles).
Electron doses typically range from
0.05 to 1,000kGy (0.005 to 100 Mrad) and proton and helium ion
doses from 1E9 to 1E13 ions/cm². Irradiation is carried out
with high uniformity and reproducibility and products are handled
in an ISO class 7 cleanroom environment. Services are
performed in accordance with written procedures within our Quality
Management System which is certified to BS EN ISO 9001.
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