20-09-2013, 04:06 PM
Development of the Next Generation of Insulated Gate Bipolar Transistors based on Trench Technology
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Abstract
This paper presents preliminary results towards developing the next generation
of Insulated Gate Bipolar Transistors for high voltage applications. Technological
issues such as the trench pro le, the gate oxide quality, the trench inversion layer
mobility and lay-out design are discussed. Optimization of 1.8 kV Trench IGBTs
using extensive numerical simulations and physical analysis is carried out. New
termination techniques are proposed.
Introduction
The Trench Insulated Gate Bipolar Transistor has been recognised by several leading companies
and research groups as one of the most promising switching devices for high voltage, high
current applications 1-4 . Recently, we reported on the on-state physical behaviour of Trench
IGBTs given by a dual PIN diode - PNP transistor mechanism. We have also shown that
the Trench IGBT o ers decisive advantages over the equivalent DMOS structure such as an
enhanced carrier modulation at the cathode side due to the PIN diode e ect, a larger SOA
due to reduced action of the parasitic thyristor inherent in the IGBT structures, and a more
exible design and geometry 5-7
Technology
The standard vertical structure is shown in Fig. 1a. The thickness and the resistivity of the
n-base are 250 m and 100 cm respectively. The trench depth was typically 5 m.
The measured and simulated doping pro le of the cathode side is shown in Fig. 1b. The
trench was formed using a special dry etch process using uorine. The trench shape and
smoothness were satisfactory. The trench was rounded" at the bottom see Fig. 2a thus
eliminating high electric elds which would otherwise lead to premature breakdown. The
typical thickness of the gate oxide was 1200 A and a critical electric eld of 5106 V cm was
obtained.
Termination Techniques
Trench devices are particularly prone to premature edge breakdown on account of the electric
eld developed at the last active trench corners. Using no termination protection only 25 of
the bulk breakdown voltage is achieved . This is due to the fact that in the bulk the trench
bodies act as eld plates to each other and the only uncovered" trench is the trench placed at
the edge of the device. Using a novel termination technique which consists of several p+ oating
rings placed under inactive trench bodies at the edge of the device the electric eld at the edge
trenches is substantially decreased. The potential lines are pushed away from the trench corners
and gradually released in the bulk. 95 of the bulk breakdown voltage is achieved in this case.
In Fig. 5 the breakdown for a wide trench csmall spacing between trenches and narrow
trench blarge spacing between the trenches, using the new termination technique and for
the non-terminated trench structure a are shown.
Conclusion
We have developed a trench process suitable for high voltage applications. The trench oxide
quality, the trench geometrical pro le and smoothness were satisfactory and excellent values
for the channel mobility have been extracted from the measured I-V characteristics. Numerical
simulations, to characterise in detail the Trench IGBT performances were carried out. 1.8 kV
Trench IGBTs have been optimised and simulated using real doping pro le data and dimensions.
A novel termination technique which can be implemented speci cally in trench devices has been
proposed. In the light of these results we believe that the Trench IGBT has the potential to be
the key structure for the next generation of high voltage power control devices.