IGBT Modules - Technologies, Driver and Application (Second Edition) - page 31

Fig. 1.10
Methods ofmanufacturing siliconwafers
In both the CZ and the FZ process, the basic doping of the mono-crystal is done by
adding the relevant doping substance to the melt. In the CZ process, the doping
substance is added to the liquid melt in the crucible. The concentration of the doping
changes accordingly, and with it the axial resistance of the mono-crystal along the
length, as shown in
In the FZ process, the doping material is present in the
form of a gas and is added to themolten zone in gas form. It is thus possible to control
the doping profile and the axial resistance very precisely. However, even in the FZ
process, process-related fluctuations cause isolated microscopic fluctuations in the
doping, known as striations, which run in concentric circles. This causes problems for
the high blocking voltages (≥3.3kV), especially for power semiconductors, which require
homogenous doping. Assuming the FZ process yields a mono-crystal, this crystal is
subjected to neutron irradiation, and the radiation effects the desired homogenous
Fig. 1.11
Relative resistance distribution of the mono-crystal in the CZ and FZ
1...,21,22,23,24,25,26,27,28,29,30 32,33,34,35,36,37,38,39,40,41,...548
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