INVESTIGATION OF HEAT TRANSFER PROCESSES IN A HEATING DEVICE FOR THERMAL MIGRATION OF LIQUID INCLUSIONS IN SILICON

Abstract

Liquid inclusions migrate in solids in the direction of the temperature gradient. This gives a
unique opportunity to form crystal perfect structures in silicon wafers with through-doped epitaxial
channels or closed cells, which are of interest in the design of power semiconductor devices and
photovoltaic converters. Moreover, there are no competitive methods of manufacturing such structures,
since the rate of thermal migration is four orders of magnitude higher than the rate of solidstate
diffusion. However the practical application of the thermomigration (TM) method in semiconductor
electronics is hindered by the unsolved problem of creating the necessary homogeneous
temperature gradient field in a silicon wafer. Violation of the uniformity of the temperature gradient
leads to a deviation of the trajectories of discrete liquid inclusions from the normal and distorts
the specified topology of inclusions on the starting surface of the plate and makes it impossible
to use group technology to obtain subsequent manufacturing operations of semiconductor
devices. In this paper, a computer simulation of heat transfer processes in a heating device is performed
in order to achieve a homogeneous temperature gradient field in a silicon wafer created by
a flat resistive heating element in the form of a spiral. The causes of periodic and monotonous
radial inhomogeneities of the temperature gradient field that distort the trajectories of liquid inclusions
and the shape of the resulting channels are revealed. Ways to reduce and eliminate these
distortions are proposed. The main controls for the configuration of the temperature gradient field
in the silicon wafer turned out to be a cassette holding the wafer at a certain distance from the
heating element and front screens with holes coaxial to the silicon wafer. The dimensions and
mutual arrangement of the elements of a heating device providing the required uniformity of the
temperature gradient field for industrial applications of thermal migration of a system of linear
inclusions of zones on silicon wafers with a diameter of 100 mm have been determined and experimentally
confirmed.