US 4,900,887 AGranted

Floating zone drawing circuitry for semiconductor rods

AssigneeSiemens Aktiengesellschaft

InventorWolfgang Keller

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Abstract

For floating zone drawing of semiconductor rods having diameters greater than 100 mm, at the beginning of the zone drawing process, in particular during melting on of the seed crystal to the semiconductor rod to be drawn, a high load change and impedance change occurs. The power from the high-frequency (HF) generator is no longer coupled thereto optimally. Heating up the feed line to the induction heating coil is the result. This heating is avoided by connecting the HF generator via a feed line to a tank circuit device. A variable tank circuit capacitor connected in parallel and to the series oscillator circuit coil feeding one side of a parallel circuit of a heating circuit capacitor and the induction heating coil. The variable oscillator circuit capacitor is adjusted as a function of the voltage drop across the induction heating coil.

Claims4

Dependent claims

A circuit for float zone drawing of semiconductor rods, the circuit comprising:

a high-frequency generator having an output;
a coupling circuit connected to the output of the high-frequency generator, the coupling circuit comprising a variable capacitor connected to the output and a series coupling coil connected between the output and a parallel heating circuit, the series coupling coil inductively coupling the output of the high-frequency generator to the parallel heating circuit, the heating circuit comprising an inductive heating coil and a heating capacitor connected in parallel to each other, the heating coil having an inductance and the series coupling coil having an inductance larger than the inductance of the heating coil, the coupling circuit capacitor being variable in capacitance, and
means for adjusting the variable capacitor responsive to a voltage potential directly across the inductive heating coil to compensate for a change in value of the inductance of the heating coil to avoid a mismatch between the output of the high-frequency generator and the coupling circuit.

Dependencies are inferred from the claim text.