Method and apparatus for floating zone melting of a semiconductor rod

Claim 3

The method according to claim 1, comprising the steps of determining the volume of the part of the melting zone determining growth of the semiconductor rod by linearly scanning the part with a diameter of the melting zone established per line; squaring and adding the information representative of the diameter and determining from the pulses obtained by linear scanning the diameter at the solidifying front and the angle at the projecting points of the molten zone, the solidifying front, melting front and the turning point.

Claim 4

The method according to claim 2 wherein a prescribed geometric form of the conical rod part is determined by the respective diameter and the respective angle as a function of the distance covered by the solidifying front.

Claim 5

The method according to claim 3 comprising the step of determining the diameter and the respective projecting angle as a cosine function dependent on the distance covered by the solidifying front.

Claim 6

The method according to claim 3, comprising the step of controlling the supplied energy in accordance with the respective desired projection angle as a function of the distance covered by the solidifying front as a function of the diameter.

Claim 7

Apparatus for floating-zone melting of a semi-conDuctor rod, particularly a silicon semiconductor rod, comprising: a pair of rod mounts holding the rod vertically, said rod mounts being axially shiftable relative one another along the direction of the rod axis; a rod mount actuator connected to one of said rod mounts for axially moving said one mount; an induction heating coil surrounding the rod; variable energizing supply means connected to said coil for energizing said coil to heat the rod and create a melting zone; a supply actuator connected to said supply means for controlling the energy supplied to the rod; an electronic television camera operating to linearly scan the melting zone perpendicular to the rod axis and produce actual value information signals corresponding to rod diameter and profile angle of the melting zone and the crystalization front thereof; a data processor receiving the information signals; first and second multi-stage control systems connected to said data processor and to said rod mount actuator and said supply actuator, respectively; monitoring means adjacent the rod for monitoring the position of the crystalization front and requesting first and second magnitudes from said data processor corresponding to the diameter at the crystalization front and to the angle of the melting zone profile at the crystalization front, respectively, said first magnitude applied to said first control system and said second magnitude applied to said second control system; a calculator connected between said television camera and said control systems for providing respective signals which are proportional to the signals representing actual value information; first comparison stages in the respective control systems for comparing the respective values received from said calculator with those received from said data processor to provide respective control signals; means for sensing actual values of rod diameter, profile angle, and heating coil energization; means for integrating the control signals; second stages in the respective control systems for comparing the sensed actual value with the integrated control signal; and third stages in the respective control systems, each having a feedback circuit, coupled directly to said rod mount actuator and said supply actuator, respectively.

Claim 8

Apparatus for floating-zone melting of a semi-conDuctor rod, particularly a silicon semiconductor rod, comprising: a pair of rod mounts holding the rod vertically, said rod mounts being axially shiftable relative one another along the direction of the rod axis; a rod mount actuator connected to one of said rod mounts for axially moving said one mount; an induction heating coil surrounding the rod; variable energizing supply means connected to said coil for energizing said coil to heat the rod and create a melting zone; a supply actuator connected to said supply means for controlling the energy supplied to the rod; an electronic television camera operating to linearly scan the melting zone perpendicular to the rod axis and produce actual value information signals corresponding to rod diameter and profile angle of the melting zone and the crystalization front thereof; a data processor receiving the information signals; first and second multi-stage control systems connected to said data processor and to said rod mount actuator and said supply actuator, respectively; monitoring means adjacent the rod for monitoring the position of the crystalization front and requesting first and second magnitudes from said data processor corresponding to the diameter at the crystalization front and to the angle of the melting zone profile at the crystalization front, respectively, said first magnitude applied to said first control system and said second magnitude applied to said second control system; a calculator connected between said television camera and said control systems for providing respective signals which are proportional to the signals representing actual value information; first comparison stages in the respective control systems for comparing the respective values received from said calculator with those received from said data processor to provide respective control signals; means for sensing actual values of rod diameter, profile angle, and heating coil energization; means for integrating the control signals; second stages in the respective control systems for comparing the sensed actual value with the integrated control signal; and third stages in the respective control systems, each having a feedback circuit, coupled directly to said rod mount actuator and said supply actuator, respectively.

Claim 9

Apparatus according to claim 6, wherein said data processor is a calculator for calculating respective control signals representing rod diameter and profile angle at a monitored position, and said data processor is connected to said first stages of said control system.

Claim 10

Apparatus according to claim 6, wherein said data processor includes a memory for storing information corresponding to rod diameter and profile angle and is responsive to said monitoring means to provide signals associated with the monitored position to said first stages of said control systems.

Claim 11

Apparatus according to claim 6, wherein said first control system comprises said first stage, an integrating stage as a part of said integrating means connected to said first stage as a second stage and an amplifier having inputs connected to said calculator and to said integrator and an output connected to said third stage.

Claim 12

Apparatus according to claim 9 wherein said calculator comprises means for supplying a sum of the squares of the pulses per scanning cycle generated by the television camera and a diameter value assigned to the image of the actual melting zone, and operates to evaluate the pulses as to rod diameter.

Claim 13

Apparatus according to claim 10, wherein said third stage includes an amplifier connected to said rod mount actuator, a tachometer included in the feedback circuit of said third stage and connected to and operated by said rod mount actuator to create a feedback voltage, and means connecting said feedback voltage to said amplifier of said third stage.

Claim 14

Apparatus according to claim 6 wherein said first stage of said second control system is operable to proVide a signal which is proportional to the deviation of the profile angle, and comprising a potentiometer connected to an auxiliary voltage source, a potentiometer actuator connected to said first stage and operated thereby to provide a control value, a correction amplifier in said second stage of said second control system connected to receive said control value and connected to said heating coil to receive a signal value representative of heating coil energization.

Claim 15

Apparatus according to claim 12, wherein the connection between said correction amplifier and said heating coil includes rectifier means.

Claim 16

Apparatus according to claim 12, wherein said correction amplifier of said second control system is connected to said third control stage, said third control stage including an amplifier, and said feedback circuit of said third control stage comprising a resistor connected from the output of said amplifier to and input thereof, said output of said third stage amplifier connected to and controlling the operation of said supply actuator for varying the energy supplied to said melting zone.

Claim 17

Apparatus according to claim 14, wherein said variable energizing supply means includes a high frequency generator variable in frequency for supplying high frequency energy to said induction heating coil, a resonant circuit including said heating coil loosely coupled to said high frequency generator, said high frequency generator being steadily variable over a frequency range which includes the resonant frequency of said resonant circuit.