JPS5910959B2 - A crucible-free zone melting method for semiconductor materials that controls the diameter to be constant using three controlled variables. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a molten zone formed in a semiconductor rod is inductively moved in the rod axis direction through the semiconductor rod by a heating coil of a heating current circuit supplied from a high frequency oscillator. The melt volume of the melt zone and the diameter of the solidified portion of the melt zone of the semiconductor rod are controlled by stretching or compressing the semiconductor rod and adjusting the radio frequency energy supplied to the melt zone by the oscillator frequency. .

In particular, the present invention relates to a crucibleless melting method and apparatus for a semiconductor material made of silicon. Such methods are known and are described in detail in, for example, DE 95-1277813.

Basically, a heating coil surrounding a semiconductor rod in a ring shape is moved in the longitudinal direction of the rod, and the surrounded portion of the semiconductor rod is melted by induction heating. The movement of the molten zone through the semiconductor rod converts the semiconductor rod from polycrystalline to single crystal material, refines the material, and controls the rod diameter. The rod diameter depends first of all on the size and shape of the melt volume of the melt zone, which can be determined by the expansion control mechanism and the supply of radio frequency energy.

Using such a method, using the anode current or the heating circuit voltage and the oscillator frequency as control variables, from a thin seed crystal according to a predetermined program for the oscillator frequency and the anode current (one heating current). The transition to the required diameter of the semiconductor rod and the constant value diameter are also controlled. Conventional electrical diameter control using two control variables, anode current (one heating current) or heating circuit voltage and oscillator frequency, does not allow deviations from the set diameter to be controlled to an order of 5%, for example in the copy method. , this is 100
It is clear that this is insufficient to meet the requirements for manufacturing semiconductor rods with large diameters of mm or more.

Such deviations are due, for example, to the fact that the melt volume of the melting zone of the semiconductor rod inductively coupled to the heating current circuit has a different shape and volume as the zone melting process progresses. Different shapes of the melt zone create different coupling resistances and the impedance of the heating current circuit changes with oscillator frequency.

This gives different resonance curves. That is, the resonant frequency, the maximum resonant value, the Q value (selectivity) and the half width of the heating circuit change depending on the shape of the melted zone. Nevertheless, this curve intersects at the operating point of the zone melting process. As a result, even if the rod diameter is controlled using two control variables, it will fluctuate within a certain range as the band melting process progresses, and this fluctuation will not be stabilized.

An object of the present invention is to eliminate the diameter deviation in diameter control that has conventionally been performed using two controlled variables.

This problem can be solved by using a heating coil supplied with electrical high-frequency energy that surrounds the semiconductor rod axis and moves parallel to the axis to inductively create a molten zone that passes through the semiconductor rod. When melting a crucibleless zone, setting of the control amount that determines the state of the melting zone, simultaneously with the axial distance between the two solid parts of the semiconductor rod that holds the melting zone in the first control, and the energy supply to the melting zone in the second control. The control variables are the oscillator frequency of the heating current supplied from the high-frequency oscillator to the heating coil via the heating circuit formed as an electric oscillation circuit and the anode current supplied to the high-frequency oscillator. In the method using the strength of According to the method of the present invention, the control mechanism is connected for controlling the axial spacing or the oscillator frequency, and the other two control variables are connected temporally and periodically for controlling the oscillator frequency or the stretching control mechanism. It will be resolved.

The invention provides the advantage that the diameter deviation of the semiconductor rod can be controlled to the order of 2% over the band melting method using two control variables. Next, an apparatus for carrying out the method according to the present invention will be explained using FIG. The device of the present invention has a first control mechanism (expansion/contraction control mechanism 13) that determines the distance between both solid parts of the semiconductor rod 1 that holds the melting zone, and a high-frequency oscillator 4 that controls melting by the oscillator frequency of the current supplied from the high-frequency oscillator 4. The second step determines the energy supply to the belt.
control mechanism (frequency control mechanism), present value meters 6, 7, 8 and set value and present value general fixed value comparison devices 9, 10, 11, and in order to operate both control processes, an exchange circuit 12 is provided which is actuated by each of the partial control circuits, and for each actuation of this exchange circuit 12 at least one of the two control mechanisms is The circuit is characterized in that one of the partial control circuits is connected thereto.

In the method according to the invention, a molten zone is created in the semiconductor rod 1 by means of this device;
A high frequency vibration circuit is formed from the.

Heating circuit voltage, oscillator frequency and anode current are measured by meter 6,
7, 8, and each current value general fixed value comparison device 9,
10 and 11.

The control deviation is applied to the control motor of the expansion/contraction control mechanism 13 or the frequency control mechanism of the high-frequency oscillator 4, and is selected in the exchange circuit 12 according to a predetermined program. In this invention, a measured value of one of the three control variables is connected to the control motor of the frequency control mechanism of the expansion/contraction control mechanism 13 or the high frequency oscillator 4, while the exchange circuit 1
Via the switching device 2, the measured value of one of the other two control variables is connected to the control motor of the frequency control mechanism or the telescopic control mechanism 13.

When the control motor operates and the current value of the selected controlled variable becomes equal to the set value of that controlled variable, the measured value of the initially unselected controlled variable among the other two controlled variables is switched. The device connects the control motor in exchange, and repeatedly compares the current value of the controlled variable with the set value. In this way, the control deviation is periodically connected in exchange to the control motor in order to control the diameter of the semiconductor rod.

FIG. 2 shows an embodiment of an exchange circuit 12 with contacts, by means of which a measured value can be cyclically exchanged with a control motor of a telescopic control mechanism or a frequency control mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an apparatus for implementing the method of the present invention, and FIG. 2 is a specific circuit diagram of the exchange circuit 12 in FIG. 1. 1...Semiconductor rod, 2...Heating coil, 3
... Capacitor, 4 ... High frequency oscillator, 5 ... Coil, 6, 7, 8 ... Instrument, 9, 10, 11 ...・Current value set value comparison device, 12... exchange circuit, 13... expansion/contraction control mechanism.

Claims (1)

[Claims] 1. Using a heating coil supplied with electrical high-frequency energy, which surrounds the axis of the semiconductor rod and moves parallel to the axis,
When melting the semiconductor rod in a crucibleless zone by inductively creating a melting zone that passes through the semiconductor rod, the axial spacing between both solid parts of the semiconductor rod that maintains the melting zone in the first control and at the same time the melting zone in the second control is increased. The energy supply is controlled by the deviation from the set value of the control variable that determines the state of the molten zone, and the controlled variable is supplied from a high-frequency oscillator to the heating coil via a heating circuit formed as an electric oscillation circuit. In the method using the oscillator frequency of the heating current to be generated and the strength of the anode current supplied to the high-frequency oscillator, the Q of the heating circuit, which is grasped by the voltage of the heating circuit, is used as the third control variable.
Using a value, one of the three control variables, namely oscillator frequency, anode current and heating circuit voltage, is connected for the control of said axial spacing or oscillator frequency, and the other two control variables are connected in time and periodically to the oscillator. A method for melting a semiconductor material in a crucible-less zone, controlling the diameter to a constant value by means of three control variables, characterized in that exchange connections are used to control the frequency or the axial spacing. 2. Energy supply to the molten zone is controlled by the first control mechanism (expansion control mechanism 13) that determines the distance between both solid parts of the semiconductor rod 1 that holds the molten zone, and the frequency of the current supplied from the high-frequency oscillator 4. It has a second control mechanism (frequency control mechanism) that determines the three control variables, namely, oscillator frequency, anode current, and heating circuit voltage, with current value meters 6, 7, and 8, and a set value and current value-set value comparison device. 9, 10, 11, and an exchange circuit 12 operated by each of the partial control circuits for operating both control steps, each activation of exchange circuit 12 at least one of the two control mechanisms. A crucibleless belt melting device for a conductive material that is controlled to a constant diameter by three control variables, characterized in that one of the other partial control circuits is connected to the crucible belt melting device.