DE1153908B - Method and device for crucible-free zone melting with changing the spacing of the rod ends - Google Patents

Description

The invention relates to a method for crucible-free zone melting of a rod made of semiconductor base material, held at its ends, in particular made of high-purity silicon, one of which is inductive heating by a high-frequency coil The melt zone generated between the two supported ends of the rod is guided along in the direction of the rod axis and the melt zone cross section is influenced by a change in the distance of a rod end, in particular for the production of a monocrystalline semiconductor rod.

There is already known a zone melting method in which to manufacture a thin semiconductor rod from a relatively thick semiconductor rod during zone melting, the rod ends during the drawing process be moved apart.

In contrast, it is the basic idea of the present invention, a method and an apparatus specify in order to create a monocrystalline semiconductor rod in a more defined, d. H. in to produce a desired area of constant thickness. According to the invention of a High-frequency current source fed into the coil surrounding the semiconductor rod, which is in itself Changing the thickness of the rod also changes, used to control a device that adjusts the distance of the holders of the semiconductor rod is able to change, this device the two Mounts approaching each other or moving away from each other until the current in the high frequency coil returns has the desired value.

This high-frequency coil is very short compared to the length of the semiconductor rod. It is appropriate but not essential that the one used to control the thickness of the semiconductor rod The high-frequency coil simultaneously heats the melting zone. If necessary, it can be used for thickness control a separate coil, which is fed by a separate high-frequency generator, can also be provided.

The invention and further details are to be explained in more detail by the description of the figures which now follows explained.

With reference to Fig. 1, the basic process of the thickness control will first be described. 1 is a semiconductor rod, e.g. B. made of silicon, which is held at both ends 2 and 3. In the exemplary embodiment, the high-frequency coil 5 also serves to Heating of zone 4. This entire arrangement is located in a quartz tube (not shown here) in a protective gas atmosphere. A support field coil can also be used to enlarge the melting zone be provided. Support field coil and high method and device

for crucible zone melting

with a change in the distance between the rod ends

Applicant:

Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Dr. Theodor Rummel, Munich,

Hans-Friedr. Quast, Freiburg (Breisgau),

and Dr. Wolfgang Keller, Pretzfeld (QFr.),

have been named as inventors

frequency coils 5 are arranged so that they are guided along the rod at a predetermined speed can be. If the melting zone z. B. out in the direction indicated by arrow 18, so According to the invention, the device for upsetting and stretching the rod during the zone drawing arranged at the end of the semiconductor rod denoted by 2. Generally it is always at the end of the rod arranged, which solidifies last, because then the by compressing and pulling the rod possibly Any defects that occur in the crystal lattice can be eliminated by the subsequent melting zone, so that rods with good crystal perfection are obtained.

To compensate for the inductive reactance of the coil 5, for. B. a capacitor 6 of the High frequency coil can be connected in parallel. This has the advantage that the high-frequency generator 7 only that caused by the heating power and the ohmic losses of coil 5 and capacitor 6 must deliver conditional active current, which is much smaller than the reactive current flowing through the coil.

The resonant circuit formed by the coil 5 and the capacitor 6, the one against the inner transmitter resonant circuit of the generator is out of tune, is capacitively or inductively coupled to the transmitter oscillating circuit. The coupling is so loose that also

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In the event of a further detuning of the heating circuit caused by the change in thickness of the semiconductor rod, the generator-heating circuit system oscillates at one frequency. ']' ...

The high-frequency current flowing in the coil 5 induces a voltage in the part of the semiconductor rod surrounding the coil, which voltage causes a current whose magnetic field counteracts the one generated by the coil. This part of the semiconductor rod can therefore be compared with a coil turn. As is known, the coupling factor of such coil assemblies is proportional to a function of the geometric dimensions of the coils and the diameter of the inner coil. If, therefore, the thickness of the semiconductor rod changes while the method according to the invention is being carried out, the coupling factor and thus the resistance Z _{n of} the heating circuit measured between terminals 12 and 13 also change. This change in load results in a change in the anode current, which is displayed by the instrument 8. A very specific value of the anode current corresponds to a certain thickness of the rod. The resistor 9 is set at the beginning of the method according to the invention in such a way that an anode current, as it corresponds to the desired thickness, causes a voltage drop across this resistor which is equal to the voltage output by the battery 10, so that the; polarized relay 11 is in the rest position 15. If the thickness of the semiconductor rod changes in the course of the process and thus the anode current of the generator changes, the relay picks up and closes, depending on the direction in which the current change occurs; the contact 16 or 17. By closing one of these contacts, the gear 19 is set in motion along the rack 20 by a motor 21 via a gear (not shown) and the semiconductor rod is stretched or compressed depending on the direction of rotation of the gear.

In FIG. 2, the power N delivered by the generator is shown as a function of the ratio of load resistance Z _H to the output resistance of transmitter Z ₅ . As is well known, the output power is greatest with adaptation, ie Z _n = Z _5. In the method proposed by the invention, the load resistance Z _n z. B. chosen so that with that thickness of the semiconductor rod that is to be maintained by the control, the power output by the generator corresponds approximately to that in the point, so work is carried out in the rising branch of the curve. From what has already been stated above, it follows that for a rod that is becoming thinner, the coupling factor becomes smaller, ie the coupling between the high-frequency coil and the TeE of the semiconductor rod symbolized by a coil turn becomes looser and thus Z _n becomes larger. From the diagram in FIG. 2 it can be seen that the adaptation then becomes better, ie the output power and therefore also the anode current increases. Conversely, if the semiconductor rod becomes thicker, i.e. the coupling becomes stronger, then Z _n becomes smaller and so does the anode current.

The load resistance Z _n can also be chosen so that work is carried out in the sloping branch of the curve, i.e. approximately at point B , that is, as the rod becomes thinner, i.e. increasing Z _n , the power N- and thus the anode current output by the generator decrease. In order to ensure that the thickness control takes place in the desired direction, the relay 11 must then be polarized in the opposite way to the method in which the operating point is in the rising branch of the curve, that is, approximately at A.

If the working point is in the rising branch of the curve, then as the rod becomes thinner, the through the increases Instrument 8 displays anode current. The relay 11 must be polarized so that it is z. B. contact 16 closes, whereby a rotation of the motor 21 is caused, which the gear 19 in the direction of the arrow 22 moved so that the semiconductor rod is upset, i.e. H. that the two ends 2 and 3 are mutually exclusive approach until the anode current has the desired value again and the relay 11 falls back into the rest position 15.

As the rod becomes thicker, the anode current becomes smaller, the relay 11 closes z. B. contact 17, whereby the motor 21 sets the gear in the direction of arrow 23 in rotation, so that the semiconductor rod is stretched until the anode current returns to the desired value and thus the relay 11 drops out.

In order to increase the thickness of the semiconductor rod during the drawing in this method according to the invention change, z. B. between the terminals 12 and 13, the heating system shown in Fig. 3 is connected. Additionally to the high-frequency coil 24, which surrounds the semiconductor rod 1, is a second coil 25 in series switched. The reactance of these two coils can, for. B. compensated again by a capacitor 26 will. For example, by immersing or pulling out a metal body 27, the The inductance of the coil 25 can be changed and thus the load resistance effective between the terminals 12 and 13 of the system, i.e. the anode current or the thickness of the semiconductor rod.

Claims (8)

PATENT CLAIMS: 1. A method for crucible-free zone melting of a rod of semiconductor base material, in particular of high-purity silicon, held at its ends, in which a melting zone generated by means of inductive heating by a high-frequency coil is guided along between the two supported ends of the rod in the direction of the rod axis and the melting zone cross-section by changing the spacing of a rod end is influenced, in particular for the production of a monocrystalline semiconductor rod, characterized in that the current fed from a high-frequency current source into a coil surrounding the melting zone of the semiconductor rod, which current also changes with changing thickness of the rod, is used to control a device which the The distance between the holders of the semiconductor rod is able to change, and that this device approaches or removes the two holders from one another until the current in the high-frequency coil has the desired value again. 2. The method according to claim 1, characterized in that the melting zone of the very short, essentially only the melting zone comprehensive high-frequency coil is generated and the change in the thickness of the rod resulting from the change in the melting effect High frequency current to control the Distance of the brackets regulating device is used. 3. The method according to claim 1 or 2, characterized in that by the device that the distance between the holders of the semiconductor rod changes, adjusted that end of the rod that will ultimately freeze. 4. The method according to any one of claims 1 to 3, characterized in that one to the High frequency power source mismatched high frequency coil is used. 5. The method according to claim 4, characterized in that the high frequency coil to the The high frequency power source is so mismatched that as the thickness of the rod decreases, the high frequency power source delivers a higher current. 6. The method according to any one of claims 1 to 5, characterized by the use one of the high frequency coils connected in parallel capacitor. 7. The method according to any one of claims 1 to 6, characterized in that to the thickness of the semiconductor rod during the pulling process, in addition to the high-frequency coil that surrounds the semiconductor rod, a second coil is connected in series, the inductance of which through Immersion or extraction of a metal body is changed. 8. Device for performing the method according to one of claims 1 to 7, characterized characterized in that the resonant circuit of the transmitter detuned from the resonant circuit of the consumer is and both are only more or less firmly connected to each other via a coupling member are. Considered publications:
German patent application S 36 998 VIIIc / 21g (published on June 23, 1955). 1 sheet of drawings