DE1272900B - Device for pulling monocrystalline rods from a melt - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

BOIj

German class: 12 g -17/18

Number: 1272900

File number: P 12 72 900.9-43 (N 23970)

Filing date: November 23, 1957

Opening day: July 18, 1968

Devices for the production of monocrystalline rods, in particular from a semiconductor material, like germanium or silicon, by pulling a monocrystalline rod through one on a melt of the material floating body consisting of a crucible, a heater for the melt and a device for pulling up a single crystal which is in contact with the melt at its end, are known. Often a crucible made of graphite is used, which by means of a high-frequency coil is heated. This crucible has a cylindrical side wall with an inside diameter that is a lot is larger than the diameter of the pulled crystal. Most often, such a crucible is initially not whole filled with the melt. During the pulling process of the crystal, the melt level drops in the crucible. A body floats on the melt, through the opening of which the rod is pulled.

The monocrystalline rods produced in this way are many, especially when it comes to semiconducting rods, divided into smaller bodies and used for semiconducting devices, such as Transistors or crystal diodes.

The monocrystalline rods produced with the above-mentioned known devices have a relatively high degree of accuracy high content of crystal defects, e.g. B. Faults and lattice dislocations that are also distributed unevenly on the cross section of the rod. These faults and dislocations affect the physical properties of the single crystal, e.g. B. its conductivity. The unevenness of the bar across the cross-section can interfere with further processing, z. B. affect diffusion or alloying processes.

It is also known to use two crucibles when pulling up, in particular semiconductor crystals, in which the smaller crucible floats on the melt in the larger crucible. The melt enters the smaller crucible through a channel in the wall of the smaller crucible, from which the monocrystalline rod is pulled up. Because the volume of the melt in the small crucible remains constant, a monocrystalline rod can be drawn with doping that is constant over its length. In such a known arrangement, the crucible has a cylindrical inner wall which protrudes fairly high above the melt in the inner crucible and is somewhat conical at the upper edge for easier supply of material. However, the diameter of the drawn rod is much smaller than the inner diameter of the smaller apparatus for drawing single crystal rods
from a melt

Applicant:

N. V. Philips' Gloeilampenfabrieken,

Eindhoven (Netherlands)

Representative:

Dipl.-Ing. E. E. Walther, patent attorney,

2000 Hamburg 1, Mönckebergstr. 7th

Named as inventor:

Marcel Pieter Alfons Frangois, Brussels

Claimed priority:

Netherlands 28 November 1956 (212 549)

Crucible. The conical part of the inner wall of the smaller crucible is so high above in this device the melting level located that this part for irradiation on the surface of that rod part in which the temperature is above the softening temperature does not contribute. The conical part forms with the rod axis at an angle of less than 30 °.

In the case of crucible-free zone melting, it is known to use one to heat the molten zone Apply the rod surrounding the heating ring, which is tapered towards the inside and short conical Has surfaces. In this known device, the task was to concentrate the heat very closely and thus to limit the molten zone to a very small length of the rod. A compensation the radiation on the surface of the already solidified rod part was not intended and because of the small size of the area, it was not achieved either.

It is known that dislocations arise after crystallization essentially as a result of thermal effects Tensions in the freshly grown monocrystalline, which is still at a high temperature Rod. It is also known that thermal stresses in a circular cylindrical rod are due to the radial heat dissipation in the rod and that they can be avoided by

809 570/513

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in the rod along its axis a constant temperature flat washer with a rectangular cross-section, temperature gradient is generated and maintained. Particularly good results are achieved with a ring die Invention aims to achieve a device disc that is thinner than 5 mm. for pulling monocrystalline bodies from a melt it is essential that the radiation be given, in which this task is at least as close to the surface as it is practically without contact is approximated solved, without the described is possible, connects to the rod, because just the Difficulties arise. It relies on the parts of this area that are near the rod Recognition that in that part of the already existing, to a considerable extent to compensate grown monocrystalline rod in which to contribute. Theoretical considerations also have thermal stresses, distortions and ver io result in a practically ideal balance Settlements can occur, a constant tem- a certain temperature gradient in the rod temperature gradient can be maintained. By choosing a certain ratio of the This constant temperature gradient then prevents the outer diameter to the inner diameter of the ring occurrence thermal stresses and eliminated disc-shaped radiation surface is achievable. In accordingly, the cause of the distortions and misunderstandings, excellent results are obtained, Subsidence. To do this, the broadcast on if this ratio is between 2 and 3, with in other words, if the outside diameter of the crystalline rod that has a temperature which is two to three times the radiating area the softening temperature of the substance exceeds, is rod diameter, it should also be noted, occurring heat loss due to irradiation of 20 that the ring width, d. H. half the difference Heat should be balanced as possible. With the difference between the outer diameter and the inner diameter, The softening temperature of a substance is the lowest to the extent that it has to be chosen greater than that Means temperature at which is lower in this substance due to the temperature gradient. It can be under a thermostat Stresses nor distortions would be beneficial rather than dimensions be guided. The softening temperature of the radiation surface on the temperature gradient Germanium is around 400 ° C and that of the adapt by cooling the rod part, which is Silicon about 800 ° C. already at a lower temperature than that In the known arrangements, the softening temperature now radiates, the Temperatar-Wärme of the surface of the melt and of gradients the dimensions of the radiation surface to adapt the crucible wall 30 protruding beyond the melt, expediently by cooling in one on the staff. The radiation coefficient is the fixed distance from the radiating body, so that However, the usual melting is very low and always contributes a constant, forced by cooling little to compensate for the radiation. It has developed a temperature gradient It turned out further that the vertical inner case of the body, the upper limit of which is a The surface of the crucible wall is unsuitable; it is a surface that slopes downwards from the melt level so distributed heat radiation on the upper is inclined above, the inclination of the conical area of the grown rod to cause part, d. H. the angle that the generating this the desired constant temperature gradient is formed by the conical part with the axis of the rod, will. in particular greater than 30 °, expediently between

It has been found that it can be chosen for an approximate 40, 40 and 50 °.

The radiation ring is expediently made of conductive, rotationally symmetrical radiation body to be used with the highest possible radiation level, which is made as close as possible to the edge of the solidification coefficient. Preferably, a radiation ring starting from an area and extending radially into a large ent graphite is used, extending at a distance from the rod. The device according to the invention will therefore be explained in more detail by means of exemplary embodiments using the device for the production of monocrystalline rods, some of which are shown in the schematic drawing, in particular from a semiconductor material. Drawing a monocrystalline rod through a to Fig. 1, 2, 3 and 4 show in section some of a melt of the material floating body formations of a device according to the invention for according to the invention the drawing opening of the body with 50 pulling a monocrystalline rod; some clearance to fit the rod, the outside F i g. 5 is a graphical representation of the diameter of the body at least twice the length of the etch pit density as a function of the rod diameter and the upper stock of the axis for a rod which, by means of delimitation of the body, is an area which is in that of a device according to F. i g. 1 plane of the phase boundary solid-liquid or, of which 55 is, and for a rod that is made in a known manner without a melting level at the drawing point, obliquely using a radiating body. is inclined upwards and its radiation In Fig. 1 contains the z. B. consisting of graphite coefficient greater than the radiation coefficient of the crucible 10 is a germanium melt 11 and is the surface of the melt. by means of one of the high-frequency coil 3 generated By the term "radiation coefficient" is heated, while the ratio between the floats from a top through the opening of the graphite ring disk 2, the surface element of a normal hot body and on the melt 11 60 high-frequency electromagnetic field, an element is drawn from a surface element of the same size, crystalline rod 1 with a diameter of the same temperature and high as a completely black one, which, with the exception of some leeway, has stowed the amount of radiation emitted by the inner body of the disc. The radiation area den (emission ratio). on the upper side of the disk causes the off-after a preferred embodiment of the same as the heat radiated by the rod. According to the invention, the radiating body is in the form of a rod part located within the disk 2

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essential still melted. To prevent the high frequency field from being heated directly; the education that the contact between the rod and that of the melt can be achieved by thermal radiation The melt is interrupted when it is pulled up, the radiation disk is introduced and controlled the thickness of the radiation disk can be suitably smaller.

chosen as 5 mm. 5 The latter two measures after the

Calculations show that a practically full invention also have the advantage that the There is only one ideal balance with a wall of the crucible perpendicular to the radiation disk can be reached, which is heated up to the rod at a relatively low temperature, extends and to a temperature of so that the heat emitted by it, which the

ίο reached the surface of the monocrystalline rod and. the desired radiation distribution disturbs, is reduced. The considerations on which the invention is based have namely also led to the knowledge that heating is carried out by a vertical radiation wall, T _{sm being} the melting temperature of the 15 z. B. the crucible wall protruding above the melt, for the rod in degrees Kelvin and ε the radiation pulling up the rod is the desired beam coefficient of the radiation surface. For a radiation compensation disruptive radiation distribution a graphite disc that creates a radiation; The deviations occur in particular in the coefficient of around 1, this means a most sensitive part of the rod, in the part directly adjacent to the temperature of the solidification surface. It is that

half desirable to reduce the radiation of such a wall as possible.

= 1.191 nm * Fig. 2 is a schematic representation of a

Apparatus which arises when the invention is taken into account that ideal circumstances of a known apparatus for pulling-on do not occur in practice, is used in which crystalline rods are used, with which a practice can expediently achieve an even higher temperature - Crystalline rod can be produced, the temperature in the longitudinal direction preferably between 1.2 T _sm and 1.5 T _sm . an essentially constant specific cons because the graphite crucible wall has a high degree of resistance. The monocrystalline rod 1 is drawn up from a radiation disk 4 in front of the high-frequency drawing crucible 15, which shields the electromagnetic field in the melt 11, the beam of a larger crucible 16 floats and through a ventilation disk essentially indirectly from the channel 17 with the melt 11 of the larger crucible heated melt. The radiation disc therefore has 16 connected. The liquid level in the one temperature, the temperature of the melt in both crucibles are the same or almost the same. After equals or is only slightly higher. As a result of ^the invention, the floating crucible 15 has not achieved ideal compensation, but its opening has an annular disc-shaped edge surface already a significant improvement over the 18, preferably with the above-mentioned externally known method without a special radiation diameter, the upper side of which has the compensating ring obtain. In the absence of the radiation disk forming a radiation surface and the lower side of which acts only the surface of the melt as the melt 11 floats out, so that the heat radiating body glides into the liquid. This level in the crucible is approximately level with the edge, but in practice it has reached due to the low surface; In this case, the drawing crucible 15, 18 has such a radiation coefficient of the molten substance or the drawing speed of the single element has proven to be inadequate. By increasing the crystalline rod so that the radiation coefficient of the radiation surface, in the front diameter of the monocrystalline rod with the exception of a lying case by using a floating clearance, the inner diameter of the flat graphite disk, the compensation will already correspond to the crucible edge surface.

much improved. Instead of the Strardungskoeffizien- In the F i g. 3 and 4 are devices according to

To increase the radiation area, one can show the invention, in which the heat with increase their temperature with the same effect. After 50 radiators from one coaxial to the rod According to the invention, the temperature of the radiation body consists of the inner side of which has little disc can be increased by the fact that in the least in the part is conical in the direction of pull vertical walls of the crucible z. B. ten one extended, the solidification surface and one at cuts are provided that are so narrow, e.g. B. this adjacent, already grown a-0.25 mm, are that the melt as a result of its upper crystalline rod part, which is on a surface tension not yet flow through them from the crucible chung temperature exceeding temperature can. Circular high frequency currents in det, surrounds.

the crucible wall are thereby bound to a large extent in the schematic in FIG. 3 in section. A relatively large part of the provided device according to the invention, which for Radiofrequency field can then be determined by the radiation disk 60 pulling up a single crystal rod, and heat them directly. comes according to the device according to FIG. 1

According to the invention, the temperature of a radiation ring floating on the melt floating radiation disc also up above for use. This radiation ring 30 has a the melting temperature can be increased, in which a in the drawing direction of the rod, d. H. of the Crucible made of insulating material, e.g. B. a quartz crucible, to- 65 melt away, the conically widening part, the Samman merges into a cylindrical part with a radiation disk made of conductive below. Of the Material, e.g. B. graphite is used. Radiation ring also floats on the melt in such a way that in this case, the radiation disk is only the conical part protruding from the melt.

The device of FIG. 4 corresponds to essential of FIG. 2; only is the flat, annular disk-shaped edge surface 18 of the drawing crucible 15 according to Figure 2 in Figure 4 by a conical Part 35 of the inner wall of the drawing crucible 15 is replaced. According to the invention, the drawing crucible floats 15 so in the melt that above the liquid level 36 in the drawing crucible only the conical extending part 35 of the inner wall is located. In this way the raised rod only receives the radiation from the conical inner wall.

Those described in the explanation of FIG Means for increasing the temperature of the floating radiating body can also be very advantageous the devices according to FIGS. 2, 3 and 4 applied will.

The effect of the invention is explained in more detail with reference to FIG. 5, which is a graphic representation of the results with the device according to FIG. 1 is. The density of the etch pits per square centimeter is plotted vertically in any unit; this density is a measure of the density of impurities in the crystal. The distance from the dash-dotted line axis XX of the rod is plotted horizontally.

Curve A represents the etch pit distribution over the cross-sectional area that occurs in the case of a monocrystalline rod which is used in a device according to FIG. 1 is received. Curve B represents the etching pit distribution in the case of a monocrystalline rod drawn up without a radiating body. It can be seen that in the monocrystalline rod obtained in the device according to the invention, the etching pit density is smaller and the etching pits are more evenly distributed over the cross-sectional area. Only at the edge RR of the rod does the etch pit density increase considerably. In this context, however, it should be noted that the temperature of the floating radiating body was lower than the temperature required for ideal compensation. Even so, there has already been a considerable improvement.

Claims (12)

Patent claims: 1. Device for the production of single-crystal rods, in particular from a semiconductor material, by pulling a monocrystalline rod through one floating on a melt of the material Body, characterized in that the opening of the body with something Clearance around the rod fits that the outside diameter of the body at least twice of the rod diameter and the upper limit of the body is an area that is in the level of the phase boundary solid-liquid or, based on the melt level at the drawing point, is inclined upwards to it and its radiation coefficient is greater than the radiation coefficient the surface of the melt. 2. Apparatus according to claim 1, characterized in that the radiating body has the shape has a flat washer (2) with a rectangular ring cross-section. 3. Apparatus according to claim 2, characterized in that the annular disc (2) thinner than 5 mm. 4. Apparatus according to claim 2, characterized in that the annular disc as a Rand.-surface (18) with a drawing crucible (15) which is coaxial to the rod and floating on the melt a lower opening (17) is formed. 5. The device according to claim 1 when using a body inclined obliquely upward upper boundary surface, characterized in that the body is below the Melt level as a drawing crucible floating on the melt, coaxial to the rod with a the lower opening (17) continues. 6. Apparatus according to claim 1 or 5, characterized in that the inclination dei upper boundary surface of the body compared to the rod axis is more than 30 °. 7. Apparatus according to claim 6, characterized in that the inclination is 40 to 50 ° amounts to. 8. Device according to claims 1 to 7, characterized in that the by high frequency Induction currents heated melt is arranged in a crucible, which consists of an electrically conductive material and the wall of which is provided with incisions that are dimensioned in this way are that the melt remains in the crucible, but the high-frequency currents are interrupted are. 9. Device according to claims 1 to 7, characterized in that the by high frequency Induction currents heated melt in a crucible from an electric Insulating material is arranged and that the radiation body consists of an electrical conductor. 10. Device according to claims 1 to 9, characterized in that the radiating body consists of graphite. 11. Device according to claims 1 to 10, characterized in that the solidified Part of the rod that has a temperature above the softening temperature of the rod material has, a cooling device is arranged. 12. The device according to claim 11, characterized in that the cooling device in one is arranged constant distance from the radiation body. Considered publications:
British Patent No. 754767; Legacy Patents Considered:
German Patent No. 1044 768. 1 sheet of drawings 809 570/513 7.68 © Bundesdruckerei Berlin