RU2324017C1 - Process to manufacture silicon hollow monocrystals - Google Patents

Abstract

FIELD: chemistry; profiled silicon monocrystals manufacturing.

SUBSTANCE: silicon monocrystals are produced by crucible-free vertical float-zone method, which implies induction generation of a melt drip on initial vertical silicon ingot, seeding of monocrystal being grown on a seed [111] oriented silicon monocrystal, building-up of crystal conical portion to specified diameter, while moving initial ingot and coil in horizontal plane, under conditions, which provide for convex crystallisation front, and emergence of face (111) at melt centre surface at the moment the monocrystal specified diameter is reached. This is followed by hollow monocrystal growing, melt column, which connects the melt ring resting on the growing monocrystal with the drip on initial ingot, being positioned between edge of (111) face and cylindrical surface of the growing monocrystal.

EFFECT: production of silicon hollow (tubular) dislocation-free high-purity perfectly structured monocrystals with [111] orientation.

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Description

The invention relates to the field of non-ferrous metallurgy engaged in the production of profiled single crystals of various materials for various purposes. The invention, in particular, allows to obtain hollow (tubular) dislocation-free silicon single crystals of high purity and perfection, on the basis of which new-generation semiconductor devices can be manufactured.

The known method of Stepanov [1], in which shaped crystals, including hollow, are obtained by drawing from the melt using a special shaper. Currently, Stepanov’s method is practically the only one that allows one to grow hollow single crystals.

The disadvantages of this method are the contact of the former with the melt, which makes it possible to contaminate the grown crystal, and a rather complicated design of the technological device. The complexity of the thermal unit does not always allow creating conditions for growing high-quality single crystals. In particular, in this way it is not possible to obtain hollow (tubular) dislocation-free silicon single crystals of high purity.

There is another method for producing hollow cylindrical crystals [2, prototype], in which hollow crystals are pulled out of the melt using a seed in the form of a tube.

However, it is not possible to grow single-crystal tubes from a silicon melt due to the lack of high-quality hollow single-crystal seeds (tubes) and the difficulties of overcoming the thermal shock that occurs when the melt contacts the seed at the time of seeding, which leads to the appearance of several crystallization centers and as a result of the growth of the polycrystalline tube.

The problem solved by the invention is the production of hollow silicon single crystals.

The technical effect is to provide the ability to obtain hollow (tubular) dislocation-free silicon single crystals of high purity and perfection.

The effect is achieved due to the fact that in the known method for producing hollow silicon single crystals, including the growth of single crystals by seed, in contrast to the known growth is carried out by the method of vertical crucible-free zone melting, which includes the formation of a melt drop on an upright silicon ingot using an inductor; seeding of the grown single crystal on the seed in the form of a silicon single crystal oriented in the [111] direction; growing the conical part of the grown single crystal to a given diameter when the starting ingot and inductor are displaced in a horizontal plane and under growing conditions that provide a convex crystallization front on the growing single crystal and when the specified diameter of the grown single crystal reaches the exit of the (111) face to the surface in the center of the melt, and then - growing a hollow single crystal with the position of the melt column connecting the melt ring resting on the growing single crystal with a drop on the original ingot, between the edge of the (111) face and the cylindrical surface of the growing crystal.

The proposed method is new, since at the present time similar methods are not known, allowing to grow hollow single crystals of a high degree of purity and perfection. The differences of the proposed method consist in the cultivation of a hollow single crystal by the method of crucible-free zone melting (BZP) under certain growing conditions.

The technical effect consists in the fact that, thanks to the differences, the proposed method provides hollow (tubular) dislocation-free silicon single crystals of a high degree of perfection and purity, on the basis of which new-generation semiconductor devices can be manufactured.

The method of growing single crystals using vertical BZP, as is known, allows one to grow single-crystal, high-purity single crystals of semiconductor materials, in particular silicon, in the form of ingots, even of large diameter. However, to date, it is not known to obtain tubular silicon single crystals of this quality by this method. So far, it has not been possible to realize the advantages of the BZP method for solving the problem - obtaining hollow silicon single crystals.

The non-obviousness of the invention lies in the fact that the conditions for growing silicon single crystals by the BZP method are found, which make it possible to obtain hollow single crystals, which is not known from the state of the art.

The essence of the claimed invention lies in the fact that in the usual method of vertical BZP of cylindrical rods with a displacement in the horizontal plane of the initial ingot and inductor, the detected growth conditions do not violate the dislocation-free crystallographic crystal growth around the crystallized face (111), forming a tube wall.

After the formation of a melt drop on the initial ingot using an inductor, the diameter of which is larger than the diameter of the initial ingot, a melt drop is connected to a seed (pickling), which uses a silicon single crystal oriented in the [111] direction.

At the next stage, the conical part of the grown single crystal is expanded to a predetermined diameter by shifting the initial ingot and inductor in a horizontal plane and conditions are created under which a melt zone is formed consisting of a part located on the end face of the growing single crystal, a small diameter column and a melting surface of the initial ingot. All three parts of the melt zone are continuously interconnected during the entire growing process. In the process of growth, thermal conditions are created that ensure the formation of a convex crystallization front in the central region of the growing single crystal with access to the melt surface - at the moment of reaching the specified diameter of the grown single crystal - the crystallographic plane (111), which crystallizes, forming a ring zone of the melt. The necessary thermal conditions are created, as you know, by changing the power of the inductor's power source and the growth rate.

It was found that under the above conditions, while continuing the growth process, the growth of a single crystal occurs with the formation of a cavity in the central part. In this case, the crystal structure is not violated and, as a result, a hollow, dislocation-free single crystal (tube) of high quality is grown.

The invention is illustrated in figure 1, 2, 3, a schematic representation of the sequence of the main steps of the method, where:

1 - lower stem with a seed holder,

2 - seed [111],

3 - conical part of the grown single crystal,

4 - convex crystallization front,

5 - melt zone,

6 - ring inductor,

7 - source ingot,

8 - upper collet for attaching the original crystal,

9 - upper stock

10 - direction of rotation of the upper rod,

11 - direction of rotation of the lower rod,

12 - direction of movement of the upper rod,

13 - direction of movement of the lower rod,

14 - direction of displacement in the horizontal plane of the upper rod,

15 - direction of displacement in the horizontal plane of the inductor,

16 is a column of melt,

17 - crystallographic plane (111) of the crystallization front, which emerged on the surface of the melt,

18 - melt ring,

19 is a melted surface of the original ingot,

20 - hollow single crystal.

To implement the proposed method, a known device for vertical BZP of cylindrical rods is used, the growth unit of which consists of a lower rod with a seed holder 1, in which a single crystal seed 2 is fixed - a silicon single crystal with [111] orientation; ring inductor 6; the upper rod 9 with a collet 8, in which the original ingot is fixed 7. The lower rod 1 rotates in the direction 11 and moves in the direction 13. The upper rod 9 rotates in the direction 10, moves in the direction 12 and moves in the horizontal plane in the direction 14. The inductor 6 shifts in the horizontal plane in the direction of 15.

The proposed method is as follows. Inductor 6 creates a drop of melt on the original ingot 7 and, using a seed 2, a silicon single crystal with [111] orientation, the conical part of the single crystal 3 is grown. By changing the power of the inductor’s power supply and the growth rate, the thermal conditions are created for the formation of a convex crystallization front 4 at least in the central part of the grown crystal. The growth of the cone to a predetermined diameter is carried out as in a conventional BZP with a melt zone 5 (Fig. 1). Then, displacing the initial crystal by displacing the upper rod 9 in direction 14 and inductor 6 in direction 15, a small-diameter melt column 16 is formed and placed between the central part of the melt and the surface of the grown crystal. By changing the power of the power source and the magnitude of the speed of movement of the upper and lower rods, thermal conditions are created for the central convex part of the crystallization front 4, containing the (111) 17 plane, to reach the melt surface. The central region of the melt, located on the growing crystal, crystallizes and a ring of melt 18 is formed, which is connected by a column 16 to the fusing surface 19 of the original ingot 7 (Fig. 2). The appeared ring of the melt 18 provides crystallization of the hollow single crystal 20 of a given diameter, without violating its crystallographic orientation (figure 3). As a result, a hollow single crystal is grown on a continuous conical base.

An example of a specific application of the method is the implementation of the proposed method on known devices for a vertical BZP installation Crystal 206, Crystal 107, Crystal 108, Crystal 114 (developed by VNIITVCh named after V.P. Vologdin).

Hollow silicon single crystals were grown on a continuous conical base with an external diameter of 28 mm, an internal diameter of 12 mm, and a crystallographic orientation [111]. The original silicon ingot of the KP-4 brand had a diameter of 28 mm. The seed is a single crystal of silicon with a section of 3 × 3 mm, a length of 70 mm, a resistance of 50.0 Ohms, doped with phosphorus. An annular inductor from a copper water-cooled tube with a diameter of 4 was used; inner diameter - 30 mm. The rods rotated at a speed of 31 rpm and moved vertically at a speed of 2 mm / min. The upper rod was displaced in the horizontal plane by 8 mm, and the inductor by 4 mm. During the growth of a hollow single crystal — a tube — the melt ring was 8 mm wide and the diameter of the melt column was 8 mm. Hollow silicon single crystals with an outer diameter of 28 mm and an inner diameter of 12 mm with a crystallographic orientation of [111] and a dislocation density of 10 ^-2 cm ^-2 were obtained

Thus, the present invention allows using standard technological equipment for growing semiconductor crystals using the BZP method to obtain tubular dislocated silicon single crystals with a crystallographic orientation [111] of high purity, on the basis of which new-generation semiconductor devices can be manufactured.

Information sources

1. A.V. Stepanov. A new method for producing products (sheets, pipes, rods of various profiles, etc.) directly from the melt. Zh.T.F., vol. 29, issue 3, 1959, p. 381.

2. V.M. Byndin, V.I. Dobrovolskaya, D.G. Ratnikov. Induction heating in the production of highly pure materials. High Frequency Thermist Library. L .: Engineering, 1980, p.40 (prototype).

Claims (1)

A method for producing hollow silicon single crystals, including the growth of single crystals by seed, characterized in that the growth is carried out by the method of vertical crucible-free zone melting, including the creation of a melt drop on an upright silicon ingot using an inductor, the seed of the grown single crystal on the seed, in the form oriented in the direction [111] a silicon single crystal, expanding the conical part of the grown single crystal to a predetermined diameter when the initial fusion is displaced ka and inductor in the horizontal plane and under growing conditions, providing a convex crystallization front on the growing single crystal and, at the moment of reaching the specified diameter of the grown single crystal, the exit of the (111) face to the surface in the center of the melt, and then growing a hollow single crystal with the position of the melt column connecting a melt ring resting on a growing single crystal with a drop on the initial ingot, between the edge of the (111) face and the cylindrical surface of the growing single crystal.

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