Device for producing a monocrystal by crystallizing said monocrystal in a melting area

Abstract

A device for producing a single crystal by crystallizing the single crystal in a melt zone, comprising a housing, an inductor for generating heat in the melt zone, a reheater which surrounds and applies thermal radiation to the crystallizing single crystal, and a separating bottom which delimits downward an intermediate space between the reheater and a wall of the housing at a lower end of the reheater.

Claims

1. A device for producing a single crystal by crystallizing the single crystal in a melt zone, comprising a housing, an inductor for generating heat in the melt zone, a reheater below the melt zone which surrounds and applies thermal radiation to the crystallizing single crystal, the single crystal crystallizing below the melt zone, and a separating bottom which delimits an intermediate space between the reheater and a wall of the housing downward at a lower end of the reheater, wherein barriers are arranged on outer sides of the separating bottom to shorten or close gaps between the reheater and the separating bottom and between the separating bottom and the wall of the housing.

2. The device of claim 1, wherein the reheater is a reflector.

3. The device as claimed in claim 1, wherein the reheater is an active radiating heater.

4. The device of claim 1, wherein an upper edge of the reheater lies at the level of a triple point of a crystallization boundary.

5. The device of claim 4, wherein the reheater has an axial length which is not larger than 1.5 times a diameter of the single crystal produced.

6. The device of claim 1, wherein the barriers arranged on outer sides of the separating bottom between the separating bottom and the wall of the housing are constructed of steel.

7. The device of claim 1, wherein the barriers arranged between the outer sides of the separating bottom and the reheater are constructed of silver or quartz glass.

8. The device of claim 1, wherein the barriers reduce or eliminate convective flow of gas to the melt zone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail below using drawings.

(2) FIG. 1 is a schematic representation which represents the prior art.

(3) FIG. 2 is a schematic representation of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The reheater is preferably a reflector or an active radiating heater, for example a heating resistor.

(5) Disruption of the temperature field is caused by the thermal expansion of protective gas, for example argon, in the housing, as a result of which heat is drawn in an uncontrollable way from the crystallizing single crystal and the melt zone.

(6) Conventional measures such as applying a positive pressure of protective gas to the housing in order to avoid secondary reactions and in order to prevent electrical sparking at the inductor or at its electrical leads, and arranging a reflector around the crystallizing single crystal, promote the creation of convection which is stimulated by thermal expansion of protective gas. The intermediate space between the crystallizing single crystal and the reflector thus acts as a vent, which promotes the thermal expansion of protective gas.

(7) The aim of the present invention is to substantially prevent disruptive thermal expansion of protective gas. This aim is achieved by a separating bottom, which stands in the way of the flowing protective gas as a barrier. The separating bottom is arranged in the housing in such a way that an intermediate space between the reheater and a wall of the housing is delimited downward by it at a lower end of the reheater.

(8) It is furthermore preferable for gaps, which may be present between the reheater and the separating bottom and between the wall of the housing and the separating bottom, to be shortened or closed by means of barriers, in order to hinder the thermal expansion of the protective gas even more strongly or entirely block it. Suitable barriers are for example rings of metal such as, for example, steel, silver or quartz glass, which cover the gaps. The gap between the wall of the housing and the separating bottom is preferably covered with a ring of steel, and the gap between the reheater and the separating bottom is preferably covered with a ring of silver or quartz glass.

(9) The arrangement of the separating bottom prevents protective gas from drawing heat from the melt zone and the crystallizing single crystal in an uncontrolled way, and therefore also consequential damage which can occur owing to the resulting disruption of the temperature field. Furthermore, the lack of heat extraction has further advantages. The heating power of the inductor can be reduced, which makes events such as electrical sparking at the inductor or at its electrical leads less likely and reduces thermal stresses in the crystallizing single crystal.

(10) The upper edge of the reheater preferably lies at the level of the triple point of the crystallization boundary. The reheater has an axial length which is preferably not longer than 1.5 times the diameter of the single crystal to be produced. The radial distance between the single crystal and the repeater is preferably not more than 30 mm, a radial distance from 10 mm to 20 mm being particularly preferred.

(11) The invention is preferably used for the production of silicon single crystals having a comparatively large diameter of at least 150 mm. Both the FZ method and the GFZ method may be envisioned as production methods.

(12) FIG. 1 shows a sectional representation of a device for producing a single crystal by crystallizing the single crystal in a melt zone. This device may be equated to the prior art. Only features which contribute to the explanation of the invention are represented. The single crystal 1 grows in a melt zone 2, which is supplied with heat by an inductor 3. Arranged at the level of the triple point ETP, there is a reflector 4 which surrounds the crystallizing single crystal and has an axial length which is shorter than the length of the single crystal being produced. The reflector 4 divides the interior of a housing into an intermediate space between the crystallizing single crystal 1 and the reflector 4 and an intermediate space between the reflector 4 and the wall 5 of the housing. Block arrows indicate the closed path of a flow of a protective gas contained in the housing, driven by thermal expansion.

(13) FIG. 2 shows a device according to FIG. 1, and additionally, features of the invention. Features which are of the same type are provided with the same reference numbers. The device according to the invention is distinguished by a separating bottom 6, which delimits the intermediate space between the reflector 4 and the wall 5 of the housing downward. The reflector 4 may be replaced by an active radiation heater. Block arrows depicted as thinner in comparison with FIG. 1 show a gas flow, driven by thermal expansion, which is greatly impeded owing to the arrangement of the separating bottom 6.

(14) The gas flow may be impeded even more strongly up to the extent of full blockage, preferably by arranging barriers 7 on outer sides of the separating bottom 6, which shorten or close gaps between the reflector 4 and the separating bottom 6 and between the separating bottom 6 and the wall 5 of the housing.