CH619007A5 - Process and device for the manufacture of preformed single crystals with multiple doping - Google Patents

Abstract

Preformed single crystals with multiple doping are manufactured continuously by the pendant drop method, the composition of the material used to manufacture the single crystal being varied during the manufacture. The device, which makes it possible to implement this process comprises especially a system for multiple feed of the material used to manufacture the single crystal, that is to say one comprising at least two independent storage vessels. The single crystals with variable doping find many applications, especially in electronics.

Description

The present invention relates to a method and a device for the production of preformed single crystals with 5U doping by the hanging drop method.

The holder's Swiss patent n ° 612 596 covers a continuous manufacturing process of a single crystal of predetermined shape consisting of:

(a) placing material used to manufacture the single crystal 55 in a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said capillary of said molten material, at the temperature and at the pressure considered,

(b) bringing said material to a temperature above its (10 melting point,

(c) bringing a suitably oriented preformed crystalline seed into contact with the hanging drop formed at the bottom of said capillary orifice,

(d) pulling the germ down while feeding said material into the crucible, so that the quantity of material supplied per unit of time is at all times substantially equal to the quantity of material drawn in the form of single crystal.

(e) removing the single crystal formed at selected time intervals,

as well as a device allowing the continuous production of monocrystals of predetermined shape comprising:

(a) a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said capillary of the molten material used to manufacture the single crystal at the temperature and pressure considered,

(b) a heating device surrounding said crucible,

(c) a system for feeding the material used to manufacture the single crystal, placed above said crucible,

(d) an enclosure provided with a device allowing its cooling surrounding said crucible and said supply system and comprising a lower orifice allowing the passage of the single crystal produced, orifices allowing the circulation of a gas constituting the working atmosphere, and orifices allowing passage to the heating system,

(e) a seed carrier system supporting the preformed single crystal seed,

(f) a system allowing said seed carrier to move up and down and to rotate on itself,

(g) a regulation system linking the traction speed of the single crystal formed to the speed of supply of the material used to manufacture the single crystal.

If the composition of the material supplied remains identical during manufacture, a single crystal is obtained having an identical composition over its entire length.

An object of the present invention is to obtain single crystals having a different composition over their length.

According to the present invention, the composition of the material used to manufacture the single crystal is varied during manufacture.

This variation in the composition of the material used to manufacture the single crystal is obtained according to the invention with a multiple supply system comprising two or more reservoirs supplying the crucible simultaneously or successively.

The process of the present invention therefore consists in:

(a) placing material used to manufacture the single crystal, the composition of which varies in a predetermined and adjustable manner, in a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said molten material, at the temperature and pressure considered,

(b) bringing said material to a temperature above its melting point,

(c) bringing a suitably oriented preformed crystalline seed into contact with the hanging drop formed at the bottom of said capillary orifice,

(d) pulling the germ down while feeding said material into the crucible, so that the quantity of material supplied per unit of time is at all times substantially equal to the quantity of material drawn in the form of a single crystal,

(e) removing the single crystal formed at selected time intervals.

The material used to manufacture the single crystal is preferably supplied in the form of powder or small beads.

The work is carried out under an appropriate atmosphere depending on the chemical nature of the crystal and the material constituting the crucible. One can work for example under nitrogen, under argon free of oxygen or in air.

The working pressure can be atmospheric pressure or a lower pressure. You can if necessary work under a vacuum of up to 10 ~ 3 mm Hg.

The temperature to which the material used to manufacture the single crystal is brought must be sufficiently higher than the

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melting point of said material so that it is well melted.

The speed of traction of the germ downwards is usually between 10 and 500 mm / h

The device of the present invention comprises: s

(A) a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said capillary of the molten material used to manufacture the single crystal at the temperature and pressure considered, m

(b) a heating device surrounding said crucible,

(c) a system for multiple feeding of the material used to manufacture the single crystal, placed above said crucible and comprising at least two independent reservoirs,

(d) an enclosure provided with a device allowing its i - ■ cooling surrounding said crucible and said supply system and comprising a lower orifice allowing the passage of the single crystal produced, orifices allowing the circulation of a gas constituting the atmosphere working, and orifices allowing passage to the heating system,; u

(e) a seed carrier system supporting the preformed single crystal seed,

(f) a system allowing said seed carrier to move up and down and to rotate on itself,

(g) a control system linking the traction speed of the monocrystal formed to the speed of supply of the material used to manufacture the monocrystal.

The crucible is made of a material chemically inert with respect to the material used to manufacture the single crystal at the working temperature. m

The enclosure is made of any suitable material, for example quartz. It can also be metallic. The enclosure must be cooled in certain cases, in particular for the manufacture of alumina and silicon single crystals. The cooling can be carried out by any suitable means, for example the enclosure can be provided with a jacket in which cooling water is circulated.

The section of the capillary orifice has a shape adapted to the desired shape of the section of the single crystal, it is for example circular for a single crystal in the form of wire and rectangular 4 "for a single crystal in the form of plate.

The heating system is made up of any suitable device, for example a resistance heater or else a high frequency induction heater fitted with turns adapted to the shape and material of the crucible, working at 20 to 500 KHz to ensure coupling with crucible materials and developing up to 50 Kw.

The multiple feeding system allows to obtain at the bottom of the capillary a liquid of variable composition and adjustable at 50 will.

It should be noted that the small amount of molten material involved: a few cm 3, makes it possible to obtain a clear change in the doping of the manufactured crystal corresponding to the variation in the composition. 53

One can thus obtain single crystals with dopings or different compositions along their length. For example, one can obtain a silicon crystal in an N-type strip over part of its length, then of the P-type simply by having two reservoirs each filled with silicon powders (l (, suitably doped to give one of the silicon P, the other silicon N.

It is also possible to obtain a doping crystal varying over its entire length according to a program determined in advance.

For example, it is possible to obtain a laser ruby with a chromium doping increasing gradually and linearly from the start, from the crystallized part to the end determined by the cessation of crystallization.

A first supply system of powder A1203 doped with Cr203 is installed so that 200 ppm by weight of Cr is obtained relative to A1203 in the crystal. A second A1203 powder supply system much more heavily doped with Cr203 is installed.

During the crystallization, the program of the two power supplies is arranged for the following operations:

- we start with the first power supply. The start of the crystal contains 200 ppm Cr / Al203,

- gradually, the second supply is put into operation so that the chromium content increases linearly. Care is taken that the overall quantity of powder A1203 brought into the crucible remains constant, that is to say that the flow rate of the first is reduced as much as the flow rate of the second is increased,

- We arrive at the end of the crystallization to obtain a crystal containing for example 1000 ppm of Cr / Al203.

The same result can be obtained with two feeds, one loaded with pure A1203 powder, the other with Al203-Cr203 powder and by programming their mixing in an appropriate manner.

The present invention, which makes it possible to obtain variable chemical and / or physical properties on the same monocrystalline support, without any physical junction of any kind, finds numerous applications, in particular in electronics.

The following examples illustrate the invention.

Example 1

Manufacturing of a sapphire and ruby single crystal

The crucible is made of iridium, with a total volume of 20 cm3, pierced in its lower part with a capillary duct of rectangular section 1 × 15 mm. The crucible is enclosed in an enclosure swept by a stream of argon without oxygen. Thanks to a first distributor tank, the crucible is supplied with monocrystalline pure alumina balls with a diameter of 0.05 to 0.1 mm, or with a pure alumina powder of 5 to 50 μm. of diameter. The crucible is brought to a temperature of 2075 ± 10 ° C (melting point of alumina a = 2050 ° C) using a high frequency generator working at 20 KHz and constantly developing a power of 20 Kw . Once the drop has formed at the bottom of the capillary duct, we put in contact with it a thin monocrystalline plate previously oriented with dimensions 1 × 15 mm, which serves as a germ and, once the drop stuck to this germ, we begin to pull the germinates downwards at the speed of 30 mm / hour. The alumina crucible is fed at the same time at a speed of 18 g / h. After 10 minutes of drawing, a thin sapphire plate is obtained, approximately 1 × 15 mm in a rectangular section and 50 mm in length.

At this point, the supply of pure alumina is stopped and, simultaneously, the crucible is supplied with a second distributor tank which contains doped alumina powder with 500 parts per million of chromium relative to the weight of alumina . The plate is continued to be drawn at the same speed and after 10 minutes, the plate has a total length of 100 mm.

This plate is transparent, monocrystalline, with the first colorless part and the second pink, with a zone of separation of the 2 parts of a few millimeters which gradually changes from colorless to pink.

Example 2

Manufacture of a single crystal in Si of type N and P

The crucible is made of sintered silicon carbide, with a total volume of 20 cm3 with a capillary conduit of rectangular section 1 × 15 mm. The crucible, with the supply system, is contained in a quartz enclosure swept by a stream of argon without oxygen. The crucible is supplied with high purity silicon powder doped with boron, with a particle size of 0.1 to 1 mm and the mixture is brought to

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a temperature of 1500 ° C ± 10 ° C (Si melting point: 470 ° C) thanks to a high frequency generator working at 300 KHz and constantly developing a power of 10 Kw. One puts in contact with the drop that has formed at the lower end of the capillary duct an oriented silicon plate which serves as a germ of dimensions 1 × 15 mm, and the drop is glued to this germ. We start to pull the germ down at the speed of 50 cm / hour and, at the same time, we feed the crucible at the average speed of 19 g / h in silicon powder. After 10 minutes of drawing, a silicon wafer with a cross section of approximately 1 × 15 mm and a length of approximately 75 mm is obtained.

At this time, the supply of boron-doped silicon powder is stopped and, simultaneously, the crucible is supplied with a second distributor reservoir which contains phosphor-doped silicon powder. The plate is continued to be drawn at the same speed and after 10 minutes, the plate reaches a total length of 150 mm. This plate is monocrystalline with a first part doped with boron (type P) and a second part doped with phosphorus (type N). The separation zone of the two parts is a few mm during which one goes from m boron doping to phosphorus doping.

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Claims (2)

619 007 2 CLAIMS 1. Process for the continuous production of a pre-formed single crystal with multiple doping, characterized in that it consists in: (a) placing material used to manufacture the single crystal, the composition of which varies in a predetermined manner and is adjustable during the process, in a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said capillary of said molten material, at the temperature and at the pressure considered, (b) bringing said material to a temperature above its m melting point, (c) bringing a suitably oriented preformed crystalline seed into contact with the hanging drop formed at the bottom of said capillary orifice. (d) pulling the germ down while feeding said material into the crucible, so that the quantity of material supplied per unit of time is at all times substantially equal to the quantity of material drawn in the form of a single crystal, (e) removing the single crystal formed at selected time intervals. 2. Device for implementing the method according to claim 1, characterized in that it comprises: (a) a crucible comprising at its lower part a capillary orifice having a height greater than or equal to the height of retention in said capillary of the molten material used to manufacture the single crystal at the temperature and pressure considered, (b) a heating device surrounding said crucible, (c) a multiple material feed system serving to manufacture the single crystal, placed above said crucible and 3 "comprising at least two independent reservoirs, (d) an enclosure provided with a device allowing its cooling surrounding said crucible and said supply system and comprising a lower orifice allowing the passage of the single crystal produced, orifices allowing the circulation of a gas constituting the working atmosphere , and orifices allowing passage to the heating system, (e) a seed carrier system supporting the preformed single crystal seed, (f) a system allowing said seed carrier 40 to move up and down and to rotate on itself, (g) a regulation system linking the traction speed of the single crystal formed to the speed of supply of the material used to manufacture the single crystal.