EP3554723B1 - Separating device for polycrystalline silicon - Google Patents

Description

The subject matter of the invention is a deposition device for polysilicon.

Polycrystalline silicon (polysilicon for short) is used as a starting material for the production of monocrystalline silicon for semiconductors using the Czochralski (CZ) or zone melting (FZ) process, as well as for the production of monocrystalline or multicrystalline silicon using various drawing and casting processes Production of solar cells for photovoltaics.

Polycrystalline silicon is usually manufactured using the Siemens process. For most applications, the polycrystalline silicon rods produced in this way are broken up into small fragments, which are then usually classified according to size. Usually, screening machines are used to sort or classify polycrystalline silicon into different size classes after comminution.

Alternatively, polycrystalline silicon granules are produced in a fluidized bed reactor. After it has been produced, the polysilicon granules are usually divided into two or more fractions or classes (classification) by means of a screening plant.

A screening machine is generally a machine for screening, i.e. the separation (separation) of solid mixtures according to grain sizes. Depending on the movement characteristics, a distinction is made between plan vibratory screens and throw screens. The screening machines are usually driven electromagnetically or by unbalance motors or gears. The movement of the screen lining serves to transport the feed material further in the longitudinal direction of the screen and to allow the fine fraction to pass through the screen openings. In contrast to plane vibratory screens, throw screens experience not only horizontal but also vertical screen acceleration.

When polysilicon is crushed, packaged and transported, dust particles and fines are produced in such significant quantities that without further screening or separation, there is a loss of yield during crystal pulling.

Therefore, there is a need to separate small particles and dust from the polysilicon prior to crystal growth.

Separating devices according to the prior art, such as bar screens, however, tend to become clogged when separating fines. The consequence of this is that these separating devices have to be cleaned cyclically and thus do not achieve a continuous, consistent separation accuracy. In addition, this requires plant downtimes and additional effort for cleaning.

DE 43 07 138 A1 discloses a separating device with at least one screen plate, comprising a feed area for polysilicon, a profiled V-shaped area and a sink, an area adjoining the profiled area with screen openings, and a removal area, with the screen openings widening in the direction of the removal area, and a Separation plate arranged below the screen openings.

EP 0 982 081 A1 discloses a device for classifying which has at least one blowing device (5) and at least one deflection device (3).

WO 97/26495 A2 discloses a conveying device made of a profiled separating base, on which a bar rake is formed at the end facing away from the opening of the residue conveying chute. The bar screen covers a fine debris discharge port and terminates at a coarse debris outlet.

EP 0 139 783 A1 discloses a device for processing scrap, waste or the like, e.g. non-ferrous scrap, by dividing it into at least two components, consisting of at least one sorting plate arranged inclined to the horizontal and an input device arranged above the sorting plate, from which the material to be processed falls freely onto the Sorting plate can be brought, wherein the sorting plate can be moved both horizontally and vertically by means of at least one drive unit.

DE 826 211 C discloses a device for sorting fruit, characterized in that a carrier conveyor belt and a wall made of individual circulating conveying means conveying in the same direction are arranged in the form of a trough and a passage opening of a specific cross-section is provided between every two of these conveying means, with the conveying means forming the conveying wall having a higher speed as the conveyor belt circulate

Out of DE 198 22 996 C1 is a separating device for elongate solid parts, which has a vibrating base with a number of longitudinal grooves extending in the conveying direction, which are followed by screen openings for separating the elongate solid parts, the groove depth of the longitudinal grooves decreasing in the conveying direction. In order to avoid blockages and to ensure that the flow of solids is as liquid as possible, one embodiment provides for the screen openings to widen in the conveying direction. On jammed in the screen opening solid parts, a force is exerted in the conveying direction by the following solid. The jammed solid part can be moved in the conveying direction and then falls through the widening screen opening.

U.S. 2015/090178 A1 discloses a separating device for polysilicon with at least one screen plate, comprising a feed area for polysilicon, a profiled area with peaks and valleys, an area adjoining the profiled area with screen openings, and a removal area, with the screen openings widening in the direction of the removal area, and a Separating plate arranged below the screen openings, which is horizontally displaceable.

However, through the in DE 198 22 996 C1 proposed device a complete separation of small silicon particles and dust can not be achieved.

The task of the invention arose from the problems described.

The object of the invention is achieved according to claim 1 by a separating device for polysilicon with at least one screen plate comprising a feed area for polysilicon, a profiled area with peaks and valleys, an area adjoining the profiled area with screen openings, and a removal area, with the screen openings in the direction of the removal area, characterized in that below the screen openings there is a separating plate which can be displaced horizontally in order to vary the position of the separating plate in the direction of the removal area and which can be displaced vertically in order to vary the distance to the screen openings.

The screen plate according to the invention provides a separating plate which is arranged below the screen openings or the area with screen openings.

It has been shown that this is necessary to increase the selectivity and to ensure a separation rate that is as constant as possible. The effective size of the screen openings can be varied by shifting the separating plate in the conveying direction. For example, the separating plate can be arranged in such a way that polysilicon with a size of less than or equal to 4 mm falls through the screen opening and is separated from the remaining polysilicon via the separating plate.

In addition, the separating plate may be inclined from the vertical such that the separated polysilicon is received in a catch bin, while larger polysilicon, although also falling through the screen openings, is received in another catch bin located downstream of the separating plate.

Thus, two fractions can also be separated from the polysilicon fed in by the sieve plate in conjunction with the separating plate.

By varying the vertical distance between the separating plate and the screen openings, it can be ensured that oblong polysilicon fragments are not also separated off.

The partition plate can therefore fulfill very different functions.

The object is also achieved by a method in which polysilicon is placed on the screen plate of a separating device according to the invention, which is made to vibrate in such a way that the polysilicon moves in the direction of the removal area, with small-sized polysilicon collecting in the depressions of the screen plate and through the screen openings of the screen plate falls over the separating plate into a collection container and is thereby separated from the polysilicon that has been fed in, with the polysilicon that has been fed in being processed further without the separated, small-sized polysilicon.

In one embodiment, the position and height of the separator plate is chosen depending on how much the polysilicon has been vibrated. The separating plate is preferably at a distance from the screen section of 5 mm to 20 mm, a distance of 1 mm to 5 mm being particularly preferred.

Small-scale polysilicon is to be understood as meaning a subset of the quantity of polysilicon that is to be separated off by means of the screening plant. The small-scale polysilicon thus corresponds to the fraction to be separated.

In the following, small-scale polysilicon should be understood to mean polycrystalline fragments whose longest distance between two points on the surface of a silicon fragment (=max. length) is less than or equal to 4 mm. This should also include fines, small silicon particles and silicon dust (size less than or equal to 100 μm).

The screen plate includes a feed area where the polysilicon is fed.

In one embodiment, the polysilicon is conveyed to the screening plant by means of a conveyor trough and delivered to the feed area of the screen plate.

The screen plate also includes a profiled area with ridges or grooves or generally indentations and elevations, so that the profiled area has depressions and peaks.

During the movement of the polysilicon on the profiled area, small fragments or silicon particles (small in relation to the target fraction) or fines accumulate in the depressions of the profiled area.

The screen plate includes - adjoining the profiled area - an area with screen openings. The screen openings are arranged in the conveying direction directly behind the sinks of the profiled area. As a result, the fine fractions of the polysilicon located in the depressions of the profiled area are guided to the screen openings in a targeted manner.

In one embodiment, the peaks of the profiled area also continue into the area with screen openings, so that the entire screen plate is profiled, but the screen plate has screen openings instead of depressions at its rear end in the conveying direction.

The profile of the profiled area can deviate from the profile in the area of the screen openings in terms of cross section and angle. The latter can be advantageous in particular when the screen section or the parts of the screen section that come into contact with the polysilicon are made of plastic.

The fines or small fragments/particles are separated via the screen openings of the screen plate in connection with the separating plate.

In one embodiment, the separated fines or small fragments/particles are collected by a collection container arranged below the screen openings of the screen plate.

Larger fragments are guided in the profiled area over the tips to the removal area.

In one embodiment, the removal area is connected to a conveyor trough, via which the larger fragments are removed. Another sieve plate can also follow in order to separate another fraction from the polysilicon.

The invention therefore provides a screen plate that can be used in all types of screening plants, in which the fines or small-sized silicon collects in depressions in the first area of the screen plate and is selectively separated in the last area of the screen plate by widening screen openings.

The design of the profiled area of the screen plate depends on the fraction to be separated. The depth and angle of the depressions in the profiled area must be designed in such a way that the fraction to be separated, e.g. the fine fraction, collects there.

The invention thus relates to a screening section in which the fine fraction collects in sinks in the first area of the device and is selectively separated in the last area of the device by widening screen openings. Thus, not the entire fraction is fed to the screen slot.

The separating device essentially consists of a screening section which can be divided into two areas. The first area is the entry area. In this area, the fines collect in the sinks and are thus fed to the screen openings (which are located in the second area, at the end of the screening section). The separating cut for the separation takes place in the second area of the screening section via the screen openings introduced there, which widen in the conveying direction. The desired Si fraction is separated off through these screen openings or the fines. Due to the fact that the screen openings widen in the conveying direction, this system does not tend to clog.

In an advantageous embodiment, the screen openings extend as far as the end of the separating device located in the conveying direction. The screen openings are therefore designed to be open towards the end. This is an essential feature to ensure that no silicon fragments accumulate in the separator or the screen opening becomes blocked.

The screen openings preferably have an opening angle of 1 to 20° and particularly preferably 5-15°.

The screen openings preferably have a length of 5 mm to 50 mm, particularly preferably a length of 20 to 40 mm.

In order to avoid blockages, a further advantageous embodiment provides that the screen openings widen further at the end in the conveying direction.

The opening angle of this second widening is preferably 40-150°, particularly preferably 60 to 120°.

In one embodiment, the angle of the screen openings can be changed using suitable devices. For example, elements made of an elastic material can be used for this purpose. It has been shown that this is advantageous for avoiding clogging.

In a preferred embodiment of the separating device, a suction device is attached below the screen openings, which is positioned in such a way that the suction device is preferably located between the start of the screen openings and the separating plate.

The suction is preferably at a distance from the lower sieve plate of 1 mm to 50 mm, a distance of 5 mm to 20 mm is particularly preferred.

A further preferred embodiment of the separation according to the invention is the installation of a gas stream above the screen openings.

This includes one or more gas nozzles which are directed towards the screen openings.

Depending on the configuration of the gas nozzles, the gas jet can be soft or hard.

A soft jet is particularly suitable for supporting the separation of dust. A hard jet, on the other hand, is particularly suitable for depositing the smaller polysilicon fragments, 0.1mm to 4mm. The gas flow can also be designed as a laminar flow.

Clean room air according to DIN EN ISO 14644-1 (ISO1 to ISO6), clean dry air, nitrogen and argon can be considered as gases.

The gas flow should preferably be positioned between the start of the screen openings and the separating plate.

In one embodiment, the removal area is connected to a conveyor trough, via which the larger fragments are removed. Another sieve plate can also follow in order to separate another fraction from the polysilicon.

In one embodiment, the screen path consists of one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, silicon or metal, fused silica lined metal and silicon lined metal

In one embodiment, the screen section is lined or coated with one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, and silicon.

In one embodiment, the portions of the screen that come into contact with the polysilicon are lined or coated with one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon, and silicon.

In one embodiment, the screening section comprises a metallic base body and a coating or lining made from one or more materials selected from the group consisting of plastic, ceramic, glass, diamond, amorphous carbon and silicon.

In one embodiment, the screening section comprises a base body made of plastic and a coating or lining made of one or more materials selected from the group consisting of ceramic, glass, diamond, amorphous carbon and silicon.

In one embodiment of the invention, the plastic used in the aforementioned versions is selected from the group consisting of PVC (polyvinyl chloride), PP (polypropylene), PE (polyethylene), PU (polyurethane), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene).

In one embodiment, the screening section includes a coating of titanium nitride, titanium carbide, aluminum titanium nitride, DLC (Diamond Like Carbon), silicon carbide, nitride-bonded silicon carbide, or tungsten carbide.

The fraction sizes (BG) 1, 2, 3 can preferably be used via this screening device. Typically, these fractional sizes have the following dimensions. Fraction size 1 3 to 15mm Fraction size 2 10 to 40mm fraction size 3 20 to 60mm

Typically, the individual fragment size classes have small and larger fragments. The proportion of larger and smaller fragments can each be up to 5%.

In particular, the screening device is suitable for separating small pieces of polysilicon, which have a diameter of about 0.05 to 2 mm and typically a length of up to 4 mm.

In a further embodiment, the separating device comprises a hopper for feeding in the polysilicon material, two conveyor units and two screening sections, with a screening section following each conveyor unit. A conveyor unit and a screening section form one unit. The first unit is called unit 1 and the second unit is called unit 2. The polysilicon delivery rate in kg/min can be set separately for each unit. The flow rate of unit 1 is preferably the same as that of unit 2.

The delivery rate of unit 1 is particularly preferably smaller than the delivery rate of unit 2, because this can result in the polysilicon fragments being isolated on unit 2, with the result that the small polysilicon fragments and the dust can be separated off better.

Of course, several units can also be attached one after the other.

Such a measure improves the separation of small pieces of polysilicon and dust.

At the end of the last screening section there is a removal area.

The removal area is designed in such a way that the polysilicon material slides into the container provided.

This extraction area can also be vibrated to ensure that no polysilicon material is left behind.

The angle of this outlet is preferably 5 to 45° and more preferably 15 to 25°.

There is no clogging of the sieve, which means that a consistent sieving quality is achieved. This eliminates the cleaning steps (increasing system runtimes, falling personnel costs). The separation accuracy is also significantly higher than with bar screens, which means that significantly less defective grain is separated. The features specified with regard to the above-mentioned embodiments of the method according to the invention can be correspondingly transferred to the device according to the invention. Conversely, the features specified with regard to the above-described embodiments of the device according to the invention can be correspondingly transferred to the method according to the invention.

Brief description of the characters

• 1 shows the schematic structure of a screen plate of a separating device according to the invention.
• 2 shows schematically a separating device with suction and separating plate.
• 3 shows schematically a separating device with suction and gas flow.

List of reference symbols used

1

sieve plate

2

task area

3

Profiled area of the sieve plate

31

Lowering of the profiled area

32

Peaks of the profiled area

4

Area with sieve openings

41

Sieve opening with opening angle a1

5

picking area

6

Widening with opening angle a2

7

partition plate

8th

suction

9

supply of gas flow

The screen plate 1 comprises a feed area 2 in which the polysilicon is fed. The polysilicon can, for example, be conveyed to the screening plant by means of a conveyor trough and delivered to the feed area 2 of the screen plate 1 .

The screen plate 1 also includes a profiled area 3. This profiled area 3 provides grooves or other types of depressions, so that the profiled area 3 has depressions 31 and peaks 32 .

The fine fraction contained in the polysilicon collects during the movement of the polysilicon on the profiled area 3 in the depressions 31 of the profiled area 3.

The screen plate 1 comprises— adjoining the profiled area 3 —an area 4 with screen openings 41 . As a result, the fine fractions of the polysilicon located in the depressions 31 of the profiled area 3 are guided to the screen openings 41 of the area 4 in a targeted manner.

The peaks 32 of the profiled area 3 preferably also continue in area 4 , so that the entire screen plate 1 is profiled, but has screen openings 41 in area 4 instead of depressions 31 .

The fines are thus separated off via the sieve openings 41 of the sieve plate 1 . The separated fines can be received, for example, by a collecting container arranged below the sieve openings 41 of the sieve plate 1 .

Larger fragments are guided to the removal area 5 in the profiled area via the tips 32 .

The screen openings 41 widen in the conveying direction by an opening angle a1. The screen openings 41 have a further widening 6 at the end of the area 4 , characterized by an opening angle a2.

In a preferred embodiment of the separating device, a suction device 8 is fitted below the screen openings 41 , which is positioned in such a way that the suction device 8 is preferably located between the start of the screen openings 41 and the separating plate 7 .

Another preferred embodiment of the separation according to the invention is the installation of a gas flow 9 above the screen openings 41.

examples

The bagged polysilicon material supplied by the polysilicon manufacturer also contains smaller fragments and fines. The fine material, especially with grain sizes smaller than 4 mm, has a negative impact on the drawing process and must therefore be removed before use. Poly break size 2 was used for the test.

The polysilicon material used for the test with fractional poly fractions of 2 was sieved using an analysis sieve (DIN ISO 3310-2) with a nominal hole width W = 4 mm (square holes) and made available for the tests. The separated fine material was collected and weighed.

10 kg of test polysilicon material of fragment size 2 (without fines <4 mm) were placed on a conveyor unit. The loading of the test polysilicon material is preferably done via a hopper. The container to be filled is positioned at the end of the screening section above the first conveyor unit so that the test polysilicon material can be conveyed into the container without any problems.

The fines separated in advance for the test are used for this test. When filling the conveyor unit, 2 g of separated fine material are added after each 2 kg of test polymer material, so that at the end a total of 10 g of fine material was added for this test.

Then the conveyor unit and the screening section were started. The flow rate was set to 3kg +/- 0.5kg per minute before the test. The fines removed were collected and reweighed. The experiments were carried out five times per setting.

Table 1 shows the mean results:

test 1

A conveyor unit plus a screening section without suction and without gas flow from above was used for this.

test 2

A conveyor unit plus a screening section with suction but without gas flow from above was used for this.

test 3

A conveyor unit plus a screening section with suction and a gas stream from above was used for this.

test 4

Two conveyor units plus two screening sections without suction and without gas flow from above were used for this, with a screening section following each conveyor unit.

test 5

Two conveyor units plus two screening sections with suction and without gas flow from above were used for this, with a screening section following each conveyor unit. <b>Table 1</b> test Amount of poly BG2 in kg Addition of fine material in g Fines removed in g Removal Rate in % 1 10 10 8.3 83 2 10 10 9.0 90 3 10 10 9.1 91 4 10 10 9.1 91 5 10 10 9.6 96

The results show that the use of suction and top gas flow resulted in an 8% improvement in removal rate.

A further improvement in the removal rate is possible if two screen sections are used and suction is provided.

In one embodiment, the separating device therefore comprises two screen plates, each comprising a feed area for polysilicon, a profiled area with peaks and valleys, an area adjoining the profiled area with screen openings, and a removal area, with the screen openings in Widen in the direction of the removal area, and a separating plate arranged below the screen openings, which can be moved horizontally and vertically, and a suction device below the screen openings. The removal area of the first screen plate connects to the feed area of the second screen plate, ie polysilicon that was not separated in the first screen section is fed to the second screen section. In both screen sections, suction is provided below the screen openings.

The foregoing description of exemplary embodiments is to be understood as an example. The disclosure thus made will enable those skilled in the art to understand the present invention and the advantages attendant thereto, while also encompassing variations and modifications to the described structures and methods that would become apparent to those skilled in the art.

The scope of the invention is limited by the appended claims.

Claims (10)

1. Separating apparatus for polysilicon with at least one screen plate (1), comprising a feed area (2) for polysilicon, a profiled area (3) with peaks (32) and depressions (31), a region (4) adjoining the profiled region (3) and having sieve openings (41), and a removal region (5), the sieve openings (41) widening in the direction of the removal region (5), characterized in that a separating plate (7) is arranged below the sieve openings, which separating plate (7) can be displaced horizontally in order to adjust the position of the separating plate in the direction of the removal area, and which can be moved vertically to vary the distance to the screen openings.
2. The separating apparatus of claim 1, wherein an opening angle of the widening of the screen openings (41) is greater than or equal to 1° and less than or equal to 20°.
3. The separating apparatus of claim 2, wherein an opening angle of the widening of the screen openings (41) is greater than or equal to 5° and less than or equal to 15°.
4. The separating apparatus according to any one of claims 1 to 3, wherein said screen openings are (41) have a length of 5 mm to 50 mm.
5. The separating apparatus according to claim 4, wherein the screen openings (41) have a length of 20 mm to 40 mm.
6. The separating apparatus according to any one of claims 1 to 5, wherein the screen openings (41) widen a second time in the direction of the removal region after a first widening, wherein an opening angle of this second widening is 40- 150°.
7. The separating apparatus according to claim 6, wherein an opening angle of the second expansion is 60 to 120°.
8. The separating apparatus according to any one of claims 1 to 7, comprising a suction device (8) below the screen openings (41).
9. The separating apparatus according to any one of claims 1 to 8, comprising means for directing a gas stream (9) from above onto the screen openings (41).
10. A method wherein polysilicon is applied to the screen plate (1) of a separating apparatus according to any one of claims 1 to 9, which is vibrated such that the polysilicon is caused to move in the direction of the removal region (5), whereby small-particle polysilicon collects in the depressions (31) of the screen plate (1) and falls through the screen openings (41) of the screen plate (1) via the separating plate (7) into a collecting container and is thereby separated from the fed polysilicon, whereby the fed polysilicon is further processed without the separated small-particle polysilicon.

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