EP3043929A1

EP3043929A1 - Classifying of polysilicon

Info

Publication number: EP3043929A1
Application number: EP14752593.5A
Authority: EP
Inventors: Andreas Schneider; Peter Gruebl; Rainer Hauswirth; Reiner Pech
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2013-09-09
Filing date: 2014-08-07
Publication date: 2016-07-20
Anticipated expiration: 2034-08-07
Also published as: CN105612011A; WO2015032584A1; US20180169704A1; KR20160047580A; US10589318B2; KR101789607B1; CA2923110A1; US20160214141A1; EP3043929B1; JP2016534873A; NO2960429T3; TW201509548A; MY188174A; CN105612011B; CA2923110C; DE102013218003A1; JP6290423B2; TWI577459B

Abstract

A method for mechanically classifying crushed or granulated polycrystalline silicon with an oscillating screening machine, wherein crushed or granulated silicon is located on one or more screens each comprising a screen lining and made to oscillate in such a way that the crushed silicon or granulated silicon is set in motion, whereby the crushed silicon or granulated silicon is separated into different size classes, wherein a screen index, which is defined as the ratio of the acceleration produced by the oscillating motion to the gravitational acceleration vertically in relation to the plane of the screen and is characterized by the formula K_v = r * ω² * sin(α + β)/(g*cos(ß)), where r: is the oscillation amplitude; ω: is the angular velocity; α is the throwing angle; β: is the angle of inclination of the screen; and g: is the gravitational constant, is greater than or equal to 0.6 and less than or equal to 9.0.

Description

Classifying polysilicon

The invention relates to a method for classifying polysilicon. Polycrystalline silicon (polysilicon in short) serves as a starting material for the production of monocrystalline silicon for semiconductors according to the Czochralski (CZ) or zone melt (FZ) process, and for the production of monocrystalline or multicrystalline silicon after various drawing and casting processes. Process for the production of solar cells for photovoltaics.

Polycrystalline silicon is usually produced by means of the Siemens process. In this process, carrier bodies, usually thin filament rods made of silicon, are heated by direct passage of current in a bell-shaped reactor ("Siemens reactor") and a reaction gas comprising hydrogen and one or more silicon-containing components is introduced ₃ , TCS) or a mixture of trichlorosilane with dichlorosilane (SiH ₂ Cl ₂ , DCS) and / or with tetrachlorosilane (SiCl ₄ , STC), but silane (SiH ₄ ) is used more rarely but also on an industrial scale Filament rods are placed vertically in electrodes located at the bottom of the reactor, where they are connected to the power supply.The heated filament rods and the horizontal bridge deposit high-purity polysilicon, which increases in diameter over time.After cooling the rods, the reactor bell is opened the bars are made by hand or with the help of special Vo taken from so-called development aids for further processing or for temporary storage. For most applications, polycrystalline silicon rods are broken down into small fragments, which are usually subsequently sized.

Polycrystalline silicon granules or polysilicon granules for short is an alternative to the polysilicon produced in the Siemens process. While the polysilicon produced in the Siemens process as a cylindrical silicon rod, the time-consuming and costly crushed into fragments prior to further processing and may need to be cleaned again, polysilicon granules has bulk material properties and can directly as raw material for example for single crystal production for the photovoltaic and electronics industry be used. Polysilicon granules are produced in a fluidized bed reactor. This is done by fluidization of silicon particles by means of a gas flow in a fluidized bed, which is heated by a heater to high temperatures. By addition of a silicon-containing reaction gas a pyrolysis reaction takes place on the hot particle surface. Here, elemental silicon is deposited on the silicon particles and the individual particles grow in diameter. Due to the regular withdrawal of grown particles and the addition of smaller silicon particles as seed particles, the process can be operated continuously with all the associated advantages. The silicon-containing starting gas used may be silicon-halogen compounds (eg chlorosilanes or bromosilanes), monosilane (SiH ₄ ), as well as mixtures of these gases with hydrogen.

The polycrystalline silicon granules are divided after its preparation by means of a sieve plant into two or more fractions.

The smallest sieve fraction (Siebunterkorn) can then be processed in a grinding plant to seed particles and added to the reactor.

The screening target fraction is usually packed. US 2009081108 A1 discloses a workbench for manual sorting of polycrystalline silicon according to size and quality. An ionization system is implemented to neutralize electrostatic charges by active air ionization. Ionizers penetrate the clean room air with ions in such a way that static charges on insulators and ungrounded conductors are dissipated.

Usually screening machines are used to sort or classify polycrystalline silicon after comminution into different size classes.

A screening machine is generally a machine for sifting, ie the separation (separation) of solid mixtures according to grain sizes.

According to the movement characteristics, a distinction is made between planing vibrating screens and throwing machines. The drive of the screening machines is usually electromagnetic or by unbalance motors or gearbox.

The movement of the Siebbelags serves the further transport of the feedstock in Sieblängsrichtung and the passage of the fine fraction through the mesh openings.

In contrast to Planschwangsiebmaschinen occurs in throwing machines in addition to the horizontal and a vertical Siebbeschleunigung. In the litter screening machines, vertical throwing motions overlap with slight turning movements. As a result, the sample material spreads over the entire surface of the sieve bottom and at the same time the particles experience an acceleration in a vertical direction (thrown up). In the air they can make free turns and are compared with the mesh of the screen fabric when falling back on the screen. If the particles are smaller than these, they pass through the sieve, they are larger, they are thrown up again. The rotational movement ensures that they have a different orientation on the next sieve on the mesh and so maybe pass through a mesh opening.

In planing sifters, the sieve tower completes a horizontal circular movement in one plane. As a result, the particles on the screen fabric largely retain their orientation. Planeting machines are preferably used for needle-shaped, platelet-shaped, elongated or fibrous screening goods in which throwing up the sample good is not necessarily advantageous.

A special type is the Mehrdecksiebmaschine, which can fractionate several grain sizes simultaneously. They are designed for a multitude of sharp separations in the middle of the finest grain range.

The drive principle is based on two-deck planer on two counter-rotating unbalance motors that produce a linear vibration. The screen material moves in a straight line over the horizontal separating surface. The machine works with low vibration acceleration.

Through a modular system, a variety of screening decks can be assembled into a stack of sieves. Thus, if necessary, different grain sizes can be produced in a single machine, without having to change screen coverings. By repeated repetition of the same Siebdeckfolgen the screening material can be offered much screen area.

US 8021483 B2 discloses an apparatus for sorting polycrystalline silicon pieces comprising a vibratory motor assembly and a step bottom classifier attached to the vibratory motor assembly. The vibratory motor assembly causes the pieces of silicon to move over a first bottom containing grooves. In a fluidized bed area, dust is removed by a stream of air through a perforated plate. In a profiled area of the first floor, the pieces of silicon settle in holes of grooves or remain on ridges of the grooves. At the end of the first bottom, pieces of silicon smaller than a gap fall through it onto a conveyor belt. Larger pieces of silicon move across the gap and fall to the second floor. The parts of the device that come in contact with the polycrystalline silicon pieces are made of materials that minimize contamination of silicon. Examples are tungsten carbide, PE, PP, PFA, PU, PVDF, PTFE, silicon and ceramics.

US 2007235574 A1 discloses a device for crushing and sorting polycrystalline silicon, comprising a polysilicon rough-cut feeder in a crusher, the crusher, and a polysilicon-collapse classifier, the device being provided with a controller comprising a allows variable adjustment of at least one crushing parameter in the crusher and / or at least one sorting parameter in the sorting system. Particularly preferably, the sorting plant consists of a multi-stage mechanical screening plant and a multi-stage optoelectronic separation plant. Preference Schwingsiebmaschinen that are driven by an unbalance motor used. As Siebbelag mesh and perforated sieves are preferred.

The screening levels can be successively or in another structure, such. B. a tree structure, be arranged. Preferably, the sieves are arranged in three stages in a tree structure.

The freed from fines polysilicon fraction is preferably sorted by means of optoelectronic separation plant. Sorting of polysilicon fracture can be done according to all criteria that are state of the art in image processing. It is preferably carried out according to one to three of the criteria selected from the group length, area, shape, morphology, color and weight of polysilicon fragments, particularly preferably length and area.

This allows the preparation of the following fractions:

Fraction 0: fraction sizes with a distribution of about 0 to 3 mm

Fraction 1: fraction sizes with a distribution of about 1 mm to 10 mm

Fraction 2: fraction sizes with a distribution of about 10 mm to 40 mm

Fraction 3: fraction sizes with a distribution of about 25 mm to 65 mm

Fraction 4: fraction sizes with a distribution of about 50 mm to 1 10 mm

Fraction 5: fraction sizes with a distribution of approx.> 90 mm to 250 mm

About the exact distribution of fraction sizes within the fractions US 2007235574 A1 gives no information. US 5165548 A discloses an apparatus for size separation of silicon pieces suitable for semiconductor applications, comprising a cylindrical screen connected to a device for rotating the cylindrical screen, the surfaces of the screen contacting the silicon pieces in the screen

Substantially consist of silicon suitable for semiconductor applications.

No. 7959008 B2 claims a method for screening out first particles from granules comprising first and second particles by conveying the granulate lo along a first screen surface, preferably starting from a vibrating device, the first particles having an aspect ratio a1 with a1> n: 1 and n = 2, 3,> 3, in particular with a1> 3: 1, and the second particles have a dimensioning which allows a passage through the meshes of the first screen surface, characterized in that the granules along the screen surface between this and a

15 extends along the screen surface extending cover and that due to the cover, the first particles are aligned with their longitudinal axes along the screen surface, wherein length of each first elongate member is greater than the mesh size of the first screen forming screen and the same length of the second particle or smaller than the mesh size. 0

EP 1454679 B1 describes a screening device with a first oscillating body, which is provided with first cross members, and a second oscillating body, which is provided with second cross members, which first and second cross members are arranged alternately and have clamping devices, so that elastic 5 Siebbeläge between each one the first and ever a second cross member are clamped, and a drive unit which is coupled directly to the first oscillating body and over which the first oscillating body is constrained, so that the clamped elastic Siebbeläge between a stretched and a compressed layer are moved back and forth, wherein the second oscillating body is forcibly guided relative to the first oscillating body.

In US 6375011 B1, a method for promoting silicon breakage is proposed, in which the silicon fragments are guided over a conveying surface made of hyperpure silicon of a vibrating conveyor. Here, sharp-edged silicon pieces are rounded when they are conveyed on the vibrating conveyor surface of a vibrating conveyor. The specific surfaces of the silicon fragments are reduced, superficial adhering contaminations are abraded. The rounded by a first vibratory conveyor unit silicon break can via a second vibratory conveyor unit are performed. Their conveying surface consists of parallel arranged hyperpure silicon plates, which are fixed by lateral fastening devices. The hyperpure silicon plates have through openings, for example in the form of openings. The conveyor edges, which serve as a lateral boundary of the conveyor surfaces, are likewise made of hyperpure silicon plates and are fixed, for example, by hold-downs. The conveyor surfaces made of hyperpure silicon slabs are supported by steel plates and optionally damping mats.

US 2012052297 A1 discloses a process for the production of polycrystalline silicon, comprising breaking into thin pieces of polycrystalline silicon deposited on thin rods in a Siemens reactor, classifying the fragments in size classes from about 0.5 mm to greater than 45 mm, treating the silicon fragments using compressed air or dry ice to remove silicon dust from the debris without chemical wet cleaning. The polycrystalline silicon is classified as follows: Breakage size 0 (BG0) in mm: approx. 0.5 to 5; Break size 1 (BG1) in mm: approx. 3 to 15; Fracture size 2 (BG2) in mm: approx. 10 to 40; Crack size 3 (BG3) in mm: approx. 20 to 60; Fracture size 4 (BG4) in mm: approx.> 45; in each case at least 90% by weight of the fracture fraction being within the stated size range. This corresponds to the specification of the various fraction sizes into which the silicon is to be classified. The application gives no information on the actual result of the classification or sorting of the silicon and the size distributions within the individual size classes.

US 2009120848 A1 describes a device which enables a flexible classification of broken polycrystalline silicon, characterized in that it comprises a mechanical screening plant and an optoelectronic sorting plant, wherein the poly-fraction through the mechanical screening plant into a silicon fines and a silicon remainder is separated and the silicon residue is separated via an optoelectronic sorting in further fractions.

The mechanical screen is preferably a vibrating screen, which is driven by an unbalance motor.

In the case of mechanical classification by sieving using vibrating screening machines according to the prior art, material wear occurs on the screen lining and is introduced into the product. This leads to contamination of the polysilicon with components contained in the screen coating. In addition, it is disadvantageous in the prior art that the fractions into which the polysilicon is classified clearly overlap.

In the prior art, some overlap was already accepted in the specifications.

In US 2012052297 A1 the overlap between fraction size 2 and fraction size 1 is max. 5 mm, between fraction size 1 and fraction size 0 max. 2 mm. This concerns the specification to classify. The actual distribution of the fractionally large deviates usually from it.

According to US 2007235574 A1, the overlap between a fraction 1 and a fraction 0 is also max. 2mm. Especially in the fraction with smaller fragment sizes of 30 mm or less, such an overlap is undesirable.

From this problem, the task of the invention resulted. The object of the invention is achieved by a method for mechanically classifying polycrystalline silicon fracture or granules with a vibrating screen, wherein silicon fracture or granules are on one or more screens each comprising a screen lining, which are vibrated such that the silicon break or the silicon granules make a movement, whereby the silicon fraction or the silicon granules are separated into different size classes, characterized in that a Siebkennziffer greater than or equal to 0.6 and less than or equal to 9.0.

The sieve index is defined as the ratio of the acceleration generated by the sieve movement to the gravitational acceleration vertical to the sieve plane:

K _v = r * ω ² * sin (a + β) / (g * cos (β)), where

r: oscillation amplitude;

ω: angular velocity;

a: throw angle;

ß screen angle; g: gravitational constant.

It indicates how strongly an object accelerates vertically at maximum relative to the gravitational acceleration g of the earth.

If the sieving index is <1, then there is pure sliding movement (without throwing motion), since the resulting vertical acceleration is smaller than the falling acceleration.

For a throwing motion, the sieving index must be> 1.

It has surprisingly been found that significantly worse sieving results both in processes with a sieving index of less than 0.6 and in processes with a sieve index of greater than 9.0 than in the inventive range of 0.6-9.0.

Preferably, the screen index is greater than or equal to 0.6 and less than or equal to 5.0. By classifying with a sieve index of 0.6 to 5.0, a further improvement of the sieve results could be achieved. In particular, the selectivity is better than with a Siebkennziffer of greater than 5.0.

The movement of silicon fracture or granulate is particularly preferably a throwing movement, the sieving index being 1, 6 to 3.0. It has been shown that this results in even improved sieving results, in particular an even higher selectivity between the different size classes.

The oscillation amplitude is preferably 0.5 to 8 mm, particularly preferably 1 to 4 mm. The rotational speed ω / 2π is preferably 400 to 2000 rpm, more preferably 600 to 1500 rpm.

The throwing angle is preferably 30 to 60 °, particularly preferably 40 to 50 °. The screen tilt angle with respect to the horizontal is preferably 0 to 15 °, particularly preferably 0 to 10 °. The screening machine preferably comprises a feed area in which the screenings are fed and a discharge area in which classified screenings are removed.

Preferably, the size of the sieve openings increases in the direction of discharge. Fractions / break sizes are preferably separated by successively arranged discharges.

Preferably, the screening machine comprises mutually arranged screen decks. This oil has the advantage that large fragments can not damage fine-meshed screen coverings. Preferably, fractions / break sizes are separated by discharges arranged one below the other.

Preferably, the screening machine comprises a frame-sieve system. This allows a quick screen change. Also, the monitoring of any contamination is facilitated.

Such a frame-sieve system provides that screen coverings are screwed to the frame, glued, plugged or potted, that the frames made of wear-resistant 0 plastic (preferably PP, PE, PU), possibly with steel reinforcement, or at least with wear-resistant plastic are lined. Preferably, the frames are sealed by vertical clamping. This can avoid contamination and material loss. It is preferred to use screen linings made of particularly wear-resistant plastics, namely elastomers having a hardness greater than 65 Shore A, more preferably having a hardness greater than 80 Shore A. The Shore hardness is specified in the DIN 53505 and DIN 7868 standards , In this case, one or more screen coverings or their surfaces may consist of such an elastomer.

0

Both one or more screen coverings or their surfaces as well as all product-contacting components and linings are preferably made of plastics with a total contamination (metals, dopants) of less than 2000 ppmw, preferably less than 500 ppmw and particularly preferably less than 100 ppmw.5

The maximum contamination of the plastics with the elements Al, Ca, P, Ti, Sn and Zn should be less than 100 ppmw, more preferably less than 20 ppmw. The maximum contamination of the plastics with the elements Cr, Fe, Mg, As, Co, Cu, Mo, Sb and W should be less than 10 ppmw, more preferably less than 0.2 ppmw.

The determination of the impurities by means of ICP-MS (mass spectrometry with inductively coupled plasma).

The screen coverings of plastics preferably comprise a reinforcement or filling of metals, glass fiber, carbon fiber, ceramic or composite materials for stiffening.

Preferably, the screenings are dedusted. The mechanical sieving mobilizes most of the fine dust adhering to the bulk material on the individual screen decks. This effect is used in the invention to dedust the bulk material during the screening process.

It is important in this case that the freed fine dust is transported away in an exhaust passage by a corresponding gas guide, so he can not get back into the product. The gas flow can be generated either by a suction or by a gas purging.

Suitable visual gases are purified air, nitrogen or other inert gases.

In the screening machine, a gas velocity of 0.05 to 0.5 m / s, more preferably 0.2 to 0.3 m / s should be present.

A gas velocity of 0.2 m / s can be set, for example, with a gas throughput or a suction capacity of about 720 NrrrVh per m ² screen area. As fine dust particles are understood that are smaller than 10 pm.

In addition to dedusting in the screening machine, dedusting by means of countercurrent air classification in the discharge lines of the individual sieve fractions is optionally carried out.

In this case, the classifying gas is fed into the lower area of the flue ducts and the dust-laden exhaust gas is discharged in the upper area immediately in front of the screening machine. As a sight gas again the above media come into question. The advantage of this dedusting method is that the visual flow can be adapted to the particle size of the sieve fraction. With a coarse sieve fraction, for example, a high visual flow can be set without fine product being carried along. This gives a very good dedusting and the desired low particulate matter in the product.

Preferably, the speed is temporarily increased up to 4000 rev / min, to free the screen coverings of Steckkorn. For this purpose, alternatively, the

Oscillation amplitude temporarily increased up to 15 mm.

Likewise, it is preferred to use free-blow balls made of plastic or hyperpure silicon in order to free the screen coverings from sticking grain. Preferably, the oscillation amplitude decreases towards the discharge. Particularly preferably, the ratio of the vibration amplitude at the discharge is up to 50% less than at the inlet. It has been shown that both wear and product contamination can be further reduced. As a drive for the screening machine come linear, circular or elliptical oscillator in question. The drive preferably provides a vertical acceleration component to reduce screen wear and to avoid pinch.

It is preferable to use certain shapes of the sieve openings.

As advantageous rectangular openings have been found. It shows less wear due to smaller contact surfaces. Plug / clamp grain can be avoided more easily.

By contrast, round openings lead to a higher selectivity with regard to the particle size.

Square openings are also preferred. With them advantages of rectangular and round openings can be combined. Preferably, the screening tray and the Siebauslässe inside are completely lined with silicon or with a thermoplastic or elastomeric plastic. Steel body of the screening machine are preferably provided with welded PP lining segments. Preference is also the use of interior linings made of PU. As side linings, steel-reinforced PU castings have proven to be particularly suitable.

For fixing the screen frame preferably quick release devices are used.

It is also preferable to use silicon hole strips as the screen covering. One or more screen coverings can be designed in this way. These are preferably perforated square rods made of hyperpure silicon. These preferably have at least in part a conical hole shape, i. the cross-sectional area is smaller at the top than at the bottom. This contributes to avoiding pinch.

The cone preferably has an angle of 1 to 20 °, particularly preferably 1 to 5 °.

Preferably, an edge rounding of the holes with a radius of 0.1 to 2 mm is provided on the upper Sieboberseite to avoid breakouts and wear, which would lead to a deterioration of the selectivity.

Preferably, only the lower part of the hole is conical and the upper part is cylindrical, so that the hole is not expanded too quickly due to wear.

Preferably plastic-coated metal support strips are provided for stabilizing the breakage of the Si strips, to avoid contamination and to secure against loosening of fragments in inguinal hernia.

Preferably, individual Si strips are provided with hard metal end strips, which are braced horizontally or vertically. Thus, a cost-effective replacement of individual strips is possible depending on the wear. The hard metal used is preferably WC, SiC, SiN or TiN. Preferably, the Si perforated screen is placed on a base, glued or screwed. This allows higher strength, larger areas and the use of thinner or thicker screens possible. Breakage is easier to avoid.

It is particularly preferred to use both Si perforated sieves and sieves made of plastic or sieves with a plastic covering.

An Si-hole sieve with a hole diameter of 5 mm to 50 mm is preferably used as the first sieve cut. The large fragments can clean the sprue grains and thus prevent clogging.

For further separation of the fine fractions one or more screens made of plastic or plastic coverings are used.

Preferably, for silicon fracture with particle sizes greater than 15 mm (max particle length), an additional pre-screen with a plastic coating and with a mesh ratio to the underlying screen deck of 1.5: 1 to 10: 1 is used.

As a result, the plastic wear on the lower screen deck can be reduced. The outlets of both screen decks are merged. The Vorsiebdeck preferably has a lower wire tension. This serves to minimize wear.

The process according to the invention (litter motion, sieve index 1, 6-3.0) leads to polycrystalline silicon fragments with a sharp particle size distribution without large overlap or with a high selectivity classified polycrystalline silicon granules, which was previously not feasible in the prior art.

The invention therefore also relates to Classified polycrystalline silicon fragments, characterized by a particle size classification in fractional size classes 2, 1, 0 and F, wherein it applies to the fragments that at fraction size 2 max. 5 wt .-% less than 1 1 mm and max. 5% by weight greater than 27 mm; at fraction size 1 max. 5% by weight smaller than 3.7 mm and max. 5% by weight greater than 14 mm; at fraction size 0 max. 5% by weight less than 0.6 mm and max. 5 wt% greater than 4.6 mm; at fraction size F max. 5 wt .-% less than 0.1 mm and max. 5 wt .-% are greater than 0.8 mm.

The fracture size is defined in each case as the longest distance of two points on the surface of a silicon fragment (= maximum length). It follows:

• Fraction size F (BG F) in mm: 0.1 to 0.8;

• Fraction size 0 (BG 0) in mm: 0.6 to 4.6;

• Breakage size 1 (BG 1) in mm: 3.7 to 14;

· Breakage size 2 (BG 2) in mm: 1 1 to 27.

In each case at least 90% by weight of the fracture fraction are within the stated size range. This results in an overlap range of the 5% by weight quantile of the coarse fraction size to the 95% by weight quantile of the fine fraction size of:

Breakage size 2 to breakage size 1: max. 3 mm;

Break size 1 to breakage size 0: max. 0.9 mm;

Fraction size 0 to fraction size F: max. 0.2 mm.

The polycrystalline silicon fragments having the improved grain size classification preferably have a very low surface contamination: Tungsten (W):

Fraction size 1 <100,000 pptw, more preferably <20000 pptw;

Fraction size 0 <1000000 pptw, more preferably <200000 pptw;

Fraction size F <10,000,000 pptw, more preferably <2,000,000 pptw; Cobalt (Co):

Fraction size 2 <5000 pptw, more preferably <500 pptw;

Fracture size 1 <50,000 pptw, more preferably <5,000 pptw;

Fraction size 0 <500,000 pptw, more preferably <50,000 pptw;

Fraction size F <5000000 pptw, more preferably <500000 pptw;

Iron (Fe):

Crack size 2 <50,000 pptw, more preferably <1000 pptw;

Fraction size 1 <500,000 pptw, more preferably e 10000 pptw;

Fraction size 0 <5000000 pptw, more preferably <100000 pptw;

Fraction size F <50,000,000 pptw, more preferably <1,000,000 pptw;

Carbon (C):

Fraction size 2 <1 ppmw, more preferably <0.2 ppmw; Fraction size 1 <10 ppmw, more preferably <2 ppmw;

Fraction size 0 <100 ppmw, more preferably <20 ppmw;

Fraction size F <1000 ppmw, more preferably <200 ppmw; Cr, Ni, Na, Zn, Al, Cu, Mg, Ti, K, Ag, Ca, Mo per single element:

Fraction size 2 <000 pptw, more preferably <100 pptw;

Crack size 1 <2000 pptw, more preferably <200 pptw;

Fraction size 0 <10000 pptw, more preferably e 1000 pptw;

Fraction size F <100000 pptw, more preferably e 10000 pptw;

Particulate matter (silicon particles less than 10 pm in size):

Fraction size 2 <5 ppmw, more preferably <2 ppmw;

Fraction size 1 <15 ppmw, more preferably <5 ppmw;

Fraction size 0 <25 ppmw, more preferably <10 ppmw;

Fraction size F <50 ppmw, more preferably <20 ppmw.

The invention also relates to classified polycrystalline silicon granules, classified at least in the two size classes Siebzielkorn and Siebunterkorn, wherein a selectivity between Siebzielkorn and Siebunterkorn is more than 0.86.

It is preferably classified polycrystalline silicon granules, classified in Siebzielkorn, Siebunterkorn and Sieboberkorn, wherein a selectivity between Siebzielkorn and Siebunterkorn and between Siebzielkorn and Sieboberkorn is more than 0.86.

Classified polycrystalline silicon granules preferably have the following impurities with metals on the surface: Fe: <800 pptw, more preferably <400 pptw; Cr: <100 pptw, more preferably <60 pptw; Ni: <100 pptw, more preferably <50 pptw; Na: <100 pptw, more preferably <50 pptw; Cu: <20 pptw, more preferably <10 pptw; Zn: <2000 pptw, more preferably <1000 pptw.

Classified polycrystalline silicon granules preferably have a surface carbon contamination of less than 10 ppmw, more preferably less than 5 ppmw.

Classified polycrystalline silicon granules preferably have a surface particulate contamination of less than 10 ppmw, most preferably niger than 5 ppmw, on. Fine dust is defined as silicon particles with a size of less than 10 [im.

Examples and Comparative Examples

The advantages of the invention are shown below with reference to examples and comparative examples.

Example 1 and Comparative Example 2 relate to the classification of polycrystalline silicon fragments in fractions of 2, 1, 0 and F.

Example 3 and Comparative Example 4 relate to classifying polycrystalline silicon granules (sieve grain size 0.75 - 4 mm). example 1

Table 1 a shows the essential parameters of the screening machine.

Table 1 a

Table 1 b shows which sieve set was used in the example. Three sieve decks with different sieve mesh sizes were used. Table 1 b

Table 1 c shows the composition of the screen coverings.

Table 1 c

The sieving results obtained with regard to the particle size distribution are shown in Tables 1 d and 1 e. Table 1d

Table 1e

Table 1f shows the contaminants of the classified fragments with surface metals, carbon, dopants and particulate matter.

Table 1f

Comparative Example 2

Table 2a shows the essential parameters of the screening machine used for this purpose. Table 2a

Wire width b [mm] 600

Sieve length 1 [mm] 1600

Frequency n [Hz] 20

Speed [rpm] 1200

Angular velocity ω [1 / s] 125.7

Amplitude [mm] 2,4

Amplitude r [mm] 1, 2

Screen inclination ß [°] 0

Throw angle α [°] 45

Sieving code Kv [-] 1, 4

Throughput [kg / h] 700

N ₂ sealing gas [Nm ³ / h] NN

Table 2b shows which sieve set was used in Comparative Example 2. Three sieve decks with different sieve mesh sizes were used.

Table 2b

Table 2c shows the composition of the screen coverings used.

Table 2c

The sieving results obtained with regard to the particle size distribution are shown in Tables 2d and 2e.

Table 2d

Table 2e

BG 2/1 BG1 / 0 BG0 / F

Overlap 5% by weight /

95% by weight [mm] 5 2 0.31 The overlap is significantly higher than in example 1. This is due to the changed parameters of the screening machine, in particular to the lower sieve index. Table 2f shows the contaminants of the classified fragments with surface metals, carbon, dopants and particulate matter.

Table 2f

The impurities are consistently higher than in Example 1. This shows the influence of the composition of the screen coverings on the surface contamination of the fragments after classification.

Example 3

Table 3a shows the essential parameters of the screening machine.

Table 3a

Table 3b shows which sieve set was used in Example 3. Three sieve decks with different sieve mesh sizes were used. Table 3b

Table 3c shows the composition of the screen coverings. Table 3c

The sieving results achieved with regard to the particle size distribution are shown in Tables 3cf and 3e.

3d table

Table 3e

Table 3f shows the contaminants of the sized granules with surface metals, carbon, dopants and particulate matter. Table 3f

Comparative Example 4

Table 4a shows the essential parameters of the screening machine. Table 4a

Table 4b shows which sieve set was used in Comparative Example 4. Three sieve decks with different sieve mesh sizes were used.

Table 4b Table 4c shows the composition of the screen coverings used.

Table 4c

The sieving results achieved with regard to the particle size distribution are shown in Tables 4d and 4e.

Table 4d

Table 4e The selectivity of Siebzielkorn / Siebunterkorn is worse than in Example 3. This is due to the comparison with Example 3 lower Siebkennziffer. Table 4f shows the contaminants of the sized granules with surface metals, carbon, dopants and particulate matter.

Table 4f

The impurities are consistently higher than in example 3.

The following measuring methods were used to determine the specified parameters. The determination of carbon contamination is carried out by means of an automatic analyzer. This is described in detail in the not yet published US application with the application number 13 / 772,756 and in the German application with the file number 102012202640.1. The determination of the dopant concentrations (boron, phosphorus, As) is carried out according to ASTM F1389-00 on monocrystalline samples. The determination of the metal impurities is carried out according to ASTM 1724-01 with ICP-MS.

The fine dust measurement is carried out as described in DE 10 2010 039 754 AI.

The particle sizes (minimal chord) are determined by means of dynamic image analysis according to ISO 13322-2 (measuring range: 30 m - 30 mm, type of analysis: dry measurement of powders and granules).

Claims

claims

1 . A method of mechanically classifying polycrystalline silicon fracture or granules with a vibrating screening machine, wherein silicon fracture or granules are on one or more screens each comprising a screen lining vibrated such that the silicon fracture or the granular silicon undergoes agitation, whereby the silicon fraction or the silicon granules are separated into different size classes, characterized in that a sieve index is greater than or equal to 0.6 and less than or equal to 9.0.

2. The method of claim 1, wherein the screen index is greater than or equal to 0.6 and less than or equal to 5.0.

3. The method of claim 2, wherein a litter screening machine is used, and the screen index is greater than or equal to 1, 6 and less than or equal to 3.0.

4. The method according to any one of claims 1 to 3, wherein the movement of silicon or silicon granules is characterized by a vibration amplitude of 0.5 to 8 mm, a speed of 400 to 2000 U / min and a throw angle of 30 to 60 ° relative to a screen plane, wherein the screen plane is inclined at an angle of 0 to 15 ° relative to the horizontal.

5. The method according to any one of claims 1 to 4, wherein the screening machine comprises a plurality of mutually arranged screen decks.

6. The method according to any one of claims 1 to 5, wherein the screen coverings are each mounted on a frame made of plastic or a frame comprising a plastic lining.

7. The method according to any one of claims 1 to 6, wherein one or more of the screen coverings made of an elastomer having a hardness greater than 65 to Shore A or have a surface of an elastomer having a hardness of greater than 65 to Shore A.

8. The method according to any one of claims 1 to 7, wherein one or more of the Siebbeläge or the surfaces of one or more of Siebbeläge and all other silicon fracture or silicon granules contacting components and their linings are made of plastics with a total impurity of less than 2000 ppmw.

9. The method according to any one of claims 1 to 6, wherein in one or more of the screen coverings silicon perforated strips are used, wherein the holes at least partially have a conical shape.

10. The method according to any one of claims 1 to 9, wherein both Si perforated strips and plastic are used as Siebbeläge, wherein at least in a first screening step, a sieve with a Si-perforated strip is used.

1 1. Classified polycrystalline silicon fragments, characterized by a size classification in size classes 2, 1, 0 and F, whereby for the fragments:

at fraction size 2 max. 5 wt .-% less than 1 1 mm and max. 5% by weight greater than 27 mm;

at fraction size 1 max. 5% by weight smaller than 3.7 mm and max. 5% by weight greater than 14 mm;

at fraction size 0 max. 5% by weight less than 0.6 mm and max. 5 wt% greater than 4.6 mm;

at fraction size F max. 5 wt .-% less than 0.1 mm and max. 5 wt .-% are greater than 0.8 mm.

12. Classified polycrystalline silicon fragments according to claim 1 1, wherein overlap areas each of the 5 wt .-% quantile of the coarse fraction size to 95

% By weight quantile of the fine breaking size for fraction size 2 to fraction size 1 not more than 3 mm, for fraction size 1 to fraction size 0 not more than 0.9 mm and for fraction size 0 to fraction size F not exceeding 0.2 mm.

13. Classified polycrystalline silicon granules, classified at least into the two size classes Siebzielkorn and Siebunterkorn, wherein a selectivity between Siebzielkorn and Siebunterkorn is more than 0.86.

14. Classified polycrystalline silicon granules according to claim 13, further characterized by surface impurities of Fe less than 800 pptw, Cr less than 100 pptw, Ni less than 100 pptw, Na less than 100 pptw, Cu less than 20 pptw, Zn less than 2000 pptw, of carbon less than 10 ppmw, of particulate matter less than 10 ppmw.