DE102010039754B4 - Method for determining the concentration of particulate matter in bulk silicon materials - Google Patents

Abstract

Method for determining the concentration of fine dust in silicon bulk materials, wherein a product sample of the silicon bulk material is placed in a sieve, the particulate matter are completely separated by a fluid from the bulk material and pass through the sieve, form a suspension with the fluid and the suspension continuously conveyed with the detached fine dust particles by means of a pump to a particle meter, measured there and then returned to the sample.

Description

The invention relates to a method for determining the concentration of fine dust in silicon bulk materials.

High-purity silicon bulk materials in the form of powders, granules and fragments of various sizes are used in industry as a raw material for further processing in the solar and semiconductor industries. Due to the manufacturing process and transport, these bulk materials are more or less contaminated with silicon dust. Since this particulate dust, which partly adheres strongly to the surface of the fragments, can have an undesired influence during further processing in the respective process, the concentration of the fine dust and the size of the particles must be clearly determinable.

The determination of the dust concentration of high-purity polycrystalline silicon bulk materials (fracture, granulate) is required for process and quality control. Fine silicon dust can degrade the subsequent product quality and disturbs, for example, the drawing process of the production of silicon crystals. Due to the large surface of dust particles, a high dust content has a negative impact on the purity of the silicon if the environment is not clean. Further negative influences of the dust are known in the melting of the silicon for the production of single crystals for the electronics or photovoltaic industry. Due to their high surface tension, particulate matter floats on the melt and creates a risk of dislocation during the formation of the crystal. Dust is also known as a nucleating agent for the formation of silicon carbide (SiC), which also causes dislocations in the crystal. Dust also has an insulating effect and can cause problems during melting. Another aspect is that discharged dust leads to contamination of the drawing system.

An early shutdown is then the result. Fine silica dust also carries a high risk potential because the dust is very reactive. There is a risk of possible ignition in the air due to the oxidation with atmospheric oxygen present.

Thus, the fine dust content in silicon bulk materials can be qualified and the manufacturing processes can be optimized in this regard, thus a reliable determination of the dust concentration is essential.

The literature describes a number of measuring methods for determining the concentration of very fine particles. In general, the determination of the dust concentration in the steps of separation of the dust particles, in the determination of the mass fraction, and the particle size of the fine dust fraction is divided.

Methods are known for separating fine-grained particles which also adhere to coarser particles by means of sifting (air jet screening), sedimentation, wet sieving / filtration (eg vibrating screening machine) or by impact. The dust concentration is usually determined gravimetrically or by turbidity measurement.

However, these general methods are not suitable for the high requirements in the measurement of lowest particulate matter concentrations in silicon bulk materials for the solar and semiconductor industry with particle sizes smaller than 10 microns and concentrations less than 50 ppmw because of insufficient sensitivity.

Out EP 1768927 the determination of the dust concentration of silicon granules is known. In this process, the fine dust is sucked off during the transfer of silicon granules and the separated dust is collected by means of a filter. About the dust content is closed to the dustiness of the product. A disadvantage of this method is that it is not measured directly on the product and no particle size distribution of the dust can be determined.

DE 10 2008 010 764 A1 discloses a dust detection method in which dust is picked up with a dust collecting unit in a dust detection unit and a reaction unit is fabricated based on a reaction, characterized in that a dust dispersion is generated from the collected dust and a dispersion liquid in a dust dispersion unit a reagent is mixed, so that a reaction between the dust dispersion and the reagent takes place, which causes a color change, a change in electrical properties and / or a change in temperature of the mixture of the dust dispersion and the reagent, which with a on an optical, electrical and / or thermal functional principle based detection unit is detected.

DE 10 2006 016 324 A1 discloses a device which enables a flexible classification of broken polycrystalline silicon, characterized in that it comprises a mechanical sieve and an optoelectronic sorting plant, wherein the poly-break is separated by the mechanical sieve into a silicon fines and a silicon remainder and the silicon Residue is separated via an optoelectronic sorting system into other fractions.

From the periodical "Rein Raum Technik" ("High-purity silicon dust as a source of contamination", Crößmann, Derzmann, April 2006, page 30/31, Verlag GIT Verlag) a method for the determination of the proportion of adhering dust particles on silicon fragments is known. However, the described method is only suitable for large silicon fragments (greater than 20 mm). A disadvantage of this process is still a complicated separation of the solid from the liquid used. Such a method is also described in Grössmann, Ivo; Derzmann, Magnus: High-purity silicon dust as a source of contamination: A method for the determination of silicon particles. GIT, Vol. 50, 2006, No. 1, pp. 54-55; ISSN 0016-3538.

The object was to provide a measuring method for the determination of the concentration of fine dust in silicon bulk materials, whose detection limit is better with respect to the fine dust concentration than in the measuring methods of the prior art.

The invention relates to a method for determining the concentration of fine dust in silicon bulk materials, wherein for measurement a product sample of the silicon bulk material is placed in a sieve, the particulate matter are completely separated by a fluid from the bulk material and form a suspension in the fluid and the suspension with the detached particulate matter continuously fed by a pump to a particle measuring device, there measured and then returned to the sample.

Surprisingly, it has now been found that a method with a combination of the separation of the finest particles and the determination of the particle size within a measuring method and in which the determination of the dust content of silicon bulk material is carried out directly on the product for particle sizes smaller than 10 microns and concentrations less than 50 ppmw suitable is. Since the particle size range over the proportion is determined, this is freely selectable in contrast to the methods of the prior art. In the method according to the invention, the separation of the fine dust, the determination of the amount of fine dust and the measurement of the particle size of the fine dust fraction are carried out in a single analysis step. This makes the method very easy to perform and the analysis times are very short. Due to the low scatter of the measured values in multiple measurements, the inventive method shows very reproducible results. Small amounts of false grain (no dust), which lead to poor results in the methods known from the prior art, do not influence the measurement result in the method according to the invention. Since the particle size distribution is measured, the particle size range over which the proportion is to be determined freely selectable.

The measuring method according to the invention can be applied to all forms of bulk materials of the polysilicon production, preferred are bulk materials in the form of fragments, granules or mixtures thereof. The invention can also be applied to sands, glass, gemstones, semi-precious stones, plastic granules, hard coal, activated carbon, fertilizer granules, washing powder granules, etc.

The determination of the dust content on silicon bulk materials preferably extends for granules to a particle size range of 0 to 15 mm and for silicon fragments to fractional sizes up to 200 mm. The concentration of fine dust is measured over the entire spectrum (up to 100 μm). With the method according to the invention dust concentrations can be measured at particles <10 microns to less than 5 ppmw.

The invention will be explained below with reference to a figure.

1 schematically shows an apparatus for carrying out the method.

The measurement is a sample 1 of the silicon bulk material in a sieve 2 presented in a sample vessel (dispersion unit) 3 located. This sample vessel is then placed in a particle measuring device 4 brought in. The fine dust particles are removed by flushing a fluid 5 completely separated from the bulk material. The fluid with the detached particulate matter is continuously during the measurement by means of a pump 6 to a suitable particle measuring device 7 promoted, measured there and in the dispersion 3 recycled.

As fluid all liquids can be used, which do not react with the bulk material to be examined, and this does not solve. Ethanol and water or mixtures thereof are preferred. With this method, the coarser grain adhering particles are separated and measured. The separation of the fine particles (deagglomeration) can be improved by adding a surfactant to the fluid. Particular preference is given to anionic and amphoteric surfactants and nonionic surfactants.

The fluid can be used both at ambient temperature and at elevated temperatures. Preference is given to room temperature.

A high fluid velocity prevents settling or adhesion of particulate matter on the wall. Via level sensors-the amount of fluid in the measuring system is automatically adjusted.

In a particular embodiment, mechanical dispersing aids, preferably ultrasound and / or a stirrer, are used to improve the separation of the fine dust particles.

The devices used are devices with polarization intensity differential scattering (PIDS) technology, laser diffraction, laser scattering, photo-optical devices, MIE scattering and back reflection, and laser measuring devices are preferred. Particular preference is given to using a laser measuring device from Beckmann Coulter, type LS 13320 with a liquid module. The device uses Fraunhofer laser diffraction and PIDS technology as the measurement method. The measuring range of the coulter ranges from 0.04 to 2000 μm.

The measuring time is 30 to 600 seconds, preferably 60 to 180 seconds.

For calibration, the solids concentration output from the meter must be checked at regular intervals. For this purpose, a sample is washed out analogously to the measuring method, the suspension is concentrated and the solids content is determined gravimetrically. Deviations from the device may be readjusted on the measuring device. Alternatively, the meter can be adjusted with a sample in which a known amount of particulate matter has been mixed in. In addition to the particle size distribution, the measuring device used should also determine the solids concentration. Based on the measured values obtained, the sample weight and the fluid quantity, the dust concentration can be determined. The maximum particle size corresponds to the mesh size of the sieve used (2).

The sieve can be made of all materials that are not attacked or loosened during the measurement. Preference is given to sieves made of metals or plastics, particularly preferably of precious metals or nylon (polyamide) or mixtures thereof. The screen can be made as a solid basket or flexible, for example in the form of a stocking.

The mesh size of the screen depends on the bulk material used. In this case, the lower limit is a mesh size through which the smallest grain of the granulate or fracture just can not pass. Preference is given to mesh sizes of 20 to 1000 .mu.m, particularly preferably from 100 to 500 .mu.m and very particularly preferably from 150 to 250 microns.

The invention will be explained in more detail with reference to the following examples.

example 1

Determination of the fine dust concentration of silicon breakage / high dust concentration

In a measuring apparatus according to the invention, cf. 1 , 5 samples with 200 g silicon fractions each were examined for their fine dust content from one batch of process. The measuring instrument used was a laser measuring instrument from Beckmann Coulter, type LS 13320 with a liquid module. The device uses Fraunhofer laser diffraction and PIDS technology as the measurement method. In addition to the fine dust concentration, in this example it should be checked how homogeneous the fine dust is distributed within a batch. For this purpose, during the production at different times samples were taken from the process. The fluid used was 800 ml ultrapure water (deionized water). The screen used was a flexible screen made of polyamide with a mesh width of 160 μm. The measurement duration was 90 seconds. The measurements showed that the distribution of particulate matter within the batch is relatively homogeneous. The results are in Table 1 is compiled. Table 1 Particle size [μm] Fine dust concentration [ppmw] Pr. 1 (batch start) Pr. 2 Pr. 3 (batch center) Pr. 4 Pr. 5 (end of batch) 0.04 0.0 0.0 0.0 0.0 0.0 0.05 0.0 0.0 0.0 0.0 0.0 0.05 0.0 0.0 0.0 0.0 0.0 0.06 0.0 0.0 0.0 0.0 0.0 0.06 0.1 0.1 0.1 0.1 0.1 0.07 0.1 0.2 0.1 0.1 0.1 0.08 0.3 0.3 0.3 0.3 0.2 0.08 0.5 0.5 0.5 0.5 0.4 0.09 0.8 0.9 0.8 0.8 0.7 0.10 1.1 1.3 1.2 1.1 1.1 0.11 1.6 1.8 1.6 1.6 1.5 0.12 2.1 2.4 2.1 2.1 1.9 0.13 2.7 3.1 2.7 2.7 2.5 0.15 3.4 3.8 3.4 3.4 3.1 0.16 4.1 4.7 4.1 4.1 3.8 0.18 4.9 5.6 4.9 4.9 4.6 0.20 5.8 6.6 5.8 5.8 5.4 0.21 6.8 7.6 6.7 6.7 6.3 0.24 7.8 8.8 7.7 7.7 7.3 0.26 8.9 10.0 8.8 8.8 8.3 0.28 10.0 11.3 9.9 10.0 9.4 0.31 11.3 12.6 11.1 11.2 10.6 0.34 12.6 14.1 12.4 12.6 11.9 0.38 14.1 15.6 13.8 14.0 13.3 0.41 15.6 17.2 15.2 15.5 14.7 0.45 17.1 18.9 16.7 17.0 16.2 0.50 18.8 20.6 18.2 18.7 17.9 0.54 20.5 22.5 19.9 20.4 19.6 0.60 22.4 24.4 21.6 22.2 21.4 0.66 24.3 26.3 23.4 24.2 23.3 0.72 26.3 28.4 25.3 26.2 25.4 0.79 28.5 30.6 27.3 28.3 27.5 0.87 30.8 32.9 29.4 30.6 29.8 0.95 33.1 35.3 31.6 33.0 32.2 1.05 35.6 37.8 34.0 35.5 34.7 1.15 38.3 40.4 36.5 38.1 37.3 1.26 41.0 43.2 39.0 40.9 40.1 1.38 43.9 46.0 41.7 43.7 43.0 1.52 46.8 48.9 44.5 46.7 46.0 1.67 49.9 51.9 47.4 49.7 49.0 1.83 52.9 54.9 50.3 52.8 52.1 2.01 55.9 57.9 53.2 55.9 55.1 2.21 58.9 60.8 56.0 58.9 58.1 2.42 61.8 63.6 58.7 61.9 61.0 2.66 64.6 66.2 61.3 64.7 63.9 2.92 67.2 68.8 63.8 67.4 66.5 3.21 69.8 71.1 66.1 70.0 69.1 3.52 72.2 73.4 68.3 72.4 71.6 3.86 74.6 75.7 70.4 74.9 74.0 4.24 77.1 77.9 72.6 77.4 76.5 4.66 79.6 80.3 74.8 79.9 79.0 5.11 82.2 82.7 77.1 82.4 81.5 5.61 84.8 85.2 79.5 85.0 84.1 6.16 87.3 87.6 81.7 87.4 86.5 6.76 89.6 89.7 83.7 89.6 88.7 7.42 91.5 91.5 85.4 91.4 90.5 8.15 93.0 92.8 86.5 92.7 91.8 8.94 94.0 93.6 87.3 93.6 92.7 9.82 94.7 94.2 87.7 94.1 93.3 10.78 95.3 94.6 88.1 94.5 93.9 11.83 96.1 95.3 88.6 95.0 94.5 12,99 97.2 96.2 89.4 95.8 95.5 14,26 98.8 97.6 90.5 97.1 96.8 15.65 100.6 99.3 91.9 98.6 98.4 17.18 102.5 100.9 93.3 100.1 100.0 18.86 104.3 102.3 94.6 101.5 101.4 20.71 105.8 103.5 95.6 102.6 102.7 22.73 107.1 104.5 96.5 103.5 103.8 24,95 108.4 105.5 97.3 104.3 104.9 27.39 109.8 106.5 98.3 105.2 106.0 30.07 111.3 107.8 99.3 106.2 107.3 33.01 113.0 109.1 100.4 107.3 108.5 36.24 114.8 110.6 101.6 108.6 109.8 39,78 116.6 111.9 102.7 109.7 111.0 43.67 118.3 113.2 103.8 110.8 112.1 47.94 119.9 114.3 104.7 111.7 113.1 52.63 121.5 115.4 105.6 112.6 114.0 57.77 123.2 116.5 106.5 113.3 114.8 63.42 125.0 117.6 107.4 114.1 115.5 69.62 126.9 118.8 108.3 114.9 116.1 76.43 128.9 119.9 109.3 115.8 116.8 83,90 131.2 121.2 110.2 116.9 117.5 92.10 133.7 122.4 111.1 118.0 118.4 101.10 136.3 123.6 111.9 119.1 119.2

Example 2:

Determination of the fine dust concentration of silicon granules / low dust concentration <10 μm

The procedure was analogous to Example 1. However, the samples used from one batch of process had only a very low concentration of fine dust. The measurements showed that the distribution of particulate matter within the batch is very homogeneous. The results are summarized in Table 2. Table 2 Particle size [μm] Fine dust concentration [ppmw] Pr. 1 Pr. 2 Pr. 3 Pr. 4 Pr. 5 0.04 0.0 0.0 0.0 0.0 0.0 0.05 0.0 0.0 0.0 0.0 0.0 0.05 0.0 0.0 0.0 0.0 0.0 0.06 0.0 0.0 0.0 0.0 0.0 0.06 0.1 0.1 0.1 0.1 0.1 0.07 0.1 0.1 0.1 0.1 0.1 0.08 0.1 0.2 0.2 0.1 0.2 0.08 0.2 0.2 0.2 0.2 0.2 0.09 0.3 0.3 0.3 0.3 0.3 0.10 0.4 0.4 0.4 0.4 0.4 0.11 0.5 0.5 0.5 0.5 0.5 0.12 0.6 0.6 0.6 0.6 0.7 0.13 0.7 0.8 0.8 0.7 0.8 0.15 0.8 0.9 0.9 0.8 0.9 0.16 1.0 1.0 1.0 0.9 1.0 0.18 1.1 1.2 1.2 1.1 1.2 0.20 1.2 1.3 1.3 1.2 1.3 0.21 1.4 1.5 1.5 1.3 1.5 0.24 1.5 1.6 1.6 1.4 1.6 0.26 1.6 1.7 1.7 1.6 1.7 0.28 1.7 1.9 1.9 1.7 1.9 0.31 1.8 2.0 2.0 1.8 2.0 0.34 1.9 2.1 2.1 1.8 2.1 0.38 2.0 2.2 2.2 1.9 2.2 0.41 2.1 2.3 2.3 2.0 2.2 0.45 2.2 2.3 2.3 2.1 2.3 0.50 2.2 2.4 2.4 2.1 2.3 0.54 2.3 2.4 2.4 2.1 2.4 0.60 2.3 2.4 2.4 2.1 2.4 0.66 2.3 2.4 2.4 2.1 2.4 0.72 2.3 2.4 2.4 2.1 2.4 0.79 2.3 2.4 2.4 2.1 2.4 0.87 2.3 2.4 2.4 2.1 2.4 0.95 2.3 2.4 2.4 2.1 2.4 1.05 2.3 2.5 2.4 2.1 2.4 1.15 2.3 2.5 2.5 2.1 2.4 1.26 2.4 2.5 2.5 2.1 2.4 1.38 2.5 2.6 2.6 2.2 2.5 1.52 2.7 2.8 2.7 2.3 2.6 1.67 2.9 2.9 2.9 2.5 2.8 1.83 3.2 3.2 3.2 2.9 3.1 2.01 3.4 3.4 3.4 3.2 3.4 2.21 3.6 3.6 3.6 3.4 3.6 2.42 3.7 3.7 3.7 3.6 3.7 2.66 3.7 3.7 3.7 3.6 3.7 2.92 3.8 3.8 3.8 3.6 3.8 3.21 3.8 3.8 3.8 3.6 3.8 3.52 3.8 3.8 3.8 3.6 3.8 3.86 3.8 3.8 3.8 3.6 3.8 4.24 3.8 3.8 3.8 3.6 3.8 4.66 3.8 3.8 3.8 3.6 3.8 5.11 3.8 3.8 3.8 3.6 3.8 5.61 3.8 3.8 3.8 3.6 3.8 6.16 3.8 3.8 3.8 3.6 3.8 6.76 3.8 3.8 3.8 3.6 3.8 7.42 3.8 3.8 3.8 3.6 3.8 8.15 3.8 3.8 3.8 3.6 3.8 8.94 3.8 3.8 3.8 3.6 3.8 9.82 3.8 3.8 3.8 3.6 3.8 10.78 3.8 3.8 3.8 3.6 3.8

Comparative Example 1

As a comparison to the process according to the invention, the sample from Example 1 was subjected to an analysis by means of an air-jet sieve according to the prior art. An air-jet screen of the company Rhewum (air-jet precision screen, type: LPS 200 K) was used, with a mesh size of 32 μm. The sample amount was 154.39 g. The air throughput was 70 m ³ / h, the nozzle speed 30 U / min and the sieving time 3 min. The result was a sieve residue of 154.37 g and dust of 0.02 g (130 ppmw).

Due to the low dust content, the residue could not be determined precisely due to the lack of suitable weighing technology. Furthermore, no statement about the particle size distribution of the separated fine dust fraction could be obtained from this process.

Claims (8)

Method for determining the concentration of fine dust in silicon bulk materials, wherein a product sample of the silicon bulk material is placed in a sieve, the particulate matter are completely separated by a fluid from the bulk material and pass through the sieve, form a suspension with the fluid and the suspension continuously conveyed with the detached fine dust particles by means of a pump to a particle meter, measured there and then returned to the sample. A method according to claim 1, characterized in that the bulk materials are used in the form of fragments, granules or mixtures thereof. A method according to claim 1 to 2, characterized in that are used as the fluid ethanol, water or mixtures thereof. A method according to claim 1 to 3, characterized in that the separation of the particulate matter is improved by adding one or more surfactants to the fluid. A method according to claim 1 to 4, characterized in that mechanical dispersing aids are used to improve the separation of the particulate matter. A method according to claim 1 to 5, characterized in that the sieve used is made of metal or plastic. A method according to claim 1 to 6, characterized in that the mesh size of the screen is chosen so that the smallest loose grain of the granules or the break, just no longer fits through. A method according to claim 7, characterized in that the mesh size is 20 to 1000 microns.

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