Method for sorting silicon chunks

Abstract

The present invention relates to the following singulating the chunk at a singulation area; - recording, by at least one first measuring device, a projected area of ​​the chunk in a 2D profile plane; - recording at least one height information item above and / or below the 2D profile plane by means of at least one further measuring device; calculating a size of the chunk from the projected area and height information items; controlling at least one deflection device as a function of the calculated size; The present invention relates to a method for sorting chunks, comprising: The invention further relates to a device for carrying out the method.

Description

[Technical Field]

[0001] The present invention relates to a method for sorting silicon chunks. [Background technology]

[0002] Polycrystalline silicon (polysilicon) is traditionally produced by the Siemens process (chemical vapor deposition). In this process, thin silicon filament rods are heated in a reactor by direct current flow through them, and a reactive gas containing a silicon-containing component (e.g., monosilane or halosilane) and hydrogen is introduced. The surface temperature of the filament rods traditionally exceeds 1000°C. At these temperatures, the silicon-containing component of the reactive gas decomposes, and elemental silicon is deposited from the vapor phase on the surface of the rod as polysilicon, causing the rod to increase in diameter. After a predetermined diameter is reached, deposition is stopped, and the resulting polysilicon rod is removed.

[0003] Polysilicon is the starting material for the production of monocrystalline silicon, for example, by the Czochralski process. It is also required for the production of polycrystalline silicon, for example, by ingot casting. For both methods, the polysilicon rod must be crushed into chunks, which are conventionally sorted according to their size in a separating device.

[0004] The separation device may be a multi-stage screening machine that mechanically separates the fragmented polysilicon into different size classes. For example, U.S. Patent No. 6,375,011 discloses a vibrating conveyor that allows separation into three size classes.

[0005] Improvement of separation, or even separation by optical criteria, can be achieved by optical-pneumatic sorting equipment. US Patent Application Publication No. 2007 / 0235574 discloses such equipment, which is placed downstream of a crushing device for polysilicon. The shadow area of ​​the crushed polysilicon chunks projected onto a plane is used in this case for size separation.

[0006] Furthermore, U.S. Patent No. 6,265,683 describes an opto-pneumatic device for sorting semiconductor materials, where size separation is performed with camera assistance by recording the projected area of ​​the material to be sorted. Optionally, sorting of materials according to their surface condition can also be performed here. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 6,375,011 [Patent Document 2] US Patent Application Publication No. 2007 / 0235574 [Patent Document 3] U.S. Patent No. 6,265,683 Summary of the Invention [Problem to be solved by the invention]

[0008] Known methods based on two-dimensional (2D) projections of chunks using transmitted light have the disadvantage that chunks are recorded only from one side. Chunks can vary greatly in terms of their shape. For example, a chunk may be unfavorably oriented so that its longest extent is in front of or behind the projection area (i.e., perpendicular to it) at the moment its projection area is recorded. This results in an incorrect estimation of chunk size (sorting error).

[0009] This problem gives rise to the object of the present invention, namely to provide an improved sorting method in which the orientation of the chunks to be sorted plays only a secondary role. [Means for solving the problem]

[0010] This object is achieved by a method for sorting chunks, in particular silicon chunks, comprising the following steps:

[0011] singulating the chunks in a singulation area; recording, by at least one first measuring device, a projected area of ​​the chunk in a 2D profile plane; - recording by means of at least one further measuring device at least one item of height information above and / or below the 2D profile plane, calculating the size of the chunk from the projected area and height information items; Controlling the at least one deflection device as a function of the calculated size.

[0012] By using additional measuring devices, the projection area of ​​the chunks acquired with the help of the first measuring device can be supplemented with height information. In this case, the measuring devices are preferably arranged at different positions around the chunks, thus inspecting the chunks from different viewing angles. This allows information items to be acquired about the extent of the chunks above and / or below the profile plane (in the direction of the application axis (z-axis)) to prevent sorting errors. In this way, the quality of the separation is improved.

[0013] The chunks are preferably crushed polysilicon, for example crushed polysilicon rods from the Siemens process.

[0014] Singulation of the chunks is intended to mean, in particular, that the chunks are separated from one another and therefore no longer located on top of one another or partially overlapping. This can be done, for example, by a rocking movement on a conveyor belt. For recording by the measuring device, it is not necessarily necessary that the chunks are arranged in a line (behind one another or next to one another).

[0015] Preferentially, the first measuring device and at least one of the further measuring devices is a photoelectric transmission or reflection light measuring system having a detection area through which the chunk passes.

[0016] Preferably, the silicon chunk passes through the detection region in free fall.

[0017] The reflected light measurement system preferentially comprises a light section sensor and / or at least one camera system.

[0018] The light section method implemented with a light section sensor is based on optical triangulation and requires relative motion between the sensor and the chunk. In this case, the chunk is linearly illuminated with the aid of an appropriate light source, and the resulting light stripe is recorded by an area scan camera (a component of the sensor). In this case, the surface normals of the light source and the camera are inclined relative to each other by the triangulation angle.

[0019] The camera system may also in principle be just a camera recording the projected area of ​​the chunk with the aid of ambient light as a light source, however preferably the camera is supplemented with an external light source.

[0020] The camera system may also be a camera system for photometric stereo analysis, which is a method for analyzing the projected area and reflection of the surface of an object (chunk) in three-dimensional (3D) space. Traditionally, an external light source is moved towards the object to acquire multiple images of the resulting light scenario. In the case of a moving object, such as a chunk in free fall, multiple cameras with different viewing angles are used instead of a moving light source. Alternatively, multiple light sources with different illumination directions and one camera or multiple light sources and multiple cameras can be used in combination.

[0021] The transmitted light measurement system preferably includes a photoelectric barrier, a light curtain, or a light grid. In this case, a light beam (e.g., an infrared beam) is emitted from a light emitter (photoelectric barrier) or from multiple emitters spaced apart from each other (light grid / light curtain) to a corresponding receiver. If one or more of the beams is interrupted, a signal is sent to a control device, which may consequently trigger, for example, a deflection device. The resolution of the light grid and light curtain may be determined by the distance between the beams. Typical examples of such measurement systems are optical micrometers, optical band micrometers, profile projectors, CCD laser micrometers, and laser sensors with photoelectric barrier functionality.

[0022] According to a preferred embodiment, the first measuring device is a camera system, which in particular comprises a light source and a camera for recording the projection area.

[0023] The further measuring device is preferably a light curtain or a light grid, especially if a camera system is selected as the first measuring device.

[0024] Preferably, the recording of the projection area and the recording of the height information item are performed at a time interval of 0 to 100 ms, preferentially 0 to 50 ms, particularly preferentially simultaneously. The shortest possible time interval ensures that the position of the chunk does not change substantially, especially in free fall.

[0025] The deflection devices involved in sorting the chunks may be pneumatic and / or mechanical deflection devices.

[0026] The pneumatic deflection device preferably comprises at least one nozzle through which a gas (e.g., air, inert gas) or a liquid (e.g., high-purity water) is ejected at a pressure of 3 to 20 bar. In this regard, reference may be made to US Pat. No. 6,265,683.

[0027] The method according to the invention is preferably an opto-pneumatic sorting method.

[0028] The chunk size calculation can be performed using an evaluation device (for example a software-assisted process control station, for example MATLAB (MathWorks)) connected to both the measurement device and the deflection device.

[0029] The basic measurement information acquired by the first measuring device is the projected area of ​​the chunk, which contains information about the chunk's shape, even if only in 2D as a contour. From the projected area, the evaluation device can obtain various length specifications, especially the diameter, which allow conclusions about the chunk's size. Many methods are generally known for determining length specifications or diameters. For example, there is the determination of the diameter (circumference-equivalent diameter) derived from an equivalent circle, or the determination of the ferret diameter, which includes a whole group of characteristic quantities, all of which are defined by the distance between two tangents to the contour of the projected area in a fixed measurement direction.

[0030] The height information items obtained by the further measuring device, for example a photoelectric barrier, may in particular be height values ​​(units of length). The combination of the acquired measurement information items is for example a 3D point cloud consisting of the contour acquired by the first measuring device and the contour displaced by the height values.

[0031] The maximum range can be calculated from the length of the vector between the points located furthest from each other.

[0032] A cloud of points as a vector X = {[x1,y1,z1], [x2,y2,z2], ..., [xn,yn,zn]} Combining all points with each other and calculating the distance in 3D: L(i,j)=[(xi-xj) 2 +(yi-yj) 2 +(zi-zj) 2 ] 0.5 Determining the maximum value of L(i,j).

[0033] The more detailed the height information items of the further measuring device, the smaller the measurement error.

[0034] A further aspect of the invention relates to a device for sorting chunks, in particular silicon chunks, comprising: a singulation area for singulating the chunk; at least one first measuring device for recording a projected area of ​​the chunk in a 2D profile plane; at least one further measuring device for recording height information items above and / or below the 2D profile plane; at least one deflection device; an evaluation device for calculating the size of the chunk from the projection area and height information items and for controlling the deflection device as a function of this size; Equipped with.

[0035] Preferably, the device is a device for carrying out the described method.

[0036] The singulation area preferably comprises at least one vibrating conveyor trough and / or conveyor belt. Optionally, the singulation area may also comprise a screening plate or a oscillating screen for removing fine fragments. Generally, this may also be a segment of a conveyor belt to which the chunks are individually applied. Suction for dust particles may also be provided. The singulation area is preferentially a singulation area as described in EP 0 983 804 A1.

[0037] Preferentially, the device comprises a large number of first and / or further measurement devices to allow high throughput sorting. A large number of measurement devices in combination with high computational power of the evaluation device may minimize the distance between singulated chunks.

[0038] Preferably, the deflection device is a pneumatic or mechanical deflection device, in particular a pneumatic deflection device comprising an array or matrix of individual nozzles.

[0039] With regard to the measuring and evaluation devices, reference is made to the above comments and to EP-A-0 983 804. [Brief explanation of the drawings]

[0040] [Figure 1] A device according to the invention having a light grid (transmitted light measurement system). [Figure 2] A device according to the invention comprising a light section sensor (reflected light measuring system).

[0041] List of references used [Explanation of symbols]

[0042] 10. Vibrating conveyor belt 12 Movement Arrows 20 sliding surface 22 End of sliding surface 30 chunks 32 projection areas 40 Camera 42 Light source 44 detection area 50 Light Grid 52 Emitter Strip 54 IR beam paths 56 Receiver Strip 60 Light cutting sensor 62 Laser scanner 63 Static Laser Lines 64 Receiving optical system 65 Reflected light 70 Deflection Device 80 First Collection Container 81 Separation elements 82 Second Collection Container 90 Evaluation Devices 100 Sorting Device 200 Sorting Device DETAILED DESCRIPTION OF THE INVENTION

[0043] 1 shows a sorting device 100 with a vibrating conveyor belt 10 as singulation area and an inclined sliding surface 20. The forward feed direction of the singulated chunks 30 is indicated by a movement arrow 12.

[0044] A camera 40 with an external light source 42 is positioned below the slideway 20 as a first measuring device. The camera 40 is, for example, a CCD camera with an optical resolution of 0.05 mm to 2.0 mm. The light source 42 is, for example, an LED with diffuse area illumination. The detection area 44 of the first measuring device, which corresponds to the chunk 30, is indicated by an asterisk. A light grid 50 is attached to the lower end 22 of the slideway 20 as a further measuring device. It consists of an emitter strip 52 with five infrared light sources (laser or LED light sources, or even visible light points, could also be considered), each of which emits light indicated by a dashed line 54, and a corresponding receiver strip 56 with five sensors. Below the first measuring device is a pneumatic deflection device 70, and below the first measuring device 70 are first and second collection containers 80, 82. The collection containers 80, 82 are connected to each other by a separation element 81 with a triangular cross section. Furthermore, both the sensor strip 56 of the first measuring device, the camera 40 and the light source 42 of the second measuring device, and the deflection device 70 are connected to an evaluation device 90. The evaluation device is a computer with image processing software, for example MATLAB.

[0045] When the chunks 30, e.g., pyramidal chunks, singulated by the oscillating motion of the vibrating conveyor belt 10, reach the inclined sliding surface 20, they are oriented so that their center of gravity is as low as possible. This can generally be adapted to the chunk size by the sliding surface 20, whose angle is adjustable. After reaching the end of the sliding surface 22, the chunks 30 pass over the light grid 50 with their elongated sides facing the z-direction, thus recording their entire length. The chunks 30 then pass in free fall through the detection area 44 of the camera 40, which records only the projection area 32 corresponding to the bottom surface of the chunks 30. From the two items of information, namely the projection area 32 and the height information item acquired by the light grid 50, the evaluation device 90 calculates the size of the chunks 30 and transfers this information to the pneumatic deflection device 70, so that the undeflected chunks 30 are collected in a second collection container 82 and the chunks 30 deflected by the pneumatic pulse are collected in the first collection container 82. A separation element 81 facilitates this separation.

[0046] FIG. 2 shows a further sorting device 200 according to the invention, which substantially corresponds to the sorting device of FIG. 1 (corresponding elements have corresponding reference numerals, and the evaluation device, deflection device, and collection container are omitted). The sorting device 200 has a light section sensor 60 as a further measuring device. It consists of a laser projector 62 and receiving optics 64. The light section sensor 60 determines height information items (3D profile recordings) using the principle of triangulation. A special optical system expands the laser beam to form a laser line 63 (represented by a thin dashed line) which is projected onto the surface of the passing chunk 30. The receiving optics 64 images the light 65 reflected by the surface (represented by a coarse dashed line) onto the sensor matrix. An evaluation device (not shown) connected to the light section sensor 60 can calculate the height information items (z-axis) of the passing chunks from the matrix image acquired along the laser line (x-axis). This information item can then be output in a two-dimensional coordinate system fixed relative to the sensor. In the case of a moving object, or if it passes across the sensor, 3D measurements may also be taken.

[0047] Comparative Example 1 Classification of crushed (fractured) polysilicon with chunk size (CS)2.

[0048] The size class of a polysilicon chunk is defined as the longest distance between two points on the surface of the silicon chunk (corresponding to the maximum length).

[0049] CS0 0.1 to 5mm CS1 3 to 15mm CS2 10 to 40mm CS3 20 to 60mm CS4 45 to 120mm CS5 100 to 250mm The polysilicon sample material used in the tests was generated from a mixture of 9,000 chunks in the length range of 10 to 40 mm (CS2) and 1,000 chunks in the length range of 40 to over 65 mm, i.e., the portion to be separated. To prepare the sample material, a mechanical screening method (analytical screening according to DIN ISO 3310-2, typically with a hole width of W = 4 mm (square drilling)) was used to remove chunks between 0 and 10 mm. The maximum lengths of both the chunks in the length range of 10 to 40 mm and the chunks in the length range of 40 to 65 mm, which were to be separated, were determined manually (with a vernier caliper), and then the polysilicon sample material was mixed.

[0050] This polysilicon sample material was subjected to conventional opto-pneumatic sorting of portions greater than 40 mm.

[0051] The opto-pneumatic sorting device used was equipped with a first 2D measuring device (CCD camera and light source according to Figure 1) for recording the projected area of ​​the chunks. The chunks passed through the detection area of ​​the measuring device individually on an inclined slide (traditionally with a distance between chunks of 0.5 to 10 mm). The measuring device was connected to an evaluation device at a process control station. A deflection device with a nozzle strip approximately 50 cm wide, with two rows of 100 nozzles each, was also connected to this control station. A separation distance of 40 mm was set at the control station.

[0052] At the end of sorting, the deviation of the separation method was determined by manual analysis (calipers) in conjunction with manual counting of chunks and was 0.1%.

[0053] Example 1 The polysilicon sample material described in the comparative example was separated in an opto-pneumatic sorting device having substantially the same design (with a separation distance of 40 mm). However, in contrast to comparative example 1, the device had a second 2D measurement device, which was a light grid as described with reference to FIG. 1.

[0054] One possible way of evaluating the information items acquired by the measuring device is presented below, which was carried out using MATLAB (MathWorks).

[0055] Image recording by the first measuring device, configured as an array of sensors, yields per unit time the shadow cast by the chunk as a vector x with grayscale values ​​[0...255].

[0056] At the same time, the value of a height information item is recorded by a second measuring device: scalar z [mm]. The individual measurements are combined as a function of time t to form an image: image [x,y] with greyscale values ​​[0..255, 0..255].

[0057] The height information items are combined as a function of time t to form a vector and assigned to the ordinate: vector [z], with a value of [mm].

[0058] The images thus formed are repeatedly evaluated.

[0059] An adjustable grayscale value (for example, grayscale value 128) converts grayscale values ​​[0..255] into binary values ​​[0=dark or 1=light].

[0060] A list of chunks is obtained by searching for contiguous regions of [0=dark] in the image.

[0061] The calculation is repeated for each chunk.

[0062] Calculate the edge points of the region as a list and convert to [mm]: list [xi,yi][mm].

[0063] Assigning height values ​​to a list: [xi,yi,zi][mm].

[0064] For all points in the list [xi,yi,zi], calculate the maximum distance in 3D relative to each other: chunk maximum extent scalar [mm].

[0065] If the adjustable limit of the chunk's maximum extent [mm] is exceeded, an instruction is given to blow the chunk away in the area of ​​the nozzle strip where the chunk is located [min(xi), max(xi)].

[0066] This post-sort deviation was manually established as above and was 0.0%.

[0067] Comparative Example 2 Classification of crushed polysilicon in CS3.

[0068] First, a polysilicon sample material was generated consisting of 9000 chunks ranging in length from 20 to 60 mm (CS3) and 1000 chunks (the part to be separated) ranging in length from 60 to over 85 mm.

[0069] The chunk length was verified manually, after which polysilicon sample material was prepared by mixing.

[0070] The polysilicon sample material was sorted using the opto-pneumatic sorting device described in Comparative Example 1, but with a separation distance of 60 mm.

[0071] This post-sort deviation was manually established as above and was 1.0%.

[0072] Example 2 The polysilicon sample material described in Comparative Example 2 was in this case sorted with an opto-pneumatic sorting device according to Figure 2. It therefore had a second measuring device in the form of a light-section sensor consisting of a laser projector and receiving optics.

[0073] This post-sort deviation was manually established as above and was 0.0%.

[0074] It could be shown that the sorting results can be significantly improved by an additional item of height information determined by a second measuring device, especially in the case of pyramidal objects. The goal of any sorting is essentially clean separation intervals with no deviations in relation to chunk size.

Claims

1. 1. A method for sorting chunks, comprising: singulating the chunks in a singulation region; - recording, by at least one first measuring device, a projected area of ​​the chunk in a 2D profile plane; - recording by means of at least one further measuring device at least one item of height information above and / or below the 2D profile plane; calculating the size of the chunk from the projected area and height information items; controlling at least one deflection device according to a function of the calculated size; 10. A method for sorting chunks, comprising:

2. 2. The method according to claim 1, characterized in that the first measuring device and at least one of the further measuring devices are photoelectric transmission or reflection measuring systems having a detection area through which the chunk passes.

3. 3. The method of claim 2, wherein the silicon chunk passes through the detection area in free fall.

4. 4. The method according to claim 2 or 3, characterized in that the reflected light measurement system comprises a light section sensor and / or at least one camera system.

5. 5. The method according to claim 4, wherein the camera system is a camera system for photometric stereo analysis.

6. 4. The method according to claim 2 or 3, characterized in that the transmitted light measurement system comprises a photoelectric barrier, a light curtain or a light grid.

7. The method of claim 1 , wherein the first measuring device is a camera system.

8. 2. The method according to claim 1, wherein the further measuring device is a light curtain or a light grid.

9. 2. A method according to claim 1, characterized in that the steps of recording the projection area and recording the height information items are performed at a time interval of 0 to 100 ms, preferentially 0 to 50 ms, particularly preferentially simultaneously.

10. 2. The method of claim 1, wherein the deflection device is a pneumatic or mechanical deflection device.

11. 1. A device for sorting chunks, comprising: a singulation area for singulating the chunk; - at least one first measuring device for recording the projected area of ​​the chunk in a 2D profile plane; - at least one further measuring device for recording height information items above and / or below the 2D profile plane; at least one deflection device; a software-assisted controller that calculates the size of the chunk from the projection area and height information items and controls the deflection device according to a function of this size; 1. A device for sorting chunks, comprising:

12. 12. The device according to claim 11, characterized in that the singulation area comprises at least one vibrating conveyor trough and / or conveyor belt.

13. 13. The device according to claim 11 or 12, characterized in that the deflection device is a pneumatic or mechanical deflection device.

14. 14. The device according to claim 13, characterized in that the pneumatic deflection device comprises a row or matrix of individual nozzles.

Images