WO2009077199A2

WO2009077199A2 - METHOD AND INSTALLATION FOR TREATING OR CLEANING Si BLOCKS

Info

Publication number: WO2009077199A2
Application number: PCT/EP2008/010871
Authority: WO
Inventors: Heinz Kappler
Original assignee: Gebr. Schmid Gmbh & Co.
Priority date: 2007-12-19
Filing date: 2008-12-19
Publication date: 2009-06-25
Also published as: DE102007063169A1; WO2009077199A3

Abstract

The invention relates to a method and installation for treating or cleaning Si blocks (17) to produce wafers for solar cells. According to the method, the Si blocks (17) are conveyed through various treatment modules (16, 30, 37, 45, 55) on a continuous, horizontal conveyor belt (14). In a first step or a cleaning module (16), the Si blocks are subjected to an alkaline cleaning step and then rinsed. In a second step or an etch-polish module (30), the blocks are subjected to etching polishing, an etching solution being applied to the Si blocks from all four sides. The blocks are then rinsed in a rinse module after etching polishing.

Description

Description Method and system for processing or cleaning Si blocks

Field of application and state of the art

The invention relates to a method for processing or for cleaning of silicon blocks and a system designed for this purpose.

To produce wafers for the photovoltaic industry, so-called ingots are first of all cast from silicon and then divided into individual blocks of the desired edge length. From these blocks, the individual wafers are then produced or sawed out. The problem often arises when sawing, the silicon blocks break or larger cracks that can make the wafer unusable. There is also the problem that cracks caused by sawing can be triggers for further cracks.

Task and solution

The invention is based on the object to provide an aforementioned method for processing or cleaning of silicon blocks and a corresponding system with which problems of the prior art can be eliminated and in particular after dividing the silicon ingots into silicon Blocks a treatment of the exposed outsides of the silicon blocks is possible.

This object is achieved by a method having the features of claim 1 and a system having the features of claim 12. Advantageous and preferred embodiments of the invention are the subject of the other claims and are explained in more detail below. Although some of the features of the plant are described mainly in the context of the process, they also serve to explain the plant and are generally applicable. Furthermore, the wording of the priority application DE 102007063169.5 of 19 December 2007 by the same applicant by expressly referring to the content of the present description. The wording of the claims is incorporated herein by express reference.

According to the invention, the silicon blocks for the process are transported on a continuous, horizontal transport path. In a first step, an alkaline cleaning and rinsing of the silicon blocks takes place, this advantageously taking place one after the other, and particularly advantageously so that rinsing takes place only after the end of the alkaline cleaning. Later, a polishing step is performed in a second step, wherein the polishing etching a corresponding etching solution is brought from all four sides or on all sides of the silicon blocks. After polishing, a further rinse of the silicon blocks takes place. This can happen immediately afterwards, but it does not have to. Likewise, an intermediate step can be carried out between the first step and the second step.

By this treatment or processing of the silicon blocks, existing cracks on the outside of the silicon blocks, which can then subsequently lead to further cracking and destruction during sawing of the wafers or in the finished wafers, are smoothed or removed by etching. By alkaline cleaning in front of a silicon block is cleaned of foreign bodies. The later polishing sets will then eliminate the microcracks.

The above-described first step can be designed so that a silicon block is first cleaned alkaline with a cleaning solution and then just, as has been described, is rinsed clean or is rinsed with water. This is advantageously carried out in a treatment module or a first treatment module of a correspondingly constructed system according to the invention for processing or cleaning silicon blocks. In each case after the above-described first step of the alkaline cleaning or the rinsing contained therein and additionally or alternatively after the second above-described step of the polishing etch, liquid is removed from the silicon blocks in each case, which takes place by air circulation or targeted and possibly strong blow-off. As a result, the silicon blocks can even be completely dried, if desired or needed, so that the liquid is completely removed. In an embodiment of the method, after the step of polishing etching, the etching solution is removed before a subsequent step for cleaning rinsing, so that the liquid is loaded or polluted for cleaning rinsing with less etching solution. In this case, although etching solution can be largely completely removed, with a cleaning rinsing is still necessary for good cleaning. As described above, blowing off can also be provided for removing the etching solution.

In a further embodiment of the invention, a so-called KOH process step can take place after the step of cleaning rinsing after polishing. In this case, a silicon block is wetted with KOH etching solution, which may for example be 5% to achieve a further advantageous treatment of the outsides of the silicon block. After the KOH process step, this KOH solution can be rinsed off again, advantageously again with water. This can be done in a single treatment module of a corresponding plant to save space.

Advantageously, the silicon blocks along the transport path are not transported continuously, but run at intervals through the plant. This means, in particular, that the silicon blocks are moved into a treatment module and there either remain dormant or else are moved back and forth intermittently during the respective step. As a result, at certain predetermined treatment periods during the individual steps, the length of the system compared to a pure, continuous flow system can be kept lower. For example, at the step of polishing etching, a sufficiently long treatment time at high throughput To achieve this, two or even more treatment modules can be provided in parallel or in succession for a higher throughput.

Especially for increasing the throughput it can be provided that the step of rinsing after the step of polishing etch in a separate treatment module takes place, in a treatment module for rinsing or on a specially designed collection container. In particular, it is also possible with multiple treatment modules for polishing etching to provide a single treatment module for rinsing.

On the one hand, it is possible, at least in the step of polishing etch, to spray or spray the silicon blocks from above and along the longitudinal sides and also from below with etching solution, which under certain circumstances can also take place with large amounts of etching solution. In this case, etching solution can also be used circulating, so that the total vorzuhaltende amount of etching solution is not too large. Alternatively, at least the polishing etching can be carried out by at least partially immersing a silicon block in the etching solution or an etching bath. This can be done either from a further spraying of the silicon block from above.

Advantageously, however, a silicon block can be completely immersed in an etching bath. This can be done such that the silicon block is introduced into a chamber of the treatment module for polishing etching, in particular at the same height of the horizontal transport path of the system. Subsequently, advantageously without lowering the silicon block, the chamber is sealed laterally and downwardly, for example by flaps, in particular in the case of rigid side walls by inlet flaps and outlet flaps. After sealing the chamber, the etching solution can be introduced, advantageously as mentioned above from above and with increasing fill level, particularly advantageously until a silicon block is completely immersed. When the desired treatment time has been reached, the etching solution is drained off, then the flaps are opened and the silicon block is removed. Advantageously, the volume of the chamber of the treatment module is only slightly larger than the silicon block itself. Especially this is advantageously about 10% to 30%, so that when the silicon block is completely immersed in the etching solution, its total amount required is not too great. In a treatment module for spraying the silicon blocks, the treatment module is advantageously considerably larger form, since spray nozzles or the like. must be provided.

A rinsing process either after the alkaline cleaning or polishing, possibly also after the KOH process, is advantageously carried out with water, it being particularly advantageous for water of different purity to be used. It is possible, for example, to perform a last rinse in a rinsing sequence on a silicon block with fresh water, which is collected after rinsing. In the next flushing sequence at the next silicon block, this water is then used for a penultimate rinse, and then used, for example, in the next cycle in the next rinse sequence as the third last or first rinse. Thus, virtually the water used for rinsing is gradually used and thereby more polluted, but in each case it is ensured that subsequent rinses are performed in a rinsing sequence, each with a little clean or less polluted water. Advantageously, a final rinse each with fresh water. It can also be provided that for this last rinse less water is used as for the rinses before, which also the fresh water consumption can be lowered. For this purpose, a system according to the invention with a plurality of treatment modules each have corresponding water tanks or basins and corresponding valves and pumps to provide the waterways and use.

The intermittent movement of a silicon ingot during a process step is advantageously provided in polishing etching. In practice, this is relatively easy to accomplish that a transport path is formed for example by appropriate transport rollers and they are driven accordingly. In order to be able to reduce the consumption of etching solution similarly to the water, it may be provided that the etching solution for polishing etching, and under certain circumstances also the alkaline cleaning liquor or the KOH treatment liquid, is sprayed onto the silicon blocks in a recirculating system , This achieves the absolutely required amount of treatment liquid. It can be provided that always a certain part is removed or always new treatment liquid is tracked. Alternatively, permanent cleaning options such as filters or the like. possible, depending on the type of treatment liquid.

Thus, the system according to the invention for carrying out the above-described method has several own treatment modules, wherein in each case a treatment module is provided at least for the alkaline cleaning and the polishing etching. Advantageously, a separate treatment module is provided for the KOH process. In order to increase the throughput, either several such systems can be provided or they can work at least partially in parallel. The treatment modules are designed essentially like conventional treatment modules for such wet processes in the in-line method. In some treatment modules, the rinsing step can be installed with water through appropriate nozzles and corresponding water tank. Advantageously, a separate rinsing module is provided behind the treatment module for polishing etching and before the treatment module for the KOH process, in particular also in order to increase the throughput precisely at the time-consuming step with the polishing etching.

A drying module for removing treatment liquid from a silicon block or also for direct drying advantageously has at least one fan, possibly also thermal dryers such as heat radiators or heaters.

These and other features are apparent from the claims and from the description and the drawings, wherein the individual features in each case alone or more in the form of sub-combinations in a Embodiment of the invention and be realized in other areas and can represent advantageous and protectable versions for which protection is claimed here. The subdivision of the application into subheadings and individual sections does not limit the general validity of the statements made thereunder.

Brief description of the drawings

An embodiment of the invention is shown schematically in the drawings and will be explained in more detail below. In the drawings show:

1 is a schematic side view of a system consisting of several modules for cleaning silicon blocks,

Fig. 2 is a schematic functional representation of a cleaning module with different liquid tanks and

Fig. 3 is a schematic representation of a Polierätz module with immersion of the silicon blocks in a Polierätz liquid.

Detailed description of the embodiments

In Fig. 1 is a side view of a system 11 according to the invention for performing the method described above. The system 11 consists of several treatment modules, which are explained in detail below.

On the left, an infeed module 13 is shown, which consists essentially of a transport track 14 with conventional transport rollers. Before the inlet module 13 is, for example, a shape of the silicon blocks from the aforementioned silicon ingots.

After the inlet module 13 is a cleaning module 16, which is formed with a closed housing, as is conventional and known per se. In the cleaning module 16 are different sized silicon blocks 17 dar- as can be seen in Fig. 2 in magnification with a functional representation. The cleaning module 16 has two spray devices 18a and 18b with the spray device 18a above the transport path 14 and thus over the silicon blocks and the spray device 18b below. Further spraying devices, not shown, can be arranged on the longitudinal sides.

The spray devices 18 are fed from a tank 21 for alkaline cleaning liquor 21 and from a tank 23 for rinsing water 24 and from a fresh water connection 26. Via two pumps 27a and 27b and valves 28a-c, the feed to the spray devices 18 is controlled. The drain from the cleaning module 16 or a corresponding trough into the tanks 20 or 23 is controlled via valves 28 d and e. The process here is such that first by means of the pump 27a and opened valves 28a and d and otherwise closed valves, the silicon blocks 17 are sprayed with the cleaning liquor 21 from the tank 20 for a predetermined time. The silicon blocks can either stand still on the transport path 14 or be moved intermittently forward and backward.

After sufficient spraying with the cleaning liquor 21 is flushed by means of the pump 27b and opened valves 28b and e and otherwise closed valves in a first rinse with the rinse water 24 from the rinsing water tank 23 via the spray devices 18 a first time. Thereafter, the valves are closed again. Then, the valves 28c and 28e are opened and the other valves are closed, so that is sprayed from the fresh water connection 26 or with fresh water on the spray devices 18. The contaminated by the flushing fresh water then passes through the valve 28e in the flushing water tank 23, so that only slightly polluted water is supplied here. A cleaning or renewal of both the cleaning liquor 21 and the rinse water 24 is easily possible for the expert. Thus, the above-described two-stage rinsing is performed. In the same way could be done with two different rinse water different levels of contamination a three-stage flushing. After the cleaning module 16, the silicon blocks 17 are retracted into a polishing etching module 30. In Fig. 1, two of which are shown one behind the other, and it is also still possible to arrange several of them next to each other, ie in parallel, in order to create a higher overall throughput. Furthermore, it is of course also possible here, silicon blocks 17 first in the left Polierätzmodul 30 and then in the right Polierätzmodul

30 consecutively.

It can be seen from the functional illustration with magnification according to FIG. 3 that a polishing etching module 30 has flaps 31a and b which can be moved downwards and form a sealed basin with a bottom 32 below the transport path 14 and in cooperation with side walls (not shown) , After retracting the silicon blocks 17, the flaps 31 are driven down to produce the liquid-tight pool. Then, by means of the spraying devices 33, etching solution for polishing etching from a liquid tank 34 is applied to the silicon blocks 17, thereby filling the basin with a filling level beyond the blocks. Under certain circumstances, with a movement of the silicon blocks 17 in an intermittent manner, a predetermined period of time is awaited. About 25 μm are removed from the silicon material of the silicon blocks. Then, the etching solution is discharged and returned to the liquid tank 34, and then the flaps

31 moved up and transported the silicon blocks 17 on the transport path 14 to the right.

Behind the Polierätzmodulen 30 is a flushing module 37. This is similar to the cleaning module 16 and has a spray device 38 above the silicon blocks and, similarly as shown in Fig. 2, corresponding spray devices below the silicon blocks 17 fed the spray device 38 or is flushed with rinse water 41 from a rinse water tank 40 and fresh water from a fresh water connection 43. This can be done at least two stages as described with reference to FIG. 2 and the cleaning module. After the flushing module 37, the KOH process module 45 follows again with a similar structure as the cleaning module 16. It has spraying devices 46, advantageously both above and below the silicon blocks 17 and the transport path 14. These serve to dispense KOH etching solution 49 from a liquid tank 48, rinse water 51 from a rinse water tank 50 and fresh water from a fresh water connection 52. The process sequence is basically as described for the cleaning module, only the treatment times may vary. After the KOH process module 45, a drying module 55 is provided. Here, the flushed silicon blocks 17 are retracted by the KOH process and blown dry by means of fans 56 and air nozzles 57. At the top of the drying module 55 filters 58 are provided for filtering the air.

Behind the drying module 55 is an outlet module 60, with which the silicon blocks 17 are transported further for further processing after cleaning and drying.

For the method steps described above, an alkaline cleaning liquid from the prior art can be used. The etching solution for polishing etching may be a mixture of 49% HF solution and 69% HNO ₃ solution in a ratio of 1: 4 to 1: 7. The process temperature can be between 15 ° C and 25 ° C, ie essentially at room temperature. For the KOH process 5% KOH solution is used, also at a temperature of 15 ° C to 25 ° C. The cycle time for such a system can be about two and a half minutes. The etching time in each case during the alkaline cleaning as well as during polishing, in some circumstances also during the KOH process, can be about one and a half minutes.

The continuous transport path 14 is important and advantageous. The intermittent movement of the silicon blocks in the individual treatment modules is also advantageous in order to increase the exposure time or the process time. The rinsing in the rinsing module 37 therefore takes place separately from the polishing etching module 30, in order to increase the throughput in this process, which actually requires the longest process time, and also to prevent too much polishing etching solution 35 from entering the wastewater. This is less critical in the KOH process module 45.

Claims

claims

A method for processing or cleaning of Si blocks, wherein the Si blocks are transported on a continuous, horizontal transport path, wherein in a first step, an alkaline cleaning and rinsing of the Si blocks takes place and then in a second step Polishing etch, wherein the polishing etching an etching solution is brought from all four sides of the Si blocks, wherein after the polishing etch rinsing takes place once again.

2. The method according to claim 1, characterized in that in the first step is first cleaned alkaline with cleaning solution and then rinsed with water, preferably in a first treatment module of a plant.

3. The method according to claim 1 or 2, characterized in that after the first step of the alkaline cleaning or rinsing and after the second step of the polishing etching liquid is removed from the Si blocks or they are dried by air circulation or blowing off, preferably wherein liquid is completely removed.

4. The method according to any one of the preceding claims, characterized in that after the step of polishing etching, the etching solution is removed before a subsequent step for cleaning rinsing, wherein in particular the etching solution is removed by blowing off.

5. The method according to claim 4, characterized in that after the step of cleaning rinsing a KOH process step takes place, preferably as the last step with treatment liquid, in particular with subsequent cleaning rinse and preferably with final drying, wherein in the KOH process step KOH solution the Si blocks is brought.

6. The method according to any one of the preceding claims, characterized in that the step of cleaning rinse after the step of polishing etch in a treatment module for rinsing or via a collecting container is carried out separately from the treatment module for polishing etching.

7. The method according to any one of the preceding claims, characterized in that the transport or passage of the Si blocks along the transport path is not carried out continuously or at intervals or intermittently.

8. The method according to any one of the preceding claims, characterized in that during polishing the Si blocks are sprayed from above and from all four sides and from below with etching solution.

9. The method according to any one of claims 1 to 7, characterized in that the polishing etching is carried out by at least partial immersion of the Si blocks in etching solution, preferably complete immersion, in particular the Si blocks are introduced into a chamber of the treatment module for polishing etching, in particular at the same height of the horizontal transport path, wherein then the chamber is sealed laterally and downwardly and filled with etching solution for the duration of the step of polishing etch.

10. The method according to any one of the preceding claims, characterized in that rinsing with water of different purity occurs, preferably a last rinse in a rinsing sequence with fresh water and this is collected after rinsing and at the next rinsing sequence for a penultimate rinse before the last rinse is used, wherein preferably after spraying the Si blocks with the cleaning liquor rinsing first with water of the last rinse cycle of the previous rinsing sequence is carried out and then rinsed as a final rinse with fresh water, in particular for the last rinse less water is used as for the rinsing before.

11. The method according to any one of the preceding claims, characterized in that the etching solution for polishing etching, in particular the other treatment liquids are sprayed in a recirculating system on the Si blocks.

12. Plant with several treatment modules for carrying out the method according to any one of the preceding claims, characterized in that each separate treatment modules of the continuous system for the treatment of Si blocks are provided for the first step of pre-cleaning and the second step of the polishing etch and the other Step with the KOH process.

13. Plant according to claim 12, characterized in that for a rinsing step after the polishing and prior to the KOH process, a rinsing module is provided between these two and preferably after the treatment module for the KOH process, a drying module is provided with fans or drying agents.

14. Plant according to claim 12 or 13, characterized in that for a rinsing step after the first step with the alkaline cleaning and rinsing of the Si blocks and before polishing a rinsing module between these two is provided.