Method and device for treating silicon wafers

A method and device for treating silicon wafers. In a first step, the silicon wafers (22) are conveyed flat along a continuous, horizontal conveyor belt (12, 32) and nozzles (20) or the like spray an etching solution (21) from the top onto the wafers to texture them, only little etching solution (21) being applied to the silicon wafers (22) from below. In a second step, the silicon wafers (22), which are aligned as in the first step, are wetted exclusively from below with the etching solution (35) to etch-polish them.

FIELD OF APPLICATION AND PRIOR ART

The invention relates to a method and also a device for treating silicon wafers, in particular for texturing and polish-etching with etching solution.

It has been known practice hitherto to etch away approximately 5 μm from silicon wafers using etching solution from both sides of the silicon wafers. It is thereby possible, firstly, to eliminate sawing damage. Furthermore, it is possible to produce a textured top side, which is significant for the performance of the solar cell produced from the silicon wafer. Furthermore, the underside should be as smooth and lustrous as possible in order that light which has passed through is reflected and its energy can be utilized in the course of return travel.

OBJECT AND HOW IT IS ACHIEVED

The invention is based on the object of providing a method mentioned in the introduction and also a device mentioned in the introduction for carrying out the method with which problems in the prior art can be solved and, in particular, an advantageous further development is possible and also improved and efficient etching of the silicon wafers.

This object is achieved by means of a method of treating silicon wafers, the method comprising the steps of transporting the silicon wafers in a horizontal position along a horizontal transport path. The texturing etching solution for texturing the silicon wafers is applied or sprayed on from above during transport by means of nozzles or the like, while little or no texturing etching solution is applied to the silicon wafers from below. In a second method step, the silicon wafers, with the same orientation as in the first method step, are wetted with a polish etching solution for polish-etching from below. The object is also achieved by a device for carrying out the method. The device has a texturing module for texturing the silicon wafers by applying or spraying on said texturing etching solution from above onto said top side of the silicon wafers. The device also has a horizontal transport path with tranport rollers or the like, and also nozzles or the like for applying or spraying the texturing etching solution. Advantageous and preferred embodiments of the invention are explained in greater detail below. Although some features of the device are described principally in connection with the method, they simultaneously serve for elucidating the device and are generally applicable thereto. Furthermore, the wording of the priority application DE 102007063202.0 of Dec. 19, 2007 in the name of the same applicant is incorporated by express reference in the content of the present description. The wording of the claims is incorporated by express reference in the content of the description.

According to the invention, it is provided that, in a first method step, the silicon wafers are transported in a horizontal position, to be precise along a horizontal transport path. Etching solution for texturing is applied or sprayed on from above, for which purpose nozzles, surge pipes or the like can be used, which are known per se for such a purpose. From below the silicon wafers, either no liquid at all or only little liquid is applied to the silicon wafers or the underside thereof in this method step. At all events, no etching liquid is sprayed on or the like from the underside. For this purpose, a device embodied in a correspondingly suitable manner can have, above the transport path, said nozzles or surge pipes or the like for wetting the top side. Below the underside, such nozzles or the like are not provided at all.

In a later or second method step, the silicon wafers, in the same way or with the same orientation as in the first method step, in a horizontal position on the transport path, are wetted with etching solution for polish-etching from below. Advantageously, in this case the etching solution is actually applied exclusively from below and also exclusively to the underside. This is because precisely if transport rollers or the like are used for the transport path, in the first method step some etching solution from above can also pass onto said transport rollers and then be transferred to the underside of the silicon wafers by the transport rollers. Since this is a manageable amount, however, the etching effect can remain very small here. It can even be advantageous, for example in preparation for the second method step.

In this way, approximately 4 μm to 6 μm of material, preferably approximately 5 μm, can be removed in a first method step for eliminating the sawing damage and for texturing the top side. The method duration can here be approximately 80 to 120 seconds. In this case, the silicon wafers are advantageously moved in a continuous fashion or moved through a corresponding texturing module on the transport path.

In the first method step, approximately 2 μm of material is removed or etched away on the underside. As a result, here as well, a portion of the sawing damage has already been eliminated, while surface texturing, which is undesired here, has not yet taken place correctly. After the method step of texturing, the silicon wafers can be rinsed, advantageously with water.

The etching solution used for the first method step can be a customary etching solution for texturing, preferably comprising a mixture of HF and HNO3. In the first method step or when the latter is carried out in the texturing module, etching solution for texturing can be applied in a plurality of regions successively along the transport path. For this purpose, a plurality of groups of nozzles or the like for spraying on the etching solution are advantageously provided successively, advantageously on surge pipes or the like running transversely with respect to the transport path. This, too, is known in principle.

The texturing module is advantageously provided with a collecting trough below the transport path, such that etching solution that runs away can be collected and reused. Said rinsing of the silicon wafers after wetting with etching solution in the first method step in the texturing module is advantageously effected in said texturing module, particularly advantageously at the end thereof. A section of the texturing module can be embodied for rinsing with water, wherein a collecting trough is provided here separately from the collecting trough for etching solution, for the purpose of separating the two liquids in order that a reduced cleaning outlay arises. The intensity of rinsing with water on the silicon wafers, that is to say the amount of water, can be considerably greater than that for wetting with etching solution.

Advantageously, the silicon wafers move after the first method step or from the texturing module directly to the next or second method step, which takes place in a polish-etching module. Here etching solution for polish-etching is applied, wherein the silicon wafers are in any event transported in a continuous fashion on a transport path through the polish-etching module. The silicon wafers are wetted exclusively at their underside. This can be effected, in one instance, by slight spraying from below. A method and also a device in the polish-etching module in accordance with DE 10 2005 062 528 A1, to which reference is explicitly made, are advantageously used for this purpose. In this case, transport rollers for the silicon wafers are for the most part immersed in a bath containing the etching solution for polish-etching. Upon rotation, etching solution adheres to a top side and is then brought to the undersides of the silicon wafers, where it performs the polish-etching. An etching removal 3 μm to 10 μm can thus be achieved at the underside, thereby very good polish-etching is actually possible with a very good result with regard to a smooth and lustrous rear side. This method step can here last somewhat longer than in the preceding method step, and in particular can last approximately 200 seconds. Here as well, the etching removal can be determined by the method duration. The etching solution used for polish-etching is one similar to that used during texturing, although with a larger HNO3proportion. The etching processes can be carried out at room temperature, a temperature range extending from approximately 4° C. to approximately 40° C.

These and further features emerge not only from the claims but also from the description and the drawings, wherein the individual features can be realized in each case by themselves or as a plurality in the form of subcombination in an embodiment of the invention and in other fields and can constitute advantageous and inherently protectable embodiments for which protection is claimed here. The subdivision of the application into individual sections and sub-headings do not restrict the general validity of the statements made thereunder.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1illustrates a texturing module11with a transport path12, which is formed by a plurality of transport rollers13in a conventional manner. The texturing module11has a housing15containing a collecting trough16, and from the left an inlet18at the transport path12.

Above the collecting trough16and the transport path12, a plurality of surge pipes19are provided parallel to one another, which surge pipes can run transversely with respect to the transport path12. They have downwardly directed nozzles20which output etching solution21. Said nozzles20are also known per se to the person skilled in the art. They can be rigidly aligned or else movable. Furthermore, the nozzle20can also, under certain circumstances, be activatable individually or in groups in order to achieve a specific profile of the discharge of the etching solution21.

Silicon wafers22are transported on the transport rollers13in a horizontal position along the transport path12. The top sides23later form the front sides of solar cells, and the undersides24bearing on the transport rollers13form the rear sides of said solar cells.

As can be discerned fromFIG. 1, etching solution21is discharged only onto the top sides23of the silicon wafers22. Consequently, the texturing of the silicon wafers22or of the top sides23thereof is principally effected here in the first method step. In this case, it is clear, of course, that a certain amount of etching solution21overflows in particular over the front edges and their edges of the silicon wafers22and is then situated on the transport rollers13. Subsequent silicon wafers22lying on the transport rollers13are then wetted with this etching solution21on their underside24as well. However, the amount of etching solution21is considerably smaller here, such that considerably less etching is effected as well. Since, however, as is illustrated, the targeted application of the etching solution21from above is effected by means of the nozzles20, this is referred to as applying etching solution from above within the meaning of the invention.

It is possible to establish whether the nozzles20are, for example, arranged above the transport rollers13or oriented toward the latter, such that etching solution21is applied to the transport rollers13if there is not actually a silicon wafer22underneath, which intensifies the wetting of the undersides24of the next silicon wafers22with etching solution21. If the nozzles20are arranged or oriented differently, this effect is considerably weaker. Furthermore, this effect of etching at the underside can also be influenced by the targeted driving of the nozzles20or by a targeted discharge of the etching solution21onto the top sides23of the silicon wafers22.

In the texturing module11continued toward the right, the nozzle20illustrated on the far right can be designed not to output etching solution21, but rather water or rinsing water26. Etching solution21can thereby be cleaned from the silicon wafer22in this region for its top side23. The separator28is provided for this purpose in the collecting trough16, such that etching solution21that has dipped away is situated to the left of said separator and the rinsing water26admixed with a small proportion of etching solution is situated to the right of said separator. The number of successive surge pipes19with nozzles20for applying etching solution21can vary and be varied in accordance with the desired transport speed and method duration. Likewise, it is advantageously possible to provide a plurality of nozzles20for rinsing water26for rinsing the silicon wafers22.

FIG. 2illustrates a polish-etching module31. The latter also has a transport path32, which is the continuation of the transport path12fromFIG. 1. Likewise, the polish-etching module31is advantageously provided and installed relatively directly in succession with respect to the texturing module11. The transport path32is formed by transport rollers33. For a detailed description of the polish-etching module31, reference is primarily made to DE 10 2005 062 528 A1, which describes in detail how the etching solution35for polish-etching is brought from the bath37to the undersides24of the silicon wafers22by means of the transport rollers33. They serve, therefore, for transporting the wafers and for wetting the underside thereof. The etching solution35for polish-etching is as described above. It can also be discerned from the illustration ofFIG. 2that, in the second method step, no etching solution35whatsoever can pass onto the top side23of the silicon wafers22, but rather only to the undersides24. As can be seen inFIG. 2, the etching solution bath level can be between a center diameter level and a top level of the rollers.

The bath37has an outlet40between two supply pipes38, which introduce new etching solution35into the bath37. Said outlet, in addition to the lateral overflow over the edge of the bath37, ensures that etching solution35is exchanged in such a way that not only in the region of the exit of the supply pipes38is there fresh etching solution35, but the latter is also moved in the direction of the outlet40and, therefore, there as well can be brought to the undersides24of the silicon wafers22by the transport rollers33. In the method sequence of the treatment of the silicon wafers22, the polish-etching in the polish-etching module31is also followed by further rinsing, advantageously once again with water.

The polish-etching module31is also provided in a housing34. Extraction of vapors of the etching solutions can be provided, of course, in both modules.

The substrates are typically flat, planar silicon wafers22having a round contour with a diameter of approximately 60 mm to 250 mm or a rectangular contour with edge length of 60 mm to 250 mm. A preferred thickness lies in the range of 0.1 mm to 2 mm.