EP2430664A2

EP2430664A2 - Method and device for treating a wafer

Info

Publication number: EP2430664A2
Application number: EP10720400A
Authority: EP
Inventors: Werner Andreas Maurer
Original assignee: Gebrueder Schmid GmbH and Co
Current assignee: Gebrueder Schmid GmbH and Co
Priority date: 2009-05-13
Filing date: 2010-05-12
Publication date: 2012-03-21
Also published as: WO2010130786A2; WO2010130786A3; MX2011011985A; IL216309A0; CA2761459A1; KR20120018155A; AU2010247404A1; CN102439730B; JP2012526914A; SG175365A1; TW201108449A; US20120052611A1; CN102439730A; DE102009022337A1

Abstract

In a method for coating a wafer to produce solar cells, a metal such as nickel, copper, or silver is deposited on the wafer in a continuous process in a coating bath containing said metal. A wafer is inserted into the coating bath, and at a time at which a first area of the wafer already extends into the coating bath but a second area does not yet extend into the coating bath, a current surge is applied to the second area of the wafer to initiate the galvanic deposition of the metal on the first area of the wafer reaching into the coating bath for a subsequent further automatic coating, with the wafer completely inserted into the coating bath, also of the remaining area of the wafer without further current surge or current flow.

Description

Description Method and device for treating a wafer

Field of application and state of the art

The invention relates to a method for treating a wafer for producing solar cells in a continuous process in a coating bath as well as to a device or treatment installation suitable for carrying out this method.

It is known to apply chemically depositable metals to wafers for solar cell production by applying a voltage to the wafers. In this case, there are a multiplicity of electrical contact means for the solar cell wafers, for example as stationary wipers, moving contact rollers or the like. However, such electrical contacting can not always be carried out without the risk of mechanical damage to the solar cell wafer. Furthermore, it takes considerable effort to provide contact means for the entire length of the pass through a coating bath and to also maintain these, in particular to clean them.

Task and solution

The invention has for its object to provide an aforementioned method and an aforementioned device with which disadvantages of the prior art can be avoided and in particular Kontaktierungsprobleme can be reduced or avoided in practicable structure of a device for performing the method. This object is achieved by a method having the features of claim 1 and a device having the features of claim 1 1 or 12. Advantageous and preferred embodiments of the invention are the subject of further claims and are explained in more detail below. Some of the features listed below are mentioned only for the method or only for the device. However, they should be able to apply to both the process and the device independently. The wording of the claims is incorporated herein by express reference.

It is envisaged that metals, in particular copper, silver or nickel, or metal layers in general or metal structures are deposited on the wafer in the coating bath. According to the invention, in the method a wafer is introduced into the coating bath and, at a time when this wafer already reaches into the coating bath with a front first area while it does not yet reach into the coating bath with a rear second area, at this second area of the coating Wafers a short current impulse applied or a short current flow takes place to initiate an automatic deposition of the metal on the reaching into the coating bath first portion of the wafer. The first area must extend with top and bottom into the coating for the electrical contact. Said generation of a current surge or current flow can take place in different ways, as will be discussed in more detail below. The wafer is then driven further into the coating bath for a subsequent further coating respectively of the part or of the growing first region, which already reaches into the coating bath. For this further coating of exactly this wafer then no further current surge or current flow or no application of voltage is required. In particular, after the first short burst even in the situation that is not yet in the rear surface of the wafer should be larger than the coating bath, no further current surge or current flow is necessary. It has surprisingly been found in the context of the invention that a said short current surge is sufficient to initiate the deposition of the corresponding metal from the coating bath onto the wafer. After this abutment, the coating process runs automatically and does not need to be restarted or maintained by current flow. The duration of such a short current surge is advantageously a few seconds, more advantageously less than two seconds and may even be shorter than one second.

Depending on the manner in which the current pulse is generated, it can be achieved, in particular, advantageously that the current surge can occur in a region of the wafer, namely the second region, which is still always clean outside the coating bath and, so to speak, clean and free from chemical solvents during the process front first area is already in contact with the coating bath. Light sources or contact means or the like. need not be provided in the coating and thus not in contact with the chemistry, which significantly improves their training, operation and maintenance and simplifies. Because of the electrical conduction characteristics of a given wafer, the generation of a current surge at a second region of the wafer is sufficient to initiate the coating at another first region. Then it is automatically increasingly on the entire wafer when it is gradually retracted completely into the coating.

According to a basic embodiment of the invention, the application or generation of the short current impulse can be effected by irradiating the second region of the wafer with light. For this purpose, a correspondingly formed light source may be provided, for example, one or two line-like light sources transversely to the passage direction of the Wafer. Thus, the second region of the wafer, which is not yet located in the coating bath, is irradiated with light over as large a surface area as possible in order to achieve a sufficiently intense irradiation at high throughput speed in order to generate a sufficient current impulse.

The irradiation of the wafer with light or a contact can be done from one side. It can be done either from below with a mounted below the pass line light source or from above with a correspondingly mounted above the light source. Decisive criteria here can be, on the one hand, the space available at a coating plant and the question on which side of the wafer a metal separation should take place. A metal deposit on the underside of the wafer is considered to be advantageous since it can be held more easily in full contact with the treatment liquid or the coating bath in a continuous process. For the basic operation and also for the implementation of such an abutment of a metal deposit in a coating bath by irradiation, ie a light-induced metal deposition, reference is made to DE 43 33 426 C1 and EP 542 148 A1.

According to another basic embodiment of the invention, the short current impulse is generated by applying voltage to the second region of the wafer, that is to say no light-induced current surge, but rather electrical contacting. Corresponding contact means, which may be formed as known from the prior art and described in the introduction, are advantageously arranged outside the coating bath. They advantageously extend to just before the coating bath, so that on the one hand it is ensured that they do not come into contact with the coating bath in order to avoid the aforementioned problems. Even with a current surge through direct electrical contact, a very short current surge is sufficient with the - -

called time periods, so that the contact means do not have to extend over a particularly long length. So it is sufficient, for example, not particularly large wafers, if already immersed in the coating bath first area only a few inches of the second area still out, so that the contact means can rest here on the second area or lighting is done for the short surge. Particularly suitable contact means are circumferential contact rollers, as they are known for example from DE 10 2005 038 450 A1.

The contact means are advantageous only on the side to be coated of the wafer, particularly advantageous, as described above, on the lower side. So it is only here to provide contact means. The applied voltage is a negative polarity DC voltage on the lower side of the wafer.

According to a further embodiment of the invention, a current impulse can take place for so long or an irradiation with light or an application of voltage can be carried out until the wafer has completely moved into the coating bath. Then, the time during which the protruding second area can be reached is maximized. As described above, the time can also be chosen to be shorter, since it has been found within the scope of the invention that even very short current pulses can be transmitted with e.g. less than one second duration sufficient for the abutment of the coating.

In the coating bath, the wafer is guided in such a way that it is at least partially immersed with both sides, that is to say top and bottom, or wetted with the coating bath. Then the coating can begin. Of course, the wafer is advantageously completely immersed in the coating bath when it is completely retracted into the coating system. - -

One application of a metallic coating of a wafer by the method described herein, or in the device described herein, is to coat one side of the wafer for solar cells with elongated conductor fingers, for which nickel or copper are offered as metal. The exact structure to be produced is created by pretreating the wafer surface, as is well known.

These and other features will become apparent from the claims but also from the description and drawings, wherein the individual features each alone or more in the form of sub-combination in one embodiment of the invention and in other areas be realized and advantageous and protectable Represent embodiments for which protection is claimed here. The subdivision of the application into individual sections and subheadings does not limit the statements made thereunder in their generality.

Brief description of the drawings

Embodiments of the invention are shown schematically in the drawings and are explained in more detail below. In the drawings show:

Fig. 1 is a schematic side sectional view through a

Coating system with galvanic contacting for the initial current surge and

Fig. 2 is a similar sectional view of an alternative coating system with light sources for an initial surge.

Detailed description of the embodiments In Fig. 1, a coating system 11 is shown, as it may be formed according to a first variant of the invention. The coating system 11 has an outer tub 12 with an outer lock 25. In it is a coating trough 13 with the bath 14. The bath 14 has a corresponding coating liquid in which a metal is dissolved, for example, the aforementioned as copper, silver or nickel. Furthermore, a pump 15 is provided to pump out or overflowed coating liquid from the outer tub 12 into the coating trough 13, if necessary together with the cleaning step, filtering step and / or additional enrichment.

There is a transport path 16 provided by the coating system 11, which in the present case extends on a single continuous plane. The transport path 16 has a multiplicity of upper transport rollers 17 and a multiplicity of lower transport rollers 18 which are at least partially driven in order to transport a substrate or a wafer 28 to be described in more detail below. Furthermore, two cathodic rollers 19 are shown instead of lower transport rollers 18 otherwise arranged at this point. These cathodic rollers 19 are provided close to an inner lock 26 in the coating trough 13, which will be explained in more detail below. The cathodic rollers 19 are further connected to a power source 21 and its negative pole. The current source 21 is further connected with its positive pole to an anode 23 in the coating trough 13 and in the bath 14, respectively, to apply a voltage that may be generated by a DC rectifier, so that a current causing a coating then flows.

As regards the function, the wafers 28 are introduced from the left on the transport path 16, with their top side 29 related to this treatment step upwards and the corresponding bottom side 30 downwards. Shown are three wafers in - o -

three positions, namely the wafer 28a, the wafer 28b and the wafer 28c, representative of the respective position.

The wafer 28a or generally a wafer at this position is indeed already in the coating system 11, but even before the inner lock 26 to the coating 14 and before the cathodic rollers 19. So nothing is happening to him.

As soon as the wafer 28b on the transport path 16 comes into contact with the left cathodic roller 19, it is connected to the negative pole of the current source. However, no electricity can flow yet. If the wafer 28 passes through the inner lock 26 into the bath 14 and is wetted there on its underside 30, but also on its upper side 29, with the bath 14 and is thus connected via the anode 23 to the positive pole of the current source 21 flows a current and the galvanic coating with the metal from the bath 14 at the bottom 30 begins. If the right-hand cathodic roller 19 is not provided, then the wafer 28b is connected to both the left-hand cathodic roller 19 and the anode 23 only approximately as long as it has retracted approximately halfway into the bath 14. However, this is sufficient to initiate the coating as described above. Once the coating process has taken place, a temporary galvanic coating is started, which builds up a thin metal layer from the bath 14 on the underside 30. By appropriate chemical deposition or coating from the bath 14, the coating then continues to run with the metal. For this purpose, the bath 14 is designed accordingly. Because the left cathodic roller 19 is arranged outside of the bath 14, there are no problems with contamination or it is not coated with metal.

In order to ensure that not only the front region of the wafer 28 is galvanically coated, but also the rear and thus a normal If the entire coating is ensured, the right-hand cathodic roller 19 can be provided. This ensures that the wafer 28 is already completely running in the bath 14 as long as it is still connected to the current source 21 or as long as the galvanically enforced coating is running. For this purpose, the right cathodic roller 19 could also be arranged further to the left and close to the inner lock 26. Under certain circumstances, it is even possible to form the lower transport roller 18 directly on the inner lock 26 as a cathodic roller 19. In this case, the problem here is that the inner cathodic roller 19 is coated metallically and then cleaned accordingly. But this is justifiable for a good coating. At least the number of cathodic rollers 19 running in the bath 14 can thus be essentially limited to one.

Overall, with this arrangement, in which even arranged within the bath 14 cathodic roller 19 is disposed very close to the beginning of the coating or near the inner lock 26, a coating is galvanically initiated and then continued chemically.

In the position of the right wafer 28c, the latter is no longer connected to the power source 21, but is only guided by the transport rollers 17 and 18 on the transport path 16. Here then takes place only a chemical coating from the bath 14 on the bottom 30, but just continues to run smoothly by the abutment described above.

In a modified coating system 1 11 according to FIG. 2, an outer trough 112 is also provided with a coating trough 113 therein, which receives a bath 114. There is also provided a pump 115 for circulating. On a transport path 116 with upper transport rollers 1 17 and lower transport rollers 118, all of which are all the same, at least in each case inside or outside of the bath 1 14, wafers 128 are transported from left to right as shown in FIG. 1 in positions 128a, 128b and 128c.

Near the inner lock 126, light sources 132 are provided below the wafers 128, that is to say with the beam direction toward the lower sides 130. These may be formed, for example, in the form of fluorescent tubes or arranged in rows LED with emission direction upwards.

Although the very left wafer 128a has already passed through the outer lock 125 of the outer tub 112, it is not yet blasted with light and thus nothing is happening here.

The middle wafer 128b is irradiated on its underside 30 on its way from the left, coming from the left, with the right front area, so that the charge carriers already separate here. As soon as the wafer 128a with its right front region enters the bath 114 through the inner lock 126, the top 129 and bottom 130 are electrically connected to each other by the bath 114. In principle, similar to the above-described galvanic coating, a current flows which effects a galvanic metal coating from the bath 114 on the irradiated underside 130, since this has a negative potential. This galvanic coating runs as long as the bottom 130 is irradiated by the left light source 132 and thus also current flows. This means that, similar to the above-described electrical contacting with the left cathodic roller 19 according to FIG. 1, the left end region of the wafer 128 is no longer irradiated with light when it enters the bath 114. Therefore, in addition, the right light source 132 can be provided, which ensures that the wafer 128b is already complete and to some extent within the bath 114 for a galvanic metal deposition forced by current flow. However, the right light source 132 is not absolutely necessary. It causes similarly as explained for the right-hand cathodic roller 19, a longer illumination of the underside 130 of the wafer 128b for the galvanic buildup of a layer, in turn, then in turn, the chemical coating from the bath 114 continues fully and independently. In the position of the right wafer 128c, in turn, similar to that described for FIG. 1, a chemical coating continues to run automatically.

While the left light source 132 is relatively easy to dispose outside the bath 114 and should hardly cause any problems during operation, this is a bit more expensive for the right light source 132. To here possible sealing problems odgl. It could also be envisaged to make the coating trough 113 so transparent in the left-hand area and to arrange the left-hand light source 132 in such a way that it also radiates into the bath 114. Thus, it can also irradiate there the bottom 130, as shown by the right light source 132. Also possible here would be facilities such as mirrors or light guides or the like.

The cathodic rollers 19 may be designed differently, for example according to DE 10 2005 038 450 A1. With regard to the design of the light sources 132, reference is made to known prior art, for example DE 10 2007 038 120 A1.

A coating of nickel takes place on a front grid on a wafer 28, in which case it has been patterned by means of either chemical opening or laser structuring of the anti-reflection layer. Furthermore, a nickel coating can take place on a phosphorus-doped silicon wafer, in which case the nickel is deposited only thinly and serves as a conductive layer, in order subsequently to be reinforced with a galvanic coating. This subsequent galvanic coating can be done, for example, with silver or copper. Furthermore, it is just possible to operate both the current source 21 and the light sources 132 not continuously, but pulsed. Again, an improvement of the coating can be achieved, as it is known for example from the aforementioned DE 10 2007 038 120 A1.

Claims

- o ~ claims

A method for treating a wafer for solar cell production in a continuous process in a coating bath, wherein in the coating bath, metal such as nickel, copper or silver is deposited on the wafer, characterized in that a wafer is retracted into the coating bath and at a time, to the wafer already reaches into the coating bath with a first area and does not yet protrude into the coating bath with a second area, a brief rush of current occurs to initiate the automatic deposition of the metal on the first area of the wafer extending into the coating bath Wafers for a subsequent further coating with wafers fully retracted into the coating bath also on its remaining surface without further impulse or other activation from the outside.

2. The method according to claim 1, characterized in that the short current pulse is effected by irradiation of the second region of the wafer with light.

3. The method according to claim 2, characterized in that the irradiation of the underside of the wafer to be coated takes place with light from below.

4. The method according to claim 1, characterized in that the brief impulse occurs by applying voltage to the second region of the wafer, preferably arranged by outside of the coating bath contact means, in particular rotating contact rollers.

5. The method according to claim 4, characterized in that the contact means are provided before the coating bath on the side to be coated of the wafer to apply the voltage as DC voltage, wherein they are applied in particular with negative polarity on the lower side of the wafer.

6. The method according to any one of the preceding claims, characterized in that the wafer is wetted in the coating bath on both sides at least partially with the coating bath, preferably on both sides and completely immersed.

7. The method according to any one of the preceding claims, characterized in that the coating on the underside of the wafer takes place in the coating bath.

8. The method according to any one of the preceding claims, characterized in that a maximum of as long as an irradiation of the wafer with light or an application of voltage to the wafer takes place, as the wafer has not been fully driven into the coating bath.

9. The method according to any one of the preceding claims, characterized in that the duration of the current impulse is less than 5 sec, preferably less than 2 sec.

10. The method according to any one of the preceding claims, characterized in that in the coating with nickel or copper elongated conductor fingers are applied to the wafer, preferably on the underside of the wafer.

1 1. A device for carrying out the method according to any one of the preceding claims, characterized in that it comprises a coating bath having a passage path and a light source below or above the passage path for short-term irradiation of a retracting wafer with light for coating in the coating.

12. Device for carrying out the method according to one of claims 1 to 10, characterized in that it comprises a coating bath having a passage path and contact means below or above the passage path for short-term electrical contacting of a retracting wafer for coating in the coating bath.