WO2008131790A1

WO2008131790A1 - Process and apparatus for electrolytic metallization of treatment good

Info

Publication number: WO2008131790A1
Application number: PCT/EP2007/003747
Authority: WO
Inventors: Norbert BÜRGER; Lütke Notarp DIETMAR
Original assignee: Rena Sondermaschinen GmbH
Current assignee: Rena Sondermaschinen GmbH
Priority date: 2007-04-27
Filing date: 2007-04-27
Publication date: 2008-11-06
Anticipated expiration: 2009-10-27
Also published as: TW200848554A

Abstract

The invention relates to the electrical contacting of treatment good (1) that is to be electroplated using e.g. continuous pass equipment, immersion bath equipment, so called cup-platers or fountain-platers and the like. The electrical contacts for feeding-in the bath current to the surface that is to be electroplated are metallized together with the treatment good. The necessary de-metallization of the contacts occurs inside the same treatment chamber together with the electrolyte (10) that fills the same. In practice, this de-metallization does not occur completely. At the contact (2), in the region of the electrolyte/air boundary (10), a metal ring (19) develops that must be manually removed. According to the present invention, the natural electrolyte/air boundary at the contacts (2) is appropriately moved e.g. by a controlled air stream (12) against the flow direction or the surface of the electrolyte. The air stream is switched on and directed in a way such that the region of the electrolyte/air boundary (10) that develops during metallization is entirely immersed during de-metallization. As a result of this, the contacts are completely de-metallized. A metal ring (19) cannot develop.

Description

Process and apparatus for electrolytic metallization of treatment good

The invention relates to the electrolytic metallization of treatment good in electroplating devices that have at least one contact for the electrical contacting of the treatment good, in particular in continuous pass equipment, immersion bath equipment, so called cup-platers or fountain-platers and the like.

The surface of the good that is to be electrolytically treated as well as an anode are located within the electrolyte of a treatment chamber. The treatment good's surface that is to be electroplated is cathodically switched by means of at least one electrical contact and a bath current source. As a negative an undesired result, also the at least one contact is electrolytically metallized. This contact metallization has to be removed by an additional process step. Usually, this is achieved by using the same electrolyte for the de- metallization of the at least one contact against a cathodic auxiliary electrode.

Devices with such contacts for electroplating of wafers are disclosed e.g. in WO 99/16936 figure 4, DE 600 25 773 T2 figure 1, and US 6,001,235 figure 1. The contacts which are electrically connected with the bath current source vertically protrude from the electrolyte. During the processing of the treatment good, also the contacts are metallized up to the electrolyte/air boundary, or up to an at least partially present isolating layer. Since this isolation layer at the contacts is often subject to wear, this layer is often omitted. A further drawback of such a layer resides in the fact that an electrical isolation does not or not sufficiently adhere to the base material, which usually consists of an electrochemically inert material such as titanium or niobium. The unavoidable oxide formation at the surface of such metals is the reason for the insufficient adhesion of such an isolation layer to the contacts. The metallization of the metallic blank contact regions must thus repeatedly be removed during ongoing production. For this purpose, the contacts in the treatment chamber are switched anodically against a cathodic auxiliary electrode. During this electrolytic de- metallization it is observed that in the vicinity of the contact's electrolyte/air boundary only an incomplete removal of the metallized layer takes place. As a result and despite several interim de-metallization steps, more and more metal builds up on the contact in this border region more or less annularly. Additionally, crystals of the electrolyte used can be deposited in this region. Automatic de-metallization and cleaning of the contacts therefore is insufficient for an uninterrupted production. Every now and then, manual interventions for the removal of the interfering annular deposits are necessary.

The same problem of insufficient de-metallization occurs with electroplating devices that use horizontally positioned or tilted contacts that may also serve as supports for the good. A part of these contacts is wetted by the electrolyte streaming out of the treatment chamber. Therefore, the contacts that are permanently mechanically fixed with respect to the treatment chamber become metallized up to the electrolyte/air boundary. During the electrolytic de- metallization, the above described imperfect de-metallization and cleaning appears at this boundary.

Figure 1 of the accompanying drawings depicts a typical prior art electroplating device in form of a fountain-plater for the treatment of planar goods such as wafers or solar cells. Details in the region of an electrical contact are shown enlarged. The electrolyte 17 that streams into the treatment chamber 3 is fed in by a pump 4. Circularly, the electrolyte streams over an overflow edge 5 into a reservoir 6. The streaming electrolyte reaches both the bottom side 7 of the treatment good 1 that is to be electroplated and the contacts 2 that are arranged at contact mounts 14 that may also serve as supports for the treatment good. These contact mounts serve for the electrical connection to the contacts 2, and thus to the treatment good 1. The flow of the electrolyte 17 is represented by flow direction arrows 8. A soluble or insoluble anode 9 is arranged within the treatment chamber 3. For the depicted case of metallization, the treatment good 1 is being switched cathodic against the anode 9 by a bath current source 15. Accordingly, the wetted bottom side 7 of the treatment good 1 and the wetted region of the metallic blank contacts 2 are being electroplated by the electrolyte up to the electrolyte/air boundary 10. Depending on the electrolyte, in particular on its metal content, crystals can deposit at this boundary as well. After each or several metallization procedures, the contacts 2 must be electrolytically de- metallized and cleaned. For this purpose, they are poled anodic against a cathodically switched counter electrode. In this region of the contacts 2, however, the electrolytic de- metallization is incomplete. If no other measures are taken, only a few metallization and de-metallization procedures will cause the electroplating metal to grow on the contacts in the region of the electrolyte/air boundary 10 in an almost annular or stripe-shaped form. This disturbing deposition is subsequently referred to as metal ring 19 and usually has to be removed manually, thus interrupting the automatic production process.

A multiple extension of the de-metallization time probably could electrolytically dissolve the metal ring 19 to a large extent. However, this is associated with a loss of the system's production capacity and thus should be avoided. Another possibility of electrolytically dissolving or etching the metal ring 19 could be the increase of the circulated electrolyte flow volume during de-metallization. However, this would necessitate a more complex arrangement and cause the disadvantage of an increased drag-in of air into the electrolyte due to a pushed and therefore more disturbed flow.

The air affects the additives of the electrolyte, resulting in a disadvantageous rise of its consumption. However, since for the present invention the de-metallization time preferably is very short compared to the plating time, the temporary flow increase has only a minor influence on the electrolyte system.

The object of the present invention is to provide a method and an apparatus which overcome the above drawbacks of the prior art and ensure a complete de-metallization and cleaning of electrically non-isolated contacts of treatment chambers, even when these are fixed and invariably arranged with respect to said treatment chambers.

Accordingly, the method according to claim 1 and the apparatus according to claim 5 are provided. Preferred embodiments are subject matter of respective independent claims.

The at last one electrical contact for the power supply to the bottom side of the good is electrolytically de-metallized after one or several metallization procedures within the same electrolyte. In order to avoid an annular build-up of metal at the electrolyte/air boundary of each contact, the apparatus according to the present invention additionally comprises means that serve to move the electrolyte/air boundary at the contact and/or the surface of the electrolyte for metallization and de-metallization in relation to the natural electrolyte/air boundary. Thereby, the flow rate of the electrolyte can be nearly or exactly the same for both cases. For the movement of the electrolyte/air boundary, two preferred embodiments exist that are subsequently referred to as case 1 and case 2 and comprise said means in the form of at least one gas distributor that, preferably, has at least one valve 16 that can be opened, choked, or closed for controlling the gas stream 12 emanating from at least one opening or nozzle 18.

In case 1, the electrolyte and thus the electrolyte/air boundary in the vicinity of each contact is moved towards the treatment chamber by at least one gas stream, preferably an air stream, during metallization of the treatment good. In case of vertically arranged contacts, this can be achieved by a gas stream that is directed close to each contact against the surface level of the electrolyte inside the treatment chamber. In case of horizontally arranged or tilted contacts, the flow direction of the gas is pointed towards the approximate center of the treatment chamber, i.e. towards the natural flow direction at the surface of the electrolyte. In both cases, the electrolyte/air boundary is moved towards the treatment chamber.

The de-metallization of the anodically switched contact (s) then occurs without the good by a gas stream being shut off or choked, e.g. due to the valve 16 being shut off or choked. In this manner, the natural electrolyte/air boundary at each contact is moved from the original boundary position that exists during metallization to the outward direction. Therefore, each contact is completely wetted also in the critical boundary area by the electrolyte, and a total de- metallization takes place in the electrolytic cell that is spatially extended in absence of a gas stream.

In case 2, the displacement or movement of the electrolyte/air boundary at each contact during de-metallization takes place in the opposite direction. During the precedent metallization, the electrolyte that streams out of the treatment chamber over its overflow edge and along each contact is not affected or displaced, even though it may be sufficient to reduce the gas stream, e.g. by appropriately closing or choking the valve 16. Thus, a natural electrolyte/air boundary is formed at the contact. The de-metallization of the almost horizontally positioned or tilted and anodically switched contact again takes place without the good. Therefore, by means of a gas stream, the electrolyte/air boundary at each contact is displaced or moved from the treatment chamber towards the outside (the contact mount 14) , such that the electrolyte/air boundary at each contact reaches an area of the contact that has not yet been wetted during metallization. For nearly vertically arranged contacts, the gas stream is directed distant to the contacts against the level of the electrolyte in the treatment chamber in such a way, that the level rises at each contact and wets a region represented by the original natural electrolyte/air boundary at each contact. Again, a total electrolytic de-metallization takes place, since the contact's area that has to be de-metallized is entirely positioned within the electrolyte.

According to a preferred embodiment, the electrolyte/air boundary during de-metallization of the at least one contact is sufficiently moved by any of the following steps which can be performed alone or in combination, such that the boundary that is formed during previous metallization is entirely positioned within the electrolyte at least in the vicinity of the at least one contact: a) directing a gas stream in-line with the flow direction of the electrolyte at the contact or against the surface of the electrolyte; b) lowering the at least one contact for de-metallization into the electrolyte, e.g. by providing a temporary mechanical tiltability for each contact; c) locally applying electrolyte onto the at least one contact; d) elevating the level of the electrolyte by elevation of the overflow edge, e.g. by using mechanical blinds or the like; and/or e) elevating the level of the electrolyte by increasing its flow. The electrolytic de-metallization of the contacts can be carried out with a significantly higher current density than it is applicable for the metallization of the treatment good. Thus, the metallization time becomes short, e.g. 20 seconds in comparison to a metallization time of 10 to 30 minutes or longer .

According to the invention, the complete de-metallization and cleaning of each contact during each de-metallization allows for an uninterrupted automatic treatment of good in an electroplating device. For enhancement of the electrical and mechanical properties of the at least one contact that usually is made from oxidizing metals, its surface can be covered with an electrically conductive diamond layer and/or partially covered with an electrically insulating layer.

In the following, the present invention is described in more detail by referring to the schematic and not-to-scale figures 2 to 4.

Figure 2a shows in a detail a stretched contact during metallization of the treatment good according to case 1.

Figure 2b shows the situation during the de-metallization of the stretched contact.

Figure 3a shows in a detail an angled contact during metallization of the treatment good according to case 1.

Figure 3b shows the situation during the de-metallization of the angled contact.

Figure 4a shows in a detail an angled contact during metallization of the treatment good according to case 2.

Figure 4b shows the situation during the de-metallization of the angled contact. The invention solves the problem by a complete removal of the entire contact metallization 11 during each de-metallization process, thus a metal ring 19 even cannot develop. This is achieved by moving the electrolyte/air boundary 10 to different regions of the contacts 2 during metallization and de-metallization. These two regions are depicted by the detail views of a device or a treatment apparatus in figures 2 and 3 for the case 1, and in figure 4 for the case 2.

Figure 2a illustrates the situation during metallization of the good 1. The contact 2, having e.g. a circular or rectangular shape, contacts and supports the good. In case of a circular shape, the good rests on at least three contacts 2 over the treatment chamber 3. For quadratic or rectangular goods, usually more than three contacts are used for the contacting and carrying over the treatment chamber 3. Alternatively, the treatment chamber can comprise only one support that is substantially ring-shaped and located close to the inner tank wall (not shown) . The electrolyte 17 that is delivered by a pump (not shown) streams along the bottom side 7 of the good 1, and from there over the overflow edge 5 in an only partially visible reservoir 6. Due to the electrolyte 17 that streams out of the treatment chamber 3, a natural electrolyte/air boundary 10 develops more or less diffusely in the border region of the good 1 and therefore close to the overflow edge 5. This boundary and thus also the region of the contact that is metallized during each metallization step up to the electrolyte/air boundary 10 is, during electroplating, displaced in direction of the center of the treatment chamber 3 by means of at least one gas stream 12 that preferably is an air stream. For each of the device's contacts, the air stream 12 emanates from at least one individual opening or nozzle 18, that is arranged at gas distributors 13, preferably at gas distribution pipes. The gas distributors 13 are fed e.g. with compressed air by at least one compactor or compressor (not shown) . By using a not depicted controlling device, the air stream 12 can be controlled and therefore switched on, choked, and turned off by means of a valve 16, a flap or the like. At least for each treatment chamber, the emanating gas or air, respectively, can be controlled collectively in groups. This purpose is served by the flaps or valves 16 that are located between the compressor and the nozzles 18.

Amount and velocity of each emanating air stream are adjusted in a manner such that the electrolytic de-metallization that follows metallization without gas stream 12 results in a complete de-metallization and cleaning of the contacts within the shortest possible time. In case of using almost horizontally arranged or tilted contacts, the electrolyte/air boundary 10 during metallization is sufficiently moved back towards the center of the treatment chamber 3, such that, during subsequent de-metallization with the gas stream being choked of shut off, the electrolyte/air boundary formed during metallization is entirely positioned within the electrolyte. During de-metallization with the air stream choked or shut off the electrolyte/air boundary 10 is shifted in direction of the contact. This natural boundary is then located in the region of the contact 2 that was not metallized or contaminated during metallization, because it stayed dry due to the air stream 12. Therefore, a complete de-metallization of each contact is achieved in each de-metallization process.

In case of using vertically arranged contacts, the gas stream is directed against the surface of the electrolyte during metallization, so that the level of the electrolyte inside the treatment chamber 3 is lowered at least in the vicinity of the contacts, also resulting in a displacement of the electrolyte/air boundary 10.

Figure 2b illustrates the situation at the beginning of the de-metallization of the contact metallization 11 with the air stream 12 being shut off. The electrolyte/air boundary 10 that develops naturally has been shifted outwards. The contact metallization 11 is completely positioned within the electrolyte enabling its complete electrolytic dissolution. Eventually formed crystals are also dissolved by the electrolyte stream. Even after many metallization and de- metallization processes, a metal ring 19 cannot develop at the at least one contact .

Figures 3a and 3b relate to case 1 and show details of a similar electroplating device with both process situations (metallization in figure 3a; de-metallization in figure 3b) .

In this case, the contact mount 14 is arranged above the highest level of the electrolyte 17. Thus, the electrolyte cannot spread itself up to the contact mount 14 when the air is shut off.

Figure 4a relates to case 2 and shows an angled contact 2 during electrolytic metallization. The electrolyte streams over the overflow edge 5 of the treatment chamber 3 into the reservoir 6. This gives rise to the development of the natural electrolyte/air boundary 10 at the depicted region of the angled contact 2. For complete de-metallization and cleaning of the contact from the contact metallization 11, this boundary has to be entirely positioned within the electrolyte during de-metallization. This preferably takes place by means of at least one gas stream 12 directed in-line with the streaming electrolyte, as e.g. exemplified in figure 4b. In absence of a good inside the treatment chamber, a gas stream 12 emanates from at least one nozzle 18 and causes the electrolyte or the electrolyte stream, at least in the vicinity of the contacts 2, to be displaced in a manner such that the newly developing electrolyte/air boundary 10, in relation to the original natural electrolyte/air boundary, is moved against gravity, i.e. outwards. This region of the contacts was not reached by the electrolyte during metallization and therefore not metallized.

For the de-metallization of vertically arranged contacts, the at least one gas stream is directed against the surface of the electrolyte such that the level of the electrolyte within the treatment chamber 3 rises at least in the vicinity of each contact, thereby elevating the electrolyte/air boundary 10. In case of almost horizontally arranged contacts, the gas stream is also directed almost horizontal in direction of the contact mount 14, as depicted in figure 4b. Due to the different electrolyte/air boundaries 10 upon metallization and de- metallization, a complete de-metallization and cleaning of the contacts 2 is obtained in each de-metallization process.

De-metallization usually takes place against a counter electrode that is used as an auxiliary electrode. In figures 2, 3 and 4, the counter electrode (not shown) can also be the soluble or insoluble anode that is located within the treatment chamber 3. For this processing, the anode is cathodically switched against the contacts 2 that are to be de-metallized. Thus, the metal that has been dissolved from the contacts 2 and deposited onto the anode, can usefully be recycled. During the next electroplating process, it is re- dissolved from there and used for metallization of the good 1.

The invention is suitable for all typical electrolytic devices and for all planar goods such as wafers, solar cells, circuit boards, and hybrids. Furthermore, all metals that are suitable for electrolytic depositing and dissolving can be used, e.g. such as copper, nickel, tin, and silver. List of reference marks

1 treatment good

2 contact

3 treatment chamber 4 pump

5 overflow edge

6 reservoir

7 bottom side of good

8 flow direction arrow 9 anode

10 electrolyte/air boundary

11 contact metallization

12 gas stream, air stream

13 gas distributor, gas distributor pipe 14 contact mount

15 bath current source

16 valve

17 electrolyte

18 opening, nozzle 19 metal ring

Claims

1. Process for the electrolytic metallization of treatment good (1) in electroplating devices that have at least one contact (2) for the electrical contacting of the treatment good, wherein said at least one contact (2) is partially immersed in an electrolyte and comprises at least one surface area that, in the region of the electrolyte, is at least partially not electrically isolated, characterized in that the electrolyte/air boundary (10) that is naturally formed at the at least one contact (2) during electrolytic metallization of the good and the contact, or during electrolytic de-metallization of the at least one contact, is moved.

2. Process according to claim 1, characterized in that, during metallization, the electrolyte/air boundary (10) at the at least one contact (2) is sufficiently moved back at least in the vicinity of said contact by means of at least one gas stream (12) that is directed against the natural flow direction of the electrolyte or to the surface of the electrolyte at the contact, such that, during subsequent de-metallization of the at least one contact (2) with the at least one gas stream being choked or shut off, the electrolyte/air boundary (10) formed during metallization is entirely positioned within the electrolyte. 3. Process according to claim 1, characterized in that, during de-metallization of the at least one contact (2), the electrolyte/air boundary (10) at the at least one contact (2) is sufficiently moved by (a) means of at least one gas stream (12) that is directed in-line with the flow direction of the electrolyte at the at least one contact or against the surface of the electrolyte, (b) lowering the at least one contact into the electrolyte, (c) locally applying electrolyte onto the at least one contact, (d) elevating the level of the electrolyte by elevation of the overflow edge, and/or (e) elevating the level of the electrolyte by increasing its flow, such that the natural electrolyte/air boundary (10) that is formed during previous metallization is entirely positioned within the electrolyte at least in the vicinity of the at least one contact (2) .

4. Method according to any of claims 1 to 3, characterized in that the at least one contact is arranged at a contact mount (14) and that the electrolyte is sufficiently moved back from the at least one contact (2), such that, during metallization, a wetting of the contact mount (14) is also avoided.

5. Apparatus for the electrolytic metallization of treatment good (1) in electroplating devices that have at least one contact (2) for the electrical contacting of the treatment good, wherein said at least one contact (2) is partially immersed in an electrolyte and comprises at least one surface area that, in the region of the electrolyte, is at least partially not electrically isolated, characterized in that the apparatus further comprises at least one means to move the electrolyte/air boundary (10) that is naturally formed at the at least one contact (2) during electrolytic metallization of the good (1) and the contact, or during electrolytic de-metallization of the at least one contact β. Apparatus according to claim 5, characterized in that said means are selected from the group consisting of (a) at least one gas stream (26) , (b) means to lower the at least one contact into the electrolyte, (c) means to locally apply electrolyte onto said at least one contact, (d) means to elevate the overflow edge, and/or (e) means to elevate the level of the electrolyte by increasing its flow.

7. Apparatus according to claim 5 or 6, characterized in that said means to move the electrolyte/air boundary is at least one gas distributor (13) with at least one opening (18) being located at and directed to the at least one contact (2) and/or the surface of the electrolyte (24) contained in the treatment chamber (3) in such a manner that the electrolyte/air boundary (10) at the at least one contact is movable in relation to the natural electrolyte/air boundary by means of the gas stream (12) emanating from each opening (18) .

8. Apparatus according to claim 6 or 7, characterized in that it further comprises a valve (16) to control the gas stream (12), wherein the valve is open towards the treatment chamber (3) during metallization of the treatment good in order to move the natural electrolyte/air boundary .(10) at the at least one contact (2), and wherein the valve is closed or choked during the subsequent electrolytic de- metallization of the at least one contact (2) .

9. Apparatus according to claim 6 or 7, characterized in that it further comprises a valve (16) to control the gas stream

(12), wherein the valve is open from the treatment chamber (3) towards the outside during de-metallization of the at least one contact (2) in order to move the natural electrolyte/air boundary (10) at the at least one contact (2), and wherein the valve is closed or choked during electrolytic metallization of the good (1) and the at least one contact (2) .

10. Apparatus according to any of claims 5 to 9, characterized in that it further comprises a soluble or insoluble anode (9) that also serves as a counter electrode during the de- metallization of the at least one contact (2) .

11. Apparatus according to any of claims 5 to 10, characterized in that the at least one contact (2) has a surface that is covered with an electrically conductive diamond layer and/or partially covered with an electrically insulating layer.

12. Apparatus according to any of claims 5 to 11, characterized in that the at least one contact (2) is arranged at a contact mount (14) that is positioned above the level of the electrolyte located inside the treatment chamber (3) .