Device for electrochemically depositing a material on a plate- shaped substrate.

DESCRIPTION The invention relates to a device for electrochemically depositing a material on at least one side of a plate-shaped substrate having a circumferential edge, said device comprising an electrolytic bath with an electrolytic solution therein, which electrolytic bath has at least one inlet opening and at least one outlet opening for feeding and discharging the electrolytic solution to and from the electrolytic bath, respectively, a substrate holder for positioning the substrate in the electrolytic bath such that the substrate is connected as a cathode, an anode arranged in the electrolytic solution opposite the substrate, and a screening member between the anode and the substrate for screening the substrate locally at the circumferential edge of the substrate. The invention relates more in particular to the application in wafers for the manufacture of semiconductor components such as transistors, diodes, or microprocessors. Even more specifically, the invention is specially aimed at the deposition of so-termed bump, stud, pad, and/or redistribution metal layers of, for example, nickel, gold, palladium, silver, lead, tin, and copper on wafers during the so-termed back end processing in the semiconductor component manufacturing process. Examples of such processes and the devices used therein are described in, for example, US 6,132,587, WO 2005/042804 A2, WO 2004/072331 A2, and WO 2004/081261 A2. De device according to the opening paragraph corresponds to the device as described in the publication mentioned last above and shown in figure 6 therein.

A problem that arises in the electrolytic deposition of material on at least one side of a plate-shaped substrate, also referred to as electroplating, as can be performed by the device of WO 2004/081261 A2, is formed by the so-termed "dog bone" effect, which results in a non-uniform thickness of the layer of material deposited on the substrate. More in particular, the thickness of the layer of material may be greater at the circumferential edge of the substrate owing to a higher density of the field lines and resulting stronger currents flowing in that location between the anode and the substrate. To offer a solution to this problem, WO 2004/081261 A2 describes the use of a regulating plate 232 adjacent the substrate, which is a wafer

W, between this wafer and the anode 214. A central hole is provided in this regulating plate whose diameter is smaller than the diameter of the wafer, so that the circumferential edge of the wafer is screened to a certain extent. Although the regulating plate does lead to better results as regards the uniform thickness distribution of the deposited layer of material compared with the situation in which the regulating plate is not present, it still remains difficult, if not downright impossible, to realize an even electric field by which a uniform thickness of the deposited layer of material is achieved.

Between the regulating plate 232 and the anode 214, furthermore, there is provided an annular nozzle pipe 220 comprising a number of nozzles 222 that are aimed at the centre of the wafer, through which nozzles electrolytic solution is propelled to the substrate via the central passage in the regulating plate 232. Upon reaching the centre of the substrate, the direction of flow is deflected radially to the outside along the surface of the substrate so as to promote a continuous supply of electrolytic solution to the substrate.

The present invention has for its object to provide a device with which it is possible in a comparatively easy manner to create a uniform electric field between the anode and the substrate such that the "dog bone" effect is avoided without any adverse effect on the possibility of continuously and efficiently supplying and discharging the electrolytic solution to and from the substrate. To achieve this, the present invention is characterised in that the screening member is tubular in shape, while at least one flow passage is provided in the wall of the tubular screening member, which passage can serve as the inlet opening or as the outlet opening for the electrolytic solution. The tubular shape of the screening member renders it possible to capture the field lines present therein and align them parallel to one another such that an even supply of metal ions is achieved so as to prevent said "dog bone" effect. The provision of at least one flow passage, which can serve as the inlet opening or the outlet opening, in the wall of the tubular screening member achieves that the supply and discharge of the electrolytic solution to and from the substrate is not hampered by the tubular screening member.

Preferably, the tubular screening member has a centerline that is oriented perpendicularly to the substrate, so that also the field lines extending between the anode and the substrate will tend to be oriented perpendicularly to the substrate.

In order to be able to expose the substrate fully to the field lines, i.e. also the region between along the circumference of the substrate, the tubular screening member preferably surrounds the substrate.

As a further measure for "aligning" the field lines, it is highly advantageous if a distributor body is provided between the anode and the substrate for homogenizing field lines that extend between the anode and the substrate, or for evening out the electric field between the anode and the cathodic substrate.

It is to be preferred, for this very purpose of distributing the field lines as homogeneously as possible and thus also the currents that flow between the anode and the substrate, that the distributor body is constructed so as to be plate- shaped with a number of passages for the field lines, wherein more preferably said passages are regularly distributed.

The distributor body in this case is preferably connected to the tubular screening member, so that the screening member serves not only for aligning the field lines, but also for fastening the distributor body in the device, i.e. no separate provisions need be made for this purpose, which provisions could give rise to disturbances of the electrical and physical flows within the electrolytic bath.

Preferably, furthermore, the distributor body has a diameter that is at least as large as the diameter of the tubular screening member. The distributor member is thus suitable for closing off the tubular screening member, either inside the tubular screening member or outside the latter at one end of the tubular screening member, such that all flows of liquid and field lines are forced to run through the passages in the distributor body, and the electrolytic process can be satisfactorily controlled in this manner. Preferably, furthermore, the distributor body has a circumferential edge that adjoins the inner side of the tubular screening member, so that the distributor body is not any larger than is necessary for achieving the advantages mentioned above.

It is further preferred that the distributor body is provided at an extremity of the tubular screening member; however, this does not exclude that the distributor body is provided Gust) inside the tubular screening member, so that the length of the tubular screening member can be optimally utilized while the dimensions of the electrolytic bath can remain limited in this manner.

In order to prevent field lines from scattering in a region between

the tubular screening member and the substrate, which would still involve a risk of the "dog bone" effect mentioned above arising, the tubular screening member adjoins the substrate in a particularly important embodiment. This matching connection may be effected at the circumference of the substrate as well as on the at least one side of the substrate.

Although the at least one flow passage may in principle act either as the inlet opening or as the outlet opening within the framework of the present invention, it is preferred that the at least one flow passage acts as the inlet opening. This renders it possible to supply an electrolytic solution of high quality, i.e. with few impurities, to the substrate in that said electrolytic solution is subjected to a cleaning treatment, for example by means of a filter, immediately or at least shortly before it is moved through the flow passage.

The flow passage here preferably has an exit flow direction that is directed at least substantially parallel to the substrate. This offers the possibility of introducing electrolytic solution into the immediate vicinity of the entire surface area of the at least one side of the substrate, so that an optimum deposition of material on the at least one side of the substrate can be realized. A strong renewal of the electrolytic solution at the surface of the substrate is generated thereby, and any gas bubbles that are evolved in some plating processes are driven out. In the case of an at least substantially disc-shaped substrate, it is furthermore preferred in general that the at least one flow passage has an exit flow direction that has at least a radial component relative to the disc shape of the substrate, and more preferably that the at least one flow passage has an exit flow direction that has a tangential component relative to the disc shape of the substrate. Exit flow directions thus orientated provide further improved possibilities for serving the at least one longitudinal side of the plate-shaped substrate as fully as possible with electrolytic solution that is supplied to the substrate via the at least one flow passage.

Especially in view of the advantage last mentioned above, it is furthermore preferred that a plurality of flow passages is provided, evenly distributed over the wall of the tubular screening member.

The positive effects of the provision of the at least one flow opening in the tubular screening member are especially noticeable if the distance between the at least one flow passage and the substrate measured in a direction

perpendicular to the substrate is at most 15 mm.

The positive effects of the tubular screening member itself on the

"alignment" of the field lines are especially obtained in a further preferred embodiment in which the distance between the substrate and the extremity of the tubular screening member located at the side of the anode is between 20 mm and

100 mm.

According to a particularly preferred embodiment, the at least one inlet opening and the at least one outlet opening are mutually positioned such that the electrolytic solution flows at least for the major part from the substrate in the direction of the anode. This creates the unique condition that the liquid flow of the electrolytic solution is opposed to the direction of the electric current, which flows from the anode to the cathode, i.e. to the substrate.

To further stimulate the "alignment" of the filed lines, the tubular screening member is preferably made of a dielectric material. The dielectric material is advantageously a plastic.

The invention will be explained in more detail below by means of a description of the preferred embodiment thereof, which is schematically depicted in a vertical cross-section in the accompanying figure.

The device 1 representing a preferred embodiment of the invention comprises an electrolytic bath 2 with an electrolytic solution 3 therein. The electrolytic bath 2 essentially consists of two parts, i.e. an electrolytic part 4 and an overflow part 5, which parts 4 and 5 are separated from one another by a partition wall 6 in the electrolytic bath 2. A discharge line 7 and a feed line 8, arranged in the overflow part 5 and in the electrolytic part 6, respectively, are provided in the bottom 27 of the bath 2. Electrolytic solution 3 can leave the bath 2 through the discharge line 7, while electrolytic solution 3 can be supplied to the bath 2 again through the feed line 8. For this purpose a circulation line 9 with a pump 10 accommodated therein is arranged between the discharge line 7 and the feed line 8 outside the bath 2. In addition, cleaning means, such as a filter, are included in the circulation line 9 upstream or downstream of the pump 10. The liquid level in the electrolytic part 4 of the electrolytic bath 2 is higher than the partition wall 6 owing to the action of the pump 10, so that electrolytic solution 3 will flow over the partition wall 6 at the location of reference numeral 11 into the overflow part 5 of the electrolytic bath 2, where by contrast the liquid level is lower than the partition wall 6.

A dielectric tubular screening member 12 is provided in the electrolytic part 4, which member is composed of various components that are to be described in more detail below. The length of the screening member 12 (reference numeral 30) is approximately 50 mm. Furthermore, an anode basket 13 is present in the electrolytic part 4 of the electrolytic bath 2 for receiving an anodic material (not shown in any detail) therein from the upper side, for example in the form of balls. Such anode baskets are well known to those skilled in the art. A substrate holder 14 is further provided in the electrolytic part 4 of the electrolytic bath 2, which holder 14 serves to position a disc-shaped substrate 15, having a side 28 of which a material is to be electrochemically deposited by means of the device 1. The substrate 15 is present at the side of the substrate holder 14 facing the screening member 12. The exact construction of the substrate holder 14 is not relevant to the present invention. Substrate holders in a wide variety of designs are known to those skilled in the art.

The device 1 further comprises a rectifier 16 whose positive side 16a connects to the anode basket 13 and thus to the anodic material contained therein, and whose negative side 16b connects to the substrate 15.

The screening member 12 is at least substantially built up from a number of tubular or annular segments made of plastic such as PP or PEEK that together form the tubular screening member 12. More in particular, these are, viewed in the direction from the substrate holder 14: a sealing ring 17 with a circumferential rubber gasket 18, a flow tube 19, an exchange tube 20, and a retaining ring 21 for retaining a distributor plate 22 in the screening member 12. An annular chamber 23, into which the feed line 8 discharges, is present in the screening member 12. The flow tube 19 further comprises, as viewed in circumferential direction and at regular distances from one another, a number of discharge channels 24 that extend between the annular chamber 23 and the inner side of the flow tube 19. The centerlines of the discharge channels 24 in the present embodiment are oriented parallel to the substrate 15 and are radially directed at the centerline 25 of the tubular screening member 12. The distance (referenced 29) in axial direction between the discharge channels 24 and the substrate 15 is approximately 5 mm. The liquid flow in the electrolytic bath 2 is directed from the substrate 15 towards the anode basket 13, i.e. the liquid flows from right to left in the figure through the bores 26 (yet to be described) in the distributor plate 22.

Alternatively, it would be quite possible within the scope of the present invention to give the centerlines of the discharge channels 24 also a tangential component with respect to the disc-shaped substrate 15, so that electrolytic solution 3 entering the interior of the tubular screening member 12 through the discharge channels 24 cover as it were the entire surface area of the longitudinal side 28 where anodic material is to be deposited on the substrate 15.

The exchange tube 20 can be replaced by a similar exchange tube of different axial dimension, for example if it is desirable for technological reasons in a process to give the tubular screening member 12 another axial length. The retaining ring 21 , finally, is primarily designed to position the distributor plate 22 in the tubular screening member 12. If so desired, the retaining ring 21 may also be readily replaced together with the distributor plate 22 by a different combination of retaining ring and another distributor plate, should this other retaining plate 22 be required for some reason. A large number of bores 26, whose centerlines are oriented parallel to the centerline 25 of the screening member 12, are provided in the distributor plate 22. The distributor plate 22 screens off the anodic material in the anode basket 13 from the substrate 15 to a certain extent. Owing to the regularly distributed bores 26, field lines extending between the anodic material and the substrate 15 will have a very strong tendency to distribute themselves homogeneously within the screening member 12 between the distributor plate 22 and the substrate 15. The tubular screening member promotes a parallel orientation of the field lines parallel to the centerline 25 between the distributor plate 22 and the substrate 15. The electric field within the tubular screening member 12 is thus evened out as much as possible. This is the optimum situation for obtaining also an even distribution of the deposit of anodic material on the substrate 15, so that obviously the thickness of this deposit is also distributed as homogeneously as possible over the surface of the substrate 15. This is important in particular if, after the electrolytic deposition process by means of the device 1 , the substrate 15 is split up into individual parts that are required to have the same properties.