KR100900608B1 - Method of wafer plating - Google Patents

Abstract

assignment

The present invention provides a wafer plating technique in which the plated film thickness on the entire surface of the wafer to be plated is uniform.

Resolution

The wafer is placed in the opening of the plating bath, the plating solution is supplied by bringing the outer peripheral side of the wafer into contact with the cathode electrode so that the plating solution that reaches the wafer flows in the outer circumferential direction of the surface to be plated of the wafer and faces the wafer in the plating bath. In a wafer plating method in which a plating current is supplied to a wafer by supplying a plating current by the disposed anode electrode and the cathode electrode, the anode electrode has a shape substantially the same as the surface to be plated of the wafer, and a plurality of peripheral edges of the anode electrode are provided. The peripheral edge current supply part was provided, and the central current supply part was provided at the center of the anode electrode to adjust the peripheral edge plating current supplied from the peripheral edge current supply part and the central plating current supplied from the central current supply part.

Wafer, Plating Bath, Cathode Electrode, Anode Electrode, Plating Solution, Plating Current

Description

Method of wafer plating

1 is a schematic cross-sectional view of the cup plating apparatus according to the present embodiment.

2 is a plan enlarged schematic view of the anode electrode.

3 is a plan view showing a film thickness measurement unit on a wafer to-be-plated surface.

4 is a plan enlarged schematic view of the anode electrode used in the second embodiment.

Explanation of the sign

1 plating equipment

2 plating bath

3 circumference

4 seal packing

5 plating liquid supply port

6 plating liquid outlet

A anode electrode

C cathode electrode

W wafer

ar1 ~ 4 circumferential edge current supply

ac central current supply

ATR to ABL perimeter edge current supply

AC central current supply

The present invention relates to a plating process of a semiconductor wafer.

Conventionally, when a semiconductor wafer is plated, a wafer in contact with the cathode electrode is disposed through the opening of the plating bath, the plating liquid is supplied toward the wafer, and the plating liquid reaching the wafer is placed in the outer circumferential direction of the surface to be plated of the wafer. BACKGROUND ART A wafer plating method is known in which plating is performed by supplying a plating current by an anode electrode disposed so as to flow and facing the wafer in a plating bath and the cathode electrode. This wafer plating method is widely used as suitable for the production of small lots and automation of the plating process, in that plating can be performed sequentially by replacing wafers in the openings of the plating bath. In the plating process of this wafer, it is important to make the film thickness uniform across the entire surface to be plated of the wafer, and various improvements for improving the uniformity of the film thickness have been proposed.

For example, in the case where a uniform film thickness cannot be realized on the entire surface of the wafer to be plated due to the local concentration of the plating current, a concentration of the plating current is provided by placing a shielding plate or the like in the plating bath in accordance with the variation in the film thickness. The countermeasure which alleviates this is known (patent document 1). In addition, as a countermeasure on the cathode electrode side, a current mirror circuit is formed by dividing the cathode electrode in contact with the circumferential edge of the wafer so that uniform electrolytic deposition is performed on the entire surface to be plated. A countermeasure for forming a current mirror circuit is known (Patent Document 2). Further, on the anode electrode side, an anode electrode disposed to face the wafer is divided into a plurality of peripheral anode electrodes and a center anode electrode so as to have mutually insulating regions, and the energization time of the plating treatment to the center anode electrode is transferred to the peripheral anode electrode. The method of controlling plating thickness by making it smaller than the energization time of a plating process is known (patent document 3). According to these prior arts, it becomes possible to perform a plating process on the to-be-plated surface of a wafer with the film thickness with a certain uniformity.

[Patent Document 1] Japanese Patent Application Laid-Open No. 8-74088

[Patent Document 2] Japanese Patent Application Laid-Open No. 2001-115297

[Patent Document 3] Japanese Patent Application Laid-Open No. 7-197299

However, disposing the shield plate in the plating bath or taking measures to divide the anode electrode complicates the plating apparatus structure, and when the diameter of the wafer is changed, the adjustment according to the diameter, that is, the size of the shield plate or It is necessary to adjust the divided shape of the anode electrode and the like. In addition, there are disadvantages in terms of cost, such as preparing a plurality of rectifiers in order to divide and control the anode electrodes individually. For this reason, when performing the plating process of a wafer, the plating process technology which can implement | achieve a uniform film thickness with a simpler plating apparatus structure, including maintenance of a plating apparatus, and a simpler and easier countermeasure is desired.

In addition, as a countermeasure for supplying the plating current so that the electrolytic deposition can be uniformly deposited on the wafer by the divided cathode electrodes, the plating process in the peripheral portion of the wafer can be controlled, but the plated surface including the center portion of the wafer can be controlled. The film thickness control on the front surface was not sufficient.

In addition, in the semiconductor industry, a large diameter of a wafer size, for example, a diameter of 12 inches (about 300 mm) has recently emerged, and a more uniform film thickness can be easily realized on the entire surface to be plated for such a large diameter wafer. There is a strong demand for a plating technology that can be used.

Accordingly, an object of the present invention is to improve the plating process of a conventional wafer, and to provide a wafer plating method capable of plating a uniform film thickness on the entire surface to be plated even in a large diameter wafer.

Means to solve the problem

In order to solve the above problems, the present invention arranges the wafer in the opening of the plating bath, supplies the plating liquid by contacting the outer peripheral side of the wafer and the cathode electrode, so that the plating liquid reaching the wafer flows in the outer circumferential direction of the surface to be plated of the wafer. In the wafer plating method in which a plating current is supplied to the wafer by supplying a plating current by the anode electrode and the cathode electrode disposed to face the wafer in the plating bath, the anode electrode has a shape substantially the same as the surface to be plated of the wafer. In addition, a plurality of peripheral edge current supply units are provided at the peripheral edges of the anode electrode, and a central current supply unit is provided at the center of the anode electrode, and the peripheral edge plating current supplied from the peripheral edge current supply unit and supplied from the central current supply unit. By adjusting the central plating current It was. According to this plating method, it is possible to perform a plating process of uniform film thickness on the entire surface to be plated of a wafer without having to arrange a shielding plate in a plating bath or to modify the plating apparatus into a special structure.

It is preferable to provide at least three or more circumferential edge current supply parts in the wafer plating method of the present invention at least three places, more preferably four or more places. Moreover, even if too many circumferential edge current supply parts are provided, the effect of contributing to the uniformity of the film thickness tends to decrease. Considering the large-diameter wafer or the like to be plated, the peripheral current supply portion is preferably 10 or less. Practically, it is preferable to provide four to eight peripheral edge current supply units.

In the wafer plating method of the present invention, the adjustment of the circumferential edge plating current in the anode electrode and the central plating current supplied from the central current supply portion is to distribute the total plating current. That is, the plating current of a predetermined ratio is supplied to the center current supply part among the total plating currents supplied to the anode electrode, and the plating current corresponding to the remaining amount is allocated to the peripheral edge current supply part. For example, in the case where the center of the wafer to be plated is plated with a thicker film thickness than the peripheral portion, 40% of the total plating current is supplied to the central current supply, and the remaining 60% is allocated to the peripheral edge current supply. Supply it. The adjustment ratio of this plating current may be suitably determined in accordance with the uneven plating thickness state. For the current adjustment to be supplied, a method of differently setting the current value itself supplied from the center and the circumferential edge, a method of differentiating the plating treatment time (the energization time) of the center and the circumferential edge, and the like can be adopted.

In addition, in the wafer plating method of the present invention, it is preferable to use an anode electrode serving as a flat plate and to provide a plurality of perforations in the flat plate to adjust the plating current distribution. When a plurality of perforations are provided in the anode electrode of the flat plate, the plating liquid passes through the perforations. By adjusting the number and the formation positions of the perforations, the plating current distribution on the plated surface of the wafer can be adjusted. By controlling the supply of the plating current to the anode electrode, and by adjusting the plating current distribution, the plating treatment with a more uniform film thickness becomes possible.

In the wafer plating method of the present invention, it is preferable to employ an anode electrode provided with a platinum film and an iridium oxide film on the surface of the intermediate layer on the titanium electrode substrate. By using the anode electrode having such a structure, it is possible to realize the improvement of the uniformity of the plating thickness while suppressing the increase of the electrode cost drastically, and the stability of the plating liquid is also maintained because of the excellent corrosion resistance to the plating liquid (for electrolytic plating treatment). Properties that do not destroy the plating liquid. In particular, in the case of performing a gold plating process on a wafer, even if a gold plating process is performed for a long time as long as it is an anode electrode having such a structure, precipitation of gold does not occur on the electrode surface and maintenance of the electrode becomes easy.

Implement the invention  Best form for

First Embodiment Hereinafter, an embodiment of the present invention will be described. FIG. 1: shows the outline of the plating tank cross section of the cup type plating apparatus in this embodiment. As shown in FIG. 1, the cup type plating apparatus 1 of this embodiment is able to place the wafer W along the opening part of the plating bath 2, and the outer peripheral part 3 of the wafer W and The ring-shaped cathode electrode C is arranged to be in contact. Under the cathode electrode C, a seal packing 4 for preventing leakage of the plating liquid is disposed.

The plating bath 2 is provided with a plating solution supply port 5 at the center of the bottom portion, and the plating solution supplied in an upward flow toward the wafer W placed on the opening 2 is transferred to the outside of the plating bath 2. One plating liquid outlet 6 is provided so that it can flow out. In addition, an anode electrode A is provided on the bottom side of the plating bath 2 so as to face the wafer W placed thereon.

2 is a plan enlarged schematic view of the anode A shown in FIG. 1. The anode A is provided with a plurality of perforations 10, and the plating solution can be passed through the perforations 10. In addition, the anode A is subjected to Pt plating (thickness of 0.5 to 2 µm) on a disc-shaped electrode base material Ti, and further plated Ir (thickness of 1 to 2 µm) on the Pt, by an electric furnace. by heat treatment in an air atmosphere it was used as the iridium oxide (IrO ₂₎ is covered with an electrode surface (see Patent Document Japanese Unexamined Patent Application Publication No. 2006-22379 call).

The anode electrode A is provided with four peripheral edge current supply terminals ar1 to ar4 and a central current supply terminal ac at the center thereof, and the respective terminals are supplied with plating current. A power source (not shown) was connected. In addition, about the ring-shaped cathode electrode C, the connection terminal provided in four surroundings of the electrode was connected to the plating current supply source.

Next, the result of having performed the wafer plating process evaluation test by the cup type plating apparatus in above-mentioned this embodiment is demonstrated. In this test, a wafer with a seed metal having a TiW film (3000 mmW) formed on a surface to be coated of a wafer having a diameter of 8 inches (about 200 mm) and an Au seed metal film (1000 mmW) formed on the surface thereof was used. As for the anode A, a 204 mm diameter and 1 mm thick Ti plate was subjected to heat treatment by Pt plating and Ir plating, and then a hole having a diameter of 8 mm was uniformly formed at 161 places on the entire surface of the electrode. (See Japanese Patent Laid-Open No. 2006-22379).

The plating treatment was non-cyanic, and a weakly alkaline high purity gold plating solution was used (manufactured by Nihon Electroplating Engineers, product name MICOFAB Au660). Plating conditions using this gold plating solution were performed at a liquid temperature of 60 ° C., pH 7 to 8, and a plating current density of 0.8 A / dm 2, with a film thickness of 18 μm as the target plating thickness. In addition, a 25 μm-thick resist was coated on the surface of the seed metal film of the wafer, and a bump formation pattern (opening area of 0.35 dm 2) used in forming a plurality of columnar bumps for liquid crystal was formed in the resist. It was plated. The plating current supply amount was adjusted such that the peripheral edge plating current value (total plating current value of four terminals of ar1 to ar4) and the central plating current value in the anode electrode during the plating treatment were in a ratio of 3: 7. The ratio of this supply amount is to prepare a plated wafer by setting the supply amount of the plating current so that the supply amount of the center plating current value and the peripheral edge plating current value is evenly distributed throughout the anode electrode. It determined by comparing the plating thickness of the vicinity and the peripheral edge part. In the ratio adjustment between the peripheral edge plating current value (total plating current value of the four terminals of ar1 to ar4) and the plating current supply amount of the central plating current value, the center plating current is not supplied after first supplying only the central plating current for a predetermined time. It was performed by supplying the peripheral plating current for a predetermined time without the state.

For comparison, in the cup plating apparatus shown in Fig. 1, Pt plating (thickness 4) is used as the anode electrode having a mesh shape of Ti (expanded metal having a diameter of 204 mm, a long axis of about 11 mm, and a short axis of about 8 mm rhombus opening). The gold plating process was performed using the thing of (micrometer). About the anode electrode of this mesh image, the plating current supply terminal is provided in one place (position corresponded to ar1 of FIG. 2), and it is made to supply plating current from this one terminal to an anode electrode. Other plating treatment conditions were the same as above.

Evaluation of the plating treatment test was performed by peeling the resist of the wafer after the plating treatment and measuring the height (plating thickness) of the columnar bumps. This bump height (plating thickness) was measured using the stylus type step measuring instrument (KLA-Tencor P11) for bumps formed on the surface to be coated. As specifically, shown in FIG. 3, 13 bump heights W1-W13 were measured about the columnar bump formed in the center of the to-be-drawn surface of the wafer, and the peripheral part. Table 1 shows the average value (Avg.), Maximum value (MAX.), Minimum value (MIN.), Deviation width (Range.), And deviation width (Range.) / Average value (Avg.) Obtained from this bump height measurement result. . In addition, the unit of average value (Avg.), Maximum value (MAX.), Minimum value (MIN.), And deviation width (Range.) Shown in Table 1 is micrometer, and the deviation width (Range.) / Average value (Avg.) Of The unit is%.

The Example shown in Table 1 is a result of supplying a plating current from four places and the center of an anode electrode circumference edge, and the comparative example shows the result of having performed plating current from one place of an anode electrode circumference edge every time. From this result, it turned out that the Example has become much smaller than the comparative example in the difference of the maximum value and the minimum value, ie, the variation range (Range.) Of a film thickness. In addition, the Range./Avg. Value (the value obtained by dividing the deviation width by the average value) clearly showed a small value in the examples, and it was confirmed that the plating treatment had a very high uniformity in plating thickness.

In addition, in the comparative example, it was found that the portion of the wafer-plated surface corresponding to the current supply terminal portion provided at one place of the anode electrode was plated extremely thickly, which increased the variation width of the plating thickness. there was. On the other hand, in the case of the Example, it turned out that the plating thickness of the periphery of the wafer to-be-plated surface is also processed uniformly. In this embodiment, the current supply on the cathode electrode side is not divided, but the current supply on the cathode electrode side is divided, specifically, at the time of supply of the plating current, By controlling the supply of the plating current by combining the division supply method and the division supply method on the anode electrode side of the present embodiment, the uniformity of the plating thickness on the entire surface of the wafer to be coated is improved, especially the plating thickness near the outer circumference of the surface to be coated. It is possible to improve uniformity.

Second Embodiment Next, another embodiment of the present invention will be described. In this 2nd Embodiment, the cup type plating apparatus (FIG. 1) of the same structure as the said 1st Embodiment was used. However, the plating apparatus of this second embodiment is capable of processing a wafer size of 12 inches in diameter (about 300 mm in diameter). In addition, the used anode electrode A was Pt-plated and Ir-plated and heat-treated to a Ti disc of 294 mm in diameter and 2 mm in thickness, and thereafter, a hole having a diameter of 10 mm was uniformly formed at 361 places on the entire surface of the electrode. (The manufacturing method of the anode electrode A is the same as that of the said 1st Embodiment). As for the anode electrode A, as shown in Fig. 4, the peripheral edge current supply terminals ATR, AR, ABR, ATL, AL, ABL and the central portion are provided at equal intervals at six positions of the peripheral edge. The center current supply terminal AC was provided, and each of these terminals was connected to a plating current supply power supply (not shown). In addition, about the ring-shaped cathode electrode C, like the said 1st Embodiment, the connection terminal provided in seven surroundings of the ring-shaped cathode electrode C was connected to the plating current supply power supply. In addition, the distance of the wafer facing the anode electrode A, that is, the distance between the poles, was set to 21 mm.

Next, the result of having performed the wafer plating process evaluation test by the cup type plating apparatus in above-mentioned this embodiment is demonstrated. In this test, a wafer having a TiW film (3000 mm) and a seed metal film (1000 mm) with Au formed on the surface to be coated of a wafer 12 inches in diameter (about 300 mm) was used. Gold bumps of a predetermined shape were formed on the surface, and the formed gold bump height was measured to examine the uniformity of the plating treatment. In this test, two types of gold bumps were formed and evaluated respectively. One is to form a plurality of bumps having a target bump height of 23 占 퐉 on the wafer surface on the wafer surface (total bump formation total area on the wafer surface of about 0.1 dm 2: bump <A>). The other is likewise forming a plurality of bumps having a target bump height of 16 탆 on the wafer surface on the wafer surface (total bump formation total area of about 1.0 dm 2: bump <B> on the wafer surface). These two types of bumps are required as a product specification to be formed in the range of 2 micrometers from the target bump height (the difference of the maximum value and the minimum value in all the bumps which measured bump height is less than 2 micrometers).

In the gold plating process for bump formation, the same gold plating solution as in the first embodiment was used. Plating conditions were 60 degreeC of liquid temperature, pH 7-8, and plating current density of 0.8 A / dm <2>. The surface of the seed metal film of the wafer was coated with a resist having a predetermined thickness corresponding to each bump height, and a bump formation pattern for forming a plurality of columnar bumps was formed in the resist, followed by gold plating.

The plating current was supplied to the anode electrode during the plating treatment by the following method. Specifically, when the plating current is supplied from all six locations around the anode electrode shown in FIG. 4 (first method), when supplied from one location of ATL shown in FIG. 4 (second method), the ABR of FIG. 4, Formation of gold bumps by four kinds of plating current supply methods in the case of supplying from two places of ABL (third system), that is, supplying from the AC of FIG. 4, i.e., the center of the anode electrode (fourth system) Was performed.

Evaluation of the plating treatment test was performed by peeling the resist and measuring the height (plating thickness) of the columnar bumps after the plating treatment as in the case of the first embodiment. The bump height (plating thickness) was measured on the gold bumps formed on the surface to be plated using a stylus step gauge (KLA-Tencor P11). Specifically, as shown in FIG. 3, the bump heights W1 to W13 of a total of 13 locations were measured for the columnar bumps formed at the center of the plated surface of the wafer and the peripheral portion thereof. Table 2 shows the average value (Avg.), The maximum value (MAX.), The minimum value (MIN.), And the deviation width (Range.) Obtained from this bump height measurement result. In addition, the unit of the average value (Avg.), The maximum value (MAX.), The minimum value (MIN.), And the deviation width (Range.) Shown in Table 2 is micrometer.

As shown in Table 2, in the case of forming bumps <A>, it is possible to form gold bumps that can satisfy the deviation range of 2 µm, which is required as a product specification, by the plating current supply of the first method or the third method. It turned out. On the other hand, in the case of bump <B>, in all of the 1st-4th systems, the gold bump which can satisfy | fill the 2 micrometers of deviation width calculated | required as a product specification was able to be formed. In the results shown in Table 2, the tendency is different in the case of bump <A> and bump <B>, but this means that the total plating area in the formation of bump <A> is much smaller than that of bump <B>. It can be thought of as a point.

As described above, according to the present invention, even a large-diameter wafer can be plated with a uniform film thickness on the entire surface to be plated of the wafer without significantly changing the structure of the plating apparatus.

Claims (3)

The wafer is placed in the opening of the plating bath, the plating solution is supplied by bringing the outer peripheral side of the wafer into contact with the cathode electrode so that the plating solution that reaches the wafer flows in the outer circumferential direction of the surface to be plated of the wafer and faces the wafer in the plating bath. A wafer plating method in which a plating current is supplied to a wafer by supplying a plating current by the disposed anode electrode and the cathode electrode, The anode electrode has the same shape as the surface to be plated of the wafer, a plurality of peripheral edge current supplies are provided at the peripheral edge of the anode electrode, and a central current supply unit is provided at the center of the anode electrode. A circumferential edge plating current supplied from said circumferential edge current supply portion and a center plating current supplied from a central current supply portion are adjusted. The wafer plating method according to claim 1, wherein the anode electrode is a flat plate, and the plating current distribution is adjusted by providing a plurality of perforations on the flat plate. The wafer plating method according to claim 1 or 2, wherein the anode electrode is provided with a platinum film as an intermediate layer on an electrode substrate made of titanium and an iridium oxide film on the surface of the intermediate layer.

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