JP2006022379A - Electrolytic plating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of easily forming a plated film with a uniform thickness, even when electrolytically plating an article like a wafer, to which an extremely precise plated thickness and the uniformity are required. <P>SOLUTION: This electrolytic plating apparatus for forming the plated film on the surface of the wafer, through supplying a plating solution into a plating tank to contact the wafer with the plating solution and supplying a plating current to the wafer, has: a cup-shaped plating tank having an opening around which a cathode electrode for contacting with a periphery of the wafer is arranged; and an anode electrode arranged in the plating tank so as to face the wafer mounted on the opening, wherein the anode electrode comprises an electrode substrate made of titanium, a platinum coating as an intermediate layer formed thereon, and an iridium oxide coating formed on the surface of the intermediate layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electroplating apparatus, and more particularly, to an electroplating apparatus suitable for performing an electroplating process that requires high-precision plating thickness uniformity, such as a semiconductor wafer.

  Conventionally, the electroplating process is used not only for decoration and surface protection, but also in various fields, for example, as processing of electrical / electronic materials. Among these, for semiconductor wafers, circuits, bumps, and the like are formed by coating a metal such as copper or gold by electrolytic plating.

  As an electroplating apparatus for semiconductor wafers, for example, a plating tank having an opening in which a ring-shaped cathode electrode in contact with the peripheral portion of the wafer is disposed, and a wafer placed in the opening are opposed to each other. It has an anode electrode arranged inside the plating tank, and supplies the plating solution into the plating tank to bring the wafer and the plating solution into contact with each other. There is. In this electroplating apparatus, a soluble anode electrode (anode: hereinafter abbreviated as an anode in some cases) made of plated metal, an insoluble anode electrode made of Pt (platinum), Ti (titanium), or the like is used.

  The characteristics required for the plating treatment on the wafer include uniformity of the plating thickness, smoothness (leveling) of the plating surface, and plating coverage. In particular, the plating thickness is strictly required to be uniform over the entire surface to be plated of the wafer. Therefore, as a method for improving the uniformity of the plating thickness, a method of making the current distribution of the plating current uniform is generally adopted.

  Factors governing the uniformity of the plating current distribution include the primary current distribution, which is affected by the geometry of the anode and cathode electrodes, and the secondary, which depends on the resistance based on the polarization caused by the current flowing through the electrodes. There is a current distribution. By controlling these current distributions, an electrolytic plating process with a more uniform plating thickness is performed.

  In order to control the primary current distribution, for example, the anode electrode shape is made similar to the cathode electrode (to-be-plated body) shape. In addition, the plating current tends to be concentrated at the end portion of the electrode, so that the plating treatment tends to proceed intensively to the end portion. Therefore, in order to alleviate the current concentration at the electrode end, a so-called mask or shielding plate is arranged to make the plating thickness uniform at the end and other parts (for example, Patent Documents). 1).

JP-A-8-74088

  As described above, the current distribution is controlled by various methods in accordance with the shape of the object to be plated, the type of the plating solution, and the like. However, when gold or copper is plated on the surface of a semiconductor wafer, extremely high-precision plating properties including the plating thickness are required. In particular, regarding the plating thickness, a uniform thickness is required over the entire plating surface of the wafer. This is because variations in thickness directly affect the production yield of a large number of electronic components (chips) manufactured from a wafer. In recent years, the diameter of wafers has been increased, and it is required to perform electrolytic plating treatment with a uniform plating thickness on the entire surface of a wafer having a large area such as 12 inches in diameter. In addition to this large area, the establishment of a manufacturing technology aimed at improving manufacturing efficiency by supplying a large plating current to the wafer is also desired, and a large plating current is supplied. Even in this case, it is also required that the electrolytic plating treatment with a more uniform thickness can be performed on the entire surface of the wafer.

  Therefore, the present invention improves the anode electrode in the electroplating apparatus, so that even in a plating process that requires extremely strict plating thickness uniformity, such as a wafer, an electroplating process with a uniform thickness can be easily performed. The purpose is to provide technology that can be used.

  In order to solve the above-described problems, the present invention is configured so that a cup-shaped plating tank having an opening in which a ring-shaped cathode electrode that contacts a peripheral edge of a wafer is disposed, and a wafer placed in the opening. And an anode electrode disposed in the plating tank, supplying a plating solution into the plating tank to bring the wafer into contact with the plating solution, and supplying a plating current to the wafer to perform plating on the wafer surface. In the electroplating apparatus, the anode electrode was formed by providing a platinum film as an intermediate layer and an iridium oxide film on the surface of the titanium electrode base material.

  In the present invention, the anode electrode is improved to achieve higher precision plating thickness uniformity. The inventors tried to improve the plating thickness uniformity by improving the anode electrode. For the following reason. In the past, the present inventor has taken various measures such as masking and liquid agitation in order to achieve a uniform plating thickness. Considering that the anode electrode is not sufficient, the anode electrode serving as the supply source of the plating current was considered again.

  As the anode electrode of this electrolytic plating apparatus, a soluble one made of a plating metal such as copper or nickel and an insoluble one such as titanium or platinum are used. Insoluble anodes with a small number of times are frequently used in the electroplating process of wafers in order to simplify the plating operation and improve the production yield. As a typical example of this insoluble anode electrode, an anode electrode (hereinafter referred to as a Pt / Ti anode electrode) in which a platinum film is applied on a titanium electrode substrate in consideration of corrosion resistance and the like is known. . This Pt / Ti anode electrode generally has a platinum coating of several microns in consideration of corrosion resistance, electrical conductivity, and cost.

  With respect to such a Pt / Ti anode electrode, the present inventor performed plating treatment on the wafer surface using a Pt / Ti anode electrode in which the thickness of the platinum film was increased ignoring the cost of the electrode. It has been found that the uniformity of the plating thickness is improved with the increase in the thickness. Usually, the platinum coating thickness is about 4 to 5 μm, but it was found that when the coating amount was increased 4 to 5 times (16 to 25 μm thickness), the uniformity of plating was clearly improved. In addition, it was confirmed that the overvoltage value during the plating treatment was clearly reduced as the platinum coating thickness was increased.

This was considered to indicate that the uniformity of the plating thickness was influenced by the material physical properties of the anode electrode surface, that is, the physical properties of platinum coated on the outermost surface of the Pt / Ti anode electrode. And this inventor estimated the material physical property to the specific resistivity which directly affects the electrical conductivity of an electrode. It is said that a material with a small specific resistivity value is likely to carry electricity. Platinum (resistivity 10.6 × 10 ⁻⁶ Ωcm <Source: “Science Handbook Basic 4th Revised Edition” September 30, 1993 The specific resistance of the Japan Society of Science, Japan Society of Sciences (the same shall apply hereinafter) is as small as about one-fourth that of titanium (42.0 × 10 ⁻⁶ Ωcm). As a result of studying a material having a small resistivity value and satisfying characteristics such as corrosion resistance to the plating solution, the present inventor has focused on iridium. This is because iridium (5.3 × 10 ⁻⁶ Ωcm) has a specific resistivity value that is half that of platinum and has high corrosion resistance.

  As a result of such diligent research, the present inventors have adopted an anode electrode in which a platinum film as an intermediate layer and an iridium oxide film on the surface of the intermediate layer are provided on an electrode substrate made of titanium. It can be said that the anode electrode according to the present invention is obtained by further coating iridium oxide on the platinum-coated surface of a conventionally used Pt / Ti anode electrode. As a result, it was possible to improve the uniformity of the plating thickness while suppressing a significant increase in electrode cost. The anode electrode according to the present invention has corrosion resistance to the plating solution and can maintain the stability of the plating solution (a property that does not destroy the plating solution in the electrolytic plating process). Since the present invention is not a complicated mechanism such as a mask or a shielding plate, it is possible to easily improve the uniformity of the plating thickness by adopting it as an electrode of a conventionally used electrolytic plating apparatus. . In addition, iridium is more advantageous in price than platinum, and thus can be said to be an anode electrode that suppresses the cost increase to some extent.

  In addition, according to the study of the present inventor, it has been confirmed that the anode electrode according to the present invention is less likely to deposit the plating metal on the electrode surface than the conventional anode electrode. For example, when a conventional Pt / Ti anode electrode is used in the gold plating process, gold deposition occurs on the electrode surface after a long plating process. However, the anode electrode of the present invention does not cause gold deposition on the electrode surface even after a long gold plating treatment. That is, the electrolytic plating apparatus of the present invention also facilitates electrode maintenance.

  The anode electrode in the electrolytic plating apparatus of the present invention preferably has a platinum coating thickness of 1.0 to 8.0 μm and an iridium oxide coating thickness of 1.0 to 5.0 μm. When the platinum coating thickness is less than 1.0 μm, pinholes are likely to be formed in the platinum coating, and the adhesion of the iridium oxide coating tends to decrease. On the other hand, if it exceeds 8.0 μm, the electrode cost increases excessively and becomes impractical. When the iridium oxide coating thickness is less than 1.0 μm, the effect of uniforming the plating thickness is reduced when the platinum coating is 1 μm. On the other hand, even if the thickness exceeds 5.0 μm, the effect of uniformity does not change, and it is very difficult at present to apply such a thickness of iridium oxide coating, which is not practical. The anode electrode in the electroplating apparatus of the present invention is not particularly limited in the electrode shape itself, and can be applied to various shapes such as mesh and plate.

  According to the present invention, even in a plating process that requires extremely strict plating thickness uniformity such as a wafer, an electrolytic plating process with a uniform thickness can be easily performed.

  The best mode for carrying out the present invention will be described.

First Embodiment : In this first embodiment, the results of investigating the uniformity of plating thickness using a beaker test plating apparatus capable of simple electrolytic plating treatment with an anode electrode coated with iridium oxide will be described.

  The beaker test plating apparatus used in the first embodiment is capable of simple plating as shown in FIG. In this beaker test plating apparatus, a plate-shaped object 2 to be a cathode is disposed in a plating tank 1, and an anode electrode 3 is disposed on one side of the object 2 to be plated. Further, a stirring member 4 is disposed at the bottom of the plating tank 1 so that the plating solution is stirred by a so-called stirrer.

  In this first embodiment, a to-be-plated body 2 is obtained by dividing a φ6 inch Si wafer into quarters. This wafer split test piece was coated with gold having a thickness of 0.1 μm as a seed metal layer on one side which becomes the surface to be plated (the back side was coated with a resist). Then, a resist (thickness 20 μm) was coated on the seed metal layer, and a resist pattern was formed so that a plurality of 100 × 100 μm square bumps were formed at equal intervals on the resist. Bumps having a bump height target of 18 μm were formed on the surface to be plated of the wafer division test piece having such a pattern formed by gold plating. The plating solution was a non-cyanide, weakly alkaline, high-purity gold plating solution (product name: MICROFAB Au140, manufactured by Nippon Electroplating Engineers). This gold plating solution has a pH of 7.6 to 8.0 and a specific gravity of 11 to 25 baume. As anode electrodes, three types of anode electrodes shown in Table 1 were prepared, and bumps were formed using each of them.

All of the anode electrodes in Table 1 were in the form of an expanded mesh and had the same area as the surface to be plated of the wafer split test piece. The anode electrode A was obtained by coating only Pt on the electrode base material Ti, and the anode electrode B was further coated with Ir on Pt plated on the electrode base material Ti. The anode electrode C is formed by directly coating Ir on the electrode base material Ti by plating. The anode electrodes B and C coated with Ir were iridium oxide (IrO ₂ ) by performing heat treatment in an air atmosphere with an electric furnace. Using these three types of anode electrodes, gold bumps were formed on the wafer split test piece. The gold plating treatment conditions for bump formation were a liquid temperature of 60 ° C. and a current density of 0.5 A / dm ² .

  In addition, as a running test, plating was performed from the start to 1.0 MTO, and gold bumps were formed every 0.2 MTO of 0.2, 0.4, 0.6, 0.8, 1.0 MTO, The bump formation characteristics were examined. Here, the unit MTO (metal tern over) indicates the consumption amount of the plating metal in the plating solution. When the plating process is performed continuously, the gold concentration in the plating solution consumed by the plating is appropriately supplemented to keep the gold concentration in the plating solution constant. For example, 1.0 MTO is the initial value. When the amount of gold contained in the plating solution is 10 g, this indicates the time when the amount of gold appropriately supplemented to the plating solution reaches 10 g.

The gold plating process described above was performed at the start and in the case of bump formation every 0.2 MTO. In addition, the gold plating process other than the bump formation uses a gold dummy panel (2 × 3 cm square) instead of the wafer division test piece, and anode electrodes made of the same material are arranged on both sides of the dummy panel. The gold plating process was continuously performed. The gold plating treatment conditions at this time were a liquid temperature of 60 ° C. and a current density of 0.5 A / dm ² .

  In the evaluation in the first embodiment, the height of the bump, the hardness of the bump, and the appearance of the top surface of the bump were observed. The bump height was measured after the gold plating treatment for bump formation, by peeling the resist to expose the gold bump, and measuring the gold bump height. The measuring method uses a stylus type bump height measuring device (P-11 manufactured by tencor), and the height (from the seed metal surface to the bump top) at the 90 μm width L (see FIG. 2) of the top surface of the bump. The distance) was measured continuously, and the average bump height, maximum height, and minimum height were determined. In addition, the measurement was performed on a total of five bumps in one wafer-divided test piece, that is, a bump located in the center and four bumps located in four directions 20 mm away from the central bump. The measurement results of the bump height are shown in Tables 2 to 4.

The uniformity values in Tables 2 to 4 are calculated by the following formula.
Uniformity (%) = (maximum height−minimum height) / average height × 100
Moreover, the dispersion | distribution in a table | surface was computed from the value of five measurement bump heights.

From the results of Tables 2 to 4, anode electrodes B and C coated with iridium oxide (IrO ₂ ) had a smaller thickness dispersion value than the conventional anode electrode A. Further, when the dispersion value of the thickness with respect to the lapse of time for the plating treatment was observed, the anode electrodes B and C had a smaller variation in dispersion value than the conventional anode electrode A, and a tendency to be stable was observed. Further, it was found that the anode electrode C was most excellent in terms of thickness uniformity. From the result in the first embodiment, it was found that the uniformity of the plating thickness can be improved by using the anode electrode whose outermost surface is coated with iridium oxide (IrO ₂ ).

Second Embodiment : In this second embodiment, in the cup type electroplating apparatus shown in FIG. 3, various anode electrodes shown in Table 5 were used for electroplating treatment, and the uniformity of the plating thickness was investigated. As the anode electrode, an IrO ₂ / Pt / Ti anode electrode (Example 1), a Pt / Ti anode electrode (Comparative Examples 1 to 5), and an Ir / Ti anode electrode (Examples 6 and 7) were used.

  The cup type electroplating apparatus 10 shown in FIG. 3 is configured so that the wafer 30 can be placed along the upper opening of the plating tank 20 and is in a ring shape so as to be in contact with the peripheral edge 40 of the wafer 30 over the entire circumference. The cathode electrode 50 is arranged. A seal packing 60 for preventing leakage of the plating solution is disposed under the cathode electrode 50. In addition, the plating bath 20 has a plating solution supply port 70 at the center of the bottom, and the plating solution supplied from the plating solution supply port 6 in an upward flow toward the placed wafer 30 can flow out of the plating bath 20. A plating solution outlet 80 is provided. Further, on the bottom of the plating tank 20, an anode electrode 90 facing the mounted wafer 30 is installed.

The object to be plated was a wafer having a diameter of 8 inches, and one having a surface to be plated coated with gold having a thickness of 0.15 μm as a seed metal layer was used. In the plating process, a resist (thickness 25 μm) was coated on the seed metal layer to form a 23.5 μm × 63.5 μm square bump-shaped pattern (plating area 0.34 dm ² ). Gold bumps were formed on the surface of the wafer having such a pattern formed by performing a gold plating process. The same plating solution as that in the first embodiment was used. The plating treatment conditions were such that a bump with a target height of 18 μm was formed with a current density of 0.5 dm ² and a plating time of about 60 minutes. In this embodiment, in order to accurately grasp the influence on the plating process of only the anode electrode, the arrangement of the current density control shielding plate or the anode electrode mask or the like usually performed in the plating process of the product wafer is I did not do anything.

  After the plating treatment, the wafer was removed from the cup-type electrolytic plating apparatus, and the wafer after the plating treatment was washed with water and dried. After the resist was peeled off, the wafer was washed with water and dried again. And in order to evaluate the uniformity of plating thickness, the height of the bump located in the 17-point part of the wafer surface shown in FIG. 4 was measured. The measurement method, conditions, etc. are the same as in the first embodiment. Table 6 shows the measurement results of the bump height.

From the results of Comparative Examples 1 to 5 in Table 6, it was confirmed that the uniformity of the thickness was improved as the Pt thickness of the anode electrode was increased. Moreover, when the voltage value at the time of a plating process was measured, it turned out that a voltage value becomes low as Pt thickness increases. From this, it was expected that the electrical conductivity of the anode electrode itself affects the uniformity of the plating thickness. On the other hand, in the anode electrode coated with iridium oxide (IrO ₂ ), the uniformity of the plating thickness is improved as compared with the conventional anode electrode (Comparative Example 1) from the results of Example 1 and Comparative Examples 6 and 7. There was found. The disk-shaped anode electrode of Comparative Example 7 showed the most improved thickness uniformity. Moreover, it turned out that the anode electrode of Example 1 has improved the uniformity of plating thickness to the same level as Comparative Example 4. The data shown in Table 6 shows that the bump height accuracy is very bad. This is because, as described above, in the plating process of this embodiment, the influence of only the anode electrode is observed. This is because no arrangement of a current distribution adjusting shielding plate or the like was performed.

Further, for each of the anode electrodes of Example 1 and Comparative Examples 6 and 7, the adhesiveness of the Pt and IrO ₂ coatings and the appearance after the plating treatment were examined, and Comparative Examples 6 and 7 were not very good in adhesiveness. It was confirmed that the appearance was also uneven in color. On the other hand, it was confirmed that the anode electrode of Example 1 had good adhesion and no color unevenness. Furthermore, when long-time plating processing was performed, in the anode electrode of Comparative Examples 1-5, precipitation of gold | metal | money was confirmed on the electrode surface. On the other hand, as for the anode electrode of Example 1 and Comparative Examples 6 and 7, when the electrode surface was IrO ₂ , gold deposition was not confirmed even after a long plating treatment. When comprehensively judging the adhesion and appearance, the result of the gold precipitation phenomenon, and the result of the uniformity of the plating thickness described above, the practical anode electrode including the cost is considered to be Example 1. It was.

The schematic sectional drawing of the beaker test plating apparatus of a first embodiment. Bump cross-section schematic Schematic sectional view of the cup type electroplating apparatus of the second embodiment Plan view showing measurement points on wafer

Explanation of symbols

1 Plating tank
2 Plated object 3 Anode electrode
DESCRIPTION OF SYMBOLS 4 Stirring member 10 Cup type plating apparatus 20 Plating tank 30 Wafer 40 Peripheral part 50 Cathode electrode 60 Seal packing 70 Plating solution supply port 80 Plating solution outlet 90 Anode electrode

Claims (2)

A plating tank having an opening in which a cathode electrode in contact with the peripheral edge of the wafer is disposed; and an anode electrode disposed in the plating tank so as to face the wafer placed in the opening;
In an electroplating apparatus that supplies a plating solution into the plating tank to bring the wafer into contact with the plating solution, and performs a plating process on the wafer surface by supplying a plating current to the wafer.
The anode electrode is an electroplating apparatus characterized in that a platinum film as an intermediate layer and an iridium oxide film on the surface of the intermediate layer are provided on an electrode substrate made of titanium. The electroplating apparatus according to claim 1, wherein the platinum coating has a thickness of 1.0 to 8.0 µm, and the iridium oxide coating has a thickness of 1.0 to 5.0 µm.

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