An embodiment of the present invention is described below.
In the plating tank 2, a plating liquid supply port 5 is provided in the middle of the bottom, and a plating liquid outflow port 6 is provided to ensure that the plating liquid supplied as an upward flow toward the wafer W placed on the opening 2 can flow out to the outside of the plating tank 2. Furthermore, on the bottom side of the plating tank 2 is provided with an anode electrode A so as to be opposed to the placed wafer W.
Furthermore, the anode electrode A is provided with peripheral-edge current supplying terminals (ar1 to ar4) in four places of a peripheral edge thereof and a central current supplying terminal (ac) in the center thereof, each of these terminals connected to a not-shown plating current supplying power source. Incidentally, for the ring-shaped cathode electrode C, connection terminals provided in four places at the periphery of the electrode were connected to the plating current supplying power source.
Next, a description is given of results of an evaluation test of wafer plating treatment conducted by use of the cup-shaped plating apparatus in this embodiment described above. This test was conducted by using a wafer with a seed metal obtained by forming a TiW film (3000 Å) on a surface of a wafer to be plated, which has a diameter of 8 inches (approximately 200 mm), and forming a seed metal film of Au (1000 Å) on the TiW film surface. For the anode electrode A, a disk made of Ti having a diameter of 204 mm and a thickness of 1 mm was plated with Pt and Ir and after heat treatment, bores having a diameter of 8 mm were formed in 161 places uniformly on the whole surface of the electrode (refer to Japanese Patent Application Laid-Open No. 2006-22379).
The plating treatment was performed by using a non-cyanide based, weakly alkaline high-purity gold plating liquid (made by Japan Electroplating Engineers Co., Ltd., product name: MICOFAB Au660). The plating treatment using this gold plating liquid was performed under the plating conditions: liquid temperature 60° C., pH 7 to 8 and plating current density 0.8 A/dm2, and a film thickness of 18 μm as the target plating thickness. The surface of the seed metal film of the wafer was coated with a resist in a thickness of 25 μm, and a bump forming pattern (total aperture area: 0.35 dm2) used in forming a plurality of bumps for liquid crystal in the form of rectangular columns was formed on the resist and subjected to a plating treatment. And the plating current supply amount was regulated so that the proportion of the peripheral-edge plating current value (the total current value of the four terminals ar1 to ar4) and to the central plating current value in the anode electrode during the plating treatment becomes 3:7. This proportion of the supply amount was determined beforehand by fabricating a wafer subjected to a plating treatment by setting the supply amount for the central plating current value and the peripheral-edge plating current becomes uniform in the whole anode electrode, checking the coating thickness of the wafer, and comparing the coating thickness between the vicinity of the center and the peripheral edge part. The adjustment of the proportion of the plating current supply amount between the peripheral-edge plating current value (the total current value of the four terminals ar1 to ar4) and the middle-par plating current value was performed by first supplying only the central plating current for a prescribed time and thereafter supplying the peripheral-edge current for a prescribed time, with the middle-par plating current not supplied.
To make a comparison, a gold plating treatment was performed by using a mesh anode electrode made of Ti (an expand metal having a diameter of 204 mm, a rhombic opening having a major axis of 11 mm and a minor axis of approximately 8 mm) plated with Pt (thickness: 4 μm) in the cup-shaped plating apparatus shown in
The evaluation of the plating treatment test was performed by exfoliating the resist of the wafer after plating treatment and measuring the height, i.e. coating thickness, of the bumps in the form of rectangular columns. This bump height, i.e. coating thickness, was measured by use of a stylus type profiler (KLA-Tencor P11). Concretely, for the bumps in the form of rectangular columns formed at the center of the wafer surface to be plated and in the periphery thereof as shown in
In the working example shown in Table 1, the plating current supply was performed from the four places in the peripheral edge and center of the anode electrode, whereas in the comparative example, the plating current was supplied from one place of the peripheral edge of the mesh anode electrode. From the results shown in the table, it became apparent that the difference between the maximum value and the minimum value, i.e., the dispersion range (Range.) in the working example is by far smaller than in the comparative example. The Range./Avg. value, which is obtained by dividing the dispersion range by the average value) is clearly small in the working example, and it was ascertained that this plating treatment has very high uniformity in terms of the coating thickness.
In the comparative example, the plating treatment was performed in such a manner that the film thickness of a spot of the plated wafer surface corresponding to the current supplying terminal portion provided in one place of the anode electrode became extremely large, and it became apparent that this phenomenon increases the dispersion range of the coating thickness. In contrast to this, it became apparent that in the case of the working example, the plating treatment had been performed so that also the coating thickness in the vicinity of the periphery of the plated wafer surface became uniform. In this working example, the current supply on the cathode electrode side was not divided. However, by dividing the current supply on the cathode electrode side, concretely, by combining a method of divided supply on the cathode electrode side as disclosed in Japanese Patent Application Laid-Open No. 20001-115297 described above, and a method of divided supply on the anode electrode side of this working example upon supplying the plating current, the supply of the plating current is controlled, whereby it is possible to improve the uniformity of the coating thickness on the whole plated wafer surface, particularly, the uniformity of the coating thickness in the vicinity of the periphery of the plated wafer surface.
Subsequently, another embodiment of the present invention is described. In this second embodiment, a cup-shaped plating apparatus of the same construction as in the first embodiment above (
Next, a description will be given of results of an evaluation test of wafer plating treatment conducted by use of the cup-shaped plating apparatus in this embodiment described above. This test was conducted by using a wafer with a seed metal obtained by forming a TiW film (3000 Å) on a surface of a wafer to be plated, which has a diameter of 12 inches, i.e. approximately 300 mm, and forming a seed metal film of Au (1000 Å) on the TiW film surface. Gold bumps of a specified shape were formed on the surface and the uniformity of plating treatment was checked by measuring the height of the formed gold bumps. In this test, two kinds of gold bumps were formed and each of the gold bumps was evaluated. One has the shape of a rectangular column, and a plurality of bumps of this kind having a target bump height of 23 μm were formed on the surface of a wafer, more specifically the total bump-formed area on the wafer surface is approximately 0.1 dm2, called the bump <A>. The other has also the shape of a rectangular column, and a plurality of bumps of this kind having a target bump height of 16 μm were formed on the surface of a wafer, more specifically the total bump-formed area on the wafer surface is approximately 1.0 dm2, called the bump <B>. Product specifications require that these two kinds of bumps be formed with a deviation of within 2 μm from the target bump height (that the difference between the maximum value and the minimum value within all bumps whose height is measured be within 2 μm.
In the gold plating treatment for performing bump formation, the same gold plating liquid as in the first embodiment was used. For the plating conditions, the liquid temperature was 60° C., the pH value was 7 to 8 and plating current density was 0.8 A/dm2. The surface of the seed metal film of the wafer was coated with a resist in a prescribed thickness corresponding to each bump height, a bump forming pattern for forming a plurality of bumps in the shape of a rectangular column was formed on the resist, and gold plating treatment was performed thereafter.
The plating current supply to the anode electrode during the plating treatment was performed by methods as described below. Concretely, the formation of the gold bumps was performed by the following four kinds of plating current supplying methods: a method by which the plating current is supplied from all of the six places at the periphery of the anode electrode shown in
The evaluation of the plating treatment test was performed in the same way as in the first embodiment by exfoliating the resist after the plating treatment and measuring the height, i.e. coating thickness of the bumps in the shape of a rectangular column. The bump height, i.e. coating thickness was measured by use of a stylus type profiler (KLA-Tencor P11). Concretely, for the bumps in the form of rectangular columns formed at the center of the wafer surface to be plated and in the periphery of the wafer as shown in
As shown in Table 2, when the bumps <A> are to be formed, it became apparent that the first method or the third method can form gold bumps capable of meeting the dispersion range of 2 μm required by the product specifications according to the plating current supply. On the other hand, in the case of the bumps <B>, under all of the first to fourth methods, it was possible to form gold bumps capable of meeting the dispersion range of 2 μm required by the product specifications. The results shown in Table 2 reveal different tendencies between the bumps <A> and the bumps <B>. However, it can be thought that this is because in the formation of the bumps <A>, the total plated area is by far smaller than in the bumps <B>.
Number | Date | Country | Kind |
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P2006-164355 | Jun 2006 | JP | national |
P2006-339379 | Dec 2006 | JP | national |