Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-09-24
2001-12-25
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S263000, C204S22400M, C205S123000, C205S148000
Reexamination Certificate
active
06332963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for plating semiconductor wafers, and more particularly to a cup-type plating apparatus.
2. Description of the Related Art
Conventionally, a cup-type plating apparatus is a known apparatus for plating semiconductor wafers. In the cup-type plating apparatus, a wafer is placed on an upper end portion of a plating tank, and a plating solution is fed in the form of an ascending flow from a lower portion of the plating tank toward a surface-to-be-plated of the wafer (hereinafter referred simply as a “wafer surface”) to thereby plate the wafer surface. Being suitable for automation of a small-lot production or plating process, the cup-type plating apparatus is in wide use.
However, the cup-type plating apparatus involves the following two problems. First, film, such as black film, formed on the surface of an anode during plating exfoliates to become impurities in the plating solution. The impurities are carried in the ascending flow of the plating solution and reach the wafer surface, causing nonuniform plating.
Second, in the case where an insoluble anode is used, an additive added for control of plating performance is consumed in significant amounts. The reason is that use of an insoluble anode causes decomposition of the additive present in the vicinity of the insoluble anode although dissolution of an anode metal into the plating solution does not occur. Such an additive-consuming phenomenon not only complicates plating process control but also increases plating cost.
A conceivable solution to the above two problems is installation of a diaphragm within the plating tank; that is, partitioning of the interior of the plating tank into an anode-side chamber and a wafer-side chamber. Employment of such a diaphragm is disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) No. 36529/1987 and Japanese Patent Application Laid-Open (kokai) Nos. 242797/1989 and 154989/1992.
According to Japanese Utility Model Application Laid-Open (kokai) No. 36529/1987 and Japanese Patent Application Laid-Open (kokai) No. 242797/1989, the diaphragm is disposed within the plating tank and above an anode in such a manner as to cover the entire surface of the anode. This diaphragm can prevent mixing of impurities generated from the anode in a plating solution that ascends toward a wafer surface. Also, since the anode is separated from the wafer surface, the consumption of additive can be reduced in the case where an insoluble anode is used. However, in the case where the plating solution is fed at a certain position, the thus-arranged diaphragm may interrupt a direct ascending flow of a plating solution. As a result, the plating solution fails to flow smoothly. Further, bubbles and impurities generated from the anode stagnate under the diaphragm, which is disposed horizontally within the plating tank, thereby preventing stable supply of plating current.
According to Japanese Patent Application Laid-Open (kokai) No. 154989/1992, the interior of a plating tank is partitioned into an upper wafer-side chamber and a lower anode-side chamber by means of a diaphragm. These chambers are fed with a plating solution separately from each other. Through feed of the plating solution into the anode-side chamber, bubbles and impurities flow with the flowing plating solution and thus are less likely to stagnate under the diaphragm. Nevertheless, impurities and bubbles are apt to stagnate under the horizontally disposed diaphragm. Although the plating solution is fed into the upper and lower chambers separately from each other, the plating solution flowing out from the upper chamber and that flowing out from the lower chamber are mixed in a single plating solution storage tank. As a result, the impurity content of the plating solution increases, which has an adverse effect on plating.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to improve a conventional cup-type plating apparatus having a diaphragm and to provide a cup-type plating apparatus capable of preventing impurities generated from an anode from affecting plating, suppressing the consumption of additive in a plating solution, which would occur upon use of an insoluble anode, and reliably ejecting bubbles generated from the anode, as well as to provide a method for plating a wafer by use of the apparatus.
To achieve the above object, the present invention provides a cup-type plating apparatus comprising: a plating tank having a wafer support section provided on an upper end of the plating tank and adapted to hold a wafer; a solution feed section provided at the center of a bottom portion of the plating tank; an anode disposed within the plating tank; and a diaphragm for separating the anode from the wafer. The diaphragm is slanted upward from the solution feed section toward the periphery of the plating tank. A gas release port is provided in the plating tank at such a position as to release bubbles collected under an upper end portion of the diaphragm.
According to a typical structure of a cup-type plating apparatus, the solution feed section is provided at the center of the bottom portion of the plating tank and is adapted to feed the plating solution in the form of an ascending flow, and the anode is disposed to surround the solution feed section. Through disposition of the diaphragm in such a manner as to be slanted upward from the solution feed section toward the periphery of the plating tank as practiced in the present invention, the interior of the plating tank is partitioned into an anode-side chamber and a wafer-side chamber. Accordingly, impurities generated from the anode do not reach the wafer surface. Also, in the case where an insoluble anode is used, the consumption of additive can be reduced. Further, bubbles generated from the anode during plating flow along the upward slanted diaphragm and are collected under the upper end portion of the diaphragm. The thus-collected bubbles are released to the exterior of the plating tank through the gas release port provided under a connecting portion between the diaphragm and the plating tank. Accordingly, the bubbles neither reach the wafer surface nor stagnate under the diaphragm.
The diaphragm used in the present invention is not particularly limited, and a diaphragm used in an ordinary plating process may be used. In order to effect sufficient separation in terms of the plating solution, a porous diaphragm is preferred. The type of diaphragm and the size of pores may be selected in consideration of a plating solution and additive employed.
According to the cup-type plating apparatus of the present invention, in order to maintain good plating conditions over a long period of time, separate solution circulation passages are provided so as to avoid mixing a solution fed into an anode-side chamber defined in the interior of the plating tank by the diaphragm, and a solution fed from the solution feed section toward the wafer. Accordingly, the solution fed toward the wafer, i.e., a plating solution, is not oxidized by the anode, and the consumption of additive in the plating solution is suppressed. Also, impurities generated from the anode are not mixed in the plating solution, thereby facilitating control of the plating solution.
Preferably, when plating is performed by use of the cup-type plating apparatus of the present invention, an electrolytic solution that contains ions of a metal to be plated onto a wafer is fed from the solution feed section toward the wafer, whereas an electrolytic solution that does not contain ions of a metal to be plated onto the wafer is fed into the anode-side chamber, thereby preventing the electrolytic solutions from mixing. As a result, there can be reduced the consumption of the electrolytic solution that contains ions of a metal to be plated onto the wafer; i.e., the consumption of a plating solution, thereby yielding a cost advantage. Also, since the composition of the electrolytic solution fed into the anode-si
Kurihara Mika
Sakaki Yasuhiko
Arent Fox Kintner & Plotkin & Kahn, PLLC
Bell Bruce F.
Electroplating Engineers of Japan Limited
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