Cup type plating apparatus

Details Cup type plating apparatus Cup type plating apparatus

2000-03-01

2002-09-24

Nguyen, Nam (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S253000

Reexamination Certificate

active

06454918

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for plating wafers for semiconductors, and particularly relates to a cup type plating apparatus.
2. Description of the Prior Art
As an apparatus for plating wafers for semiconductors, a cup type plating apparatus is known. Generally, this cup type plating apparatus, in which wafers are plated by mounting them at the opening of a plating tank, supplying a plating solution through a tube fixed at the bottom center of the plating tank for supplying solutions, and electrically connecting an anode provided in the plating tank and wafers connected to a cathode, has become widely used because of the suitability for production in small lots and automation of plating steps are possible.
However, this cup type plating apparatus also has some points to be improved. For example, when plating is carried out, films such as black film are formed on the surface of the anode which may come off, go into the plating solution as impurities, and reach surfaces of the wafers to be plated, causing unevenness in the quality of plating.
Also, when an insoluble anode is used in the plating apparatus, control of the quality of plating may become difficult due to decomposition of additives around the insoluble anode instead of dissolution of the anode metal, causing problems in management and cost.
Taking these points in consideration, a technology of providing a conductive diaphragm in the plating tank to separate the anode and the wafer from each other have been proposed as shown in Japanese Utility Model Application Laid-Open No. 62-36529, Japanese Patent Application Laid-Open 1-242797, Japanese Patent No. 2908790. This technology is excellent in that the diaphragm separating plating solutions of the anode side and of the wafer side prevents them from mixing, thereby preventing impurities from contacting the wafer and further the whole plating solution from being deteriorated.
Incidentally, the diaphragm to be used in this case is required to have an area roughly corresponding to the cross sectional area of the plating tank for the purpose of separating the anode and the wafer from each other. However, it is considerably difficult to put diaphragms to practical use, though there are many advantages, as there are technical difficulties in the production of diaphragms with large area as the production cost of these diaphragms with increased area increases with respect to increases in geometrical ratio.
The cup type plating apparatus having a diaphragm is often formed by separating a wafer side separate chamber above the diaphragm and an anode side separate chamber below the diaphragm, both separate chambers being provided with circulation tubes for charging and discharging the plating solution so that plating solution of each separate chamber can be circulated. Here in this specification, the route for charging the plating solution into and discharging it from the cathode side separate chamber is defined as the main plating solution circulation route, and the route for charging the plating solution into and discharging it from the anode side separate chamber is defined as the auxiliary plating solution circulation route.
The purpose of providing such separate plating solution circulation routes is to prevent impurities, such as those formed from black films formed on and removed from the anode or formed in the plating solution by decomposition of additives, from getting into the plating solution to be charged into the wafer side separate chamber. Therefore, a cup type plating apparatus provided with a diaphragm can significantly reduce defective plating in plating of wafers where uniform and accurate plating quality are required.
However, plating using this cup type plating apparatus with a diaphragm may cause such undesirable situations as follows. For example, in case of plating wafers with Cu using a cupric sulfate plating solution and a soluble Cu anode, Cu concentration of the plating solution in the anode side separate chamber increases, causing imbalance of Cu concentration between plating solutions in the wafer side and the anode side of separate chambers. Although a small amount of the plating solution of the anode side separate chamber infiltrates into the cathode side separate chamber forced by the osmotic pressure, increase of Cu concentration through dissolution of the Cu anode material proceeds much faster, resulting in significant difference in Cu concentration between the anode and the cathode side separate chambers. Once this phenomenon occurs, plating current efficiency is reduced accompanied by change in quality of plating, also causing the problem that stable plating becomes impossible.
Further, the conventionally used cup type plating apparatus has an advantage of being capable of uniformly plating all over target surfaces of plating, since the plating solution is supplied as upward flow against the target surface of plating of the mounted wafer so that the plating solution contacts the plating target surface as a flow spreading from the center toward the edge.
However, as slight bump is formed resulting in an edge between the solution outlet provided beneath the mounted wafer and the target surface of plating of the wafer in this cup type plating apparatus, there occurs a phenomenon in which flow of the plating solution stagnates around the edge resulting in non-uniform plating in the periphery of the target surface of plating. This phenomenon causes undesirable yield because usable area of wafers is restricted, so that technologies capable of widening usable area of wafers is required.
Accompanying the current progress of fine wiring processing technology, very fine processing has become available for circuit patterns provided on the surface of wafers, and technologies of more homogeneous plating has become required for wafer surfaces provided with such fine wiring processing as the target surfaces of plating.
Conventional cup type plating apparatus has not been so sufficient for these requests in more uniformly plating the whole target surface provided with fine wiring since the flowing condition of the plating solution constantly forms a flow spreading from the center towards the peripheral directions. Also there was limitation in uniformly plating larger area extending to peripheries of the plating target area of the wafers.
SUMMARY OF THE INVENTION
The present invention was completed with such a background as described above, and provides a technology capable of plating wafers more homogeneously than before when plating them by using a cup type plating apparatus. Particularly, the present invention enables use of a diaphragm for the cup type plating apparatus without any problem of cost required for the diaphragm, provides a cup type plating apparatus that can respond to variation of the concentration of plating solutions to allow plating at stably maintained concentrations of the solutions, even when separate plating solutions are circulated in the anode side and wafer side separate chambers formed in a plating tank by separation with a diaphragm, and further provides a cup type plating apparatus that avoids nonuniformity at the periphery of the target surface of plating due to the flowing condition of the plating solution in a conventional cup type plating apparatus, and enables more homogeneous plating all over the target surface of plating.
In the present invention, in order to solve the aforementioned problems, a wafer is plated by supplying a plating solution through a solution supply tube provided at a center bottom of a plating tank to the wafer placed at an opening at the top of a plating tank, while electrically connecting the anode provided in the plating tank and the wafer connected to the cathode, and in a cup type plating apparatus having a diaphragm for separating an anode and a wafer, a division wall having a plurality of openings covered with diaphragms is provided between an anode and a wafer so that they can be separated from each other.
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