Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating substrate prior to coating
Reexamination Certificate
2000-01-27
2003-10-28
King, Roy (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating substrate prior to coating
C118S073000, C204S227000, C205S123000, C205S215000, C205S223000, C205S296000, C205S917000, C427S304000, C427S305000
Reexamination Certificate
active
06638411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for separating out metal copper according to an electroplating of copper using, for example, a solution of copper sulfate in order to fill copper in fine interconnection grooves formed in a surface of a substrate such as a semiconductor wafer to produce copper interconnections on the surface of the substrate.
2. Description of the Related Art
According to a conventional electroplating for plating a substrate with copper using a solution of copper sulfate, a substrate is dipped in sulfuric acid or the like so as to be activated by the acid in a pre-treatment process outside of a plating tank. Instead of such pre-treatment process, a substrate having a seed copper layer as an electrically conductive layer may be brought into contact with a solution of copper sulfate in the plating tank. A thin surface Cu layer etching without electrical current loading (de-energization) can be made for a certain period of time (activating time) in a pre-treatment process. Then, an electric current is supplied to separate out metal copper on the substrate after the pre-treatment process.
The former pre-treatment process is disadvantageous in that a tank different from the plating tank is necessary to carry out the pre-treatment process. Hence, the required facility is large and the running cost is increased.
On the other hand, the latter pre-treatment process is disadvantageous in that the plating solution and the seed copper layer on the substrate are not brought into contact with each other under constant conditions. Hence, additives such as a copper separation accelerator and a copper separation inhibitor contained in the plating solution tend to suffer initial adsorption irregularities to the surface of the seed copper layer and activation irregularities thereof Further, the substrate is susceptible to the specific adsorption of a component caused by a black film on a soluble anode positioned in confronting relation to the substrate. As a consequence, the metal copper is abnormally separated out locally on the surface of the substrate, causing the substrate to have a stained appearance. When the metal copper is nonuniformly and abnormally separated out locally, the crystal orientation of the copper and the thickness of the copper layer become irregular, making it difficult for the substrate to be polished to a flat finish by a chemical mechanical polishing (CMP) process after the plating process.
According to conventional solutions to the above problems, the activating time is increased, or the substrate is rotated or the plating solution is stirred by a device known as a squeegee, whereby adsorption irregularities and activation irregularities are eliminated. However, the activating process carried out for a long period of time tends to dissolve away the seed copper layer in its entirety because the seed copper layer provided as a fine interconnection pattern or a very thin electrode layer on the bottom of holes having a high aspect ratio is etched more than other portions, possibly making it impossible to embed metal copper according to electroplating. The other solutions referred to above are disadvantageous in that they make the entire system complex or large in size.
Further, the conventional copper plating process is problematic in that the thickness of the deposited copper film differs from location to location because of the presence of the interconnection pattern. According to this problem, specifically, the thickness of the deposited copper film is much larger in an area where fine interconnections are closely spaced than in an area which is free of fine interconnections. The hump, which is the difference between the thickness of the deposited copper film in the area where fine interconnections are closely spaced and the thickness of the deposited copper film in the area free of fine interconnections, may reach 1 &mgr;m. The hump presents difficulty in polishing the deposited copper film to a flat finish in the chemical mechanical polishing (CMP) process subsequent to the plating process. Any undesirable remaining copper film in the area where fine interconnections are closely spaced tends to cause a short circuit between the interconnections. Thus, the yield of substrates is likely to be lowered.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for plating a substrate with copper which can prevent metal copper from being separated out locally on the surface of the substrate, allow a plated copper film to be easily planarized in a chemical mechanical polishing (CMP) process after the plating process, and finish the substrate to a mirror-like glossy surface with a relatively simple facility and a process.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for plating a substrate with copper, comprising: bringing, at least once, a substrate into contact with a processing solution containing at least one of organic substance and sulfur compound which are contained in a plating solution; and bringing the substrate into contact with the plating solution to plate the substrate.
The substrate is brought into contact with the processing solution before the substrate is plated and/or while the substrate is being plated. The phrase “while the substrate is being plated” means while the plated film is being deposited in a stage before the thickness of the plated film reaches a final target thickness for the plated film.
In the above plating method, before the substrate is plated, the substrate is brought into contact with the processing solution which contains at least one of an organic substance and a sulfur compound which are contained in the plating solution. Alternatively, after the plating solution is removed from the substrate by interrupting plating of the substrate, the substrate is brought into contact with the processing solution.
The substrate may be brought into contact with the processing solution by directly dipping the substrate into the processing solution in a tank, spraying the processing solution over the substrate while the substrate is being rotated in a horizontal plane at a high speed as with a spin dryer, or supplying the processing solution by a pump into a dedicated dipping chamber in which the substrate is set at a predetermined position. When the substrate is thus brought into the processing solution, a thin film of the organic substance and/or the sulfur compound is coated on the processed surface of the substrate. Extra processing solution is preferably removed from the substrate, and then the substrate is plated with copper according to a conventional process. In this manner, metal copper is prevented from being separated out locally on the processed surface of the substrate, and the substrate is plated to provide a mirror-like glossy surface. Further, the size of humps in an area of closely spaced interconnections on the processed surface of the substrate can be suppressed.
Thereafter, it is preferable to remove the processing solution from the substrate and/or to dry the substrate to minimize any amount of processing solution carried into the plating solution to maintain a better quality of the plating solution. However, since the amount of processing solution which is coated is usually much smaller than the amount of plating solution, removing the processing solution from the substrate and/or drying of the substrate are not necessarily required. The processing solution may be removed from the substrate by simply lowering the level of processing solution, lifting the substrate out of the processing solution, rotating the substrate to spin off the processing solution from the substrate as with a spin dryer, rotating the substrate and applying a nitrogen gas blow to the substrate, or passing the substrate through a forced air flow such as an air blower. Further, the two processes including removing of the processing solution and dry
Kaneko Hisashi
Kimizuka Ryoichi
Matsuda Tetsuo
Mishima Koji
Nagai Mizuki
Ebara Corporation
King Roy
Leader William T.
Wenderoth , Lind & Ponack, L.L.P.
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