Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-05-07
2001-02-27
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S279000
Reexamination Certificate
active
06193859
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to an apparatus for treating the surface of a substrate and more particularly to an apparatus for electroplating a layer on a semiconductor wafer.
BACKGROUND OF THE INVENTION
The manufacture of semiconductor devices often requires the formation of electrical conductors on semiconductor wafers. For example, electrically conductive leads on the wafer are often formed by electroplating (depositing) an electrically conductive layer such as copper on the wafer and into patterned trenches.
Electroplating involves making electrical contact with the wafer surface upon which the electrically conductive layer is to be deposited (hereinafter the “wafer plating surface”). Current is then passed through a plating solution (i.e. a solution containing ions of the element being deposited, for example, a solution containing Cu
++
) between an anode and the wafer plating surface (the wafer plating surface being the cathode). This causes an electrochemical reaction on the wafer plating surface which results in the deposition of the electrically conductive layer.
To minimize variations in characteristics of the devices formed on the wafer, it is important that the electrically conductive layer be deposited uniformly (have a uniform thickness) over the wafer plating surface. However, conventional electroplating processes produce nonuniformity in the deposited electrically conductive layer due to the “edge effect” described in Schuster et al., U.S. Pat. No. 5,000,827, herein incorporated by reference in its entirety. The edge effect is the tendency of the deposited electrically conductive layer to be thicker near the wafer edge than at the wafer center.
To offset the edge effect, Schuster et al. teaches non-laminar flow of the plating solution in the region near the edge of the wafer, i.e. teaches adjusting the flow characteristics of the plating solution to reduce the thickness of the deposited electrically conductive layer near the wafer edge. However, the range over which the flow characteristics can be adjusted is limited and difficult to control. Thus, it is desirable to have a method of offsetting the edge effect which does not rely on adjustment of the flow characteristics of the plating solution.
Another conventional method of offsetting the edge effect is to make use of “thieves” adjacent the wafer. By passing electrical current between the thieves and the anode during the electroplating process, electrically conductive material is deposited on the thieves which otherwise would have been deposited on the wafer plating surface near the wafer edge where the thieves are located. This improves the uniformity of the deposited electrically conductive layer on the wafer plating surface. However, since electrically conductive material is deposited on the thieves, the thieves must be removed periodically and cleaned adding to the maintenance cost and downtime of the apparatus. Further, additional power supplies must be provided to power the thieves adding to the capital cost of the apparatus. Accordingly, it is desirable to avoid the use of thieves.
Nonuniformity of the deposited electrically conductive layer can also result from entrapment of air bubbles on the wafer plating surface. The air bubbles disrupt the flow of ions and electrical current to the wafer plating surface creating nonuniformity in the deposited electrically conductive layer. One conventional method of reducing air bubble entrapment is to immerse the wafer vertically into the plating solution. However, mounting the wafer vertically adds complexity and hinders automation of the electroplating process. Accordingly, it is desirable to have an apparatus for electroplating a wafer which allows the wafer to be immersed horizontally into the plating solution and yet avoids air bubble entrapment.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus for depositing an electrically conductive layer on the surface of a substrate such as a wafer comprises a flange. The flange has a cylindrical wall and an annulus extending inward from the cylindrical wall, the annulus having an inner perimeter which defines a flange central aperture. The apparatus also includes a cup for supporting the wafer along a peripheral region thereof. The cup has a cup central aperture defined by an inner perimeter of the cup, the cup being positioned above the flange.
In one embodiment, the diameter of the flange central aperture is less than the diameter of the cup central aperture. The annulus of the flange thus extends under the edge region of the wafer surface and reduces the electric current flux to this edge region during electroplating. This, in turn, reduces the thickness of the deposited electrically conductive layer on the edge region of the wafer surface. Of importance, the thickness of the deposited electrically conductive layer on the edge region of the wafer surface is reduced without the use of thieves.
The thickness of the deposited electrically conductive layer on the edge region of the wafer can be varied by adjusting the diameter of the flange central aperture. To further decrease the thickness of the layer in this region, the diameter of the flange central aperture is decreased; conversely, to increase the thickness of the layer, the diameter is increased. Thus, the thickness profile of the deposited electrically conductive layer across the wafer surface can be readily adjusted by simply modifying the diameter of the flange central aperture.
The flange can further include a plurality of apertures extending through the cylindrical wall of the flange. By locating these apertures adjacent the cup and near the edge region of the wafer surface, air bubbles entrapped on the wafer surface can readily escape through the apertures. To further enhance removal of entrapped air bubbles, the wafer can be rotated while the plating solution is directed towards the center of the wafer surface.
By modifying the width of the apertures in the cylindrical wall of the flange, the electric current flux at the edge region of the wafer surface is adjusted. This, in turn, adjusts the thickness of the deposited electrically conductive layer on the edge region of the wafer surface. Thus, the thickness profile of the deposited electrically conductive layer across the wafer surface can also be readily adjusted by simply modifying the width of the apertures in the cylindrical wall of the flange.
In accordance with another embodiment of the present invention, a method of depositing an electrically conductive layer on the wafer surface includes providing a cup attached to a flange, the cup having an inner perimeter which defines a cup central aperture, the flange having an annulus. The wafer is then mounted in the cup so that the wafer surface is exposed through the cup central aperture. The cup and flange are then placed into a plating solution, the plating solution contacting the wafer surface. An electrical field and electric current flux is then produced between the wafer surface and an anode in the plating solution wherein the annulus of the flange shapes the electric current flux and reduces the thickness of the deposited electrically conductive layer on the edge region of the wafer surface.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings.
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pate
Contolini Robert J.
Dukovic John Owen
Feng Jingbin
Patton Evan
Reid Jonathan
Novellus Systems Inc.
Skjerven Morrill & MacPherson LLP
Steuber David E.
Valentine Donald R.
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