Method and apparatus for electroplating a semiconductor wafer
A method, apparatus and anode for plating copper or other metals onto a barrier or seed layer of a wafer surface is described. A copper layer of uniform thickness is plated on the surface by, for instance, maintaining a constant current density between the anode and wafer surface. Several configurations of anodes are described for obtaining the constant current density.
This invention relates to the field of electroplating metals onto a semiconductor wafer.
PRIOR ARTIn the fabrication of integrated circuits, metal layers are often formed on semiconductor wafers as part of a process for forming conductive lines. More recently, the electroplating of copper is used in a damascene process because of the high conductivity of copper when compared, for instance, to aluminum.
As shown in
The deposition rate of copper in a given area on the surface 14 is directly related to the current density, that is, the more current the more copper is deposited. The seed layer or barrier layer on the surface 14 has a relatively high resistivity. As a result, the current path between electrode 10 to electrode 12 follows paths of different resistance depending upon where on the wafer surface the current enters the barrier or seed layer as it moves toward the electrode 12. The path, for example, that includes the center of the wafer has more resistance because the current must travel the full radius of the wafer. In contrast, the path nearer the electrode 12 and electrode 10 has a relatively short path, and consequently, encounters a lower resistance. For this reason, the current flow between the anode and the wafer surface 14 is not uniform across the surface of the wafer. Less current flows in the center of the wafer and more current flows toward the periphery of the wafer per unit area. This causes the thickness of the copper layer to be thicker near electrode 12 and thinner in the center of the wafer.
The generally concave shaped copper layer formed on the wafer 13 is made uniform by polishing the layer using, for instance, chemical-mechanical polishing (CMP). There are numerous disadvantages with depositing a non-uniform layer and polishing it, some of these disadvantages are discussed later.
BRIEF DESCRIPTION OF THE DRAWINGS
Electroplating methods, apparatuses, and anodes, particularly for use in forming a metal layer on a semiconductor wafer are described. The methods, apparatuses, and anodes are described for the formation of a copper layer in a damascene process. It will be apparent that the present invention may be used for forming other layers. Moreover, in the following description, numerous specific details known in the art, such as for the formation of barrier and seed layers in a damascene process, and electroplating chemistry are not set forth in detail in order not to obscure the present invention.
With some of the methods, apparatuses, and anodes described below, a relatively uniform current density is achieved between the anode of the electroplating apparatus and the surface of the semiconductor wafer upon which the layer is plated. Several anode configurations are discussed below for providing this uniform current density. This uniform current provides a layer of relatively uniform thickness. Thus, for instance, in the formation of a copper layer in a damascene process, less polishing is required to provide a flat surface and to define the inlaid conductors. This more readily allows the use of mechanically weaker, lower k dielectrics. The need for a hard mask may be eliminated in some processes because of the uniform layer. Less polishing is needed which shortens the processing time. Other advantages will be apparent to one skilled in the art.
Referring first to
While not specifically shown in
The barrier layer, even with the seed layer, are not particularly conductive. Consequently, as described above, there is a significant voltage drop associated with the current flow between the first electrode 22 and the anode 26 as a function of the distance the current must travel.
The anode 26 of
In one embodiment, the density of the rods is greater at the center of the anode 26 than it is at a distance away from the center. For instance, as shown in
The rods are coupled to a source of potential with respect to the clamp/electrode 22. In
The anode 26 of
In another embodiment, the rods may be of uniform density within the anode 26 and the different voltages shown in
In yet another embodiment shown in
For all the embodiments, including the prior art, a reduction reaction occurs at the wafer and an oxidation reaction occurs at the anode. The wafer is negative relative to the anode and the Cu+2 ions in the plating solution, in which the electrode and wafer are submerged, are attracted to the wafer surface.
In the embodiment of
In the embodiment of
The cell 42 is filled with a plating solution. In practice, while not illustrated, the outlet 53 is a relatively short distance from the surface 41. Enough space is provided to allow the plating fluid to escape from a gap between the surface 41 and the outlet 53, as shown by the arrows. The plating solution first flows upward and then escapes through the gap between the cell and the wafer surface 41. Once the liquid has escaped the cell, it drains downward and away from the surface of the wafer. Consequently, only a fraction of the wafer surface is exposed to the electroplating solution at any given time.
The entire surface 41 can be electroplated by moving the cell relative to the surface 41. The anode voltage 60 is varied as the electroplating cell is moved. More voltage is applied near the center region than at the region near the electrode 52. This voltage variation provides a constant current density, and consequently, a constant plating rate. This results in a layer of uniform thickness.
Alternatively, the voltage 60 may remain constant and the rate at which the cell 40 is moved can be varied. For instance, the cell can be moved at a slower rate near the center of the wafer than at the periphery of the wafer. This again allows for a layer of uniform thickness since the plating rate at the center will be slower than at the periphery because of the added resistance at the center from the barrier or seed layer. A combination of the varied voltages and varied rate of movement can be used.
Thus, the method of the present invention is to provide an anode the results in a uniform layer being formed on a wafer surface. In some cases, as shown above, this is achieved by having a greater voltage drop between the anode and wafer surface at the peripheral regions of the surface. For instance, this occurs with the anode of the
Claims
1-9. (canceled)
10. An apparatus for electroplating a wafer comprising:
- a conductive clamp for engaging the periphery of a wafer; and
- an anode disposed above the wafer, comprising a plurality of conductive elements disposed in an insulative member, the conductive elements being coupled to at least one source of potential.
11. The apparatus of claim 10, wherein the conductive elements comprise a plurality of rods having a uniform density in the insulative member.
12. The apparatus of claim 10, wherein the conductive elements comprise a plurality of rods having a higher density in a center of the anode when compared to a distance away from the center of the anode.
13. The apparatus of claim 10, wherein the conductive elements include a plurality of concentric, annular members.
14. The apparatus of claim 10, wherein a plurality of voltages are applied to the conductive elements with a higher voltage being applied to conductive elements disposed at a center of the anode, when compared to conductive elements disposed at a distance away from the center of the anode.
15. The apparatus of claim 10, wherein the conductive elements comprise copper.
16. The apparatus of claim 11, wherein the conductive elements comprise copper.
17. The apparatus of claim 12, wherein the conductive elements comprise copper.
18. The apparatus of claim 13, wherein the conductive elements comprise copper.
19. The apparatus of claim 14, wherein the conductive elements comprise copper.
20. An apparatus for electroplating a wafer comprising:
- a conductive clamp disposed about the periphery of the electrode,
- a lenticular shaped anode disposed above a surface of the wafer such that the anode is closer to the wafer at a center of the wafer when compared to the periphery of the wafer.
21. The apparatus of claim 20, wherein the anode is copper.
22. An apparatus for electroplating a wafer comprising:
- an electrode disposed about the periphery of the wafer;
- a cell having an inlet and an outlet facing a surface of the wafer, the cell carrying an electroplating fluid and being movable such that the outlet of the cell, sweeps over substantially the entire surface of the wafer;
- an anode disposed within the cell; and
- a source of potential applied between the electrode and the anode.
23. The apparatus of claim 22, wherein the source of potential is varied as the cell moves.
24. The apparatus of claim 23, wherein the rate at which the cell moves is varied.
Type: Application
Filed: Apr 25, 2005
Publication Date: Sep 1, 2005
Inventor: James Powers (Aloha, OR)
Application Number: 11/114,312