1. Field of the Invention
Generally, the present disclosure relates to the manufacture of sophisticated semiconductor devices, and, more specifically, to an adjustable current shield that may be employed in electroplating processes that are performed to form a conductive metal material.
2. Description of the Related Art
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. There are two general types of electroplating equipment: fountain plating equipment and vertical plating equipment. Both have relative advantages in some applications. Although the orientation of the surface of the wafer to be plated is different in the two different processes—horizontal in fountain plating equipment and vertical in vertical plating equipment—the process operations are very similar.
In general, electroplating involves making electrical contact with a so-called conductive “seed” layer that is formed on the wafer surface upon which the electrically conductive layer, e.g., copper, is to be deposited. 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 conductive seed layer on the wafer plating surface that acts as a cathode. The seed layer carries the electrical plating current from the edge of the wafer, where electrical contact is made, to the center of the wafer, including through embedded structures, trenches and vias. This causes an electrochemical reaction on the wafer plating surface which results in the deposition of the electrically conductive layer. Ideally, the final layer of material that is electrodeposited on the seed layer should completely fill the embedded structures, and it should have a specific thickness profile across the surface of the wafer. Generally, in electroplating processes, the thickness profile of the deposited metal should be controlled as much as possible.
In an attempt to minimize variations in the deposited material, it is important that the electrically conductive seed layer have a uniform thickness over the wafer plating surface. However, even with highly uniform seed layers, conventional electroplating processes produce a non-uniform deposition due to the so-called “edge effect” associated with such plating processes. In general, the edge effect refers to the tendency of the deposited electrically conductive layer to be thicker near the wafer edge than at the wafer center, i.e., an “edge-thick” profile. This edge-thick profile in the final layer is caused by, among other things, a decrease in current flow through the seed layer in the middle region of the wafer as compared to the current flowing near the edge region of the wafer. That is, since the conductive seed layer is contacted at the periphery of the wafer and the magnitude of the current flowing through the seed layer drops as one moves from the edge of the wafer toward the center of the wafer, there is less conductive material, e.g., copper, plated at the center of the wafer as compared to the edge region of the wafer.
The formation of such edge-thick layers of material makes subsequent processing more difficult. For example, such edge-thick layers of material make subsequent chemical mechanical polishing operations more difficult to perform, i.e., it makes it more difficult to obtain a substantially planar surface after the polishing process has been performed. As another example, various processing parameters of the electroplating process may be adjusted in an attempt to combat this tendency to produce conductive material layers with an edge-thick profile. However, such processing changes may result in producing a conductive layer that is too thin in the middle area of the wafer, thereby leading to the formation of defective wiring features that are not as thick as intended by the design process. Such defective wiring features may reduce the useful life of an integrated circuit product and, in a worst-case scenario, may lead to complete device failure.
One technique that has been employed in an effort to avoid or reduce the magnitude of the production of such edge-thick conductive layers involves the use of so-called current shields. Current shields are typically positioned between the anode and the wafer and they act to reduce the electrical field at the edge region of the wafer, which reduces the amount of the conductive material formed on the edge region of the wafer. The current shields may be made of a variety of materials, such as non-conductive, inert materials, like plastic. The current shields may be fixed or adjustable in terms of their area that is positioned between the anode and the wafer. In one example, a fixed current shield has a radial width of about 20-30 mm and a thickness on the order of about 2-3 mm. Such fixed current shields are typically sized and configured for a particular process flow and/or device by a trial and error process. Once acceptable results are achieved, the specifically designed current shield is used in production operations. Unfortunately, when there is a change in the design of the wafer or the process conditions, the existing current shield may not produce acceptable results. In that case, a new design of a current shield may need to be determined (by trial and error) and then put into production service. Alternatively, processing engineers may try to “make-do” with the less than desirable original current shield, which may lead to the production of conductive layers that do not have the desired or target thickness profile and the problems associated with such layers as discussed above.
The present disclosure is directed to a novel adjustable current shield that may solve or reduce one or more of the problems identified above.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
Generally, the present disclosure is directed to a plating tool that includes an adjustable current shield that may be employed in electroplating process operations. One illustrative plating apparatus disclosed herein includes a substrate holder that is adapted to receive a substrate, an anode and an adjustable current shield positioned between the substrate holder and the anode. In this illustrative embodiment, the adjustable current shield includes a stationary member, a moveable member that is adapted to be moved relative to the stationary member and a plurality of current shield members that are operatively coupled to either the stationary member or the moveable member, wherein each of the current shield members is rotatably pinned to either the stationary member or the moveable member and wherein each of the current shield members is adapted to rotate when there is relative movement between the moveable member and the stationary member.
Another illustrative plating apparatus disclosed herein includes a substrate holder that is adapted to receive a substrate, an anode and an adjustable current shield positioned between the substrate holder and the anode. In this illustrative embodiment, the adjustable current shield includes a stationary ring, a moveable ring that is adapted to be moved relative to the stationary ring and a plurality of current shield members operatively coupled to the stationary ring and the moveable ring, wherein each of the plurality of current shield members is rotatably pinned to either the stationary ring or the moveable ring and wherein each of the current shield members is adapted to rotate when there is relative movement between the moveable ring and the stationary ring, thereby moving a portion of each of the current shield members radially inward or outward depending upon the direction of the relative movement.
Yet another illustrative plating apparatus disclosed herein includes a substrate holder that is adapted to receive a substrate, an anode and an adjustable current shield positioned between the substrate holder and the anode, wherein the adjustable current shield includes a plurality of segmented shielding members that may be moved so as to effectively change a size of an opening of the adjustable current shield.
The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
The present disclosure is directed to an electroplating tool that includes an adjustable current shield that may be employed in electroplating process operations. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the methods and devices disclosed herein may be employed in a variety of different manufacturing applications and techniques, e.g., standard plating operations to form a uniform conductive layer, patterned plating applications, etc. Moreover, the methods and devices disclosed herein may also be employed in manufacturing a variety of different devices, including, but not limited to, logic devices, memory devices, etc. With reference to the attached figures, various illustrative embodiments of the methods and devices disclosed herein will now be described in more detail.
Also shown in
The illustrative electroplating bath 14 is a conventional bath that typically contains the metal to be plated, together with associated anions, in an acidic solution. Copper electroplating is usually performed using a solution of CuSO4 dissolved in an aqueous solution of sulfuric acid. In addition to these major constituents of the electroplating bath 14, it is common for the bath 14 to contain several additives, which are any type of compound added to the plating bath 14 to change the plating behavior. Three types of electroplating bath additives are in common use, subject to design choice by those skilled in the art: suppressors, accelerators and levelers. Suppressor additives retard the plating reaction and increase the polarization of the cell. Accelerator additives are normally catalysts that accelerate the plating reaction under suppression influence or control. Levelers behave like suppressors, but are highly electrochemically active (i.e., are more easily electrochemically transformed), losing their suppressive character upon electrochemical reaction. Levelers also tend to accelerate plating on depressed regions of the surface undergoing plating, thus, tending to level the plated surface. Of course, as will be appreciated by those skilled in the art after a complete reading of the present application, the inventions disclosed herein are not limited to use with any type of plating bath, as the inventions disclosed herein may be employed with a variety of different bath chemistries.
General aspects of a typical plating process will now be described. As will be appreciated by those skilled in the art, the container wall 16 of the plating apparatus 10 functions as an overflow weir. During typical operations, the substrate holder 20 is partially submerged in the plating bath 14 such that the electrolytic plating fluid wets plating surface 22F of the substrate 22 but does not wet the upper portions of substrate holder 20. In general, the plating fluid overflows the container/weir 16, as indicated by the arrows 32, into the space between the main plating bath container 12 and container wall 16. Thereafter, as indicated by the arrows 34, the plating fluid flows to the inlet 36 of a circulating pump 38. During operations, the circulating pump 38 typically continuously circulates plating fluid to the plating bath 14, as indicated by the arrow 26. In this manner, the bath height 18 may be maintained during plating operations. Generally, the plating solution flows upwards through openings (not shown) in the anode 30 and around the anode 30 toward the substrate 22. During use, the power supply 24 biases the wafer 22 to have a negative potential relative to the anode 30, causing an electrical current to flow from the anode 30 to the substrate 22. This also causes an electric current flux from the anode 30 to the substrate 22, wherein the electric current flux is defined as the number of lines of forces (field lines) through an area. This causes an electrochemical reaction (e.g., Cu+++2e−=Cu) which results in the deposition of the electrically conductive layer (e.g., copper) on the on the front face 22F of the substrate 22. The ion concentration of the desired metal in the plating solution may be replenished during the plating cycle by dissolving a metal of the anode 30, e.g., copper, in the plating solution.
With reference to
In the example depicted in
The effective width of the current shielding members 130 may be adjusted as follows. Rotation of the moveable ring 112 relative to the stationary ring 102 (by means of the lever 115 or the motor 140/gear teeth 113/142) in the direction indicated by the arrow 150 causes a portion of the current shielding members 130 to be extended radially inward, in the direction indicated by the arrow 150A, to thereby increase the effective width of the adjustable current shield 100. During this process, the current shielding members 130 pivot around the pin 108 on the stationary ring 102. The slot 134 cooperates with the pin 118 on the moveable ring 112 to allow the movement of the current shielding member 130. The amount or extent to which the current shielding members 130 may move radially inward depends upon the desired effective width of the adjustable current shield 100 and the specific design of the plating apparatus. Normally, the adjustable current shield 100 will have a limit on how far the moveable ring 112 may be rotated relative to the stationary ring 102, which will correspond to a maximum displacement of the current shielding members 130 (not shown) in the radially inward direction 150A. In some cases, to the extent that each of the current shielding members 130 overlapped with an adjacent current shielding member 130 when the adjustable current shield 100 was in its fully closed position (as shown in
As will be appreciated by those skilled in the art after a complete reading of the present application, the adjustable current shield 100 provides several advantages as it relates to performing plating operations. For example, to the extent that there is a change in the design of the substrates to be processed through the plating apparatus 10, or a change in the processing parameters, the adjustable current shield 100 provides a readily adjustable means by which a process engineer may attempt to reduce or eliminate the problems associated with producing plated metal layers with an edge-thick profile. Moreover, by adjusting the shape, size and/or number of current shielding members 130, as well as the extent to which portions of the current shielding members 130 may be positioned radially inward, a process engineer has greater processing flexibility to “tune” plating operations as necessary. In one embodiment, the subject matter disclosed herein is directed to a plating apparatus that includes a plurality of segmented shielding members that may be actuated simultaneously or individually to effectively change the size (effective diameter) of the opening or aperture of a substantially circular current shield.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.