US20090211900A1

US20090211900A1 - Convenient Replacement of Anode in Semiconductor Electroplating Apparatus

Info

Publication number: US20090211900A1
Application number: US12/036,177
Authority: US
Inventors: Robert Rash; Frederick Wilmot; Mitchell Gee
Original assignee: Novellus Systems Inc
Current assignee: Novellus Systems Inc
Priority date: 2008-02-22
Filing date: 2008-02-22
Publication date: 2009-08-27

Abstract

The convenient replacement of an anode in a semiconductor electroplating apparatus is disclosed. For example, in one disclosed embodiment, an electroplating system comprises an electroplating cell having an anode chamber, a cathode chamber, a selective transport barrier separating the anode chamber and the cathode chamber, and an anode disposed within the anode chamber. The anode comprises a plurality of pieces of anode material disposed within a removable anode holder.

Description

BACKGROUND

Electroplating is commonly used in integrated circuit manufacturing processes to form electrically conductive structures. For example, in a copper damascene process, electroplating is used to form copper lines and vias within channels previously etched into a dielectric layer. In such a process, a seed layer of copper is first deposited into the channels and on the substrate surface via physical vapor deposition. Then, electroplating is used to deposit a thicker copper layer over the seed layer such that the channels are completely filled. Excess copper is then removed by chemical mechanical polishing, thereby forming the individual copper features.
Some electroplating processes utilize consumable copper anodes. As copper is reduced out of solution at the substrate (cathode) surface, copper at a consumable anode is oxidized, thereby adding copper ions to the solution and reducing the mass of the anode. A consumable anode may be periodically replaced to replenish the mass of copper at the anode. Anode replacement generally involves bringing an electroplating system generally off-line during replacement, and therefore may reduce system throughput. To mitigate this by lessening the frequency at which replacement is performed, anodes having a large mass of copper may be used. However, such anodes may be expensive to produce due to the cost of the raw material and to the machining used to produce the anodes. Further, such anodes may be heavy and difficult to handle during replacement.

SUMMARY

Accordingly, the convenient replacement of an anode in a semiconductor electroplating apparatus is disclosed herein. For example, in one disclosed embodiment, an electroplating system comprises an electroplating cell having an anode chamber, a cathode chamber, a selective transport barrier separating the anode chamber and the cathode chamber, and an anode disposed within the anode chamber. The anode comprises a plurality of pieces of anode material disposed loosely within a removable anode holder.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an embodiment of a semiconductor electroplating system.

FIG. 2 shows a view of an embodiment of a portion of an anode in a semiconductor electroplating system.

FIG. 3 shows an exploded view of the embodiment of FIG. 2.

FIG. 4 shows a flow diagram depicting an embodiment of a method of changing an anode in a semiconductor electroplating system.

DETAILED DESCRIPTION

Prior to discussing the convenient replacement of an anode in a semiconductor electroplating assembly, an example use environment is described. FIG. 1 shows a block diagram of an embodiment of a semiconductor electroplating system 100. Electroplating system 100 comprises an electroplating cell 102 with an anode chamber 104 and a cathode chamber 106. The anode chamber 104 is defined by a selective transport barrier 108 that separates the anode chamber 104 from the cathode chamber 106, and includes an anode indicated schematically at 110.
The anode chamber 104 comprises an anolyte solution associated with the anode 110. The cathode chamber 106 comprises a “plating bath”, or catholyte, associated with a cathode 112. In one embodiment, the cathode 112 comprises a semiconductor wafer having trenches etched on its surface for damascene processing.
During electroplating, an electric field is established between the anode 110 and the cathode 112. This field drives positive ions from the anode chamber 104 through the selective transport barrier 108 and into the cathode chamber 106 and onto cathode 112. At the cathode, an electrochemical reaction takes place in which metal cations are reduced to form a solid layer of the metal on the surface of the cathode 112. An anodic potential is applied to the anode 110 via an anode electrical connection 114, and a cathodic potential is provided to the cathode 112 via a cathode electrical connection 116. In one embodiment, the metal ions are copper ions and copper metal is deposited in the trenches on the semiconductor wafer. In some embodiments, the cathode/substrate may be rotated during plating.
The selective transport barrier 108 allows a separate chemical and/or physical environment to be maintained within the anode chamber 104 and the cathode chamber 106. For example, the selective transport barrier 108 may be configured to prevent non-ionic organic species from crossing the barrier while allowing metal ions to cross the barrier. The catholyte may contain various organic additives, such as levelers, accelerators and suppressors, that aid in plating copper onto the cathode 112 but that may poison the anode 110 or otherwise harm anode performance. Therefore, the selective transport barrier 108 may be configured to prevent such organic additives in the catholyte from contaminating the anolyte while allowing copper from the anolyte to reach the catholyte.
The selective transport barrier 108 may be made from any suitable material or materials. In some embodiments, the selective transport barrier may be made from a material or material that is porous and that allows passage of both anions and cations. Examples of suitable materials include, but are not limited to, porous glasses, porous ceramics (e.g. alumina and zirconia), silica aerogels, organic aerogels, and porous polymeric materials such as Kynar, sintered polyethylene or sintered polypropylene. For many materials, the thickness, pore size, etc. can be adjusted to increase ionic conductance or decrease non-ionic diffusion. Generally, reducing the thickness and increasing pore size may increase the ionic conductance while also increasing non-ionic diffusion. Likewise, increasing the thickness and reducing pore size may decrease both of these parameters. Therefore, suitable thickness and/or pore sizes may be selected depending upon a desired balance between these characteristics.
In yet other embodiments, a multi-layer structure comprising one or more layers of a material with smaller pores and one or more layers of a material with larger pores may be used. For example, in one specific embodiment, the selective transport barrier 108 has a three-layer structure comprising a thin small pore size material sheet sandwiched between two thicker larger pore size material sheets. In a specific embodiment, the thin small pore size material is a sheet of porous polyolefin (such as polypropylene) having a thickness of approximately 10-50 microns and an average pore size of less than about 0.5 microns (e.g. 0.01-0.2 microns), while the thicker, large pore size material is a sheet of polyolefin having an average pore size of approximately 5-20 microns. The middle layer provides a large resistance to fluid flow through the selective transport barrier (due to the small pore size) while allowing good ionic conductivity (due to thickness), while the outer layers provide mechanical strength and extra resistance to flow.
The catholyte may be circulated between the cathode chamber 106 and a catholyte reservoir 120. The temperature and composition of the catholyte may be controlled within the catholyte reservoir 120. For example, concentrations of non-ionic organic plating additives may be controlled in the catholyte reservoir 120. Catholyte may be circulated between the catholyte reservoir 120 and the cathode chamber 106 via a combination of gravity and one or more pumps 122.
Likewise, the anolyte in the anode chamber 104 may be stored in and replenished from an anolyte reservoir 124. The temperature and composition of the anolyte may be controlled in the anolyte reservoir 124. Anolyte may be circulated through the anolyte reservoir 124 and the anode chamber 104 via a combination of gravity and one or more pumps 126. In some embodiments, anolyte from the anolyte reservoir 124 is introduced into the anode chambers via one or more outlets arranged to create a flow of anolyte laterally across the anode. This may facilitate mixing and help prevent any impurities present from poisoning the anode surface.
It will be understood that in some integrated circuit fabrication systems, plating operations maybe performed in parallel on multiple wafers using multiple electrofill modules. In such cases, central catholyte and/or anolyte reservoirs may supply multiple plating cells with catholyte and/or anolyte.
FIG. 2 shows a cut-away view of the plating cell 102 depicting anode 110 in more detail, and FIG. 3 shows an exploded view of the anode 110. In these views, the selective transport barrier 108, cathode 112, and other structures are omitted for clarity. The anode comprises a plurality of anode holders 202, one of which is shown in FIG. 2 and all of which are shown in FIG. 3, each containing a plurality of pieces of an anode material, which are referred to hereinafter as anode pieces 204. The anode holders 202 rest on a charge plate 206 configured to conduct electrical current to/from the anode holders 202 and the anode pieces 204. Further, a porous filter 208 is disposed between the charge holder and an anolyte outlet that leads to the anolyte reservoir 124.
The anode pieces 204 are disposed loosely within the anode holders 202 in that they are not connected to the anode holders 202 with bolts or other fasteners. The use of an anode holder 202 to hold loose anode pieces 204 offers various advantages compared to the use of a solid anode. For example, as mentioned above, a solid anode of sufficient thickness for high-volume industrial use may be quite heavy (e.g. greater than 60 lbs. for a 300 mm wafer plating cell), and therefore difficult to handle during installation. Further, the costs of machining such an anode may be quite expensive. Even when divided into a number of smaller segments (for example, three wedge-shaped segments each comprising 120 degrees of a cylindrical anode), the individual pieces still may be difficult to machine and handle. Additionally, solid anodes are generally connected to the anode chamber wall via fasteners such as bolts. Therefore, changing such an anode generally involves unbolting the used anode and then reinstalling the bolts to secure the new anode in place.
In contrast, the use of anode pieces 204 loosely disposed within an anode holder 202 may greatly reduce replacement and servicing costs. For example, such anode pieces 204 may be easily handled relative to large, solid anodes. Further, whereas solid anodes are generally bolted to a bottom portion of a plating cell, the anode holders 204 on the bottom of the plating cell. Therefore, servicing the anode 110 involves simply lifting the anode holders 202 out of the plating cell 102 via a handle 210 on each anode holder 202, pouring out the anode pieces, and then adding replacement anode pieces, without removing/reinstalling any bolts or other fasteners.
The anode pieces may have any suitable shape or size. Examples of suitable anode pieces include, but are not limited to, generally rounded or oval anode pieces having an average radius of approximately 0.5-0.75 inch. In one specific embodiment, the anode pieces have a generally rounded shape with an average diameter of approximately ½ inch. The use of relatively larger anode pieces 204 may facilitate the flow of anolyte solution through the anode pieces, while the use of relatively smaller anode pieces 204 may increase the mass of copper that can be held within the anode holders 202, and therefore reduce a frequency at which anode servicing is performed. It will be understood that the above-specified shapes and size ranges are disclosed for the purpose of example, and that anode pieces may have any other suitable shape and/or size.
The anode holders 202 likewise may have any suitable configuration. Suitable configurations include, but are not limited to, configurations that permit the free flow of anolyte through the anode holder and that help to prevent the escape of anode pieces 204 from the anode holder 202 as the anode pieces 204 reduce in size due to consumption. In the depicted embodiment, the anode holders 202 each take the form of an open basket defining a ninety-degree wedge of a circle (due to the circular cross-section of the plating cell 102). In other embodiments, either more or fewer anode holders 202 than four may be used, and the anode holders 202 may other suitable shapes. Generally, the user of larger anode holders 202 may allow the use of fewer total anode holders 202. This may allow a greater mass of copper to be held in the anode, as less total anode space is occupied by the anode holders 204. However, this also may lead to a greater weight for each anode holder 202 when loaded with new anode pieces 204, which may increase the difficulty of handling during anode replenishment. Likewise, the use of smaller anode holders 202 may increase the ease of handling during replenishment, but also may reduce the mass of copper in the anode due to the greater amount of space occupied by the anode holders 202.
Each anode holder 202 comprises a plurality of elongate openings 212 configured to admit a flow of anolyte into and out of the sides and bottom of the anode holder 202. The depicted openings 212 have a smallest dimension (i.e. the vertical dimension in FIGS. 2-3) configured to prevent used anode pieces 204 of an average reduced size from passing through the openings 202, and a largest dimension of sufficient size to avoid any openings being plugged shut by an anode piece 204. While the depicted openings 212 have an elongate oval shape, it will be understood that the openings may have any other suitable shape that enables anolyte flow while preventing escape of anode pieces and plugging by anode pieces. Examples include, but are not limited to, rectangular, trapezoidal, other polygonal shapes, other rounded shapes, and combinations of all of the above-described shapes.
The charge plate 206 is configured to be coupled to an electrical connection to deliver electric charge to the anode holders 202 and anode pieces 204. In the depicted embodiment, the anode holders 202 rest on the charge plate 206 without the use of any fasteners to connect the structures together. This allows the anode holders to be removed from the charge plate 206 in a quick and easy manner during anode servicing. However, in other embodiments, the anode holders 202 may be fastened to the charge plate 206.
The charge plate 206 may have any suitable configuration for transferring charge to the anode holders 202. In the depicted embodiment, the charge plate 206 comprises two halves 214, 216 each configured to be fixed within the anode chamber 104 via two bolts 217 (for a total of four bolts 217). In other embodiments, the charge plate may have a single piece, or more than two pieces. Further, the charge plate comprises a plurality of support feet 218 configured to support the charge plate 206 against the weight of the anode holders 202. Additionally, the charge plate 206 defines openings 220 configured to permit anolyte to flow out of the bottom of the anode holders 202 and into an anolyte outlet for transport to the anolyte chamber 124. In the depicted embodiment, the openings are positioned below a substantial portion of the bottoms of the anode holders 202, and the charge plate 206 contacts the anode holders 202 around a perimeter region of the bottom surface of the anode holders 202. However, the charge plate 206 may have any other suitable configuration other than that shown. Further, while the depicted charge plate is fixed within the anode chamber 104 via four bolts 217, it will be understood that either more or fewer bolts, or any other suitable fastener or fasteners, may be used.
The charge plate 206 and anode holders 202 may be made from any suitable material or materials. Suitable materials include materials that are inert to the anolyte solution used in a desired plating process. In the specific example of a copper plating process that utilizes a sulfuric acid/copper sulfate solution as an anolyte, one example of a suitable material is titanium. Further, the anode holders 202 may be partly or fully coated with a protective coating, such as a PTFE (polytetrafluoroethylene) coating or other polymer coating, to insulate the anode holder material from plating solutions, such as a copper sulfate solution. When the anode pieces become small (i.e. near end of life but before requiring replenishment), the anode holder 202 may pass current to a wafer during processing. This may cause electrolysis in the plating solution, and may introducing air bubbles under the selective transport barrier 108, which can disrupt the plating process. By coating a portion of the anode holder with such a protective coating (for example, the upper ¾ of the height of the anode holder), the electrical potential between the wafer and the anode holder may be reduced, and the anode pieces may remain the primary electrical source, thereby reducing the production of air bubbles.
The filter 208 is configured to prevent any anode pieces or fragments that escape from the anode holders 202 from being circulated toward the anolyte chamber 124, as such anode pieces or fragments may harm the pumping mechanisms used to circulate anolyte. Any suitable type of filter may be used as filter 208. In one embodiment, the filter 208 comprises a polypropylene mesh having a pore size of approximately 120 microns. Other suitable materials and/or other suitable filter pore sizes may be used in other embodiments. The depicted filter 208 comprises a plurality of holes 222 configured to accommodate the bolts 217 that fix the charge plate within the anode chamber 104, and a plurality of holes 224 configured to accommodate the charge plate support feet 218, but a filter may accommodate these structures in any other suitable manner than the depicted holes.
The filter 208 may be periodically changed to ensure proper anolyte fluid flow through the filter 208. The filter 208 may be changed each time the anode pieces 204 are changed, or on either a more frequent or less frequent basis. Because changing the filter involves removing only the four bolts 217 that hold the charge plate in the anode chamber 104, and does not involve the removal of any other fasteners, the filter change may not add any significant amount of time to the anode changing process, and therefore may be performed during anode servicing without substantially adding to system downtime.
As described above, the embodiments of anodes described herein may be easily serviced to replenish the copper mass of the anode, to replace the filter, and/or to service or change other parts. FIG. 4 shows an embodiment of a method 400 of changing an anode in a semiconductor electroplating device. Method 400 first comprises, at 402 removing electroplating fluids (i.e. the anolyte and catholyte) from the anode chamber and cathode chamber of a plating cell. Then, method 400 comprises, at 404, opening an access into the anode chamber. As described above, the plating cell embodiments disclosed herein comprise a selective transport barrier 108 that prevent additives in the catholyte from diffusing into the anolyte. Therefore, opening access to the anode chamber may comprise removing the selective transport barrier, as indicated at 406, or otherwise opening an access through the selective transport barrier.
Once access has been gained to the anode chamber, the anode holder or holders are removed from the electroplating cell at 408, and used anode pieces are removed from the anode holder at 410. Generally, all of the used anode pieces are removed from the anode holder during anode replacement, but under some circumstances, only a portion of the used anode pieces may be removed. Also, once the anode holders are removed from the anode chamber, the charge plate may be removed, the filter located between the charge plate and an anolyte outlet may be changed, and then the charge plate may be replaced.
Continuing with FIG. 4, method 400 next comprises, at 412, adding replacement anode pieces to the anode holder. Any suitable quantity of replacement anode pieces may be added to the anode holder. For example, if it is desired to maximize the amount of time or the number of plating cycles that pass between anode replacement, then the anode holders may be substantially completely filled with anode pieces. Alternatively, it may be desired under some circumstances to fill one or more anode holders only partially with anode pieces.
After adding replacement anode pieces to the anode chamber, method 400 next comprises closing access to the anode chamber, as indicated at 414. Closing access to the anode chamber may comprise, for example, placing the previously removed selective transport barrier (or a replacement barrier) back into the cell, as indicated at 416, or otherwise closing an access through the selective transport barrier. Then, as indicated at 418, the anolyte and catholyte electroplating fluids may again be added to the plating cell.
It be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.

Claims

1. An electroplating system, comprising:

an electroplating cell comprising an anode chamber, a cathode chamber, and a selective transport barrier separating the anode chamber and the cathode chamber; and

an anode disposed within the anode chamber and comprising a plurality of pieces of anode material disposed within a removable anode holder.

2. The electroplating system of claim 1, wherein the anode pieces comprise copper pieces.

3. The electroplating system of claim 2, wherein the copper pieces have a rounded shape with a radius in the range of 0.5-0.75 inches.

4. The electroplating system of claim 1, wherein the anode holder comprises a titanium basket.

5. The electroplating system of claim 1, wherein the anode holder comprises a plurality of elongate openings to admit a flow of an anolyte.

6. The electroplating system of claim 1, further comprising a plurality of anode holders.

7. The electroplating system of claim 1, wherein the anode holder is at least partially coated with a protective coating.

8. The electroplating system of claim 1, further comprising a charge plate on which the anode holder rests.

9. The electroplating system of claim 8, wherein the charge plate comprises one or more openings configured to pass a flow of plating solution received through the bottom surface of the anode holder, and wherein the electroplating system further comprises a filter disposed between the anode holder and a plating solution outflow.

10. An electroplating system, comprising:

an electroplating cell comprising an anode chamber, a cathode chamber, and a selective transport barrier separating the anode chamber and the cathode chamber;

a plurality of removable anode holders disposed within the anode chamber, each anode holder comprising a basket with one or more faces having a plurality of openings configured to admit a flow of anolyte through the anode holder; and

a plurality of copper anode pieces disposed loosely within each anode holder.

11. The electroplating system of claim 10, wherein the removable anode holders each comprise titanium baskets.

12. The electroplating system of claim 10, wherein at least some openings in the anode holders have an elongate shape with a small dimension that is smaller than an average smallest dimension of a used anode piece.

13. The electroplating system of claim 12, wherein the openings have an oval or rectangular shape.

14. The electroplating system of claim 10, wherein the anode holder is at least partially coated in a protective polymer coating.

15. The electroplating system of claim 10, further comprising a charge plate on which the anode holder rests, wherein the charge plate comprises one or more openings configured to pass a flow of plating solution received through a bottom of the anode holder, and wherein the electroplating system further comprises a filter disposed between the anode holder and a plating solution outflow.

16. In an electroplating system having an electroplating cell comprising an anode chamber, a cathode chamber separated from the anode chamber by a selective transport barrier, and an anode comprising a plurality of anode pieces contained within an anode holder, a method of servicing the anode, comprising:

removing electroplating fluids from the cathode chamber and the anode chamber;

opening an access to the anode chamber;

removing the anode holder from the electroplating cell;

removing at least some used anode pieces from the anode holder;

adding at least some replacement anode pieces to the anode holder;

closing the access between the cathode chamber and the anode chamber; and

adding electroplating fluids to the cathode chamber and the anode chamber.

17. The method of claim 16, wherein opening an access between the cathode chamber and the anode chamber comprises removing the selective transport barrier.

18. The method of claim 16, wherein the anode pieces comprise copper pieces.

19. The method of claim 16, wherein the anode comprises a plurality of anode holders, and wherein removing the anode holder from the electroplating cell comprises removing each anode holder from the plating cell.

20. The method of claim 16, wherein the electroplating system comprises a filter disposed fluidically between the anode holder and an electroplating fluid outlet, and further comprising replacing the filter before adding electroplating fluid to the anode chamber.