Background of the Related Art Sub-quarter micron, multi-level metallization is one of the key technologies for the next generation of ultra large scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, lines and other features. Reliable formation of these interconnect features is very important to the success of ULSI and to the continued effort to increase circuit density and quality on individual substrates and die.

As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to less than 250 nanometers, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i. e., their height divided by width, increases. Many traditional deposition processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), have difficulty filling structures where the aspect ratio exceeds 4: 1, and particularly where it exceeds 10: 1. Therefore, there is a great amount of ongoing effort being directed at the

formation of void-free, nanometer-sized features having high aspect ratios wherein the ratio of feature height to feature width can be 4: 1 or higher. Additionally, as the feature widths decrease, the device current remains constant or increases, which results in an increased current density in the feature.

Elemental aluminum (Al) and its alloys have been the traditional metals used to form lines and plugs in semiconductor processing because of aluminum's perceived low electrical resistivity, its superior adhesion to silicon dioxide (Si02), its ease of patterning, and the ability to obtain it in a highly pure form. However, aluminum has a higher electrical resistivity than other more conductive metals such as copper, and aluminum also can suffer from electromigration leading to the formation of voids in the conductor.

Copper and its alloys have lower resistivities than aluminum and significantly higher electromigration resistance as compared to aluminum. These characteristics are important for supporting the higher current densities experienced at high levels of integration and increase device speed. Copper also has good thermal conductivity and is available in a highly pure state. Therefore, copper is becoming a choice metal for filling sub-quarter micron, high aspect ratio interconnect features on semiconductor substrates.

Despite the desirability of using copper for semiconductor device fabrication, choices of fabrication methods for depositing copper into very high aspect ratio features, such as a 4: 1, having 0.35 micron (or less) wide vias are limited. As a result of these process limitations, plating, which had previously been limited to the fabrication of lines on circuit boards, is now being used to fill vias and contacts on semiconductor devices.

Metal electroplating is generally known and can be achieved by a variety of techniques.

A typical method generally comprises physical vapor depositing a barrier layer over the feature surfaces, physical vapor depositing a conductive metal seed layer, preferably copper, over the barrier layer, and then electroplating a conductive metal over the seed layer to fill the structure/feature. Finally, the deposited layers and the dielectric layers are planarized, such as by chemical mechanical polishing (CMP), to define a conductive interconnect feature.

Fig. 1 is a flow circuit schematic diagram of a prior art electrochemical plating system 100 for depositing copper or other metals on a wafer or other substrate. The plating system 100 includes an electroplating tool platform 102 which has one or more electroplating cells 104 in which an electrolyte containing the material to be deposited, is circulated through each cell, to deposit the deposition material onto a wafer disposed within the cell 104. The deposition material is added to the electrolyte typically in the form of a chemical composition such as, for example, copper sulfate. The process of adding the deposition chemical to the electrolyte is often referred to as"dosing"and is usually performed by an electrolyte replenishment platform such as that indicated at 106.

The electrolyte replenishment platform 106, also often referred to as chemical cabinet,"typically includes a large tank 108 in which the deposition chemical is mixed with the electrolyte. An analyzer 110 analyzes the chemical composition of the electrolyte and indicates whether additional deposition chemical or other chemicals should be added to the electrolyte in the tank 108 to maintain a desired composition of the electrolyte.

The electrolyte replenishment platform 106 typically includes a pump 112 to pump the electrolyte from the main tank 108 though a supply line 114 to the electroplating tool platform

102. To provide a sufficient flow of electrolyte to the cells 104 of the electroplating tool platform 102, the supply line 124 is often relatively large. For example, to provide a flow of 30 gallons per minute from the electrolyte replenishment platform 106 to the electroplating tool platform 102, the supply line 124 often has an inner diameter of 1 inch (25 mm) in many systems. Moreover, to save valuable clean room space adjacent to the electroplating tool platform 102, the electrolyte replenishment platform 106 is often located a relatively large distance from the platform 102, including being located on another floor of the factory. Hence, many systems have a second, booster pump 116 positioned on the electroplating tool platform 102 to provide sufficient head pressure to the plating cells 104.

Prior to admitting the electrolyte into the cells 104, many electroplating tool platforms have one or more filters 118 positioned upstream of the inlets to the cells 104, to filter the electrolyte from the electrolyte replenishment platform 106. Positioned downstream of the cells 104, the electroplating tool platform often has one or more intermediate holding tanks 120 to collect the flow of electrolyte from the cells 104. The electrolyte is then pumped by yet another pump 122, via a return line 124, back to the main tank 108 of the electrolyte replenishment platform 106 for analyzing and dosing if needed. Another filter or set of filters 126 is often provided on the electrolyte replenishment platform 106 to filter the electrolyte before it is admitted to the main tank 108 of the electrolyte replenishment platform 106.

To maintain the quality of the deposition onto the substrate in the cells, it is often desirable to closely control the temperature of the electrolyte to facilitate the desired chemical reaction in the electrolytic cells 104. In many systems such as that shown in Fig. 1, the main holding tank 108 of the electrolyte replenishment platform 106 typically has a chiller unit installed in the tank 108 to cool the electrolyte to the desired temperature prior to recirculating

the electrolyte back into the cells 104.

The intermediate holding tanks 120 and the main holding tank 108 also usually have various sensors to monitor the electrolyte levels in the tanks. To avoid a potential overflow of hazardous electrolyte from the tanks, the flow rates by the various pumps 112,116 and 122 are controlled to lower an excessive level of electrolyte in one tank and pump the excess to the other tank.

Brief Description of the Drawings Figure 1 is a flow circuit schematic diagram of a prior art electrochemical plating system.

Figure 2 is a perspective view of an electroplating system in accordance with one embodiment of the inventions.

Figure 3 is a mechanical schematic view of the electroplating system of Fig. 2.

Figure 4 is a fluid flow circuit schematic diagram of the electroplating system of Figs. 2 and 3.

Figures 5A and 5B are fluid flow schematic diagrams showing the reservoir-cell recirculation circuit of the electroplating tool platform of Fig. 4 in greater detail.

Figure 5C is a fluid flow schematic diagram showing the reservoir-dosing system recirculation circuit of Fig. 4 in greater detail.

Figure 6 is a fluid flow schematic diagram of a dosing system platform in accordance with an alternative embodiment.

Summary of the Illustrated Embodiments In one illustrated embodiment of the present inventions, a method and apparatus for electroplating semiconductor substrates is provided which comprises recirculating electrolyte

between an electrolyte reservoir and at least one electrolytic plating cell through a reservoir-cell fluid recirculation circuit disposed in an electroplating tool plafform ; and recirculating electrolyte between the reservoir and a dosing unit through a reservoir-dosing unit fluid recirculation circuit which couples a dosing system platform to the electroplating tool platform. The electrolyte is dosed in the dosing system platform with additives using the dosing unit.

As explained in greater detail below, in one embodiment, the majority of the electro- chemical deposition solution, which in this embodiment is an electrolyte, recirculates locally in the electroplating tool platform. A relatively small flow of electrolyte may be diverted to the dosing system platform to be analyzed and dosed as needed. In addition, dosing may be achieved in a pressurized flow line rather than in an unpressurized reservoir or holding tank. As a consequence of these and other features discussed below, the complexity of the overall system can be substantially reduced and the reliability increased.

It should be understood that the preceding is merely a brief summary of one embodiment of the present inventions and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the inventions. The preceding summary, therefore, is not meant to limit the scope of the inventions. Rather, the scope of the inventions is to be determined only by the appended claims and their equivalents.

Detailed Description of the Drawings Figure 2 is a perspective view of an electro-chemical deposition system 150 in accordance with one embodiment of the inventions. Figure 3 is a mechanical schematic view of the electro-chemical deposition system of Fig. 2. Referring to both Figures 2 and 3, the electro-

chemical deposition system 150 includes an electroplating tool platform 152 and a dosing system platform 154, which doses an electro-chemical deposition solution for the electroplating tool platform 152. As explained in greater detail below, in one embodiment, the majority of the electro-chemical deposition solution, which in this embodiment is an electrolyte, recirculates locally in the electroplating tool platform 152. A relatively small flow of electrolyte is diverted to the dosing system platform 154 to be analyzed and dosed as needed. In addition, dosing may be achieved in a pressurized flow line rather than in an unpressurized reservoir or holding tank.

As a consequence of these and other features discussed below, the complexity of the overall system 150 can be substantially reduced and the reliability increased.

In the illustrated embodiment, the electroplating tool platform 152 generally comprises a loading station 210, a thermal anneal chamber 211, a spin-rinse-dry (SRD) station 212 and a mainframe 214. Preferably, the electroplating tool platform 152 is enclosed in a clean environment using panels such as plexiglass panels. The mainframe 214 generally comprises a mainframe transfer station 216 and a plurality of processing stations 218. Each processing station 218 includes one or more processing cells 220.

An architecture system and method in accordance with the present invention is applicable to a variety of electro-chemical deposition systems and electro-chemical deposition processes. Thus, the electro-chemical deposition system may utilize a variety of different types of electro-chemical deposition cells. An example of a suitable fountain type electroplating cell is described in copending application Serial No. 09/263,126, filed March 5,1999 and entitled "Apparatus for Electro-Chemical Deposition of Copper Metallization with the Capability of In-Situ Thermal Annealing"and assigned to the assignee of the present application. Similarly, the electro-chemical deposition system may utilize a variety of different electro-chemical deposition

solutions including electrolytes.

The dosing system platform 154 receives a relatively small flow of electrolyte via flow lines 222 from the electroplating tool platform 152 to dose with the appropriate chemicals prior to returning the electrolyte to the electroplating tool platform 152. The dosing system platform 154 may be positioned adjacent the electroplating tool platform 152 or at a substantial distance from the electroplating tool platform 152 such as on another floor of the factory. The electroplating tool platform 152 also includes a control system 223a, typically comprising a programmable microprocessor. The control system 223a may control the dosing system platform 154 as well, either as a complete controller or in combination with another controller 223b disposed on the dosing system platform 154. The controller 223b, like the controller 223a typically comprises a programmable microprocessor.

The loading station 210 preferably includes one or more wafer cassette receiving areas 224, one or more loading station transfer robots 228 and at least one wafer orientor 230. The number and positions of the wafer cassette receiving areas, loading station transfer robots 228 and wafer orientors included in the loading station 210 can be configured according to the desired throughput of the system. As shown for one embodiment-in Figures 2 and 3, the loading station 210 includes two wafer cassette receiving areas 224, two loading station transfer robots 228 and one wafer orientor 230. A wafer cassette 232 containing wafers 234 is loaded onto the wafer cassette receiving area 224 to introduce wafers 234 into the electroplating tool platform. The loading station transfer robot 228 transfers wafers 234 between the wafer cassette 232 and the wafer orientor 230. The loading station transfer robot 228 comprises a typical transfer robot commonly known in the art. The wafer orientor 230 positions each wafer 234 in a desired orientation to ensure that the wafer is properly processed.

The loading station transfer robot 228 also transfers wafers 234 between the loading station 210 and the SRD (spin-rinse-dry) station 212 and between the loading station 210 and the thermal anneal chamber 211.

Figure 4 shows a fluid flow circuit schematic diagram of the electro-chemical deposition system 150 of Figs. 2 and 3. Referring to Figs. 2-4, the electroplating tool platform 152 includes a main reservoir or holding tank 250 for the electrolyte. The main reservoir 250 is coupled by a first fluid recirculation circuit 252, which recirculates the electrolyte from the reservoir 250 to the electrolytic cells 220 and back to the main reservoir 250 of the electroplating tool platform 152. It should be appreciated that, in this embodiment, the electrolyte recirculates between the main reservoir and the processing cells 220 while remaining primarily in the electroplating tool platform 152. By recirculating locally in this reservoir-cell recirculation circuit 252, the complexity of the overall system can be substantially reduced.

To achieve this, it has been recognized by the present inventors that a relatively small flow of electrolyte may be diverted from the electroplating tool platform 152 and directed by a second fluid recirculation circuit 260 to the dosing system platform 154 to be dosed and returned to the reservoir 250 of the electroplating tool platform 152. In this manner, the electrolyte flowing through the processing cells 220 circulates primarily through the reservoir- cell recirculation circuit 252 of the electroplating tool platform 152. However, by diverting a relatively small flow through the reservoir-dosing system recirculation circuit 260 to the dosing system platform 154, the electrolyte flowing through the processing cells may be maintained at the desired chemical composition by the dosing system platform 154.

In another feature of the illustrated embodiments, the dosing system platform 154 has a dosing unit 262, which does not require any dosing reservoir on the dosing system platform 154 during normal dosing operations. Instead, as explained in greater detail below, the dosing unit 262 of the illustrated embodiment is primarily a pressurized flow line 264 having a plurality of inlets 266 for each fluid chemical to be added to the flow of electrolyte flowing through the flow line 264 of the dosing unit 262. As a consequence, the complexity of the system may be substantially reduced.

For example, the electro-chemical deposition system 150 of the illustrated embodiment has only a single pump 280, which is disposed in the electroplating tool platform 152. Since the dosing system platform 154 does not utilize an unpressurized reservoir for dosing, a pump which would be used to pump electrolyte from such a dosing reservoir may be eliminated. It is believed that the single pump 280 disposed in the electroplating tool platform 152 is sufficient to recirculate the electrolyte through the primary recirculation circuit 252 of the electroplating tool platform 152 and to recirculate the lesser flow of electrolyte through the secondary recirculation circuit 260 coupling the dosing system platform 154 to the electroplating tool platform 152.

Because the flow of electrolyte flowing the reservoir-dosing system recirculation circuit 260 may be relatively small (such as. 1-5 gallons per minute (. 38-18.9 liters), for example), the supply and return lines of the recirculation circuit 260 may be made relatively small (such as a 3/4 inch (19 mm) inner diameter, for example). By comparison, the supply and return lines of the primary recirculation circuit 252 may be on the order of 1 1/2 inch (38 mm) inner diameter or larger, to provide an electrolyte flow of 30 gallons (113.5 liters) per minute, for example, depending upon the size and number of processing cells in the tool platform 152.

For example, the average flow cross-sectional area of the primary recirculation circuit 252 may be 100-300 % larger than that of the reservoir-dosing system recirculation circuit 260, to provide an average flow rate in the primary recirculation circuit 252 that is 600-3000 % larger than that of the reservoir-dosing system recirculation circuit 260. The relative sizes of the recirculation circuits will of course depend upon the particular application. However, reducing the size of the supply and return lines of the recirculation circuit 260 is particularly convenient should the dosing system platform 154 be located a large distance (such as 20 feet (6 meters) for example) or even on a different floor from the electroplating tool platform 152.

For example, the dosing system platform 154 may be separated from the electroplating tool platform by 1-50 meters (3.3-164 feet) or more. Notwithstanding a large separation between the dosing system platform 154 and the electroplating tool platform 152, it is believed that an additional boost pump such as the pump 116 of the prior art system, for pumping the electrolyte from a chemical cabinet may be eliminated in many applications of an electroplating system in accordance with the present invention. However, in some applications, particularly those having a very large separation between the two platforms, a booster pump may be appropriate.

Still further, by eliminating a dosing reservoir from the dosing platform, the need for complex controls to balance the electrolyte level of such a dosing reservoir with the electrolyte level of a reservoir in the tool platform can be reduced or eliminated. Instead, if desired, the electro-chemical deposition system 150 may utilize a single reservoir 250 during plating operations such that the volume of the system may be readily fixed at a particular level. As a consequence, the controls may be substantially simplified.

In addition, the reservoir-cell recirculation circuit 252 has a filter or set of filters 282 and 324 disposed in the electroplating tool platform 152. It is believed that these filters are sufficient to filter the electrolyte such another set of filters disposed in the dosing system platform 154 to filter the electrolyte flowing through the secondary recirculation circuit 260 may be avoided if desired.

Figures 5A and 5B are schematic diagrams showing the reservoir-cell recirculation circuit 252 of the electroplating tool platform 152 in greater detail. As depicted therein, the reservoir-cell recirculation circuit 252 includes a main supply line 300 (Fig. 5A), which couples a drain outlet 250a of the main reservoir 250 to the inlet of the pump 280 which pumps a flow of electrolyte from the main reservoir 250 to the array of processing cells 220 (Fig. 5B) via the supply line 300. The pump speed and activation time is controlled by the controller 223a (Figs.

2 and 3), which monitors the flow through the supply line 300. A pressure sensor 302 and a flow meter 304 coupled to the supply line 300 provide output signals to the controller 223a, which are indicative of the pressure and flow rate, respectively, of electrolyte through the supply line 300. The main filter 282 is also disposed in the main supply line to filter the electrolyte being pumped to the array of processing cells 220 (Fig. 5B). A bleed indicated generally at 306 bleeds bubbles from the filter 282 and vents into the main reservoir 250. The main supply line 300 also includes suitable shut-off and control valves 310a, which may be controlled manually or by the controller 223a.

Referring now to Fig. 5B, in the illustrated embodiment, the main supply line 300 of the reservoir-cell recirculation circuit 252 of the electroplating tool platform 152 includes two branched supply lines 300a, each of which includes two branched supply lines 300b. Each supply line 300a has a control and/or shut off valve 310b. Each supply line 300b supplies a

flow of electrolyte to the inlet of one of the processing cells 220 of the array. To control the electrolyte flow rate into the inlet 220a of each processing cell, each processing cell supply line 300b includes a control loop comprising a control valve 312 and a flow meter 314. The flow rate control loop for each processing cell 220 may be controlled by the controller 223a or manually, if desired.

The reservoir-cell recirculation circuit 252 further includes a plurality of return lines 320, each of which is coupled to an electrolyte discharge outlet 220b of an associated processing cell 220. Each return line 320 may have a shutoff and/or control valve 31 Oc and a filter 324 to filter the electrolyte being discharged from the associated processing cell 220. The outlet of each filter 324 is coupled to the main reservoir 250. In this manner, the recirculation circuit 252 provides a complete circuit for recirculating the electrolyte from the main reservoir 250 to the array of processing cells and back to the main reservoir. In the illustrated embodiment, the electrolyte flow remains substantially local within the electroplating tool platform 152 while flowing in the reservoir-cell recirculation circuit 252.

In addition to the return lines 320, other return lines feed into the main reservoir 250.

More specifically, each filter 324 of the array of processing cells 220 has a bypass line 326 with an associated shut-off control valve 31 Od which permits the flow of electrolyte to bypass the filter 324 and return to the main reservoir 250 should it be desired. An anode bypass line 220b exchanges fresh electrolyte across the anode surface of the cell. The supply line 300b for each processing cell 220 is coupled to a bypass line 328 with an associated shut-off control valve 31 Oe, which permits the flow of electrolyte to bypass the associated processing cell and return to the main reservoir 250. Also, the main supply line 300 is coupled to a bypass line 330 with an associated pressure drop valve 31 Of, which permits the flow of electrolyte to bypass the

processing cells and return to the main reservoir 250.

The reservoir-dosing system recirculation circuit 260 includes a dosing system supply line 350 (Fig. 5A) having an inlet coupled to an outlet 352 of the main supply line 300 of the reservoir-cell recirculation circuit 252. As shown in Fig. 5C, the dosing system supply line 350 diverts a small flow of electrolyte from the main supply line 300 to an inlet 264a of the dosing system flow line 264 of the dosing unit 262, and thus provides a pressurized flow of electrolyte through the dosing system flow line 264. The dosing unit 262 includes a plurality of additive supply lines 360, each of which is coupled to one of a plurality of inlets 266 of the dosing system flow line 264. Each additive supply line 360 is coupled to one of a plurality of source tanks 364 (Fig. 3) to provide the various constituent chemicals of the desired electrolyte to the dosing system flow line 264. In the illustrated embodiment, an additive supply line 360 is provided for each of the constituents, copper sulfate CuS04, sulfuric acid H2SO4, and hydrochloric acid HCI. The particular additives may vary, depending upon the desired electro- chemical solution and the desired electro-chemical deposition process.

The reservoir-dosing system recirculation circuit 260 further includes a dosing system return line 380 having an inlet coupled to an outlet 264b of the dosing system flow line 265. As shown in Fig. 5A, the dosing system return line 380 is coupled to the main reservoir 250 of the electroplating tool platform 102. In this manner, the recirculation circuit 260 provides a complete circuit for recirculating the electrolyte from the main reservoir 250 to the dosing unit 262 of the dosing system platform 154 and back to the main reservoir. In the illustrated embodiment, the electrolyte remains pressurized within the dosing system platform 154 while flowing in the dosing unit 262. The electrolyte does not become unpressurized until it flows back into the unpressurized reservoir 250 of the tool platform 102. The electrolyte in the

reservoir-dosing recirculation unit circuit 260 is pressurized by the pump 280 which is shared with the reservoir-cell recirculation circuit 252.

As shown in Fig. 5C, the chemical composition of the electrolyte flowing through the reservoir-dosing system recirculation circuit 260 is analyzed by an analyzer 400 disposed in the dosing system platform 154. The reservoir-dosing system recirculation circuit 260 includes an analyzer sample supply line 402 coupled to the supply line 350 through a controller 403, which diverts a small sample flow of electrolyte from the supply line 350 to the analyzer 400 for chemical analysis. An analyzer sample return line 404 returns the sample flow of electrolyte to the return line 380 at a point downstream of the dosing unit 262. In the illustrated embodiment, the sample flow of electrolyte through the sample supply line 402, the analyzer 400 and the sample return line 404 remains pressurized.

The supply line 300 has a pressure drop 406 which may be set at a particular value (such as 1 gallon (3.8 liters) per minute, for example) to provide the desired flow into the sample supply line 402. A bypass line 408 continues the flow of pressurized electrolyte to the sample return line 404.

The analyzer 400 of the illustrated embodiment is a titration and CBS type analyzer ("Bantam"model) and is manufactured by Parker Technology. Other commercially available analyzers may be used as well. The analyzer 400 has a syringe to withdraw a sample from the sample flow for analysis. The analyzer 400 is electrically coupled to one or more of the controllers 223a and 223b and provides electrical signals to the appropriate controller, which are representative of the chemical analysis of the sample drawn from the electrolyte flowing through the analyzer. In response the controller, as needed, opens the appropriate control

valves 410 (Fig. 3) coupled to the additive inlets 266 to admit the appropriate quantities of additives to mix with the flow of electrolyte flowing through the dosing flow line 264 of the dosing unit 262 to achieve the desired chemical composition of the electrolyte in the system 150. The control valves 410 may include appropriate flow meters to measure the flow of additive in the associated additive inlet to provide a suitable flow control loop for each additive inlet 266.

Because a pressurized flow line is used to perform dosing rather than a large reservoir, the size or footprint of the dosing system platform 154 may be substantially reduced as compared to many prior chemical cabinets. Furthermore, a single dosing system platform 154' may be used to dose and/or analyze the electrolyte from a plurality of electroplating tool plafforms152a-152c as shown in Fig. 6 while maintain a relatively small footprint. The dosing system platform 154'may use one set of additive sources 364 (Fig. 3) to supply the additives for each of the dosing units of the platform 154'. A single analyzer 400 may be used to analyze the electrolyte from each of the tool platforms or alternatively, separate analyzers may be disposed on the platform 154'for use with the electrolyte from each tool if more complete separation of the flow lines is desired.

The reservoir 250 of the tool platform 152 further has a heat exchanger 500 which is coupled by supply and return lines 502 to a chiller unit 504. It is believed that the primary source of undesirable heating of the electrolyte is the pump or pumps of the system. In a system in accordance with the present invention, the size and number of pumps may be reduced because most of the electrolyte circulates locally on the electroplating too platform 152. The need to overcome a large head loss resulting from shuttling most or all of the system electrolyte to and from a remote chemical cabinet can be reduced or eliminated. As a

consequence, the drop in pump horsepower which the system may require can reduce the system cooling requirements at the same time. Moreover, it is believed that the electrolyte temperature may be more effectively controlled in many applications because the heat exchanger is located close to the point of delivery to the processing cells. In one embodiment, the reservoir 250 (and associated heat exchanger 500) may be located immediately adjacent to the processing cells 220. Alternatively, the reservoir 250 may be spaced less than 1 or 2 meters (3.3 or 6.6 feet) from the processing cells but is preferably spaced less than 5 meters (16.4 feet) from the processing cells to reduce pumping needs and increase temperature control accuracy. Of course, the actual distance may vary depending upon the particular application.

The dosing system platform 154 has a maintenance reservoir 600 (Fig. 5c) and associated maintenance plumbing indicated generally at 602. The reservoir 600 is not intended to be used during dosing but to provide a drain receptacle to permit the dosing system to be repaired or otherwise serviced when not in operation. Similarly, the plating tool platform 152 has maintenance plumbing indicated generally at 604,606 and 608 which is generally not used during plating but provide a drain system for servicing the plating platform when not in operation.

Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.