Abstract:
A plating chemical replenishment system is described having a tank for supporting a chemical solution used in a plating fluid, a container having a pre-determined volume, a first valve for selectively coupling the chemical solution from the tank to the container to form a pre-determined volume of the chemical solution within the container, and a second valve for selectively dispensing the pre-determined volume of the chemical solution from the container to a plating fluid reservoir. Also disclosed is a method of dispensing a plating solution to a plating fluid reservoir, comprising the steps of forming a pre-determined volume of the plating solution; and dispensing the pre-determined volume of the plating solution to the plating fluid reservoir. In addition, a plating system is provided for plating a surface of an article, comprising a plating fluid tank for supporting a plating fluid reservoir, a plating apparatus for using plating fluid from the plating fluid reservoir to plate the surface of the article; and a plating chemical replenishment system. The replenishment system has a chemical solution tank for supporting a chemical solution used in a plating fluid; a container having a pre-determined volume; a first valve for selectively coupling the chemical solution from the chemical solution tank to the container to form a pre-determined volume of the chemical solution within the container; and a second valve for selectively dispensing the pre-determined volume of the chemical solution from the container to the plating fluid reservoir.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to plating systems, and in particular, to a system, apparatus and method for replenishing a plating fluid reservoir used in plating wafers, substrates, and other articles. Although the disclosure uses the plating of a wafer to exemplify the invention, it shall be understood that the plating of other articles including ceramic substrates is within the scope of the invention. 
     BACKGROUND OF THE INVENTION 
     The plating of wafers, substrates and other articles involves many parameters that need to be controlled to achieve a desired plating characteristics. These parameters may include the electrostatic field between the anode and the cathode in contact with the article to improve the uniformity of the plating deposition across the surface of the wafer, the ion concentration gradient between the anode and the cathode contact with the article to improve the plating rate, and the placement of the wafer within a plating bath to improve the plating of via holes on the wafer. There are many other parameters that affect the plating characteristic of a wafer. 
     One particular plating parameter of interest to the invention is the chemical composition of the plating fluid used in plating wafers, substrates, and other articles. A typical plating fluid comprises a mixture of different chemical solutions including de-ionized (DI) water. In order to obtain a desired plating characteristic across the surface of a wafer, the plating fluid should include the proper concentrations of these chemical solutions. If the proper concentrations of these chemical solutions are not present in the plating fluid, the desired plating characteristic across the surface of a wafer may not be achieved. Therefore, it is desired to properly set and maintain the desired concentrations of the chemical solutions in the plating fluid prior to and during the plating of a wafer. 
     One impediment to maintaining the desired concentrations of the chemical solutions in a plating fluid during the plating cycle is that these concentrations are continuously changing. One reason for this is that the chemical solutions continuously dissipate, decompose, and/or combine with other chemicals during the plating cycle. Thus, the concentrations of the various chemicals in a plating fluid will change with time if the plating fluid is left alone. Accordingly, plating apparatus provide specialized devices to control the concentrations of the chemicals in the plating fluid during the plating cycle. 
     One such specialized device is a chemical real time analyzer (RTA). An RTA is a device that probes the plating fluid and periodically determines the concentrations of the chemicals in the plating fluid. Using the information of the current concentrations of the chemicals in the plating fluid, the RTA then determines which and amount of chemical solutions that need to be added to the plating fluid and the amount of plating fluid that needs to be drained prior to adding the chemicals in order to achieve the desired concentrations for the chemicals in the plating fluid. This information is used to control a chemical replenishment system that precisely drains the plating fluid reservoir and precisely adds the proper quantities of chemical solutions to the plating fluid to achieve the desired concentrations for the chemicals in the plating fluid. The measuring and replenishing of the plating fluid occurs periodically during a plating cycle. 
     The invention provides a plating system, a plating chemical replenishment apparatus and method that precisely adds the right quantities of chemical solutions and precisely drains the plating fluid under the control of an RTA to achieve the desired concentrations for the chemicals in the plating fluid. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is a plating chemical replenishment system, comprising a tank for supporting a chemical solution used in a plating fluid; a container having a pre-determined volume; a first valve for selectively coupling the chemical solution from the tank to the container to form a pre-determined volume of the chemical solution within the container; and a second valve for selectively dispensing the pre-determined volume of the chemical solution from the container to a plating fluid reservoir. In the preferred embodiment, the plating chemical replenishment system includes a bleed line fluidly coupled to the container to remove gases formed within the container. Also in the preferred embodiment, the plating chemical replenishment system includes a pressurized gas source to force the chemical solution out of the container during the dispensing of the pre-determined volume of chemical solution to the plating fluid reservoir. The replenishment system may also be used to drain plating fluid from the plating fluid reservoir. 
     A second aspect of the invention is a method of dispensing a plating solution to a plating fluid reservoir, comprising the steps of forming a pre-determined volume of the plating solution, and dispensing the pre-determined volume of the plating solution to the plating fluid reservoir. In the preferred implementation of the dispensing method, a step is provided to remove gas from a container during the step of forming the pre-determined volume of plating solution. In addition, a step is provided to force the pre-determined volume of plating solution from the container using pressurized gas during the dispensing step. 
     A third aspect of the invention is a plating system for plating a surface of an article, comprising a plating fluid tank for supporting a plating fluid reservoir; a plating apparatus for using plating fluid supplied from the plating fluid reservoir to plate the surface of the article; and a plating chemical replenishment system to periodically replenish the plating fluid reservoir during plating. The replenishment system a chemical solution tank for supporting a chemical solution used in the plating fluid; a container having a pre-determined volume; a first valve for selectively coupling the chemical solution from the chemical solution tank to the container to form a pre-determined volume of the chemical solution within the container; and a second valve for selectively dispensing the pre-determined volume of the chemical solution from the container to the plating fluid reservoir. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a block diagram of an exemplary plating system in accordance with the invention; 
     FIG. 2 illustrates a simplified block diagram of a portion of a chemical solution dispensing apparatus in accordance with the invention; 
     FIG. 3 illustrates a simplified block diagram of another chemical solution dispensing apparatus in accordance with the invention; 
     FIG. 4 illustrates a schematic diagram of an exemplary plating chemical replenishment system in accordance with the invention; 
     FIG. 5 illustrates a block diagram of a dispensing apparatus  500  that can be used for dispensing a pre-determined volume of plating chemical solutions or DI-water; and 
     FIGS. 6A-6C are front, top and side views of a preferred embodiment of a plating chemical replenishment system in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. Plating System with Plating Chemical Replenishment System 
     FIG. 1 illustrates a block diagram of an exemplary plating system  100  in accordance with the invention. The plating system  100  preferably comprises a plating fluid reservoir  102  for supplying fresh plating fluid to a plating apparatus  104 . The plating apparatus  104  uses the fresh plating fluid to form a plating deposition across the surface of a wafer, substrate or article (not shown). The plating apparatus  104  may be of the types described in pending patent application Ser. No. 09/348,768, filed on Jul. 7, 1999, now U.S. Pat. No. 6,197,182, entitled “Improved Apparatus and Method For Plating Wafers, Substrates and Other Articles” and pending patent application Ser. No. 09/407,635, filed on Sep. 28, 1999, entitled “Anode Having Separately Excitable Sections to Compensate for Non-Uniform Plating Deposition Across the Surface of a Wafer Due to Seed Layer Resistance.” These applications are incorporated herein by reference. After the fresh plating fluid is used by the plating apparatus  104 , the used plating fluid is fed to a filter  106  to remove contaminants, and then recycled back to the plating fluid reservoir  102 . 
     As it was previously discussed, the concentrations of the various chemicals in the plating fluid should be properly set and maintained to achieve the desired plating characteristic. However, the concentrations of these chemicals change over time due to dissipation, decomposition, and undesired chemical reactions. Thus, the plating fluid reservoir  102  should be periodically tested and replenished during plating to maintain the proper concentrations of the chemicals in the plating fluid so that the desired plating characteristics are achieved. In this respect, the plating system  100  comprises a chemical real time analyzer (RTA)  108  and a plating chemical replenishment system  110 . The RTA  108  periodically measures the concentrations of the various chemicals in the plating fluid by way of a sense line. The RTA  108  then uses this measurement to determine the quantity of plating fluid to drain from the plating fluid reservoir  102  and the quantity of the various chemical solutions including de-ionized (DI) water to add to the plating fluid reservoir to maintain the desired concentrations for the various chemicals in the plating fluid. 
     The RTA  108  uses the information regarding the quantity of plating fluid to drain and chemicals to add to control, via a control line, the plating chemical replenishment system  110 . The replenishment system  110 , under the control of the RTA  108 , precisely drains the plating fluid reservoir and precisely dispenses the quantities of the various chemicals including DI-water to the plating fluid reservoir  102  to achieve the desired concentrations of the chemicals in the plating fluid. For instance, the plating fluid may comprise five different chemical solutions labeled in FIG. 1 as Chm. Sol. 1-5 and DI-water. The replenishment system  110  independently controls the dispensing of Chm. Sol. 1-5 and DI-water. The dispensing of the chemicals (Chm. Sol. 1-5) including DI-Water and draining of the plating fluid reservoir should be controlled very precisely to achieve the desired concentrations of the chemicals (Chm. Sol. 1-5) in the plating fluid. The dispensing methodology of the invention achieves this precision dispensing of the chemicals and DI-water, and draining of the plating fluid reservoir  102 . 
     II. Dispensing Methodology 
     FIG. 2 illustrates a simplified block diagram of a chemical solution dispensing apparatus  200  used to illustrate the dispensing methodology in accordance with the invention. The dispensing apparatus  200  may be used to dispense the chemical solutions (Chm. Sol. 1-5) or DI-Water separately as part of the replenishment system  110 . The dispensing apparatus  200  comprises a tank  202  containing the chemical solution or DI-Water to be dispensed. The tank  202  includes an outlet that may be selectively coupled to a pre-determined volume  206  by way of a valve  204 . The valve  204  receives a signal CNTL  1  that controls the opening and closing of the valve  204 . The pre-determined volume  206  includes an outlet coupled to a second valve  208  for selectively dispensing the pre-determined volume  204  of the chemical solution to the plating fluid reservoir  102 . The valve  208  receives a signal CNTL  2  that controls the opening and closing of the valve  204 . 
     Prior to dispensing, the control signals CNTL  1 - 2  are set such that both valves  204  and  208  remain closed. To dispense a discrete pre-determined volume of chemical solution into the plating fluid reservoir  102 , the control signal CNTL  1  is set to open valve  204  so that the chemical solution flows from tank  202  into pre-determined volume  206 . Once the pre-determined volume  206  is filled with the chemical solution, the control signal CNTL  1  is set to close valve  204 . Then, the control signal CNTL  2  is set to open valve  208  to allow the chemical solution in the pre-determined volume to flow to the plating fluid reservoir  102 . Once the pre-determined volume is drained, the control signal CNTL  2  is set to close valve  208 . This process is repeated a number of times as required by the RTA  108  so that the proper quantity of chemical solution is dispensed into the plating fluid reservoir  102 . The pre-determined volume  206  should be sized to the desired incremental volume resolution. 
     The draining of the plating fluid reservoir  102  using this dispensing methodology is accomplished in a similar manner, except that in this case, the tank  202  is replaced with the plating fluid reservoir  102  and the output of valve  208  is fluidly coupled to a waste tank. In a similar fashion, control signal CNTL  1  is set to open valve  204  to allow plating fluid to drain from the plating fluid reservoir  102  into the pre-determined volume  206 . Once the pre-determined volume  206  is filled, the control signal CNTL  1  is set to close valve  204 . Then, the control signal CNTL  2  is set to open valve  208  so that the plating fluid in the pre-determined volume  206  flows to the waste tank. Once this occurs, control signal CNTL  2  is set to close valve  208 , and the process is repeated until the desired amount of plating fluid is drained from the plating fluid reservoir  102 . As in the dispensing case, the pre-determined volume  206  in the draining case should be sized at the desired decremental volume resolution. 
     FIG. 3 illustrates a simplified block diagram of another chemical solution dispensing apparatus  300  used to illustrate the dispensing methodology in accordance with the invention. As with dispensing apparatus  200 , the dispensing apparatus  300  may be used to dispense the chemical solutions (Chm. Sol. 1-5) or DI-Water separately as part of the replenishment system  110 . The dispensing apparatus  300  differs from dispensing apparatus  200  in that the former provides a technique to remove trapped gas in the pre-determined volume  306  when it is being filled. During filling of the pre-determined volume  306 , air or other gases may sneak their way into the pre-determined volume  306 . As a result, the amount of chemical solution in the pre-determined volume  306  may be less than the pre-determined volume due to the presence of trapped gases. Thus, there is a need to remove the trapped gas to insure that the volume of the chemical solution is substantially the same as the volume of the pre-determined volume  306 . 
     In the preferred embodiment, the dispensing apparatus  300  comprises a tank  302  containing the chemical solution or DI-Water to be dispensed into the plating fluid reservoir  102 . The tank  302  includes an outlet that may be selectively coupled to a pre-determined volume  306  by way of a valve  304 . The valve  304  receives a signal CNTL  3  that controls the opening and closing of the valve  304 . The pre-determined volume  304  includes an outlet coupled to a one-pole, two-throw valve  308 . A control signal CNTL  4  is used to selectively couple the input of the valve  308  to either output. One of the outputs of valve  308  is fluidly coupled to the plating fluid reservoir  102  and the other output is fluidly coupled to a bleed line  310 . The bleed line  310  gives the dispensing apparatus  300  the ability to remove trapped gas in the pre-determined volume  306  prior to dispensing the chemical solution from the pre-determined volume  306  into the plating fluid reservoir  102 , as discussed in detail as follows. 
     Prior to dispensing, the control signal CNTL  3  is selected to set valve  304  in a closed position, and control signal CNTL  4  is selected to set valve  308  such that its input is coupled to the output connected to the bleed line  310 . To dispense a discrete pre-determined volume of chemical solution into the plating fluid reservoir  102 , the control signal CNTL  3  is set to open valve  304  so that the chemical solution flows from tank  302  into the pre-determined volume  306  and into the bleed line  310 . After sufficient amount of chemical solutions is dispensed from the tank  302  to fill the pre-determined volume  306  and to at least partially fill the bleed line  310 , the control signal CNTL  3  is set to close valve  304 . 
     The end of the bleed line is preferably positioned above the pre-determined volume  306  so that substantially all the trapped gas within the pre-determined volume  306  flows due to buoyancy into the bleed line  310 . After a sufficient time to allow substantially all the gas to leave the pre-determined volume  306 , the control signal CNTL  4  is set to fluidly couple the input of valve  308  to the output that is coupled to the plating fluid reservoir  102 , thereby dispensing the pre-determined volume of chemical solution into the plating fluid reservoir  102 . This process is repeated a number of times as required by the RTA  108  so that the proper quantity of chemical solution is dispensed into the plating fluid reservoir  102 . The pre-determined volume  306  should be sized at the desired incremental volume resolution. 
     The draining of the plating fluid reservoir  102  using this dispensing methodology is accomplished in a similar manner, except that in this case, the tank  302  is replaced with the plating fluid reservoir  102  and one of the outputs of valve  308  is fluidly coupled to a waste tank. In a similar fashion, control signal CNTL  3  is set to open valve  304  to allow plating fluid to drain from the plating fluid reservoir  102  into the pre-determined volume  306  and the bleed line  310 . Once the pre-determined volume  306  is filled and the bleed line  310  is at least partially filled, the control signal CNTL  3  is set to close valve  304 . After a sufficient time to allow substantially all the gas to leave the pre-determined volume  306 , the control signal CNTL  4  is set to fluidly connect the input of valve  308  to the output that is coupled to the waste tank, thereby draining the pre-determined volume of plating fluid from the plating fluid reservoir  102 . This process is repeated a number of times as required by the RTA  108  so that the proper quantity of chemical solution is drained from the plating fluid reservoir  102 . The pre-determined volume  306  should be sized at the desired decremental volume resolution. 
     III. The Preferred Embodiment of the Plating Chemical Replenishment System 
     A. Preferred Elements of the Plating Chemical Replenishment System 
     FIG. 4 illustrates a schematic diagram of an exemplary plating chemical replenishment system  400  in accordance with the invention. The replenishment system  400  comprises at least one tank for each chemical solution required for the plating fluid. In this case, for example, the replenishment system  400  includes five chemical solution tanks  402 - 1  through  402 - 5 . The replenishment system  400  also includes an inlet  402 - 6  for DI-water as required by the plating fluid mixture. The outputs of the chemical solution tanks  402 - 1  through  402 - 5  are fluidly coupled to respective normally-closed (N.C.) inputs of one-pole, two-throw pneumatic valves  404 - 1  through  404 - 5 . The DI-water inlet  402 - 6  is fluidly coupled to one-a normally-closed (N.C.) input of one-pole, two-throw pneumatic valve  404 - 6  by way of T-fitting  403 , which has a port fluidly coupled to a DI-water drain  405 . The chemical solutions tanks  402 - 1  through  402 - 5  are fluidly coupled to vent/clean line  406  by way T-fittings  408 - 1  through  408 - 4 . The vent/clean line  406  is fluidly coupled to an output port (C) of one-pole, two-throw pneumatic valve  410 . The valve  410  has a normally-open (N.O.) input fluidly coupled to a vent  412 , and a normally-closed (N.C.) input fluidly coupled to a compressed dry air (CDA)/DI-water select inlet  414  by way of T-fitting  416 . 
     The valves  404 - 1  through  404 - 6  respectively have normally-open (N.O.) inputs fluidly coupled to a low pressure CDA/clean line  418  by way of T-fittings  420 - 1  through  420 - 5 . The CDA/clean line  418  is fluidly coupled to an output port (C) of one-pole, two-throw pneumatic valve  422 . The valve  422  has a normally-closed input (N.C.) fluidly coupled to T-fitting  416 , and a normally-open (N.O.) input fluidly coupled to an output port of valve  424 . The valve  424  has an input fluidly coupled to a low pressure CDA source  426 . The valves  404 - 1  through  404 - 6  also respectively have output ports (C) fluidly coupled to respective inputs (C) of one-pole, two-throw pneumatic valves  428 - 1  through  428 - 6 . The valves  428 - 1  through  428 - 6  respectively have normally-closed (N.C.) outputs fluidly coupled to autodose line  430  by way of T-fittings  432 - 1  through  432 - 5 . The autodose line  430  is selectively coupled to either the plating fluid reservoir or a waste tank. The valves  428 - 1  through  428 - 5  also respectively have normally-open (N.O.) outputs fluidly coupled to respective bleed lines  434 - 1  through  434 - 5 . The bleed lines  434 - 1  through  434 - 5 , in turn, are fluidly coupled back to respective chemical solution tanks  402 - 1  through  402 - 5 . Valve  428 - 6  has a normally-open (N.O.) output coupled to vent line  436 . 
     The pre-determined volumes  438 - 1  through  438 - 5  for the respective chemical solutions 1-5 and DI-water is the piping that fluidly couples the respective (C) ports of valves  404 - 1  through  404 - 6  and valves  428 - 1  through  428 - 6 , respectively, plus some displacement in the respective valves. The piping is selected so that the pre-determined volume is sized at the desired incremental volume resolution. The piping can be changed to different size pipings to alter the desire incremental volume resolution. 
     B. Preferred Dispensing Method of the Plating Chemical Replenishment System 
     The description of the preferred dispensing method of the plating chemical replenishment system  400  is discussed as follows. The dispensing of chemical solution no. 2 will be used to exemplify the invention. The dispensing of the other chemical solutions and DI-water operate in the same manner. Prior to dispensing, the valves  404 ,  410 ,  422 , and  428  are set to their respective normally-open (N.O.) positions. Valve  424  is initially set closed. The first step in the dispensing operation is to position valves  404 - 2  in their normally-closed (N.C.) position. This step allows chemical solution in tank  402 - 2  to flow through valve  404 - 2  and fill the pre-determined volume  438 - 2  and at least partially fill the bleed line  434 - 2  by way of valve  428 - 2 . Preferably, the chemical solution flows under hydrostatic pressure. During this operation, the valve  410  is set to its normally-open (N.O.) position to fluidly couple the tank vent  412  to the tank  402 - 2  so that the chemical solution is allowed to freely flow under hydrostatic pressure. The bleed line  434 - 2  provides an outlet for gas (e.g. air) that is present in the pre-determined volume  438 - 2 . 
     The next step in the preferred dispensing method of the plating chemical replenishment system  400  is to position valve  404 - 2  into its normally-open (N.O.) position to remove the fluid coupling between the chemical solution tank  402 - 2  and the pre-determined volume  438 - 2 . Then, valve  428 - 2  is set to its normally-closed (N.C.) position to fluidly couple the pre-determined volume  438 - 2  to the plating fluid reservoir by way of the autodose line  430 . Then, valve  424  is opened to apply low pressure CDA  426  to the normally-open (N.O.) port of valve  404 - 2  so that the chemical solution in the pre-determined volume  438 - 2  is forced out of the pre-determined volume  438 - 2  and dispensed to the plating fluid reservoir. After this occurs, valve  428 - 2  is set to its normally-open (N.O.) position so that the low pressure CDA  426  pushes the remaining chemical solution in the bleed line  434 - 2  back into the chemical solution tank  402 - 2 . After this step, valve  424  is closed, and the process is repeated again for dispensing another discrete pre-determined volume of chemical solution into the plating fluid reservoir. 
     This process is repeated a number of times as required by the RTA so that the desired quantity of the chemical solution is dispensed into the plating fluid reservoir. The process of providing the desired quantity of chemical solutions to the plating fluid reservoir through a series of dispensing procedure is defined herein as a dispensing interval. The RTA measures the concentrations of the chemicals in the plating fluid, for example, once a few minutes. It then instructs the replenishment system  400  to dispense a certain amount of quantity of at least one chemical or D.I. water. Then, the replenishment system  400  undergoes a dispensing interval to provide the desired quantity of at least one chemical solution or D.I. water by dispensing a series of pre-determined volumes of chemical solution as described above. After this occurs, the RTA takes another measurement of the concentrations of the chemicals in the plating fluid, and the dispensing interval process is undertaken again. This process of measuring and replenishing the plating fluid continues until the plating process is complete. 
     C. Preferred Cleaning Method of the Plating Chemical Replenishment System Between Dispensing Intervals 
     As previously discussed, the plating process may require the RTA to periodically take several measurements of the concentrations of the chemicals in the plating fluid, and periodically cause the replenishment system  400  to undergo a dispensing interval so that the desired chemical concentrations for the plating fluid is maintained. In between dispensing intervals, it may be desirable to clean the pre-determined volumes  438 - 1  through  438 - 6  to remove any chemical solution residue. To begin the cleaning process after completion of a dispensing interval, the valves  404 - 1  through  404 - 6  are set to their respective normally-open (N.O.) positions, and valves  428 - 1  through  428 - 6  are set to their respective normally-closed (N.C.) positions. The autodose delivery line  430  is then selectively coupled to a waste tank. Then, valve  422  is set to its normally-closed (N.C.) position and CDA/DI-water  414  is set to provide DI-water to substantially flush the pre-determined volumes  438 - 1  through  438 - 6  with DI-water and remove any chemical residue therein. The used DI-Water drains into a waste tank (not shown) by way of the autodose delivery line  430 . After the control volumes  438 - 1  through  438 - 6  are properly flushed, the CDA/DI-Water select  414  is set to deliver CDA to substantially dry the pre-determined volumes  438 - 1  through  438 - 6 . After this cleaning process is complete, the valves are set to their normally-open positions (N.O.). 
     D. Preferred Cleaning Method of the Plating Chemical Replenishment System After Completion of Plating Cycle 
     After completion of a plating cycle, it may be desirable to clean the chemical solutions tanks, the pre-determined volumes, and all other conduits that are exposed to the chemical solutions. To perform this cleaning operation, all the valves (i.e. valves  404 -series,  410 ,  422 , and  428 -series) are set to their respective normally-closed (N.C.) positions. This step fluidly couples the CDA/DI-Water select  414  to the chemical solution tanks  402 - 1  through  402 - 5 , the pre-determined volumes  438 - 1  through  438 - 5 , the valves  404 - 1  through  404 - 5 , the valves  428 - 1  through  428 - 5 , and autodose delivery line  430  so that rinsing of these elements occurs. During this cleaning process, the valves  428 - 1  through  428 - 5  may be set to their respective normally-open (N.O.) positions to direct DI-water into and flush the bleed lines  434 - 1  through  434 - 5 . After the rinsing cycle, the CDA/DI-water select  414  is set to deliver CDA to substantially dry the elements of the replenishment system  400  previously rinsed. 
     E. Alternative Embodiment for the Dispensing Apparatus 
     FIG. 5 illustrates a block diagram of a dispensing apparatus  500  that can be used in place of the dispensing valve arrangement depicted in FIG.  4 . The dispensing apparatus  500  preferably comprises an input check valve  502 , an output check valve  506 , and a pre-determined volume  504  interposed between the check valves  502  and  506 . The check valves  502  and  506  allow fluid to flow in one direction (as indicated by the arrows in FIG.  5 ), and prevent fluid flow in the opposite direction. In a dispensing application, the input check valve  502  is fluidly coupled to the corresponding chemical solution tank or D.I. water inlet, and the output check valve  506  is fluidly coupled to the plating fluid reservoir. In a draining application, the input check valve is fluidly coupled to the plating fluid reservoir, and the output check valve  506  is fluidly coupled to a waste tank. The dispensing apparatus  500  further includes an occluding mechanism such as plunger  508  situated within the pre-determined volume  504  and a driver  510  that controls the lateral movement of the plunger  508 . The driver  510  may comprise a pneumatic driver, a solenoid driver, an electric motor or a rotating cam. 
     Prior to a dispensing or draining action, the plunger  508  is positioned within the pre-determined volume  504  to prevent fluid flow from the input check valve  502  into the pre-determined volume  504 . During a dispensing or draining action, the driver  510  is actuated to cause the plunger  508  to move laterally away from the pre-determined volume, and allow fluid flow from the input check valve  502  into the pre-determined volume  504 . After the pre-determined volume  504  is filled, the driver  510  is actuated to cause the plunger  508  to move laterally into the pre-determined volume  504  and push the fluid into and through the output check valve  506 . The input check valve  502  prevents the fluid to flow from the pre-determined volume  504  into the input check valve  502 . 
     IV. The Preferred Physical Embodiment of the Plating Chemical Replenishment System 
     FIGS. 6A-6C are front, top and side views of a preferred physical embodiment of a plating chemical replenishment system  600  in accordance with the invention. The plating chemical replenishment system  600  is the physical implementation of the schematically represented replenishment system  400  of FIG.  4 . The reference numbers for elements in FIG. 6 are the same reference numbers for corresponding elements in FIG. 4, except that the most significant digit is a “ 6 ” instead of a “ 4 .” Thus, the detailed discussions of the elements should be referred to the section of the specification that describes replenishment system  400 . It should be noted that the chemical solution tanks  602 - 1  through  602 - 5  are elongated vertically, and are securely positioned adjacent to each other by a mainframe  642 . The chemical solution tanks  602 - 1  through  602 - 5  have respective external fluid level indicators  640 - 1  through  640 - 6 . The pre-determined volumes  638 - 1  through  638 - 6  are configured as relatively short pipes that provide a pre-determined volume displacement. As previously discussed, the pre-determined volumes  638 - 1  through  638 - 6  also include some displacements introduced by the valves on either side of the pipes. In order to change the pre-determined volumes  638 - 1  through  638 - 6 , the pipes may be changed to provide a different volume displacement. 
     CONCLUSION 
     While the invention has been described in connection with various embodiments, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptation of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains.