Abstract:
A single substrate cleaning apparatus that prevents galvanic corrosion is provided. The apparatus includes a spindle configured to rotatably support a substrate. A moveable dispense arm disposed over the spindle is included. The dispense arm supports a first supply line and a second supply line. The first supply line has a first nozzle affixed to an end of the first supply line, and the second supply line has a second nozzle affixed to an end of the second supply line. The first nozzle is positioned behind the second nozzle such that a fluid dispensed from the second nozzle is dried by application of a fluid simultaneously dispensed from the first nozzle in manner that protects the substrate from galvanic corrosion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional application of U.S. patent application Ser. No. 10/013,211, filed on Dec. 7, 2001, and entitled “METHOD FOR CONTROLLING GALVANIC CORROSION EFFECTS ON A SINGLE-WAFER CLEANING SYSTEM,” which claims priority from U.S. Provisional Patent Application No. 60/305,372 filed Jul. 13, 2001 and entitled “Drying substrate using a combination of substrate processing techniques.” Each of these applications is herein incorporated by reference in their entirety for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates generally to semiconductor manufacturing and more specifically to a cleaning method and apparatus for a single-wafer cleaning system, which minimizes galvanic corrosion.  
         [0004]     2. Description of the Related Art  
         [0005]     Galvanic corrosion is induced in an environment where two dissimilar metals are coupled through an electrolyte. One of the metals in the galvanic cell becomes an anode and corrodes faster than it would normally, while the other metal becomes a cathode and corrodes slower than it would normally.  FIG. 1  illustrates prior art diagram  100  of a basic galvanic cell. Two dissimilar metals,  104  and  106 , are coupled through electrolyte  102 . The anode  106  donates electrons and has its corrosion rate increased while the cathode  104  has its corrosion rate reduced.  
         [0006]     Metal interconnects used in semiconductors are often constructed from dissimilar metals such as Copper/Tantalum (Cu/Ta) or Copper/Tantalum Nitride (Cu/TaN). During cleaning operations following processing operations such as etch and chemical mechanical planarization (CMP), the dissimilar metals are brought into electrical contact through an electrolyte, such as water from an aqueous based cleaner or a semi-aqueous based cleaner. As a result, corrosion of one of the metals is accelerated, thereby creating the potential for device failure.  FIG. 2  illustrates prior art diagram  110  depicting one example of where dissimilar metals can form a galvanic cell. Diagram  110  illustrates a dual damascene structure where trench  120  includes a via  122  down to copper metallization line  112 . Liner  114  encases copper metalization line  112  around 3 sides and acts a copper diffusion barrier. Dielectric layer  118  is typically a low K dielectric disposed over barrier  116 . As can be seen in diagram  110  the via  122  is slightly misaligned over copper metalization line  112 . Consequently, two dissimilar metals are exposed, the copper of copper metallization line  112  and the liner  114  since liner  114  is typically tantalum or tantalum nitride for dual damascene applications. An additional misaligned via on a second metal line (not shown), which is not in contact with the metallization line  112 , can also introduce the potential for a galvanic cell once the dissimilar metals exposed in isolated lines are brought into contact through an electrolyte. It should be appreciated that the via need not be misaligned as the copper can be brought into contact with a second metal exposed in a different region of substrate  124 . Thus dissimilar metals of even perfectly aligned structures can be brought into contact through an electrolyte during cleaning and rinsing operations. Additionally, while a dual damascene structure is presented in diagram  110 , traditional metallization processes using aluminum can also create the potential for a galvanic cell.  
         [0007]     During cleaning operations, substrates are exposed to cleaning chemistries. In the case of single-wafer cleaning operations the cleaning chemistries are formulated to be fast acting and the stoichiometry of the components is critical to the performance of the cleaning chemistry. For example, semi-aqueous cleaning chemicals for single-wafer cleaning operations typically include a solvent to remove organic material, a chelator to enhance metal contaminant removal from surfaces exposed to sputtering from the etch process, and a surfactant to passivate sensitive surfaces, especially those vulnerable to corrosion. Examples of commercially available single-wafer cleaning chemistries used for post via etch applications include NE-89 from Ashland Inc. of Dublin, Ohio and EKC 640 from EKC Technology, Inc. of Hayward, Calif.  
         [0008]     The surfactant of the cleaning chemicals for the single-wafer cleaning operations are formulated to help improve wetting of difficult-to-access features such as vias and contacts, and also to control galvanic effects where necessary, however, if the surfactant is diluted then its passivation capacity is reduced or inhibited, thereby leaving the substrate more vulnerable to galvanic corrosion effects. For example, where the cleaning chemistry is puddled on the substrate and then rinsed off with de-ionized (DI) water, the water acts as an electrolyte to initiate the mechanism for galvanic corrosion. The galvanic corrosion may occur within the first few seconds of rinsing, where the cleaning chemistry and the surfactant are initially diluted upon rinsing of the cleaning chemistry. The dilution of the cleaning chemistry upsets a chemical equilibrium established to protect the substrate surface from corrosion. Since the surfactant concentration is modified by dilution through rinsing, the semiconductor substrate is vulnerable to corrosion when the diluted surfactant concentration is insufficient to inhibit corrosion.  
         [0009]      FIG. 3  illustrates a prior art diagram displaying the various concentration gradient regions formed during the rinsing operations from a vantage point above the substrate  126 . Substrate  126  is spinning in the direction of arrow  134 . Region  128  depicts the region containing the cleaning chemistry puddled onto the substrate  126  through a nozzle or other delivery mechanism (not shown). To rinse of the cleaning chemistry from the substrate  126 , DI water is sprayed onto the substrate  126  through a nozzle (not shown) directed toward the outer edge of the substrate  126  while the substrate is spinning. As the DI water is sprayed on the substrate  126 , regions of differing gradients will form on the substrate  126 . Region  130  contains a mixture of the cleaning chemistry and DI water, which forms as the DI water is initially sprayed onto the substrate  126 . After a period of time, enough DI water is sprayed onto the substrate  126  where the cleaning chemistry is displaced and region  132  containing only DI water forms. While  FIG. 3  provides a snapshot of one instance during the rinsing process, it should be appreciated that the edges of regions  132  and  130  are moving toward the edge of substrate  126  as depicted by arrows  136 . The DI water rinse continues until eventually all of the cleaning chemistry is displaced from the substrate  126 .  
         [0010]     As mentioned above, region  130  includes a mixture of cleaning chemistry and DI water. Thus, the chemical equilibrium under which the cleaning chemistry is designed to function has been shifted. As a result of the dilution of the surfactant by the DI water, the corrosion protection of the surfactant is inhibited, which in turn exposes the substrate  126  to the effects of galvanic corrosion. As mentioned above, the effects of corrosion, especially galvanic corrosion, can occur within seconds.  
         [0011]     In view of the foregoing, there is a need to provide an apparatus and method to rinse the cleaning chemistry from a substrate in a manner which protects the exposed metals of the substrate from galvanic corrosion.  
       SUMMARY OF THE INVENTION  
       [0012]     Broadly speaking, the present invention fills these needs by providing an apparatus and a method which quickly removes the cleaning chemistry from the surface of a semiconductor substrate. It should be appreciated that the present invention can be implemented in numerous ways, including as an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.  
         [0013]     In one embodiment, a method for minimizing galvanic corrosion effects in a single-wafer cleaning system is provided. The method initiates with applying a cleaning chemistry containing corrosion inhibitors to a surface of a wafer. Then, the surface of the wafer is exposed to the cleaning chemistry for a period of time. Next, a concentration gradient at an interface of the cleaning chemistry and the surface of the wafer is refreshed. Then, a rinsing agent and a drying agent are applied simultaneously to remove the cleaning chemistry, wherein the drying agent dries the surface of the wafer prior to a concentration of the corrosion inhibitors being diluted to a level insufficient to inhibit corrosion.  
         [0014]     In another embodiment, a method for quickly drying a surface of a semiconductor substrate is provided. The method initiates with applying a cleaning chemistry including a surfactant to the surface of the semiconductor substrate. Then, the surface of the semiconductor substrate is exposed to the cleaning chemistry for a defined time period. Next, a rinsing agent and a drying agent are applied simultaneously to the surface of the semiconductor substrate to remove the cleaning chemistry, wherein the drying agent inhibits the rinsing agent from forming a diluted region of the cleaning chemistry from residing on the surface of the semiconductor substrate for a time period sufficient to allow corrosion of the substrate.  
         [0015]     In yet another embodiment, a chemical sequencing method for single-wafer cleaning of a residue on a surface of a semiconductor substrate is provided. The chemical sequencing method is configured to maintain a concentration gradient at an interface between a cleaning chemistry and a residue on the semiconductor substrate. The method initiates with applying a cleaning chemistry to the surface of the semiconductor substrate. Then, the cleaning chemistry is allowed to react with the residue. Next, the cleaning agent is removed to reduce exposure of the semiconductor substrate to corrosion. Then, the applying, the allowing and the removing steps are repeated such that the concentration gradient is refreshed to more effectively remove the residue on the surface of a semiconductor substrate.  
         [0016]     In still another embodiment, a method for minimizing galvanic corrosion effects in a single-wafer cleaning system while maintaining a concentration gradient at an interface between a cleaning chemistry and a residue on a wafer is provided. The method initiates with applying the cleaning chemistry containing corrosion inhibitors to a surface of a wafer. Then, the surface of the wafer is exposed to the cleaning chemistry for a period of time. Next, a concentration gradient at an interface of the cleaning chemistry and the surface of the wafer is refreshed. Then, the wafer is rinsed with the cleaning chemistry and simultaneously dried with a drying agent to remove the cleaning chemistry and dry the wafer.  
         [0017]     In another embodiment, a system for cleaning a single substrate is provided. The system includes a spindle adapted to support the substrate where the spindle is configured to spin the substrate. A substrate surface having a layer of a cleaning chemistry disposed thereover is included. A first nozzle positioned over the substrate surface is also included. The first nozzle is configured to apply a rinsing agent on the substrate surface while the substrate is spinning. A second nozzle positioned over the substrate surface is included. The second nozzle is configured to apply a drying agent on the substrate surface while the first nozzle is applying the rinsing agent. A dispense arm to which the first and second nozzles are rigidly attached is included. The dispense arm is configured to advance radially above the substrate surface from a center of the substrate to an edge of the substrate while the substrate is spinning and while the first and second nozzles are applying the rinsing agent and the drying agent, respectively. The substrate surface is dried quickly to reduce exposure of the substrate surface to corrosion. Alternative configurations can be incorporated to increase the speed of rinsing and drying, such as incorporating multiple nozzle pairs.  
         [0018]     In yet another embodiment, a single substrate cleaning apparatus that prevents galvanic corrosion is provided. The apparatus includes a spindle configured to rotatably support a substrate. A moveable dispense arm disposed over the spindle is included. The dispense arm supports a first supply line and a second supply line. The first supply line has a first nozzle affixed to an end of the first supply line, and the second supply line has a second nozzle affixed to an end of the second supply line. The first nozzle is positioned behind the second nozzle such that a fluid dispensed from the second nozzle is dried by application of a fluid simultaneously dispensed from the first nozzle in manner that protects the substrate from galvanic corrosion.  
         [0019]     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, in which like reference numerals designate like structural elements.  
         [0021]      FIG. 1  illustrates prior art diagram of a basic galvanic cell.  
         [0022]      FIG. 2  illustrates prior art diagram depicting one example of where dissimilar metals can form a galvanic cell.  
         [0023]      FIG. 3  illustrates a prior art diagram displaying the various concentration gradient regions formed during the rinsing operations from a vantage point above the substrate.  
         [0024]      FIG. 4  illustrates an exemplary drying system in accordance with one embodiment of the invention.  
         [0025]      FIG. 5  provides a detailed view of dispense nozzles positioned over a substrate in accordance with one embodiment of the invention.  
         [0026]      FIG. 6  illustrates a detailed diagram of the surface of the substrate in the region where the rinsing agent and drying agent are impinging on the surface of the substrate to remove a cleaning chemistry layer in accordance with one embodiment of the invention.  
         [0027]      FIG. 7  illustrates a diagram providing a detailed view of the interface between the substrate and the cleaning chemistry layer in accordance with one embodiment of the invention.  
         [0028]      FIG. 8  illustrates a flowchart depicting a method for minimizing galvanic corrosion effects in a single-wafer cleaning system in accordance with one embodiment of the invention.  
         [0029]      FIG. 9  illustrates a flowchart depicting a chemical sequencing method for single-wafer cleaning of a residue on a semiconductor substrate in accordance with one embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     An invention is described which provides a method and apparatus for removing a cleaning chemistry from the surface of a semiconductor substrate without exposing the substrate to corrosion effects during a single-wafer cleaning operation. In addition, the method and apparatus provide a more effective means for removing the residue during cleaning operations without increasing the consumption of the cleaning chemistry. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to obscure the present invention.  
         [0031]     The embodiments of the present invention provide a method and apparatus for applying and removing a cleaning agent from a semiconductor substrate without exposing the substrate to galvanic corrosion effects. In one embodiment, the precisely formulated cleaning chemistry applied to the semiconductor substrate is removed in a manner to reduce dilution of the components of the cleaning chemistry. In another embodiment, the cleaning chemistry includes a surfactant to inhibit corrosion. As used herein, surfactant also refers to corrosion inhibitors. The cleaning chemistry is removed from the surface of the semiconductor substrate in a manner where the dilutive effects of the rinsing agent are counteracted by quickly removing the cleaning chemistry from the surface of the substrate. By quickly drying the surface of the substrate during the rinsing process, the semiconductor remains protected from corrosion.  
         [0032]     In addition, a method and apparatus for more effectively removing the cleaning chemistry from the surface of the semiconductor substrate during single-wafer cleaning is provided in another embodiment. The fast acting formulations of the cleaning chemistries for single-wafer cleaning processes perform optimally when a concentration gradient between the cleaning chemistry and the residue to be removed at the surface of the semiconductor substrate is maintained by removal of the boundary layer formed from reaction of the cleaning chemistry with the residue. More particularly, the retarding effects of the reactant species produced by the interaction of the cleaning chemistry and the residue is minimized by a chemical sequencing process to refresh the cleaning chemistry in order to maintain the concentration gradient. The refreshing process can include removing cleaning chemistry from the surface of the substrate and replacing it with fresh cleaning chemistry or continually recycling the cleaning chemistry to maintain the concentration gradient as will be discussed in more detail below.  
         [0033]      FIG. 4  illustrates an exemplary drying system  140  in accordance with one embodiment of the invention. The drying system  140  includes a hollow spindle  142  configured to hold a substrate  148  and disposed within and over a drip tray  150 . Dispense arm  152  is positioned over a top surface of the substrate  148 . Dispense arm  152  is supported by dispense arm support post  154  which is mechanically connected (not shown) to a dispense arm drive shaft (not shown) disposed within a dispense arm drive shaft housing  156 . Substrate  148  is affixed to hollow spindle  142  with fingers  158 . Hollow spindle  142  is configured to rotate, which in turn rotates the substrate  148 . Spindle motor  160  is configured to provide rotational energy which is applied to hollow spindle  142  with drive belt  162 , which spins the substrate  148  locked to the hollow spindle  142  in fingers  158 .  
         [0034]     Surrounding hollow spindle  142 , fingers  158 , and substrate  148  is spray shield  164 . Spray shield  164  is configured to contain any liquid from the rinsing and drying process to the region around hollow spindle  142 . In one embodiment of the invention, spray shield  164  is configured with a door (not shown) that is magnetically coupled to a semi-circular pneumatic system to provide lateral access to the hollow spindle  142  for the insertion and removal of substrates  148 .  
         [0035]     In another embodiment of the invention, a rinsing agent and a drying agent are simultaneously applied to the top surface of substrate  148 . The rinsing agent is applied through nozzle  166  and the drying agent is applied through nozzle  168  in one embodiment. Examples of rinsing agents include de-ionized water (DIW) and Isopropyl alcohol. Examples of drying agents include isopropyl alcohol (IPA), IPA vapor, heated Nitrogen (N 2 ) gas, and other inert gasses or vaporized chemicals. Some drying agents produce by-products or result in excess vapors that can become trapped within drip tray  150 . An exhaust  170  is provided for the release of airborne chemicals or vapors, and a drain  172  is provided to drain any liquid residue of both cleaning and drying agents.  
         [0036]     Dispense arm  152  provides for the supply of rinsing and drying agents through dispense nozzles  166  and  168  through corresponding supply lines  174  and  176  to substrate  148  positioned in fingers  158  on the hollow spindle  142 . The drying agent and the rinsing agent are supplied from separate reservoirs (not shown) and are routed along dispense arm  152  to dispense nozzles  168  and  166 , respectively. Nozzles  166  and  168  direct streams of drying agent and the rinsing agent to a top surface of substrate  148 .  
         [0037]     In one embodiment, positioning of the dispense arm  152  across the top and surface of substrate  148  is controlled by a dispense arm controller (not shown) and a dispense arm drive shaft (not shown) contained within a dispense arm drive shaft housing  156 . The dispense arm drive shaft is mechanically connected to the dispense arm support post  154  providing a direct mechanical connection between the drive shaft and the dispense arm  152  to position the dispense arm  152 . The dispense arm  152  is configured to pivot about the dispense arm support post  154  to move the dispense arm  152  and move the dispense nozzles  166  and  168  radially across a top surface of a substrate. In one embodiment of the invention, the rinsing and drying agents are dispensed along a radius of a spinning substrate from a center region of the substrate to a peripheral region of the substrate. The dispense arm  152  is therefore moved along the surface of the spinning substrate from the center region outward to a peripheral region. In another embodiment, the nozzles  166  and  168  are positioned so that the drying agent is applied to the surface of the substrate directly behind the rinsing agent as the dispense arm  152  traverses across the surface of the substrate  148 . As will be described in more detail below, applying the drying agent simultaneously with the rinsing agent and in a manner which quickly dries the surface of the substrate  148  in a single-wafer cleaning operation protects the substrate from corrosion effects. It should be appreciated that  FIG. 4  is provided as an exemplary illustration of one embodiment of an apparatus and not meant to be limiting.  
         [0038]      FIG. 5  provides a detailed view of dispense nozzles  166  and  168  positioned over substrate  148  in accordance with one embodiment of the invention. Dispense arm  152  traverses a path radially across the surface of the substrate  148  in a plane above the substrate as indicated by arrow  180 . Therefore, as the substrate  148  is spinning about its axis, nozzles  166  and  168  are directing a flow of rinsing agent and a flow of drying agent across the surface of the substrate  148 . By rinsing the cleaning chemistry and immediately drying the surface of the substrate  148 , the corrosion inhibitors of the cleaning chemistry do not remain on the surface of the substrate  148  in a diluted state unable to inhibit corrosion effects. Since galvanic corrosion can be initiated in a matter of seconds, the immediate drying of the substrate reduces or prevents the onset of the corrosion effects as the substrate is quenched as described above.  
         [0039]      FIG. 6  illustrates a detailed diagram of the surface of the substrate  148  in the region where the rinsing agent  182  and drying agent  184  are impinging on the surface of the substrate  148  to remove a cleaning chemistry layer  188  in accordance with one embodiment of the invention. Rinsing agent  182  is applied through dispense nozzle  166  simultaneously while drying agent  184  is applied through dispense nozzle  168 . In one embodiment, the nozzles  166  and  168  are positioned so that the fluid streams  190  and  192 , emanating from nozzles  166  and  168 , respectively, are directed at an angle to the surface of the substrate  148  and in the same plane as the direction of the movement  180  of the dispense arm. The rinsing agent  182  is applied ahead of the drying agent  184  to a top surface the spinning substrate  148  while moving from a center region of the substrate  148  towards a periphery region of the substrate  148 . The rinsing agent is configured to rinse the surfaces of the substrate  148  to remove the cleaning chemistry layer  188 . In one embodiment, the rinsing agent is DIW. The drying agent is formulated such that it reduces the surface tension of the rinsing agent and the movement of the liquid and residue is enhanced thereby drying the surfaces of the substrate quickly, without allowing a diluted region of the cleaning chemistry layer to remain on the surface of the substrate  148 .  
         [0040]     It should be appreciated that by simultaneously applying the drying agent  184  and the rinsing agent  182  of  FIG. 6 , the substrate surface is quickly dried so that any region containing a mixture of the cleaning chemistry and the rinsing agent  182  is minimized. Moreover, by simultaneously applying the rinsing agent  182  and the drying agent  184 , the surface of the substrate  148  is quickly dried. Therefore, even if the diluted region of the cleaning chemistry is formed, it is quickly dried without allowing the opportunity for corrosion effects to initiate.  
         [0041]      FIG. 7  illustrates a diagram providing a detailed view of the interface  194  between the substrate  148  and the cleaning chemistry layer  188  in accordance with one embodiment of the invention. Substrate surface  196  contains a residue from a previous operation, such as etch or CMP in one embodiment. During a single-wafer cleaning operation, the cleaning chemistry applied to the substrate surface  196  is configured to quickly dissolve the residue to enable rinsing the residue from the surface of the substrate. The cleaning chemistry typically includes at least a solvent to dissolve organic materials, a chelator to dissolve metals and a surfactant to inhibit corrosion. As mentioned above, the cleaning chemistry is precisely formulated for the single-wafer cleaning process to be fast acting. The pH, concentration of the chemical species and the concentration of water of the semi-aqueous cleaning chemistries are carefully formulated to provide the desired cleaning result. Additionally, the reactions taking place at the interface  194  occur in seconds.  
         [0042]     Therefore, at the interface  194  of  FIG. 7  as the cleaning chemistry is dissolving or reacting with the residues from a previous operation, the chemical equilibrium is shifted, which in turn retards the activity of the cleaning chemistry. The reactant species resulting from the chemical reactions occurring at the interface  194  reduces the concentration gradient between the active chemicals of the cleaning chemistry and the residue with which the cleaning chemistry is interacting. Therefore, in another embodiment of the invention, a chemical sequencing method is employed to refresh the concentration gradient. As will be explained in reference to  FIG. 9 , the chemical sequencing operation includes applying the cleaning chemistry to the substrate for a specified time period, quickly removing the cleaning chemistry as discussed above with reference to  FIGS. 4-6  and repeating the applying and removing. In this embodiment, while the cleaning chemistry is applied at least twice, the absolute amount of cleaning chemistry used is not increased. For example, where the cleaning chemical is applied twice, each application uses half the amount as when the cleaning chemistry is applied once as explained in reference to  FIG. 9 . In another embodiment, the cleaning chemistry is recycled, i.e., as it is removed from the surface of the substrate it is captured and re-applied to the surface of the substrate. It should be appreciated that as the cleaning chemistry is continuously sprayed on the surface of the substrate, the concentration gradient remains substantially constant.  
         [0043]      FIG. 8  illustrates flowchart  198  depicting a method for minimizing galvanic corrosion effects in a single-wafer cleaning system in accordance with one embodiment of the invention. Flowchart  198  initiates with operation  200  where a cleaning chemistry is applied to the wafer (also referred to as a semiconductor substrate). In one embodiment the cleaning chemistry includes a surfactant for inhibiting corrosion. In another embodiment, the surfactant protects the wafer from galvanic corrosion. One skilled in the art would appreciate that the cleaning chemistry can be puddled in a bulk application or sprayed on the wafer continuously. The method then advances to operation  202  where the wafer is exposed to the cleaning chemistry for a defined period of time. In one embodiment, the cleaning chemistry for a single-wafer cleaning method is designed to dissolve the residues between about 30 seconds to about one minute. The method then proceeds to operation  204  where a concentration gradient is refreshed. Here, the gradient between the cleaning chemistry and the residue at an interface of the wafer is refreshed by continuously spraying the cleaning chemistry onto the surface of the wafer in one embodiment. In another embodiment, the continuously sprayed cleaning chemistry is collected as it falls off the surface of the spinning wafer and recycled. For example, the drip tray of  FIG. 4  can collect the cleaning chemistry for recycling. In another embodiment, the concentration gradient is refreshed through a chemical sequencing process where the cleaning chemistry is puddled or sprayed onto the substrate for a period of time and then removed. Fresh cleaning chemistry is then applied again to the substrate to refresh the concentration gradient.  
         [0044]     The method of  FIG. 8  then advances to operation  206  where a rinsing agent and a drying agent are applied simultaneously to the surface of the wafer to remove the cleaning chemistry. In operation  206  the cleaning chemistry is removed quickly i.e., without allowing a diluted region of surfactant to remain on the wafer for a period of time which allows for corrosion to occur on the wafer. In one embodiment, the rinsing agent and the drying agent are applied as discussed with respect to  FIGS. 4-6 . In another embodiment, the rinsing agent is one of DIW, or any other liquid which can displace and quench the cleaning chemistry such as isopropyl alcohol, and the drying agent is one of IPA, IPA vapor, nitrogen, heated nitrogen or other inert gas.  
         [0045]      FIG. 9  illustrates flowchart  208  depicting a chemical sequencing method for single-wafer cleaning of a residue on a semiconductor substrate in accordance with one embodiment of the invention. The method initiates with operation  210  where a cleaning chemistry is applied to a surface on the semiconductor substrate. In one embodiment, the cleaning chemistry is one of NE-14 and NE-89 from Ashland Inc. of Dublin, Ohio and EKC 640 from EKC Technology, Inc. of Hayward, Calif. In another embodiment, the single-wafer cleaning method is being applied after an etch or CMP operation which leaves residues on the surface of the semiconductor substrate. The method then advances to operation  212  where the cleaning chemistry is allowed to react with the residue on the surface of the semiconductor substrate. Here, the cleaning chemistry resides on the surface of the wafer for a defined period of time to dissolve the residue. In one embodiment, the defined period of time is between about 30 seconds and about one minute.  
         [0046]     The method of flowchart  208  then moves to operation  214  where the cleaning chemistry is removed quickly to reduce exposure of the semiconductor substrate to corrosion. In one embodiment, the cleaning chemistry is removed quickly as described in reference to  FIGS. 4-6  where a rinsing agent and a drying agent are simultaneously applied to the surface of the semiconductor substrate to remove the cleaning chemistry. The method then advances to operation  216  where operations  210 ,  212  and  214  are repeated. The concentration gradient is refreshed by repeating operations  210 ,  212  and  214 , so that the activity of the cleaning chemistry is not diminished by the build-up of reactant species at the interface between of the cleaning chemistry and the surface of the semiconductor substrate. As described with reference to  FIG. 7 , a reactant species resulting from the chemical reactions occurring at the interface reduces the concentration gradient between the active chemicals of the cleaning chemistry and the residue with which the cleaning chemistry is interacting. Thus, the chemical equilibrium under which the cleaning chemistry is most effective is shifted by this build-up.  
         [0047]     By refreshing the cleaning chemistry, the optimal chemical equilibrium is re-established. In one embodiment, the method of flowchart  208  consumes substantially the same amount of cleaning chemistry as a single application process. More specifically, if the single application process consumes about 10 ml to about 100 ml, then the chemical sequencing operation where the cleaning chemistry is removed once and re-applied consumes half the amount for each application i.e., between about 5 ml to about 50 ml. Therefore, the absolute quantity of cleaning chemistry consumed does not increase. Additionally, the total amount of time for the single-wafer cleaning method of flowchart  208  is substantially the same as for a single application of the cleaning chemistry. Since the concentration gradient is refreshed, the summation of the residence time for the cleaning chemistry for each application of the chemical sequencing method is substantially similar to the single application residence time. For example, the processing time for a chemical sequencing operation where the cleaning chemistry is applied, then removed and re-applied is substantially similar to the processing time of a single application of the cleaning chemistry. That is, the cleaning chemistry for the chemical sequencing is applied twice, however, each application has a residence time of about half of the residence time for the single application, since the gradient is refreshed in between applications during chemical sequencing. Therefore, the total processing time remains substantially similar.  
         [0048]     It should be appreciated that more than two applications of the cleaning chemistry may be utilized. For example, the cleaning chemistry may be applied three or more times in one embodiment. In this embodiment, the amount of cleaning chemistry consumed remains substantially similar as well as the processing time when compared to the single application. In another embodiment, the cleaning chemistry can be continually applied to the surface of the semiconductor substrate. Here, the cleaning chemistry sprayed or puddled onto the surface of the substrate is recycled as it is removed from the substrate surface. In this embodiment the concentration gradient would be continually refreshed.  
         [0049]     In yet another embodiment of the invention, the cleaning chemistry is applied to the substrate using the apparatus of  FIGS. 4-6 . Here, the cleaning chemistry is applied to the surface of the substrate simultaneously with the drying agent i.e., the cleaning chemistry replaces the rinsing agent. For example the cleaning chemistry is initially applied to the substrate and exposed to the substrate for a period of time. Here the cleaning chemistry can be puddled, sprayed or continuously sprayed and recycled for a period of time as discussed above. In the continuous spray mode, the cleaning chemistry is recycled to refresh the concentration gradient continuously in one embodiment. After the period for the exposure is complete the cleaning chemistry is rinsed form the wafer using the apparatus as described in reference to  FIGS. 4-6 . In one embodiment, the cleaning chemistry replaces DI water or any liquid which is used to displace and quench the cleaning chemistry as a rinsing agent.  
         [0050]     For the embodiment where the cleaning chemistry replaces the rinsing agent discussed above, it should be appreciated that the cleaning chemistry will be easily captured and recycled if desired. In turn, the waste effluent quantity would be reduced as the cleaning chemistry is not diluted with DI water or other rinsing agent, thus the cleaning chemistry can be recycled and reused. Furthermore, galvanic corrosion effects would be minimized as the cleaning chemistry is not diluted by the rinsing agent. Therefore, the chemical equilibrium established for the surfactants or corrosion inhibitors of the cleaning chemistry is maintained and refreshed to control galvanic corrosion effects.  
         [0051]     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.