Abstract:
A brush-cleaning apparatus is disclosed for use in cleaning a semiconductor wafer after polishing. Embodiments of the brush-cleaning apparatus implemented with a multi-branch chemical dispensing unit are applied beneficially to clean semiconductor wafers, post-polish, using a hybrid cleaning method. An exemplary hybrid cleaning method employs a two-chemical sequence in which first and second chemical treatment modules are separate from one another, and are followed by a pH-neutralizing-rinse that occurs in a treatment module separate from the first and second chemical treatment modules. Implementation of such hybrid methods is facilitated by the multi-branch chemical dispensing unit, which provides separate chemical lines to different chemical treatment modules, and dispenses chemical to at least four different areas of each wafer during single-wafer processing in an upright orientation. The multi-branch chemical dispensing unit provides a flexible, modular building block for constructing various equipment configurations that use multiple chemical treatments and/or pH neutralization steps.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to wet cleaning processes and equipment and, in particular, to wet cleaning of integrated circuit wafers in the semiconductor industry following chemical-mechanical polishing (CMP). 
         [0003]    2. Description of the Related Art 
         [0004]    Wet chemical processing and wet cleaning are frequently executed steps used to fabricate integrated circuits on semiconductor wafers. In particular, various types of wet chemical processes typically are used to etch wafers, to clean wafers following etching, to polish wafers, and to clean wafers following polishing. Wet processing equipment used in all four of these operations generally is designed to include multiple processing modules such as one or more chemical processing modules, one or more water rinse modules, and a wafer dryer. The processes and equipment needed for such wet processing operations are similar in some respects and quite different in other respects. 
         [0005]    Some conventional wet chemical wafer cleaning operations entail immersing wafers in a tank, wet chemical processing for etching and associated post-etch cleaning. Typically, batches of wafers or single wafers are held upright in a vertical orientation within immersion tanks during wet processing. Chemical immersion tanks are typically made from non-reactive materials such as, for example, polytetrafluoroethylene (PTFE, known as “teflon”), or stainless steel. Following chemical treatment, wafers can be moved to a separate rinse module such as a water rinse tank, to receive a treatment that arrests chemical reactions occurring on the wafer surface. Water rinse tanks are also used to achieve pH neutralization following exposure of wafers to acidic or basic chemicals during processing in the chemical immersion tanks. Thus, the water tanks are exposed to chemicals used in the steps that precede the pH neutralization step, which means the water tank materials must also be resistant to such chemicals. Spray processing modules are one alternative to immersion tanks for chemical and/or water processing. Spray processing typically entails spraying individual wafers that are held in a horizontal position. 
         [0006]    Some chemical immersion tanks and/or water rinse tanks are equipped with a sonic vibration system to assist in removing particles from wafer surfaces by vibrating the water while the wafer is submerged. Once particles are dislodged by the sonic vibrations, the particles can float away from the wafer surface. When the sonic vibration system operates at a vibration frequency in the MHz range, the process is referred to as a “megasonic” clean. 
         [0007]    Wafer dryers can use, for example, nitrogen gas and/or a solvent such as isopropyl alcohol (IPA) to evaporate rinse water from the wafers. Additionally or alternatively, a high-speed spinning machine can drive water from the wafers by the action of a centrifugal force. 
         [0008]    Single wafers or groups of wafers are typically transported between processing modules by one or more automated transport devices such as industrial manufacturing robots. Such robots can be designed to function in an aqueous environment and/or which may be chemically resistant. Such robots can be single axis, dual axis, or triple axis robots. 
         [0009]    Some chemical immersion tanks and/or water rinse tanks are equipped with brushes that assist in removing particles from the wafer surfaces. Brushes are especially useful for removing slurry particles that may remain on the wafer surface after completing a CMP process. Brush cleaning typically entails scrubbing the front side of each individual wafer to remove particulates from at least partially formed integrated circuits. 
         [0010]    Typically, neither etching nor post-etch cleaning involves scrubbing wafers with slurry or brushes. On the other hand, existing post-polish wafer cleaning equipment typically uses slurry and brushes combined with water or dilute acidic detergents, as opposed to concentrated chemicals and/or complex sequences of chemicals to clean the wafer. The design of wet cleaning equipment depends in large part on what chemicals are used. For example, the type of chemical to be used in the cleaning system determines the materials allowed for the tanks, delivery lines, hardware, filters, and even soldering methods used to plumb the delivery lines. Furthermore, different types of chemicals can require different safety features that impact equipment design. The design of post-polish cleaning equipment is therefore different from that of post-etch cleaning equipment in that the handling, delivery, and disposal of water and detergents containing particulate slurries will differ significantly from those needed for concentrated corrosive chemicals such as sulfuric acid, ethylene glycol, and the like that are typically used in post-etch cleaning. 
       BRIEF SUMMARY 
       [0011]    A brush-cleaning apparatus is disclosed for use in cleaning semiconductor wafers after CMP, using a hybrid clean process. A hybrid cleaning method described employs a two-chemical sequence in which first and second chemical treatment modules are separate from one another, and are followed by a pH-neutralizing rinse that occurs in a treatment module separate from the first and second chemical treatment modules. 
         [0012]    Embodiments of the brush-cleaning apparatus are implemented with a multi-branch chemical dispensing unit that is applied beneficially in conjunction with the hybrid cleaning method described herein as an illustrative example. Implementation of the hybrid cleaning method, as well as other multi-chemical processing sequences, is facilitated by the multi-branch chemical dispensing unit, which includes separate chemical lines to supply the different chemical treatment modules. The multi-branch chemical dispensing unit also dispenses chemical to at least four different areas of each wafer during single-wafer processing in an upright orientation. Furthermore, the multi-branch chemical dispensing unit provides a flexible, modular building block for constructing various equipment configurations that use multiple chemical treatments and/or pH neutralization steps. Use of a rail system and a pallet for changing the order of various treatment modules further facilitates experimental development of more complex processes and subsequent implementation to support manufacturing. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]    In the drawings, identical reference numbers identify similar elements. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. 
           [0014]      FIG. 1A  is a top plan view of a semiconductor wafer map showing locations of surface defects following an in-line metrology step, with four top plan micrographs that highlight specific defects. 
           [0015]      FIG. 1B  is a perspective view of a conventional wafer cleaning brush apparatus used to scrub the wafer having the defects shown in  FIG. 1A . 
           [0016]      FIG. 2A  is a high-level flow diagram illustrating a sequence of operations within a conventional post-CMP wet cleaning process, according to the prior art. 
           [0017]      FIG. 2B  is a high-level flow diagram illustrating a sequence of operations within a post-CMP hybrid wet cleaning process, as disclosed herein. 
           [0018]      FIGS. 3A and 3B  are block diagrams of equipment configurations used to execute post-CMP sequences of operations such as those shown in  FIGS. 2A and 2B , respectively. 
           [0019]      FIG. 4  is a pictorial perspective view of tanks shown in  FIG. 3B  and described herein. 
           [0020]      FIG. 5  is a detailed process flow diagram showing steps in a post-CMP hybrid wet cleaning process as described herein. 
           [0021]      FIG. 6  is a pictorial perspective view of a modular multi-branch chemical dispensing unit for use in re-configuring the equipment configuration shown in  FIG. 3B  to run the post-CMP hybrid wet cleaning process described herein. 
           [0022]      FIGS. 7A-10B  are pictorial perspective views of various alternative equipment configurations that combine modular multi-branch chemical dispensing units to support different cleaning sequences, according to further embodiments described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of semiconductor processing comprising embodiments of the subject matter disclosed herein have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
         [0024]    Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
         [0025]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
         [0026]    Reference throughout the specification to integrated circuits is generally intended to include integrated circuit components built on semiconducting substrates, whether or not the components are coupled together into a circuit or able to be interconnected. Throughout the specification, the term “layer” is used in its broadest sense to include a thin film, a cap, or the like. 
         [0027]    Reference throughout the specification to conventional thin film deposition techniques for depositing silicon nitride, silicon dioxide, metals, or similar materials include such processes as chemical vapor deposition (CVD), low-pressure chemical vapor deposition (LPCVD), metal organic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), plasma vapor deposition (PVD), atomic layer deposition (ALD), molecular beam epitaxy (MBE), electroplating, electro-less plating, and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain deposition techniques should not be limited to those described. For example, in some circumstances, a description that references CVD may alternatively be done using PVD, or a description that specifies electroplating may alternatively be accomplished using electro-less plating. Furthermore, reference to conventional techniques of thin film formation may include growing a film in-situ. For example, in some embodiments, controlled growth of an oxide to a desired thickness can be achieved by exposing a silicon surface to oxygen gas or to moisture in a heated chamber. 
         [0028]    Reference throughout the specification to conventional etching techniques known in the art of semiconductor fabrication for selective removal of polysilicon, silicon nitride, silicon dioxide, metals, photoresist, polyimide, or similar materials includes such processes as wet chemical etching, reactive ion etching (RIE), washing, wet cleaning, pre-cleaning, spray cleaning, scrubbing, chemical-mechanical planarization (CMP) and the like. Specific embodiments are described herein with reference to examples of such processes. However, the present disclosure and the reference to certain etching and/or polishing techniques should not be limited to those described. In some instances, two such techniques may be interchangeable. For example, stripping photoresist may entail immersing a sample in a wet chemical bath or, alternatively, spraying wet chemicals directly onto the sample. 
         [0029]    Reference throughout the specification to processing a semiconductor wafer in a vertical orientation is synonymous with an upright orientation. For a semiconductor wafer semiconductor wafer, processing in a vertical orientation means the wafer is held on edge as opposed to lying flat. 
         [0030]    Specific embodiments are described herein with reference to equipment configurations for use in cleaning semiconductor wafers following chemical-mechanical polishing processes. However, the present disclosure and the reference to certain materials, dimensions, and the details and ordering of processing operations or processing steps are exemplary and should not be limited to those shown. The term “planarize” is used in its broadest sense, to include polishing the wafer, as well as other approaches. 
         [0031]    In the figures, identical reference numbers identify similar features or elements. The sizes and relative positions of the features in the figures are not necessarily drawn to scale. 
         [0032]      FIG. 1A  shows an example of an in-line metrology wafer scan  100  of a silicon wafer  102  following a conventional post-CM P wet chemical cleaning process. The silicon wafer  102  bears a pattern of printed circuits  104  that are at least partially fabricated. The full wafer scan  100  shows that an exemplary ring defect mode  105  that is present on the wafer  102 . In particular, the full wafer scan  100  shows a pattern of dots representing the ring defect mode  105 , that lie approximately along the perimeter of a circle of radius r. Four exemplary magnification inserts  106 ,  108 ,  110 , and  112  show top plan view micrographs of the wafer surface at locations corresponding to certain ones of the defects,  105   a ,  105   b ,  105   c , and  105   d , respectively. Under magnification, the defects  105   a - 105   d  are recognizable as gouges. Other types of defects that may also occur following CMP include scratches, crystalline growth defects, and the like, which generally become more problematic as circuit dimensions continue to shrink. 
         [0033]      FIG. 1B  illustrates an exemplary conventional wafer cleaning brush apparatus  114  for use in post-CMP cleaning. The conventional wafer cleaning brush apparatus  114  can be mounted within a wet chemical immersion tank or within a water rinse tank, as shown in  FIG. 3 . The wafer cleaning brush apparatus  114  includes wafer edge rollers  116 , a pair of rotating brushes  118 , and a chemical dispense tube  120 . The wafer edge rollers  116  are mounted on spindles  122  that set the wafer edge rollers  116  in a rotational motion. When a wafer  102  is oriented vertically in the wafer cleaning brush apparatus  114  such that the edge of the wafer  102  is in contact with the wafer edge rollers  116 , counterclockwise rotation of the wafer edge rollers  116  causes counterclockwise rotation of the wafer  102 . Meanwhile, the rotating brushes  118  contact opposite sides of the wafer  102  as the wafer  102  rotates. One or both of the rotating brushes  118  can also rotate against a respective surface of the wafer  102 , or the rotating brushes  118  can remain fixed while the wafer rotates. 
         [0034]    Returning to  FIG. 1A , a logical conclusion consistent with the exemplary circular pattern of defects  105  is that surface particles, perhaps slurry particles from the previous CMP step, have gouged the surface of the wafer  102  during contact with one or more of the rotating brushes  118  during the post-CMP wet chemical cleaning process. Such gouges could be caused, for example, by a mis-adjustment of the brush position, or by insufficient particle removal during the cleaning operation.
       In  FIG. 2A , a first sequence of operations in the conventional post-CMP wet cleaning process  124  includes a first brush clean operation  130 , a second brush clean operation  132  that repeats the first brush clean operation  130 , and an isopropyl alcohol (IPA) drying operation  134 . The first and second brush clean operations  130  and  132 , respectively, use de-ionized (DI) water or a single chemical detergent. Such a conventional post-CMP wet cleaning process  124  can be used for wafers bearing circuits having a characteristic feature size of about 45 nm. The wet cleaning process  124  was used to clean the gouged wafer shown in  FIG. 1A .       
 
         [0036]      FIG. 2B  illustrates a hybrid wet chemical cleaning process  126  according to one embodiment of the innovations disclosed herein. The sequence of operations shown in  FIG. 2B  is carried out following a polishing step, such as CMP. In one embodiment, the hybrid wet chemical cleaning process  126  is a sequence of operations that includes a first brush clean operation  140 , a second brush clean operation  142 , a DI water rinse with megasonics  143 , and an isopropyl alcohol (IPA) drying operation  144 . The first and second brush clean operations  140  and  142 , respectively, can use, for example, two different chemicals such as a first acidic chemical and a second basic chemical. Alternatively, the first and second brush clean operations can be repeated chemical processes using the same chemical or different concentrations of the same chemical. For example, in one embodiment, the hybrid wet chemical cleaning process  126  uses an acid chemical that includes a 60:1 dilute citric acid solution, such as CX-100, available from CANI, Inc., WAKO chemical, and other industrial chemical suppliers. Such a hybrid wet chemical cleaning process  126  has been shown to reduce or substantially eliminate the exemplary ring defect mode shown in  FIG. 1A , for wafers bearing circuits having a characteristic feature size of 32 nm. Experiments using the hybrid wet chemical cleaning process  126  have shown that such a process is useful in reducing or substantially eliminating other defect modes as well, at one or more layers of the 32 nm technology node process, or in fabrication processes designed for other technology nodes. Furthermore, such a hybrid wet chemical cleaning process  126  may be useful in other contexts within, or outside of, the semiconductor industry. In other industries in which the object being cleaned is volumetric instead of a wafer, a modified brush apparatus can be substituted for the wafer cleaning brush apparatus  114  described herein, with similar results. 
         [0037]      FIG. 3A  illustrates an exemplary equipment configuration  150  that was used to execute the sequence of operations  130 ,  132 , and  134  in the conventional post-CMP wet cleaning process  124  described above with respect to  FIG. 2A . The equipment configuration  150  includes five modules that process one wafer  102  at a time. From left to right, the processing modules are: a wet loading station  152 ; a two-stage vertical double-sided brush scrubber  154  having a first brush scrubber stage  156  that carries out the first brush clean operation  130 ; a second brush scrubber stage  158  that carries out the second clean operation  132 ; a vertical spin rinse dryer  160 ; and a dry unload station  162 . The brush scrubber stages  156  and  158  contain DI water supplied by the DI water lines  159 . The vertical spin rinse dryer  160  is also supplied by the DI water supply line  159 , as well as a local source of IPA via IPA line  161 . The dotted lines  165  indicate transfer paths of wafers through the various modules, for increased throughput. 
         [0038]    At the wet loading station  152 , a wet robot loads a single wafer  102  into the first brush scrubber stage  156  of the two-stage vertical double-sided brush scrubber  154 . In the first stage  156 , the wafer  102  receives “rough” processing in a relatively dirty tank containing DI water, in which particles tend to accumulate. The first brush scrubber stage  156  may be dirty despite use of a filter, continuous replenishing of the DI water, and other such measures. Subsequently, the wafer  102  is loaded into the second brush scrubber stage  158  of the two-stage vertical double-sided brush scrubber  154 , for second stage cleaning processing in a relatively clean tank also containing DI water. Inside the first and second brush scrubber stages  156  and  158 , the DI water lines  159  terminate in water dispense tubes  120  for dispensing DI water at two locations on opposite sides of the wafer  102 . Rotating brushes  118  are positioned to scrub both sides of the wafer  102  at the same time. Next, the wafer  102  is transferred to the vertical spin rinse dryer  160  where the wafer  102  is immersed in isopropyl alcohol vapor at the drying operation  134 , while spinning at high speed to drive off moisture. Finally, the wafer  102  exits the equipment configuration  150  via the dry unload station  162 , where a dry robot flips the wafer  102  to a horizontal orientation and unloads the wafer  102 . Processing carried out using the equipment configuration  150  is limited to water-based processing because there are no chemical supply lines feeding either of the brush scrubber stages  156  and  158 . In addition, the water is delivered to only one location on either side of the wafer. 
         [0039]      FIG. 3B  illustrates one exemplary equipment configuration  166  that would be desirable to use in executing the sequence of operations  140 ,  142 ,  143 , and  144  in the hybrid post-CMP wet chemical cleaning process  126  described with respect to the inventive concepts of  FIG. 2B . The equipment configuration  166  includes six modules that process one wafer  102  at a time. From left to right, the processing modules include: the wet loading station  152 , a two-stage vertical double-sided brush scrubber  161  having a first brush scrubber stage  163  that carries out the first brush clean operation  140 ; a second brush scrubber stage  169  that carries out the second brush clean operation  142 ; a vertical megasonic tank  167  that carries out the DI water rinse with megasonics  143 , the vertical spin rinse dryer  160  that carries out the drying operation  144 , and the dry unload station  162 . The brush scrubber stages  163  and  169  contain a chemical supplied by the chemical supply line  168 , or DI water supplied by the DI water lines  159 . The vertical spin rinse dryer  160  is also supplied by the DI water supply line  159 , as well as a local source of IPA via IPA line  161 . The dotted lines  165  indicate transfer paths of wafers through the various modules, for increased throughput. 
         [0040]    At the wet loading station  152 , a wet robot loads a single wafer  102  into the first brush scrubber stage  163  of the two-stage vertical double-sided brush scrubber  161 . In the first stage  163 , the wafer  102  can receive chemical processing or water processing. Subsequently, the wafer  102  is loaded into the second brush scrubber stage  169  of the two-stage vertical double-sided brush scrubber  161 , for second stage cleaning. In the second stage  169 , the wafer  102  can receive chemical processing or water processing. Next, the wafer  102  is transferred to the vertical spin rinse dryer  160  where the wafer  102  is immersed in isopropyl alcohol while spinning at high speed to drive off moisture. Finally, the wafer  102  exits the equipment configuration  166  via the dry unload station  162 , where a dry robot flips the wafer  102  to a horizontal orientation and unloads the wafer  102 . 
         [0041]      FIG. 4  shows a perspective view of tanks  164 , containing the double-sided brush scrubber stages  163  and  169 . The double-sided brush scrubber stages  163  and  169  may include an alignment mechanism that is configured to position the semiconductor wafer  102  in a vertical orientation. Processing carried out using the equipment configuration  166  is limited to water-based processing or processing with one chemical because there is only one set of shared chemical delivery lines  168  feeding both of the brush scrubber stages  163  and  169 . In addition, chemical is delivered to only one location on either side of the wafer. Inside the first and second brush scrubber stages  163  and  169 , the shared set of chemical delivery lines  168  terminate in chemical dispense tubes  120  for dispensing chemical at two locations on opposite sides of the wafer  102 . Rotating brushes  118  are positioned to scrub both sides of the wafer  102  at the same time. The shared set of chemical delivery lines  168  feed both of the brush scrubber stages  156  and  158  and that the dispense tubes  120  dispense chemical to only two locations—one adjacent to the top of the front side of the wafer  102  and one adjacent to the top of the back side of the wafer  102 . Thus, processing options are limited by the structure of the chemical delivery system used in the equipment configuration  166 . With such a limited configuration, it is not possible to implement the hybrid post-CMP wet chemical cleaning process sequence  126  as desired because separate chemical lines are not provided to each of the two processing tanks  164 . 
         [0042]      FIG. 5  shows a first embodiment of a modular, multi-branch chemical dispensing unit  170  that can be substituted for the shared set of chemical delivery lines  168  inside the two-stage vertical double-sided brush scrubber  161 . Such a modular approach supports execution of the hybrid post-CMP cleaning process and other types of cleaning processes. Use of the multi-branch chemical dispensing units  170  permits a first set of chemical delivery lines  172  to supply the first brush scrubber stage  163  and a second set of chemical delivery lines  174  to the second brush scrubber stage  169 . Use of separate chemical delivery lines for the first and second stages allows use of different chemical treatments at these stages instead of simply having a first “dirty” stage and a second “clean” stage of the same chemical treatment, and/or a water rinse. For example, the first set of chemical delivery lines  172  can be plumbed with an acid and the second chemical delivery lines  174  can be plumbed with a base to support a hybrid cleaning sequence. In addition, use of a second chemical in the second brush scrubber stage  158  can passivate the wafer surface by inhibiting the first chemical reaction faster than use of a wafer rinse which simply dilutes the previous chemical but may not stop the chemical reaction completely. 
         [0043]    Furthermore, the multi-branch chemical dispensing unit  170  provides four chemical dispense tubes  120  in each tank  164  instead of two chemical dispense tubes. A pair of chemical dispense tubes  120   a  are mounted on an upper branch, and a pair of chemical dispense tubes  120   b  are mounted on a lower branch of each multi-branch dispensing unit  170 . The multi-branch chemical dispensing unit  170  thus allows fresh chemical to reach more areas of the wafer  102  substantially simultaneously, resulting in a more uniform process, and higher particle removal efficiency. In addition, vertical positions  175  of the chemical dispense tubes  120  along each branch of the multi-branch chemical dispensing unit  170  can be adjusted for best chemical dispersion efficiency. Also, use of the multi-branch chemical dispensing unit  170  permits measurement and adjustment of a distance of the chemical dispense tubes  120  from the wafer surface. The measurement and adjustment can be performed by an alignment mechanism internal to the tank  164 . As a result, the hybrid post-CMP wet chemical cleaning process  126 , when operated using the equipment configuration  166  in which the two-stage vertical double-sided brush scrubber  161  is configured with multi-branch chemical dispensing units  170 , has been shown to substantially reduce the ring defect  105  as well as other defects at multiple post-CMP cleaning operations, as demonstrated by in-line wafer metrology scans. 
         [0044]      FIG. 6  shows a sequence of steps  200  in the exemplary hybrid post-CMP wet chemical cleaning process  126  according to one embodiment. 
         [0045]    At  201 , a single wafer  102  enters the equipment configuration  166  via the wet loading station  152  and is transferred into the first brush scrubber stage  163  of the two-stage vertical double-sided brush scrubber  161 . In the first brush scrubber stage  163 , a first chemical is dispensed into the first dual-brush module at  202 . 
         [0046]    At  204 , the wafer  102  then receives chemical processing in the first chemical, for example, a solution containing 25% citric acid. Other acid solutions may be used. The wafer  102  is then loaded into the second brush scrubber stage  169  of the two-stage vertical double-sided brush scrubber. 
         [0047]    At  206 , a second chemical is dispensed into the second dual-brush module. 
         [0048]    At  208 , the wafer receives chemical processing in the second chemical, for example, a base solution. The base can contain sodium bicarbonate, or another base chemical. 
         [0049]    At  210 , the wafer is transferred to the vertical megasonic tank  167  to cease the second chemical reaction and to neutralize the pH of the wafer surface. The vertical megasonic tank  167  contains a neutralizing solution such as DI water that is supplied by the DI water supply lines  159 . In the vertical megasonic tank  167 , sonic vibrations dislodge remaining slurry particles prior to the drying operation. Alternatively, the vertical megasonic tank  167  can be filled with a chemical via a neutralization chemical supply line  173  to provide megasonics-enhanced chemical processing. 
         [0050]    At  212 , the wafer  102  is transferred to the vertical spin rinse dryer  160  where the wafer  102  is immersed in isopropyl alcohol (IPA) vapor while spinning at high speed to drive off moisture. IPA is supplied to the vertical spin rinse dryer  160  via the local dryer chemical supply line  161 . 
         [0051]    At  214 , the wafer  102  exits the equipment configuration  166  via the dry unload station  162 . 
         [0052]    In a second exemplary embodiment shown in  FIGS. 7A-7C , groups of multi-branch chemical dispensing units  170  are combined to support different types of hybrid cleaning processes. For example,  FIG. 7A  shows a dual-hybrid cleaning sequence  176  in which four of the multi-branch chemical dispensing units  170  are used to process the wafer  102  twice through each of two different chemicals.  FIG. 7B  shows a quad-hybrid cleaning sequence  178  in which four of the multi-branch chemical dispensing units  170  are used to process the wafer  102  through a succession of four different chemicals.  FIG. 7C  shows a tri-hybrid cleaning sequence  180  in which three of the multi-branch chemical dispensing units  170  are used to process the wafer  102  through one chemical twice and through another chemical once. Thus, the use of the multi-branch chemical dispensing units  170  affords great flexibility in building the best and most efficient cleaning sequence at each layer in the overall integrated circuit fabrication process. 
         [0053]    In a third exemplary embodiment shown in  FIG. 8 , two multi-branch chemical dispensing units  170  are combined to support a hybrid cleaning process in which a neutralization module  182  that may contain for example, water, a dilute acid, or a dilute base, is inserted between the two multi-branch chemical dispensing units  170 . Using such a configuration, the wafer is immersed in a liquid in a tank so it can be pH-neutralized before it moves from a first brush cleaning step that uses, for example, an acidic chemical, to a second brush cleaning step that uses, for example, a basic chemical. The addition of such a neutralization operation prevents pH shock-induced defects from forming on the surface of the wafer  102 . Shock-induced defects can cause surface charge to accumulate on the wafer  102 , for example. The neutralization module  182  can be configured using either a regular tank or a megasonics tank that are full of liquid into which the wafer is immersed. 
         [0054]    In a fourth exemplary embodiment shown in  FIGS. 9A-9B , three or four multi-branch chemical dispensing units  170  are combined to support a hybrid cleaning process in which a neutralization module  182  containing, for example, water, a dilute acid, or a dilute base, is inserted between multiple multi-branch chemical dispensing units  170 . For example,  FIG. 9A  illustrates use of the neutralization module  182  following dual processing by a first chemical, and preceding dual processing by a second chemical.  FIG. 9B  illustrates use of the neutralization module  182  following dual processing by a first chemical, and preceding single processing by a second chemical. In the fourth embodiment, the neutralization module  182  can be inserted among pairs of multi-branch chemical dispensing units  170  to achieve an efficient hybrid cleaning process. 
         [0055]    In a fifth exemplary embodiment shown in  FIGS. 10A-10B , further flexibility is provided by the use of a rail system  184  to switch positions of the neutralization module  182  or any one of the multi-branch chemical dispensing units  170  so as to change the order of operations within the wafer cleaning process. For example,  FIG. 10A  illustrates use of the neutralization module  182  inserted to follow dual processing by a first chemical and single processing by a second chemical, and to precede single processing by a third chemical.  FIG. 10B  illustrates use of the neutralization module  182  inserted to follow single processing by a first chemical and to precede dual processing by a second chemical. To move from the sequence shown in  FIG. 10A  to the sequence shown in  FIG. 10B , the first chemical processing module can be removed, the third chemical module can be plumbed with the second chemical, and the neutralization module  182  can be placed on a track and transported via the rail system  184  to the position shown between the first and second chemical processing modules. In particular, a car, pallet, or holder is mounted on tracks that form the rail system  184 . The module  182  can be moved to any location in the sequence of cleaning stations to provide the desired neutralizing clean. Similarly, the various stations  163  and  169  can be moved as well. 
         [0056]    The use of multi-branch chemical dispensing units  170  in conjunction with one or more neutralization modules  182  and the rail system  184  thus greatly facilitates experimentation with different cleaning sequences during development and/or manufacturing of wet cleaning processes. 
         [0057]    The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
         [0058]    It will be appreciated that, although specific embodiments of the present disclosure are described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, the present disclosure is not limited except as by the appended claims. 
         [0059]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.