Patent Publication Number: US-2007119544-A1

Title: Apparatus and method for single substrate processing using megasonic-assisted drying

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of co-pending U.S. patent application Ser. No. 10/826,458 (APPM/010533.C1), filed Apr. 16, 2004, which is a continuation of co-pending U.S. patent application Ser. No. 10/010,240 (APPM/010533), filed Dec. 7, 2001, issued U.S. Pat. No. 6,726,848. Each of the aforementioned related patent applications is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to the field of surface preparation systems and methods for semiconductor substrates and the like.  
      2. Description of the Related Art  
      In certain industries there are processes that must be used to bring objects to an extraordinarily high level of cleanliness. For example, in the fabrication of semiconductor substrates, multiple cleaning steps are typically required to remove impurities from the surfaces of the substrates before subsequent processing. The cleaning of a substrate, known as surface preparation, has for years been performed by collecting multiple substrates into a batch and subjecting the batch to a sequence of chemical and rinse steps and eventually to a final drying step. A typical surface preparation procedure may include etch, clean, rinse and dry steps. An etch step may involve immersing the substrates in an etch solution of HF to remove surface oxidation and metallic impurities and then thoroughly rinsing the substrates in high purity deionized water (DI) to remove etch chemicals from the substrates. During a typical cleaning step, the substrates are exposed to a cleaning solution that may include water, ammonia or hydrochloric acid, and hydrogen peroxide. After cleaning, the substrates are rinsed using ultra-pure water and then dried using one of several known drying processes.  
      Currently, there are several types of tools and methods used in industry to carry out the surface preparation process. The tool most prevalent in conventional cleaning applications is the immersion wet cleaning platform, or “wet bench.” In wet bench processing, a batch of substrates is typically arranged on a substrate-carrying cassette. The cassette is dipped into a series of process vessels, where certain vessels contain chemicals needed for clean or etch functions, while others contain deionized water (“DI”) for the rinsing of these chemicals from the substrate surfaces. The cleaning vessels may be provided with piezoelectric transducers that propagate megasonic energy into the cleaning solution. The megasonic energy enhances cleaning by inducing microcavitation in the cleaning solution, which helps to dislodge particles off of the substrate surfaces. After the substrates are etched and/or cleaned and then rinsed, they are dried. Often drying is facilitated using a solvent such as isopropyl alcohol (IPA), which reduces the surface tension of water attached to the substrate surface.  
      Another type of surface preparation tool and method utilized in the semiconductor industry is one in which a number of surface preparation steps (e.g. clean, etch, rinse and/or dry) may be performed on a batch of substrates within a single vessel. Tools of this type can eliminate substrate-transfer steps previously required by wet bench technology, and have thus gained acceptance in the industry due to their reduced risk of breakage, particle contamination and their reduction in footprint size.  
      Further desirable, however, is a chamber and method in which multiple surface preparation steps can be performed on a single substrate (e.g. a 200 mm, 300 mm or 450 mm diameter substrate), as opposed to a batch of substrates. It is thus an object of the present invention to provide a chamber and method for performing one or more surface preparation steps on a single substrate.  
     SUMMARY OF THE INVENTION  
      In one aspect of the present invention, a single substrate is positioned in a single-substrate process chamber and subjected to wet etching, cleaning and/or drying steps. According to another aspect of the present invention, a single substrate is exposed to etch or clean chemistry in the single-substrate processing chamber as boundary layer thinning is induced in the region of the substrate. According to yet another aspect of a method according to the present invention, boundary layer thinning is induced in a zone within the single-substrate process chamber, and a single substrate is translated through the zone during a process within the chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a schematic illustration of a single substrate processing chamber, showing the substrate positioned in the lower interior region of the chamber.  
       FIG. 1B  is a schematic illustration of a single substrate processing chamber, showing the substrate positioned in the upper interior region of the chamber.  
       FIG. 1C  is a block diagram illustrating one example of a fluid handling system useable with the chamber of  FIG. 1A .  
       FIG. 1D  is a block diagram illustrating a second example of a fluid handling system useable with the chamber of  FIG. 1A .  
       FIGS. 2A-2C  are a sequence of cross-section views of the chamber interior, illustrating movement of the substrate between the upper interior region and the lower interior region.  
       FIG. 3A  is a cross-sectional perspective view of a second embodiment of a single substrate processing chamber showing the fluid manifold in the closed position. The figure also shows automation provided for transporting a substrate into, out of, and within the chamber.  
       FIG. 3B  is a cross-sectional perspective view of the single substrate processing chamber of  FIG. 3A  showing the fluid manifold in the opened position. The transport automation shown in  FIG. 3A  is not shown in  FIG. 3B .  
       FIG. 4  is a cross-sectional perspective view of the upper manifold and a portion of the tank of the second embodiment of  FIG. 3A .  
       FIG. 5  is a cross-sectional side view of the second embodiment of  FIG. 3A .  
       FIG. 6  is a perspective view of an end effector of the second embodiment of  FIG. 3A . The end effector is shown carrying a substrate.  
       FIG. 7A  is a perspective view of one prong of a second embodiment of an end effector during transport of a substrate.  
       FIG. 7B  is a perspective view showing the end effector of  FIG. 7A  during transport of a substrate into or out of the chamber.  
       FIG. 7C  is a perspective view showing the end effector, substrate and chamber during transport of the substrate into or out of the chamber, with the substrate beginning to make contact with the bottom notch of the chamber.  
       FIG. 7D  is a perspective view showing the end effector, substrate and chamber during processing of the substrate within the chamber.  
       FIG. 7E  is a perspective view similar to the view of  FIG. 7A  showing one prong of the end effector during processing of the substrate within the chamber.  
       FIG. 8  is a cross-section view of a chamber according to a third embodiment. 
    
    
     DETAILED DESCRIPTION  
      Three embodiments of single substrate chambers and associated processes are described herein. Each of the described chambers/methods performs wet processing steps such as (but not limited to) etching, cleaning, rinsing and/or drying on a single substrate (such as, for example a semi-conductor wafer substrate) using a single chamber. As will be appreciated from the description that follows, such chambers and methods are beneficial in that each substrate treated using the chamber/method is exposed to the same process conditions to which the other substrates undergoing the same process are exposed. This yields higher precision processing than seen in a batch system, in which a substrate positioned in one part of a substrate batch may be exposed to slightly different process conditions (such as fluid flow conditions, chemical concentrations, temperatures, etc.) than a substrate positioned in a different part of the batch. For example, a substrate at the end of a longitudinal array of substrates may see different conditions than a substrate at the center of the same array. Such variations in conditions can yield batches lacking in uniformity between substrates.  
      Single substrate chambers/methods such as those described herein are further beneficial in that each substrate is exposed to process fluids for a shorter amount of time than is required in batch processing. Moreover, for applications where only a few substrates need processing (e.g. in a prototype engineering context), the individuals requiring the processed substrates need only wait a few minutes to receive the treated substrates, rather than waiting a full hour or more for the substrates to be processed in a batch-type chamber. Moreover, the chambers/methods described herein can be practiced using the same or smaller volumes of process fluids (on a substrate-per-substrate basis) than would be used in corresponding batch processes.  
     First Embodiment—Structure  
      Features of a first embodiment of a single substrate processing chamber are schematically shown in  FIGS. 1A-1D . Referring to  FIG. 1A , a first embodiment 2 of a single substrate processing chamber includes a chamber  10  having sidewalls  11  defining a lower interior region  12   a  proportioned to receive a substrate S for processing, an upper interior region  12   b , and an opening  14  in the upper interior region  12   a.    
      The first embodiment includes a substrate transport device  28 . Transport device includes an end effector  30  configured to engage a substrate S, and is driven by conventional automation (not shown) to move the substrate S through opening  14  into and out of the chamber  10  in an edgewise direction. Transport device  28  is further configured to cause end effector  30  to move the substrate between the lower interior region  12   a  and the upper interior region  12   b , as described below in connection with operation of the device.  
      Transport device  28  may also carry a lid  29  that closes against opening  14  when the end effector  30  is lowered. The lid  29  may remain in place, even as the end effector moves the substrate between regions  12   a ,  12   b  during processing, and be later withdrawn so that the end effector  30  can remove substrate S from the chamber.  
      The upper end of the lower interior region  12   a  may be narrowed to include a throat section to increase the velocity of fluid flowing through the throat section from the lower section of the chamber. The bottom of the chamber  10  may be flat or contoured to conform to the shape of the lower edge of the substrate.  
      Fluid Handling System  
      The first embodiment  2  is preferably provided with a fluid handling system  26  configured to carry various process fluids (e.g. etch fluids, cleaning fluids, rinse water, etc.) into the lower interior region  12   b  of chamber  10 .  
      There are various ways in which the fluid handling system  26  can be configured. For example, as shown in  FIGS. 1A and 1B . a window  16  may be formed in the lower interior region  12   b  and one or more manifolds may be moveable into place at the window  16  to direct process fluids into the chamber  10 . The manifolds and the window  16  are preferably sealed within the fluid handling system  26 , a sealed housing that exhausts fumes, gases, etc. that may be released from the manifolds so as to prevent their escape into the surrounding environment.  
      A fluid manifold  18  is position able to direct process fluids (e.g. chemistries for etching, and DI water for rinsing) into the lower interior  12   a  of chamber  10  via window  16 . Fluid manifold  18  includes at least one, but preferably multiple, openings  20  through which fluid is directed into the chamber  10 . The fluid manifold  18  is moveable between a closed position ( FIG. 1A ) in which the manifold is oriented to direct fluids into the window  16  via openings  20 ,and an open position ( FIG. 1B ) in which the openings  20  are positioned away from the window  16 . The fluid manifold  18  may be moveable between the closed and open positions using standard automation. Fluid manifold  18  may optionally include a megasonic transducer (not shown) having one or more transducers for directing megasonic energy into fluids in the chamber as will be described in greater detail below. For simplicity, the term “megasonic transducer” will be used herein to encompass transducer assemblies comprised of a single transducer or an array of multiple transducers.  
      A second fluid manifold, which will be referred to as the megasonics manifold  22 , is provided and includes one or more inlets  24 . Like the fluid manifold  18 , the megasonics manifold  22  is moveable between a closed position ( FIG. 1B ) in which the inlets  24  are oriented to direct fluid (e.g. cleaning solutions and DI water for rinsing) from the megasonics manifold  22  through window  16 , and an opened position ( FIG. 1A ) in which the inlets  24  are spaced from the window  16 , permitting the manifold  18  to be brought into its closed position. The megasonics manifold  22  may be moveable between the closed and open positions.  
      The megasonics manifold  22  includes a megasonic transducer, which may include a single transducer or an array of multiple transducers, oriented to direct megasonic energy into the chamber interior via the window. When the megasonic transducer(s) direct megasonic energy into fluid in the chamber, they induce acoustic streaming within the fluid—i.e. streams of microbubbles that aid in removal of contaminants from the substrate and that keep particles in motion within the process fluid so as to avoid their reattachment to the substrate.  
      Referring to the block diagram of  FIG. 1C , the fluid handling system  26  may include a system of valves and conduits for directing fluids into the manifolds  18 ,  22 . A DI water source and a source of etch fluid are fluidly coupled to manifold  18 , and valves  19   a ,  19   b  govern flow of these fluids into the manifold  18 . It should be appreciated that while the etch plumbing is shown configured for injection into a DI water stream, etch fluid may alternatively be independently directed into the manifold  18 . Similarly, valves  23   a ,  23   b  and associated conduits couple sources of DI water and cleaning fluid to megasonics manifold  22 .  
      The configuration of the fluid handling system shown in  FIG. 1C  provides two means for evacuation of fluid from the chamber  10 . First, dedicated sealed containers  31   a ,  31   b  are provided for rapidly withdrawing fluids from the chamber. Preferably, each sealed container is dedicated to a particular type of process fluid, e.g. an etch fluid or a cleaning fluid, so as to prevent cross-contamination of process fluids.  
      Each container  31   a,    31   b  is coupled to the chamber  10  by valves  27   a ,  27   b  and associated drain plumbing  29   a ,  29   b . Alternatively, the valves and drain plumbing may couple the sealed containers  31   a ,  31   b  to the manifolds  18 ,  22 . The sealed containers  31   a ,  31   b  are maintained at negative pressure and the valves  27   a ,  27   b  are kept closed except when they are opened for evacuation of the chamber. At the end of the etch process, the valve  27   a  may be opened, causing rapid removal of the etch fluid into the negative pressure container  31   a  for subsequent re-use. This rapid removal of the fluid helps to shear etch solution from the substrate surface. It also optimizes uniformity across the substrate surface by creating a sharp transition between exposure of the substrate to the etch solution and separation of the substrate from the bulk etch solution—thus minimizing surface variations between the top portion of the substrate and the lower portion of the substrate. This transition may be sharpened further, and the shearing of the etch solution from the substrate may be enhanced, by using the end effector to pull the substrate into the upper interior region  12   b  during the rapid fluid removal.  
      The second evacuation means provided in the embodiment of  FIG. 1C  utilizes the megasonics manifolds  18 ,  22 , which are moved to the opened position to dump fluid from the chamber into a drain (not shown).  
      As another example of a fluid distribution system, a fluid manifold  23  as shown in the block diagram of  FIG. 1D  may be provided with multiple dedicated valves  33   a ,  33   b , and  33   c  feeding process fluids into the manifold  23 . In such a configuration, one valve may feed etch solution into the manifold, whereas another may feed cleaning solution and another may feed rinse water. This type of dedicated configuration is desirable in that it minimizes the number of common plumbing components (i.e. those that are exposed to multiple process chemicals) and thus minimizes the amount of rinsing required for the plumbing between process steps.  
      In this example, manifold  23  may include a megasonic transducer, or a megasonic transducer may be positioned in a lower region of the chamber  10 . The manifold  23  may be fixed or moveable to an opened position for a rapid evacuation of the chamber  10 . Sealed negative pressure containers  31   a ,  31   b  may also provide an additional means of evacuation as described with respect to the  FIG. 1C  embodiment. The sealed containers  31   a ,  31   b  may be coupled to the manifold itself, or to the chamber  10  as shown in  FIG. 1D .  
      Upper Megasonics  
      Referring again to  FIGS. 1A and 1B , an overflow weir  34  is formed along the chamber periphery at the top of the lower interior region  12   a . Process fluid flowing into the chamber from manifolds  18 ,  22  cascades into the weir  34  and into overflow plumbing  35  for recirculation or disposal. A pair of megasonic transducers  32   a ,  32   b , each of which may include a single transducer or an array of multiple transducers, are positioned at an elevation below that of the weir  34 , and are oriented to direct megasonic energy into an upper portion of lower interior region  12   a  of the chamber  10 . Transducer  32   a  directs megasonic energy towards the front surface of a substrate, while transducer  32   b  directs megasonic energy towards the rear surface of the substrate.  
      The transducers are preferably positioned such that the energy beam interacts with the substrate surface at or just below the gas/liquid interface, e.g. at a level within the top 0-20% of the liquid in the lower interior  12   a . The transducers may be configured to direct megasonic energy in a direction normal to the substrate surface or at an angle from normal. Preferably, energy is directed at an angle of approximately 0-30 degrees from normal, and most preferably approximately 5-30 degrees from normal. Directing the megasonic energy from transducers  32   a,b  at an angle from normal to the substrate surface can have several advantages. For example, directing the energy towards the substrate at an angle minimizes interference between the emitted energy and return waves of energy reflected off the substrate surface, thus allowing power transfer to the solution to be maximized. It also allows greater control over the power delivered to the solution. It has been found that when the transducers are parallel to the substrate surface, the power delivered to the solution is highly sensitive to variations in the distance between the substrate surface and the transducer. Angling the transducers reduces this sensitivity and thus allows the power level to be tuned more accurately. The angled transducers are further beneficial in that their energy tends to break up the meniscus of fluid extending between the substrate and the bulk fluid (particularly when the substrate is drawn upwardly through the band of energy emitted by the transducers)—thus preventing particle movement towards the substrate surface.  
      Additionally, directing megasonic energy at an angle to the substrate surface creates a velocity vector towards overflow weir  34 , which helps to move particles away from the substrate and into the weir. For substrates having fine features, however, the angle at which the energy propagates towards the substrate front surface must be selected so as to minimize the chance that side forces imparted by the megasonic energy will damage fine structures.  
      It may be desirable to provide the transducers  32   a ,  32   b  to be independently adjustable in terms of angle relative to normal and/or power. For example, if angled megasonic energy is directed by transducer  32   a  towards the substrate front surface, it may be desirable to have the energy from transducer  32   b  propagate towards the back surface at a direction normal to the substrate surface. Doing so can prevent breakage of features on the front surface by countering the forces imparted against the front surface by the angled energy. Moreover, while a relatively lower power or no power may be desirable against the substrate front surface so as to avoid damage to fine features, a higher power may be transmitted against the back surface (at an angle or in a direction normal to the substrate). The higher power can resonate through the substrate and enhance microcavitation in the trenches on the substrate front—thereby helping to flush impurities from the trench cavities.  
      Additionally, providing the transducers  32   a ,  32   b  to have an adjustable angle permits the angle to be changed depending on the nature of the substrate (e.g. fine features) and also depending on the process step being carried out. For example, it may be desirable to have one or both of the transducers  32   a ,  32   b  propagate energy at an angle to the substrate during the cleaning step, and then normal to the substrate surface during the drying step (see below). In some instances it may also be desirable to have a single transducer, or more than two transducers, rather than the pair of transducers  32   a ,  32   b.    
      Vapor inlet ports  36 , fluid applicators  37 , and gas manifold  38  extend into upper interior region  12   b  of the chamber  10 . Each is fluidly coupled to a system of conduits that deliver the appropriate vapors and gases to the ports as needed during processing. The fluid applicators  37  are preferably configured to inject a stream or streams of process fluid into the upper interior region  12   b . It is preferable that the stream(s) of injected fluid collectively extend for a width at least as wide as the diameter of the substrate, such that fluid may be uniformly applied at high velocity across the width of the substrate as the substrate is moved past the stream(s). To this end, the fluid applicators may comprise a pair of narrow elongate slots in the wall of the upper region  12   b  of the chamber. It is also preferable that the fluid applicators  37  are spaced from the substrate by a very close distance.  
     First Embodiment—Operation  
      The system  2  may be used for various processes, including those requiring one or more of the steps of wet etching, cleaning, rinsing and drying. Its use will be described in the context of an etch, clean and drying process, in which rinses are performed following etching and cleaning. Performance of this combination of steps is efficient in that it allows multiple steps to be performed in a single chamber, and it minimizes post-treatment particle reattachment since substrates leave the chamber dry. Moreover, performance of the multiple steps in a single chamber minimizes buildup of particles and residue in the process chamber, since each time a substrate goes through the sequence of processes, the chamber itself is cleaned and dried. Naturally, various other combinations of these or other process steps may be performed without departing from the scope of the present invention.  
      Etching  
      If processing is to begin with an etch procedure, operation of the first embodiment begins with fluid manifold  18  in the closed position as shown in  FIG. 1A . The lower portion  12   a  of the chamber  10  is filled with process fluids necessary for the etching procedure (for example, hydrofluoric acid (HF), ammonium fluoride and HF, or buffered oxide). These fluids may be injected into a DI water stream entering fluid manifold  18  (using, for example, the fluid handling configuration shown in  FIG. 1C ), causing them to flow into the chamber  10  with the DI water. Alternatively, the etch solution may flow directly into manifold  18  and into chamber, or, if the fluid handling configuration of  FIG. 1D  is used, the solution may enter manifold  23  and chamber  10  via dedicated valve  33   b . In either case, the solution cascading over weir  34  may be recirculated back into the chamber  10  throughout the etch process, such as by collecting it into a (preferably) temperature-controlled vessel and circulating it back to manifold  18  for re-introduction into the chamber  10 . Alternatively, the etch process may be a “one-pass” process in which the overflowing etch solution is directed to a drain for disposal. As a third alternative, the flow of etch solution may be terminated once the lower portion  12   a  of the chamber has been filled.  
      Substrate S is engaged by end effector  30  and moved into the etch solution by the substrate transport device  28 . Substrate S is positioned in the lower portion  12   a  of the chamber, i.e. at an elevation below that of the weir  34 , so that the substrate is fully immersed in the etch solution.  
      In wet processing, a relatively stagnant fluid layer known as a “boundary layer” is typically present at the substrate surface. A thick boundary layer can inhibit the ability of an etch or cleaning solution to reach and react with the substances that are to be removed from the substrate surface. It is thus desirable to minimize the thickness of the boundary layer of fluid attached to the substrate surface so that the etch chemicals can more effectively contact the substrate surface. Boundary layer thinning may be accomplished by inducing turbulence in the etch fluid using disturbances formed into the sidewalls of the chamber. For example, a random or patterned topography may be machined into the side walls so that fluid flowing through the chamber  10  from the manifold is turbulent rather than laminar. Turbulence may be further increased by using relatively high fluid flow rates and temperatures. As another alternative, additional inlet ports (not shown) may b-e formed into the side walls and process fluids may enter the chamber via these ports as well as via manifold  18  so as to cause disruptions in the flow from the manifold  18 . As yet another alternative, a megasonic transducer of a type that could withstand the etch fluids (e.g. sapphire, fluoroplastic, PFA, Halar, ECTFE, coated metal, or polytetrafluoroethylene (PTFE) sold under the trade name Teflon) could be positioned in the chamber  10  to cause turbulent flow of the etch fluid and to thus induce or contribute to boundary layer thinning.  
      Post-Etch Quench and Rinse  
      At the end of the etch procedure, flow of etch solution is terminated and a post-etch rinsing step may be carried out to remove etch solution from the substrate and chamber. The post-etch rinsing step may be initiated in one of several ways. In one example, manifold  18  is moved to the opened position ( FIG. 1B ), draining the etch solution from the chamber  10  into a drain (not shown), from which it is directed for collection/disposal. The manifold is then closed and DI rinse water is introduced into the chamber via fluid manifold  18  and caused to cascade through the chamber and over weir  34 . Alternatively, the step of opening the manifold  18  may be eliminated, in which case flow of DI water is permitted to continue until the etch solution is thoroughly rinsed from the substrate, manifold and chamber.  
      As another alternative, the etch fluid may be rapidly removed from chamber  10  by opening valve  27   a  ( FIG. 1C ), causing the fluid to be suctioned into sealed negative pressure container  31  a for later re-use or disposal. As discussed in the “Structure” section above, this type of rapid removal of etch solution minimizes etch variations across the substrate surface by more sharply ending the exposure of the substrate to the bulk etch fluid. This process is preferably enhanced by simultaneously using the end effector  30  to withdraw the substrate from the chamber lower portion  12   a  into the upper portion  12   b . Withdrawal may be carried at any desired speed, although a rate of 25-300 mm/sec has been found beneficial.  
      The post-etch rinse process may preferably include a boundary layer thinning process to accelerate diffusion of the etch chemistry from the surface of the substrate out of the boundary layer of fluid attached to the substrate and into the surrounding bulk fluid. This diffusion process is known in the art as “quenching” and is instrumental in terminating etching of the substrate surface. A megasonic transducer positioned at or near the chamber bottom (e.g. a transducer provided as part of fluid manifold  18 , or a transducer mounted separately within the chamber, or the transducer of megasonics manifold  22 ) may also be utilized for this purpose.  
      The accelerated quench is preferably performed in combination with the rapid removal of the bulk etch fluid (e.g. in approximately less than 1.0 second), such as by suction of the fluid into the negative pressure container  31   a  ( FIG. 1C ) and the simultaneous withdrawal of the substrate into the upper portion  12   b  of the chamber. However, any of the evacuation processes described above, such as opening of the manifold  18 , may also be used preferably in combination with the lifting of the substrate from the chamber  10 .  
      Next, the chamber  10  is rapidly filled with a quenchant such as DI water. Since at this time the substrate is in the upper portion  12   b  of the chamber, rapid filling can be performed without concern that the substrate will be splashed—an occurrence which could lead to lack of uniformity across the substrate&#39;s surface. As the chamber  10  begins to fill, the megasonic transducer in the chamber bottom (i.e. depending on the fluid handling system, this may be the transducer of manifold  22 , manifold  18 , or a lower chamber transducer) is operated at low power. The megasonic power is increased as the chamber fills with DI water. Once the lower portion  12   a  of the chamber has been partially filled, the substrate is lowered into the quenchant. The turbulence created by the megasonic energy facilitates boundary layer thinning that thus facilitates diffusion of etch chemistry from the boundary layer into the bulk rinse water.  
      The megasonic power is increased as the volume of quenchant in the chamber increases. Beginning at a lower power and increasing the power as the chamber fills minimizes the chance of high power megasonic energy causing splashing of quenchant onto the substrate, and also minimizes the likelihood that residual etch solution on the substrate and in the tank would aggressively etch the bottom portion of the substrate immersed in the water.  
      The flow of DI water or other quenchant into the chamber preferably continues even after the substrate is fully immersed. The upper megasonic transducers  32   a ,  32   b  are energized. These transducers impart megasonic energy into an adjacent region of the DI water. The energy creates a zone Z ( FIGS. 2A through 2C ) in which the turbulence created by the megasonic energy causes boundary layer thinning and thus facilitates gettering of the etch material away from the substrate and into the quenchant. The zone Z is a band of megasonic energy extending across the chamber. The substrate transport  28  pulls the substrate through zone Z so as to expose the entire substrate to the zone Z. The area of the band is preferably selected such that when the substrate passes through the zone, up to 30% of the surface area of a face of the substrate is positioned within the band. Most preferably, as the center of the substrate passes through the zone, only approximately 3-30% of the surface area of a face of the substrate is positioned within the band.  
      The substrate is raised and lowered through zone Z one or more times as needed for a thorough quench. The raising and lowering may be performed at any desired speed, although a rate of approximately 25-300 mm/sec has been found to be beneficial. As the substrate passes from the upper region  12   b  into the bulk rinse fluid, particles entrained at the substrate surface are released at the gas/liquid interface and are flushed over the weir and out of the chamber. The expression “gas/liquid interface” as used herein refers to the interface between air present in the chamber (and/or gas or vapor introduced into the chamber) and fluid in the lower region  12   a  of the chamber. Preferably the zone Z is created slightly below the gas/liquid interface.  
      It should be noted that the lower megasonic transducer may remain powered on while the substrate is translated through the zone Z.  
      The quenching process may be enhanced by a stream of DI water preferably directed into upper region  12   b  through fluid applicators  37 . As the substrate transport  28  pulls the substrate through the chamber, the substrate passes through zone Z and through the stream of fresh water. During movement of the substrate upwardly past the fluid stream, the fluid stream applies a thin layer of fresh rinse fluid to the portion of the substrate at which the boundary layer was just thinned by zone Z. The substrate may be moved upwardly and downwardly through the zone Z and the fluid stream one or more times as needed for a thorough quench.  
      The timing of energization of the transducers  32   a ,  32   b  may be selected depending on the goals of the process or the nature of the substrate surface (e.g. whether it is hydrophobic or hydrophilic). In some instances it may be desirable to energize the transducers  32   a ,  32   b  only during extraction of the substrate from lower region  12   a  into upper region  12   b , or only during insertion of the substrate into lower region  12   a , or during both extraction and insertion.  
      After quenching, DI water may continue to circulate through the chamber until such time as the chamber, end effectors and substrate have been thoroughly rinsed.  
      Cleaning  
      A substrate cleaning step may also be performed utilizing the first embodiment. If etching is performed, the cleaning step may occur before and/or after the etch process. Prior to cleaning, the chamber is drained by moving the fluid manifold  18  away from the window  16 . If the fluid handling configuration of  FIG. 1C  is used, the megasonics manifold  22  is moved to the closed position covering the opening. During the cleaning process, a cleaning solution (for example, a solution of water, NH 2 OH and H 2 O 2  that is known in the industry as “SC1”) is introduced into the chamber  10  via megasonics manifold  22  and caused to cascade over weir  34 . Alternatively, if a fluid handling configuration such as that shown in  FIG. 1D  is used, the cleaning solution enters the manifold  23  and chamber  10  via the appropriate one of the dedicated valves  33   c.    
      Megasonic transducers  32   a,b  are energized during cleaning so as to impart megasonic energy into an adjacent region of the process fluid—and in doing so create zone Z ( FIGS. 2A through 2C ) of optimum performance within the chamber. If necessary to prevent fine feature damage, one of the transducers may by operated at low power or zero power.  
      Throughout cleaning, the substrate transport  28  moves the substrate upwardly and downwardly one or more times (as required by the specifics of the process) to move the entire substrate through the zone Z of optimum performance. The substrate may be translated through the zone at any desired speed, although a rate of approximately 25-300 mm/sec has been found beneficial.  
      As with the quenching process, the timing of energization of the transducers  32   a ,  32   b  may be selected depending on the goals of the process. In some instances it may be desirable to energize the transducers  32   a ,  32   b  only during extraction of the substrate from lower region  12   a  into upper region  12   b , or only during insertion of the substrate into lower region  12   a , or during both extraction and insertion.  
      The zone Z is a band of megasonic energy extending across the chamber, preferably slightly below the gas/liquid interface. The substrate transport  28  pulls the substrate through the band so as to expose the entire substrate to the zone Z. The area of the band is preferably selected such that when the substrate passes through the zone, up to 30% of the surface area of a face of the substrate is positioned within the band. Most preferably, as the center of the substrate passes through the zone, only approximately 3-30% of the surface area of a face of the substrate is positioned within the band.  
      Creation of zone Z is optimal for cleaning for a number of reasons. First, cleaning efficiency is enhanced by minimizing the thickness of the boundary layer of fluid that attaches to the substrate surface—so that the cleaning solution can more effectively contact the substrate surface and so that reaction by products can desorb. The megasonic energy from transducers  32   a ,  32   b  thin the boundary layer by creating regional turbulence adjacent the substrate. Since transducers  32   a ,  32   b  are directed towards the front and back surfaces of the substrate, this boundary layer thinning occurs on the front and back surfaces. The megasonic energy further causes microcavitation within the fluid, i.e. formation of microbubbles that subsequently implode, releasing energy that dislodges particles from the substrate. The megasonic turbulence keeps particles in the fluid suspended in the bulk and less likely to be drawn into contact with the substrate. Lastly, high velocity fluid flow through the chamber and over the weir moves particles away from the zone and thus minimizes re-attachment. This high velocity flow may be enhanced as discussed using a narrowed throat region in the upper end of the chamber, or using an active mechanism such as a bellows-type device, to accelerate fluid flow through the zone.  
      Further optimization of cleaning at zone Z may be achieved by introducing a gas such as nitrogen, oxygen, helium or argon into upper interior region  12   b  via gas inlet port  38 . The gas diffuses into the volume of cleaning solution that is near the surface of the cleaning solution and increases the microcavitation effect of the megasonic transducers in the zone Z of optimal performance.  
      The lower megasonic transducer associated with manifold  22  (or, in the case of the  FIG. 10  embodiment, a megasonic transducer associated with manifold  23  or separately positioned in the lower portion of the chamber) may be activated during the cleaning process, to as to create an acoustic streaming effect within the chamber, in which streams of microbubbles are formed that keep liberated particles suspended in the bulk fluid until they are flushed over the weir  34 , so as to minimize particle re-attachment to the substrate. It has been found to be desirable, but not required, to operate the lower megasonic transducer while the upper megasonic transducers  32  are also activated and while the substrate is being translated through the zone Z.  
      It should be noted that while some minimal boundary layer thinning may be caused by activation of the lower transducer(s), boundary layer thinning is not the objective of activation of the megasonics associated with this transducer. Creating the zone Z in which the boundary layer is thinned as described above, rather than relying upon acoustic streaming procedures for boundary layer thinning of the entire substrate surface, is advantageous in that by keeping the boundary layer relatively thicker outside the zone, the chance of particle reattachment is minimized.  
      To further minimize the chance of particle reattachment, a particle gettering surface (not shown) may be positioned in the chamber near zone Z. During cleaning, a charge is induced on the gettering surface such that particles liberated from the substrate surface are drawn to the gettering surface and thus away from the substrate. After the substrate has passed out of zone Z, the polarity of the gettering surface is reversed, causing release of particles from the gettering surface. These released particles are flushed out of the chamber  10  and into the weir by the flowing cleaning fluid.  
      A charge may also be induced on the end effector  30  so as to draw particles off of the substrate when the end effector is in contact with the substrate. Later, the polarity of the end effector is reversed, causing particles gettered into the end effector to be released into the flowing cleaning fluid in the chamber and to be flushed into the weir.  
      The cleaning process will result in release of gases from the cleaning solution into the upper interior region  12   b , some of which may contact exposed regions of the substrate and cause pitting at the substrate surface. To avoid such exposure, select vapors are introduced into the upper chamber region  12   b  via vapor inlet port  36 . The vapors condense on the substrate to form a protective film. If any released gas should condense on the substrate, it will react with the protective film rather than reacting with the silicon surface of the substrate. For example, an SC1 cleaning solution will cause off-gassing of ammonia into the chamber. In this example, hydrogen peroxide vapor would be introduced into the upper region  12   b  to form a protective film on the substrate. Ammonia released by the cleaning solution will react with the protective film rather than pitting the substrate surface.  
      After the substrate has been exposed to cleaning solution for the required process time, the substrate is rinsed using a rinse solution. The rinse solution naturally will be dependent on the cleaning process being carried out. Following back end of the line (BEOL) cleaning, an isopropyl alcohol or dilute acid rinse may be carried out. After front end cleaning process such as SC1 cleaning, a DI water rinse is preferable. Rinsing may be accomplished in various ways. For example, with the substrate preferably elevated above the cleaning solution in the chamber, the cleaning solution may be suctioned back through the manifold  22  into a low pressure container  31   b  in the manner described in connection with the etch process. Next, rinse fluid is introduced into the chamber  10  (via, for example, manifold  22  of  FIG. 1C , manifold  23  of  FIG. 1D ) and cascades over the weir  34 .  
      The substrate is lowered into the rinse water and the water rinses the cleaning solution from the chamber  10  and from the surface of the substrate. Alternatively, with the substrate remaining in the cleaning solution, rinse fluid may be introduced into the lower region chamber, thereby flushing the cleaning solution from the chamber  10  into the weir  34  as it rinses the chamber and substrate.  
      Megasonic energy from the side transducers  32   a ,  32   b  and/or the lower transducer is optionally directed into the rinse water chamber so as to enhance the rinse process. The substrate may be passed through zone Z multiple times (again at a rate that may, but need not be, within the range of 25-300 mm/sec) as needed for thorough rinsing. A gas such as nitrogen, oxygen, helium or argon may be introduced into upper interior region  12   b  via gas inlet port  38 . The gas diffuses into the volume of rinse fluid that is near the gas/liquid interface (i.e. the interface between the upper surface of the rinse fluid and the gas or air above it) and surface of the rinse fluid and increases the microcavitation effect of the megasonic transducers in zone Z.  
      The power state of the transducers is selected as appropriate for the stage of the rinsing process and the surface state of the substrate. Preferably, both of the side transducers  32   a ,  32   b  and the lower transducer are powered “on” during insertion of the substrate into the rinse fluid. Depending upon the surface state of the substrate (e.g. whether it is hydrophilic or hydrophobic), the side transducers  32   a ,  32   b  may be on or off during extraction of the substrate into the upper region  12   b.    
      Reactive Gas Rinse  
      At some point during wet processing, the substrate may be exposed to a reactive gas (such as, for example, ozone, chlorine or ammonia) so as to interact with the substrate surface. Preferably, the reactive gas is dissolved in a rinse fluid and the substrate is exposed to the rinse fluid for an appropriate length of time.  
      The reactive gas rinse may be carried out with megasonic energy being used to create a turbulent flow of the reactive gas rinse fluid. The turbulent flow thins the boundary layer of fluid attached to the substrate, so as to enhance reactive gas diffusion through the boundary layer into contact with the substrate surface. Turbulence may be created using a megasonic transducer positioned in the bottom of the chamber as reactive gas rinse fluid flows into the chamber via one of the fluid manifolds. Alternatively, reactive gas may be introduced, via nozzles  36  or additional nozzles, into the upper interior  12   b  of the chamber as rinse water flows into the chamber via one of the fluid manifolds. The gas dissolves into the rinse water near the surface of the rinse water. The upper megasonic transducers  32   a ,  32   b  are energized to cause boundary layer thinning in zone Z, creating a zone of optimal absorption of reactive species onto the substrate surface. The substrate is translated through the zone Z one or more times as needed for the reactive gas to effectively treat the substrate surface.  
      Pre-Dry Rinse  
      In certain processes it may be desirable to perform a pre-dry passivating rinse using hydrofluoric acid (HF), hydrochloric acid (HCl) or de-gassed DI water.  
      In such processes, the lower portion  12   a  of the chamber  10  is filled with passivation fluid. The passivation fluid may be injected into a DI water stream entering fluid manifold  18  (using, for example, the fluid handling configuration shown in  FIG. 1C ), causing it to flow into the chamber  10  with the DI water. Alternatively, the passivation fluid may flow directly into manifold  18  and into chamber, or, if the fluid handling configuration of  FIG. 1D  is used, the fluid may enter manifold  23  and chamber  10  via dedicated valve  33   b . In either case, the solution cascading over weir  34  may be recirculated back into the chamber  10  throughout the pre-dry rinse process, such as by collecting it into a (preferably) temperature-controlled vessel and circulating it back to manifold  18  for re-introduction into the chamber  10 . Alternatively, the pre-dry rinse process may be a “one-pass” process in which the overflowing fluid is directed to a drain for disposal. As a third alternative, the flow of fluid may be terminated once the lower portion  12   a  of the chamber has been filled.  
      Substrate S is engaged by end effector  30  and moved into the solution by the substrate transport device  28 . Substrate S is positioned in the lower portion  12   a  of the chamber, i.e. at an elevation below that of the weir  34 , so that the substrate is fully immersed in the passivation solution. As with the reactive gas step, the upper megasonic transducers  32   a ,  32   b  may be energized to cause boundary layer thinning in zone Z, creating an optimal zone for contact between the passivating rinse fluid and the substrate surface. The substrate is translated through the zone Z one or more times as needed for the passivating rinse fluid to effectively passivate the substrate surface. The use of megasonic energy may also prevent particle deposition onto the substrate, which can often occur using low-pH passivation solutions such as HF or HCl.  
      Drying  
      After the final treatment and rinse steps are carried out, the substrate is dried within the chamber. Drying may be performed in a number of ways—three of which will be described below. Each of the three examples described utilize an IPA vapor preferably carried into the chamber by a nitrogen gas flow. In each example, the IPA vapor is preferably generated in an IPA generation chamber remote from the chamber  10 , using one of a variety of IPA generation procedures known those skilled in the art. For example, IPA vapor may be created within the IPA generation chamber by injecting a pre-measured quantity of IPA liquid onto a heated surface within the IPA generation chamber. The IPA is heated on the heated surface to a temperature preferably less than the boiling point of IPA (which is 82.4° C. at 1 atmosphere). Heating the IPA increases the rate at which IPA vapor is generated and thus expedites the process, creating an IPA vapor cloud. When the IPA vapor is needed in the chamber  10 , nitrogen gas is passed through an inlet into the IPA generation chamber, and carries the IPA vapor out of the IPA generation chamber via an outlet that is fluidly coupled to the vapor inlet port  36  in chamber  10 .  
      The three examples of drying processes using the IPA vapor will next be described. In one embodiment, the bulk water used for the final rinse may be rapidly discharged from the chamber  10  by rapidly withdrawing the fluid into a negative pressure container, or by performing a “quick dump” by moving megasonics manifold  22  to the opened position (or, if drying follows an HF last process and rinse, fluid manifold  18  is moved from the closed to opened position). Then a vapor of isopropyl alcohol is introduced into the chamber  10  via vapor inlet port  36 . The IPA vapor passes into the lower portion  12   a  of the chamber and condenses on the surface of the substrate where it reduces the surface tension of the water attached to the substrate, and thus causes the water to sheet off of the substrate surfaces. Any remaining liquid droplets may be evaporated from the substrate surface using gas, such as heated nitrogen gas, introduced through gas inlet port  38 . Gas inlet port  38  may include a gas manifold having outlets that are angled downwardly. The end effector  30  may be used to move the substrate past this manifold to accelerate evaporation of remaining IPA/water film from the surface of the substrate.  
      In an alternative drying process, an atmosphere of IPA vapor may be formed in the upper interior region  12   b  by introducing the vapor via vapor inlet port  36 . According to this embodiment, the substrate transport  28  lifts the substrate from the lower interior region  12   a  into the IPA atmosphere in the upper interior region  12   b , where the IPA vapor condenses on the surface of the substrate, causing the surface tension of the water attached to the substrate to be reduced, and thus causing the water to sheet from the substrate surface.  
      The megasonic transducers  32   a ,  32   b  may be energized as the substrate is pulled from the DI water so as to create turbulence in zone Z to thin the boundary layer of fluid attached to the substrate. With the boundary thinned by zone Z. IPA can diffuse more quickly onto the surface of the substrate, thus leading to faster drying with less IPA usage. Thus, the substrate may be withdrawn into the IPA atmosphere relatively quickly, i.e. preferably at a rate of 30 mm/sec or less, and most preferably at a rate of between approximately 8 mm/sec-30 mm/sec. This is on the order of ten times faster than prior extraction drying methods, which utilize a slow withdrawal (e.g. 0.25 to 5 mm/sec) to facilitate a surface-tension gradient between fluid attached to the substrate and the bulk rinse water.  
      Again, gas such as heated nitrogen may be introduced via manifold  38  to evaporate any remaining IPA and/or water film, and the substrate may be translated past the manifold  38  to accelerate this evaporation process.  
      In a third alternative embodiment, slow extraction-type drying may be utilized. The substrate may thus be slowly drawn from the bulk DI water into the IPA vapor. Using this embodiment, the IPA condenses on the liquid meniscus extending between the substrate and the bulk liquid. This results in a concentration gradient of IPA in the meniscus, and results in so-called Marangoni flow of liquid from the substrate surface. Gas such as heated nitrogen gas may be directed from manifold  38  onto the substrate to remove some of the residual water and/or IPA droplets and/or film. The substrate may be moved past gas manifold  38  to accelerate this evaporation step.  
      In each of the above three embodiments, care should be taken to maintain the static pressure within the chamber during the various steps in the drying processes.  
     Second Embodiment—Structure  
       FIG. 3A  shows a second embodiment  100  of a single substrate processing chamber utilizing principles of the present invention.  
      Second embodiment  100  generally includes a process chamber  102 , a containment vessel  104 , an end effector  106  (see  FIG. 6 ), a rotational actuator  108  and a vertical actuator  110 .  
      Referring to  FIG. 3A , process chamber  102  includes closely spaced chamber walls  111  defining a lower interior region  113   a  and an upper interior region  113   b . An overflow weir  114  is positioned in the lower region  113   a , slightly below upper region  113   b . Overflow weir  114  includes a wall section  115  over which fluids cascade into the weir  114  during certain processing steps. At the bottom of the chamber  102  is a lower opening  135 , and at the top of the chamber is an upper opening  142  ( FIG. 4 ).  
      A vapor/gas manifold  116  is provided for directing vapors/gases into upper region  113   b  of the chamber. Manifold  116  (best shown in  FIG. 4 ) includes walls  120  on opposite sides of upper region  113   b . Vapor/gas ports  122   a  (see  FIG. 4 ),  122   b  (see  FIG. 5 ) extend through walls  120  and are fluidly coupled to vapor/gas conduits  124   a ,  124   b . A plurality of orifices  126   a ,  126   b  extend from conduits  124   a ,  124   b  into the chamber  102 . The orifices  126   a ,  126   b  may be downwardly angled as shown. The angles are preferably (but are not required to be) within the range of 45°-80° relative to the normal to walls  120 . Each port  122   a ,  122   b  is coupled to plumbing that delivers process vapors/gases through the ports  122   a,b  and into chamber  102  via conduits  124   a , b and orifices  126   a ,  126   b.    
      Referring to  FIG. 5 , manifold  116  additionally includes drain ports  128  extending from overflow weirs  114 . Drain ports  128  are fluidly coupled to plumbing (not shown) that carries overflow fluids from weir  114  and away from the chamber for recirculation or disposal.  
      Within containment vessel  104  is a fluid manifold  130 , which includes an elongated conduit  132 , and a plurality of openings  134  extending from conduit  132  into the lower region of the chamber  102 . Fluid ports  133  are coupled to conduit  132  and are fluidly coupled to a network of plumbing. This plumbing network selectively delivers a selection of different process chemistries through the fluid ports  133  into manifold  130  and thus into the chamber  102 . Manifold  130  is moveable to an opened position as shown in  FIG. 3B  to permit fluid in the chamber to be rapidly discharged through lower opening  135  into a drain (not shown). Automation  137  is provided for moving the fluid manifold between the open and closed position.  
      An end effector of the type shown in  FIG. 6  may be used for either of the first or second embodiments. End effector  136  includes a block  138  and a pair of gripping members  140  that engage a substrate S between them by engaging opposite edges of the substrate as shown. Vertical actuator  110  ( FIG. 3A ) moves block  138  and gripping members  140  between a withdrawn position in which the substrate S is fully removed from the chamber  102 , and an advanced position in which the substrate S is fully disposed within the lower region  113   a . When in the advanced position, block  138  closes against opening  142  ( FIG. 4 ) of chamber  102  so as to contain gases and vapors and so as to prevent migration of particles into the chamber.  
      When the end effector is in the withdrawn position, rotational actuator  108  ( FIG. 3A ) is configured to rotate the end effector to a lateral orientation. This is particularly desirable for large substrates (e.g.  300  mm) that are customarily housed in a horizontal arrangement in a storage device or carrier. The end effector can be made to retrieve and deposit substrates directly from/to such a carrier, or from a separate robotic end effector provided for unloading/loading substrates from/to the carrier. The vertical and horizontal actuators preferably utilize conventional robotics of the type known to those of skill in the art, and these as well as other automated features (e.g. those relating to measurement and injection of process fluids/vapors/gases are controlled by a conventional controller such as a PLC controller.  
       FIGS. 7A through 7E  show an alternative end effector  106   a  having an engaging mechanism found particularly beneficial when used with the described embodiments. An alternative chamber having a different shape than the chamber  102  is also described, although various other chamber shapes may be utilized with the end effector  106   a . As will be understood from the description that follows, the end effector  106   a  has two positions relative to the substrate: a transport position in which the substrate is securely held by the end effector, and a process position in which the end effector stabilizes the substrate while permitting process fluids to flow into contact with the substrate&#39;s surface.  
      Referring to  FIG. 7A , the end effector  106   a  includes a pair of support members  150 , each of which includes an upper support  152 , lower support  154 , upper transport slot  156  and lower transport slot  158 . During transport of the substrate, upper and lower transport slots  156 ,  158  receive the edge of the substrate S as shown in  FIGS. 7A and 7B , thereby supporting the substrate as it is moved into/out of/within the chamber  102   a.    
      As illustrated in  FIGS. 7B-7D , a bottom notch  160  is mounted within the chamber  102   a  (for example, to a chamber wall  111   a  as shown). As the substrate is lowered into the process position in the chamber, the bottom edge of the substrate contacts bottom notch  160 . Continued downward movement of the end effector  106  causes the substrate to edge to slip out of the upper and lower transport slots  156 ,  158 . Once the substrate has been fully lowered into the process position within the chamber ( FIG. 7D ), its weight is supported by the bottom notch  160  and support members  152 ,  154  function to stabilize the substrate in this process position. Specifically, as illustrated in  FIG. 7E , the substrate edge is disposed between a slot in support member  152 , which restricts forward/backward movement of the substrate but preferably does not grip the substrate—thereby keeping the substrate stable while allowing process fluid to flow through the slot. Support member  154  (which preferably does not include a slot) extends towards the substrate edge and restricts lateral movement of the substrate.  
      Because the chamber walls  111  a are closely spaced, the chamber walls preferably include recessed sections  162  ( FIGS. 7B-7D ) which provide additional space for receiving end effector members  150 .  
     Second Embodiment—Operation  
      As with the first embodiment, the second embodiment may be used for a variety of steps, including but not limited to wet etch, clean, rinse and drying operations either alone or in combination with one another or with other process steps. Operation of the second embodiment will be described in the context of an etch, clean and drying process, with rinses being performed following etching and cleaning. However it should be understood that various other combinations of processes might be performed without departing from the scope of the present invention. It should also be understood that various steps described in connection with the first embodiment may be practiced using the second embodiment, including the described methods for boundary layer thinning, megasonic-assisted quenching, cleaning, rinsing and/or drying, ozone passivation, chemical injection and exhaustion. Moreover, the rates and other values given as examples in connection with the first embodiment may also be applied to use of the second and third embodiments.  
      Operation of the second embodiment begins with fluid manifold  130  in the closed position as shown in  FIG. 5 . DI water is directed into fluid ports  133 , through manifold conduit  132  and into the chamber  102  through openings  134 . The DI water passes through the lower interior region  113   a  and cascades over wall  115  into weir  114  and out drain ports  128 . At the same time, nitrogen gas flows slowly into the uppermost of the fill ports  122   a,b  in the vapor/gas manifold, causing the nitrogen gas to flow through the associated conduits  124   a ,  124   b  and into the upper region  113   b  of the chamber  102  via orifices  126   a ,  126   b . This low flow maintains a slight positive pressure within the chamber  102 . Preferably, this nitrogen flow continues throughout etching, cleaning, rinsing and drying.  
      Substrate W is engaged by end effector  106  and moved into the cascading DI water by the automation system. Substrate S is positioned in the lower interior  113   a  of the chamber. Process fluids necessary for the etching procedure (e.g. HF) are injected into the DI water being delivered to fluid ports  133  into manifold, and are thus passed into the chamber  102  via fluid manifold  130 . At the end of the etch procedure, delivery of etch solution into the chamber  102  is terminated. The etch solution may be exhausted from the chamber and rinsing may be carried out preferably using one of the rinse procedures described above. For example, pure DI water may continue to flow into the chamber  102  to flush the etch solution from the chamber and to rinse the substrate, manifold, and chamber.  
      In an alternative etch procedure, the lower interior  113   a  may be filled with etch solution, and then the substrate lowered into the static volume of etch solution. After the required dwell time, a cascading rinse or other type of rinse is preferably carried out as described above.  
      Once the substrate is thoroughly rinsed, a cleaning solution (for example, a solution of water, NH 2 OH and H 2 O 2  that is known in the industry as “SC1” is introduced into the chamber  102  via manifold  130  and caused to cascade over wall  115  into weir  114 . After the substrate has been exposed to the cleaning solution for the desired period of time, injection of the cleaning solution into the DI stream is terminated, and pure DI water flows into the chamber  102  to rinse the substrate.  
      After the final treatment and rinse steps are carried out, the substrate is dried within the chamber  102 . Drying may be performed in a number of ways—each of which preferably utilizes IPA vapor generated in a manner similar to that described above.  
      In one example of a drying process, the bulk water used for the final rinse may be rapidly discharged from the chamber  102  by moving fluid manifold  130  to the opened position ( FIG. 3B ). A vapor of isopropyl alcohol is then introduced into the upper portion  113   b  of the chamber by passing the IPA vapor through the vapor/gas inlet port  122   a,b,  into the corresponding conduit  124   a,b  and thus into the chamber via openings  126   a,b.  The IPA vapor flows into lower portion  113   a  of the chamber, where it condenses on the surface of the substrate where it reduces the surface tension of the water attached to the substrate, and thus causes the water to sheet off of the substrate surfaces. Any remaining liquid droplets may be evaporated from the substrate surface using a gas (e.g. heated nitrogen gas) introduced through the vapor/gas inlet ports  126   a,b.    
      Alternatively, an atmosphere of IPA vapor may be formed in the upper interior region  113   b  by introducing the vapor via gas/vapor openings  126   a,b.  According to this embodiment, the end effector  106  lifts the substrate from the lower interior region  113   a  into the IPA atmosphere in the upper interior region  113   b . Withdrawal of the substrate into the IPA atmosphere may occur quickly, i.e. approximately 8 to 30 mm/sec. The IPA vapor condenses on the surface of the substrate, causing the surface tension of the water attached to the substrate to be reduced, and thus causing the water to sheet from the substrate surface. A third opening similar to openings  126   a,b  may be provided just above overflow weir  114  to allow a vacuum to be applied so as to accelerate evaporation of the IPA or IPA/water mixture. Again, gas such as heated nitrogen may be introduced to dry remaining IPA and/or droplets/film from the substrate.  
      As another alternative, the substrate may be slowly drawn from the bulk DI water into the IPA vapor. Using this embodiment, the IPA condenses on the liquid meniscus extending between the substrate and the bulk liquid. This results in a concentration gradient of IPA in the meniscus, and results in so-called Marangoni flow of liquid from the substrate surface. Gas (e.g. heated nitrogen gas) may be used following the Marangoni process to remove any residual water droplets.  
     Third Embodiment—Structure  
      Referring to  FIG. 8 , a third embodiment  200  of a single substrate processing chamber includes a chamber  210  having a lower interior region  212   a  proportioned to receive a substrate S for processing, an upper interior region  212   b , and an opening  214  in the upper interior region  212   a.    
      A substrate transport device (not shown) is provided and includes an end effector configured to engage a substrate S, preferably in the manner shown in  FIG. 6 . The transport device is driven by conventional automation (not shown) to move the substrate S through opening  214  into, out of, and within the chamber  210  in an edgewise direction.  
      A lid  215  is provided for sealing opening  214 . The lid  215  may be operable with the automation that also drives the end effector, or with separate automation.  
      A fluid handling system (not shown) is configured to carry various process fluids (e.g. etch fluids, cleaning fluids, rinse water, etc.) into the lower interior region  212   a  of the chamber  210 . The fluid handling system may take a variety of forms, including those described with respect to  FIGS. 1A-1D , and  5 .  
      One or more megasonic transducers (not shown) are provided in the lower region  212   a  of the chamber  210 . The lower transducer may be mounted to the walls of the chamber  210  in a manner known in the art, or it may comprise a portion of a manifold assembly as described above. When the lower megasonic transducer directs megasonic energy into fluid in the chamber, it induces acoustic streaming within the fluid—i.e. streams of microbubbles that aid in removal of contaminants from the substrate by keeping particles in motion within the process fluid so as to avoid their reattachment to the substrate.  
      Vapor inlet ports, fluid applicators, and gas manifolds extend into the upper interior region  212   b  of the chamber  210 . Each is fluidly coupled to a system of conduits that deliver the appropriate fluids, vapors and gases to the ports as needed during processing.  
      An upper overflow weir  234  is positioned below the opening  214 . Process fluid flowing through the chamber and past substrate S cascades into the weir  434  and into overflow conduits  235  for recirculation back into the fluid handling system and re-introduction into the chamber, or into drain  233 . One more megasonic transducers  232  (one shown in  FIG. 8 ), which may include a single transducer or an array of multiple transducers, is positioned at an elevation below that of the weir  234 , and is oriented to direct megasonic energy into an upper portion of the chamber  210 .  
      The energy interacts with the substrate as the substrate is moved upwardly and downwardly though the chamber  210  by the end effector. It is desirable to orient the transducer such that its energy beam interacts with the substrate surface at or near the surface of the process fluid, e.g. at a level within the top 0-20% of the chamber region lying below the elevation of upper weir  234 . The transducers may be configured to direct megasonic energy in a direction normal to the substrate surface or at an angle from normal. Preferably, energy is directed at an angle of approximately 0-30 degrees from normal, and most preferably approximately 5-30 degrees from normal. The power and orientation of the transducer(s) may be adjustable in the manner described in connection with the first embodiment.  
      When energized, the transducer  232  creates a zone Z (see  FIGS. 2A-2C ) of optimal performance within the process fluid in the chamber. As will be discussed in greater detail below, energization of the zone enhances post-etch quenching, cleaning, rinsing and drying processes through regional boundary layer thinning and microcavitation. A lower weir  240  is positioned beneath the elevation of the transducer  232 . Lower weir  240  optionally includes a door  242  having a closed position, which prevents flow of fluid into the weir. When weir  240  is in the closed position, fluid flowing into the chamber flows past transducer  232  and cascades over upper weir  234 . When lower weir  240  is in the opened position, fluid flowing into the chamber cascades through weir  234  and does not flow Into contact with transducer  232 . The lower weir  240  is used to shunt away harsh chemicals (such as an etch solution utilizing hydrofluoric acid) that can damage the megasonic transducer. Although some transducer materials such as sapphire or Teflon can resist the harsh effects of such chemicals, those materials are very expensive and will increase the overall cost of the chamber. Moreover, providing a separate weir for harsh chemicals also helps to keep those chemicals out of conduits used to carry other solutions, such as the conduits  235  that re-circulate cleaning and rinsing solutions, and thus minimizes cross-contamination of fluids.  
     Third Embodiment—Operation  
      Use of the chamber  200  will be described in the context of an etch, clean and drying process, in which rinses are performed following etching and cleaning. Naturally, various other combinations of these or other process steps may be performed without departing from the scope of the present invention.  
      Etching  
      An etch operation preferably begins with the lower portion  212   a  of the chamber  210  filled with process fluids necessary for the etching procedure (for example hydrofluoric acid (HF), ammonium fluoride and HF, or buffered oxide). These fluids are introduced via the fluid handling system that directs process fluids into the lower end of the chamber.  
      A substrate S is engaged by the end effector (such as end effector  30  of  FIG. 6 ) and is moved into the etch solution. Substrate S is positioned in the lower portion  212   a  of the chamber such that its upper edge is below the elevation of lower weir  240 . If provided, the door  242  of lower weir  240  is moved to the opened position. Etch solution continues flowing into the chamber  210 , and cascades into weir  240 .  
      The etch preferably includes boundary layer thinning to assist the etch solution in reaching and thus reacting with the substances that are to be removed from the substrate surface. Boundary layer thinning may be accomplished by inducing turbulence in the flowing etch fluid using disturbances formed into the sidewalls of the chamber. The induced turbulence may be enhanced using relatively high fluid flow rates and temperatures for the etch solution. Other mechanisms for inducing turbulence in the etch solution, including those described in connection with the first and second embodiments, may also be utilized.  
      Post-Etch Quench and Rinse  
      At the end of the etch procedure, flow of etch solution is terminated and a post-etch rinsing step may be carried out to remove etch solution from the substrate and chamber.  
      The post-etch rinse process preferably includes a quenching process, which accelerates diffusion of the etch chemistry from the surface of the substrate out of the boundary layer of fluid attached to the substrate and into the surrounding bulk fluid. Quenching is preferably initiated using a rapid removal (e.g. in preferably, but not limited to, less than approximately 1.0 second), of etch solution from the lower end chamber  210 , such as using sealed pressure chambers such as the chambers  31  a described in connection with  FIG. 1C . Quickly removing the bulk etch solution from the chamber minimizes etch variations across the substrate surface by more sharply ending the exposure of the substrate to the bulk etch fluid. This process is preferably enhanced by simultaneously withdrawing the substrate from the chamber lower portion  212   a  into the upper portion  212   b  using the substrate transport.  
      Next, the lower weir  240  is moved the closed position and the chamber  210  is rapidly filled with a quenchant such as DI water. Since at this time the substrate is in the upper portion  212   b  of the chamber, rapid filling can be performed without concern that the substrate will be splashed—an occurrence which could lead to lack of uniformity across the substrate&#39;s surface. As the chamber  210  begins to fill, the megasonic transducer in the chamber bottom is operated at low power. Once the lower portion  212   a  of the chamber has been partially filled, the substrate is lowered into the quenchant. The turbulence created by the megasonic energy facilitates boundary layer thinning that thus facilitates diffusion of etch chemistry from the boundary layer into the bulk rinse water.  
      The megasonic power is increased as the volume of quenchant in the chamber increases. Beginning at a lower power and increasing the power as the chamber fills minimizes the chance of high power megasonic energy causing splashing of quenchant onto the substrate, and also minimizes the likelihood that residual etch solution on the substrate and in the tank would aggressively etch the bottom portion of the substrate immersed in the water.  
      The flow of DI water or other quenchant into the chamber preferably continues even after the substrate is fully immersed. Because lower weir  240  is closed, the fluid level rises above megasonic transducer  232  and cascades into upper weir  234 . The upper megasonic transducer  232  is energized and imparts megasonic energy into an adjacent region of the DI water in zone Z ( FIGS. 2A through 2C ). In zone Z, the turbulence created by the megasonic energy causes boundary layer thinning and thus facilitates gettering of the etch material away from the substrate and into the fresh quenchant. The substrate is pulled through zone Z and is raised and lowered through zone Z one or more times as needed for a thorough quench. As with prior embodiments, the area of the band is preferably selected such that when the substrate passes through the zone, up to 30% of the surface area of a face of the substrate is positioned within the band. Most preferably, as the center of the substrate passes through the zone preferably approximately 3-30% of the surface area of one face of the substrate is positioned within the band.  
      As the substrate is lowed from the upper region  212   b  into the bulk rinse fluid, particles entrained at the substrate surface are released at the air/liquid interface and are flushed over the weir and out of the chamber  210 .  
      The quenching process may be enhanced by a stream of DI water preferably directed into upper region  212   b  through fluid applicators (such as applicators  37  described in connection with the first embodiment) located in the upper region. As the substrate transport pulls the substrate through the chamber, the substrate passes through zone Z and through the stream of fresh water. During movement of the substrate upwardly past the fluid stream, the fluid stream applies a thin layer of fresh rinse fluid to the portion of the substrate at which the boundary layer was just thinned by zone Z. The substrate may be moved upwardly and downwardly through the zone Z and the fluid stream one or more times as needed for a thorough quench.  
      As previously discussed, the timing of energization of the transducers  232  may depend on the goals of the process or the nature of the substrate surface (e.g. whether it is hydrophobic or hydrophilic). In some instances it may be desirable to energize the transducers  232  only during extraction of the substrate from lower region  212   a  into upper region  212   b , or only during insertion of the substrate into lower region  212   a , or during both extraction and insertion.  
      After quenching, DI water may continue to circulate through the chamber until such time as the chamber, end effectors and substrate have been thoroughly rinsed.  
      Cleaning  
      Prior to cleaning, the chamber is drained in using one of a variety of methods, including one of the methods described above. During the cleaning process, a cleaning solution (e.g. an “SC1” solution or a back-end cleaning solution) is introduced into the chamber  210  using the fluid handling system. Lower weir  240  remains in closed position and thus allows the cleaning fluid to rise above transducer  232  and to cascade over upper weir  234 .  
      Megasonic transducer  232  is energized during cleaning so as to impart megasonic energy into zone Z. The substrate transport moves the substrate upwardly and downwardly one or more times in an edgewise direction to move the entire substrate through the zone Z. As with the quenching process, the timing of energization of the transducers  232  may be selected depending on the goals of the process.  
      The zone Z optimizes cleaning for a number of reasons. First, cleaning efficiency is enhanced by creating regional turbulence that thins the boundary layer and thus allows the cleaning solution to effectively contact the substrate surface. The megasonic energy further causes microcavitation within the fluid, i.e. formation of microbubbles that subsequently implode, releasing energy that dislodges particles from the substrate. Microcavitation may be enhanced by introducing a gas such as nitrogen, oxygen, helium or argon into upper interior region  212   b  via a gas inlet port, such that the gas diffuses into the volume of cleaning solution that is near the surface of the cleaning solution.  
      Second, the megasonic turbulence also keeps particles in the fluid suspended in the bulk and less likely to be drawn into contact with the substrate. Finally, high velocity fluid flow through the chamber and over the weir moves particles away from the zone and thus minimizes re-attachment.  
      A megasonic transducer in the lower region  212   b  may be activated during the cleaning process, so as to create an acoustic streaming effect within the chamber, keeping liberated particles suspended in the bulk fluid until they are flushed over the weir  234 . This minimizes the chance of particle reattachment. To further minimize the chance of particle reattachment, a particle gettering surface (not shown) may be positioned in the chamber near zone Z. During cleaning, a charge is induced on the gettering surface such that particles liberated from the substrate surface are drawn to the gettering surface and thus away from the substrate. After the substrate has passed out of zone Z, the polarity of the gettering surface is reversed, causing release of particles from the gettering surface. These released particles are flushed out of the chamber  10  and into the weir by the flowing cleaning fluid.  
      The cleaning process will result in release of gases from the cleaning solution into the upper interior region  212   b , some of which may contact exposed regions of the substrate and cause pitting at the substrate surface. To avoid such exposure, select vapors are introduced into the upper region  212   b  via a vapor inlet port so as to form a protective film on the substrate. If reactive gases released from the cleaning solution condense on the substrate, they will react with the protective film rather than reacting with the silicon surface of the substrate. For example, an SC1 cleaning solution will cause off-gassing of ammonia into the chamber. In this example, hydrogen peroxide vapor would be introduced into the upper region  212   b  to form a protective film on the substrate. Ammonia released by the cleaning solution will react with the protective film rather than pitting the substrate surface.  
      After the substrate has been exposed to cleaning solution for the required process time, the substrate is rinsed using a rinse solution. The rinse solution naturally will be dependent on the cleaning process being carried out. Rinsing may be accomplished in various ways. In one example, the substrate is elevated above the cleaning solution in the chamber and the cleaning solution is withdrawn from the chamber using a low pressure container such as container  31   b  described above. Rinse fluid is introduced into the chamber  210  and cascades over the upper weir  234 .  
      The substrate is lowered into the rinse fluid and the fluid rinses the cleaning solution from the chamber  210  and from the surface of the substrate. Megasonic energy from the side transducers  232  and/or a lower transducer is optionally directed into the chamber so as to enhance the rinse process. The substrate may be passed through zone Z multiple times as needed for thorough rinsing. A gas such as nitrogen, oxygen, helium or argon may be introduced into upper interior region  212   b . The gas diffuses into the volume of rinse fluid that is near the gas/liquid interface (i.e. the interface between the upper surface of the rinse fluid and that gas above it) and increases the microcavitation effect of the megasonic transducers in zone Z.  
      The power state of the transducers is selected as appropriate for the stage of the rinsing process and the surface state of the substrate. Preferably, the side transducer  232  and the lower transducer are powered “on” during insertion of the substrate into the rinse fluid. Depending upon the surface state of the substrate (e.g. whether it is hydrophilic or hydrophobic), the side transducer  232  may be on or, off during extraction of the substrate into the upper region  12   b.    
      Drying  
      The final rinse may be followed by any of a variety of drying processes, including (but not limited to) those described in connection with the first and second embodiments.  
      Three embodiments utilizing principles of the present invention have been described. These embodiments are given only by way of example and are not intended to limit the scope of the claims—as the apparatus and method of the present invention may be configured and performed in many ways besides those specifically described herein. Moreover, numerous features have been described in connection with each of the described embodiments. It should be appreciated that the described features may be combined in various ways, and that features described with respect to one of the disclosed embodiments may likewise be included with the other embodiments without departing from the present invention.  
      While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.