Abstract:
Apparatuses and methods are disclosed for submerged cleaning of substrates and the like. The apparatus includes a container holding a bath of cleaning fluid and, within the container, the combination of a submerged brush scrubber, submerged megasonic transducer and Marangoni drying devices. In operation, at least a portion of a substrate is submerged in the bath of cleaning fluid where its surfaces are contacted by one or more brush scrubbers while beams produced by megasonic transducers are directed parallel to the surface of the substrate along the surface of the substrate. The substrate is removed from the bath of cleaning fluid and rinsed with rinse water. A Marangoni flow is induced on the surface of the substrate and the substrate is allowed to dry through one or more means of drying, thereby rendering the substrate free from particulate contamination and dried of any residual fluid from the cleaning process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention is directed generally to cleaning a surface and, more particularly, to cleaning the surface of a semiconductor substrate following a chemical, mechanical, or chemical mechanical polishing of the substrate surface. 
     Integrated circuits are typically constructed by depositing layers of various materials to form circuit components on a wafer shaped semiconductor substrate. The formation of the circuit components in each layer generally produces a rough, or nonplanar, topography on the surface of the wafer. A rough surface on an underlying layer increases the likelihood of a defect occurring in subsequently deposited layers that can result in flawed or improperly performing circuitry. Thus, the efficient production of integrated circuits depends, in part, on the ability to produce smooth, or planarized, surfaces on which subsequent circuitry can be precisely deposited. 
     A smooth surface on the layers is generally provided by performing a planarization process. There are numerous processes used to planarize a surface, which are generally classified in the art as chemical planarization (such as etching), mechanical planarizing, and/or chemical-mechanical planarizing. 
     While each of the planarization processes generally provides for a more smooth surface, residual chemicals and/or particles may remain on the surface following the process. The residual chemicals and particles also must be removed to prevent defect formation in subsequent layers. Such defects may result either physically from the presence of particles or chemically via the interaction of the residual chemicals or particles with the composition of the subsequently deposited layer. 
     Post-planarization cleaning of the surface is often performed using various methods depending upon the composition of the layer and any residual chemicals and particles that may be present on the layer. The cleaning methods are generally wet cleaning procedures that include chemical cleaning, mechanical scrubbing and other surface agitation techniques. 
     For example, some cleaning methods are purely chemical or mechanical, such as those described in U.S. Pat. No. 5,181,985 and Japanese Patent Abstract Publication No. 02-281,733, respectively. As might be expected, these methods are generally more suitable for the removal of either residual chemicals or particles, respectively. Other methods, such as those described in U.S. Pat. Nos. 5,475,889, 5,442,828, 5,529,638, and 5,555,177 employ mechanical brush scrubbers that are used to brush particles from the surface, while liquid jet sprays are used to wet the surface, and possibly dislodge particles, with deionized water and/or cleaning solutions. While many of these methods provide both chemical and mechanical cleaning of the surfaces, the cleaning results derived from the methods are subject to variation due to uneven chemical distribution on the surface of the substrate which contributes to varying mechanical cleaning effectiveness and the potential for uneven drying of the surface subsequent to cleaning. 
     Still other methods rely on other forms of agitation to remove the residual chemicals or particles. For example, U.S. Pat. No. 5,451,267 discloses an apparatus in which a cleaning solution is agitated by bubbling a gas through the cleaning vessel to produce liquid flow past the surface to be cleaned. U.S. Pat. Nos. 3,893,869, 4,804,007, 4,869,278, 4,998,549, 5,037,481, 5,365,960, 5,368,054, 5,427,622, 5,533,540, and 5,534,076 disclose cleaning systems in which cleaning solutions and surfaces are acoustically agitated. The efficiency of these agitation methods depends upon the effectiveness of the flowing liquid or the acoustic energy at dislodging particles from the surface. It is expected that the effectiveness of the methods will depend upon the composition of the particle and the layer, as well as the particle sizes and surface affinity. It is therefore difficult to provide an effective cleaning procedure given the expected variations in residual chemicals and particle distributions during production processing of semiconductor substrates. 
     Following wet cleaning procedures, as the fluid on the surface of the substrate evaporates, particles and other contaminants contained in the residual cleaning fluid may settle on the surface to form water marks. Therefore, it is desirable to dry the surface following a wet cleaning procedure in a manner that minimizes evaporation and the resulting formation of water marks. A number of methods, such as those described in U.S. Pat. Nos. 5,660,642, 5,569,330, 5,653,045, 5,634,978, 5,601,655, and 5,571,337, utilize the formation of a Marangoni flow to decrease the surface tension of fluid on the surface, thereby facilitating the removal of the water from the surface prior to evaporation. 
     As is evident from the aforementioned discussion, a number of difficulties remain with present cleaning methods that need to be overcome to provide an effective cleaning method for surfaces. The present invention serves to provide methods and apparatuses for cleaning surfaces, in particular, the surfaces of semiconductor substrate layers. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to surface cleaning and drying methods and apparatuses that provide for improved cleanliness of surfaces. The apparatus generally includes a chamber suitable for retaining cleaning fluids and receiving at least one substrate having a surface that is to be cleaned. The chamber preferably includes mechanical scrubbers, generally in the form of cylindrical brushes or pads, submerged in the cleaning fluids within the chamber and positioned to contact and scrub at least one substrate submerged in the cleaning fluid. In a preferred embodiment, the substrates are fully submerged during the scrubbing, although the portion not being contacted by the scrubber need not be submerged. The chamber may further include at least one discharge for spraying a fluid, such as deionized water, onto the substrate to rinse the residual cleaning fluid from the substrate. In a preferred embodiment, the discharge is located within the same chamber as the mechanical scrubbers. The chamber may further include a mechanism for drying the substrate once the cleaning and rinsing processes have been completed. In a preferred embodiment, the drying mechanism utilizes the formation of a Marangoni flow to remove fluid from the surface of the substrate before it evaporates. Also in a preferred embodiment, the drying apparatus is included in the same chamber as the scrubbing apparatus, although in alternative embodiments, separate chambers may be used for one or more of the individual scrubbing, rinsing, and drying apparatus. 
     The apparatus also preferably includes a cleaning fluid recirculation loop that is used to remove residual chemicals, particles, and other contaminants from the cleaning fluid and to replenish the cleaning fluid. In this manner, the substrate surfaces can be more uniformly contacted by chemical cleaning fluids and the composition of the cleaning fluid can be more precisely controlled. In the embodiment in which the cleaning, rinsing, and drying processes are performed within the same chamber, the recirculation loop is additionally used to drain the cleaning and rinsing fluids from the chamber so that the rinsing and drying process may be initiated. 
     An embodiment of the mechanical scrubbing apparatus may additionally include megasonic enhancement to the mechanical scrubbing process. Megasonic cleaning is known in the art and involves generating a megasonic signal (0.2-5 MHz) within the bath of cleaning fluid and directing it substantially parallel to the submerged surface of the substrate to be cleaned. The megasonic signal causes the cleaning fluid through which the signal passes to become agitated. The action of the fluid agitation against the surface of the substrate causes minute particles to become dislodged from the substrate. Such particles are generally tenaciously adhered to the substrate and would not otherwise be readily dislodged by mechanical scrubbing methods without an increased potential for damage to the substrate caused by increased direct contact to the surface of the substrate brought on by additional brushing or scrubbing. Mechanical scrubbing with megasonic enhancement thus provides a benefit over purely mechanical methods of brushing or scrubbing in that it serves to remove additional particulate matter from the surface of the substrate without contacting the substrate. As such, the potential for damage to the substrate from additional brushing or scrubbing is also removed. 
     In an embodiment of the drying method, the cleaning fluid preferentially produces a surface composition that is hydrophilic. The formation of such a hydrophilic surface thus aides in the evacuation of fluid from the surface of the substrate, thereby reducing the potential for deposition of contaminants at the interface of hydrophilic and hydrophobic portions of the surface. In a further aspect of the drying method, after the cleaning process, the surface of the substrate is flushed with a rinsing fluid to remove the cleaning fluid from the surface of the substrate. However, after the rinse a thin film of fluid often remains on the surface of the substrate. If the film is allowed to evaporate on the surface of the substrate, impurities held by the fluid will be deposited on the surface of the substrate. Drying methods such as gravity flow and spin drying, are thus used to evacuate the fluid from the surface of the substrate before it is allowed to evaporate. However, such methods alone have proven ineffective in removing sufficient quantities of fluid from the surface of the substrate prior to evaporation. The present invention thus calls for the formation of a surface tension gradient, or Marangoni gradient, on the surface of the substrate to enable the rapid removal of the film of fluid remaining from the surface of the substrate. Such a Marangoni drying process is achieved by the passive introduction (by natural evaporation and diffusion of vapors) of surface tension-reducing volatile organic compounds, in the vicinity of the film of fluid adhering to the surface of the substrate. The compounds will diffuse into the film of fluid, resulting in surface tension gradients (Marangoni gradients) and causing the surface tension of the film of fluid to decrease. After reducing the surface tension, the film of fluid can then be more easily removed from the surface of the substrate by way of gravity flow, spin drying, or other removal techniques as are known in the art. Marangoni drying thus has the benefit of expediting the removal of the film of water from the surface of the substrate while avoiding the potentially deleterious effects brought on by using heat, air flow, or direct physical contact to dry the surface of the substrate. Marangoni drying also has the additional benefit of inducing the film of water to leave the surface of the substrate without allowing it to evaporate while on the surface of the substrate and deposit any impurities contained therein on the surface of the substrate. 
     Accordingly, the present invention overcomes the aforementioned problems to provide apparatuses and methods that provide for improved cleanliness of surfaces, such as semiconductor wafer substrates. These advantages and others will become apparent from the following detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying Figures wherein like members bear like reference numerals and wherein: 
     FIG. 1 is a semi-schematic view of an embodiment of the apparatus of the present invention; 
     FIG. 2 is a cut-away view of the wafer conveyor of the embodiment shown in FIG. 1; 
     FIG. 3 is a cut-away side view of the wafer conveyor of the embodiment of FIG. 1; 
     FIG. 4 is a side view of the roller of the embodiment of FIG. 1; and 
     FIG. 5 is a semi-schematic view of another embodiment of the apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The operation of the submerged cleaning apparatus  1  will be described generally with reference to the drawings for the purpose of illustrating the present preferred embodiments of the invention only and not for purposes of limiting the same. Referring now to the drawings, the figures show a submerged cleaning apparatus for mechanically cleaning semiconductor substrates. More particularly, and with reference to FIG. 1, the submerged scrubber is shown generally as  1 . The preferred construction of the submerged cleaning apparatus  1  of the present invention, as shown in FIG. 1, includes a submersion chamber  10  and a drying chamber  30 . Preferably, a recirculation system  40  and a loading area  50  are also provided. 
     In the present embodiment, the drying chamber  30 , is preferably located adjacent to and above the submersion chamber  10 . The submersion and drying chambers  10  and  30 , respectively, are separated by a wall  32 . The wall  32  thus forms the ceiling of the submersion chamber  10  and the floor of the drying chamber  30  and thereby serves to prevent communication of fluid  4  between the submersion chamber  10  to the drying chamber  30 . Wafers  3  to be cleaned enter the apparatus on wafer trays  2  at a loading area  50 , located on the side of the apparatus  1  at the lower end of the submersion chamber  10 . Upon entering the loading area  50 , the door  52  to the loading area  50  is closed and the seal  13  separating the loading area  50  from the submersion chamber  10  is opened. As such, the wafers  3  are submerged in the bath of cleaning fluid  4 . The wafers  3  move into the submersion chamber  10  on wafer tray conveyor  14 . Upon entering the submersion chamber  10 , the individual wafers  3  are transferred by suitable handling apparatus from the wafer tray  2  to a wafer conveyor  15  which carries the individual wafers  3  through a series of submerged mechanical and megasonic cleaning apparatus  26  and  28 ; respectively. After leaving the bath of cleaning fluid  4 , the wafers  3  enter a drying chamber  30  and are transferred back to a wafer tray  2 . After drying operations in the drying chamber  30 , wafers  3  exit the apparatus  1  at a door  52  located on the side of the drying chamber  30  at the upper end of the apparatus  1 . 
     The submersion chamber  10  provides a contained environment suitable for holding a bath of chemical cleaning fluid  4  therein. The composition of the bath of chemical cleaning fluid  4  is dependent upon the surface to be cleaned and the contaminants to be removed. However, one preferred chemistry is dilute TMAH. The submersion chamber  10  is preferably constructed as a tank that is impervious to the chemicals contained in the bath of cleaning fluid  4 . Preferably, the submersion chamber  10  is constructed from polytetrafluoroethylene (PTFE). A wafer tray conveyor  14  is positioned within the chamber  10  along the floor for moving wafer trays  2  containing wafers  3  from the loading area  50  into the submersion chamber  10 . Adjacent to the conveyor  14 , a set of opposing parallel rail members  16  and  18  define the path of wafer conveyor  15 . Preferably, wafer conveyor  15  is oriented perpendicular to the tray conveyor  14  and is positioned such that individual wafers  3  may be drawn directly from the wafer tray  2  into the wafer conveyor  15 . 
     As shown in particular in FIGS. 2 and 3, the wafer conveyor  15  includes two generally parallel rail members  16  and  18  that run along the length of the submersion container  10 . Each rail member  16  and  18 , has a set of rollers  17  and  19 , respectively, mounted thereon. The rail members  16  and  18  are preferably U-shaped in cross-section. However, it will be appreciated that additional cross-sectional configurations resembling, for example “C” or “V” are also suitable for the design of the rail members  16  and  18 . The opposing sets of rollers  17  and  19  are rotatably connected along the length of the inner edge of each of the rail members  16  and  18 , respectively. As shown in particular in FIG. 4, each of the rollers  22  and  19  preferably has a notch  17  therein. The notch  22  in each of the rollers  17  and  19  preferably has oppositely angled walls  23  and  24  such that the notch  22  is widest around the circumference of each roller  17  and  19  and tapers toward the center axis of each roller  17  and  19 . In operation, the two opposing sets of rollers  17  and  19  are preferably spaced from each other by a distance that is less than the diameter of one wafer  3 . Thus, as shown in particular in FIG. 3, wafers  3  are held between the opposing sets of rollers  17  and  19 , with minimal contact to the surface of the wafer  3  by the walls of the notch  23  and  24 . When the sets of rollers  17  and  19  are driven by a motor (not shown), the wafers  3  held therebetween will be transported along the length of the wafer conveyor  15 . It will further be appreciated that in additional embodiments, alternative designs such as motorized belts (not pictured) or individual wafer trays (not pictured) could also be used to hold the individual wafers  3  within the wafer conveyor  15 . 
     Mechanical brush scrubbers  26  are positioned to contact both surfaces of the wafer  3  as it is moved along the length of the wafer conveyor  15 . Such brushes  26  are well known in the art and are manufactured and sold, for example, by Syntak, Incorporated. The brushes  26  are typically cylindrical and have surfaces (not shown) populated with a plurality of protrusions. The geometry of the protrusions may be that of circular knobs, linear ridges, or any other pattern known in the art. In operation, when the cylindrical brush  26  is rotated, the protrusions physically contact the surface of the wafer  3  and work to remove impurities deposited thereon. Preferably, the cylindrical brushes  26  are positioned on either side of the wafer conveyor  15  such that both sides of the wafer  3  may be cleaned simultaneously. 
     Preferably, the mechanical brush scrubbers  26  are augmented by megasonic cleaning apparatuses as are known in the art. The megasonic enhancement of the mechanical brushes  26  includes a series of transducers  28  positioned below the surface of the chemical bath  4  within the submersion chamber  10 . The transducers  28  are oriented relative to the surface of the wafers  3  held in the wafer conveyor  15  such that they direct a high frequency (megasonic) signal through the bath of cleaning fluid  4  substantially parallel to the surfaces of the submerged wafers  3 . Preferably, the frequency of the signal emitted by the transducers  28  will be made to vary between 0.2 and 5 MHz. In operation, the high frequency of the signal causes the fluid  4  through which the path of the signal passes to become agitated. In particular, the fluid  4  directly surrounding the surfaces of the wafers  3  is agitated. The action of the agitated fluid  4  against the surface of the wafer  3  serves to enhance the removal of minute particles from the surface of the wafer  3 , that would otherwise require additional mechanical brush scrubbers  26  to remove. 
     The drying chamber  30  is located above the submersion chamber  10  and may be separated therefrom by a wall  32 . As such, the wall  32  prevents the chemical bath  4  contained in the submersion chamber  10  from entering the drying chamber  30 . Preferably, the wall  32  contains gap  31  therein through which the wafer conveyor  15  passes from the submersion chamber  10  to the drying chamber  30 . The gap  31  thus enables the wall  32  to inhibit the interaction of the atmospheres of the two chambers  10  and  30 , while allowing the wafers  3  held within the wafer conveyor  15  to pass from the submersion chamber  10  into the drying chamber  30 . Within the drying chamber  30 , the wafer conveyor  15  meets a second wafer tray conveyor  56 . The conveyor  56  is designed to hold a wafer tray  2  thereon and to position the tray  2  such that wafers  3  may be transferred directly from the wafer conveyor  15  into the tray  2 . The drying chamber  30  further includes a series of spray nozzles  33 . The spray nozzles  33  are supplied with a rinsing fluid and are positioned to direct a stream of the rinsing fluid onto the surfaces of the wafers  3  to flush the surface of the wafers  3  and to remove any residual fluids remaining on the surface of the wafers  3  from the cleaning fluid  4  from the surface of the wafer  3 . Preferably, the composition of the rinsing fluid will include de-ionized water. The nozzles  33  are also supplied with surface tension reducing compounds and are equipped to flush the surface of the wafers  3  with the surface tension-reducing compounds to induce surface tension gradients (Marangoni gradients) between the surface of the wafer  3  and any fluid remaining on the surface of the wafer  3  after the rinse process has been completed. The resulting Marangoni flow is known in the art and is commonly used to remove fluid from surfaces prior to the evaporation of that fluid. In operation, a stream of fluid from the nozzles  33  is directed at the surfaces of the wafers  3 . The stream diffuses into any fluid remaining on the surface of the wafers  3 , resulting in a Marangoni gradient and causing the surface tension of the fluid already on the surfaces of the wafers  3  to decrease. The reduced surface tension of the fluid on the surfaces of the wafer  3  thus enables the fluid to be more easily removed from the surfaces of the wafers  3  by means of gravity flow, spin drying, or other like drying techniques known in the art. Preferably, the surface tension-reducing compound sprayed by the nozzles  33  onto the surfaces of the wafers  3  will include volatile organic compounds such as isopropyl alcohol. However, it will be understood that additional compounds having similar surface tension reducing properties such as ethanol may also be used. 
     The drying chamber  30  is preferably provided with a door  57  through which the wafer tray conveyor  56  travels. When the door  57  is closed, the environment within the drying chamber  30  is unable to communicate with the environment outside the chamber  30 . However, when the door  57  is opened, an empty wafer tray  2  may be inserted into the chamber  30 , or a wafer tray  2  with wafers  3  therein removed from the chamber  30 . 
     A loading chamber  50  is also preferably provided from which a wafer tray  2  containing wafers  3  to be cleaned may be inserted into the apparatus  1 . In operation, a wafer tray  2  containing wafers  3  is placed onto a wafer elevator  51 . The elevator  51  lowers the wafer tray  2  into the loading chamber  50 . Once within the loading chamber  50 , the door  52  of the loading chamber  50  is closed, sealing the loading chamber  50  from the outside atmosphere and the door  13  linking the loading chamber  50  and the submersion chamber  10  is opened allowing the inside of the loading chamber  50  to communicate with the inside of the submersion chamber  10 . The tray  2  is then moved on conveyor  14  to the submersion chamber  14  on conveyor  11  and positioned to load the wafers  3  contained thereon into the wafer conveyor  15 . 
     A recirculation system  40  is preferably provided for replenishing the volume of chemical cleaning fluid  4  in the submersion chamber  10 . Such a recirculation system  40  is known in the art and is capable of removing residual chemicals, particles, and other contaminants from the chemical cleaning fluid  4  and returning the cleaned fluid  4  to the submersion chamber  10 . The recirculation system  40  is also used to drain and fill the submersion chamber  10  and the loading chamber  50  with cleaning fluid  4  as is needed to facilitate the submerged cleaning process. 
     In a further embodiment of the present invention shown in FIG. 5, the submerged mechanical scrubbing and drying operations are conducted within a single container  9 . As such, the container  9  performs the function of the submersion chamber  10  and the drying chamber  30  described herein with regard to previous embodiments and like embodiments will be similarly numbered. 
     As seen in FIG. 5, the container  9  is adapted to hold a bath of cleaning fluid  4  therein and to remain impervious to the effects of the chemicals that make up the bath of cleaning fluid  4  for prolonged periods of time. A wafer conveyor  15 ′ is contained within the container  9 . The conveyor  15 ′ follows a generally U-shaped path through the container  9 . As such, the ends  59  and  60  of the conveyor  15 ′ are above the surface of the bath of cleaning fluid  4 , while the remainder of the conveyor  15 ′ remains submerged within the bath of cleaning fluid  4 . The general design and operation of the wafer conveyor  15 ′ is otherwise identical to that of other embodiments of the wafer conveyor  15  described herein above. As is the case with previous embodiments, scrubber brushes  26  are positioned beneath the surface of the bath of cleaning fluid  4  along the path of the conveyor  15 ′. The design and operation of the brushes  26  are otherwise identical to that of other embodiments of the brushes  26  described herein above. As such, the brushes  26  contact and clean the surface of the wafers  3  contained in the conveyor  15 ′. Adjacent to the brushes  26  lies a series of one or more transducers  28 . The transducers  28  are oriented to direct beams of megasonic energy parallel to the surfaces of the wafers  3  held within the wafer conveyor  15 ′ as the wafers pass the brushes  26 . The design and operation of the transducers  28  are otherwise equivalent to that of the transducers  28  described previously herein above. Adjacent to the portion of the conveyor  15 ′ lying after the brushes  26  and above the surface of the bath of cleaning fluid  4  are a series of spray nozzles  33 . The design and operation of the nozzles  33  are otherwise identical to those of other embodiments of the nozzles  33  described herein above. 
     Wafer tray conveyors  53  and  56  may also be provided for use in loading and unloading trays  2  of wafers  3  from the container  9 . Preferably, the loading conveyor  53  intersects one end  59  of the wafer conveyor  15 ′. When a tray  2  of wafers  3  is positioned on the conveyor  53  above the end  59  of the wafer conveyor  15 ′, the wafers  3  may be fed directly into the wafer conveyor  15 ′. Similarly, an unloading conveyor  56  intersects the end  60  of the wafer conveyor  15 ′. When a tray  2  of wafers  3  is positioned on the conveyor  56  above the end  60  of the wafer conveyor  15 ′, the wafers may be fed directly from the wafer conveyor  15 ′ into the wafer tray  2 . Thus, after being loaded into the container  9  at  59 , the wafer tray  2  may be advanced along the loading conveyor  53 , onto unloading conveyor  56 , and positioned above  60  to receive a load of cleaned wafers  3  being unloaded from container  9 . 
     The present embodiment of the invention also preferably includes a cleaning fluid  4  recirculation system  40  for recirculating and replenishing the cleaning fluid  4  in the container  9  as is needed to facilitate the cleaning process, the design and operation of which is identical to those embodiments described previously herein above. The design and operation of the recirculation system  40  is otherwise identical to that of the recirculation system  40  previously described herein with regard to other embodiments of the present invention. 
     In operation, a wafer tray  2  with wafers  3  therein is positioned on the loading conveyor  53  and moved to the end  59  of the wafer conveyor  15 ′. The wafers  3  are loaded from the wafer tray  2  onto the wafer conveyor  15 ′. The wafer conveyor  15 ′ transports the wafers  3  into the bath of cleaning fluid  4 . Beneath the surface of the bath of cleaning fluid  4 , the wafers  3  are moved along the wafer conveyor  15 ′ past a series of the rotating cylindrical brushes  26 . The surfaces of the wafers  3  are contacted and cleaned by the brushes  26 . In conjunction with the brushes  26 , transducers  28  direct megasonic signals parallel to the surfaces of the wafers  3  so as to create agitation in the fluid  4  along the surface of the wafers  3  and to remove impurities therefrom. After passing through the scrub brushes  26  and transducers  28 , the wafer conveyor  15 ′ emerges from the bath of cleaning solution  4  and passes a series of spray nozzles  33 . As with previous embodiments, the nozzles  33  first flush the surface of the wafers  3  with a rinsing solution to remove the residual chemical cleaning solution  4  from the surface of the wafers  3 . The nozzles  33  then spray the surface of the wafers  3  with a surface tension-reducing compound to induce a Marangoni flow on the surface of the wafers  3  to dry the surfaces of the wafers  3  of any residual fluid or chemicals before those chemicals are allowed to evaporate on the surface of the wafer  3 . The wafers  3  are then unloaded directly into a waiting wafer tray  2  sitting atop the unloading conveyor  56  at end  60  of the wafer conveyor  15 ′. 
     Those of ordinary skill in the art will appreciate that a number of modifications and variations that can be made to specific aspects of the method and apparatus of the present invention without departing from the scope of the present invention. Such modifications and variations are intended to be covered by the foregoing specification and the following claims.