Patent Abstract:
A substrate cleaning apparatus is provided. The apparatus includes a transducer capable of resonating at a high frequency and a brush material attached to a surface of the transducer. The brush material includes at least one passage extending to the surface of the transducer and is configured to be applied to a surface of a substrate. When the transducer resonates at the high frequency, the transducer is capable of imparting acoustic energy to the surface of the substrate at a location of the at least one passage.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to substrate surface cleaning and, more particularly, to a method and apparatus for improving semiconductor substrate cleaning following fabrication processes. 
   2. Description of the Related Art 
   As is well known to those skilled in the art, the fabrication of semiconductor devices involves numerous processing operations. These operations include, for example, impurity implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography patterning, etching operations, chemical mechanical polishing (CMP), etc. Typically, these operations generate contaminants such as particles, residue, or absorbed components (e.g., chemicals), which are adhered to the wafer surface and/or wafer topography features. It is well established that contaminants should be removed as the presence of such contaminants has detrimental effects on the performance of the integrated circuit devices. To achieve this task, wafer surfaces and topography features are cleaned so as to dislodge and remove contaminants. 
   Common cleaning operations may involve brush scrubbing of the wafer surfaces wherein the wafer surfaces are cleaned purely by applying mechanical energy. Another widely use cleaning operation involves megasonic cleaning of the wafer surfaces in order to dislodge any adhered contaminants. 
   The brush scrubbing operation is usually performed by either a double-sided horizontal wafer scrubber or horizontal wafer scrubber designed to clean top and bottom surfaces of a wafer. Top and bottom surfaces of the wafer are brushed by a pair of brushes, each mounted on a corresponding brush core. Each of the brush cores includes a respective shaft, each connected to a fluid inlet. The outer surfaces of the brushes are typically covered with a plurality of nodules. The wafer is engaged by a pair of rollers while the top and bottom surfaces of the wafer are scrubbed by the brushes. The wafer is cleaned as the brushes come in contact with top and bottom surfaces of the wafer, thus removing the contaminants. 
     FIG. 1A  shows a simplified, partial, exploded, cross sectional view of an exemplary prior art brush scrubbing operation. A brush  12  having a plurality of nodules  14  is shown to be applied to the wafer surface  8 ′ so as to clean planer surface as well as the topography features  8   a – 8   d  defined on the wafer surface  8 ′. As can be seen, a plurality of contaminants  10   a – 10   f  is adhered to the planer surface of the wafer surface  8 ′ or in deep topography features  8   a – 8   d . For instance, contaminants  10   a ,  10   b ,  10   d , and  10   e  are adhered to the planer surface of the wafer surface  8 ′ while contaminant  10   c  is adhered inside the feature  8   b , and contaminant  10   f  is adhered inside the feature  8   d.    
   Normally, wafer surface  8 ′ is brush scrubbed using chemicals so as to remove any contaminants adhered to the wafer surface  8 ′. The wafer surface  8 ′ is then rinsed by flushing the wafer surface  8 ′ with DI water, thus disposing the contaminant  10   a – 10   e . At this point, the cleaned wafer is removed from the brush scrubber, allowing the next wafer to be placed in the brush scrubber. In this fashion, each wafer is scrubbed and rinsed in the prior art brush box. 
   Unfortunately, brush scrubbing operations can generally only dislodge contaminants defined on planer surfaces, i.e.,  10   a ,  10   b ,  10   d , and  10   e . This occurs as the brush materials  12  may not penetrate through very high aspect ratio features  8   a – 8   d  (e.g., trenches and vias, etc.) so as to clean contaminants  10   c  and  10   f  defined deep within the features. As a result, brush scrubbing operations may exhibit a rather poor cleaning capacity when cleaning surface topography features such as trenches or vias open to the wafer surface  8 ′. For instance, at the conclusion of the brush scrubbing operation, contaminants defined on the planer surface of the wafer surface (i.e.,  10   a ,  10   b ,  10   d , and  10   e ) have been removed while, in some cases, contaminants  10   c  and  10   f  may still remain adhered to the wafer surface  8 ′. In some circumstance, this limitation associated with brush scrubbing operations becomes more noticeable as the feature sizes get smaller (e.g., smaller than 0.2 microns). As can be appreciated, smaller feature sizes may prevent penetration of the brush material into the topography features, thus limiting or blocking access to the contaminants lodged therein. 
   Another commonly used cleaning operation is cleaning of wafer surface  8 ′ using a megasonic cleaner shown in the simplified, partial, exploded, cross sectional view of  FIG. 1B , in accordance with the prior art. As shown, a megasonic transducer is fabricated using a plurality of crystals  32  of piezoelectric material bonded to a resonator  30 . The crystals  32  are powered, thus causing the resonator  30  to vibrate. The vibration of the high frequency acoustic energy transducer creates sonic pressure waves in the liquid medium or the meniscus present. In this manner, contaminants  10   a – 10   f  are expected to be removed by cavitation and sonic agitation generated in the high frequency acoustic energy cleaner. 
   Megasonic cleaning has proven to be more than reliable in cleaning and dislodging contaminants defined deep into the topography features  8   a – 8   d  defined on the wafer surface  8 ′. However, megasonic cleaning may achieve an inadequate cleaning of the planer surfaces. By way of example, contaminant  10   c  lodged deep into the feature  8   b  and contaminant  10   f  lodged into the feature  8   d  are easily dislodged and removed by megasonic cleaning. Contaminants  10   a ,  10   b ,  10   d , and  10   e , nevertheless may still remain on the wafer surface  8 ′ subsequent to the megasonic cleaning. Furthermore, as shown, megasonic cleaning may not be capable of dislodging contaminants pressed onto the wafer surface  8 ′, such as contaminant  10   d.    
   In an attempt to compensate the limitations associated with either brush scrubbing or megasonic cleaning operations, typical wafer cleaning processes of the prior art involve performing cleaning operations in multiple stand alone modules in a given order. For instance, as shown in  FIG. 1C , the prior art cleaning operation starts by brush scrubbing wafer surfaces in a stand alone brush box  2  for a specific period of time subsequent to which the cleaned wafer is removed from the brush box  2  and transferred into the stand alone megasonic cleaner  4 . At this point, the wafer surfaces are cleaned in the stand alone megasonic cleaner  4  for a particular time after which the cleaned wafer is transferred to a spin, rinse, and dry (SRD) module  6 . Next, the wafer is spin-rinsed and dried. In this fashion, each wafer is scrubbed, megasonically cleaned, and spin-rinsed in accordance with the prior art. 
   As can be appreciated, each wafer has to be brush scrubbed, megasonically cleaned, and spin rinsed, separately and for a corresponding period of time, in three different stand alone modules, thus making the cleaning process of the prior art an extended and lengthy process. Prolonging the cleaning period even more is the transition time necessary for removing and transferring of wafers between the stand alone modules. In this manner, the cleaning cycle for each wafer is significantly and unnecessarily increased. As can be appreciated, this reduces the overall wafer throughput. 
   In view of the foregoing, a need therefore exists in the art for a method and apparatus capable of producing a substantially clean patterned and/or unpatterned semiconductor substrate, while maximizing cleaning efficiency and minimizing semiconductor substrate cleaning cycle. 
   SUMMARY OF THE INVENTION 
   Broadly speaking, the present invention fills this need by providing a system for cleaning semiconductor substrates by concurrently using a combination of high frequency acoustic energy cleaning and brush scrubbing in a stand alone cleaning module or clustered with other modules. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below. 
   In one embodiment, a substrate cleaning apparatus is provided. The apparatus includes a transducer capable of resonating at a high frequency and a brush material attached to a surface of the transducer. The brush material includes at least one passage extending to the surface of the transducer and is configured to be applied to a surface of a substrate. When the transducer resonates at the high frequency, the transducer is capable of imparting acoustic energy to the surface of the substrate at a location of the at least one passage. 
   In another embodiment, a substrate cleaner is provided. The substrate cleaner includes a transducer that includes a first side and a second side, a brush, a housing, and an arm. The brush is disposed on the first side of the transducer and is configured to include a plurality of openings. The plurality of openings is configured to facilitate transmission of high frequency acoustic energy imparted by the transducer to a surface of a substrate at a respective location of each opening of the plurality of openings. The housing is configured to cover the brush and the transducer and an arm coupled to a backside of the housing. The arm is configured to controllably apply the brush disposed on the transducer onto the surface of the substrate. 
   In yet another embodiment, a brush scrubbing-high frequency acoustic energy (AE) cleaning system is provided. The system includes a brush core having a first end, a second end, and an outer surface, a shaft, a fluid inlet, a transducer, and a brush. The brush core includes a plurality of orifices extending from a center of the brush core to the outer surface of the brush core. The shaft is connected to the first end of the brush core. The fluid inlet is configured to deliver a fluid medium to the brush core through the shaft. The transducer is disposed on an outer surface of the brush core and is capable of resonating at a high frequency. The brush includes a plurality of openings and is configured to cover the transducer. When the transducer resonates at the high frequency, high energy acoustic energy is imparted from the transducer to a surface of a substrate at respective locations of each of the plurality of openings. 
   In still another embodiment, another brush scrubbing-high frequency acoustic energy (AE) cleaning system is provided. The system includes a brush core having a first end, a second end, and an outer surface, a shaft, a transducer, and a brush. The shaft is connected to the first end of the brush core. The transducer is disposed on an outer surface of the brush core and is capable of resonating at a high frequency. The brush includes a plurality of openings and is configured to cover the transducer. When the transducer resonates at the high frequency, high energy acoustic energy is imparted from the transducer to a surface of a substrate at respective locations of each of the plurality of openings. 
   In still another embodiment, a method for making a brush scrubbing-high frequency acoustic energy cleaning assembly is provided. The method includes making a plurality of orifices in a brush core. The method also includes disposing a plurality of transducers on an outer surface of the brush core such that a subset of the plurality of orifices in the brush core is exposed to a brush. The plurality of transducers is capable of resonating at a high frequency. Also included is making a plurality of openings in the brush and placing the brush over the plurality of transducers such that the plurality of transducers is exposed to a subset of the plurality of openings in the brush. When the transducer resonates at the high frequency, high energy acoustic energy is imparted from the plurality of transducer to a surface of a substrate at respective locations of each of the plurality of openings. 
   In yet another embodiment, a method for making a brush scrubbing-high frequency acoustic energy cleaning assembly is provided. The method includes disposing a plurality of transducers on an outer surface of a brush core and making a plurality of openings in a brush. The method further includes covering the brush over the plurality of transducers such that the plurality of transducers is exposed to a subset of the plurality of the openings in the brush core. 
   In still another embodiment, a method for making a brush scrubbing-high frequency acoustic energy (AE) cleaning assembly is provided. The method includes making an opening in a brush. The opening extends through the brush. The method also includes disposing the brush over a transducer capable of resonating at a high frequency. When the transducer resonates at the high frequency, high energy acoustic energy is imparted from the transducer to a surface of a substrate at a location of the opening. 
   The advantages of the present invention are numerous. Most notably, the embodiments of the present invention concurrently utilize brush scrubbing and high frequency acoustic energy cleaning, thus achieving a substantially improved cleaning operation. Another advantage of the present invention is that performing of brush scrubbing-AE cleaning in a single cleaning module enhances the substrate cleaning efficiency. Another advantage of the embodiments of the present invention is that by concurrently performing brush scrubbing and AE cleaning, the cleaning cycle per wafer is substantially reduced, ultimately leading to an increase in wafer throughput. Still another advantage of the present invention is that single semiconductor wafers can be cleaned substantially eliminating the possibility of recontamination of the wafer by contaminants set free during the cleaning of other semiconductor wafers. Yet another advantage of the present invention is that in the cleaning module of the present invention the cleaning operation can easily be switched between contact cleaning (brush scrubbing), non-contact cleaning (AE cleaning), or contact-noncontact cleaning, depending on the application requirements. Yet another advantage is that the embodiments of the present invention can be implemented in a multi-station cleaning module designed to clean a plurality of substrates in individual combination cleaning modules. 
   Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
       FIG. 1A  shows a simplified, partial, exploded, cross sectional view of an exemplary prior art brush scrubbing operation. 
       FIG. 1B  shows a simplified cross sectional view of an exemplary prior art megasonic cleaning. 
       FIG. 1C  shows a simplified schematic diagram illustrating cleaning modules implemented in a prior art cleaning operation. 
       FIG. 2A  is a simplified cross sectional view of an exemplary cleaning module, in accordance with one embodiment of the present invention. 
       FIG. 2B  is a simplified, exploded, cross sectional view of an exemplary flat brush scrubbing-AE cleaning assembly, in accordance with one embodiment of the present invention. 
       FIG. 2C  is a simplified cross sectional view illustrating cleaning of the wafer top surface by an exemplary brush scrubbing-AE cleaning assembly, in accordance with another embodiment of the present invention. 
       FIG. 2D  is an exploded, simplified, cross sectional view of a portion of the flat brush of the brush scrubbing-AE cleaning assembly, in accordance with one embodiment of the present invention. 
       FIG. 3A  is a simplified bottom view of an exemplary circular-shaped flat brush scrubbing-AE cleaning assembly, in accordance with another embodiment of the invention. 
       FIG. 3B  is a simplified bottom view of an exemplary quarter-arc flat brush scrubbing-AE cleaning assembly, in accordance with yet another embodiment of the invention. 
       FIG. 3C  is a simplified bottom view of an exemplary eight-arc flat brush scrubbing-AE cleaning assembly, in accordance with still another embodiment of the invention. 
       FIG. 4  is a simplified top view of an exemplary flat brush scrubbing-AE cleaning assembly cleaning a wafer top surface, in accordance with still another embodiment of the invention. 
       FIG. 5A  is a simplified three-dimensional view of a pair of exemplary roller-type brush scrubbing-AE cleaning assemblies, in accordance with one embodiment of the invention. 
       FIG. 5B  is a simplified cross sectional view or the roller-type brush scrubbing-AE cleaning assembly being applied to the top surface of the wafer, in accordance with still another embodiment of the invention. 
       FIG. 5C  is a simplified cross sectional view of an exemplary roller-type brush scrubbing-AE cleaning assembly, in accordance with still another embodiment of the invention. 
       FIG. 5D  is a simplified, exploded, cross sectional view of yet another exemplary roller-type brush scrubbing-AE cleaning assembly, in accordance with still another embodiment of the invention. 
       FIG. 5E  is a simplified top view of an unrolled exemplary roller-type brush, in accordance with one embodiment of the present invention. 
       FIG. 6  is a simplified three-dimensional view of a pair of exemplary roller-type brush scrubbing-AE cleaning assemblies, in accordance with still another embodiment of the present invention. 
       FIG. 7  is a simplified cross sectional view of an exemplary multi-station cleaning module including a plurality of single-wafer combination cleaning assemblies, in accordance with yet another embodiment of the present invention. 
       FIG. 8  is a flowchart diagram of method operations performed in making a brush scrubbing-AE cleaning assembly, in accordance with still another embodiment of the present invention. 
       FIG. 9  is a flowchart diagram of method operations performed in making a roller-type brush scrubbing-AE cleaning assembly, in accordance with yet another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Several exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings.  FIGS. 1A ,  1 B, and  1 C are discussed above in the “Background of the Invention” section. 
   The embodiments of the present invention provide an apparatus and a method for cleaning a semiconductor substrate by concurrently using a combination of high frequency acoustic energy cleaning and brush scrubbing in a stand alone cleaning module. In one embodiment, a brush scrubbing-high frequency acoustic energy cleaning assembly capable of substantially removing contaminants lodged on wafer planer surfaces or deep wafer topography features. In one embodiment, a flat brush scrubbing-acoustic energy (AE) cleaning assembly is provided. The flat brush scrubbing-AE cleaning assembly includes a housing, a transducer having a crystal bonded to a resonator, and an arm configured to move the housing and thus the flat brush scrubbing-AE cleaning assembly. A flat brush having a plurality of openings functioning as AE passageways are defined in the brush. In another embodiment, a roller-type brush scrubbing-AE cleaning assembly is provided. The roller-type brush scrubbing-AE cleaning assembly includes a plurality of transducers defined on the outer surface of a brush core. In such an embodiment, each pair of adjacent transducers can be separated by a portion of the brush material. In one embodiment, fluid medium is introduced onto the wafer surfaces through the brush. In another embodiment, fluid medium is dripped onto the wafer surface through a nozzle. 
   In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIG. 2A  is a simplified cross sectional view of an exemplary cleaning module  100 , in accordance with one embodiment of the present invention. A chamber  111  of the cleaning module  100  is shown to include a flat (i.e., pancake) brush scrubbing-AE assembly  120 , an arm  118 , a nozzle  126 , and a wafer  108  engaged by a pair of rollers  124   a  and  124   b . The flat brush scrubbing-AE assembly  120  is connected to an arm control module  116  by an arm  118 . The arm  118  is configured to move in a movement direction  122 , thus causing the flat brush scrubbing-AE cleaning assembly  120  to scan the wafer top surface in the movement direction  122  during the brush scrubbing-AE cleaning operation. In this manner, in one embodiment, maximized wafer coverage and averaging of cleaning efficiency can be achieved by scanning the flat brush scrubbing-AE cleaning assembly  120  from the center of the wafer  108  to the edge of the wafer  108 . Fluid medium  127  is introduced onto the wafer surface through the nozzle  126 . 
   As can be appreciated, in one embodiment, the flat brush scrubbing-AE cleaning assembly may be configured to symmetrically clean the wafer backside. In such an implementation, the chamber  111  further includes a second brush scrubbing-AE assembly  120 ′ connected to a second arm control module  116 ′ using an arm  118 ′. The wafer backside  108   b  is cleaned as the second brush scrubbing-AE assembly  120 ′ scans the wafer backside in the movement direction  122 . A fluid medium  127 ′ is introduced into the cleaning interface using a second nozzle  126 ′. 
   As can be seen, the wafer  108  is engaged by the rollers  124   a  and  124   b  during the cleaning operation. The rollers  124   a  and  124   b  are respectively placed in the chamber  111  using corresponding spindles  128   a  and  128   b  of a chuck. In one example, the rollers  124   a  and  124   b  are configured to rotate, thus causing the wafer  108  to rotate during the cleaning operation. In another embodiment, the cleaning module  100  may include a third roller (not shown in  FIG. 2A ). In such example, the third roller is configured to rotate while the rollers  124   a  and  124   b  are designed to remain stationary. The rotation of the third roller is configured to cause the wafer  108  to rotate during the cleaning operation. In one example, the cleaning efficiency is averaged by rotating the wafer  108  and/or the brush scrubbing-AE cleaning assembly  120  and  120 ′. 
   Reference is made to a simplified, exploded, cross sectional view of an exemplary flat brush scrubbing-AE cleaning assembly  120  shown in  FIG. 2B , in accordance with one embodiment of the present invention. As shown, a transducer  133  includes a crystal  132  bonded to a resonator  130  defined in a housing  134 . In one example, the crystal  132  is a piezoelectric crystal. The crystal is shown to be defined on a backside of the resonator  130 , facing away from the wafer  108  to be cleaned. 
   A brush  112  is shown to be placed on the face of the resonator  130 . In one example, as shown in the embodiment of  FIG. 2B , the brush  112  covers the sidewalls of the resonator  130  and portions of the resonator  130  sidewalls. A plurality of openings  112   a – 112   f  defined in the brush  112  is configured to function as AE passageways and facilitate the transmission of acoustic energy onto the wafer surface. 
     FIG. 2C  is a simplified cross sectional view illustrating cleaning of the wafer top surface  108   a  by an exemplary brush scrubbing-AE cleaning assembly  120 , in accordance with one embodiment of the present invention. The brush  112  is shown to be applied onto the wafer top surface  108   a  while the crystal  132  is powered by the electrical connection module  138 . In this manner, the electrical connection is used to apply power to the transducers. As shown, the plurality of openings  112   a – 112   f  faces the wafer top surface  108   a  during the brush scrubbing-AE cleaning operation. 
   In the embodiment shown in  FIG. 2C , the flat brush scrubbing-AE cleaning assembly  120  scans the top surface  108   a  of the wafer  108  in the movement direction  122  while rotating in a rotation direction  119 . In this manner, the brush scrubbing-assembly  120  can be implemented to clean almost the entire wafer top surface  108   a . In one embodiment, a diameter of the transducer  133  can be smaller than the diameter of the wafer  108 . In another embodiment, the diameter of the transducer  133  can be substantially equivalent to the diameter of the wafer  108  or be slightly larger than the diameter of the wafer  108 . 
   The fluid medium  127  is shown to be introduced onto the wafer top surface  108   a  through nozzles  126   a  and  126   b  creating a layer of meniscus  136  on the wafer top surface  108   a . In this manner, the brush  112  is saturated with fluid medium  127  as the fluid medium  127  is applied to the wafer top surface  108   a . In one preferred embodiment, the fluid medium  127  and thus the meniscus  136  propagate into the openings  112 – 112   f . In this manner, the fluid medium  127  defined in the exemplary openings  112   a – 112   f  is implemented to transmit high frequency acoustic energy imparted by the resonator to the wafer top surface  108  during the cleaning operation. 
   One having ordinary skill in the art must appreciate that any suitable number of nozzles can be implemented to introduce the fluid medium  127  onto the wafer surfaces. Furthermore, in one example, the mechanical energy created to clean the wafer surfaces is created by the linear velocity of the brush scrubbing-cleaning assembly and the wafer. For instance, linear velocity can be created by rotating brush scrubbing-cleaning assembly, rotating brush scrubbing-cleaning assembly and scanning the wafer surface using the brush scrubbing-cleaning assembly, or rotating the wafer. For instance, as the wafer  108  rotates, the fluid medium introduced onto the wafer surface is spread on the wafer surface due to the centrifugal force, thus causing the fluid medium to be substantially evenly distributed on the wafer surface. In one embodiment, the wafer is configured to rotate approximately about 1 and 200 RPMs, and a more preferred range of approximately about 5 and 50 RPMs and most preferably approximately about 5 RPMs during the cleaning operation. In another embodiment, the brush scrubbing-cleaning assembly can be configured to linearly move back and forth on the wafer surface while the wafer  108  rotates. 
   In one exemplary embodiment, the vibration of the high frequency acoustic energy transducer  133  creates sonic pressure waves in the fluid medium  127  defined in the openings  112   a – 112   f  as well as the meniscus  136 . As the transducer  133  scans across the wafer  108  using the fluid medium  127 , the contaminants are removed by cavitation and sonic agitation generated by the high frequency acoustic energy. 
     FIG. 2D  is an exploded, simplified, cross sectional view of a portion of the flat brush of the brush scrubbing-AE cleaning assembly  120 , in accordance with one embodiment of the present invention. As can be seen, fluid medium  127  substantially fills the opening  112   c . In one embodiment, the brush  112  is saturated with the fluid medium  127  as the fluid medium  127  is continuously introduced onto the wafer top surface  108   a  and the cleaning interface. In this manner, once the brush  112  is applied onto the wafer top surface  108  with pressure, excess fluid medium  127  is squeezed out of the brush  112  in a direction  138  and into the opening  112   c , substantially filling the opening  112   c . As a result, the wafer top surface  108   a  is concurrently cleaned by both mechanical action as well as high frequency acoustic energy imparted by the resonator. For instance, the portions of the brush  112  surrounding the opening  112   c  are applied to the wafer top surface  108   a , cleaning the wafer top surface  108   a  as shown the mechanical energy  139   a . In comparison, the portion of the wafer top surface  108   a  defined beneath the opening  112   c  is cleaned using the high frequency acoustic energy  139   b . Of course, as the brush scrubbing-AE cleaning assembly  120  rotates and scans the wafer top surface  108   a , each section of the wafer top surface  108   a  is most likely exposed to both, the high frequency acoustic energy as well as mechanical action. In this manner, limitations associated with separately performing brush scrubbing and AE cleaning in different brush scrubbing modules and AE cleaning modules are eliminated. 
   In one embodiment, sonic agitation subjects the fluid medium  127  to acoustic energy waves. In one example, the acoustic energy waves are configured to occur at frequencies between approximately about 0.4 Megahertz (MHz) and about 1.5 MHz, inclusive. In one implementation, the sonic agitation can have a frequency of between approximately about 400 kHz to about 2 MHz. By way of example, in typical implementations, the megasonic energy ranges typically between approximately about 700 kHz to about 1 MHz. For instance, lower frequencies can be used for cleaning applications in the ultrasonic range, which are used mainly for part cleaning. However, preferably, the higher frequencies are used to clean wafers and semiconductor substrates, substantially reducing the possibility of damage to the substrates, which is known to occur at the lower frequencies. 
   In one embodiment, the top and bottom transducers  133  and  133 ′ are configured to create acoustic pressure waves through sonic energy with frequencies approximately about 1 Megahertz. In this manner, the brush scrubbing and AE cleaning are performed simultaneously and in concert, each augmenting the cleaning power of the other. 
   In one example, high frequency acoustic energy originating from the top or bottom transducers  133  and  133 ′ is respectively transmitted through top and bottom resonators  130  and  130 ′. Thereafter, the top and bottom resonators  130  and  130 ′ propagate the acoustic energy to the top and bottom surfaces  108   a  and  108   b  of the wafer  108 . 
   It must be appreciated that the performance of the transducer is determined by the material properties of the piezoelectric crystals as well as the bonding method of the crystal  132  to the resonator  130 . The piezoelectric crystal  132  can be made of any appropriate piezoelectric material (e.g., piezoelectric ceramic, lead zirconium tintanate, piezoelectric quartz, gallium phosphate, etc.). In a like manner, the resonators  130  can be made of any appropriate material (e.g., ceramic, silicon carbide, stainless steel, aluminum, quartz, etc.). In one preferred embodiment, the resonator  130  is constructed from a material that is compatible with the cleaning chemistries (i.e., fluid medium) used. In another embodiment, the resonator  130  can be protected from the fluid medium a coating. 
   One having ordinary skill in the art must further appreciate that a thickness of the crystal  132  depends on the design of the crystal, mechanical strength of the crystal material, and type of crystal material. In one example, the thickness of the crystal  132  is configured to range between approximately about 1 mm and approximately about 6 millimeter, and a more preferred range of approximately about 2 mm and approximately about 4 mm and most preferably between approximately about 1 mm to approximately about 2 millimeters. In one embodiment, wherein the crystals are ceramic type crystals, the thickness of the crystals  132  is configured to range between approximately about 1 to about 4 millimeters. 
     FIGS. 3A through 3C  are simplified bottom views of exemplary flat brush scrubbing-AE cleaning assemblies, in accordance with several embodiments of the present invention. The flat brush scrubbing-AE cleaning assembly of  FIG. 3A  has a circular-shaped brush, wherein the brush  112  includes a plurality of openings such as  112   a – 112   c . In one embodiment, a size of the circular shaped brush  112  can be substantially equivalent to the size of the semiconductor substrate while in another embodiment, the size of the circular shaped brush  112  can be different than the size of the semiconductor substrate. 
   In one embodiment, the openings are configured to occupy a substantial portion of the brush so as to allow undisturbed transfer of high frequency acoustic energy. In one embodiment, the openings occupy between approximately about 10 and approximately about 80, and a more preferred range of approximately about 20 and approximately about 70 and most preferably approximately about 50% of the brush surface. 
   The brush  112 ′ of  FIG. 3B  is shown to have the shape of a quarter-arc length of a circle  113  while the embodiment  112 ″ shown in  FIG. 3C  has the shape of an eight-arc length of a circle  113 , wherein a radius R of the circle  113  is equivalent to a radius of the wafer  108 . As can be appreciated, in one preferred embodiment, the brush  112 ′ of the flat brush scrubbing-AE cleaning assembly  120  of  FIG. 3B  is designed such that the brush scrubbing-AE cleaning assembly  112 ′ covers, at least partially, a center C′ of the assembly  112 ′. In a like manner, brush  112 ″ of the brush scrubbing-AE cleaning assembly  120  of  FIG. 3C  is designed such that the brush  112 ″ covers, at least partially, a center C″ of the assembly  112 ″. In this manner, the centers C′ and C″ are substantially cleaned despite the brushes  112 ′ and  112 ″ having smaller sizes than the wafer  108 . As can be appreciated, the brushed  112 ′ and  112 ″ are shown to include the plurality of exemplary openings  112 ′ a–c  and  112 ″ a – 112   c ″, respectively. One of ordinary skill in the art must appreciate that the brushes  112 ′ and  112 ″ can be configured to remain stationary, to rotate, or to rotate and scan while cleaning the wafer top surface  108 . Furthermore, one having ordinary skill in the art must appreciate that the brush-transducers of the present invention can be configured to have any appropriate shape. 
     FIG. 4  is a simplified top view of an exemplary flat brush scrubbing-AE cleaning assembly  120  cleaning a wafer top surface  108 , in accordance with another embodiment of the present invention. As shown, the wafer  108  is engaged with three rollers  124   a – 124   c , each rotating in a respective rotation direction  125   a ,  125   b , and  125   c . The rotation of the driving roller  124   a  is designed to cause the wafer  108  to rotate in the rotation direction  125 . The flat brush scrubbing-AE assembly  120  is shown to clean the wafer top surface  108   a  as the assembly  120  moves over the wafer top surface  108   a . In one embodiment, the assembly  120  can scan over the wafer top surface  108   a  in a linear direction  122   a  while in a different embodiment, the assembly is configured to move in a radial direction  122   b . The assembly  120  of the present invention can be implemented to clean substantially the entire wafer top surface  108   a , even the edge of the wafer  108  being engaged by the rollers  124   a – 124   c . In this manner, the brush scrubbing-cleaning assembly can thus be moved onto the wafer surfaces horizontally through the spaces defined between adjacent rollers. 
   In one exemplary embodiment, the wafer surface is cleaned by changing the liner velocity of the brush scrubbing-cleaning assembly, as the brush scrubbing-cleaning assembly is cleaning the center of the surface versus the edge of the wafer. For instance, the liner velocity of the brush scrubbing-cleaning assembly can be configured to be reduced as the brush scrubbing-cleaning assembly moves from the center of the wafer to the edge of the wafer. In one embodiment, the arm control defines the applied pressure, velocity, and trajectory. For instance, in one embodiment, the brush  212  can have a thickness between approximately about 0.25 and 0.5 inch. In such embodiment, the compression of the brush  212  can be between approximately about 0.5 mm and approximately about 14 mm, and a more preferred range of approximately about 1 mm and approximately about 10 mm and most preferably approximately about 2 and approximately about 3 mm. 
     FIG. 5A  is a simplified three-dimensional view of a pair of exemplary roller-type brush scrubbing-AE cleaning assemblies  200   a  and  200   b , in accordance with one embodiment of the present invention. As shown, the top roller-type brush scrubbing-AE cleaning assembly  200   a  includes a top brush  212  mounted on a top brush core  240  that includes a top shaft  215  connected to a top fluid inlet  246 . As shown, the surface of top brush  212  is covered by a plurality of openings such as  212   a – 212   d . The top brush  212  is shown to be rotating in a rotation direction  222  as the rollers  224   a – 224   c  rotate, thus causing the wafer  108  to rotate in the direction  125 . 
   In one example, the wafer  108  can be engaged by two engaging rollers  224   a  and  224   b  and a driving roller  224   c . As can be seen, during the brush scrubbing-AE cleaning operation, the wafer  108  is held horizontally by the engaging rollers  224   a  and  224   b  and the driving roller  224   b  and top brush  212 . In such an embodiment, the wafer  108  is rotated in the wafer rotation direction  125  by the driving roller  224   c.    
   In accordance with one implementation, the backside of the wafer  108  can be cleaned using a bottom roller-type brush scrubbing-AE cleaning assembly  200   b . Similar to the top roller-type assembly  200   a , the bottom roller-type brush scrubbing-AE cleaning assembly  200   b  includes a bottom brush  212 ′ mounted on a bottom brush core  240 ′ that includes a bottom shaft  215 ′ connected to a bottom fluid inlet  246 ′. The surface of the bottom brush  212 ′ is shown to be covered by a plurality of openings such as  212 ′ a – 212 ′ d . The bottom brush  212 ′ is shown to be rotating in a rotation direction  222 ′ as the wafer is rotated in the direction  125 . 
   As can be seen, top and bottom brushes  212  and  212 ′ are configured to rotate around an axis of rotation in respective rotation directions  222  and  222 ′. In this manner, top and bottom surfaces of the wafer  108  are cleaned as top and bottom brushes  212  and  212 ′ come into contact with top and bottom surfaces  108   a  and  108   b , applying equal but opposite forces to the wafer top and bottom surfaces  108   a  and  108   b , respectively. Additional information with respect to the mechanism of the roller-type brush scrubbing-AE cleaning assemblies  200   a  and  200   b  are provided below with respect to  FIGS. 5B–5D . 
   In one embodiment, top and bottom brushes  212  and  212 ′ are polyvinyl alcohol (PVA) brushes (i.e., a very soft sponge), which can dislodge contaminants such as particles and residues using the fluid medium. In must be noted, however, that in another example, top and bottom brushes  212  and  212 ′ can be constructed from any suitable material so long as the material can dislodge particles and residues remaining on top and bottom surfaces of the wafer  108 . 
   In one embodiment, top and bottom surfaces  108   a  and  108   b  are cleaned using de-ionized water or any aqueous or semi-aqueous chemical solution. It must be appreciated by one having ordinary skill in the art that the fluid medium  227  can be any suitable fluid medium capable of cleaning top and bottom surfaces of the wafer and transmitting high frequency acoustic energy (e.g., Standard Cleaning I (SC1), DI water, ammonia containing chemical mixtures, HF containing chemical mixtures, surfactant containing chemical mixtures, etc.). In one implementation, the scrubbing-AE cleaning fluid medium  227  may be a cleaning fluid as described in U.S. Pat. No. 6,405,399, issued on Jun. 18, 2002, having inventors Jeffrey J. Farber and Julia S. Svirchevski, and entitled “Method and System of Cleaning a Wafer After Chemical Mechanical Polishing or Plasma Processing.” This U.S. Patent, which is assigned to Lam Research Corporation, the assignee of the subject application, is incorporated herein by reference. 
   The cleaning operation using the roller-type brush scrubbing-AE cleaning assembly  200   a  can further be understood with respect to the simplified, exploded, cross sectional view shown in  FIG. 5B , in accordance with one embodiment of the present invention. In the embodiment shown in  FIG. 5B , the roller-type brush scrubbing-AE cleaning assembly  200   b  is being applied to the top surface of the wafer  108 . The roller-type brush scrubbing-AE cleaning assembly is shown to include the brush core  240 , the fluid inlet  246 , and a plurality of transducers  233 , each including crystals  232  and respective resonators  230 , and the brush  212 . Each crystal  232  of the plurality of crystals  232  is bonded to a face of a respective resonator  230 , on the first side, and is attached to the brush core  240 , on the second side. In one example, the brush  212  is configured to be disposed over the brush core  240  such that the resonators  230  are entirely covered by the brush  212 . In this manner, the face of each resonator  130  is bonded to the corresponding crystal  132  while the back of each resonator  130  is in contact with the brush  212 . The plurality of openings such as  212   a – 212   i  is defined in the brush  212  so as to facilitate traveling of AE. 
   A plurality of orifices  240   a – 240   h  is defined in the brush core  240 . The fluid medium  227  is shown to be initially introduced into the brush core  240  through the fluid inlet  246 . Thereafter, the fluid medium  227  is guided to the respective gaps  231  defined between each pair of adjacent resonators  232 , and ultimately into the brush  112  and the openings such as  212   a – 212   i.    
   In the embodiment of  FIG. 5B , the roller-type brush scrubbing-AE cleaning assembly cleans the wafer as follows: The fluid medium  227  is implemented to saturate the brush  212  and form a meniscus  236  on the wafer top surface  108   a . The fluid medium  227  is guided to the brush  212  and thus the wafer surface  108  first through the orifices  240   a – 240   e  and then the nearby gaps  231 . In this manner, while the brush  212  is applied to the wafer top surface  108   a  with pressure, extra fluid medium  227  in the brush  212  is squeezed out as excess fluid  237  into the openings  212   a – 212   i . In this embodiment, saturation of the brush  212  further leads to formation of the layer of meniscus  236  on the wafer surface. The meniscus  236  and the excess fluid  237  facilitate the transmission of AE to the wafer surface during the cleaning operation. 
   The application of the brush  212  onto the wafer top surface  108   a  using the fluid medium  227  enables mechanical cleaning of the wafer top surface  108   a , thus defining areas  239 . In this manner, contaminants defined on the planer surface of the wafer top surface  108   a  can easily be removed by brush scrubbing. Embodiments of the present invention, however, simultaneously clean the wafer top surface  108   a  using high frequency acoustic energy imparted from the resonators  232  to the wafer top surface  108   a  through the excess liquid  237  defined in the exemplary openings  212   a – 212   i . The AE cleaning areas are shown as areas  239   b . The high frequency acoustic energy cleaning can be implemented to dislodge contaminants defined deep within the topography features, substantially enhancing the cleaning operation performed by brush scrubbing. 
     FIG. 5C  is a simplified cross sectional view of an exemplary roller-type brush scrubbing-AE cleaning assembly, in accordance with one embodiment of the present invention. As can be seen, the plurality of transducers  233 , as shown by the resonators  232  and the brush  212  are disposed on the outer surface of the brush core  240  in an alternate arrangement. That is, each pair of transducers  233  is separated by at least a portion of brush  212 . In this manner, the high frequency acoustic energy imparted by the resonators can easily travel through the small openings  212  and onto the wafer top surface  108   a . As can be appreciated, each of the plurality of orifices  240   a – 240   d  is in contact with a portion of the brush  212 , introducing fluid medium  227  into the cleaning interface through the brush  212 . In one example, excess fluid medium  227  further creates the layer of meniscus on the wafer surface. In this manner, the high frequency acoustic energy imparted by the resonators  232  can travel through the fluid medium  227  in the exemplary openings  212   a–h  and the meniscus  236  on to the wafer surface. 
     FIG. 5D  is a simplified, exploded, cross sectional view of yet another exemplary roller-type brush scrubbing-AE cleaning assembly, in accordance with another embodiment of the present invention. In the embodiment of  FIG. 5D , each of the plurality of crystals  332  is shown to be electrically connected to a electrical connection  332 . As can be seen, the plurality of resonators  232  and brush  312  are dispose on the outer surface of the brush core  240  in an alternate arrangement. In this manner, power can be integrated in the brush core to be provided to the transducers. By powering the crystals  232  using the electrical connections  334 , high frequency acoustic energy can be generated. 
   In one embodiment, the transducers  233  can cover substantially the entire outer surface of the brush core  240 . In another embodiment, the transducers  233  can be defined on the outer surface of the brush core  240  such that transducers  233  cover less than an entire surface of the brush core  240 . In such an embodiment, the openings  212   a – 212   i  defined in the brush  312  can be configured to merely cover the transducers rather than the entire surface of the brush core. Furthermore, as can be appreciated, a length of the transducers can be configured to be equivalent to the diameter of the wafer  108 . 
   In one exemplary embodiment, a brush  312  can include a plurality of slits  312   a  and brush patches  312   b , in accordance with one embodiment as shown in  FIG. 5E . The embodiment of  FIG. 5E  illustrates an unrolled exemplary roller-type brush  312 . As shown, the brush  312  includes a plurality of slits  312   b , with each slit  312   b  including a plurality of brush patches  312   a . In one preferred embodiment, each slit  312   b  is configured to be disposed over the brush core  240  such that each of the brush slits  312  is defined over a transducer. The brush patches  312   a  are configured to improve the strength of the brush  312 , substantially reducing the possibility of having a tear in the brush  312 . One must appreciate that the brush patches are defined out of phase. In this manner, lack of generation of acoustic energy resulting form being covered by each of the brush patches  312  is compensated by the adjacent transducers. 
     FIG. 6  is a simplified three-dimensional view of a pair of exemplary roller-type brush scrubbing-AE cleaning assemblies  200 ′ a  and  200 ′ b , in accordance with one embodiment of the present invention. As shown, fluid medium  227  is introduced onto the brush  212  and the wafer top surface  108   a  through a top nozzle  226 . In this manner, fluid medium  227  is dripped onto the brush  212 , saturating the brush  212  while creating a meniscus on the wafer top surface  108   a . The fluid medium  227  defined in the exemplary openings  212   a–h  of the brush  212  enables the high frequency acoustic energy to travel and be applied on the wafer top surface  108   a . In this manner, the wafer top surface  108   a  is cleaned by substantially concurrently using both mechanical action and the generated high frequency acoustic energy. 
   In accordance with one implementation, the wafer backside  108   b  of the wafer  108  can be cleaned using a bottom roller-type brush scrubbing-AE cleaning assembly  200 ′ b . Similar to the top assembly  200 ′ a , in one embodiment, the fluid medium  227  is sprayed onto the wafer backside  108   b  using a pressurized nozzle  226   b  (not shown in this Figure). 
     FIG. 7  is a simplified cross sectional view of an exemplary multi-station cleaning module  400  including a plurality of single-wafer combination cleaning assemblies  400   a – 400   c , in accordance with one embodiment of the present invention. As can be seen, the cleaning module  400  includes a chamber  411 , an arm control module  416 , and an electrical connection module  450 . The first single-wafer combination cleaning assembly  400   a  includes top and bottom brush-scrubbing-AE cleaning assemblies  120   a  and  120   a ′, each connected to the arm control module  416  using a respective arm  418   a  and  418 ′ a . The wafer  108  is engaged by a pair of rollers  424   a  and  424 ′ a , each connected to the electrical connection module  450 . Nozzles  126   a  and  126   a ′ are configured to respectively spray fluid medium onto the wafer top and bottom surfaces  108   a  and  108   b . The fluid medium introduced into the cleaning interface is configured to create a layer of meniscus on the wafer surfaces  108   a  and  108   b  and to saturate the brushes in the brush-scrubbing cleaning assemblies  120   a  and  120 ′ a . As described in more detail above, the high frequency acoustic energy can easily travel through the fluid medium, allowing the acoustic energy imparted by the resonators to be applied on to the wafer surfaces. 
   Still referring to  FIG. 7 , the second single-wafer combination cleaning assembly  400   b  includes a top and bottom brush-scrubbing-AE cleaning assemblies  120   b  and  120   b ′, each connected to the arm control module using a respective arm  418   b  and  418 ′ b . The wafer  108 ′ is engaged by a pair of rollers  424   b  and  424 ′ b , each connected to the electrical connection module  450 . Nozzles  126   b  and  126   b ′ are configured to respectively spray fluid medium onto the wafer top and bottom surfaces  108 ′ a  and  108 ′ b . The fluid medium introduced into the cleaning interface is configured to create a layer of meniscus on the wafer surfaces  108 ′ a  and  108 ′ b  and to saturate the brushes in the brush-scrubbing cleaning assemblies  120   b  and  120 ′ b.    
   The third single-wafer combination cleaning assembly  400   c  includes a top and bottom brush-scrubbing-AE cleaning assemblies  120   c  and  120 ′ c , each connected to the arm control module using a respective arm  418   c  and  418 ′ c . The wafer  108 ″ is engaged by a pair of rollers  424   c  and  424 ′ c , each connected to the electrical connection module  450 . Nozzles  126   c  and  126   c ′ are configured to respectively spray fluid medium onto the wafer top and bottom surfaces  108 ″ a  and  108 ″ b . The fluid medium introduced onto the cleaning interface is configured to create a layer of meniscus on the wafer surfaces  108 ″ a  and  108 ″ b  and to saturate the brushes in the brush-scrubbing cleaning assemblies  120   c  and  120 ′ c.    
   As can be seen, each pair of adjacent single-wafer combination cleaning assemblies  400   a – 400   c  is separated by a shield  450   a  and  450   b , respectively. In this manner, fluid medium introduced into each of the single-wafer combination cleaning assembly  400   a – 440   c  cannot contaminate the cleaning operation performed in the adjacent cleaning assemblies. Furthermore, several wafers, each made of different materials, can be cleaned substantially simultaneously in the multi-station cleaning module of the present invention. As can be appreciated, the embodiments of the present invention prevent the introduction of chemicals implemented in different single-wafer combination cleaning assembly to contaminate the adjacent stations. Of course, multiple wafers can be simultaneously cleaned implementing both a brush scrubber and high frequency acoustic energy, removing contaminants defined in the planer surfaces as well as deep topography features of the wafer. 
     FIG. 8  is a flowchart diagram  800  of method operations performed in making a brush scrubbing-AE cleaning assembly, in accordance with one embodiment of the present invention. The method begins in operation  802  in which a transducer is provided. The transducer includes a resonator and a crystal. The crystal is defined on the first side of the resonator. The method continues to operation  804  in which a plurality of openings is defined in a brush. In one embodiment, the brush is a flat brush. In one embodiment, the plurality of openings can perform the function as nodules during the cleaning operation. Next, in operation  806 , the brush is placed over the second side of the resonator. 
     FIG. 9  is a flowchart diagram  900  of method operations performed in making a roller-type brush scrubbing-AE cleaning assembly, in accordance with another embodiment of the present invention. The method begins in operation  902  in which a brush core is provided followed by operation  904  in which a plurality of orifices is defined in the brush core. Continuing to operation  906 , a plurality of transducers is defined on the brush core. Thereafter, in operation  908 , each transducer is defined on the brush core without covering all of the orifices in the brush core. In one embodiment, the entire outer surface of the brush core can be covered by transducers. In such scenario, the brush can cover the entire outer surface of the brush core. In another embodiment, transducers are defined on certain portion of the brush core. In such embodiment, openings are defined on the sections of the brush configured to be disposed on the transducers. Proceeding to operation  910 , a brush having a plurality of openings is provided. In operation  912 , the brush is defined over the brush core and the transducers such that the openings in the brush are defined at least partially on the transducers. 
   It should be appreciated that the brush scrubbing-high frequency acoustic energy cleaning assembly of the present invention can be implemented to clean wafer surfaces vertically or horizontally. Additionally, although the embodiments described herein have been primarily directed toward cleaning semiconductor substrates, it should be understood that the brush scrubbing-AE cleaning assembly of the present invention is well suited for cleaning any type of substrate. The invention has been described herein in terms of several exemplary embodiments. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. The embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims.

Technology Classification (CPC): 7