Abstract:
A sonic cleaning tank is provided that transmits energy from a side-wall-mounted transducer, parallel to a wafer, and reflects the sonic energy out of the plane of the wafer via an angled side wall positioned on the side of the wafer opposite the transducer. The angled side wall preferably forms a vertical V. Internal partitions may be optionally employed to partition reflected energy from the wafer. By configuring the relative angles and positions of tank walls and internal partitions, the path of reflected energy is advantageously controlled. Multiple reflections ensure that any reflected energy which impacts the wafer is sufficiently attenuated so as not to interfere with wafer cleaning.

Description:
BACKGROUND OF THE INVENTION 
     Conventional megasonic cleaning tanks employ a fluid filled tank having substrate supports therein and a source of megasonic energy, (e.g., a transducer) coupled to the fluid for directing sonic energy through the fluid to the surfaces of a substrate or wafer supported therein. During megasonic cleaning, the transducer oscillates between a positive and a negative position at a megasonic rate so as to generate positive and negative pressures within the fluid (and thereby coupling megasonic energy to the fluid. As the energy imparted to the fluid oscillates between positive and negative pressure, cavitation bubbles form in the liquid during negative pressure and collapse or shrink during positive pressure. This bubble oscillation and collapse gently cleans the surface of the wafer. 
     Particles cleaned from the wafer are carried upward via a laminar flow of fluid and flushed into overflow weirs coupled to the top of the cleaning tank. Thus, a supply of clean fluid is continually introduced to the cleaning tank from the bottom of the side walls thereof. Cleaning fluid distribution nozzles are positioned along the bottom of the sidewalls to supply various cleaning fluids through the same nozzles or through dedicated sets of nozzles. 
     Most conventional cleaning tanks position one or more transducers along the bottom of the cleaning tank. Acoustic waves from these transducers reflect from the surface of cleaning fluid back into transducers, and interference results in reduced power density in the tank and reduced cleaning efficiency. Due to the limited area of the tank&#39;s bottom, the number, size, placement and shape of the transducers, fluid inlets, etc., often can not be freely selected for optimal performance. Particularly, positioning the transducer elsewhere would allow a higher laminar flow of fluid from the fluid inlets, and would decrease cleaning/processing time. 
     Accordingly, a need exists for an improved sonic cleaning tank that provides high laminar fluid flow yet avoids the interference of incident and reflected waves. 
     SUMMARY 
     The present invention provides a sonic cleaning tank having a side wall transducer and having a cleaning tank configured to reflect sonic waves away from the wafer, and to thereby avoid interference . Specifically, sonic waves are reflected out of the plane of the wafer, and thereafter undergo further reflection. By generating a plurality of reflections within the tank, the inventive tank design ensures that any reflected wave which impacts the wafer is sufficiently attenuated to avoid the negative effects of interference. 
     In a first aspect of the invention, a transducer is mounted on a first wall of the cleaning tank, a substrate receiving area is provided for supporting a substrate in parallel with energy wave rays emitted from the transducer and a second wall is located across the substrate receiving area from the first wall, and is angled such that energy wave rays emitted by the transducer impact the second wall and reflect out of the plane of the wafer. Preferably the second wall is angled to form a vertical V. 
     In a second aspect of the invention, one or more internal partitions extend from the first wall forming one or more partitioned regions to partition energy wave rays which impact the second wall and reflect out of the plane of the wafer. 
     In a third aspect, the second wall is angled to form a vertical V, and the angle of the V and the position of a side wall (coupled between the first and second walls) relative to the V are such that energy wave rays reflect from the V to the side wall and reflect from the side wall upwardly toward an air/liquid interface of the tank. 
     Other aspects of the invention position the apex of the second wall&#39;s V toward or away from the wafer and/or in line with the wafer or inline with an internal partition, to achieve desired reflection paths. 
     The various aspects of the invention provide a cleaning tank that is virtually free of interference from reflected energy wave rays yet maintains an open bottom for high laminar fluid flow. The resultant cleaning tank boasts high transducer efficiency and faster cleaning times due to the combination of transducer efficiency and high laminar flow. 
     Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are a front perspective view and a top plan view, respectively, of a first preferred sonic cleaning tank embodying the invention; 
     FIGS. 2A and 2B are a front perspective view and a top plan view, respectively, of a second preferred cleaning tank embodying the invention; and 
     FIGS. 3A and 3B are a front perspective view and a top plan view, respectively, of a third preferred cleaning tank embodying the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A and 1B are a front perspective view and a top plan view, respectively, of a first cleaning tank  11   a . As described below, the first cleaning tank  11   a  employs a pair of partitioned regions  13   a ,  13   b  having sloped bottom walls  15   a ,  15   b , respectively, to partition reflected energy wave rays from a wafer  17 , and to further reflect the energy wave rays upward from the partitioned regions  13   a ,  13   b  to an air/liquid interface  19 . 
     The first cleaning tank  11   a  comprises a first wall  21  having a transducer  23  mounted thereto. The transducer  23  is dimensioned for maximum power density, and preferably has a length greater than the diameter of a wafer to be cleaned. Similarly, the width of the transducer  23  is preferably equal to the width of the wafer to be cleaned plus the tolerance required for wafer placement. By thus minimizing the width of the transducer  23  the volume of the tank is minimized. A wafer support mechanism is provided to support the wafer  17  in a wafer receiving area  25  so that the wafer  17  is parallel to energy wave rays emitted from the transducer  23 . A second wall  27  is positioned across the wafer receiving area  25  from the first wall  21 , and is angled so that energy wave rays emitted from the transducer  23  impact the second wall  27  and reflect out of the plane of the wafer  17 , and into either the first partitioned region  13   a  or the second partitioned region  13   b . Specifically, the second wall  27  is angled to form a V, which is oriented so that the point thereof extends vertically (i.e., a vertical V) as shown in FIG.  1 A. The V comprises a first region  27   a , and a second region  27   b  which angle away from the internal region of the first cleaning tank  11   a , (i.e., the V points toward the wafer receiving area  25  of the first cleaning tank  11   a ). The point of the V is in line with the wafer  17 . 
     The first partitioned region  13   a  comprises the sloped bottom  15   a  and a first internal partition  29   a  that extends from the first wall  21 . The position of the first internal partition  29   a , (e.g., the length which the first internal partition  29   a  extends from the first wall  21 , and the distance between the first internal partition  29   a  and a back wall  31  which couples between the first wall  21  and the second wall  27 ) preferably is selected with reference to the position of the wafer  17 , and the position (e.g., the length and the angle) of the second wall  27 &#39;s first region  27   a  so that an energy wave ray which impacts any portion of the first region  27   a  reflects into the first partitioned region  13   a , and is partitioned from the wafer  17  via the first internal partition  29   a . Once inside the first partitioned region  13   a , the reflected energy wave ray undergoes further reflection and eventually reflects upward to the air/liquid interface  19  by the first sloped bottom wall  15   a.    
     Similarly the second partitioned region  13   b  comprises the sloped bottom  15   b  and a second internal partition  29   b  that extends from the first wall  21  and is located across the transducer  23  from the first internal partition  29   a . The position of the second internal partition  29   b  (e.g., the length which the second internal partition  29   b extends from the first wall  21 , and the distance between the second internal partition  29   b  and a front wall  33  which couples between the first wall  21  and the second wall  27 ) preferably is selected with reference to the position of the wafer  17 , and the position (e.g., the length and the angle) of the second wall  27 &#39;s second region  27   b  so that an energy wave ray which impacts any portion of the second region  27   b  reflects into the second partitioned region  13   b , and is partitioned from the wafer  17  via the second internal partition  29   b . Once inside the second partitioned region  13   b , the reflected energy wave ray undergoes further reflection and eventually reflects upward to the air/liquid interface  19  by the second sloped bottom wall  15   b.    
     The first cleaning tank  11   a  also comprises a plurality of fluid inlets positioned along a bottom wall  35 , as generally represented by the dotted arrows  37   a-b , an overflow weir coupled along the entire top perimeter of the first cleaning tank  11   a , as generally represented by the dotted arrow  39 , and a wafer supporting mechanism such as a plurality of supports  41  positioned along the lower edge of the wafer  17 . Preferably each support  41  is small, so as to minimize wafer shadowing and has a v-groove formed therein to minimize wafer contact. 
     The distance between the internal partitions  29   a ,  29   b  is equal to the width of the transducer  23 , plus an additional 0 to 50% of transducer  23 &#39;s width. The angle between the first and second regions  27   a ,  27   b  of the second wall  27  is greater than 90°, so that acoustic waves reflected from the first and second regions  27   a ,  27   b  reflect from the front and back wall  33 ,  31  at an angle less than 90°. The internal partitions  29   a ,  29   b  extend forward so that the rays reflected from a location near a point  27   c  (where the first and second regions  27   a ,  27   b  meet) strike the first or second regions  29   a ,  29   b , but rays from the edges of the transducer  23  reflect from the first and second regions  27   a ,  27   b  to the front and back walls  31 ,  33  into the internal partitions  29   b ,  29   a , respectively, and are trapped in the partitioned regions  13   a ,  13   b.    
     In operation, the transducer  23  is energized and a plurality of energy wave rays are emitted from the transducer  23 , such that the rays parallel to the wafer  17 , and travel across the wafer receiving area  25  to the second wall  27 . As the energy wave rays travel through the wafer receiving area  25  they sonically clean the wafer  17 . A continuous laminar flow of cleaning fluid  37   a-c  is emitted from the tank bottom and sweeps particles dislodged from the surface of the wafer  17  up and into the overflow weir as represented by the dotted arrow  39 . Preferably the supports  41   a-c  rotate causing the wafer  17  supported thereon to rotate such that each portion of the wafer  17  is cleaned. For simplicity, only a single representative energy wave ray is shown, as represented by arrows  45   a-d . The first arrow  45   a  represents the energy wave ray emitted from the transducer  23  prior to any reflection thereof. After impacting the second wall  27 , the energy wave ray reflects out of the plane of the wafer and impacts the front wall  33  as represented by the second arrow  45   b . After impacting the front wall  33  the energy wave ray reflects into the second partitioned region  13   b  and impacts the second sloped bottom wall  15   b  as represented by the third arrow  45   c . After impacting the second sloped bottom wall  15   b  the energy wave ray reflects upward to the air/liquid interface  19  where the energy wave ray is partially reflected back and partially exits the first cleaning tank  11   a  as represented by the fourth arrow  45   d.    
     Thus, within the first cleaning tank  11   a  each of the plurality of energy wave rays emitted from the transducer  23  are reflected out of the plane of the wafer  17  and are partitioned from the wafer  17  via the first partitioned region  13   a  and the second partitioned region  13   b . Because the point of the V is in line with the wafer  17 , the wafer  17  shadows the point from energy wave rays, preventing energy wave rays from reflecting from the point into the wafer receiving area  25 . The energy wave rays emitted closer to the surface  19 , after reflection from the back or front walls  31 ,  33  impinge on the first or second internal partition  29   c ,  29   b  and may go through multiple reflections prior to striking the sloped bottom wall  15   a ,  15   b  and reflecting therefrom, as represented by arrow  45   d.    
     FIGS. 2A and 2B are a front perspective view and a top plan view, respectively, of a second cleaning tank  11   b . As described below, the second cleaning tank  11   b  employs a single partitioned region  13  having a sloped bottom wall  15 , to partition reflected energy wave rays from the wafer  17 , and to further reflect energy wave rays upward from the partitioned region  13  to the air/liquid interface  19 . The use of a single partitioned region  13  simplifies the tank&#39;s design and manufacture. 
     The first cleaning tank  11   a  and the second cleaning tank  11   b  differ primarily in the relative position and angling between the second wall  27  and the internal partition  29 . Specifically, in the second cleaning tank  11   b  the V of the second wall  27  points away from the wafer receiving area  25  and is positioned in line with the internal partition  29 . Thus, the first region  27   a  of the second wall  27  is positioned across the wafer receiving area  25  from the transducer  23 , and the second region  27   b  of the second wall  27  is positioned in front of the sloped bottom wall  15 . The position of the internal partition  29  preferably is selected with reference to the position of the wafer  17  and the position of the second wall  27 , so that an energy wave ray which impacts any portion of the first region  27   a  of the second wall  27  is reflected to the second region  27   b  of the second wall  27 , and is reflected from the second region  27   b  into the partitioned region  13 . Once inside the partitioned region  13 , the reflected energy wave ray undergoes further reflection and eventually reflects upward to the air/liquid interface  19  by the sloped bottom wall  15 . 
     Other than the difference described above, the first cleaning tank  11   a  and the second cleaning tank  11   b  comprise the same components. The description of common components and their operation is therefore not repeated. Accordingly the path of the energy wave rays as they reflect within the second cleaning tank  11   b  are now described. For simplicity, only a single representative energy wave ray is shown, as represented by the arrows  45   a-d.    
     In operation, an energy wave ray is emitted from the transducer  23 , parallel to the wafer  17  and travels across the wafer receiving area  25  to the first region  27   a  of the second wall  27 , as represented by the first arrow  45   a . After impacting the second wall&#39;s first region  27   a , the energy wave ray reflects into the partitioned region  13  and impacts the sloped bottom wall  15 , as represented by the third arrow  45   c . After impacting the sloped bottom wall  15  the energy wave ray reflects upward to the air/liquid interface  19  where it is partially reflected back and partially exits the second cleaning tank  11   b.    
     Thus, within the second cleaning tank  11   b  each of the plurality of energy wave rays emitted by the transducer  23  are reflected out of the plane of the wafer  17  and are partitioned from the wafer  17  via the partitioned region  13 ; yet tank design and manufacture are simplified. To further simplify design and manufacture, internal partitions may be omitted and the tank walls themselves configured to reflect energy wave rays out of the wafer plane, and away from the wafer, as exemplified by FIGS. 3A and 3B. 
     FIGS. 3A and 3B are a front perspective view and a top plan view, respectively, of a third cleaning tank  11   c . As described below, the third cleaning tank  11   c , like the second cleaning tank  11   b , employs a single partitioned region  13  having a sloped bottom wall  15 , to partition reflected energy wave rays from the wafer  17 , and to further reflect energy wave rays upward from the partitioned region  13  to the air/liquid interface  19 . The use of a single partitioned region  13  simplifies the tank&#39;s design and manufacture. 
     The second cleaning tank  11   b  and the third cleaning tank  11   c  differ primarily in the relative position and angling between the second wall  27  and the internal partition  29 . Specifically, in the third cleaning tank  11   c  the second wall  27 , rather than forming a V, extends in a line between the back wall  31  and the front wall  33  such that the second wall  27  slants away from the wafer receiving area  25 . The position of the internal partition  29  preferably is selected with reference to the position of the wafer  17  and the slant of the second wall  27 , so that an energy wave ray which impacts any portion of the second wall  27  is reflected into the partitioned region  13 . Once inside the partitioned region  13 , the reflected energy wave ray undergoes further reflection and eventually reflects upward to the air/liquid interface  19  by the sloped bottom wall  15 . 
     Other than the difference described above, the second cleaning tank  11   b  and the third cleaning tank  11   c  comprise the same components. The description of common components and their operation is therefore not repeated. Accordingly the path of the energy wave rays as they reflect within the third cleaning tank  11   c  are now described. For simplicity, only a pair of representative energy waves are shown, as represented by the arrows  47   a-d  and  49   a-d.    
     In operation, an energy wave ray is emitted from the transducer  23 , parallel to the wafer  17  and travels across the wafer receiving area  25  to the second wall  27 , as represented by the first arrows  47   a ,  49   a . After impacting the second wall  27 , the energy waves ray reflect therefrom to the front wall  33  as represented by the arrows  47   b ,  49   b . Thereafter, the energy wave rays either impact the internal partition  29  and reflect therefrom to impact the sloped bottom wall  15  (arrows  49   c  and  49   d ) or reflect directly from the front wall  33  into the sloped bottom wall  15  (arrow  47   c ). After impacting the sloped bottom wall  15  the energy wave ray reflects upward to the air/liquid interface  19  where it is partially reflected back and partially exits the third cleaning tank  11   c.    
     Thus, within the third cleaning tank  11   c  each of the plurality of energy wave rays emitted by the transducer  23  are reflected out of the plane of the wafer  17  and are partitioned from the wafer  17  via the partitioned region  13 ; yet tank design and manufacture are simplified. 
     The foregoing description discloses only the preferred embodiments of the invention, modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. Specific dimension and angles for exemplary tanks described above have not been provided, as armed with the present teachings, a person of ordinary skill in the art will be able to design any number of cleaning tanks, by varying angles and dimensions to achieve a desired energy wave ray path and to comply with limitations of a given space. For instance, the second wall may be angled in a number of configurations such as a horizontally oriented V, or a plurality of V&#39;s. As used herein, a substrate or a wafer includes, but is not limited to a semiconductor wafer with or without material layers thereon, whether patterned or unpatterned. 
     Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.