Abstract:
Embodiments of the present invention relate to semiconductor device manufacturing, and more particularly to a horizontal megasonic module for cleaning substrates. In one embodiment an apparatus for cleaning a substrate is provided. The apparatus comprises a tank adapted to contain a cleaning fluid, a movable housing having a first side adapted to be placed in the cleaning fluid, a plurality of rotatable rollers coupled to the first side of the housing, the rollers positioned and including grooves to securely hold the substrate in a horizontal orientation, and one or more transducers adapted to direct vibrational energy through the cleaning fluid in the tank toward the substrate, wherein at least one of the transducers directs vibrational energy toward the substrate and substantially parallel to a major surface of the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 60/871,914, filed Dec. 26, 2006, which is herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate to semiconductor device manufacturing, and more particularly to a horizontal megasonic module for cleaning substrates. 
         [0004]    2. Description of the Related Art 
         [0005]    In certain industries there are processes that must be used to bring objects to an extraordinarily high level of cleanliness. For example, in the fabrication of semiconductor substrates, multiple cleaning steps, known as surface preparation, are typically required to remove impurities from the surfaces of the substrates before subsequent processing. A typical surface preparation procedure may include etch, clean, rinse and dry steps. An etch step may involve immersing the substrates in an etch solution of HF to remove surface oxidation and metallic impurities and then thoroughly rinsing the substrates in high purity deionized water (DI) to remove etch chemicals from the substrates. During a typical cleaning step, the substrates are exposed to a cleaning solution that may include water, ammonia or hydrochloric acid, and hydrogen peroxide. After cleaning, the substrates are rinsed using ultra-pure water and then dried using one of several known drying processes. The effectiveness of a substrate fabrication process is often measured by two related and important factors, which are device yield and the cost of ownership (CoO). These factors are important since they directly affect the cost to produce an electronic device and thus a device manufacturer&#39;s competitiveness in the market place. The CoO, while affected by a number of factors, is greatly affected by the system and chamber throughput, or simply the number of substrates per hour processed using a desired processing sequence. In an effort to reduce CoO, electronic device manufacturers often spend a large amount of time trying to optimize the process sequence and chamber processing time to achieve the greatest substrate throughput possible given the tool architecture limitations and the chamber processing times. 
         [0006]    For the foregoing reasons, there is a need for a tool that can meet the required device performance goals, has a high substrate throughput, and thus reduces the process sequence CoO. 
       SUMMARY OF THE INVENTION 
       [0007]    Embodiments of the present invention relate to semiconductor device manufacturing, and more particularly to a horizontal megasonic module for cleaning substrates. In one embodiment an apparatus for cleaning a substrate is provided. The apparatus comprises a tank adapted to contain a cleaning fluid, a movable housing having a first side adapted to be placed in the cleaning fluid, a plurality of rotatable rollers coupled to the first side of the housing, the rollers positioned and including grooves to securely hold the substrate in a horizontal orientation, and one or more transducers adapted to direct vibrational energy through the cleaning fluid in the tank toward the substrate, wherein at least one of the transducers directs vibrational energy toward the substrate and substantially parallel to a major surface of the substrate. 
         [0008]    In another embodiment an apparatus for cleaning multiple substrates is provided. The apparatus comprises a tank adapted to contain a cleaning fluid, a first movable housing having a first side adapted to be placed into the cleaning fluid, a first plurality of rotatable rollers coupled to the first side of the first housing, the rollers positioned and including grooves to securely hold a first substrate in a horizontal orientation, a second movable housing having a first side adapted to be placed into the cleaning fluid, a second plurality of rotatable rollers coupled to the first side of the second housing, the rollers positioned and including grooves to securely hold a first substrate in a horizontal orientation, and a first transducer positioned between the first housing and the second housing, wherein the first transducer is adapted to generate vibrations that may propagate horizontally toward both housings and the substrates held therein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0010]      FIG. 1  is a schematic cross-sectional view of a horizontal megasonic module provided in accordance with one embodiment of the present invention; and 
           [0011]      FIG. 2  is a schematic cross-sectional view of a multiple-substrate horizontal megasonic module in accordance with one embodiment of the present invention. 
       
    
    
       [0012]    To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that elements and/or process steps of one embodiment may be beneficially incorporated in other embodiments without additional recitation. 
       DETAILED DESCRIPTION 
       [0013]    In semiconductor device processing, chemical-mechanical polishing (CMP) processes are typically followed by one or more cleaning procedures in which loose substrate particles and slurry resulting from the polishing process are removed from the surface of a substrate. One of the conventional techniques for cleaning substrates is megasonic cleaning, in which a substrate is submerged in a fluid bath and subjected to megasonic frequency vibrations (500 kHz or greater) which dislodge the particles and/or slurry residue from the substrate surfaces. 
         [0014]    Embodiments of the present invention provide an apparatus or module for horizontal megasonic substrate cleaning in which a substrate may be subjected to megasonic vibrations while positioned in a horizontal orientation. One or more transducers may generate megasonic vibrations directed substantially parallel to the major surface(s) of a horizontally oriented substrate. The present invention also provides an apparatus or module in which multiple horizontally oriented substrates may be subjected to megasonic vibrations. 
         [0015]    One of the advantages of a horizontal megasonic module in comparison with a vertically-oriented module is that a horizontal megasonic module may be able to more evenly distribute vibrational energy across the surface of a substrate. The improved energy distribution enables a lower wattage to be applied; the lower wattage, in turn, reduces wear on rollers and other components of the module. Control of the grip on a substrate (e.g., by rollers) also may be improved. 
         [0016]    Additionally, transfer of a substrate into or out of a horizontal module is generally more stable and efficient because the substrate is held (in part) by gravity against the transferring device (such as a robot). Because other polishing and/or cleaning modules may process substrates horizontally, a single robot can generally serve all of the modules of a polishing and cleaning system. Further advantages are discussed in conjunction with the following description of embodiments of the present invention. 
         [0017]      FIG. 1  is a schematic cross-sectional view of a horizontal megasonic module  100  provided in accordance with the present invention. As shown, the module  100  comprises a generally horizontally extending housing  110  supported above by a shaft member  115 . During a cleaning operation, as shown, the housing  110  may be submerged in a cleaning fluid contained in a tank  120 . The cleaning fluid may comprise deionized water (DIW), a cleaning chemistry (SCI), surfactants, acids, bases and/or any other suitable cleaning solution. The tank  120  may be made of any material compatible with the cleaning fluid. 
         [0018]    Rollers  131 ,  132  are coupled to and extend from a lower edge  114  of the housing  110 . While only two rollers  131 ,  132  are shown in the cross-sectional view of  FIG. 1 , in some embodiments the module  100  may include three rollers spaced 120 degrees apart in the horizontal plane (e.g., to securely support a substrate). A greater number of rollers, such as four rollers, may also be used. 
         [0019]    A motor  140 , which may be disposed in the housing or in any other suitable location, is operatively coupled to one or both of the rollers  131 ,  132  such that the rollers can rotate. In some embodiments, a separate drive mechanism may be included for each roller. In other embodiments, only a single roller may be driven and the remaining rollers may rotate passively. 
         [0020]    Each of the rollers  131 ,  132  include a groove  135 ,  136  which can be V-shaped as shown or may be otherwise shaped, such as U-shaped. The rollers  131 ,  132  may be positioned on the housing  110  so as to surround a substrate  105  of a particular diameter in a horizontal orientation. 
         [0021]    In some embodiments, the motor  140  or another motor (not shown) may move one or more of the rollers  131 ,  132  a small distance horizontally to position the rollers  131 ,  132  in or out of gripping contact with the substrate  105  for receiving or releasing the substrate  105 . When in gripping contact, the rollers  131 ,  132  exert sufficient force on the edge of the substrate  105  to firmly secure the substrate  105  in place within the grooves  135 ,  136  while allowing the substrate  105  to rotate with the rotation of the rollers  131 ,  132 . 
         [0022]    A controller  150  may be coupled to the motor  140  and control the motion and/or rotation of the rollers  131 ,  132  and/or the raising and/or lowering of the housing  110 . The controller  150  may also receive signals from a rotation sensor (not shown) that monitors the rotation of the rollers  131 ,  132 , and provides an indication of the rotational speed of the substrate  105 . For example, one or more of the rollers  131 ,  132  may include a magnet (not shown), and the rotation of the magnet may be used to indicate roller and substrate rotation rate. 
         [0023]    One or more transducers  161 ,  162 ,  163  may be positioned within or on the outside of the tank  120  to generate vibrational energy within the fluid of the tank  120  at a megasonic or other frequency. The transducers  161 ,  162 ,  163  may be implemented, for example, using piezoelectric actuators, or any other suitable mechanism that can generate vibrations at megasonic frequencies of suitable amplitude. While three transducers are shown in  FIG. 1 , fewer or a larger number of transducers may be used. The embodiment depicted shows advantageous configurations where transducers may be placed to direct vibrational energy effectively toward the substrate  105 . 
         [0024]    A first transducer  161  may be directly coupled to or positioned adjacent to an external surface of a first side  127  of the tank  120 . The first transducer  161  is oriented to generate vibrational energy that travels through the tank  120  and cleaning fluid to impact the substrate  105  from the side, substantially parallel to the major surface(s) of the substrate  105 . In some embodiments, the vibrational energy is directed at an angle of about 10 degrees or less from a plane defined by the major surface(s) of the substrate  105  and/or within about 10 degrees of horizontal. When vibrational energy is directed substantially parallel to the substrate&#39;s major surface(s), the vibrational wave fronts stream along the upper and lower surfaces of the substrate, impacting particles along their path. 
         [0025]    A second transducer  162  may be directly coupled or positioned externally adjacent to the bottom of the tank  120  and may be oriented to generate vibrational energy that travels via the tank  120  and cleaning fluid to impact the bottom major substrate surface from below, approximately perpendicular to the substrate surface. In some embodiments, the second transducer  162  may have a surface area approximately the same size as (or larger than) the surface area of the substrate  105  in order to generate vibrational energy that encompasses the entire surface area of the substrate  105 . 
         [0026]    A third transducer  163  may be positioned adjacent to a second side  128  of and/or inside the tank  120 , wholly or partially submerged in the cleaning fluid. The third transducer  163 , like the first transducer  161 , may be oriented to generate vibrational energy which impacts the substrate  105  from the side, substantially parallel to the major surface(s) of the substrate, e.g., within about 10 degrees of the major surface(s) of the substrate and/or horizontal. However, unlike the first transducer  163 , the third transducer  163  may be in contact with the cleaning fluid and may transmit vibrational energy through the fluid directly. 
         [0027]    It is noted that the transducers  161 ,  162 ,  163  may be placed in other suitable locations. Additionally, all three transducers need not be used together. For example, the first transducer  161  may be used alone, or one or both of the second and third transducers  162 ,  163  may be used without the first transducer  161 . As in these example embodiments, it may be useful to have at least one transducer that provides vibrational energy substantially parallel to the major surface(s) of the substrate  105 . The controller  150  may be adapted to control operation of the transducer  161 ,  162  and/or  163 . Each transducer may provide energy continuously, periodically or at any suitable cycle time. 
         [0028]      FIG. 2  is a schematic cross-sectional view of a multiple-substrate horizontal megasonic module  200  according to the present invention. The multiple-substrate module  200  can accommodate two (as shown) or more substrates simultaneously, increasing the throughput of the cleaning process. The module  200  includes separate housings  210 ,  211  for each substrate handled, which may be positioned adjacent to each other (as shown) or behind or in front of each other within a single tank  220  filled with cleaning fluid. 
         [0029]    Each housing  210 ,  211  is supported from above by a respective shaft  215 ,  216  and supports, in turn, respective sets of rollers  231 ,  232  (first housing  210 ) and  233 ,  234  (second housing  211 ). Each housing  210 ,  211  may include one or more motors  240 ,  241 . The motors  240 ,  241  may also be located at any other suitable location for driving the rollers  231 ,  232  and  233 ,  234  (e.g., each roller, a single roller in each set of rollers, etc.). In some embodiments, a single motor may be used to drive both sets of rollers and/or a single roller in each set (e.g., via gears, belts or the like). The respective sets of rollers  231 ,  232  and  233 ,  234  of the housings  210 ,  211  are positioned so as to each surround and support a substrate  205 ,  206  of a particular diameter and in a horizontal orientation. The rollers  231 ,  232  and  233 ,  234  include grooves  236 ,  237 ,  238  and  239  adapted to hold and secure the edge of a substrate  205 ,  206 ; the grooves  236 ,  237 ,  238 ,  239  may be V-shaped (as shown) or any other suitable shape. 
         [0030]    A single controller  250  (as shown) or multiple controllers may be coupled to the motors  240 ,  241  and thereby control the motion and/or rotation of the rollers  231 ,  232 ,  233  and  234  and/or the raising and/or lowering of the housing  210 ,  211 . The controller  250  may also receive signals from rotation sensors (not shown) that monitor the rotation of the rollers  231 ,  232 ,  233 ,  234  and/or the substrates  205 ,  206  (as previously described). 
         [0031]    One of the advantageous features of the multiple-substrate module  200  is that vibrational energy produced by a transducer may be distributed over multiple substrates, which can reduce power needs and costs. For example, as shown in  FIG. 2 , a first transducer  261  may be positioned between the housings  210 ,  211  wholly or partially submerged within the cleaning fluid in the tank  220 . Lateral back-and-forth movements of the transducer  261  generate vibrations that may propagate horizontally toward both housings  210 ,  211  and the substrates  205 ,  206  held therein. 
         [0032]    As in the embodiment depicted in  FIG. 1 , additional or alternative transducers may be included that direct vibrational energy primarily perpendicularly onto the substrates  205 ,  206 . For example, a second transducer  262  may be positioned adjacent to the bottom of the tank  120  and oriented to generate vibrational energy that travels through the tank  220  and cleaning fluid to impact the bottom surface of substrate  205  from below, approximately perpendicular to the bottom major surface of the substrate  205 . The second transducer  262  may have a size that is similar to the size of the substrate  205  in order to generate vibrational energy that encompasses the entire area of the substrate  205 . Similarly, a third transducer  263  may be positioned adjacent to the bottom of the tank  120  and oriented to generate vibrational energy that travels through the tank  220  and cleaning fluid to impact the bottom major surface of the substrate  206  (e.g., approximately perpendicularly). Fewer or a larger number of transducers may be used. The controller  250  may be adapted to control operation of the transducers  261 ,  262 , and/or  263 . Each transducer may produce energy continuously, periodically or at any suitable cycle time. 
       Exemplary Operation of the Horizontal Megasonic Module 
       [0033]    The following describes the operation of a single horizontal megasonic module. However, the description applies equally to a multi-substrate module unless otherwise indicated. 
         [0034]    In operation, according to some embodiments of the present invention, before mega sonic cleaning commences, a substrate is brought to the housing  110  by a transfer device (not shown) such as a robot. The housing  110  at this point may be positioned above the tank  120 , out of contact with the cleaning fluid. To receive a substrate, the motor  140  or another mechanism moves one or more of the rollers  131 ,  132  horizontally outward into a receiving position, and the robot moves the substrate between the rollers  131 ,  132  and at the level of the grooves  135 ,  136 . The motor  140  or other mechanism then moves the previously-moved roller(s) back into a gripping position ( FIG. 1 ). Enough force is applied by the rollers  131 ,  132  to secure the substrate in place and for the rollers  131 ,  132  to be in frictional contact with the edge of the substrate. The robot then releases the substrate and moves out of the module  100 . 
         [0035]    With the substrate in place, the housing  110  is lowered via the shaft  115  into the tank  120 . In some embodiments, the housing  110  may descend into the tank  120  at a tilt to avoid air being trapped beneath the housing  110 , which could lead to bubble formation. The tilt may be at or around 10 degrees from horizontal, for example, although larger or smaller tilt angles may be used. The housing  110  may be lowered until at least the substrate is completely submerged in the cleaning fluid and preferably until the rollers  131 ,  132  are completely submerged as well. The housing  110  may remain tilted or be returned to an approximately horizontal orientation. 
         [0036]    Once submerged, the motor  140  may start the rotation of one or more of the rollers  131 ,  132  which, in turn, cause rotation of the substrate by frictional contact. The transducer(s)  161 ,  162  and/or  163  are activated to direct and transmit vibrational energy through the fluid to the substrate. In some embodiments, at least one of the transducers may direct vibrational energy substantially parallel to the major surface(s) of the substrate. In various embodiments and configurations, additional transducers may be used, one or more of which may direct vibrational energy perpendicularly with respect to the major surface(s) of the substrate. The vibrational energy unsettles and/or dislodges particles from substrate surfaces. Due to the rotation of the substrate, the vibrational energy is distributed over the substrate surface, which improves the efficiency and accuracy of the cleaning. 
         [0037]    Fresh cleaning fluid may be continuously, periodically or otherwise supplied from a conduit (not shown) which may force used cleaning fluid to overflow the tank  120 . The overflow may be captured by a reservoir (not shown) and either recycled or disposed of downstream. 
         [0038]    Operation of the multi-substrate horizontal megasonic module  200  may be similar to that of the single substrate module  100  described above. A first substrate may be cleaned using the first housing  210  while a second substrate may be cleaned using the second housing  211  at the same time, at a different time, independently of or in coordination with the first substrate. 
         [0039]    Accordingly, while the present invention has been disclosed in connection with specific 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.