Patent Document

FIELD OF THE INVENTION  
         [0001]    The present invention relates to chemical mechanical polishing (CMP) tools, and more particularly, to cleaning apparatuses for use in CMP tools.  
         BACKGROUND  
         [0002]    Chemical mechanical polishing (CMP) tools are typically used to planarize the surface of a semiconductor wafer or to remove a portion of a layer formed on the semiconductor wafer, undergoing fabrication of circuits thereon, by processes such as the damascene and dual damascene. Some CMP tools also include a mobile or stationary carrier to hold a wafer, and a mobile or stationary platen or table equipped with a polish pad. The CMP tool imparts relative motion between the wafer surface and the polish pad. The CMP tool causes the polish pad and the wafer surface to come into contact, typically applying a specified pressure between the polish pad and the wafer surface sufficient to thereby polish the wafer surface, by removal of some material from its surface. In addition, the CMP tool typically introduces a slurry or reactive chemical at the interface between the polish pad and the wafer surface. The slurry can have abrasive particles suspended in a chemical solution that reacts with selected materials on the wafer surface. The pressure, slurry and relative motion effectuate the polishing process.  
           [0003]    Typically at the end of a CMP process step there is a subsequent cleaning step to remove debris and residual slurry. Some cleaning apparatuses place the wafer in a horizontal position with a cleaning solution being applied to permit effective cleaning with the brush. Because each wafer is being cleaned in a horizontal position, the cleaning apparatus may occupy a relatively large footprint, especially if multiple wafers are being cleaned. Further, the trend in the industry is to increase wafer size, which will tend to further increase cleaning apparatus footprints. Moreover, horizontal apparatuses undesirably have a relatively large contact area between the wafer and the fabrication environment, which might increase the risk of contamination of the wafer and/or the clean room environment. Additionally, due to industry demand for increased throughput, there is a need for the ability to clean multiple wafers simultaneously. Therefore, there is a need for an alternative to prior art apparatuses and methods of cleaning wafers.  
         SUMMARY  
         [0004]    In accordance with embodiments of the present invention, a multiple wafer (or workpiece) cleaning apparatus is provided that permits cleaning of multiple wafers simultaneously while maintaining a relatively small footprint in the fabrication environment.  
           [0005]    In one embodiment of the present invention, the cleaning apparatus includes a first pair of spaced-apart brushes with supports for holding a workpiece, and a second pair of spaced-apart brushes, with supports for holding another workpiece. The brushes are rotatable, with one of each pair of brushes movable axially toward the other brush of the pair so that the brushes contact a workpiece with a controlled pressure.  
           [0006]    In another embodiment the invention utilizes a controller in communication with pairs of brushes. The controller causes the brushes to rotate and come into contact with the workpieces. Parameters such as the axial brush forces, cleaning cycle duration, brush rotation speeds, and rotation directions of the pairs of brushes are controllable via signals provided by the controller in this embodiment.  
           [0007]    In a further embodiment of the present invention, the diameter of each brush assembly may be greater than the radius of the wafers. During the cleaning process, the workpieces are loaded into the machine and supported, with the center of the workpiece being offset from the center of rotation of the brushes. During cleaning, the brushes are brought into contact with opposite sides of the wafers and the brushes are rotated, thereby causing the workpiece to rotate through frictional forces. This embodiment of the invention advantageously eliminates the need for a separate unit to rotate the workpieces, although such a unit may be used in conjunction with the brushes, as described here.  
           [0008]    According to another embodiment of the present invention, the brushes can each rotate at the same speed, different speeds or in different directions, thereby creating a differential relative velocity between the brushes and the workpiece surfaces resulting in forces tangential to the workpiece surfaces that assist in cleaning the workpieces. Cleaning fluid can be introduced to the workpiece surface or issued directly through the brush material or through distribution holes in the brushes.  
           [0009]    In another embodiment of the present invention, a cleaning fluid is introduced to at least a portion of the workpieces to facilitate the cleaning process. The fluid can be used to flush away and/or react with debris, which has accumulated on the workpieces. In yet another embodiment of the present invention, the apparatus includes a tank or tanks to hold the fluid, with at least a portion of the workpieces being submerged so that the workpieces rotate through the fluid. This allows the workpieces to more readily contact the cleaning solution to assist the brushes in the cleaning the workpieces. In still another embodiment the tanks can be filled to completely submerge the wafers.  
           [0010]    In a further embodiment of the invention, a megasonic transducer is introduced into the cleaning solution tanks so that sonic waves further assist in cleaning portions of the workpieces submerged in the cleaning solution, as the workpieces rotate.  
           [0011]    Additionally, in yet another embodiment of the invention there are no brushes, but instead the workpiece rests on support rollers at least one of which is coupled to a drive motor. This embodiment allows for brushless cleaning primarily using the cleaning solution, optionally in conjunction with the megasonic transducers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The foregoing embodiments and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying illustrative drawings that are not necessarily to scale, wherein:  
         [0013]    [0013]FIG. 1 is an isometric view of a dual wafer vertical cleaning apparatus according to an embodiment of the invention.  
         [0014]    [0014]FIG. 2 is a schematic cross sectional front view of a dual wafer vertical cleaning apparatus according to an embodiment of the invention.  
         [0015]    [0015]FIG. 3 is a schematic cross sectional side view of a dual wafer vertical cleaning apparatus according to an embodiment of the invention.  
         [0016]    [0016]FIG. 4 is an exploded view showing pertinent detail of one of the wafer vertical cleaner modules of a dual wafer vertical cleaning apparatus according to an embodiment of the invention.  
         [0017]    [0017]FIG. 5 is an isometric view of a dual wafer vertical cleaning apparatus according to another embodiment of the invention.  
         [0018]    [0018]FIG. 6 is a block diagram according to another embodiment of the invention, illustrating a controller integrated into a dual vertical wafer cleaner.  
         [0019]    [0019]FIG. 7 is a schematic cross sectional side view of a dual wafer vertical cleaning apparatus according to an embodiment of the invention.  
         [0020]    [0020]FIG. 7A is a schematic cross sectional front view of an embodiment of a drive system for a brushless cleaner. 
     
    
     DETAILED DESCRIPTION  
       [0021]    A vertical cleaning apparatus according to the present invention potentially reduces clean room costs by achieving a reduced footprint as compared to a horizontal cleaning apparatus. The vertical cleaning apparatus also allows for multiple workpiece cleaning, due to its modular design, and therefore can be configured to clean any number of workpieces. In addition, a vertical apparatus according to the present invention potentially reduces the risk of contamination by reducing the contact area between the workpiece and its cleaning solution, and the clean room environment. The present invention in one embodiment uses a velocity differential between brushes and workpieces to achieve cleaning, while the workpieces are in a vertical position. Further, a vertical cleaning apparatus according to the present invention permits a megasonic cleaning process of both sides of a workpiece concurrently with cleaning using brushes and having one or more transducers, thereby eliminating the need for a separate subsequent megasonic cleaning step. An embodiment of a vertical cleaning apparatus according to the present invention is described herebelow, with reference to attached figures.  
         [0022]    [0022]FIG. 1 illustrates a dual wafer vertical cleaning apparatus  10  according to one embodiment of the invention. This embodiment includes a first cleaning module  12  and a second cleaning module  14  with the potential for additional modules to be added as necessary. The modules function independently of each other, providing the advantage that one may continue to operate if the other were to experience a disabling failure. Additionally, due to the functional independence in certain embodiments, each module can operate using a different cleaning protocol as needed.  
         [0023]    [0023]FIG. 2 is a schematic cross sectional front view of a dual wafer vertical cleaning apparatus according to an embodiment of the invention. The dual wafer cleaner may be divided into two sections by a vertical plane c-c, as shown in the illustration. Relative to this plane, we define an “inner” component to mean one closer to plane c-c, and “outer” to be one further from the plane. Thus, the inner brushes are  21   a  and  22   a.    
         [0024]    Referring to FIGS. 2 and 3, each module  12  and  14  contains a spaced-apart brush assembly  21  and  22  respectively. Workpieces  25  are loaded between brushes  21   a ,  21   b ,  22   a ,  22   b  of spaced apart brush assemblies  21  and  22 . First brush assembly  21  has an inner brush  21   a  and an outer brush  21   b  relative to line c-c, and second brush assembly  22  has an inner brush  22   a  and an outer brush  22   b  relative to line c-c. The workpieces  25  rest on the rotatable supports  27 . The rotatable supports  27  are each located between and below the irrespective brush assemblies. In this embodiment, the rotatable supports  27  include a set of four rollers (see FIG. 2) but in other embodiments more or less rollers could be used, so long as the workpieces  25  are adequately supported throughout the cleaning process in a vertical orientation.  
         [0025]    During operation, each brush within its assembly rotates independently of the other. The downforce assembly  23  (detailed in FIG. 4) applies force to the outer brush  21   b  and  22   b  of each brush assembly. The pressure applied, in combination with the rotation of the brushes of the brush assemblies, imparts a rotational motion onto the workpieces  25 . The workpieces  25  may rotate at a slower rate than the brushes of each brush assembly thereby creating a velocity differential between the workpieces  25  and the brush assemblies which in turn allows the brushes to slide across the workpiece surfaces creating tangential forces that sweep and dislodge debris from the surface of the workpieces  25 . The individual brushes of each set may rotate at the same angular velocity or, alternatively, the brush velocities may differ to obtain a different cleaning format with the velocity of rotation of the brushes independently set in this or other embodiments of the dual wafer vertical cleaning apparatus  10 . Further, brushes with different characteristics (e.g. stiffeners, materials, etc.) may be used with differing angular velocities.  
         [0026]    In a further refinement, the relative velocity can be changed as desired during the cleaning operation. For example, the relative velocity can be changed during the cleaning operation by causing the brush that was initially rotating faster than the slower brush to reduce its angular velocity and become the brush that is rotating slower. Any number of these directional reversal cycles can be used to obtain the desired cleaning profile.  
         [0027]    In this embodiment (referring to FIGS. 2 and 3), workpieces  25  are disposed between the spaced-apart brush assemblies  21  and  22  so that a portion of the each workpiece  25  extends beyond an edge of brushes. Preferably, the contact area between the workpieces and the brushes, combined with rotation of the workpieces, are designed so that the entire surface of each workpiece  25  will come into contact with brushes with a workpiece rotating at a velocity relative to the brushes. In other embodiments the brushes may completely cover the workpieces (e.g., the spaced-apart brushes may have a greater diameter than the workpiece, for example twice the diameter of the workpiece). In such an embodiment, the first and second brush assemblies can be rotated with the centers of rotation of the brushes being offset with respect to the center of rotation of the workpieces.  
         [0028]    As shown in FIGS. 2 and 3, dual wafer vertical cleaning apparatus  10  may include a tank  28 , for each spaced-apart brush assembly  21  and  22 , each tank containing cleaning solution  26 . Support members  27  are located in the tanks  28  so that as the brush assemblies  21 ,  22  are rotated, a portion of each of the workpieces  25  rotates through the cleaning solution  26  in the respective tank  28 , and then continues on to rotate into contact with the respective brushes. Cleaning solution  26  adhering to the surface of the workpieces  25  assists the brushes in cleaning the workpiece surfaces. This embodiment additionally has a drain hole  24  located along the base of each tank  28  to facilitate removal of the cleaning solution  26 . In other embodiments, the spaced-apart brush assemblies may be located or sized so that the brushes are not submerged in the cleaning solution  26 , which may help lengthen the useful life of the brushes.  
         [0029]    In still a further refinement, dual wafer vertical cleaning apparatus  10  may include a megasonic transducer  29  disposed within each tank  28 . Each megasonic transducer  29  is submerged in the cleaning solution  26  contained in each tank  28 . Support members  27  are positioned in the each tank  28  so that at least part of each workpiece  25  is submerged in the cleaning solution  26 , as shown in FIG. 2. Activation of megasonic transducers  29  results in the generation of sonic pulses in the cleaning fluid  26  to further clean workpieces  25 . This embodiment allows megasonic cleaning in conjunction with brush cleaning and allows for the placement of the megasonic transducers  29  anywhere in the tank  28  below the fluid surface to facilitate the cleaning process. Thus, the addition of megasonic transducers  29  into this dual wafer vertical cleaning apparatus  10  can eliminate a step in a cleaning process (i.e., a prior or subsequent separate megasonic step), and allows for a reduction in footprint of the overall cleaning process (i.e., the footprint of a separate megasonic cleaning station).  
         [0030]    [0030]FIG. 4 is an exploded view of a single wafer vertical cleaner module of dual wafer vertical cleaning apparatus  10  according to one embodiment of the invention. In this embodiment wafer  25  is loaded between the spaced-apart inner brush  21   a  and spaced-apart outer brush  21   b . Spaced-apart brushes  21   a  and  21   b  each have a platen  103  with an attached brush pad  102 . In this embodiment, brush pads  102  are respectively attached to platens  103  such as, for instance, by a mechanical attachment. For example, the brushes may be fitted with an elastic band, which may be stretched to fit over the platen. Brush pad  102  may also be affixed to the platen by other mechanical means, fittings, or by chemical adhesives, preferably so that the brush pad  102  may be removed and replaced when worn out. Brush pads  102  and  103  are configured in a pancake style configuration with the workpiece supported or sandwiched between the two pads. The pad is not necessarily equipped with bristles, but with a surface adapted for cleaning the workpiece surface. Thus, any type of pad suited to the cleaning operation can be implemented and is herein known as a “brush,” or “brush pad” so long as it meets the requirements of the application. In light of the disclosure, brushes can be implemented by those skilled in the art of CMP tools without undue experimentation, an example of which is produced by Syntak Division, San Jose, Calif.  
         [0031]    As shown in FIG. 4, one or more support rollers  27  are located between and below the spaced-apart brushes  21   a  and  21   b  to provide support for workpiece  25  during the cleaning process. These supports are preferably rotatable, and are located within the tank  28  so that as the spaced-apart brushes  21   a  and  21   b  are rotated, a portion of the supported workpiece  25  rotates through a cleaning solution in tank  28 . In this embodiment, as shown in FIG. 4, tank  28  includes a first tank half  28   a , a second tank half  28   b , and a tank cover  28   c . Megasonic transducer  29  is disposed within tank  28 . The megasonic transducer  29  provides sonic emissions that are transmitted via the cleaning fluid to the workpiece to provide additional cleaning of the workpiece  25  in concert with brush cleaning provided by the brushes  21   a  and  21   b . In one embodiment the transducer&#39;s length is approximately equivalent to the distance between the furthest edges of spaced-apart brushes  21   a  and  21   b . Alternatively, megasonic transducer  29  can be of a different size, so long as it can be contained inside and below the cleaning solution level in tank  28 . The fluid  26  (as depicted in FIG. 3) in tank  28  enters the tank  28  through fill hole  112  and can be of any suitable cleaning fluid such as, for example, an ammonium hydroxide solution.  
         [0032]    The embodiment of FIGS. 2 and 4 also provides drive mechanisms for each brush of brush assemblies  21  and  22 . The drive mechanisms comprises a motor coupled to a gear box as illustrated by gear/motor assembly  113  and located below each tank  28 . Each motor provides drive to the brushes  21   a  and  21   b  respectively via a shaft, belt and pulley system. This shaft and pulley system includes a motor shaft pulley  110  in communication with the motor and the platen shaft pulley  108  by way of a drive belt  109 . The platen shaft pulley  108  imparts a drive motion onto platen shaft  107 , which in turn drives either the inner spaced-apart brush  21  a or the outer spaced-apart brush  21   b . Platen shaft  107  rotates with the platen shaft clamp  120  which applies downforce to the platen shaft  107 , and thus to a workpiece  25  via thrust bearing  124 . Thrust bearing  124  is contained in thrust bearing housing  123 . Force is supplied by a downforce air cylinder  122 , which is contained in a downforce bracket  121 .  
         [0033]    In this embodiment cleaning brushes  102  contact the workpiece  25  with a pressure of about 0.5 to about 1.2 psi, although the pressure can range from about 0 psi to about 6 psi, depending on the cleaning application. In one embodiment, thrust bearing housing  123  is configured to move brush  102  of spaced-apart brush  21   a  toward the opposing brush  102  with a downforce of about 1 psi. In a further embodiment of the invention, the pressure can be varied during a workpiece cleaning operation. For example, the pressure can be reduced in conjunction with a reversal of the relative differential rotational direction. In this embodiment, the workpiece is subjected to the cleaning process for about 30 seconds. The duration of the cleaning process may vary from about 20 to about 120 seconds, and in other embodiments it may vary, typically depending on the type of brushes being used, the cleaning fluid, the rotational velocity of the brush assemblies, the workpiece, etc. Still further, the rotational velocity and pressure can be optimized for particular brush pads and cleaning applications. For example, these parameters can be controlled and adjusted one or more times during a single cleaning operation, for an optimal cleaning operation.  
         [0034]    [0034]FIG. 5 is another embodiment that includes a first cleaning module  12  and a second cleaning module  14 . The cleaning modules are placed in echelon, having the same orientation as compared to previous embodiments, which were in opposition.  
         [0035]    In a further embodiment detailed in FIG. 6, a controller  61  is used to communicate with the brush assemblies  21  and  22 . The controller  61  would cause the required motors to drive spaced-apart brushes  21   a ,  21   b ,  22   a , and  22   b  of the assemblies to rotate and to contact the workpieces with a desired pressure, thereby causing the workpieces to rotate. The controller  61  could be configured to independently control the speed of each spaced-apart brush within brush assembly  21  or  22 . For example, the controller could cause each individual brush of a brush assembly to rotate in the same or opposite direction and with the same or different angular speed. The controller may also respond to input from sensors placed in the system to monitor pH, pressure, chemical concentration, speed, reflectivity, conductivity, motor current or other inputs as part of a closed loop control system. The controller  61  can be of any suitable type ranging from a manual controller to a controller using a microprocessor. Other embodiments may use other types of controllers (e.g., sequential state machines or other combinatorial logic circuits).  
         [0036]    [0036]FIG. 7 is a schematic cross sectional side view of a dual wafer vertical cleaning apparatus according to another embodiment of the invention. In this embodiment, support rollers  27  support the workpieces  25  with at least one roller from each set of support rollers  27  in mechanical communication with a drive motor. The driven rollers cause the workpieces  25  to rotate through cleaning solution  26  contained within tanks  28 . In conjunction with the cleaning fluid  26  are megasonic transducers  29  located below the fluid level in each tank  28  and applying sonic pulses to assist in the cleaning. The result of this embodiment is brushless cleaning of the workpieces  25 .  
         [0037]    [0037]FIG. 7A illustrates an embodiment of mechanical communication between drive motor  113  and support roller  27  via drive shaft  71 . Any number of support rollers can be mechanically driven by this method depending on the requirements of the application. Other methods, which would produce acceptable cleaning results, can be used to provide drive to the support roller  27  so long as an acceptable cleaning results can be maintained.  
         [0038]    Although the description above refers to cleaning wafers, other embodiments of the present invention can be adapted for cleaning other types of workpieces. For example, a workpiece may be semiconductor wafer, a bare silicon or other substrate with or without active apparatus or circuitry, a partially processed wafer, a silicon or insulator structure, a hybrid assembly, a flat panel display, a micro electromechanical structure (MEMS), a disk for a hard drive memory, or any other material that would benefit from cleaning or planarization such as mirrors, lenses or dishes.  
         [0039]    The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Technology Category: b