Abstract:
A wafer cleaning system is provided. The wafer cleaning system comprises a first brush, a second brush, a brush motor, and a controller. The second brush is positioned parallel to the first brush. The brush motor moves at least one of the first and second brushes from a first position to a second position according to a driving current of the brush motor.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to semiconductor manufacturing and more particularly to a system for cleaning wafers.  
         [0002]     Polishing slurries used for planarization processes, such as chemical-mechanical polishing (CMP) processes, are typically aqueous suspensions, comprising metal oxide abrasive, organic acids, surfactants, and a suitable oxidizing agent. The oxidizing agent enhances mechanical removal of material via a corrosion assisted process. Such oxidizing agents employed in commercially available or proprietary slurries are typically inorganic metal salts such as FeNO 3 , or KIO 3 , and also hydrogen peroxide. Other chemicals, such as organic acids, are added-to slurries to improve dispersion and/or enhance performance. Sodium, potassium, and iron salts and/or compounds are frequently used in slurry formulations, and significant measurements of these metal ion impurities remain on the wafer after polishing and post-polish cleaning. The particulate materials are extremely difficult to remove without adversely affecting the polished surface.  
         [0003]      FIG. 1A  illustrates a brush assembly employed in a conventional post-CMP cleaning process.  FIG. 1A  illustrates a simplified three dimensional diagram of a pair of brushes  120   a  and  120   b  for scrubbing a top surface and a bottom surface, respectively, of a wafer  130 . Typically, the wafer  130  is caused to rotate in a particular direction while the brushes  120   a  and  120   b  roll around an axis, and the surfaces of the brushes  120   a  and  120   b  press against the surfaces of the wafer  130 . The brushes  120   a  and  120   b  are mounted on brush cores  100   a  and  100   b , respectively. Brushes  120   a  and  120   b  are generally made of (polyvinyl alcohol) PVA, and expand during the lifetime thereof. Typically, positions of brush cores  100   a  and  100   b  are fixed during the lifetime of the brushes  120   a  and  120   b.  As the brushes expand, the surfaces of the brushes  120   a  and  120   b  exert increased pressure on the wafer  130 . Referring to  FIGS. 1B and 1C , the distance between brush cores  100   a  and  100   b  is d. In  FIG. 1C , brushes  120   a  and  120   b  expand, and more pressure is exerted on wafer  130 . Additionally, as the brushes exert increased pressure on the wafer surface, severe particulate contamination may occur.  
       SUMMARY  
       [0004]     Wafer cleaning systems are provided. An exemplary embodiment of a wafer cleaning system comprises: a first brush; a second brush; a brush motor, and a controller. The second brush is positioned parallel to the first brush. The brush motor rolls the first and second brushes, respectively. The controller moves at least one of the first and second brushes from a first position to a second position according to a driving current of the brush motor.  
         [0005]     Workpiece processing methods are provided. An exemplary embodiment of a workpiece is cleaned with a pair of rolling brushes positioned at a first position. A measurement of a driving current is received, wherein the driving current is utilized to roll the brush when it is at the first position. A preset schedule is provided, specifying the relationship between the driving current and the distance between the outer surfaces of the first and second brushes. A second brush position is determined according to the measurement of the driving current and the preset schedule. The brushes are moved from the first position to the second position. The workpiece is cleaned with the pair of rolling brushes positioned at the second position.  
         [0006]     Methods for controlling a brush assembly are also provided. An exemplary embodiment of a brush assembly used for wafer cleaning comprises a pair of brushes positioned at a first position rolling when cleaning a wafer. A preset schedule is provided, specifying the relationship between the driving current and the distance between the outer surfaces of the first and second brushes. A measurement of a driving current is received, wherein the driving current utilized to roll the brush when it is at the first position. A second position for the pair of brushes is determined according to the measurement of the driving current and the preset schedule.  
         [0007]     The method for controlling a brush assembly may take the form of program code embodied in a tangible media. When the program code is loaded into and executed by a machine, the machine becomes a system for practicing embodiments of the invention.  
         [0008]     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0010]      FIGS. 1A  to  1 C illustrate a brush assembly and a wafer processed by a conventional wafer cleaning process;  
         [0011]      FIG. 2  is a schematic view of an embodiment of a manufacturing system;  
         [0012]      FIG. 3A  illustrates a simplified three dimensional diagram of a pair of brushes;  
         [0013]      FIG. 3B  is a partial frontal view of an embodiment of a scrubbing cleaner; and  
         [0014]      FIG. 4  is a flowchart of an embodiment of a method of wafer cleaning.  
     
    
     DETAILED DESCRIPTION  
       [0015]     The present invention will now be described with reference to FIGS.  2  to  4 , which generally relate to a manufacturing system implementing a method for operating a brush assembly.  
         [0016]     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration of specific embodiments. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The leading digit(s) of reference numbers appearing in the Figures corresponds to the Figure number, with the exception that the same reference number is used throughout to refer to an identical component which appears in multiple Figures.  
         [0017]      FIG. 2  is a schematic view of an embodiment of a manufacturing system according to the invention. Manufacturing system  200  is a semiconductor manufacturing system performing CMP and cleaning processes on a semiconductor wafer.  
         [0018]     The manufacturing system  200  comprises a processing station  20 , a Computer Integrated Manufacturing system (CIM)  23 , and a Fault Detection Control system (FDC)  25 . The CIM  23  and FDC  25  connect to databases  24  and  26 , respectively.  
         [0019]     The processing station  20  performs a CMP process and a post-CMP cleaning process, comprising a CMP tool  210  and a cleaning tool  230 .  
         [0020]     The CMP tool  210  comprises platens  211 ˜ 213 . Platens  211 ,  212 , and  213  are used for different CMP stages, wherein different types of polishing slurry and different processing recipes are used in those different CMP stages. For example, a first CMP stage is performed at platen  211 , wherein a buck of material, such as Cu, is removed. An eddy current endpoint mechanism is used in the first stage for detecting a process endpoint. A second CMP stage is performed at platen  212 , wherein a lower down force is implemented, and the wafer surface is further polished. An i-scan endpoint mechanism is used in the second stage for detecting a process endpoint. A third CMP stage is performed at platen  213 , wherein a final polishing is performed. A processing time mechanism is used in the third stage for determining a process endpoint.  
         [0021]     The cleaning tool  230  comprises a megasonic cleaner  231 , scrubbing cleaners  232  and  233 , and a dryer  234 . The megasonic cleaner  231  performs a cleaning process on a wafer using a megasonic mechanism after the wafer is processed by the CMP tool  210 . The scrubbing cleaners  232  and  233  perform a wafer cleaning process using a brush assembly, respectively. The structure and operation of the scrubbing cleaners  232  and  233  are detailed in the following. The dryer  234  uses isopropyl alcohol (IPA) drying mechanism to remove water and moisture from the wafer processed by the megasonic cleaner  231  and scrubbing cleaners  232  and  233 .  
         [0022]      FIG. 3A  illustrates a simplified three dimensional diagram of a pair of brushes  32   a  and  32   b  for scrubbing a top surface and a bottom surface, respectively, of a wafer  30 . Typically, the wafer  30  is caused to rotate in a particular direction while the brushes  32   a  and  32   b  roll around an axis, and the surfaces of the brushes  32   a  and  32   b  press against the surfaces of the wafer  30 . The brushes  32   a  and  32   b  are mounted on brush cores  31   a  and  31   b , respectively. The brushes are generally made of (polyvinyl alcohol) PVA, and expand during the lifetime thereof. Rolling of the brushes  320   a  and  320   b  is driven by a driving current. Measurement of the driving current used during the cleaning processes is obtained and stored by the scrubbing cleaners  232  and  233 , respectively. The measurement is transmitted to CIM  23 , and stored in database  24  as record  241 . The FDC  25  periodically retrieves the record  241  from the database  24  via the CIM  23 . A preset schedule  261  is stored in database  26 , specifying the relationship between the driving current and the distance between the pair of brushes. The FDC  25  calculates an average of driving current for measurements obtained during processing of each wafer within a lot, and controls the positioning of the pair of brushes according to the average and the preset schedule  261 .  
         [0023]      FIG. 3B  is a partial frontal view of an embodiment of a scrubbing cleaner of the invention. As shown in  FIG. 3B , initially brushes  32   a  and  32   b  are at positions  391   a  and  391   b , respectively (indicated by dashed circles). Wafer  30  is then inserted vertically between brushes  32   a  and  32   b  by a robotic arm (not shown). Brushes  32   a  and  32   b  are then moved towards each other to positions  395   a  and  395   b,  respectively. Typically, brushes  32   a  and  32   b  move approximately 0.5 inches between positions  391   a  and  395   a,    391   b  and  395   b,  respectively. At positions  395   a  and  395   b,  brushes  32   a  and  32   b  contact first and second surfaces  30   a  and  30   b , respectively, of wafer  30 . The level of the driving current for rolling brushes  32   a  and  32   b  is proportional to perpendicular component of force (force exerted perpendicular to planes formed by surfaces  30   a  and  30   b  of wafer  30 ) exerted by brush  32   a  (and brush  32   b ) on wafer  30 .  
         [0024]     As shown in  FIG. 3B , brush  32   a  is rotated clockwise and brush  32   b  is rotated counterclockwise. A plurality of spray nozzles, such as spray nozzles  351 ,  352 ,  353 , and  354 , spray liquid on brushes  32   a  and  32   b , and wafer  30 , respectively. The liquid can be a surfactant and/or be de-ionized water. The combination of the scrubbing action on the surfaces  30   a  and  30   b  of wafer  30  caused by the rotation of brushes  32   a  and  32   b  along with liquid supplied through spray nozzles  351 ˜ 354 , removes particulates from surfaces  30   a ,  30   b  of wafer  30 . In particular, particulates are scrubbed from surfaces  30   a  and  30   b  by brushes  32   a  and  32   b , respectively. These particulates are flushed from brushes  32   a  and  32   b  by the liquid supplied to brushes  32   a  and  32   b  through brush cores  31   a  and  31   b.  Further, particulates which are loosened by the scrubbing action of brushes  32   a  and  32   b , but remain on surfaces  30   a  and  30   b  of wafer  30 , are flushed from surfaces  30   a  and  30   b  by liquid sprayed from sets of spray nozzles. By orienting wafer  30  vertically instead of horizontally, the removal of particulates from the surfaces  30   a  and  30   b  is enhanced.  
         [0025]      FIG. 4  is a flowchart of an embodiment of a method of the invention.  
         [0026]     First, a preset schedule is provided, specifying the relationship between the driving current and the distance between the outer surfaces of the first and second brushes (step S 41 ). The preset schedule can be determined by experimenting and/or historical process data recorded during previous processes.  
         [0027]     In step S 42 , a workpiece is cleaned with a pair of rolling brushes, wherein the pair of the brushes is positioned at a first position.  
         [0028]     During the cleaning process, a measurement of a driving current for the brush rolling is obtained when the pair of brushes is positioned at the first position (step S 43 ). The measurement is obtained by a cleaning tool, transferred to and stored in a CIM system. The CIM system stores measurements obtained during a plurality of process runs in a database. The stored measurements are retrieved from the CIM system, and used for cleaner adjustment periodically. Typically, a cleaning brush, such as a PVA brush, undergoes cleaning processes for 400˜500 wafers before it is severely worn. The texture and size of the brush changes during its lifetime, causing changes in a downward pressure exerted on a workpiece. Here, the data retrieval and cleaner adjustment can be performed at a lower frequency during the early in the life of the brush, and a higher frequency later in the life of the brush.  
         [0029]     In step S 44 , stored measurements are retrieved from the CIM system, and used for cleaner adjustment. In step S 45 , a second position for the pair of brushes is determined according to the preset schedule and the retrieved measurements. Moving the pair of brushes from the first position to the second position compensates for brush wear. In step S 46 , the pair of brushes is moved from the first position to the second position. In step S 47 , a cleaning process is performed using the pair of brushes positioned at the second position.  
         [0030]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. Those skilled in this technology can still make various alterations and modifications without departing from the scope and spirit of this invention. Therefore, the scope of the present invention shall be defined and protected by the following claims and their equivalents.