Abstract:
A polishing apparatus comprises a housing defining a chamber wherein articles to be polished are subject to polishing and cleaning operations; partition walls for dividing the chamber of the housing into a plurality of sections; and, an air exhaust device. The exhaust device comprises a plurality of air exhaust conduits which are fluidly connected to the sections in the housing to exhaust air from the sections; valves for closing and opening the respective air exhaust conduits, respectively; and, a control for independently controlling the respective valves to regulate air flows exhausted through the conduits. The conduits have inlet openings located in a vicinity of spaces where any air pollutant is generated in the sections of the housing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a system for polishing articles such as semiconductor wafers, which is provided with an air exhaust system for creating a negative pressure in a housing of the polishing system.  
           [0002]    In the production of semiconductor devices, it is common to use a polishing system in which semiconductor wafers are subjected to a so-called chemical mechanical polishing (CMP) process to form a highly planarized surface for formation of an integrated circuit- In a chemical mechanical polishing process, semiconductor wafers are slidably engaged with and moved relative to a polishing surface, which surface is usually provided on the upper side of a turntable, and a chemical polishing liquid referred to as slurry is concurrently supplied onto the polishing surface.  
           [0003]    Semiconductor devices are produced in a clean room, and a polishing system such as that mentioned above is installed in the clean room. In a polishing operation pollutants are generated: these may include: particles of polishing liquid scattered from a polishing surface; debris generated from a wafer or from a polishing surface; particles generated in driving assemblies for driving a turntable, and in cleaning machines for cleaning wafers which have been polished, and also in wafer transporting devices; and harmful gases emitted from a chemical cleaning liquid. It is necessary to prevent such pollutants from leaving a housing of a polishing system and entering a cleaning room space. To this end, a pressure In a housing of a polishing system is kept lower than that in a clean room by exhausting or drawing out air from the housing.  
           [0004]    However, since a volume of a housing of a polishing system is large, a large amount of energy is required to create a negative pressure in the housing relative to a clean room.  
         SUMMARY OF THE INVENTION  
         [0005]    Accordingly, it is an object of the present invention to provide a polishing system with an air exhaust system which can efficiently exhaust or draw out air from the housing to create negative pressures In the housing which are required to prevent pollutants, such as particles of a polishing liquid, from leaking from the housing.  
           [0006]    According to one aspect of the present invention, there is provided a polishing system comprising:  
           [0007]    a housing defining a chamber in which articles to be polished are subject to polishing and cleaning operations;  
           [0008]    partition walls for dividing the chamber of the housing into a plurality of sections; and,  
           [0009]    an air exhaust device comprising:  
           [0010]    a plurality of air exhaust conduits which are fluidly connected to sections in the housing to exhaust air from the sections:  
           [0011]    valves for closing and opening respective air exhaust conduits, the conduits having inlet openings located in a vicinity of spaces where any air pollutant is generated in the sections of the housing; and,  
           [0012]    a control for independently controlling the respective valves to regulate air flows exhausted through the conduits,.  
           [0013]    In the polishing system of the present invention, since the inlet openings of the conduits are positioned in a vicinity of spaces where an air pollutant may be generated in the polishing system housing, any air pollutant can be efficiently discharged from the housing to prevent leakage of an air pollutant from the housing into the space of the clean room, even in a case that a negative pressure employed in the housing is not as great as that employed in a housing of a conventional polishing system having an air exhaust system. Further, in the polishing system of the present invention, it is possible to independently control the respective valves. This makes it possible for the air exhaust system to perform an efficient and effective air exhaust operation, by conducting such an operation on the basis of various conditions such as an air pressure In various sections in the housing of the polishing system, a degree of air pollutant in the same and so on. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Further objects and advantages of the present invention will be apparent from the following description made with reference to the accompanying drawings showing a preferred embodiment of the present invention.  
         [0015]    In the drawings:  
         [0016]    [0016]FIG. 1 is a top plan view of a polishing system in accordance with an embodiment of the subject invention, with the ceiling wall of a housing of the polishing system cut away to provide a clear view of the inside of the housing; and,  
         [0017]    [0017]FIG. 2 is a schematic cross sectional side elevation view of the main portion of the polishing system of FIG. 1 showing an air exhaust system installed in the polishing system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    As shown in FIGS. 1 and 2, a polishing system in accordance with a preferred embodiment of the present invention has a housing  10  which is divided by partition walls  13  into a pair of polishing sections  11 ,  11 , and a cleaning section  12  and a wafer intake/outtake section  25 , the outside of which is adapted to receive wafer storage cassettes  27 - 1 ,  27 - 1 ,  27 - 3  and  27 - 4 .  
         [0019]    In each of the polishing sections  11 ,  11 , a turntable  15  is provided, along with a motor M for drivingly rotating the turntable  15  about its vertical axis. As shown in FIG. 2, the polishing sections are divided by a partition wall  14  into an upper area in which a turntable  15  is provided, with a cup-like slurry drainage member  16  being provided to surround the turntable  15 , and a lower area in which the motor M is provided. Each of the polishing sections  11 ,  11  is further provided with a wafer carrier  29 , and a pair of wafer transfer trays  17 ,  17  adapted to be horizontally moved by corresponding motors such as air cylinders  17 - 1 ,  17 - 2  to either a left position or a right position, as shown in FIG. 1. The wafer carrier  29  is pivotable about a vertical axis  29 - 1  between a position shown in FIG. 1 where the wafer carrier brings a wafer into contact with the polishing surface provided on the upper side surface of the turntable  15 , and a position where the wafer carrier  29  is positioned above the wafer transfer tray  17  at the left position to receive a pre-pollshlng wafer from the wafer tray  17 , or to return a post-polishing wafer onto the wafer tray  17 . In FIG. 2, reference numeral  18 - 1  denotes a first wafer lift having a motor such as air cylinder provided at its lower end for moving the first wafer lift either up or down to transfer a wafer from the wafer tray  17  at the left position to the wafer carrier  29 , and vice versa. Reference numeral  18 - 2  denotes a second wafer lift which is also provided at its lower end with a motor for moving the second wafer lift  18 - 2  either up or down to transfer a wafer from the wafer tray  17  at the right position to a reverser  30  provided over the wafer tray  17 , and vice versa. The reverser  30  is adapted to turn upside down a wafer received from a transfer robot  23  provided inside the cleaning section  12  (to be described in detail later) to pass the wafer to the second wafer lift  18 - 2 , and also to turn upside down a wafer received from the second wafer lift  18 - 2  to pass it to the transfer robot  23 .  
         [0020]    In the cleaning section  12 , there a pair of primary cleaning machines  19 ,  19  is provided along with a pair of secondary cleaning machines  20 ,  20  arranged in tandem. In the center area of the cleaning section  12 , there are provided the transfer robot  23  and a wafer table  24 . The transfer robot  23  is adapted to take up a pre-polishing wafer supplied onto the table  24  from the wafer intake/outtake section  25  and transfer it to the reverser  30  in the polishing section  11 , and to take up a polished wafer from the reverser  30  to transfer it first to the primary cleaning machine  19 , and then to the secondary cleaning machine  20  The secondary cleaning machine  20  can perform a spinning dry operation in addition to the wafer cleaning operation so that the wafer is substantially completely dried.  
         [0021]    In the wafer intake/outtake section  25 , there is provided a transfer robot  26  adapted to take out a pre-polishing wafer from any one of the wafer storage cassettes  27 - 1 ,  27 - 2 ,  27 - 3  and  27 - 4  and place it on the wafer table  24  in the cleaning section  12  and to take up a polished wafer from the secondary cleaning machine  20  and return it to one of the wafer storage cassettes.  
         [0022]    [0022]FIG. 2 shows an air exhaust system provided in the polishing system. The air exhaust system comprises a plurality of conduits L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7  that are fluidly connected to the housing  10 ; specifically, the upper and lower parts of the polishing section  11  and the cleaning section  12  of the housing. The conduits L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7  have outlet openings (not shown) connected to air draw means (not shown), for example a vacuum pump, and input openings which are, with the exception of conduit L 5 , positioned in a vicinity of spaces where an air pollutant is generated. Specifically, the inlet opening of the conduit L 1  is provided in the slurry drainage member  16  near the turntable  15  since during a polishing operation polishing liquid and debris are scattered from both a wafer being polished and the polishing surface. The inlet opening of the conduit L 2  is open to the inside of the motor casing enclosing the drive assembly of the motor M, since particles may be generated therefrom as a result of frictional engagement between movable elements of the drive assembly. The inlet openings of the conduit L 4  and L 3  are positioned near the air cylinders or motors  17 - 1 ,  17 - 2  of the wafer trays  17 ,  17 , and the air cylinders or motors of the lifts  18 - 1 ,  18 - 2 , respectively. The inlet openings of the conduit L 6 , L 7  are open to the inside of the primary and secondary cleaning machines  19 ,  20 , respectively. The conduits L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7  are provided with valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7 , respectively, which are connected to a control  22  for controlling opening and closing of the respective valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7  to independently regulate air exhausted through the conduits L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7 .  
         [0023]    The conduit L 5  is provided with a return branch to return air drawn from the cleaning section  12  to the same section through a filter  21  mounted on the top of the housing  10 . The polishing section  11  is provided with an additional air vent conduit (not denoted by any reference numeral) at the left upper portion thereof.  
         [0024]    Operation of the air exhaust system described above will now be explained. As stated above, to maintain a negative pressure in the inside of the system housing  10  relative to the clean room to prevent air leakage from the system housing  10  into the clean room, it is essential for the air exhaust system to be operated. Further, the air exhaust system is capable of generating different pressures in different sections in the system housing  10  divided by the partition walls  13  and  14 . Specifically, a pressure in the polishing section  11  which, generally, is the most susceptible to contamination by air pollutants, is made lower than that in the cleaning section  12 . Although no air exhaust conduits for the wafer intake/outtake section  25  is shown, the pressure in the section  25  is also controlled by means of air vent conduits similar to those described above. Specifically, the section  25  is usually kept at a higher pressure than the clean room as well as the sections  11  and  12 . An air supply system (not shown) may be provided to supply a clean air from the outside to the section  25  to, for example, keep the section at a high pressure relative to the other sections  11  and  12  and the clean room.  
         [0025]    The control  22  controls the valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7  taking into account air pressure and/or air contaminant conditions in respective spaces in the system housing; and it is possible to selectively open any of the valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7 . For example, during a polishing operation, only valves V 1  and V 7  will be opened when it is determined that it is sufficient to exhaust air through the conduits L 1  and L 7  to prevent pollutants generated in the polishing operation from leaking into the clean room. Such control of the valves leads to an effective saving of energy expended in creating negative pressures needed to prevent pollutant leakage into the clean room. Further, during a waiting period for a next polishing operation, only the valve V 1  may be opened while the other valves are closed, as it is generally unnecessary to conduct air exhaust through the conduits L 2 -L 7 . In a polishing system in accordance with this embodiment, while a total amount of air to be exhausted through all of the conduits L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , and L 7  amounts to 52 m 3 , an amount of air exhausted through L 1  amounts to 11 m 3 , whereby the energy for exhausting air from the polishing system is greatly decreased Furthermore, it is possible to open the valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7  intermittently during an air-exhaust operation.  
         [0026]    The control of the valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7  may be performed on the basis of air pressures in the housing sensed by pressure sensors S provided at predetermined positions in the housing. Specifically, valve control may be conducted on the basis of comparison of the sensed pressures with predetermined pressure values.  
         [0027]    Although a specific embodiment of the present invention has been described in the foregoing, it should be understood that the present invention is not limited to this embodiment, and a variety of modifications and changes are possible within the spirit and scope of the present invention. For example, the valve control as described above will be applicable to control an air supply conduit system with which the polishing system described above may be provided, to the extent that a control independently controls valves provided in the respective air supply conduits of the air supply conduit system fluidly which are connected to respective sections of the housing of the polishing system. Further, it should be noted that the present invention is applicable to the apparatuses as disclosed in Japanese Patent Applications 7-344797, 9-33784, 11-545612, 10-189704 and 2000-250392.