Patent Publication Number: US-6982009-B2

Title: Method and device for cleaning abrasive plates on an abrasive machine

Description:
REFERENCE TO RELATED SPECIFICATION 
     This is a divisional application of application Ser. No. 09/992,191, filed Nov. 6, 2001, now U.S. Pat. No. 6,807,701. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of cleaning abrasive plates of an abrasive machine and a cleaning device, more precisely relates to a method, in which abrasive faces of an upper abrasive plates and a lower abrasive plates, which are mutually faced and rotated, are cleaned by water jetted from a nozzle moving along the abrasive faces, and a cleaning device executing said method. 
     Both side faces of a wafer-shaped work piece, e.g., silicon wafer, are abraded by an abrasive machine. A lapping machine, which is a kind of abrasive machines, is shown in  FIG. 10 . 
     In  FIG. 10 , the lapping machine has an upper abrasive plate  20 , whose lower face is an abrasive face for lapping work pieces  10 , e.g., silicon wafers, and keys  21  are keyed in an upper face of the upper abrasive plate  20 . An air cylinder unit  22  is provided above the upper abrasive plate  20 . The air cylinder unit  22  is fixed to an upper part of a gate-shaped frame  14 . The upper abrasive plate  20  is rotatably connected to a lower end of a piston rod  22   a  of the air cylinder unit  22  by a rotary plate  23  and connecting rods  27 . By employing a connector  22   b,  the piston rod  22   a  cannot rotate; the rotary plate  23  and the upper abrasive plate  20 , which are connected by the connecting rods  27 , can be rotated with respect to the piston rod  22   a  and held at the lower end thereof. With this structure, weight or a pressing force of the upper abrasive plate  20 , which works to a lower abrasive plate  30 , can be controlled by adjusting a lifting force of the cylinder unit  22 . 
     Note that, in some cases, the pressing force working to the lower abrasive plate  30  is controlled by adjusting a pressing force applied to the upper abrasive plate  20 . 
     Since the keys  21  engage with key grooves of a rotary member  54  which is rotated by a motor  70 , the upper abrasive plate  20  is rotated by a driving force of the motor  70 . A shaft  54   a  is downwardly extended from the rotary member  54 . A gear  54   b,  which is fixed to a lower end of the shaft  54   a,  is engaged with an idle gear  63 , and the idle gear  63  is engaged with a gear  64 , which is fixed to a spindle  60 . With this structure, the driving force or torque of the motor  70  can be transmitted to the upper abrasive plate  20  via the rotary member  54 . 
     Since the upper abrasive plate  20  and the rotary member  54  are connected by the keys  21 , a clearance between the upper abrasive plate  20  and the lower abrasive plate  30  can be made wider by actuating the air cylinder unit  22  when the work pieces  10  are set or discharged or maintenance is executed. 
     Carriers  40  are rotated by an external gear  50  and an internal gear  52 . A first hollow shaft  50   a,  which is coaxial to the shaft  54   a,  is connected to the external gear  50 , and a gear  50   b,  which is fixed to the first hollow shaft  50   a,  is engaged with a gear  65  of the spindle  60 . 
     A second hollow shaft  30   a,  which is coaxial to the first hollow shaft  50   a,  is connected to the lower abrasive plate  30 , and a gear  30   b,  which is fixed to a mid part of the second hollow shaft  30   a,  is engaged with a gear  61  of the spindle  60 . 
     A third hollow shaft  52   a,  which is coaxial to the second hollow shaft  30   a,  is connected to the internal gear  52 , and a gear  52   b,  which is fixed to the third hollow shaft  52   a,  is engaged with a gear  62  of the spindle  60 . The spindle  60  is connected to an adjustable reduction unit  69 , which is connected to the motor  70 , e.g., an electric motor, a hydraulic motor, by a belt. 
     The upper abrasive plate  20 , the lower abrasive plate  30 , the external gear  50  and the internal gear  52  are rotated by one motor  70  via the reduction unit  69 , the gears and the shafts. 
     An upper abrasive face of the lower abrasive plate  30  has discharging grooves  12  and  16 , which run like lattice as shown in  FIG. 11 , so as to discharge abraded dusts, which are produced by abrading the work pieces  10 , and slurry from the abrasive face. The discharging grooves  12  and  16  are formed in the lower abrasive face of the upper abrasive plate  20 , too. 
     The abraded dusts and slurry gradually deposit in the discharging grooves  12  and  16 , and they damage surfaces of the work pieces  10 . To prevent the damage of the work pieces  10 , the clearance between the abrasive plates  20  and  30  is widen by actuating the air cylinder unit  22  after a prescribed number of abrasive works are completed so as to clean the abrasive faces of the abrasive plates  20  and  30 . 
     However, the abraded dusts and slurry are solidified in the grooves  12  and  16  of the abrasive faces of the abrasive plates  20  and  30 , so they must be manually removed. Namely, a metal plate is manually inserted into the grooves  12  and  16  so as to scrape out the solidified dusts from the grooves  12  and  16 . It takes a long time to completely clean the abrasive faces, and the abrasive faces are sometimes damaged. 
     To automatically clean the abrasive faces, a cleaning device was disclosed in the Japanese Patent Gazette No. 7-9342 (see  FIG. 12 ). In the conventional cleaning device shown in  FIG. 12 , front end sections of two nozzles  100   a  and  100   b  are respectively enclosed by brush members  102 . The nozzles  100   a  and  100   b  are provided to a front end of a shaft  106  and respectively headed upward and downward. With this structure, pressurized water is jetted upward and downward from the nozzles  100   a  and  100   b.  The shaft  106  is vertically and horizontally moved together with the nozzles  100   a  and  100   b.    
     In the cleaning device shown in  FIG. 12 , front ends of the brush members  102  simultaneously contact the abrasive faces of the upper abrasive plate  20  and the lower abrasive plate  30 , and the pressurized water, whose pressure is about 50–100 atm., is simultaneously jetted from the nozzles  100   a  and  100   b  toward the abrasive faces rotating (see  FIG. 13 ). The nozzles  100   a  and  100   b  are moved in the radial direction with respect to the abrasive faces, so that abraded dusts deposited in the grooves  12  and  16  of the abrasive faces can be removed. 
     The cleaning device shown in  FIGS. 12 and 13  can automatically clean the abrasive faces of the abrasive plates  20  and  30 . 
     When the pressurized water is jetted from the nozzles  100   a  and  100   b  toward the abrasive faces, the nozzles  100   a  and  100   b  are respectively formed by the brush members  102  and the abrasive faces, so that the jetted water cannot be scattered outside. 
     However, outer edges of the abrasive plates  20  and  30  must be washed so as to clean the whole abrasive faces. When the nozzles  100   a  and  100   b  are moved to the outer edged of the abrasive plates  20  and  30 , gaps are respectively formed between the outer edges of the abrasive plates  20  and  30  and the brush members  102  as shown in  FIG. 14 , so that the jetted water is scattered outside from the gaps. 
     The water jetted outside from the gap between the outer edge of the lower abrasive plate  30  and the brush member  102  for cleaning the lower abrasive plate  30  is received and introduced outside of the cleaning device via a discharging section  31   a  (see  FIG. 10 ). The discharging section  31   a  is formed along the outer edge of the lower abrasive plate  30 . As shown in  FIG. 10 , the internal gear  52  is provided in the discharging section  31   a,  so a width of the discharging section  31   a  is narrow. Therefore, the water, which has once passed through the discharging section  31   a,  is not returned to the abrasive face via the discharging section  31   a.    
     On the other hand, the water jetted outside from the gap between the outer edge of the upper abrasive plate  20  and the brush member  102  for cleaning the upper abrasive plate  20  is scattered into a space, in which an abrading mechanism is set. 
     The water, which is scattered into the space, includes the abraded dusts and used slurry, so it makes abraded products dirty. 
     Especially, the abrasive machine for abrading silicon wafers, is located in a clean room, so the water jetted from the nozzle  100   a  and scattered into the clean room via the gap of the upper abrasive plate  20  makes degree of cleanliness of the clean room lower. 
     If a moving range of the nozzles  100   a  and  100   b  is limited so as to prevent the water jetted from the nozzle  100   a  from scattering outside via the gap of the upper abrasive plate  20 , the outer edge portions of the abrasive faces of the abrasive plates  20  and  30  cannot be cleaned, and the portions must be manually cleaned. Therefore, it is difficult to automatically clean the whole abrasive faces of the abrasive plates  20  and  30 . 
     Further, in the cleaning device shown in  FIGS. 12 and 13 , the pressurized water is simultaneously jetted from the nozzles  100   a  and  100   b  so as to simultaneously wash the abrasive faces of the abrasive plates  20  and  30 . Therefore, the water washing the lower abrasive face of the upper abrasive plate  20  falls onto the upper abrasive face of the lower abrasive plate  30 , so that the upper abrasive face of the lower abrasive plate  30  is made dirty again by the water washing the lower abrasive face of the upper abrasive plate  20 . 
     In the case that width and density of the discharging grooves  12  and  16  of the upper abrasive plate  20  are different from those of the lower abrasive plate  30 , proper moving speed for washing the upper abrasive plate  20  is different from that for washing the lower abrasive plate  30 . In the cleaning device shown in  FIGS. 12 and 13 , the moving speed of the both nozzles  100   a  and  100   b  are equal, so one of the abrasive faces cannot be cleaned properly. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a method of cleaning abrasive plates, which is capable of cleaning whole abrasive faces of an upper abrasive plate and a lower abrasive plate without scattering jetted water into a space in which an abrading mechanism is set, and a cleaning device for executing said method. 
     A second object is provide to a method of cleaning abrasive plates, which is capable of cleaning the abrasive faces of the both abrasive plates rotating, which are mutually faced, without making the upper abrasive face of the lower abrasive plate dirty with water washing the lower abrasive face of the lower abrasive plate, and a cleaning device for executing said method. 
     To achieve the first object, the inventors of the present invention studied and found that scattering the jetted water into the space in which an abrading mechanism is set can be prevented by the steps of: moving a nozzle, which jets pressurized water and which is formed by a brush and the abrasive face of the upper abrasive plate, toward an outer edge of the upper abrasive plate; and closing a gap between the outer edge of the upper abrasive plate and the brush by another brush when the gap is formed. 
     Namely, the first object can be achieved by the following method. It is a method of cleaning abrasive faces of an upper abrasive plate and a lower abrasive plate of an abrasive machine, which are mutually faced, by a cleaning device including: 
     a nozzle for jetting water toward the abrasive faces of the abrasive plates rotating; 
     means for moving the nozzle along the abrasive faces; 
     means for preventing the jetted water from scattering in the air, the preventing means enclosing the nozzle; and 
     means for closing a gap between the preventing means and an outer edge of the upper abrasive plate, 
     the method is characterized by the steps of: 
     jetting water from the nozzle toward the abrasive face of the upper abrasive plate; 
     moving the nozzle toward the outer edge of the upper abrasive plate; and 
     closing the gap by the closing means when the gap is formed between the preventing means and the outer edge of the upper abrasive plate. 
     In this method, as described in BACKGROUND OF THE INVENTION, the jetted water for cleaning the abrasive face of the lower abrasive plate is not scattered into a space, in which an abrading mechanism is set, even if the jetted water is jetted from the gap between the preventing means and the outer edge of the lower abrasive plate. 
     Therefore, if no water is jetted outside from the gap between the preventing means and the outer edge of the upper abrasive plate while cleaning the upper abrasive plate, the whole abrasive faces of the both abrasive plates can be cleaned without scattering water into the space in which the abrading mechanism is set. 
     In the method of the present invention, the nozzle, which jets the water toward the abrasive face of the upper abrasive plate and which is formed by the abrasive face of the upper abrasive plate and the preventing means, is moved toward the outer edge of the upper abrasive plate, and the closing means closes the gap between the preventing means and the outer edge of the upper abrasive plate. 
     With this action, the whole abrasive faces of the both abrasive plates can be cleaned without scattering water into the space in which the abrading mechanism is set. 
     To achieve the second object, the inventors of the present invention studied and found that contamination of the abrasive face of the lower abrasive plate can be prevented by the steps of: washing the lower abrasive face of the upper abrasive plate; and secondly washing the upper abrasive face of the lower abrasive plate after the upper abrasive plate is washed, whereby the water washing the upper abrasive plate can be securely removed when the lower abrasive plate is washed. 
     The second object can be achieved by the following method. It is a method of cleaning abrasive faces of an upper abrasive plate and a lower abrasive plate of an abrasive machine, which are mutually faced, by a cleaning device including: 
     a pivotable nozzle for jetting water toward the abrasive faces of the abrasive plates rotating; 
     means for pivoting the nozzle; and 
     means for moving the nozzle along the abrasive faces, 
     the method is characterized by the steps of: 
     jetting water from the nozzle toward the abrasive face of the upper abrasive plate; 
     moving the nozzle so as to clean the abrasive face of the upper abrasive plate; 
     pivoting the nozzle toward the abrasive face of the lower abrasive plate; 
     jetting water from the nozzle toward the abrasive face of the lower abrasive plate; and 
     moving the nozzle so as to clean the abrasive face of the lower abrasive plate. 
     In this method, firstly the lower abrasive face of the upper abrasive plate is cleaned by the water jetted from the nozzle. Then, the nozzle is pivoted toward the upper abrasive face of the lower abrasive plate, and the upper abrasive face of the lower abrasive plate is cleaned by the jetted water. With this action, the water washing the upper abrasive plate and falling onto the upper abrasive face of the lower abrasive plate can be securely removed when the lower abrasive plate is washed, so that the contamination of the lower abrasive plate can be fully prevented. 
     Further, in this method, width and density of discharging grooves, which discharge abraded dusts and slurry outside, of the upper abrasive plate may be different from those of the lower abrasive plate, and 
     moving speed of the nozzle for cleaning the abrasive face of the upper abrasive plate and that for cleaning the abrasive face of the lower abrasive plate may be independently controlled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which: 
         FIG. 1  is a partial sectional view of an embodiment of a cleaning device of the present invention; 
         FIG. 2  is an explanation view of the cleaning device shown in  FIG. 1 ; 
         FIG. 3  is an explanation view of another embodiment of the cleaning device; 
         FIGS. 4A and 4B  are partial front views of another nozzle of the cleaning device shown in  FIG. 3 ; 
         FIG. 5  is a partial front view of another nozzle of the cleaning device shown in  FIG. 3 ; 
         FIG. 6  is an explanation view showing moving directions of the nozzle shown in  FIG. 3 ; 
         FIGS. 7A and 7B  are explanation views of another embodiment of the cleaning device; 
         FIGS. 8A and 8B  are explanation views of another embodiment of the cleaning device; 
         FIG. 9  is an explanation view of another embodiment of the cleaning device; 
         FIG. 10  is an explanation view of a lapping machine, which is an example of the abrasive machines; 
         FIG. 11  is a partial plan view of an abrasive face of a lower abrasive plate of the lapping machine shown in  FIG. 10 ; 
         FIG. 12  is an explanation view of a conventional cleaning device; 
         FIG. 13  is an explanation view of a nozzle section of the conventional cleaning device shown in  FIG. 12 ; and 
         FIG. 14  is an explanation view showing a state, in which the nozzle section shown in  FIG. 13  is located in the vicinity of outer edges of abrasive plates. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     An embodiment of the cleaning device of the present invention is shown in  FIG. 1 . In the cleaning device shown in  FIG. 1 , two nozzles  100   a  and  100   b , each of which is enclosed by a brush  102  for preventing jetted water from scattering in air, are respectively provided to an upper end and a lower end of a shaft  106 , which is extended along abrasive faces of an upper abrasive plate  20  and a lower abrasive plate  30 , and the water, which is pressurized and supplied by a high pressure pump  104 , is upwardly and downwardly jetted from the nozzles  100   a  and  100   b  as well as the conventional cleaning device shown in  FIG. 12 . 
     Front ends of the brushes  102 , which respectively enclose the nozzles  100   a  and  100   b , contact and wash the abrasive faces of the abrasive plates  20  and  30 . Each of the brushes  102  forms a space, which defines a range of scattering water jetted from the nozzle  100   a  or  100   b , with the abrasive face. Since the water can flow out from the brushes  102 , no water is stored in the brushes  102 . 
     The shaft  106 , to which the nozzles  100   a  and  100   b  are provided, can be vertically moved by elevating means, e.g., a handle  108 ; the shaft  106  can be horizontally moved by moving means, e.g., a motor  110 . 
     The cleaning device shown in  FIG. 1  is capable of cleaning the abrasive faces of the abrasive plates  20  and  30 . The cleaning device shown in  FIG. 1  inserts the brushes  102  into a space between the abrasive faces of the rotating abrasive plates  20  and  30 , which are mutually faced. The ends of the brushes  102  simultaneously contact the abrasive faces, and the pressurized water, whose pressure is about 50–100 atm., is jetted toward the abrasive faces from the nozzles  100   a  and  100   b , which are also inserted in the space together with the brushes  102 . The nozzles  100   a  and  100   b  jetting the water are moved along the abrasive faces so as to remove abraded dusts, etc. deposited in discharging grooves  12  and  16  of the abrasive faces. 
     When the abrasive faces of the abrasive plates  20  and  30  are cleaned, the nozzles  100   a  and  100   b  are respectively located in spaces, each of which is formed by the brush  102  and the abrasive face to be cleaned, so that the nozzles  100   a  and  100   b  jet the water in the spaces without scattering the water outside. 
     The cleaning device shown in  FIG. 1  has a shaft  11  and the brush  18 , which is provided to a front end of the shaft  11 . The brush  18  can move to and away from the upper abrasive plate  20 . The brush.  18  can contact an outer circumferential face of the upper abrasive plate  20 . 
     The brush  18  is used as closing means as shown in  FIG. 2 . When the edge portions of the abrasive plates  20  and  30  are cleaned, the nozzles  100   a  and  100   b  are moved to the outer edges of the abrasive plates  20  and  30 . Then gaps are formed between the outer edges of the abrasive plates  20  and  30  and inner edges of the brushes  102 . 
     The gap between the outer edges of the abrasive plate  20  and the inner edge of the brush  102  for cleaning the upper abrasive plate  20  is closed by the brush  18 . With this action, the water jetted from the nozzle  100   a  is not scattered outside. 
     On the other hand, the water jetted from the nozzle  100   b  can be discharged from the gap between the outer edges of the abrasive plate  30  and the inner edge of the brush  102  for cleaning the abrasive plate  30 . 
     When the abrasive face of the lower abrasive plate  30  is cleaned by the water jetted from the nozzle  100   b  of the cleaning device shown in  FIG. 1 , the water jetted outside from the gap between the outer edge of the lower abrasive plate  30  and the brush member  102  for cleaning the lower abrasive plate  30  is received and introduced outside of the cleaning device via the discharging section  31   a  (see  FIG. 10 ) as shown in  FIG. 2 . The discharging section  31   a  is formed and opened along the outer edge of the lower abrasive plate  30  so as to discharge slurry, etc. outside. As shown in  FIG. 10 , the internal gear  52  is provided in the discharging section  31   a , so the width of the discharging section  31   a  is narrow. Therefore, the water, which has once passed through the discharging section  31   a , is not returned to the abrasive face via the discharging section  31   a.    
     In the cleaning device shown in  FIGS. 1 and 2 , the whole abrasive faces of the both abrasive plates  20  and  30  of the abrasive machine, by the water jetted from the nozzles  100   a  and  100   b , without scattering the water into a space, in which the abrading mechanism is set. 
     In the cleaning device shown in  FIGS. 1 and 2 , the whole abrasive faces of the both abrasive plates  20  and  30  are simultaneously cleaned, so the water which has cleaned the lower abrasive face of the upper abrasive plate  20  falls onto and contaminates the upper abrasive face of the lower abrasive plate  30 . 
     If width and density of the discharging grooves  12  and  16  of the upper abrasive plate  20  are different from those of the lower abrasive plate  30 , proper moving speed for cleaning the upper abrasive plate  20  is different from that for cleaning the lower abrasive plate  30 . Then, if the moving speed of the both nozzles  100   a  and  100   b  are equal, one of the abrasive faces cannot be cleaned properly. 
     The contamination of the lower abrasive plate  30  can be prevented by a cleaning device shown in  FIG. 3 . 
     The cleaning device shown in  FIG. 3  includes: an air cylinder unit  24  having a piston rod  24   a  for vertically moving a moving unit  26 ; a pump  38  for supplying the pressurized water to a nozzle section  32 ; and a tank  39  for supplying water to the pump  38 . 
     The moving unit  26  includes: a casing; a motor  28 ; and a ball bearing screw  36 , which is rotated in a normal direction and a reverse direction by the motor  28 . By rotating the ball bearing screw  36  by the motor  28 , a moving body  25  is moved along a rail  44 , which is fixed on an upper face of the casing. A shaft  29  is rotatably connected to the motor  45 , which is mounted on the moving body  25 , and extended along the abrasive faces of the abrasive plates  20  and  30 . The nozzle section  32  is provided to a front end of the shaft  29 . 
     With this structure, the nozzle section  32  can be moved along the abrasive faces of the abrasive plates  20  and  30  with the movement of the moving body  25 . Further, by actuating the motor  45  to turn the nozzle section  32 , the nozzle section  32  is capable of heading to and jetting the water toward the abrasive face of the upper abrasive plate  20  or the abrasive face of the lower abrasive plate  30 . 
     To detect stroke ends of the movement of the moving body  25 , position detecting sensors  41  and  42 , e.g., photo sensors, are respectively provided to ends of the rail  44 . 
     A nozzle  35  is included in the nozzle section  32 , which is fixed to the front end of the shaft  29 . The water is introduced from the pump  38  to the nozzle  35  via a pipe  33 . The nozzle  35  is enclosed by a brush  34 . Front end of the brush  34  is capable of contacting the abrasive face of the abrasive plate  20  or  30  to wash the abrasive face. Further, the brush  34  defines a range of scattering the water jetted from the nozzle  35 . Since the water can flow out from the brushes  34 , no water is stored in a space enclosed by the brush  34 . 
     A control valve  37 , e.g., an electromagnetic valve, is provided to a mid part of the pipe  33  so as to control water supply to the nozzle  35 . 
     A shaft  17  is extended and retracted by an air cylinder unit  19 , and the brush  18  is provided to a front end of the shaft  17 . By actuating the air cylinder unit  19 , the brush  18  can be moved to and away from the outer circumferential face of the upper abrasive plate  20 . 
     The motors  28  and  45  of the moving unit  28 , the pump  38 ,the air cylinder units  19  and  24 , and the control valve  37  are controlled by a control unit  43 . 
     In the case of cleaning the abrasive faces of the abrasive plates  20  and  30  of the lapping machine shown in  FIG. 10 , firstly the cylinder unit  22  of the lapping machine is actuated so as to upwardly move the upper abrasive plate  20  and widen the clearance between the abrasive plates  20  and  30 , which are not rotated. 
     Then, the control unit  43  drives the motors  28  and  45  and actuates the cylinder unit  24  so as to insert the nozzle section  32  into the wide clearance between the abrasive plates  20  and  30  and turn the nozzle section  32  to head to the lower abrasive face of the upper abrasive plate  20 . With this action, the water can be jetted toward the lower abrasive face of the upper abrasive plate  20 . 
     Successively, the abrasive plates  20  and  30  are rotated, and the water is jetted toward the lower abrasive face of the rotating upper abrasive plate  20 , so that the lower abrasive face of the upper abrasive plate  20  can be cleaned. After the lower abrasive face of the upper abrasive plate  20  is cleaned, the nozzle section  32  is turned to head to the upper abrasive face of the lower abrasive plate  30 . 
     Then, the upper abrasive face of the lower abrasive plate  30  is cleaned by the water jetted from the nozzle  35 . 
     When the abrasive face of the rotating upper abrasive plate  20  is cleaned, the control unit  43  drives the motor  28  of the moving unit  26  and actuates the cylinder unit  24  so as to make the brush  34  of the nozzle section  32  contact the outer edge part of the rotating upper abrasive plate  20 . Then, the control unit  43  drives the pump  38  and opens the valve  37  so as to jet the water from the nozzle  35  toward the abrasive face of the upper abrasive plate  20 . Proper temperature of the water for easily wash the abrasive face is 10–90° C., preferably about 40° C.; proper pressure of the jetted water at an outlet of the pump  38  is 10.79 MPa or more, preferably 11.76 MPa or more. 
     Note that, amount of jetting water can be reduced by increasing water pressure. 
     While the nozzle section  32  cleans the abrasive face of the upper abrasive plate  20 , the control unit  43  drives the motor  28  so as to move the nozzle section  32  jetting the water from the outer edge portion of the upper abrasive plate  20  toward the center thereof. 
     When the nozzle section  32  reaches the center, the control unit  43  drives the motor  28  so as to move the nozzle section  32 , whose brush  34  is contacting the abrasive face of the upper abrasive plate  20  and whose nozzle  35  is jetting the water thereto, toward the outer edge of the upper abrasive plate  20 . 
     When the nozzle section  32  approaches to the outer edge of the upper abrasive plate  20 , a gap is formed between the outer edge of the upper abrasive plate  20  and an inner edge of the brush  34 . At that time, the control unit  43  actuates the cylinder unit  19  so as to make the brush  18  contacts the outer circumferential face of the upper abrasive plate  20  and close the gap (see  FIG. 2 ). 
     After the contact, the nozzle section  32  is moved from the outer edge portion of the upper abrasive plate  20  to the center thereof. When the gap between the outer edge of the upper abrasive plate  20  and the brush  34  is disappeared, the control unit  43  actuates the cylinder unit  10  so as to leave the brush  18  from the outer circumferential face of the upper abrasive plate  20 . 
     Since the nozzle section  32 , whose brush  34  is contacting the abrasive face of the upper abrasive plate  20  and whose nozzle  35  is jetting the water thereto, is reciprocatively moved along the abrasive face of the upper abrasive plate  20 , the whole abrasive face of the upper abrasive plate  20  can be cleaned. 
     Proper time for cleaning the abrasive face of the abrasive plate  20  was previously known by experiments, and it is inputted to a timer. When the set time elapsed, cleaning of the upper abrasive plate  20  is completed. 
     Note that, the control unit  43  can know if the nozzle section  32  reaches the outer edge or the center of the upper abrasive plate  20  by signals from the sensors  41  and  42 . 
     When the control unit  43  receives a signal from the timer which indicates the termination of the cleaning of the upper abrasive plate  20 , the control unit  43  stops the pump  38  and closed the valve  37 , then drives the motor  45  so as to turn and head the nozzle section  32  to the upper abrasive face of the lower abrasive plate  30 . 
     When the brush  34  of the nozzle section  32  contacts an outer edge portion of the lower abrasive plate  30 , the control unit  43  drives the pump  38  and opens the valve  37 , so that the water is jetted from the nozzle  35  toward the abrasive face of the lower abrasive plate  30  so as to clean the abrasive face of the lower abrasive plate  30 . 
     As well as the abrasive face of the upper abrasive plate  20 , the abrasive face of the lower abrasive plate  30  is cleaned by controlling the motor  28  so as to reciprocatively move the nozzle section  32 , whose brush  34  is contacting the abrasive face of the lower abrasive plate  30  and whose nozzle  35  is jetting the water thereto, between the outer edge of the lower abrasive plate  30  and the center thereof. 
     As described above, when the lower abrasive pate  30  is cleaned, the water, which has once passed through the discharging section  31   a  (see  FIG. 10 ), is not returned to the abrasive face of the lower abrasive plate  30 . Therefore, means for closing a gap between the outer edge of the lower abrasive plate  30  and the inner edge of the brush  34  is not required, but the closing means may be provided for the lower abrasive plate  30 . 
     Preferably, the moving speed of the nozzle  35  for cleaning the upper abrasive plate  20  and that for cleaning the lower abrasive plate  30  are independently defined so as to properly remove abraded dusts deposited in the grooves  12  and  16  (see  FIG. 11 ) of the abrasive faces. The proper speed for the abrasive plates  20  and  30  were respectively known by experiments and stored in the control unit  43 . 
     Since the proper moving speed of the nozzle section  32  depends on the width and density of the discharging grooves  12  and  16  of each abrasive face, the moving speed for cleaning the upper abrasive plate  20  and the lower abrasive plate  30  were previously defined on the basis of experiments and stored in the control unit  43 . 
     By reciprocatively moving the nozzle section  32 , whose brush  34  is contacting the abrasive face of the lower abrasive plate  30  and whose nozzle  35  is jetting the water thereto, the whole abrasive face of the lower abrasive plate  30  can be cleaned. While moving the nozzle section  32 , the abraded dusts can be removed from the abrasive face of the lower abrasive plate  30 . Further, the water, which has washed the abrasive face of the upper abrasive plate  20  and fallen onto the abrasive face of the lower abrasive plate  30 , also can be removed, so that the contamination of the lower abrasive plate  30  can be securely prevented. 
     Proper time for cleaning the abrasive face of the lower abrasive plate  30  was also previously known by experiments, and it is inputted to the timer. When the set time elapsed, cleaning of the lower abrasive plate  30  is completed. 
     When the control unit  43  receives a signal from the timer which indicates the termination of the cleaning of the lower abrasive plate  30 , the control unit  43  stops the pump  38  and closed the valve  37 . 
     After the cleaning of the abrasive faces of the both abrasive plates  20  and  30  are completed, the nozzle section  32  is moved out from the clearance between the abrasive plates  20  and  30 . 
     The moving speed of the nozzle section  32  may be fixed. And, the moving speed may be varied on the basis of area of cleaning the abrasive face and peripheral speed of the abrasive plates  20  and  30 . For example, the cleaning area of the outer edge portion of the abrasive face is broader than that of the center portion thereof, and the peripheral speed of the outer edge portion is higher than that of the center portion. Therefore, the moving speed of the nozzle section  32  for cleaning the outer edge portion may be lower than that for cleaning the center portion so as to make the cleaning area in the outer edge portion broader. 
     The nozzle section  32  shown in  FIG. 3  has one nozzle  35 . To shorten the time for cleaning the abrasive faces of the both abrasive plates  20  and  30 , a plurality of the nozzles  35  may be provided as shown in  FIGS. 4A and 4B . A plurality of the nozzles  35  may be arranged parallel in the direction of moving the nozzle section  32 (see  FIG. 4A ) or serially arranged in said direction (see  FIG. 4B ). 
     Further, all or some of the nozzles  35  may jet the water with supersonic waves. In this case, for example, some nozzles  35  jets the high pressure water, whose pressure at the outlet of the pump  38  is 10.79 MPa or more; other nozzles  35  jets low pressure water, whose pressure at the outlet of the pump  38  is less than 10.79 MPa, and irradiate supersonic waves toward the low pressure water. By using the high pressure water and the low pressure water to which the supersonic waves are irradiated, the abraded dusts deposited in the grooves  12  and  16  can be broken by the supersonic waves, and they can be scraped out by the high pressure water. 
     Note that, some of the nozzles  35  may jet a liquid including an anticorrosive agent. 
     In the cleaning device shown in  FIGS. 3–4B , length of hairs of the brush  34 , which encloses the nozzle  35 , are fixed, but the length of the hairs of the brush  34  may be varied as shown in  FIG. 5 . The brush  34  shown in  FIG. 5  has a dual structure including an inner brush  34   a  and an outer brush  34   b.  The length of hairs of the inner brush  34   a  is shorter than that of the outer brush  34   b.  In  FIG. 5 , the short inner brush  34   a  contacts and cleans the abrasive face of the upper abrasive plate  20 ; the long outer brush  34   b  enters and cleans the grooves  12  and  16  of the abrasive face. 
     In the cleaning device shown in  FIGS. 3–5 , the nozzle section  32  is linearly moved between the outer edge and the center of the abrasive plate. In  FIG. 6 , this structure is shown as the device “A”. On the other hand, the nozzle section  32  may be turned with respect to the abrasive plate. The turnable device “B” is also shown in  FIG. 6 . Of course, the both devices “A” and “B” may be combined. 
     In the cleaning device shown in  FIGS. 1 and 2  too, the abrasive face of the lower abrasive plate  30  can be cleaned after the abrasive face of the upper abrasive plate  20  is cleaned as well as the cleaning device shown in  FIGS. 3–5 . In this case, for example, two pipes for supplying the water are connected to each of the nozzles  100   a  and  100   b , and a control valve, e.g., an electromagnetic valve, is provided to each pipe. The control valves may be controlled by a control unit. The control unit opens the valve for supplying the water to the nozzle  100   a  so as to clean the abrasive face of the upper abrasive plate  20 . After the upper abrasive plate  20  is cleaned, the control unit opens the valve for supplying the water to the nozzle  100   b  so as to clean the abrasive face of the lower abrasive plate  30 . 
     In the cleaning device shown in  FIGS. 3–6 , the nozzle  35  firstly cleans the lower abrasive face of the upper abrasive plate  20 , then the nozzle  35  is turned to clean the upper abrasive face of the lower abrasive plate  30 . With this structure, working efficiency of the cleaning device shown in  FIGS. 3–6  is lower than that of the cleaning device shown in  FIGS. 1 and 2 , which is capable of simultaneously jetting the water from the nozzles  100   a  and  100   b.    
     This disadvantage can be solved by a cleaning device shown in  FIGS. 7A , in which a plurality of the nozzle sections  32   a,    32   b  and  32   c  are linearly arranged on a shaft  29  with regular separations. 
     By linearly providing the nozzle sections  32   a,    32   b  and  32   c  on the shaft  29  with the regular separations, the nozzle section  32   c,  which is located on the motor  45  side, corresponds to the outer edges of the abrasive plates  20  and  30 , and the nozzle section  32   a  corresponds to inner portions of the abrasive plates  20  and  30  (see  FIG. 7B ). Since a plurality of the nozzles  32   a,    32   b  and  32   c  are linearly arranged on the shaft as shown in  FIG. 7A , strokes of the nozzle sections  32   a,    32   b  and  32   c  can be shorter than the stroke of the nozzle section  32  shown in  FIG. 3 , in which one nozzle section  32  is provided on the shaft  29 . Therefore, working efficiency can be improved. 
     Since the shaft  29  is turned by the motor  45  together with the nozzle sections  32   a,    32   b  and  32   c,  the nozzle sections  32   a,    32   b  and  32   c  can be simultaneously headed to the same direction. Namely, the nozzle sections  32   a,    32   b  and  32   c  are firstly headed to the lower abrasive face of the upper abrasive plate  20 , and the water is simultaneously jetted from the nozzle sections  32   a,    32   b  and  32   c  so as to clean the lower abrasive face of the upper abrasive plate  20 . After the upper abrasive plate  20  is cleaned, the nozzle sections  32   a,    32   b  and  32   c  are turned and headed to the upper abrasive face of the lower abrasive plate  30 , and the water is simultaneously jetted from the nozzle sections  32   a,    32   b  and  32   c  so as to clean the upper abrasive face of the lower abrasive plate  30 . 
     Note that, in the cleaning device shown in  FIG. 7A , structural elements shown in  FIG. 3  are assigned the same symbols and explanation is omitted. 
     The working efficiency of cleaning the abrasive plates can be improved by a cleaning device shown in  FIG. 8A , too. The cleaning device includes: a nozzle section  32   d  including a nozzle  35   d  for jetting water toward the lower abrasive face of the upper abrasive plate  20 ; and a nozzle section  32   e  including a nozzle  35   e  for jetting water toward the upper abrasive face of the lower abrasive plate  30 . The nozzle sections  32   d  and  32   e  are independently moved. 
     If the nozzle sections  32   d  and  32   e  are moved together, the water which has washed the lower abrasive face of the upper abrasive plate  20  falls onto and contaminates the upper abrasive face of the lower abrasive plate  30 . To solve the disadvantage, the water falls onto the lower abrasive plate  30  is removed as shown in  FIG. 8A . Namely, the movement of the nozzle section  32   e  is a prescribed time behind the movement of the nozzle section  32   d  so as to securely remove the water fallen onto the upper abrasive face of the lower abrasive plate  30 , so that the contamination of the lower abrasive plate  30  can be securely prevented. 
     The nozzle section  32   e  may be provided immediately below the nozzle section  32   d  (see  FIG. 8A ); the nozzle sections  32   d  and  32   e  may be arranged with a proper separation (see  FIG. 8B ). 
     Note that, in  FIG. 8A , heading of the nozzle sections  32   e  and  32   e  may be fixed. 
     The cleaning devices shown in  FIGS. 8A and 8B  are separated from the abrasive machine, but they may be assembled in the abrasive machine. 
     The closing brush  18  may include a nozzle, to which the water is supplied via the hollow shaft  11 . By jetting the water from the nozzle, the brush  18  can wash the outer circumferential face of the upper abrasive plate  20 . Of course, the brush  18  can close the gap between the outer edge of the upper abrasive plate  20  and the inner edge of the brush  34  of the nozzle section  32 , so that scattering the jetted water from the gap can be prevented. 
     In the cleaning devices shown in  FIGS. 1–8B , the brush  18  (the closing means) is provided to the front end of the shaft and moved close to and away from the outer circumferential face of the upper abrasive plate  20 . 
     In a cleaning device shown in  FIG. 9 , an enclosing member  15  encloses a space including the abrasive plates  20  and  30  and prevents the water, which is jetted from the nozzle  35 , from scattering outside. By employing the enclosing member  15 , the closing means, e.g., the brush  18 , can be omitted. 
     In the cleaning device shown in  FIG. 9 , structural elements shown in  FIG. 3  are assigned the same symbols and explanation will be omitted. 
     Further, the structures shown in  FIGS. 4A–8B  may be employed in the cleaning device shown in  FIG. 9 . Note that, their explanation will be omitted, too. 
     In the above described cleaning devices, the brush  34  encloses  35  as the preventing means, but the preventing means is not limited to the brush  34 . Net, cloth, etc., which are capable of preventing the water from scattering outside, may be used as the preventing means. 
     Further, the closing means, which closes the gap formed between the outer edge of the upper abrasive plate  20  and the brush  34  or  102 , is also not limited to the brush  18 . Net, cloth, etc., which are capable of preventing the water from scattering from the gap, may be used as the closing means. 
     The above described cleaning devices may be used for cleaning polishing plates of a polishing machine which polishes both side faces of a work piece, e.g., a silicon wafer. In this case too, proper temperature of the water for cleaning the polishing plates is 10–90° C., preferably about 40° C.; proper pressure of the jetted water at an outlet of a pump is 10.79 MPa or more, preferably 11.76 MPa or more. 
     In the cleaning device of the present invention, the whole abrasive faces of the upper abrasive plate and the lower abrasive plate can be cleaned without scattering the water, which has been jetted toward the abrasive face, into the space in which the abrading mechanism is set. 
     Even if the abrasive machine is installed in a clean room, no dirty water is scattered into the clean room. Therefore, degree of cleanliness of the clean room can be maintained high. The cleaning device is especially proper for a polishing machine which is installed in a high clean room and polishes silicon wafers. 
     Further, in the cleaning device of the present invention, the abrasive face of the lower abrasive plate is cleaned after the abrasive face of the upper abrasive plate is cleaned. With this action, the water washing the upper abrasive plate and falling onto the upper abrasive face of the lower abrasive plate can be securely removed when the lower abrasive plate is washed, so that the contamination of the lower abrasive plate can be fully prevented. 
     Since the upper abrasive plate and the lower abrasive plate are separately cleaned, the moving speed of the nozzle can be easily adjusted on the basis of the width and density of the discharging grooves of each abrasive face. Therefore, the abrasive faces can be fully cleaned. 
     By fully cleaning the abrasive faces of the abrasive plates, damaging work pieces, which is occurred by abraded dusts, etc. deposited in the abrasive faces, can be securely prevented, and yield of abraded products can be improved. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.