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 22a of the air cylinder unit 22 by a rotary plate 23 and connecting rods 27. By employing a connector 22b, the piston rod 22a 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 22a 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 54a is downwardly extended from the rotary member 54. A gear 54b, which is fixed to a lower end of the shaft 54a, 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 50a, which is coaxial to the shaft 54a, is connected to the external gear 50, and a gear 50b, which is fixed to the first hollow shaft 50a, is engaged with a gear 65 of the spindle 60.
A second hollow shaft 30a, which is coaxial to the first hollow shaft 50a, is connected to the lower abrasive plate 30, and a gear 30b, which is fixed to a mid part of the second hollow shaft 30a, is engaged with a gear 61 of the spindle 60.
A third hollow shaft 52a, which is coaxial to the second hollow shaft 30a, is connected to the internal gear 52, and a gear 52b, which is fixed to the third hollow shaft 52a, 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 100a and 100b are respectively enclosed by brush members 102. The nozzles 100a and 100b 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 100a and 100b. The shaft 106 is vertically and horizontally moved together with the nozzles 100a 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 100a and 100b toward the abrasive faces rotating (see FIG. 13). The nozzles 100a and 100b 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 100a and 100b toward the abrasive faces, the nozzles 100a and 100b 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 100a and 100b 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 31a (see FIG. 10). The discharging section 31a 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 31a, so a width of the discharging section 31a is narrow. Therefore, the water, which has once passed through the discharging section 31a, is not returned to the abrasive face via the discharging section 31a. 
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 100a 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 100a and 100b is limited so as to prevent the water jetted from the nozzle 100a 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 100a and 100b 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 100a and 100b are equal, so one of the abrasive faces cannot be cleaned properly.