Patent Publication Number: US-6338669-B1

Title: Polishing device

Description:
TECHNICAL FIELD 
     The present invention relates to a polishing machine comprising a turntable having a polishing surface for polishing a semiconductor wafer or the like, and a polishing liquid supply unit for supplying a polishing liquid onto the polishing surface of the turntable. 
     BACKGROUND OF THE INVENTION 
     In a semiconductor wafer manufacturing process, a polishing machine is used to planarize semiconductor wafer surfaces. 
     The polishing machine of the this kind comprises a turntable having a polishing surface and adapted to be turned at a predetermined rotating speed, a wafer carrier that holds a semiconductor wafer rotates at a predetermined rotating speed and presses a surface of the semiconductor wafer against the polishing surface of the turntable onto which a polishing liquid is being supplied so as to polish the surface of the semiconductor wafer, a dressing tool that is brought into contact with the polishing surface of the turntable while supplying a dressing liquid onto the polishing surface of the turntable to dress the polishing surface, and an airtight housing containing the turntable, the wafer carrier and the dressing tool therein. 
     As shown in FIG. 1, in a conventional polishing machine, a polishing surface of a turntable  201 , which polishing surface is usually formed by attaching a polishing pad  202  to the upper surface of the turntable  201 , is supplied with various kinds of liquids, including a polishing liquid and a dressing liquid which are needed for performing certain operations such as polishing of semiconductor wafers, dressing of the polishing surface and so on, through a nozzle  203  which is set above the turntable and connected to a liquid supply tube  205 . 
     However, this conventional polishing machine has the following problems. 
     (1) The nozzle  203  and the liquid supply tube  205 , which are fixedly held above the turntable  201  hinder maintenance work which includes replacing the polishing pad  202  attached to the upper surface of the turntable  201  with a new one. 
     (2) Although it is desired that the liquid discharged from the nozzle  203  falls onto the polishing surface of the turntable  201  at a position suitable for the liquid to be appropriately spread over the polishing surface of the turntable  201  by a centrifugal force, i.e., a position near the center of rotation of the turntable  201 , the position on the polishing surface of the turntable  201  where the liquid falls may be different from such a desired position depending on the flow rate and velocity of the discharged liquid. 
     The present invention has been made in view of those problems and it is therefore an object of the present invention to provide a polishing machine with a liquid supply system that does not hinder maintenance work such as the exchange of polishing pads and is capable of positively supplying a liquid at an optimum position on a polishing surface of a turntable. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a polishing machine is provided with a liquid supply system comprising a movable arm, and a nozzle supported on the movable arm to supply a liquid onto a polishing surface of a turntable. 
     The movable arm is movable between a liquid supply position whereby the nozzle is positioned substantially vertically above a portion of the polishing surface onto which the liquid is to be discharged, and at least one retracted position whereby the nozzle is positioned outside the periphery of the turntable. The polishing machine further comprises a holding device for holding the arm at either the liquid supply position or the retracted position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side elevational view of an arrangement of a turntable and a nozzle in a conventional polishing machine; 
     FIG. 2 is a schematic plan view of a polishing machine in a preferred embodiment of the present invention; 
     FIG. 3 is an enlarged plan view of a turntable and an arm with a liquid supply nozzle unit included in the polishing machine of the preferred embodiment; 
     FIG. 4 is a schematic sectional view taken along a line  4 — 4  in FIG. 3; 
     FIG. 5 is a plan view, similar to FIG. 3, showing a plurality of positions where the arm with the nozzle unit is positioned; 
     FIG. 6 is a partly cutaway plan view of the arm with the nozzle unit; 
     FIG. 7 is a partly cutaway side elevational view of the arm with the nozzle unit; 
     FIG. 8 is a plan view of an arm with the nozzle unit in accordance with a second embodiment of the present invention; 
     FIG. 9 is a side elevation of the arm shown in FIG. 8; 
     FIG. 10 is a side elevational view of a movable nozzle included in the nozzle unit of the arm shown in FIG. 9; 
     FIG. 11 is a sectional view taken along a line  11 — 11  in FIG. 10; and 
     FIG. 12 is a sectional view taken along a line  12 — 12  in FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The best mode embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
     FIG. 2 shows a schematic view of an entire construction of a polishing machine  60  in accordance with an embodiment of the present invention. Referring to FIG. 2, the polishing machine  60  has a polishing unit  70  that performs a polishing operation, and a cleaning unit  90  contiguous with the polishing unit  70 . The units  70  and  90  are contained in an airtight housing. 
     In the polishing unit  70 , a turntable  73  is disposed at the center of the polishing unit  70 , and a carrier assembly  77  and a dresser assembly  81  are respectively disposed on either side of the turntable  73 . The carrier assembly  77  includes a wafer carrier  75  in the shape of a disk and capable of holding a wafer to be polished and of bringing the wafer into contact with a polishing surface of the turntable. The dresser assembly  81  includes a dressing tool  79  in the shape of a disk for dressing the polishing surface of the turntable  73 . A workpiece transfer device  83  is disposed near the carrier assembly  77  to transfer a semiconductor wafer from the polishing unit  70  to the cleaning unit  90  and vice versa. 
     The polishing machine performs a polishing operation and a dressing operation as described below. 
     A semiconductor wafer to be polished is received through a delivery station a of the cleaning unit  90 . The semiconductor wafer is carried through the cleaning unit  90  onto the workpiece transfer device  83  of the polishing unit  70 . 
     The wafer carrier  75  of the carrier assembly  77  is turned from a position shown in FIG. 2 along a path indicated by an arrow A, picks up the wafer from the workpiece transfer device  83  to hold it on its lower surface, rotates about its axis while returning along the path indicated by the arrow A to a position above the turntable  73 , and is then lowered to press the wafer against a polishing pad  74  attached to the upper surface of the turntable for the polishing operation. During the polishing operation, a polishing liquid is supplied onto the polishing pad  74  through a liquid supply arm  10 . 
     After the polishing operation has been completed, the semiconductor wafer is returned to the work transfer device  83  so that the wafer is cleaned and dried by the cleaning unit  90  and, thereafter, taken outside through the delivery station a. 
     After the polishing operation has been completed, the dressing tool  79  is pressed against the polishing pad while being rotated about its axis and swung along the path designated by an arrow B over the turntable  73  so as to dress the polishing pad  74 . During the dressing operation, a dressing liquid is supplied onto the polishing pad  74  through the liquid supply arm  10 , the detail of which is explained hereinafter. 
     The polishing machine according to the embodiment is provided with a liquid supply system for supplying a polishing liquid, a dressing liquid and so on which will be described hereinafter. However, prior to describing the liquid supply system, a liquid draining system will briefly be explained as follows. 
     Referring to FIGS. 3 and 4, the polishing machine according to the embodiment of the present invention is provided with a splash cover  101  to prevent a liquid such as the polishing liquid supplied onto the turntable  73  by the liquid supply system from scattering beyond the periphery of the turntable  73  as the turntable  73  is rotated. The splash cover  101  is provided with a notch  103 . An annular trough  111  is disposed under the periphery of the turntable  73 . The liquid stopped by the splash cover  101  is collected in the annular trough  111  and is drained from the polishing unit  70  through a drain pipe, not shown. 
     The liquid supply system will now be described. The liquid supply system includes the liquid supply arm  10 . The liquid supply arm  10  has one end portion supported by a pivot shaft  50  on a frame  121 . A nozzle assembly comprising four nozzles  23  for selectively discharging a polishing liquid or a dressing liquid is held on the other end portion of the liquid supply arm  10 . 
     A detent mechanism  15  is provided near the pivot shaft  50  supporting the liquid supply arm  10 . The detent mechanism  15  is able to selectively hold the liquid supply arm  10  at a liquid supply position F (the position shown in FIG. 3) for supplying the liquid, a first retracted position D close to the periphery of the turntable  73  or a second retracted position E radially separated from the periphery of the turntable  73 . 
     The liquid supply arm  10  has a slide mechanism  12  on the upper surface of its forward end portion, the slide mechanism including a slide member  14 . The nozzle assembly  40  is fastened to a forward end portion of the slide member  14  with screws or the like. A cover  13  is detachably attached to the nozzle assembly  40  so as to cover the latter. As shown in FIG. 7, the liquid supply arm  10  can be moved vertically by a hydraulic or pneumatic piston-cylinder actuator. 
     The detent mechanism  15  comprises an elastic member disposed at a predetermined position on the frame  121 , a ball pressed against the lower surface of the base end portion of the liquid supply arm  10  by the elastic member, and recesses formed in the lower surface of the base end portion of the liquid supply arm  10 . The liquid supply arm  10  is held at the liquid supply position F, the first retracted position D or the second retracted position E when the ball engages with the corresponding one of the recesses. When a torque exceeding a predetermined value is applied to the liquid supply arm  10 , the arm  10  can be released from the position where it was held by the detent mechanism. 
     The slide member  14  is supported for sliding on the slide mechanism  12 . However, the slide member  14  is restrained from sliding off the slide mechanism  12  in a direction X by a detent mechanism similar to the detent mechanism  50 . 
     The nozzle assembly has a nozzle holding member  40 . A forward end portion of the nozzle holding member  40  projects downward from an opening  21  formed in a forward end portion of the lower wall of the cover  13 . The nozzles  23  are held by the nozzle holding member  40  so that the distal end portions thereof project vertically downward from the lower surface  19  of the nozzle holding member  40 . The proximal ends of the nozzles  23  are respectively connected to supply tubes  25  via connectors  24 . If the distal ends of the nozzles  23  are flush with the lower surface  19 , liquids such as a polishing liquid and dressing liquid discharged from the nozzles  23  have a tendency such that little quantities thereof remain on the lower surface  19  of the nozzle holding member  40  due to their surface tension, whereby a mixing of the remaining liquids or a contamination can result. However, in this embodiment, since the distal end portions of the nozzles  23  are projected from the lower surface  19  of the nozzle holding member  40  and are spaced apart from each other, such a mixing or contamination can be avoided. 
     While the four supply tubes  25  are extended out from the cover  13 , they are inclined at a predetermined angle θ relative to a horizontal plane to prevent the liquids from remaining in the supply tubes  25 . 
     A polishing liquid, a dressing liquid, a dispersant or cleaning liquid and chemical liquids such as an oxidizer liquid or the like may be supplied to the supply tubes  25 , respectively. Specifically, the supply tubes  25  may be connected to different tanks T or sources of such liquids, respectively, as shown in FIG.  7 . The number and construction of the nozzles  23  and the supply tubes  25  are determined as required. 
     The operation of the liquid supply arm  10  will be described hereinafter. 
     When the liquid supply arm  10  is located and held by the detent mechanism  15  at the liquid supply position F as shown in FIG. 5, the center of the arrangement of the four nozzles  23  coincides with the turning axis of the turntable  73 . When polishing the semiconductor wafer by holding the semiconductor wafer on the lower surface of the wafer. 
     The polishing liquid thus discharged falls vertically on the central portion of the turntable  73 , and is forced to spread uniformly over the entire surface of the turntable  73  by a centrifugal force. 
     When the dressing tool  79  is operated for a dressing operation, a dressing liquid is discharged through another nozzle  23  for the dressing liquid. The dressing liquid falls vertically on the central portion of the turntable  73  and is forced to spread uniformly over the entire surface of the polishing pad  74 . 
     While the nozzle in the conventional polishing machine as shown in FIG. 1 discharges a liquid obliquely onto the turntable, the nozzles  23  supported by the liquid supply arm discharge liquids vertically onto the central portion of the turntable  73  and, as a result, the liquids can be supplied accurately onto a desired region of the polishing surface of the turntable  73 . 
     The liquids can be vertically supplied onto the turntable  73  by a different method without arranging the nozzles  23  to extend vertically as shown in FIG.  7 . In the different method, flow regulating valves V are provided in the lines connecting the nozzles  23  and the tanks T storing the liquids to control the flow rates of the liquids supplied to the nozzles  23  so that the liquids discharged from the nozzles  23  will instantaneously fall vertically even if the tip end portions of the nozzles  23  are extended obliquely. 
     When replacing the polishing pad  74  attached to the upper surface of the turntable  73  with a new one, the liquid supply arm  10  is turned by hand to the first retracted position D shown in FIG.  5 . The liquid supply arm  10  is then held stationary at the first retracted position D by the detent mechanism  15 . Consequently, there is nothing immediately above the polishing pad  74  of the turntable  73 , so that the replacement of the polishing pad  74  can easily be conducted. 
     During the polishing pad replacement operation, the nozzles  23  supported on the forward end portion of the liquid supply arm  10  located at the first retracted position D are positioned just above the notch  103  of the splash cover  101 , whereby liquids which may remain inside and drop from the nozzles  23  after ceasing the supply of the liquids to the nozzles  23  fall through the notch  103  into the annular trough  111 ; and thus, the surroundings of the turntable  73  is not contaminated by the dropping liquids. 
     The drainage system also makes it possible that a pure water source is additionally connected to the tubes  25  so that pure water can be flowed through the tubes and nozzles after the supply of the polishing liquid, the dressing liquid and so on to clean the and nozzles without contaminating the surroundings of the turntable  73 . 
     The liquid supply arm  10  is moved to the second retracted position E and held by the detent mechanism when it is necessary to carry out maintenance work of the polishing machine which cannot be done with the liquid supply arm  10  located at the liquid supply position F or the first retracted position D. The maintenance work includes dismounting the nozzle assembly  40  from an arm body  11  of the liquid supply arm to measure supply or discharging rates of the liquids discharged from the nozzles  23 , removing pieces of a semiconductor wafer broken on the turntable  73 , removing the splash cover  101  to remove the pieces of broken semiconductor wafer from the annular trough  111 , inspecting the entire turntable  73  and repairing the liquid supply system, removing pieces of a semiconductor wafer broken on the turntable  73 , removing the splash cover  101  to remove the pieces of broken semiconductor wafer from the annular trough  111 , inspecting the entire turntable  73  and repairing the liquid supply system. 
     In this state, nothing overlies the turntable  73  and the splash cover  101  and hence the maintenance work can easily be conducted. 
     Since the second retracted position E is close to a side wall of the polishing unit  70 , the maintenance of the liquid supply system can easily be performed from the outside of the polishing unit  70 . A retracted position G shown in FIG. 5 may be used instead of the second retracted position E. 
     The discharging rate at which the liquid is discharged through each nozzle  23  must be measured to adjust the rate to an appropriate value. In this embodiment, the discharging rate is measured by either of the following two methods. 
     In a first measuring method, the liquid discharged from each nozzle  23  is directly measured by a graduated cylinder or the like. The measurement may be carried out by, for example, placing the liquid supply arm  10  at the first retracted position D or removing the nozzle unit  40  together with the slide member  14  from the liquid supply arm and placing it on a place convenient for the measurement. To remove the nozzle assembly from the arm  10 , screws  16  (FIGS. 6 and 7) are first removed and then the nozzle assembly with the slide member  14  is moved in the direction X to thereby be separated from the arm. 
     In a second measuring method, the cover  13  is pulled in the direction designated by an arrow Y to remove the cover  13  from the slide member  14 . The supply tubes  25  are then disconnected from the connector  24 , the free end portions of the supply tubes  25  are moved to a place convenient for the measurement and, thereafter, the flow rates of the liquids discharged from the free ends are measured. 
     The second measuring method does not measure quantities of the liquids discharged from the nozzles  23 . Therefore, it is possible that a discharging rate measured by the second measuring method may include an error greater than an error which may be included in the measurement by the first measuring method. However, the second measuring method is more convenient and simpler than the first measuring method where slide member  14  and associated elements are removed from the arm body  11  of the liquid supply arm. 
     In this embodiment, the liquid supply arm  10  is turned on the pivot shaft  50  and the position of the liquid supply arm  10  can easily be detected by a position sensor combined with the pivot shaft  50 . Therefore, it is possible to improve the polishing machine in terms of safety by providing an interlocking mechanism which controls the drive of the polishing machine so that, when it is detected that the liquid supply arm is not appropriately located at the liquid supply position F in a polishing operation, the driving of the polishing machine is stopped. For example, it is possible to avoid damaging the liquid supply arm  10  and the dressing unit  81  by a collision therebetween which may be brought about by a turn of the dressing unit  81  about its pivot shaft when the liquid supply arm  10  is at a position out of the liquid supply position F. 
     As shown in FIG. 3, a dog  131  is attached to the splash cover  101  at a predetermined position, and a sensor  133  is attached to the arm body  11  at a position which is close to and opposite the dog  131  when the splash cover  101  is set correctly in place (FIGS. 1 and 3) so that it is easy to determine whether the splash cover is set correctly or not. The splash cover  101  is vertically movable and is lowered when performing the maintenance of the turntable  73 . If the polishing operation is performed with the splash cover  101  lowered, the polishing liquid and such are scattered around. A drive motor for driving the turntable  73  is therefore adapted to be prevented from being activated when the splash cover  101  is lowered and thus the sensor  133  does not detect the dog  131 . 
     Further, it is possible to lower the splash cover  101  to the predetermined regular position or to raise the arm body  11  by a predetermined distance when the splash cover  101  is raised excessively so that it becomes impossible for the sensor  133  to detect the dog  131 . Although in this embodiment both of the arm body  11  and the splash cover  101  are made to be vertically movable, it is possible for the arm body  11  not to move vertically. 
     The polishing machine in this embodiment has three positions where the liquid supply arm  10  can be held stationary by the detent mechanism  15 . However, this invention is not limited to such an arrangement. The polishing machine may have at least one liquid supply position and at least one retracted position. 
     If the liquid supply arm  10  is arranged to be turned by a piston-cylinder actuator provided between the fixed frame of the polishing machine and the liquid supply arm  10 , any mechanism like the detent mechanism  15  for holding the liquid supply arm  10  stationary is not needed. When such a piston-cylinder actuator is employed, a position sensing switch may be associated with the piston-cylinder actuator to sense and control the position of the liquid supply arm  10 . A rotary actuator may be employed instead of the piston-cylinder actuator. Further, if the liquid supply arm  10  is driven for turning by a stepping motor, the liquid supply arm  10  can accurately be stopped and held at desired positions without any detent mechanism. 
     In this embodiment, the liquid supply position F is such a position that makes the center of the arrangement of the four nozzles  23  in the forward end portion of the liquid supply arm  10  coincide with the turning axis of the turntable  73 . However, the liquid supply position F is not limited to such a position. For example, when the periphery of a semiconductor wafer  300  is not moved to the center of the turntable  73  in the polishing operation, the center of the arrangement of the four nozzles  23  may, as shown in FIG. 5, be located at any position in a circular center area of the polishing pad having a radius H which is not used for polishing the semiconductor wafer  300 . This is because the liquid supplied onto such a circular center area will be appropriately spread over the polishing pad and supplied to the semiconductor wafer  300  which is being polished. 
     In the second embodiment, a liquid supply arm  10 ′ includes fixed nozzles  23 ′ fixedly held on a forward end portion of a body  11 ′ of the arm  10 ′, and a movable nozzle  23 ″ longitudinally movably supported on the arm body  11 ′. The fixed nozzles  23 ′ are formed from a tip or free end portions of tubes  25 ′ connected to liquid supply sources including a dressing liquid source (not shown). The free end portions of the tubes  25 ′ are passed through vertical through holes formed in the forward end portion of the liquid supply arm  10 ′ and secured to the liquid supply arm  10 ′ by a fixing member  27 . The movable nozzle  23 ″ is formed from a tip or free end portion of a tube  25 ″ connected to a polishing liquid source (not shown). The free end portion of the tube  25 ″ is passed vertically through longitudinal slots  28  formed in the arm body  11 ′ and is held at a desired position by a movable fixing device  30 . More specifically, the arm body  11 ′ is a tubular member having a circular cross section and the longitudinal slots  28  are diametrically opposite each other in the vertical direction. The movable fixing device  30  includes a sliding member  32  which has a substantially circular cross section and is longitudinally slidably fitted in the arm body  11 ′, a tube holding member  36  positioned below a lower surface of the arm body  11 ′, and a bolt  34  which passes through the longitudinal slots  28  in the vertical direction and is threadably engaged with the tube holding member  36 . The free end portion of the tube  25 ″ passing through the slots  28  is fastened to the tube holding member  36  by a fastening member  38 . 
     The bolt  34  is passed through a vertical hole formed in the sliding member  32  and is threadably engaged with a threaded hole formed in the tube holding member  36 . The tube holding member  36  can thus be lifted and lowered relative to the arm body  11 ′ by turning the bolt  34  about its axis so that the sliding member  32  is fixedly engaged with and disengaged from the arm body. 
     In the embodiment shown in FIG. 8, the movable nozzle  23 ″ is located at a radial position on the polishing surface of the turntable corresponding to the center of a wafer  300  which is being subjected to the polishing operation, while the fixed nozzles are positioned at the center of the polishing surface of the turntable. Although, in this embodiment, only the nozzle for discharging a polishing liquid is made to be movable, any other nozzles may be made to be movable as required. For example, it is preferable that the nozzles for discharging a dispersant liquid and the nozzle for discharging an oxidizer liquid are movable so that those nozzles can be located at the same position as the polishing liquid. 
     INDUSTRIAL APPLICABILITY 
     As is apparent from the foregoing description, according to the present invention, (1) since the liquid supply arm can be located outside the turntable as required, the maintenance work which includes changing the polishing pads can easily be carried out without being hindered by the liquid supply arm, thereby shortening the time for the maintenance operation and, (2) since the liquids discharged from the nozzles are directed vertically, the liquids can be appropriately supplied onto a desired position on the turntable.