Patent Publication Number: US-6705929-B1

Title: Cloth cleaning device and polishing machine

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cloth cleaning device and a polishing machine including the cloth cleaning device. 
     A surface of a semiconductor wafer must be precisely polished like a mirror face with uniform thickness before integrated circuits are formed thereon. 
     Many types of polishing machines have been used to polish semiconductor wafers, etc. 
     One of the conventional polishing machines is shown in FIGS. 8 and 9. The polishing machine  10  has a polishing plate  12  having an upper face which is covered with a polishing cloth and which is rotated in a horizontal plane. A center roller  14 , which is capable of rotating freely, is arranged at a center of the polishing plate  12 . A plurality of work plates  16  are arranged on the polishing cloth. Work pieces to be polished, e.g., semiconductor wafers, are adhered to a bottom face of each work plate  16 , and their bottom faces contact the polishing cloth. 
     FIG. 10 shows a state in which the semiconductor wafers  17  are adhered to the work plate  16 . Guide rollers  18  are arranged in the vicinity of an outer edge of the polishing plate  12  as shown in FIG. 9, and outer circumferential faces of the work plates  16  contact the center roller  14  and the guide rollers  18 . The polishing plate  12  is rotated in a direction of an arrow “A”, but the work plates  16  are held at predetermined positions by the center roller  14  and the guide rollers  18 . 
     As shown in FIG. 9, the guide rollers  18  are moved vertically by an elevating mechanism, and their strokes of vertical movement are equal to or more than the thickness of the work plates  16 . When the guide rollers  18  are at their lowest positions, they are located close to the outer edge of the polishing plate  12  so as to contact the outer circumferential face of the work plates  16  and when the guide rollers  18  are at their highest positions, they are moved away from the outer edge of the polishing plate  12  so as to allow the work plates  16  to pass through a space between the center roller  14  and the guide rollers  18  with the rotation of the polishing plate  12 . 
     The guide rollers  18  may be moved between positions close to the outer edge of the polishing plate  12  and positions away therefrom by, for example, swinging arms of the guide rollers  18 . The moving mechanism of the guide rollers  18  is not always necessary. In some constructions, the guide rollers  18  may be fixed at predetermined positions or no guide rollers  18  are required. 
     Press heads  20  are moved vertically. When the press heads  20  are at their lowest positions, the press heads  20  respectively press the work plates  16  and the semiconductor wafers onto the polishing cloth with an appropriate force. Therefore, the bottom faces of the semiconductor wafers can be polished by the polishing cloth which is rotated together with the polishing plate  12 . 
     The press heads  20  can be freely rotated about their axes. 
     While polishing the semiconductor wafers, alkaline slurry including abrasive grains, e.g., silica grains, is fed to the rotating polishing cloth. Therefore, the bottom faces of the semiconductor wafers can be mechanically and chemically polished like mirror faces. 
     A holding member  23  is arranged on a front end of an arm  22  for enabling the polishing cloth to be cleaned. More specifically, a brush (not shown) for brushing the surface of the polishing cloth is arranged on a bottom face of the holding member  23 . 
     The arm  22  is capable of swinging or rotating about a rotary shaft  24  which is located outside of the polishing plate  12 . While the semiconductor wafers are polished, the arm  22  is located outside of the polishing plate  12  and while the polishing cloth is cleaned, the arm  22  is swung, about the rotary shaft, above the polishing plate  12 . 
     To clean the polishing cloth, wash water is directed in a radial direction from the center roller  14  onto the polishing cloth. 
     The polishing cloth must be cleaned because abraded grains, which are formed by abrading the semiconductor wafers, and reaction products gradually permeate and deposit in the polishing cloth. As a result, the polishing efficiency of the polishing cloth is reduced during the course of its use. 
     However, in the conventional polishing machine, the polishing cloth is cleaned by merely supplying the wash water from the center roller  14  and brushing. As a result, the polishing cloth cannot be fully cleaned, and the polishing efficiency of the polishing cloth cannot be recovered. Further, the holding member  23  must have a prescribed width, so the holding member  23  must be moved backward from the center roller  14  so as not to collide with the center roller  14  when the arm  22  is swung, so that a part of the polishing cloth in the vicinity of the outer circumferential face of the center roller  14  cannot be cleaned well. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a cloth cleaning device and a polishing machine which are capable of fully cleaning a polishing cloth including a part in the vicinity of a center roller. 
     To achieve this object, a cloth cleaning device of a polishing machine in accordance with the present invention comprises an arm movable in a plane parallel to a polishing cloth arranged on an upper face of a polishing plate between a first position, above the polishing cloth and a second position outside of the polishing cloth; a jet nozzle attached to the arm and arranged to direct high pressure water toward the polishing cloth; and an enclosing member enclosing the jet nozzle so as to prevent the high pressure water, which has been directed out from the jet nozzle, from scattering. The jet nozzle is headed or oriented toward a center roller arranged at the center of the polishing plate and the high pressure water is directed toward a part of the polishing cloth in the vicinity of the center roller when the arm moves the jet nozzle close to the center roller. 
     A polishing machine in accordance with the present invention comprises a polishing plate having an upper face covered with a polishing cloth; a driving mechanism for rotating the polishing plate; a center roller arranged at a center of the polishing plate; a work plate arranged on the polishing cloth and to which a work piece to be polished is adhered and whose outer circumferential face contacts an outer circumferential face of the center roller such that the work piece contacts the polishing cloth; a press head for pressing the work plate onto the polishing cloth; a slurry feeding mechanism for feeding slurry to the polishing cloth; an arm movable in a plane parallel to the polishing cloth between a first position above the polishing cloth and a second position outside of the polishing cloth; a jet nozzle attached to the arm and arranged to direct high pressure water toward the polishing cloth; and an enclosing member enclosing the jet nozzle so as to prevent the high pressure water which has been directed out from the jet nozzle, from scattering. The jet nozzle is headed or oriented toward the center roller and the high pressure water is directed toward a part of the polishing cloth in the vicinity of the center roller when the arm moves the jet nozzle close to the center roller. 
     The polishing machine may further comprise a guide roller arranged in the vicinity of an outer edge of the polishing plate, and an outer circumferential face of the work plate may contact outer circumferential faces of the center roller and the guide roller. 
     In the present invention, an angle of the jet nozzle may be changed between a first angle, at which the jet nozzle is headed toward the center roller, and a second angle, at which the jet nozzle is vertical with respect to the polishing cloth. 
     A sectional shape of a jet form of the high pressure water may be longer in the direction of moving the arm. 
     The enclosing member may be a plastic net enclosing the jet nozzle. 
     In the cloth cleaning device and the polishing machine of the present invention, the polishing cloth including the part in the vicinity of the center roller can be fully cleaned, so that the work piece can be precisely polished with a higher polishing efficiency and the longevity of the expensive polishing cloth can be increased. 
    
    
     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 schematic view of a first embodiment of the cloth cleaning device of the present invention; 
     FIG. 2 is an enlarged view in the vicinity of a jet nozzle; 
     FIG. 3 is a perspective view of a plastic net, which acts as an enclosing member; 
     FIG. 4 is a schematic view of the plastic net; 
     FIG. 5 is a schematic view showing a sectional shape of a jet form of high pressure water; 
     FIG. 6 is a perspective view of a plastic net of a second embodiment; 
     FIG. 7 is a perspective view of a plastic net of a third embodiment; 
     FIG. 8 is a schematic view showing the outline of the conventional polishing machine; 
     FIG. 9 is a plan view of the polishing plate of the conventional polishing machine; and 
     FIG. 10 is a top view of the work plate on which the semiconductor wafers are adhered. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     Basic structures of the polishing machines of the present embodiments are substantially the same as those in the conventional polishing machine described above with reference to FIGS. 8-10 and the elements of the present embodiments in common with the conventional polishing machine are assigned the same reference numerals and an explanation thereof will not be repeated in its entirety. 
     The polishing machine  10  includes the polishing plate  12 , whose upper surface is covered with a polishing cloth  12   a ; a driving mechanism (e.g., a motor  33 ) for rotating the polishing plate  12 ; the center roller  14  arranged at the center of the polishing plate  12 ; the work plates  16  arranged on the polishing cloth  12   a  and to each of which work pieces (e.g., semiconductor wafers) to be polished are adhered and whose outer circumferential faces contact the outer circumferential face of the center roller  14  such that the work pieces contact the polishing cloth  12   a ; the press heads  20  for pressing the work plates  16  onto the polishing cloth  12   a ; a slurry feeding mechanism  15  for feeding alkaline slurry to the polishing cloth  12   a ; and a cloth cleaning device  30 . The cloth cleaning device  30  comprises an arm  22  rotatable about the rotary shaft  24  in a plane parallel to the polishing cloth  12   a  between a first position above the polishing cloth  12   a  and a second position outside of the polishing cloth  12   a ; a jet nozzle  31  attached to the arm  22  and jetting (directing) high pressure water toward the polishing cloth  12   a ; and an enclosing member  40  enclosing the jet nozzle  31  so as to prevent the high pressure water which has been directed out from the jet nozzle  31  from scattering. The jet nozzle  31  is headed or oriented toward the center roller  14 , and the high pressure water is directed toward a part of the polishing cloth  12   a  in the vicinity of the center roller  14  when the arm  12  moves the jet nozzle  31  close to the center roller  14 . 
     The polishing machine in accordance with one embodiment of the invention thus comprises the polishing plate  12 , whose upper surface is covered with the polishing cloth  12   a ; the driving mechanism  33  for rotating the polishing plate  12 ; the center roller  14  arranged at the center of the polishing plate  12 ; the work plates  16  arranged on the polishing cloth  12   a  and to each of which the work pieces are adhered and whose outer circumferential faces contact the outer circumferential face of the center roller  14  such that the work pieces contact the polishing cloth  12   a ; the press heads  20  for pressing the work plates  16  onto the polishing cloth  12   a ; the slurry feeding mechanism  15  for feeding slurry to the polishing cloth  12   a ; the arm  22  rotatable about the rotary shaft  24  in a plane parallel to the polishing cloth  12   a  between the first position above the polishing cloth  12   a  and a second position outside of the polishing cloth  12 ; the jet nozzle  31  attached to the arm  22  and directing high pressure water toward the polishing cloth  12   a ; and the enclosing member  40  enclosing the jet nozzle  31  so as to prevent the high pressure water from scattering. The jet nozzle  31  is headed or oriented toward the center roller  14 , and the high pressure water is directed toward a part of the polishing cloth  12   a  in the vicinity of the center roller  14  when the arm  12  moves the jet nozzle  31  close to the center roller  14 . 
     In each of the examples, the guide rollers  18  are arranged in the vicinity of the outer edge of the polishing plate  12 , and the outer circumferential faces of the work plates  16  contact the center roller  14  and the guide rollers  18 . 
     As described above, characteristic features of the present invention are the cloth cleaning device  30  and the polishing machine including the cloth cleaning means. 
     FIG. 1 shows the arm  22  and the jet nozzle  31  of the cloth cleaning device  30  a first embodiment of the invention. 
     A base end of the arm  22  is fixed to the rotary shaft  24 , and the arm  22  is swung or rotated in the plane parallel to the polishing cloth  12   a . In this manner, a front end of the arm  22  can be moved between the first position above the polishing plate  12  and the second position outside thereof. 
     The rotary shaft  24  is rotated by the motor  33 , which includes a reduction unit  32 . 
     A sensor  34  detects rotational angle of the rotary shaft  24 , so that rotational angle of the arm  22  can be determined. 
     A holder box  36  is fixed to the front end of the arm  22 . The jet nozzle  31  is diagonally pierced through the holder box  36  and fixed to the holder box  36  by a fixing member  37 . 
     A cylindrical hood  38  covers a side of the jet nozzle  31  and is fixed to a bottom face of the holder box  36 . Further, the enclosing member  40  is fixed to the hood  38  and encloses sides of the water jet of the high pressure water and prevents the high pressure water from scattering. 
     The enclosing member  40  includes a cylindrical holding member  41  fixed to a lower end of the hood  38  and cylindrical plastic nets  42  fixed to the holding member  41 . Each of the plastic nets is formed, for example, like a screen. 
     In the first embodiment, as shown in FIGS. 3 and 4, a pair of the plastic nets  42 , each of which is folded such that a folding line makes a lower edge, are placed one against the other to form a pile of plastic nets  42 . The piled plastic nets  42  are sandwiched and fixed, by bolts (not shown), between the holding member  41  and a frame-shaped member  43 . In this manner, the plastic nets  42  constitute a four-net-structure. 
     The mesh size of each plastic net  42  is about 1 mm, and thickness thereof is 0.5 mm. Therefore, the plastic nets  42 , which constitute the four-net-structure, have enough flexibility. 
     The mesh size and hardness of the plastic nets  42  may be optionally designed. Further, the plastic nets  42  are not limited to the four-net-structure, so other structures (e.g., two-net-structure, six-net-structure) may be employed. 
     The jet nozzle  31  is arranged diagonally. More specifically, a lower end of the jet nozzle  31  is directed toward the center roller  14  when the arm  22  is located on a line connecting the rotary shaft  24  and the center roller  14 , so that the high pressure water, which is diagonally directed out from the jet nozzle  31 , can be directed toward the polishing cloth  12   a  in the vicinity of the outer edge of the center roller. 
     As clearly shown in FIG. 2, when the arm  22  is located at this position, the plastic nets  42  are very close to the outer circumferential face of the center roller  14  and the high pressure water  31   a  is directed toward the lower end of an inner face of the plastic nets  42 , which is on the side of the center roller  14 . In the first embodiment, the jetted water  31   a  reaches a position 7 mm away from the outer edge of the center roller  14 . 
     The high pressure water is supplied to the jet nozzle  31  via a pressure-resisting hose  44 . The pressure of the high pressure water (e.g., 30 kg/cm 2  (2.94 Mpa) or more) may be optionally set. 
     The operation of the polishing machine will now be explained. 
     When the polishing cloth  12   a  is cleaned, the guide rollers  18  are moved upward and the arm  22  is swung by the motor  33 . The rotational angle of the arm  22  is detected by the sensor  34 , which detects the rotational angle of the rotary shaft  24 , so that the swing movement of the arm  22  can be controlled so as not to move the jet nozzle  31  away from the polishing cloth  12   a.    
     A pump (not shown) is driven to supply the high pressure water, and the high pressure water  31   a  is directed from the jet nozzle  31  toward the polishing cloth  12   a , so that abraded grains and reaction products, which have been deposited in the polishing cloth  12   a , are washed away by the high pressure water  31   a . The water including the grains and the reaction products is introduced onto the polishing cloth  12   a  via meshes of the plastic nets  42  and a gap between the lower ends of the plastic nets  42  and the polishing cloth  12   a . Further, the grains and the reaction products are introduced outside of the polishing cloth  12   a  by water, which is radially directed out from the center roller  14 . In this manner, the grains and the reaction products, which have been deposited in the polishing cloth  12   a , can be removed from the polishing cloth  12   a , so that the polishing cloth  12   a  can be recovered and reused with high polishing efficiency. 
     Since the plastic nets  42  have the four-net-structure, the pressure of the high pressure water  31   a  is decreased and the water  31   a  is discharged together with the reaction products, etc., so that the water  31   a  including the reaction products, etc., cannot be scattered to the periphery The periphery can thus be kept clean. 
     As described above, the structure of the plastic nets  42  is not limited. Thus, any structures which are capable of preventing the high pressure water  31   a  from scattering in the periphery can be employed as the enclosing member  40 . The structure may be optionally changed according to operating conditions. 
     In the first embodiment, the plastic nets  42  are folded along the lower ends. The lower ends may be welded in the circumferential direction. With proper welding width, raveling plastic fibers of the plastic nets  42  can be prevented even if the lower ends of the plastic nets  42  are abraded, so that span of life of the plastic nets  42  can be longer. 
     When the arm  22  is located on the line connecting the rotary shaft  24  and the center roller  14 , the plastic nets  42  are very close to the outer circumferential face of the center roller  14 . Also, the high pressure water  31   a  is directed from the jet nozzle  31 , which is arranged diagonally to cause the high pressure water  31   a  to head for the center roller  14 , toward the lower end of the inner face of the plastic nets  42 , so that the polishing cloth  12   a  including the part in the vicinity of the center roller  14  can be fully cleaned. 
     As described above, the outer circumferential faces of the work plates  16  contact the outer circumferential face of the center roller  14 . Outer edges of the work pieces, e.g., semiconductor wafers  17 , are 7 mm separated away from the outer edge of the work plate  16 , so that they are about 7 mm separated away from the outer circuferential face of the center roller  14 . Therefore, the part of the polishing cloth  12   a , which is 7 mm away from the outer circumferential face of the center roller  14 , polishes the bottom faces of the semiconductor wafers  17 . In this manner, the abraded grains and the reaction products deposit in the part of the polishing cloth  12   a , which is close to the outer edge of the center roller  14 , but the conventional means cannot fully remove the abraded grains, etc. from this part of the polishing cloth  12   a.    
     In the first embodiment, the outer edges of the semiconductor wafers  17  are 7 mm separated away from the outer edge of the work plate  16 . The present invention can also be applied to the situation in which a distance between the outer edges of the semiconductor wafers  17  and the outer edge of the work plate  16  is less than 7 mm, etc. 
     FIG. 5 is a schematic view showing a sectional shape of a jet form of the high pressure water  31   a.    
     In the present embodiment, an outlet of the jet nozzle  31  is designed to make the sectional shape of the jet form of the high pressure water  31   a  longer in the direction “B” of movement of the arm  22 . The sectional shape of the jet form of the high pressure water  31   a  is shown in FIG. 5 as a black long ellipse. The outlet of the jet nozzle  31  is also formed into a long elliptic shape. 
     Since the jet form is formed into the long ellipse whose long axis is extended in the direction “B”, the high pressure water  31   a  can be directed to one point on the polishing cloth  12   a  for a long time, so that the part in the vicinity of the center roller  14 , which cannot be fully cleaned by the conventional means, can be fully cleaned. 
     The sectional shape of the jet form of the high pressure water  31   a  is not limited to the long ellipse, it may be a circle, etc. 
     In the first embodiment, as shown in FIG. 5, the jet form is formed into the long ellipse whose long axis is extended in the direction “B”, so the plastic nets  42  and the holding member  41  are also long in the direction “B”. In this case, corners of the plastic nets  42  and the holding member  41  are rounded, the plastic nets  42  and the holding member  41  are not interfered with by the center roller when the arm  22  is swung. In this manner, the plastic nets  42 , the holding member  41  and the jet nozzle  31  can be moved further close to the center roller  14 . 
     Preferably, an inclination angle of the jet nozzle  31 , with respect to the vertical line from the polishing cloth  12   a , is about 10°. 
     If the inclination angle is larger, energy of the high pressure water  31   a  colliding with the polishing cloth  12   a  is decreased. 
     If the angle of the jet nozzle  31  is changed between a first angle, at which the jet nozzle  31  is headed toward the center roller  14 , and a second angle, at which the jet nozzle  31  is vertical with respect to the polishing cloth  12   a , the polishing cloth  12   a  can be effectively cleaned. 
     To change the angle of the jet nozzle, the jet nozzle  31  is, for example, rotatably attached to a shaft and is moved between two points corresponding to the first and second angles by a cylinder unit or a motor. 
     When changing the angle of the jet nozzle  31 , the sensor  34  detects the rotational angle of the arm  22 , then the jet nozzle  31  is inclined to clean the periphery of the center roller  14  if the jet nozzle  31  is located near the center roller  14 . On the other hand, the jet nozzle  31  is made vertical to the polishing cloth  12   a  if the jet nozzle  31  is located far from the center roller  14 . With this control, the polishing cloth  12   a  can be efficiently cleaned. 
     The structure of the enclosing member  40  is not limited to the plastic nets  42 . For example, a cylindrical brush which encloses the jet nozzle  31  may be employed as the enclosing member  40 . 
     A second embodiment is shown in FIG. 6, which is a perspective view of another enclosing member. 
     In this embodiment, a plurality of pieces of curtain-shaped cloth  46 , whose material is equal to that of the polishing cloth  12   a , are fixed to the holding member  41  instead of the plastic nets  42 . Inner cloth  46  and outer cloth  46 , which are made of the same material and have the same size, are piled. They are sandwiched, by bolts, between the holding member  41  and the frame-shaped member  43 . 
     Slits  47  of the inner cloth  46  and slits of the outer cloth  46  are not in correspondence with one another. In this manner, the entire curtain-shaped cloth  46  has an appropriate flexibility. 
     A passage  48  is formed in a lower end section of a rear part of the curtain-shaped cloth  46  so as to introduce the high pressure water outside. 
     The abraded grains and reaction products, which have been deposited in the polishing cloth  12   a , are washed away by the high pressure water  31   a . The water including the grains and the reaction products is introduced onto the polishing cloth  12   a  via the passage  48  and the slits  47 . 
     Since the high pressure water directed from the nozzle  31  collides with the inner face of the curtain-shaped cloth  46 , the pressure of the high pressure water is decreased, so that the water including the reaction products, etc. cannot be scattered to the periphery. The periphery can thus be kept clean. 
     The inner cloth  46  and the outer cloth  46  are made of the same material, so mutual abrasion can be prevented. 
     The passage  48  may be omitted. The number, size, etc. of each piece of the curtain-shaped cloth  46  may be optionally designed according to operating conditions, e.g., the pressure of the high pressure water. 
     A third embodiment is shown in FIG. 7, which is a perspective view of another enclosing member. 
     In this embodiment, four pieces of curtain-shaped cloth  50 , whose material is equal to that of the polishing cloth  12   a , are fixed to the holding member  41  instead of the plastic nets  42 . They are sandwiched, by bolts, between the holding member  41  and the frame-shaped member  43 . 
     Each piece of the curtain-shaped cloth  50  is arranged on a respective side of the present enclosing member. Slits  51  are respectively formed at corners so that the curtain-shaped cloth  50  has proper flexibility. The passage  48  is formed in a lower end section of a rear part of the curtain-shaped cloth  50  so as to introduce the high pressure water outside. The passage  48  may be omitted. 
     The action of the enclosing member of the third embodiment is almost equal to that of the second embodiment (FIG.  6 ), so an explanation thereof will be omitted. 
     In the above described embodiments, the jet nozzle  31  and the enclosing member  40  are moved by the arm  22 . However, the present invention is not limited to the embodiments. Any other means which is capable of moving the jet nozzle  31  and the enclosing member  40  in a plane parallel to the polishing cloth  12   a , between the first position, which is located above the polishing cloth  12   a , and the second position, which is located outside of the polishing cloth  12   a , can be employed instead of the arm  22 . 
     For example, an elongated arm, which is linearly and reciprocally moved, may be employed instead of the arm  22 . The elongated arm may be moved linearly along a linear guide, which is arranged outside of the polishing plate  12  and guides the elongated arm in the radial direction of the polishing plate  12 , so as to move close to and away from the center roller  14 . The elongated arm may be driven by, for example, a driving mechanism including a ball screw or a chain-sprocket unit and a servo motor. By using the servo motor, the elongated arm can be positioned at the first and the second positions. 
     When employing the elongated arm, the jet nozzle  31  can be properly moved close to the center roller  14  as well as the swing able arm  22 . Further, if the jet nozzle  31  is inclined and the lower end of the jet nozzle  31  is oriented toward the center roller  14 , the high pressure water can be directed toward the part of the polishing cloth  12   a  which is in the vicinity of the center roller  14  so that the polishing cloth  12   a  can be properly cleaned. 
     In the above described embodiments, the semiconductor wafers  17  are polished as the work pieces. The work pieces are, of course, not limited to the semiconductor wafers. 
     In the cloth cleaning device and the polishing machine of the present invention, the polishing cloth including the part in the vicinity of the center roller can be fully cleaned, so that the work piece can be precisely polished with higher polishing efficiency and span of life of the expensive polishing cloth can be made longer. 
     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.