Patent Publication Number: US-2020298363-A1

Title: Polishing device and polishing method

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-052002, filed Mar. 19, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a polishing device and a polishing method. 
     BACKGROUND 
     Semiconductor devices, such as memory devices and logic devices, are manufactured by depositing films on a substrate and etching films repeatedly to form a desired circuit pattern on the substrate. During depositing of films and etching of films, for example, a convex defect, which protrudes from the surface of the substrate, may be occasionally formed on the substrate. 
     When the surface of the substrate has such a convex defect, an unfavorable situation, known as defocusing, arises in a lithography step for forming a circuit pattern to hinder formation of the circuit pattern as desired. In particular, this situation becomes more serious as a minimum size of circuit patterns decreases in accordance with progress in microfabrication of semiconductor devices. 
     When a film is further deposited over the convex defect, for example, an enlarged convex defect is formed on the buried convex defect. As the stacking number of films increases, the convex defect continues to be enlarged. This increases a region where defocusing hinders formation of the desired circuit pattern, and consequently, the above-described unfavorable situation becomes even more serious. 
     When memory cells of a memory device have a three-dimensional configuration, for example, the stacking number of films formed on a substrate drastically increases. This increases an influence of the convex defect on formation of circuit patterns, thus decreasing the yield of semiconductor devices. Consequently, it is desirable to effectively remove the convex defect on the surface of the substrate. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic diagrams illustrating a polishing device according to a first embodiment. 
         FIG. 2  is a diagram illustrating a polisher of the polishing device according to the first embodiment. 
         FIGS. 3A to 3C  are diagrams illustrating functions and effects of the polishing device and a polishing method according to the first embodiment. 
         FIGS. 4 and 5  are diagrams illustrating functions and effects of the polishing method according to the first embodiment. 
         FIGS. 6A and 6B  are schematic diagrams illustrating a polishing device according to a second embodiment. 
         FIGS. 7A and 7B  are schematic diagrams illustrating a polishing device according to a third embodiment. 
         FIGS. 8A and 8B  are schematic diagrams illustrating a polishing device according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments provide a polishing device and a polishing method that effectively remove convex defects on a surface of a substrate. 
     In general, according to an embodiment, a polishing device includes a substrate holder, a dispenser configured to dispense an abrasive to a surface of a substrate held by the substrate holder, a polisher including an elastic body configured to polish the surface of the substrate as the elastic body is rotated with respect to the surface of the substrate. An area of contact between the elastic body and the surface of the substrate during polishing is smaller than a surface area of a region of the substrate that is to be polished by the elastic body. The elastic body is moved, while the elastic body is rotated, with a downward velocity component prior to contacting the surface of the substrate and with an upward velocity component after the elastic body comes into contact with the surface of the substrate. 
     Description will now be made on embodiments of the present disclosure with reference to the drawings. In the following description, the same or similar components are denoted with identical reference numerals and signs, and components described once will not be elaborated repeatedly unless necessary. 
     Hereinafter, a polishing device and a polishing method according to each of the embodiments will be described with reference to the drawings. 
     First Embodiment 
     A polishing device according to a first embodiment includes: a holder configured to hold a substrate; a dispenser configured to dispense abrasive to a surface of the substrate; and a polisher including an elastic body and configured to polish the surface of the substrate using the elastic body. An area of contact between the elastic body and the surface of the substrate is smaller than a surface area of the substrate. A direction of a component of a velocity vector of the elastic body in polishing in a normal direction of the surface of the substrate is reversed after the elastic body comes into contact with the surface of the substrate. 
     A polishing method according to the first embodiment includes: dispensing abrasive to a surface of a substrate; bringing an elastic body into contact with the surface of the substrate in such a manner that an area of contact between the elastic body and the surface of the substrate is smaller than a surface area of the substrate; and moving the elastic body in such a manner that a direction of a component of a velocity vector of the elastic body in a normal direction of the surface of the substrate is reversed after the elastic body comes into contact with the surface of the substrate so as to polish the surface of the substrate. 
       FIGS. 1A and 1B  are schematic diagrams illustrating the polishing device according to the first embodiment.  FIG. 1A  illustrates a cross-sectional view of the polishing device, and  FIG. 1B  illustrates a top view of the polishing device. A polishing device  100  according to the first embodiment polishes a surface of a substrate such as a semiconductor wafer. 
     The polishing device  100  according to the first embodiment includes a stage  10  (also referred to as the holder), a support shaft  12 , an abrasive dispensing nozzle  14  (also referred to as the dispenser), a polisher  16 , a first rotation mechanism  18 , a movement mechanism  20 , a housing  22 , and a controller  24 . The polisher  16  includes a polishing pad  16   a  (also referred to as the elastic body) and a rotation shaft  16   b.    
     A semiconductor wafer W (also referred to as the substrate) to be polished is placed on the stage  10 . The semiconductor wafer W is secured on the stage  10  by, for example, vacuum suction from a rear surface side. A front surface of the semiconductor wafer W faces upward. That is, the front surface of the semiconductor wafer W is on an opposite side to the stage  10  side. 
     The support shaft  12  supports the stage  10 . The support shaft  12  secures the stage  10 . 
     The abrasive dispensing nozzle  14  dispenses slurry to the front surface of the semiconductor wafer W. The slurry is an example of the abrasive. 
     The slurry includes abrasive grains. The abrasive grains are particles including silicon oxide, aluminum oxide, or cerium oxide, for example. 
     The polisher  16  is disposed on the semiconductor wafer W side of the stage  10 . The polisher  16  polishes the front surface of the semiconductor wafer W. 
     The polisher  16  includes the polishing pad  16   a  and the rotation shaft  16   b . The polishing pad  16   a  is disposed around the rotation shaft  16   b.    
     The polishing pad  16   a  is an example of the elastic body. An storage modulus of the polishing pad  16   a  is, for example, equal to or higher than 0.01 GPa and equal to or less than 10 GPa. The storage modulus of the polishing pad  16   a  is measured by a method provided in JIS K7244-4 “Plastics—Determination of dynamic mechanical properties—Part 4: Tensile vibration —Non-resonance method”. 
     The polishing pad  16   a  includes resin or non-woven fabric, for example. The polishing pad  16   a  is made of a material such as polyurethane resin. 
     The polishing pad  16   a  is circular or elliptic in cross-section perpendicular to the front surface of the semiconductor wafer W.  FIG. 1A  illustrates a case where a surface of the polishing pad  16   a  is circular in cross-section perpendicular to the front surface of the semiconductor wafer W. 
     The rotation shaft  16   b  extends in a direction parallel to a surface of the stage  10 . The rotation shaft  16   b  is parallel to the front surface of the semiconductor wafer W. Rotation of the rotation shaft  16   b  causes the polishing pad  16   a  to rotate about the rotation shaft  16   b  in a circumferential direction of the polishing pad  16   a . The polishing pad  16   a  makes rotary movement. 
       FIG. 2  is a diagram illustrating the polisher  16  of the polishing device  100  according to the first embodiment.  FIG. 2  is an enlarged view of the polisher  16  and the front surface of the semiconductor wafer W.  FIG. 2  illustrates a state where the front surface of the semiconductor wafer W is being polished. 
       FIG. 2  illustrates a state of the polishing pad  16   a  in contact with the front surface of the semiconductor wafer W. When the polishing pad  16   a  comes into contact with the front surface of the semiconductor wafer W, the polishing pad  16   a  is elastically deformed. 
     A contact portion (S in  FIG. 2 ) where the polishing pad  16   a  polishing the front surface of the semiconductor wafer W is in contact with the front surface of the semiconductor wafer W has a contact area smaller than a surface area of the semiconductor wafer W. In other words, the polishing pad  16   a  is only in contact with part of the front surface of the semiconductor wafer W. A minimum width (Wmin) of the contact portion S is, for example, equal to or less than 1/100 of a diameter of the semiconductor wafer W. 
     A direction of a component of a velocity vector of the polishing pad  16   a  in polishing in a normal direction of the front surface of the semiconductor wafer W is reversed after the polishing pad  16   a  comes into contact with the front surface of the semiconductor wafer W. For example, a velocity vector before the polishing pad  16   a  in rotation comes into contact with the front surface of the semiconductor wafer W is a vector Va in  FIG. 2 . For example, a velocity vector after the polishing pad  16   a  in rotation comes into contact with the front surface of the semiconductor wafer W is a vector Vb in  FIG. 2 . 
     A component of the vector Va in the normal direction of the front surface of the semiconductor wafer W is a vector Vax in  FIG. 2 . A component of the vector Vb in the normal direction of the front surface of the semiconductor wafer W is a vector Vbx in  FIG. 2 . The vector Vax and the vector Vbx have reversed directions. 
     The first rotation mechanism.  18  causes the polishing pad  16   a  to rotate about the rotation shaft  16   b  in the circumferential direction of the polishing pad  16   a . The first rotation mechanism  18  includes components such as a motor and a bearing to rotatably hold the rotation shaft  16   b.    
     The movement mechanism  20  causes the polisher  16  to move relative to the semiconductor wafer W in directions parallel to the front surface of the semiconductor wafer W. The movement mechanism  20  moves the polisher  16  in the directions parallel to the front surface of the semiconductor wafer W. When the polisher  16  is moved using the movement mechanism  20 , the front surface of the semiconductor wafer W can be wholly polished. The movement mechanism  20  includes components such as a motor and a conversion mechanism to convert rotary motion of the motor into linear motion. 
     The housing  22  contains components such as the stage  10 , the support shaft  12 , the abrasive dispensing nozzle  14  (the dispenser), the polisher  16 , the first rotation mechanism  18 , and the movement mechanism  20 . The housing  22  protects components such as the stage  10 , the support shaft  12 , the abrasive dispensing nozzle  14  (the dispenser), the polisher  16 , the first rotation mechanism  18 , and the movement mechanism  20 . 
     The controller  24  controls the abrasive dispensing nozzle  14 , the polisher  16 , the first rotation mechanism  18 , and the movement mechanism  20 . For example, the controller  24  controls a dispensing start and end of the slurry from the abrasive dispensing nozzle  14  and a dispensing amount of the slurry. The controller  24  respectively controls the first rotation mechanism  18  and the movement mechanism.  20  to control a rotation speed and a movement speed of the polishing pad  16   a . The controller  24  may be hardware such as a circuit board or a combination of hardware and software such as a control program stored in a memory. 
     Next, the polishing method according to the first embodiment will be described. A case of using the polishing device  100  according to the first embodiment will be described as an example. 
     In the polishing method according to the first embodiment, the front surface of the semiconductor wafer W is polished. A circuit pattern is formed on the semiconductor wafer W to be polished, for example, by depositing films and etching films repeatedly. At least one of an insulating film and a conductive film, for example, is exposed on the front surface of the semiconductor wafer W to be polished. 
     First, the semiconductor wafer W is conveyed into the housing  22  and placed on the stage  10 . The semiconductor wafer W is secured on the stage  10  by, for example, vacuum suction from the rear surface side. 
     Next, the slurry is dispensed to the front surface of the semiconductor wafer W. The slurry is dispensed from the abrasive dispensing nozzle  14 . 
     Next, the polishing pad  16   a  of the polisher  16  is brought into contact with the front surface of the semiconductor wafer W. The contact portion (S in  FIG. 2 ) where the polishing pad  16   a  is in contact with the front surface of the semiconductor wafer W has a contact area smaller than the surface area of the semiconductor wafer W. 
     The polishing pad  16   a  is rotated about the rotation shaft  16   b  in the circumferential direction of the polishing pad  16   a . The direction of the component of the velocity vector of the polishing pad  16   a  in polishing in the normal direction of the front surface of the semiconductor wafer W is reversed after the polishing pad  16   a  comes into contact with the front surface of the semiconductor wafer W. The front surface of the semiconductor wafer W is polished by the polishing pad  16   a . A surface of the polishing pad  16   a  has a plurality of uneven portions. While the front surface of the semiconductor wafer W is being polished, the slurry remains in the plurality of uneven portions. 
     With the polishing pad  16   a  being kept rotating, the polisher  16  is moved in directions parallel to the front surface of the semiconductor wafer W, as indicated with the arrows in  FIG. 1B . The polisher  16  is moved to polish the entire front surface of the semiconductor wafer W. 
     After polishing the entire front surface of the semiconductor wafer W is ended, dispensing the slurry to the front surface of the semiconductor wafer W is ended. Then, the semiconductor wafer W is conveyed out of the housing  22 . 
     Next, functions and effects of the polishing device  100  and the polishing method according to the first embodiment will be described. 
     When a front surface of a semiconductor wafer has a convex defect in manufacturing a semiconductor device, an unfavorable situation, known as defocusing, arises in a lithography step to hinder formation of a desired circuit pattern. In particular, this situation becomes more serious as a minimum size of circuit patterns decreases in accordance with progress in microfabrication of semiconductor devices. 
     When a film is further deposited over the convex defect, for example, an enlarged convex defect is formed on the buried convex defect. As the stacking number of films increases, the convex defect continues to be enlarged. This increases a region where defocusing hinders formation of the desired circuit pattern, and consequently, the above-described unfavorable situation becomes even more serious. 
     The polishing device and the polishing method according to the first embodiment enable effective removal of convex defects on a front surface of a semiconductor wafer. 
       FIGS. 3A to 3C  are diagrams illustrating functions and effects of the polishing device and the polishing method according to the first embodiment.  FIG. 3A  is a schematic diagram illustrating a convex defect.  FIG. 3B  is a diagram illustrating a polishing method according to a comparative example.  FIG. 3C  is a diagram illustrating the polishing method according to the first embodiment. 
     Suppose, for example, that such a convex defect  30  as illustrated in  FIG. 3A  exists on the semiconductor wafer W. The convex defect  30  is formed by forming a film over foreign matter  29  in a lower layer. 
     The convex defect  30  illustrated in  FIG. 3A  is not attached to the front surface of the semiconductor wafer W but is integral to the surface. Therefore, it is difficult to remove the convex defect  30  by cleaning of a small mechanical action such as wet etching cleaning and brush cleaning. 
       FIG. 3B  illustrates a polishing method in which a polishing pad  17  is moved parallel to the front surface of the semiconductor wafer W. In this case, the convex defect  30  is removed by shearing stress applied in a direction parallel to the front surface of the semiconductor wafer W. 
     The polishing pad  17  continues to be moved laterally, and the shearing stress is continuously applied. Consequently, for example, the removed convex defect  30  is dragged on the front surface of the semiconductor wafer W by the polishing pad  17  and may unfortunately form a large scratch in the front surface of the semiconductor wafer W. Moreover, for example, the foreign matter  29  buried in the lower layer may be drawn out and dragged on the front surface of the semiconductor wafer W and may form an even larger scratch in the front surface of the semiconductor wafer W. 
     In the polishing method according to the first embodiment, in a similar manner to the comparative example, shearing stress is applied in a direction parallel to the front surface of the semiconductor wafer W in the contact portion of the polishing pad  16   a  so as to remove the convex defect  30 . The polishing method according to the first embodiment differs from the comparative example in that the polishing pad  16   a  is rotated. Consequently, after removing the convex defect  30 , the polishing pad  16   a  is moved upward. Therefore, no scratch is formed by dragging the convex defect  30  and by drawing out the foreign matter  29  buried in the lower layer and dragging the foreign matter  29 . 
     The polishing device and the polishing method according to the first embodiment enable effective removal of convex defects on a front surface of a semiconductor wafer without scratching the front surface of the semiconductor wafer. 
       FIG. 4  is a diagram illustrating functions and effects of the polishing method according to the first embodiment. As illustrated in  FIG. 4 , preferably, a circumferential width (Wx in  FIG. 4 ) of the portion where the polishing pad  16   a  is in contact with the semiconductor wafer W is equal to or less than a minimum size of a pattern formed on the semiconductor wafer W. In the case illustrated in  FIG. 4 , the minimum size of the pattern formed on the semiconductor wafer W is a width (L 1  in  FIG. 4 ) of wiring  40  or an interval (L 2  in  FIG. 4 ) between pieces of the wiring  40 . 
     When the above-described condition is satisfied, a length of a scratch formed by the polishing pad  16   a  dragging the convex defect  30  or such matter becomes equal to or less than the minimum size of the pattern formed on the semiconductor wafer W. This prevents, for example, disconnection of the wiring  40  and short-circuiting between pieces of the wiring  40 . 
       FIG. 5  is a diagram illustrating functions and effects of the polishing method according to the first embodiment.  FIG. 5  illustrates a case where the polisher  16  is moved horizontally relative to the semiconductor wafer W. 
     As illustrated in  FIG. 5 , preferably, a distance (d in  FIG. 5 ) of movement of a point (A in  FIG. 5 ) in the polishing pad  16   a  on the front surface of the semiconductor wafer W while the point is in contact with the semiconductor wafer W is equal to or less than the minimum size of the pattern formed on the semiconductor wafer W. In the case illustrated in  FIG. 5 , the minimum size of the pattern formed on the semiconductor wafer W is the width (L 1  in  FIG. 5 ) of the wiring  40  or the interval (L 2  in  FIG. 5 ) between pieces of the wiring  40 . 
     When the above-described condition is satisfied, a length of a scratch formed by the polishing pad  16   a  dragging the convex defect  30  or such matter becomes equal to or less than the minimum size of the pattern formed on the semiconductor wafer W. This prevents, for example, disconnection of the wiring  40  and short-circuiting between pieces of the wiring  40 . 
     The storage modulus of the polishing pad  16   a  is preferably equal to or higher than 0.01 GPa and equal to or less than 10 GPa and more preferably equal to or higher than 0.1 GPa and equal to or less than 1 GPa. When the storage modulus is higher than the lower limit value, removal efficiency of the convex defect, for example, is increased. When the storage modulus is less than the upper limit value, abrasion of a region other than the convex defect is prevented. 
     In view of removing the convex defect effectively, preferably, the polishing pad  16   a  includes resin or non-woven fabric. 
     As described above, the polishing device and the polishing method according to the first embodiment enable effective removal of convex defects. 
     Second Embodiment 
     A polishing device according to a second embodiment differs from the first embodiment in that the polishing device according to the second embodiment further includes a second rotation mechanism to rotate the holder to revolve the substrate about the center of the substrate. A polishing method according to the second embodiment differs from the first embodiment in that the polishing method according to the second embodiment revolves the substrate about the center of the substrate. In the following description, some of the contents overlapping with the first embodiment will not be repeated. 
       FIGS. 6A and 6B  are schematic diagrams illustrating the polishing device according to the second embodiment.  FIG. 6A  illustrates a cross-sectional view of the polishing device, and  FIG. 6B  illustrates a top view of the polishing device. A polishing device  200  according to the second embodiment polishes a surface of a substrate such as a semiconductor wafer. 
     The polishing device  200  according to the second embodiment includes the stage  10 , the support shaft  12 , the abrasive dispensing nozzle  14 , the polisher  16 , the first rotation mechanism  18 , the movement mechanism  20 , the housing  22 , the controller  24 , and a second rotation mechanism  26 . The polisher  16  includes the polishing pad  16   a  and the rotation shaft  16   b.    
     The second rotation mechanism  26  rotates the stage  10  to revolve the semiconductor wafer W about the center C of the semiconductor wafer W. The second rotation mechanism  26  rotates the support shaft  12 . 
     The second rotation mechanism  26  includes components such as a motor and a bearing to rotatably hold the support shaft  12 . The second rotation mechanism  26  is controlled by the controller  24 . 
     In the polishing method according to the second embodiment, the semiconductor wafer W is revolved about the center C of the semiconductor wafer W. Revolving the semiconductor wafer W increases shearing stress at the contact portion of the polishing pad  16   a . This improves removal performance of convex defects. 
     As described above, the polishing device and the polishing method according to the second embodiment enable more effective removal of convex defects than the first embodiment. 
     Third Embodiment 
     A polishing device according to a third embodiment differs from the first embodiment in that the polishing device according to the third embodiment includes a plurality of polishers. In the following description, some of the contents overlapping with the first embodiment will not be repeated. 
       FIGS. 7A and 7B  are schematic diagrams illustrating the polishing device according to the third embodiment.  FIG. 7A  illustrates a cross-sectional view of the polishing device, and  FIG. 7B  illustrates a top view of the polishing device. A polishing device  300  according to the third embodiment polishes a surface of a substrate such as a semiconductor wafer. 
     The polishing device  300  according to the third embodiment includes the stage  10 , the support shaft  12 , the abrasive dispensing nozzle  14 , the polishers  16 , the first rotation mechanism  18 , the movement mechanism  20 , the housing  22 , the controller  24 , and the second rotation mechanism  26 . The polishers  16  each include the polishing pad  16   a  and the rotation shaft  16   b.    
     The polishing device  300  includes the plurality of polishers  16 .  FIGS. 7A and 7B  illustrate an example of two polishers  16 . The polishing device  300  may include three polishers  16  or more. 
     The polishing device  300  including the plurality of polishers  16  can shorten polishing time. 
     As described above, the polishing device according to the third embodiment enables effective removal of convex defects in a similar manner to the first embodiment. Furthermore, polishing time can be shortened. 
     Fourth Embodiment 
     A polishing device according to a fourth embodiment differs from the first embodiment in that the elastic body has a length larger than a maximum length of the substrate. In the following description, some of the contents overlapping with the first embodiment will not be repeated. 
       FIGS. 8A and 8B  are schematic diagrams illustrating the polishing device according to the fourth embodiment.  FIG. 8A  illustrates a cross-sectional view of the polishing device, and  FIG. 8B  illustrates a top view of the polishing device. A polishing device  400  according to the fourth embodiment polishes a surface of a substrate such as a semiconductor wafer. 
     The polishing device  400  according to the fourth embodiment includes the stage  10 , the support shaft  12 , the abrasive dispensing nozzle  14 ), the polisher  16 , the first rotation mechanism  18 , the movement mechanism  20 , the housing  22 , the controller  24 , and the second rotation mechanism  26 . The polisher  16  includes the polishing pad  16   a  and the rotation shaft  16   b.    
     The polishing pad  16   a  of the polishing device  400  has a length (L 3  in  FIG. 8B ) larger than a maximum length (diameter D in  FIG. 8B ) of the semiconductor wafer W. 
     Since the length L 3  of the polishing pad  16   a  is larger than the diameter D of the semiconductor wafer W, the polishing device  400  can shorten polishing time. 
     As described above, the polishing device according to the fourth embodiment enables effective removal of convex defects in a similar manner to the first embodiment. Furthermore, polishing time can be shortened. 
     In describing the first to fourth embodiments as examples, the surface of the polishing pad  16   a  is circular in cross-section perpendicular to the front surface of the semiconductor wafer W. However, the surface of the polishing pad  16   a  may be elliptic in cross-section. 
     In describing the first to fourth embodiments as examples, the polishing pad  16   a  makes rotary movement. However, the polishing pad  16   a  may make reciprocating movement like a pendulum. In this case, for example, a cross-sectional shape of the polishing pad  16   a  may be part of a circle to reduce the polishing pad  16   a  in size. For example, the cross-sectional shape of the polishing pad  16   a  may be a fan shape. 
     In describing the first, third, and fourth embodiments as examples, the stage  10  is secured, and the polisher  16  is moved horizontally. However, the polisher  16  may be secured, and the stage  10  may be moved horizontally. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.