Patent Publication Number: US-2016229026-A1

Title: Retainer ring, polishing apparatus, and manufacturing method of semiconductor device

Description:
CROSS REFERENCE TO RELATED 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2015-020854, filed on Feb. 5, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a retainer ring, a polishing apparatus, and a manufacturing method of a semiconductor device. 
     BACKGROUND 
     In a manufacturing process of a semiconductor device, chemical mechanical polishing (hereinafter referred to as “CMP”) is used to flatten, for example, an insulating film, a metallic film, or a polycrystalline silicon film buried in a trench which is provided in a surface of a polishing object by patterning. A CMP apparatus generally holds the rear surface (the surface opposite to a polishing surface) of the polishing object by a polishing head to press the surface (polishing surface) of the polishing object onto a polishing pad to which slurry is supplied, and relatively rotate the polishing head and the polishing pad, thereby flattening the insulating film, the metallic film, or polycrystalline silicon buried in the trench in the surface of the polishing object. 
     The polishing head which holds the polishing object is provided with a mechanism which applies pressure to the rear surface of the polishing object, and a retainer ring which prevents the polishing object from protruding to outside of the polishing head during the relative rotation of the polishing head and the polishing pad. 
     The retainer ring as well as the polishing object is pressed onto the polishing pad. Therefore, if the fracture toughness is low, wear rapidly progresses due to the repetition of polishing, and the frequency of replacement increases, so that the costs of consumable materials increase, and time loss caused by replacement work is a problem. 
     Impact from the polishing object is also applied to the retainer ring. Therefore, partial wear occurs such that wear more significantly progresses on the side of the polishing object than on the side opposite to the polishing object. In this case, the outer peripheral part of the polishing object is excessively polished. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is an example of a perspective view showing a schematic configuration of a polishing apparatus (CMP apparatus) according to one embodiment; 
         FIG. 2  is an example of a sectional view of a polishing pad provided in the polishing apparatus shown in  FIG. 1 ; 
         FIG. 3  is an example of a perspective view showing a schematic configuration of a retainer ring according to one embodiment; 
         FIG. 4  is an example of a flowchart illustrating the outline of a manufacturing method of the retainer ring shown in  FIG. 3 ; 
         FIG. 5  is a table showing an example of an experimental result showing wear amounts of various ceramic materials; 
         FIG. 6  is an example of a diagram illustrating force which is applied to the retainer ring during polishing; 
         FIG. 7  is an example of a diagram illustrating a rebound from the polishing pad in an initial state of use; 
         FIG. 8  is an example of a diagram illustrating a rebound from the polishing pad after the partial wear of the retainer ring has progressed; 
         FIG. 9  is an example of a graph showing the relation between the polishing rate and the distance from the center of a polishing object by the comparison between the initial state and the state in which the partial wear has already progressed in the retainer ring; 
         FIG. 10  is an example of a graph showing the relation between the fracture toughness of the retainer ring and the incidence of chipping; 
         FIG. 11  is an example of a diagram illustrating how the side surface of the polishing object is chipped by stress resulting from the collision with the retainer ring; 
         FIG. 12  is an example of a graph showing the relation between the Young&#39;s modulus of the retainer ring and the incidence of chipping in the polishing object; and 
         FIG. 13  is an example of a table showing the fracture toughness and Young&#39;s modulus for each ceramic material. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with an embodiment, a polishing apparatus includes a polishing table and a polishing head. A retainer ring is attached to a surface of the polishing head. The surface of the polishing head faces the polishing table. The retainer ring includes a ceramic material, The fracture toughness of the ceramic material is 4 MPa·m 1/2  or more. 
     Embodiments will now be explained with reference to the accompanying drawings, Like components are provided with like reference signs throughout the drawings and repeated descriptions thereof are appropriately omitted. It is to be noted that the accompanying drawings illustrate the invention and assist in the understanding of the illustration and that the shapes, dimensions, and ratios and so on in each of the drawings may be different in some parts from those in an actual apparatus. 
     First, a polishing apparatus according to one embodiment is described with reference to  FIG. 1  to  FIG. 3 . 
       FIG. 1  is an example of a perspective view showing a schematic configuration of a polishing apparatus (CMP apparatus) according to the present embodiment. 
     A polishing apparatus  1  shown in  FIG. 1  includes a polishing table  2 , a polishing head  3 , a diamond dresser  4 , a polishing solution supply opening  5 , a pure water supply opening  6 , and a cleaning solution supply opening  7 . 
     A polishing pad  8  is attached to the upper surface (the surface facing the polishing head  3 ) of the polishing table  2 . The polishing table  2  is configured to be rotatable and drivable by a driver (not shown) including a motor. 
     The polishing head  3  is configured to be rotatable and drivable by a driver (not shown) including a motor. This polishing head  3  is configured to be able to press the upper surface (the surface facing the polishing head  3 ) of the polishing pad  8  with predetermined pressure while rotating, for example, a semiconductor wafer W (see  FIG. 2 ) which is a polishing object. The detailed configuration of the polishing head  3  will be described later in detail. 
     The diamond dresser  4  conditions the surface of the polishing pad  8 . The diamond dresser  4  is rotated and driven by a driver (not shown) including a motor, and is configured to be pressed by the polishing pad  8 . 
     The polishing solution supply opening  5 , the pure water supply opening  6 , and the cleaning solution supply opening  7  are configured to be able to respectively supply a polishing solution (e.g. slurry), pure water, and a cleaning solution onto the polishing pad  8  at predetermined flow volumes. 
     The specific structure of the polishing head  3  is described with reference to  FIG. 2 ,  FIG. 2  is an example of a sectional view along the cutting-plane line A-A in  FIG. 1 . 
     The polishing head  3  includes circular-plate-shaped head body  10 , a membrane  12 , and a retainer ring  11  corresponding to one embodiment. The head body  10  is configured to be supported by an arm (not shown). The membrane  12  is held by the retainer ring  11  so as to contact the lower surface (the surface facing the polishing pad  8 ) of the head body  10 . The retainer ring  11  is attached to the lower surface of the head body  10 , and holds the semiconductor wafer W in such a manner that the surface of the semiconductor wafer W opposite to the polishing surface contacts the lower surface of the membrane  12 . 
     The semiconductor wafer W thus held by the retainer ring  11  is pressed to the polishing pad  8  by the head body  10  and the membrane  12 . 
     A schematic configuration of the retainer ring  11  is shown in a perspective view in  FIG. 3 , The retainer ring  11  according to the present embodiment is manufactured by the use of a ceramic material as a whole, and has a fracture toughness of 4 MPa·m 1/2  or more and a Young&#39;s modulus of 400 GPa or less. 
     The outline of a manufacturing method of this retainer ring  11  is described with reference to  FIG. 4 , In the present embodiment, a ceramic is formed by the use of a cold isostatic press (CIP) method. 
     Specifically, a ceramic material (powder) is put into a rubber-state mold formed to adapt to the shape of a target retainer ring (step  1 ), and the mold is then inserted into a high-pressure container (step  2 ) and isotropically pressurized via a pressure medium (liquid) (step  3 ). As the ceramic material, for example, zirconia (ZrO 2 ), alumina (Al 2 O 3 ), silicon carbide (SiC), silicon nitride (SiN), yttria (Y 2 O 3 ), and cordierite (2MgO·2Al 2 O 3 ·5SiO 2 ) can be used (see  FIG. 13 ). 
     A primary process to form a groove (not shown) of the retainer ring is then performed (step  4 ), and a sinter process is performed to eliminate holes in the ceramic material (step  5 ). Finally, a finish process is performed as a secondary process, and the retainer ring  11  is thereby obtained (step  6 ). 
       FIG. 5  shows the wear amounts that are obtained by conducting experiments under the same experimental environment for each of the above-mentioned ceramic materials. As obvious from  FIG. 5 , it is confirmed that the ceramic materials can reduce the wear amounts 50 times or more as compared to polyphenylene sulfide (PPS) which is a generally used retainer ring material. 
     The degree of fracture toughness is a problem in the manufacture of the retainer ring. This is because if the retainer ring is manufactured by the use of a material having a fracture toughness of less than 4 MPa·m 1/2 , the retainer ring may break due to insufficient pressure during the CIP formation or may break from a slight crack or the like occurring during mechanical processing for forming the grooves in the primary process. 
     In contrast, when a material having a fracture toughness of 4 MPa·m 1/2  or more is used to manufacture the retainer ring by the CIP formation method, it was confirmed that the retainer ring can be satisfactorily manufactured without breakage or the like. 
     In CMP, the polishing head  3  and the polishing pad  8  are relatively rotated to flatten the surface of the semiconductor wafer W. Therefore, force from the polishing pad  8  is applied to the retainer ring  11  as indicated by the arrow AR 1  in  FIG. 6 , and force which causes the semiconductor wafer W to protrude to the outside of the polishing head  3  as indicated by the arrow AR 2  in  FIG. 6  is also repeatedly applied to the retainer ring  11  for every polishing. As a result of the repetition of such impacts in a lateral direction (a direction level with the surface of the polishing pad  8  facing a processing surface of the semiconductor wafer W), the inner surface of the retainer ring  11  may be chipped as indicated by the sign CP 1  in  FIG. 6 . 
     In an initial state of use of the retainer ring  11 , rebounds from the polishing pad  8  equally occur inside and outside the retainer ring  11  as shown in  FIG. 7 . However, if a chip CP 1  occurs in the inner surface of the retainer ring  11 , wear progresses from the crack, and partial wear progresses accordingly. The progress of the partial wear affects the state of a rebound from the polishing pad. For example, as shown in  FIG. 8 , rebounds from the polishing pad  8  concentrate inside the retainer ring  11 , and a polishing rate is enhanced at a wafer edge, thus resulting in a wafer edge excessive polishing state. 
     An example of this wafer edge excessive polishing state is shown in a graph of  FIG. 9 . It is obvious from  FIG. 9  that in the region of a wafer edge, due to the repetition of the polishing process, the polishing rate after the partial wear has progressed is significantly higher than the polishing rate in the initial state. 
       FIG. 10  is an example of a graph showing the relation between the fracture toughness of the retainer ring and the incidence of chipping. From  FIG. 10  it is confirmed that the incidence of chipping is 0 when the fracture toughness is 4 MPa·m 1/2  or more. 
     The retainer ring  11  according to the present embodiment has a fracture toughness of 4 MPa·m 1/2  or more, thus chipping in the inner surface of the retainer ring  11  is inhibited. Consequently, the occurrence of the partial wear can be inhibited. 
     Meanwhile, the impact by the (lateral) force during polishing which causes the semiconductor wafer W to protrude to the outside of the polishing head  3  is not only applied to the retainer ring  11  but also applied to the side of the semiconductor wafer W, and stress is repeatedly generated by collision between the semiconductor wafer W and the retainer ring  11 . Therefore, if a retainer ring  11  manufactured by the use of a hard material is used, a chip CP 2  may occur in the side surface of the semiconductor wafer W by receiving repetitive stress in the direction of the arrow AR 3 , as shown in  FIG. 11 . 
     One index that indicates the hardness (the degree of the elastic modulus) of a material is the Young&#39;s modulus (the physicality value [GPa] that indicates the difficulty of deformation). Stronger impact is applied to the semiconductor wafer W in the case of materials that are less deformable, so that the degree of the impact applied to the semiconductor wafer W can be judged by the degree of the Young&#39;s modulus of the retainer ring  11 . 
       FIG. 12  is an example of a graph showing the relation between the Young&#39;s modulus of the retainer ring  11  and the incidence of chipping in the semiconductor wafer W. From  FIG. 12  it is confirmed that desired buffering effect required to inhibit the chipping in the semiconductor wafer W can be obtained if the Young&#39;s modulus of the retainer ring  11  is 400 GPa or less. 
     The fracture toughness and Young&#39;s modulus of respective selectable ceramic materials are shown in a table of  FIG. 13 . As obvious from  FIG. 13 , it is possible to manufacture a retainer ring  11  having a fracture toughness of 4 MPa·m 1/2  or more and a Young&#39;s modulus is 400 GPa or less by the use of SiN. However, the material is not limited to SIN, and it is also possible to manufacture a retainer ring having desired physicality by selecting purity and the kind of binder or by combining the ceramic materials when, for example, other ceramic materials shown in  FIG. 13  are used. 
     The retainer ring according to at least one embodiment described above includes the ceramic material, so that the progress of wear can be inhibited. 
     In addition, the retainer ring according to at least one embodiment described above has a fracture toughness of 4 MPa·m 1/2  or more, so that the progress of partial wear can be inhibited. 
     Furthermore, the retainer ring according to at least one embodiment described above has a Young&#39;s modulus is 400 GPa or less, so that it is possible to prevent the polishing object from being damaged. 
     The polishing apparatus  1  according to at least one embodiment described above includes the retainer ring including the ceramic material, so that the frequency of the replacement of the retainer ring decreases, the throughput of the polishing process improves, and the polishing object can be thus polished at low cost. 
     In addition, the polishing apparatus  1  according to at least one embodiment described above includes the retainer ring having a fracture toughness of 4 MPa·m 1/2  or more, so that the polishing object can be polished without uneven polishing and without the chipping in the retainer ring. 
     Furthermore, the polishing apparatus  1  according to at least one embodiment described above includes the retainer ring having a Young&#39;s modulus of 400 GPa or less, so that it is possible to inhibit the polishing object from being damaged. 
     Next, a manufacturing method of a semiconductor device according to one embodiment is described. The manufacturing method according to the present embodiment includes a polishing process using the polishing apparatus  1  shown in  FIG. 1 . 
     First, a semiconductor wafer W in which an insulating film, a metallic film, a polycrystalline silicon film, and others are formed by, for example, patterning is prepared. 
     The semiconductor wafer W is then brought into contact with the polishing pad  8  in such a manner that the polishing surface of the semiconductor wafer W faces the polishing pad  8  while the semiconductor wafer W is held by the polishing head  3 . 
     The polishing table is then rotated, for example, in the direction of the arrow AR 10  in  FIG. 1  while a polishing solution such as slurry, pure water, and a cleaning solution are respectively supplied onto the polishing pad  8  at predetermined flow volumes via the polishing solution supply opening  5 , the pure water supply opening  6 , and the cleaning solution supply opening  7 . Moreover, while the semiconductor wafer W is held by the retainer ring  11 , the semiconductor wafer W is pressed to the polishing pad  8  by the head body  10  and the membrane  12  and at the same time rotated, for example, in the direction of the arrow AR 20  in  FIG. 1 , Thus, polishing targets such as the silicon film, the metallic film, and the insulating film formed on the semiconductor wafer W are polished by the relative rotation of the polishing pad  8  and the semiconductor wafer W. A semiconductor device is manufactured on the semiconductor wafer W by the repetition of the film formation process and the polishing process. 
     During polishing, the surface part of the semiconductor wafer W is returned to the initial state before polishing by the diamond dresser  4  in order to prevent the surface part of the polishing pad  8  from being worn or being clogged with abrasive grains included in an abrasive due to the polishing of the semiconductor wafer W. 
     The polishing pad  8  and the polishing head  3  are preferably rotated and driven together, from the perspective of eliminating the unevenness of the polishing amount of the semiconductor wafer W. When these portions are rotated and driven, the rotation direction of the polishing pad  8  and the rotation direction of the polishing head  3  are preferably the same as shown in  FIG. 1 . Although both the polishing pad  8  and the polishing head  3  respectively rotate in the directions of the arrows AR 10  and AR 20  in the case shown in  FIG. 1 , it should be understood that these portions do not exclusively rotate in this direction, and may rotate in directions opposite to the above directions. 
     According to the manufacturing method of the semiconductor device in at least one embodiment described above, the substrate is polished by the use of the polishing apparatus  1  provided with the retainer ring  11  including the ceramic material, so that the costs of consumable materials are reduced, and the manufacturing costs of the semiconductor device can be reduced. 
     In addition, according to the manufacturing method of the semiconductor device in at least one embodiment described above, the substrate is polished by the use of the polishing apparatus  1  provided with the retainer ring  11  having a fracture toughness of 4 MPa·m 1/2  or more, so that it is possible to prevent the excessive polishing of a substrate edge region resulting from the partial wear of the retainer ring. Consequently, the substrate can be accurately polished, so that it is possible to improve the yield of the semiconductor device. 
     Furthermore, according to the manufacturing method of the semiconductor device in at least one embodiment described above, the substrate is polished by the use of the polishing apparatus  1  provided with the retainer ring  11  having a, Young&#39;s modulus of 400 GPa or less, so that it is possible to prevent the substrate from being chipped, and improve the yield of the semiconductor device. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to emit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems 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.