Patent Publication Number: US-9849558-B2

Title: Polishing pad dresser, polishing apparatus and polishing pad dressing method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2015-32012, filed on Feb. 20, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a polishing pad dresser, a polishing apparatus and a polishing pad dressing method. 
     BACKGROUND 
     When a semiconductor device is manufactured, a film on a substrate is often polished to planarize the film or to make the film thinner. For example, such polishing is performed with a chemical mechanical polishing (CMP) apparatus. However, when the semiconductor device with a large vertical dimension such as a three-dimensional memory is manufactured, such polishing performed with an existing CMP apparatus takes long time of approximately 100 seconds. Therefore, a technique is required in which a polishing target such as the film on the substrate can be polished faster. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a structure of a polishing apparatus of a first embodiment; 
         FIGS. 2A and 2B  are cross-sectional views illustrating a structure of a first polishing pad dresser of the first embodiment; 
         FIGS. 3A and 3B  are cross-sectional views illustrating a structure of a second polishing pad dresser of the first embodiment; 
         FIGS. 4A to 4C  are cross-sectional views illustrating an example of usage of the first polishing pad dresser of the first embodiment; 
         FIGS. 5A to 5C  are cross-sectional views illustrating an example of usage of the second polishing pad dresser of the first embodiment; 
         FIG. 6  is a graph illustrating measurement results of polishing rates of a wafer by using a polishing pad of the first embodiment; 
         FIGS. 7A to 7F  are plan views illustrating examples of layout for convex portions of the first polishing pad dresser of the first embodiment; 
         FIGS. 8A to 8C  are cross-sectional views illustrating a first example of a method of fabricating the first polishing pad dresser of the first embodiment; 
         FIGS. 9A to 9C  are cross-sectional views illustrating a second example of the method of fabricating the first polishing pad dresser of the first embodiment; 
         FIG. 10  is a cross-sectional view illustrating a structure of a polishing apparatus of a second embodiment; 
         FIGS. 11A and 11B  are cross-sectional views illustrating a structure of a polishing pad dresser of the second embodiment; and 
         FIGS. 12A and 12B  are plan views illustrating structures of the polishing pad dresser of the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be explained with reference to the accompanying drawings. 
     In one embodiment, a polishing pad dresser includes a first base portion, and first convex portions provided in a first region of the first base portion. Furthermore, a width of the first convex portions is 1 to 10 μm, a height of the first convex portions is 0.5 to 10 μm, and a density of the first convex portions in the first region is 0.1 to 50%. 
     First Embodiment 
       FIG. 1  is a cross-sectional view illustrating a structure of a polishing apparatus of a first embodiment. 
     The polishing apparatus in  FIG. 1  is a CMP apparatus for polishing a wafer (substrate)  1  by CMP. The polishing apparatus in  FIG. 1  includes a surface plate  2 , a polishing pad  3 , a polishing head  4 , a slurry feeder  5 , a controller  6 , a first polishing pad dresser  11 , a first arm  12 , a first standby module  13 , a second polishing pad dresser  21 , a second arm  22  and a second standby module  23 . 
       FIG. 1  illustrates an X-direction and a Y-direction which are parallel to a placing surface of the polishing apparatus and perpendicular to each other, and a Z-direction perpendicular to the placing surface of the polishing apparatus. In the specification, the +Z-direction is regarded as an upward direction and the −Z-direction is regarded as a downward direction. For example, positional relation between the wafer  1  and the surface plate  2  is expressed as that the surface plate  2  is positioned below the wafer  1 . The −Z-direction of the present embodiment may coincide with the direction of gravity or may not coincide with the direction of gravity. 
     The polishing head  4  holds the wafer  1  which is a polishing target, and the surface plate  2  holds the polishing pad  3  which is a polishing member. The polishing apparatus causes the wafer  1  to rotate with the polishing head  4 , causes the polishing pad  3  to rotate with the surface plate  2 , and feeds slurry on the surface of the polishing pad  3  from the slurry feeder  5 . The polishing apparatus then brings the wafer  1  into contact with the polishing pad  3  using the polishing head  4  to press the wafer  1  on the polishing pad  3 . In this way, the surface of the wafer  1  is polished by the polishing pad  3 . Operations of the surface plate  2 , the polishing head  4  and the slurry feeder  5  are controlled by the controller  6 . The controller  6  controls various operations of the polishing apparatus. 
     The first and second polishing pad dressers  11  and  21  are used for dressing the surface of the polishing pad  3 . The dressing can improve or recover the performance of the polishing pad  3 . 
     The first polishing pad dresser  11  is held by the first arm  12 . When the wafer  1  is polished by the polishing pad  3 , the first polishing pad dresser  11  is standing by in the state where it is immersed in water inside the first standby module  13 . When the polishing pad  3  is dressed by the first polishing pad dresser  11 , the first arm  12  moves the first polishing pad dresser  11  to the position of the arrow P, rotates the first polishing pad dresser  11 , and presses the first polishing pad dresser  11  on the polishing pad  3 . In this way, the surface of the polishing pad  3  is dressed by the first polishing pad dresser  11 . The operation of the first arm  12  is controlled by the controller  6 . 
     The second polishing pad dresser  21  is held by the second arm  22 . When the wafer  1  is polished by the polishing pad  3 , the second polishing pad dresser  21  is standing by in the state where it is immersed in water inside the second standby module  23 . When the polishing pad  3  is dressed by the second polishing pad dresser  21 , the second arm  22  moves the second polishing pad dresser  21  to the position of the arrow P, rotates the second polishing pad dresser  21 , and presses the second polishing pad dresser  21  on the polishing pad  3 . In this way, the surface of the polishing pad  3  is dressed by the second polishing pad dresser  21 . The operation of the second arm  22  is controlled by the controller  6 . 
       FIGS. 2A and 2B  are cross-sectional views illustrating a structure of the first polishing pad dresser  11  of the first embodiment. 
       FIG. 2A  is a cross-sectional view illustrating the first polishing pad dresser  11  in dressing the polishing pad  3 .  FIG. 2B  is an expanded sectional view in which the frontside-to-backside direction of the first polishing pad dresser  11  is reversed. 
     As illustrated in  FIG. 2A , the first polishing pad dresser  11  includes a base portion  11   a  and convex portions  11   b  provided on the base portion  11   a . The convex portions  11   b  of the present embodiment are edge patterns protruding from a surface of the base portion  11   a . The first polishing pad dresser  11  dresses the polishing pad  3  with these convex portions  11   b . The base portion  11   a  is an example of a first base portion. The convex portions  11   b  are an example of first convex portions. 
     A part of the base portion  11   a  is formed of a first material  11   1 . The remaining part of the base portion  11   a  and the convex portions  11   b  are formed of a second material  11   2  different from the first material  11   1 . In this manner, the convex portions  11   b  of the present embodiment are formed of the same material as a portion of the base portion  11   a . Alternatively, the convex portions  11   b  of the present embodiment may be formed of the same material as the entirety of the base portion  11   a.    
     The convex portions  11   b  are desirable to be formed of a hard material because they are used for dressing the polishing pad  3 . Examples of the material of the convex portions  11   b  are a Si-based material containing silicon (Si), a Ti-based material containing titanium (Ti), an Al-based material containing aluminum (Al) and the like. Specifically, the convex portions  11   b  are oxides, nitrides or carbides containing Si, Ti or Al. Examples of the material of the convex portions  11   b  are silicon (Si), silicon oxide (SiO 2 ), silicon nitride (SiN), silicon carbide (SiC), titanium nitride (TiN), aluminum oxide (Al 2 O 3 ) and the like. 
     The base portion  11   a  has a first surface S 1A , a second surface S 1B , and an end face S 1C  between the first and second surfaces S 1A  and S 1B . The convex portions  11   b  are provided in a region R 1  corresponding to the first surface S 1A  of the base portion  11   a . The region R 1  is an example of a first region. 
       FIG. 2B  illustrates a width W 1  of the convex portions  11   b , a height H 1  of the convex portions  11   b , and a density D 1  of the convex portions  11   b  in the region R 1 . The width W 1  of the convex portions  11   b  of the present embodiment is set to be 1 to 10 μm (1 μm≦W 1 ≦10 μm). The height H 1  of the convex portions  11   b  of the present embodiment is set to be 0.5 to 10 μm (0.5 μm≦H 1 ≦10 μm). The density D 1  of the convex portions  11   b  in the region R 1  of the present embodiment is set to be 0.1 to 50% (0.1%≦D 1 ≦50%). 
     The density D 1  of the present embodiment is calculated by dividing the total area of the convex portions  11   b  in the region R 1  by the area of the region R 1  and expressing it in percentage. It is noted that these areas represent the areas of the region R 1  and the convex portions  11   b  in the XY-plane. The area of the region R 1  of the present embodiment represents the area of the first surface S 1A  and is expressed by πr 1   2  where r 1  is the radius of the first surface S 1A . 
       FIGS. 3A and 3B  are cross-sectional views illustrating a structure of the second polishing pad dresser  21  of the first embodiment. 
       FIG. 3A  is a cross-sectional view illustrating the second polishing pad dresser  21  in dressing the polishing pad  3 .  FIG. 3B  is an expanded sectional view in which the frontside-to-backside direction of the second polishing pad dresser  21  is reversed. 
     As illustrated in  FIG. 3A , the second polishing pad dresser  21  includes a base portion  21   a  and convex portions  21   b  provided on the base portion  21   a . The convex portions  21   b  of the present embodiment are diamond particles attached onto a surface of the base portion  21   a . In this manner, the convex portions  21   b  of the present embodiment are formed of diamond. The second polishing pad dresser  21  dresses the polishing pad  3  with these convex portions  21   b.    
     The base portion  21   a  has a first surface S 2A , a second surface S 2B , and an end face S 2C  between the first and second surfaces S 2A  and S 2B . The convex portions  21   b  are provided in a region R 2  corresponding to the first surface S 2A  of the base portion  21   a.    
       FIG. 3B  illustrates a width W 2  of the convex portions  21   b , a height H 2  of the convex portions  21   b , and a density D 2  of the convex portions  21   b  in the region R 2 . The width W 2  of the convex portions  21   b  of the present embodiment is set to be greater than 10 μm (W 2 &gt;10 μm), for example, 100 to 200 μm. The height H 2  of the convex portion  21   b  of the present embodiment is set to be greater than 10 μm (H 2 &gt;10 μm), for example, 100 to 200 μm. The density D 2  of the convex portions  21   b  in the region R 2  of the present embodiment is set to be higher than 50% (D 2 &gt;50%). 
     The density D 2  of the present embodiment is calculated by dividing the total area of the convex portions  21   b  in the region R 2  by the area of the region R 2  and expressing it in percentage. It is be noted that these areas represent the areas of the region R 2  and the convex portions  21   b  in the XY-plane. The area of the region R 2  of the present embodiment represents the area of the first surface S 2A  and is expressed by πr 2   2  where r 2  is the radius of the first surface S 2A . 
     As described above, the first polishing pad dresser  11  of the present embodiment includes fine convex portions  11   b  whose width W 1  and height H 1  are 10 μm or less, and the second polishing pad dresser  21  of the present embodiment includes course convex portions  21   b  whose width W 2  and height H 2  exceed 10 μm. Moreover, the density D 1  of the convex portions  11   b  in the first polishing pad dresser  11  of the present embodiment is set to be 50% or less so that the convex portions  11   b  are arranged sparse, and the density D 2  of the convex portions  21   b  in the second polishing pad dresser  21  of the present embodiment is set higher than 50% so that the convex portions  21   b  is arranged dense. 
       FIGS. 4A to 4C  are cross-sectional views illustrating an example of usage of the first polishing pad dresser  11  of the first embodiment. 
       FIG. 4A  illustrates the first polishing pad dresser  11  in dressing the polishing pad  3 . Since the first polishing pad dresser  11  of the present embodiment includes the fine and low-density convex portions  11   b , it can form fine scratches  3   a  on the surface of the polishing pad  3  by dressing the polishing pad  3  ( FIG. 4B ). 
       FIG. 4C  illustrates polishing of the wafer  1  using the polishing pad  3  which has been dressed by the first polishing pad dresser  11 . Sign  7  designates slurry particles fed from the slurry feeder  5 . The slurry particles  7  come into the scratches  3   a  of the polishing pad  3 . The slurry particles  7  which have got into the scratches  3   a  contribute to improvement of the polishing rate of the wafer  1  with the polishing pad  3 . Therefore, the present embodiment makes it possible, by dressing the polishing pad  3  with the first polishing pad dresser  11 , to enhance the polishing rate compared to that before the dressing. 
       FIGS. 5A to 5C  are cross-sectional views illustrating an example of usage of the second polishing pad dresser  21  of the first embodiment. 
       FIG. 5A  illustrates the second polishing pad dresser  21  in dressing the polishing pad  3 . Since the second polishing pad dresser  21  of the present embodiment includes the course and high-density convex portions  21   b , it can form coarse scratches  3   b  on the surface of the polishing pad  3  by dressing the polishing pad  3  ( FIG. 5B ). 
       FIG. 5C  illustrates polishing of the wafer  1  using the polishing pad  3  which has been dressed by the second polishing pad dresser  21 . Sign  7  designates the slurry particles fed from the slurry feeder  5 . The slurry particles  7  come into the scratches  3   b  of the polishing pad  3 . The slurry particles  7  which have got into the scratches  3   b  contribute to improvement of the polishing rate of the wafer  1  with the polishing pad  3 . Therefore, the present embodiment makes it possible, by dressing the polishing pad  3  with the second polishing pad dresser  21 , to enhance the polishing rate compared with that before the dressing. 
     In the present embodiment, the polishing pad  3  dressed by the first polishing pad dresser  11  has the fine scratches  3   a , and the polishing pad  3  dressed by the second polishing pad dresser  21  has the coarse scratches  3   b . Therefore, it is considered that the slurry particles  7  are more liable to be trapped in the scratches  3   a  than in the scratches  3   b . Accordingly, the polishing rate of the polishing pad  3  can be enhanced more in the case of using the polishing pad  3  dressed by the first polishing pad dresser  11  of the present embodiment than in the case of using the polishing pad  3  dressed by the second polishing pad dresser  21 . 
     The second polishing pad dresser  21  is normally used in dressing the polishing pad  3  of the present embodiment. Meanwhile, the first polishing pad dresser  11  is used when the polishing rate of the polishing pad  3  is desired to be largely improved. For example, the second polishing pad dresser  21  is used when low protrusions are desired to be removed by the polishing. On the other hand, the first polishing pad dresser  11  is used when high protrusions are desired to be removed by the polishing. In this manner, the first and second polishing pad dressers  11  and  21  in the present embodiment can be separately used depending on the intended purpose. 
     The scratches  3   a  by the first polishing pad dresser  11  are finer than the scratches  3   b  by the second polishing pad dresser  21 . Therefore, the present embodiment makes it possible, by dressing the polishing pad  3  with the first polishing pad dresser  11 , to reduce the abrasion amount of the polishing pad  3  compared with the case of dressing the polishing pad  3  with the second polishing pad dresser  21 . Therefore, the present embodiment can extend the operation life of the polishing pad  3 . 
       FIG. 6  is a graph illustrating measurement results of polishing rates of the wafer  1  by using the polishing pad  3  of the first embodiment. 
       FIG. 6  presents the polishing rate in the case of using the polishing pad  3  dressed by the first polishing pad dresser  11  (edge dressing), and the polishing rate in the case of using the polishing pad  3  dressed by the second polishing pad dresser  21  (diamond dressing). From the measurement results in  FIG. 6 , it is understood that the polishing rate in the case of using the first polishing pad dresser  11  increases by 1.4 times compared with the polishing rate in the case of using the second polishing pad dresser  21 . 
       FIGS. 7A to 7F  are plan views illustrating examples of layout for the convex portions  11   b  of the first polishing pad dresser  11  of the first embodiment. 
     Each of the convex portions  11   b  in  FIG. 7A  has a square planar shape and has a columnar shape extending in the Z-direction. The width W 1  of these convex portions  11   b  is the length of one side of the square. 
     Each of the convex portions  11   b  in  FIG. 7B  has an annular planar shape and has a tubular shape extending in the Z-direction. The inner circumference and the outer circumference of the annular shape are square. The width W 1  of these convex portions  11   b  is the length of one side of the outer circumferential square. Each convex portion  11   b  in  FIG. 7B  has a shape having four convex portions  11   b  in  FIG. 7A  connected to one another, and has approximately 8 times the volume of each convex portion  11   b  in  FIG. 7A . The width W 1  of the convex portions  11   b  in  FIG. 7B  is approximately 3 times the width W 1  of the convex portions  11   b  in  FIG. 7A . 
     Each convex portion  11   b  in  FIG. 7C  has a shape in which a center cavity of each convex portion  11   b  in  FIG. 7B  is closed. Therefore, each of the convex portions  11   b  in  FIG. 7C  has a square planar shape and has a columnar shape extending in the Z-direction. The width W 1  of these convex portions  11   b  is the length of one side of the square. It is noted that the length of one side of the square in  FIG. 7C  is reduced to be ⅔ times the length of one side of the outer circumferential square in  FIG. 7B . Therefore, the width W 1  of the convex portions  11   b  in  FIG. 7C  is approximately twice the width W 1  of the convex portions  11   b  in  FIG. 7A . Each convex portion  11   b  in  FIG. 7C  has approximately 4 times the volume of each convex portion  11   b  in  FIG. 7A . 
     In the case where a convex portion  11   b  has a columnar shape, the planar shape of the convex portion  11   b  may be other than square. Similarly, in the case where a convex portion  11   b  has a tubular shape, the inner circumferential and outer circumferential planar shapes of the convex portion  11   b  may be other than square. Moreover, the layout of the convex portions  11   b  is not limited to the examples in  FIGS. 7A to 7C . For example, the convex portions  11   b  may be arranged in a triangular grid instead of being arranged in a rectangular grid. Other examples of the convex portions  11   b  of the present embodiment are illustrated in  FIGS. 7D to 7F . 
     The convex portions  11   b  in  FIGS. 7D and 7E  have strip planar shapes extending in the X-direction. The width W 1  of these convex portions  11   b  is the length of the short side of the strip shapes. The width W 1  of the convex portions  11   b  in  FIGS. 7D and 7E  is herein set to be approximately the same as the width W 1  of the convex portions  11   b  in  FIG. 7A . 
     Each of the convex portions  11   b  in  FIG. 7F  has a cross planar shape containing strip portions extending in the X-direction and strip portions extending in the Y-direction. The width W 1  of these convex portions  11   b  is the length of the short sides of these strip portions. The width W 1  of the convex portions  11   b  in  FIG. 7F  is set to be approximately the same as the width W 1  of the convex portions  11   b  in  FIG. 7A . 
       FIGS. 8A to 8C  are cross-sectional views illustrating a first example of a method of fabricating the first polishing pad dresser  11  of the first embodiment. In the first example, the first polishing pad dresser  11  is fabricated by semiconductor manufacture processing. 
     First, the second material  11   2  is formed on the first material  11   1 , and a photoresist film  11   3  is formed on the second material  11   2  ( FIG. 8A ). Examples of the first material  11   1  are a semiconductor substrate and an insulating substrate. Examples of the second material  11   2  are a conductive layer, a semiconductor layer and an insulating layer. The first material  11   1  or the second material  11   2  may be a stacked film including plural layers. 
     Next, the photoresist film  11   3  is patterned by photolithography and etching ( FIG. 8B ). As a result, convex portions  11   c  are formed of the photoresist film  11   3 . 
     Next, the second material  11   2  is etched by using the photoresist film  11   3  as a mask ( FIG. 8C ). As a result, the convex portions  11   c  are transferred onto the second material  11   2  to form the convex portions  11   b  of the second material  11   2 . In this way, the first polishing pad dresser  11  including the base portion  11   a  and the convex portions  11   b  is fabricated. 
     The etching in  FIG. 8C  may be stopped before the first material  11   1  is exposed, or may be continued until the first material  11   1  is exposed. In the former case, the base portion  11   a  is to include the first material  11   1  and a part of the second material  11   2 . In the latter case, the base portion  11   a  is to include only the first material  11   1 .  FIG. 8C  represents the former case. This is the same as the case in  FIGS. 2A and 2B . 
     The polishing pad dresser  11  of the present embodiment may be formed by forming the photoresist film  11   3  on the first material  11   1 , patterning the photoresist film  11   3 , and etching the first material  11   1  by using the photoresist film  11   3  as a mask. In this case, both of the base portion  11   a  and the convex portions  11   b  are formed of only the first material  11   1 . 
       FIGS. 9A to 9C  are cross-sectional views illustrating a second example of the method of fabricating the first polishing pad dresser  11  of the first embodiment. In the second example, the first polishing pad dresser  11  is fabricated by metallic molding. 
     First, a metallic mold  14  having a first opening  14   a  for forming the base portion  11   a  and second openings  14   b  for forming the convex portions  11   b  is prepared ( FIG. 9A ). The second openings  14   b  are provided at the bottom of the first opening  14   a.    
     Next, the material of the first polishing pad dresser  11  is poured into the first and second openings  14   a  and  14   b  ( FIG. 9B ). In this way, the first polishing pad dresser  11  including the base portion  11   a  and the convex portions  11   b  is fabricated with the metallic mold  14 . 
     Next, the first polishing pad dresser  11  is taken out of the metallic mold  14  ( FIG. 9C ). In this way, the first polishing pad dresser  11  completes. 
     As described above, the first polishing pad dresser  11  of the present embodiment includes the fine and low-density convex portions  11   b . Specifically, the width W 1  of the convex portions  11   b  of the present embodiment is set to be 1 to 10 μm, the height H 1  of the convex portions  11   b  of the present embodiment is set to be 0.5 to 10 μm, and the density D 1  of the convex portions  11   b  in the region R 1  of the present embodiment is set to be 0.1 to 50%. 
     Therefore, the present embodiment can form, by dressing the polishing pad  3  with the first polishing pad dresser  11 , the fine scratches  3   a  on the polishing pad  3 , which can effectively enhance the polishing rate of the polishing pad  3 . Therefore, the present embodiment makes it possible, by using such a polishing pad  3 , to enable fast polishing of a polishing target such as the wafer  1 . 
     Second Embodiment 
       FIG. 10  is a cross-sectional view illustrating a structure of a polishing apparatus of a second embodiment. In the description of the second embodiment, explanations on the matters common to those of the first embodiment are omitted. 
     The polishing apparatus in  FIG. 10  includes a polishing pad dresser  31 , an arm  32  and a standby module  33  in place of the first polishing pad dresser  11 , the first arm  12 , the first standby module  13 , the second polishing pad dresser  21 , the second arm  22  and the second standby module  23 . 
     The polishing pad dresser  31  is used for dressing the surface of the polishing pad  3 . The dressing can improve or recover the performance of the polishing pad  3 . 
     The polishing pad dresser  31  is held by the arm  32 . When the wafer  1  is polished by the polishing pad  3 , the polishing pad dresser  31  is standing by in the state where it is immersed in water inside the standby module  33 . When the polishing pad  3  is dressed by the polishing pad dresser  31 , the arm  32  moves the polishing pad dresser  31  to the position of the arrow P, rotates the polishing pad dresser  31 , and presses the polishing pad dresser  31  on the polishing pad  3 . In this way, the surface of the polishing pad  3  is dressed by the polishing pad dresser  31 . The operation of the arm  32  is controlled by the controller  6 . 
       FIGS. 11A and 11B  are cross-sectional views illustrating a structure of the polishing pad dresser  31  of the second embodiment. 
     As illustrated in  FIGS. 11A and 11B , the polishing pad dresser  31  includes a first dresser module  31   a , and a second dresser module  31   b  adjacent to the first dresser module  31   b . The first dresser module  31   a  of the present embodiment has a circular planar shape. The second dresser module  31   b  of the present embodiment has a circular ring-like planar shape and surrounds the first dresser module  31   a.    
     The first dresser module  31   a  is configured to be movable relative to the second dresser module  31   b , and therefore can move in the vertical direction relative to the second dresser module  31   b  (Z-direction). In  FIG. 11A , the first dresser module  31   a  is sucked in the upward direction as indicated by the arrow A 1 . In  FIG. 11B , the first dresser module  31   a  is pressed in the downward direction as illustrated by the arrow A 2 . 
     Similarly to the first polishing pad dresser  11  of first embodiment, the first dresser module  31   a  includes the base portion  11   a  and the convex portions  11   b  provided on the base portion  11   a . Similarly to the first embodiment, the convex portions  11   b  of the present embodiment are edge patterns protruding from the surface of the base portion  11   a . The first dresser module  31   a  can dress the polishing pad  3  with these convex portions  11   b . The base portion  11   a  is an example of the first base portion. The convex portions  11   b  are an example of the first convex portions. 
     The base portion  11   a  has the first surface S 1A , the second surface S 1B , and the end face S 1C  between the first and second surfaces S 1A  and S 1B . The convex portions  11   b  are provided in the region R 1  corresponding to the first surface S 1A  of the base portion  11   a . The region R 1  is an example of the first region. 
     The width W 1  of the convex portions  11   b , the height H 1  of the convex portions  11   b , and the density D 1  of the convex portions  11   b  in the region R 1  are set similarly to the first embodiment (refer to  FIG. 2B ). Namely, the width W 1  of the convex portions  11   b  is set to be 1 to 10 μm, the height H 1  of the convex portions  11   b  is set to be 0.5 to 10 μm, and the density D 1  of the convex portions  11   b  in the region R 1  is set to be 0.1 to 50%. The density D 1  is calculated by dividing the total area of the convex portions  11   b  in the region R 1  by the area of the region R 1  and expressing it in percentage. 
     Similarly to the second polishing pad dresser  21  of the first embodiment, the second dresser module  31   b  includes the base portion  21   a  and the convex portions  21   b  provided on the base portion  21   a . Similarly to the first embodiment, the convex portions  21   b  of the present embodiment are diamond particles attached onto the surface of the base portion  21   a . The second dresser module  31   b  can dress the polishing pad  3  with these convex portions  21   b . The base portion  21   a  is an example of a second base portion. The convex portions  21   b  are an example of second convex portions. 
     The base portion  21   a  has the first surface S 2A , the second surface S 2B , an outer end face S 2C  between the first and second surfaces S 2A  and S 2B , and an inner end face S 2D  between the first and second surface S 2A  and S 2B . The base portion  21   a  is adjacent to the base portion  11   a . The inner end face S 2D  of the base portion  21   a  is adjacent to the end face S 1C  of the base portion  11   a . The convex portions  21   b  are provided in the region R 2  corresponding to the first surface S 2A  of the base portion  21   a . The region R 2  is an example of a second region. 
     The width W 2  of the convex portions  21   b , the height H 2  of the convex portions  21   b , and the density D 2  of the convex portions  21   b  in the region R 2  are set similarly to the first embodiment (refer to  FIG. 3B ). Namely, the width W 2  of the convex portions  21   b  is set to be longer than 10 μm, the height H 2  of the convex portions  21   b  is set to be greater than 10 μm, and the density D 2  of the convex portions  21   b  in the region R 2  is set to be higher than 50%. The density D 2  is calculated by dividing the total area of the convex portions  21   b  in the region R 2  by the area of the region R 2  and expressing it in percentage. 
     The base portion  11   a  (first dresser module  31   a ) is configured to be movable relative to the base portion  21   a  (second dresser module  31   b ), and therefore can move in the vertical direction relative to the base portion  21   a.    
     In  FIG. 11A , the base portion  11   a  is sucked in the upward direction. As a result, the first surface S 1A  of the base portion  11   a  is higher than the first surface S 2A  of the base portion  21   a . Therefore, the polishing pad dresser  31  in  FIG. 11A  can dress the polishing pad  3  only with the convex portions  21   b  of the second dresser module  31   b.    
     In  FIG. 11B , the base portion  11   a  is pressed in the downward direction. As a result, the first surface S 1A  of the base portion  11   a  is lower than the first surface S 2A  of the base portion  21   a . Therefore, the polishing pad dresser  31  in  FIG. 11B  can dress the polishing pad  3  with the convex portions  11   b  and  21   b  of the first and second dresser modules  31   a  and  31   b  or only with the convex portions  11   b  of the first dresser module  31   a.    
       FIGS. 12A and 12B  are plan views illustrating structures of the polishing pad dresser  31  of the second embodiment. 
     In the polishing pad dresser  31  of the present embodiment, the second dresser module  31   b  surrounds the first dresser module  31   a  as illustrated in  FIG. 12A . As a result, the second region R 2  of the base portion  21   a  surrounds the first region R 1  of the base portion  11   a . Therefore, the convex portions  11   b  of the present embodiment are arranged so as to be surrounded by the convex portions  21   b.    
     Nevertheless, the convex portions  11   b  and  21   b  of the present embodiment may be arranged in another layout. For example, in the polishing pad dresser  31  of the present embodiment, the first dresser module  31   a  may surround the second dresser module  31   b  as illustrated in  FIG. 12B . In this case, the convex portions  11   b  of the present embodiment are arranged so as to surround the convex portions  21   b.    
     As described above, the polishing pad dresser  31  of the present embodiment includes the fine and low-density convex portions  11   b  and the coarse and high-density convex portions  21   b . Therefore, the polishing pad dresser  31  of the present embodiment can realize similar functions to those of the first and second polishing pad dressers  11  and  21  of the first embodiment. 
     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 dressers, apparatuses and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the dressers, apparatuses and methods 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.