Patent Publication Number: US-2002009953-A1

Title: Control of CMP removal rate uniformity by selective heating of pad area

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] The following co-pending application is related and hereby incorporated by reference:  
                                       Serial No.   Filing Date   Inventor(s)                  TI-30582       Swanson                  
 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The invention is generally related to the field of semiconductor processing and more specifically to chemical-mechanical polishing semiconductor wafers.  
       BACKGROUND OF THE INVENTION  
       [0003] Chemical-mechanical polishing (CMP) for planarizing semiconductor wafers during fabrication is becoming more and more common. A CMP system generally consists of a polishing pad, wafer carrier, and slurry. As a wafer carrier positions a semiconductor wafer against the polishing pad, slurry is added between the polishing pad and the wafer. The wafer, the pad, or, more typically, both are moved to planarize the surface of the wafer. CMP employs both a mechanical removal of material (due to the physical abrasion of the polishing pad and slurry particles against the surface of the wafer) and a chemical removal (etch) of material (due to the chemical components of the slurry).  
       [0004] Three basic types of architecture are currently being manufactured. The first type is a rotary polisher. In a rotary polisher, the platen (and the polishing pad it holds) has a radius that is slightly larger than the diameter of the semiconductor wafer. Both the platen and the wafer are typically rotated. The second type of CMP machine is an orbital polisher. In an orbital polisher, the platen diameter is slightly larger than the wafer diameter. The wafer is rotated, but the pad is not. The wafer&#39;s center orbits around an axis of rotation offset slightly from the pad center. The third type of CMP machine is a linear belt polisher. In a linear belt polisher, a continuously fed belt is moved over the platen. The wafer is rotated during polishing.  
       [0005] The planarization uniformity on many polishing machines is difficult to control. This can be due to such process irregularities as pad conditioning, down force, and slurry delivery. Hence, achieving good planarization across a wafer is difficult. This is especially true for copper CMP, which is currently under development.  
       SUMMARY OF THE INVENTION  
       [0006] The invention is an improved CMP machine and/or process that uses selective heating of the polishing pad/belt to improve uniformity. A heating mechanism is used to create a temperature gradient across the polishing pad/belt by heating a selected area such as the perimeter of the pad or belt. Heating the selected area improves the removal rate in that area. For example, heating along the perimeter of the pad improves the removal rate at the perimeter of the semiconductor wafer.  
       [0007] An advantage of the invention is a CMP machine and/or process having improved planarization uniformity.  
       [0008] This and other advantages will be apparent to those of ordinary skill in the art having reference to the specification in conjunction with the drawings.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] In the drawings:  
     [0010] FIGS.  1 A- 1 C are top views of a rotary polisher modified to include a heating mechanism according to the invention;  
     [0011] FIGS.  2 A- 2 B are top views of an orbital polisher modified to include a heating mechanism according to the invention; and  
     [0012] FIGS.  3 A- 3 B are top views of a belt polisher modified to include a heating mechanism according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
     [0013] The invention will now be described in conjunction with three separate CMP machine architectures. It will be apparent to those of ordinary skill in the art that the invention may be applied to other machine architectures as well.  
     [0014] It is known that the copper removal rate during polish increases as the pad and slurry temperature rises. This is due to the fact that the chemical component of the CMP process is thermally activated. In the invention, the temperature of selective areas of the pad is adjusted to improve the uniformity across a wafer during CMP. For example, heat may be applied to selective areas the pad that correspond to areas of the wafer having a low removal rate.  
     [0015] In copper CMP removal rate is lower near the edges of a wafer (˜2-5 cm inset from the edge of the wafer by a few mm) than near the center of the wafer. In order to improve the removal rate uniformity across the wafer, the area of the polishing pad that polishes more of the edge of the wafer than the center is heated. The heat, in turn, increases the removal rate in that area making it more uniform across the wafer.  
     [0016] FIGS.  1 A-C show a rotary polisher  100  modified to include a heating mechanism  110  for heating selective areas of the polishing pad  120 . In a rotary polisher  100 , the platen  140  had a radius that is slightly larger than the wafer  150  diameter. Platen  140  is used to hold pad  120 . Wafer  150  is held against polishing pad  120  and rotated by a wafer carrier (not shown).  
     [0017] Heating mechanism  110  heats selective areas of the polishing pad  120  where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer. Therefore, to improve this non-uniformity, the periphery  130  of the polishing pad  120  is heated since this area contacts the outer portions of the wafer  150 .  
     [0018] Heating mechanism  110  may be located within platen  140  as shown in FIG. 1A. In this case, heating mechanism  110  could include an array of heaters  112 . Alternative heating mechanisms will be apparent to those of ordinary skill in the art. For example, heating mechanism  110  may be located above pad  120 , as shown in FIG. 1B. In this case, heating mechanism  110  may comprise radiant heaters  114  (e.g., lamps). Heating mechanism may alternatively comprise heated wires  116  embedded in selective areas of pad  120 , as shown in FIG. 1C.  
     [0019] Heaters  112  are placed in areas of the platen where increased removal rate is desired. To improve copper CMP non-uniformity, heaters  112  are placed around the periphery of the platen to heat the overlying area  130  of the pad  120  that polishes the outer portions of the wafer  150 . Of course, heaters may be placed throughout the platen for greater flexibility. Then, only those heaters below specific areas of the pad  120  could be used. Alternatively, heaters  114  may be placed above area  130  of pad  120  or wires  116  may be placed in area  130  of pad  120 .  
     [0020] If desired, temperature monitoring may be used to actively control the temperature profile. For example, optical IR (infrared) radiometers  170  could be used to monitor the pad  120  surface temperature during CMP. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.  
     [0021] In operation, slurry  160  is applied to the pad  120 . Wafer  150  is pressed against pad  120  with the desired downforce and both the pad and wafer are rotated. Selected areas of the pad  120  are heated using heating mechanism  110  to improve the removal rate in those areas. For copper CMP, the periphery  130  of the pad  120  is heated. This results in a more uniform removal rate across the wafer  150 . The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C.  
     [0022] FIGS.  2 A-B show an orbital polisher  200  modified to include a heating mechanism  110  for heating selective areas of the polishing pad  220 . In an orbital polisher  200 , the platen  240  had a diameter that is slightly larger than the wafer  150  diameter. Platen  240  is used to hold pad  220 . Wafer  150  is held against polishing pad  220  and rotated by a wafer carrier (not shown).  
     [0023] As with the rotary polisher, heating mechanism  110  heats selective areas of the polishing pad  220  where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer. Therefore, to improve this non-uniformity, the periphery  230  of the polishing pad  220  is heated since this area contacts the outer portions of the wafer  150 .  
     [0024] Heating mechanism  110  may be located within platen  240  as shown in FIG. 2A. In this case, heating mechanism  110  could include an array of heaters  112 , as discussed above. Alternative heating mechanisms will be apparent to those of ordinary skill in the art. For example, heating mechanism  110  may comprise heated wires  116  embedded in selective areas of pad  220 , as shown in FIG. 2B. Radiant heating from above is difficult in this type of polisher because almost the entire pad  220  is covered by wafer  150  during polishing. The heat source would need to be placed above the wafer  150  in the wafer carrier.  
     [0025] If desired, temperature monitoring may be used to actively control the temperature profile. For example, thermocouples  280  located behind the wafer  150  or beneath the pad  220  may be used to provide feedback for effective process control. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.  
     [0026] In operation, slurry  160  is applied to the pad  220  through holes in the pad  220 . Wafer  150  is pressed against pad  220  with the desired downforce and both the pad  220  and wafer  150  are rotated. Selected areas of the pad  120  are heated using heating mechanism  110  to improve the removal rate in those areas. For copper CMP, the periphery  230  of the pad  220  is heated. The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C. This results in a more uniform removal rate across the wafer  150 .  
     [0027] A linear belt polisher  300  modified to include heating mechanism  110  is shown in FIGS.  3 A- 3 B. Linear belt polisher  300  comprises a continuously fed belt  320 . Wafer  150  is held against polishing belt/pad  320  and rotated by a wafer carrier (not shown).  
     [0028] Heating mechanism  110  heats selective areas of the polishing belt  320  where an increased removal rate is desired. For example, in copper CMP the removal rate is lower near the edge of the wafer  150 . Therefore, to improve this non-uniformity, the outer portion  330  of the polishing belt  320  is heated since this area contacts the outer portions of the wafer  150 .  
     [0029] Heating mechanism  110  may be located below the polishing belt  320 , as shown in FIG. 3A or above, as shown in FIG. 3B. Heating mechanism  110  could include an array of radiant lamp heaters  114 . Alternative heating mechanisms will be apparent to those of ordinary skill in the art. Heaters  114  are placed over or under the polishing belt  320  just prior to the belt  320  moving under wafer  150 . To improve the removal rate at the outer regions of wafer  150 , the heaters  114  are placed at the outer edges of polishing belt  320 .  
     [0030] If desired, temperature monitoring may be used to actively control the temperature profile. For example, optical IR (infrared) radiometers could be used to monitor the pad  320  surface temperature during CMP. The amount of heating could then be increased or decreased as desired to establish and maintain the proper temperature. Alternative means for temperature monitoring will be apparent to those of ordinary skill in the art.  
     [0031] In operation, slurry  160  is applied to the pad  320 . Wafer  150  is pressed against pad  320  with the desired downforce and both the pad and wafer are rotated. Selected areas of the pad  320  are heated using heating mechanism  110  to improve the removal rate in those areas. For copper CMP, the periphery  330  of the pad  320  is heated. The temperature difference between the selected areas and the other areas of the pad may be on the order of 15° C. In the preferred embodiment, the selected areas are heated to a temperature of approximately 35-40° C. A maximum temperature is on the order of 70° C. This results in a more uniform removal rate across the wafer  150 .  
     [0032] While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.