Abstract:
Polishing equipment, comprising a polishing head ( 30 ) having an opened hollow mixing tank ( 32 ) on the opposite side of the side thereof where a polishing pad ( 36 ) is installed, a slurry feed mechanism ( 50 ) for feeding slurry into the mixing tank ( 32 ), an additive liquid feed mechanism ( 60 ) for feeding additive liquid used by adding to the slurry into the mixing tank ( 32 ), and a mixed liquid feed tube ( 34 ) extending from the mixing tank ( 32 ) into the polishing head ( 30 ) and opened to near the rotating center of the polishing pad ( 36 ), wherein the slurry fed by the slurry feed mechanism ( 50 ) and the additive liquid fed by the additive liquid feed mechanism ( 60 ) are fed from the mixed liquid feed tube ( 34 ) to the outside of the polishing pad ( 36 ) in the mixed state in the mixing tank ( 32 ).

Description:
[0001]     This is a continuation of PCT Application No. PCT/JP03/03150 filed Mar. 17, 2003, which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to polishing equipment, which is used to planarize an object to be polished such as a silicon wafer, and more particularly to polishing equipment that polishes a surface of an object chemically and mechanically with a slurry being supplied onto the surface. The present invention also relates to a method of manufacturing a semiconductor device, in which this polishing equipment is used for polishing a surface of a semiconductor wafer.  
       BACKGROUND OF THE INVENTION  
       [0003]     Nowadays, the number of layers that realize multilayered wiring in a semiconductor substrate tends to increase correspondingly to the progress in the miniaturization and complication of IC structures. Accordingly, the process that planarizes the surface of a substrate after each succesive thin film is formed thereon has increased in importance. If the unevenness of the surface after the planarization process, which is performed after the formation of each thin film, is relatively large because the planarization process lacks precision, then a defect in insulation can occur and cause a short circuit. Also, in the process of lithography, the unevenness or irregularity of the surface of a semiconductor substrate makes the projection on the surface too fuzzy to create microcircuits.  
         [0004]     As a prior-art technique for planarizing a semiconductor substrate at a high precision, a method of CMP (Chemical Mechanical Polishing) is known, in which so-called CMP equipment is used. This equipment generally comprises a polishing pad, which is mounted on a polishing head. In the equipment, the polishing pad is brought into contact with a surface to be polished of a semiconductor substrate while a liquid abrasive containing silica particles is being supplied onto the surface (this abrasive is referred to as “slurry”).  
         [0005]      FIG. 3  shows schematically such prior-art CMP equipment as an example. This CMP equipment comprises a surface table  92 , which holds substantially horizontally a semiconductor substrate  91  as an object to be polished, and a polishing head  93 , which is positioned above the surface table  92  and has a polishing pad  95  attached on its bottom surface. For polishing the semiconductor substrate  91 , the surface table  92 , which holds the semiconductor substrate  91 , is rotated around its vertical axis while the is polishing head  93  is also rotated around its vertical axis. In this condition, the polishing pad  95  is lowered onto the upper surface of the substrate  91 . In design, the diameter of the polishing pad  95  is smaller than that of the semiconductor substrate  91 , so to polish the surface uniformly, the polishing head  93  reciprocates (oscillates) in (horizontal) directions that are parallel to the contacting surface with the semiconductor substrate  91 . During the polishing, a slurry is sucked from a slurry tank  96  by a pump  97  and delivered through a slurry supply tube  98  and through a slurry supply tube  94  provided inside the polishing head  93  and supplied onto the polished surface of the semiconductor substrate  91  externally with respect to the polishing pad  95 .  
         [0006]     Furthermore, in another case for polishing a semiconductor substrate  91 , an additive liquid (liquid chemical) necessary for achieving a specific purpose is added to the above mentioned slurry. As such an additive, an additive liquid that is known to facilitate the planarization of the surface of the substrate is mixed with the slurry, so that the mixture is supplied onto the surface being polished of the semiconductor substrate  91 . In this case, the liquid mixture of the additive liquid and the slurry is prepared in the slurry tank  96  and supplied onto the surface being polished of the semiconductor substrate  91  in the same manner as in the above mentioned case where only the slurry is supplied.  
         [0007]     By the way, in the above case where the slurry is mixed with an additive liquid for application, there is a problem that if the additive liquid is mixed with the slurry beforehand, then the effectiveness of the additive liquid is not demonstrated sufficiently. To solve this problem, it is preferable that the slurry and the additive liquid be mixed just before the mixture is supplied onto the surface being polished. However, if the above mentioned conventional polishing equipment is used, then there is no way for such mixing, so the slurry and the additive liquid must be mixed before use with the equipment. In this case, the effectiveness of the additive liquid is not brought up sufficiently.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention has been conceived to solve such a problem. It is an object of the present invention to provide polishing equipment that mixes a slurry and an additive liquid just before this mixture is supplied onto a surface to be polished of a substrate, so that the effectiveness of the additive liquid is sufficiently brought up to improve the precision of the polishing.  
         [0009]     It is another object of the present invention to provide a method of manufacturing a semiconductor device in which the above polishing equipment is used for polishing a surface of a semiconductor wafer.  
         [0010]     Polishing equipment according to the present invention comprises a surface table, which holds an object to be polished, and a polishing head, which has a polishing pad attached on a face that faces a surface to be polished of the object held on the surface table. For polishing the surface of the object, the polishing pad is brought into contact with the surface of the object. The polishing equipment further comprises a slurry feed mechanism, an additive liquid feed mechanism and a mixed liquid feeder. The slurry feed mechanism supplies a slurry to the polishing head, and the additive liquid feed mechanism supplies also to the polishing head an additive liquid, which is added to the slurry. The mixed liquid feeder, which is provided inside the polishing head, mixes the slurry supplied by the slurry feed mechanism and the additive liquid supplied by the additive liquid feed mechanism and feeds this mixture through an opening provided in the vicinity of the rotational center of the polishing pad to the outside of the polishing pad.  
         [0011]     In the polishing equipment according to the present invention, it is preferable that a stirrer member fixed either on the polishing head or on a polishing head retaining body, which retains the polishing head rotatably, be positioned in the mixed liquid feeder. In this case, it is also preferable that the stirrer member have a configuration of projections or spiral grooves. In addition, it is preferable that a stirrer member having a configuration of projections or spiral grooves be provided on at least part of the inner walls of the mixed liquid feeder. Furthermore, it is preferable that the surface table hold the object to be polished in a condition where the surface to be polished of the object faces upward and that the polishing pad come from above into contact with the object.  
         [0012]     The present invention also provides a semiconductor device manufacturing method, which uses the polishing equipment described above for polishing a surface of a semiconductor wafer (object to be polished). According to this manufacturing method, semiconductor devices of high precision can be manufactured at a high throughput and a high yield.  
         [0013]     Therefore, high quality semiconductor devices can be manufactured with reduced costs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic view of the construction of CMP equipment as an embodiment of polishing equipment according to the present invention.  
         [0015]      FIG. 2  is an enlarged sectional partial view of the CMP equipment shown in  FIG. 1 .  
         [0016]      FIG. 3  is a schematic view of prior-art CMP equipment as an example.  
         [0017]      FIG. 4  is a flowchart showing an example of semiconductor device manufacturing method according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Now, a preferred embodiment of the present invention is described in reference to the drawings.  FIG. 1  is a schematic view of the construction of CMP equipment  10  as an embodiment of polishing equipment according to the present invention, and  FIG. 2  is an enlarged sectional view showing a part of the CMP equipment  10 . The CMP equipment  10  comprises an equipment body that includes a surface table  20 , a polishing head  30  and a polishing head retaining body  40 , which are mounted on a frame (not shown), and a slurry feed mechanism  50  and an additive liquid feed mechanism  60 , which are detailed later in this section. The surface table  20  holds substantially horizontally a semiconductor substrate  1  as an object to be polished, and the polishing head  30  is attached with a polishing pad  36  facing the surface to be polished (in this case, the upper surface) of the semiconductor substrate  1 , which is held on the surface table  20 . The polishing head retaining body  40  retains the polishing head  30  rotatably around its vertical axis.  
         [0019]     The surface table  20  is mounted on the upper end of a rotating column  21 , which extends substantially vertically. While the rotating column  21  rotates around its axis, the surface table  20  rotates correspondingly in a (substantially horizontal) plane that is perpendicular to the axis. A suction chuck (not shown) is provided on the upper surface of the surface table  20 , and the suction chuck holds by suction the lower surface of the semiconductor substrate  1 , which is an object to be polished.  
         [0020]     The polishing head  30  comprises a rotating body  31  and a polishing pad  36 , and the rotating body  31  comprises a trunk portion  31   a  and a circular disc portion  31   b , which is positioned below the trunk portion  31   a . The polishing pad  36  is attached on the lower face of the circular disc portion  31   b  of the rotating body  31  (in other words, the polishing pad  36  is positioned to face the surface to be polished of the semiconductor substrate  1 , which is held on the surface table  20 ). The trunk portion  31   a  of the rotating body  31  is provided with a hollow portion (hereinafter referred to as “mixing tank  32 ”) that is open upward at the side located opposite to the circular disc portion  31   b  (with the polishing pad  36 ). The lower face of the circular disc portion  31   b  is planarized at a high degree of precision, so that the polishing pad  36  is attached precisely horizontally. The polishing pad  36  is made of such a raw material as nonwoven fabric or urethane in a thin circular disc with a diameter substantially equal to that of the circular disc portion  31   b  of the rotating body  31 . The polishing pad  36  as a consumable item is attached on the lower face of the circular disc portion  31   b  by an adhesive, an adhesive bandage or the like, so it can be removed relatively easily.  
         [0021]     The polishing head retaining body  40  is mounted on the frame (not shown as mentioned above) through a plurality of stages, whose movements are controlled by a plurality of motors (not shown), so the polishing head retaining body  40  is three dimensionally movable. As shown in  FIG. 2 , the polishing head retaining body  40  further comprises an extending portion  41 , which extends vertically downward, and a bearing  43 , which is provided around the extending portion  41 . The extending portion  41  is placed from above into and positioned in the above described mixing tank  32 , which is provided in the rotating body  31  of the polishing head  30 , so that the extending portion  41  supports, through the bearing  43 , the whole of the polishing head  30  rotatably around its vertical axis.  
         [0022]     The polishing head  30  is provided with a driven gear  37  around the circular disc portion  31   b  of the rotating body  31 , and the driven gear  37  always meshes with a drive gear  39 , which is driven by a motor  38 . As a result, when the motor  38  is activated, the rotational power of the motor is transmitted from the drive gear  39  to the driven gear  37 , rotating the whole of the polishing head  30  around its vertical axis.  
         [0023]     As shown in  FIG. 2 , the polishing head retaining body  40  is provided with a first fluid passage  44  and a second fluid passage  45 , which extend vertically and in parallel with each other inside the extending portion  41  and open radially outward at outlets provided on the lateral side of the extending portion  41 . Furthermore, a retaining body side stirrer portion  42 , which protrudes outward in projections, is provided at the lower periphery of the extending portion  41  while a mixing tank side stirrer portion  33 , which protrudes inward in projections in the mixing tank  32 , is provided on the inside wall of the mixing tank  32 . Moreover, a mixed liquid feed passage  34  is provided inside the rotating body  31  of the polishing head  30 , extending downward from the mixing tank  32 , branching and opening at a plurality of positions in the vicinity and the periphery of the rotational center of the polishing pad  36 .  
         [0024]     The slurry feed mechanism  50  comprises a slurry storage tank  51 , a slurry supply tube  52  and a first pump  53 . The slurry storage tank  51  stores a slurry, which is an abrasive liquid that includes ceria particles. One end of the slurry supply tube  52  is positioned in the slurry storage tank  51 , and the other end of the slurry supply tube  52  is threaded into and connected to the upper opening of the first fluid passage  44 , which is provided in the polishing head retaining body  40 . The first pump  53  is placed somewhere along the slurry supply tube  52 , so that the first pump  53  pumps the slurry from the slurry storage tank  51  into the first fluid passage  44 . Furthermore, the additive liquid feed mechanism  60  comprises an additive liquid storage tank  61 , an additive liquid supply tube  62 , and a second pump  63 . The additive liquid storage tank  61  stores an additive liquid (liquid chemical), which is used in mixture with the slurry. One end of the additive liquid supply tube  62  is positioned in the additive liquid storage tank  61 , and the other end of the additive liquid supply tube  62  is threaded into and connected to the upper opening of the second fluid passage  45 , which is provided in the polishing head retaining body  40 . The second pump  63  is placed somewhere along the additive liquid supply tube  62 , so that the second pump  63  pumps the additive liquid from the additive liquid storage tank  61  into the second fluid passage  45 . Here, the slurry supply tube  52  and the additive liquid supply tube  62  are flexible hoses (for example, rubber hoses), whose inner diameter is relatively small, so they can bend and follow the three dimensional movement of the polishing head retaining body  40 .  
         [0025]     For planarizing and polishing a semiconductor substrate by the CMP equipment  10 , which is constructed as described above, at first, a semiconductor substrate  1  (for example, a silicon wafer) as an object to be polished is placed and fixed by suction on the surface table  20 , with the surface to be polished of the semiconductor substrate  1  facing upward. In this case, it is preferable that the semiconductor substrate  1  be placed and positioned such that the center of the semiconductor substrate  1  is at the rotational center of the surface table  20 . After the semiconductor substrate  1  is held on the surface table  20 , the surface table  20  with the semiconductor substrate  1  is rotated in a horizontal plane. Then, the polishing head  30  is rotated around its vertical axis by the activation of the motor  38  (this action also resulting in the rotation of the polishing pad  36  in a horizontal plane), and the polishing head retaining body  40  is lowered to bring the polishing pad  36  downward and into contact with the surface to be polished of the semiconductor substrate  1 . After the polishing pad  36  has come into contact with the surface, starting a polishing process, the polishing head retaining body  40  is moved in a direction that is parallel to the plane where the semiconductor substrate  1  and the polishing pad  36  are in contact with each other (in this case, in a horizontal direction) to polish the entire surface.  
         [0026]     Just before the polishing of the semiconductor substrate  1  starts, the mixture or mixed liquid of the slurry and the additive liquid is supplied onto the surface to be polished of the semiconductor substrate  1 . This supply of the mixed liquid is executed by the activation of the first pump  53 , which delivers the slurry from the slurry storage tank  51  through the slurry supply tube  52  and through the first fluid passage  44  in the polishing head retaining body  40  into the mixing tank  32 , and by the activation of the second pump  63 , which delivers the additive liquid from the additive liquid storage tank  61  through the additive liquid supply tube  62  and through the second fluid passage  45  in the polishing head retaining body  40  into the mixing tank  32 . In this way, the slurry, which is supplied by the slurry feed mechanism  50 , and the additive liquid, which is supplied by the additive liquid feed mechanism  60 , are mixed in the mixing tank  32 , and then the mixed liquid is supplied through the mixed liquid feed passage  34 , which is provided in the rotating body  41  of the polishing head  40 , extending to a plurality of outlets in the vicinity and periphery of the rotational center of the polishing pad  36 , to the outside of the polishing pad  36  (in other words, the mixed liquid is led onto the lower face of the polishing pad  36 ). By the way, it is necessary that the slurry in the slurry tank  32  be always agitated to prevent solid constituents from separating and settling from liquid constituents.  
         [0027]     In this way, while the surface to be polished of the semiconductor substrate  1 , which is held on the surface table  20 , receives the mixed liquid, which is the mixture of the slurry and the additive liquid being supplied thereon, the entire surface is polished uniformly because of the rotation of the semiconductor substrate  1  itself and the rotation and rocking movements of the polishing head  30  (i.e., the polishing pad  36 ). As a result, the polished surface of the semiconductor substrate  1  is planarized up to a high degree of precision. However, if the above described polishing is continued, then the polishing pad  36  deteriorates gradually, so there are changes (degradations) in the polishing property of the equipment. To solve this problem, it is necessary that the polishing pad be reconditioned (dressed) periodically by a conditioner (not shown).  
         [0028]     According to the CMP equipment  10 , as mentioned above, the slurry, which is supplied by the slurry feed mechanism  50 , and the additive liquid, which is supplied by the additive liquid feed mechanism  60 , are both supplied into and mixed in the mixing tank  32 , which is a hollow space provided in the polishing head  30 , and then the mixed liquid, i.e., the mixture of the slurry and the additive liquid, is supplied through the mixed liquid feed passage  34 , which extends from the mixing tank  32  through the polishing head  40  to the outlets provided in the vicinity of the rotational center of the polishing pad  36 , to the outside (lower face) of the polishing pad  36 . Therefore, the slurry and the additive liquid are mixed with each other just before they reach the polished surface of the semiconductor substrate  1 . This mixing timing of the CMP equipment  10  according to the present invention brings the effectiveness of the additive liquid more sufficiently than in a case with prior-art CMP equipment, so an improvement is made in the precision of the polishing of a semiconductor substrate. Moreover, after the mixed liquid, which is the mixture of the slurry and the additive liquid mixed in the mixing tank  32 , comes out of the polishing pad  36 , the mixed liquid scatters radially outward by the centrifugal force generated by the rotation of the polishing head  30 . In the CMP equipment  10 , because the mixed liquid feed passage  34 , which is a passageway provided in the polishing head  30  for the mixed liquid, opens in the vicinity of the center of the polishing pad  36 , the mixed liquid is spread uniformly over the entire polished surface of the semiconductor substrate  1 .  
         [0029]     Furthermore, in the CMP equipment  10 , the extending portion  41  of the polishing head retaining body  40  is positioned in the mixing tank  32  of the polishing head  30 , and the polishing head  30  rotates around the extending portion  41 . While the polishing head  30  is rotating, the extending portion  41  rotates around its axis in the mixing tank  32  as a relative motion. This relative rotation of the extending portion  41  agitates effectively and mixes the slurry and the additive liquid in the mixing tank  32 . Moreover, in the CMP equipment  10 , because the retaining body side stirrer portion  42 , which has projections, is provided around the periphery of the extending portion  41  as mentioned above, the slurry and the additive liquid are mixed efficiently and uniformly into the mixed liquid. Also, because the mixing tank side stirrer portion  33 , which has projections, is provided on the inner wall of the mixing tank  32 , the mixing of the mixed liquid is more effective. By the way, the retaining body side stirrer portion  42  and the mixing tank side stirrer portion  33  may be provided also in spiral grooves, not only in the form of projections as described above.  
         [0030]     The rotation of the extending portion  41  in the mixing tank  32  is achieved as a relative motion because of the rotation of the polishing head  30 , and no other power source is involved. Therefore, this stirring mechanism is simple in construction, which is a merit. It is possible to provide a construction of independent stirring mechanism that mixes the slurry and the additive liquid in the mixing tank  32 , but it will require another power source to drive a stirrer member and make the construction of the equipment more complicated than the CMP equipment  10 .  
         [0031]     A preferred embodiment of the present invention has been described above. However, the scope of the present invention is not limited to the above description. For example, in the above described embodiment, the surface table holds the semiconductor substrate in a condition where the surface to be polished faces upward, and the polishing pad comes from above into contact with the surface to be polished (upper surface) of the semiconductor substrate. On the contrary, in an alternative construction, the surface table may hold the semiconductor substrate in a condition where the surface to be polished faces downward, and the polishing pad may come from below into contact with the surface to be polished (lower surface) of the semiconductor substrate. However, in the latter construction, the pressure required for delivering the slurry and the additive liquid through the first and second fluid passages  44  and  45  in the polishing head retaining body  40  and through the mixed liquid feed passage  34  in the polishing head  30  to the outside of the polishing pad  36  must be much higher because the feeding of the slurry and the additive liquid in this case is against the gravity.  
         [0032]     Also, in the above described two embodiments, the polishing head is rotated around its vertical axis in addition to that the surface table, which holds the semiconductor substrate, is rotated. However, for polishing the surface of the semiconductor substrate, it is necessary only that the semiconductor substrate be moved relatively to the polishing head (polishing pad). Therefore, it is not necessary to rotate the surface table. Furthermore, the slurry to be used may contain alumina, silica and the like in addition to ceria. Moreover, the present invention may be applied also to a case where a plurality of additives are used and mixed with the slurry.  
         [0033]     Now, an embodiment of method for manufacturing a semiconductor device according to the present invention is described.  FIG. 4  is a flowchart showing a process for manufacturing a semiconductor device. After the start of the semiconductor-manufacturing process, at first, at step S 200 , an appropriate process from the following steps S 201 ˜S 204  is selected, and the operational flow proceeds to the selected step. Here, step S 201  is an oxidization process, which oxidizes a surface of a wafer. Step S 202  is a CVD process, which forms an insulation film or a dielectric film on a surface of a wafer by CVD. Step S 203  is an electrode formation process, which forms electrodes on a wafer by vapor deposition. Step S 204  is an ion injection process, which injects ions into a wafer.  
         [0034]     After the CVD process (S 202 ) or the electrode formation process (S 203 ), the flow proceeds to step S 205 , which is a CMP process. In the CMP process, polishing equipment according to the present invention is used for planarization of an interlayer-insulation film or for polish of a metal film or a dielectric film on a semiconductor device, for example, to create damascene.  
         [0035]     After the CMP process (S 205 ) or the oxidization process (S 201 ), the flow proceeds to step S 206 , which is a photolithography process. In this process, the wafer is coated with a resist, the wafer is exposed and printed with a circuit pattern by an exposure device, and the circuit pattern on the wafer is developed. Then, the next step S 207  is an etching process, where the part excluding the resist image, which has been developed, is etched by etching, and then the resist is separated and removed because it is unnecessary after the etching.  
         [0036]     At step S 208 , a determination is made whether all necessary steps are completed or not. If all steps are not yet completed, then the flow returns to step S 200  and repeats the above mentioned steps to create a circuit pattern on the wafer. If the result of the determination at step S 208  is that all necessary steps are completed, then the operational flow ends.  
         [0037]     In the above semiconductor device manufacturing method according to the present invention, polishing equipment according to the present invention is used in the CMP process, so the throughput of the CMP process is improved. An effect of this method is that semiconductor devices are manufactured with costs lower than those in a case where they are manufactured by a prior-art semiconductor device manufacturing method. Furthermore, polishing equipment according to the present invention may be applied to a CMP process of a semiconductor device manufacturing method other than that described above. Because a semiconductor device manufacturing method according to the present invention achieves a high throughput, the semiconductor devices manufactured accordingly are cost-effective.  
         [0038]     As described above, polishing equipment according to the present invention mixes a slurry and an additive liquid just before they are applied onto a surface to be polished of a polished object. Therefore, in the polishing equipment, the effectiveness of the additive liquid is demonstrated more effectively than in prior-art polishing equipment. As a result, the polished objects achieve an improved degree of precision in polished condition. Furthermore, the mixed liquid of the slurry and the additive liquid, after coming out of the polishing pad, scatters radially outward by the centrifugal force generated by the rotation of the polishing head. In the polishing equipment according to the present invention, because the mixed liquid feed passage, which is a passageway provided in the polishing head for the mixed liquid, opens in the vicinity of the center of the polishing pad, the mixed liquid is spread uniformly over the entire polished surface of the polished object.  
         [0039]     Also, by a semiconductor device manufacturing method that uses the polishing equipment in a process that polishes a surface of a semiconductor wafer, semiconductor devices of high precision can be manufactured at a high throughput and a high yield. As a result, high quality semiconductor devices can be manufactured with reduced costs, and these high quality semiconductor devices can be distributed at relatively low prices.