Abstract:
An apparatus for multiple component slurry distribution during semiconductor wafer polishing operations. Concurrent polishing pad conditioning is obtained by means of a novel polishing pad design where polishing pads are mounted in a cylindrical configuration as opposed to the conventional flat surface configuration. A polishing pad conditioner is provided to refurbish the polishing pad.

Description:
This is a division of patent application Ser. No. 09/195,654, filing date Nov. 19, 1998 now U.S. Pat. No. 6,235,635, A Novel Linear Cmp Tool Design Using In-Situ Slurry Distribution And Concurrent Pad Conditioning, assigned to the same assignee as the present invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of Chemical Mechanical Polishing (CMP). More particularly, the present invention relates to methods and apparatus for chemical mechanical polishing of substrates, such as semiconductor substrates, on a rotating polishing pad in the presence of a chemically and/or physically abrasive slurry, and providing fresh supply of slurry onto the surface of the substrate which is mounted on the polishing pad while the substrate is being polished. Additionally, the present invention includes a pad conditioning apparatus to condition the polishing pad while the polishing pad is being used to polish semiconductor substrates. Additionally, the present invention includes a new slurry delivery system where multi-component slurries can be used that can be metered very accurately during slurry flow and which completely eliminates the use of the conventional peristaltic pump. 
     DESCRIPTION OF THE PRIOR ART 
     Chemical Mechanical Polishing is a method of polishing materials, such as semiconductor substrates, to a high degree of planarity and uniformity. The process is used to planarize semiconductor slices prior to the fabrication of semiconductor circuitry thereon, and is also used to remove high elevation features created during the fabrication of the microelectronic circuitry on the substrate. One typical chemical mechanical polishing process uses a large polishing pad that is located on a rotating platen against which a substrate is positioned for polishing, and a positioning member which positions and biases the substrate on the rotating polishing pad. Chemical slurry, which may also include abrasive materials therein, is maintained on the polishing pad to modify the polishing characteristics of the polishing pad in order to enhance the polishing of the substrate. 
     The use of chemical mechanical polishing to planarize semiconductor substrates has not met with universal acceptance, particularly where the process is used to remove high elevation features created during the fabrication of microelectronic circuitry on the substrate. One primary problem which has limited the used of chemical the polishing pad is difficult. Providing a fresh supply of slurry to all positions of the substrate is even more difficult. As a result, the uniformity and the overall rate of polishing are significantly affected as the slurry reacts with the substrate. 
     The polishing process is carried out until the surface of the wafer is ground to a highly planar state. During the polishing process, both the wafer surface and the polishing pad become abraded. After numerous wafers have been polished, the polishing pad becomes worn to the point where the efficiency of the polishing process is diminished and the rate of removal of material from the wafer surface is significantly decreased. It is usually at this point that the polishing pad is treated and restored to its initial state so that a high rate of uniform polishing can once again be obtained. 
     In the conventional approach, the wafer is held in a circular carrier, which rotates. The polishing pads are mounted on a polish platen which has a flat surface and which rotates. The rotating wafer is brought into physical contact with the rotating polishing pad; this action constitutes the Chemical Mechanical Polishing process. Slurry is dispensed onto the polishing pad typically using a peristaltic pump. The excess slurry typically goes to a drain, which means that the CMP process has an open loop slurry flow. In addition, the conventional approach uses orbital motion where there is a relative motion at any point of the wafer that poses severe problems of non-uniformity across the die and across the wafer in addition to problems of planarity. Also, the conventional approach uses and dispenses with an excessive amount of slurry that adds significantly to the processing cost. There also is no method for exactly controlling slurry flow. The present invention addresses and solves the indicated problems. Since both the wafer and the polishing pad are rotating there exists a velocity differential across the wafer. This velocity differential wafer polishing uniformity and planarity suffer across the die and across the wafer. This limits the application of the conventional CMP approach especially in Shallow Trench Applications, copper damascene, etc., which are involved in sub-quarter micron technology modes. 
     FIG. 1 shows a Prior Art CMP apparatus. A polishing pad  20  is affixed to a circular polishing table  22  which mechanical polishing in the semiconductor industry is the limited ability to predict, much less control, the rate and uniformity at which the process will remove material from the substrate. As a result, CMP is labor intensive process because the thickness and uniformity of the substrate must be constantly monitored to prevent overpolishing or inconsistent polishing of the substrate surface. 
     One factor, which contributes to the unpredictability and non-uniformity of the polishing rate of the CMP process, is the non-homogeneous replenishment of slurry at the surface of the substrate and the polishing pad. The slurry is primarily used to enhance the rate at which selected materials are removed from the substrate surface. As a fixed volume of slurry in contact with the substrate reacts with the selected materials on the surface of the substrate, this fixed volume of slurry becomes less reactive and the polishing enhancing characteristics of that fixed volume of slurry is significantly reduced. One approach to overcoming this problem is to continuously provide fresh slurry onto the polishing pad. This approach presents at least two problems. Because of the physical configuration of the polishing apparatus, introducing fresh slurry into the area of contact between the substrate and rotates in a direction indicated by arrow  24  at a rate in the order of 1 to 100 m RPM. A wafer carrier  26  is used to hold wafer  18  face down against the polishing pad  20 . The wafer  18  is held in place by applying a vacuum to the backside of the wafer (not shown). The wafer carrier  26  also rotates as indicated by arrow  32 , usually in the same direction as the polishing table  22 , at a rate on the order of 1 to 100 RPM. Due to the rotation of the polishing table  22 , the wafer  18  traverses a circular polishing path over the polishing pad  20 . A force  28  is also applied in the downward or vertical direction against wafer  18  and presses the wafer  18  against the polishing pad  20  as it is being polished. The force  28  is typically in the order of 0 to 15 pounds per square inch and is applied by means of a shaft  30  that is attached to the back of wafer carrier  26 . Slurry  21  is deposited on top of the polishing pad  20 . 
     FIG. 2 shows a typical Prior Art slurry delivery system. Slurry  21  of uniform chemical and mechanical composition is contained in the slurry vat  34  from where the slurry  21  is pumped by the diaphragm pump  36  in direction  38 . The peristaltic pump  40  deposits controlled and intermittent amounts of slurry  21  onto the polishing pad  20  while the balance  44  of the slurry that had been pumped by the diaphragm pump  36  is returned to the slurry vat  34 . The rate at which the slurry  42  is provided by the two pumps  36  and  40  can be under control of conditions of operation and environment such as type of surface being polished, rate of rotation of either the wafer  18  and/or the polishing table, etc. 
     U.S. Pat. No. 5,688,360 (Jairath) shows cylindrical and conical polishing pads. 
     U.S. Pat. No. 5,709,593 (Guthrie et al.) shows a slurry delivery system and slurry wiper bar. 
     U.S. Pat. No. 5,785,585 (Manfredi et al.) discloses a polishing pad conditioner with radical compensation. 
     U.S. Pat. No. 5,792,709 (Robinson et al.) shows a polishing pad disk. 
     U.S. Pat. No. 5,782,675 (Southwick) discloses an apparatus to recondition a polishing pad. 
     U.S. Pat. No. 5,679,039 (Talieh) discloses a polishing pad with grooves to deliver slurry. 
     U.S. Pat. No. 5,775,983 (Shendon et al.) teaches a conical roller to condition the polishing pad. 
     SUMMARY OF THE INVENTION 
     The present invention teaches an in-situ slurry distribution and concurrent pad conditioning process and apparatus. The novelty of the present invention is that the polishing pads are mounted on a cylindrical platform that consists of a pad/core arrangement, instead of the conventional flat platform on which the polishing pads are placed. 
     The cylindrical pad has motion in the X-Y-Z directions; the cylindrical pad in addition has rotational motion. The novelty of the present design consists of as unique pad/core design with the polishing pads mounted on the surface of the core. Evenly spaced openings are provided within the pad/core assembly for the location of slurry ports. 
     The center of the core is hollow; slurry is pumped through the center of the core and exits the core through the slurry ports to the polishing pads and the pad conditioners. 
     The present invention in addition incorporates a new slurry delivery arrangement. The slurry, which can consist of a combination of more than one type or composition of slurry, is pumped in the conventional manner (for instance using diaphragm pumps) and flows through an orifice-flow meter where the multi-component slurries are combined and pumped through a single tube mixing coil. The actual mixing of the different slurries occurs within the mixing coil. The mixed slurry flows through a rotating driver that 
     In this way, a constantly renewed supply of fresh slurry can be provided to the wafers which are being polished thus eliminating previously experienced problems associated with stationary or used slurry. This aspect of the present invention is of particular importance for the polishing of metal surfaces. 
     Using this approach of the present invention, the slurry can be metered very accurately unlike the slurry flow of conventional applications where the peristaltic pump causes a great deal of irregularities in the flow of the slurry. In addition, the present invention allows for the complete elimination of the peristaltic pump. 
     As part of the present invention, a pad conditioner disc used. This disc is of the same shape as the pad/core assembly and fits snuggly around this assembly. The pad conditioner conditions the polishing pads at the same time that the polishing operation takes place. The friction between the pad conditioner and the pad/core assembly can be varied during and as part of the polishing process thus further adding a parameter of control for the polishing operation. 
     The method used for increasing the friction or pressure between the pad conditioner and the pad/core assembly can be of a number of designs, for instance air-actuated cylinders can be used for this purpose. This allows for very accurate control of this application parameter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows Prior Art polishing and slurry supply tools. 
     FIG. 2 shows a Prior Art slurry delivery system. 
     FIG.  3 A and FIG. 3B show an overview of the implementation of the present invention. 
     FIG.  4 A and FIG. 4B show a cross sectional view of the pad/core assembly. 
     FIG. 5 shows a detailed view of the pad conditioner disk. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now specifically to FIG. 3 a , there is shown an exploded view of the polishing apparatus of the present invention. The plan view  50  in the top left corner shows the positioning of the wafers  52  that are being polished with the wafer carrier  53 . The diagram  51  at the center of this cross sectional view indicates that the wafer carrier  53  has freedom of motion in the X-Y-Z direction in addition to the rotating motion  57 . 
     The pad/core assembly  54  is further detailed FIG. 3 b . Mounted on the outside of the hollow core  56  and in parallel with this core is an arrangement of four polishing pads  58 . The number of polishing pads provided in this manner is not limited to the number of four as shown in FIG. 3 b , any number of pads can be used which best suits and satisfies the need of a particular application. 
     Adjacent to the pad/core assembly  54  is presented one pad conditioner disk  60 . The number of pad conditioner disks that can be used within the scope of this invention can vary and is determined by optimum results obtained for a particular application of the present invention. 
     Air actuated cylinders  62  can be used to urge the pad/core assembly  54  toward the wafer carrier  53 . By increasing the pressure by which the pad/core assembly  60  is urged toward the wafer carrier  53 , the process of polishing the wafers  52  can be controlled. 
     The process of wafer polishing is as follows: the pad/core assembly  54  rotates around its axis  82  stimulated by the rotary actuator  64 . The diagram  86  within this cross sectional view indicates that the pad/core assembly  54  has freedom of motion in the X-Y-Z direction in addition to the rotating motion. The direction of rotation of the pad/core assembly  54  is, within the scope of the present invention, not critical. 
     The wafers  52  that are to be polished are, in the conventional manner, affixed to the wafer carrier  53 , the wafer carrier  53  also rotates around its axis, the direction of rotation  57  is, within the scope of the present invention, not critical. 
     The pad/core assembly  54  is mounted above and in close physical proximity to the wafers  52  affixed to the wafer carrier  53  such that the polishing pads  58  are in physical contact with the wafers  52  thus allowing the polishing pads  58  to polish the wafers  52 . 
     While this polishing action is taking place, the polishing pad conditioner  60  is or can be brought into contact with the rotating polishing pads  58 . This latter contact between the polishing pads  58  and the polishing pad conditioner disc  60  refreshes or conditions the polishing pads  58 . 
     The number of polishing pad conditioners  60  that is mounted on the pad/core arrangement  54  may vary and is dictated by requirements of particular applications. It is clear from the above that a large part of the outside surface of core  56  can be covered with pad conditioners  60 , care must be taken that the pad conditioners  60  do not physically interfere with the top surface of the wafer carrier  53 . 
     The rotary driver  64  rotates that pad/core assembly  54  around its central axis  82 . The rotary driver  64  can be of any conventional design; the design of the rotary driver  64  is not part of the present invention. Pumped through the rotary driver is the slurry  81  after it exits the slurry-mixing coil  66 . The slurry is forced into the slurry-mixing coil from the slurry junction box  68 . The slurry enters this box  68  from one or more sources of slurry, the rate at which this slurry from the various sources enters the junction vessel  68  is controlled at the entry points into the vessel by means of preset and adjustable-openings  84  into the vessel  68 . 
     Shown in FIG. 3 b  are two diaphragm pumps  72  that pump the slurry in direction  70 , that is towards and into the slurry junction vessel  68 . The slurry used for the polishing process is contained in the two slurry supply containers  74  and  76  which contain respectively slurry component  1  and slurry component  2 . At the center of core  56  are provided channels or hollow zones  78  that run in the same direction as the axis  82  of the pad/core assemblage  54 . These channels  78  are further connected to slurry ports (not shown in FIG. 3 b ) through which the slurry  80  is deposited and distributed to the polishing pads  58 . 
     FIG. 4 a  shows a cross sectional view of the pad/core combination with a set of four polishing pads  58 , the core  56  and the slurry ports  89 . 
     FIG. 4 b  shows a cross sectional view of the pad/core combination. The cross sectional view shows that the center  78  of the core  56  is hollow. The slurry ports  89  are also indicated. 
     The flow of the slurry is as follows: the slurry is forced into the hollow zones or channels  78  provided for this purpose in the core  56  by the rotary driver  64  and exits these channels  78  via the slurry ports  89 . The core is mounted on the core shaft or axis  82 , which in turn is connected to the rotary driver  64 . 
     FIG. 5 shows the exploded view of the pad conditioner disc. The inside  88  of the conditioner disk is seeded with diamond in order to improve the effectiveness of the polishing pad renewal process. The conditioner disk itself ( 86 ) can be made using stainless steel or any other appropriate material. 
     From the foregoing it will be clear that, although a specific embodiment of the present invention has been described herein for purposes of illustration, various modifications to the present invention may be made without deviating from the spirit and scope of the present invention. Accordingly, the present invention is not limited except as by the appended claims.