Abstract:
A method and polishing system for planarizing a substrate having one or more materials formed thereon. The method generally includes positioning the substrate in proximity with a polishing pad, dispensing a polishing fluid to the polishing pad, the polishing fluid being subjected to carbonation prior to being dispensed to the polishing pad, and polishing the substrate. The polishing system generally includes a polishing platen having a polishing pad disposed thereon and in proximity to the substrate, a controller configured to cause the polishing pad to contact the substrate, and a polishing fluid delivery system to deliver a polishing fluid to the polishing pad, the polishing fluid delivery system including a carbonation system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of U.S. Provisional Patent Application Ser. No. 60/463,358, filed Apr. 16, 2003, which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to planarization of semiconductor devices and to methods and compositions for material removal. 
   2. Description of the Related Art 
   Multilevel interconnects are formed by the sequential deposition and removal of materials from a substrate surface to form conductive interconnect features. As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface, thereby requiring planarization. Planarization, or “polishing” a surface, is a process where material is removed from the substrate surface to form a generally even, planar surface. Planarization is useful in damascene processes to remove excess deposited material and to provide an even surface for subsequent levels of metallization and processing. Planarization may also be used to remove undesired surface topography and surface defects such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. 
   Chemical mechanical planarization (CMP) systems generally utilize a polishing head to retain and press a substrate against a polishing surface of a polishing material while providing motion therebetween. A polishing fluid is generally disposed between the substrate and the polishing material during polishing to provide chemical activity to assist in removing material from the substrate. Some polishing fluids further contain abrasives to assist in removal. 
   CMP processes may utilize a fixed abrasive polishing pad, which contains fixed abrasive particles held in a containment medium, such as a backing sheet, and a plurality of geometric abrasive composite elements adhered to the containment medium. 
   One problem that is encountered is that fixed abrasive planarization may cause surface irregularities, such as scratches on the substrate surface. The abrasive treatment used to modify a substrate should be designed to simultaneously modify the metal and dielectric materials without scratching the surface of either material. Therefore, there is a need for a polishing fluid that will reduce surface irregularities. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention generally include a method of planarizing a substrate having one or more materials formed thereon. The method generally includes positioning the substrate in proximity with a chemical mechanical polishing pad, dispensing a polishing fluid to the chemical mechanical polishing pad, the polishing fluid being subjected to carbonation prior to being dispensed to the chemical mechanical polishing pad, and chemical mechanical polishing the substrate. 
   Embodiments of the present invention further include a polishing fluid for a fixed abrasive polishing pad configured to remove materials formed on a substrate surface. The polishing fluid generally includes potassium hydroxide, deionized water, and carbon dioxide. 
   Embodiments of the present invention further provide a polishing system for planarizing one or more materials formed on a substrate surface. The polishing system generally includes a polishing platen having a fixed abrasive polishing pad disposed thereon and in proximity to the substrate, a controller configured to cause the fixed abrasive polishing pad to contact the substrate, and a polishing fluid delivery system to deliver a polishing fluid to the fixed abrasive polishing pad, the polishing fluid delivery system including a bubbling apparatus configured to carbonate the polishing fluid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope. 
       FIG. 1  illustrates a specific embodiment of a polishing system for polishing a substrate. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a specific embodiment of a polishing system  100  for polishing a substrate  112 . The substrate  112  may have one or more dielectric materials formed thereon. The dielectric materials may include silicon dioxide, silicon nitride, silicon oxy-nitride, phosphorus-doped silicon glass (PSG), boron-doped silicon glass (BSG), boron-phosphorus-doped silicon glass (BPSG), silicon dioxide derived from tetraethyl orthosilicate (TEOS), and silane, which are deposited by various chemical vapor deposition (CVD) techniques, and combinations thereof. The polishing system  100  generally includes a polishing fluid delivery system  102  to control the distribution of a polishing fluid  114  across a polishing material  108 . Although the polishing fluid and its delivery system  102  are described in reference to the illustrative polishing system  100 , the embodiments described below may be used in other polishing systems that utilize a polishing fluid. 
   Generally, the polishing system  100  includes a platen  104  and a polishing head  106 . The platen  104  is generally positioned below the polishing head  106  that holds the substrate  112  during polishing. The platen  104  is generally disposed on a base  122  of the system  100  and coupled to a motor (not shown.) The motor rotates the platen  104  to provide at least a portion of a relative polishing motion between the polishing material  108  disposed on the platen  104  and the substrate  112 . It is understood that relative motion between the substrate  112  and the polishing material  108  may be provided in other manners. For example, at least a portion of the relative motion between the substrate and the polishing material  108  may be provided by moving the polishing head  106  over a stationary platen  104 , moving the polishing material linearly under the substrate  112 , or moving both the polishing material  108  and the polishing head. 
   The polishing material  108  is generally supported by the platen  104  so that a polishing surface  116  faces upward towards the polishing head  106 . Generally, the polishing material  108  is fixed to the platen  104  by adhesives, vacuums, or mechanical clamping during processing. Optionally, and particularly when the polishing material  108  is configured as a web, the polishing material  108  is releasably fixed to the platen  104 , typically by use of a vacuum disposed between the polishing material  108  and the platen  104 , as described in U.S. Pat. No. 6,244,935, the subject matter of which is hereby incorporated by reference. 
   The polishing material  108  is preferably a fixed abrasive material, although embodiments of the invention may be used with any polishing material. Fixed abrasive polishing materials are generally comprised of a plurality of abrasive particles suspended in a resin binder that is disposed in discrete elements on a backing sheet. Fixed abrasive polishing materials may be utilized in either pad or web form. As the abrasive particles are contained in the polishing material itself, systems utilizing fixed abrasive polishing materials generally utilize polishing fluids that do not contain abrasives. Examples of fixed abrasive polishing materials are disclosed in U.S. Pat. No. 5,692,950, issued Dec. 2, 1997 and U.S. Pat. No. 5,453,312, issued Sep. 26, 1995, both of which are hereby incorporated by reference. 
   The polishing head  106  generally is supported above the platen  104 . The polishing head  106  retains the substrate  112  in a recess  120  that faces the polishing surface  116 . The polishing head  106  typically moves toward the platen  104  and presses the substrate  112  against the polishing material  108  during processing. The polishing head  106  may be stationary or rotate, move orbitally, linearly or a combination of motions while pressing the substrate  112  against the polishing material  108 . 
   The polishing fluid delivery system  102  generally includes a delivery arm  130 , a plurality of nozzles  132  disposed on the arm  130  and at least one polishing fluid source  134 . The delivery arm  130  is configured to dispense polishing fluid  114  at different locations along the arm  130  to control the distribution of polishing fluid  114  on the polishing surface  116  of the polishing material  108 . As the polishing fluid  114  is generally supplied from a single source, the polishing fluid  114  is disposed on the polishing material  108  in a uniform concentration but in different locations along the width (or diameter) of the polishing material  108 . 
   The delivery arm  130  is generally coupled to the base  122  proximate the platen  104 . The delivery arm  130  generally has at least a portion that is suspended over the polishing material  108 . The delivery arm  130  may be coupled to other portions of the system  100  as long as the portion is positionable to deliver polishing fluid  114  to the polishing surface  116 . The plurality of nozzles  132  are disposed along the portion of the delivery arm  130  that is disposed above the platen  104 . In one embodiment, the nozzles  132  comprise at least a first nozzle  140  and a second nozzle  142 . Typically, the first nozzle  140  is positioned on the arm  130  radially inward of the second nozzle  142  relative to the center of rotation of the polishing material  108 . The distribution of polishing fluid  114  across the polishing material  108  is controlled by selectively flowing polishing fluid  114  from either the first nozzle  140  or from the second nozzle  142 , or from both the first nozzle  140  and the second nozzle  142 . The polishing fluid  114  may be supplied to the polishing surface  116  at a flowrate of from about 5 mL/min to about 500 mL/min. 
   The polishing fluid source  134  is generally disposed externally to the system  100 . In one embodiment, the polishing fluid source  134  generally includes a reservoir  152  and a pump  154 . The pump  154  generally pumps the polishing fluid  114  from the reservoir  152  through the supply line  124  to the nozzles  132 . The polishing fluid source  134  further includes a carbonation system  160 . 
   In operation, the substrate  112  is positioned in the polishing head  106  and brought in contact with the polishing material  108  supported by the rotating platen  104 . The polishing head  106  may hold the substrate stationary, or may rotate or otherwise move the substrate to augment the relative motion between the polishing material  108  and substrate  112 . The polishing fluid delivery system  102  flows carbonated polishing fluid  114  through the supply line  124  to the first polishing nozzle  140 . After a predetermined amount of material is removed from the substrate  112 , the flow of polishing fluid  114  is stopped from the first nozzle  140  and started from the second nozzle  142 . The change in location (i.e., distribution) of polishing fluid  114  on the polishing surface  116  results in a change in the local polishing rate across the width of the substrate. 
   Polishing Fluid 
   The carbonated polishing fluid  114  contained in the reservoir  152  generally includes one or more pH adjusting agents can be present in an amount sufficient to adjust the pH of the polishing fluid to provide a pH of from about 2.5 to about 12 and can include any of various bases, such as potassium hydroxide (KOH), or inorganic and/or organic acids, such as acetic acid, phosphoric acid or oxalic acid. The pH is adjusted based on the composition of the various components of the composition. Preferably, the pH adjusting agent is added in an amount sufficient to provide a pH of from about 9.5 to about 11.5. The polishing fluid may further include up to about 35 wt. % of abrasive particles, such as silica. 
   The polishing fluid may also include one or more buffers to increase the scratch performance, e.g., reduction of scratches, of the polishing fluid. In addition, buffers may be added to the polishing fluid to control the pH and thus mitigate pH changes caused by minor dilution from rinse water and/or the difference in the pH of the deionized water. As mentioned above, the pH can have a significant effect on the nature of the dielectric surface, and the dielectric removal rate. The buffer may include one or more organic compounds, which assist in selectively modifying the removal rate of one or more dielectric materials in relation to another dielectric material. Examples of organic compounds include amino acids having amino (—NH2) and carboxyl (—COOH) terminal ends, and derivatives thereof, such as glycine, proline, arginine, lysine, and combinations thereof. Preferably, the polishing solution includes L-proline. Polishing additives, for example, chelating agents and surfactants, may be added to the polishing composition. 
   Embodiments of the invention include carbonating the polishing fluid to further increase scratch performance, e.g., adding carbon dioxide (CO 2 ) to the polishing fluid. The polishing fluid may be carbonated in the reservoir  152  as shown in  FIG. 1 , or at any other time prior to contacting the polishing surface  116 . The CO 2  may be added to the reservoir  152  by any carbonation system  160  known to one skilled in the art, such as via a bubbling apparatus having a conduit configured to deliver the CO 2  to the reservoir  152 . A bubbling apparatus is generally operably connected to a gas regulator configured to control the gas flowrate into the tank. Generally the gas flowrate is from about 100 cc/min to about 1000 cc/min. The polishing fluid may be carbonated for a period of time from about 5 to about 1000 seconds. Preferably, the polishing fluid is carbonated for about 100 to about 660 seconds. 
   The pH of the polishing fluid may be remeasured upon carbonation and adjusted accordingly to obtain a desired pH level. For example, additional KOH may be added to the polishing fluid to obtain a polishing fluid pH of about 9.5 after carbonation. 
   The embodiments described above generally result in increased scratch performance. For example, a polishing fluid having a pH of 9.5 and which was carbonated for 600 seconds exhibited zero scratches. The surface finish of the substrate may be evaluated by methods known to one skilled in the art. For example, defects may be detected by the Orbot or Compass systems available from Applied Materials, Santa Clara, Calif. 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.