Abstract:
A Chemical Mechanical Planarization (CMP) Pad. The CMP pad may be hydrophobic due to the incorporation of metal complexing agents. The CMP pad substantially retaining planarazation characteristics throughout planarization applications. Shearing, hardness, wearing, water absorbtion and electrical characteristics of the CMP pad remain substantially constant during CMP applications.

Description:
BACKGROUND 
     Embodiments described relate to Chemical Mechanical Planarization (CMP) Pads. In particular, embodiments relate to CMP Pads which display substantially resilent character throughout CMP applications. 
     BACKGROUND OF THE RELATED ART 
     In the fabrication of semiconductor devices, materials of varying purposes are deposited on a semiconductor substrate. The semiconductor substrate is often a wafer of monocrystaline silicon materials having oxide layers such as silicon dioxide. Materials deposited thereon may include copper, aluminum and other metals to form metal lines within trenches of the semiconductor substrate. Additional circuit features and material layers may be formed on the semiconductor substrate throughout the fabrication process. A process of chemical mechanical planarization (CMP) follows the deposition of materials on the substrate in order to ensure that circuit features, such as the described metal lines, are discrete and isolated within the semiconductor substrate. 
     The CMP process may involve removing unwanted portions of deposited materials on the semiconductor substrate in order to planarize and isolate circuit features as described above. Planarization of the semiconductor substrate ensures a smooth and uniform surface thereon for subsequent material depositions and device fabrication. CMP is generally achieved by application of a CMP pad to the surface of the semiconductor substrate. The CMP pad, in combination with an aqueous slurry, are of particular chemical and mechanical properties configured to planarize the semiconductor substrate as the CMP pad is driven across the surface thereof. 
     A CMP pad is generally of a polyurethane or other flexible organic polymer. The particular characteristics of the CMP pad are key in developing the CMP process to be employed. For example, factors such as hardness, porosity, and rigidity of the CMP pad and its surface are taken into account when developing a particular CMP process for planarization of a particular semiconductor surface. In this manner, the CMP process may be precisely tailored for the type and amount of material to be planarized from the semiconductor surface. 
     Unfortunately, wear, hardness and other characteristics of the CMP pad may change over the course of a given CMP process. This is due in part to water absorption as the CMP pad takes up some of the aqueous slurry when encountered at the wafer surface during CMP. This sponge-like behavior of the CMP pad leads to alteration of CMP pad characteristics, notably at the surface of the CMP pad. Altering the character of the CMP pad in this manner, makes a particular planarization process extremely difficult, if not entirely impossible, to establish with a high degree of precision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional perspective view of an embodiment of Chemical Mechanical Planarization (CMP) material formation. 
         FIG. 2  is a side view of an embodiment of a CMP log formed of the CMP material of  FIG. 1 . 
         FIG. 3  is a side view of an embodiment of a hydrophobic CMP pad taken from the CMP log of  FIG. 2  and applied to a semiconductor substrate. 
         FIG. 4  is an exploded view of an embodiment of a hydrophobic CMP pad and semiconductor substrate taken from  4 - 4  of  FIG. 3 . 
         FIG. 5  is an exploded view of the hydrophobic CMP pad and semiconductor substrate of  FIG. 4  following application of an embodiment of Chemical Mechanical Planarization. 
         FIG. 6  is a flow-chart summarizing embodiments of forming a hydrophobic CMP pad. 
         FIG. 7  is a flow-chart summarizing an embodiment of planarization with a hydrophobic CMP pad. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments are described below with reference to certain Chemical Mechanical Planarization (CMP) pads and methods of making and using CMP Pads. In particular, hydrophobic CMP pads are described having resilent planarization characteristics. For example, embodiments of hydrophobic CMP pads may be employed in planarization applications while avoiding significant change in hardness, wear, water absorption, cross-link density, electrical, and other planarization characteristics. 
     Referring now to  FIG. 1 , an embodiment of a molding chamber  101  is shown having CMP material  100  therein. In the embodiment shown, the CMP material  100  includes an organic polymer which may initially be in the form of a polymer forming liquid provided by a polymer inlet  120 . The CMP material  100  also includes a metal agent provided by way of an agent inlet  110 . Additional additives and fillers may also be provided to tailor properties of the CMP material  100  as desired. In the embodiment shown, the molding chamber  101  also includes a mold container  175  for securing the CMP material  100 . A heater  150  and a gas inlet  130  may also be provided as shown. These features may be employed, as described further below, in the formation of a CMP log  200  (see  FIG. 2 ) from the liquid CMP material  100 . 
     With additional reference to  FIG. 6 , and embodiment of forming a hydrophobic CMP pad  250  as shown in  FIG. 2 . is summarized in the form of a flow-chart.  FIG. 6  is referenced throughout portions of the description to follow as an aid in describing formation of a hydrophobic CMP pad  250 . 
     Continuing with reference to  FIGS. 1 and 6 , the polymer forming liquid of the CMP material  100  may include a liquid urethane formed from a polyol and a di-isocyanate. The urethane may be polyether based. To encourage cross-linking as described below, the urethane selected may be reactive with a polyfunctional amine, diamine, triamine, a polyfunctional hydroxyl compound, and mixed functionality compounds including hydroxyl amines. In this manner, a polymer matrix may be formed as the CMP material  100  is later cured. A metal agent is also introduced via the agent inlet  110  and mixed with the organic polymer as indicated above and at  620 . In this manner, the CMP material  100  is formed. The metal agent itself may induce further cross-linking. As described below, additional mechanisms may be employed such that a reaction takes place by which the CMP material  100  takes the form of the CMP log  200  as shown in  FIG. 2 . 
     In one embodiment, the CMP material  100  is delivered to the mold container  175  along with foaming and curing agents. Curing agents may be provided to the CMP material  100  as indicated at  630  via the agent inlet  110  such that the CMP material  100  takes the form of a solidifiable polyurethane foam. Metal agent such as that described above may be employed as a foaming agent. Polyurethane is often selected as a CMP material due to inherent shear, wear, and hardness characteristics. 
     To tailor the porosity of the foam to a desired level, an inert gas may be simultaneously introduced through a gas inlet  130  and dissolved within the CMP material  100  as indicated at  640 . This may take place following addition of curing agent. Additionally, conditions within the molding chamber  101 , such as pressure and temperature may be regulated during the curing of the CMP material  100 . For example, in the embodiment shown, a heater  150  is provided to ensure that a desired temperature of the CMP material  100  is regulated during the curing process. In one embodiment, heat is applied to expedite the curing process as indicated at  635 . As also indicated at  635 , pressure may be reduced within the molding chamber  101 . This may encourage curing in a manner that promotes a desired level of porosity. 
     Continuing with reference to  FIG. 1 , and as described above, a polymeric matrix may be formed by use of the selected materials. This matrix may be formed from urethanes as described, in addition to melamines, polyesters, polysulfones, polyvinyl acetates, fluorinated hydrocarbons, including mixtures and copolymers thereof. Additionally, a metal agent is introduced as the CMP material  100  is formed. Generally, the metal agent is organically soluble and delivered dissolved within an organic solvent. The metal agent aids in the cross-linking formation of a matrix which includes metal-polymer complexes. As described further herein, these complexes provide hydrophobicity and control over the resistivity of the final product. Thus, a hydrophobic CMP pad  250  (see  FIG. 2 ) may be formed which is able to maintain a reliable character during planarization applications. That is, shear, hardness, wear, water absorption and other characteristics of a hydrophobic CMP pad  250  may be substantially and reliably maintained, including at the pad surface  475  throughout planarization applications (see  FIG. 4 ). 
     Embodiments of metal agents which may be employed as described above include metal β-diketonates having structures such as that shown here: 
     
       
                 
         
             
             
         
      
     
     As shown above, M may be a divalent metal cation including Copper, Cobalt, Palladium, Nickel, and Zinc, or a tetravalent metal cation including Titanium, Zirconium, and Hafnium. Additionally, R 1 , R 2 , R 3 , R 4 , R 5  and R 6  may be any combination of Hydrogen, aryls, perfluoroaryls, alkyls, and perfluoroalkyls. However, other embodiments may also be employed, including derivatives of metal β-diketonates and Lewis base adducts. In one preferred embodiment, all of R 1 -R 6  are t-butyl groups. These groups may be chosen to help limit isomerization reactions and instill a higher thermal stability to the organic polymer matrix formed. In another embodiment, all of R 1 -R 6  are perfluoroalkyl groups. 
     Referring now to  FIGS. 1 ,  2  and  6 , the CMP material  100  is cured as described above and a solidified CMP log  200  is removed as indicated at  650 , from the mold container  175  and chamber  101 . A CMP saw  275  is used to saw individual hydrophobic CMP pads  250  from the CMP log  200 . In this manner, a single CMP log  200  provides several hydrophobic CMP pads  250  as indicated at  660 . A hydrophobic CMP pad  250  may then be treated, conditioned, and available for use in planarization (see  FIGS. 3-5 ). 
     Referring to  FIGS. 3-5 , a hydrophobic CMP pad  250  is shown employed in a planarization process applied to a semiconductor wafer  300   FIG. 7 , a flow-chart summarizing an embodiment of planarization, is also referenced herein as an aid in and indicated describing planarization. As shown in  FIG. 3 , and indicated at  730 , the hydrophobic CMP pad  250  is positioned on a CMP apparatus  301 . A dispenser  325  then delivers an aqueous slurry  350  to the surface  475  of the hydrophobic CMP pad  250  as indicated at  740 . The semiconductor wafer  750  is positioned above the hydrophobic CMP pad  250  as indicated at  750 . The aqueous slurry  350  includes slurry particles  450  and chemistry providing certain chemical and mechanical properties thereto. Thus, an aqueous slurry  350  may be configured for a particular planarization application, depending on the material of the semiconductor wafer  300  to be planarized. 
     During a planarization application, the hydrophobic CMP pad  250  is moved in a given direction (see arrow  375 ), generally in a rotable manner. Similarly, the semiconductor wafer  300  to be planarized is positioned above the hydrophobic CMP pad  250  and moved in an opposite direction to that of the hydrophobic CMP pad  250  (see arrow  380 ), generally also in a rotable manner. In this manner, shearing forces are applied from the hydrophobic CMP pad  250  to the surface  430  of the semiconductor wafer  300  for planarization as indicated at  760 . 
     The effects of the shearing forces described above are illustrated with particular reference to  FIGS. 4 and 5 . In the embodiment shown, the semiconductor wafer  300  includes a metal line  420  between dielectric material  410 . A planarization application is applied to the semiconductor wafer  300  to remove excess metal  425 . In this embodiment, planarization is used to isolate the metal line  420  as shown in  FIG. 5 . That is, the surface  430  of the semiconductor wafer  300  is planarized and reduced from the position shown in  FIG. 4  to that shown in  FIG. 5  during a planarization application. As shown in  FIG. 5 , the metal line  420  is now entirely isolated between dielectric material  410  of the semiconductor wafer  300 . Planarization may also be used in other embodiments for removal of other material types, including dielectric materials, in other applications. 
     Throughout the planarization process described above, the hydrophobic CMP pad  250  substantially retains reliable wear, shearing, hardness, water absorption, electrical and other planarization characteristics. This is because the material of the hydrophobic CMP pad  250  is tailored as described above with a degree of hydrophobicity necessary to prevent any substantial intake of aqueous slurry  350 . That is, the aqueous slurry  350  is substantially prevented from crossing the surface  475  of the hydrophobic CMP pad  250 . In this manner, the hydrophobic CMP pad  250  maintains reliable physical characteristics as noted above while also maintaining a stable electrical character, unaffected by any significant uptake of a liquid media such as the aqueous slurry  350 . Additionally, pores  460  throughout the hydrophobic CMP pad  250  remain substantially void further stabilizing its character. 
     Referring to  FIGS. 6 and 7 , embodiments of forming and using a hydrophobic CMP pad are summarized in the form of flow-charts as previously indicated. With particular reference to  FIG. 6 , an organic polymer is mixed with a metal agent to form the initial liquid CMP material as indicated at  620 . As shown at  630 , a curing agent is then added to the CMP material which may be followed by application of reduced pressure and elevated heat as indicated at  635 . An inert gas is then dissolved into the CMP material as indicated at  640 . As shown at  650  a cured and solidified CMP log may then be removed and sawed into individual hydrophobic CMP pads as shown at  660 . With particular reference to  FIG. 7 , a hydrophobic CMP pad may be provided as indicated at  730  for the planarization of a semiconductor wafer. An aqueous slurry may be applied to the hydrophobic CMP pad as indicated at  740 . However, as described above, the hydrophobic CMP pad is able to avoid significant uptake of the aqueous slurry and substantially maintain its physical and electrical characteristics. Therefore, a semiconductor wafer may be positioned above the hydrophobic CMP pad as shown at  750  and planarized as indicated at  760  in a reliable and predictable manner throughout the planarization process. 
     Embodiments described above may substantially prevent intake of aqueous slurry by a CMP pad during a planarization application. As a result, wear, hardness, shearing, electrical and other characteristics of the CMP pad remain fairly constant throughout the planarization. Therefore, planarization applications may be established with a high degree of precision due to the reliable character and performance of the CMP pad. 
     While the above embodiments are described with reference to a particulate hydrophobic CMP pad, method of manufacture, and use, other embodiments and features may be employed. For example, the metal agent incorporated into the CMP material may be selected in light of metal features of the semiconductor wafer to be planarized. That is, where copper metal lines are to be isolated within the semiconductor wafer during planarization, the metal agent may include copper. Thus, the effect of any metal leeching from the CMP pad may be substantially minimized. Additionally, various other features and methods may be employed which are within the scope of the described embodiments.