Abstract:
A system and method for filling a plurality of closely-spaced apart recesses to form a high-density pattern in the surface of a substrate. The metallization system and process includes providing a substrate, which includes a first surface defining a plurality of recesses; overlaying a resistive foil on the first surface; and subjecting the substrate to a pressure to cause said resistive foil to enter said plurality of recesses.

Description:
BACKGROUND  
         [0001]    1. Field of Invention  
           [0002]    The present invention relates to a method for forming a layer of an electrically conductive material on a substrate surface; and, more particularly, to a method of filling a plurality of closely-spaced apart recesses in the surface of the substrate.  
           [0003]    2. Related Art  
           [0004]    In the semiconductor industry, metal films can be formed as part of high-density metallization processing, which employ “damascene” (or “in-laid”) technology, of particular utility in integrated circuit semiconductor device and circuit board manufacture. The metal films can be used in semiconductor manufacturing technology, to form electrically conductive contacts to active, as well as passive, device regions or components formed in or on a semi-conductor substrate, as well as for filling via holes, inter-level metallization, and interconnection routing patterns for wiring together the components and/or regions.  
           [0005]    Typically, metallization patterns are formed in a damascene processing sequence to create, for example, back-end contacts, vias, interconnections, routing, and the like, in a semi-conductor device formed in or on a semi-conductor wafer substrate. The pattern of recesses, may include grooves, trenches, holes, and the like, formed, for example, by etching in the surface of a dielectric layer deposited or otherwise formed over the semiconductor substrate. A suitably conductive metal layer is deposited over the etched recesses as a blanket layer of excess thickness, so as to overfill the recesses and cover the exposed upper surface of the dielectric layer. The excess thickness of the metal layer over the surface of the dielectric layer is removed using a chemical-mechanical polishing (CMP) process, including moving the wafer while urging the wafer surface into contact with a facing surface of a polishing pad and providing a slurry, including abrasive particles, in the area of contact. As a result of polishing, the portions of the metal layer overlying the surface of the dielectric layer are substantially completely removed, while the metal portions remain in the recesses with their exposed upper surfaces substantially co-planer with the surface of the dielectric layer.  
           [0006]    Unfortunately, a problem associated with damascene processing of metallic materials arises from the phenomena of increased rates of erosion by CMP of high-density conductor patterns, such as patterns where the surface coverage by the layer of electrically conductive material forming the pattern is above 80% of the available surface area. Such increased erosion rates of regions of high-density metallization patterns by CMP also results in greater erosion of the dielectric layer portions intermediate the metallization features. As a consequence, non-planarity can occur across the surface of a wafer substrate. Moreover, typical methods for forming high-density in-laid metallization patterns by a damascene technique can include reduced electrical conductivity of the metallization features and reduce dielectric isolation resulting in degradation of device properties.  
         SUMMARY  
         [0007]    The present invention provides a system and method for filling a plurality of closely-spaced apart recesses forming a high-density pattern in the surface of the substrate. As a result, the exposed upper surface of the layer is substantially co-planer with non-recessed areas of the substrate surface. The method of the present invention also increases manufacturing through-put, and improves product quality.  
           [0008]    In one aspect, a method of metallization is provided which includes providing a substrate, which includes a first surface defining a plurality of recesses; overlaying a resistive foil on the first surface; and subjecting the substrate to a pressure to cause said resistive foil to enter said plurality of recesses.  
           [0009]    In another aspect, a system is provided for metallizing a substrate. The system includes a process chamber, which defines a cavity configured to receive a substrate. The substrate can have a plurality of recesses and may include a foil disposed on a surface thereof. The system also includes a pressurizing device for applying a pressure to the substrate. The pressure can cause the foil to move into each of the plurality of recesses.  
           [0010]    These and other features and advantages of the present invention will be more readily apparent from the detailed description of the embodiments set forth below taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]    The present invention may be better understood, and it&#39;s numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.  
         [0012]    [0012]FIG. 1 is a simplified illustration of a processing chamber including a pressurizing device in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is a simplified illustration of a portion of a substrate in accordance with the present invention;  
         [0014]    [0014]FIGS. 3A and 3B are simplified illustrations of an embodiment of the pressurizing device of FIG. 1;  
         [0015]    [0015]FIG. 4 is a simplified illustration of another embodiment of a pressurizing device of FIG. 1;  
         [0016]    [0016]FIG. 5 is a simplified illustration of an embodiment of the present invention;  
         [0017]    [0017]FIG. 6 is a simplified illustration of an embodiment of the present invention; and  
         [0018]    [0018]FIG. 7 is a flow chart of a process in accordance with the present invention.  
         [0019]    Embodiments of the present invention will be described with reference to the aforementioned figures. These figures have been simplified for ease of describing and understanding the embodiments. The use of the same reference symbols in different drawings indicates similar or identical items. 
     
    
     DETAILED DESCRIPTION  
       [0020]    The present invention will be discussed primarily in terms of selectively overlaying a metal film on a surface of a substrate, including a plurality of recesses. The plurality of recesses can include grooves, trenches, holes, and the like, formed, for example, by etching in the surface of a dielectric layer deposited or otherwise formed over the semiconductor substrate. It should be understood that that the overlaying process is not limited to any one type of surface but is applicable to metallizing any surface.  
         [0021]    [0021]FIG. 1 is a simplified cross-sectional view of one embodiment of a processing chamber  10  in accordance with an embodiment of the present invention. Processing chamber  10  includes a housing  12 , which defines an enclosed space  14 . Housed within space  14  can be susceptor  16 , including substrate support standoffs  18  (hereinafter “standoffs  18 ”), and a pressurizing device  20 , embodiments of which are described in greater detail below. It should be understood that processing chamber  10  includes heating, insulatory and other structural components, the use of which are well known to those of ordinary skill in the art, for the proper operation of the processing chamber.  
         [0022]    Externally, housing  12  may be metallic, preferably made of aluminum, stainless steel, or similar metal. Housing  12  has an opening (not shown) provided on a face of housing  12 , which is configured to receive a substrate loader (not shown), such as a robotic arm. The opening allows for the loading and unloading of substrates from housing  12  before and after processing. The opening may be a relatively small opening, but with a width large enough to accommodate substrates, for example substrate  22 . The relatively small opening size can help to reduce radiation heat loss from space  14 . The small opening size keeps down the number of particles entering enclosed space  14  and allows for easier maintenance of the isothermal temperature environment.  
         [0023]    To conduct a process, housing  12  is capable of being pressurized. For example, housing  12 , can be made to withstand internal pressures of about 0.001 Torr to 10 5  Torr, preferably between about 0.1 Torr and about 7600 Torr.  
         [0024]    Susceptor  16 , mounted within internal space  14  of housing  12 , includes a platen that is fabricated of aluminum or other thermally conductive material with a top surface having a generally circular shape for supporting a semiconductor wafer within processing chamber  10 . Typically, susceptor  16  includes a shaft, which is coupled to the bottom of the platen and supports the platen in processing chamber  10 . A heating element can be mounted in or under the platen and arranged to be in thermally conductive contact with the surface of the platen such that substrate  22  supported by the platen can be heated during processing. Susceptor  16  includes standoffs  18  positioned on the surface of the platen, which can support substrate  22  during processing. Standoffs  18  may be any high temperature resistant material, such as quartz. Standoffs  18  may have a height of between about 50 μm and about 20 mm.  
         [0025]    [0025]FIG. 2 is an enlarged view of a portion of substrate  22  in accordance with the present invention. In one embodiment, substrate  22  includes plurality of recesses  24 , which provide electrical contact areas, vias, interlevel metallization, and interconnection routing. Recesses  24  can have a depth d between about 0.05 μm to about 0.10 mm and a width w between about 0.05 μm to about 0.10 mm, or a diameter of between about 0.05 μm and 0.10 mm. In some embodiments, recesses  24  are actual holes that can extend through substrate  22 . Suitable substrates  22  can include inorganic and organic substances, such as glass, ceramics, porcelain, resins and the like.  
         [0026]    [0026]FIG. 2 is a simplified illustration showing foil  26  overlaid onto substrate  22  as a self-supporting thin sheet. Thin metal foils are of use in various well-known applications. Most foils are manufactured by a mechanical process involving extrusion and pressing of metal sheets. Very thin metal foils may be fabricated using a vacuum vapor deposition. In such a process, a metal is vaporized and subsequently condensed onto a solid substrate to form a thin foil on the substrate. In another known process, a thin unbacked metal foil may be formed by a process, which includes depositing a layer of metal onto one side of a soluble substrate film so as to form a layer of metal foil thereon, and subsequently dissolving the film in a suitable solvent so as to leave the deposited layer of metal as an unbacked foil sheet. In one embodiment, foil  26  can have a thickness t up to about 1000 μm. Foil  26  can be made from any suitably conductive material, such as gold, aluminum, nickel, cobalt, silver, tungsten, titanium, tantalum, copper and alloys thereof.  
         [0027]    Once fabricated, foil  26  can be manually transferred to a suitable supporting structure, such as substrate  22 . When transferred to substrate  22 , foil  26  fits loosely over the substrate surface. In most cases, foil  26  can be tightened before the metallization process occurs. In some cases, the application of heat from susceptor  16  (FIG. 1) is sufficient to tighten foil  26  on the surface of substrate  22 .  
         [0028]    [0028]FIG. 3A is a simplified illustration of an embodiment of pressurizing device  20  (FIG. 1). In this embodiment, pressurizing device  20  includes a roller assembly  40 , which may be used to provide the metallization of substrate  22 . Roller assembly  40  can include a roller  42  and an actuator  44 . Roller  42  can be, for example, a spherically or cylindrically shaped device used to provide pressure to a surface of substrate  22 . Roller  42  can be heated to a temperature between about 100° C. and about 800° C.  
         [0029]    In this embodiment, actuator  44  provides a conventional means for making roller assembly  40  operable to roll over substrate  22 . Actuator  44  may be configured to move roller  42  in a continuous or a back and forth, rolling motion across substrate  22 . One of ordinary skill in the art should recognize that actuator  44  may include, but is not limited to, conventional drivers and motion translation mechanisms, such as linear motors, stepper motors, hydraulic drives, and the like, and gears, pulleys, chains, linkages, and the like.  
         [0030]    [0030]FIG. 3B, is a simplified illustration of roller assembly  40  in operation. After foil  26  has been applied to surface  46  of substrate  22 , actuator  44  causes roller  42  to move over foil  26  and substrate surface  46 . The pressure imparted to surface  46  from roller  42 , causes foil  26  to be forced into recesses  24  until recesses  24  are filled with the desired amount of foil  26 . The amount of pressure needed may vary, depending on the type of foil  260 . Typically, recesses  24  are filled until the foil material in each recess  24  is substantially co-planer with substrate surface  46 .  
         [0031]    [0031]FIG. 4 is a simplified illustration of another embodiment of pressurizing device  20  (FIG. 1) in accordance with the present invention. In this embodiment, pressurizing device  20  includes a pressure applicator  50 . Pressure applicator  50  can include a nozzle  52  or similarly performing device coupled to a reservoir  54 . A fluid held in reservoir  54 , either a liquid or a gas, is emitted from nozzle  52  as a stream  56 , which impinges on the foil covered surface  46  of substrate  22 . The fluid pressure causes foil  26  to enter recesses  24  to fill recesses  24 . The amount of pressure forced upon foil  26  and substrate surface  46  can vary depending on, for example, the type of foil  26  being used, the depth of recesses  24  and the desired rate at which the processes is to proceed. For example, for a gold metal foil having a thickness of about 0.10 μm, the pressure impinging on substrate surface  46  can range from between about 0.001 Torr to 10 5  Torr, preferably between about 0.1 Torr and about 7600 Torr. Typically, recesses  24  are filled until the foil material filling each recess  24  is substantially co-planer with substrate surface  46 .  
         [0032]    Although, the embodiment of FIG. 4 shows pressure applicator  50  impinging on only a portion of substrate  22 , one of ordinary skill should understand that any amount of the substrate surface  46  of substrate  22 , including the entire substrate surface  46  can be simultaneously subjected to the pressure from pressurizing device  50 .  
         [0033]    [0033]FIG. 5 is a simplified illustration of another embodiment of the present invention. In this embodiment, a process system  60  includes process chamber  62 , pump  64  and fluid reservoir  66 . Process chamber  60  defines an internal cavity  68 , which can be completely pressurized. Accordingly, substrate  22  can be placed in cavity  68 . In this embodiment, foil  26  can be tightened before the metallization process occurs to create a first pressure Pa within recesses  24 . Pump  62  can be used to draw a gas from reservoir  66  to fill cavity  68  and place it under a chamber pressure Pc. Chamber pressure Pc can be made greater than pressure Pa in recesses  24  to cause foil  26  to be forced into recesses  24  to fill recesses  24 . The amount of pressure Pc forced upon foil  26  and substrate surface  46  can vary depending on, for example, the type of foil  26  being used, the depth of recesses  24 , pressure Pa and the desired rate at which the processes is to proceed. For example, chamber pressure Pc impinging on substrate  22  can range from between about 20 psig and 300 psig. Typically, recesses  24  are filled until the foil material filling each recess  24  is substantially co-planer with substrate surface  46 .  
         [0034]    [0034]FIG. 6 is a simplified illustration of another embodiment of the present invention. In this embodiment, a process system  80  includes a chamber  82 , pump  84  and fluid reservoir  86 . Chamber  82  includes a fluid bath  88  and a substrate holder  90 , which can be operably coupled together to be completely pressurized. Accordingly, substrate  22  can be placed and secured onto substrate holder  90  in an inverted position, such that recesses  24  are facing down and opposed to fluid bath  88 . Foil  26  can be tightened over substrate  22  before the metallization process begins. Pump  84  can be used to draw a fluid  89 , such as deionized water, from reservoir  86  to fill fluid bath  88 . Fluid  89  fills fluid bath  88  causing a chamber pressure Pc to impinge on foil  26 . Chamber pressure Pc causes foil  26  to be forced into recesses  24  to fill recesses  24 . The amount of pressure Pc forced upon foil  26  and substrate surface  46  can vary depending on, for example, the type of foil  26  being used, the depth of recesses  24  and the desired rate at which the processes is to proceed. For example, chamber pressure Pc impinging on substrate  22  can range from between about 20 psig and 300 psug. Typically, recesses  24  are filled until the foil material filling each recess  24  is substantially co-planer with substrate surface  46 . Once the operation is complete, chamber  82  can be pumped down and substrate  22  can be removed.  
         [0035]    [0035]FIG. 7 is a flow diagram of a process  70  in accordance with the present invention. In describing process  70 , reference is made to the embodiments of FIGS.  1 - 6 . In action  72 , substrate  22  is provided. Substrate  22  includes a plurality of recesses  24  and/or holes defined on substrate surface  46 . In action  74 , substrate  22  and thus, substrate surface  46  including recesses  24  are overlaid with a resistive material. In one embodiment, the resistive material includes foil  26 , for example, a metal foil, which may be made of gold, aluminum, nickel, cobalt, silver, tungsten, titanium, tantalum, copper and alloys thereof.  
         [0036]    Once foil  26  is in position, in action  74  a part to all of foil  26  is moved into the plurality of recesses  24 . Movement of foil  26  into recesses  24  can be accomplished using pressurizing device  20 , which is used to subject substrate surface  46  to a pressure, which forces foil  26  into recesses  24 . In one embodiment, pressurizing device includes a roller assembly  40 , which includes a roller  42  made to roll over substrate surface  46  using actuator  44 . Roller  42 , which can be heated to facilitate the movement of foil  26 , applies a rolling pressure to surface  46  causing foil  46  to enter each recess  24 . In another embodiment, pressurizing device  20  can include a pressure applicator  50 . Pressure applicator  50  causes a fluid, such as a gas or liquid, to impinge on substrate surface  46  causing foil  26  to enter recesses  24 . In yet another embodiment, substrate  22  having foil  26  overlaying substrate surface  46  can be placed in process chamber  62  and subjected to chamber pressure Pc. Chamber pressure Pc impinges on substrate surface  46  and is substantially high enough to cause foil  46  to enter recesses  24  on substrate  22 .  
         [0037]    While the principles of the invention have been described in connection with certain embodiments, it is to be understood that this description is not a limitation on the scope of the invention. Persons skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention. Thus, the invention is limited only by the following claims.