Abstract:
A method and apparatus for applying conservative amounts of a fluid to coat a silicon wafer surface. The surface is rotated and the fluid is applied to the surface through multiple application ports. Centrifugal forces spread the fluid across the wafer surface.

Description:
BACKGROUND OF THE INVENTION 
     Silicon wafers are chemically etched to form semiconductor circuits. As part of the etching process a chemical typically referred to as photoresist is uniformly applied to the surface of the silicon wafer. A mask is then interposed between the silicon wafer and an energy source such as a light projector. The energy source is applied through the mask and exposes the photoresist. The photoresist is then dissolved with developers, leaving a pattern which is used to etch an image upon the silicon wafer. 
     Typically, photoresist is applied to the silicon wafer through a nozzle located at the center of the wafer. The wafer is rotated and centrifugal force distributes the photoresist along the surface of the wafer. Photoresist is expensive and it is therefore desirable to avoid applying more photoresist to a wafer surface than is required to properly coat the surface. 
     SUMMARY OF THE INVENTION 
     The present invention may improve the efficiency of coating a silicon wafer with a fluid. In one embodiment, the fluid is applied at the center of the silicon wafer and at a point between the center of the silicon wafer and the silicon wafer&#39;s edge. In another embodiment, the progress of the fluid across the rotating wafer is monitored. The flow of the fluid is controlled such that excess fluid is not applied to the wafer. In yet another embodiment a first fluid application nozzle is located at the center of the silicon wafer. A second fluid application nozzle is interposed between the first application nozzle and the edge of the silicon wafer. A fluid is applied at the first nozzle and the wafer is rotated. As the photoresist progresses towards the edge of the silicon wafer, a sensor monitors the fluid progress and when the fluid reaches a predetermined point or radius, the flow of the fluid from the first nozzle is changed and the fluid is then dispensed through the second nozzle. 
     Another embodiment involves a method of applying fluid to a silicon wafer surface. A receiving surface is rotated about an axis. The receiving surface has an edge remote from the axis. A fluid is dispensed from a first nozzle onto the receiving surface at the axis from a first nozzle. Fluid is also dispensed onto the receiving surface from a second nozzle interposed between the first nozzle and the edge of the receiving surface. 
     Another embodiment involves an apparatus for uniformly coating a silicon wafer surface. A receiving surface is rotated about an axis. A first nozzle is positioned over the receiving surface proximate the axis. A second nozzle is over the receiving surface remote from the first nozzle. 
     In another embodiment, a method is disclosed for applying a fluid to a silicon wafer surface by rotating a receiving surface about an axis and dispensing a fluid onto a receiving surface proximate the axis. An energy stream is projected against the receiving surface. The energy reflected from the receiving surface is monitored to gather information about the receiving surface. The gathered information is used to then control the flow of the fluid to the receiving surface. 
     Another embodiment involves an apparatus for applying fluid to a silicon wafer surface. A receiving surface is rotatable about an axis. A nozzle is positioned over the receiving surface near the axis. An emitter projects an energy stream against the receiving surface. A receiver monitors the portion of the energy stream reflected from the receiving surface. A controller is in communication with the receiver. A conduit is in a fluid communication with the nozzle. A meter is disposed in the conduit. The meter is in communication with the controller and the meter is adapted to control the flow of the fluid through the conduit to the nozzle. 
     Another embodiment involves a method for applying fluid to a silicon wafer. A receiving surface is rotated about an axis. A fluid is dispensed from a first nozzle over the receiving surface proximate the axis onto the receiving surface. The outward flow of the fluid along the receiving surface is monitored and a fluid is dispensed from a second nozzle onto the receiving surface when the outward fluid flow reaches a predetermined radius from the axis. 
     In another embodiment, an apparatus for applying a fluid to a silicon wafer includes a receiving surface rotatable about an axis. The receiving surface has an exterior edge. A first conduit has a discharge orifice over the receiving surface near the receiving surface axis. The second conduit has a discharge orifice over the receiving surface between the axis and the exterior edge of the receiving surface. A first meter is adapted to control the flow of a fluid through the first conduit. A second meter is adapted to control the flow of the fluid through the second conduit. A monitor is adapted to detect the outward flow of the fluid along the receiving surface. A controller is in communication with the monitor and the meters and is adapted to control the meters. 
     In another embodiment a receiving surface is rotated about an axis and a fluid is dispensed onto the receiving surface at a first radius from the axis. The outward flow of the fluid is monitored and the fluid is dispensed from a second radius from the axis when the fluid dispensed at the first radius flows to a predetermined radius. 
     In yet another embodiment a method for coating a silicon wafer surface involves rotating a receiving surface about an axis. A fluid is dispensed onto the receiving surface at a first radius from the axis. The fluid is sensed at a second radius from the first axis. The flow of the fluid onto the receiving surface at the first radius from the axis is altered and the fluid is dispensed onto the receiving surface near the second radius. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an embodiment of the present invention. 
     FIG. 2 is a perspective view of another embodiment of the present invention. 
     FIG. 3 is a schematic representation of an aspect of one embodiment of the present invention. 
     FIG. 4 is a schematic representation of an alternate embodiment of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a silicon wafer  12  is mounted on a spindle  14 . The spindle  14  is rotatable. A first nozzle  16  is adjacent the center of the silicon wafer  12 . A second nozzle  18  is interposed between the first nozzle  16  and the edge  20  of the silicon wafer  12 . A third nozzle  22  is interposed between the second nozzle  18  and the edge  20  of the silicon wafer  12 . Flow of a fluid, such as photoresist, through the first, second, and third nozzles is independently controlled. 
     The fluid is first applied through the first nozzle  16 . The silicon wafer  12  is rotated and centrifugal forces spread the fluid outwardly along the receiving surface of the wafer  12 . After a predetermined time, the fluid flow from the first nozzle  16  may be stopped or decreased and the fluid may then be dispensed from the second nozzle  18 . After a predetermined time, the fluid flow from the second nozzle  18  may be stopped or decreased and the fluid may then be dispensed from the third nozzle  22 . The flow of fluid to the first, second, and third nozzles  16 ,  18 ,  22  may be stopped or ramped down as the subsequent nozzle flow begins or is ramped up so that the flow of fluid to the wafer  12  remains constant. This process provides an even and efficient distribution of a fluid, such as photoresist, across the surface of the silicon wafer  12 . 
     For a twelve-inch diameter wafer, the first, second, and third nozzles  16 ,  18 ,  22  may be approximately two inches apart in one illustrative embodiment. In another illustrative embodiment, initially, photoresist may be applied to the silicon wafer  12  from the first nozzle  16  for 0.5 seconds. After the first 0.5 seconds of the process, 0.3 cc of photoresist may be dispensed from the second nozzle  18  for 0.5 seconds. After the first 1.0 seconds of the process, 0.3 cc of photoresist may then be flowed from the third nozzle  22  for 0.5 seconds. Thus, in this example, 1.1 cc. of photoresist is applied in 1.5 seconds. 
     In an alternate embodiment shown in FIG. 2, a fluid is applied to the center of the silicon wafer through a first nozzle  16 . The silicon wafer  12  is rotated on a spindle  14 . A first energy source  24 , such as an infrared or visible light emitter, projects energy to a first observation point  26  on the surface of the silicon wafer  12 . A first receiver  28  monitors energy reflected from the first observation point  26 . A second energy source  30  projects energy against the surface of the silicon wafer at a second observation point  32 . A second receiver monitors  34  the energy reflected from the second observation point  32 . 
     When the applied fluid is detected at the first observation point  26 , for example, because of the effect of the fluid on surface reflectivity, the flow of fluid through the first nozzle  16  may be reduced or stopped. Fluid may then be dispensed from the second nozzle  18  until the fluid is detected at the second observation point  32 . When the fluid is detected at the second observation point  32 , the flow from the second nozzle  18  may be stopped or reduced and fluid may then be dispensed from the third nozzle  22  for a predetermined period. The first and second observation points  26 ,  32  may be at the same radius as the second and third nozzles  18 ,  22 . Alternatively, it may be advantageous to position the observation points  26 ,  32  inward from the second and third nozzles  18 ,  22 . 
     As shown in FIG. 3, fluid may be dispensed from the first nozzle  16  by activating the first pump  36 . A processor  38  receives information from the first receiver  28  indicating the fluid has spread to the first observation point  26 . The processor  38  can then deactivate the first pump  36  and activate the second pump  40  which dispenses photoresist through the second nozzle  18 . When the processor  38  receives information from the second receiver  34  indicating the photoresist has spread to the second observation point  32 , the processor  38  may deactivate the second pump  40  and activate the third pump  42  for a predetermined period. 
     Alternatively, as shown in FIG. 4, fluid may be dispensed from the first nozzle  16  by activating the pump  44  and valve  46 . A processor  38  receives information from the first receiver  28  indicating the fluid has spread to the first observation point  26 . The processor  38  can then activate the nozzle  18  by controlling the valve  46 . When the processor  38  receives information from the second receiver  34  indicating the photoresist has spread to the second observation point  32 , the processor  38  may activate the valve  42  to disperse liquid from the nozzle  22  for a predetermined period. 
     The foregoing describes various embodiments of the claimed invention. The claimed invention is not limited to the embodiments described above. It is contemplated that numerous alternative constructors exist that would fall within the claimed invention.