Abstract:
Apparatuses are disclosed for use in dispensing a process liquid onto a surface of a wafer. The apparatus may include a bowl having a bottom and a side defining an interior region. An air ring is disposed in the interior region to define an upper plenum in fluid communication with a lower plenum. The air ring may have at least one flow path therethrough to said lower plenum, preferably in the form of a plurality of holes in a circumferential groove. Also in a preferred embodiment, a top ring is provided to further define the upper plenum. A semiconductor wafer that has a liquid dispensed thereon, may be supported within the bowl to contact portions of the air ring to remove excess liquid migrating to the underside of the wafer. The excess liquid may be drained through the air ring into the lower plenum wherein it is removed by a drain. A solvent dispenser may be provided in the air ring to apply a solvent to the underside of the wafer. Excess solvent and liquid may be drained through the air ring to the lower plenum.

Description:
This a divisional application of U.S. patent application Ser. No. 08/667,705 filed on Jun. 21, 1996 now U.S. Pat. No. 5,861,061. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to containers and methods for use in dispensing process liquids onto a surface. More particularly, the present invention relates to a bowl and method for use in a spin coating apparatus for the coating of wafer shaped semiconductor material. 
     2. Description of the Invention Background 
     Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or “wafer”. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonapthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing salvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose-corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete. 
     Photoresist and developer materials are typically applied to the wafer using a spin coating technique in which the photoresist is dispensed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the photoresist over the surface of the material and exerts a shearing force that separates the excess photoresist from the wafer thereby providing a thin layer of photoresist on the surface of the wafer. Spin coating operations are performed in a clean room environment, and it is necessary to contain not only the excess coating material that is separated from the wafer, but also the vapor resulting from the evaporation of the solvent. In addition, photoresist materials are generally very expensive, ranging from $500 to $2300/gallon, therefore, reducing the amount of coating material used in the process can significantly reduce the overall cost of producing semiconductor devices. Also, a build up of excess coating material in the bowl requires additional downtime to remove and clean the bowl that further increases production costs. 
     FIG. 1 shows a side view of a typical bowl  200  and a porous wafer support chuck  202  of the prior art, such as is disclosed in U.S. Pat. No. 5,289,222 issued Feb. 22, 1994 to Hurtig. The wafer support chuck  202  is supported by a shaft  204  that passes through a hole  206  in the bowl  200  and attaches to a spin motor  208  in a motor compartment  209 . A wafer  210  having a top and a bottom surface,  212  and  214  respectively, is placed on the wafer support chuck  202  and is secured using a vacuum (not shown). The wafer  210  is spun and coating material, such as photoresist or developer, is dispensed onto the top surface  212  of the wafer  210 . The rotation of the wafer  210  causes the coating material to distribute over the top surface  212  and exerts a shear force on the coating material that separates excess coating material from the surface  212 . 
     Some of the solvent in the excess coating material vaporizes upon leaving the surface producing dry aerosol particles of the coating mixed with the liquid drops which accumulate over time on wall  216  of the bowl  200 . Also, the excess coating material has a tendency to creep around the edge of the wafer  210  and contaminate the bottom surface  214 . If the coating material on the bottom surface  214  migrates to the chuck  202  a loss of vacuum could occur and the wafer  210  will be released, possibly damaging the wafer. A solvent spray nozzle  218  is attached to the bowl  200  and is directed toward the edge of the wafer  210  to rinse the bottom surface  214 , thereby preventing a buildup of coating material. Solvent spray holes (not shown) are also provided in the bottom  217  of the bowl  200  to rinse the coating solution from the bottom surface. 
     The excess liquid coating and liquid solvent are drained from the bowl  200  using drain line  220  and the solvent vapors are purged from the bowl  200  with air through air purge line  222 . Solvent vapors are exhausted from the motor compartment  209  through a safety exhaust line  224 . The drain line  220 , the air purge line  222  and the safety exhaust line  224  are connected to an exhaust manifold and the vapor and liquid are separated and either reclaimed or disposed accordingly. 
     One problem that exists with the prior art design shown in FIG. 1 is that in the region between the bottom surface  214  of the wafer  210  and the bottom of the bowl  217  a low pressure zone is created that results in a recirculation zone being formed that increases the amount of contamination that reaches the bottom surface  214  of the wafer  210 , the bottom of the bowl  217 , the chuck  202 , and the motor  208 . The recirculation zone results in a lower production yield due to contamination of the wafers and an increase in the overall processing time due to the increased downtime required to clean the bowl  200 . 
     One prior art effort to eliminate the recirculation zone, shown in FIG. 2, employs a bowl  200  having a bottom  217  that is in close proximity to the bottom surface  214 . While this design does eliminate the recirculation zone beneath the bottom surface  214 , the pressure differential between the edge of the wafer and the axis of rotation and the proximity of the bottom  217  to the bottom surface  214  produces a wicking effect that draws coating material in toward the center of the bowl  200 . The proximity of the bottom surface  214  to the bottom  217  of the bowl  200  also makes it more difficult to rinse the coating material off the bottom surface  214  using the solvent spray nozzle  218 . 
     Another problem is that proior art bowls are generally segregated, such as by divider  226 , to prevent the excess coating material from getting splashed or drawn onto the bottom surface  214  of the wafer  210 . While this design is effective for that purpose, the solvent is also segregated from the excess coating material that is removed from the wafer  210  and the dry aerosol particulates that are produced as the solvent n the coating evaporates, all of which makes it more difficult to remove the liquid and solid coating material from the bowl  200 . The problems of the liquid coating drying and forming a build up occurs not only in the bowl, but in the drain lines leading to the exhaust manifold, which, of course, leads to increased downtime to clean the bowl and the drain lines. The amount of downtime required to clean the bowl in the prior art is further increased by the fact that in order to fully clean the bowl or the chuck and motor or to perform maintenance, the bowl and chuck have to be disassembled to separate the components. Thus, it is apparent that a need exists for an improved spin coating bowl design and method of using the same which overcomes, among others, the above-discussed problems so as to provide a spin coating bowl that requires less maintenance and the maintenance that is performed requires less overall downtime. 
     SUMMARY OF THE INVENTION 
     The above objects and others are accomplished by an apparatus and method in accordance with the present invention. The apparatus is used in the process of spin coating a top surface of a wafer with a coating material, the wafer having an edge and a bottom surface that is supported and rotated by a rotatable chuck attached by a shaft to a spin motor. The apparatus includes a bowl having a bottom and a side defining an interior region, the bottom containing an opening in which the shaft is movable. The rotatable chuck is attached to the shaft within the interior region and an air ring having an inner rim, an outer rim, a top surface and a bottom surface. The air ring is seated on the bottom and disposed around the opening. The top surface includes depressions having a base and an edge with the edge being in close proximity to the bottom surface of the wafer. The bottom surface of the air ring and the bottom of the bowl define a lower plenum and the top surface and said side defining an upper plenum, said outer rim being oriented to allow fluid communication between said upper plenum and said lower plenum and the depressions containing at least one flow path from the top surface to the lower plenum. In a preferred embodiment, and the depressions consist of at least one circumferential groove in the top surface of the air ring. Also in a preferred embodiment, a top ring is provided having a bottom face and an inner lip having dimensions smaller than the outer rim and larger than the wafer, the top ring being seated on the side of the bowl and the bottom face being separated from the top surface of the air ring by a plenum region which is part of the upper plenum. Preferably, the bottom of the bowl includes a raised portion containing the opening and the raised portion of the bottom and the inner rim of the top surface form a first circumferential groove and a second circumferential groove is provided in close proximity to the edge of the wafer to minimize the amount of coating material that migrates along the bottom surface of the wafer. Also preferred is that the raised portion of the bottom of the bowl includes integral solvent dispense nozzle directed toward the bottom surface of the wafer above the first circumferential groove to rinse any coating material may reach the second groove. 
     Accordingly, the present invention provides an effective solution to problems associated with contamination of the bottom surface of the wafer by eliminating the recirculation zone beneath the wafer through the use of the air ring and preventing capillary forces from being produced between the top surface and the air ring by the inclusion of vented depressions in the surface of the air ring. These and other details, objects, and advantages of the invention will become apparent as the following detailed description of the present preferred embodiment thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the present invention will be described in greater detail with reference to the accompanying drawings, wherein like members bear like reference numerals and wherein: 
     FIG. 1 is a side cross sectional view of a prior art spin coating apparatus; 
     FIG. 2 is a side cross sectional view of another prior art spin coating apparatus; 
     FIG. 3 is a side cross sectional view of a preferred embodiment of the present invention with a wafer supported by a chuck in a process position; 
     FIG. 4 is a perspective cross sectional view of the bowl with the wafer chuck disposed in the wafer loading position; 
     FIG. 5 is a side cross sectional view of the bowl with the wafer chuck disposed in the maintenance position; 
     FIG. 6 is an exploded perspective view of the bowl with the air ring, top ring and baffle; 
     FIG. 7 is a top plan view of the air ring; 
     FIG. 8 is a side view of the exhausted drain attached to the bowl; 
     FIG. 9 is a cross-sectional side view of another embodiment of the present invention supporting a wafer thereon. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The operation of the apparatus  10  will be described generally with reference to the drawings for the purpose of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same. The apparatus  10  of the present invention includes a process bowl  12  through which a rotatable chuck  14  is disposed to support a wafer  16  having a diameter D, a top surface  13 , a bottom surface  15  and an edge  17  during a spin coating of a coating material onto the wafer  16 . The bowl  12  is attached to an exhausted drain system  18  to allow for the removal of excess liquid and vapor coating material spun off the wafer  16  during the spin coating operation, as well as solvent materials. While preferred embodiments of the invention will be discussed with respect to spin coating material onto a circular surface of a wafer, one skilled in the art will appreciate that the invention can be suitably modified to coat any number of surfaces. 
     In a preferred embodiment, the process bowl  12  is circularly shaped having a central axis A—A, and a bottom  20  and a side  22  defining an interior region  24 . The side  22  has an upper edge  21  with a vertical lip  23  extending therefrom. The bottom  20  includes a generally cylindrically shaped raised portion  26  surrounding central axis A—A having an upper surface  25  containing a central opening  28  surrounded by an annular lower portion  27 . The upper surface  25  of the raised portion  26  has a peripheral surface  32  that is sloped toward the lower portion  27  leading to a circumferential step  34 . Solvent dispense nozzles  30  are internally formed in the raised portion  26  circumferentially around the central axis A—A and are attached to a solvent source (not shown) and directed at the bottom surface  15  of the wafer  16 . The dispense nozzles  30  are distributed circumferentially and are directed radially away from the axis A—A A through peripheral surface  32 . The circumferential step  34  contains notched leakage paths  36  corresponding to the location of the dispense nozzles  30  to allow solvent provided through the solvent dispense nozzles  30  to drain to the lower annular portion  27 . The interior region  24  is unsegregated or unpartitioned to facilitate the flow of excess liquid and vapor to the drain system  18 . Alternatively, the interior region  24  could be partitioned to form segregated plenum and mutual fluid communication between the partitioned plenum and the drain system  18  could be provided. 
     A circular air ring  40  is provided having an inner rim  42 , an outer rim  44  and top and bottom surfaces,  46  and  48 , respectively. The top and bottom surfaces,  46  and  48 , respectively, are crowned wherein the crown forms a circle having a diameter less than that of the wafer  16  and defining an inner sloped surface  50  and an outer sloped surface  52 . The inner rim  42 ,  42  is seated on the circumferential step  34  and the inner sloped surface  50  and the sloped peripheral surface  32  define a first circumferential groove  54  having two edges,  55  and  56 , respectively and a base  58 . The solvent is dispensed using the dispense nozzle  30  and the solvent and the excess coating material are directed toward the bottom surface  15  of the wafer  16  above the groove  54  drained through the notched leakage paths  36 . Preferably a second circumferential groove  60  is formed at the crown of the top surface  46  in close proximity to the edge  17  of the wafer  16 , when the wafer  16  is supported by the chuck  14 . The groove  60  is defined by edges,  56  and  62 , respectively, and base  64  contains perforations  66  extending from the top surface  46  through the bottom surface  48 . The bottom surface  48  and the bottom  20  of the bowl  12  define a lower plenum  70  that extends annularly around the raised portion  26 . The top surface  46  and the side  22  of the bowl  12  define an upper plenum  72  that extends annularly between the outer rim  44  of the air ring  40  and the side  22 . When the inner rim  42  is seated on the circumferential step  34 , the outer rim  44  is preferably not in contact with the bowl  12 , thereby providing fluid communication between the upper and lower plenums,  70  and  72 , respectively. 
     Preferably, a top ring  80  is provided having an inner lip  82  that extends into the interior region  24  having a diameter greater than the diameter of the wafer  16  and an outer diameter containing two circumferential steps  84  that mate with side edge  21  and lip  23 . The top ring  80  has a bottom face  86  that extends toward the bottom  20  of the bowl  12  and opposes the top surface  46  and preferably slopes from the inner lip  82  to the outer diameter, such that bottom face  86  is above the wafer  16  near the inner lip  82  and below the wafer  16  near the side  22 , when the wafer  16  is being supported in a process position, as shown in FIG. 3, and the bottom face  86  and the top surface  46  form a plenum region that is part of the upper plenum  72 . The bowl  12 , air ring  40  and top ring  80  are preferably constructed from a material that is resistant to, but wetted, by the spin coating chemicals and can be easily cleaned, such as Teflon, although other material can be incorporated to suit the particular needs of the practitioner. 
     In a preferred embodiment, the exhausted drain system  18  includes a single drain  88  in the bottom  20  of the bowl  12 , which is in close proximity to the outer rim  42  and in fluid communication with the lower and upper plenums  70  and  72 , respectively, thereby providing unsegregated or unpartitioned access to the drain system  18 . The unsegregated access to the drain  88  reduces the amount of material that precipitates or drys in the bowl  12  resulting in fewer maintenance shutdowns to clean the bowl. The use of a single drain provides for higher flow rates near the drain which maintain particles in suspension and leads to increased mixing of the solvent and the excess coating material allowing the coating material to be carried out of the system. Also, the use of a single drain and an unsegregated bowl maintains the solvent vapors in contact with coating material preventing additional evaporation of the solvent and drying of the coating material in the bowl  12  and in the drain lines. The exhausted drain  88  is connected to an exhaust manifold  90  through piping  92 . The liquid and the vapor are gravitationally separated in the exhaust manifold  90  with the vapor exiting through exhaust pipe  96  and the liquid exiting through drain  98 . A negative pressure is applied to the exhausted drain system  18  through exhaust pipe  96 , which draws vapor and liquid from the interior region  24  of the bowl  12 . A semicircular cylindrical baffle  100  is attached to the bottom  20  around the drain  88  to more uniformly distribute the flow in the interior region  24 . The presence of the exhausted drain  88  on one side of the bowl  12  would tend to preferentially exhaust vapor from the portion of the bowl  12  nearest to the drain  88 . The baffle  100  forces the vapor and liquid to flow into the drain  88  in a predetermined direction resulting in a more uniform flow field in the interior region  14  that further enhances the mixing of the solvent and the coating material providing for a cleaner bowl  12 . In an alternative embodiment, the bottom  20  can be sloped to further aid the flow of the solvent and-coating material to the drain  88 . 
     The drainage performance of the single drain  88  is enhanced through the use of the chuck  14  that is dimensionally smaller than the opening  28  in the bowl  12 . The chuck  14  is disk shaped and attached by a shaft  102  to a spin motor (not shown) for rotation of the shaft  102  and the chuck  14  and to servomotor (not shown), or other lift means, which is used to reciprocate the chuck  14  through the opening  28  between a maintenance position (FIG.  5 ), a process position (FIG. 3) and a wafer receiving position (FIG.  4 ). Because the chuck  14  is dimensionally smaller than the opening  28 , the processing position can be lowered with respect to the raised portion  26  and the air ring  40 , which allows the practitioner of the present invention to control the resistance of the flow path from between the wafer  16  and the raised portion  26  and the chuck  14  and the opening  28 . An important aspect of controlling the resistance is that the flow of solvent vapors through the opening  28  can be minimized, because the path of least resistance will be through or around the air ring  40  to the exhausted drain  88 . Also, because the chuck  14  can be reciprocated through the opening  28 , the spin motor and the servomotor can be separated from the bowl  12 , so that small amounts of solvent vapor that may travel through the opening  28  can be processed with the system air all of which combine to eliminate the need to have a dedicated vapor exhaust. In addition, the chuck  14  can be reciprocated to its maintenance position and the bowl  12  or the chuck  14  and lift means can be maintained separately without the need to disassemble either component, which greatly reduce maintenance time. For example, if a process bowl  12  is to be cleaned, the chuck  14  can be lowered to the maintenance position and the process bowl  12  can be switched out and replaced with another bowl so that the spin coating apparatus can be operating while the cleaning is being performed which significantly reduces the downtime of the processor. The chuck  14  is preferably a hard plastic, such as Teflon or polyphenylene sulfide (PPS), or a metal oxide through which a vacuum can be drawn using port  108  to secure the wafer  16  on the chuck  14  and which also has a low thermal conductivity to minimize the amount of heat generated by the spin motor that is transferred to the wafer  16 . In a preferred embodiment, the top surface  104  has a circumferential raised rim  106  that allows the wafer  16  to be supported in sufficiently close proximity to the top surface  104  to allow the vacuum to hold the wafer  16 , but the gap between the wafer  16  and the top surface  104  further reduces the heat transfer to the wafer  16 . 
     In the operation and method of the present invention, the air ring  40  is inserted into the bowl  12  with the inner rim  42  seated on the circumferential steps  84  and the top ring  80  is positioned so that the circumferential steps  84  mates with side edge  21  and lip  23  on the side  22  of the bowl  12 . The chuck  14  is initially in the maintenance position and then is moved through the process position to the wafer receiving, or loading, position using the servomotor. A wafer  16  is placed on the chuck  14  and a vacuum is drawn on the chuck  14  to secure the wafer  16  and the chuck  14  is lowered to the process position. The spin motor is activated to rotate the chuck  14  and wafer  16  and a negative pressure is applied through the exhaust  96  as the coating material is then dispensed onto the wafer  16  using a dispense assembly connected to a coating source. The rotation of the wafer  16  causes the coating material to distribute over the top surface  13  of the wafer  16  and the majority of the excess coating material will be spun off the wafer  16  into the upper plenum  72  and will contact the downwardly sloping surfaces of either the top surface  48  of the air ring  40 , the side  22 , or the bottom face  86 , which serve to direct the flow of material toward the lower plenum  70  and drain  88 . Some of the excess coating material will creep around the edge  17  of the wafer  16  onto the bottom surface  15 . The excess coating material will travel along the bottom surface  15  until it encounters circumferential edge  62  which allows coating material to move downwardly along the surface  52  or toward base  64 . If the material is not removed by edge  62 , the excess coating material traveling toward axis A—A will next encounter edge  56  which also allows the excess coating material to flow downwardly to base  64  or on surface  50 , both of which are in fluid communication with the lower plenum  70 . Excess coating material that passes edge  56  is sprayed by solvent nozzles  30 , which are directed away from axis A—A toward the bottom surface  15 . The solvent and excess coating material run down the downwardly sloping surfaces  50  and  32  and are drained through notched leakage paths  36  into the lower plenum  70 . The proximity of the bottom surface  13  of the wafer  16  to the raised portion  26  of the bowl  12  as a result of the chuck  14  having smaller dimension than the opening  28  serves to minimize the flow of solvent back through the opening  28 . The use of a single drain provides for an unsegregated exhaust system that allows the solvent to mix freely with the excess coating material, thereby minimizing the amount of dry coating material that remains in the bowl  12  and the drain lines when the solvent evaporates. After the coating operation is complete, the rotation of the wafer  16  and chuck  14  is stopped and the chuck is raised using the servomotor to the wafer receiving position and the wafer is removed and another wafer is placed onto the chuck  14  or the chuck  14  is lowered to the maintenance position, at which time the bowl  12  can be removed for cleaning or maintenance can be performed on the chuck  14 , spin motor and/or servomotor. 
     FIG. 9 depicts another embodiment of the present invention wherein the bowl  12 , air ring  40 , and top ring  80  are integrally formed out of a single material of the type described above. The skilled artisan will appreciate that this embodiment functions identically to the embodiment described above. 
     Those of ordinary skill in the art will appreciate that the present invention provides significant advantages over the prior art. In particular, the subject invention eliminates the recirculation zone beneath the wafer and prevents capillary forces from being produced between the air ring that can result in damage to the wafer by the inclusion of vented depressions in the surface of the air ring. The subject invention also improves the drainage of the process bowl so as to provide a cleaner process bowl, thereby reducing the extent of downtime required to clean the bowl. Also, the subject invention has the advantage of allowing the wafer chuck and motor assembly to be separated from the process bowl without disassembly of either component and provides added versatility in the positioning of the wafer within the process bowl, which was not present in the prior art. While the subject invention provides these and other advantages over the prior art, it will be understood, however, that various changes in the details, materials and arrangements of parts and steps which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.