METHOD AND APPARATUS FOR SPIN-COATING CHEMICALS

Abstract: An apparatus (100) and a method for spin-coating chemicals over a surface of a substrate (130) is disclosed. The apparatus includes a bowl (102) for supporting a substrate (130), a plurality of drain holes defined below the level of the substrate (130), a lid (101) having a flat surface that mates with the bowl (102), and a plurality of injection holes (121) defined in the bowl (102) for applying a solvent to an underside of the substrate, are included. The plurality of injection holes (121) are defined in along an injection ring (227) that is configured to receive the liquid solvent that is to be applied near an outer radius of the underside of the substrate, and the injection ring (227) is spaced apart from the underside of the substrate (130).

Description: METHOD AND APPARATUS FOR SPIN-COATING CHEMICALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to semiconductor fabrication, and more particularly, to apparatuses and methods for spin-coating substrates used in the fabrication of semiconductor devices. 2. Description of the Related Art The fabrication of a large variety of solid state devices such as semiconductors requires the use of planar substrates, otherwise known to those skilled in the art as wafers. An important consideration in the fabrication of these devices is the final number (i.e., yield) of functional dies remaining from each manufactured wafer. The functional dies are packaged, undergo testing (both electrical and otherwise), and substantially all of the packaged dies that pass the requisite testing are sold. It is therefore of utmost importance for manufacturers of these products to take advantage of economies of scale realized by increasing their production yield. Typically, depending on the individual die dimensions, upwards of 1000 or more dies may be fabricated on a single wafer. These wafers are typically on the order of six to twelve inches in diameter. A typical fabrication process requires numerous steps, where several layers of material are cumulatively applied and patterned on the surface of the wafer. Once complete, these layers form the desired semiconductor structure necessary for the resulting circuit, or device. As can be appreciated, the final functional yield critically depends upon the proper application of each layer during the various process steps. Proper application of these layers typically depends, in turn, upon the ability to form uniform coatings of material on the surface of the wafer in an efficient, environmentally benign, and production worthy manner. Various fabrication process steps implemented in making semiconductor devices utilize photolithography to define the desired patterns on the surface of a wafer. As is well known, photolithography is the process where light energy is applied through a reticle mask (using a stepper exposure camera) onto a photoresist material that is applied to the wafer to define patterns where subsequent etching will occur. These surface patterns represent a two dimensional layout of the desired structure that is fabricated on the surface of the wafer. It is therefore important that the photoresist material be applied in uniformly distributed coatings, while at the same time ensuring that particulate generation is minimized. As is well known in the art, when particulate generation is minimized or eliminated, it is possible to increase the resolution of the desired patterns, as well as increase pattern density. Conventionally, the application of photoresist coatings on the surface of a wafer is accomplished by casting a photoresist fluid on a wafer that is spinning at high speeds within a stationary exhausted bowl. In general, the stationary exhausted bowl is used to catch any excess fluids and remove particulates. Once the photoresist fluid is applied, the centrifugal force that result from the high rotational speed of the wafer overcomes the surface tension of the photoresist fluid, which causes the photoresist fluid to spread over the surface of the wafer. A side effect of spinning the wafer is the inducement of air flows in the air immediately above and adjacent to the wafer surface. Unfortunately, this air flow tends to induce particles of photoresist to leave the wafer surface at the wafer's edge. When the photoresist leaves the wafer's edge, the free floating photoresist particulates have the potential to back contaminate the remainder of the wafer surface where a fresh coating of photoresist has just been applied. Although these particles may be removed by an exhaust system that may be part of the stationary bowl, the exhaust has the undesirable effect of drying out photoresist solvent films unevenly and, thus, producing a non-uniform coating of photoresist over the surface of the wafer during the spinning process. Back side contamination of the photoresist film with photoresist particulates and uneven drying of the photoresist film are therefore, undesirable yield reducing side effects of conventional spin- coating processes. Another problem associated with conventional spin coating methods is photoresist fluid beading at the outer edge of the spinning wafer. Specifically, it is believed that surface tension and adhesion of the photoresist film to the wafer surface experienced during spinning causes the photoresist to from a "zone of increased thickness" at the edge of the wafer. This beading can typically contribute to a significant loss in functional devices that lie at and near the outer edge of the wafer. Yet another problem associated with the beading effect at the edges of the wafers is that wafers are commonly stored in cassettes and, the increased thickness at the edges has the unfortunate effect of fracturing the wafers when they come in contact with the storage cassette. Of course, when wafers are fractured in any way, an instant loss in yield is experienced. Figure 1 is an illustration of a conventional open bowl apparatus 10 for spin coating a wafer 16. A wafer 16 is typically placed upon a rotatable chuck 14 which is rigidly connected to a spinning motor unit 20 by a shaft 18. As shown, the spinning chuck 14 and the wafer 16 are located within an open stationary bowl 12. The open stationary bowl 12 may include suitable exhaust passages 22 that are used to purge out particulates that may be produced within open stationary bowl 12 during a spin coating process. Unfortunately, conventional methods for removing particulates produced during spin coating operations have been less than adequate. During a spin coating operation, a number of air flows 17 may be produced in the air immediately above and adjacent to the spinning chuck 14. As described above, the air flows 17 tend to produce particles of photoresist that further complicate the back contamination problems described above. In view of the foregoing, there is a need for apparatuses and methods that facilitate the application of substantially uniform spin coated materials over the surface of a wafer while reducing the amount of yield reducing particulates. SUMMARY OF THE INVENTION Broadly speaking, the present invention fills these needs by providing methods and apparatuses for uniformly spin-coating materials over the surface of wafers. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below. In one embodiment, an apparatus for spin coating chemicals over a surface of a substrate is disclosed. The apparatus includes a bowl for supporting a substrate, the bowl has a plurality of drain holes defined below the level of the substrate. The apparatus further includes a lid having a flat surface configured to lie at a predetermined distance above the substrate and mate with the bowl. Further, a plurality of injection holes are located under the bowl for applying a solvent to an underside of the substrate. The plurality of injection holes are located adjacent to a solvent injection ring that is configured to receive the liquid solvent applied from the outside of the bowl and driven into the bowl by centrifugal force to an outer radius of the underside of the substrate. The applied liquid solvent is configured to substantially reduce beading at an edge of the substrate and rinse off particulates that may be on the underside of the substrate. In another embodiment, an apparatus for spin coating a workpiece is disclosed. The apparatus includes a bowl for holding the work piece and a lid mounted on a top surface of the bowl. A plurality of lower drain holes are preferably defined along an outer circumference of bowl. A plurality of injecting holes each have a first end located on the outer lower surface of the bowl, and each of the plurality of injecting holes have a corresponding second end located on an inner surface of the bowl, such that the first end and second end are connected to define a path. Further, the plurality of injection holes are located at a first radial distance that is less than a second radial distance of the second end of the plurality of injection holes. In yet another embodiment, a method for spin coating a chemical over a substrate is disclosed. The method includes applying a chemical over a substrate and enclosing the substrate in a closed bowl configured to hold the substrate. The method also includes spinning the closed bowl to cause the chemical to spread over a top surface of the substrate. Then, injecting a solvent into the closed bowl such that the injected solvent is applied at an under surface of the substrate while the closed bowl is spinning, the injected solvent being configured to reduce edge beading of the chemical applied over the substrate and to rinse off particulates which may collect on the underside of the wafer. In addition, the solvent advantageously cleans the interior of the bowl by rinsing waste resist and chemicals from the interior of the bowl. One advantage of the above embodiments is that the lid is configured to enclose the wafer and seal out the environment above the wafer surface during a spin coating process. The plurality of injection holes defined through the underside of the spinning bowl are well suited for applying a fluid solvent to the underside of the wafer, and thereby rinse the underside of the wafer to suppress edge beading. In the preferred embodiment, the plurality of injection holes are located in a ring that is well suited to receive the fluid solvent that is applied to the outside of the spinning bowl. The applied fluid solvent is driven by the spinning centrifugal force through the holes and up onto the backside of the wafer. The solvent fluid is then driven by the centrifugal force to the edge of the wafer rinsing both the underside of the wafer, the edge of the wafer and the inner regions of the bowl. In an alternative embodiment, an apparatus for spin coating chemicals over a substrate is disclosed. The apparatus includes a bowl having a raised support for holding the substrate. The bowl includes curved walls that define a cavity capable of holding a fluid near an outer region of the bowl. The apparatus further includes a lid configured to mate with the curved walls. The lid preferably has a substantially flat underside that is positioned in close proximity to a top surface of the substrate. Further, the apparatus includes fluid injector holes defined along an ejection ring that is defined under the substrate. The fluid injector holes are directed at an underside of the substrate that is near the outer diameter of the substrate. The apparatus also includes a plurality of drain holes that are defined on a floor region of the bowl. The plurality of drain holes are spaced apart from the outer region of the bowl to enable the cavity to hold a fluid while the bowl is spinning, and to drain the fluid when the bowl begins to come to a substantial stop. A method for spin coating a substrate in accordance with the alternative embodiment is also disclosed. The method includes applying a chemical to be spin coated over a substrate that is supported within a bowl. The bowl has a fluid retaining cavity at an outer edge of the bowl. The method further includes encapsulating the substrate in the bowl, and spinning the encapsulated bowl to cause the applied chemical to be spin coated over the surface of the wafer. Further, the method includes injecting a solvent to an underside edge of the wafer to remove an excess chemical beading from the edge of the wafer, and collecting the solvent and the excess chemical beading that flows off of the substrate in the fluid retaining cavity while the encapsulated bowl is spinning. Further, the method includes draining the excess chemical beading and the solvent that is collected in the fluid retaining cavity when the encapsulated bowl nears a non-spinning state. An advantage of the alternative embodiment is that the lid is configured to enclose the wafer and seal out the environment above the wafer surface during a spin coating process. The plurality of injection holes defined in the floor of the spinning bowl are well suited for applying a solvent to the underside of the wafer to rinse the edge of the wafer to prevent edge beading of the applied chemicals (e.g., photoresist, SOG, and other spun on dielectrics). Generally, the solvent that is applied to the underside of the wafer is driven into the spinning bowl by the centrifugal forces produced when the bowl is spinning. Accordingly, the applied solvent may also be used to clean the inside of the bowl after each spin coating operation to reduce chemical build up, which may cause yield reducing defects. Furthermore, the fluid retaining cavity of the alternative embodiment in the bowl is well suited to hold any excess chemicals that are spin coated over the wafer as well as any solvent material that may be applied to the underside of the wafer. Preferably, substantially all fluids are retained within the cavity while the bowl is spinning, and when the bowl comes to a stop, the fluids may drain out through drain holes defined in the floor of the bowl. As an additional advantage, by capturing the fluids within the cavity during a spin coating operation, substantially less yield reducing particulates are produced. In a further embodiment, an extension of the bowl is well suited to form a labyrinth with a splash ring of a catch cup, and thereby substantially further reduce the possibility of air borne particulates outside to the bowl/catch cup system. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. Figure 1 is a cross-sectional view of a substrate spin coated in a conventional open bowl arrangement. Figure 2 A is an exploded view of a rotatable bowl and a lid in accordance with one embodiment of the present invention. Figure 2B is a top view of a rotatable bowl in accordance with one embodiment of the present invention. Figure 2C is a cross-sectional view showing the rotatable bowl containing a wafer and a locking shaft for mechanically applying and removing the lid to the rotatable bowl in accordance with one embodiment of the present invention. Figure 2D is a top view of the lid used in accordance with one embodiment of the present invention. Figures 2E is an enlarged side view of a portion of a rotatable bowl having a fluid drain hole in accordance with one embodiment of the present invention. Figure 2F is a diagrammatic cross-sectional view of a wafer during a typical spin coat cycle in accordance with one embodiment of the present invention. Figure 2G is a cross sectional view of a wafer having a substantially uniform coating layer after a spin coating procedure in accordance with one embodiment of the present invention. Figures 3 illustrates an exemplary spin coating system including a catch cup in accordance with one embodiment of the present invention. Figure 4A is an exploded view of a rotatable bowl and a lid in accordance with one embodiment of the present invention. Figure 4B is a side cross sectional view of the rotatable bowl of Figure 4A in accordance with one embodiment of the present invention. Figures 4C is an enlarged side view the rotatable bowl of Figure 4B illustrating a cavity for holding fluids during a wafer spin coating operation in accordance with one embodiment of the present invention. Figure 5 A is a cross sectional view of the applied coating fluid captured in the cavity during the spin coating operation in according with one embodiment of the present invention. Figure 5B is a cross sectional view of the applied coating after a solvent back rinse operation is performed in accordance with one embodiment of the present invention. Figures 6A is an exemplary spin coating system including a catch cup and splash rings in accordance with one embodiment of the present invention. Figures 6B is a magnified cross sectional view of a labyrinth formed by an extension of the rotatable bowl and a splash ring of the catch cup of Figure 6 A in accordance with one embodiment of the present invention DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An invention for a closed semiconductor process bowl that provides improved spin coat uniformity is disclosed. Although the present invention is particularly well suited for the application of photoresist materials, other chemicals such as spin-on-glass (SOG) may also find the application process well suited to improve coating uniformity. The various embodiments of the present invention may be implemented in any form, and may find particular use in the application of both high viscosity and lower viscosity materials to the surface of a planar wafer. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. In accordance with one embodiment, a closed process bowl is disclosed where chemicals are spin coated over a substrate during a fabrication process. In a preferred embodiment, the substrate is a wafer that may be used to make semiconductor devices. Generally, the wafer is placed on a rotatable bowl that is rigidly affixed to a motor driven shaft. During the coating process, a chemical such as photoresist is applied to the surface of the wafer before a lid is secured to the rotatable bowl having curved walls. The spinning of the bowl causes the chemical to spread over the surface of the wafer. To combat the aforementioned edge beading problems, a solvent is preferably injected on the back side (i.e., back side rinse) of the spinning wafer near its outer diameter after the photoresist has spread over the surface of the wafer. Preferably, the solvent is injected through a plurality of solvent injector holes that extend from an outer surface of the rotatable bowl to an interior region of the rotatable bowl. When applied, the solvent is forced into the rotatable bowl by the centrifugal force produced by the spinning action. In one embodiment, the applied solvent acts to substantially reduce beading at the outer regions of the wafer. Further, the applied solvent also acts to reduce particle contamination to the under surface of the wafer. Any dissolved material and excess solvent is generally removed from the closed bowl system through drain holes that are located at an outer diameter edge of the bowl. In manner, the dissolved material and excess solvent generally flows out of the closed bowl system during the photoresist coating operation and the back side rinse operation used to prevent edge bead formation. Once the back side rinse operation is complete, a top side rinse operation may also be performed. In general, the top side rinse operation involves removing the lid of the closed bowl system and applying a solvent over the top of the resist coated wafer. Preferably, the bowl containing the coated wafer is spun while the solvent is applied to the surface of the wafer to complete the top side rinse. Any solvent chemicals that spin off of the surface of the wafer while the bowl is spinning (and when the bowl comes to rest) are therefore allowed to exit the bowl through the aforementioned drain holes that are positioned below the surface height of the wafer. The back side rinse and top side rinse operations have the advantageous effect of cleaning the inner regions of the bowl of excess photoresist in addition to providing superior edge bead removal in a controlled environment. Figure 2 A is an exploded view of a closed semiconductor process system 100 including a bowl 102 and a lid 101. In this embodiment, the lid 101 preferably has a circular shape having an upper beveled surface 110, a lower flat surface 114, and a hollow internal region 111 that is accessible through a top opening 113. In accordance with the present embodiment, the bowl 102 is integrally connected to a motor driven axial shaft 135. As shown, the axial shaft 135 has an axially located vacuum chamber 118 extending substantially along the length of axial shaft 135 and terminating in a vacuum orifice 119. Vacuum orifice 119 is preferably centrally located on a support surface 104 of bowl 102. As shown, support surface 104 of bowl 102 is preferably configured to hold a suitable workpiece. In a prefeπed embodiment, the work piece is a silicon wafer used in the fabrication of semiconductor integrated circuits. However, it should be appreciated that the various embodiments of the present invention may be equally applicable to other technologies where precision chemical spin-coating is desirable (i.e., photoresist, spin-on- glass (SOG), compact disc recordable (CDR) dye chemicals, etc.). Generally, a support ring 126 defines the outer circumference of support surface 104 of bowl 102 and is configured to support a wafer 130, as shown in Figure 2C. In this example, lid 101 will preferably have a circular recessed groove 112 defined in the lower flat surface 114. Circular recessed groove 112 is preferably configured to mate with a circular protruded lip 124 that is located around the outer wall portions of bowl 102. Also shown are a plurality of drain holes 125 that are aπanged at the outer radius of bowl 102. Preferably, drain holes 125 are vertically lower than support surface 104. In this manner, when wafer 130 is placed over support surface 104, the wafer lies above drain holes 125. Because chemicals that are applied to the surface of a spinning wafer slide off of the wafer at high rates, the chemicals will preferably be channeled down and along the curved walls to the drain holes 125. As such, this curved wall surface is well suited to receive the chemicals being released from the wafer surface in a manner that directs the chemicals out of the closed bowl system. Preferably, between about 8 and about 16 drain holes 125 are defined around the outer radius of bowl 102 to enable the applied chemicals to exit during a spin coating cycle. In this embodiment, drain holes 125 are between about 1 mm and about 3 mm in diameter. Of course, the diameter may be modified to suit depending on the viscosity of the applied chemicals and the solvent materials injected in through injection holes 121. In any event, drain holes 125 are generally large enough to ensure that a sufficient pathway is defined to drain out the injected solvent and dissolved coating materials. Figure 2B is a top view of bowl 102 in accordance with one embodiment of the present invention. As shown, support surface 104 of bowl 102 has a plurality of supports 128 that extend radially outward from the centrally located vacuum orifice 119 to the support ring 126. Supports 128 are used to support the substrate that is held in place by vacuum suction supplied by vacuum orifice 119 and vacuum chamber 118. A plurality of locking pins 122 are shown aπanged around the top portion of bowl 102 to assist in securing lid 101 to bowl 102. Generally, locking pins 122 are configured to mate with suitable recessed pin holes 122a located on lid 101 as shown in Figure 2D below. Of course, other suitable lid attachment techniques will work as well. This view also provides a good illustration of a plurality of solvent injector holes 121 that are defined on a solvent ejector ring 127. In one embodiment, about 100 solvent injection holes 121 are defined around the solvent ejector ring 127 for applying solvent chemicals used in back side rinse operations. The back rinse function of solvent injector holes 121 will be described in greater detail with reference to Figure 2E. Figure 2C shows a wafer 130 placed upon support surface 104 of bowl 102 in accordance with one embodiment of the present invention. As described above, a vacuum supplied by a vacuum pump (not shown) is coupled to the vacuum chamber 118 which leads to the support surface 104 for securing wafer 130 during operation. In this view, the lid 101 has been coupled to bowl 102 in order to encapsulate wafer 130. Preferably, the lower flat surface 114 of lid 101 is separated from the upper surface 132 of wafer 130 by a distance that is small enough to reduce convective vortices from forming near the surface lying above the spinning wafer. In one embodiment, the distance is between about 1 mm and about 10 mm, and more preferably, between about 1.5 mm and about 3 mm, and most preferably about 2 mm. During a spin coating operation, a coating material is preferably applied to the inner radius of the upper surface 132 of wafer 130 before lid 101 is secured to the bowl 102. After the coating material has been applied, lid 101 is secured to bowl 102 by mating circular recessed groove 112 to circular protruded lip 124 as described above. In one embodiment, axial shaft 135 is connected to a motor (not shown) that preferably rotates axial shaft 135 to operational speeds sufficient to spread the coating materials. To ensure that lid 101 remains secured to bowl 102 during rotation, a locking shaft 160 is secured to lid 101. In addition, locking shaft 160 is used to mechanically apply and remove lid 101 from bowl 102 during and between spin coating cycles. As shown by Figure 2D, opening 113 defines a shape that is configured to receive locking shaft 160 (having a similar shape) into hollow internal region 111. Once the locking shaft 160 is lowered into hollow internal region 111, locking shaft 160 is rotated approximately 120 degrees in either direction. In this manner, the now opposing shapes of the locking shaft 160 and opening 113 prevent lid 101 from detaching during spin coating. From this top view of lid 101, the plurality of recessed pin holes 122a are shown defined along the outer diameter of lid 101 such that the plurality of pins 122 illustrated in Figures 2 A and 2B mate with the plurality of pin holes 122a. As described above and illustrated in Figure 2E, bowl 102 includes a plurality of solvent injection holes 121. Solvent injection holes 121 have one end E, defined within a solvent injector ring 123 that is located a radial distance r, from the center of rotation of bowl 102. Further, an internal end E 2 of the solvent injection holes 121 is located at about a radial distance r 2 from the center of rotation of bowl 102. Generally, radial distance r, is less than radial distance r 2 , therefore the injector holes 121 form angled conduit paths (e.g., between about 30 and 50 degrees) through bowl 102, connecting solvent injector ring 123 and solvent ejector ring 127. In a preferred embodiment, solvent ejector ring 127 has a diameter that extends about 150 mm. As described above, solvent that is passed in through the injector holes are well suited to complete back side rinsing of wafer 130, thereby reducing the possibility of edge bead formation. It should also be appreciated that wafer 130 is positioned a distance "Hw" above drain holes 125. In one embodiment, the distance Hw is at least between about 3 mm and about 5 mm, and more preferably at least between about 3 mm and about 4 mm, and most preferably at least about 3 mm. In this manner, chemicals that are spun off of the surface of wafer 130 are preferably not reflected back onto the surface of wafer 130. As described above, the inner wall surface of bowl 102 is preferably curved enough to allow chemicals to slide off wafer 130 and down the wall surface toward drain holes 125. A further advantage of having the drain holes 125 below the top surface 132 of wafer 130 is that any turbulence flows produced near the inner edge of bowl 102 is preferably contained below wafer 130. When turbulent flows are directed away from the surfaced wafer 130, the spun on coatings are produced with improved uniformity, thereby reducing yield reducing imperfections. Figure 2F shows a cross sectional view of wafer 130 during a typical spin coat procedure. As bowl 102 rotates, the produced centrifugal forces assist the coating material in spreading over the surface 132 of wafer 130, thereby forming a coating layer 140. Unfortunately, the typical coating procedure produces a beading 150 at the edge of wafer 130. As described above, beading 150 presents a number of undesirable yield reducing problems. To reduce the possibility of beading 150, a solvent material is injected in through solvent injector 121 and applied as a temporary solvent coating 141. In this example, the solvent coating 141 is caused to spread out towards the beading 150 by the same centrifugal forces that spread coating layer 140. Accordingly, the solvent coating 141 assists in dissolving beading 150 to produce a more uniformly coated edge. The dissolved coating material and excess solvent will then flow out of bowl 102 through drain holes 125 as described above. Figure 2G is a diagrammatic cross sectional view of wafer 130 having the spun on coating material layer 140 after the solvent coating 141 was applied to remove beading 150. As shown, the coating layer 140 is now more uniform throughout the surface of wafer 130. Figures 3 illustrates an exemplary spin coating system 180 that may be used in conjunction with the closed bowl spin coating system described above. As shown, bowl 102 and lid 101 are preferably assembled within a catch cup 182. Catch cup 182 may include a splash ring 183 that is used to block particulates generated out of drain holes 125 from exiting catch cup 182. Catch cup 182 also includes a drain hole 190 that is well suited to channel chemicals out of catch cup 182 and into a drain manifold (not shown). An exhaust manifold 188 may also be provided to assist in the removal of air borne particulates. A HEPA filter (not shown) may also be positioned above spin coating system 180 to capture any particulates that may escape catch cup 182. In the embodiment shown, a plenum 192 is coupled to bowl 102 to provide a channel 194 used for applying the aforementioned solvent chemicals to the solvent injector holes 121. In addition, plenum 192 provides a surface for receiving the exhaust manifold 188. Of course, any number of well known exhaust manifolds 188 may be implemented as well. In an alternative embodiment, an invention for a closed semiconductor process bowl that reduces particulate generation and provides improved spin coat uniformities is disclosed. Although the present invention is particularly well suited for the application of photoresist materials, other chemicals, such as, spin-on-glass (SOG) and spin-on-dielectrics (SODs) may also find the application processes described herein particularly advantageous for achieving improved coating uniformities and reducing particulates. Furthermore, the various embodiments of the present invention may be implemented in any form, and may find particular use in the application of both high viscosity and lower viscosity materials. In this alternative embodiment, any dissolved coating material and excess solvent that is produced during a spin coating process is preferably captured in a concave region located at an interior edge of the bowl, while the spin coating process is in progress. Once spin coating is complete (e.g., the spinning bowl comes to a substantial halt), the captive dissolved coating material and excess solvent are allowed to flow out of the spinning bowl through drain holes that are located on the lower surface of the bowl. That is, while the bowl is spinning, the centrifugal force acts to holds the dissolved coating material in the concave region. However, once the centrifugal forces diminish, the liquid will be allowed to flow out of the closed bowl system. It should be appreciated that substantially all particulates are advantageously contained within the closed bowl system during the spin coat operation, thereby reducing backside contamination problems as well as environmental contamination. In accordance with a further embodiment of the present invention, the back side and sometimes top side edge bead removal (EBR) process steps enable the generation of substantially uniform coatings within a controlled environment that reduces particulate generation. Furthermore, the EBR process steps advantageously assist in automatically rinsing the bowl after each coating operation. Of course, maintaining the bowl clean during a spin coating session is particularly important to reduce the possibility of contaminating cuπent wafers with particulates of previous spin coating sessions. Figure 4A is an exploded view of a closed semiconductor process bowl 200 including a bowl 202 and a lid 201, and Figure 4B is an assembled view in accordance with one embodiment of the present invention. In this embodiment, the lid 201 preferably has a circular shape with an upper beveled surface 210, a lower flat surface 214, and a hollow internal region 211 that is accessible through a top opening 213. Preferably, the bowl 202 is integrally connected to a motor driven axial shaft 235 that includes an axially located vacuum chamber 218 extending along the length of the axial shaft 235 and terminating in a vacuum orifice 219. Vacuum orifice 219 is preferably centrally located within bowl 202 for securing wafers to a support surface 204. As shown in Figure 4B, support surface 204 of bowl 202 is well suited to hold a wafer 230 during spin coating operations. In a prefeπed embodiment, the substrate is a silicon wafer used in the fabrication of semiconductor integrated circuits. However, it should be appreciated that the various embodiments of the present invention may be equally applicable to other technologies where precision chemical (i.e., photoresist, spin-on-glass (SOG), spin-on-dielectrics (SODs), compact disc recordable (CDR) dye chemicals, mask plates, liquid crystal display panels, multi-chip carriers, etc.) spin-coating is desirable. In this embodiment, a support ring 226 defines the outer diameter of support surface 204. In this example, lid 201 will preferably have a circular recessed groove 212 defined in the lower flat surface 214. Circular recessed groove 212 is preferably configured to mate with a circular protruded lip 224 that is located around the outer portion of bowl 202. Further, a separation of between about 1 mm and about 10 mm is preferably defined between the lower flat surface 214 of lid 201 and the top surface of wafer 230, and more preferably, the separation is between about 1.5 mm and about 3, and most preferably about 2. As mentioned above, bowl 202 preferably includes a cavity 250 for holding any dissolved coating material and excess solvent during the spin coating process. Therefore, while bowl 202 and lid 201 are spinning, the centrifugal forces will hold the excess liquid in cavity 250, and when the forces diminish, the liquid will preferably flow out through a plurality of drain holes 225. Preferably, between about 8 and about 16 drain holes 225 are defined along the floor of bowl 202 to enable the applied chemicals to exit after a spin coating application. Referring to Figure 4B, bowl 202 also includes a plurality of solvent injection holes 221 that have a first end located within a solvent injector ring 223 (at a radial distance r, from the center of bowl 202), and a second end located approximately at the mid-line of a solvent ejector ring 227 (at a radial distance r 2 from the center of bowl 202). Generally, radial distance r, is less than radial distance r 2 , therefore solvent injection hole 221 forms an angled conduit (e.g., between about a 30 and 50 degrees) through bowl 202 connecting solvent injector ring 223 and solvent ejector ring 227. Bowl 202 also includes a circular extension 260 that extends from the outer region of bowl 202 to reduce the possibility of particulate contamination. As will be described in greater detail below with reference to Figure 6B, circular extension 260 forms a labyrinth with a stationary catch cup splash ring to prevent substantially all generated particulates from exiting the system and contaminating the spin coated chemicals. To ensure that lid 201 remains secured to bowl 202, a locking shaft 261 is placed near the lower surface 214 of lid 201. By way of example, locking shaft 261 conforms to the shape of the top opening 213 of lid 201, thereby accessing hollow internal region 211. Once inserted into hollow internal region 211, locking shaft 261 is rotated approximately 120° in either direction. In this manner, locking shaft 261 is firmly affixed near the lower surface 214 of lid 201 to ensure that lid 201 does not detach during a spin coating process. Additionally, a plurality of locking pins 122/222 shown in Figures 4A and 2B are arranged about the top portion of the walls of bowl 202 to assist in securing lid 201 during processing. Generally, locking pins 122/222 are configured to mate with suitable recessed pin holes located on the underside of lid 201. In another embodiment, lid 201 may include magnetic latches (not shown) for securing lid 201 to bowl 202. Generally, the magnetic latches may be composed of a plurality of attracting magnet pads that are well balanced along the top portion of the walls of bowl 202 and along the underside of the lid 201. In this manner, the magnet pads of the bowl 202 and the lid 201 are not required to mate in the same fixed orientation each time the lid 201 is applied to the bowl 202. As an advantage, a more rapid sealing of bowl 202 may be performed which, in some cases, may prevent premature drying of the chemicals that applied to the wafer 230. Figure 4C is a magnified cross sectional view of Figure 4B having the plurality of drain holes 225 spaced a distance "y" from the outer edge of bowl 202 (excluding circular extension 260). In this manner, the plurality of drain holes 225 (being between about 1 and 3 mm in diameter) lie under wafer 230 to ensure that cavity 250 will hold the excess solvent and dissolved photoresist during a spin coating operation. For this reason, cavity 250 is preferably large enough to accommodate a volume of between about 10 cubic centimeters and about 20 cubic centimeters. Figure 5A is a more magnified view of cavity 250 holding solvent fluids provided through solvent injection holes 221 and dissolved chemicals that spread off of the wafer 230 in accordance with one embodiment of the present invention. As described above, while bowl 202 is spinning during a spin coating process, the centrifugal force will ensure that the excess chemicals will be contained in cavity 250 during the spin coating process. Therefore, when a chemical, such as, photoresist is applied over a top surface 232 of wafer 230, a photoresist beading 254 will unfortunately occur at the edge of wafer 230. To eliminate beading 254, a solvent 241 is applied from under bowl 202 against injection ring 223, through injection holes 221, and onto the back side of wafer 230. Once the solvent 241 is applied to an under surface 231 of wafer 230, the solvent material spreads in an outward manner due to the centrifugal forces of the spinning motion of bowl 202. When the solvent 241 reaches the edge of wafer 230, the solvent bead 251 is believed to interact with a beading 254 of a chemical coating 240. When solvent 241 comes in contact with beading 254, the beading 254 will begin to dissolve and fall into cavity 250. As an advantage, substantially all of the excess fluids are captured in cavity 250 during a spin coating operation, and substantially all uncontrolled solvents and coating chemicals are prevented from exiting bowl 202 where undesirable particulates may be generated. Figure 5B is a cross sectional view of the chemical coating 240 applied in a substantially uniform manner to the entire top surface of wafer 230 in accordance with one embodiment of the present invention. As described above, bowl 202 having cavity 250 advantageously reduces the amount of produced particulates during a spin coating operation. Further, the closed bowl configuration assists in maintaining coating uniformities by preventing the premature drying of the applied solvents. As a result, chemical coating 240 may be applied more evenly, while substantially preventing the yield reducing defects associated with beading and premature solvent drying. Figure 6 A illustrates an exemplary spin coating system 300 that may be used to reduce particulate generation in accordance with one embodiment of the present invention. As shown, bowl 202 and lid 201 are partially contained within a catch cup 302 that includes a first splash ring 303 and a second splash ring 304. Catch cup 302 also includes exemplary floor drain holes 310 that drain chemicals that flow out of drain holes 225, and then removed to a drain manifold. An exhaust manifold 308 may also be used to assist in the removal of air borne particulates. Of course, any number of well known exhaust manifolds 308 may be implemented as well. In this embodiment, the second splash ring 304 is preferably well suited to meet circular extension 260 and form a labyrinth to substantially prevent the escape of air borne particulates into the environment suπounding the spin coating system 300. Figure 6B is an exploded view of the exemplary spin coating system 300 illustrating the labyrinth in accordance with one embodiment of the present invention. As shown, when chemicals are being spin coated over the wafer, some chemicals may fly out of cavity 250 through the drain holes 225, causing particulates 320 to spread into catch cup 302. However, the particulates 320 that are contained within catch cup 302 are typically not a problem because they are removed by exhaust manifold 308. Because the second splash ring 304 is designed to almost contact the circular extension 260 of bowl 202, for particulates to escape, the particulates would have to traverse an unlikely path 350 before exiting the spin coating system 300. As a result of the labyrinth created between bowl 202 and second splash ring 304, as well as the fluid capturing cavity 250, the amount of yield reducing particulates are substantially eliminated. Therefore, the closed bowl spin coating system 300 provides semiconductor manufacturers with a powerful tool for increasing yields and maintaining substantially particulate free uniform chemical coatings. Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. By way of example, the methodology described herein may also be used to provide superior coating uniformities for square substrates, such as, mask plates, liquid crystal display panels and multi-chip carrier modules. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims. What is claimed is:

Claims: CLAIMS 1. A chemical applicator for spin coating chemicals over a surface of a substrate, comprising: a bowl for supporting a substrate, the bowl having a plurality of drain holes defined below the level of the substrate; a lid having a flat surface configured to lie a predetermined distance above the substrate and mate with the bowl; and a plurality of injection holes defined in the bowl for applying a solvent to an underside of the substrate. 2. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, wherein the plurality of injection holes are aπanged in a ring, the ring being coupled to a solvent injection ring that is configured to receive the liquid solvent that is to be applied near an outer radius of the underside of the substrate. 3. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 2, wherein the ring has an internal surface that is spaced apart from the underside of the substrate. 4. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, further comprising a locking shaft for mechanically applying the lid over the bowl, and the locking shaft being configured to secure the lid to the bowl during a spin coating process. 5. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 4, wherein the bowl includes a plurality of pins that are configured to mate and secure the lid to the bowl. 6. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 4, wherein the lid has a hollow internal region that is configured to receive the locking shaft. 7. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, wherein the predetermined distance is between about 2 mm and about 10 mm. 8. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, wherein the predetermined distance is between about 2 mm and about 4 mm. 9. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, wherein the bowl is secured in a catch cup having a draining system and an exhaust system. 10. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 9, wherein the catch cup includes a first splash ring configured to sit over a top portion of the catch cup. 11. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 10, wherein the catch cup includes a second splash ring that is configured to mate with the first splash ring, the second splash ring further being configured to substantially retain particulates exiting the plurality of drain holes within the catch cup. 12. A chemical applicator for spin coating chemicals over a surface of a substrate as recited in claim 1, wherein the substrate is a semiconductor wafer. 13. A spinning chemical applicator for spin coating a work piece, comprising: a bowl for holding the work piece; a lid mounted on a top surface of the bowl; a plurality of lower drain holes being defined along an outer circumference of bowl; and a plurality of injecting holes, the plurality of injecting holes each have a first end located under the bowl on an outer surface, and each of the plurality of injecting holes have a coπesponding second end located on an inner surface of the bowl such that the first end and the second end are connected to define a path. 14. A spinning chemical applicator for spin-coating a work piece as recited in claim 13, wherein the first end of the plurality of injection holes is located at a first radial distance that is less than a second radial distance of the second end of the plurality of injection holes. 15. A spinning chemical applicator for spin-coating a work piece as recited in claim 13, wherein the lid encapsulates the bowl and workpiece. 16. A spinning chemical applicator for spin-coating a work piece as recited in claim 14, wherein the plurality of drain holes provide a drain path leading from the plurality of injector holes. 17. A spinning chemical applicator for spin-coating a work piece as recited in claim 14, wherein the plurality of drain holes are defined substantially near a lower portion of the bowl. 18. A spinning chemical applicator for spin-coating a work piece as recited in claim 14, wherein the plurality of injector holes are vertically lower and spaced apart from the workpiece. 19. A spinning chemical applicator for spin-coating a work piece as recited in claim 14, wherein the bowl contains a vacuum channel for securing the work piece to the bowl. 20. A spinning chemical applicator for spin-coating a work piece as recited in claim 19, wherein vacuum channel is connected to a vacuum pump. 21. A spinning chemical applicator for spin-coating a work piece as recited in claim 13, wherein the lid contains a plurality of pin holes configured to mate with a plurality of pins defined on a top lip of the bowl. 22. A spinning chemical applicator for spin-coating a work piece as recited in claim 13, wherein the work piece is a semiconductor wafer. 23. A method for spin coating a chemical over a substrate, comprising: applying a chemical over a substrate; enclosing the substrate in a closed bowl configured to hold the substrate; spinning the closed bowl to cause the chemical to spread over a top surface of the substrate; and injecting a solvent into the closed bowl such that the injected solvent is applied at an under surface of the substrate while the closed bowl is spinning, the injected solvent being configured to reduce an edge beading of the chemical applied over the substrate. 24. A method for spin coating a chemical over a substrate as recited in claim 23, further comprising: dissolving the chemical beading formed over the top surface of the substrate when the solvent injected at the under surface of the substrate contacts the chemical beading. 25. A method for spin coating a chemical over a substrate as recited in claim 24, wherein the dissolving of the chemical beading produces a substantially uniform chemical coating over the top surface of the substrate. 26. A method for spin coating a chemical over a substrate as recited in claim 25, wherein the spinning of the closed bowl assists in injecting the solvent through a plurality of injecting holes defined in an underside of the closed bowl. 27. An apparatus for spin coating chemicals over a substrate, comprising: a bowl having a raised support for holding the substrate, the bowl having curved walls that define a cavity capable of holding a fluid near an outer region of the bowl; a lid configured to mate with the curved walls, the lid having a substantially flat underside that is positioned in close proximity to a top surface of the substrate; fluid injector holes defined along an ejection ring that is under the substrate, the fluid injector holes being directed at an underside of the substrate that is near the outer diameter of the substrate; and a plurality of drain holes defined on a floor region of the bowl, the plurality of drain holes being spaced apart from the outer region of the bowl to enable the cavity to hold a fluid while the bowl is spinning at a high rate, and drain the fluid when the bowl slows down. 28. An apparatus for spin coating chemicals over a substrate as recited in claim 27, wherein the fluid that is applied to the substrate is caused to spread over the substrate by a centrifugal force when the bowl is spinning, the centrifugal force further acting to hold the fluid that spreads off of the substrate in the cavity while the bowl is spinning. 29. An apparatus for spin coating chemicals over a substrate as recited in claim 27, wherein the bowl includes an extension defined outwardly from an outer edge of the curved walls. 30. An apparatus for spin coating chemicals over a substrate as recited in claim 28, wherein the fluid injector holes are defined at an angle ranging between about 30 degrees and about 50 degrees. 31. An apparatus for spin coating chemicals over a substrate as recited in claim 27, further comprising a catch cup configured to receive the bowl having the extension defined outwardly from an outer edge of the curved walls, the catch cup further including at least one splash ring that that defines a particulate reducing labyrinth with the extension. 32. -An apparatus for spin coating chemicals over a substrate as recited in claim 30, wherein the substantially flat underside of the lid is between about 2 mm and about 3 mm separated from a top surface of the substrate. 33. An apparatus for spin coating chemicals over a substrate as recited in claim 32, further including an injector ring that is defined on an under surface of the bowl for channeling a solvent through the fluid injector holes. 34. An apparatus for spin coating chemicals over a substrate as recited in claim 33, wherein the fluid applied to the substrate is a chemical selected from the group consisting of a photoresist chemical and a spin-on-glass chemical. 35. An apparatus for spin coating chemicals over a substrate as recited in claim 33, wherein the solvent is applied to the underside of the substrate that is near the outer diameter of the substrate, the solvent being configured to remove a beading of the chemical at an edge of the substrate. 36. An apparatus for spin coating chemicals over a substrate as recited in claim 35, wherein the applied solvent and applied chemical is captured in the cavity by the centrifugal force when the bowl is spinning. 37. An apparatus for spin coating chemicals over a substrate as recited in claim 36, further comprising a locking shaft for mechanically applying the lid over the bowl, and the locking shaft being configured to secure the lid when the bowl is spinning. 38. An apparatus for spin coating chemicals over a substrate as recited in claim 36, wherein the bowl includes a plurality of magnetic pads for securing the lid to the bowl. 39. An apparatus for spin coating chemicals over a substrate as recited in claim 36, wherein the cavity is configured to hold a volume of between about 10 cubic centimeters and about 20 cubic centimeters. 40 A method for spin coating a substrate, comprising: applying a chemical to be spin coated over a substrate that is supported within a bowl, the bowl having a fluid retaining cavity at an outer edge of the bowl; encapsulating the substrate in the bowl; spinning the encapsulated bowl to cause the applied chemical to be spin coated over the surface of the wafer; injecting a solvent in a vicinity of an underside edge of the wafer to remove an excess chemical beading from the edge of the wafer; and collecting the solvent and the excess chemical beading that flows off of the substrate in the fluid retaining cavity while the encapsulated bowl is spinning. 41. A method for spin coating a substrate as recited in claim 40, further comprising: draining the excess chemical beading and the solvent that is collected in the fluid retaining cavity when the encapsulated bowl nears a non-spinning state. 42. A method for spin coating a substrate as recited in claim 41, wherein the excess chemicals collected in the fluid retaining cavity are drained through a plurality of drain holes defined in a base region of the bowl. 43. A method for spin coating a substrate as recited in claim 42, wherein the plurality of drain holes are spaced apart from the outer perimeter of the bowl to establish the fluid retaining cavity. 44. A method for spin coating a substrate as recited in claim 41, wherein the fluid retaimng cavity is configured to hold a volume of between about 10 cubic centimeters and about 20 cubic centimeters. 45. A method for spin coating a substrate as recited in claim 41, further comprising: retarding chemical evaporation of the applied chemical when the bowl is encapsulated during the spinning, the retarded chemical evaporation being configured to result in a more uniform spin coating on a top surface of the substrate. 46. A method for spin coating a substrate as recited in claim 41, further comprising: providing a bowl extension along an outer edge of the bowl. 47. A method for spin coating a substrate as recited in claim 46, further comprising: providing a catch cup for holding the encapsulated bowl during the spinning, the catch cup having at least one splash ring; forming a labyrinth between the at least one splash ring and the bowl extension, the labyrinth being configured to reduce the amount of particulates that escape the catch cup. 48. A method for spin coating a substrate as recited in claim 46, further comprising: cleaning the bowl of excess chemicals after each spin coating operation with the solvent that is injected into the bowl. 49. A spin coating device, comprising: means for applying a chemical to be spin coated over a substrate that is supported within a bowl, the bowl having a fluid retaining cavity at an outer edge of the bowl; encapsulating means to contain the substrate in the bowl; means for spinning the encapsulated bowl to cause the applied chemical to be spin coated over the surface of the wafer; injector means to apply a solvent to an underside edge of the wafer, the solvent application being configured to remove an excess chemical beading from the edge of the wafer; and means for collecting the solvent and the excess chemical beading that flows off of the substrate in the fluid retaining cavity while the encapsulated bowl is spinning. 50. A spin coating device as recited in claim 49, further comprising: drain means for removing the excess chemical beading and the solvent that is collected in the fluid retaining cavity from the bowl when the bowl comes to a substantial stop. 51. A spin coating device as recited in claim 50, further comprising: means for cleaning an interior of the bowl after each substrate is spin coated. 52. A spin coating device as recited in claim 50, further including a labyrinth defined between the bowl and a catch cup splash ring, the labyrinth being configured to substantially prevent particulates from exiting the catch cup during a spin coating operation. 53. A spin coating device as recited in claim 52, wherein the chemical is selected from the group consisting of a photoresist chemical and a spin-on-glass chemical.

Inventors: BATCHELDER WILLIAM T, MAHNEKE PETER, BATCHELDER, WILLIAM, T., MAHNEKE, PETER
Applicants: FAIRCHILD CORP, THE FAIRCHILD CORPORATION
Application year: 1998
Main classification: B05D3
IPC codes: B05C11, B05D1, G03F7, H01L21