Abstract:
Disclosed is method and apparatus for distributing a chemical over the surface of a substrate. The method includes depositing the chemical on a portion of the surface of a substrate near the center of the substrate. The method further includes controlling the temperature of the surface of a substrate so that the viscosity of the chemical is calibrated to cause the chemical to be deposited on the surface of the substrate in a substantially uniform manner.

Description:
This is a Divisional application of prior application Ser. No. 08/807,680 filed on Feb. 27, 1997, now U.S. Pat. No. 5,916,368, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to compact disc manufacturing, and more particularly, to methods and apparatus for temperature controlled spin-coating systems. 
     2. Description of the Related Art 
     Compact disc recordable (CDR) technology has received increased popularity due to increased consumer demands for storage devices having large storage capacities and fast reading and writing capabilities. Generally, CDR discs are similar to well known read-only compact discs (CDs) used in the music recording industry and computer software industry. However, fabricating CDR discs requires various processing steps that are dissimilar to those employed by CD manufactures. Initially, CDR disc manufactures use well known molding machines that are configured to receive a polycarbonate (i.e., plastic) material from one end and output a warm clear plastic disc at the other end. Once output from the molding machine, the discs are cooled and inspected for defects or abnormalities which may have been introduced during the molding process. If the polycarbonate disc meets quality control tolerances, the disc is moved to a chemical application station where a solvent based chemical is coated over the clear polycarbonate disc. Suitable well known solvent based chemicals may be obtained from CMR Technology, Inc., Trumble, Conn. 
     In “record once” recordable CDR technology, the solvent based chemical coated over the surface of the polycarbonate disc is a critical layer that typically defines the resulting performance ratings of recording and reading operations. The solvent based chemical generally acts as a programmable layer that changes characteristics when a recording laser is directed at the underside of the polycarbonate disc. Accordingly, during a subsequent reading operation, a reading laser is scanned across the disc and a sensor is able to distinguish recorded signals from non-recorded regions by examining the reflected light from the reading laser. 
     Nonuniformities in the chemical coating affect the reaction of the chemical coating to the reading laser. Therefore, the solvent based chemical applied over the polycarbonate disc must be extremely uniform in order to produce CDR discs that are sufficiently fast at both recording and subsequent reading operations. If the solvent based chemical is applied in a non-uniform manner over the surface of the polycarbonate disc, the recording and reading responses will suffer and therefore produce a slower recording and reading CDR disc. 
     As is well known in the art, CDR discs are classified and marketed as either 2X, 4X, 6X, 8X, etc., depending the CDR disc&#39;s recording speed. Although manufacturing costs associated with fabricating CDR discs having 2X, 4X, 6X, or 8X speeds are substantially equal, typical market prices for 2X discs are substantially lower than that of 8X discs. However, generating uniform chemical coatings over the surface of a polycarbonate disc has been found to be extremely challenging due to a number of factors, including increased temperatures generated in conventional spin-coating systems. By way of example, most commonly used spin-coating systems have chucks for holding discs in place while rotating the chuck at high revolutions per minute (RPMs). Of course, in order to rotate the chuck and disc at speeds suitable for spin-coating solvent based chemicals used in CDR technology, the mechanical friction and motors to rotate the chuck generate increased temperatures. 
     As CDR discs are spin coated in a manufacturing line where hundreds or thousands of discs are spin-coated one after another, the temperatures of the spin-coating systems may increase to temperatures reaching about 35 degrees °C. Typically, when discs are placed over a chuck for spinning, the disc is only in contact with the chuck near the center radius where no information is written. The polycarbonate material which makes up the disc is a relatively good thermal insulator. Therefore, when a disc is placed in contact with the warm chuck, the disc will generally be warmer near the center radius and cooler near the edges. As a result, the solvent based chemical will be less viscous (i.e., thinner) near the center and more viscous (i.e., thicker) near the outer radius. The solvent also tends to be more viscous at the edge as a result of evaporation. Consequently, undesirable nonuniformities are introduced which degrade the quality of reading and writing operations. 
     FIG. 1 is a cross-sectional view of a CDR disc having non-uniformities believed to be caused in part by elevated temperatures in conventional spin coating systems. In this example, a disc  32  is shown having various chemical layers applied over the disc&#39;s surface. As described above, a solvent based chemical  36  is initially applied near an inner radius of the disc  32  in order to spread the chemical over the top surface of the disc once the disc is rotated to equilibrium speeds. As shown, the applied solvent based chemical  36  has a wavy top surface having a thinner profile near the radius and a thicker profile near the outer radius. 
     As illustrated, when the center of the disc  32  has a higher temperature, the solvent based chemical  36  is will be less viscous and therefore exhibit a thinner profile  36   b.  Conversely, the outer radius of the disc  32  will have a lower temperature because it is not in contact with the chuck. As a result, the solvent based chemical will be more viscous and have a thicker profile  36   a.    
     Once the solvent based chemical  36  is applied over disc  32 , disc  32  is removed from the spin coating system and placed into a sputtering machine where a gold material  38  is sputtered over solvent based chemical  36 . Although the gold material  38  may have a more uniform profile throughout the disc surface, the non-uniformities of the underlying solvent based chemical  36  unfortunately mirror up. Once the gold material is sputtered on, the disc  16  is moved to another station where a suitable protective lacquer coating  40  is applied over the gold layer  38  and solvent based chemical  36 . As is well known in the art, protective layer coating  40  serves to seal the various layers from ambient conditions and prolongs a CDR&#39;s useful life. 
     Once the lacquer coating  40  is applied, the disc  16  is placed into an ultraviolet curing station where lacquer coating  40  is appropriately hardened. At this point, the core CDR fabrication steps are complete and the CDR disc may then be recorded with suitable information using a recording head  46  that applies a recording layer beam  48  to an under surface of the CDR disc. During recording, the recording laser beam  48  reacts with solvent based chemical  36  which changes the chemical properties of solvent based chemical  36 . As a result, the changed chemical properties produce a recorded spot  35  which identifies a recorded event. Of course, it should be appreciated that the non-uniform wavy characteristics of solvent based chemical  36  may detrimentally affect recording an reading speeds which consequently impact a CDR disc&#39;s value. 
     In view of the foregoing, there is a need for methods and apparatuses for controlling the viscosity of the chemical during spin-coating process to reduce non-nonuniformities in coatings which have changing viscosity as a result of temperature variation and evaporation. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing methods and apparatuses for uniformly spin-coating chemicals over uniformity and precision sensitive CDR discs. In addition, the present invention controls the evaporation of the solvent component in solvent based chemicals through the precise temperature controlling features of the present invention. 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, a method of distributing a chemical over the surface of a substrate is disclosed. The method includes depositing the chemical on a portion of the surface of a substrate near the center of the substrate. The method further includes controlling the temperature of the surface of a substrate so that the viscosity of the chemical is calibrated to cause the chemical to be deposited on the surface of the substrate in a substantially uniform manner. 
     In a further embodiment, the substrate may be placed in contact with a cooled chuck that is in the vicinity of a cooled mounting plate having a network of cooling coils. Advantageously, any heat generated by mechanical friction and motors used to spin a spin coating apparatus is controlled to ensure that the chemical applied to the surface of the substrate results in a substantially uniform layer. 
     In yet another embodiment, a temperature controlled dispense arm is implemented to ensure that the temperature of the chemicals being applied to the surface of a substrate are maintained at optimum process temperature during application. The temperature controlled dispense arm is also preferably suited to dispense a plurality of chemicals that may include a primary chemical, a test chemical and a cleaner. 
     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, wherein like reference numerals designate like structural elements, and in which: 
     FIG. 1 is a cross-sectional view if a disc spin coated using conventional methods. 
     FIG. 2 is an exploded view of a spinning bowl including an internal chuck and a lid in accordance with one embodiment of the present invention. 
     FIG. 3A is a cross-sectional view of a process station in accordance with one embodiment of the present invention. 
     FIG. 3B is a cross-sectional view of a process station for an “open bowl” process in accordance with one embodiment of the present invention. 
     FIG. 4 is a more detailed illustration of a base region of the process bowl that is shown in direct contact with the mounting plate in accordance with one embodiment of the present invention. 
     FIGS. 5A and 5B are solvent viscosity versus disc radius, and disc temperature versus disc radius graphs in accordance with one embodiment of the present invention. 
     FIGS. 6A through 6C illustrate an exploded diagram of the mounting plate in accordance with one embodiment of the present invention. 
     FIG. 7A is a diagrammatic representation of a chemical coating station in accordance with one embodiment of the present invention. 
     FIG. 7B illustrates the internal cooling system of the chemical coating station of FIG. 7A in accordance with one embodiment of the present invention. 
     FIG. 7C is an overview flowchart diagram of the timing associated with monitoring and changing chemicals in TANKS  1  and  2  of FIG. 7A in accordance with one embodiment of the present invention. 
     FIGS. 8A and 8B illustrate alternative embodiments for implementing a dispense arm in accordance with one embodiment of the present invention. 
     FIG. 9 is an exploded diagram of a temperature controlled dispense arm  750  in accordance with one embodiment of the present invention. 
     FIG. 10 is an exploded diagram of cooling plate  902  of FIG. 9 in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An invention is disclosed for methods and apparatuses for temperature controlled spin-coating systems. 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. 
     It should be understood that the temperature controlling embodiments of the present invention may be practiced using any spin-coating system which may include “open” and “closed” bowl arrangements. For ease of description, FIG. 2 illustrates a closed bowl arrangement which is disclosed in U.S. patent application Ser. No. 08/797,819 filed on Feb. 7, 1997, now U.S. Pat. No. 5,840,365, naming Andreas Ebert and Abdul Ghafar, and entitled “Method and Apparatus for Spin-Coating Compact Discs.” This application is hereby incorporated by reference. 
     FIG. 2 is an exploded view of a spinning bowl including an internal chuck and a lid. A spinning bowl  102  is shown as a circular bowl having a hollow internal region that is accessible through a top opening. In this embodiment, a chuck base  106  and a shaft  108  are placed into and fixedly attached to an internal base region  121  of spinning bowl  102 . By way of example, shaft  108  is passed through a chuck receiving hole  120  located at internal base region  121  where a chuck base  106  is securely attached to spinning bowl  102 . Although any suitable attaching method may be implemented, conventional screws (now shown) passed through a set of receiving holes  119  may be used to secure chuck base  106  to spinning bowl  102 . 
     Finally, a chuck plate  104  that is preferably integrally connected to chuck base  106  is provided for holding a suitable work piece. In a preferred embodiment, the work piece is a polycarbonate disc used in the compact disc (CD) and compact disc recordable (CDR) industries. However, it should be appreciated that the various embodiments of the present invention may be equally applicable to other semiconductor technologies where precision chemical (i.e., resist, spin on glass, etc.) spin-coating is desirable. 
     As shown, chuck plate  104  preferably has a top surface region  117  that is configured to hold a suitable polycarbonate disc. Generally, top surface region  117  includes three supporting rings near a center radius of chuck plate  104  that are used to hold a disc in a manner that protects the disc&#39;s under surface from coming into contact with top surface region  117  of chuck plate  104 . 
     By way of example, typical polycarbonate discs include a molded protruded ring near an inner radius of its under surface. This protruded ring is generally configured to mate with the various complementary protruded rings provided as part of chuck plate  104 . In this example, chuck plate  104  includes an inner protruded ring  130 , a middle protruded ring  128 , and an outer protruded ring  126 . Thus, when a polycarbonate disc having a protruded ring is placed over chuck plate  104 , the protruded ring on the polycarbonate disc may preferably sit between middle protruded ring  128  and outer protruded ring  126 . In this manner, sensitive portions of the polycarbonate disc are maintained slightly above and apart from top surface region  117 . However, when the temperature of chuck plate  104  increases, the temperature of the inner radius of a disc will also increase. 
     Once chuck plate  104 , chuck base  106 , and rotation rod  108  are inserted into chuck receiving hole  120  of spinning bowl  102 , a lid  110  may be placed over spinning bowl  102  to encapsulate chuck plate  104  and chuck base  106  within spinning bowl  102 . In this example, lid  110  will preferably have a circular recessed groove at its under portion (not shown for ease of explanation) which will preferably mate with a circular protruded lip  103  located at a topmost region near an opening of spinning bowl  102 . 
     Preferably, spinning bowl  102  has a base region which is at a slight incline and wall regions which are curved and inclined at an angle towards the center of spinning bowl  102 . As illustrated, spinning bowl  102  therefore resembles a saucer shape that includes curved angled walls. Further, a plurality of floor drain holes  116  are useful in draining any excess chemicals during a spin coating process. To ensure that lid  110  remains attached to spinning bowl  102 , a plurality of pins  122  arranged about the top portion of spinning bowl  102 . Generally, pins  122  will appropriately mate with suitable recessed pin holes located at an under surface of lid  110 . In yet a further embodiment, lid  110  may include a center pin (not shown) which preferably inserts down into a center top portion of chuck plate  104 . 
     Spinning bowl  102  also includes a plurality of upper vent holes  112  arranged about a midway point of the side walls of spinning bowl  102 . Further shown are a plurality of venting drain holes  114  arranged about an outer lower region of the side walls of spinning bowl  102 . Generally, venting drain holes  114  are defined near a radial distance (i.e., from the center) where the curved walls of spinning bowl  102  integrally meet a base region of spinning bowl  102 . It should be appreciated that upper vent holes  112  are preferably located at radial distance that is less than the radial distance of venting drain holes  114 . In this embodiment, venting drain holes  114  are slightly larger in diameter than the upper vent holes  112  to ensures that a pathway sufficient for both ventilation and drainage is available. 
     FIG. 3A is a cross-sectional view of a process station  200  in accordance with one embodiment of the present invention. As shown, spinning bowl  102  is mounted within a process bowl  202  that surrounds spinning bowl  102  in a circular manner. In a preferred embodiment, process bowl is manufactured from an aluminum material. However, it should be understood that other metals or alloys may be substituted therefor. Process bowl  202  is preferably a single unit having a base portion that lies below spinning bowl  102 . Further, process bowl is preferably in direct contact with and mounted on a mounting plate  208 . As will be described in greater detail below, mounting plate  208  is preferably a temperature controlled aluminum plate having a network of cooling coils  210 . In this manner, heat generated by a motor  226  and related mechanical friction is dissipated and the temperature is controlled to improve the uniformity (e.g., reduce viscosity variations) of chemicals applied within spinning bowl  102 . 
     Process bowl  202  may also include a splash ring  204  that surrounds a top ridge of process bowl  202  to prevent chemicals being output from venting drain holes  114  from dispersing out of the process station  200 . As described above, spinning bowl  102  is preferably coupled to shaft  218  which directly mounts to chuck  106 . Shaft  218  therefore extends in a downward direction into a shaft housing  230  which holds a driven sprocket  220 . Accordingly, shaft  218  spans the vertical distance of shaft housing  230 . In this embodiment, shaft  218  preferably includes a hollow vacuum channel  118  that extends up into chuck  106  and up to an under surface of disc  316 . In general, the vacuum generated through the vacuum assists in securing disk  316  to chuck plate  104  during a spinning operation. 
     Accordingly, the vacuum channel  118  may be split into a pair of vacuum channels  118  that are shown existing shaft housing  230 . In this manner, the vacuum channels  118  may be connected to a suitable vacuum device. In this embodiment, shaft  108  preferably rotates about a pair of upper and lower bearings  234  and  232  contained within shaft housing  230 . Driven sprocket  220  contained within shaft housing  230  is also shown connected to a driving sprocket  222  which is connected to motor  226 . In this manner, a belt  224  causes driven sprocket  220  to rotate upon the rotation of driving sprocket  220  which is turned by motor  226 . Motor  226  may be any motor capable of driving sprocket driven belt. By way of example, motor  226  may be a 3.5 horse power Servo motor. 
     During a spin coating operation, the solvent based chemical is preferably applied to the inner radius of the top surface of disc  316  before lid  110  is secured to the top of spinning bowl  102 . In one embodiment, motor  226  preferably rotates spinning bowl  102  to process equilibrium speeds which may be between about 3,000 rpms and about 10,000 rpms, and more preferably, between about 5,000 rpms and 8,500 rpms, and most preferably, about 7,000 rpms. 
     As the spin-coating process proceeds, excess solvent based chemical may be output from venting drain holes  114  of spinning bowl  102  which then caused the solvent based chemical to fall on the lower surface and walls of the process bowl  202 . Because the solvent based chemical may be a very expensive chemical re-using or recycling of such chemical would be advantageous. To accomplish such recycling, excess chemicals are drained out through suitable pipes  212  that are channeled to a suitable receptacle for holding the excess chemicals. Because part of the solvent component of the solvent based chemical evaporates into a vapor form during the coating process, the vapors are preferably pumped away from the process area through a channel  203  lying between the inner and outer walls of process bowl  202 . 
     Channel  203  is therefore coupled to a manifold  216  that may be connected to a flexible pipe  214  for safely diverting such process vapors away from the processing area. Although manifolds  216  appears to be rectangular in shape in this cross-sectional view, it should be appreciated that manifold  216  is preferably a circular manifold attached to an under surface of mounting plate  208 . To further assure that vapor chemicals are safely diverted from the process station  200 , a flow of air pictorially illustrated by flow lines  240  are shown directing air in a downward direction at process station  200 . Once the ambient air is directed downward towards process station  200 , the air and process vapors are preferably diverted through channels  203  and out through pipes  214 . 
     FIG. 3B is a cross-sectional view of a process station  200  for an “open bowl” process in accordance with one embodiment of the present invention. In this embodiment, a second circular splash ring  206  is placed over splash ring  204  to further ensure that chemicals being applied in the open bowl process are contained within process bowl  202 . To create an open bowl process station, spinning bowl  102  of FIG. 2 is simply detached from chuck  106  at a lower portion. However, it should be appreciated that the heat generated by motor  226  as well as the rotational friction during operation is still conducted up to discs placed over chuck plate  104 . 
     Advantageously, the cooling coils  210  assist in cooling mounting plate  208  to a temperature that is slightly below room temperature. By maintaining mounting plate  208  to this lower temperature, the temperature of chuck  106  as well as chuck plate  104  is reduced to slightly below room temperature. As a result, the temperature of the inner radius of a disc placed in contact with chuck plate  104  is also reduced. Therefore, it should be appreciated that the temperature controlling features of the present embodiment applicable to both an open and a closed bowl spin-coating process. 
     FIG. 4 is a more detailed illustration of a base region of process bowl  202  that is shown in direct contact with mounting plate  208  in accordance with one embodiment of the present invention. As shown, shaft  108  is directly coupled to a lowermost portion of chuck  106 . As described above, the heat transfer from a warmer process bowl  202  to a temperature controlled mounting plate  208  preferably assists in removing thickness variations of chemical applied over disc  316 . By way of example, during full rotational operation, it is believed that the temperature of chuck  106  may reach temperatures close to about 35° C. after a number of discs are spin-coated. 
     In accordance with one embodiment of the present invention, the disc lying over chuck plate  104  will preferably have cooler temperature near the inner radius where the disc is in contact with chuck plates  104 . Preferably, the temperature of the inner radius may be between about 17° C. and about 20° C., and the outer radius of the disc may increase up to about room temperature (i.e., about 22° C.). To transfer this lower temperature to the inner radius of the disc, the mounting plate  208  is cooled to a temperature of between about 16° C. and about 20° C. with the aforementioned network of cooling coils  210 . In one embodiment, cool fluids are preferably circulated through the mounting plate  208  and a refrigerating system. Of course, the provided temperature ranges are merely exemplary and the applied temperature ranges may vary depending on the parameters of the process. 
     To elaborate further, chuck  106  lies in direct contact with shaft  108  which is surrounded by the cooled mounting plate  208 . Further, mounting plate  208  is preferably a large enough plate that its size and magnitude assists in absorbing the heat generated in process station  200 . As shown in FIGS. 3A and 3B above, shaft housing as well as motor  226 , generate heat which is advantageously dissipated by the network of cooling coils contained within mounting plate  208 . 
     FIGS. 5A and 5B are solvent viscosity versus disc radius, and disc temperature versus disc radius graphs in accordance with one embodiment of the present invention. It should be borne in mind that disc  316  is in direct contact with chuck plate  104  at an inner radius of disc  316 . In other words, disc  316  is in contact with chuck plate  104  near the inner radius where the temperature of chuck plate  104  is controlled by the network of cooling coils  210  in mounting plate  208 . As a result, during an equilibrium spin-coating state, disc  316  itself has a cooler temperature near an inner radius  506  which increases to about room temperature near an outer radius  508  as illustrated in FIG.  5 B. 
     As will be described with reference to FIG. 5A, the increasing (i.e., from the inner radius to the outer radius) temperature variation caused on disc  316  is a beneficial aspect when applying the solvent based chemical over disc  316 . By way of example, a line “A” illustrates a case where the usual amount of “solvent component” evaporates from the surface of disc  316  and the center of the disc in not cooled. As the solvent based chemical migrates from the center of the disc to the edge, the solvent component evaporates, causing the solvent based chemical to become more viscous. As a result, the viscosity of the solvent based chemical tends to increase from a point  502  (Vis 2 ) to about a point  504   a  (Vis 3 ). When this happens, the thickness of the applied chemicals will tend to be greater near the outer radius as shown in FIG.  1 . 
     To avoid this problem, in one embodiment, the present invention causes the solvent based chemical to be cooler near the center of the disc and warmer near the edges so that the tendency of the solvent based chemical viscosity to decrease with higher temperature substantially cancels the tendency of the solvent based chemical to increase as a result of evaporation. The aforementioned cooling network contained within mounting plate  208  is implemented to cool the disc at its center. Because the polycarbonate disc is a relatively good thermal insulator, the temperature near the outside of the disc remains high when the center of the disc is cooled. By way of example, line “C” illustrates for a fluid which does not evaporate as it migrates outward, thus lowering of the viscosity of the fluid in contact with the disc surface when the inner radial region of the disc is cooler than the outer radial region of the disc. Thus, the viscosity decreases from a point (Vis 2 ) to a point (Vis 1 ) at an outer radius point  504   c  of the disc where the temperature is warmer than the inner cooled radius. In one embodiment, the outer radius of the disc  316  is preferably at about room temperature (i.e. about 22° C.) and the inner radius of the disc  316  is at a temperature that is slightly below room temperature (i.e., about 18-20° C.). 
     Advantageously, when the inner radius of the disc  316  is cooled as described above, the resulting viscosity over the surface of disc  316  is believed to be substantially uniform as shown by line “B”. The tendency of the solvent based chemical&#39;s viscosity to increase as a result of evaporation near the outer edge of the disc is substantially canceled by the tendency of the solvent based chemical&#39;s viscosity to decrease as a result of increasing temperature near the outer edge of the disc. Accordingly, the viscosity is shown being at about (Vis 2 ) from between point  502  to about a point  504   b.  (It should be noted that the graphs in FIGS. 5A and 5B both extend from zero radius to the disc radius R. Of course, in most CD applications, there is a hole in the center of the disc. It will be appreciated that the above analysis does not change in such applications where the solvent based chemical is applied at a point near the center instead of the center) 
     FIGS. 6A through 6C illustrate an exploded diagram of mounting plate  208  in accordance with one embodiment of the present invention. For ease of illustration, a thin bottom plate  208   b  is shown in FIG.  6 A. That is, thin bottom plate  208   b  is preferably the surface that underlies process station  200  of FIGS. 3A and 3B. In one embodiment, thin bottom plate  208   b  is preferably a thin aluminum sheet that covers a network of copper piping that makes up cooling coils  210  shown in FIG.  6 B. Preferably, cooling coils  210  are inset into grooves defined within a thicker top plate  208   a.  As shown, thin bottom plate  208   b  preferably includes a pair of process station holes  606  and a pair of dispense arm holes  610  that suited to match up with complementary holes  606  and  610  contained on thicker top plate  208   a.    
     Once assembled, thicker bottom plate  208   b  will define the internal roof section of a chemical coating station  700  of FIG. 7A which will be described below. In this embodiment, the network of cooling coils  210  are preferably suited to maintain the temperature of mounting plate  208  at a temperature that is slightly below room temperature ranging between about 14° C. and about 21° C., and more preferably between about 16° C. and 20° C., and most preferably between about 18° C. and 19° C. In this manner, suitable heat transfer will occur down from a warmer chuck  106  shown in FIG.  4 . 
     FIG. 7A is a diagrammatic representation of a chemical coating station  700  in accordance with one embodiment of the present invention. In this embodiment, the chemical coating station  700  preferably has an insulated wall and floor structure  702  that is preferably suited to insulate chemicals and components from outside ambient conditions. As described above, maintaining the solvent based chemicals contained in a TANK  1  and a TANK  2  at or slightly below room temperature, is an important aspect of the present invention. When the temperature is appropriately controlled through the cooling processes described above, the chemical coating process produces more uniform layers over disc  316 . In this embodiment, a pair of process stations  200  are mounted to mounting plate  208  to increase the throughput of the chemical coating station  700 . 
     To maintain the internal areas of the chemical coating station  700  at a constant temperature that is slightly below room temperature, the internal walls of the housing structure  702  are preferably provided with suitable cooling coils (shown in FIG. 7B below) that surround the internal walls around the chemicals contained within TANK  1 , TANK  2 , and a reservoir  722 . As illustrated, a reservoir  722  preferably has sensor electronics  723  that is coupled to a pair of lines  742   a  and  742   b  leading to TANK  1  and TANK  2 , respectively. 
     In this manner, sensor electronics  723  detect when either one of the two tanks are about to reach any empty state. By way of example, sensor electronics  723  may detect an empty state when line  742   a  or line  742   b  detects a slight air bubble coming from the internal region of TANKS  1  and TANKS  2 . In a preferred embodiment, chemicals contained within a TANK  1  are used first and fed through line  742   a  to reservoir  722  for dispensing through one of the dispense arms  750 . As shown, each dispense arm  750  is coupled to reservoir  722  to ensure that during a line-manufacturing coating process, chemicals as the required process temperatures are continuously available to dispense arms  750 . By way of example, when an air bubble is detected by sensor electronics  723  coming from line  742   a  that leads to TANK  1 , the sensor electronics  723  will detect that TANK  1  is nearly empty and a switch contained within sensor electronics  723  switches to TANK  2  through line  742   b.  In this manner, it is advantageous that the coating process does not need to be slowed down or stopped while the chemicals contained within TANK  1  are replaced are brought down to a suitable cool temperature. 
     By way of example, while suction was occurring through TANK  1 , the chemicals in TANK  2  were maintained at a temperature that is slightly below room temperature by the aforementioned cooling coils contained within housing walls  702 . Therefore, when TANK  1  is replaced, TANK  2  is already stabilized at a suitable process temperature. Further, once the chemicals contained in TANK  1  are replaced and placed back into housing  702 , a insulated cover (not shown) may be placed over the front portion of housing  702  to ensure that the temperature within the housing is precisely controlled to reduce nonuniformities in the coating process. 
     It is further noted that once TANK  1  is replaced and slid back into housing  702 , it is back in a temperature controlled unit. Accordingly, once TANK  2  reaches an empty state which is detected by an air bubble flowing through line  742   b  by sensor electronic  723 , again the system will switch back to TANK  1  through line  742   a.  At this point, it is noted that TANK  1  is now sitting within housing  702  and ready for use. Accordingly, the process of switching back and forth between TANK  1  and TANK  2  allows the continuous coating processes to be uninterrupted. Further, the temperatures of the chemicals contained within TANK  1  and TANK  2  are always maintained at appropriate coating process temperature. 
     In this embodiment, chemicals pumped into reservoir  722  are preferably applied through dispense arm  750  through a filter and pump unit pair. As shown, lying on the left-hand side of the chemical coating station  700 , is a filter  726   a  that is coupled to reservoir  722  via a line  740   a.  In this manner, the filter provides appropriate filtering of the solvent based chemicals to avoid introducing impurities or contaminants through dispense arm  750  during a coating application. Coupled to filter  726   a  is a pump  724   a  that is used to pump the chemicals from reservoir  722  up through a line  748   a  to dispense arm  750 . 
     In a like manner, on the right side of the chemical coating station is a filter  726   b  which is connected to reservoir  722  via a line  740   b.  Filter  726   b  is likewise connected to pump  724   b  that is connected to dispense arm  750  via a line  748   b.  Accordingly, appropriate filtering and pumping of the chemicals from reservoir  722  are performed and applied through dispense arm  750  during operation. Further shown is a pipe  212  which is used to collect excess solvent based chemical being applied to a disc during a coating operation. This excess solvent based chemical is then passed out of the housing  702  to a tank  747 . 
     In this embodiment, tank  747  is used for recycling excess chemicals being applied at the coating stations. As described above, the solvent based chemicals may be very expensive chemicals that may be recycled. By way of example, the recycled solvent based chemicals may be shipped back to the manufacturer where the solvent based chemical is adjusted to appropriate solvent concentrations for appropriate re-use. In yet a further embodiment, dispense arms  750  are also equipped with a separate line  746  for applying a cleaner solution contained within a tank  749 . Although the cleaner solution tank is not shown connected to the dispense arm on the right-hand side of the chemical coating station  700 , it is assumed that suitable cleaning solutions may also be coupled to the dispense arm  750  on the right-hand side. 
     Furthermore, the chemical coating station  700  is equipped with a test chemical canister  720  having a valve  721  connected through a line  744  leading to dispense arm  750 . The test chemical canister  720  is preferably used for applying new chemicals through the dispense arms without having to drain and waste expensive solvent based chemicals contained within reservoir  722 . Further, having the separate test chemical canisters  720  eliminates the need for replacing (i.e., cleaning out) the filters and the pumps associated with applying the solvent based chemicals contained in TANK  1  and TANK  2 . It should be noted that having test chemical canister  720  is an important feature which further allows a user to test chemicals in the coating stations without having to replace and drain reservoir  722 . 
     As is well known in the art, when reservoir  722  is emptied and the filters and pumps are replaced, substantial amounts of the solvent based chemicals are wasted and may not be appropriately re-used. Further, replacement of the solvent based chemicals contained within reservoir  722  and the pumps and filters of the chemical coating station  700 , further introduces downtime which may be unsuitable where throughput is an important feature of production. It should be noted that it is highly advantageous to implement side-by-side dual coating stations  200  and two dispense arms  750 . Having this side-by-side arrangement allows for the simultaneous spin coating of discs which increases coating throughput. 
     By way of example, an entire coating process for a single disc may take about 16 seconds, however, by implementing the dual coating system, throughput speed may be increased to enable coating speeds up to about one disc per every 8 seconds. As can be appreciated, such throughputs have commercial advantages over single coating systems implemented in prior art designs. 
     FIG. 7B illustrates the internal cooling system of chemical coating station  700  of FIG. 7A in accordance with one embodiment of the present invention. As shown, the cooling system contained within the internal walls of the chemical coating station  700  are preferably copper cooling coils. As shown, there are preferably left side cooling coils  730 , middle cooling coils  734  and right side cooling coils  732 . As described above, the copper cooling coils contained with the internal walls of the chemical coating station  700  allow for precise temperature control of the chemicals stored within the housing structure  702 . 
     FIG. 7C is an overview flowchart diagram of the timing associated with monitoring and changing chemicals in TANKS  1  and  2  of FIG. 7A in accordance with one embodiment of the present invention. The method begins at an operation  780  where chemicals are applied through dispense arms. Preferably, dispensing is performed through one dispense arm at one time, however, simultaneous dispensing may also be practiced. While chemicals are being applied through the dispense arms, chemicals are preferably being pulled from a current tank in a chemical application station. The method then proceeds to a decision operation  782  where it is determined whether the contents of the current tank are depleted. 
     By way of example, when a sensor detects that at least one air bubble is flowing through a line connected to the current tank, the sensor may determine that the first tank has become depleted of chemicals. If it is determined in operation  782  that the chemicals in the first tank are not depleted, then the method will proceed back to operation  780  where chemical application through the dispense arms continues. When it is determined in operation  782  that the chemicals in the first tank are depleted, the method will proceed to an operation  784  where a switch is made to the second tank contained within the chemical coating station. Once switched, the chemicals will now be drawn from a backup tank to prevent the dispense arms from running out of chemicals during a dispense operation. 
     The method now proceeds to an operation  786  where the depleted tank is replaced with fresh chemicals and allowed to cool to process conditions while dispensing is occurring through the backup tank in the chemical coating station. Accordingly, while the backup tank is being used for chemical application, the replaced tank is undergoing cooling to process conditions (which are preferably slightly below room temperature). The process then moves to a decision operation  788  where it is determined if the dispensing process should be terminated. If it is determined that the process should be terminated, the process will end. 
     On the other hand, the method will again proceed to decision operation  782 . As such, the method will again determine if the contents of a current tank are depleted. If they are, the method will again proceed to operation  784  where a switch is performed to the backup tank to prevent the dispense arms from running out of chemicals. Of course, when the switch is made to the backup tank, the backup tank will have cooled down to the appropriate process conditions. Accordingly, the process will continue detecting the status of the tanks in use and replacing tanks while allowing the temperature of the replaced tank to be brought down to process temperature before being implemented in the chemical application station. 
     FIGS. 8A and 8B illustrate alternative embodiments for implementing a dispense arm  750  in accordance with one embodiment of the present invention. By way of example, FIG. 8A illustrates a dispense arm  750  having three feedlines coupled to a chemical tank  808 , a cleaner container  849 , and a test chemical container  820 . As shown, a mounting plate having cooling coils  210  is used for mounting a process station  200 . In operation, dispense arm  750  may be either moved mechanically towards (e.g., rotated to process station  200  from a fixed axis) process station  200  for applying one of the liquids connected to dispense arm  750 . 
     As shown, dispense arm  750  preferably includes cooling coils  751  that are contained within a top cavity of dispense arm  750 . The cooling cavity and the cooling coils contained within dispense arm  750  will be described in greater detail in FIGS. 9 and 10 below. By providing dispense arm  750  with its own cooling system, the chemicals being applied to the surface of a disc contained within process station  200  will be applied at the appropriate process temperature. Any excess chemicals applied over a disc in process station  200 , may be funneled back into chemical tank  808  for re-use. Of course, if such re-use is performed, it may be necessary to recondition the chemical tank to bring it back up to its appropriate solvent concentration levels. 
     Although not shown, a separate concentration equilibrium tank may be used to bring the chemicals contained within chemical tank  808  to their appropriate concentration level before being funneled back in through dispense arm  750 . Further, if application to a test chemical is desired, test chemical container  820  may be used to funnel chemicals to dispense arm  750 . Such application may be performed using any suitable pump and filtering technique as described with reference to FIG.  7 A. 
     FIG. 8B illustrates an embodiment where dispense arm  750  is rotated or moved towards process station  200 . As shown, chemicals contained within chemical tank  808  or test chemical container  820  may be applied over the surface of a disc contained within process station  200 . Alternatively, an appropriate cleaning solution contained within cleaner container  849  may be applied to the internal portions of process station  200  to clean the process station  200  after a coating session or before a new chemical is used. 
     FIG. 9 is an exploded diagram of a temperature controlled dispense arm  750  in accordance with one embodiment of the present invention. As shown, dispense arm  750  includes a base portion  906  having a plurality of channels which include channels  908 ,  910  and  912  for routing separate dispensing lines as described with reference to FIGS. 8A and 8B. As an example, a shaft  926  is preferably a pipe fixture that contains a plurality of flexible Teflon lines that curve up to the topmost surface of the base portion  906 . 
     In this embodiment, shaft  926  is shown having three lines,  926   a,    926   b,  and  926   c  that may be used for dispensing a primary chemical, a secondary chemical, and a cleaner. Lines  926   a,    926   b,  and  926   c  preferably have an inter diameter of about 4 mm to ensure suitable application of varying viscosity chemicals through dispense arm  750 . Of course, any suitable number of chemical lines may be passed through shaft  926 . Shaft  926  is preferably connected to a collar  924 , which is an adjustable collar for positioning dispense arm  750  upwards or downwards with respect to a mounting plate  208  (as shown in FIG.  3 A). Coupled to collar  924  is a mounting block  930  that is preferably coupled to the base portion  906  by a suitable pin (not shown) that allows vertical movement of the dispensing end (i.e., the front end) relative to the rear end of base portion  906  near mounting block  930 . 
     Further, a cam  920  which is of a semi-circular shape, is placed below base portion  906 . As shown, cam  920  is in direct contact with a bearing  922  that is attached an under lip  931  of the base portion  906 . In this manner, base portion  906  is pivoted about shaft  926  and rotationally moves along cam  920 . In a preferred embodiment, cam  920  has a portion which is vertically higher than other portions. The vertically higher region is used to elevate dispense arm  750  when it is rotated over the process station  200 . Through this elevation, dispense arm  750  is raised to avoid contact with process bowl  202  as shown in FIG.  3 A. Also illustrated is the exemplary continuation of line  926   a  which is preferably a flexible Teflon pipe that is connected to a coupler  928 . The coupler  928  is preferably used to connect down to a stainless steel pipe  927  which is run within channel  908 . 
     In one embodiment, stainless steel pipe  927  preferably has inner diameters ranging between about 1 mm and about 2 mm, depending on the viscosity of chemicals being applied through dispense arm  750 . Although not shown for ease of illustration, a similar dispense line  926   b  and  926   c  will be run up through collar  924 , mounting block  930 , through the base portion  906 , and then fit in along channels  910  and  912 . Once the lines are properly channeled in the respective channels  908 ,  910  and  912 , a dispense line separator  904  is preferably secured down to the front region of base portion  906 . In this embodiment, dispense line separator  904  is preferably used to hold in place the various stainless steel pipes which are fit in channels  908 ,  910  and  912 . 
     Once dispense line separator  904  has been secured to the front region of base portion  906 , holding in place the various dispense lines, a cooling plate  902  is secured to the topmost portion of dispense line separator  904  as well as base portion  906 . As will be described in more detail below, coupling plate  902  preferably includes copper cooling coils which are suited for running cooling fluids to ensure that chemicals being dispensed are dispensed at a proper dispensing temperature. 
     FIG. 10 is an exploded diagram of cooling plate  902  of FIG. 9 in accordance with one embodiment of the present invention. As shown, cooling plate  902  preferably has an inset groove which is suited to receive cooling coils  751 . Once cooling coils  751  are inset into cooling plate  902 , cooling plate  902  may be set down onto and over dispense line separator  904  as well as center portions of base portion  906 . It should be appreciated that maintaining the process temperature of the chemicals being applied through dispense arm  750  is a major improvement over prior art dispensers which merely funnel chemicals to a process station. Consequently, maintaining the temperature of the chemicals at about room temperature or slightly below is an important feature that reduces premature evaporation of the solvent materials applied through dispense arm  750  and also controls the viscosity of the solvent based chemical when it is applied to the disc. 
     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. 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.