Abstract:
An apparatus including a dispense line, a solvent line, and a solvent vapor bath having a purge section is disclosed. The purge section of the apparatus has a cleaning member disposed therein containing at least one dispense hole corresponding to the dispense line. The purge section contains a plurality of ports to receive the dispense line and the solvent line. The solvent line is directed toward the cleaning member when the dispense line extends through the dispense hole. A method of cleaning a dispense line is also disclosed. In the method, a solvent vapor bath comprising a purge region having a cleaning member disposed therein and containing at least one dispense hole is provided. The purge region contains a plurality of ports to receive the dispense line and a solvent line, the solvent line being directed toward the cleaning member when the at least one dispense line extends through the at least one dispense hole. The method includes disposing the dispense line through one of the ports of the purge region and the dispense hole of the cleaning member, disposing a solvent dispense line through one of the ports of the purge region, and dispensing solvent from the solvent dispense line toward the cleaning member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application arising from U.S. patent application Ser. No. 08/667,784, filed on Jun. 21, 1996, now U.S. Pat. No. 5,849,084. 
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to fluid dispense arm assemblies and methods of using the same. More particularly, the present invention relates to a fluid dispense arm assembly and methods for dispensing photoresist and developer compounds on semiconductor substrate material. 
     DESCRIPTION OF THE INVENTION BACKGROUND 
     Integrated circuits are typically constructed by depositing a series of individual layers of predetermined materials on a wafer shaped semiconductor substrate, or “wafer”. The individual layers of the integrated circuit are in turn produced by a series of manufacturing steps. For example, in forming an individual circuit layer on a wafer containing a previously formed circuit layer, an oxide, such as silicon dioxide, is deposited over the previously formed circuit layer to provide an insulating layer for the circuit. A pattern for the next circuit layer is then formed on the wafer using a radiation alterable material, known as photoresist. Photoresist materials are generally composed of a mixture of organic resins, sensitizers and solvents. Sensitizers are compounds, such as diazonaphthaquinones, that undergo a chemical change upon exposure to radiant energy, such as visible and ultraviolet light resulting in an irradiated material having differing salvation characteristics with respect to various solvents than the nonirradiated material. Resins are used to provide mechanical strength to the photoresist and the solvents serve to lower the viscosity of the photoresist so that it can be uniformly applied to the surface of the wafers. After a photoresist layer is applied to the wafer surface, the solvents are evaporated and the photoresist layer is hardened, usually by heat treating the wafer. The photoresist layer is then selectively irradiated by placing a radiation opaque mask containing a transparent portion defining the pattern for the next circuit layer over the photoresist layer and then exposing the photoresist layer to radiation. The photoresist layer is then exposed to a solvent, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble, which removes the photoresist in the pattern defined by the mask, selectively exposing portions of the oxide insulating layer. The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. It is important that the remaining photoresist be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. Following the etching process, the next circuit is deposited and the remaining photoresist is stripped from the surface of the wafer typically through the use of a solvent. 
     Photoresist and developer materials are typically applied to the wafer using a spin coating technique in which the photoresist is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the photoresist over the surface of the material and exerts a shearing force that separates the excess photoresist from the wafer thereby providing a thin layer of photoresist on the surface of the wafer. It is necessary to produce a highly uniform photoresist layer to enable the subsequent circuit layers to be precisely placed on the wafer; however, a number of process conditions, such as photoresist temperature, system temperature, photoresist dispensing velocity, rotational speed, system air flow and solvent evaporation rate, greatly affect the characteristics of the photoresist layer. 
     Many of the prior art attempts to provide a dispense system that produces a more uniform photoresist or developer coating have generally focussed on only a limited number of the aforementioned conditions. For instance, U.S. Pat. No. 5,427,820 issued to Biche discloses a photoresist dispense line which incorporates an annular flow path, surrounding an internal photoresist dispense line, in which a heat transfer medium is circulated to control the temperature of the photoresist and related U.S. Pat. No. 5,289,222 issued to Hurtig discloses a method for controlling the solvent evaporation rate in the spin coating apparatus. Also, U.S. Pat. No. 5,405,813 issued to Rodrigues discloses a method to distribute photoresist on the wafer by varying the rotational speed of the wafer during the dispensing and drying process. U.S. Pat. Nos. 5,020,200 issued to Mimasaka and 5,429,912 issued to Neoh disclose nozzle designs directed toward decreasing the force with which the photoresist or developer contacts the wafer surface by redirecting the flow of photoresist prior to contacting the surface of the wafer. 
     The prior art apparatuses and methods have only provided limited insight as to solutions to the problem of a nonuniform air flow field caused by the presence of the dispense line above the spinning wafer. The Biche patent notes that prior art heat transfer dispense devices are sufficiently large so as to block air flow which leads to non-uniform coatings (col. 2, lines 34-38) and suggests that the dispense line of the Biche patent was sufficiently small so that minimal interference to air flow occurs which results in uniform coatings (col. 6, lines 28-31). However, the presence of the dispense line remains an obstruction that causes nonuniformities in the air flow near the wafer. 
     The present invention is directed to apparatuses and methods for which overcome, among others, the above-discussed problems so as to provide a flow field having increased uniformity over the prior art resulting in more uniform coating being formed on the wafer and an apparatus that is easily maintained during operations. 
     SUMMARY OF THE INVENTION 
     The above objects and others are accomplished by a method and apparatus in accordance with the present invention. The apparatus is a dispense arm that includes first and second dispense lines connected to at least one liquid source to permit the dispensing of liquids from the first and second dispense lines on to a rotating surface. In a preferred embodiment, the first and second dispense lines are tubular and have first and second dispense tubes disposed within the interior region of the first and second dispense lines, respectively. The first and second dispense tubes define first and second annular regions in the dispense lines, which are preferably connected by a fluid channel. A heat exchanger is attached to the first and second annular region to enable a heat transfer medium to be circulated through the first and second annular regions and the fluid channel to control the temperature of the liquid to be dispensed. 
     Also in a preferred embodiment, a solvent dispense line is disposed between the first and second dispense lines and a vapor solvent bath is provided containing a purge section including a cleaning member to allow excess coating material to be rinsed from the first and second dispense lines. 
     Accordingly, the present invention provides an improved apparatus and method to control the air flow surrounding a rotating surface and to dispense liquids on the rotating surface in more than one position to provide the capability to fully coat larger surface in a cost effective and timely manner. These and other details, objects, and advantages of the invention will become apparent as the following detailed description of the present preferred embodiment thereof proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will be described in greater detail with reference to the accompanying drawings, wherein like members bear like reference numerals and wherein: 
     FIG. 1 is a perspective view of a preferred embodiment of the present invention raised out of a stored position in part of a spin coating system; 
     FIG. 2 is a perspective view of a preferred embodiment with an exploded view of a preferred nozzle assembly; 
     FIG. 3 is a cross sectional view of a dispense line along line  3 — 3  in FIG. 2; 
     FIG. 4 is a schematic despiction of the purge section of the solvent bath; 
     FIG. 5 is a side cross sectional view of the solvent bath, along line  5 — 5  in FIG. 1; and 
     FIG. 6 is a front cross sectional cutaway view showing the flow paths through the dispense lines and solvent line. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The operation of the apparatus  10  will be described generally with reference to the drawings for the purpose of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same. As illustated in FIG. 1; and apparatus  10  of the present invention is a dispense arm that includes first and second dispense lines  12  and  14  through which liquids flow and are dispensed onto a rotating wafer surface  15 . A solvent dispense line  16  is provided between the first and second dispense lines,  12  and  14 , to clean excess coating material off the dispense lines  12  and  14  and to fill a solvent bath  18 . While preferred embodiments of the invention will be discussed with respect to dispensing photoresist, developer and rinse solution for use in manufacturing silicon wafers for semiconductors, one skilled in the art will appreciate that the invention can be suitably modified to apply other types of process liquids to a surface. 
     As may be seen in FIG. 2,  3  and  6 , the first and second dispense lines,  12  and  14 , respectively, are identical cylindrical tubular lines having dispense ends  20  and  22 , source ends  24  and  26 , interior regions  28  and  30 , respectively, and a uniform cross sectional dimension perpendicular to the direction of flow. The first and second dispense lines,  12  and  14 , are aligned in parallel and the dispense ends  20  and  22 , respectively, are directed substantially perpendicular toward the rotating surface  15 . The first and second dispense lines,  12  and  14 , contain opposing ports,  21  and  23 , respectively, adjacent to the dispense ends  20  and  22 , respectively. The dispense lines are preferably constructed of stainless steel, although any material of suitable strength and rigidity can be used with the scope of the invention. Alternatively, the first and second dispense lines,  12  and  14 , respectively, do not have to be identical or aligned in parallel, but can be varied to achieve the result desired by the skilled practitioner. In addition, it may be desirable to include additional dispense lines to ensure complete coverage of a large surface area where it would be inefficient and impractical to coat the surface using only one dispense line. 
     The solvent line  16  is also preferably aligned parallel to and disposed between the first and second dispense lines,  12  and  14 . The solvent line  16  is cylindrically shaped having a dispense end  32  directed substantially perpendicular to the rotating surface  15 , an inlet end  34  and an interior region  36 . An internal solvent dispense tube  38  is disposed within the interior region  36  of the solvent line  16  and is connected to a solvent source to provide for the dispensing of solvent out of the dispense end  32 . In developer applications, the solvent line  16  is used to dispense water onto the surface of the wafer to rinse the developer solution off the wafer. In photoresist stripping applications, solvents are dispensed onto the surface of the wafer using the solvent line  16  to strip any remaining photoresist off the wafer following processing. In this manner, the arrangement of the dispense lines,  12  and  14 , and the solvent line  16  can be used for all of the processing and storage without having to commingle solvents and coatings in the same lines. 
     In a preferred embodiment for a spin coating application, the dispense lines,  12  and  14 , respectively, are ½ inch diameter tubes with a two inch spacing centerline to centerline and the solvent line  16  is a ⅜ inch diameter tube positioned between the dispense lines,  12  and  14 , respectively, to provide a gap of ⅝ inch. We have found that reducing the gap spacing to ½ inch, (i.e. one tube diameter) adversely affects the air flow performance of the apparatus  10 , thus it is preferred to maintain a gap spacing greater the diameter of the dispense lines,  12  and  14 . In addition, better air flow performance is derived if the solvent line  16  has a smaller diameter than the dispense lines,  12  and  14 . An important consideration in the determination of the number and cross sectional dimensions of the dispense lines to be used in the present invention is to minimize the cross sectional dimension and the total cross sectional area of all of the dispense lines. 
     Preferably, first and second dispense tubes,  40  and  42 , respectively, are disposed within the interior regions the first and second dispense lines,  12  and  14 , respectively, to define first and second annular regions,  44  and  46 , respectively. The dispense tubes,  40  and  42 , are preferably identical, have dispense and source ends,  41  and  43 , respectively, and are constructed of plastic tubing or other flexible material that can be fed through the rigid dispense lines,  12  and  14  and can be easily changed. Alternatively, the dispense tubes can be constructed from rigid material and also may be fixed within the dispense lines, such as through the use of spacers. The source ends  43  of the dispense tubes,  40  and  42 , respectively, are connected to one or more liquid sources. Generally, the source ends  43  will be connected to the same liquid source  45 ; however, there is no requirement that the same source be used or that the number of sources  45  be limited to one as shown in FIG. 1. A fluid channel  48  is perpendicularly connected between the opposing ports  21  and  23  in the first and second dispense lines,  12  and  14 , adjacent to the dispense end  20  to provide fluid communication between the first and second annular regions,  44  and  46 . A conventional heat exchanger  47  is attached to the annular regions,  44  and  46 , between the two source ends,  24  and  26 , to form a circulation system through which a heat transfer medium is circulated into the first annular region  44  at the source end  24 . The heat transfer medium flows through the first annular region  44  and the fluid channel  48  into the second annular region  46 . The heat transfer medium flows through the second annular region  46  and returns to the heat exchanger  47  through the source end  26 . An advantage of having all of the dispenses lines in a common heat exchange system is that the temperature in the dispense lines can be commonly controlled, thereby eliminating problems associated with synchronizing separate circulation systems. 
     In a preferred embodiment, the solvent line  16  passes through the fluid channel  48  so as to minimize disturbances in the flow field, but does not fluidly communicate with the channel  48 . The fluid channel  48  has a dimension in the direction perpendicular to the direction of flow that is substantially equal to or less than the cross section of the dispense lines, but is greater than the dimension of the solvent line  16 , so that the solvent line  16  does not prevent fluid communication within the fluid channel  48  by blocking the flow path. Alternatively, the solvent line  16  does not have to pass through fluid channel  48 ; however, this would tend to make the flow field somewhat less uniform around the apparatus  10 , which is considered undesirable. 
     Also in a preferred embodiment, the dispense ends  20  and  22 , include nozzle assemblies,  60  and  62 , respectively, that are removably attached such as by threading. In a preferred embodiment, the nozzle assemblies,  60  and  62  includes a tubular fitting  64  having first and second ends,  66  and  68 , respectively. The first ends  66  are inserted into and provide fluid communication with the dispense ends  41  of the dispense lines  40  and  42 , respectively, and are secured by collars  70  around the outside of the dispense lines  40  and  42 , respectively. The fitting  64  has an outer surface  72  containing two circumferential recesses that are sized to receive two O-ring gaskets  74  used to seal the interior regions  28  and  30 . The nozzles  76  are connected to the second end  68  of the fitting  64  to provide fluid communication with the dispense tubes,  40  and  42 , respectively, and secured by nozzle housings  78  to the dispense lines,  12  and  14 . 
     As illustrated in FIGS. 4 and 5 the solvent bath  18  provides for storage and cleaning of the nozzle assemblies,  60  and  62 , respectively between coating evolutions. The bath  18  includes a purge section  80 , a bath section  82  and a vapor return section  84 . The purge section  80  includes a bottom portion  86  and a top  88  containing three ports  90  that are sized to receive the first and second dispense lines,  12  and  14 , respectively, and the solvent line  16 . The purge section  80  further includes a cleaning member  92  containing two holes  94 . As such, the cleaning member  92  is disposed within the purge section  80  proximate to the top  88  and the holes  94  are aligned with the ports  90  in the top  88  so that the first and second dispense ends,  20  and  22 , respectively, extend through the ports  90  and the holes  94 . The cleaning member  92  has a top surface  96  that is preferably sloped toward the holes  94  to direct the flow of solvent introduced into the purge section  80  through the solvent dispense tube  38  to rinse excess coating material off the nozzle assemblies,  60  and  62 , respectively. The bottom  86  of the purge section  80  contains an exhausted drain  98  to remove the excess solvent and coating material from the purge section  80 . 
     The bath section  82  includes a top  100  containing three ports  102  that are sized to receive the first and second dispense lines,  12  and  14 , respectively, and the solvent line  16 , a liquid region  104  and vapor region  106 . The bath section  82  is connected to the purge section  80  by an opening  108 , which defines the maximum height of the liquid region  104 . The solvent line  16  is used to maintain liquid solvent in the bath section  82 . The vapor return section  84  is connected to the vapor region  106  of the bath section  82  and to the exhausted drain  98 . 
     In the operation of the present invention, the apparatus  10  is initially in a stored position with the first and second dispense ends,  20  and  22 , respectively, and the solvent dispense end  32  disposed in the bath section ports  102 . The solvent dispense tube  38  is connected to a solvent source and the bath section  82  is filled to opening  108  with liquid solvent using dispense tube  38 . The solvent evaporating from the liquid region  104  contacts the nozzles  76 , thereby preventing the coating material contained in the nozzles from drying out and the excess vapor is drawn through the vapor return section  84  to the exhausted drain  98 . The heat transfer medium is introduced into the source end  24  of the first dispense line  12 , flows through the annular region  44  into fluid channel  48  and exits the apparatus  10  through the annular region  46  and source end  26  of the second dispense line  14 . The apparatus  10  is then raised by mechanism  110  to lift the dispense ends  20  and  22 , respectively, and solvent dispense end  32  out of the port  102  in the bath section  82 , as shown in FIG.  1 . The apparatus  10  is then moved into position over a coating bowl  112  containing the rotating surface  15  of the wafer supported by a rotatable chuck  114  attached by a shaft  116  to a spin motor  118 . The coating liquid is introduced from the liquid sources into source ends  43  of the dispense tubes,  40  and  42 , respectively, and the coating liquid moves through the dispense tubes,  40  and  42 , respectively, and the nozzles  76  onto the rotating surface  15 . After the coating liquid has been dispensed, the apparatus  10  is moved away from the rotating surface  15  and the dispense ends  20  and  22 , respectively, and the solvent dispense end  37  are placed through ports  90  in the purge section  80 , the nozzles  76  passing through the holes  94 . Solvent is introduced from the solvent source through solvent dispense tube  38  toward the top surface  96  which directs the solvent toward the dispense ends,  20  and  22 , so as to rinse the liquid residue off the nozzle assemblies,  60  and  62 , respectively. The first and second dispense tube,  40  and  42 , respectively, can then be purged and the purged coating liquid and the used solvent exit the purge section  80  through the exhausted drain  98 . The apparatus  10  is then be returned to the stored position in the bath section  82 . 
     While the present invention has been described with respect to a two dispense line apparatus, the utility of the present invention can be extended to include any number of dispense lines. In fact, an increase in the number of dispense lines should coincide with a decrease in the diameter that will serve to further increase the uniformity of the flow field. The capability to provide for a relatively uniform flow field with multiple nozzles is of particular importance if the apparatus is being employed to dispense coating material onto a surface that is sufficiently large that one dispense line will not reliably be able to provide full coverage of the surface. An example of which would be in spin coating a large diameter wafer, where the dispense lines could be employed at regular intervals to more fully ensure full coverage of the wafer surface. 
     Those of ordinary skill in the art will appreciate that the present invention provides several advantages over the prior art. In particular, the subject invention provides a more uniform flow of air near the wafer surface to provide for a more uniform coating. The subject invention also provides an apparatus for use in dispensing liquids at a number of different positions over larger surfaces where it would be impractical to dispense process liquids over the surface using a single dispense line. While the subject invention provides these and other advantages over prior art, it will be understood, however, that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.