Abstract:
A multi-nozzle gas spray arm for a spin coating apparatus. In a typical embodiment, the invention comprises a primary spray arm and a secondary spray arm which is confluently connected to the primary spray arm. The primary spray arm ejects a narrow, relatively high-velocity nitrogen stream against a substrate while the secondary spray arm ejects a diffuse, relatively low-velocity nitrogen stream against the substrate as the gas spray arm is typically swept across the surface of the wafer. The diffuse nitrogen flow characteristic of the nitrogen ejected from the secondary spray arm is effective in eliminating water and chemical droplets which otherwise would tend to remain and form dry spots on the wafer surface.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to spin coating apparatus used to coat a photoresist on a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to a new and improved gas purge arm which facilitates a diffuse spray pattern of nitrogen purge gas against a substrate surface after a photoresist coating process in a spin coating apparatus.  
         BACKGROUND OF THE INVENTION  
         [0002]    The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.  
           [0003]    Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic or photolithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate.  
           [0004]    The numerous processing steps outlined above are used to cumulatively apply multiple electrically conductive and insulative layers on the wafer and pattern the layers to form the circuits. The final yield of functional circuits on the wafer depends on proper application of each layer during the process steps. Proper application of those layers depends, in turn, on coating the material in a uniform spread over the surface of the wafer in an economical and efficient manner.  
           [0005]    During the photolithography step of semiconductor production, light energy is applied through a reticle mask onto a photoresist material previously deposited on the wafer to define circuit patterns which will be etched in a subsequent processing step to define the circuits on the wafer. Because these circuit patterns on the photoresist represent a two-dimensional configuration of the circuit to be fabricated on the wafer, minimization of particle generation and uniform application of the photoresist material to the wafer are very important. By minimizing or eliminating particle generation during photoresist application, the resolution of the circuit patterns, as well as circuit pattern density, is increased.  
           [0006]    Photoresist materials are coated onto the surface of a wafer by dispensing a photoresist fluid typically on the center of the wafer as the wafer rotates at high speeds within a stationary bowl or coater cup of a spin coating apparatus. The coater cup catches excess fluids and particles ejected from the rotating wafer during application of the photoresist. The photoresist fluid dispensed onto the center of the wafer is spread outwardly toward the edges of the wafer by surface tension generated by the centrifugal force of the rotating wafer. This facilitates uniform application of the liquid photoresist on the entire surface of the wafer.  
           [0007]    Spin coating of photoresist on wafers is carried out in an automated track system using wafer handling equipment which transport the wafers between the various photolithography operation stations, such as vapor prime resist spin coat, develop, baking and chilling stations. Robotic handling of the wafers minimizes particle generation and wafer damage. Automated wafer tracks enable various processing operations to be carried out simultaneously. Two types of automated track systems widely used in the industry are the TEL (Tokyo Electron Limited) track and the SVG (Silicon Valley Group) track.  
           [0008]    A typical conventional spin coating apparatus for coating semiconductor wafers with a photoresist liquid is generally indicated by reference numeral  8  in FIGS. 1 and 2. The spin coating apparatus  8  includes a coater cup  3  which includes a top opening  6  and partially encloses a wafer support stage or chuck  1  on which is supported the wafer  2 . A chemical dispensing system  10  includes a nitrogen gas spray arm  12 , an acid dispensing arm  13  and a deionized (DI) water spray arm  14 , each of which extends from a corresponding arm slot  7  in an arm mount  11 . As shown in FIG. 2, each of the arms  12 ,  13 ,  14  is capable of swinging or pivoting from a stored position on the side of the coater cup  3 , over the top of the coater cup  3  for dispensing the corresponding liquid through the top opening  6  onto the wafer  2 . In operation, the chuck  1  rotates the wafer  2  at high speeds, typically as high as 4,000 rpm, either after or as the liquid photoresist (not shown) is dispensed onto the center of the spinning wafer  2 , through the top opening  6 . By operation of centrifugal force imparted to the wafer  2  by the rotating chuck  1 , the dispensed photoresist liquid is spread across and uniformly coated on the surface of the wafer  2 . Exhaust solvent gases and photoresist particles generated during the process are vented from the coater cup  3  through an exhaust pipe  4  which may be connected to an exhaust manifold  5 .  
           [0009]    After the liquid photoresist is applied to the wafer  2 , the acid dispensing arm  13  sweeps over the center of the coater cup  3  and back to the “home” position on the side of the coater cup  3  as acid is dispensed from the arm  13  through the top opening  6  onto the surface of the spinning wafer  2  at a pressure of typically about 0.3 psi. This step removes excess photoresist, as well as photoresist particles, from the wafer  2 . Next, the water spray arm  14  sweeps over the center of the coater cup  3  and back to the “home” position on the side of the coater cup  3  to spray DI water, at a pressure of typically about 20-40 psi, through the top opening  6  and onto the wafer  2  to remove residual acid from the wafer  2 . Finally, the nitrogen gas spray arm  12  is initially positioned over the center of the coater cup  3  and then sweeps back to the “home” position on the side of the coater cup  3  to blow nitrogen gas, at a pressure of typically about 15 psi, onto the surface of the spinning wafer  2 . This final step dries most of the DI water remaining on the wafer  2 .  
           [0010]    As shown in FIG. 3, the nitrogen spray arm  12  includes a central dispensing tube  15  that terminates in a nozzle opening  16  at the end of the nitrogen spray arm  12 . The nozzle opening  16  typically has a relatively small diameter of about 1.0 mm to about 1.5 mm, and this tends to eject the nitrogen gas onto the surface of the wafer  2  in a narrow, forceful stream  18 . The nitrogen gas stream  18  tends to blow or splash water droplets  17  from localized areas on the surface of the wafer  2  contacted directly by the nitrogen gas stream  18  while spreading the water droplets  17  to adjacent areas on the wafer  2 . Consequently, some of the water droplets  17  remain on the wafer  2 , forming chemical and water spots on the surface of the wafer  2  after the cleaning process. Chemical and water spots remaining on the wafer  2  after the photoresist application process tend to adversely affect device performance and reduce the yield of devices on the wafer  2 .  
         SUMMARY OF THE INVENTION  
         [0011]    An object of the present invention is to provide a gas spray arm which is capable of applying a drying gas in a diffuse pattern to the surface of a substrate.  
           [0012]    Another object of the present invention is to provide a gas spray arm which is effective in drying water and chemicals from a substrate.  
           [0013]    Still another object of the present invention is to provide a gas spray arm for preventing the formation of water or chemical spots on a substrate after a process is carried out on the substrate typically in a spin coating apparatus.  
           [0014]    Another object of the present invention is to provide a multi-nozzle gas spray arm which includes at least two spray arms for ejecting a gas, particularly nitrogen, against a substrate to remove water or other liquid droplets from the substrate.  
           [0015]    Yet another object of the present invention is to provide a multi-nozzle gas spray arm for drying liquid from a substrate and preventing the formation of water or liquid spots on the substrate.  
           [0016]    A still further object of the present invention is to provide a multi-nozzle gas spray arm which combines a high-pressure, narrow gas stream with a lower-pressure, diffuse gas stream to facilitate effective drying of a substrate surface.  
           [0017]    In accordance with these and other objects and advantages, the present invention is directed to a multi-nozzle gas spray arm for a spin coating apparatus, which multi-nozzle gas spray arm in a typical embodiment comprises a primary spray arm and a secondary spray arm which is confluently connected to the primary spray arm. The primary spray arm ejects a narrow, relatively high-velocity nitrogen stream against a substrate while the secondary spray arm ejects a diffuse, relatively low-velocity nitrogen stream against the substrate as the gas spray arm is typically swept across the surface of the wafer. The diffuse nitrogen flow characteristic of the nitrogen ejected from the secondary spray arm is effective in eliminating water and chemical droplets which otherwise would tend to remain and form dry spots on the wafer surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    The invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0019]    [0019]FIG. 1 is a schematic view of a typical conventional spin-coating apparatus for substrates;  
         [0020]    [0020]FIG. 2 is a top view of a typical conventional spin-coating apparatus;  
         [0021]    [0021]FIG. 3 is a schematic view illustrating removal of residual liquid from a substrate surface in operation of a typical conventional spin-coating apparatus;  
         [0022]    [0022]FIG. 4 is a schematic view illustrating removal of residual liquid from a substrate surface in implementation of the present invention;  
         [0023]    [0023]FIG. 5 is a schematic view of a spin coating apparatus in implementation of the present invention;  
         [0024]    [0024]FIG. 6 is a top view of the spin coating apparatus of FIG. 5;  
         [0025]    [0025]FIG. 7 illustrates removal of particles and water droplets from a via or other aperture formed in the surface of a substrate in implementation of the present invention; and  
         [0026]    [0026]FIG. 8 is a perspective view, partially in section, of an illustrative embodiment of the gas spray arm of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The present invention has particularly beneficial utility in the removal of residual water or other liquid droplets from the surface of a semiconductor wafer substrate after spin-coated deposition of a photoresist layer on the substrate. However, the invention is not so limited in application, and while references may be made to such spin-coated apparatus, the present invention may be applicable to removing water or other liquids from surfaces in a variety of industrial and mechanical applications.  
         [0028]    An illustrative embodiment of a spin coating apparatus which utilizes the nitrogen spray arm of the present invention is generally indicated by reference numeral  28  in FIG. 5. While the spin coating apparatus  28  has particular features hereinafter described, it is understood that the present invention may be equally applicable to spin coating apparatus or other process tools having features which depart from the following description. The spin coating apparatus  28  includes a coater cup  23  which is provided with a top opening  26  and partially encloses a wafer support stage or chuck  21  on which is supported a wafer substrate  22 . A chemical dispensing system  30  includes a dual-nozzle gas spray arm  32  of the present invention, the details of which will be hereinafter described, and may additionally include an acid dispensing arm  47  and a deionized (DI) water spray arm  48 , as well as additional fluid dispensing arms (not shown), each of which may extend from a corresponding arm slot  27  in an arm mount  31 . Each of the arms  32 ,  47 ,  48  is engaged by an arm swinging mechanism (not shown) which may be conventional and is typically housed inside the chemical dispensing system  30 . Accordingly, as shown in FIG. 6, each of the arms  32 ,  47 ,  48  is capable of swinging or pivoting from a stored, or “home”, position on the side of the coater cup  23 , over the top of the coater cup  23 , in conventional fashion, for dispensing the corresponding fluid through the top opening  26  onto the wafer  22 .  
         [0029]    As shown in FIG. 8, the dual-nozzle gas spray arm  32  of the present invention typically includes a primary spray arm  33  which is typically constructed of stainless steel. The primary spray arm  33  includes a horizontal segment  60  the proximal end  63  of which is engaged by the arm swinging mechanism (not shown) in the arm slot  27  of the dispensing system  30 . A downward arm bend  61  in the primary spray arm  33  defines a vertical segment  62  which terminates in a primary spray nozzle  35 . As shown in FIG. 4, a primary spray tube  34 , which may be constructed of Teflon® (polytetrafluoroethylene), extends through the center of the primary spray arm  33  and is connected in fluid communication with a source (not shown) of inert gas, typically nitrogen, in the chemical dispensing system  30 , typically in conventional fashion. The discharge end of the primary spray tube  34  terminates at a nozzle opening  36  in the primary spray nozzle  35 . In a preferred embodiment, the nozzle opening  36  has a size of about 1 mm in diameter or width, but may alternatively have a larger or smaller size.  
         [0030]    As further shown in FIGS. 4 and 8, a secondary spray arm  41 , typically constructed of stainless steel, is mounted on the side of the primary spray arm  33  and includes a horizontal segment  64 , a downward arm bend  65  and a vertical segment  66  which may be attached to those respective segments of the primary spray arm  33 . The secondary spray arm  41  is confluently attached to the primary spray arm  33  typically through a connecting bridge  38 , as illustrated in FIG. 4. Accordingly, a connecting tube  39 , which may be constructed of Teflon® (polytetrafluoroethylene), confluently connects the primary spray tube  34  of the primary spray arm  33  to a secondary spray tube  42  which extends through the center of the secondary spray arm  41 . As further shown in FIG. 4, the discharge end  45  of the secondary spray tube  42  terminates inside a secondary spray nozzle  43 , provided on the end of the secondary spray arm  41 , in spaced-apart relationship to a nozzle opening  44  in the secondary spray nozzle  43 . In a preferred embodiment, the nozzle opening  44  has a diameter or width of about 4 mm, although the diameter or width may be smaller or larger, as desired. Typically, the nozzle opening  44  has a larger diameter or width than that of the nozzle opening  36  in the primary spray nozzle  35 . In a typical embodiment, the primary spray tube  34 , the connecting tube  39  and the secondary spray tube  42  each has a size of about 3 mm in diameter or width, although each of these elements may have a larger or smaller size.  
         [0031]    In typical operation of the spin coating apparatus  28 , the chuck  21  rotates the wafer  22  at high speeds, typically as high as 4,000 rpm, either after or as a liquid photoresist (not shown) is dispensed onto the center of the spinning wafer  22 , through the top opening  26 . By operation of centrifugal force imparted to the wafer  22  by the rotating chuck  21 , the dispensed photoresist liquid is spread across and uniformly coated on the surface of the wafer  22 . Exhaust solvent gases and photoresist particles generated during the process are vented from the coater cup  23  through an exhaust pipe  24  which may be connected to an exhaust manifold (not shown).  
         [0032]    After the liquid photoresist is applied to the wafer  22 , the acid dispensing arm  47  of the chemical dispensing system  30  sweeps over the center of the coater cup  23  and back to the “home” position on the side of the coater cup  23  as acid is dispensed from the arm  47  through the top opening  26  onto the surface of the spinning wafer  22  at a pressure of typically about 0.3 psi. This step removes excess photoresist, as well as photoresist particles, from the wafer  22 . Next, the water spray arm  48  sweeps over the center of the coater cup  23  and back to the “home” position on the side of the coater cup  23  as DI water is sprayed from the arm  48  at a pressure of typically about 20-40 psi, through the top opening  26  and onto the wafer  22  to remove residual acid from the wafer  22 . Because residual water remains on the wafer  22 , the water must be removed from the water  22  prior to further processing thereof. Accordingly, the dual-nozzle gas spray arm  32  is initially positioned over the center of the coater cup  23 , in the direction indicated by the arrow  25  in FIG. 4. Next, pressurized nitrogen gas is introduced into the primary spray arm  33  at a pressure of typically about 20 psi, flows through the primary spray tube  34 , and is ejected from the nozzle opening  36  of the primary spray nozzle  35 . The ejected nitrogen gas forms a narrow, relatively high velocity nitrogen gas stream  54  which strikes the surface of the wafer  22  and dislodges water droplets  51  remaining on the surface of the wafer  22  after the water rinsing step. While some of these water droplet  51  evaporate from the wafer  22 , other water droplets “splash” onto the surrounding areas of the wafer  22 . It is understood that the nitrogen gas may be ejected from the gas spray arm  32  both while the gas spray arm  32  is being swept from the “home position” at the side of the coater cup  3  to the center of the wafer  22 , as indicated by the arrow  25 , and as the gas spray arm  32  returns to the “home” position at the side of the coater cup  3 , as indicated by the arrow  37 .  
         [0033]    As the pressurized nitrogen gas is ejected from the nozzle opening  36  of the primary spray nozzle  35 , some of the pressurized nitrogen flows from the primary spray tube  34  and into the secondary spray tube  42  of the secondary spray arm  41 , through the connecting tube  39 . The nitrogen gas is thus ejected from the discharge end  45  of the secondary spray tube  42 , where the nozzle opening  44  of the secondary spray nozzle  43  widens the spray path of the nitrogen gas to define relatively low-velocity, diffuse gas streams  55 . The diffuse gas streams  55  contact a wider area on the surface of the wafer  22  than does the narrow, high-velocity gas stream  54  ejected from the primary spray nozzle  35 . Accordingly, as the spray arm  32  begins to sweep back to the “home” position on the side of the coater cup  23 , as indicated by the arrow  37 , water droplets  51  remaining on the wafer  22  are blown and evaporated therefrom by the diffuse gas streams  55  of the secondary spray nozzle  43 .  
         [0034]    As shown in FIG. 7, the diffuse gas streams  55  ejected from the secondary spray nozzle  43  are effective in removing particles  52 , as well as water droplets  51 , from vias or other openings  57  formed in the surface of the wafer  22 . This results in enhanced cleaning and drying of the wafer  22  and increases the yield of devices on the wafer  22 .  
         [0035]    While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.