Abstract:
A wafer treatment method semiconductor wafer is disclosed. The method may include supporting the wafer and flowing a continuous sheet of liquid in a predetermined non-perpendicular orientation relative to the wafer. The continuous sheet of liquid is applied to the wafer.

Description:
This is a division of U.S. Pat. No. 08/823,815, filed Mar. 24, 1997, now U.S. Pat. No. 5,954,877. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a nozzle and a method for dispensing process liquids onto a surface. More particularly, the present invention relates to a fluid dispense nozzle and method for dispensing developer chemicals onto a rotating semiconductor substrate material. 
     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 chemical, known as developer, in which either the irradiated or the nonirradiated photoresist is soluble and the photoresist is removed in the pattern defined by the mask, selectively exposing portions of the underlying insulating layer. 
     The exposed portions of the insulating layer are then selectively removed using an etchant to expose corresponding sections of the underlying circuit layer. The photoresist must be resistant to the etchant, so as to limit the attack of the etchant to only the exposed portions of the insulating layer. 
     Alternatively, the exposed underlying layer(s) may be implanted with ions which do not penetrate the photoresist layer thereby selectively penetrating only those portions of the underlying layer not covered by the photoresist. The remaining photoresist is then stripped using either a solvent, or a strong oxidizer in the form of a liquid or a gas in the plasma state. The next layer is then deposited and the process is repeated until fabrication of the semiconductor device is complete. 
     Developer solution and other process liquids are typically applied to the wafer using a spin coating technique in which the process liquid is sprayed on the surface of the wafer as the wafer is spun on a rotating chuck. The spinning of the wafer distributes the liquid over the surface of the material. When developer chemicals are applied to the surface, it is necessary to quickly and gently produce a deep puddle of developer on the wafer to ensure that the photoresist layer is dissolved uniformly in areas that are soluble in the developer. 
     A common practice in the prior art is to spray the process liquid onto the surface of the wafer from a source positioned high enough above the wafer to ensure that the spray fully covers the wafer. However, the process liquid develops a significant amount of momentum prior to contacting the surface that greatly disturbs the surface of photoresist material. Although the surface of the wafer is very smooth, the impact of the process liquid being dispensed onto the wafer results in a nonuniform distribution of the process liquid. In the case of applying developer solution, the turbulence caused by the impact of the developer increases the possibility that air bubbles will form in the developer and that uneven salvation of the photoresist will occur due to agitation caused by local mixing. Both of these problems decrease the uniformity and contribute to defects which reduce the overall yield of properly performing chips from the wafer. 
     Several attempts have been made in the prior art to minimize the aforementioned problems, such as disclosed in U.S. Pat. No. 5,002,008 issued to Ushijima et al., U.S. Pat. No. 5,020,200 issued to Mimasaka et al. and U.S. Pat. No. 5,429,912 issued to Neoh. The Ushijima patent discloses a nozzle having a trumpet shaped tip to prevent inadvertent dripping of the process material onto the wafer and threaded to the dispense arm to minimize the leakage of air into the nozzle itself. The nozzle is positioned in close proximity to the wafer and dispenses the process material perpendicular to the surface. The process material is distributed over the surface of the wafer by the spinning motion of the wafer on the chuck. 
     The Neoh patent discloses a nozzle apparatus that contains a well immediately upstream of the dispense end of the nozzle. The well provides a large flow area that slows the flow of the process material, allowing air pockets that may have been formed during the pumping of the material to the well to separate from the process material as a result of buoyancy and be removed from the nozzle. As with the Ushijima patent, the nozzle is positioned in close proximity to the wafer and dispenses the process material perpendicular to the surface. The process material is distributed over the surface of the wafer by the spinning motion of the wafer on the chuck. While the Ushijima and Neoh patents disclose nozzles that provide the aforementioned improvements, the process material is dispensed perpendicular to the surface in a small area proximate to the nozzle, which can cause nonuniformities in the surface of the coating layer due to the impact of the material as discussed previously. 
     The Mimasaka patent discloses a cylindrically shaped nozzle that contains a plurality of holes through the side of the nozzle in a direction parallel to the surface of the wafer. The nozzle produces a lower impact velocity of the process material by forcing the flow, which initially is perpendicular to the surface of the wafer to turn 180° after encountering blockage at the bottom of the nozzle and to exit the nozzle through holes in the side of the nozzle. The impact velocity of the process material is substantially lowered because the fluid has lost almost all of its momentum perpendicular to the wafer when it encountered the blockage in the nozzle; therefore only the gravitational acceleration of the fluid over the short distance from the holes in the nozzle to the surface of the wafer will contribute to the perpendicular component of the impact velocity. 
     Certain difficulties exist with the use of the Mimasaka nozzle. For instance, because the flow does not exit from the bottom of the nozzle, the nozzle must be positioned off the centerline of the wafer so that the flow exiting the holes contacts the center of the spinning wafer. The off-centerline positioning of the nozzle is not necessarily a less favorable orientation; however, the placement of the Mimasaka nozzle requires far more precision than the bottom dispense nozzles of the prior art. Both the bottom dispense and the Mimasaka nozzles have to be radially positioned over the centerline of the wafer to ensure full coverage requiring accuracy in the positioning of the nozzle on a scale of the liquid stream dimensions. The Mimasaka nozzle, however, must additionally be angularly positioned so that one hole on the circumference of the nozzle is aligned with the centerline of the wafer, while maintaining the proper radial alignment. The additional complexity of the alignment procedure was apparently recognized in the Mimasaka patent as an alternative embodiment also provides holes in the bottom of the nozzle. This embodiment, however, is fraught with the same problems as other prior art designs in which the fluid exits perpendicular to the surface of the wafer. Also, the use of a plurality of holes increases the potential for the liquid to drip onto the surface of the wafer after dispensing is completed, because the holes can act as vents and drains for the flow that facilitates the formation of drops. 
     In addition, because the flow generally must turn 180° and must exit through flow holes the flow path is necessarily extremely tortuous. In fact, the tortuous path is the means by which the Mimasaka nozzle lowers the impact velocity of the process material. The tortuosity of the flow path produces turbulence in the flow, even at low Reynolds numbers, which greatly increases the possibility that air will get trapped in the process material and that chaotic motion of the flow will disrupt the coating layer. 
     Thus, it is apparent that a need exists for an improved nozzle for spin dispensing apparatuses which overcomes, among others, the above-discussed problems so as to produce a more uniform layer of process liquid over the surface of the wafer. 
     BRIEF SUMMARY OF THE INVENTION 
     The above objects and others are accomplished by an apparatus and method for dispensing process liquid from a liquid source onto a surface of a semiconductor wafer in accordance with the present invention. The apparatus includes a nozzle having a bore with a longitudinal axis in fluid communication with the liquid source and a flow surface having a perimeter. The flow surface is oriented at a first angle relative to the axis and in fluid communication with the bore to dispense a sheet of process liquid from the perimeter onto a wafer surface. In a preferred embodiment, the nozzle is axisymmetric and includes a housing having a source portion connected to the liquid source and a dispense portion, and the bore traverses the source and dispense portions. An insert is provided having a first section disposed in the dispense portion of the bore adjacent to said source portion and a second section including the flow surface which is fully circumferential and continuous. The flow surface is in close proximity to the dispense portion, so as to define a flow path along the flow surface to control the flow of the process liquid. In the method of the invention, the nozzle is positioned to dispense a fully circumferential continuous sheet of process liquid onto the wafer surface, while the surface is being rotated. The nozzle is radially offset from the center of the surface such that a portion of the continuous sheet of process liquid is dispensed directly onto the center of the wafer surface. 
     Accordingly, the present invention provides an improved nozzle that allows process liquid to be dispensed more uniformly on a rotating surface, which provides for a more uniform distribution of the process liquid on the surface of the layer, while requiring less process liquid and slower rotational speed to ensure full coverage of the surface. 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 an exploded perspective view of a preferred embodiment of the present invention; 
     FIG. 2 is a cross sectional exploded perspective view of a preferred embodiment of the present invention along line  2 — 2 ; 
     FIG. 3 is a cross sectional assembled perspective view of a preferred embodiment of the present invention along line  2 — 2 ; 
     FIG. 4 is a top plan view of a second alternative embodiment of the apparatus; 
     FIG. 5 is a side cross sectional assembled view of a first alternative embodiment of the present invention along line  5 — 5 ; 
     FIG. 6 is a top plan view of a second alternative embodiment of the insert; 
     FIG. 7 is a top plan view of a second alternative embodiment of the apparatus; 
     FIG. 8 is a side cross sectional assembled view of a second alternative embodiment of the apparatus along line  8 — 8 ; 
     FIG. 9 is an exploded perspective view of a third alternative embodiment of the present invention; 
     FIG. 10 is a cross sectional exploded perspective view of an alternative embodiment of the present invention along line  10 — 10 ; 
     FIG. 11 is a cross sectional assembled perspective view of an alternative embodiment of the present invention along line  10 — 10 ; and, 
     FIG. 12 is a cross sectional assembled perspective view of a preferred embodiment of the present invention along line  2 — 2  in a spin dispensing assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The operation of the apparatus  10  will be described generally with reference to the drawings for the purpose of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same. The apparatus  10  of the present invention includes a nozzle  11  having a housing  12  attached to an insert  14  for use in dispensing a process liquid from a liquid source onto, for example, a rotating surface of a semiconductor wafer. 
     In a preferred embodiment, as shown in FIGS. 1-3, the nozzle  11  is axisymmetric about a longitudinal axis A—A. The housing  12  is bell shaped having a source portion  16  and a dispense portion  18  which are traversed by a central bore  20  defined by an inner surface  22  parallel to the longitudinal axis A—A. The central bore  20  has first and second diameters, respectively, corresponding to the source and dispense portions,  16  and  18 , respectively. The second diameter of the central bore  20  is larger than the first diameter and abruptly changes between the source portion  16  and the dispense portion  18 . The inner surface  22  of dispense portion  18  is also provided with a circumferential groove  24  for securing the insert  14  in the central bore  20  and the source portion  16  is provided with a flange  26  for attachment to a spin dispensing assembly. The dispense portion  18  has a dispense end  28  in which the inner surface  22  defining the bore  20  diverges at a second angle β with respect to the longitudinal axis A—A to form a dispense surface  23 . 
     Also in a preferred embodiment, the insert  14  is generally circular shaped having first and second end sections,  30  and  32 , respectively, separated by a middle section  34 . The first section  30  has an outer surface  40  that conforms to the inner surface  22  of the housing  12  and includes a circumferential lip  42  that mates with the circumferential groove  24  in the housing to secure the insert  14  in substantial contact with the housing  12 . The first section  30  prevents any substantial flow of liquid from occurring between the first section  30  and the inner surface  22 . The insert  14  contains a fluid passage  36  extending between the first section  30  and a plurality of fluid ports  38  in the middle section  36  to provide fluid communication with the central bore  20  around the first section  30  of the insert  14 . The fluid passage  36  is a centrally located second bore in the first section  30  and has the same diameter as the first diameter of the central bore  20  and is aligned with the central bore  20  to minimize the amount of turbulence generated in the flow by the transition. In one embodiment, the fluid passage  36  extends through the middle section  36  and past the fluid ports  38 , terminating in the second section of the insert  14 . The extension of the fluid passage  36  beyond the fluid ports  38  reduces the momentum of the process liquid perpendicular to the surface of the wafer, further lowering the impact velocity of the process liquid. However, the reduction in momentum is somewhat offset by the increased turbulence of the air surrounding the nozzle in this design. 
     The middle section  34  of the insert  14  has a diameter less than second diameter of the central bore  20  near the dispense portion  18  so that an annular region  44  is formed between the middle section  34  and the inner surface  22  of the housing  12 . The fluid ports  38  are circumferentially oriented and distributed around the middle section  34  to fully distribute the flow in the annular region  44 . A preferred embodiment incorporates circular fluid ports  38  because of the ease of manufacturing circular ports; however, the fluid ports  38  can be any shape necessary to accommodate the design. Although the ports  38  are preferably distributed uniformly around the circumference of the middle section  34 , the skilled practitioner may distribute the ports to achieve other desired flow patterns in the nozzle  11 . 
     In a current preferred embodiment, the second section  52  of the insert  14  is a circular shaped disc having a diameter greater than the second diameter of the central bore  20 . The second section  52  is attached at its center to the middle section  34  of the insert  14 . The second section  32  extends beyond the dispense portion  18  and has a top flow surface  50  defined by an edge or perimeter  52  that has a diameter that is greater than the outer diameter of the housing  12 . The top flow surface  50  forms a first angle α with the longitudinal axis A—A of the central bore  20  as measured from a portion of the longitudinal axis A—A extending through and opposite to the flow surface  50 , so that process liquid dispensed onto the top flow surface  50  will be directed toward the edge or perimeter  52 , as shown in FIG.  12 . The first angle α can range from 0° to 180°; however, it is preferred that the angle be between 45° and 90° so that the major component of the flow direction is parallel to the wafer surface (i.e., perpendicular to the longitudinal axis A—A). It may alternatively be desirable in some instances to have the flow surface  50  be oriented at an angle between 90° and 180° to form a pool of process liquid within the nozzle, which would spill over the perimeter  52  onto the wafer surface. 
     The second section  32  also includes a bottom surface  54  defined by edge  52  that is generally perpendicular to the central bore  20 . In a preferred embodiment, the bottom surface  54  has a beveled circumferential region  56  near the edge  52  that facilitates the creeping of the process liquid from the flow surface  50  around the edge  52  onto the bottom surface  54 , which is beneficial when utilizing a meniscus to contact a portion of the surface of the wafer, as further discussed within. 
     The flow surface  50  of the insert  14  and the dispense end  28  are in close proximity and define a narrow fully circumferential (360°) flow path  58  along the flow surface  50 . The continuous flow path  58  provides for a 360° flow of the process liquid on the flow surface  50  resulting in the dispensing of a continuous sheet of process liquid onto the wafer surface. Preferably, the second angle β is less than or equal to the first angle α, to provide the continuous flow path  58  with a converging or constant cross sectional flow area as defined by the flow surface  50  and the dispense surface  23 . A converging or constant cross-sectional area is desirable to dampen any flow instability introduced upstream in the nozzle  11 . The resistance to the flow of the process liquid through the nozzle  11  can be controlled by varying the size of the flow path  58  to produce a uniform flow field exiting the nozzle  11  either by varying the distance separating the flow surface  50  and the dispense surface  23  or the first and second angles, α and β, respectively. The impact velocity of the process liquid will be substantially reduced compared to prior art nozzles because the full perimeter  52  of the nozzle  11  is used to dispense the process liquid providing for a larger flow area and a corresponding lower fluid velocity. In addition, the fully circumferential flow path  58  allows for a continuous 360° sheet of process liquid to be dispensed from the perimeter  52  of the nozzle  11  in a circumferentially uniform manner, thereby overcoming the problems in the prior art with having to precisely align the nozzle  11  both radially and angularly to ensure that the liquid will contact the center of the wafer. Also, after the dispensing of the process liquid is completed, the fully circumferential flow path  58  retains the liquid remaining in the nozzle  11  and reduces the potential for the liquid to drip onto the surface compared to the multiple flow paths designs in the prior art. 
     Two alternative embodiments of the insert  114  are shown in FIGS. 4-8. In these embodiments, the source portion  116  and the dispense portion  118  have equal outer diameters providing for a fully cylindrical housing  112 . Also, the first and second diameters of the central bore  120  are comparable. In one embodiment of the nozzle  111  shown in FIGS. 4 and 5, the first section  130  of the insert  114  is sized to conform to the inner surface  122  of the dispense portion  118  and the diameter of the fluid passage  136  in the first section  130  is smaller than the diameter of the central bore  120  and the first section  130  is shaped to channel process liquid into the fluid passage  136  from the central bore  120 . In another embodiment of the nozzle  211 , shown in FIGS. 6-8, the insert  214  is a solid member that is sized such that the flow passage  236  is defined by the annular gap  244  between the insert  214  and the inner surface  222  of the housing  212 . The circumferential lip  242  is slotted to allow communication over the full length of the housing  212 , as shown in FIG.  8 . The embodiments  111  and  211  shown in FIGS. 4-8 provide a constant cross sectional area that provides for better air flow characteristics in the spin dispensing process chamber than the preferred embodiments shown in FIG. 1; however, the process liquid will be dispensed over a smaller area resulting in generally higher velocities when using the embodiments shown in FIGS. 4-8. 
     In an alternative embodiment of the nozzle  311  shown in FIGS. 9-11, the dispense portion  318  has an increasing outer diameter from the source portion  316  toward the dispense end  328 . The dispense portion  318  includes an integral distribution portion  360  extending across the central bore  320  and consisting of distribution ports  362  circumferentially distributed around a solid portion  364 . The distribution ports  362  feed the annular plenum  344  at the dispense end  328 . A distribution plate  366  having a top surface  368  and a bottom surface  370  is attached to the solid portion  364  by conventional methods, such as a pin  372 , so that the top surface  368  and the dispense end  328  are in close proximity and define the fully circumferential continuous flow path  358  in fluid communication with the annular plenum  344 . 
     A method and use of a preferred embodiment of the present invention will be described with respect to dispensing developer from a spin dispensing apparatus  10 , as shown in FIG.  12 . The source portion  16  of the nozzle  11  is attached using flange  26  to a liquid source  80 , containing the process liquid to be dispensed, which in the present example is a developer solution. The liquid source  80  generally includes a liquid dispense arm that attaches to and positions the nozzle  11  in the spin dispensing apparatus  10  and the dispense arm is plumbed to provide the process liquid from a source, as is known in the art. A wafer  82  having a surface  84  to be coated is positioned on a support surface  85  of a rotatable chuck  86  that spins the wafer  82  around central axis C—C. 
     The nozzle  11  is positioned above the surface  84  of the wafer  82  and is radially offset from the center of wafer  82  so that the fully circumferential continuous sheet of developer solution emerging from the nozzle  11  contacts the center of the wafer  82 . The chuck  86  is rotated for a period of time according to predetermined specifications. The developer solution is dispensed from the liquid source  80  in an axial direction (represented by arrows  23  in FIG. 12) into central bore  20  of the nozzle  11  in the source portion  16  and the developer solution flows through the central bore  20  and into the flow passage  36  in the first section  30  of the insert  14 . The developer solution flows through the first section  30  into the middle section  34  via the fluid passage  36 . 
     At this point, the flow turns to exit through ports  38  and a significant amount of the momentum of the developer solution in the direction parallel to the central bore  20  is lost in the form of an irrecoverable shock loss. The developer solution exits the fluid passage  36  through ports  38  into the annular region  44 . The flow of the developer solution in the annular region  44  is generally turbulent as a result of the turning of the flow and the area change associated with passing through the ports  38 . The developer solution passes through the annular region  44  contacting the flow surface  50  and enters the continuous flow path  58 , which provides a high resistance path relative to the annular region  44 . The narrow pathway provided by flow path  58  stabilizes the flow field by dampening the turbulence produced entering the annular region  44  and also circumferentially distributes the flow around the flow path  58 . 
     The developer solution then uniformly exits the flow path  58  in a 360° continuous sheet flowing over the flow surface  50  off the edge or perimeter  52  in a 360° continuous circular sheet of developer solution onto the surface  84  of the wafer  82  forming a puddle  87 . In a preferred method of dispensing the developer solution, the nozzle  11  is positioned in sufficiently close proximity to the surface  84  of the wafer  82  that the developer solution forms a meniscus  88  between the wafer surface  84  and the bottom surface  54  of the insert  14 . In this way, full contact of the developer solution with the surface  84  near the center of the wafer  82  is better ensured. The beveled circumferential region  56  further provides for the developer solution to creep around the edge  52  onto the bottom surface  54  to provide a continuous source of developer solution to maintain the meniscus  88 . 
     The nozzle of the present invention can also suitably modified to dispense process liquids at a wide range of flow rates by modifying the nozzle to have a variable flow area. The flow area can be varied by biasing the nozzle  11  such that the pressure of the impacting process liquid in the nozzle would bias the continuous flow path open to a greater extent, providing more flow area and thereby lowering the impact velocity of the process liquid. The biasing could be performed using conventional methods such as by incorporating a diaphragm or a spring load mechanism into the nozzle. 
     Those of ordinary skill in the art will appreciate that the present invention provides significant advantages over the prior art. In particular, the subject invention provides a more uniform and easily controlled dispensing of process liquids onto the surface of the semiconductor wafer, while lowering the potential for the formation of air bubbles in the resulting liquid layer formed on the surface by reducing the turbulence produced during the dispensing of the process liquid. 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 and steps which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.