Abstract:
An exemplary method of depositing photoresist material on an integrated circuit wafer is described. This method can include providing a cross-shaped resist dispenser including a plurality of resist dispense nozzles; dispensing photoresist material through the plurality of resist dispense nozzles to an integrated circuit wafer; and rotating at least one of the cross-shaped resist dispenser and the integrated circuit wafer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 09/760,243, filed Jan. 12, 2001, entitled DISC-SHAPED RESIST DISPENSING SYSTEM AND METHOD, filed by Yu et al. on the same day and assigned to the same assignee as this application. 
    
    
     FIELD OF THE INVENTION 
     The present specification relates generally to the field of integrated circuits and to methods of manufacturing integrated circuits. More particularly, the present specification relates to a cross-shaped resist dispensing system and method. 
     BACKGROUND OF THE INVENTION 
     Generally, conventional integrated circuit manufacturing processes involve the transfer of geometric shapes on a mask to the surface of a semiconductor wafer or layer above the semiconductor wafer. The semiconductor wafer corresponding to the geometric shapes, or corresponding to the areas between the geometric shapes, is etched away. The transfer of the shapes from the mask to the semiconductor wafer typically involves a lithographic process. Conventional lithographic processes include applying a pre-polymer solution to the semiconductor wafer, the pre-polymer being selected to form a radiation-sensitive polymer which reacts when exposed to ultraviolet light, electron beams, x-rays, or ion beams. The solvent in the pre-polymer solution is removed by evaporation resulting from baking the pre-polymer film on the wafer. The film is exposed to radiation, such as, ultraviolet light, through a photomask supporting the desired geometric patterns. 
     The images in the photosensitive material are then developed by soaking the wafer in a developing solution. The exposed or unexposed areas are removed in the developing process, depending on the nature of the radiation-sensitive material. Then, the wafer is placed in an etching environment which etches away the areas not protected by the radiation-sensitive material. Due to their resistance to the etching process, the radiation sensitive-materials are also known as photoresists. 
     The high cost of photoresist pre-polymer solutions makes it desirable to devise methods of improving the efficiency of the coating process to minimize the amount of the polymer solution required to coat a substrate. Furthermore, thickness uniformity of the photoresist layer is an important criterion in the manufacture of integrated circuits. When the radiation is focused through the mask onto the coating, variations in thickness of the coating prevent the precise focus of the radiation over the entire surface of the wafer. Such precision is necessary to ensure satisfactory reproduction of the geometric patterns on the semiconductor wafer. Moreover, high precision is particularly important for advanced circuits with line width dimensions approaching 0.25 micron line widths and smaller. 
     Photoresist is often deposited to a substrate, or more particularly a wafer, by means of forming a puddle followed by spinning (i.e., spin coating). A large puddle of photoresist covering more than half of the substrate area is applied via a dispenser that directs a steady flow of resist in liquid form. The thickness on the puddle is on the order of a millimeter. The substrate is then spun at a speed ranging from 1,000 to 10,000 RPM to thoroughly spread out and remove the excess resist. This spinning results in a film thickness on the order of between a fraction of micrometer and a few micrometers. Therefore, only a small percentage of the photoresist material actually remains on the substrate. Most of the photoresist material dispensed is wasted, resulting in high cost and waste disposal problems. 
     In conventional systems, photoresist deposition utilizes a single pipe or a nozzle to dispense or spray coat the photoresist. Use of a single pipe or nozzle for photoresist deposition on a spinning wafer is taught in numerous patents, such as, U.S. Pat. Nos. 4,416,213; 5,254,367; 5,366,757; and 5,378,511. However, such conventional dispensing and spraying mechanisms use much more resist material than actually remains on the wafer. This inefficiency is costly, particularly due to the high cost of photoresist material. 
     Thus, there is a need to dispense photoresist material in a more efficient manner. Further, there is a need to dispense photoresist material that limits waste and increases uniformity of the dispensed photoresist material. Yet further, there is a need for a cross-shaped resist dispensing system and method. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment is related to a method of depositing photoresist material on an integrated circuit wafer. This method can include providing a cross-shaped resist dispenser including a plurality of resist dispense nozzles; dispensing photoresist material through the plurality of resist dispense nozzles to an integrated circuit wafer; and rotating at least one of the cross-shaped resist dispenser and the integrated circuit wafer. 
     Another exemplary embodiment is related to a method resist dispensing system used in the dispensing of photoresist material on a wafer in an integrated circuit fabrication process. This system can include a wafer supporting structure which supports a wafer; and a cross-shaped platter having a plurality of dispensing nozzles for dispensing resist material on the wafer. 
     Another embodiment is related to an apparatus for coating a substrate with a soluble material. This apparatus can include a spin chamber; a cross-shaped dispenser located in the spin chamber, the cross-shaped dispenser having a plurality of dispensing nozzles; a substrate support which locates a substrate within a proximity distance of the cross-shaped dispenser; and means for spinning the substrate such that the soluble material is distributed about the substrate. 
     Other principle features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exemplary embodiments will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
     FIG. 1 is a perspective view of a photoresist dispensing system in accordance with an exemplary embodiment; and 
     FIG. 2 is a representation of a spin chamber configured to dispense photoresist on a wafer in accordance with an exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring to FIG. 1, a photoresist dispensing system  10  includes a cross photoresist dispenser  12  and an integrated circuit (IC) wafer  14 . As used in this application, the term wafer refers to any substrate used in IC fabrication processes or layer above such a substrate. The substrate or layer above can be conductive, semiconductive, or insulative. 
     Cross photoresist dispenser  12  is generally comprised of a first rectangular member  18  and a second rectangular member  19 . Members  18  and  19  preferably occupy the same plane and are integrally joined at a center point  21 . Alternatively, member  18  can be disposed above member  19  or vice versa. Members  18  and  19  are preferably the same size in length, width, and height. Alternative shapes or configurations for cross photoresist dispenser  12  are possible, including cross shaped dispensers where the angle between members  18  and  19  is not 90 degrees. Generally, cross photoresist dispenser  12  can have a similar length to the diameter of wafer  14 . 
     In an exemplary embodiment, cross photoresist dispenser  12  can be described as a cross like apparatus including hundreds (or possibly thousands) of photoresist dispense nozzles  16  directed downward to IC wafer  14 . In an exemplary embodiment, the length of members  18  and  19  of cross photoresist dispenser  12  is substantially similar to the diameter and shape of IC wafer  14 . For example, the length of members  18  and  19  of cross photoresist dispenser  12  is 200 mm. Photoresist material is provided to cross photoresist dispenser  12 , which preferably rotates in the opposite direction of the rotation of IC wafer  14  while dispensing photoresist material onto IC wafer  14 . 
     According to other embodiments, the size of cross photoresist dispenser  12  can vary. For example, if wafer  14  is a 6 inch wafer, dispenser  12  has members  18  and  19  with lengths of 150 mm. If wafer  14  is a 3 inch wafer, members  18  and  19  can have lengths of 75 mm. If wafer  14  is a 10 inch wafer, members  18  and  19  can have lengths of 250 mm. Generally, members  18  and  19  can have lengths of slightly smaller or the same as the diameter of wafer  14  with which it is used. Dispenser  12  (including members  18  and  19 ) can be either the same diameter/length or 2 to 5 percent smaller than wafer  14 . 
     In an exemplary embodiment, dispense nozzles  16  are separated from each other by a distance of 1 mm on center. In alternative embodiments, dispense nozzles  16  are separated by a distance of 0.5 mm. Dispense nozzles  16  can have a width of 0.2 mm for a 0.5 mm separation. Alternatively, dispensing nozzles  16  can have a width of 0.5 mm for a separation of 1 mm to 2 mm. In an exemplary embodiment, cross photoresist dispenser  12  has over 10,000 dispensing nozzles  16 . 
     Preferably, one nozzle is centered at the center of wafer  14  to insure coating of center portion of wafer  14 . The pattern of nozzles  16  is circular to match wafer  14 . The size of each nozzle can be 500 micrometers (μm). Nozzles  16  are large enough to allow photoresist material to easily pass yet small enough to avoid excessive puddling on wafer  14 . 
     During conventional photoresist spin coating processes, a large percentage of photoresist is wasted. Conventional spin coating processes have a single pipe or nozzle which deposits a puddle of photoresist material onto a wafer. The puddle of photoresist material is distributed by spinning the IC wafer. Much of the photoresist material from the puddle is spun off the IC wafer. Furthermore, the resist thickness uniformity is hard to control using conventional single nozzle or pipe systems. Thickness uniformity is particularly hard to control on topographic patterns with conventional photoresist coating processes. 
     Advantageously, cross photoresist dispenser  12  greatly reduces the photoresist consumption and improves the overall photoresist thickness uniformity. Conventional photoresist spin coating processes deposit a puddle of photoresist material on an IC wafer which is then distributed over the wafer by spinning the wafer. Cross photoresist dispenser  12 , advantageously, deposits a smaller amount of photoresist material than is deposited using the conventional single nozzle photoresist dispenser. As such, less resist is needed to cover the whole wafer. 
     Referring now to FIG. 2, photoresist material is introduced through a channel  22  to cross photoresist dispenser  12 . Channel  22  introduces photoresist material to a spin chamber  24 . In an exemplary embodiment, cross photoresist dispenser  12  is coupled to a rotatable member  26  and IC wafer  14  is located on a substrate support  28  which is coupled to a rotatable member  30 . During the dispensing of the photoresist material, cross photoresist dispenser  12  can be rotated while IC wafer  14  is rotated. In an exemplary embodiment, cross photoresist dispenser  12  spins in an opposite direction as the rotation of IC wafer  14 . 
     Photoresist material passes from cross photoresist dispenser  12  through dispense nozzles  16  to IC wafer  14 . Cross photoresist dispenser  12  is separated from IC wafer  14  by a distance  32 . In an exemplary embodiment, distance  32  is 0.5 mm. Advantageously, the puddles of photoresist material formed on IC wafer  14  from dispense nozzles  16  are smaller in size than the puddle of photoresist material dispensed from conventional single nozzle or pipe photoresist dispensing systems. In an exemplary embodiment, puddles of photoresist material on IC wafer  14  from dispense nozzles  16  are 2 mm in size. The multiple puddles of photoresist material are dispensed about IC wafer  14  by the spinning motion of IC wafer  14 . 
     Once photoresist material is disposed on IC wafer  14 , photoresist material is dried. In an exemplary embodiment, photoresist material is dried by a baking process in spin chamber  24 . 
     In an exemplary embodiment, circular wafer  14  has a diameter of 200 mm. The target photoresist thickness is chosen to be 1 μm as an example. With this photoresist thickness, the range of dispensed photoresist thickness before high-speed spin is 3 μm to 5 μm. A 3 μm to 5 μm dispensed resist thickness requires 0.05 ml to 0.09 ml of resist respectively per 8 inch wafer. Comparing with conventional techniques requiring at least 3.5 ml of resist, a 65× to 40× saving of resist material is realized for the 3 μm to 5 μm thick dispensed thickness, respectively. 
     The size of dispense nozzles  16  is chosen to be sufficiently small that surface tension of the liquid resist prevents it from dripping. Yet, dispense nozzles  1   6  are chosen to be sufficiently large to facilitate dispense nozzles  16  fabrication and to prevent too much surface tension which hinders dispensing. In an exemplary embodiment, nozzles  16  have a size as to hold the resist when there is no pressure, but when pressure is applied, tiny jets or streams of resist come out of nozzles  16 . The usable range of dispense nozzles  16  size is between 0.1 mm and 2 mm. Whereas, the preferred range is between 0.2 mm and 0.5 mm. Dispense nozzles  16  are located as close as physically permitted to each other. The nozzle-to-substrate proximity distance ranges from 500 μm to 10 mm. 
     Preferred slow spin speed ranges from 0.1 to 100 rpm. High-speed spin ranges from 500 to 20,000 rpm. The preferred liquid resist dispense time is between 1 and 10 seconds. Using a dispense time of 3 seconds while the substrate support  28  rotates at 20 rpm, the resist flow rate is 0.017 ml/sec for a 3 μm dispensed resist thickness or 0.03 ml/sec for a 5 μm dispensed thickness. 
     While the embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. Other embodiments may include, for example, different spinning techniques as well as different mechanisms to dispense photoresist onto cross resist dispenser  12 . Further, other embodiments may utilize the methods and systems described to dispense any soluble material. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that nevertheless fall within the scope and spirit of the appended claims.