Abstract:
An apparatus and system for removing photoresist or other organic material from a substrate such as a semiconductor wafer is provided. The apparatus and system includes a chamber for partially immersing the substrate in a solvent (e.g., deionized water), a chamber for receiving an oxidizing gas (e.g., ozone), and a mechanism for rotating or otherwise moving the substrate through the solvent to coat a thin film of solvent over the organic component on the substrate surface and expose the solvent-coated substrate to the ozone gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of Ser. No. 09/688,757, filed Oct. 16, 2000, now U.S. Pat. No. 6,558,477. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the fabrication of semiconductor devices. More particular, the invention relates to a method and system of removing photoresist or other organic materials from a substrate in a semiconductor manufacture. 
     BACKGROUND OF THE INVENTION 
     Photolithography processes are used in semiconductor manufacture to remove portions of the top layers on a wafer surface and create a desired pattern. Generally, this involves utilizing a polymeric resist that reacts to ultraviolet light, as for example, a novolak/diazonaphtoquinone or novolak/quinonediazide resist. 
     Typically, this technique involves coating the wafer with a layer of a light-sensitive polymeric photoresist material, transferring the desired pattern formed in a reticle into the photoresist layer, and exposing the photoresist to light (e.g., UV light) to image the pattern on the reticle onto the photoresist layer. This changes the character of the exposed or unmasked portions of the pattern, and the resist layer then undergoes development, for example, using chemical solvents, to selectively remove the unmasked portions of the resist to provide a desired pattern having open areas in the resist layer. Etchants are then applied to remove an underlying substrate, such as silicon, metal or an insulator, that is exposed through the mask openings. Photoresist masks are used in processing steps such as etching, ion implantation, reworks, and high temperature postbakes. After etching is completed, the photoresist layer is no longer needed and must be removed prior to subsequent processing of the wafer. The main object of a photoresist removal is to quickly and completely strip the photoresist without effecting the underlying substrate surface. 
     There are many conventional resist removal processes that are known to those skilled in the art, including, for example, wet chemical processing and dry plasma etching processing. A typical wet chemical etch involves immersing the wafer in an inorganic resist stripper. A common mixture is a solution of sulfuric acid (H 2 SO 4 ) and an oxidant such as hydrogen peroxide (H 2 O 2 ), which attacks organic materials and converts the carbon in the resist to CO 2  gas. However, wet cleaning has several drawbacks, including particle generation, difficulties with drying, high expense, and chemical waste disposal. In addition, wet cleaning may require mechanical scrubbing to remove all remnants of the resist. 
     An alternative to wet cleaning to remove resist and other organic films from a wafer is the use of ozone (O 3 ) as the primary chemical agent. One technique involves exposing the photoresist to an O 3 -containing gaseous atmosphere while heating the substrate on which the photoresist layer is disposed. The ozone oxidizes the resist and other organics into by-products such as water, carbon monoxide (CO) and carbon dioxide (CO 2 ). Ozone is highly selective to organic materials, and does not etch silicon, silicon dioxide, or aluminum. However, in a gas phase process, ozone must react with the organic material until it volatilizes into a gas phase. 
     Methods have also been described that utilize ozonated deionized (DI) water to remove resist and resist residues. In one known method, the wafers are immersed in a chilled water bath (about 5° C.) and ozone is diffused into the water to strip the resist. A drawback of this method is the low strip rate for the resist. 
     Another process involves heating the wafers and steam-treating with an ozonated water mixture. A process has also been described in which wafers mounted in a carrier are sprayed with ozonated water within a process chamber. In either process, the resist is stripped as the water runs down the wafer surface. However, such methods do not adequately strip the resist and resist residues from the wafer surface. Additionally, residual resist can remain on the wafer at the contact points between the wafer and the carrier. In the use of spray systems, specific control elements and a more complex system than desirable is needed, and the spray mechanisms may not provide a suitable misting of the wafer surface resulting in poor uniformity of removal. 
     In another process, the wafers are spun at high revolutions per minute (RPM) and simultaneously sprayed with warm water while ozone is pumped into the reaction chamber. However, it is difficult to maintain a suitably thin layer of water on the surface of the wafer for effective permeation of the ozone to the surface of the wafer. 
     In view of the foregoing, there is a need for a method of removing photoresist or other organic materials from a substrate that overcomes these problems. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of known methods in providing an improved method and system for removing photoresist and, more generally, organic components, from the surface of a substrate such as a semiconductor wafer. The method can be used in conjunction with other compatible methods used for organic material removal. 
     According to the method of the invention, at least a portion of a wafer or other substrate having an organic component on the surface, is submerged in a solvent, preferably deionized water, and the substrate is then moved relative to the solvent such that a thin layer of solvent is deposited over the organic component on the surface of the substrate, which is then exposed to ozone gas for removal of the organic component. 
     In one embodiment of the method, the substrate such as a semiconductor wafer is rotated through a solvent section and a gaseous section of the reaction chamber of a cleaning module. Rotation of the wafer through the solvent is controlled so that a thin film or layer of solvent is formed over the organic component on the surface of the substrate which is then exposed to ozone gas in the gaseous section of the reaction chamber. The thickness of the solvent layer is sufficiently thin to facilitate diffusion of the ozone gas therethrough to react with the organic material and remove at least a portion of the organic material from the substrate surface. 
     As the wafer or other substrate is rotated and passes through the solvent and into the gaseous section, a meniscus of solvent forms at the interface between the solvent and the surface of the wafer, while a thin layer of the solvent is formed over the organic component on the surface of the substrate. Preferably, the ozone gas reacts with the organic component on the surface of the substrate through the meniscus as well as the solvent layer. In addition, water vapor may condense onto the organic component on the surface of the wafer, and the ozone gas can also react with the organic component through the water vapor layer. Gaseous by-products such as CO and CO 2  that are formed by the reaction are exhausted from the reaction chamber. 
     In another embodiment of the method, the substrate can be vertically moved into and out of the solvent section and the gaseous section. Such vertical movement is controlled similarly to the above described rotational movement to form a suitably thin layer of solvent over the organic component on the surface of the substrate as it is drawn upward out of the solvent into the gaseous section whereupon exposure to the ozone gas effectively removes the organic component from the surface of the substrate. 
     In the use of the method in a semiconductor process, a plurality of semiconductor wafers or other substrates can be loaded into a carrier and moved into a cleaning module that includes a reaction chamber having a gaseous section for containing ozone gas and a section containing a solvent, preferably deionized water, to provide a solvent bath. The solvent section can comprise structure such as a container for holding the solvent therein. The solvent section is adapted to receive the wafer carrier such that the semiconductor wafers are at least partially submerged in the solvent. The solvent section can include a mechanism for contacting the wafer carrier and the semiconductor wafers, and moving the wafers relative to the solvent section and the gaseous section, for example, by vertical or rotational movement. Preferably, the mechanism is operable to rotate the wafers through the solvent and gaseous sections of the reaction chamber. The carrier is loaded into the reaction chamber of the cleaning module and positioned in the solvent such that the wafers are at least partially submerged within the solvent, and the rotating or moving mechanism is placed in contact with the semiconductor wafers. Ozone gas is flowed into the reaction chamber and the moving mechanism is activated to move the wafers through the solvent to form a thin layer of solvent over the organic component on the surface of the wafers and then into the gaseous section to expose the solvent layer to the ozone gas. As the solvent-covered substrate passes through the gaseous section, the ozone gas diffuses through the solvent layer to react with and remove at least a portion of the organic component from the substrate surface. 
     Also provided is a system embodying a cleaning apparatus for use in the method of the invention. The system includes a reaction chamber comprising a gaseous section for containing ozone gas and a solvent section than can include structure such as a container for holding the solvent. The solvent section is adapted to receive at least one wafer at least partially submerged within the solvent. The system also includes a mechanism to contact and move the substrate relative to the solvent section and the gaseous section, for example by vertical movement and/or preferably by rotational movement. The system further includes a source of ozone gas such as an ozone generator that is in flow communication with the gaseous section of the reaction chamber. The system can further include a conveyor mechanism that moves the wafers or other substrate through the reaction chamber and the solvent, an exhaust pump for removing gaseous by-products from the reaction chamber, and an element for heating the solvent. 
     Advantageously, the present invention provides an improved method and system for removing substantially all traces of photoresist or other organic components from the surface of a substrate. In addition, the invention provides a method and system for removing organic material that is efficient, low cost, and adaptable to volume semiconductor manufacture. The invention eliminates mechanisms such as spray nozzles and conventional cycling mechanisms, requires fewer control devices than conventional systems, and provides a uniform rate of resist removal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings which are for illustrative purposes only. Throughout the following views, reference numerals will be used on the drawings, and the same reference numerals will be used throughout the several views and in the description to indicate same or like parts. 
     FIG. 1 is a schematic diagram of an embodiment of a system for removing photoresist according to the invention. 
     FIG. 2 is a diagrammatic perspective view depicting a semiconductor wafer (with the carrier not shown) and rotor mechanism of the system of FIG.  1 . 
     FIG. 3 is a diagrammatic cross-sectional view of a semiconductor wafer (carrier not shown) with a layer of photoresist being removed using the system shown in FIG.  1 . 
     FIG. 4 is a schematic diagram of another embodiment of a system for removing photoresist according to the invention. 
    
    
     DETAILED DESCRIPTION 
     In a semiconductor device fabrication process, a polymeric resist is applied on a substrate to form a resist layer that typically has a thickness of about 0.5 microns to about 1.5 microns. After an etch process, the resist layer is then removed. The present invention provides a method and system for removing photoresist or other organic components from a substrate such as a wafer used in the fabrication of semiconductor devices. 
     The method and system of the invention will be described generally with reference to the drawings for the purpose of illustrating the present preferred embodiments of the invention only and not for purposes of limiting the same. FIGS. 1-3 illustrate processing steps for use in the fabrication of semiconductor devices in accordance with the present invention. It should be readily apparent that the processing steps are only a portion of the entire fabrication process. The present invention particularly deals with the method of removing photoresist and other carbon-based materials that are used in the fabrication of semiconductor devices. 
     A first embodiment of a method of the present invention for cleaning photoresist or other organic component from the surface of a substrate in the form of a semiconductor wafer is described with reference to FIGS. 1-3. According to the method, a reaction chamber  12  is provided that includes a gaseous section  14  and a solvent section  15  comprising a container  16  to contain a solvent  18 , preferably deionized water. The wafers  20  are moved into the reaction chamber  12 , typically by means of a carrier or boat  22  that holds the wafers  20  in a vertical orientation. The wafers  20  are placed in the solvent  18  such that about half  24   a  of the wafer is immersed in the solvent and about half  24   b  extends into the gaseous section  14  of the chamber  12 . Ozone gas  26  is then supplied to the gaseous section  14  of the chamber  12 , and the wafers  20  are continuously rotated such that the wafers  20  pass through the solvent  18  and then the gaseous section  14  of the chamber  12  to expose the solvent-coated surface  28  of the wafer to the ozone gas  26 . 
     Referring to FIGS. 2 and 3, as the wafer  20  is rotated or otherwise moved through the surface  30  of the solvent  18  into the gaseous section  14 , a meniscus  32  of water or other solvent forms at the interface  34  between the wafer and the solvent, and a thin film  36  of solvent forms over the organic component  38  on the surface  28  of the wafer. The rotation of the wafer is at a speed effective to cause a thin layer  36  of the solvent to form that will effectively wet the surface and remain as a film or coating over a majority of the organic component  38  while the wafer is moved through the gaseous section  14 . In addition, water vapor  39  from the solvent bath can condense on a portion of the wafer to wet the surface and the organic component  38 . The solvent layer  36  and water vapor layer  39  are sufficiently thin to allow the ozone (O 3 ) gas to diffuse through the solvent layer  36  to the underlying photoresist or other organic component  38 . Preferably, a solvent layer  36  having a thickness of about 0.001 to about 100 microns, more preferably about 0.001 to about 50 microns is formed over the organic component  38 . Water vapor layer  39  is preferably about 0.001 to about 100 microns thick, preferably about 0.001 to about 50 microns. It is also preferred that the speed of rotation of the wafer  20  is about 1 to about 10 mm/second. Ozone (O 3 ) can also be dissolved or mixed into (e.g., bubbled into) the solvent (e.g., deionized water) to increase the resist strip rate and increase the effectiveness of the method. 
     As the wetted surface of the wafer  20  is passed into and through the gas-phase section  14  of the reaction chamber  12 , the ozone gas  26  permeates through the thin layer  36  of solvent and water vapor  39 , and preferably through the meniscus  32 , to react with and dissolve the resist or other carbon-based (organic) component  38  on the surface  28  of the wafer. The ozone (O 3 ) decomposes into diatomic oxygen and atomic oxygen (O), and the photoresist or other organic component  38  is oxidized into CO and CO 2  reaction products, which are exhausted from the system. Any solid by-products are rinsed from the surface of the wafer  20  as the wafer is moved from the gaseous section  14  and through the solvent section  18 . 
     The ozone gas  26  is flowed into the reaction chamber  12  to provide a concentration effective to diffuse through the solvent layer  36  and water vapor layer  39  and react with the resist or other organic component  38  to remove at least a portion of the organic component  38  from the wafer surface  28  as the wafer  20  passes through the gaseous section  14  of the chamber  12 . The flow of ozone  26  into the reaction chamber  12  can range from about 2000 to about 9000 sccm, preferably about 3000 to about 7000 sccm, to provide a concentration of ozone gas in the reaction chamber of about 80 to about 300 grams per m 3 , preferably about 150 to about 250 grams per m 3 . 
     Preferably, a pressure of about 1 mTorr to about 10 Torr is maintained in the reaction chamber  12  during the removal process. The temperature of the solvent  18  is preferably maintained at about 80° C. to about 95° C., more preferably about 85° C. to about 90° C. The gaseous section  14  of the reaction chamber  12  can be maintained at about ambient temperature. 
     The process is performed for a predetermined period of time necessary to remove the photoresist or other organic component  38  from the surface  28  of the wafer. The time period is determined, at least in part, by the thickness of the organic component to be removed, the concentration of ozone in the reaction chamber, and the nature of the solvent that is used. A treatment period of up to about 10 minutes is generally effective to remove resists up to about 3 microns thick at a strip rate of about 1,500 angstroms per minute. Longer time periods can be utilized as necessary to remove resist layers that are greater than 3 microns. 
     Referring to FIG. 1, an embodiment of a system  10  for use in removing organic materials from a wafer according to the invention is illustrated. As shown, the system  10  includes a reaction chamber  12  containing a gaseous section  14  and a solvent section  15  which includes structure such as a tank or other container  16  containing the solvent  18 , preferably deionized water. A gas supply unit  54 , for example, an ozone generator, can be used to supply a gaseous atmosphere containing ozone  26  (“ozone gas”) into the gaseous section  14  of the reaction chamber  12  through an inlet  40  at a predetermined rate. A flow control mechanism  42 , such as a valve, can be included to regulate the flow of gas  26  into the reaction chamber. In general, the ozone generator converts oxygen to ozone. Such devices are commercially available and well known in the art. 
     The reaction chamber  12  is a sealed chamber designed to contain the ozone gas  26  at about room temperature or greater, and a pressure of about 1 mTorr to about 10 Torr (atmospheric pressure). The reaction chamber  12  includes an outlet or vent  44  for exhausting reactive by-products  46 . The container  16  receives the solvent  18  (e.g., deionized water) from a source  48  through a conduit  49 . The solvent  18  can be drained from the container  16  through a conduit  50 . The temperature of the solvent can be maintained using a temperature control device  52 . 
     Wafers  20  to be cleaned are moved through the reaction chamber  12  and into and out of the solvent  18  by conventional means that are readily available and known in the art (not shown). The wafers  20 , positioned vertically in a carrier  22 , are loaded into the container  16  (i.e. water bath) such that a portion  24   a  of the wafer is immersed in the solvent  18 , and a portion  24   b  is positioned in the gaseous section  14  of the reaction chamber for exposure to the ozone gas  26 . The reaction chamber  12  is sealed and purged, for example, with an inert gas such as argon or helium. The flow of ozone gas  26  from the gas supply unit  54  is initiated, and the wafers  20  are moved by rotational movement in accordance with the invention to solubilize the resist or other organic material  38 . The ozone gas  26  is flowed into the reaction chamber  12  in an amount sufficient to diffuse through the layer or film  36  of solvent and condensed water vapor layer  39  that forms on the wafer  20  in the practice of the invention, and to react with and remove the photoresist or other organic component  38  disposed on the surface  28  of the wafer  20 . As the wafers  20  are rotated through the solvent  18  and then exposed to the ozone gas  26 , the organic component  38  is oxidized into CO and CO 2  reaction products, which are exhausted from the system  10  through the vent  44 . When the process is completed, the wafers  20  are removed from the solvent  18  and conveyed onto the next processing step. 
     The wafers  20  are typically transported inside a conventional flat wafer carrier or boat  22  that is adapted to support the wafers  20  in slots (not shown) in a vertical position. The carrier  22  is typically loaded with about fifty wafers, which are similarly processed simultaneously according to the present method. Preferably, the wafers  20  are mounted in a carrier  22  that facilitates rotation of the wafers to expose the entire surface  28  of the wafer to both the solvent  18  and the ozone gas  26 . A useful wafer carrier for the present invention is described, for example, in U.S. Pat. No. 5,000,208 (Ludwig et al.), using a standard Fluorware low mass carrier, the disclosure of which is incorporated by reference herein. Briefly, the wafers are set vertically into slots and retained in the carrier by a pair of support rods that bear against and support the top edges of the wafers (not shown). 
     In a preferred embodiment of the system  10 , a motor-driven roller mechanism  56  is positioned on the bottom  58  of the container  16  to contact and rotate the wafers  20  through the solvent  18 . As shown in FIG. 1, the carrier  22  is placed into the container  16  to straddle the roller mechanism  56 . As the bottom edges  60  of the wafers  36  are brought into contact with the roller mechanism  56 , the wafers are raised upward about {fraction (1/16)} th  inch to move the wafers out of direct contact with the carrier  22 . As the roller  56  is turned in the direction of arrow  62 , the wafers  20  are rotated in the direction of arrow  64 . 
     Referring to FIG. 4, in another embodiment of the method of the invention and a system  70  for utilizing that method, the wafers  20  can be moved into and out of the solvent section  15  by vertical movement. A thin film or layer  36  of solvent is formed over the organic components  38  on the surface  28  of the wafer  20  as the wafer is drawn upward out of the solvent  18 , and is exposed to the ozone gas  26  in the gaseous section  14  of the reaction chamber  12 . To facilitate such vertical movement, a wafer carrier  22  can be mounted on a device  72  operable to move the carrier  22  vertically through the solvent  18  and into the gaseous section  14 , and back down into the solvent, as depicted by arrow  74 . Preferably, the device  72  includes a member  76  that is structured to contact and raise the wafers out of direct contact with the carrier  22 , for example, about {fraction (1/16)} th  inch, when the carrier is placed onto the mechanism  72 . This ensures coverage of the solvent  18  and exposure to the ozone gas  26  over the entire surface of the wafer  20  for complete removal of the photoresist or other organic material  30  from the surface  28  of the wafer. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.