Abstract:
A system and method for processing substrates, such as porous low-K semiconductor wafers, using ultraviolet (UV) radiation is disclosed. The substrates are first cleaned in a wet processing module and then dried in a UV module under reduced pressure and at a temperature below 100 C., preferably at or below 80 C. A robot module transfers the substrates from the wet processing module to the UV module. The UV module can include a pulse xenon excimer lamp providing incoherent vacuum ultraviolet (VUV) radiation at 172 nm.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. Provisional Application Ser. No. 60/586,773, filed Jul. 9, 2004, the entirety of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to systems and methods for processing substrates, especially systems and methods for cleaning and/or drying silicon wafer or photomask substrates. The invention also relates to single wafer cleaning and drying methods and apparatus.  
         [0003]     The use of ultraviolet radiation during various substrate processing steps, such as the removal of organic compounds or cleaning, is known. However, existing systems are less than optimal in that the processing takes too long or does not achieve optimal end result requirements.  
         [0004]     Single wafer wet processing systems have become available and are being used commercially, among which are the “Goldfinger” single wafer megasonic cleaning system, “Sahara” single wafer drying system, “Rotagoni,” and “Oasis” single wafer spin drying systems which result in wafers previously considered to be sufficiently dry for further processing. Such single wafer wet processing systems are described in U.S. Pat. Nos. 6,754,980; 6,732,749; 6,684,891; 6,681,782; 6,463,938; 6,295,999; 6,140,744; 6,122,837; 6,039,059; 5,556,479; 5,556,479; 5,286,657; 5,090,432; all assigned or previously to Verteq, Inc., Goldfinger LLC, Akrion LLC, and IMEC; and in U.S. patent Publication US 2002/0029788 A1; and U.S. Pat. No. 6,843,855 (&#39;855), assigned to Applied Materials, Inc., all of which are hereby incorporated by reference in their entireties.  
         [0005]     The aforementioned &#39;855 patent discloses the fact that conventional SiO 2  has a relative dielectric constant of roughly 4, but that the semiconductor industry has recently introduced dielectric materials having relative dielectric constants of less than 4, referred to as “low-K” materials, that many of such low-K materials rely on the inclusion of pores or voids to achieve their low-K properties, and that when liquids are used in a conventional wet cleaning and drying process, especially the aforementioned conventional single wafer wet processing systems, capillary forces draw the liquid into such pores or voids. The trapped liquids can be water, reagent, or other rinsing or cleaning fluids. Conventional spin dry, IPA spin dry, or other drying methods used in wet processing apparatus do not dry such trapped liquid(s).The solution proposed in the &#39;855 patent was adding either a supercritical drying chamber or a low-pressure chamber and substrate transferring chamber to a conventional wet-cleaning chamber in order to dry the trapped fluid.  
         [0006]     The &#39;855 patent supercritical fluid drying chamber used, for example, carbon dioxide drying gas. The &#39;855 low pressure drying chamber using temperatures of 100-200° C. and pressures below 10 Torr to dry such trapped fluid from low-K substrates which have been cleaned and dried in a wet process. There are several reasons why the use of supercritical fluid drying is undesirable, and there are also reasons why the use of 100-200° C. temperature in a low pressure drying chamber is undesirable, for example at such high temperatures sodium, lithium, potassium, and/or other ions can migrate. We have recognized a need to provide a drying system and method for low-K substrates which avoids supercritical fluids and also avoids heating to 100-200° C.  
       SUMMARY OF THE INVENTION  
       [0007]     This and other needs are met by the present invention which in one aspect is a method for cleaning a substrate comprising cleaning the substrate in a wet-cleaning module; drying the substrate in the wet-cleaning module; transferring the substrate from the wet-cleaning module to a UV module, the UV module having a source of UV radiation; and drying the substrate in the UV module using UV radiation at subatmospheric pressure and at a temperature below 100° C.; wherein the wet-cleaning module and the UV module are coupled to a substrate transferring module which transfers the substrate to and from the wet-cleaning module and the UV module.  
         [0008]     The system aspect of the invention is an apparatus for cleaning a substrate comprising a UV module having a source of UV radiation; a wet-cleaning module having drying means; a substrate transferring module having means to transfer a cleaned substrate from the wet-cleaning module to the UV module; means to reduce pressure in the UV module; and a source of UV radiation in the UV module capable of drying the substrate at sub-atmospheric pressure and at a temperature below 100° C.  
         [0009]     Preferably the temperature does not exceed 80° C. The invention is especially useful for hard to dry substrates such as certain reticles and especially low-K materials having pores. Preferably the drying in the UV module is carried out for 60 to 90 seconds, although longer and shorter drying times are certainly feasible.  
         [0010]     The preferred source of UV radiation is a pulse xenon excimer lamp providing incoherent vacuum ultraviolet (VUV) radiation at 172 nm at a temperature not exceeding 80° C. without cooling. In some embodiments the source of UV radiation is a pulse xenon excimer lamp providing incoherent vacuum ultraviolet (VUV) radiation at 172 nm at a temperature not exceeding 80° C. without cooling. In other embodiments wherein the UV module comprises a VUV light box having three UV light sources and a reflector which providing incoherent VUV radiation at 172 nm in a nitrogen atmosphere and a VUV processing module having gas distribution manifolds, a vacuum manifold, and sensor ports.  
         [0011]     Controllers and pressure valves can be used to control the subatmospheric pressure below 10 Torr.  
         [0012]     The optional ultraviolet transmissive window is preferably made of fluorinated glass or sapphire. The UV light box may contain a reflector for providing uniform ultraviolet radiation transmission.  
         [0013]     The controller may activates components for creating a cleaning gas atmosphere upon activating the components for reducing pressure, thereby backfilling the first module with cleaning gas as undesirable gases are removed.  
         [0014]     The apparatus can include a source of inert gas is selected from the group consisting of nitrogen and argon, and can also include two or more of the UV modules.  
         [0015]     The UV module can include a process chamber having means for supporting at least one substrate; means for reducing pressure within the process chamber below atmospheric pressure; a source of ultraviolet (UV) radiation for providing UV radiation to a substrate supported in the process chamber; optionally means for creating an inert gas atmosphere in the UV module; and optionally a UV transmissive window separating the process and the UV chamber(s).  
         [0016]     A sensor for detecting intensity of ultraviolet radiation can be provided in the process chamber or in the UV chamber to ensure that the UV lamp is working properly. It is also preferable that the process chamber be capable of being sealed when a substrate is positioned therein. The means for supporting the at least one substrate can be adjustable in height and preferably supports the at least one substrate in a substantially horizontal orientation.  
         [0017]     The UV module can be positioned above or below a wet processing module. The inert gas atmosphere in the UV module can be made of nitrogen and the cleaning gas atmosphere can comprise oxygen and/or ozone.  
         [0018]     In another aspect, the invention is an apparatus for processing at least one substrate comprising: a first module having a substrate support; means for reducing pressure within the first module below atmospheric pressure; a source of a gas fluidly coupled to the first module; a UV module having a source of ultraviolet radiation for providing ultraviolet radiation to a substrate supported in the first module; a source of inert gas fluidly coupled to the UV module; and an ultraviolet transmissive window separating the first and second modules.  
         [0019]     In yet another aspect, the invention is an apparatus for processing at least one substrate comprising: a first module having a substrate support; means for reducing pressure within the first module below atmospheric pressure; a source of a cleaning gas fluidly coupled to the first module; a second module having a source of ultraviolet radiation for providing ultraviolet radiation to the first module; and an ultraviolet transmissive window separating the first and second modules.  
         [0020]     Still in another aspect, the invention is an apparatus for cleaning at least one substrate comprising: a hermetically sealable first module having a substrate support; means to reduce pressurize within the first module below atmospheric pressure; means to produce a gaseous atmosphere comprising at least one gas for processing a substrate in the first module; a second module having a wall in common with the first module; an ultraviolet transmissive window forming at least a portion of the common wall; a source of ultraviolet radiation positioned in the second module so as to emit ultraviolet radiation through the window and into the first module when activated; and means to produce a substantially inert gaseous atmosphere in the second module.  
         [0021]     In a still further aspect, the invention is an apparatus for cleaning at least one substrate comprising: a hermetically sealable first chamber having a substrate support; means to reduce pressurize within the first chamber below atmospheric pressure; means to produce a gaseous atmosphere comprising at least one gas for processing a substrate in the first chamber; a source of ultraviolet radiation for providing ultraviolet radiation to a substrate positioned on the substrate support.  
         [0022]     In a yet further aspect, the invention is an apparatus for providing ultraviolet radiation to at least one substrate comprising: a chamber containing a source of ultraviolet radiation; an ultraviolet transmissive window forming at least a portion of a wall of the chamber; and means to produce a substantially inert gaseous atmosphere in the chamber.  
         [0023]     Another aspect of the invention is a method of cleaning at least one substrate comprising supporting the substrate in a first module; reducing pressure within the first module to a sub-atmospheric pressure; creating a cleaning gas atmosphere in the first module; and exposing the substrate(s) to ultraviolet radiation.  
         [0024]     The UV module is preferably maintained at a slight vacuum to ensure fast drying times. The source of UV radiation preferably a UV lamp that produces UV radiation having a wavelength within a range of 100 to 300 nanometers, most preferably 172 nanometers. One suitable UV lamp is an Osram Xeradex® brand which emits incoherent vacuum ultraviolet (VUV) radiation at 172 nm without ever exceeding 80° C., without the need for water or other cooling. This type of VUV lamp also provides additional cleaning beyond that provided by a wet processing module, although it is still preferred to have a prior wet processing module as disclosed in the &#39;855 patent and the other aforementioned patents. These VUV type lamps produce ozone and oxygen radicals to dry and clean low-K substrates better than achievable with wet processing systems alone.  
         [0025]     Preferably, the ultraviolet radiation is created by a source of ultraviolet radiation such as a UV lamp positioned in a second module, the first and second modules being separated by an ultraviolet transmissive window through which the ultraviolet radiation passes. It is also preferable that an inert gas atmosphere, such as nitrogen or argon, be created in the second module. The second module can be maintained at atmospheric pressure. The substrate can be a semiconductor wafer or a reticle substrate.  
         [0026]     It is further preferable that a ultraviolet transmissive window be provided and made of fluorinated glass or sapphire. Additionally, a reflector can be provided in the UV module for providing uniform ultraviolet radiation transmission. A controller can be provided that activates the means for creating a gas atmosphere in the process module upon activating the means for reducing pressure, thereby backfilling the process module with cleaning gas as undesirable gases are removed therefrom.  
         [0027]     When the substrate is a photomask, the intensity of the ultraviolet radiation can be monitored and the distance between the substrate and the source of the ultraviolet radiation can be adjusted to a desired distance. The ultraviolet radiation most preferably has a wavelength of approximately 172 nanometers and the substrate can be supported in a substantially vertical or horizontal orientation. The cleaning gas atmosphere can comprise oxygen or nitrogen.  
         [0028]     In another aspect, the invention is method of providing ultraviolet radiation to at least one substrate comprising: supporting a substrate in a first chamber; providing a second chamber adjacent to the first chamber, the second chamber containing a source of ultraviolet radiation and an ultraviolet transmissive window that forms at least a portion of a wall of the second chamber; providing a substantially inert gas atmosphere in the second chamber; activating the source of ultraviolet radiation so that the ultraviolet radiation is emitted through the window and into the first chamber, thereby exposing the substrate to the ultraviolet radiation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0029]      FIG. 1  is a front perspective view of a substrate processing apparatus according to an embodiment of the present invention in an open position for receiving a substrate.  
         [0030]      FIG. 2  is a rear perspective view of the substrate processing apparatus of  FIG. 1 .  
         [0031]      FIG. 3  is a front perspective view of the UV chamber and substrate process chamber of the substrate processing apparatus of  FIG. 1  with the UV light box housing removed.  
         [0032]      FIG. 4  is a side cross sectional view of the UV chamber and substrate process chamber of the substrate processing apparatus of  FIG. 1  in a closed position and supporting a substrate.  
         [0033]      FIG. 5  is illustrates an embodiment of an apparatus which includes wet processing modules, UV drying modules, and a substrate transferring module. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0034]      FIGS. 1 and 2  schematically illustrate a one UV drying module  100  embodiment of the present invention. The substrate process apparatus  100  comprises a support frame assembly  101  that supports the various components for operating the apparatus, including an ultraviolet (“UV”) light box  102 , a substrate process chamber  103 , a mask platen  104 , an ultraviolet lamp power supply  105 , a gas box  106  containing mass flow controllers, and a pumping system  109 . Substrate process system  100  is a two chamber system for the purpose of irradiating photomask, reticle substrates, and semiconductor substrates with ultraviolet radiation in a reduced pressure environment for the purposes of removing contamination in the form of residual films and particles. Substrate process system  100  comprises a substrate process chamber  103  and a separate UV chamber  127  (shown in  FIG. 4 ). The substrate process chamber  103  and the UV chamber  127  are substantially vertically aligned, wherein the UV chamber  127  is atop the process chamber  103 .  
         [0035]     Referring to  FIGS. 3 and 4 , the UV light box  102  forms a UV chamber  127  that contains UV lamps  110  that are a source of UV radiation. Preferably, the UV lamp  110  creates UV radiation having a wavelength of approximately 172 nanometers. During operation, the UV chamber  127  is preferably maintained at atmospheric pressure and filled with nitrogen gas so as to form an inert nitrogen gas atmosphere. An inert gaseous atmosphere is maintained in the UV chamber  127  to minimize/reduce absorption of the UV radiation in this gas space. The nitrogen gas is supplied (and removed) via a purge connection  111  that is fluidly coupled to a source/reservoir of nitrogen gas (not shown). Alternatively, other inert gases may be used. Mass flow controllers, pumps, and valves can be incorporated as needed on the inert gas supply line in order to meet operability requirements.  
         [0036]     Additionally, a faceted reflector  112  is shown in conjunction with the UV lamp  110  to provide a uniform UV radiation exposure to the surface of a substrate supported in the process chamber  103 . Absorption of the UV radiation in the UV chamber would render this reflector useless, hence, the inert gaseous atmosphere in the UV chamber  127 .  
         [0037]     Process chamber  103  has an open and closed position. When in the open position, the mask platen  104  is in a lowered position away from the UV chamber  127  (as illustrated in  FIG. 1 ). The mask platen  104  comprises a substrate/mask support  108  for supporting a substrate/photo mask  107  thereon. When in the open position, a substrate/photo mask  107  can be positioned in a substantially horizontal orientation atop the substrate/mask support  108 . The mask platen  104  is then raised until it compresses the chamber O-ring seal  117  positioned in a fully vented dove tail groove, thereby contacting the side walls  116  of the process chamber  103  and forming a substantially sealed fit. The process chamber  103  is preferably all stainless steel and, when closed, has a leak rate no more than 1×10 −7  Std CC/sec Air. Once closed and sealed, the process chamber  103  can be run at sub-atmospheric conditions by applying a vacuum force. Process gases, such as cleaning gases, can be supplied to the process chamber  103  via a gas port  120  ( FIG. 3 ) that is fluidly coupled to the appropriate gas sources/reservoirs.  
         [0038]     Referring solely to  FIG. 3 , the mask platen  104  is shown in the lowered position. Mask platen  104  can be raised through the use of a pneumatic lifter in combination with guide shafts  118 . Alternatively, mask platen  104  can be maintained in a stationary position while the UV light box  102  ( FIG. 1 ) and sidewalls  116  ( FIG. 4 ) of process chamber are raised and/or lowered. Mask platen  104  is preferable made of stainless steel. Chamber supports  119  help support the chambers  103  in a stationary raised position. In yet another alternative embodiment, the process chamber  103  can comprise sealable openings that allow for the insertion and removal of a substrate/photo mask with and automated handling system.  
         [0039]     Referring back to  FIG. 4 , positioned between the UV chamber  127  and the process chamber  103  is a UV transmissive window  113  made from special fluorinated glass or sapphire. The UV transmissive window  113  is held in place with a window clamp assembly  114  and an O-ring seal  115  which is provided to seal, thereby isolating, the UV chamber  127  from the process chamber  103 . The UV transmissive window  113  is thick enough to withstand pressure differences across this window that result from the process chamber  103  and the UV chamber  127  being maintained at different pressures.  
         [0040]     Isolating chambers  103  and  127  from one another allows for the process chamber  103  to be simultaneously run at a different pressure than the UV chamber  127 . More specifically, during preparation for processing, the process chamber  103  is first run at sub-atmospheric pressures to remove the undesirable gases from the processing environment while backfilling the process chamber  103  with the specific gas composition desired for processing, such as cleaning and/or the surface treatment of photomask, reticle substrates and semiconductor substrates.  
         [0041]     A UV power detector  121  is integrated into the mask platen  104  for monitoring the intensity of the UV radiation throughout processing. Alternatively, an integrated UV radiation detection system can be included in the UV chamber  127 . A UV power detector  121  is desirable because UV lamps typically have a short lifetime.  
         [0042]     The introduction of oxygen gas into the process chamber  103  during processing will produce ozone in proportion to the amount of oxygen present. However ozone is a very strong absorber of the 172 nm wavelength so the concentration of ozone should be closely controlled so that the short wavelength, high energy radiation gets to the surface of the substrate/photo mask  107  where it facilitates the chemical activity. Accordingly, ozone detector  122  is coupled to process chamber  103  to perform such monitoring.  
         [0043]     With each new loading of a new substrate/photo mask, the precise process gas composition within the process chamber  103  must be re-established. The sub-atmospheric pressure capabilities of the present invention will provide the capability to do this rapidly to provide a system with high productivity.  
         [0044]     The substrate/photo mask support  108  is preferably adjustable in height with respect to the mask platen  104  when in the closed position to position the substrate/photo mask  107  at a pre-determined distances from the UV window  113 . Mass flow controllers for nitrogen, oxygen and an auxiliary port for future use (argon) can be provided to allow for a completely inert environment (pure nitrogen or argon environment) for surface treatment applications in addition to the ability to precisely control the oxygen composition for organic removal applications. For cleaning applications the UV source produces ozone and free radical oxygen to oxidize organic contamination on the substrate.  
         [0045]     A roughing valve  123  and a vent valve  124  ( FIG. 2 ) with a soft vent to CDA are also operably coupled to process chamber  103 . Additionally, a thermocouple vacuum gauge  125  can be provided as illustrated in  FIG. 3 .  
         [0046]     Referring now to  FIG. 5 , an embodiment of the invention is illustrated wherein a wafer processing apparatus  500  comprises a wet-cleaning chamber  502 , a UV drying chamber  504 , and a substrate transferring chamber  506  used for processing a substrate such as a wafer. More than one wet-cleaning chamber  502  and more than one UV drying chamber  504  can be included in the apparatus  500  depending throughput requirements. The apparatus  500  can include an inspection chamber  510  which may include tools (not shown) to inspect the substrates that have been processed in the apparatus  500 . The tools may include devices that inspect the wafer to see if all of the liquids are removed from the wafer.  
         [0047]     The wafer processing apparatus  500  can include a cluster including several single wafer processing chambers, for example, the two wet-cleaning chambers  502 , the two UV drying chambers  504 , and the substrate transferring chamber  506 . The apparatus  500  can also include other positioned about the robot arm assembly  509 . The illustrated apparatus  500  also includes a number of wafer cassettes  512  and  514 , each holding a plurality of wafers to be cleaned and dried.  
         [0048]     In one example, a wafer is processed first in a wet-cleaning chamber  502  for macroscopic cleaning to remove all visibly detectable residues or liquids (e.g., particles and reagents). Then, the wafer is moved to the UV drying chamber  504  to remove the liquids that are not visibly detectable but that are trapped in the voids or pores of the films formed on the wafer. The cleaning processes of the wafer in the apparatus  500  proceeds in a sequence timed to optimize the use of available space and the robot arm assembly  509 . One possible sequence for cleaning and drying wafers that has film(s) formed upon it includes: the robot arm assembly  509  take an unclean wafer from a wafer cassette  512 , install the wafer into a wet-cleaning chamber  502 , remove a clean wafer from another wet-cleaning chamber  502 , place this clean wafer into a UV drying chamber  504 , and take a dried wafer from another UV drying chamber  504  and place the dried wafer into the wafer cassette  514 . This movement from the wafer cassette  512  to one wet-cleaning chamber  502 , to a UV drying chamber  504 , and so on will optimize wafer cleaning times. Other sequence variations may be used to select an optimal wafer cleaning and drying cycle time.  
         [0049]     While the invention has been described and illustrated in sufficient detail that those skilled in this art can readily make and use it, various alternatives, modifications, and improvements should become readily apparent without departing from the spirit and scope of the invention.