Abstract:
A method and apparatus for reduction and prevention of residue formation and removal of residues formed in an immersion lithography tool. The apparatus including incorporation of a cleaning mechanism within the immersion head of an immersion lithographic system or including a cleaning mechanism in a cleaning station of an immersion lithographic system.

Description:
BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0001]     The present invention relates to the field of semiconductor manufacturing processes; more specifically, it relates to method and apparatus for cleaning a semiconductor substrate in an immersion lithography system.  
         [0002]     Immersion lithography is emerging as a technology for extending optical photolithography to smaller image sizes than currently printable with conventional optical lithography tools. Immersion lithography tools place an immersion liquid in direct contact with the photoresist layer to be exposed and the final image-focusing lens of the immersion lithography system is either immersed in the liquid or placed in very close proximity to the immersion liquid. The immersion liquid allows an increase of the capture angle of the Raleigh criterion of resolution (thus increasing resolution) by application of Snell&#39;s law of refraction and thus smaller images can be formed than could otherwise be possible in lithography systems with only air between the photoresist layer and the final image-focusing lens.  
         [0003]     However, a significant problem with immersion lithography is the creation of contaminant residues on the photoresist surface and on the surface of the semiconductor substrate in regions where the photoresist is subsequently developed away. These residues can cause physical yield and reliability defects as well as degradation of electrical parameters of the integrated circuit devices being fabricated.  
         [0004]     Therefore, there is a need for a method and apparatus for preventing or reducing formation of contaminant residues and for removing contaminant residues formed during immersion lithography.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention addresses the problem of reduction or prevention of contaminant residue formation and removal of contaminant residues formed in an immersion lithography tool by in situ cleaning of the semiconductor substrate by incorporation of a cleaning mechanism within the immersion head of an immersion lithographic system or by incorporation of a cleaning mechanism in a cleaning station of an immersion lithographic system.  
         [0006]     A first aspect of the present invention is an apparatus, comprising: a chamber having a top and a sidewall and a bottom opening, the top transparent to selected wavelengths of light; an inlet and an outlet in the sidewall of the chamber; a plate extending outward from a bottom edge of the chamber; a set of concentric grooves formed in a bottom surface of the plate, the grooves centered about the chamber, means for applying a vacuum to a first groove and a fourth groove of the set of grooves, the first groove nearest the bottom opening of the chamber; means for supplying an inert gas or the inert gas and a solvent vapor mixture to a second groove and a fifth groove of the set of grooves, the second groove between the first and the fourth groove and the fifth groove outside of the fourth groove; and means for supplying a cleaning fluid to a third groove of the set of grooves, the third groove between the second groove and the fourth groove.  
         [0007]     A second aspect of the present invention is an apparatus, comprising: a circular plate and a opening formed in bottom surface of the plate; a set of concentric grooves formed in the bottom surface of the plate, the grooves centered about the opening; means for supplying a cleaning fluid to the opening; means for applying a vacuum to a first groove of the set of grooves, the first groove closest to the opening; and means for supplying an inert gas or the inert gas and a solvent vapor mixture to a second groove of the set of grooves, the second groove outside of the first groove.  
         [0008]     A third aspect of the present invention is an immersion exposure system for exposing a photoresist layer on a top surface of a wafer to light, comprising: a light source, one or more focusing lenses, a mask holder, a slit, an immersion head and a wafer stage, the light source, the one or more focusing lenses, the mask holder, the slit, and the immersion head aligned to an optical axis, the wafer stage moveable in two different orthogonal directions, each the orthogonal direction orthogonal to the optical axis, the mask holder and the slit moveable in one of the two orthogonal directions, the immersion head having a chamber having a top, a sidewall and a bottom opening, the top transparent to selected wavelengths of light; means for filling the chamber of the immersion head with an immersion liquid, the chamber aligned to the optical axis; and means for cleaning a top surface of the photoresist layer.  
         [0009]     A fourth aspect of the present invention is a method for exposing a photoresist layer on a top surface of a wafer to light, comprising: (a) placing a portion of a top surface of the photoresist layer in contact with an immersion liquid and forming regions of exposed and unexposed photoresist in the portion of the photoresist layer; after (a), (b) removing any immersion liquid remaining on the top surface of the portion of the photoresist layer; after (b), (c) rinsing the top surface of the portion of the photoresist layer with an inert gas or the inert gas and a solvent vapor mixture; after (c), (d) cleaning the top surface of the portion of the photoresist layer with a cleaning fluid; after (d), (e) removing the cleaning fluid; and after (e), (f) rinsing the top surface of the portion of the photoresist layer with an additional inert gas or the additional inert gas and an additional solvent vapor mixture. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]     The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a pictorial representation of an exemplary immersion lithography system according to a first embodiment of the present invention;  
         [0012]      FIG. 2  is a top view of a first immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention;  
         [0013]      FIG. 3  is a cross-sectional view through line  3 - 3  of  FIG. 2 ;  
         [0014]      FIG. 4  is a cross-sectional view of a second immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention;  
         [0015]      FIG. 5  is a cross-sectional view of a third immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention;  
         [0016]      FIG. 6  is cross-sectional view of a fourth immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention;  
         [0017]      FIG. 7  is a partial cross-sectional view of a fifth immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention;  
         [0018]      FIGS. 8 and 9  are pictorial representations of an immersion lithography system according to a second embodiment of the present invent;  
         [0019]      FIG. 10  is a cross-sectional view of a first immersion head for use in the immersion lithography system of  FIGS. 8 and 9  according to the present invention;  
         [0020]      FIG. 111  is a flowchart of the method of cleaning a semiconductor substrate in a immersion lithography system according to the first embodiment of the present invention; and  
         [0021]      FIG. 12  is a flowchart of the method of cleaning a semiconductor substrate in an immersion lithography system according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     For the purpose of the present invention the term wafer will be used to indicate any semiconductor substrate, examples of which include but are not limited to bulk silicon substrates, silicon-on-insulator (SOI) substrates, silicon-germanium substrates, sapphire substrates, and other semiconductor substrates used for the manufacturing of integrated circuits.  
         [0023]      FIG. 1  is a pictorial representation of an exemplary immersion lithography system according to a first embodiment of the present invention. In  FIG. 1 , an immersion lithography system  100  includes a controlled environment chamber  105  and a controller  110 . Contained within controlled environment chamber  105  is a focusing mirror  115 , a light source  120 , a first focusing lens (or set of lenses)  125 , a mask  130 , an exposure slit  135 , a second focusing lens (or set of lenses)  140 , a final focusing lens  145 , an immersion head  150  and a wafer chuck  155 . Immersion head  150  includes a transparent window  160 , a central chamber portion  165 , a surrounding plate portion  170 , an immersion liquid inlet  175 A and an immersion liquid outlet  175 B. An immersion liquid  185  fills central chamber portion  165  and contacts a photoresist layer  186  on a top surface  188  of a wafer  190 . Plate portion  170  is positioned close enough to photoresist layer  186  to form a meniscus  192  under plate portion  170 . Window  160  must be transparent to the wavelength of light selected to expose photoresist layer  186 . In one example window  160  is transparent to a wavelength of about 190 nm or less.  
         [0024]     Focusing mirror  115 , light source  120 , first focusing lens  125 , a mask  130 , exposure slit  135 , second focusing lens  140 , final focusing lens  145 , immersion head  150  are all aligned along an optical axis  200  which also defines a Z direction. An X direction is defined as a direction orthogonal to the Z direction and in the plane of the drawing. A Y direction is defined as a direction orthogonal to both the X and Z directions. Wafer chuck  155  may be moved in the X and Y directions under the direction of controller  110  to allow formation of regions of exposed and unexposed photoresist in photoresist layer  186 . As XY-stage moves, new portions of photoresist layer  186  are brought into contact with immersion liquid  185  and previously immersed portions of the photoresist layer are removed from contact with the immersion liquid. Mask  130  and slit  135  may be moved in the Y direction under the control of controller  110  to scan the image (not shown) on mask  130  onto photoresist layer  186 . In one example, the image on mask  130  is a 1× to a 10× magnification version of the image to be printed and includes one or multiple integrated circuit chip images.  
         [0025]     When exposure is complete, wafer  190  must be removed from controlled environment chamber  105  without spilling immersion fluid  185 . To this end, controlled environment chamber  105  also includes a cover plate  195  that may be moved to first abut with wafer chuck  155  and then move with the wafer chuck as the wafer chuck is moved out of position from under immersion head  150 , the cover plate replacing the wafer chuck under immersion head  150 .  
         [0026]      FIG. 2  is a top view of a first immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention. In  FIG. 2 , plate portion  170  of immersion head  150  contains concentric circular grooves  210 ,  215 ,  220 ,  225  and  230  formed into a bottom surface of the plate portion. Each circular groove is open to multiple inlets or outlets evenly positioned along the groove. Groove  210  is connected to outlets  235 . Groove  215  is connected to inlets  240 . Groove  220  is connected to inlets  245 . Groove  225  is connected to outlets  250 . Groove  230  is connected to inlets  255 .  
         [0027]      FIG. 3  is a cross-sectional view through line  3 - 3  of  FIG. 2 . In  FIG. 3 , window  160 , sidewall  260  of chamber portion  165  of immersion head  150  and photoresist layer  186  define an immersion chamber  265  having a height H 1  in which the bulk of immersion liquid  185  is contained. Plate portion  170  of immersion head  186  is positioned a height H 2  above photoresist layer  186 . In one example H 1  is about 1 to about 5 mm. In one example H 2  is about 5 to about 100 microns. A small portion of immersion fluid  185  is contained in meniscus  192  between plate portion  170 , photoresist layer  186  and groove  210 .  
         [0028]     Groove  210  is the innermost groove of grooves  210 ,  215 ,  220 ,  225  and  230  relative to chamber portion  165  and outlets  235  are connected to a vacuum source. Groove  215  is positioned outside of groove  210  relative to chamber portion  165  and inlets  240  supply, to groove  215 , an inert gas such as nitrogen or an inert gas/solvent vapor mixture such as a nitrogen and methanol vapor mixture, a nitrogen ethanol vapor mixture or a nitrogen and propanol or isopropanol vapor mixture which is dispersed on photoresist layer  186 . Other inert gases may be substituted for nitrogen and other organic solvents may be substituted for methanol, ethanol and propanol or isopropanol. Groove  210  collects any immersion liquid  185  leaking past meniscus  192  or left on photoresist layer  186  as well as the inert gases or inert gases/solvent vapor mixtures dispersed on photoresist layer  186  from groove  220 .  
         [0029]     Groove  220  is positioned outside of groove  215  relative to chamber portion  165  and inlets  245  supply a cleaning fluid to groove  225  that then is dispersed onto photoresist layer  186 . Thus groove  220  may be considered a “cleaning” groove. The cleaning fluid may be selected based on the composition of immersion liquid  185  and photoresist layer  186 . In a first example, if immersion liquid  185  is water or a water based material, then the cleaning fluid may comprise, a polar solvent, a chelating agent, a hydroxylamine, an alkanolamine and combinations thereof. Examples of chelating agents include, but are not limited to organic acids, thiophenol, ethylene diamine teracarboxylic acid, ethylene diamine tetra acetic acid, hydroxybenzene and derivatives thereof. Examples of polar solvents include but are not limited to water, alcohols, glycols and glycol ethers.  
         [0030]     In a second example, if immersion fluid  185  is a glycerol, then the cleaning fluid may comprise an alcohol. Examples of alcohols include but are not limited to methanol, ethanol, propanol or isopropanol.  
         [0031]     In a third example, if immersion fluid  185  is oil based, then the cleaning fluid may comprise a non-polar solvent. Examples of non-polar solvents include but are not limited to alkanes, cyclic alkanes and alkenes, ketones, and chlorinated solvents.  
         [0032]     Groove  225  is positioned outside of groove  220  relative to chamber portion  165  and outlets  250  are connected to a vacuum source. Groove  230  is positioned outside of groove  225  relative to chamber portion  165  and inlets  255  supply, to groove  230 , an inert gas such as nitrogen or an inert gas/solvent vapor mixture such as a nitrogen and methanol vapor mixture, a nitrogen ethanol vapor mixture or a nitrogen and propanol or isopropanol vapor mixture which contacts photoresist layer  186 . Other inert gases may be substituted for nitrogen and other organic solvents may be substituted for methanol, ethanol propanol and isopropanol. Groove  225  collects cleaning fluid dispersed onto photoresist layer  186  from groove  220  as well as the inert gases or inert gases/solvent vapor mixtures dispersed on photoresist layer  186  from groove  230 .  
         [0033]     As wafer  190  is moved under immersion head  150  during exposure, immersion fluid  185  is constantly circulated through immersion chamber  265  from inlet  175 A to outlet  175 B. Simultaneously inert gases or inert gas/solvent vapor mixtures are supplied by inlets  240  and  255  to grooves  215  and  225  respectively and dispersed on photoresist layer  186 , cleaning fluid is supplied to groove  220  by inlets  245  dispersed on photoresist layer  186  and vacuum is applied to grooves  210  and  225  by outlets  235  and  250  respectively to remove cleaning fluid and inert gases or inert gases and solvent vapor mixtures. Thus fresh cleaning fluid and inert gases or inert gas/solvent vapor mixtures are constantly being applied to and removed from photoresist layer  186  before and after immersion and exposure of the photoresist layer. The photoresist surface is thus cleaned of any contaminants attaching to it from the immersion fluid and the contaminants are removed in a very short period of time after exposure to immersion fluid. Additionally, by cleaning the surface of photoresist later  186  before the surface come into contact with immersion fluid  185 , potential contamination of the immersion fluid is reduced or eliminated.  
         [0034]     Temperature control in an immersion lithography system is important. Therefore, the ambient atmosphere of controlled environment chamber  105 , immersion fluid  185 , all inert gases or inert gas/solvent vapor mixtures and all cleaning fluids supplied to grooves  210 ,  215 ,  225  and  230  in plate portion  170  of immersion head  150  are temperature controlled. In one example, the ambient atmosphere of controlled environment chamber  105 , immersion fluid  185 , all inert gases or inert gas/solvent vapor mixtures are controlled to room temperature (about 18° C. to about 24° C.) plus or minus about 0.1° C. by any number of means well known in the art. Additionally the humidity of controlled environment chamber  105  may be controlled to about 40% relative humidity or less. And all non-aqueous inert gas/solvent mixtures and cleaning fluids may be selected or treated to contain less than about 1% water by weight.  
         [0035]      FIG. 4  is a cross-sectional view of a second immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention. In  FIG. 4 , an immersion head  150 A is similar to immersion head  150  of  FIGS. 2 and 3  except that additional grooves  270 ,  275  and  280  and corresponding sets of inlets  285 , outlets  290  and inlets  295  are added to plate portion  170 .  
         [0036]     Groove  270  is positioned outside of groove  230  relative to chamber portion  165  and inlets  285  supply a second cleaning fluid to groove  270  that is dispersed on photoresist layer  186 . Thus groove  270  may be considered a “cleaning” groove. The cleaning fluid may be selected based on the composition of immersion liquid  185  and the first cleaning fluid being supplied to groove  220  by inlets  245 . The second cleaning fluid may comprise any of the cleaning fluids described supra in reference to groove  220  or may comprise any of the inert gas or inert gas/solvent vapor mixtures described supra in reference to grooves  215  and  230 . Groove  275  is positioned outside of groove  270  relative to chamber portion  165  and outlets  290  are connected to a vacuum source. Groove  280  is positioned outside of groove  275  relative to chamber portion  165  and inlets  295  supply any of the inert gases or inert gases/solvent vapor mixtures described supra.  
         [0037]      FIG. 5  is a cross-sectional view of a third immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention. In  FIG. 5 , an immersion head  150 B is similar to immersion head  150 A of  FIG. 4  except that grooves  230  and  275  and corresponding inlets  255  and outlets  290  are eliminated. This embodiment of the present invention is useful when the first and second cleaning fluids supplied by inlets  245  and  285  do not form any harmful reaction products and can both be allowed to be captured in groove  225  and removed through outlets  250 .  
         [0038]     In a first mode of operation, cleaning fluid is supplied to groove  220  for immersion heads  150  (see  FIG. 3 ), immersion head  150 A (see  FIG. 4 ) and immersion head  150 B (see  FIG. 5 ) and to groove  270  for immersion heads  150 A and  150 B at all times during exposure of photoresist layer  186 . In a second mode of operation, cleaning fluid is supplied to groove  220  for immersion heads  150  (see  FIG. 3 ), immersion head  150 A (see  FIG. 4 ) and immersion head  150 B (see  FIG. 5 ) and to groove  270  for immersion heads  150 A and  150 B only when wafer  190  is moving relative to immersion head  150 ,  150 A or  150 B as the case may be.  
         [0039]      FIG. 6  is cross-sectional view of a fourth immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention. In  FIG. 6 , an immersion head  150 C is similar to immersion head  150  of  FIGS. 2 and 3  except a set of ultrasonic generators  300  are positioned between grooves  220  and  225 . Radio frequency (RF) power is supplied to each ultrasonic generator  300  by RF cables  305 . Cleaning fluid dispersed from groove  220  onto photoresist layer  186  passes under ultrasonic generators  300  before being captured and removed by grooves  225 . The ultrasonic energy supplied by ultrasonic generators aids in removing contaminants from photoresist layer  186 . In a third mode of operation, ultrasonic generators are powered whenever cleaning fluid is supplied to groove  220 . In a fourth mode of operation, ultrasonic energy is only supplied when cleaning fluid is supplied to groove  220  and wafer  190  is moving relative to immersion head  150 C. In a fifth mode of operation ultrasonic generators  300  are not used.  
         [0040]      FIG. 7  is a partial cross-sectional view of a sixth immersion head for use in the immersion lithography system of  FIG. 1  according to the present invention. In  FIG. 7 , an immersion head  150 D is similar to immersion head  150 C of  FIG. 6  except a second set of ultrasonic generators  310  are positioned between grooves  270  and  275 . RF power is supplied to each ultrasonic generator  310  by RF cables  315 . Cleaning fluid dispersed from groove  270  onto photoresist layer  186  passes under ultrasonic generators  310  before being captured and removed by grooves  275 . The ultrasonic energy supplied by ultrasonic generators aids in removing contaminants from photoresist layer  186 . In a sixth mode of operation, ultrasonic generators are powered whenever cleaning fluid is supplied to groove  270 . In a seventh mode of operation, ultrasonic energy is only supplied when cleaning fluid is supplied to groove  270  and wafer  190  is moving relative to immersion head  150 D. In an eighth mode of operation ultrasonic generators  310  are not used.  
         [0041]     In  FIGS. 6 and 7 , ultrasonic generators  300  and  310  are shown imbedded in plate  170 . Ultrasonic generators  300  and  310  may be placed in slots formed in the bottom surface of plate  170 , in slots formed in a top surface of plate  170 , or simply positioned on top surface  170 .  
         [0042]     Any combination of mode  1  or  2 , and/or mode  3 ,  4  or  5 , and/or mode  6 ,  7  or  8  may be employed in the operation of an immersion head according to the present invention, provided that the mode(s) selected is supported by the physical immersion head fitted to the immersion lithography system.  
         [0043]     Returning to  FIG. 5 , ultrasonic generators (not shown) can be added to immersion head  150 B between grooves  220  and  225 , between grooves  270  and  280  or between both grooves  220  and  225  and between grooves  270  and  280 .  
         [0044]      FIGS. 8 and 9  are pictorial representations of an immersion lithography system according to a second embodiment of the present invention. In  FIG. 8 , a photolithography exposure tool  350  includes a load/unload station  355 , a wafer transfer station  360 , an immersion lithography station  365  and a cleaning station  370 . Immersion lithography station  365  includes an immersion lithography system  100 A. Immersion lithography system  100 A is similar to immersion lithography system  100  of  FIG. 1  described supra, except that the immersion head of immersion lithography system  100 A is a conventional immersion head. Alternatively, the immersion head of immersion lithography system  100 A may be an immersion head according to the present invention. Clean station  370 , includes a cleaning head  400  illustrated in  FIG. 10  and described infra. In  FIG. 9 , a photolithography exposure tool  380  includes a load/unload station  385 , a cleaning station  390  and an immersion lithography station  395 . Immersion lithography station  395  includes immersion lithography system  100 A.  
         [0045]      FIG. 10  is a cross-sectional view of a first immersion head for use in the immersion lithography system of  FIGS. 8 and 9  according to the present invention. In  FIG. 10 , a cleaning head  400  contains no immersion chamber but includes a circular plate  405  symmetrical about a longitudinal axis  407  and having a central opening  410  aligned with axis  407  and containing concentric circular grooves  415  and  420  and optional grooves  425 ,  430  and  435  formed into a bottom surface of the plate. Each circular groove is open to multiple inlets or outlets evenly positioned along the groove. Groove  415  is connected to outlets  445 . Groove  420  is connected to inlets  450 . Groove  425  is connected to inlets  455 . Groove  430  is connected to outlets  460 . Groove  435  is optional. A set of ultrasonic generators  475  are positioned in plate  405  between central opening  410  and groove  415 . RF power is supplied to each ultrasonic generator  475  by RF cables  480 . A second optional set of ultrasonic generators  485  are positioned in plate  405  between groove  425  and groove  430 . RF power is supplied to each ultrasonic generator  485  by RF cables  490 .  
         [0046]     Central opening  410  is supplied with a first cleaning fluid by inlet  470 . Thus central opening  410  may be considered a “cleaning” opening. In a first example, first cleaning fluid comprises a polar solvent, a chelating agent, a hydroxylamine, an alkanolamine and combinations thereof. Examples of chelating agents include, but are not limited to ethylene diamine, ethylene diamine tetra-acetate (EDTA), ethylene glycol-bis-(2-aminoethyl)-N,N,N′N′-tetra-acetate (EGTA), tris-carboxymethylamine, nitrilo-acetic acid, nitrilo-acetate, citrates, tartrates, triethanol-amine, salicylic acid, dimercaptopropanol, phosphates, polysaccharides, and carbohydrates. Examples of polar solvents include but are not limited to water, alcohols, glycols and glycol ethers. In a second example, first cleaning fluid comprises an alcohol. Examples of alcohols include but are not limited to methanol, ethanol, propanol and isopropanol. In a third example, first cleaning fluid comprises a non-polar solvent. Examples of non-polar solvents include but are not limited to non-polar solvents such as alkanes, cyclic alkanes and alkenes, ketones, and chlorinated solvents.  
         [0047]     Groove  415  is the innermost groove of grooves  415 ,  420 ,  425 ,  430 , and  435  relative to central opening  410  and outlets  445  are connected to a vacuum source. Cleaning fluid dispersed from central opening  410  onto photoresist layer  186  passes under ultrasonic generators  475  before being captured and removed by grooves  415 . Groove  420  is positioned outside of groove  415  relative to central opening  410  and inlets  450  supply, to groove  420 , an inert gas or inert gas/solvent vapor mixture such as those described supra which is dispersed on photoresist layer  186 .  
         [0048]     Groove  425  is positioned outside of groove  420  relative to central opening  410  and inlets  455  supply a second cleaning fluid to groove  425  that is dispersed on photoresist layer  186 . Thus groove  425  may be considered a “cleaning” groove. In one example, the second cleaning fluid may comprise any of the cleaning fluids described supra or may comprise any of the inert gas or inert gas/solvent vapor mixtures described supra. Groove  430  is positioned outside of grooves  425  relative to central opening  410  and outlets  460  are connected to a vacuum source. Cleaning fluid dispersed from groove  425  onto photoresist layer  186  passes under ultrasonic generators  485  before be captured and removed by grooves  430 . Groove  435  is positioned outside of groove  430  relative to central opening  410  and inlets  465  supply, to groove  430 , an inert gas or insert gas/solvent vapor mixture such as those described supra which is dispersed on photoresist layer  186 .  
         [0049]     Ultrasonic generators  475  and  485  are optional, and one or both sets of ultrasonic generators are not present in alternative cleaning heads according to the present invention. Similarly grooves  425 ,  430  and  435  and inlets  455  and  465  and outlets  460  are not present in alternative cleaning heads according to the present invention.  
         [0050]     In a first mode of operation, ultrasonic generators  475  and  485  are powered whenever cleaning fluid is supplied to central opening  410  or groove  420  respectively. In a second mode of operation, ultrasonic energy is only supplied when cleaning fluid is supplied to central opening  410  or groove  420  respectively and wafer  190  is moving relative to cleaning head  400 . In a third mode of operation ultrasonic generators  475  are not used. In a fourth mode of operation ultrasonic generators  485  are not used. In a fifth mode of operation ultrasonic generators  475  and  485  are not used.  
         [0051]      FIG. 11  is a flowchart of the method of cleaning a semiconductor substrate in an immersion lithography system according to the first embodiment of the present invention. In step  500 , inlet inert gas or inert gas/solvent vapor mixture is turned on to the immersion head. In step  505 , outlet vacuum is turned on to the immersion head. In step  510 , immersion fluid is turned on to the immersion head. In step  515 , a photoresist-coated wafer is loaded under the immersion head. In step  520 , the operational mode(s) is selected and the cleaning fluid(s) and ultrasonic generator(s) turned on based on the selected mode and physical capability of the immersion head as described supra for the first embodiment of the present invention. In step  525 , the wafer is moved under the immersion head and the photoresist layer exposed while cleaning according to the mode(s) selected is performed. In step  530 , the cleaning fluid(s) is turned off and in step  535  the wafer is unloaded from under the immersion head. Steps  515  through  535  are repeated for each wafer to be exposed.  
         [0052]      FIG. 12  is a flowchart of the method of cleaning a semiconductor substrate in an immersion lithography system according to the second embodiment of the present invention. The steps listed below may be performed in the following sequences: 1) steps  540 ,  545 ,  550 ,  555 ,  560 ,  565 ,  570 ,  575  and  580  (START 1 to END 2); or 2) steps  540 ,  545 ,  550 ,  555 ,  560  and  565  (START 1 to END 1); or 3)  555 ,  560 ,  565 ,  570 ,  575  and  580  (START 2 to END 2). In other words, cleaning may be performed before exposure, after exposure, or both before and after exposure.  
         [0053]     In step  540 , the wafer is loaded into the cleaning station and positioned under the cleaning head. In step  545 , the operational mode(s) is selected and the cleaning fluid(s) and ultrasonic generator(s) turned on based on the selected mode and physical capability of the cleaning head as described supra for the second embodiment of the present invention. In step  550 , the cleaning fluid(s) is turned off and the wafer is unloaded from under the cleaning head.  
         [0054]     In step  555 , the photoresist-coated wafer is moved (or loaded if steps  540 ,  545  and  550  were not performed) under the immersion head. In step  560 , the photoresist layer on the wafer is exposed. In step  565 , the wafer is unloaded from the exposure station.  
         [0055]     In step  570 , the exposed wafer is moved to the cleaning station and positioned under the cleaning head (or moved out of the tool if steps  570 ,  575  and  580  are not to be performed). In step  575 , the operational mode(s) is selected and the cleaning fluid(s) and ultrasonic generator(s) turned on based on the selected mode and physical capability of the cleaning head as described supra for the second embodiment of the present invention. In step  580 , the cleaning fluid(s) is turned off and the wafer is unloaded from the cleaning station.  
         [0056]     In the first embodiment of the present invention, when two cleaning grooves are supplied, photoresist developer may be supplied to the innermost of the two “cleaning” grooves instead of a cleaning fluid in order to develop the latent image formed in the photoresist layer by the exposure process and a rinse solvent may be supplied to the outermost of the two “cleaning” grooves to rinse away the developer and dissolved photoresist.  
         [0057]     In the second embodiment of the present invention, when both a central opening and a cleaning groove is supplied, photoresist developer may be supplied to the central opening instead of a cleaning fluid in order to develop the latent image formed in the photoresist layer by the exposure process and a rinse solvent may be supplied the “cleaning” groove to rinse away the developer and dissolved photoresist.  
         [0058]     Thus, the present invention provides a method and apparatus for preventing or reducing formation of contaminant residues and for removing contaminant residues formed during immersion lithography.  
         [0059]     The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. For example, while the wafers described in the present invention are circular discs, the present invention is applicable to wafers having other geometric shapes such as squares and rectangles. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.