Abstract:
A support bar member for supporting an electrode member of a pulsed laser system is described. The support bar member includes an aerodynamic nose configured to reduce an aerodynamic load applied against a blower assembly of the laser system by the support bar member. The nose provides an aerodynamic cut-off region on the support bar member such that, when the blower assembly is operating, the blower assembly does not vibrate significantly.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/157,067, filed Sep. 18, 1998, pending, titled “Reliable, Modular, Production Quality Narrow-Band High Rep Rate Excimer Laser.” 
     The following applications and patent are incorporated herein by reference: Ser. No. 09/041,474, filed Mar. 11, 1998, now U.S. Pat. No. 5,991,324, titled “Reliable, Modular, Production Quality Narrow-Band KrF Excimer Laser”; Ser. No. 09/034,870, filed Mar. 4, 1998, now U.S. Pat. No. 6,005,879, titled “Pulsed Energy Control for Excimer Laser”; Ser. No. 08/995,832, filed Dec. 22, 1997, now U.S. Pat. No. 5,982,795, titled “Excimer Laser Having Pulse Power Supply with Fine Digital Regulation”; Ser. No. 08/842,305, filed Apr. 23, 1997, now U.S. Pat. No. 5,835,520, titled “Very Narrow-band KrF Laser”; and U.S. Pat. No. 5,719,896, issued Feb. 17, 1998, titled “Low Cost Corona Preionizer for Laser.” 
    
    
     FIELD OF THE INVENTION 
     This invention relates to laser systems and, more specifically, to a support bar for supporting an electrode member of the laser system. 
     BACKGROUND OF THE INVENTION 
     Pulsed laser systems, such as excimer lasers, are well known. FIG. 1 is an end cross sectional view of a laser chamber, generally illustrated as  10 , used in a conventional pulsed laser system. The laser chamber  10  comprises a pair of electrode members  12 , which include a cathode  14  and an anode  16 . The area between the cathode  14  and the anode  16  is referred to as an electrical discharge area  18 . A support bar member  20  supports the anode  16 . A heat exchanger  22 , and a blower assembly  24  are also disposed within the laser chamber  10 . As is well known by those skilled in the art, the pulsed laser system produces energy pulses from a gas mixture in the electrical discharge area  18 . The mixture of gas, which typically includes krypton and fluorine, is maintained at a high pressure (e.g., 3 atm.). The electrode members  12  ionize the gas mixture to produce a high energy discharge. 
     The blower assembly  24  plays the important role of circulating the gases in the laser chamber  10  of the pulsed laser system. The circulation of the gases has many purposes, including maintaining the temperature of the gases at the most efficient level of reaction, maximizing the life cycle of the gases, and facilitating the overall operation of the pulsed laser system. 
     The blower assembly  24  comprises a plurality of blades or vanes  26  which are driven in a clockwise direction, as indicated by arrow  28 , for circulating the gases about the laser chamber  10 . The directional flow of the gases, as indicated by arrows  30 , is through the electrical discharge area  18 , with a clockwise circulation about the heat exchanger  22 , and through the blower assembly  24 . The gases pass between the blades  26  of the blower assembly  24 , as illustrated by the arrow  30 . 
     The support bar member  20 , configured to support the anode  16 , includes a cut-off point, as indicated by numeral  21 . The cut-off point  21  is a general region on the support bar member  20 , located adjacent to the blower assembly  24 , which defines the inlet side and the outlet side of the blower assembly  24 . 
     Each time one of the blades  26  passes the cut-off point  21 , the support bar member  20  applies an aerodynamic load to the blower assembly  24 . The aerodynamic load agitates the blower assembly  24 , causing the blower assembly  24  to vibrate. As the rotational speed of the blades  26  increases, so does the aerodynamic load, and, thus, the vibration of the blower assembly  24 . The effect of the rotational speed of the blades  26 , i.e., the blower speed, on the vibration of the blower assembly  24  is illustrated in FIG.  2 . Curve A illustrates the vibration response in the range of 2500 to 4000 vibrations per minute corresponding to blower speeds of 2500 RPM to 4000 RPM. Curve B illustrates the vibrational response associated with twice the rotational speed, and curve C illustrates the vibrational response associated with 23 times the rotational speed (i.e., 23 vanes or blades  26 ). 
     Furthermore, the vibration of the blower assembly  24  is highly detrimental to our application due to the nature of beam stability as it travels through. In the past any reduction of rotating mass vibration was necessarily associated with blower speed reduction. Blower speed reduction results in gas flow reduction. Gas flow reduction disabled the function of the laser. The vibration reduces the output efficiency of the blower assembly  24  by about 10%. The vibration also increases the noise produced by the blower assembly  24 . Moreover, the vibration causes deterioration and failure of the mechanical components of the blower assembly  24 , such as the blower assembly&#39;s  24  bearing members, driver shaft, and other moving components. As a result, it would be advantageous to reduce the vibration of the blower assembly  24 . 
     SUMMARY 
     An improved laser chamber is disclosed which does not suffer from the above-described drawbacks. The laser chamber has a pair of electrode members—an anode and a cathode—defining an electrical discharge area for producing a high energy discharge. The laser chamber includes a blower assembly for the proper circulation and the efficient flow of gases during the operation of the electrode members. 
     The laser chamber further includes a support bar member for supporting one of the electrode members, e.g., the anode. The support bar member comprises an aerodynamic nose configured to reduce an aerodynamic load that is applied against the blower assembly by the support bar member when the blower assembly is rotatably driven. As a result, the blower assembly does not vibrate significantly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an end cross sectional view of a conventional laser chamber used in a pulsed laser system, including a conventional support bar member; 
     FIG. 2 is a graph illustrating the vibration of a blower assembly of the pulsed laser system versus blower speed, the vibration being caused by an aerodynamic load applied to the blower assembly by the conventional support bar member; 
     FIG. 3 is an end cross sectional view of a laser chamber used in a pulsed laser system, including the support bar member of the present invention configured to support an electrode member; 
     FIG. 4 is an exterior, elevational view of one end of the laser chamber of FIG. 3; 
     FIG. 5 is a schematic, side cross sectional view of the laser chamber of FIG. 3; 
     FIG. 6 is a partial, side cross sectional view of the laser chamber, taken in the direction of the arrows and along the plane of line  4 — 4  of FIG. 3; 
     FIGS. 7-12 are end cross sectional views of various embodiments of the support bar member of the present invention; and 
     FIG. 13 is a graph illustrating the reduced vibration of a blower assembly of the pulsed laser system versus blower speed, the vibration being caused by an aerodynamic load applied to the blower assembly by the support bar member of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring in detail now to the drawings wherein similar parts of the present invention are represented by like reference numerals, there is seen in FIGS. 3-6 a laser chamber  40 , similar to Excimer Laser Model 5000, produced by CYMER, Inc., San Diego, Calif. The laser chamber  40  is thoroughly disclosed in U.S. Pat. No. 4,959,840 to Akins et al., assigned to the assignee of the present invention, and incorporated herein by reference in its entirety as if repeated verbatim immediately hereinafter. The laser chamber  40  is formed by a pair of half-housing members, an upper housing member  42  and a lower housing member  44 , coupled together and sealed. The coupled half-housing members  42  and  44  are, in essence, interconnected walls, collectively and/or individually illustrated as  46 . The interconnected walls  46  define a laser cavity  48  which contains various components of the laser chamber  40 . The walls  46  of the laser chamber  40  can be manufactured from any suitable material that is compatible with the specific gases (e.g., fluorine and krypton) used in the laser chamber  40 , such as nickel plated aluminum, tin, monel, and gold. 
     Located within the laser cavity  48  are electrode members, generally illustrated as  50 . The electrode members  50  include a cathode  52  and an anode  54 , separated by a distance defining an electrical discharge area  56 . 
     The cathode  52  and the anode  54  can be manufactured from any suitable high purity, insulated metal capable of resisting erosion so as to avoid contaminating the gases which are introduced into the laser cavity  48 . For example, the electrode members  50  can be manufactured from brass insulated with a ceramic compound, such as alumina. 
     A support bar member  60 , made from a suitable conducting material, supports the anode  54  with threaded rods  62 . The support bar member  60  is structurally defined by a first side  64  (FIGS.  7 - 10 ), a second side  66  opposing the first side  64 , and an aerodynamic nose  68  commonly extending from the first and second sides  64 ,  66 . The nose  68  provides a means for reducing the vibration of a blower assembly  90 , the details of which will be discussed later in the application. 
     In a first embodiment, as illustrated by the end cross sectional view of FIGS. 3 and 7, the nose  68  is structurally defined by a generally convex wall  70  (FIG. 7) extending into a generally concave wall  72 . A lip  74  protrudes from the second side  66  of the support bar member  60 . The lip  74  comprises a lip wall  76  that is in common with and extending from the concave wall  72 . Illustrative dimensional specifications for the support bar member  60 , including the nose  68 , shown in FIGS. 3 and 7 are provided in Table I below: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 mm 
                 inches 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 A 1   
                 30.50 
                 1.201 
               
               
                 A 2   
                 15.90 
                 0.626 
               
               
                 A 3   
                 19.76 
                 0.778 
               
               
                 A 4   
                 24.90 
                 0.980 
               
               
                   
               
             
          
         
       
     
     In a second embodiment, as illustrated by FIG. 8, the nose  68  is structurally defined, as illustrated in the end cross sectional view, by a planar wall  78  and a lip  80  protruding from the second side  66  of the support bar member  60 . The lip  80  has a lip wall  82  that is in common with and extending from the planar wall  78 . The lip wall  82  is geometrically defined by a radius of curvature, indicated by R 1 . Illustrative dimensional specifications for the support bar member  60 , including the nose  68 , shown in FIG. 8, are provided in Table II below: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
               
                   
                 mm 
                 inches 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 B 1   
                 30.50 
                 1.201 
               
               
                 B 2   
                 15.90 
                 0.626 
               
               
                 B 3   
                 9.00 
                 0.354 
               
               
                 B 4   
                 4.50 
                 0.177 
               
               
                 B 5   
                 25.40 
                 1.000 
               
               
                 B 6   
                 35.03 
                 1.379 
               
               
                 B 7   
                 0.76 
                 0.030 
               
               
                 R 1   
                 43.43 
                 1.710 
               
               
                   
               
             
          
         
       
     
     Referring to FIG. 9 for the third embodiment, the nose  68  is structurally defined, as illustrated in the end cross sectional view, by a generally convex wall  84  having a radius of curvature R 2 . Illustrative dimensional specifications for the support bar member  60 , including the nose  68 , shown in FIG. 9, are provided in Table III below: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE III 
               
               
                   
                   
               
               
                   
                 mm 
                 inches 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 C 1   
                 30.50 
                 1.201 
               
               
                 C 2   
                 24.74 
                 0.974 
               
               
                 C 3   
                 15.90 
                 0.626 
               
               
                 C 4   
                 7.95 
                 0.313 
               
               
                 R 2   
                 9.82 
                 0.387 
               
               
                   
               
             
          
         
       
     
     The fourth embodiment is similar to the third embodiment but for the inclusion of a lip  86 . As illustrated in FIG. 10, the lip  86  protrudes from the second side  66  of the support bar member  60 . The lip  86  comprises a lip wall  88  that is in common with and extending from the convex wall  84 . The lip wall  88  is geometrically defined by a radius of curvature, as illustrated by R 3 . Illustrative dimensional specifications for the support bar member  60 , including the nose  68 , shown in FIG. 10, are provided in Table IV below: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE IV 
               
               
                   
                   
               
               
                   
                 mm 
                 inches 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 D 1   
                 30.50 
                 1.201 
               
               
                 D 2   
                 24.74 
                 0.974 
               
               
                 D 3   
                 15.90 
                 0.626 
               
               
                 D 4   
                 9.00 
                 0.354 
               
               
                 D 5   
                 19.76 
                 0.778 
               
               
                 D 6   
                 55.90 
                 2.201 
               
               
                 D 7   
                 35.03 
                 1.379 
               
               
                 D 8   
                 7.95 
                 0.313 
               
               
                 R 2   
                 9.82 
                 0.387 
               
               
                 R 3   
                 43.27 
                 1.704 
               
               
                   
               
             
          
         
       
     
     It should be understood that other structural and geometrical designs of the nose  68  can be implemented in the support bar member  60  of the present invention, examples of which are illustrated in FIGS. 11 and 12. FIG. 11 shows the nose  68  being structurally defined by a protruding wall  87  tapering into a generally concave wall  89  towards the second side  66 . FIG. 12 shows the nose  68  being structurally defined by a rounded corner  91 . 
     It should be further understood that the above-given values or dimensions are only illustrative and not limiting such that other dimensions can be used for the support bar member  60  and the nose  68  of the present invention. 
     Referring to FIG. 3, the blower assembly  90 , provides for the proper circulation and efficient flow of gases during the operation of the laser chamber  40 . The blower assembly  90  is described in application Ser. No. 09/141,068, Cymer docket number 97-0055-1, to Kyle Webb, entitled “A Blower Assembly For a Pulsed Laser System Incorporating Ceramic Bearings,” assigned to the assignee of the present invention and incorporated herein by reference in its entirety as if repeated verbatim immediately hereinafter. 
     The blower assembly  90  comprises a plurality of blades or vanes (e.g., 23 blades)  92  which are driven in a clockwise direction  94  for circulating the gases about the laser cavity  48 . The flow of the gases is illustrated by arrows  96 . 
     The nose  68  provides an enlarged, aerodynamic area on the support bar member  60  which would have otherwise defined the cut-off point  21  of FIG.  1 . The nose  68 , by including the aforementioned geometrical shapes of FIGS. 7-11, in effect, enlarges the cut-off point  21  to an aerodynamic cut-off region (i.e., a general region on the support bar member  60  which defines the inlet side and the outlet side of the blower assembly  90 ), as indicated by encircled area  100  in FIGS.  3  and  7 - 11 . The modification of the prior art cut-off point  21  (FIG. 1) to a cut-off region  100  reduces the aerodynamic load that the support bar member  60  applies to the blower assembly  90 . Accordingly, the blower assembly  90  does not vibrate significantly. 
     FIG. 13 is a graph illustrating the vibration of the blower assembly  90  when the nose  68  is employed. Curve A illustrates the magnitude of vibration of the blower assembly  90  corresponding to blower speeds of 2500 RPM to 4700 RPM. Curve B illustrates the magnitude of vibration at twice the rotational speed, and curve C illustrates the magnitude of vibration at 23 times the rotational speed(i.e., 23 blades or vanes  92 ). The maximum amount of vibration of the blower assembly  90  is about 0.14 mm/sec rms, which is 0.185 mm/sec rms less than the maximum vibration caused by the conventional support bar member  20  (see FIG. 2 for a comparison). 
     Referring again to FIG. 3, a spacer member  102  contacts the cathode  52 . The spacer member  102  is disposed adjacent to a main insulator  104 . The main insulator  104  separates and insulates high voltage connectors  106  from one another. The high voltage connectors  106  engage the spacer member  102  to introduce a high voltage to the cathode  52 . The high voltage connectors  106  extend through insulating bushings  108 , which are made from any suitable material including ceramics or plastics. 
     A high energy discharge can be produced in the electrical discharge area  56  by the application of a high voltage, e.g., 20 kilovolts, to the cathode  52 . More specifically, the application of a high voltage to the cathode  52  through the high voltage connectors  106  and the spacer member  102  produces the high energy discharge in the electrical discharge area  56 . The high energy discharge ionizes the gases, illustrated by the shaded region  110 , in the vicinity of the electrical discharge area  56  and causes these gases to react chemically. For example, the gases may include a mixture of krypton (Kr) and fluorine (F 2 ), which chemically react to produce KrF. The formation of KrF produces an energy radiation in a very narrow band of wavelengths such as in the excimer range. Referring to FIGS. 4 and 5, the energy radiation is directed to an optical element  112 A (e.g., a window) at one end and to a corresponding optical element  112 B at an opposing end. The energy radiation is reflected between the opposing optical elements  112 A and  112 B and is reinforced in each reflection. A portion of the energy radiation moving in each cycle between the opposing optical elements  112 A and  112 B passes through one of the optical elements such as the optical element  112 A. 
     Pre-ionizers, generally illustrated as  114  can be disposed in the laser cavity  48  to facilitate the ionization of the gases, the details of which are included in U.S. Pat. No. 5,337,330 to Larson, assigned to the assignee of the present invention and fully incorporated herein by reference in its entirety as if repeated verbatim immediately hereinafter. 
     The laser chamber  40 , moreover, can include a gas scoop (omitted from the Figures) for allowing a portion of the gases circulating about the laser cavity  48  to be siphoned for filtering by a filter  116 , as illustrated in FIG.  4 . The filter  116  can be an electrostatic precipitator, the details of which are described in U.S. Pat. No. 5,048,041 to Akins et al., assigned to the assignees of the present invention and fully incorporated herein by reference in its entirety as if repeated verbatim immediately hereinafter. 
     The high energy discharge produces a large amount of local heating in the gases. Accordingly, a heat exchanger  118  is disposed within the laser cavity  48  to decrease the temperature of the gases. The heat exchanger  118  is supported on the walls  46  of the laser chamber  40  by end caps, one of which is illustrated as  120  in FIG. 4. A fluid coolant is introduced through conduit  122  of the heat exchanger  118  to cool the circulating gases. 
     While particular embodiments of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications can be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall with the true spirit and scope of the this invention.