Abstract:
An excimer or molecular fluorine gas discharge laser which may comprise a pair of electrodes extending longitudinally across a lasing chamber forming a discharge region, and method of operating same, is disclosed which may comprise a fan providing sufficient gas movement to allow for arc-free laser operation at a selected laser output light pulse repetition rate; a flow guiding mechanism extending longitudinally across the lasing chamber along the length of the discharge region configured to optimize the fan power consumption at a selected fan speed, e.g., that is greater than an arc free fan speed; and a flow speed increasing mechanism selectively positioned along the length of the flow guiding mechanism selectively increasing the lasing gas flow rate in the vicinity of the flow increasing mechanism to thereby enable running at the selected fan speed at a reduced power consumption level in the fan.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation in part of co-pending U.S. application Ser. No. 11/095,976, entitled 6 KHZ AND ABOVE GAS DISCHARGE LASER SYSTEM, filed on Mar. 31, 2005, Attorney Docket No. 2004-0010-01, the disclosure of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to gas discharge excimer or fluorine laser system gas circulation flow.  
       BACKGROUND OF THE INVENTION  
       [0003]     In excimer or molecular fluorine gas discharge lasers lasing occurs in a lasing gas medium created by an electrical discharge between electrodes in a chamber containing the lasing gas mixture, e.g., for ArF, KrF, XeCl, XeF, F 2  or the like gas discharge lasers. Typically the lasing gas mixture is circulated by a circulation fan, e.g., a squirrel-cage cross-flow fan, such as described in the above referenced co-pending application Ser. No. 11/095,976. This can provide sufficient flow in the region between the electrodes, which essentially extend across most of the length of the chamber in the longitudinal axis of the electrodes, to both replace the spent gas mixture between the electrodes between successive electrical discharges and move the spent gas sufficiently far from the region of the next successive discharge between the electrodes so that arcing does not occur, e.g., through ions still remaining in the spent gas.  
         [0004]     Depending on the composition of the gas a certain fan or blower speed is needed to accomplish this and is referred to by applicant as arc-free blower speed (“AFBS”) or arc-free fan speed (“AFFS”), hereinafter AFFS. As the pulse repetition rates of the types of laser mentioned above have steadily increased, e.g., up to 4 kHz it has become increasingly more difficult to attain and maintain AFFS with given size motors capable of operation at a selected RPM and torque within an allowed power consumption. Applicant&#39;s assignee has in the past developed a variety of fan configurations, and flow path improvements to address the need to add more RPM and/or torque to attain sufficient gas movement due to the fan operation to achieve an AFFS that is acceptable in terms of, e.g., fan power consumption. This is becoming even more critical a design issue as the pulse repetition rates climb by 50% to 6 kHz operation.  
         [0005]     The present application relates to further such improvements.  
       SUMMARY OF THE INVENTION  
       [0006]     An excimer or molecular fluorine gas discharge laser which may comprise a pair of electrodes extending longitudinally across a lasing chamber forming a discharge region, and method of operating same, is disclosed which may comprise a fan providing sufficient gas movement to allow for arc-free laser operation at a selected laser output light pulse repetition rate; a flow guiding mechanism extending longitudinally across the lasing chamber along the length of the discharge region configured to optimize the fan power consumption at a selected fan speed, e.g., that is greater than an AFFS; and a flow speed increasing mechanism selectively positioned along the length of the flow guiding mechanism selectively increasing the lasing gas flow rate in the vicinity of the flow increasing mechanism to thereby enable running at the selected fan speed, e.g., an arc free fan speed, at a reduced power consumption level in the fan. The method and apparatus may comprise the flow speed increasing mechanism being selectively positioned in a plurality of discrete positions along the length of the flow guiding mechanism, which may comprise the two ends of the flow guiding mechanism. The flow guiding mechanism may comprise an electrode support optimizing the fan power consumption at a selected fan speed by being formed to have a plurality of flow slots separated by respective support member; and the flow speed increasing mechanism may comprise the absence of a slot at a selected position along the length of the flow guiding mechanism. The electrode support may comprise an anode support bar, which may comprise a flue comprising a pocket formed along the longitudinal extent of the anode support bar and/or a pocket formed in the vicinity of the flow speed increasing mechanism. The position of the flow speed increasing mechanism may be selected to reduce arcing downstream of the position of the flow speed increasing mechanism that occurs in the selected position at the selected fan speed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  shows a perspective orthogonal view of an anode support bar illustrating aspects of an embodiment of the present invention;  
         [0008]      FIG. 2  shows an opposite perspective orthogonal view of the anode support bar of  FIG. 1 .  
         [0009]      FIG. 3  shows a cross-sectional view along lined  3 - 3  in  FIG. 2 ; and  
         [0010]      FIG. 4  shows a cross-sectional view along lines  4 - 4  in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0011]     Applicant has examined the role of end effects in arc free fan speed (“AFFS”) variability, and determined that there is a relatively small effect that flow shaping elements have on the flow speed near the chamber walls, i.e., at either end of the anode support bar holding the anode in typical laser chambers, e.g., of the kind contained in applicant&#39;s assignees 6XXX, 7XXX and XLA-XXX series laser systems currently on the market. Applicant has also been made aware of the apparent relatively large effect that filling in the ends of the MI had on the AFFS. Considering end effects from different anode support bar geometries, applicant concluded that the anode support bar also had a large effect on end flow. Applicant then concluded that one could change the geometry of the anode support bar only at the ends of the chamber and improve flow in that region, while maintaining other effects of, e.g., flow shaping elements. This can have the effect of, e.g., maximizing or optimizing flow rate in critical areas while minimizing overall fan power consumption. Applicant has discovered that certain anode support bar geometries draw less power for a given fan speed, e.g. a pocketed anode support bar, e.g., as disclosed in the above referenced co-pending &#39;976 application. Applicant also has found that, such anode support bars also deliver slightly lower flow speeds. Therefore, according to aspects of an embodiment of the present invention, applicant proposes to provide for changes in the anode support bar geometry over the length of the chamber, such that flow speed might be tuned to minimize downstream arcing in critical areas, such as at the ends of the electrodes where, e.g., the flow speed has been seen to drop.  
         [0012]     The AFFS being defined as the fan speed/blower speed at which unwanted arcing will occur within the chamber, e.g., through the ions in the spent lasing gas medium moving from the discharge region between the electrodes, the blower speed must be at least greater than the AFFS. With some built in margin for insuring arcing does not occur, the fan speed should be selected to be above the AFFS by such margin, e.g., at least 10% margin. By selecting the fan speed as this AFFS plus an appropriate margin for a slotted only anode support bar, according to aspects of an embodiment of the present invention applicants then propose to configure the anode support bar as discussed herein to then enable running the fan/blower at the selected speed, but at a power level to the fan/blower that is reduced according to the configuration of the anode support bar.  
         [0013]     Turning now to  FIGS. 1-4  there is shown an electrode support structure  10  according to aspects of an embodiment of the present invention. The support structure  10  may serve as an anode support bar in a gas discharge laser of the type referenced above and may serve to support an anode electrode (not shown) and adjacent flow shaping fairings (not shown) and also to ground the electrode the laser chamber, e.g., by being constructed of a conducting material and being connected to the chamber as further described below.  
         [0014]     The electrode support structure  10  may comprise an upper support surface  12  through which may be formed electrode connecting pin holes  14 , which may serve to fasten the, e.g., anode electrode to the electrode support structure  10 . The electrode support structure may have formed therein a support member fairing  16  which may form a leading edge  20 . Between the electrode support structure  10  and the support member fairing  16  may be formed a plurality of flow slots  22 , which may be structurally supported by a plurality of ribs  24 .  
         [0015]     The electrode support structure may have a flue  30  at least a portion of which may extend substantially between the opposing interior side walls of the laser chamber (not shown) and thereby define a flow channel for the laser gas medium flowing around the interior of the chamber. The flue  30  may have a concave surface  32 . The electrode support member may have a first end  34  and a second end  36 . at each of the first end  34  and second end  36  there may be formed a flow cutout  40 , which together with the elimination of a slot  16  so that the electrode support member  10  is solid from the leading edge  20  to the downstream side of the electrode support member over a region substantially corresponding to the length of the cutout  40 .  
         [0016]     The electrode support structure  10  may be formed on the first end  34  and on the second end  36  with, e.g., a mounting bracket  44  and a mounting lip  46 , for attachment of the electrode support structure  10  to the laser chamber (not shown).  
         [0017]     It will be understood by those skilled in the art that AFFS may be defined as the blower speed above which arcing occurs and below which arcing does not occur as noted above, however this speed is not a precise, e.g., RPM number as, e.g., it may vary with conditions in the chamber, e.g., pulse repetition rate, operating voltage for the gas discharge between the electrodes, fluorine content in the lasing gas mixture, which varies during laser system operation, and other factors. In addition those skilled in the art may select various levels of acceptable margin for error to insure arcing does not occur. Therefore, AFFS as used in the present application and the appended claims includes the concept of a speed found acceptable to prevent arcing over whatever range of conditions may impact that speed and with whatever margin for error is found acceptable, whereby according to aspects of embodiments of the present invention, whatever this speed is selected to be the configuration of the anode support bar enables a reduction in the required power to achieve this selected speed or perhaps even various different AFFSs selected based on particular operating conditions and/or particular margins for error.  
         [0018]     While the particular aspects of embodiment(s) of the HYBRID ELECTRODE SUPPORT BAR described and illustrated in this patent application in the detail required to satisfy 35 U.S.C. §112 is fully capable of attaining any above-described purposes for, problems to be solved by or any other reasons for or objects of the aspects of an embodiment(s) above described, it is to be understood by those skilled in the art that it is the presently described aspects of the described embodiment(s) of the present invention are merely exemplary, illustrative and representative of the subject matter which is broadly contemplated by the present invention. The scope of the presently described and claimed aspects of embodiments fully encompasses other embodiments which may now be or may become obvious to those skilled in the art based on the teachings of the Specification. The scope of the present HYBRID ELECTRODE SUPPORT BAR is solely and completely limited by only the appended claims and nothing beyond the recitations of the appended claims. Reference to an element in such claims in the singular is not intended to mean nor shall it mean in interpreting such claim element “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to any of the elements of the above-described aspects of an embodiment(s) that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Any term used in the specification and/or in the claims and expressly given a meaning in the Specification and/or claims in the present application shall have that meaning, regardless of any dictionary or other commonly used meaning for such a term. It is not intended or necessary for a device or method discussed in the Specification as any aspect of an embodiment to address each and every problem sought to be solved by the aspects of embodiments disclosed in this application, for it to be encompassed by the present claims. No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element in the appended claims is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”.  
         [0019]     It will be understood by those skilled in the art that the aspects of embodiments of the present invention disclosed above are intended to be preferred embodiments only and not to limit the disclosure of the present invention(s) in any way and particularly not to a specific preferred embodiment alone. Many changes and modification can be made to the disclosed aspects of embodiments of the disclosed invention(s) that will be understood and appreciated by those skilled in the art. The appended claims are intended in scope and meaning to cover not only the disclosed aspects of embodiments of the present invention(s) but also such equivalents and other modifications and changes that would be apparent to those skilled in the art. In additions to changes and modifications to the disclosed and claimed aspects of embodiments of the present invention(s) noted above others could be implemented.