Abstract:
An assembly, including: a nozzle including a first chamber with a first orifice arranged to receive a stream of gas; a second chamber with a second orifice to emit the stream; a throat connecting the nozzle chambers; and a collector including: top and bottom walls with first and second openings; a third chamber bounded by the top and bottom walls and including a third opening connected to the second orifice to receive the stream; and a fourth opening. The first chamber tapers from the first orifice to the throat. The second chamber expands in size from the throat to the second orifice. The third chamber expands in size from the third opening to the fourth opening. The collector is arranged to: entrain, in the stream, debris entering the third chamber through first or second opening; and emit the stream, with the entrained debris, from the fourth opening.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/738,342, filed Dec. 17, 2012, which application is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to apparatus, a system and methods for separating gases and mitigating debris in a controlled pressure environment. In particular, the present disclosure relates to apparatus, system and method for generating a controlled gas stream with nozzles and passing the gas stream through a collector to entrain debris associated with generation of extreme ultra-violet light. 
       BACKGROUND 
       [0003]    Plasma sources are used to generate light, such as extreme ultra-violet (EUV) for use in semi-conductor applications, such as semi-conductor inspection systems in low pressure environments. Typically, the light is transmitted in an axial direction to, for example, a chamber including optical components for the inspection station. A by-product of the light generation is debris that can migrate into sensitive portions of the inspection system, for example, degrading light quality or contaminating optical components, adversely impacting the function and service life of the optical components and/or requiring more frequent purging of the inspection system, all of which are undesirable. 
         [0004]    S R Mohanty, T Sakamoto, Y Kobayashi, et al., disclose a gas curtain to address debris from a EUV source. The design uses an annular nozzle to create an annular curtain coaxial with the source (S R Mohanty, T Sakamoto, Y Kobayashi, et. al., “Influence of electrode separation and gas curtain on extreme ultraviolet emission of a gas jet z-pinch source”, Applied Physics Letters, 89, 041502, 2006). The method used by Mohanty et al. does not stop debris travelling in the axial direction from the source. Thus, the method of Mohanty et al. is unsuitable for controlling debris associated with the axial transmission of the EUV emission. For example, for a semi-conductor inspection system, the method of Mohanty et al. cannot prevent debris from the EUV light source from entering the chamber in an axial direction and contaminating the optical components in the chamber. 
       SUMMARY 
       [0005]    According to aspects illustrated herein, there is provided a nozzle for producing a controlled gas stream in a low pressure environment, including: a first chamber with a first orifice arranged for connection to a source of gas and to receive a stream of gas from the source; a second chamber with a second orifice arranged to emit the stream; a throat connecting the first and second chambers; and a longitudinal axis extending from the first orifice to the second orifice in a first direction. The first chamber tapers from the first orifice to the throat. The second chamber expands in size from the throat to the second orifice. 
         [0006]    According to aspects illustrated herein, there is provided a collector for entraining and ejecting debris in a gas flow for a low pressure system, including: a top wall, a bottom wall, and first and second side walls connecting the top and bottom walls; first and second openings in the top and bottom walls, respectively; and a first chamber: formed by the top wall, the bottom wall, and the first and second side walls; including a third opening arranged to receive a stream of gas and a fourth opening; and expanding in size from the first opening to the second opening. The collector includes a longitudinal axis extending in a first direction from the third opening to the fourth opening. The collector is arranged to: entrain, in the stream, debris entering the first chamber through the first or second opening; and emit the stream, with the entrained debris, from the fourth opening. 
         [0007]    According to aspects illustrated herein, there is provided an assembly for removing debris from a controlled pressure environment, including: a nozzle including a first chamber with a first orifice arranged for connection to a source of gas and to receive a stream of gas from the source a second chamber with a second orifice arranged to emit the stream; a throat connecting the first and second chambers; and a collector including top and bottom walls with first and second openings, respectively, a third chamber bounded in part by the top and bottom walls and including a third opening connected to the second orifice and arranged to receive the stream, and a fourth opening; and, a longitudinal axis passing through the first and second orifices and the third and fourth openings in a first direction. The first chamber tapers from the first orifice to the throat. The second chamber expands in size from the throat to the second orifice. The third chamber expands in size from the third opening to the fourth opening. The collector is arranged to: entrain, in the stream, debris entering the third chamber through first or second opening; and emit the stream, with the entrained debris, from the fourth opening. 
         [0008]    According to aspects illustrated herein, there is provided a method for removing debris from a controlled pressure environment, including: flowing gas, in a first direction, through a first chamber for a nozzle while simultaneously reducing, along the first direction, a first area, in second and third directions orthogonal to the first direction, of a stream of the gas in the first chamber; flowing the gas through a throat connecting the first chamber to a second chamber for the nozzle; flowing the gas, in the first direction, through the second chamber while simultaneously increasing, along the first direction, a second area, in the second and third directions, of the steam of the gas in the second chamber; flowing the gas from the second chamber into a third chamber for a collector; flowing the gas through the third chamber in the first direction, while simultaneously increasing, along the first direction, a third area, in the second and third directions, of the stream of the gas in the third chamber; entraining, in the stream of the gas, debris located in the third chamber; and emitting, in the first direction, the stream of the gas with the entrained debris from the third chamber through a first opening of the collector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: 
           [0010]      FIG. 1  is a top view of a nozzle for producing a controlled gas stream in a low pressure environment; 
           [0011]      FIG. 2  is a side view of the nozzle in  FIG. 1 ; 
           [0012]      FIG. 3  is cross-sectional view generally along line  3 - 3  in  FIG. 1 ; 
           [0013]      FIG. 4  is a cross-sectional view generally along line  4 - 4  in  FIG. 2 ; 
           [0014]      FIG. 5  is a front view of the nozzle in  FIG. 1  showing an exit orifice; 
           [0015]      FIG. 6  is a top view of a nozzle for producing a controlled gas stream in a low pressure environment; 
           [0016]      FIG. 7  is a side view of the nozzle in  FIG. 6 ; 
           [0017]      FIG. 8  is cross-sectional view generally along line  8 - 8  in  FIG. 6 ; 
           [0018]      FIG. 9  is a cross-sectional view generally along line  9 - 9  in  FIG. 7 ; 
           [0019]      FIG. 10  is a front view of the nozzle in  FIG. 6  showing an exit orifice; 
           [0020]      FIG. 11  is a top view of a collector for entraining and ejecting debris in a gas flow for a low pressure system; 
           [0021]      FIG. 12  is a side view of the collector in  FIG. 11 ; 
           [0022]      FIG. 13  is cross-sectional view generally along line  13 - 13  in  FIG. 11 ; 
           [0023]      FIG. 14  is a cross-sectional view generally along line  14 - 14  in  FIG. 12 ; 
           [0024]      FIG. 15  is a top view of an assembly for mitigating contamination in a low pressure environment; 
           [0025]      FIG. 16  is a side view of the assembly in  FIG. 15 ; 
           [0026]      FIG. 17  is cross-sectional view generally along line  17 - 17  in  FIG. 15 ; 
           [0027]      FIG. 18  is a cross-sectional view generally along line  16 - 16  in  FIG. 15 ; 
           [0028]      FIGS. 19A and 19B  are graphs showing calculated and actual performance of the nozzle in  FIGS. 1 through 5 ; and, 
           [0029]      FIGS. 20A and 20B  are graphs showing calculated and actual performance of the nozzle in  FIGS. 6 through 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
         [0031]    Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure. 
         [0032]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure. 
         [0033]      FIG. 1  is a top view of nozzle  100  for producing a controlled gas stream in a low pressure environment. 
         [0034]      FIG. 2  is a side view of nozzle  100  in  FIG. 1 . 
         [0035]      FIG. 3  is cross-sectional view generally along line  3 - 3  in  FIG. 1 . 
         [0036]      FIG. 4  is a cross-sectional view generally along line  4 - 4  in  FIG. 2 . 
         [0037]      FIG. 5  is a front view of the nozzle in  FIG. 1  showing an exit orifice. The following should be viewed in light of  FIGS. 1 through 5 . Nozzle  100  includes chambers  102  and  104  and throat  106  linking chambers  102  and  104 . Chamber  102  includes orifice  108  arranged for connection to a source of gas G, for example, tube T. Chamber  104  includes exit orifice  110  arranged to emit gas G in gas stream, or flow, GS. Chamber  102  tapers from orifice  108  to throat  106  and chamber  104  expands in size from throat  106  to orifice  110 . 
         [0038]    Nozzle  100  includes longitudinal axis LA extending in direction D1 from orifice  108  to orifice  110  through chambers  102  and  104  and throat  106 . In an example embodiment as shown in  FIG. 3 , chamber  102  tapers in direction D2, orthogonal to direction D1 and, as shown in  FIG. 4 , a size of chamber  102  in direction D3, orthogonal to the directions D2 and D3, is substantially uniform. That is, distance  112  between top surface  114  and bottom surface  116  of chamber  102  decreases moving in direction D1 and distance  118  between sides wall  120  and  122  of chamber  102  remains substantially uniform (unchanging) between orifice  108  and throat  106 . 
         [0039]    In an example embodiment as shown in  FIG. 3 , chamber  104  expands in direction D2 and, as shown in  FIG. 4 , a size of chamber  104  in direction D3 is substantially uniform. That is, distance  124  between top surface  126  and bottom surface  128  of chamber  104  increases moving in direction D1 and distance  130  between sides wall  132  and  134  of chamber  104  remains substantially uniform (unchanging) between throat  106  and orifice  110 . 
         [0040]    In an example embodiment, height  136  of orifice  110  in direction D2 is less than width  138  of orifice  110  in direction D3. That is, orifice  110  has a rectangular shape in a plane defined by directions D2 and D3. It should be understood that a configuration and shape of orifice  110  is not limited to the configuration and shape shown in  FIG. 5  and that other configurations and shapes are possible. For example, the angular corners shown in  FIG. 5  can be rounded and the continuous straight lines shown in  FIG. 5  can be rounded and/or made discontinuous. 
         [0041]    In an example embodiment, maximum dimension, or length,  140  for chamber  104  in direction D1 is greater than maximum dimension, or length,  142  for chamber  102  in direction D1. In an example embodiment, maximum height  124  for chamber  104  is greater than maximum height,  112  for chamber  102 . 
         [0042]    In an example embodiment, gas stream GS reaches supersonic speed in chamber  104 . 
         [0043]      FIG. 6  is a top view of nozzle  200  for producing a controlled gas stream in a low pressure environment. 
         [0044]      FIG. 7  is a side view of nozzle  200  in  FIG. 6 . 
         [0045]      FIG. 8  is cross-sectional view generally along line  8 - 8  in  FIG. 6 . 
         [0046]      FIG. 9  is a cross-sectional view generally along line  9 - 9  in  FIG. 7 . 
         [0047]      FIG. 10  is a front view of the nozzle in  FIG. 6  showing an exit orifice. The following should be viewed in light of  FIGS. 6 through 10 . Nozzle  200  includes chambers  202  and  204  and throat  206  linking chambers  202  and  204 . Chamber  202  includes orifice  208  arranged for connection to a source of gas G, for example, tube T. Chamber  204  includes exit orifice  210  arranged to emit gas stream, or flow, GS. Chamber  202  tapers from orifice  208  to throat  206  and chamber  204  expands in size from throat  206  to orifice  210 . 
         [0048]    Nozzle  200  includes longitudinal axis LA extending in direction D1 from orifice  208  to orifice  210  through chambers  202  and  204  and throat  206 . In an example embodiment as shown in  FIG. 8 , chamber  202  tapers in direction D2 and, as shown in  FIG. 9 , chamber  202  tapers in direction D3. That is, distance  212  between top surface  214  and bottom surface  216  of chamber  202  decreases moving in direction D1 and distance  218  between side wall  220  and  222  of chamber  202  decreases moving in direction. 
         [0049]    In an example embodiment as shown in  FIG. 8 , chamber  204  expands in direction D2 and, as shown in  FIG. 9 , chamber  204  also expands in direction D3. That is, distance  224  between top surface  226  and bottom surface  228  of chamber  204  increases moving in direction D1 and distance  230  between side wall  232  and  234  of chamber  104  also increases moving in direction D1. 
         [0050]    In an example embodiment, height  236  of orifice  210  in direction D2 is less than width  238  of orifice  210  in direction D3. That is, orifice  210  has a rectangular shape in a plane defined by directions D2 and D3. It should be understood that a configuration and shape of orifice  210  is not limited to the configuration and shape shown in  FIG. 10  and that other configurations and shapes are possible. For example, the angular corners shown in  FIG. 10  can be rounded and the continuous straight lines shown in  FIG. 10  can be rounded and/or made discontinuous. 
         [0051]    In an example embodiment, maximum dimension, or length,  240  for chamber  204  in direction D1 is greater than maximum dimension, or length,  242  for chamber  202  in direction D1. In an example embodiment, maximum dimension, or height,  244  for chamber  104  in direction D2 is greater than maximum dimension, or height,  246  for chamber  202  in direction D2. 
         [0052]    In an example embodiment, gas stream GS reaches supersonic speed in chamber  204 . 
         [0053]      FIG. 11  is a top view of collector  300  for entraining and ejecting debris in a gas flow for a low pressure system. 
         [0054]      FIG. 12  is a side view of collector  300  in  FIG. 11 . 
         [0055]      FIG. 13  is cross-sectional view generally along line  13 - 13  in  FIG. 11 . 
         [0056]      FIG. 14  is a cross-sectional view generally along line  14 - 14  in  FIG. 12 . The following should be viewed in light of  FIGS. 11 through 14 . Collector  300  includes top wall  302 , bottom wall  304 , and side walls  306  and  308  connecting top wall  302  and bottom wall  304 . Collector  300  opening  310  in top wall  302  and chamber  312  formed wholly or at least partly by walls  302 ,  304 ,  306 , and  308 . Chamber  312  includes opening  314  and opening  316 . Chamber  312  expands in size from opening  314  to opening  316 . Chamber  312  is arranged to accept a gas stream, or flow to entrain, in the gas, debris entering chamber  312  through opening  310  and eject the gas, with entrained debris, from opening  316 . 
         [0057]    Collector  300  includes longitudinal axis LA extending in direction D1 from opening  314  to opening  316  through chamber  312 . In an example embodiment as shown in  FIG. 13 , a size of chamber  312  in direction D2 is substantially uniform for portion  312 A of chamber  312  and chamber  312  expands in direction D3 as shown in  FIG. 14 . That is, distance  318  between side walls  320  and  322  of chamber  312  increases moving in direction D1 and distance  324 A between top wall  324  and bottom wall  326  of portion  312 A remains substantially uniform (unchanging) between openings  314  and  316 . 
         [0058]    In an example embodiment as shown in  FIG. 13 , a size of chamber  312  in direction D2 is expands for portion  312 B of chamber  312  and chamber  312  expands in direction D3 as shown in  FIG. 14 . That is, distance  318  between side walls  320  and  322  of chamber  312  increases moving in direction D1 and distance  324 B between top wall  324  and bottom wall  326  of portion  312 B increases in direction D1. 
         [0059]    In an example embodiment, bottom wall  304  includes opening  328 . At least respective portions of openings  310  and  328  are aligned in direction D2. In an example embodiment, an entirety of opening  310  is aligned with opening  328  in direction D2. In an example embodiment, diameter DM1 of opening  328  is larger than diameter DM2 of opening  310  to accommodate cone-shaped a light beam passing through the collector. In an example embodiment, openings  310  and  328  have common center line CL. 
         [0060]    In an example embodiment, collector  300  includes collar  330  extending from edge  332  opening  310  in direction D2. Collar  330  is arranged to create a seal with an opening for a partition plate separating collector  300  from another chamber as discussed below. 
         [0061]    In an example embodiment, openings  310  and  328  are only partially enclosed by walls  302  and  304 , respectively. For example, gap  334  is present to accommodate a nozzle, such as nozzle  100 . 
         [0062]      FIG. 15  is a top view of assembly  400  for mitigating contamination in a low pressure environment. 
         [0063]      FIG. 16  is a side view of assembly  400  in  FIG. 15 . 
         [0064]      FIG. 17  is cross-sectional view generally along line  17 - 17  in  FIG. 15 . 
         [0065]      FIG. 18  is a cross-sectional view generally along line  16 - 16  in  FIG. 15 . The following should be viewed in light of  FIGS. 15 through 18 . Assembly  400  includes nozzle  100  or  200  and collector  200 . Nozzle  200  is shown in  FIGS. 15-18 ; however, it should be understood that the discussion of  FIGS. 15-18  is applicable, unless stated otherwise, to assembly  400  with nozzle  100 . Orifice  210  of nozzle  200  is connected to opening  314  of collector  300 . 
         [0066]    In an example embodiment, assembly  400  includes partition plates  402  and  404  (not shown in  FIG. 15 ) with openings  406  and  408 , respectively. Collector  300  is located between plates  402  and  404  in direction D2. At least respective portions of openings  310 ,  328 ,  406 , and  408  are aligned in direction D2 In an example embodiment, respective diameters for openings  404 ,  310 ,  328 , and  406  become progressively larger in the preceding sequence to accommodate cone-shaped light beam LB passing through the collector. In an example embodiment, openings  310 ,  328 ,  406 , and  408  have common center line CL. 
         [0067]    In an example embodiment, plates  402  and  404  are substantially parallel in a plane formed by directions D1 and D3. In an example embodiment, plates  402  and  404  are in contact with walls  302  and  304 , respectively, and co-planar with walls  302  and  304 , respectively. 
         [0068]    In an example embodiment, plasma source PL is located in chamber  410  partially formed by plate  402  and optical components (not shown) are located in chamber  412  partially formed by plate  404 . For example, the optical components are for a semi-conductor inspection system. In an example embodiment, pressure in chamber  410  is controlled independent of system  400 . For example, chamber  410  contains a buffer gas, such as argon, and pressure in chamber  410  is controlled by a vacuum pump (not shown). 
         [0069]    The dimensions and proportions of nozzles  100  and  200 , as well as the pressure of gas G entering nozzles  100  and  200  are selectable to obtain a desired flow rate and flow pattern of gas G from nozzles  100  and  200 , for example, into collector  200  in assembly  300 . The discussion below is directed to assembly  300 ; however, it should be understood that portions of the discussion directed to nozzles  100  and  200  and collector  200  also are applicable to nozzles  100  and  200  and collector  200  outside of assembly  300 . 
         [0070]    In an example embodiment as shown in  FIG. 18 , the nozzle orifice, for example orifice  210 , and opening  314  for chamber  300  have complementary curved shapes. 
         [0071]    As noted above, plasma sources are used to generate light, such as EUV for use in semi-conductor applications, such as semi-conductor inspection systems in low pressure environments. However, a by-product of the light generation is debris that can migrate into sensitive portions of an inspection system, for example, degrading light quality or contaminating optical components. Thus, the debris adversely impacts the function and service life of the optical components and/or requires more frequent purging of the inspection system, all of which are undesirable. Advantageously, assembly  300  provides a means for entraining and removing such debris as described above and further below. 
         [0072]    In some instances, it is desirable to generate a gas flow pattern, in direction D1, into collector  200  expanding in direction D2 and remaining substantially uniform in direction D3. Nozzle  100  provides such a flow pattern as shown in  FIGS. 1 and 2 . For example, as shown in  FIG. 1 , extent  148  of stream GS in direction D3 is substantially equal to width  138  of exit orifice  110 . Further, as shown in  FIG. 2 , extent  150  of stream GS in direction D2 expands as the flow moves in direction D1 into the collector. 
         [0073]    In some instances, it is desirable to generate a gas flow pattern, in direction D1, into collector  200  expanding in direction D3 and remaining substantially uniform in direction D2. Nozzle  200  provides such a flow pattern as shown in  FIGS. 6 and 7 . For example, as shown in  FIG. 6 , extent  248  of stream GS in direction D3 expands as the flow moves in direction D1 into the collector. Further, as shown in  FIG. 7 , extend  250  of stream GS is substantially equal to height  236  of exit orifice  210 . In an example embodiment, extent  248  matches the expansion of collector  200 , along direction D1, in direction D3, for example, flowing along side walls  306  and  308  with nominal contact with walls (to preserve the velocity of the gas and prevent turbulence). In an example embodiment, extent  250  matches extent  324  of the collector and gas G flows along top wall  302  and bottom wall  304  with nominal contact with walls (to preserve the velocity of the gas and prevent turbulence). Thus, the gas stream through the chamber is controlled and the gas stream is directed to where gas flow is most needed and useful. Minimizing the extent of the gas stream in direction D2 enables use of collector  400  with a minimal dimension in direction D2, advantageously reducing the space needed for system  400 . 
         [0074]    It should be understood that any gas or combination of gases known in the art can be used with system  400 . 
         [0075]    The following are example advantages of system  400 : 
         [0076]    1. Nozzles  100  and  200  shape supersonic gas flows at low Reynolds number regimes (R˜1,000) in vacuum by shaping the dimensions of chambers  102 ,  104 ,  202 , and  204  and throats  106  and  206 . 
         [0077]    2. Nozzles  100  and  200  reduce condensation in some gases and assist in the acceleration of heavy gases. For example, nozzle  100  can be heated before or after throat  106  and nozzle  200  can be heated before or after throat  206  to reduce or eliminate condensation. 
         [0078]    3. A shape of collector  400  collects a high fraction of curtain gas, for example from nozzles  100  and  200  such that the collector itself becomes a pump. 
         [0079]    4. Stops debris and undesirable gas species from passing through an opening, such as opening  310  for passing a light beam, while minimizing absorption of light by the entraining gas and minimizing the development of larger gas pressures in regions near the gas curtain. 
         [0080]    5. The shape of the gas stream produced, for example, by nozzle  200  (narrowly focused in direction D2 and spreading in direction D3) enables the size of openings  310  and  328  (for passing a light beam) to be minimized, further reducing the transmission path for debris to enter the chamber. 
         [0081]    6. System  400  shapes a gas stream with minimal undesirable impact on gas pressures outside of the curtain. For example, stream GS can be such that there is little or no flow into chamber  410 , which is a relatively closed area, improving EUV transmission. 
         [0082]    7. System  400  shapes a gas stream with minimal undesirable impact on gas pressures outside of the curtain. For example, stream GS can be such that there is little or no flow into chamber  414 , which is a relatively open area, improving EUV transmission. 
         [0083]    8. Collector  300  enables collection of the gas stream and entrained debris (at opening  316 ) while gas G has a relatively large density, enabling easier removal of the gas and entrained debris. 
         [0084]    9. The design gas collector  300  prevents a gas species located on one side of system  400 , for example, in chamber  410 , from diffusing around system  400  to the other side of system  400 , for example, to chamber  414 . 
         [0085]    10. The complimentary designs of nozzles  100 / 200  and collector  300  eliminate dead space in the collector, for example as described above for nozzle  200  and collector  300 . 
         [0086]    11. The complimentary designs of nozzles  100 / 200  and collector  300  closely matches a shape of the high-speed region of stream GS such that the entire volume of the collector is continually swept by the gas flowing through the collector, for example as described above for nozzle  200  and collector  300 . 
         [0087]    12. To affect and/or control the flow rate of buffer gas, for example in chamber  410 , and the distribution of the buffer gas in the chamber, the gas pressure in system  400  can be controlled. For example, increasing gas pressure in system  400  reduces the flow rate of buffer gas from chamber  410  into collector  300 . 
         [0088]    13. To affect and/or control the flow rate of buffer gas, for example in chamber  410 , and the distribution of the buffer gas in the chamber, the respective temperatures of the buffer gas in chamber  410  and gas G in system  400  can be controlled. 
         [0089]      FIGS. 19A and 19B  are graphs  500  and  600 , respectively, showing calculated and actual performance of nozzle  100  in  FIGS. 1 through 5 .  FIGS. 19A and 19B  are for nozzle  100  having a rectangular orifice  110  (wider in direction D3).  FIGS. 19A and 19B  depict gas velocity values in direction D1 taken 3 centimeters away from nozzle  100  in direction D1. Lines  502  and  602  are calculated values. Points  504 ,  506 , and  604  are actual, measured values. The vertical axes in  FIGS. 19A and 19B  are velocity of gas G as measured by a Pitot tube. The horizontal axis in  FIG. 19A  is distance in direction D3 and the horizontal axis in  FIG. 19B  is distance in direction D2. 
         [0090]      FIGS. 19A and 19B  show that peak velocities  508  and  606  are substantially aligned in direction D1 with a center point (in the D2/D3 plane) of orifice  110 , for example, along axis LA. Lesser peak velocities  510  are symmetrically disposed from peak  508 . Lesser peak velocities  608  are symmetrically disposed from peak  606 . Thus, nozzle  100  produces a dual-conical gas stream focused about axis LA. 
         [0091]      FIGS. 20A and 20B  are graphs  700  and  800 , respectively, showing calculated and actual performance of nozzle  200  in  FIGS. 6 through 10 .  FIGS. 20A and 20B  are for nozzle  200  having a rectangular orifice  210  (wider in direction D3).  FIGS. 20A and 20B  depict gas velocity values taken 3 centimeters away from nozzle  200  in direction D1. Lines  702  and  802  are calculated values. Points  704  and  706 , and points  804  and  806  are actual, measured values. The vertical axes in  FIGS. 20A and 20B  are velocity of gas G as measured by a Pitot tube. The horizontal axis in  FIG. 20A  is distance in direction D3 and the horizontal axis in  FIG. 20B  is distance in direction D2. 
         [0092]      FIGS. 20A and 20B  show that peak velocities  708  and  808  are substantially symmetrically displaced from a center point (in the D2/D3 plane) of orifice  210 , for example, about axis LA. Thus, nozzle  200  produces a gas stream with a relatively small extent in direction D2 and a larger extent in direction D3, for example, a gas stream well suited to fill collector  300  while maintaining peak velocities close to the walls of collector  300 . 
         [0093]      FIGS. 19A ,  19 B,  20 A, and  20 B each show excellent correlation between calculated and measured results, thus providing empirical evidence for the characteristics described above for nozzles  100  and  200 , collector  300 , and system  400 . 
         [0094]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.