Abstract:
A chemical vapor deposition (CVD) process employs a vented cold ring. The vented cold ring includes the capability of resisting the movement of a wafer that is being processed during a throttling operation. The vented cold ring also resists the buildup of unwanted deposition during CVD processing.

Description:
TECHNICAL FIELD  
         [0001]    Embodiments of the present invention relate to articles and methods that are used in semiconductor processing. More particularly, an embodiment relates to a vented cold ring system that is used during chemical vapor deposition for semiconductor processing.  
         BACKGROUND INFORMATION  
         [0002]    Description of Related Art  
           [0003]    Integrated circuits (ICs) are processed in a high-volume manufacturing scheme by use of expensive processing tools such as a chemical vapor deposition (CVD) chamber. A CVD chamber is useful during several stages of process integration such as for depositing metal films, metal compound films, dielectric films, and others. During extended use, the CVD chamber becomes fouled under ordinary processing conditions. A preventative maintenance (PM) is therefore scheduled, based upon operator experience, such that an optimum number of wafers is processed before the CVD chamber has become too fouled to assure a useful process yield.  
           [0004]    When the CVD chamber is taken off-line for a PM, several parts must be cleaned to the level of a pristine new part. PM cleaning is time-consuming, and it often may take 24 hours or longer. However, cleaning of the CVD chamber is unavoidable, and the cleaning process must be undertaken periodically.  
           [0005]    During CVD processing, the number of particulates that occur on the wafer has a direct effect on die yield. Accordingly, a cleaner process results in a higher yield, and a periodic cleaning also results in a higher yield.  
           [0006]    Known CVD processing technology include a kit such as the TxZ® kit made by Applied Materials, Inc. of Santa Clara, Calif. The TxZ® kit is useful for the advanced integrated processing schemes of devices including 0.35 micron (micrometer) processing, 0.25 micron processing, 0.18 micron processing, 0.15 micron processing, 0.13 micron processing, 0.10 micron processing, and for future-generation processing.  
           [0007]    [0007]FIG. 1 is a cross-sectional elevation of an existing CVD system. The system  100  includes a heater  110 , a wafer chuck  112 , and a cold ring  114 . The cold ring  114  is seated upon two washer-like rings  116  and  118 . A bottom purge is undertaken in which a purge gas (indicated as the meandering flow)  120  is flowed upwardly to counter deposition at unwanted areas. Unwanted deposition occurs as a first deposition  122  at the edge of the wafer chuck  112  and as a second deposition  124  between the heater  110  and the cold ring  114 . The first deposition  122  and the second deposition  124  represent decomposed materials from CVD processing.  
           [0008]    One undesirable result in CVD processing is that the wafer moves during throttling of process gases. After a significant number of wafers has been processed, such as about 5,000 to 8,000 wafers, a PM must be undertaken to clean the first and second depositions,  122  and  124 , respectively.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    In order to understand the manner in which embodiments of the present invention are obtained, a more particular description of various embodiments of the invention briefly described above will be rendered by reference to the appended drawings. Understanding that these drawings depict only typical embodiments of the invention that are not necessarily drawn to scale and are not therefore to be considered to be limiting of its scope, the embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a cross-sectional elevation of an existing CVD system;  
         [0011]    [0011]FIG. 2 is an oblique elevation of a vented cold ring according to an embodiment;  
         [0012]    [0012]FIG. 3A is a schematic elevation of a vented cold ring according to an embodiment;  
         [0013]    [0013]FIG. 3B is a schematic elevation of a vented cold ring according to an embodiment;  
         [0014]    [0014]FIG. 3C is a schematic elevation of a vented cold ring according to an embodiment;  
         [0015]    [0015]FIG. 3D is a schematic elevation of a vented cold ring according to an embodiment;  
         [0016]    [0016]FIG. 3E is a schematic elevation of a vented cold ring according to an embodiment;  
         [0017]    [0017]FIG. 4 is a cross-sectional elevation of a vented cold ring system according to an embodiment;  
         [0018]    [0018]FIG. 5 is a cross-sectional elevation of a vented cold ring system according to an embodiment;  
         [0019]    [0019]FIG. 6 is a process flow diagram according to an embodiment; and  
         [0020]    [0020]FIG. 7 is a method flow diagram according to an embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0021]    The following description includes terms, such as first, second, etc., that are used for descriptive purposes only and are not to be construed as limiting. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. These drawings show, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the inventive concepts. Other embodiments may be used, and structural, logical, and electrical changes may be made without departing from the scope of the present invention.  
         [0022]    [0022]FIG. 2 is an oblique elevation of a vented cold ring according to an embodiment. The vented cold ring  200  includes a washer upper section  210  and an annular lower section  212 . In one embodiment, the washer upper section  210  is substantially orthogonal to the annular lower section  212 . In another embodiment, the washer upper section  210  has a pitch of about 7° that falls from its inner circumference  214  to its outer circumference  216 . Other pitches greater or less than 7° can be selected depending upon the application. The washer upper section  210  includes a characteristic width, and the annular lower section  212  includes a characteristic height. In one embodiment, the characteristic height is greater than the characteristic width. In another embodiment, the characteristic height is smaller than the characteristic width.  
         [0023]    At least one through-hole  218  is located on the annular lower section  212 . The at least one through-hole  218  is located upon the annular lower section  212  according to its ultimate orientation within a CVD chamber as is discussed below. In one embodiment, the at least one through-hole  218  includes a plurality of through-holes  218 . In one embodiment, the plurality of through-holes includes uniformly spaced holes. By “uniformly spaced”, it is meant that the holes are equidistantly spaced on through-hole centers. In one embodiment, the through-holes are uniformly spaced, incrementally sized holes as set forth below.  
         [0024]    In one embodiment, a first fastener hole  220  is located in the washer upper section  210 . In one embodiment, three occurrences of the first fastener hole  220  are located in the washer upper section  210 . Other numbers of the first fastener holes  220  can be used according to a specific application.  
         [0025]    FIGS.  3 A- 3 E represent various embodiments. In one embodiment, the at least one through-hole includes a plurality of through-holes in a range from about 2 to about 100 in number. In another embodiment, the plurality of through-holes is in a range from about 8 to about 80. In another embodiment, the plurality of through-holes is in a range from about 16 to about 40.  
         [0026]    [0026]FIG. 3A is a schematic elevation of a vented cold ring  300  according to an embodiment. The pitch between the inner circumference  314  and the outer circumference  316  of the washer upper section is also illustrated. As set forth herein, embodiments include an orientation of the vented cold ring in relation to the CVD chamber. Pressure differentials occur within the CVD chamber, particularly during gas flow operations. One source of the pressure differentials is a pump port for managing the flow of process gases. In FIG. 3A, the location of a pump port  310  in relation to the vented cold ring  300  is indicated schematically by the letter X.  
         [0027]    According to one embodiment, the at least one through-hole includes a plurality of through-holes. In a non-limiting illustration depicted in FIG. 3A, twelve ( 12 ) through-holes ( 318 ,  320 ,  322 ,  324 ,  326 , and  328 , labeled in pairs) are depicted. In this embodiment, the plurality of through-holes includes a plurality of uniformly spaced incrementally sized holes. On the annular lower section  312 , through-holes  318  have a standard hole size of ⅛ inch (0.318 centimeter). Through-holes  320  have a standard hole size of {fraction (9/64)} inch that is sized incrementally larger than through-holes  318 . Through-holes  322  have a standard hole size of {fraction (9/32)} inch (0.714 cm) sized incrementally larger than through-holes  320 . Through-holes  324  have a standard hole size of {fraction (19/64)} inch (0.754 cm) sized incrementally larger than through-holes  322 . Through-holes  326  have a standard hole size of {fraction (5/16)} inch (0.794 cm) sized incrementally larger than through-holes  324 . And through-holes  328  have a standard hole size of ¼ inch (0.635 cm) sized incrementally larger than through-holes  326 . In one embodiment, the vented cold ring  300  is represented schematically, as all through-holes on half of the circumference are depicted. Accordingly, the vented cold ring  300  has a plurality of through-holes that totals twenty-four ( 24 ) through-holes.  
         [0028]    [0028]FIG. 3B is a schematic elevation of a vented cold ring  301  according to an embodiment. In this embodiment, the plurality of through-holes includes uniformly spaced groups of same-sized holes. By “uniformly spaced, same-sized” it is meant that the groups are uniformly spaced, and among a given group, the holes of the group are same-sized. In accordance with other embodiments, it is understood that an embodiment includes an incidence of fewer through-holes and/or fewer through-hole groups that are placed proximate the location of the pump port  310 . Accordingly, the through-holes  330  are a smallest size in FIG. 3B, the through-holes  332  represent an optional at least one intermediate size, and the through-holes  334  represent a largest size. According to another embodiment, the arrangement of the through-holes  330 ,  332 ,  334  can be all same-sized holes, but the groups are incrementally clustered to have the greatest clustering at a location that is distal to the location of the pump port  310 , and the least clustering is at a location that is proximal to the pump port  310 . Other clustering schemes can be selected.  
         [0029]    [0029]FIG. 3C is a schematic elevation of a vented cold ring  302  according to an embodiment. In FIG. 3C, upper holes  336  and lower holes  338  are arrayed along the annular lower section  312  of the vented cold ring  302 . In this embodiment, the through-holes include grouped same-sized holes that are grouped in upper and lower groups. The upper-group holes  336 , although they can appear to be uniformly same-sized, can be incrementally sized according to a scheme similar to the embodiment set forth in FIG. 3A. The lower-group holes  338 , although they can likewise appear to be uniformly same-sized, can also be incrementally sized according to a scheme similar to the embodiment set forth in FIG. 3A.  
         [0030]    Another embodiment includes a combination of uniformly spaced through-holes such as is depicted in FIG. 3A, with upper or lower spaced groups of same-sized holes, such as is depicted in FIG. 3B.  
         [0031]    [0031]FIG. 3D is a schematic elevation of a vented cold ring  303  according to an embodiment. In this embodiment, the plurality of through-holes includes upper and lower uniformly spaced groups of same-sized holes. By “uniformly spaced, same sized” it is meant that the groups are uniformly spaced, and among a given group, the holes of the group are same-sized. In accordance with other embodiments, it is understood that an embodiment includes an incidence of fewer through-holes and/or fewer through-hole groups that are placed proximate the location of the pump port  310 . For the upper holes  340 ,  342 , and  344 , the through-holes  340  are a smallest size for the upper holes in FIG. 3D, the through-holes  342  represent an optional at least one intermediate size, and the through-holes  344  represent a largest size. According to another embodiment, the arrangement of the through-holes  340 ,  342 ,  344  can be all same-sized holes, but the groups are incrementally clustered to have the greatest clustering at a location that is distal to the location of the pump port  310 , and the least clustering is at a location that is proximal to the pump port  310 . Other clustering schemes can be selected.  
         [0032]    Similarly, for the lower holes  346 ,  348 , and  350 , the through-holes  346  are a smallest size for the lower holes in FIG. 3D, the through-holes  348  represent an optional at least one intermediate size, and the through-holes  350  represent a largest size. According to another embodiment, the arrangement of the through-holes  346 ,  348 , and  350  can be all same-sized holes, but the groups are incrementally clustered to have the greatest clustering at a location that is distal to the location of the pump port  310 , and the least clustering is at a location that is proximal to the pump port  310 . Other clustering schemes can be selected that include clustering upper and lower holes in relation to the location of the pump port  310  as set forth in this disclosure.  
         [0033]    [0033]FIG. 3E is a schematic elevation of a vented cold ring  304  according to an embodiment. Although a substantially circular through-hole can be an embodiment that is selected, other through-hole shapes are embodiments. In one embodiment, a slot  352  is depicted, in addition to substantially circular holes, represented generically by reference numeral  318 . In one embodiment, the slot  352  can be a single through-hole. In one embodiment, a plurality of slots can be formed on the annular lower section  312 . In one embodiment, the slot  352  is part of a mixture of holes similar to holes  318 .  
         [0034]    By the embodiments depicted in FIGS.  3 A- 3 E, it becomes clear that one of ordinary skill in the art can undertake a practical exercise to select a through-hole scheme according to a specific application. It also becomes clear that one of ordinary skill in the art can undertake an academic exercise to select a through-hole scheme according to a specific application.  
         [0035]    [0035]FIG. 4 is a cross-sectional elevation of a vented cold ring system  400  according to an embodiment. The vented cold ring system  400  includes a vented cold ring  410  that includes a washer upper section  412  and an annular lower section  414 . The annular lower section  414  can be defined by an upper region  416  and a lower region  418  that is separated by a through-hole  420 . The washer upper section  412  and the annular lower section  414  are substantially orthogonal to each other when defined by their major axes that pass through the most mass of each section as illustrated. By “substantially orthogonal” it is understood that the washer upper section  412  can have a pitch that can deviate, for example, by about 7° from the horizontal as depicted in FIG. 2. In one embodiment, the pitch of the washer upper section  412  can have an angle that deviates from the horizontal in a range from about negative 10° to about positive 10°. Unlike the structure depicted in FIG. 2, FIG. 4 depicts a substantially orthogonal configuration with no illustrated pitch.  
         [0036]    The washer upper section  412  includes an upper surface  422  and a lower surface  424 . The annular lower section  414  includes an inner surface  426  and an outer surface  428 . A prominence  430  extends downwardly from the lower surface  424  of the washer upper section  412 .  
         [0037]    Another embodiment of the vented cold ring system  400  includes an upper fastener  432  and a lower fastener  434 . In another embodiment, the upper fastener  432  and the lower fastener  434  are each vented. In one embodiment, at least one of the upper fastener  432  and the lower fastener  434  is vented. Included in the upper fastener system is a fastener seat  436 . The fastener seat  436 , when assembled with a CVD chamber, contacts a rest button (not pictured) as is known in the art. In one embodiment, the vented cold ring  410  is an aluminum structure. In one embodiment, the fastener seat  436  is a stainless steel structure.  
         [0038]    The lower fastener  434  is configured to make closure contact with the prominence  430 . In one embodiment, the lower fastener  434  is a threaded vent screw, and the prominence  430  is internally threaded to match threading of the lower fastener  434 . With the lower fastener system, a first washer, hereinafter referred to as a first spacer  438 , is disposed over the prominence  430 . The vented cold ring  410  is seated upon two washer-like rings that include a first support ring  440  and a second support ring  442 . The first spacer  438  is disposed between the washer upper section  412  and the first support ring  440 . A second washer, hereinafter referred to as a second spacer  444 , is disposed between the first support ring  440  and the second support ring  442 . The spacer ring  442  has a smaller hole that is countersunk to accept the screw  434 . FIG. 4 illustrates one embodiment where the terminal end  446  (depicted by a phantom line) of the prominence  430  terminates within the thickness of the first support ring  440  as depicted. Although the elevational cross section depicted in FIG. 4 is exploded, it is understood in one embodiment that when the cold ring system is fully assembled, the terminal end  446  of the prominence  430  terminates within the thickness of the first support ring  440 .  
         [0039]    [0039]FIG. 5 is a cross-section elevation of a vented cold ring system  500  according to an embodiment. A heater block  510  includes a wafer chuck  512 . Prior art heater blocks included complex geometries that required more elaborate cleaning processes. The heater block of this embodiment of the present invention includes a simple, substantially rectilinear geometry. In contrast to known methods and systems for cold rings, no back-side clamping is required in embodiments of the vented cold ring system.  
         [0040]    The vented cold ring system  500  includes a vented cold ring  514  that includes a washer upper section  516  and an annular lower section  518 . A bottom purge is undertaken in which a purge gas (indicated as the meandering flow)  520  is flowed upwardly to counter deposition at unwanted areas. In this embodiment, the annular lower section  518  acts to split the purge gas  520  into an outer flow  520 A and an inner flow  520 B. The inner flow  520 B substantially bypasses the through-hole  522  due to the equilibrating presence of the outer flow  520 A. Unwanted deposition occurs as a first deposition  524  at the edge of the wafer chuck  512 .  
         [0041]    The vented cold ring  514  is seated upon two washer-like rings that include a first support ring  526  and a second support ring  528 . A first washer, hereinafter referred to as a first spacer  530  is disposed between the washer upper section  516  and the first support ring  526 . A second washer, hereinafter referred to as a second spacer  532 , is disposed between the first support ring  526  and the second support ring  528 .  
         [0042]    In one embodiment, the vented cold ring system  500  includes an upper fastener and a lower fastener similar to the embodiments depicted in FIG. 4. In another embodiment, the upper fastener and the lower fastener are each vented. In one embodiment, at least one of the upper fastener and the lower fastener is vented. Included in the upper fastener system is a fastener seat similar to the embodiments depicted in FIG. 4.  
         [0043]    [0043]FIG. 6 is a process flow diagram  600  according to an embodiment. According to a process embodiment, the CVD chamber is prepared to a milliTorr atmosphere, often referred to as a “high vacuum.” The wafer resides in a transfer chamber that has been prepared up to an approximate 10 −8  Torr atmosphere, such as by a cryogenic high-vacuum pump. A robot extends into the transfer chamber, the transfer chamber valve closes, and gas begins to flow into the CVD chamber to prepare it for processing.  
         [0044]    At  610 , the wafer is meanwhile brought to a process position within the CVD chamber, and control is exercised on the CVD chamber to begin throttling the chamber to the CVD pressure. In one embodiment, the CVD process pressure is from about 1.4 Torr to about 1.6 Torr. In another embodiment, the CVD process pressure is about 1.5 Torr.  
         [0045]    At  620 , during the establishment of gas flow conditions, a bottom purge of an inert gas is also established. The bottom purge is used in a gas flow range from about 20 standard cubic centimeters per minute (sccm) to about 100 sccm. In one embodiment, a 50 sccm purge gas flow rate is used.  
         [0046]    During the first throttling, the first gas passes through at least one through-hole in the vented cold ring. By passing through the at least one through-hole in the vented cold ring, the wafer does not move to any significant degree such as it did in previous processes. Once the pressure, temperature, and other processing conditions have been achieved, the CVD gas begins to feed to the CVD chamber.  
         [0047]    A refractory metal film can be formed in the CVD process. In one embodiment, a refractory metal compound film is formed. The refractory metal that is used to form one of the refractory metal film or the refractory metal compound film includes at least one metal selected from titanium (Ti), zirconium (Zr), hafnium (Hf), or combinations thereof. In one embodiment, the refractory metal is selected from vanadium (V), niobium (Nb), tantalum (Ta), or combinations thereof. In one embodiment, the refractory metal is selected from chromium (Cr), molybdenum (Mo), tungsten (W), or combinations thereof. In one embodiment, the refractory metal is selected from cobalt (Co), rhodium (Rh), iridium (Ir), or combinations thereof. In one embodiment, the refractory metal is selected from nickel (Ni), palladium (Pd), platinum (Pt), or combinations thereof. In one embodiment, a metal wiring layer is formed. In this embodiment, a metal such as aluminum (Al), copper (Cu), silver (Ag), gold (Au), or the like, is used.  
         [0048]    In one embodiment, a metal nitride film is formed. The refractory metals that can be used to form a refractory metal film can be used to form a refractory metal nitride film. In some embodiments a metal such as aluminum (Al) is used.  
         [0049]    In one embodiment, the CVD gas is triethylaluminum (TEAL) or the like. In one embodiment, the CVD gas is selected from tetrakisdimethylamino titanium (TDMAT) or tetrakisdiethylamino titanium (TDEAT), or trimethylethylenediamine tris(dimethylamino)titanium (TMEDT), and the like.  
         [0050]    The CVD gas is bubbled with an inert gas carrier such as helium. The CVD gas is carried from the bubbling source, through a distributor such as a “shower head”, as is known in the art. A CVD process then occurs in the CVD chamber. After the CVD process, the bottom purge can be discontinued.  
         [0051]    In another embodiment, a dielectric film is formed. The dielectric film can include one of an oxide, a nitride, an oxintride, and the like. For example, an oxide film is formed by the decomposition of tetraethylortho silicate (TEOS).  
         [0052]    In one embodiment, a semiconductive film is formed. For example, a silicon source such as silane is bubbled to the CVD chamber, and deposition is carried out to form a polysilicon film.  
         [0053]    At  630 , a second throttling process is carried out. The second throttling process follows the CVD process. During the second throttling, the first gas (at a higher pressure than the second gas) passes out from under the vented cold ring through the at least one through-hole in the vented cold ring. By passing through the at least one through-hole in the vented cold ring, the wafer does not move to any significant degree such as it did in previously known CVD equipment and processes.  
         [0054]    During the second throttling process the CVD film is processed. In one embodiment the CVD film is densified. In one embodiment the CVD film is oxidized. In one embodiment the CVD film is nitrided. In one embodiment the CVD film is oxynitrided. In one embodiment the CVD film is annealed. In one embodiment the CVD film is treated to a combination of the above processes.  
         [0055]    In one embodiment the CVD film is densified by the use of hydrogen and nitrogen in a plasma environment. Before the second throttling, the gas purge is discontinued.  
         [0056]    After processing according to an embodiment, the wafer is removed from the CVD chamber for further processing, if any. A subsequent wafer is then able to be processed as set forth herein.  
         [0057]    [0057]FIG. 7 is a method flow diagram  700  according to an embodiment. Because of the vented cold ring and its effect on a reduced amount of build-up, a cleaner and higher-throughput process is achieved.  
         [0058]    At  710  a first plurality of wafers is CVD processed. The processing includes forming a CVD film, and processing the CVD film according to embodiments set forth herein.  
         [0059]    At  720 , a mini-clean operation is performed on the cold ring system. In the mini-clean operation, the vented cold ring is separated from the wafer chuck. The CVD buildup is removed from the wafer chuck. In one embodiment, the CVD buildup is removed by cleansing with a scrubbing article such as a Wilshire™ SCRUBPAD® cleansing pad made by Foamex Asia of Carlsbad, Calif. The mini-clean includes a wiping process that is carried out by wiping the wafer chuck and the heater with a cleansing fluid. According to one embodiment, the cleanser fluid is a Wilshire foam, manufactured by Foamex Asia of Carlsbad, Calif. The wiping process is continued by wiping the wafer chuck and the heater with a solvent such as isopropyl alcohol.  
         [0060]    At  730 , the vented cold ring is reinstalled, and a subsequent plurality of wafers is processed. Alternatively, after the subsequent plurality of wafers is processed, another mini-clean operation is carried out. In this embodiment, another subsequent plurality of wafers is processed. According to this embodiment, a third plurality of wafers is processed before the CVD chamber is broken down and a conventional cleaning operation is carried out as is known in the art at  740 .  
         [0061]    At  740 , after the final subsequent plurality of wafer is processed, the CVD chamber is broken down, and a conventional cleaning operation is carried out as is known in the art.  
         [0062]    In one embodiment, the first plurality of wafers is processed in a number range from about 4,000 to about 12,000 wafers. Thereafter, the mini-clean operation is carried out as set forth herein. Next the second plurality of wafers is processed in a number range from about 4,000 to about 12,000 wafers. Next, the CVD chamber is broken down, and a conventional cleaning operation is carried out as is known in the art.  
         [0063]    In one embodiment, after a series of processes have been completed, a new vented cold ring is installed. Installation of the new vented cold ring can follow the mini-cleaning operation, or it can follow the conventional cleaning operation.  
         [0064]    In a first example of the method embodiment, about 10,200 wafers were processed. At about the 9,000 th  wafer, the particle count was recorded at 10. At about the 10,200 th  wafer, the particle count was at a high of 15. At this stage of the method, the mini-clean was performed. Thereafter, the CVD chamber was reassembled with the vented cold ring, and processing continued until a total of about 15,000 wafers was processed. Except for the particle count of 10 and 15, no particle count on any wafer exceeded 8, and with the exception of five individual wafer particle counts (including the 10-count and 15-count wafers), no particle count exceeded 5 particles. Further, with the exception of seven individual wafer particle counts (including the 10-count, the 15-count, an 8-count, a 7-count, a 6-count, and two 5-count wafers, no particle count exceeded 4 particles. Further, of all the particles counted above 1, only 15 wafers had higher particle counts before the mini-clean. Similarly, of all the particles counted above 1 after the mini-clean, only 9 wafers had higher particle counts.  
         [0065]    It is emphasized that the Abstract is provided to comply with 37 C.F.R. §1.72(b) requiring an Abstract that will allow the reader to quickly ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.  
         [0066]    In the foregoing Detailed Description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description of Embodiments of the Invention, with each claim standing on its own as a separate preferred embodiment.  
         [0067]    It will be readily understood to those skilled in the art that various other changes in the details, material, and arrangements of the parts and method stages which have been described and illustrated in order to explain the nature of this invention may be made without departing from the principles and scope of the invention as expressed in the subjoined claims.