Abstract:
A method of operating a computing system to determine reticle data. The reticle data is for completing a reticle for use in projecting an image to a semiconductor wafer. The method comprises receiving circuit design layer data comprising a desired circuit layer layout, the layout comprising a plurality of circuit features. The method further comprises providing the reticle data for inclusion in an output data file for use in forming reticle features on the reticle. This providing step comprises a first iteration and a second iteration. In a first iteration, the method indicates parameters for forming a plurality of primary features and a first plurality of assist features on the reticle and it selectively removes the parameters of selected ones of the first plurality assist features. In a second iteration, the method indicates parameters for forming a second plurality of assist features on the reticle.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present embodiments relate to forming semiconductor circuit wafers and are more particularly directed to locating assist features, also referred to as sub-resolution assist features, on a mask (or reticle) for use with such wafers. 
         [0004]    The history and prevalence of semiconductor devices are well known and have drastically impacted numerous electronic devices. As a result and for the foreseeable future, successful designers constantly are improving the semiconductor fabrication process, and improvements are in numerous areas including device size, fabrication efficiency, and device yield. The present embodiments advance these and other goals by improving the methodology for developing parameters to implement sub-resolution assist features on the masks used to form semiconductor devices. 
         [0005]    By way of background and as known in the art, semiconductor devices are sometimes referred to as chips, and each chip is created from a portion of a semiconductor wafer. Typically, each chip is located in a respective area on the wafer referred to as a field. Various fabrication steps are taken to form electric circuits on each field. Some of these steps involve photolithography, whereby a light source is directed toward a mask, and light passes through only portions of the mask because so-called features have been previously formed on the mask so that the light that passes is determined by the location of the features. In other words, an image is projected through the mask based on the location of the features, where in some cases the feature is what blocks the light or in other cases the feature is what passes the light. In either case, typically the light image is further directed to a reduction lens that reduces the size of the image and the reduced image is then projected to a selected field on the wafer, where the field selection is determined by a device known as a stepper. The stepper gets its name because it causes the image to step through different fields on the wafer, that is, once the image is projected to one field on the wafer, the stepper disables the light source, re-positions either the mask or the wafer, and then enables the light source so that the same image from the same mask is then directed to a different field on the wafer, and so on for numerous fields. Thus, this process repeats until numerous images of the same type are directed to numerous respective fields on the wafer, with the stepper thereby stepping the image from one field to another on the wafer. As each image reaches a field on the wafer, typically the light reacts with a layer of photoresist that was previously deposited on the wafer. The resulting reacted photoresist layer is then etched to remove the unreacted photoresist, leaving behind structures on the wafer that correspond to the same size and shape as the reduced light that previously was directed through the mask and reducer to the wafer. These remaining wafer structures are also referred to as features and note, therefore, that each feature on the mask causes a corresponding feature on the wafer. However, each feature on the mask is larger in size, typically by some integer multiple (e.g., 2, 4, 5, 10), where the specific multiplier is implemented with respect to the wafer by the reducer lens. For example, in a case where the mask features are four times that desired on the wafer, the reducer lens reduces the size of the light image passing through the mask by a factor of four so that each resulting wafer feature will be one-fourth the size (in all dimensions) of each respective mask feature. In this manner, therefore, limitations on the mask may be at a larger size scale than on the wafer, due to the use of the reducer lens. 
         [0006]    Given the use of imaging and masks as discussed above, various aspects of semiconductor design are necessarily limited by constraints of the mask and its related technology. In other words, since the mask defines the image that passes through it and that ultimately dictates the layout of the circuit on the wafer, then limitations of the mask represent limitations of the resultant wafer circuit. For example, it is well known that features on the mask may be made only down to a certain limited width, which as of this writing are typically on the order of 250 nm (nanometers). Moreover, in developing the location of features on a mask, various designers have developed methodologies that place limits on how closely two neighboring wafer features may be formed. More specifically, it has been determined that if such neighboring wafer features are too closely formed, then the wafer features cannot be resolved optically with conventional light source and mask techniques, causing an undesirable or unacceptable image on the wafer. Such limitations are particularly evident when a desired dimension of a wafer feature is smaller than the wavelength of the light that passes through the mask. In this regard, more recently technology has advanced with the use of two techniques that permit creation of even smaller wafer features, each of which is described below. 
         [0007]    One technology used for improving wafer features in smaller circuits is known as a phase-shifting mask. In such a mask, the mask blocks light in certain areas and phase shifts light in other nearby areas typically so that the light passing through these latter areas is 180 degrees out of phase with respect to the areas that pass non-phase shifted light. As a result, in use of the mask there is overlap between the non-phase shifted and phase shifted light, causing light interference that effectively cancels some of the overlapping light and produces a clearer edge for the resulting wafer feature. 
         [0008]    Another mask technology used for improving wafer features in smaller circuits is known by various names, such as feature assist, assist features, or sub-resolution assist features, where the last connotes that the assisting feature on the mask contributes to a corresponding wafer feature with greater resolution and printing margin than that otherwise obtainable for a given light wavelength. In any event, those assist features are features that are located on a mask, but a key goal of these features is that there is not a counterpart of the mask assist feature formed on the wafer. More particularly, ideally the mask assist feature is small enough and properly located on the mask so that that the assist feature is not transferred onto the wafer because the wafer features are below the dimensional resolution of the lithography system. However, the assist feature is also large enough so that that it does affect the passage of light and thereby impacts a nearby wafer feature, sometimes referred to in this context as a primary feature and that is formed therefore in response to a primary (non-assist) feature on the mask but is further defined by the light that is manipulated by the assist feature. 
         [0009]    In view of the above, with assist (or assist feature) technology comes the complexity of a methodology for locating the assist features on the mask or reticle. Often such a method implements a rule-based computer program that considers various of the circuit attributes and layout dimensions so as to generate parameters that in turn are used to form both primary and assist features on the mask. The present embodiments, however, seek to improve upon such technology by permitting and forming additional assist features beyond those that are placed on a mask in the prior art, with the ability therefore to enhance the printability of corresponding primary features on the wafer, thereby reducing chip size, permitting greater device density per field, and improving yield for smaller dimension circuits. Various other benefits also may be ascertained by one skilled in the art, based on the remaining discussion set forth below. Thus, the prior art provides drawbacks in its limitations of achieving only certain primary feature definition and minimal wafer feature sizes, while the preferred embodiments improve upon these limitations as demonstrated below. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In the preferred embodiment, there is a method of operating a computing system to determine reticle data. The reticle data is for completing a reticle for use in projecting an image to a semiconductor wafer. The method comprises receiving circuit design layer data comprising a desired circuit layer layout, the layout comprising a plurality of circuit features. The method further comprises providing the reticle data for inclusion in an output data file for use in forming reticle features on the reticle. This providing step comprises a first iteration and a second iteration. In a first iteration, the method: (i) indicates parameters for forming a plurality of primary features on the reticle, where the primary features of the plurality of primary features corresponding to the plurality of circuit features; (ii) indicates parameters for forming a first plurality of assist features on the reticle, wherein in use of the reticle for use in projecting the image to the semiconductor wafer the first plurality of assist features, if formed on the reticle, are for assisting corresponding ones of the primary features; and (iii) selectively removes the parameters of selected ones of the assist features in the first plurality of assist features so that removed parameters are not used in forming reticle features. In a second iteration, the method indicates parameters for forming a second plurality of assist features on the reticle, wherein in use of the reticle for use in projecting the image to the semiconductor wafer the second plurality of assist features, if formed on the reticle, are for assisting corresponding ones of the primary features. 
         [0011]    Other aspects are also disclosed and claimed. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0012]      FIG. 1  illustrates a block diagram of a system for forming a reticle in accordance with the preferred embodiments. 
           [0013]      FIG. 2   a  illustrates a block diagram of a portion of the surface of the reticle from  FIG. 1  and per the prior art with a reticle assist feature symmetrically centered between two sufficiently-spaced primary features. 
           [0014]      FIG. 2   b  illustrates a block diagram of a portion of the surface of the reticle from  FIG. 1  and per the prior art with two reticle assists features symmetrically centered between two sufficiently-spaced primary features. 
           [0015]      FIG. 2   c  illustrates a block diagram of a portion of the surface of the reticle from  FIG. 1  and per the prior art with three reticle assists features symmetrically centered between two sufficiently-spaced primary features. 
           [0016]      FIG. 3  illustrates a flowchart of a methodology to be implemented in format rules and methodology file  34   2  of  FIG. 1  and per the preferred embodiments. 
           [0017]      FIG. 4   a  illustrates a block diagram of a region that will result from data designating a primary feature to be constructed on a reticle per the job deck output data file  34   3  of  FIG. 1 . 
           [0018]      FIG. 4   b  illustrates the region of  FIG. 4   a  with an area extended away from the primary feature for purposes of examining whether data indicates an assist feature to be included in the area. 
           [0019]      FIG. 4   c  illustrates the region of  FIG. 4   b  after data has been added to designate an assist feature to be added within at least part of the extended area. 
           [0020]      FIG. 5   a  illustrates a block diagram of a region that will result from data designating two primary features to be constructed on a reticle per the job deck output data file  34   3  of  FIG. 1 . 
           [0021]      FIG. 5   b  illustrates the region of  FIG. 5   a  with respective areas extended in a same dimension but in opposing directions and away from the respective primary features for purposes of examining whether data indicates an assist feature to be included in the areas. 
           [0022]      FIG. 5   c  illustrates the region of  FIG. 5   b  after data has been added to designate an assist feature to be added within at least part of the extended areas. 
           [0023]      FIG. 6   a  illustrates a block diagram of a region that will result from data designating two primary features to be constructed per the job deck output data file  34   3  of  FIG. 1  and with respective areas extended in different perpendicular dimensions and away from the respective data reticle primary features for purposes of examining whether data indicates an assist feature to be included in the areas. 
           [0024]      FIG. 6   b  illustrates the region of  FIG. 6   a  after data has been added to designate an assist feature to be added within at least part of the extended areas. 
           [0025]      FIG. 7  illustrates a block diagram of a region that will result from data designating five primary features to be constructed per the job deck output data file  34   3  of  FIG. 1 , with respective areas extended away from the respective primary features, and after data has been added to designate an assist feature to be added with at least part of each of the extended areas. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  illustrates a block diagram of a system  10  for forming a reticle  20  in accordance with the preferred embodiments. By way of introduction, the general nature of system  10  is known in the art, but novel aspects are added thereto and improve reticle  20  for reasons appreciated throughout the remainder of this document. 
         [0027]    Looking then to system  10  in general, it includes a processor system  30  that may be embodied in various different forms of hardware and software, typically including one or more processors and/or computing devices. Processor system  30  has one or more interfaces  32  coupled to a data store  34 , where data store  34  represents any of various forms of storage such as drives and memory, and where such storage may retain program or other data that may be read/written with respect to processor system  30 . Data store  34  is shown to provide two input data files  34   1  and  34   2  via interface  32  to processor system  30 , and to receive an output data file  34   3  from processor system  30 , and each of these files is discussed below. Lastly, note that system  30  may include numerous other aspects such as are common with various computing configurations, including other input devices (e.g., keyboards, mouse, touch pad, tablet, and the like), output devices (e.g., display, monitor, and the like), as well as other media, components, devices, and peripherals, although such aspects are neither shown nor described so as to simplify the present discussion. 
         [0028]    The first input data file  34   1  from data store  34  to processor system  30  is designated circuit design layer (“CDL”) data  34   1 . CDL data  34   1  is a digitization of a desired circuit layer layout features, thereby illustrating a desired corresponding image to be formed on reticle  20  so that a circuit layer may be formed later on a wafer and with features in the same shape and with scaled dimensions of the image. CDL data  34   1  is often created by one or more circuit designers, and indeed in some instances one company provides data  34   1  to another company for creation of reticle  20  to correspond to data  34   1 . The circuit layer layout data of CDL data  34   1  typically has many shapes extending in various directions and these shapes are often referred to as features. Moreover, the layout pertains to materials and layers used in semiconductor fabrication processes. For example, typical types of layers used in the process include gate layer, contact layer, and via layer, where each of these is mentioned here as introduction to one preferred embodiment aspect discussed later. In any event, therefore, CDL data  34   1  provides the layout shape and dimensions of each item, or feature, that is desired to be ultimately formed on a wafer or to establish circuit devices, or parts thereof, on the wafer. For example, for the gate layer, CDL data  34   1  may indicate locations, layout, shape, and dimensions of polysilicon to be formed on a wafer. Thus, in the example of polysilicon, and with the many transistors typically formed in a circuit design, the polysilicon layer may have numerous locations indicated as included for forming respective transistor gates throughout the layout. However, polysilicon elsewhere in the layout may have other uses, such as in resistors, capacitors, interconnect, or plasma etch load features. Thus, these other uses also may be described by information included in CDL data  34   1 . One skilled in the art will appreciate numerous other examples of types of structures and layers that may be indicated in CDL data  34   1 . 
         [0029]    The second input data file  34   2  from data store  34  to processor system  30  is designated format rules and methodology (“FRAM”) data  34   2  and in certain respects performs as known in the art. Specifically, FRAM data  34   2  includes programming information, rules, and parameters that may take various forms ascertainable by one skilled in the art, such as computer (or processor) instructions/programming and appropriate other data. FRAM data  34   2 , with the operation of processor system  30 , formats CDL data  34   1  into job deck output data file  34   3 , which sometimes may be referred to other than as a job deck, where output data file  34   3  is later used to control a lithographic write by a write device  40 ; thus, write device  40  later and ultimately forms an image on reticle  20  and that corresponds to the layout described by CDL data  34   1 . Looking then to FRAM data  34   2  in a little more detail, it is used by processor system  30  to convert the data from CDL data  34   1  into a language compatible with write device  40 , where this conversion is sometimes referred to as fracturing. The conversion divides the layout into shapes (e.g., rectangles and trapezoids) that are usable by write device  40 . FRAM data  34   2  also may make changes in size and rotation, add fiducials and internal references, and make other data alterations as known to one skilled in the art. 
         [0030]    Continuing with FRAM data  34   2 , it also includes additional novel aspects directed to the preferred embodiments. By way of introduction to these aspects, recall that the Background Of The Invention section of this document introduces sub-resolution assist features (hereafter referred to as “assist feature” or, plural, “assist features”). In this regard, FRAM data  34   2  also provides rules and a methodology, detailed later, for inclusion of assist features into job deck output data file  34   3 . These assist features are features that are not provided with circuit feature counterparts in CDL data  34   1 , but in response to FRAM data  34   2  are added to the job deck output data file  34   3  so that the assist features may be printed on reticle  20 , for assistance and in addition to the primary features that are printed on reticle  20  due to corresponding layout information in CDL data  34   1 . Further in this regard and again by way of introduction, the rules and methodology of FRAM data  34   2  preferably cause an iteration that provides an initial inclusion of assist features for placement into job deck output data file  34   3 . However, in the preferred embodiment methodology, an additional iteration is provided and examines spatial locations, corresponding to regions on reticle  20 , where assist features do not exist to a certain extent or for which assist features were designated for inclusion but were thereafter removed, and under a different set of criteria additional assist features may then be included in such locations. In any event, once job deck output data file  34   3  is complete and with all primary and assist features therein, it is used to form a reticle  20  that is later used to impinge an image on a semiconductor wafer; when reticle  20  is so used, the assist features on reticle  20  do not cause a corresponding image on the wafer but instead assist in forming and defining better resolution and dimensions in the wafer features that correspond to the primary features on reticle  20 . 
         [0031]    Completing some observations with respect to system  10 , the job deck output data file  34   3  is provided to a write device  40 . Write device  40  controls either an electron beam or laser beam  50  so that it traces a beam across the surface of reticle  20  based on the information in job deck output data file  34   3 . Specifically, reticle  20  includes a substrate  20   S , over which is a chrome layer  20   C , over which is an anti-reflection layer  20   AR , over which is a resist layer  20   R . Write device  40  performs a lithographic process by controlling the beam so that it writes to resist layer  20   R  an image, or “geometry,” that follows the data in file  34   3 , which recall should define reticle primary features that approximate that of CDL data  34   1  as provided by FRAM data  34   2 . As introduced above and detailed below, FRAM data  34   2  in this regard causes reticle assist features to be included in file  34   3  so that they will later be physically formed on reticle  20  to be positioned strategically with respect to many reticle primary features based on various considerations. In any event, the light in beam  50  reacts with resist layer  20   R  in those areas where the write occurs. Thereafter, a developing process is performed so that any resist that has been so reacted, or “exposed,” will be removed, leaving openings down to chrome layer  20   C . Next, reticle  20  is etched, that is, the portions of anti-reflection layer  20   AR  and chrome layer  20   C  that are now exposed are removed. Finally, the unreacted portions of resist layer  20   R  are removed, thereby leaving clear (or sometimes called “glass”) areas through which light may pass in the areas that were etched, while also leaving portions of anti-reflection layer  20 R elsewhere. Accordingly, reticle  20  now may be used in connection with a stepper or the like so that light may be passed through the clear areas on reticle  20  toward a wafer (not shown), while the light is blocked by the portions where anti-reflection layer  20   AR  remains, where such latter portions are often referred to as chrome, dark, or opaque. These remaining areas, therefore, include the reticle primary and assist features. 
         [0032]    Before further detailing various preferred embodiment aspects, some background to certain prior art methodologies for locating reticle assist features with respect to reticle primary features is now provided, starting with  FIG. 2   a .  FIG. 2   a  illustrates a block diagram of a portion of the surface of reticle  20  and that includes portions of chrome layer  20   C  from  FIG. 1 , where those chrome portions define a few dark areas that have been formed and, thus, are shown in the perspective of  FIG. 2   a . As known in the art and in connection with a bright field reticle, the dark areas, such as in  FIG. 2   a , are referred to as features. Similarly, however, in an opposite approach, a dark field reticle may be formed wherein the open lines are the rectangles in  FIG. 2   a  while the remainder of the reticle is darkened (i.e., covered with chrome), where in this case the open areas are referred to as features. In either event, and for sake of consistency and explanation in this document, each feature on the reticle is further identified herein as either: (i) a reticle primary feature where it is included so as to later cause the formation of a respective circuit feature (or “wafer feature” or “wafer primary feature”) on a wafer that is exposed to a light in combination with reticle  20 ; or (ii) a reticle assist feature, where the reticle assist feature is included proximate one or more reticle primary features and where the reticle assist feature is included so as to later influence the light diffraction and assist or contribute to the formation of the wafer circuit feature that is created due to the reticle primary feature that is proximate the reticle assist feature—further, when the reticle is so used, then ideally no wafer feature corresponding to the reticle assist feature should be printed on the wafer. 
         [0033]    Looking specifically to the features in  FIG. 2   a , it illustrates a reticle primary feature RPF 1 , a reticle primary feature RPF 2 , and a reticle assist feature RAF 1 . Each feature is shown to have a rectangular shape and for sake of reference has a respective major axis, shown by way of a respective dashed line—for purposes of this document, the major axis is an imaginary line that passes down the center of the longer dimension of the rectangular feature. Given the major axes, note that the axis of reticle primary feature RPF 1  is parallel to that of reticle primary feature RPF 2  and, thus, these two features are parallel to one another. For sake of distinction and not necessarily with an accurate scale, the line width LW (i.e., perpendicular to the major axis) for reticle assist feature RAF 1  is shown to be less than that of reticle primary features RPF 1  and RPF 2 . Also, while the features are all shown to have the same length, such is not required but is provided for sake of simplifying the present discussion. Still further, a primary-to-primary feature space PPSP 1  is shown between the closest edges E 1  and E 2 , respectively, of the two reticle primary features. With these introductions, and according to the prior art, where two reticle primary features are to be formed on a reticle such as shown in  FIG. 2   a , and provided the primary-to-primary feature space PPSP 1  between them is in a certain range (e.g., 330 to 430 nm), then a system such as system  10  also locates a reticle assist feature RAF 1  centered between the two reticle primary features RPF 1  and RPF 2 . Thus, in  FIG. 2   a , the primary-to-assist space, shown as PASP x  and defined as the distance from an edge of a reticle primary feature to the closest edge of an adjacent reticle assist feature, is the same with respect to both reticle primary features and reticle assist feature RAF 1 . In other words, PASP 1  and PASP 2  are equal to one another, thereby centering reticle assist feature RAF 1  between reticle primary features RPF 1  and RPF 2 . 
         [0034]    Given the illustrations of  FIG. 2   a , various observations are now made with respect thereto and for relating later to the preferred embodiments. Reticle primary features are described herein as “primary-type adjacent” relative to one another in that each is a primary type (i.e., as opposed to assist type) and they are situated such that there is not another reticle primary feature between these two reticle primary features. Thus, where two reticle primary features are primary-type adjacent in this manner and where one such reticle primary feature has at least some respective portion that is parallel to the other reticle primary feature, and presuming the reticle primary features are within a certain distance of one another and at least a predetermined minimum distance apart, then the prior art locates an assist feature equidistantly between the two. As a result, when reticle  20  is used to later write an image to a wafer, a first wafer feature will be written to the wafer by light passing around reticle primary feature RPF 1 , a second wafer feature will be written to the wafer by light passing around reticle primary feature RPF 2 , and while no third wafer feature will be formed from reticle assist feature RAF 1 , it will instead influence the light so as to provide better image quality and pattern to enable the printing of the wafer features corresponding to reticle primary features RPF 1  and RPF 2 . In this manner, therefore, reticle assist feature RAF 1  is also sometimes referred to as “shared” with respect to the reticle primary features, in that the former contributes to the wafer features created by the latter. 
         [0035]      FIG. 2   b  illustrates a block diagram of a different portion of the surface of reticle  20  in a manner comparable to  FIG. 2   a , but that includes different features so as to illustrate another prior art approach. Particularly, in  FIG. 2   b , there are shown a reticle primary feature RPF 3 , a reticle primary feature RPF 4 , and two reticle assist features RAF 2  and RAF 3 , where all of these features are (or include portions that are) parallel with respect to one another. In  FIG. 2   b , it is assumed that the primary-to-primary feature space PPSP 2  between reticle primary features RPF 3  and RPF 4  is greater than that (i.e., PPSP 1 ) in  FIG. 2   a , and therefore again at least a predetermined minimum distance apart. As a result, and also according to the prior art, a larger number of reticle assist features are located between the reticle primary features. Thus, in the example of  FIG. 2   b , rather than including one reticle assist feature as was the case in  FIG. 2   a , then two reticle assist features RAF 2  and RAF 3  are formed on the reticle surface. Per the prior art, reticle assist features RAF 2  and RAF 3  are symmetrically located between reticle primary features RPF 3  and RPF 4  such that the primary-to-assist space PASP 3  between adjacent edges E 3  and E AF2.1 , respectively, of reticle primary feature RPF 3  and reticle assist feature RAF 2 , and the primary-to-assist space PASP 4  between adjacent edges E 4  and E AF3.1 , respectively, of reticle primary feature RPF 4  and reticle assist feature RAF 3 , are the same distance (i.e., PASP 3 =PASP 4 ). The assist-to-assist space AASP 1  may vary, but note that regardless of its dimension there is still symmetry with respect to each reticle assist feature relative to its closest reticle primary feature. In this manner, when reticle  20  is used to write the image from  FIG. 2   b  to a wafer, reticle assist feature RAF 2  influences the light that will form the wafer feature corresponding to reticle primary feature RPF 3  in the same way and to the same extent that reticle assist feature RAF 3  influences the light that will form the wafer feature corresponding to reticle primary feature RPF 4 . 
         [0036]      FIG. 2   c  illustrates a prior art block diagram of yet another different portion of the surface of reticle  20  in a manner comparable to  FIGS. 2   a  and  2   b , where the space between the reticle mask features is increased farther as compared to  FIGS. 2   a  and  2   b . As a result, in  FIG. 2   c , there are shown a reticle primary feature RPF 5 , a reticle primary feature RPF 6 , and three reticle assist features RAF 4 , RAF 5 , and RAF 6 , where all of these features include portions that are parallel with respect to one another. Moreover and also according to the prior art, the number of reticle assist features is increased as compared to the earlier Figures. Further, reticle assist features RAF 4 , RAF 5 , and RAF 6  are symmetrically located between reticle primary features RPF 5  and RPF 6  such that the primary-to-assist space PASP 5  between adjacent edges E 5  and E AF4.1 , respectively, of reticle primary feature RPF 5  and reticle assist feature RAF 4 , and the primary-to-assist space PASP 6  between adjacent edges E 6  and E AF6.1 , respectively, of reticle primary feature RPF 6  and reticle assist feature RAF 6 , are the same distance (i.e., PASP 5 =PASP 6 ). Moreover, reticle assist feature RAF 5  is centered as between reticle primary features RPF 5  and RPF 6  (i.e., AASP 2 =AASP 3 ). In this manner, when reticle  20  is used to write the image from  FIG. 2   c  to a wafer, reticle assist features RAF 4  and RAF 5  influence the light that will form the wafer feature corresponding to reticle primary feature RPF 5  in the same way that reticle assist features RAF 5  and RAF 6  influence the light that will form the wafer feature corresponding to reticle primary feature RPF 6 . 
         [0037]    Additional placements of reticle assist features may be performed in various manners. For example, other placements are known in the art and are not illustrated herein but a few additional aspects are worth mentioning. While  FIGS. 2   a  through  2   c  show up to three reticle assist features, that number may be increased still further as between two primary-type adjacent reticle features that are at least a predetermined minimum distance apart. Thus, the number of reticle assist features may vary and the prior art locates them symmetrically between the primary-type adjacent reticle features. Note also that assist features also may be used with respect to a reticle primary feature that is sufficiently far away from any other primary feature so as to be considered isolated. In this “isolated” case, then reticle assist features are typically placed on both sides and at equidistant distances from the isolated reticle primary feature, again creating a symmetry, but here such that the reticle primary feature is centered with respect to the reticle assist features. Lastly, assist features may be located according to co-pending patent application Ser. No. 11/340,251, entitled “Method of Locating Sub-resolution Assist Feature(s)”, filed Jan. 25, 2006, and hereby incorporated herein by reference. 
         [0038]      FIG. 3  illustrates a flowchart of a methodology  100  to be implemented by processor system  30  per FRAM data  34   2  of the preferred embodiment in  FIG. 1  as well as its effect in creating job deck output data file  34   3 . While methodology  100  is shown by way of a flowchart, one skilled in the art will appreciate that it may be implemented in various forms and included within system  30 , such as by programming code, instructions, rules, parameters, and other data in FRAM data  34   2  and with the appropriate responses and operation by processor system  30 . Moreover, various steps may be substituted or re-arranged in the flow or occur concurrently depending on processing power and the like, and the flow also may be illustrated in other forms such as a state machine or still others. In all events, the following steps and illustration therefore are by way of example and do not exhaustively limit the inventive scope. 
         [0039]    By way of introduction, methodology  100  includes at its beginning a number of steps  110  through  170 . These steps are explored below and are shown to in effect perform a first iteration of analyses on CDL data  34   1  so that data for primary features corresponding to circuit layout data in CDL data  34   1  are written to job deck output data file  34   3 , and data for assist features are also included in output data file  34   3  so as to assist the primary features (i.e., when later forming wafer features with a reticle  20  that is constructed from output data file  34   3 ). By example, steps  110  through  170  in a preferred embodiment may include steps that are known in the prior art or, alternatively, by another example some of these steps may be modified by one skilled in the art according to various techniques but in all events to yield data, such as for inclusion in output data file  34   3 , to establish primary and assist features to be formed on reticle  20 . In any event, however, the steps following step  170  are per the preferred embodiment and, as demonstrated later, operate to provide an additional iteration that identifies any area adjacent a primary feature that is, after the preceding iteration, sufficiently empty of an assist feature; per the preferred embodiment, the methodology performs additional analyses so as to potentially indicate an assist feature to be included in the respective empty area. Each of these aspects is further explored below. 
         [0040]    Method  100  begins with a step  110 , where in response to FRAM data  34   2  processor system  30  identifies one or more wafer features in CDL data  34   1 , that is, it identifies wafer features that are to be established to correspond to the circuit features specified in CDL data  34   1 , such as per the prior art. For example, the particular wafer feature or features identified in a given operation of step  110  depends on whether the wafer feature is isolated or is nearby one or more other wafer features. In this regard, the determination of whether a given wafer feature is considered isolated or nearby one or more other features depends on distances that are evaluated from the given wafer feature. Thus, in present technology this distance may be in the approximate range of 1 to 500 nm so that if the given wafer feature has no other wafer feature within that range of it, then it is considered isolated and may be separately identified by step  110 . Alternatively, if the given wafer feature has one or more other wafer features within that range of it, then those wafer features with such a distance may all be identified for a given occurrence of step  110 . Next, method  100  continues from step  110  to step  120 . 
         [0041]    In step  120 , and again in response to FRAM data  34   2 , processor system  30  determines and stores into output data file  34   3  the size, shape, and location of one or more reticle primary (i.e., non-assist) features and one or more reticle assist features for the wafer feature(s) identified in step  110 . Further, the determined feature information is preferably stored in job deck output data file  34   3  (or in memory for later writing to output data file  34   3 ). This determination again depends on whether the step  110  identified wafer feature is isolated or adjacent one or more other wafer features, as well as the methodology in FRAM data  34   2 . For example, if a step  110  wafer feature is isolated, then step  120  preferably determines to locate a reticle primary feature of a particular size and shape, for ultimate printing on a reticle  20 , so that the primary feature will cause the formation of the corresponding isolated wafer feature. In addition, however, and consistent with the discussion in the Background Of The Invention section, step  120  may determine and store the size, shape, and location of a reticle assist feature to assist the reticle primary feature in forming the corresponding isolated wafer feature, provided such a reticle assist feature will not cause a corresponding print on a wafer. As another example, if a step  110  identified wafer feature is within a predetermined distance of another step  110  identified wafer feature (i.e., if the wafer features are primary-type adjacent); then step  120  preferably determines and stores the size, shape, and location of two respective reticle primary features, for ultimate printing on a reticle  20 , so that each reticle primary feature will cause the formation of a respective corresponding wafer feature. In addition, however, and consistent with the earlier discussion of  FIG. 2   a  and thereafter, step  120  may determine and store data for the size, shape, and location of one or more reticle assist features to later assist the reticle primary features in forming the corresponding two wafer features. These reticle assist features may be located per the data, by ways of example, as shown in  FIGS. 2   a ,  2   b , and  2   c , so as to be centered between the primary features and thereby to assist each primary feature equally. Alternatively, per the teachings of the above-incorporated U.S. patent application Ser. No. 11/340,251, the reticle assist features may be located per the data so as to assist in the formation of one step  110  identified reticle feature more than the other step  110  identified wafer feature. Still other techniques may be used to locate reticle primary and reticle assist features for step  110 , as may be ascertained by one skilled in the art. Moreover, while a single step  110  is shown for the generation of reticle primary and reticle assist feature data, this step may be separated into separate processes as well so that reticle primary feature data are established in one instance and reticle assist feature data are established in another. Following step  120 , method  100  continues to step  130 . 
         [0042]    Step  130  is a conditional step that determines whether there are additional wafer features in CDL data  34   1  that have not yet been processed per steps  110  and  120 , that is, whether there are wafer features for which a reticle primary feature and consideration of assist have not yet been made. If one or more additional such wafer features exists, then method  100  returns from step  130  to step  110 , so that the additional unprocessed wafer features are identified and data for at least a respective reticle primary feature, and possibly a reticle assist feature, is provided into output data file  34   3  for each wafer feature described by data in CDL data  34   1 . Once each such wafer feature has been identified (and processed by step  120 ), the condition of step  130  is answered in the negative, and method  100  continues from step  130  to step  140 . 
         [0043]    Steps  140  through  170  operate to remove some of the reticle assist features that were previously included by step  120  for inclusion into job deck output data file  34   3 . Specifically, the prior art recognizes that through the analyses conducted by the repeated iterations of step  120 , certain reticle assist features that were planned for inclusion, or for which data was stored, in data file  34   3  may be undesirable for one of various reasons and, therefore, are candidates for removal from output data file  34   3 . Toward this end, step  140  identifies the data for a reticle assist feature stored for inclusion or already in output data file  34   3 , and method  100  then continues to step  150 . 
         [0044]    Step  150  determines whether the step  140  identified reticle assist feature data violates any rule in FRAM data  34   2  that may indicate that the reticle assist feature is undesirable for final use on reticle  20 . In this regard, note that typically in contemporary applications of method  100  a very large number of assist features are initially indicated by the many occurrences of step  120  file of for a given CDL data  34   1 . For example, for such a file, the repeated instances of step  120 , corresponding to the many step  100  identified wafer features, may give rise to hundreds of millions of reticle assist features being indicated for inclusion into output data file  34   3 . However, in the subsequent analysis of step  150 , there is a chance for the data that provides for some of these reticle assist features to be removed from, or prevented from being written to, output data file  34   3 . For example, step  150  may determine whether a step  140  identified reticle assist feature will, when used on reticle  20 , cause a respective feature to print on a wafer; if this is the case, then the reticle assist feature is undesirable and step  150  is answered in the affirmative. As another example, step  150  may determine that a step  140  identified reticle assist feature would, if included on a reticle  20 , be located too dose to a nearby reticle primary feature, thereby improperly assisting or wrongfully affecting the wafer feature to be formed in response to the nearby reticle primary feature; again, if this is the case, then the reticle assist feature is undesirable and step  150  is answered in the affirmative. As still another example, step  150  may determine that a step  140  identified reticle assist feature would, if included on a reticle  20 , create a process violation. Still other examples may be ascertained by one skilled in the art. In any event, if step  150  is answered in the affirmative, method  100  continues to step  160 . Alternatively, if step  150  is answered in the negative, method  100  continues to step  170 . 
         [0045]    Step  160  deletes from output data file  34   3 , or prevents the writing into output data file  34   3 , the data that specifies the reticle assist feature identified and analyzed in the immediately preceding occurrence of steps  140  and  150 . Returning to the first example of the preceding paragraph, therefore, if a reticle assist feature is determined to present a risk of causing a corresponding print on a wafer, then step  160  ensures that the data that would create the reticle assist feature is not included in output data file  34   3 . Alternatively looking to the second example of the preceding paragraph, if a reticle assist feature is determined to be planned for location that is too dose or inoperative relative to the location of a nearby reticle primary feature also specified in output data file  34   3 , then step  160  ensures that the data that would create the reticle assist feature is not included in output data file  34   3 . Further, and for reasons detailed later, in one preferred embodiment, step  160  may optionally store an indication of the location that the deleted reticle assist feature would have occupied had it been left in output file  34   3  for purposes of being printed on a reticle. Following step  160 , method  100  continues to step  170 . 
         [0046]    Step  170  is a conditional step that determines whether there are data specifying additional reticle assist features in output data file  34   3  (or that are indicated, such as in memory, for inclusion into output data file  34   3 ) that have not yet been processed per steps  140  and  150 , that is, whether there are reticle assist features that have not been reviewed by step  150 . If one or more additional such assist features exists, then method  100  returns from step  170  to step  140 , so that the additional unprocessed assist feature(s) may be identified and analyzed. Once each such reticle assist feature in output data file  34   3  has been identified by step  140  and processed by step  150 , the condition of step  170  is answered in the negative and method  100  continues from step  170  to step  180 . 
         [0047]    Having reached step  180 , an overview is now presented of the results of methodology  100  thus far as well as the remaining steps of methodology  100 . From the preceding steps, one skilled in the art will appreciate that output data file  34   3  includes data specifying numerous reticle primary features as well as numerous reticle assist features. The reticle primary features were specified and included in output data file  34   3  from numerous iterations of step  120 , and note that in a typical contemporary circuit there may at this point be in the range of 100 to 500 million reticle primary features. Further, recall that by way of example there could be hundreds of millions of reticle assist features from the numerous iterations of step  120 , and note also that with numerous iterations of step  160  then on the order of 0.001%, which in the present example may be tens of thousands (or more), of those reticle assist features may be subsequently removed, or kept from, output data file  34   3 . Thus, at this point in the process, one skilled in the art could proceed, and indeed in the prior art in many instances would proceed, to use output data file  34   3  to create reticle  20 . However, in the preferred embodiments, starting with step  180  and thereafter, additional reticle assist features may be included in output data file  34   3  prior to creating a reticle  20  with that file, as further explored below. 
         [0048]    In step  180  and in response to FRAM data  34   2 , processor system  30  identifies the data specifying one or more reticle primary features in output data file  34   3 , where the particular reticle primary feature or features in a given operation of step  180  depends on whether the reticle primary feature is isolated or is nearby one or more other reticle primary features. In this regard, the determination of whether a given reticle primary feature is considered isolated or nearby one or more other features depends on a distance that is evaluated from the given primary feature. Thus, in the preferred embodiment, a reticle primary feature is considered isolated if there is no other primary feature within a distance of 1 to 850 nm from the given reticle primary feature. Alternatively, step  180  will identify multiple reticle primary features if those features are all within the distance of 1 to 850 nm from one another. Next, method  100  continues from step  180  to step  190 . 
         [0049]    In step  190 , processor system  30  examines an area adjacent to and extending away from an edge of the step  180  identified reticle primary feature(s) and then determines if a threshold-exceeding amount of a reticle assist feature already has been located (i.e., by specified data), at least in part, in that area according to the designations in output data file  34   3 , for example where such a reticle assist feature was previously indicated to be located in that area into output data file  34   3  by step  120 . To further illustrate step  190  in this regard,  FIG. 4   a  illustrates a region  300   1  that is intended, in part, to be a pictorial representation of the data in output data file  34   3  insofar as it indicates reticle primary features and reticle assist features, that is, if the data calls for the formation of either type of feature then such a feature is shown in  FIG. 4   a . Thus, in  FIG. 4   a , a data reticle primary feature DRPF 1  is shown, where the descriptor “data reticle primary feature” is intended to suggest that data in output data file  34   3  indicates by data a reticle primary feature that thereafter will be printed on a reticle  20  if that printing is done per the data in output data file  34   3 . However, region  300 , is also intended to illustrate that output data file  34   3  does not, at the instant time of step  190 , indicate that a reticle assist feature is to be formed in region  300   1  and, thus, only data reticle primary feature DRPF 1  is shown and there is no nearby assist feature. Continuing with the illustration of step  190  and looking now to  FIG. 4   b , it again illustrates region  300   1 , but it further illustrates that step  190  examines an area shown in  FIG. 4   b  by a dotted-lined enclosed area A 1.1 ; thus, in this preferred embodiment example, area A 1.1  is defined by a polygon adjacent to and extending in a direction away from a respective edge E 1.1  of data reticle primary feature DRPF 1 . In the preferred embodiment, the polygon endosing area A 1.1  is a pentagon, although other shapes may be used to define the area and the area may be symmetric or asymmetric. In any event, in the application of step  190  to data reticle primary feature DRPF 1 , processor system  30  analyzes the data in output data file  34   3  to determine if there already is a reticle assist feature specified by data to be located at least in part within area A 1.1 . More specifically, step  190  examines an area (e.g., area A 1.1 ) and determines whether the amount, if any, of a reticle assist feature in that area exceeds a threshold. This threshold may be selected by one skilled in the art and is preferably less than twenty and more preferably less than ten percent of the area; thus, in the latter example, step  190  determines whether any reticle assist feature area, within area A 1.1 , is more or less than the threshold of the area A 1.1 . So, for example, if area A 1.1  is 43,000 nm 2 , then step  190  determines if less than 4,300 nm 2  of that area includes a reticle assist feature. Note that the threshold may be reduced to any number. For example, by setting the threshold to zero percent, then step  190  determines if the examined area is devoid of or “empty” with respect to any part of a reticle assist feature. Alternatively, the threshold may be increased to somewhere between zero and ten percent to thereby determine if that area is devoid of or empty with respect to any non-negligible part of a reticle assist feature. Thus, for the remainder of this document, the examination of an area in this regard is referred to with respect to a threshold-amount of the area including any part of a reticle assist feature, where one skilled in the art should now understand that the threshold may be adjusted accordingly. Continuing then with step  190 , if the examined area already includes a threshold-exceeding portion of a reticle assist feature, then step  190  is answered in the affirmative and method  100  continues to step  210 , whereas if the examined area includes less than the threshold amount (e.g., does not include any portion) of an assist feature, then step  190  is answered in the negative and method  100  continues to step  200 . Thus, in the example of  FIG. 4   b , no reticle assist feature is included within area A 1.1  and, thus, method  100  continues to step  200 . Note also in this regard, therefore, that step  190  permits a negative finding even if some below-the-threshold portion of the examined area includes a reticle assist feature, where again the determination of the threshold may be left to one skilled in the art and may be coded such that in some instances a relatively small amount of an existing reticle assist feature may be within the examined area and yet, because that amount is below the threshold, the area is deemed to be sufficiently “empty” with respect to a reticle assist feature and the method will therefore continue to step  200 . 
         [0050]    The above demonstrates that step  200  is reached when processor system  30  determines that an area adjacent a reticle primary feature edge is not indicated to include a threshold-exceeding amount of a reticle assist feature. In response, in step  200  processor system  30  includes into data output file  34   3  sufficient data so that a reticle assist feature will be formed in the area that was examined (e.g., area A 1.1 ) and found to be sufficiently lacking (i.e., less than the threshold) of a reticle assist feature, provided that when the features of the region (e.g., region  300   1 ) are later mapped to a corresponding reticle  20  the added reticle assist feature will not cause the printing of a respective feature on the wafer when the reticle  20  is used to process the wafer. In other words and in the example of  FIG. 4   b , in an area A 1.1  adjacent to and extending away from a data reticle primary feature DRPF 1  and where no threshold-exceeding amount of a reticle assist feature was to exist after the preceding analyses and operations of step  120  (and possibly  160 ), then step  200  includes data so that a reticle assist feature will be included in that area. In this regard,  FIG. 4   c  again illustrates region  300   1 , but now it includes a data reticle assist feature DRAF 1 ; note also that the word “data” is included in this descriptor to indicate, similar to data reticle primary feature DRPF 1 , that at this point the actual reticle primary feature or reticle assist feature is not yet created but the data describing it and from which it will be created is included in output data file  34   1 . Thus, where the reticle primary feature identified in step  180  was previously unassisted by virtue of no (or relatively little) nearby reticle assist feature, then following step  200  that reticle primary feature will be assisted by a reticle assist feature, where by example in  FIG. 4   c  data reticle primary feature DRPF 1  feature DRPF 1  will create a reticle primary feature and it will be assisted by a data reticle assist feature DRAF 1  created by step  200 . In other words, where the first possible assist-inclusion iteration, step  120 , that could have included an assist feature did not do so (or that assist feature was deleted by step  160 ), then step  200  provides an additional iteration that may indeed insert such an assist feature. Given that step  200  provides data for a reticle assist feature, in the preferred embodiment step  200  also provides the particular location, shape, and size for the reticle assist feature. In the preferred embodiment, the step  200  created reticle assist feature location may be at a set distance from the primary feature to be assisted, or as shown below by example centered between two primary features to be assisted, or determined by various methodologies detailed later. Also in the preferred embodiment, the step  200  reticle assist feature shape is preferably rectangular when it is to assist a single or isolated primary feature. Lastly, note also in the preferred embodiment that preferably the step  200  created reticle assist feature has dimensions equal to or less than any reticle assist feature defined in step  120 , particularly because a larger assist feature may not have been included by step  120  (or was excluded by step  160 ) because such a larger size was unacceptable relative to the nearby reticle primary feature(s) that it would have assisted and, thus, a smaller step  200  data reticle assist feature is provided so as to reduce the chance of incurring the issue that the larger step  120  feature may have caused. Thus, the length of a step  200  reticle assist feature (e.g., shown in the vertical direction in  FIG. 4   c ) may be in the range of 85 to 200 nm, whereas the length of a step  120  reticle assist feature may be in the range of 150 to 300 nm 
         [0051]    Also in connection with steps  190  and  200 , note that the illustration of  FIGS. 4   a  through  4   c  is shown in connection with edge E 1.1 , of data reticle primary feature DRPF 1.1 . Only this single edge is discussed in order to simplify the demonstration. However, in the preferred embodiment, step  190  is performed, either in one instance or in repeated occurrences of the step, for each different linear edge of the step  180  identified data reticle primary feature. Thus, in the example of  FIG. 4   a , the same inquiry of step  190  is made for edges E 1.1 , E 1.3 , and E 1.4 , where each of those edges therefore, if adjacent to an area (e.g., comparable to area A 1.1  but extending away from the respective other edge) that does not include a threshold-exceeding part of a reticle assist feature, becomes a candidate for candidate for such an assist feature to be included by step  200 , so long as that assist feature will not cause a respective wafer feature to be later printed. Thus, once all edges E x.y  of a data reticle primary feature have been analyzed by steps  190  and  200 , then method  100  continues to step  210 . 
         [0052]    Step  210  is a conditional step that determines whether there are additional reticle primary features specified by data in output data file  34   3  (or that are indicated, such as in memory, for inclusion into data file  34   3 ) that have not yet been processed per steps  180 ,  190 , and possibly  200 , that is, whether there are data reticle primary features that have not been reviewed by step  190  to determine if an area adjacent an edge of such feature does not include at least a threshold-exceeding part of a reticle assist feature. If one or more additional such data reticle primary features exists, then method  100  returns from step  210  to step  180 , so that such additional unprocessed primary feature(s) may be identified and analyzed. Once each such primary feature has been considered, the condition of step  210  is answered in the negative, and method  100  continues from step  210  to step  215 . 
         [0053]    Step  215  is intended to include the same operations as were performed in steps  140  through  170  discussed above, where these operations now follow a negative finding in step  210 . Thus, when step  210  determines that there are not additional unprocessed primary features in output data file  34   3  to be processed by steps  180  through step  200 , then step  215  represents that for those additional reticle assist features for which data were created by occurrences of step  200 , then the operations of steps  140  through  170  are performed. Thus, for each such additional data reticle assist feature (i.e., step  140  type operation), an evaluation is made as to whether it violates any rule(s) (i.e., step  150  type operation) and, if so, that respective feature is deleted (i.e., step  160  type operation), continuing until all such additional data reticle assist features are considered (i.e., step  170  type operation). Thus, step  215  demonstrates that for step  200  added reticle assist features, these features are also each considered and deleted should any of them violate any step  150  rule. Step  215  ends with a condition like step  210  and is why a triangle is used for step  215  in the flowchart of  FIG. 3 , so that if there are any additional unprocessed data reticle assist features, the flow returns for each such feature and when all such features are processed, then preferably method  100  continues to step  220 . However, note that in an alternative embodiment method  100  may return yet again to step  180  at this point. In this manner, therefore, after additional data reticle assist features have been included by step  200  and some of those have been deleted by the step  160  type operation of step  215 , then in this alternative embodiment another occurrence(s) of step  180  could include yet additional data reticle assist features, and one skilled in the art may adjust the number of times that steps  180  through  200  are repeated in this manner. 
         [0054]    Step  220  represents the completion of method  100 , insofar as output data file  34   3  is complete and therefore ready for use to print the data reticle primary and data reticle assist features therein on a reticle  20 . Thus, consistent with the earlier discussion of  FIG. 1 , at this point output data file  34   3  is used as a job deck to drive a write device  40 , and write device  40  thereby writes to a reticle  20  the reticle primary and reticle assist features provided by the respective data in that job deck. 
         [0055]    Having demonstrated via  FIGS. 4   a  through  4   c  one example of the application of step  200  and the inclusion thereby of a data reticle assist feature into an area adjacent a data reticle primary feature that did not previously include at least a threshold-exceeding amount of a reticle assist feature, and recalling that in that example the data reticle primary feature was an isolated feature, additional Figures and discussion are now provided to demonstrate that step  180  may apply to other examples, including neighboring data reticle primary features. These examples are shown below in  FIGS. 5   a - 5   c ,  6   a - b , and  7 . 
         [0056]      FIG. 5   a  illustrates a region  300   2  that is intended to be a pictorial representation similar to  FIG. 4   a , meaning of the data in output data file  34   3  insofar as it indicates data reticle primary features and data reticle assist features (i.e., if the data calls for the formation of either type of feature then such a feature is shown in  FIG. 5   a ). Also,  FIG. 5   a , like  FIG. 4   a  above, is intended to demonstrate in part the operation of method  100  starting with step  180 , that is, after the preliminary iterations through step  170  have been taken with respect to the data in CDL file  34   1 , per the methodology in FRAM data  34   2 , so as to provide data for reticle primary and reticle assist features to be formed on a reticle. In  FIG. 5   a , and per step  180 , two data reticle primary features DRPF 2.1  and DRPF 2.2  are identified and thus shown in the Figure, meaning in this document that data in output data file  34   3  indicates that two respective data reticle primary features will be thereafter printed on a reticle  20  if constructed per output data file  34   3 . Further, there is no reticle assist feature shown in region  300   2 , thereby intending to depict that output data file  34   3  does not, as of the time of step  190 , provide for a reticle assist feature to be formed in region  300   2 ; thus, were output data file  34   3  used at this point to construct features on a reticle, then with respect to region  300   2  only reticle primary features from data reticle primary features DRPF 2.1  and DRPF 2.2  would be constructed with no nearby reticle assist feature in region  300   2 . 
         [0057]    Turning to  FIG. 5   b , it again illustrates region  300   2 , but it further illustrates that respective dotted-lined enclosed polygon areas A 2.1  and A 2.2  are examined by step  190 . In the preferred embodiment, note therefore that when areas are extended from more than one data reticle primary feature such as in the example of  FIG. 5   b , then each such area is of a same geometry. Thus, in this example, area A 2.1  is defined by a polygon extending away from a respective edge E 2.1.1  of data reticle primary feature DRPF 2.1  and in one dimension (shown horizontally) and area A 2.2  is defined by a polygon of the same geometry and extending in the same dimension but in an opposite direction, namely, away from a respective edge E 2.2.1  of data reticle primary feature DRPF 2.2 . Thus, in the present example, step  180  identifies two data reticle primary features and the subsequent step  190  extends areas, preferably of the same geometry, from respective edges of the identified features. Moreover, in step  190 , processor system  30  analyzes the data in output data file  34   3  to determine if there already is data specifying a data reticle assist feature to be located, at least spanning an area that exceeds the step  190  threshold, within either of areas A 2.1  and A 2.2 . In the example of  FIG. 5   b , it may be seen by the pictorial illustration of the data that no such reticle assist feature was previously indicated (e.g., by step  120 ) for those areas. Thus, method  100  continues to step  200 , as further explored below in connection with  FIG. 5   c.    
         [0058]      FIG. 5   c  illustrates region  300   2  following the application of  FIG. 3  step  200  to  FIG. 5   b . For  FIG. 5   c , processor system  30  of  FIG. 1  determines that an area adjacent a reticle primary feature edge is not indicated to include a threshold-exceeding amount of a reticle assist feature given that areas A 2.1  and A 2.2  are devoid of any part of a data reticle assist feature. In response, processor system  30  includes into data output file  34   3  sufficient data so that an assist feature will be formed when that file is used to process and thereby create features on a reticle. Also in the preferred embodiment,  FIG. 5   c  illustrates an example of more than one identified data reticle primary feature, and in this case the step  200  added data reticle assist feature is located so that a least a portion of the added assist feature is within the respective area for each data reticle primary feature; thus, in the example of  FIG. 5   c , a data reticle assist feature DRAF 2  is added to the data in output data file  34   3  whereby at least a portion of data reticle assist feature DRAF 2  is within both areas A 2.1  and A 2.2  again provided that the added reticle assist feature will not cause the printing of a respective feature on a wafer when a respective reticle is used to process the wafer. Further, in the preferred embodiment and where two data reticle primary features have co-aligned areas extending toward one another as is the case in  FIGS. 5   b  and  5   c , and as occurs when an imaginary perpendicular line extended perpendicularly from one edge of one of those features would contact, in substantial perpendicular orientation, an edge of the other of those features (i.e., those features are “opposing” one another in orientation), then the added assist feature is preferably centered between the two data reticle primary features to be assisted. Thus, in the example of multiple data reticle primary features, and for their respective overlapping areas A 2.1  and A 2.2  where no reticle assist feature was to exist after the preceding analyses of step  120  (and possibly  160 ), then step  200  potentially includes data so that such an assist feature will be included and centered between the two primary features. Thus, where the data reticle primary features DRPF 2.1  and DRPF 2.2  identified in step  180  were previously unassisted by virtue of no nearby reticle assist feature, then following step  200  each such primary feature will be assisted by an assist feature DRAF 2.2 . 
         [0059]    With the illustrations of  FIGS. 4   a  through  5   c , one skilled in the art should readily appreciate that the preferred embodiment methodology examines an area adjacent a data reticle primary feature(s), and if that area does not encompass, at least a threshold-exceeding amount of a reticle assist feature to be included in that area, then data for a reticle assist feature may be added so that such a feature will be formed in that area. With that appreciation,  FIG. 6   a  illustrates another example of the application of these aspects, and here in relation to a region  300   3 . Specifically, to simplify the remaining discussion and illustrations, region  300   3  is shown pictorially as an example as it would appear from corresponding data after step  190  of method  100 . Thus, looking to region  300   3 , it includes two data reticle primary features DRPF 3.1  and DRPF 3.2 . Recall that  FIG. 5   a  also illustrated two data reticle primary features, but in that case an imaginary perpendicular line extended from one edge of one of those features would contact, in perpendicular orientation, an edge of the other of those features (i.e., those features were “opposing” one another in orientation). In contrast, in  FIG. 6   a , the two data reticle primary features are oriented such that an imaginary perpendicular line L 1  extended from one edge (e.g., E 3.1.1 ) of one of those features (e.g., DRPF 3.1 ) is substantially perpendicular (i.e., 90 degrees or within a few degrees thereof) to an imaginary perpendicular line L 2  extending from one edge (e.g., E 3.2.1 ) of the other feature (e.g., DRPF 3.2 ), and the features are still sufficiently close to one another so that they are identified by step  180 . In such an example, in applying step  190  to region  300   3 , processor system  30  examines an area A 3.1  extending away from edge E 3.1.1  of feature DRPF 3.1  and an area A 3.2  extending away from edge E 3.2.1  of feature DRPF 3.2 . As in the case of  FIG. 4   b , in  FIG. 6   a  the extended areas overlap and that overlapping area does not include, at least a threshold-exceeding amount of a reticle assist feature to be created as indicated by data presently in output data file  34   3 , thereby giving rise by method  100  to a response as discussed below. 
         [0060]      FIG. 6   b  illustrates region  300   3  following step  200  as applied to the same region of  FIG. 6   a . Thus, step  200  includes data into output data file  34   3  to provide for a data reticle assist feature DRAF 3 , in at least the region of the overlapping areas A 3.1.  and A 3.2 . Recalling the perpendicular orientation of feature DRPF 3.1  relative to feature DRPF 3.2  (i.e., such that perpendicular lines L 1  and L 2  extending from the edges each perpendicularly cross one another), then preferably step  200  provides data specifying a reticle assist feature, shown in  FIG. 6   b  as data reticle assist feature DRAF 3 , that has two longer portions P 1  and P 2  (i.e., each with a length longer than its width), with one portion P 1  having a majority of its length parallel to the closest edge E 3.1.1  of one primary feature DRPF 3.1  and another portion P 2  having a majority of its length parallel to the closest edge E 3.2.1  of the other primary feature DRPF 3.2 . In this manner, when a reticle is formed using region  300   3 , then portion P 1  will tend to assist data reticle primary feature DRPF 3.1  and portion P 2  will tend to assist data reticle primary feature DRPF 3.2 . 
         [0061]      FIG. 7  pictorially illustrates data from a final example of the results from steps  180  through  200  of the preferred embodiments, where in this example more than two data reticle primary features are identified by step  180 . In the example of  FIG. 7 , five such features are shown as DRPF 4.1  through DRPF 4.5 . To simplify this discussion and in view of the previous examples,  FIG. 7  pictorially illustrates the result following the completion of step  200  with respect to region  300   4 . In applying step  190  to region  300   4 , processor system  30  examines areas A 4.1.1  through A 4.5.1  extending respectively from each edge E 4.1.1  through E 4.5.1  of each primary feature DRPF 4.1  through DRPF 4.5 . In the example of  FIG. 7 , the extended areas A 4.x  are situated toward one another, although it should be understood that step  190  also may consider comparable areas in other directions. For instance, in  FIG. 7 , area A 4.1  is considered and extends from edge E 4.1.1 , although step  190  also may consider an area extending from any of the other edges of feature DRPF 4.1 , as well as for the other features of  FIG. 7 . Returning to the example illustrated, the extended areas overlap and, while not shown as a separate figure, assume that each of the areas as of the time step  190  is applied do not include a threshold-exceeding amount of a reticle assist feature. In response, then step  200  includes data into output data file  34   3  to provide for a data reticle assist feature DRAF 4 , in the region of the overlapping areas A 4.1  through A 4.5 . In the preferred embodiment, where the extending areas correspond to more than two data reticle primary features, then preferably step  200  provides a square-shaped assist feature, as shown in  FIG. 7 . In this manner, when a reticle is formed using region  300   4 , then assist feature DRAF 4  will tend to assist each of data reticle primary features DRPF 4.1  through DRPF 4.3 . 
         [0062]    Method  100  and the preceding examples thereby demonstrate various aspects of the preferred embodiment for determining size, shape, and location for reticle assist features through the additional steps  180  through  210 . Further in this regard and as discussed partially above, the preferred embodiments may include various different methodologies for determining a specific location for such an assist feature. For example, in a case such as shown in  FIG. 7  where more than two primary features are considered and have respective areas that do not include at least a threshold-exceeding amount of an already-determined assist feature, then such an assist feature is included so that it is at least partially within, or overlapped, by the overlapping portions of the examined areas. In such an instance, the preferred embodiment methodology for locating such an assist feature could be any of the following. In one approach, the preferred embodiment determines if there were two or more assist features in the examined area that were deleted by occurrences of step  160 ; if so, then in step  200 , the location (e.g., x,y coordinate) of the step  200  added assist feature is based on the average of the locations (e.g., respective x,y coordinates) of the previously deleted assist features, where recall that step  160  may store an indication, including the intended location, of any step  160  deleted assist feature. In another approach, the preferred embodiment locates the step  200  assist feature according to a center-of-mass resulting from a sum of the individual examined areas (e.g., A 4.1  through A 4.5  in  FIG. 7 ) corresponding to the primary features being considered, and this center of mass is a coordinate, such as the center coordinate, of the step  200  assist feature. In still another approach, each examined area (e.g., A 4.1  through A 4.5  in  FIG. 7 ), corresponding to each considered primary feature, is assigned a specific x,y coordinate and the coordinates of the examined areas are averaged to arrive at the final x,y location of the step  200  assist feature. A final approach is to calculate a minimum sized geometry (e.g., rectangle or other shape) that completely contains the areas (e.g., A 4.1  through A 4.1  in  FIG. 7 ) of all primary features being considered and using the center of that shape as the center of the step  200  assist feature. Lastly, while the preceding examples are preferable for instances where two or more primary features are being considered (e.g.,  FIG. 7 ), these or modifications thereof also may apply to the instance where only two primary features are being considered (e.g.,  FIGS. 5   a - c ,  6   a - b ). 
         [0063]    From the above, it may be appreciated that the preferred embodiments provide a method for locating reticle assist features on a resulting reticle or mask for use in forming semiconductor circuits, where such features may be from either bright field or dark field reticles and such reticles may or may not use phase shifting and include other variants such as chromeless phase lithography. The method and resulting reticle herein described may have particular benefit in instances of complex semi-random circuit layouts. Thus, in a regular array of gates or contacts the need for the application of the preferred embodiments may be attenuated or bypassed, but in more random if not arbitrary layouts, the prior art may fail to locate reticle assist features or may have them deleted and in such case the preferred embodiments ultimately provide a greater amount of assist. In addition, the preferred embodiments improve upon the prior art, in that the prior art as well as step  110  through  170  herein may result in a small percentage of reticle sites with no discerned answer as to locating reticle assist features, whereas the preferred embodiments implement a secondary method to potentially place such assistance in those sites; this secondary method uses relaxed rules differing from those of the primary method and thereby increase the possibility of assistance in most sites. Further, various alternatives have been provided according to preferred embodiments, and still others may be ascertained by one skilled in the art. In all events, the preferred embodiments have been shown to provide one or more reticle assist features adjacent a reticle primary feature, where the reticle assist features may be established in a first iteration by a set of rules such as known in the art or other techniques, but in a second iteration a reticle assist feature may be added adjacent a reticle primary feature if there is an area extending from that primary feature that does not already include at least a threshold-exceeding amount of an assist feature. In this regard, therefore, in locations where no (or an insufficient amount of) reticle assist feature existed relative to a reticle primary feature in the prior art, the preferred embodiments provide the possibility of including such an assist feature, thereby further assisting with the creation of wafer features when the reticle assist feature is later used in connection with a reticle primary feature. Given the preceding, therefore, one skilled in the art should further appreciate that while the present embodiments have been described in detail, various substitutions, modifications or alterations could be made to the to the descriptions set forth above without departing from the inventive scope, as is defined by the following claims.