Abstract:
One method disclosed herein involves, among other things, identifying a plurality of features within an overall pattern layout that cannot be decomposed using the SADP process, wherein at least first and second adjacent features are required to be same-color features, decreasing a spacing between the first and second adjacent features such that the first feature and the second feature become different-color features so as to thereby render the plurality of features decomposable using the SADP process, decomposing the overall pattern layout into a mandrel mask pattern and a block mask pattern, and generating mask data sets corresponding to the mandrel mask pattern and the block mask pattern.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Generally, the present disclosure relates to the manufacture of sophisticated semiconductor devices, and, more specifically, to various methods of generating circuit layouts that are to be formed using self-aligned double patterning (SADP) techniques. 
     2. Description of the Related Art 
     Photolithography is one of the basic processes used in manufacturing integrated circuit products. At a very high level, photolithography involves: (1) forming a layer of light or radiation-sensitive material, such as photoresist, above a layer of material or a substrate; (2) selectively exposing the radiation-sensitive material to a light generated by a light source (such as a DUV or EUV source) to transfer a pattern defined by a mask or reticle (interchangeable terms as used herein) to the radiation-sensitive material; and (3) developing the exposed layer of radiation-sensitive material to define a patterned mask layer. Various process operations, such as etching or ion implantation processes, may then be performed on the underlying layer of material or substrate through the patterned mask layer. 
     Of course, the ultimate goal in integrated circuit fabrication is to faithfully reproduce the original circuit design on the integrated circuit product. Historically, the feature sizes and pitches employed in integrated circuit products were such that a desired pattern could be formed using a single patterned photoresist masking layer. However, in recent years, device dimensions and pitches have been reduced to the point where existing photolithography tools, e.g., 193 nm wavelength photolithography tools, cannot form a single patterned mask layer with all of the features of the overall target pattern. Accordingly, device designers have resorted to techniques that involve performing multiple exposures to define a single target pattern in a layer of material. One such technique is generally referred to as multiple patterning, e.g., double patterning. In general, double patterning is an exposure method that involves splitting (i.e., dividing or separating) a dense overall target circuit pattern into two separate, less-dense patterns. The simplified, less-dense patterns are then printed separately on a wafer utilizing two separate masks (where one of the masks is utilized to image one of the less-dense patterns, and the other mask is utilized to image the other less-dense pattern). Further, in some cases, the second pattern is printed in between the lines of the first pattern such that the imaged wafer has, for example, a feature pitch which is half that found on either of the two less-dense masks. This technique effectively lowers the complexity of the photolithography process, improving the achievable resolution and enabling the printing of far smaller features than would otherwise be impossible using existing photolithography tools. 
     The SADP process is one such multiple patterning technique. The SADP process may be an attractive solution for manufacturing next-generation devices, particularly metal routing lines on such next-generation devices, due to better overlay control that is possible when using an SADP process. 
       FIGS. 1A-1K  depict one illustrative example of a device  10  wherein an illustrative prior art SADP process was performed to form metal features, e.g., metal lines, in a layer of insulating material  12 . With reference to  FIG. 1A , a hard mask layer  14  is formed above the layer of insulating material  12  and a layer of mandrel material  16  was formed above the hard mask layer  14 . Also depicted is a patterned layer of photoresist material  17 , typically referred to as a “mandrel mask,” that was formed above the layer of mandrel material  16  using traditional, single exposure photolithography tools and techniques. The layer of mandrel material  16  may be comprised of a material that may be selectively etched with respect to the hard mask layer  14 . 
     Next, as shown in  FIG. 1B , an etching process is performed on the layer of mandrel material  16  while using the patterned layer of photoresist material  17  as an etch mask. This etching process results in the formation of a plurality of mandrels  16 A. In the depicted example, the mandrels are formed so as to have a pitch  16 P and a minimum width  16 W. The pitch  16 P and the width  16 W may vary depending upon the particular device  10  under construction.  FIG. 1C  depicts the device  10  after the patterned layer of photoresist  17 , i.e., the mandrel mask, has been removed. 
     Next, as shown in  FIG. 1D , a layer of spacer material  18  was deposited on and around the mandrels  16 A by performing a conformal deposition process. The layer of spacer material  18  should be a material that may be selectively etched relative to the mandrels  16 A and the hard mask layer  14 .  FIG. 1E  depicts the device  10  after an anisotropic etching process was performed on the layer of spacer material  18  to define a plurality of sidewall spacers  18 A, having a lateral width  18 W, positioned adjacent the mandrels  16 A. The width  18 W of the spacers  18 A may vary depending upon the particular device  10  under construction. Next, as shown in  FIG. 1F , the mandrels  16 A are removed by performing an etching process that is selective relative to the hard mask layer  14  and the sidewall spacers  18 A. 
       FIG. 1G  depicts the device  10  after a patterned photoresist mask  20 , a so-called block mask, is formed above the layer of spacers  18 A and the hard mask layer  14 . In one example, the block mask  20  may be formed using traditional, single exposure photolithography tools and techniques.  FIG. 1H  depicts the device  10  after an etching process has been performed to transfer the pattern defined by the combination (or union) of the sidewall spacers  18 A and the block mask  20  to the hard mask layer  14 .  FIG. 1I  depicts the device  10  after one or more process operations were performed to remove the sidewall spacers  18 A and the block mask  20  from above the now-patterned hard mask layer  14 . Next, as shown in  FIG. 1J , an etching process was performed on the layer of insulating material  12  through the patterned hard mask  14  to define illustrative trenches  22  in the layer of insulating material  12 .  FIG. 1K  depicts the device  10  after schematically depicted metal features  24 , e.g., metal lines, were formed in the trenches  22  and after the patterned hard mask layer  14  was removed. The manner in which such metal features  24  may be formed in the layer of insulating material  12  are well known to those skilled in the art. 
     In the SADP process, the metal features  24  that are formed are typically referred to as either “mandrel-metal” features (“MM”) or “non-mandrel-metal” features (“NMM”). As depicted in  FIG. 1K , the metal features  24  that are positioned under the location where the mandrels  16 A and the features of the mandrel mask  17  (both shown in dashed lines in  FIG. 1K ) were located, are so-called “mandrel-metal” features—designated as “MM” in  FIG. 1K . All of the other metal features  24  formed in the layer of insulating material  12  are “non-mandrel-metal” features—designated as “NMM” in  FIG. 1K . As it relates to terminology, the MM features and NMM features are referred to as being different “colors” when it comes to decomposing an overall pattern layout that is intended to be manufactured using an SADP process, as will be described more fully below. Thus, two MM features are said to be of the “same color” and two NMM features are said to be of the “same color, while an MM feature and an NMM feature are said to be of “different colors.” 
     To use double patterning techniques, an overall pattern layout for a circuit must be what is referred to as double patterning compliant. In general, this means that an overall pattern layout can be decomposed into two separate patterns that each may be formed using existing photolithography tools and other techniques. An overall pattern layout may have many regions or areas that cannot be directly printed because the plurality of closely spaced features in those regions are spaced too close to one another for existing photolithography tools to be able to print such closely spaced features as individual features. To the extent a particular region under investigation has an even number of such features, such a pattern is sometimes referred to as an “even cycle” pattern, while a region that has an odd number of features is sometimes referred to as an “odd cycle” pattern. Even cycle patterns can be formed using double patterning techniques, while odd cycle patterns cannot be formed using double patterning techniques. 
     One well-known double patterning technique is referred to as LELE (“litho-etch-litho-etch) double patterning. As the name implies, the LELE process involves forming two photoresist etch masks and performing two etching processes to transfer the desired overall pattern to a hard mask layer that is then used as an etch mask to etch an underlying layer of material. With respect to terminology, the different masks employed in the LELE double patterning process are said to be different “colors.” Thus, depending upon the spacing between adjacent features, the features may be formed using the same photoresist mask (“same color”) or they may have to be formed using different photoresist masks (“different color”). In an LELE process, if two adjacent features are spaced apart by a distance that can be patterned using traditional single exposure photolithography, then those two adjacent features may be formed using the same (“same color”) photoresist mask. In contrast, if the spacing between the two adjacent features is less than can be formed using single exposure photolithography, then those features must be either formed using different photoresist masks (“different color”) or the spacing between the features must be increased by changing the circuit layout such that they may be formed using the same photoresist mask. 
     As noted above, any circuit layout to be formed using double patterning techniques must be checked to confirm that it can be decomposed into two separate photoresist masks. A layout must have zero odd-cycles to be decomposable in an LELE process. To determine if a circuit layout is double-patterning compliant, a mask engineer, using very sophisticated and well-known computer programs, connects adjacent features by “drawing” a “polygon loop” that connects the centroid of the features under investigation.  FIG. 1L  contains a simplistic example of such a polygon loop  30  drawn for five (A-E) adjacent features. The polygon loop  30  is comprised of five edges  31 . In this example, due to the relative spacing between adjacent features, all of the features are required to be formed using “different color” (“DC”) masks. Thus, the polygon loop  30  has five “DC” edges connecting the various features. The polygon loop  30  represents an odd-cycle layout due to the odd number of DC edges (five total) in the polygon loop  30 . Due to the odd number of DC edges in the polygon loop  30 , the pattern reflected by the polygon loop  30  is not decomposable using double patterning techniques.  FIG. 1M  depicts one illustrative modification that may be made to the circuit layout to make it decomposable. In this example, the spacing between the features A and B is increased such that those two features may be formed using the “same color” (SC) mask. Thus, the modified polygon loop  30 A now has only four DC edges—an even number—and it may be decomposed using double patterning techniques. In short, in the LELE double patterning process, increasing the spacing between the adjacent features has the effect of “breaking” the odd-cycle polygon loop. However, increasing the spacing between adjacent features has the negative effect of increasing the area or “plot space” of silicon needed to fabricate the circuit, and increasing such spacing may have a “ripple” effect, causing additional odd-cycles that will need to be resolved. 
     In the SADP process, just like with the LELE process, a layout must have zero odd-cycles to be decomposable. However, unlike the LELE process, due to the nature of the SADP process, merely increasing the spacing between adjacent features within an odd-cycle polygon loop such that the two adjacent features must be formed using the “same color” mask will not resolve an odd-cycle situation, i.e., such an increase in spacing will not break the odd-cycle loop in the SADP process. Rather, in the SADP process, the spacing between the two adjacent features must be increased by a sufficient magnitude such that the two adjacent features are spaced so far apart that they may be formed using either the mandrel mask or the block mask—i.e., the spacing must be increased to such an extent that the features are said to be “color insensitive.” As before, increasing the spacing between adjacent features has the negative effect of increasing the area or “plot space” of silicon needed to fabricate the circuit, and increasing such spacing may have a “ripple” effect, causing additional odd-cycles that will need to be resolved by increasing the spacing between additional features. 
     The present disclosure is directed to various methods of generating circuit layouts that are to be formed using self-aligned double patterning (SADP) techniques which may solve or at least reduce one or more of the problems identified above. 
     SUMMARY OF THE INVENTION 
     The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
     Generally, the present disclosure is directed to various methods of generating circuit layouts that are to be formed using self-aligned double patterning (SADP) techniques. In one embodiment, a method is disclosed herein that is directed to the design and manufacture of reticles that may be employed in semiconductor manufacturing. Such a method involves, among other things, creating an overall pattern layout for an integrated circuit that is to be manufactured using a self-aligned double patterning (SADP) process, identifying a plurality of features within the overall pattern layout that cannot be decomposed using the SADP process, wherein at least first and second adjacent features are required to be same-color features, decreasing a spacing between the first and second adjacent features such that the first feature and the second feature become different-color features so as to thereby render the plurality of features decomposable using the SADP process, decomposing the overall pattern layout with the different-color first and second features having the decreased spacing therebetween into a mandrel mask pattern and a block mask pattern, generating a first set of mask data corresponding to the mandrel mask pattern and generating a second set of mask data corresponding to the block mask pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
         FIGS. 1A-1K  depict one illustrative example of a prior art SADP process; 
         FIGS. 1L-1M  depict illustrative examples of polygon loops and one example of resolving an odd-cycle conflict in a LELE process; and 
         FIGS. 2A-2J  depict various illustrative embodiments of various methods disclosed herein of decomposing circuit layouts that are to be formed using self-aligned double patterning (SADP) techniques. 
     
    
    
     While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
     The present disclosure is generally directed to various methods of decomposing circuit layouts that are to be formed using self-aligned double patterning (SADP) techniques. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the methods and devices disclosed herein may be employed in the fabrication of a variety of devices, such as logic devices, memory devices, ASICs, etc. With reference to the attached figures, various illustrative embodiments of the methods, devices and systems disclosed herein will now be described in more detail. 
       FIG. 2A-2J  will be referenced to discuss various aspects of the inventions disclosed herein. Reference will also be made to certain aspects of the prior art process flow described in  FIGS. 1A-1M  as needed. As indicated in the background section of this application, in an SADP process, the features that are formed, e.g., metal lines, are either mandrel-metal features (MM) or non-mandrel-metal (NMM) features. As it relates to terminology used herein and in the attached claims, the MM features and NMM feature are referred to as being different “colors” when it comes to decomposing an overall pattern layout that is to be manufactured using an SADP process technique. Thus, two MM features are said to be of the “same color,” while an MM feature and an NMM feature are said to be of “different colors.” Similarly, two NMM features are said to be of the “same color.” 
       FIG. 2A  depicts a simplistic example of a circuit layout, e.g., a plurality of metal lines  100  that are to be formed using an SADP process. The metal lines  100  may be representative of metal lines that are to be formed in the metal-2 (M2) layer of an integrated circuit product. The metal lines  100  are arranged on various tracks (“M2 tracks”), as depicted in dashed lines in  FIG. 2A . As it relates to the SADP process, the metal lines  100  may be divided into mandrel-metal lines  102  and non-mandrel-metal lines  103 . In the depicted example, the mandrel-metal lines  102  are arranged on the M2 tracks with the “0” designation, while the non-mandrel-metal lines  103  are arranged on the M2 tracks with the “1” designation. In the depicted example, each of the metal lines  100  has a critical dimension or width  104  and they have a pitch  106 . The magnitude of the width  104  and the pitch  106  may vary depending upon the particular application, and these dimensions will likely decrease as device dimensions continue to shrink as technology advances. In one example, the metal lines  100  may have a target width  104  of 24 nm and a target pitch  106  of 48 nm. However, as will be appreciated by those skilled in the art after a complete reading of the present application, the various inventions disclosed herein have broad applicability and they may be employed when manufacturing features having any desired configuration, pitch or width. Thus, the present inventions should not be considered to be limited to any of the illustrative numerical examples referenced herein, as those examples are only provided so as to facilitate an understanding of the presently disclosed inventions. 
     With reference to  FIG. 2B , various other aspects of an SADP process will now be discussed. In general, in an SADP process, the minimum width or critical dimension of a mandrel-metal feature is equal to the minimum width  16 W of the mandrel  16 A (see  FIGS. 1B and 1K ). On the other hand, the minimum width or critical dimension of a non-mandrel-metal feature is equal to the spacing between two mandrels  16 A less twice the spacer width  18 W. See  FIGS. 1B and 1E . (See dimension  19  in  FIG. 1K .)  FIG. 2B  graphically depicts various “coloring rules” for an SADP process wherein the minimum width  16 W of the mandrels  16 A is 24 nm, the minimum width  18 W of the spacers is 24 nm and the pitch  18 P of the mandrels  16 A is 96 nm. 
     With continuing reference to  FIG. 2B , if the spacing between adjacent features is 24 nm (S MIN ), then those two features must be formed with different colors—where one feature is a mandrel-metal (MM) feature and the other feature is a non-mandrel-metal (NMM) feature. When the spacing between features is greater than or equal to 72 nm (S INT ), then those features may be formed using the same color mask. If the spacing between the adjacent features is greater than 120 nm (S LRG ), then the features are insensitive to “color” and may be formed using any mask. Note that, in the case where the adjacent features are spaced apart by a distance equal to 72 nm and up to but not including 120 nm, then those features must be formed using the same color mask, i.e., both features are MM features or both features are NMM features. That is, for the condition where S INT ≦S&lt;S LRG , then the adjacent features must be formed using the same color mask. 
       FIG. 2C  depicts an example of a polygon loop  140  drawn for five (A-E) adjacent features that are part of a circuit pattern that is to be manufactured using an SADP process. The polygon loop  140  is comprised of five edges. In this example, due to the relative spacing between adjacent features A-C-E and D, those four adjacent features have to be formed using “different color” (“DC”) masks. Thus, the polygon loop  140  has three “DC” edges connecting those four features. The spacing between the feature B and its adjacent features A and D is such that the features A and B must be formed using the “same color” (“SC”) mask and the features B and C must be formed using the same color mask. In one particular example, the features A and B in the polygon loop  140  may be spaced apart by a distance equal to 72 nm and up to but not including 120 nm, e.g., the condition where S INT ≦S&lt;S LRG . Thus, the polygon loop  140  represents an odd-cycle layout due to the odd number of DC edges (three total) in the polygon loop  140 . Accordingly, due to the odd number of DC edges in the polygon loop  140 , the pattern reflected by the polygon loop  140  is not decomposable and therefore cannot be manufactured using SADP techniques. 
       FIG. 2D  depicts one aspect of the presently disclosed inventions wherein the pattern represented by the non-decomposable polygon  140  in  FIG. 2C  may be changed to a decomposable pattern  140 A using double patterning techniques. More specifically, in one embodiment disclosed herein, the spacing between adjacent features (e.g., A-B) that had to be formed using the same color mask is decreased so as to force the features (with the decreased spacing therebetween) to be formed using different color (DC) masks. For example, the spacing between the features A and B may be decreased to S MIN , e.g., 24 nm, in the example discussed herein, to thereby force the features A and B to be formed using different color masks and thus change an odd cycle loop (3 DC edges) into an even cycle loop (4 DC edges). Effecting such a change in spacing may be accomplished using several techniques. In the example depicted in  FIG. 2D , the decrease in spacing between the features A and B may be accomplished by treating one edge  110  of the feature A as being fixed and moving another edge  112  of the feature A toward the feature B. In this example, the position of the edges of the feature B remain unchanged and only feature A is modified. Stated another way, the size of the feature A is increased while the size of the feature B remains unchanged. 
     Importantly, using the methods disclosed herein, an otherwise non-decomposable pattern may be converted to a decomposable pattern without affecting the spacing relationship between other adjacent features or any area penalty.  FIGS. 2E and 2F  are side by side layouts of a portion of a non-decomposable circuit pattern ( FIG. 2E ) and a decomposable circuit pattern ( FIG. 2F ) that will be referenced to explain this point. In  FIGS. 2E and 2F , the spacing  114  between the features C and A, as well as the spacing  116  between the features B and D remain unchanged. However, using the methods disclosed herein, the spacing between the features A and B was decreased to S MIN , e.g., 24 nm (compare  FIGS. 2E and 2F ), to thereby force the features A and B to be formed using different masks. In the particular example depicted in  FIG. 2F , the decrease in spacing between the features A and B was accomplished by changing the size of both of the features A and B. More specifically, one edge  110  of both of the features A and B was treated as being fixed, while the facing edges  112  of the features A and B were moved toward one another. In this example, the position of the edges of both of the features A and B were modified. Stated another way, the size of both of the features A and B were increased to reduce the spacing between the features A and B. 
       FIGS. 2G-2H  provide another example of a pattern layout that may be transformed from a non-decomposable layout to a decomposable layout using the methods disclosed herein. Again, the numbers set forth herein are for purposes of illustration only. In the pattern  150  shown in  FIG. 2G , there are four (A-D) adjacent features that are part of a circuit pattern that is to be manufactured using an SADP process. The polygon loop is comprised of four edges. In this example, due to the relative spacing between adjacent features A-B, B-C and C-D, those three features have to be formed using “different color” (“DC”) masks. Thus, the polygon loop has three “DC” edges connecting those four features. The spacing (72 nm) between the feature D and its adjacent feature A is such that the features A and D must be formed using the “same color” (“SC”) mask. Thus, the pattern  150  represents an odd-cycle layout due to the odd number of DC edges (three total) in the polygon loop. Accordingly, the pattern  150  is not decomposable and therefore cannot be manufactured using SADP techniques. 
       FIG. 2H  depicts an example wherein the size of both of the features A and D are increased to resolve the coloring conflict by forcing the features A and D to be formed using different color (DC) masks. More specifically, in this example, the outside edges  110  of both of the features A and D were treated as being fixed, while portions of the facing edges  112  of both of the features A and D were moved toward one another until the spacing was decreased to 24 nm. Having made this spacing change, the pattern  150 A is now decomposable since the polygon has four DC edges. 
       FIGS. 2I-2J  provide yet another example of a pattern layout that may be transformed from a non-decomposable layout to a decomposable layout using the methods disclosed herein. Again, the numbers set forth herein are for purposes of illustration only. In the pattern  160  shown in  FIG. 2I , there are four (A-D) adjacent features that are part of a circuit pattern that is to be manufactured using an SADP process. The polygon loop is comprised of four edges. In this example, due to the relative spacing between adjacent features A-B, B-C and C-D, those three features have to be formed using “different color” (“DC”) masks. Thus, the polygon loop has three “DC” edges connecting those four features. The spacing (72 nm) between the feature D and its adjacent feature A is such that the features A and D must be formed using the “same color” (“SC”) mask. Thus, the pattern  160  represents an odd-cycle layout due to the odd number of DC edges (three total) in the polygon loop. Accordingly, the pattern  160  is not decomposable and therefore cannot be manufactured using SADP techniques. 
       FIG. 2J  depicts an example wherein the size of only the feature A is increased to resolve the coloring conflict by forcing the features A and D to be formed using different color (DC) masks. More specifically, in this example, the outside edge  110  of the feature A was treated as being fixed, while a portion of the inside edge  112  of the feature A was moved toward the feature D until the spacing was decreased to 24 nm. During this process, the size of the feature D remained unchanged. Having made this spacing change, the pattern  160 A is now decomposable since the polygon has four DC edges. 
     The techniques disclosed herein are in stark contrast to the methods employed in the prior art SADP processes. More specifically, in the context of attempting to resolve coloring conflicts for patterns to be manufactured using SADP techniques, the prior art methods always involved increasing spacing between adjacent features to resolve such conflicts. Such actions tended to consume additional plot space and cause additional coloring conflicts as the increase in spacing between the adjacent features tended to have a “ripple effect” in other parts of the layout with respect to other features. In contrast, the methods disclosed herein involve decreasing the spacing between adjacent features so as to force those features to be formed using different color masks to resolve odd-cycle conflicts when using an SADP process to manufacture an integrated circuit product. Thus, in contrast to the prior art techniques, using the methods disclosed herein, there may be less plot space consumed when resolving coloring conflicts and changes made to resolve such conflicts may not have adverse “rippling” effects on other parts of the circuit layout. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.