Patent Publication Number: US-2018046745-A1

Title: Methods for Multi-Wire Routing and Apparatus Implementing Same

Description:
CLAIM OF PRIORITY 
     This application is a continuation application under 35 U.S.C. 120 of prior U.S. application Ser. No. 15/181,157, filed Jun. 13, 2016, issued as U.S. Pat. No. 9,779,200, on Oct. 3, 2017, which is a continuation application under 35 U.S.C. 120 of prior U.S. application Ser. No. 14/298,206, filed Jun. 6, 2014, issued as U.S. Pat. No. 9,390,215, on Jul. 12, 2016, which is a continuation application under 35 U.S.C. 120 of prior U.S. application Ser. No. 13/918,890, filed Jun. 14, 2013, issued as U.S. Pat. No. 8,759,985, on Jun. 24, 2014, which is a continuation application under 35 U.S.C. 120 of prior U.S. application Ser. No. 13/085,447, filed Apr. 12, 2011, issued as U.S. Pat. No. 8,471,391, on Jun. 25, 2013, which is a divisional application under 35 U.S.C. 121 of prior U.S. application Ser. No. 12/411,249, filed Mar. 25, 2009, issued as U.S. Pat. No. 7,939,443, on May 10, 2011, which claims the priority benefit of U.S. Provisional Patent Application No. 61/040,129, filed Mar. 27, 2008. The disclosure of each above-identified application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     A push for higher performance and smaller die size drives the semiconductor industry to reduce circuit chip area by approximately 50% every two years. The chip area reduction provides an economic benefit for migrating to newer technologies. The 50% chip area reduction is achieved by reducing the feature sizes between 25% and 30%. The reduction in feature size is enabled by improvements in manufacturing equipment and materials. For example, improvement in the lithographic process has enabled smaller feature sizes to be achieved, while improvement in chemical mechanical polishing (CMP) has in-part enabled a higher number of interconnect layers. 
     In the evolution of lithography, as the minimum feature size approached the wavelength of the light source used to expose the feature shapes, unintended interactions occurred between neighboring features. Today minimum feature sizes are approaching 32 nm (nanometers), while the wavelength of the light source used in the photolithography process remains at 193 nm. The difference between the minimum feature size and the wavelength of light used in the photolithography process is defined as the lithographic gap. As the lithographic gap grows, the resolution capability of the lithographic process decreases. 
     An interference pattern occurs as each shape on the mask interacts with the light. The interference patterns from neighboring shapes can create constructive or destructive interference. In the case of constructive interference, unwanted shapes may be inadvertently created. In the case of destructive interference, desired shapes may be inadvertently removed. In either case, a particular shape is printed in a different manner than intended, possibly causing a device failure. Correction methodologies, such as optical proximity correction (OPC), attempt to predict the impact from neighboring shapes and modify the mask such that the printed shape is fabricated as desired. The quality of the light interaction prediction is declining as process geometries shrink and as the light interactions become more complex. 
     In view of the foregoing, techniques are sought for managing lithographic gap issues as technology continues to progress toward smaller semiconductor device features sizes. 
     SUMMARY 
     In one embodiment, a method is disclosed for defining a rectangular interlevel connector array (RICA) in a semiconductor chip layout. The method includes an operation for defining a virtual grid for interlevel connector placement. The virtual grid is defined by a first set of parallel virtual lines that extend across the layout in a first direction and by a second set of parallel virtual lines that extend across the layout in a second direction that is perpendicular to the first direction. Each intersection point between the first and second sets of parallel virtual lines is a gridpoint in the virtual grid. The method also includes an operation for placing a first plurality of interlevel connector structures at respective gridpoints in the virtual grid to form a first RICA. Neighboring interlevel connector structures of the first RICA are spaced apart from each other by a first number of gridpoints in the first direction and by a second number of gridpoints in the second direction. The first plurality of interlevel connector structures of the first RICA are placed to collaboratively connect a first conductor channel in a first chip level with a second conductor channel in a second chip level. 
     In another embodiment, a method is disclosed for wire routing in a semiconductor chip layout. The method includes an operation for defining a first conductor channel layout in a first chip level. The first conductor channel layout includes a first plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a first direction. The method also includes an operation for defining a second conductor channel layout in a second chip level. The second conductor channel layout includes a second plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a second direction that is perpendicular to the first direction. The first and second conductor channel layouts extend across each other within the chip layout at a crossing location. The method further includes an operation for defining a first RICA layout at the crossing location to connect the first conductor channel layout to the second conductor channel layout. The first RICA layout includes a first plurality of interlevel connector layout shapes placed to collaboratively connect the wire layout shapes of the first conductor channel layout to the wire layout shapes of the second conductor channel layout. 
     In another embodiment, a semiconductor chip is disclosed. The chip includes a first conductor channel defined in a first chip level. The first conductor channel includes a first plurality of parallel wires having a common electrical connectivity and oriented in a first direction. The chip also includes a second conductor channel defined in a second chip level. The second conductor channel includes a second plurality of parallel wires having a common electrical connectivity and oriented in a second direction that is perpendicular to the first direction. The first and second conductor channels extend across each other within the chip at a crossing location. The chip further includes a first RICA defined at the crossing location to connect the first conductor channel to the second conductor channel. The first RICA includes a first plurality of interlevel connectors placed to collaboratively connect the wires of the first conductor channel to the wires of the second conductor channel. 
     In another embodiment, a layout of a semiconductor chip is disclosed. The layout includes a first conductor channel defined in a first chip level. The first conductor channel includes a first plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a first direction. The layout also includes a second conductor channel defined in a second chip level. The second conductor channel includes a second plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a second direction that is perpendicular to the first direction. The first and second conductor channels extend across each other within the chip at a crossing location. The layout also includes a first RICA defined at the crossing location to connect the first conductor channel to the second conductor channel. The first RICA includes a first plurality of interlevel connector layout shapes placed to collaboratively connect the wire layout shapes of the first conductor channel to the wire layout shapes of the second conductor channel. 
     Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an illustration showing placement of wires and interlevel connectors, in accordance with one embodiment of the present invention; 
         FIG. 1B  shows an example layout in which a horizontally oriented virtual grate of an interlevel connector placement virtual grid allows for placement of interlevel connectors on adjacent virtual lines, in accordance with one embodiment of the present invention; 
         FIG. 1C  shows an example layout in which an interlevel connector placement virtual grid allows for placement of interlevel connectors on adjacent virtual lines in both the horizontal and vertical directions, in accordance with one embodiment of the present invention; 
         FIG. 2A  shows an example layout in which multiple wires are used to form a conductor channel, in accordance with one embodiment of the present invention; 
         FIG. 2B  shows a variation of the layout of  FIG. 2A  in which a horizontal position of the RICAs is reversed, in accordance with one embodiment of the present invention; 
         FIG. 3  shows an example layout in which multiple 3-wire conductor channels are interleaved and connected through a pair of overlapping RICAs, in accordance with one embodiment of the present invention; 
         FIG. 4  shows an example layout in which three 2-wire conductor channels are routed horizontally to connect with three 2-wire conductor channels that are routed vertically, in accordance with one embodiment of the present invention; 
         FIG. 5  shows an example layout in which a single-wire routing is defined within a multi-wire conductor channel, in accordance with one embodiment of the present invention; 
         FIG. 6  shows an example layout in which RICAs are used to connect two interleaved 3-wire conductor channels with two interleaved 2-wire conductor channels, in accordance with one embodiment of the present invention; 
         FIG. 7  shows an interlevel connector pattern used to connect non-interleaved horizontal and vertical multi-wire conductor channels, in accordance with one embodiment of the present invention; 
         FIG. 8  shows an example layout in which a non-interleaved conductor channel is embedded within another conductor channel, in accordance with one embodiment of the present invention; 
         FIG. 9A  shows an example of Opportunistic Strapping (OSt), in accordance with one embodiment of the present invention; 
         FIG. 9B  shows an example layout in which a non-redundant RICA is used to connect multiple horizontal conductor channels to multiple vertical conductor channels, in accordance with one embodiment of the present invention; 
         FIG. 10  shows an example routing between multiple locations in a chip layout, in accordance with one embodiment of the present invention; 
         FIG. 11  shows an example layout in which OSt strap wires are used with non-interleaved conductor channels, in accordance with one embodiment of the present invention; 
         FIG. 12A  shows use of supplemental OSt strap wires in a dense interlevel connector pattern without orthogonally adjacent interlevel connector placement, in accordance with one embodiment of the present invention; 
         FIG. 12B  shows a variation of the example layout of  FIG. 12A  in which OSt strap wires are used to connect adjacent and commonly oriented wires, in accordance with one embodiment of the present invention; 
         FIG. 12C  shows a variation of the example layout of  FIG. 12A  in which each wire of a given conductor channel is connect by a single OSt strap wire, in accordance with one embodiment of the present invention; 
         FIG. 13A  shows an example layout in which an unused fill wire is incorporated into a conductor channel by way of OSt strap wires, in accordance with one embodiment of the present invention; 
         FIG. 13B  shows the example layout of  FIG. 13A  with a shorter length fill wire, in accordance with one embodiment of the present invention; 
         FIG. 14A  shows an example layout demonstrating how OSt strap wires can connect to fill wires at any point along the length of the fill wires, in accordance with one embodiment of the present invention; 
         FIG. 14B  shows an example layout demonstrating how shorter segments of fill wires may be connected to conductor channel wires, in accordance with one embodiment of the present invention; 
         FIG. 14C  shows an example layout demonstrating how tuning wires can be used to increase the capacitance on a channel wire or other wire, or to increase interlevel connector density in an area, in accordance with one embodiment of the present invention; 
         FIG. 15  shows an exemplary chip level layout based on the dynamic array architecture, in accordance with one embodiment of the present invention; 
         FIG. 16  shows a flowchart of a method for defining a RICA in a semiconductor chip layout, in accordance with one embodiment of the present invention; and 
         FIG. 17  shows a flowchart of a method for wire routing in a semiconductor chip layout, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     Dynamic Array Architecture 
     In deep sub-micron VLSI (Very-Large-Scale Integration) design, process compensation techniques (PCTs) such as Optical Proximity Correction (OPC) or sub-resolution feature utilization, among others, enhance the printing of layout features. PCTs are easier to develop and implement when the layout is highly regular and when the quantity and diversity of lithographic interactions are minimized across the layout. 
     The dynamic array architecture represents a semiconductor device design paradigm capable of enhancing PCT development and implementation. In the dynamic array architecture, linear-shaped layout features are defined along a regular-spaced virtual grate (or regular-spaced virtual grid) in a number of levels of a cell, i.e., in a number of levels of a semiconductor chip. The virtual grate is defined by a set of equally spaced, parallel virtual lines extending across a given level in a given chip area. The virtual grid is defined by a first set of equally spaced, parallel virtual lines extending across a given level in a given chip area in a first direction, and by a second set of equally spaced, parallel virtual lines extending across the given level in the given chip area in a second direction, where the second direction is perpendicular to the first direction. In various embodiments, the virtual grate of a given level can be oriented either substantially perpendicular of substantially parallel to the virtual grate of an adjacent level. 
     A linear layout feature is defined as a layout shape that extends along a virtual line of a virtual grate without contacting a neighboring linear layout feature that extends along a different virtual line of the virtual grate. In one embodiment, a linear layout feature can be defined to have a substantially rectangular cross-section when viewed in an as-drawn state. In another embodiment, a linear layout feature can be defined to have a primarily rectangular cross-section defined by a width and length, with some allowable variation in width along its length. It should be understood, however, that in this embodiment, the linear layout feature of varying width may not contact a neighboring linear layout feature that extends along a different virtual line of the same virtual grate within the same chip level. For example, some linear layout features may have one or more variations in width at any number of locations along their length, wherein “width” is defined across the substrate in a direction perpendicular to the virtual line along which the linear layout feature is disposed. Such a variation in width may be used to define a contact head upon which a contact is to connect, or may serve some other purpose. Additionally, different linear layout features within a given chip level can be defined to have the same width or different widths, so long as the width variation is predictable from a manufacturing perspective and does not adversely impact the manufacture of the linear layout feature or its neighboring layout features. 
     In the dynamic array architecture, variations in a vertical cross-section shape of an as-fabricated linear layout feature can be tolerated to an extent, so long as the variation in the vertical cross-section shape is predictable from a manufacturing perspective and does not adversely impact the manufacture of the given linear layout feature or its neighboring layout features. In this regard, the vertical cross-section shape corresponds to a cut of the as-fabricated linear layout feature in a plane perpendicular to the centerline of the linear layout feature. 
       FIG. 15  shows an exemplary chip level layout based on the dynamic array architecture, in accordance with one embodiment of the present invention. A number of virtual lines  1501 ,  1503 ,  1505 ,  1507 ,  1509  are each defined to extend across the substrate, i.e., across the chip level layout of the portion of the chip, in a single common direction (y direction). Each of linear layout features  1511 ,  1513 ,  1515 ,  1517 ,  1519 ,  1521  is defined to extend along a single virtual line ( 1501 ,  1503 ,  1505 ,  1505 ,  1507 ,  1509 , respectively), without contacting a neighboring linear layout feature that extends along a different virtual grate line. Some linear layout features, such as  1511 ,  1515 ,  1517 ,  1521 , are defined to have a substantially rectangular cross-section when viewed in their as-drawn state. Whereas other linear layout features, such as  1513  and  1519 , are defined to have some variation in width (in x direction) along their length (in y direction). It should be appreciated that although linear layout features  1513  and  1519  vary in width along their length, neither of linear layout features  1513  and  1519  contacts a neighboring linear layout feature that extends along a different virtual grate line. 
     In one embodiment, each linear layout feature of a given chip level is substantially centered upon one of the virtual lines of the virtual grate associated with the given chip level. A linear layout feature is considered to be substantially centered upon a particular virtual grate line when a deviation in alignment between of the centerline of the linear layout feature and the particular virtual grate line is sufficiently small so as to not reduce a manufacturing process window from what would be achievable with a true alignment between of the centerline of the linear layout feature and the virtual grate line. In one embodiment, the above-mentioned manufacturing process window is defined by a lithographic domain of focus and exposure that yields an acceptable fidelity of the layout feature. In one embodiment, the fidelity of a layout feature is defined by a characteristic dimension of the layout feature. 
     In another embodiment, some linear layout features in a given chip level may not be centered upon a virtual grate line. However, in this embodiment, the linear layout features remain parallel to the virtual lines of the virtual grate, and hence parallel to the other linear layout features in the given chip level. Therefore, it should be understood that the various linear layout features defined in a layout of a given chip level are oriented to extend across the given chip level in a parallel manner. 
     In one embodiment, within a given chip level defined according to the dynamic array architecture, proximate ends of adjacent, co-aligned linear layout features may be separated from each other by a substantially uniform gap. More specifically, adjacent ends of linear layout features defined along a common virtual grate line are separated by an end gap, and such end gaps within the chip level associated with the virtual grate may be defined to span a substantially uniform distance. Additionally, in one embodiment, a size of the end gaps is minimized within a manufacturing process capability so as to optimize filling of a given chip level with linear layout features. 
     Also, in the dynamic array architecture, a portion of a chip level can be defined to have any number of virtual grate lines occupied by any number of linear layout features. In one example, a portion of a given chip level can be defined such that all lines of its virtual grate are occupied by at least one linear layout feature. In another example, a portion of a given chip level can be defined such that some lines of its virtual grate are occupied by at least one linear layout feature, and other lines of its virtual grate are vacant, i.e., not occupied by any linear layout features. Furthermore, in a portion of a given chip level, any number of successively adjacent virtual grate lines can be left vacant. Also, the occupancy versus vacancy of virtual grate lines by linear layout features in a portion of a given chip level may be defined according to a pattern or repeating pattern across the given chip level. 
     In a given chip level, some of the linear layout features may form functional structures within an integrated circuit, and other linear layout features may be non-functional with respect to integrated circuit operation. It should be understood that the each of the linear layout features, regardless of function, is defined to extend across the chip level in the common direction of the virtual grate and to be devoid of a substantial change in direction along its length. It should be understood that each of the linear layout features, regardless of function, is defined such that no linear layout feature along a given virtual grate line is configured to connect directly within the same chip level to another linear layout feature defined along a different virtual grate line. 
     Additionally, within the dynamic array architecture, vias and contacts are defined to interconnect a number of layout features in various levels so as to form a number of functional electronic devices, e.g., transistors, and electronic circuits. Layout features for the vias and contacts can be aligned to a virtual grid. In one embodiment, a virtual grid is defined as a combination of virtual grates associated with a plurality of levels to which the vias and contacts will connect. Also, in one embodiment, a combination of virtual grates used to define a virtual grid can include one or more virtual grates defined independent from a particular chip level. 
     In the dynamic array architecture, a number of layout features in various chip levels form functional components of an electronic circuit. Additionally, some of layout features within various chip levels may be non-functional with respect to an electronic circuit, but are manufactured nonetheless so as to reinforce manufacturing of neighboring layout features. It should be understood that the dynamic array architecture is defined to enable accurate prediction of semiconductor device manufacturability with a high probability. 
     In view of the foregoing, it should be understood that the dynamic array architecture is defined by placement of linear layout features on a regular-spaced grate (or regular-spaced grid) in a number of levels of a cell, such that the linear layout features in a given level of the cell are oriented to be substantially parallel with each other in their traversal direction across the cell. As discussed above, in the dynamic array architecture, each as-drawn linear layout feature, i.e., prior to PCT processing, is defined to be devoid of a substantial change in direction relative to its traversal direction across the cell. 
     Cell 
     A cell, as referenced herein, represents an abstraction of a logic function, and encapsulates lower-level integrated circuit layouts for implementing the logic function. It should be understood that a given logic function can be represented by multiple cell variations, wherein the cell variations may be differentiated by feature size, performance, and process compensation technique (PCT) processing. For example, multiple cell variations for a given logic function may be differentiated by power consumption, signal timing, current leakage, chip area, OPC, RET, etc. It should also be understood that each cell description includes the layouts for the cell in each level of a chip, as required to implement the logic function of the cell. More specifically, a cell description includes layouts for the cell in each level of the chip extending from the substrate level up through a particular interconnect level. 
     Exemplary Embodiments 
     When routing conductors in a restricted architecture, such as the dynamic array architecture, multi-wire buses and multi-wire channels may be required. Various embodiments are disclosed herein for providing multi-wire buses and multi-wire channels that are connected using interlevel connectors, such as vias and contacts, which are placed according to a virtual grid. In one embodiment, interconnect chip level features, i.e., wires, in a given interconnect chip level are placed according to a virtual grate that is spatially related to the virtual grid for interlevel connector placement. As used herein the term wire refers to an electrically conductive structure defined within a level of a semiconductor chip. By way of example, wires may be formed of metal, polysilicon, or essentially any other electrically conductive material used in the manufacture of semiconductor chips. Also, in one embodiment, a wire can be defined by a local interconnect structure formed through doping and/or salicide processes. 
       FIG. 1A  is an illustration showing placement of wires and interlevel connectors, in accordance with one embodiment of the present invention. Wires within a given chip level are centered on virtual lines of a virtual grate associated with the given chip level. In one embodiment, adjacent virtual lines within a given virtual grate are separated by a substantially uniform pitch. Vertically oriented wires  801   c  and  801   d  are placed in one interconnect chip level according to the virtual grate that includes virtual lines  803   a,    803   b,    803   c.  Horizontally oriented wires  801   a  and  801   b  are placed in another interconnect chip level according to the virtual grate that includes virtual lines  803   d,    803   e,    803   f.  As used herein, the term “vertical” refers to the Y-axis direction, and the term “horizontal” refers to the X-axis direction, wherein the X-Y plane is oriented substantially parallel to the underlying substrate of the chip. Additionally, as used herein, the term interlevel connector refers to an electrically conductive structure defined to extend between any two different chip levels to electrically connect a structure in one chip level to a structure in another chip level. Examples of interlevel connectors include without limitation vias, gate contacts, and diffusion contacts. 
     Interlevel connectors can be placed according to a virtual grid, wherein the virtual grid is defined by two perpendicularly oriented virtual grates. In one embodiment, the two perpendicularly oriented virtual grates of the virtual grid can be defined for two separate levels, e.g., for two separate interconnect chip levels in the case of vias, or for a gate chip level and an interconnect chip level in the case of gate contacts. In this embodiment, the virtual grates for the different levels may or may not have a specification dependency upon each other. Valid interlevel connector placement locations may be defined in a number of ways, including but not limited to, intersection points between virtual lines within a virtual grid, i.e., gridpoints in the virtual grid. 
     The perpendicular distance between parallel and adjacent virtual lines in a virtual grid is referred to as a virtual grid pitch, and may be determined in a number of ways. For example, the virtual grid pitch may be equal to a minimum wire, i.e., conductive feature, width plus a minimum wire-to-wire space. Also, the virtual grid pitch between adjacent vertically oriented virtual lines can be different from the virtual grid pitch between adjacent horizontally oriented virtual lines. Thus, a virtual grid for interlevel connector placement can include virtual grates associated with two different chip levels, wherein each of the virtual grates is defined by a different pitch. 
       FIG. 1A  depicts a Rectangular Interlevel Connector Array (RICA)  805  defined by the two horizontal wires ( 801   a  and  801   b ), the two vertical wires ( 801   c  and  801   d ), and the interlevel connectors ( 802   a,    802   b,    802   c,    802   d ) which connect them. It should be understood that the wires  801   a - 801   d  of  FIG. 1A  can represent any type of wire on any chip level. For example, wires  801   c  and  801   d  may represent conductive features of a gate chip level, and wires  801   a  and  801   b  may represent conductive features of a first interconnect chip level. In another example, wires  801   c  and  801   d  may represent conductive features of one interconnect chip level, and wires  801   a  and  801   b  may represent conductive features of another interconnect chip level. Also, in various embodiments, interlevel connectors  802   a - 802   d  can represent either vias or contacts, depending on the chip level and functionality of the wires  801   a - 801   d  to which they connect. It should be appreciated that in the embodiment of  FIG. 1A , wires  801   a  and  801   b  are placed on virtual grate lines  803   d  and  803   f,  respectively. Similarly, wires  801   c  and  801   d  are placed on virtual grate lines  803   a  and  803   c,  respectively. Although the embodiment of  FIG. 1A  includes a vacant virtual grate line  803   b  between wires  801   c  and  801   d,  and a vacant virtual grate line  803   e  between wires  801   a  and  801   b,  in other embodiments, the virtual grate lines  803   b  and  803   e  may be occupied by wires (related or non-related), depending on wire spacing and wire width specifications/restrictions. 
     Each wire ( 801   a - 801   d ) may extend beyond an interlevel connector ( 802   a - 802   d ) by a specified extension distance or may continue to other routing points beyond the RICA  805 . For example, wire  801   a  may be defined to have either of horizontal extensions  804   a  or  804   c.  Wire  801   b  may be defined to have either of horizontal extensions  804   b  or  804   d.  Wire  801   c  may be defined to have either of vertical extensions  804   e  or  804   g.  Wire  801   d  may be defined to have either of vertical extensions  804   f  or  804   h.  Also, horizontal/vertical extensions of wires beyond an interlevel connector may be defined in a related manner or may be defined independently. Also, an extension distance of a given wire beyond an interlevel connector location may be specified as necessary to satisfy design or layout requirements. In one embodiment, a wire may be defined to end essentially at an edge of an interlevel connector, thereby resulting in a substantially non-existent extension distance. Also, in one embodiment, a wire may be defined to partially traverse an interlevel connector, thereby resulting in a negative extension distance. 
     At a given RICA location, a  90 -degree elbow intersection, a T-intersection, or a cross intersection may be formed by linear conductive features, e.g., wires, on two or more different chip levels. An elbow intersection occurs where a first wire on one chip level connects with a second wire on another chip level by way of an interlevel connector, and wherein each of the first and second wires terminates at or just beyond the connection location defined by the interlevel connector, and wherein the first and second wires extend in a substantially perpendicular direction relative to each other. In one embodiment of the elbow intersection, the first wire and/or second wire may extend partially across the interlevel connector used to connect the first and second wires. In this embodiment, the wire that extends partially across the interlevel connector is considered to have a negative extension distance with respect to the interlevel connector. 
     A T-intersection occurs where a first wire on one chip level connects with a second wire on another chip level by way of an interlevel connector, and wherein the first wire terminates at or just beyond the connection location defined by the interlevel connector, and wherein the second wire continues substantially beyond the connection location defined by the interlevel connector, and wherein the first and second wires extend in a substantially perpendicular direction relative to each other. In one embodiment of the T-intersection, the first wire may extend partially across the interlevel connector used to connect the first and second wires. In this embodiment, the first wire is considered to have a negative extension distance with respect to the interlevel connector. A cross intersection occurs where a first wire on one chip level connects with a second wire on another chip level by way of an interlevel connector, and wherein both the first and second wires continue substantially beyond the connection location defined by the interlevel connector, and wherein the first and second wires extend in a substantially perpendicular direction relative to each other. 
     A virtual grid defined for interlevel connector placement may be specified such that orthogonally adjacent interlevel connector placements are allowed in one or both of the horizontal and vertical directions. In one embodiment, wires associated with an RICA may be placed on adjacent virtual grate lines.  FIG. 1B  shows an example where a horizontally oriented virtual grate (including virtual lines  813   d  and  813   e ) of an interlevel connector placement virtual grid (including virtual lines  813   a - 813   e ) allows for placement of interlevel connectors ( 812   a/   812   c  and  812   b/   812   d ) on adjacent virtual lines ( 813   d  and  813   e ). 
     The interlevel connector  812   a  provides for connection of wires  811   a  and  811   c  defined on different chip levels. The interlevel connector  812   b  provides for connection of wires  811   a  and  811   d  defined on different chip levels. The interlevel connector  812   c  provides for connection of wires  811   b  and  811   c  defined on different chip levels. The interlevel connector  812   d  provides for connection of wires  811   b  and  811   d  defined on different chip levels. 
       FIG. 1C  shows an example where an interlevel connector placement virtual grid (including virtual lines  823   a - 823   d ) allows for placement of interlevel connectors ( 822   a - 822   d ) on adjacent virtual lines in both the horizontal and vertical directions. The interlevel connector  822   a  provides for connection of wires  821   a  and  821   c  defined on different chip levels. The interlevel connector  822   b  provides for connection of wires  821   a  and  821   d  defined on different chip levels. The interlevel connector  822   c  provides for connection of wires  821   b  and  821   c  defined on different chip levels. The interlevel connector  822   d  provides for connection of wires  821   b  and  821   d  defined on different chip levels. 
     When designing in accordance with the dynamic array architecture or other restricted architecture, multiple wires may be used to replicate the function of a single wire of larger width.  FIG. 2A  shows an example layout in which multiple wires are used to form a conductor channel, wherein the conductor channel is electrically equivalent to a single conductor, i.e., single wire. Specifically, multiple wires  201  and  203  form a first conductor channel A 1 . Multiple wires  202  and  204  form a second conductor channel B 1 . Multiple wires  205  and  207  form a third conductor channel A 2 . Multiple wires  206  and  208  form a fourth conductor channel B 2 . In one embodiment, each of the conductor channels A 1 , A 2 , B 1 , and B 2  is defined to respectively replace a single larger wire. It should be understood that a given conductor channel may be defined by any number of wires greater than one. Also, it should be understood that conductor channels defined within different chip levels can be connected to each other by way of a RICA. A number of exemplary embodiments are disclosed herein for RICA-connected conductor channels in which the connected conductor channels extend in perpendicular directions with respect to each other. However, it should be understood that in various embodiments, RICA-connected conductor channels in different chip levels may extend in a common direction or in different directions. 
     In the example of  FIG. 2A , RICA  209  is formed by interlevel connectors  209   a - 209   d  to connect the horizontal conductor channel A 1  to the vertical conductor channel A 2 , thereby associating both conductor channels A 1  and A 2  with a common net A. Also, RICA  210  is formed by interlevel connectors  210   a - 210   d  to connect the horizontal conductor channel B 1  to the vertical conductor channel B 2 , thereby associating both conductor channels B 1  and B 2  with a common net B. The RICAs  209  and  210  are overlapped such that the interlevel connectors  209   a - 209   d  and  210   a - 210   d  are placed in a non-adjacent manner. More specifically, interleaving of the conductor channel wires  201 - 208  enables overlapping of the RICAs  209  and  210  to connect the horizontal conductor channels A 1  and B 1  to the vertical conductor channels A 2  and B 2 , respectively, without either horizontally adjacent or vertically adjacent interlevel connector placements within the RICAs  209 ,  210 . 
     Overlapped RICAs with corresponding interleaved conductor channel wires may be utilized to avoid interlevel connector placements with a center-line spacing that is equivalent to the center-line spacing of wires on levels that connect to the interlevel connector under consideration. For example, overlapped RICAs with corresponding interleaved conductor channel wires may be used in a multi-wire bus to ensure a separation of more than one wire pitch between interlevel connector, or to avoid interlevel connector placements on vertically or horizontally adjacent virtual grid lines. Placement of interlevel connectors on vertically or horizontally adjacent virtual grid lines is referred to herein as an orthogonally adjacent placement. Also, by interleaving the wires of the different conductor channels, a dense interlevel connector placement pattern can be obtained at the intersection of the vertically and horizontally oriented conductor channels (A 1 /A 2 , B 1 /B 2 ) without use of orthogonally adjacent interlevel connector placements. 
       FIG. 2B  shows a variation of the embodiment of  FIG. 2A  in which a horizontal position of RICAs  209  and  210  is reversed. The horizontal position reversal of RICAs  209  and  210  causes connected wires of the connected conductor channels to maintain an inner-to-outer sequence through the RICAs  209  and  210 . Specifically, innermost wire  204  of conductor channel B 1  is connected to innermost wire  206  of conductor channel B 2 . Also, outermost wire  201  of conductor channel A 1  is connected to outermost wire  207  of conductor channel A 2 . By maintaining the inner-to-outer conductor channel wire sequence at interlevel connector locations within the RICA, an edge relationship between adjacent wires may be averaged over a run length of the conductor channels. This technique can be employed with any number of conductor channels and with any number of wires per conductor channel. 
     Overlapping RICAs can be extended to connect any number of conductor channels and to accommodate any number of wires per conductor channel.  FIG. 3  shows an example embodiment in which interleaved 3-wire conductor channels are connected through a pair of overlapping RICAs  513  and  514 . A first conductor channel A 1  is formed by horizontal wires  501 ,  503 , and  505 . A second conductor channel B 1  is formed by horizontal wires  502 ,  504 , and  506 . A third conductor channel A 2  is formed by vertical wires  508 ,  510 , and  512 . A fourth conductor channel B 2  is formed by vertical wires  507 ,  509 , and  511 . It should be understood that horizontal wires  501 - 506  are defined in a chip level separate from vertical wires  507 - 512 . The RICA  513  includes interlevel connectors defined to connect horizontally oriented conductor channel A 1  to vertically oriented conductor channel A 2 , thereby associating both conductor channels A 1  and A 2  with a net A. The RICA  514  includes interlevel connectors defined to connect horizontally oriented conductor channel B 1  to vertically oriented conductor channel B 2 , thereby associating both conductor channels B 1  and B 2  with a net B. 
       FIG. 4  shows an example embodiment in which three 2-wire conductor channels (A 1 , B 1 , C 1 ) are routed horizontally to connect with three 2-wire conductor channels (A 2 , B 2 , C 2 ) that are routed vertically. Specifically, conductor channel A 1  (defined by wires  520  and  523 ) is routed horizontally to connect with vertically routed conductor channel A 2  (defined by wires  528  and  531 ) through RICA  534 . Conductor channel B 1  (defined by wires  521  and  524 ) is routed horizontally to connect with vertically routed conductor channel B 2  (defined by wires  527  and  530 ) through RICA  533 . Conductor channel C 1  (defined by wires  522  and  525 ) is routed horizontally to connect with vertically routed conductor channel C 2  (defined by wires  526  and  529 ) through RICA  532 . In various embodiments, the wires  520 - 525  of the horizontal conductor channels A 1 , B 1 , and C 1  can be interleaved in different orders, with the wires of the vertical conductor channels A 2 , B 2 , and C 2  correspondingly interleaved. However, in an embodiment in which the interlevel connector placement virtual grid does not support orthogonally adjacent interlevel connector placement, the wires  520 - 525  of the horizontal conductor channels A 1 , B 1 , C 1  should be arranged so as to avoid adjacent routing of multiple wires of the same conductor channel. Similarly, in this embodiment, the wires  526 - 531  of the vertical conductor channels A 2 , B 2 , C 2  should be arranged so as to avoid adjacent routing of multiple wires of the same conductor channel. 
       FIG. 5  shows an example embodiment in which a single-wire routing is defined within a multi-wire conductor channel. Wires  551  and  553  define a horizontal conductor channel A 1 . Wires  554  and  556  define a vertical conductor channel A 2 . The horizontal and vertical conductor channels A 1  and A 2  are connected together by a RICA  558  defined by interlevel connectors  558   a.  A single-wire routing net B is defined by a horizontal wire  552 , connected through an interlevel connector  557  to a vertical wire  555 . Because the single-wire routing interlevel connector  557  is placed within the RICA  558 , the single-wire routing wire  552  is placed within horizontal conductor channel A 1 , and the single-wire routing wire  555  is placed within the vertical conductor channel A 2 . It should be understood that in various embodiments, the horizontal wire  552  and/or the vertical wire  555  can be defined to extend beyond the interlevel connector  557 , and even beyond the RICA  558 . Also, it should be appreciated that essentially any number of single-wire routings can be placed within, i.e., interleaved with, one or more conductor channels. 
     RICAs may be used to connect two or more multi-wire conductor channels that have different numbers of wires per conductor channel.  FIG. 6  shows an example embodiment in which RICAs  711  and  712  are used to connect two interleaved 3-wire conductor channels (A 1  and B 1 ) with two interleaved 2-wire conductor channels (A 2  and B 2 ). Horizontal conductor channel A 1  is defined by wires  701 ,  703 , and  705 . Horizontal conductor channel B 1  is defined by wires  702 ,  704 , and  706 . Vertical conductor channel A 2  is defined by wires  708  and  710 . Vertical conductor channel B 2  is defined by wires  707  and  709 . RICA  711  includes interlevel connectors placed to connect the horizontal conductor channel A 1  with the vertical conductor channel A 2 . Therefore, RICA  711  is defined to transition the 3-wire horizontal conductor channel A 1  into the 2-wire vertical conductor channel A 2 , vice-versa. RICA  712  includes interlevel connectors placed to connect the horizontal conductor channel A 2  with the vertical conductor channel B 2 . Therefore, RICA  712  is defined to transition the 3-wire horizontal conductor channel B 1  into the 2-wire vertical conductor channel B 2 , vice-versa. Also, the interleaving of the conductor channel A 1  wires ( 701 ,  703 ,  705 ) with the conductor channel B 1  wires ( 702 ,  704 ,  706 ), and the interleaving of the conductor channel A 2  wires ( 708 ,  710 ) with the conductor channel B 2  wires ( 707 ,  709 ) allows the interlevel connectors of RICAs  711  and  712  to be placed so as to avoid orthogonally adjacent interlevel connector placements. 
     If adjacent interlevel connector placements are allowed, non-interleaving interlevel connector patterns may be employed.  FIG. 7  shows an example of an interlevel connector pattern used to connect non-interleaved horizontal and vertical multi-wire conductor channels. A horizontal conductor channel A 1  defined by wires  241  and  242  is connected through a RICA  249  to a vertical conductor channel A 2  defined by wires  247  and  248 . Also, a horizontal conductor channel B 1  defined by wires  243  and  244  is connected through a RICA  250  to a vertical conductor channel B 2  defined by wires  245  and  246 . Because the conductor channels A 1  and B 1  are non-interleaved, and because the conductor channels B 2  and A 2  are non-interleaved, the RICAs  249  and  250  do not overlap each other. Use of non-overlapping RICAs can be extended to any number of non-interleaved conductor channels, and to any number of wires per non-interleaved conductor channel. 
     Additionally, a non-interleaved conductor channel can be embedded within one or more other conductor channels, thereby causing one RICA to be embedded within another RICA.  FIG. 8  shows an example layout in which a non-interleaved conductor channel is embedded within another conductor channel. Specifically, a non-interleaved conductor channel B 1  defined by wires  262  and  263  is connected through a RICA  269  to a conductor channel B 2  defined by wires  266  and  267 . Another conductor channel A 1  defined by wires  261  and  264  is connected through a RICA  270  to a conductor channel A 2  defined by wires  265  and  268 . The horizontal conductor channel B 1  is embedded within the horizontal conductor channel A 1 . Similarly, the vertical conductor channel B 2  is embedded within the vertical conductor channel A 2 . Therefore, the RICA  269  is embedded within the RICA  270 . 
     If additional redundancy or interconnection is required, a technique referred to herein as Opportunistic Strapping (OSt) may be employed. One method to perform OSt is to place and connect strap wires between member wires of the same conductor channel, wherein the strap wires are routed perpendicularly to the routing direction of the conductor channel wires to which they connect, and wherein the strap wires are defined on a different chip level than the conductor channel wires to which they connect.  FIG. 9A  shows an example of OSt. In  FIG. 9A , RICA  309  connects horizontal conductor channel A 1  defined by wires  301  and  303  to vertical conductor channel A 2  defined by wires  305  and  307 . Also, RICA  310  connects horizontal conductor channel B 1  defined by wires  302  and  304  to vertical conductor channel B 2  defined by wires  306  and  308 . RICAs  309  and  310  are reinforced by periodic strapping of the horizontal and vertical wires to which they connect. Specifically, RICA  309  is reinforced by vertical strap wire  311  and by horizontal strap wire  313 . Similarly, RICA  310  is reinforced by vertical strap wire  312  and by horizontal strap wire  314 . It should be understood that OSt may include use of multiple commonly oriented strap wires to reinforce a given RICA. 
     OSt can also be used to add redundancy to a non-redundant RICA.  FIG. 9B  shows an example embodiment in which a non-redundant RICA  329  is used to connect a horizontal conductor channel A 1  to a vertical conductor channel A 2 , and to connect a horizontal conductor channel B 1  to a vertical conductor channel B 2 . While a non-redundant RICA, such as  329 , provides no redundancy or interconnection between wires of a common conductor channel, use of a non-redundant RICA may be more area efficient in some layout instances. To compensate for the lack of interconnection and redundancy in a non-redundant RICA, strap wires can be added down the horizontal and vertical run lengths of the conductor channels entering the non-redundant RICA. For example, strap wire  330  is connected between wires  321  and  323  of horizontal conductor channel A 1 . Strap wire  331  is connected between wires  322  and  324  of horizontal conductor channel B 1 . Strap wire  332  is connected between wires  325  and  327  of vertical conductor channel A 2 . Strap wire  333  is connected between wires  326  and  328  of vertical conductor channel B 2 . Each of strap wires  330 - 333  reinforces the interlevel connections within non-redundant RICA  329 . 
     In the OSt process, an extension of a strap wire beyond an interlevel connector to which it is connected may or may not be related to an extension of a channel wire beyond an interlevel connector in a RICA. Also, the extension of strap wires beyond their associated interlevel connectors may be specified globally or on per wire basis. 
     In the OSt process, strap wires can be distributed along an entire length of a conductor channel segment.  FIG. 10  shows an example routing between a location  400  and a location  406  in a chip layout. The routing depicted in  FIG. 10  includes five conductor channel segments  401 ,  402 ,  403 ,  404 , and  405 . A number of strap wires can be placed along each conductor channel segment  401 - 405 . Based on the degree of additional interconnect, redundancy required, desired segment capacitance and the proximity of nearby fill wires, a minimum number of OSt strap wires may be specified. In one embodiment, when local routing is completed, additional OSt strap wires are inserted in the layout as space permits. In one embodiment, a maximum number of OSt strap wires may be specified on a per route or per conductor channel segment basis. 
     If adjacent interlevel connectors are permitted by the virtual grid, non-interleaved conductor channels may employ OSt strap wires.  FIG. 11  shows an example layout in which OSt strap wires are used with non-interleaved conductor channels. A strap wire  350  is used to connect wires  341  and  342  of horizontal conductor channel A 1 . A strap wire  351  is used to connect wires  343  and  344  of horizontal conductor channel B 1 . A strap wire  352  is used to connect wires  345  and  346  of vertical conductor channel A 2 . A strap wire  353  is used to connect wires  347  and  348  of vertical conductor channel B 2 . The OSt strap wires  350 - 353  provide additional interconnect and redundancy to the interlevel connectors within the non-redundant RICA  349 . 
     A dense interlevel connector pattern without orthogonally adjacent interlevel connector placement can be supplemented by OSt strap wires to connect a multi-wire horizontal conductor channel to a multi-wire vertical conductor channel, when each of the horizontal and vertical conductor channels is defined by four or more wires, such as shown in  FIG. 12A . RICA  609  connects wires  601  and  603  of horizontal conductor channel A 1  to wires  605  and  607  of vertical conductor channel A 2 . RICA  610  connects wires  602  and  604  of horizontal conductor channel A 1  to wires  606  and  608  of vertical conductor channel A 2 . The RICAs  609  and  610  do not connect all the wires of the horizontal conductor channel A 1  to all the wires of the vertical conductor channel A 2 . However, the strap wires  615  and  616  supplement the connections made through the RICAs  609  and  610 , such that each of the wires  601 - 604  of the horizontal conductor channel A 1  is connected to each of the wires  605 - 608  of the vertical conductor channel A 2 . Additional OSt strap wires  611 ,  612 ,  613 , and  614  can also be used to reinforce the connections made by RICAs  609  and  610 . 
     If orthogonally adjacent interlevel connector placement is permitted by the virtual grid, some or all of the OSt strap wires may be placed to connect adjacent and commonly oriented wires.  FIG. 12B  shows a variation of the example layout of  FIG. 12A  in which OSt strap wires are used to connect adjacent and commonly oriented wires. Specifically, a strap wire  635  is used to connect wires  602  and  603 . Therefore, the combination of strap wires  611 ,  612 , and  635  serves to connect the wires  601 - 604  of conductor channel A 1 . A strap wire  633  is used to connect wires  605  and  606 . A strap wire  634  is used to connect wires  607  and  608 . Therefore, the combination of strap wires  616 ,  633 , and  634  serves to connect wires  605 - 608  of conductor channel A 2 . 
       FIG. 12C  shows a variation of the example layout of  FIG. 12A  in which each wire of a given conductor channel is connect by a single OSt strap wire. Specifically, a strap wire  651  is defined to connect each of the wires  601 - 604  of conductor channel A 1 . Also, a strap wire  652  is defined to connect each of the wires  605 - 608  of conductor channel A 2 . Each of the strap wires  651  and  652  reinforces the connections of both RICAs  609  and  610 . 
     If one or more unused fill wires is routed near or adjacent to a conductor channel, OSt strap wires may be used to incorporate the unused fill wire into the conductor channel, as shown in the example of  FIG. 13A . Wires  361  and  363  of horizontal conductor channel A 1  are connected to unused fill wire  376  by OSt strap wires  371  and  372 , respectively. Also, if the unused fill wire runs near or adjacent to a RICA to which its channel-by-incorporation is connected, the unused fill wire may be incorporated into the RICA. For example, in  FIG. 13A , the unused fill wire  376  is extended into RICA  369 . Therefore, RICA  369  is configured to connect conductor channel A 1 , as defined by wires  361 ,  363 , and  376 , to conductor channel A 2  defined by wires  365  and  367 . Incorporation of a fill wire into a conductor channel may serve to increase redundancy or alter the capacitance on conductor channel. Additionally, incorporation of a fill wire into a conductor channel may be used to increase the interlevel connector density in the areas around other interlevel connectors on the conductor channel. 
     It should be understood that the length of the fill wire does not need to be equal to or greater than the conductor channel segment to be incorporated into the conductor channel segment. For example,  FIG. 13B  shows the example layout of  FIG. 13A  with the fill wire  376  replaced by a shorter length fill wire  397 . A fill wire may be partially incorporated into a RICA. For example, the fill wire  397  is partially incorporated into RICA  389 . 
     Moreover, use of OSt strap wires to connect to nearby or adjacent conductor channel wires does not need to occur near a RICA. As shown in  FIG. 14A , strap wires can be used to connect to fill wires at any point along the length of the fill wires. Fill wire  901  is connected to conductor channel wire  903  by OSt strap wires  905  and  907 . Fill wire  904  is connected to conductor channel wire  902  by OSt strap wires  906  and  908 . Again, OSt strap wire connection to fill wire can be used to increase redundancy, capacitance or interlevel connector density. Also, shorter segments of fill wires may be connected to conductor channel wires as shown in  FIG. 14B . Fill wires  911  and  914  have a shorter length than conductor channel wires  912  and  913 . Fill wire  911  is connected to conductor channel wire  913  by OSt strap wires  915  and  917 . Fill wire  914  is connected to conductor channel wire  912  by OSt strap wires  916  and  918 . It should be understood that OSt strap wires can be used to connect conductor channel wires to fill wires of any length. 
     To increase the capacitance on a channel wire, or any single wire for that matter, or to increase interlevel connector density in an area, one or more tuning wires can be perpendicular connected along the run length of the subject wire, even in the case that these perpendicular tuning wires do not connect to an additional conductor channel or fill wire, as shown in  FIG. 14C . For example, perpendicular tuning wires  922 - 925  are connected to wire  921 . The frequency of these perpendicular tuning wires may be specified on a per wire basis, within a local area or globally. The perpendicular tuning wires do not need to be equally spaced along the length of the subject wire to which they are connected. Also, a minimum and maximum length may be specified for each perpendicular tuning wire. Also, a total length of all perpendicular tuning wires connected to a subject wire may be specified. The extension of a given perpendicular tuning wire beyond the interlevel connector to which it is connected can be defined independently from the extension of other perpendicular tuning wires, OSt wires, or channel wires. 
     Based on the foregoing, it should be understood that multiple RICAs can be overlapped to maintain an inner-to-outer sequence of conductor channel wires when a horizontal conductor channel transitions to a vertical conductor channel, vice-versa. Also, a RICA can be expanded to route any number of conductor channels. Also, a RICA can be expanded to connect any number of wires per conductor channel. Moreover, horizontal and vertical conductor channels defined by different numbers of wires can be connected through use of a RICA. Each extension of a wire with regard to an interlevel connector, e.g., via or contact, may be defined in a unique manner. Also, each extension of a wire may be defined as either negative, substantially zero, or positive with respect to an edge position of an interlevel connector. 
     Also, as discussed above, OSt strap wires can be used with RICAs or with any other type of interlevel connector pattern. OSt strap wires can be placed at essentially any location along the run length of a conductor channel. In one embodiment, OSt strap wires can be used to connect all wires in a multi-wire conductor channel. Also, in one embodiment, OSt strap wires can be used to connect to nearby fill wires. 
       FIG. 16  shows a flowchart of a method for defining a RICA in a semiconductor chip layout, in accordance with one embodiment of the present invention. The method includes an operation  1601  for defining a virtual grid for interlevel connector placement. The virtual grid is defined by a first set of parallel virtual lines that extend across the layout in a first direction, and by a second set of parallel virtual lines that extend across the layout in a second direction that is perpendicular to the first direction. Each intersection point between the first and second sets of parallel virtual lines is a gridpoint in the virtual grid. 
     The method also includes an operation  1603  for placing a first plurality of interlevel connector structures at respective gridpoints in the virtual grid to form a first RICA. In various embodiments, each interlevel connector structure is defined as either a via structure or a contact structure. Neighboring interlevel connector structures of the first RICA are spaced apart from each other by a first number of gridpoints in the first direction and by a second number of gridpoints in the second direction. Also, the first plurality of interlevel connector structures of the first RICA are placed to collaboratively connect a first conductor channel in a first chip level with a second conductor channel in a second chip level. The first conductor channel is defined by a first plurality of wires which are electrically equivalent to a single conductor. The second conductor channel is defined by a second plurality of wires which are electrically equivalent to a single conductor. 
     In one embodiment, the first plurality of wires of the first conductor channel are defined as parallel wires that extend in the first direction in the first chip level, and the second plurality of wires of the second conductor channel are defined as parallel wires that extend in the second direction in the second chip level, such that the first and second conductor channels are perpendicular to each other. In another embodiment, the first plurality of wires of the first conductor channel are defined as parallel wires that extend in the first direction in the first chip level, and the second plurality of wires of the second conductor channel are defined as parallel wires that also extend in the first direction in the second chip level, such that the first and second conductor channels extend in the same direction. 
     In one embodiment, the spacing between neighboring interlevel connectors is equal to one gridpoint of the virtual grid in the first direction, and one gridpoint of the virtual grid in the second direction. In another embodiment, the spacing between neighboring interlevel connectors is equal to one gridpoint of the virtual grid in the first direction, and at least two gridpoints of the virtual grid in the second direction. In yet another embodiment, the spacing between neighboring interlevel connectors is equal to at least two gridpoints in each of the first and second directions. 
     In one embodiment in which the interlevel connectors of the first RICA are spaced apart by at least two gridpoints of the virtual grid in each of the first and second directions, a non-RICA interlevel connector structure is placed at a gridpoint within the first RICA, so as to connect a first single wire with a second single wire. The first and second single wires are respectively defined in any different two levels of the chip. Each of the first and second single wires is not part of either the first or second conductor channel. 
     In one embodiment, the method includes an operation for placing a second plurality of interlevel connector structures at respective gridpoints in the virtual grid to form a second RICA that is interleaved with the first RICA. In this embodiment, the interlevel connector structures of the second RICA are placed to collaboratively connect a third conductor channel with a fourth conductor channel. The third and fourth conductor channels are respectively defined in any different two levels of the chip. In one version of this embodiment, the interlevel connectors of the first RICA are spaced apart by at least two gridpoints of the virtual grid in each of the first and second directions, and some of the second plurality of interlevel connector structures of the second RICA are placed at respective gridpoints between some of the first plurality of interlevel connector structures of the first RICA. 
     In one embodiment, the method includes an operation for placing a second plurality of interlevel connector structures at respective gridpoints in the virtual grid to form a second RICA that is embedded within the first RICA. Also in this embodiment, the interlevel connector structures of the second RICA are placed to collaboratively connect a third conductor channel with a fourth conductor channel. The third and fourth conductor channels are respectively defined in any different two levels of the chip. In this embodiment, the interlevel connectors of the first RICA are sufficiently spaced apart such that the first plurality of interlevel connector structures of the first RICA brackets the second plurality of interlevel connector structures of the second RICA in both the first and second directions. 
     In one embodiment, the method of  FIG. 16  can optionally include an operation for defining a first number of strap wires to electrically connect some of the first plurality of wires of the first conductor channel together at a location outside the first RICA. Each of the first number of strap wires is defined in any level of the chip other than the first level, and each of the first number of strap wires is oriented perpendicular to the first plurality of wires of the first conductor channel. Each connection between the first number of strap wires and the first plurality of wires of the first conductor channel is formed by an interlevel connector structure. 
     Additionally, in this embodiment, another operation can be optionally performed to define a second number of strap wires to electrically connect some of the second plurality of wires of the second conductor channel together at a location outside the first RICA. Each of the second number of strap wires is defined in any level of the chip other than the second level, and each of the second number of strap wires is oriented perpendicular to the second plurality of wires of the second conductor channel. Also, each connection between the second number of strap wires and the second plurality of wires of the second conductor channel is formed by an interlevel connector structure. 
       FIG. 17  shows a flowchart of a method for wire routing in a semiconductor chip layout, in accordance with one embodiment of the present invention. The method includes an operation  1701  for defining a first conductor channel layout in a first chip level. The first conductor channel layout includes a first plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a first direction. The method also includes an operation  1703  for defining a second conductor channel layout in a second chip level. The second conductor channel layout includes a second plurality of parallel wire layout shapes having a common electrical connectivity and oriented in a second direction that is perpendicular to the first direction. The first and second conductor channel layouts extend across each other within the chip layout at a crossing location. 
     The method further includes an operation  1705  for defining a first RICA layout at the crossing location to connect the first conductor channel layout to the second conductor channel layout. The first RICA layout includes a first plurality of interlevel connector layout shapes placed to collaboratively connect the wire layout shapes of the first conductor channel layout to the wire layout shapes of the second conductor channel layout. In one embodiment, the operation  1705  includes placing the first plurality of interlevel connector layout shapes at respective gridpoints in a virtual grid for interlevel connector placement. The virtual grid is defined by a first set of parallel virtual lines that extend across the chip layout in the first direction and by a second set of parallel virtual lines that extend across the chip layout in the second direction. Each intersection point between the first and second sets of parallel virtual lines is a gridpoint in the virtual grid for interlevel connector placement. 
     It should be understood that the methods as described herein and the resulting cell layouts can be stored in a tangible form, such as in a digital format on a computer readable medium. Also, the invention described herein can be embodied as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include hard drives, network attached storage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical and non-optical data storage devices. The computer readable medium can also be distributed over a network of coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     Any of the operations described herein that form part of the invention are useful machine operations. The invention also relates to a device or an apparatus for performing these operations. The apparatus may be specially constructed for the required purpose, such as a special purpose computer. When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. Alternatively, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network the data maybe processed by other computers on the network, e.g., a cloud of computing resources. 
     The embodiments of the present invention can also be defined as a machine that transforms data from one state to another state. The data may represent an article, that can be represented as an electronic signal and electronically manipulate data. The transformed data can, in some cases, be visually depicted on a display, representing the physical object that results from the transformation of data. The transformed data can be saved to storage generally, or in particular formats that enable the construction or depiction of a physical and tangible object. In some embodiments, the manipulation can be performed by a processor. In such an example, the processor thus transforms the data from one thing to another. Still further, the methods can be processed by one or more machines or processors that can be connected over a network. Each machine can transform data from one state or thing to another, and can also process data, save data to storage, transmit data over a network, display the result, or communicate the result to another machine. 
     While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.