# Patent

## Title
Layout design for electron-beam high volume manufacturing

## Abstract

The present disclosure relates to a method and apparatus to create a physical layout for electron-beam lithography, comprising defining a layout grid for a physical design, the layout grid further comprising vertical grid lines which coincide with stitching lines resulting from partitioning the physical design into a plurality of subfields. The physical design is assembled in accordance with design restrictions regarding interaction between design shapes and the layout grid. In some embodiments, the design restrictions are realized though layout restrictions. In some embodiments, the design restrictions are realized by shifting standard cells to minimize design shape interaction with the layout grid in a post-layout step. In some embodiments, the design restrictions are realized by exchanging positions between a plurality of standard cells for an exchange permutation which minimizes the number of interactions in a post-layout step. In some embodiments a routing grid is refined to rule out interactions between a subset of design constructs and the layout grid. Remaining design shape placement is then optimized along the routing grid relative to the stitching lines.

## Background
BACKGROUND
Electron-beam (Ebeam) lithography utilizes a focused beam of electrons to selectively pattern a wafer directly for electron-beam direct write (EDW), but may also be employed to pattern a photomask for optical photolithography. Ebeam lithography offers an increased patterning resolution over optical photolithography by utilizing an Ebeam with electron energies on the order of approximately 5 keV-100 keV, resulting in wavelengths less than that of light, and is only limited by diffraction by an electron optics slit though which the beam of electrons is passed. However, Ebeam lithography has limited throughput compared to optical photolithography as an Ebeam writer forms shapes of a pattern in a serial manner, whereas optical photolithography forms a forms shapes of a pattern in parallel manner. This makes optical photolithography more suitable for high-volume manufacturing.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1C illustrate some embodiments of a data flow for electron-beam (Ebeam) patterning.
FIGS. 2A-2E illustrate some embodiments of defect formation when dithering a subminimum sized stitch-metal shape in an Ebeam patterning data flow.
FIG. 3 illustrates some embodiments of overlay degradation for adjacent Ebeam patterning subfields containing a buffer region.
FIGS. 4A-4B illustrate a flow chart of some embodiments a method to create a physical layout for Ebeam lithography.
FIG. 5 illustrates a flow chart of some embodiments a method to create a stitching-aware physical layout for Ebeam lithography.
FIGS. 6A-6B illustrate some embodiments of a method to shift a standard cell relative to a stitching line to reduce a violation density value.
FIGS. 7A-7B illustrate some embodiments of a method to minimize a total violation density value within a row of standard cells.
FIGS. 8A-8D illustrate some embodiments of a method to minimize a total violation density value within a checking tile.
FIGS. 9A-9B illustrate some embodiments of a method to solve a minimization problem to determine placement of the plurality of shapes.
FIGS. 10A-10E illustrate some embodiments of routing grid line removal to avoid stitching lines.
FIGS. 11A-11B illustrate some embodiments of routing grid point removal to avoid subminimum sized stitch-metal shapes.
FIG. 12 illustrates some embodiments of a design tool configuration to create a physical layout for Ebeam lithography.



DETAILED DESCRIPTION
The description herein is made with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to facilitate understanding. It may be evident, however, to one of ordinary skill in the art, that one or more aspects described herein may be practiced with a lesser degree of these specific details. In other instances, known structures and devices are shown in block diagram form to facilitate understanding.
FIG. 1A illustrates some embodiments of a data flow for electron-beam (Ebeam) patterning. A physical design (e.g., GL1, OASIS, or GDSII) 102A is created using a physical design tool. The physical design 102A is subjected to an optical enhancement, wherein designed shapes of the physical design 102A are subjected to a proximity correction at 104A, adjusting edges of a respective designed shape so that the resultant shape formed on-wafer resembles the respective designed shape as closely as possible within lithographic limits. The physical design 102A is parsed into subfields, or “striped” at 106A, wherein a respective stripe spans an area between two outside edges of the physical design, and is narrow enough so that a stripe width can be written by an Ebeam patterning tool (e.g., Ebeam writer). The physical design 102A is converted into a data format at 108A which readable by the Ebeam writer. The Ebeam writer forms a pattern at 110A, the pattern comprising the designed shapes of the physical design 102A on a photomask for optical photolithography, or in resist on-wafer for EDW, resulting in an on-wafer physical layout 112A.
FIG. 1B illustrates some embodiments of partitioning a physical design 100B into a plurality of stripes 102B which abut one another and cover the entire physical design 100B. A respective stripe 102B spans an area between two outside edges 104B of the physical design 100B. For this type of partitioning, a physical design 100B of approximately 30 mm by 30 mm is partitioned into stripes for parallel writing by the Ebeam writer. State of the art Ebeam writers support “striping” widths of approximately 1 nm-10 nm.
FIG. 1C illustrates some embodiments of a detailed physical design 100C comprising a plurality of design shapes further comprising a plurality of metallization shapes 102C and a plurality of via interconnect shapes 104C. Some design shapes are located within a standard cell 106C from a library which had been previously defined for reuse. Other design shapes are located outside any standard cell 106C and are added at a level of design hierarchy other than the standard cell 106C, placed by a place and route tool to form connections between standard cells 106C, or both. The detailed physical design 100C further comprises a stripe 102B defined for EDW, wherein edges of the stripe 102B not coincident with an outside edge of the physical design 100C are defined as stitching lines 108C and serve as a boundary between two stripes 102B.
Design shapes which straddle a stitching line are subject to manufacturing defects, which can result in reduced yield, as the decomposition of the design 100C between two or more stripes 102B creates additional manufacturing overhead, because portions of the design shape are created at different times by the Ebeam writer and must subsequently be “stitched” together. “Stitching” of a decomposed shape may comprise an overlap area, or stitching area, wherein the portion of the design shape immediately surrounding the stitching line 108C is patterned twice by the Ebeam writer to assure that the shape is continuous. Manufacturing defects are particularly sensitive to design constructs such as via interconnect shapes 104C which straddle 110C a stitching line 108C and are subject to irregular metal topographies when landing on stitched metallization shapes 102C. A vertical metallization shape 102C bisected 112C by a stitching line 108C also generate a high number of defects due to large topographical and width variations. Manufacturing defects are also sensitive to a via interconnect shape 104C touching a stitch-metal shape with a size below a manufacturing minimum threshold 114C, wherein stitch-metal shape is defined as an intersection of a stripe 102B and a metallization shape 102C straddling a stitching line 108C.
Accordingly, the present disclosure relates to a method and apparatus to create a physical layout for electron-beam lithography, comprising defining a layout grid for a physical design, the layout grid further comprising vertical grid lines which coincide with stitching lines resulting from partitioning the physical design into a plurality of subfields. The physical design is assembled in accordance with design restrictions regarding interaction between design shapes and the layout grid. In some embodiments, the design restrictions are realized though layout restrictions. In some embodiments, the design restrictions are realized by shifting standard cells to minimize design shape interaction with the layout grid in a post-layout step. In some embodiments, the design restrictions are realized by exchanging positions between a plurality of standard cells for an exchange permutation which minimizes the number of interactions in a post-layout step. In some embodiments a routing grid is refined to rule out interactions between a subset of design constructs and the layout grid. Remaining design shape placement is then optimized along the routing grid relative to the stitching lines.
FIGS. 2A-2E illustrate some embodiments of defect formation when dithering a subminimum sized stitch-metal shape 114C in an Ebeam patterning data flow. FIG. 2A illustrates some embodiments of a close-up view of the stitch-metal shape with a size below a manufacturing minimum threshold 114C. FIG. 2B illustrates some embodiments of a pixel rendering 200B of the stitch-metal shape of FIG. 2A comprising a plurality of pixels 202B which cover the stitch-metal shape of FIG. 2A. FIG. 2C illustrates some embodiments of a gray-level transformation 200C of the stitch-metal shape 114C into the pixels 202B of FIG. 2B. The gray-level transformation 200C also includes a proximity correction to the via interconnect shape 104C to model effects of the Ebeam writer: diffraction, shape biasing, corner-rounding, etc. A data processing error in the gray-level transformation 200C may introduce a defect 202C to a single pixel that can propagate 204C to adjacent pixels in that have not yet been processed through subsequent steps in the Ebeam patterning data flow. FIG. 2D illustrates some embodiments of a gray-level to black-and-white representation 200D of the stitch-metal shape 114C, wherein propagation of the defect 202C has resulted in a dithering error 202D, causing voids 204D to form in the black-and-white representation 200D. The dithering error 202D results in a malformed on-wafer metallization shape 202E the embodiments of FIG. 2E, when the Ebeam writer patterns the drawn metallization shape 102C of the subminimum sized stitch-metal shape 114C, resulting in a manufacturing defect comprising an open, short, void, etc.
FIG. 3 illustrates some embodiments of overlay degradation for adjacent Ebeam patterning subfields containing a buffer region 300, comprising a first subfield 302A and a second subfield 302B. The first subfield 302A further comprises a first metallization layer subset 304A and a first via interconnect layer subset 306A. The second subfield 302B further comprises a second metallization layer subset 304B and a second via interconnect layer subset 306B. Each subfield is patterned separately, which comprises a single Ebeam writer at different times, and decreases throughput relative to optical lithography. Therefore it can be stated that the first subfield 302A is patterned by a first Ebeam and the second subfield 302B is patterned by a second Ebeam. Generally, different layers written by different Ebeams are subject to several types of patterning error, including: beam-to-beam position error on-wafer (i.e., overlay error), beam-to-beam defocus errors and variations, beam-to-beam current variation, and beam-to-beam magnification variation. The overlay error for beam-to-beam is twice that of a single beam.
The embodiments of FIG. 3 further comprise a buffer region 308, wherein a boundary 310 between the first subfield 302A and the second subfield 302B purposefully deviates from an each abutting a stitching line 1080 to minimize a number of design shapes that are stitched between subfields. When performing subfield division for subfields separated by a stitching line 108C (i.e., rectangular subfields with straight-line boundaries), the layer above (i.e., the first via interconnect layer subset 306A, or the second via interconnect layer subset 306B, respectively) will obey the division rule from the layer below (i.e., first metallization layer subset 304A, or the second metallization layer subset 304B, respectively). In this instance the same subfield in different layers written by the same Ebeam minimizes the layer to layer overlay tolerance. However, the presence of the buffer region 308 and the (non straight-line) boundary 310 may break this rule, doubling the overlay error.
As such, some embodiments of the current invention comprise a formulation for optimizing patterning of adjacent subfields without any buffer region 308 and associated (non straight-line) boundary 310, such that a boundary between the first subfield 302A and second subfield 302B always comprises a stitching line 108C, eliminating the increased overlay error within the buffer region 308. To further minimize effects' of the overlay error for design shapes that straddle the stitching line 108C, design restrictions comprising special design rules (e.g., a via interconnect landing rule or a short polygon rule), or an automated post-design modification of a layout (e.g., as a part of the proximity correction), or a combination thereof, are utilized to minimize a number of shapes that straddle the stitching line 108C to minimize a number of polygons cut by the stitching line 108C.
FIG. 4A illustrates a flow chart of some embodiments of a method 400A to create a physical layout for Ebeam lithography. While method 400A is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.
At 402A layout optimization restrictions are put into place in accordance with minimization of design shapes that straddle stitching lines in a physical design. The layout optimization restrictions may comprise direct avoidance of the stitching line, a “keep out” region which outlaws placement of certain design constructs in a vicinity of a stitching line, or a combination thereof. These layout restrictions may directly enable on-wafer geometries as drawn, or enable a post-processing step that further modifies the shape for stitching line avoidance.
At 404A a physical design (e.g., GL1, OASIS, or GDSII) is created using a physical design tool, assembling a physical design by arranging a plurality of standard cells, and recognizing a partitioning of the physical design into a plurality of subfields through the layout optimization restrictions. The layout optimization restrictions will govern partitioning of the physical design, position of one or more standard cells, may drive redesign to one or more standard cells, or a combination thereof, to minimize a number of design shapes that straddle stitching lines dividing subfields. The design shapes comprise a plurality of metallization layers or a plurality of via interconnect layers.
At 406A the physical design is subjected to a proximity correction, adjusting edges of metallization layers or via interconnect layers so that the resultant on-wafer shape resembles the respective designed shape as closely as possible within lithographic limits.
At 408A the physical design is then parsed into subfields, or “striped” in accordance with the definition of 404A.
At 410A the physical design is converted into a data format which readable by an Ebeam writer.
At 412A the Ebeam writer forms a pattern comprising the designed shapes of the physical design. In some embodiments the pattern is formed on a photomask for optical lithography. In other embodiments the pattern is formed in resist on-wafer for EDW.
At 414A several subsequent manufacturing processing steps are performed comprising development of resist, filling with an interlayer dielectric, subsequent layer formation, etc., resulting in an on-wafer physical layout.
FIG. 4B illustrates a flow chart of some detailed embodiments of a method 400B to define stitching-aware layout optimization for Ebeam lithography. The method 400B improves upon some prior art approaches by advancing recognition of the subfield division and the stitching line formation to the physical design through the layout optimization restrictions, or by modeling the stitching lines directly in the design space. This allows for generation of layouts with stitching-aware optimization.
At 402B stitching line specifications are defined which define the size and location of subfields of a physical design based upon an overall footprint (i.e., size and shape) of the physical design. The stitching line specifications are also influenced by settings of the Ebeam writer and unit processes which are used to manufacture the physical layout.
At 404B stitching-aware design constraints are defined which may comprise specialized design rules, a design utility that shows a layout designer the position of stitching lines in the layout space, an automated post-design modification of the physical design, or a combination thereof.
At 406B a physical design is produced in accordance with the stitching-aware design constraints for standard cell placement and top level wiring of the physical design by a place and route tool.
At 408 a physical design with stitching aware optimization has been produced in accordance with the stitching-aware design constraints for subsequent processing comprising subfield division, Ebeam data conversion, Ebeam writing, and downstream manufacturing processes to produce a physical layout.
FIG. 5 illustrates a flow chart of some further embodiments of a method 500 to create a stitching-aware physical layout for Ebeam lithography. The embodiments of FIG. 5 comprise a detailed description of 406B for construction of a stitching-aware physical design. Moreover, various steps of the method 500 will be revisited in subsequent embodiments.
At 502 stitching-aware detailed placement of standard cells in a physical design is performed. The stitching-aware detailed placement comprises two steps which may be performed in an arbitrary order: standard cell sliding 506 and standard cell swapping 508. Cell sliding 506 comprises assembling a portion of a physical design by arranging the plurality of standard cells into rows, recognizing interaction between a subset of design constructs and a stitching line as defined in the stitching-aware design constraints, and moving a standard cell along a direction orthogonal to a stitching line (i.e., along a row) to reduce the interactions. Cell swapping 508 comprises exchanging positions of two or more standard cells to minimize these interactions.
At 504 stitching-aware full chip routing is performed to form connections between standard cells through placement of a plurality of shapes formed on a metallization layer, wiring the physical design (e.g., chip) up to bond pads, packaging, and the like. Stitching-aware full chip routing 504 is performed in three sequential steps: global routing 510, stitching-aware layer and track assignment 512, and detailed routing for short polygon avoidance 514. At 510 global routing of the physical design is performed on a course routing grid. This step may occur with little regard to stitching-aware design constraints, or may reorder subsequent steps to incorporate stitching-aware design constraints into router restrictions. At 512 stitching-aware layer and track assignment is performed to place design shapes on a track comprising a global grid that is an integer multiple of a design shape minimum pitch, while minimizing interaction of the design shapes with the stitching lines. In some embodiments the 512 stitching-aware layer and track assignment 512 is performed after a global routing result is obtained, adjusting a track grid about a metallization wiring topology. At 514 detailed routing for short polygon avoidance is performed, wherein the routing grid is refined to outlaw routing grid lines or routing grid points in accordance with the stitching-aware design constraints, and may comprise re-routing of the global routing result.
FIGS. 6A-6B illustrate some embodiments of a method to shift a standard cell relative to a stitching line to reduce a violation (e.g., cell sliding). FIG. 6A illustrates an embodiment of a standard cell 600A placed in a physical design, which intersects a stitching line 108C. The standard cell 600A comprises design shapes further comprising a plurality of metallization shapes 102C and a plurality of via interconnect shapes 104C. A first violation 602A is defined as a via interconnect shape 104C straddling a stitching line 108C. A stitch-metal shape is also defined as an intersection of a subfield and a metallization shape 102C straddling a stitching line, and a second violation 604A is defined as a subminimum sized stitch-metal shape (e.g., a stitch metal shape with a size below a minimum manufacturing threshold). A third violation density 606A is defined by a vertical metallization shape 102C bisected by a stitching line 108C.
FIG. 6B illustrates some embodiments of minimizing violation densities 600B, comprising shifting the standard cell 600A horizontally to avoid stitching line 108C interactions with design shapes to eliminate the first violations 602A, the second violations 604A, and the third violation 606A of the embodiments of FIG. 6A.
FIGS. 7A-7B illustrate some embodiments of a method to minimize a total violation density value within a row of standard cells (e.g., cell sliding). A first violation density value is defined within a standard cell as a number of via interconnect shapes within the standard cell straddling a stitching line. A second violation density value is defined within a standard cell as a number of subminimum sized stitch-metal shapes within the standard cell straddling a stitching line. A third violation density value within a standard cell as a number of vertical metallization shapes bisected by a stitching line. A violation density value for a standard cell is defined as a sum of the first violation density value, the second violation density value, and the third violation density value.
FIG. 7A illustrates some embodiments of minimizing a total violation density value for a row configuration 700A of standard cells 702A by standard cell sliding, wherein a total violation density value is defined as a sum of the violation density values for the standard cells 702A comprising the row configuration 700A. After determining the violation density value of each standard cell 702A the row configuration 700A, a first standard cell 704A comprising a largest violation density value (i.e., 4) is moved within a row along a direction orthogonal to a stitching line 108C to minimize the largest violation density value within the first standard cell 704A. FIG. 7B further illustrates some embodiments of minimizing a total violation density value for the row configuration 700A after movement of the first standard cell 704A, by selecting a second standard cell 702B comprising a second largest violation density value (i.e., 2) for movement within the row. The second standard cell 702B is then moved along a direction orthogonal to a stitching line to minimize the second largest violation density value.
FIGS. 8A-8D illustrate some embodiments of a method to minimize a total violation density value within a checking tile by standard cell swapping. FIG. 8A shows an arrangement of standard cells 800A, wherein a checking tile 802A is defined to cover portions of two or more rows of standard cells, including a first standard cell 804A in a first row, a second standard cell 806A in a second row, and a third standard cell 808A in a third row. FIG. 8B shows the arrangement of standard cells 800A, wherein the first standard cell 804A, the second standard cell 806A, and the third standard cell 808A have been removed to reveal a first location 802B, a second location 804B, and a third location 808B, respectively.
A numerical description is formulated for a resulting number of interactions formed between standard cells and stitching lines (e.g., the total violation density) in a given arrangement, and expanded to formulate the total violation density when exchanging positions between a plurality of standard cells of equal size for all possible exchange permutations (there are six possible permutations in the embodiments of FIGS. 8A-8D). The positions of the standard cells are then exchanged for an exchange permutation which minimizes the number of interactions, as arranged in FIG. 8C, wherein the first standard cell 804A is moved to the second location 804B, the second standard cell 806A is moved to the third location 808, and the third standard cell 808A is moved to the first location 802B.
FIG. 8D illustrates some embodiments of a minimization problem for the arrangement of the standard cells of the embodiments of FIG. 8C, comprising a bipartite graph 800D denoting interactions between a first set of shapes comprising the first standard cell 804A, the second standard cell 806A, and the third standard cell 808A and a second set of shapes comprising the first location 802B, the second location 804B, and the third location 808. The standard cells and locations form vertices of the bipartite graph 800D. Each pair of vertices is connected by an edge weighted by a total violation density value resulting from placing the standard cell at the location. A total of six edges corresponding to the possible permutations in the embodiments of FIGS. 8A-8D exist in the bipartite graph 800D. This minimization problem may then be solved by numerical methods to minimize a sum of total violation density values along all edges of the bipartite graph 800D to find an optimal swapping solution for placement of the standard cells from the first set of shapes in the locations from the second set of shapes.
For the embodiments of FIG. 8D the edge weighting of an edge formed between a standard cell and a location may be refined as a sum of a product of a first weighting factor and a first violation density value resulting from placing the standard cell at the location, a product of a second weighting factor and a second violation density value resulting from placing the standard cell at the location, and a product of a third weighting factor and a number of design shapes that straddle a stitching line.
FIGS. 9A-9B illustrate some embodiments of a method to solve a minimization problem to determine placement of the plurality of design shapes. FIG. 9A illustrates a routing arrangement 900A, comprising a plurality of metallization shapes 902A, or segments S1-S6, which comprise a global routing wiring result. The routing arrangement 900A further comprises a routing grid comprising first vertical grid lines 904A spaced at integer multiples of the metallization shape 902A minimum pitch. A layout grid is further defined within the routing grid 900B comprising stitch-lines as second vertical grid lines 108C spaced at integer multiples of the metallization shape 902A minimum pitch, and wherein periodicity of the second vertical grid lines 108C is an integer multiple of periodicity of the first vertical grid lines 904A. The vertical routing grid and the layout grid are aligned resulting in coincidence between each first vertical grid line 904A and a respective second vertical grid line 108C. In some embodiments, first vertical grid lines 904A which are coincident with second vertical grid lines 108C are removed from the routing grid 900B to prevent patterning and manufacturing issues with via interconnect shapes straddling stitching lines 108C, subminimum sized stitch-metal shapes, and vertical metallization shapes bisected by a stitching lines.
FIG. 9B illustrates some embodiments of a vertical constraint graph 900B for the plurality of metallization shapes 902A, vertical constraint graph 900B comprising one vertex 902B for each shape and an edge formed between a first shape and a second shape which overlap in a horizontal direction (e.g., W12 formed between S1 and S2, which overlap). Each edge of the vertical constraint graph 900B is weighting by a value proportional to a distance between the first shape and the second shape, and a minimization problem corresponding to the vertical constraint graph is solved to determine placement of the metallization shapes relative to the routing grid 900B to minimize total edge weight.
In some embodiments the routing arrangement 900A into a plurality of tiles T1-T4, wherein the plurality of metallization shapes 902A form connections between two or more standard cells. The vertical constraint graph 900B comprising vertices for each metallization shapes 902A and edges between vertices for shapes which overlap in the horizontal direction. The edges are weighting by a value of one-half raised to a value of a distance between the first shape and the second shape, and a minimization problem equivalent to the vertical constraint graph 900B is solved to determine placement of metallization shapes 902A
FIGS. 10A-10E illustrate some embodiments of routing grid line removal to avoid stitching lines. FIG. 10A illustrates some embodiments of a gridded layout 1000A with stitching lines 108C resulting from layout partitioning. FIG. 10B illustrates a routing grid 10008 corresponding to the gridded layout 1000A, wherein a line path 1002B is placed by a place and route tool along a legal set of grid coordinates. FIG. 100 illustrates some embodiments of a physical design 1000C derived from the routing grid 1000B and line path 1002B, wherein a stitching defect 1004C is formed on a vertical segment of a metallization layer 1002C derived from the line path 1002B. To prevent the stitching defect 1004C, the routing grid 1000B may be refined by removing vertical grid lines from the routing grid 1000B that overlap with stitching lines, as demonstrated in FIG. 10D. The resulting physical design 1000E of FIG. 10E no longer contains the stitching defect 1004C as the grid line along which the stitching defect 1004C had formed in FIG. 10C is no longer legal for routing.
FIGS. 11A-11B illustrate some embodiments of routing grid point removal to avoid subminimum sized stitch-metal shapes. FIG. 11A illustrates some embodiments of a routing grid 1100A comprising grid lines 1102A which can form a routing path 1104A between a source pin 1106A and a target pin 1108A. A middle grid line of the routing grid 1100A is coincident with a stitching line 108C, resulting in a subminimum sized stitch-metal shape 114C. To avoid this, the embodiments of FIG. 11B refine the routing grid 1100A into a new routing grid 1100B by defining an intersection of the stitching 108C line and a routing grid line as an illegal point 1102B on the routing grid 1100B when the intersection is within a threshold number of routing grid points from the source pin 1106A or the target pin 1108A.
FIG. 12 illustrates some embodiments of a design tool configuration 1200 to create a physical layout for Ebeam lithography, comprising a physical design tool 1202 configured to create a physical design, a place and route tool 1212 coupled to the physical design tool 1202 and configured to place shapes within the physical design, and a detailed placement engine 1206 coupled to the physical design tool 1202 and the place and route tool 1212. The detailed placement engine 1206 is configured to optimize shape placement in the physical design tool 1202 by moving shapes according to physical design restrictions. The detailed placement engine 1206 is further configured to define shape placement by the place and route tool 1212 according to a layout grid in conjunction with physical design restrictions. A design rule checker 1210 is configured to check the physical design against a pre-defined set of layout restrictions, and communicate results of the check to the physical design tool to be accessed through a user interface 1204. The design rule checker 1210 may also communicate results of the check to the detailed placement engine 1206 so that the detailed placement engine 1206 may refine shape placement within the physical design.
The design tool configuration 1200 further comprises an Ebeam data processor 1214 configured to receive physical design data from the physical design tool 1202, and to send layout partitioning requirements for Ebeam patterning to the detailed placement engine 1206. The design tool configuration 1200 further comprises a library unit 1208 coupled to the physical design tool 1202 and configured to store a plurality of standard cells, a standard cell comprising one or more shapes, wherein the detailed placement engine 1206 is configured to refine standard cell placement in the physical design tool 1202 in accordance with partitioning requirements from the electron-beam data processor 1212. The detailed placement engine 1206 will optimize shape placement by modifying the physical design by steps comprising: shifting standard cells within a physical design, exchanging positions between the plurality of standard within the physical design, communicating to the place and route tool 1212 illegal routing grid positions resulting from layout partitioning for Ebeam lithography by the Ebeam writer 1216.
It will also be appreciated that equivalent alterations and/or modifications may occur to one of ordinary skill in the art based upon a reading and/or understanding of the specification and annexed drawings. The disclosure herein includes all such modifications and alterations and is generally not intended to be limited thereby. In addition, while a particular feature or aspect may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features and/or aspects of other implementations as may be desired. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, and/or variants thereof are used herein; such terms are intended to be inclusive in meaning—like “comprising.” Also, “exemplary” is merely meant to mean an example, rather than the best. It is also to be appreciated that features, layers and/or elements depicted herein are illustrated with particular dimensions and/or orientations relative to one another for purposes of simplicity and ease of understanding, and that the actual dimensions and/or orientations may differ substantially from that illustrated herein.
Therefore, the present disclosure relates to a method and apparatus to create a physical layout for electron-beam lithography, comprising defining a layout grid for a physical design, the layout grid further comprising vertical grid lines which coincide with stitching lines resulting from partitioning the physical design into a plurality of subfields. The physical design is assembled in accordance with design restrictions regarding interaction between design shapes and the layout grid. In some embodiments, the design restrictions are realized though layout restrictions. In some embodiments, the design restrictions are realized by shifting standard cells to minimize design shape interaction with the layout grid in a post-layout step. In some embodiments, the design restrictions are realized by exchanging positions between a plurality of standard cells for an exchange permutation which minimizes the number of interactions in a post-layout step. In some embodiments a routing grid is refined to rule out interactions between a subset of design constructs and the layout grid. Remaining design shape placement is then optimized along the routing grid relative to the stitching lines.
In some embodiments the present disclosure relates to a method to create a physical layout for electron-beam lithography, comprising assembling a physical design by arranging a plurality of standard cells, defining a layout grid for the physical design comprising first vertical grid lines spaced at integer multiples of a design shape minimum pitch, and minimizing intersection of design shapes with first vertical grid lines.
In some embodiments the present disclosure relates to a method to create a physical layout, comprising forming a plurality of standard cells, assembling a physical design by arranging the plurality of standard cells into rows, partitioning the physical design into a plurality of subfields which abut one another and cover the entire physical design, wherein a subfield spans an area between two outside edges of the physical design orthogonal to an orientation of the rows, defining a stitching line as a boundary between two subfields, and minimizing a number of design shapes that straddle the stitching line.
In some embodiments the present disclosure relates to a design tool configured to create a physical layout for electron-beam lithography, comprising a physical design tool configured to create a physical design, a place and route tool coupled to the physical design tool and configured to place shapes within the physical design, and a detailed placement engine coupled to the physical design tool and the place and route tool. The detailed placement engine is configured to optimize shape placement in the physical design tool by moving shapes according to physical design restrictions, and define shape placement by the place and route tool according to a layout grid in conjunction with physical design restrictions.

## Claims

1. A method to create layout for electron-beam lithography, comprising:
assembling a layout comprising graphical data by arranging a plurality of standard cells within a design tool, a standard cell comprising one or more design shapes;
defining a layout grid for the layout within the design tool, wherein the layout grid comprises first vertical grid lines; and
reducing an amount of intersection between the design shapes and the first vertical grid lines by shifting one or more of the design shapes relative to the first vertical grid lines;
wherein reducing the amount of intersection between the design shapes and the first vertical grid lines comprises shifting the design shapes horizontally relative to the first vertical grid lines.

2. The method of claim 1, wherein reducing the amount of intersection between the design shapes and the first vertical grid lines comprises avoiding first vertical grid lines with design shapes within the standard cell by shifting the standard cell horizontally, wherein design shapes comprise a width value below a first threshold or an area value below a second threshold.

3. The method of claim 1, wherein reducing the amount of intersection between the design shapes and the first vertical grid lines comprises:
formulating a numerical description for a resulting number of interactions formed between design shapes and first vertical grid lines when exchanging positions between a plurality of standard cells of equal size for all possible exchange permutations; and
exchanging positions between the plurality of standard cells for an exchange permutation which minimizes the number of interactions.

4. The method of claim 1, further comprising:
defining a vertical routing grid comprising second vertical grid lines, wherein periodicity of the layout grid is an integer multiple of periodicity of the vertical routing grid;
aligning the vertical routing grid to the layout grid resulting in coincidence between each first vertical grid line and a respective second vertical grid line; and
removing the respective second vertical grid line from the vertical routing grid.

5. The method of claim 1, further comprising:
forming connections between two or more standard cells through placement of a plurality of shapes formed on a metallization layer;
constructing an vertical constraint graph for the plurality of shapes comprising one vertex for each shape and an edge formed between a first shape and a second shape which overlap in a horizontal direction;
weighting the edge by a value proportional to a distance between the first shape and the second shape; and
solving a minimization problem corresponding to the vertical constraint graph to determine placement of the plurality of shapes.

6. A method to create a layout for patterning by an electron beam (e-beam) writing tool, comprising:
assembling a layout by arranging a plurality of standard cells into rows using a design tool, wherein a standard cell comprises graphical data including one or more design shapes;
partitioning the layout into a plurality of subfields, wherein neighboring subfields abut one another at a stitching line;
defining a first violation density value as a number of via interconnect shapes within the standard cell straddling the stitching line;
defining a stitch-metal shape as an intersection of one of the plurality of subfields and a metallization layer straddling the stitching line;
defining a second violation density value within the standard cell as a number of subminimum sized stitch-metal shapes within the standard cell straddling the stitching line;
defining a third violation density value within the standard cell as a number of vertical metallization shapes bisected by the stitching line;
defining a violation density value for the standard cell as a sum of the first violation density value, the second violation density value, and the third violation density value; and
shifting at least one of the one or more design shapes from the stitching line to reduce a number of design shapes that straddle the stitching line.

7. The method of claim 6, wherein the graphical data comprises a GL1, OASIS, or GDSII data format.

8. The method of claim 6, further comprising moving the standard cell along a direction orthogonal to the stitching line to reduce the violation density value.

9. The method of claim 8, further comprising:
determining the violation density value of each standard cell within a respective row of the layout;
moving a first standard cell comprising a largest violation density value within the row along the direction orthogonal to the stitching line to minimize the largest violation density value within the first standard cell; and
moving a second standard cell comprising a second largest violation density value within the row along the direction orthogonal to the stitching line to minimize the second largest violation density value within the second standard cell.

10. The method of claim 6, further comprising:
defining a checking tile to cover portions of two or more rows of standard cells within the layout;
determining a total violation density value within the checking tile as a sum of violation density values within standard cells covered by the checking tile; and
minimizing the total violation density value by swapping a first standard cell within the checking tile with a second standard cell within the checking tile.

11. The method of claim 10 further comprising swapping three or more cells by:
constructing a bipartite graph between a first set of shapes comprising a plurality of standard cells of equal size within the checking tile and a second set of shapes comprising locations of the plurality of standard cells;
weighting an edge formed between a standard cell from the first set of shapes and a location from the second set of shapes by the total violation density value resulting from placing the standard cell at the location; and
solving a minimum weight maximum bipartite matching problem to minimize a sum of total violation density values along all edges of the bipartite graph to find an optimal swapping solution for placement of the standard cells from the first set of shapes in the locations from the second set of shapes.

12. The method of claim 11, further comprising weighting an edge formed between the standard cell and a location by a sum of:
a product of a first weighting factor and a first violation density value resulting from placing the standard cell at the location;
a product of a second weighting factor and a second violation density value resulting from placing the standard cell at the location; and
a product of a third weighting factor and a number of design shapes that straddle the stitching line.

13. The method of claim 6, further comprising:
partitioning a subfield into a plurality of tiles;
forming connections between two or more standard cells within the subfield through placement of a plurality of shapes formed on one of a plurality of metallization layers;
constructing a vertical constraint graph comprising one vertex for each shape and an edge formed between a first vertex corresponding to a first shape, and a second vertex corresponding to a second shape, wherein the first shape and the second shape overlap in a horizontal direction;
weighting the edge by a value of one-half raised to a value of a distance between the first shape and the second shape; and
solving a minimization problem corresponding to the vertical constraint graph to determine placement of the plurality of shapes.

14. The method of claim 13, further comprising:
aligning each stitching line with a vertical grid line of a routing grid; and
removing vertical grid lines from the routing grid that overlap with stitching lines.

15. The method of claim 14, further comprising preventing a subminimum sized stitch-metal shape on a routing path by defining a layout restriction which identifies an intersection of a stitching line and a routing grid line as an illegal point on the routing grid when the intersection is within a threshold number of routing grid point from a pin.

16. A tool arrangement configured to create a layout for electron-beam lithography, comprising:
a design tool configured to create a layout comprising graphical data by arranging a plurality of standard cells within a layout grid, wherein a standard cell comprises one or more design shapes;
a place and route tool coupled to the design tool and configured to place design shapes within the layout;
a shape placement tool coupled to the design tool and the place and route tool and configured to reduce an intersection of the design shapes with the layout grid by shifting one or more design shapes relative to the layout grid; and
an electron-beam data processor configured to receive the graphical data from the design tool, to define the layout grid according to requirements for electron-beam patterning, and to send the layout grid to the shape placement tool.

17. The tool arrangement of claim 16, further comprising a library unit coupled to the design tool and configured to store a plurality of standard cells, a standard cell comprising one or more design shapes, wherein the shape placement tool is configured to change standard cell placement within the layout to reduce an intersection of the design shapes with the layout grid.

18. The tool arrangement of claim 16, the shape placement tool further configured to move shapes within the layout-by a method comprising:
shifting standard cells within the layout;
exchanging positions between a plurality of standard cells within the layout; and
communicating to the place and route tool illegal routing grid positions resulting from the layout grid.

19. The method of claim 6, further comprising defining a set of layout restrictions, which are programmed into a design rule checker coupled to the design tool, and which determine the violation density value for the layout.

20. The method of claim 15, further comprising verifying the layout restriction against the layout within a design rule checker coupled to the design tool.

21. The method of claim 1, wherein the first vertical grid lines are spaced periodically with a horizontal distance between adjacent first vertical grid lines that is different than a horizontal dimension of a standard cell.

22. The method of claim 6, wherein the neighboring subfields correspond to separate patterning passes of the e-beam writing tool over the layout.