Abstract:
Embodiments of the invention provide an integrated circuit (IC) having reduced through silicon via (TSV)-induced stresses and related IC design structures and methods. In one embodiment, the invention includes a method of designing an integrated circuit (IC) having reduced substrate stress, the method including: placing in an IC design file a plurality of through silicon via (TSV) placeholder cells, each placeholder cell having an undefined TSV orientation; replacing a first portion of the plurality of TSV placeholder cells with a first group of TSV cells having a first orientation; and replacing a second portion of the plurality of TSV placeholder cells with a second group of TSV cells having a second orientation substantially perpendicular to the first orientation, wherein TSV cells having the first orientation and TSV cells having the second orientation are interspersed to reduce a TSV-induced stress in an IC substrate.

Description:
BACKGROUND 
     The present invention relates generally to integrated circuits and, more particularly, to integrated circuits (ICs) and IC design structures in which through silicon via (TSV)-induced stresses in a substrate are reduced. 
     In many known ICs, TSVs are placed throughout the IC in order to facilitate the connection of IC devices. Typically, such TSVs are provided in “cells” comprising one or more TSV. Each TSV in a cell includes a longitudinal axis and, where more than one TSV is included in a cell, their longitudinal axes are typically arranged in a substantially parallel direction. 
     For example,  FIG. 1  shows a schematic representation of a portion of a surface of an IC  100  as may exist in an IC design file, wherein the IC  100  includes a substrate  10  and a plurality of TSV cells  20 A-D,  22 A-D,  24 A-D spaced throughout the surface of IC  100 . Each TSV cell includes a plurality of TSVs  30 A,  32 A,  34 A,  36 A,  38 A oriented substantially parallel to each other. For the sake of simplicity, only TSVs  30 A,  32 A,  34 A,  36 A,  38 A in TSV cell  20 A are labeled in  FIG. 1 . 
     Typically, the orientation of TSVs in a TSV cell is referred to as “horizontal” or “vertical.” Such terms are meant to refer only to the orientations of TSVs in one TSV cell as compared to an orientation of TSVs in another TSV cell. For example, in  FIG. 1 , the orientation of TSVs  30 A,  32 A,  34 A,  36 A,  38 A of TSV cell  20 A and of TSV cell  20 A as a whole may be referred to as “horizontal,” whereas orientation of TSV cell  20 D and its TSVs may be referred to as “vertical.” Other designations may be used to refer to such relative orientations, including, for example, “North-South” and “East-West.” 
     In some ICs, whether a particular TSV cell is oriented horizontally or vertically may be of importance. In many cases, however, the orientation of particular TSV cells is not of great importance and is more likely the result of convention or simplicity in IC design. As a consequence, it is not uncommon for an IC to include multiple adjacent TSV cells having the same orientation. 
     For example, referring again to  FIG. 1 , it can be seen that TSV cells  20 A,  20 B, and  20 C are all oriented horizontally. In addition, TSV cells  20 D,  22 D, and  24 D, as well as TSV cells  22 B and  24 B are all oriented vertically. Such similar orientation of adjacent TSV cells will result in increased stresses  40 ,  42 ,  50 ,  52 ,  54  in substrate  10  caused, at least in part, by differences in the thermal expansions of substrate  10  and the materials used to fill the TSVs, typically copper, tungsten, or doped polysilicon. In effect, the orientation of adjacent TSVs in the same direction acts much like a wedge within substrate  10  as the TSV materials thermally expand more quickly and/or to a greater extent than the material of substrate  10 . 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention provides a method of designing an integrated circuit (IC) having reduced substrate stress, the method comprising: placing in an IC design file a plurality of through silicon via (TSV) placeholder cells, each placeholder cell having an undefined TSV orientation; replacing a first portion of the plurality of TSV placeholder cells with a first group of TSV cells having a first orientation; and replacing a second portion of the plurality of TSV placeholder cells with a second group of TSV cells having a second orientation substantially perpendicular to the first orientation, wherein TSV cells having the first orientation and TSV cells having the second orientation are interspersed to reduce a TSV-induced stress in an IC substrate. 
     A second aspect of the invention provides an integrated circuit comprising: a substrate; and a plurality of through silicon vias (TSVs) in the substrate, the plurality of TSVs comprising: a first portion having a first orientation; and a second portion having a second orientation, wherein the first portion and the second portion are distributed within the substrate to reduce TSV-induced stresses in the substrate. 
     A third aspect of the invention provides a non-transitory computer-readable medium storing code representative of a design structure realized upon execution of the code by a computer system, the code representative of the design structure including code representing a circuit, the code comprising: code representing an integrated circuit (IC), the IC including: a substrate; and a plurality of through silicon vias (TSVs) in the substrate, the plurality of TSVs comprising: a first portion having a first orientation; and a second portion having a second orientation, wherein the first portion and the second portion are distributed within the substrate to reduce TSV-induced stresses in the substrate. 
     A fourth aspect of the invention provides a method comprising: encoding code representative of a design structure stored on a non-transitory computer readable medium of a source computer system into a set of data signals; and providing the set of data signals for use on a destination computer system distinct from the source computer system, the code representative of the design structure including code representing a circuit, the code comprising: code representing an integrated circuit (IC), the IC including: a substrate; and a plurality of through silicon vias (TSVs) in the substrate, the plurality of TSVs comprising: a first portion having a first orientation; and a second portion having a second orientation substantially perpendicular to the first orientation, wherein the first portion and the second portion are distributed within the substrate to reduce TSV-induced stresses in the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIG. 1  shows a schematic view of a known integrated circuit (IC). 
         FIGS. 2-5  show schematic views of ICs according to embodiments of the invention. 
         FIG. 6  shows a flow diagram of a method according to an embodiment of the invention. 
         FIG. 7  shows a schematic representation of an IC design flow according to an embodiment of the invention. 
     
    
    
     It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a schematic representation of a portion of an IC  200 , as may exist in an IC design file. IC  200  includes a substrate  110  upon which are placed a plurality of TSV placeholder cells  120 A-D,  122 A-D,  124 A-D. Each TSV placeholder cell  120 A-D,  122 A-D,  124 A-D includes a vertical TSV  130 A and a horizontal TSV  132 A. For the sake of simplicity, only TSVs  130 A,  132 A of TSV placeholder cell  120 A are labeled. As can be seen in  FIG. 2 , the horizontal-vertical orientation of each TSV placeholder cell  120 A-D,  122 A-D,  124 A-D is ambiguous, as each has substantially equal horizontal and vertical components. 
     Often, substrate  110  includes silicon or germanium. Other suitable materials include, for example, silicon germanium, silicon carbide, and materials consisting essentially of one or more III-V compound semiconductors having a composition defined by the formula Al X1 Ga X2 In X3 As Y1 P Y2 N Y3 Sb Y4 , where X 1 , X 2 , X 3 , Y 1 , Y 2 , Y 3 , and Y 4  represent relative proportions, each greater than or equal to zero and X 1 +X 2 +X 3 +Y 1 +Y 2 +Y 3 +Y 4 =1 (1 being the total relative mole quantity). Other suitable substrates include II-VI compound semiconductors having a composition Zn A1 Cd A2 Se B1 Te B2 , where A 1 , A 2 , B 1 , and B 2  are relative proportions each greater than or equal to zero and A 1 +A 2 +B 1 +B 2 =1 (1 being a total mole quantity). 
     As noted above, TSVs are typically filled with a filler material, such as copper, tungsten, or doped polysilicon. Other materials suitable for filling TSVs according to embodiments of the invention include other conducting and semi-conducting materials. 
     Referring again to  FIG. 2 , in designing an IC, a designer may position a plurality of TSV placeholder cells  120 A-D,  122 A-D,  124 A-D across IC  200  to indicate where connections between IC devices will be made. As noted above, the orientation of a particular TSV or TSV cell is typically of little or no importance, as connections between IC devices can often be made horizontally or vertically. 
     TSV placeholder cells  120 A-D,  122 A-D,  124 A-D are, however, mere placeholders. According to embodiments of the invention, TSV placeholder cells  120 A-D,  122 A-D,  124 A-D are replaced in the IC design file by TSV cells arranged such that their orientations reduce or eliminate TSV-induced stresses in ICs prepared from the IC design file. 
     For example,  FIG. 3  shows IC  200  in which half of the TSV placeholder cells have been replaced by horizontally-oriented TSV cells  220 A,  220 C,  222 B,  222 D,  224 A,  224 C and the other half replaced by vertically-oriented TSV cells  220 B,  220 D,  222 A,  222 C,  224 B,  224 D. As such, adjacent TSV cells have different orientations, reducing the TSV-induced stresses in substrate  110  of IC  200  in  FIG. 1 . 
     In replacing TSV placeholder cells with TSV cells, as in  FIG. 3 , an algorithm may be employed to optimize orientations among the TSV cells and their placement relative to other TSV cells. In some embodiments, horizontally-oriented TSV cells will comprise between about 40% and about 60% of the TSV placeholder cells replaced, and vertically-oriented TSV cells will comprise the remainder, or vice versa. That is, in order to ensure that all or substantially all of the TSV cells have adjacent cells having a different orientation, TSV cells of each orientation should comprise about half of the total TSV cells. The precise proportions will vary, of course, based on the placements of TSV placeholder cells in IC  200 . For example, TSV cells that will be isolated or more distantly placed from other TSV cells may not need to have an orientation different from their nearest neighboring TSV cells if the effect of their similar orientations will be negligible in terms of TSV-induced stresses in the substrate. 
     In some cases, of course, it may be necessary for an IC designer to specify that a particular TSV cell have a particular orientation. For example, in  FIG. 4 , it may be necessary, based on the IC devices to be connected, that TSV cell  320 D have the horizontal orientation depicted. In such a case, the orientations of other TSV cells may be determined, when replacing TSV placeholder cells, such that TSV cell  320 D maintains its horizontal orientation while orienting other TSV cells to reduce TSV-induced stresses, as described above.  FIG. 5  shows IC  300  following such replacement of TSV placeholder cells with TSV cells  320 A-C,  322 A-D,  324 A-D. 
       FIG. 6  shows a flow diagram of a method according to an embodiment of the invention. At S 1 , a plurality of TSV placeholder cells are placed in an IC design file. Suitable IC design files include, for example, map files, GDSII (i.e., GDS2) data files, GL1 data files, and OASIS data files. Other suitable file types will be apparent to one skilled in the art. 
     At S 2 , at least one TSV cell having a first orientation may optionally be placed in the IC design file, as described above with respect to  FIG. 4 . Similarly, at S 3 , at least one TSV cell having a second orientation may optionally be placed in the IC design file. As above, the first and second orientations refer to relative orientations of TSV cells, e.g., horizontal and vertical orientations. 
     At S 4 , a first portion of the plurality of TSV placeholder cells placed at S 1  is replaced with TSV cells having a first orientation. In some embodiments, the first orientation of the TSV cells is substantially the same as the first orientation of the at least one TSV cell optionally placed at S 2 . 
     At S 5 , a second portion of the plurality of TSV placeholder cells placed at S 1  is replaced with TSV cells having a second orientation. In some embodiment, the second orientation of the TSV cells is substantially the same as the second orientation of the at least one TSV cell optionally placed at S 3 . 
       FIG. 7  shows a block diagram of an example design flow  900 . Design flow  900  may vary depending on the type of IC (e.g.,  200 ,  300  in  FIGS. 3 and 5 , respectively) being designed. For example, a design flow  900  for building an application specific IC (ASIC) may differ from a design flow  900  for designing a standard component. Design structure  920  is preferably an input to a design process  910  and may come from an IP provider, a core developer, or other design company or may be generated by the operator of the design flow, or from other sources. Design structure  920  comprises an IC in the form of schematics or a hardware description language (HDL) (e.g., Verilog, VHDL, C, etc.). Design structure  920  may be contained on one or more machine readable media. For example, design structure  920  may be a text file or a graphical representation of an IC. Design process  910  preferably synthesizes (or translates) an IC into a netlist  980 , where netlist  980  is, for example, a list of wires, transistors, logic gates, control circuits, I/O, models, etc. that describes the connections to other elements and circuits in an integrated circuit design and recorded on at least one non-transitory computer-readable medium. This may be an iterative process in which netlist  980  is resynthesized one or more times depending on design specifications and parameters for the circuit. 
     Design process  910  may include using a variety of inputs, including, for example, inputs from library elements  930  which may house a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications  940 , characterization data  950 , verification data  960 , design rules  970 , and test data files  985  (which may include test patterns and other testing information). Design process  910  may further include, for example, standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc. One of ordinary skill in the art of IC design can appreciate the extent of possible electronic design automation tools and applications used in design process  910  without deviating from the scope and spirit of the disclosure. The design structure of the disclosure is not limited to any specific design flow. 
     Design process  910  preferably translates an embodiment of the disclosure as shown in  FIGS. 3 and 5  along with any additional IC design or data (if applicable), into a second design structure  990 . Design structure  990  resides on a non-transitory computer-readable storage medium in a data format used for the exchange of layout data of ICs (e.g. information stored in a map file, a GDSII (GDS2) data file, a GL1 data file, an OASIS data file, or any other suitable format for storing such design structures). Second design structure  990  may comprise information such as, for example, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data required by a semiconductor manufacturer to produce an embodiment of the disclosure as shown in  FIGS. 3 and 5 . Second design structure  990  may then proceed to a stage  995  where, for example, design structure  990  proceeds to tape-out, is released to manufacturing, is released to a mask house, is sent to another design house, is sent back to the customer, etc. 
     The design structure, structures and methods as described above are used in the fabrication of IC chips. The resulting IC chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes IC chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The foregoing description of various aspects of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.