Parasitic Capacitance Extraction for FinFETs
A method includes generating a three-dimensional table. The table cells of the three-dimensional table comprise normalized parasitic capacitance values selected from the group consisting essentially of normalized poly-to-fin parasitic capacitance values and normalized poly-to-metal-contact parasitic capacitance values of Fin Field-Effect Transistors (FinFETs). The three-dimensional table is indexed by poly-to-metal-contact spacings of the FinFETs, fin-to-fin spacings of the FinFETs, and metal-contact-to-second-poly spacings of the FinFETs. The step of generating the three-dimensional table is performed using a computer.
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This application claims the benefit of the following provisionally filed U.S. patent application: Application Ser. No. 61/776,738, filed Mar. 11, 2013, and entitled “Parasitic Capacitance Extraction for FinFETs,” which application is hereby incorporated herein by reference.
BACKGROUNDIntegrated circuits (“ICs”) vary in complexity from, for example, an analog circuit comprising a few basic electronic components, such as transistors and diodes, to a complex digital system including hundreds of millions of transistors. Although different design methods and Electronic Design Automation (“EDA”) tools are arranged to design ICs of various levels of complexity, the fundamental process of IC design remains unchanged. That is, IC design engineers design an integrated circuit by transforming a circuit specification into geometric descriptions of physical components that in combination form the basic electronic components. In general, the geometric descriptions are polygons of various dimensions, representing conductive features located in different processing layers. The detailed geometric descriptions of physical components are generally referred to as integrated circuit layouts. After the creation of an initial integrated circuit layout, the integrated circuit layout is usually tested and optimized through a set of steps in order to verify that the integrated circuit meets the design specification and will perform as desired.
In a typical post-design testing and optimization step, after an integrated circuit design process is completed, an initial integrated circuit layout is created. The layout is first checked against design rules and then verified to be equivalent to the desired design schematic. This step is generally referred to as Design-Rule Check (DRC) and Layout Versus Schematic (LVS).
A step of RC extraction is subsequently performed in order to “extract” electrical characteristics of the layout. The common electrical characteristics that are extracted from an integrated circuit layout include capacitance and resistance in the electronic devices and on the various interconnects (also generally referred to as “nets”) that electrically connect the aforementioned devices. This step is also referred to as “parasitic extraction” because these capacitance and resistance values are not intended by the designer but rather result from the underlying device physics of the device configurations and materials used to fabricate the IC.
The designed IC is then simulated to insure the design meets the specification with the parasitic capacitance and resistance in the IC. If the parasitic capacitance and resistance cause undesirable performance, the integrated circuit layout is typically changed through one or more design optimization cycles. If the simulation results satisfy the design specification, the design process is completed.
It is known that the parasitic capacitance and resistance can cause various detrimental effects in a designed IC, such as undesired long signal delays on the nets. Thus, the impact of the parasitic capacitance and resistance on the performance of the designed IC must be accurately predicted so that design engineers can compensate for these detrimental effects through proper design optimization steps.
It is also recognized that, when device feature sizes shrink down to the ultra-deep submicron range (less than 0.25 micron), interconnect delays begin to dominate the total delay in an IC. Moreover, when FinFET technology is used, the parasitic capacitance between gate electrodes and semiconductor fins also plays an important role in the parasitic capacitance in additional to the parasitic capacitance between gate electrodes and metal contacts. Existing EDA tools, however, are not designed to handle the complex parasitic in the FinFETs.
For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are illustrative, and do not limit the scope of the disclosure.
A method of determining parasitic capacitances for Fin Field-Effect Transistors (FinFETs) is provided in accordance with various exemplary embodiments. The variations of the embodiments are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.
As shown in
In the layouts of the integrated circuits that include FinFET 20, the layouts of fins 22 and metal contacts 28 are included in different layers of the layouts. There is no layer, however, to mark the location where metal contacts 28 overlap semiconductor fins 22. Accordingly, in accordance with some exemplary embodiments, pseudo contacts 30 (
Referring back to
Each of capacitances Cgf and Cgm is a function of spacings S1, S2, and S3 (
In some embodiments, a minimum spacing is selected for the sample FinFETs. The minimum spacing may be determined by the technology used for manufacturing the FinFETs, and may be the minimum spacing that can be achieved when the FinFETs are manufactured on physical wafers using the respective technology. Spacings S1, S2, and S3 are selected to be equal to the minimum spacing (expressed as 1×) or equal to multiple times the minimum spacing. In some embodiments, the multiple times may be equal to an integer (N) times the minimum spacing (expressed as N×), or may be equal to an integer times the minimum spacing plus a half of the minimum spacing, which is expressed as (N+0.5) times the minimum spacing (expressed as (N+0.5)×).
Next, as shown as step 104 in
An exemplary two-dimensional table 1-A is shown in
Similarly, Tables 1-B and 1-C are shown in
Table 2 includes 2-A, 2-B, and 2-C, which are illustrated in
The capacitance values Cgf and Cgm are normalized values, which are the capacitance per unit width of the respective FinFET, wherein the width is measured in the direction parallel to the lengthwise direction of gate electrode 26. An example of such width is shown as width W1 in
Referring back to
Referring again to
The capacitances of FinFETs with irregular shapes may also be calculated using the three-dimensional capacitance tables 1 and 2. For example,
Tables 1 and 2 may also be used to perform a pre-layout simulation, and the corresponding flow chart includes steps 102, 104, 106, 302, 304, 306, and 308 in
Referring to
Referring to
Referring back to
After the parasitic capacitance of the integrated circuit is obtained in accordance with the embodiments, the parasitic capacitance is back annotated to the integrated circuit. The respective step is shown as step 326 in
The process steps as in the embodiments may be performed by a computer(s), which includes software and hardware. The intermediate and final results of the embodiments may be saved on a tangible non-transitory computer-readable medium such as hard drives, discs, and the like. For example, Tables 1 and 2 (
In the embodiments of the present disclosure, by constructing three-dimensional lookup tables for FinFETs, the calculation of the parasitic capacitance of the FinFETs is simplified. The embodiments of the present disclosure may be used in the pre-layout simulation to estimate the parasitic capacitance of circuits more accurately. Hence, the performance of the integrated circuits may be found in early design stages. The number of re-design iterations may thus be reduced.
In accordance with some embodiments, a method includes generating a three-dimensional table. The table cells of the three-dimensional table include normalized parasitic capacitance values selected from the group consisting essentially of normalized poly-to-fin parasitic capacitance values and normalized poly-to-metal-contact parasitic capacitance values of FinFETs. The three-dimensional table is indexed by poly-to-metal-contact spacings of the FinFETs, fin-to-fin spacings of the FinFETs, and metal-contact-to-second-poly spacings of the FinFETs. The step of generating the three-dimensional table is performed using a computer.
In accordance with other embodiments, a method includes creating pseudo contacts for FinFETs of an integrated circuit, using the pseudo contacts to determine a poly-to-metal-contact spacing, a fin-to-fin spacing, and a metal-contact-to-second-poly spacing for each of the FinFETs, and using the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing as indices to index into a three-dimensional capacitance table. A normalized capacitance value is retrieved from a table cell indexed to by the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing. The step of retrieving is performed by a computer.
In accordance with yet other embodiments, a method includes generating a plurality of sample FinFETs, wherein poly-to-metal-contact spacings, fin-to-fin spacings, and metal-contact-to-second-poly spacings of the plurality of sample FinFETs are different from each other. The method further includes simulating normalized poly-to-fin capacitances of the plurality of sample FinFETs, and simulating normalized poly-to-metal-contact capacitances of the plurality of sample FinFETs, wherein the steps of simulating are performed using a computer. A first three-dimensional table is constructed, wherein table cells of the first three-dimensional table are the normalized poly-to-fin capacitances. The table cells of the first three-dimensional table are indexed by the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings. A second three-dimensional table is constructed, wherein table cells of the second three-dimensional table are the normalized poly-to-metal-contact capacitances. The table cells of the second three-dimensional table are indexed by the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings.
Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure.
Claims
1. A method comprising:
- generating a three-dimensional table, wherein table cells of the three-dimensional table comprise normalized parasitic capacitance values selected from a group consisting essentially of normalized poly-to-fin parasitic capacitance values and normalized poly-to-metal-contact parasitic capacitance values of Fin Field-Effect Transistors (FinFETs), and wherein the three-dimensional table is indexed by: poly-to-metal-contact spacings of the FinFETs; fin-to-fin spacings of the FinFETs; and metal-contact-to-second-poly spacings of the FinFETs, wherein the step of generating the three-dimensional table is performed using a computer.
2. The method of claim 1 further comprising generating pseudo contacts, wherein the pseudo contacts are between metal contacts of the FinFETs and fins of the FinFETs, and wherein the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings are determined from the pseudo contacts.
3. The method of claim 1, wherein the table cells of the three-dimensional table comprise the normalized poly-to-fin parasitic capacitance values.
4. The method of claim 3 further comprising an additional three-dimensional table, wherein table cells of the additional three-dimensional table comprise normalized poly-to-metal-contact parasitic capacitance values.
5. The method of claim 1, wherein the table cells of the three-dimensional table comprise the normalized poly-to-metal-contact parasitic capacitance values.
6. The method of claim 1 further comprising:
- creating pseudo contacts for FinFETs of an integrated circuit;
- using the pseudo contacts to determine a poly-to-metal-contact spacing, a fin-to-fin spacing, and a metal-contact-to-second-poly spacing for each of the FinFETs; and
- retrieving the normalized parasitic capacitance values by indexing into the three-dimensional table using the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing of each of the FinFETs as indices.
7. The method of claim 6 further comprising calculating parasitic capacitances for the FinFETs by multiplying the normalized parasitic capacitance values with FinFET widths of respective FinFETs.
8. A method comprising:
- creating pseudo contacts for Fin Field-Effect Transistors (FinFETs) of an integrated circuit;
- using the pseudo contacts to determine a poly-to-metal-contact spacing, a fin-to-fin spacing, and a metal-contact-to-second-poly spacing for each of the FinFETs;
- using the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing as indices to index into a three-dimensional capacitance table; and
- retrieving a normalized capacitance value from a table cell of the three-dimensional capacitance table indexed to by the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing, wherein the step of retrieving is performed by a computer.
9. The method of claim 8, wherein table cells of the three-dimensional capacitance table comprise normalized parasitic capacitance values selected from the group consisting essentially of normalized poly-to-fin parasitic capacitance values and normalized poly-to-metal-contact parasitic capacitance values.
10. The method of claim 8 further comprising calculating a parasitic capacitance for the each of the FinFETs by multiplying the normalized parasitic capacitance value by a FinFET width of the each of the FinFETs.
11. The method of claim 10 further comprising:
- partitioning one of the FinFETs into a plurality of FinFET regions;
- calculating a sub parasitic capacitance for each of the plurality of FinFET regions; and
- adding the sub parasitic capacitance of the plurality of FinFET regions to obtain a parasitic capacitance of the one of the FinFETs.
12. The method of claim 8 further comprising performing a pre-layout simulation using a schematic of the integrated circuit, wherein the normalized capacitance value is used in the pre-layout simulation, and wherein the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing are estimated values of the FinFETs of the integrated circuit.
13. The method of claim 12 further comprising:
- calculating a parasitic capacitance for the each of the FinFETs by multiplying the normalized parasitic capacitance value by a FinFET width of the each of the FinFETs;
- multiplying the parasitic capacitance by a pre-determined factor to obtain an estimated overall parasitic capacitance of the each of the FinFETs;
- back-annotating the estimated overall parasitic capacitance to the schematic of the integrated circuit to generate a back-annotated schematic; and
- performing the pre-layout simulation on the schematic of the integrated circuit, wherein the schematic is the back-annotated schematic.
14. The method of claim 8 comprising performing a post-layout simulation of the integrated circuit, wherein the method further comprises:
- retrieving the poly-to-metal-contact spacing, the fin-to-fin spacing, and the metal-contact-to-second-poly spacing from a layout of the integrated circuit.
15. A method comprising:
- generating a plurality of sample Fin Field-Effect Transistors (FinFETs), wherein poly-to-metal-contact spacings, fin-to-fin spacings, and metal-contact-to-second-poly spacings of the plurality of sample FinFETs are different from each other;
- simulating normalized poly-to-fin capacitances of the plurality of sample FinFETs, wherein the step of simulating is performed using a computer;
- simulating normalized poly-to-metal-contact capacitances of the plurality of sample FinFETs;
- constructing a first three-dimensional table, wherein table cells of the first three-dimensional table are the normalized poly-to-fin capacitances, and wherein the table cells of the first three-dimensional table are indexed by the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings; and
- constructing a second three-dimensional table, wherein table cells of the second three-dimensional table are the normalized poly-to-metal-contact capacitances, and wherein the table cells of the second three-dimensional table are indexed by the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings.
16. The method of claim 15, wherein the first three-dimensional table comprises a plurality of tables, wherein each of the plurality of tables is indexed by two of the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings.
17. The method of claim 16, wherein the second three-dimensional table comprises a plurality of tables, wherein each of the plurality of tables is indexed by two of the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings.
18. The method of claim 15 further comprising creating pseudo contacts for the plurality of the sample FinFETs, wherein the pseudo contacts are overlapped regions of the metal contacts of the plurality of sample FinFETs and semiconductor fins of the respective ones of the plurality of sample FinFETs.
19. The method of claim 18 further comprising determining the poly-to-metal-contact spacings, the fin-to-fin spacings, and the metal-contact-to-second-poly spacings for the plurality of sample FinFETs using locations of the pseudo contacts.
20. The method of claim 15, wherein the normalized poly-to-fin capacitances and the normalized poly-to-metal-contact capacitances are capacitances per unit width.
Type: Application
Filed: Apr 30, 2013
Publication Date: Sep 11, 2014
Applicant: Taiwan Semiconductor Manufacturing Company, Ltd. (Hsin-Chu)
Inventors: Chia-Ming Ho (Hsin-Chu), Ke-Ying Su (Taipei City), Hsiao-Shu Chao (Baoshan Township), Yi-Kan Cheng (Taipei), Ze-Ming Wu (Tainan City), Hsien-Hsin Sean Lee (Duluth, GA)
Application Number: 13/873,969