U.S. patent application number 13/873969 was filed with the patent office on 2014-09-11 for parasitic capacitance extraction for finfets.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Company, Ltd.. The applicant listed for this patent is TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD.. Invention is credited to Hsiao-Shu Chao, Yi-Kan Cheng, Chia-Ming Ho, Hsien-Hsin Sean Lee, Ke-Ying Su, Ze-Ming Wu.
Application Number | 20140258962 13/873969 |
Document ID | / |
Family ID | 51400203 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140258962 |
Kind Code |
A1 |
Ho; Chia-Ming ; et
al. |
September 11, 2014 |
Parasitic Capacitance Extraction for FinFETs
Abstract
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.
Inventors: |
Ho; Chia-Ming; (Hsin-Chu,
TW) ; Su; Ke-Ying; (Taipei City, TW) ; Chao;
Hsiao-Shu; (Baoshan Township, TW) ; Cheng;
Yi-Kan; (Taipei, TW) ; Wu; Ze-Ming; (Tainan
City, TW) ; Lee; Hsien-Hsin Sean; (Duluth,
GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIWAN SEMICONDUCTOR MANUFACTURING COMPANY, LTD. |
Hsin-Chu |
|
TW |
|
|
Assignee: |
Taiwan Semiconductor Manufacturing
Company, Ltd.
Hsin-Chu
TW
|
Family ID: |
51400203 |
Appl. No.: |
13/873969 |
Filed: |
April 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61776738 |
Mar 11, 2013 |
|
|
|
Current U.S.
Class: |
716/122 |
Current CPC
Class: |
H01L 21/845 20130101;
H01L 29/41791 20130101; H01L 21/823821 20130101; G06F 30/367
20200101; G06F 30/398 20200101 |
Class at
Publication: |
716/122 |
International
Class: |
G06F 17/50 20060101
G06F017/50 |
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.
Description
[0001] 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.
BACKGROUND
[0002] Integrated 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.
[0003] 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).
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 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:
[0009] FIG. 1 illustrates a flow chart for generating parasitic
capacitance lookup tables in accordance with some exemplary
embodiments;
[0010] FIGS. 2A and 2B illustrate a schematic perspective view and
a top view, respectively, of a Fin Field-Effect Transistor (FinFET)
in accordance with some exemplary embodiments;
[0011] FIG. 2C schematically illustrates a perspective view of
pseudo contacts in the FinFET;
[0012] FIGS. 3A, 3B, and 3C illustrate a three-dimensional lookup
table of FinFETs, wherein normalized parasitic poly-to-fin
capacitance values of the FinFETs are illustrated as the functions
of various spacings in the FinFETs;
[0013] FIGS. 4A, 4B, and 4C illustrate a three-dimensional lookup
table of FinFETs, wherein normalized parasitic
poly-to-metal-contact capacitance values of the FinFETs are
illustrated as the functions of various spacings in the
FinFETs;
[0014] FIG. 5 illustrates a FinFET having non-uniform fin
spacings;
[0015] FIG. 6 illustrates a process flow for simulating integrated
circuits in accordance with some embodiments;
[0016] FIG. 7 illustrates a perspective view of a FinFET, wherein
parasitic capacitors between various components are
illustrated;
[0017] FIG. 8 illustrates a schematic flow chart for estimating the
overall capacitance of FinFETs and using the estimated overall
capacitance in the pre-layout simulation;
[0018] FIG. 9 illustrates a portion of the integrated circuit,
wherein no parasitic capacitors and parasitic resistors are
back-annotated; and
[0019] FIG. 10 illustrates a portion of the integrated circuit with
the extracted parasitic capacitors and parasitic resistors being
back-annotated.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0020] 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.
[0021] 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.
[0022] FIG. 1 illustrates a flow chart for generating parasitic
capacitance lookup tables, and using the parasitic capacitance
lookup tables to generate Resistance-Capacitance (RC) netlists of
FinFETs. The subsequently discussed process steps are addressed
referring to the flow chart shown in FIG. 1.
[0023] FIG. 2A illustrates a schematic perspective view of FinFET
20, whose parasitic capacitance is to be extracted using the
methods in accordance with the embodiments of the present
disclosure. FinFET 20 includes semiconductor fins 22, wherein gate
dielectrics 24 are formed on the top surfaces and sidewalls of
semiconductor fins 22. FIG. 2B illustrates a top view of FinFET 20.
As shown in FIG. 2B, FinFET 20 includes a plurality of parallel
fins 22. Gate electrodes 26 are formed over gate dielectric 24, and
cross over the plurality of parallel fins 22. In some embodiments,
gate electrodes 26 comprise polysilicon, and hence are sometimes
referred to using the term "poly," "poly gate" or "PO," although
gate electrodes 26 may also be formed of other conductive materials
such as metals, metal silicides, or the like.
[0024] As shown in FIGS. 2A and 2B, metal contacts 28 cross over,
and are electrically coupled to the plurality of fins 22. Metal
contacts 28 are formed as slot contacts that are electrically
coupled to the plurality of fins 22. The portions of fins 22
electrically coupled to metal contacts 28 are parts of the source
and drain (referred to as source/drain hereinafter) regions of
FinFET 20.
[0025] 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 (FIG. 2B) are generated
in the layout files, which may be in a Graphic Database System
(GDS) format. The positions and the sizes of pseudo contacts 30 may
be used to extract the relative positions and some sizes of FinFET
20. For example, through pseudo contacts 30, the positions and the
widths of metal contacts 28 and fins 22, spacing S1 between poly
gate 26 (also marked as 26A) and metal contact 28, spacing S2
between fins 22, and spacing S3 between metal contact 28 and a
neighboring conductive line (also marked as 26B) may be extracted
and used in the embodiments. Throughout the description, spacings
S1, S2, and S3 are also referred to as a poly-to-metal-contact
spacing, a fin-to-fin spacing, and a metal-contact-to-second-poly
spacing, respective. Conductive lines 26B may be gate electrodes,
or may be dummy gate electrodes. FIG. 2C schematically illustrates
a perspective view of pseudo contacts 30, fins 22, and metal
contact 28. It is appreciated that pseudo contacts 30 are generated
in the layout files, and are not actual features formed on
wafers.
[0026] Referring back to FIG. 2A, parasitic capacitance exists
between gate electrode 26 and fins 22, which parasitic capacitance
is referred to as poly-to-fin capacitance hereinafter, and is
denoted as Cgf. Capacitance Cgf includes two components, including
a first capacitance between gate electrode 26 and the top surfaces
of fins 22, and a second capacitance between gate electrode 26 and
two sidewalls of fins 22. Capacitance Cgf is the sum of the first
capacitance and the second capacitance. In addition, parasitic
capacitance also exists between gate electrode 26 and metal
contacts 28, which parasitic capacitance is referred to a
poly-to-metal-contact capacitance, and is denoted as Cgm.
[0027] Each of capacitances Cgf and Cgm is a function of spacings
S1, S2, and S3 (FIG. 2B). In accordance with the embodiments of the
present disclosure, a plurality of sample FinFET layouts are
created, which have the structures similar to what is shown in
FIGS. 2A, 2B, and 2C. The plurality of sample FinFET layouts have
different spacings S1, S2, and S3 in different combinations. Pseudo
contacts 30 are then generated for the sample FinFET layouts. The
respective step is shown as step 102 in the process flow in FIG.
1.
[0028] 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.times.) 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.times.), 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).times.).
[0029] Next, as shown as step 104 in FIG. 1, the parasitic
capacitances Cgf and Cgm of the sample FinFETs are found, for
example, through simulation. Each of the sample FinFETs has a set
of spacings S1, S2, and S3. One capacitance Cgf and one capacitance
Cgm can be simulated for each of the sample FinFETs. Accordingly,
from the plurality of sample FinFETs, a plurality of capacitances
Cgf and Cgm is generated. The resulting Cgf and Cgm and the
respective S1, S2, and S3 values may then be used to construct
three-dimensional tables (step 106 in FIG. 1) Table 1 and Table 2,
which are shown in FIGS. 3A through 4C. The first three-dimensional
table (Table 1, which includes two-dimensional tables 1-A, 1-B, and
1-C) stores the values of capacitances Cgf of the sample FinFETs,
wherein capacitances Cgf are indexed by spacings S1, S2, and S3.
The second three-dimensional table (Table 2, which includes
two-dimensional tables 2-A, 2-B, and 2-C) stores the values of
capacitances Cgm of the sample FinFETs, wherein capacitances Cgm
are also indexed by spacings S1, S2, and S3. In accordance with
some embodiments, spacings S1 and S2 are used to index to the table
cells in each of the two-dimensional tables, and spacing S3 is used
to index to the plurality of two-dimensional tables. It is realized
other indexing schemes may be used. For example, the indexing to
the plurality of two-dimensional tables may be through spacing S1
or S2.
[0030] An exemplary two-dimensional table 1-A is shown in FIG. 3A,
wherein the fin-to-fin spacings S2 is placed as the column index,
and the poly-to-metal-contact spacing S1 is placed as the row
index. The table cell values are normalized capacitances Cgf values
per unit width. Spacings S1, S2, and S3 are represented as how many
times (represented as ".times.") the minimum spacing the respective
spacings S1, S2, and S3 equal to. Each of the table cells is filled
with a simulated normalized capacitance value, which is represented
by letter "C" followed by the values of the corresponding spacings
S1, S2, and S3. Table 1-A is obtained when spacing S3 is 1.times.,
which means spacing S3 is equal to the minimum spacing.
[0031] Similarly, Tables 1-B and 1-C are shown in FIGS. 3B and 3C,
respectively. FIG. 3B illustrates the normalized capacitance Cgf
(per unit width) when spacing S3 is equal to 2.times.. FIG. 3C
illustrates the normalized capacitance Cgf (per unit width) when
spacing S3 is equal to 3.times.. More tables may be constructed
when spacing S3 is equal to other values such as 1.5.times.,
2.5.times., 4.times., and the like. All of the two-dimensional
Tables (including Tables 1-A, 1-B, 1-C and possibly more) of the
normalized capacitance values Cgf in combination form the
three-dimensional Table 1, which is the table of capacitance values
Cgf indexed by spacings S1, S2, and S3.
[0032] Table 2 includes 2-A, 2-B, and 2-C, which are illustrated in
FIGS. 4A, 4B, and 4C, respectively. Tables 2-A, 2-B, and 2-C are
similar to Tables 1-A, 1-B, and 1-C, respectively, except that they
store normalized poly-to-metal-contact capacitance values Cgm (per
unit width) indexed by spacings S1, S2, and S3. The details of
Tables 2-A, 2-B, and 2-C are not discussed in detail herein. All of
the two-dimensional Tables (including 2-A, 2-B, and 2-C and
possibly more) of capacitance values Cgm in combination form the
three-dimensional table 2, which is the table of capacitance values
Cgm indexed by spacings S1, S2, and S3.
[0033] 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 FIG. 2B. In a unit of width (for example, a
micron), many fins may be disposed. Hence, when width W1 and
spacings S1, S2, and S3 of FinFET 20 (FIG. 2B) are extracted, the
actual capacitances Cgf of FinFET 20 (FIG. 2B) may be calculated by
indexing to Table 1 using spacings S1, S2, and S3 to find the
respective table cell value, and multiplying the respective table
cell value by width W1. For example, in FIG. 2B, assuming spacings
S1, S2, and S3 are equal to 1.times., 2.times., and 1.5.times.,
respectively, the respective table value is C.sub.1, 2, 1.5.
[0034] Referring back to FIG. 1, when tables 1 and 2 are
constructed (step 108), RC technology files may be constructed. As
is known in the art, a technology file is usually used to provide
process technology information into various extraction EDA tools.
The information may include design rules for device placement and
interconnect routing, process information for the interconnect
layers, thicknesses of conductive layers, and resistivity values of
the conductive layers. Tables 1 and 2 (FIGS. 3A through 4C) are
incorporated as a part of the technology files for future lookup,
which step is shown as step 108 in FIG. 1.
[0035] Referring again to FIG. 1, in step 110, a layout of an
Integrated Circuit (IC) is provided by a designer. Next, as shown
in step 112, the IC layout is partitioned, for example, into
portions that include a plurality of FinFETs, which are similar to
FinFET 20 in FIGS. 2A-2C and FIG. 5. For each of the FinFETs,
pseudo contacts are generated, and spacings S1, S2, and S3 are
extracted, so that Tables 1 and 2 may be looked up (step 114) to
find the normalized capacitance values Cgf and Cgm for each of the
FinFETs. The normalized capacitance values Cgf and Cgm are
multiplied by the widths of the respective FinFETs, so that the
parasitic capacitance values of the FinFETs are found. The
capacitance values of the FinFETs are then incorporated into the RC
netlist of the IC layout (step 116).
[0036] The capacitances of FinFETs with irregular shapes may also
be calculated using the three-dimensional capacitance tables 1 and
2. For example, FIG. 5 illustrates an exemplary FinFET 40 having
non-uniform fin spacings. Accordingly, FinFFT 40 may be
partitioned. In the illustrated example, FinFFT 40 is portioned to
include region 40A and region 40B. Spacings S1, S2, and S3 in
region 40A are equal to 1.5.times., 1.times., and 2.times.,
respectively. Spacings S1, S2, and S3 in region 40B are equal to
1.5.times., 3.times., and 2.times., respectively. Hence, the
parasitic capacitance Cgf of the portion of FinFET 40 in region 40A
is equal to (C.sub.1.5, 1, 2.times.W2+C.sub.1.5, 3, 2.times.W3),
wherein the values C.sub.1.5, 1, 2 and C.sub.1.5, 3, 2 are found by
indexing into Table 1. Similarly, the parasitic capacitance Cgm of
the portion of FinFET 40 in region 40B is equal to (C.sub.1.5, 1,
2.times.W2+C.sub.1.5, 3, 2.times.W3), wherein the values C.sub.1.5,
1, 2 and C.sub.1.5, 3, 2 are found by indexing into Table 2.
[0037] FIG. 6 illustrates a process flow for simulating integrated
circuits. The process flow includes the flow for pre-layout
simulation, which is performed on the schematic circuit diagram of
an integrated circuit. The process flow also includes the flow for
post-layout simulation, which is performed on the layout of the
integrated circuit. Steps 102, 104, 106, and 108 are essentially
the same as in FIG. 1, and hence the details of these steps are not
repeated herein. As shown in step 202, a layout of the integrated
circuit is generated from the schematic (which is a schematic
circuit diagram) of the integrated circuit, and the respective
pseudo contacts are created. Next, in step 204, a Layout Versus
Schematic (LVS) comparison is performed to ensure that the layout
correctly reflects the schematic of the integrate circuit. A Layout
Parameter Extraction (LPE) is also performed to extract the
parameters (such as sizes, spacings, or the like) of the layout,
during which spacings S1, S2, and S3, and the FinFET widths are
extracted. Next, an RC extraction is performed (step 206) to
extract the parasitic capacitance of the circuit. The parasitic
capacitance of FinFETs in the integrated circuit is also extracted
in this step in accordance with the aforementioned methods. The
extraction includes the lookup of Tables 1 and 2 (FIGS. 3A-4C), and
calculating the poly-to-fin capacitance Cgf and
poly-to-metal-contact capacitance Cgm using the values in Tables 1
and 2 by multiplying the looked up table values by the FinFET
widths. In step 208, a (SPICE) simulation of the integrated circuit
is performed to determine the performance of the integrated circuit
such as the timing, the drive currents, or the like. The simulation
results are then recorded (step 210). Steps 102 through 108 steps
202 through 210 are referred to as post-layout simulation steps
since they are performed on the layout of the integrated
circuits.
[0038] 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 FIG. 6. Again, in the
pre-layout simulation, Tables 1 and 2 (FIGS. 3A through 4C) are
first constructed in steps 102, 104, and 106. Tables 1 and 2 may be
incorporated into a Front-End-of-Line (FEOL) simulation model (step
302), which is the model for simulating the FEOL behavior of the
integrated circuit. The FEOL behavior includes the effect of the
circuit components that are underlying interconnect structures
(metal lines and the respective dielectric layers). In step 304, an
IC schematic netlist is provided, which netlist essentially
presents the integrated circuit in the form of a circuit diagram
(not the layout). Next, a simulation is performed to simulate the
performance of the integrated circuit, as shown in step 306. In the
simulation, although the layout of the integrated circuit is not
generated yet, some parameters related to the layout of FinFETs,
such as spacings S1, S2, and S3 in FIG. 2A, are estimated. The
estimated values are used to index into Tables 1 and 2 to determine
the parasitic capacitance of the FinFETs in the integrated circuit.
Accordingly, in the simulation, the parasitic capacitance of the
FinFETs is used. The pre-layout simulation results are then
recorded (step 210). The pre-layout simulation results in
accordance with the embodiments are more accurate than in
conventional simulation methods since the pre-layout simulation
results incorporate the estimated parasitic capacitance of
FinFETs.
[0039] Referring to FIG. 7, the parasitic capacitance of FinFET 20,
besides parasitic capacitances Cgf and Cgm, also includes
additional components. For example, the parasitic capacitance
Cap_M1_PO is a part of the parasitic capacitance of FinFET 20.
Capacitance Cap_M1_PO is the parasitic capacitance between gate
electrode 26 and metal line 42, which is the metal line in metal
layer M1. Metal line 42 is connected to metal contact 28. The
parasitic capacitance components account for roughly about 40
percent of the overall capacitance of FinFET 20, while capacitances
Cgf and Cgm account for about 60 percent of the overall capacitance
of FinFET 20. To simulate circuits more accurately, the overall
capacitance may be estimated through capacitances Cgf and Cgm. FIG.
8 illustrates a schematic flow chart for estimating the overall
capacitance and using the estimated overall capacitance in the
pre-layout simulation.
[0040] Referring to FIG. 8, steps 102, 104, 106, and 302 are
essentially the same as in FIGS. 1 and 6, and hence are not
repeated herein. In step 304, a schematic (circuit diagram) of an
integrated circuit is provided (step 304). A portion of the
integrated circuit, which is represented by the IC schematic
netlist, is illustrated in FIG. 9, which shows transistor 50 as an
example. The parasitic resistance and capacitance of transistor 50
are not determined yet, and hence are not included in the IC
schematic netlist.
[0041] Referring back to FIG. 8, in step 320, a parasitic RC
analyzer is used to analyze the overall parasitic capacitance and
parasitic resistance of the devices in the integrated circuit. The
parasitic RC analyzer is configured to estimate the spacings S1,
S2, and S3 (FIG. 2A) of the FinFETs in the integrated circuit, and
use lookup Tables 1 and 2 to find the normalized parasitic
capacitances Cgf and Cgm of the FinFETs in the integrated circuit.
As aforementioned, parasitic capacitances Cgf and Cgm accounts for
a portion (for example, about 60 percent) of the overall
capacitance of the FinFETs. Hence, the overall capacitance of the
FinFET may be estimated by multiplying the calculated parasitic
capacitances Cgf and Cgm by a pre-determined factor, which may be
between about 1.3 and about 1.5, for example, to obtain the overall
parasitic capacitance of each of the FinFETs (step 322).
Alternatively, as shown in step 324, a distribution of the overall
capacitance of the FinFET may be estimated, wherein the estimated
value includes a mean value, and the standard deviation (sigma).
Again, the mean capacitance and the standard deviation are the
functions of the calculated parasitic capacitances Cgf and Cgm.
[0042] 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 FIG. 8. FIG. 10
schematically illustrates the back-annotated transistor 50, which
include parasitic capacitors 52, whose capacitances are obtained in
steps 320, 322, and 324. In addition, the parasitic resistance of
the integrated circuit is also retrieved by the parasitic RC
analyzer. FIG. 10 also illustrates the back-annotation of the
parasitic resistors 54. Next, in step 328 of FIG. 8, a simulation
is performed on the back-annotated integrated circuit, which
includes the parasitic capacitance and parasitic resistance
obtained in steps 320, 322, and 324. The pre-layout simulation
results are then recorded, as shown in step 330.
[0043] 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 (FIGS. 3A
through 4C), the integrated circuit layout, and the generated
netlists and technology files may be saved on the non-transitory
computer-readable medium. In addition, each of the steps as shown
in the flow charts in FIGS. 1, 6, and 8 may also be executed by a
computer(s), which embodies program codes for performing the steps.
The program codes may also be saved on a tangible non-transitory
computer-readable medium such as hard drives, discs, and the
like.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
* * * * *