U.S. patent application number 11/240380 was filed with the patent office on 2006-02-16 for method for fabrication of semiconductor device.
This patent application is currently assigned to eASIC Corporation. Invention is credited to Laurance Cooke, Zvi Or-Bach.
Application Number | 20060033124 11/240380 |
Document ID | / |
Family ID | 32592950 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060033124 |
Kind Code |
A1 |
Or-Bach; Zvi ; et
al. |
February 16, 2006 |
Method for fabrication of semiconductor device
Abstract
A novel method is presented to provide ASICs with drastically
reduced NRE and with volume flexibility. The invention includes a
method of fabricating an integrated circuit, including the steps
of: providing a semiconductor substrate, forming a borderless logic
array including a plurality of Area I/Os and also including the
step of forming redistribution layer for redistribution at least
some of the Area I/Os for the purpose of the device packaging. The
fabrication may utilize Direct Write e-Beam for customization. The
customization step may include fabricating various types of devices
at different volume from the same wafer.
Inventors: |
Or-Bach; Zvi; (San Jose,
CA) ; Cooke; Laurance; (Los Gatos, CA) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20045-9998
US
|
Assignee: |
eASIC Corporation
San Jose
CA
|
Family ID: |
32592950 |
Appl. No.: |
11/240380 |
Filed: |
October 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10321669 |
Dec 18, 2002 |
6953956 |
|
|
11240380 |
Oct 3, 2005 |
|
|
|
Current U.S.
Class: |
257/202 ;
257/E23.146 |
Current CPC
Class: |
H01L 23/525 20130101;
H01L 2924/3011 20130101; H01L 2924/0002 20130101; H01L 2924/14
20130101; H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/202 |
International
Class: |
H01L 27/10 20060101
H01L027/10 |
Claims
1.-62. (canceled)
63. A device comprising: a borderless logic array; area I/Os; a
redistribution layer to redistribute one or more of said area I/Os;
and at least one pad to connect said device to at least one other
device, wherein at least one said pad overlays at least a portion
of the logic array or a portion of the area I/Os.
64. The device according to claim 63, further comprising: a
borderless memory array.
65. The device according to claim 63, wherein said logic array
comprises: a module array.
66. A device comprising: a borderless logic array, including one or
more logic array interconnections, wherein said one or more logic
array interconnections comprise metal layers and via layers, and
wherein at least one of said metal layers comprises at least one
substantially repeating pattern for a portion used for said logic
array interconnections; area I/Os; and a redistribution layer.
67. The device according to claim 66, wherein at least two of said
metal layers comprise substantially repeating patterns for portions
used for said logic array interconnections.
68. A device according to claim 66, wherein at least three of said
metal layers comprise substantially repeating patterns for portions
used for said logic array interconnections.
69. A device comprising: a borderless logic array; area I/Os
positioned in a non-surrounding fashion with respect to said
borderless logic array; and a redistribution layer to redistribute
at least some of said area I/Os.
70. A device comprising: a borderless logic array, the borderless
logic array comprising a repeating module; area I/Os positioned in
a non-surrounding fashion with respect to at least one of said
repeating modules; and a redistribution layer to redistribute at
least some of said area I/Os.
71. A device comprising: a borderless logic array, comprising a
repeating core; area I/Os, at least one of said area I/Os being a
configurable I/O; and a redistribution layer for redistributing at
least some of said area I/Os.
72. A device comprising: a borderless logic array; area I/Os,
wherein at least one of said area I/Os comprises a via-configurable
I/O.
73. The device as in claim 72, further comprising: a redistribution
layer for redistributing at least some of said area I/Os.
74. A device comprising: a logic array; and via-configurable I/Os,
wherein at least one of said via-configurable I/Os contains a
structure to enable the via-configurable I/O to be configured in
the following forms: as a single-ended input; as a single-ended
output; as a portion of a differential input pair; and as a portion
of a differential output pair.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application No. 10/321,669, filed on Dec. 18, 2002 (to issue as
U.S. Pat. No. 6,953,956), commonly assigned, and incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to logic arrays and
fabrication method for custom integrated circuit
[0004] 2. Discussion of Background Art
[0005] Semiconductor manufacturing is known to improve device
density in exponential manner over time, but such improvements do
come with a price. The cost of mask set required for each new
process technology has been increasing exponentially. In addition,
the minimum fabrication quantity due to the increases of wafer size
has also increased exponentially at the same time.
[0006] These changes represent an increasing challenge primarily to
custom products, which tend to target smaller volume and less
diverse market, therefore making the increased cost of product
development and reduction of manufacturing flexibility very hard to
accommodate.
[0007] Custom Integrated Circuits can be segmented into two groups.
The first are devices that have all their layers custom made. The
second group are devices that have at least some generic layers
used across different custom products. Well known examples of the
second kind are Gate Arrays, which use generic layers for all
layers up to contact layer, and FPGAs which utilize generic layers
for all their layers. This second group of custom integrated
circuits is also sometimes called semi-custom devices due to their
broader applicability. The generic layers in such devices are
mostly a repeating pattern structure in array form.
[0008] The use of generic layers across multiple application
provides saving for the individual custom product with respect to
the cost of masks and economies of scale. In 1996 Chip Express of
Santa Clara, Calif., introduced a logic array called CX2000 that
utilized a base logic cell equivalent to about 4 logic gates. At a
later time Lightspeed Semiconductor of Sunnyvale, Calif.,
introduced their 3G Modular Array product family. These more
advanced logic arrays use generic layers, comprising mostly
repeating pattern, also for some of the metal layers such as
contact, Metal-1, Via-1 and Metal-2. These types of logic arrays
are sometime called Module Arrays and require less custom layers. A
very advanced Module Array technology was introduced by eASIC of
San Jose, Calif., in September 2000.
[0009] That Module Arrays uses generic layers such as Metal-1 and
Metal-2 to define the logic array, in conjunction with generic
layers such as Metal-3 and Metal-4 to provide a generic
connectivity fabric. The generic connectivity fabric comprises of
repeating patterns and are also structured in array form. Such
arrangement allows to further reduce the number of custom layers
required for design customization. eASIC technology, as described
in U.S. Pat. No. 6,331,790 is going further toward the goal
minimizing the number of custom masks and requires only a single
custom via mask.
[0010] The logic array technology is based on a generic fabric that
is customized for a specific design during the customization stage.
As designs tend to be highly variable in the amount of logic and
memory each one needs, vendors of logic array create product
families with a number of Master Slices covering a range of logic
and memory size options. Yet, it is always a challenge to come up
with minimum set of Master Slices that will provide a good fit for
maximal number of designs.
[0011] U.S. Pat. No. 4,733,288 issued to Sato Shinji Sato in March
1988, discloses a method "to provide a gate-array LSI chip which
can be cut into a plurality of chips, each of the chips having a
desired size and a desired number of gates in accordance with a
circuit design." The prior art in the references cited presents few
alternative methods to utilize generic structure for a different
size of custom devices.
[0012] The array structure fits the objective of variable sizing.
The difficulty to provide variable-sized devices is due to the need
of providing I/O cells and associated pads to connect the device to
the package.
[0013] U.S. Pat. No. 5,217,916 issued to Anderson et al. on Jun. 8,
1993, discloses a configurable gate array free of predefined
boundaries--borderless--using transistor gate cells, of the same
type of cells used for logic, to serve the input and output
function. Accordingly, the input and output functions may be placed
to surround the logic array sized for the specific application.
This method presents a severe limitation on the I/O cell to use the
same transistors as used for the logic and would not allow the use
of higher operating voltage for the I/O.
[0014] It is also known in the art that I/O and pads do not need to
be at the edge of the semiconductor device. Semiconductor devices
could be using the flip chip or C-4 (controlled collapse chip
connection) technology described in U.S. Pat. Nos. 3,401,126 and
3,429,040 by Miller that had been used for over 30 years in IBM's
mainframe computer modules. In these approaches the bonding pads
are deployed in an area array over the surface of the chip known as
area bonding and may use I/O cells known as area I/O placed near
the area pads. Flip Chip packaging is known in the art to use an
additional final metal layer known as the redistribution layer, to
allow proper distribution of the device I/O to the area pads.
SUMMARY OF THE INVENTION
[0015] The present invention seeks to provide a new method for
semiconductor device fabrication that is highly desirable for
custom products. The current invention suggests the use of
direct-write e-Beam in conjunction with a continuous logic array.
The continuous array utilizes area I/O with area pads to allow
variable sizing of designs and placing them on a wafer with various
numbers of repetitions. The current invention provides solution to
the challenge of high cost of mask-set and low flexibility that
exist in the currently-common method of semiconductor fabrication.
An additional advantage of the invention that it reduces the high
cost of manufacturing the many different mask sets required in
order to provide acceptable range of master slices. The current
invention improves upon the prior art in many respects, including
the way the semiconductor device is structured and those related to
methods of fabrication of semiconductor devices.
[0016] The prior art reflected the motivation to better fit the
device size to the custom application and therefore saving on
wasted silicon. The current invention reflects the motivation to
save the cost of mask with respect to the investment that would
have been otherwise required to put in place proper set of master
slices. The current invention also seeks to provide the ability to
incorporate memory block in the custom device. The current
invention provides a method to customize the device with respect
the amount of logic and memory required.
[0017] The main point of the current invention is the use of area
I/O to provide a continuous fabric that provides a continuous
terrain of logic and I/O and also provides the ability to mix in
continuous terrain of memory with islands of special functions like
PLL and SERDES. The current invention shows that with area I/O and
redistribution layer to connect the area I/O to area pads, many of
the limitation of the prior art are overcome. A greater level of
flexibility is therefore provided. The current invention also
suggests to utilize Module Array, whereby additional layers such as
Metal-1 and Metal-2 are generic and would be part of such
borderless continuous terrain. Furthermore, the current invention
also suggests the use of segmented routing whereby some of the
connectivity layers are also generic and would be a part of the
continuous terrain. In such fabric only few layers need to be
customized while most of the layers are generic and consist
primarily of a repeating pattern. A favorable embodiment of the
current invention is a continuous terrain customizable by single
custom via layer. Furthermore, the current invention suggests the
use of direct-write e-Beam for those few custom layers. An added
advantage of the current invention is the use of direct-write
e-Beam on the continuous terrain to provide on the same wafer
different product types, with different amount of product units of
the various product types. The very large size of current wafer
allows hundreds of device units, each of different type, built on a
single wafer. Therefore the current invention allows to provide
"on-demand" semiconductor device manufacturing, where one customers
could get few units of one type of device for prototype work, while
another may get few hundreds of devices for low volume production,
all from a single wafer fabrication process.
[0018] To allow such level of flexibility with borderless terrain,
the current invention suggests wafer level customization using
equipment like direct-write e-Beam and dicing the wafer using
highly flexible dicing using equipment like laser-based dicing.
Such equipment allows mix and match of various die sizes on the
wafer, as opposed to the saw dicing commonly used in the industry,
which requires dicing along complete straight lines from one wafer
edge to the other. An added advantage of the current invention's is
the use of area pads and homogenous pad terrain so single probe
card could be use for various devices.
[0019] The present invention also seeks to provide an improved
semiconductor device including borderless logic array; area I/Os;
and a redistribution layer for redistributing at least some of the
area I/Os.
[0020] Preferably some of the pads are used to connect the
semiconductor device to other devices and overlays at least a
portion of the logic array or a portion of the area I/Os.
[0021] Preferably the semiconductor device also includes a
borderless memory array. Preferably the logic array includes a
module array. Preferably the logic array includes interconnections
within the logic array, wherein the logic array interconnections
include metal layers and via layers, and wherein at least one of
the metal layers includes at least one substantially repeating
pattern for a portion used for the interconnections. And according
to one embodiment of the invention, the logic array interconnection
includes at least two of metal layers with substantially repeating
patterns for portions used for interconnections. And according to
another embodiment of the invention, the logic array
interconnection includes at least three metal layers with
substantially repeating patterns for portions used for the
interconnections. Preferably the area I/Os are positioned in a
non-surrounding fashion with respect to the logic array.
Preferably, the logic array includes a repeating module, and
wherein the area I/Os are positioned in a non-surrounding fashion
with respect to at least one of the repeating module. Preferably at
least one of the area I/Os is a configurable I/O.
[0022] There is thus provided in accordance with a preferred
embodiment of the invention, a method of fabricating a
semiconductor device, comprising the steps of: providing a
semiconductor substrate; forming a borderless logic array,
including a plurality of area I/Os, on the semiconductor substrate;
and forming a redistribution layer for redistributing at least some
of the area I/Os.
[0023] Preferably also including the step of: forming pads to
connect the semiconductor device to other devices, and wherein at
least one of the pads overlays at least a portion of the logic
array or a portion of the area I/Os.
[0024] Preferably also including the steps of: placing and routing
a specific design on the logic array; and marking marks for an edge
of a used portion of the logic array according to the step of
placing and routing.
[0025] Preferably the step of marking comprises photolithography,
and also including a step of dicing the semiconductor substrate
according to the marks.
[0026] Preferably the step of dicing includes laser dicing.
[0027] There is thus provided in accordance with another preferred
embodiment of the invention, a method of fabricating an integrated
circuit, comprising the step of: Providing a semiconductor
substrate, forming a borderless logic array including a memory
array, a plurality of area I/Os and also including the step of
forming redistribution layer for redistribution at least some of
the area I/Os for the purpose of the device packaging.
[0028] Preferably also including the steps of: placing and routing
a specific design on the logic array and the memory array; and
marking marks for an edge of a used portion of the logic array and
the memory array according to the step of placing and routing.
[0029] Preferably the step of marking, includes photolithography,
and also including a step of dicing the semiconductor substrate
according to the marks.
[0030] Preferably the step of dicing includes laser dicing.
[0031] There is thus provided in accordance with another preferred
embodiment of the invention, a method of fabricating an integrated
circuit, comprising the step of: providing a semiconductor
substrate, forming a borderless logic array including, a plurality
of area I/Os and also including the step of forming redistribution
layer for redistribution at least some of the area I/Os for the
purpose of the device packaging and wherein the logic array
includes a module array.
[0032] There is thus provided in accordance with another preferred
embodiment of the invention, a method of fabricating an integrated
circuit, comprising the step of: Providing a semiconductor
substrate, forming a borderless logic array including a plurality
of area I/Os and also including the step of forming redistribution
layer for redistribution at least some of the area I/Os for the
purpose of the device packaging, and wherein the logic array is
interconnected by metal layers and via layers, and wherein at least
one of the metal layers comprises at least one substantially
repeating pattern for a portion used for interconnecting.
[0033] And according to one embodiment of the invention, at least
two of the metal layers include substantially repeating patterns
for portions used for interconnecting.
[0034] And according to another embodiment of the invention, at
least three of the metal layers comprise substantially repeating
patterns for portions used for the interconnecting.
[0035] There is thus provided in accordance with a preferred
embodiment of the invention, a method of fabricating a
semiconductor device, comprising the steps of: providing a
semiconductor substrate; forming a borderless logic array,
including a plurality of area I/Os, on the semiconductor substrate;
and forming a redistribution layer for redistributing at least some
of the area I/Os. And also includes the step of utilizing a direct
write technique to customize the logic array.
[0036] Preferably the step of marking utilizes a direct write
technique.
[0037] There is thus provided in accordance with a preferred
embodiment of the invention, a method of fabricating a
semiconductor device, comprising the steps of: providing a
semiconductor substrate; forming a borderless logic array,
including a plurality of area I/Os, on the semiconductor substrate;
and forming a redistribution layer for redistributing at least some
of the area I/Os, and wherein the step of forming a borderless
logic array comprises the step of positioning the area I/Os in a
non-surrounding fashion with respect to the logic array.
[0038] There is thus provided in accordance with another preferred
embodiment of the invention, a method of fabricating a
semiconductor device, comprising the steps of: providing a
semiconductor substrate; forming a borderless logic array,
including a plurality of area I/Os, on the semiconductor substrate;
and forming a redistribution layer for redistributing at least some
of the area I/Os, and wherein the logic array includes a repeating
core, and wherein the step of forming a borderless logic array
includes the step of positioning the area I/Os in a non-surrounding
fashion with respect to at least one of the repeating core.
[0039] Preferably at least one of the area I/O is configurable
I/O.
[0040] Preferably also including the step of: performing
photolithography, wherein a reticle is projected over the
semiconductor substrate, and wherein the used portion comprises
elements from two projections.
[0041] There is thus provided in accordance with a preferred
embodiment of the invention, a method of fabricating an integrated
circuit wafer, comprising the steps of: providing a semiconductor
substrate; forming a borderless logic array, including a plurality
of area I/Os, on the semiconductor substrate; and forming a
redistribution layer for redistributing at least some of the area
I/Os.
[0042] Preferably also comprising the step of: forming pads to
connect the semiconductor device to other devices, wherein at least
one of the pads overlays at least a portion of the logic array or a
portion of the area I/Os.
[0043] Preferably also including the steps of: placing and routing
a specific design on the logic array; and marking marks for an edge
of a used portion of the logic array according to the step of
placing and routing.
[0044] Preferably the step of marking comprises photolithography,
and also includes a step of dicing the semiconductor substrate
according to the marks.
[0045] Preferably the step of dicing includes a step of laser
dicing.
[0046] There is thus provided in accordance with a preferred
embodiment of the invention, a method of fabricating an integrated
circuit wafer, comprising the steps of: providing a semiconductor
substrate; forming a borderless logic array, including a memory
array, a plurality of area I/Os, on the semiconductor substrate;
and forming a redistribution layer for redistributing at least some
of the area I/Os.
[0047] Preferably also comprising the steps of: placing and routing
a specific design on the logic array and the memory array; and
marking marks for an edge of a used portion of the logic array and
the memory array according to the step of placing and routing.
[0048] Preferably the step of marking comprises photolithography,
and also comprising a step of dicing the semiconductor substrate
according to the marks.
[0049] Preferably the step of dicing includes laser dicing.
[0050] Preferably the logic array includes a module array.
[0051] Preferably the logic array is interconnected by metal layers
and via layers, and wherein at least one of the metal layers
includes at least one substantially repeating pattern for a portion
used for interconnecting.
[0052] Alternatively at least two of the metal layers include
substantially repeating patterns for portions used for the
interconnecting.
[0053] Preferably the step of placing and routing is done for a
specific design called A' and also for another specific design
called B', and wherein the location on the wafer in which design A'
is placed is independent of the location on the wafer in which
design B' is placed.
[0054] Alternatively the step of placing and routing is done for a
specific design called A' and also for another specific design
called B', and wherein a number of times that design A' is placed
on the wafer is independent of a number of times that design B' is
placed on the wafer.
[0055] Preferably the step of marking includes the step of
utilizing a direct write technique.
[0056] Preferably the step of placing and routing is done for a
specific design called A' and also for another specific design
called B', and wherein a silicon area ratio of logic array to
memory array in design A' is substantially larger than a silicon
area ratio of logic array to memory array in design B'.
[0057] Preferably the step of marking includes the step of
utilizing a direct write technique.
[0058] Preferably also including the step of probing the wafer,
wherein the step of probing utilizes the same wafer probe to test
design A' and design B'.
[0059] Preferably also comprising the step of probing the wafer,
wherein the step of probing utilizes the same wafer probe to test
design A' and design B'.
[0060] Preferably also comprising the step of probing the wafer,
wherein the step of probing utilizes the same wafer probe to test
design A' and design B'.
[0061] Preferably also comprises the step of utilizing a direct
write technique to customize the logic array.
[0062] Preferably the design A' and design B' are probed
simultaneously.
[0063] Preferably design A' and design B' are probed
simultaneously.
[0064] There is thus provided in accordance with additional
preferred embodiment of the invention, a method of fabricating an
integrated circuit wafer with improved yield, comprising the steps
of: providing a semiconductor substrate; forming a borderless logic
array, including a plurality of area I/Os, on the semiconductor
substrate; and forming a redistribution layer for redistributing at
least some of the area I/Os, and further comprising the steps of:
testing and marking modules on the logic array; placing specific
designs on the logic array so as to avoid faulty modules; and
customize the logic array according to placement of specific
designs; testing and marking the specific designs; and dicing the
logic array according to placement and marking of specific
designs.
[0065] Preferably utilizing a direct write technique to customize
the logic array.
[0066] Preferably having one or more pads dedicated to testing.
[0067] Preferably also including the step of using a probe card to
independently test one or more modules simultaneously.
[0068] Preferably one or more of the pads dedicated to testing are
not the area I/Os for the specific designs.
[0069] Preferably at least one of the area I/Os comprises a
configurable I/O.
[0070] Preferably the configurable I/O comprises multiple copies of
input, output, and pre-output cells, and wherein the semiconductor
device further comprises connections between at least one of the
input, output, and pre-output cells and area I/O pads to construct
an area I/O.
BRIEF DESCRIPTION OF THE DRAWINGS
[0071] The present invention will be understood and appreciated
more fully from the following detailed description, taken in
conjunction with the drawings in which:
[0072] FIG. 1 is a drawing illustration of a wafer marked with
reticle projections;
[0073] FIG. 2, consisting of FIGS. 2-1, 2-2, and 2-3, is a drawing
illustration of a repeating core;
[0074] FIG. 3A is a drawing illustration of a area pads;
[0075] FIG. 3B is a pictorial illustration of a area
pads--soldering balls;
[0076] FIG. 3C is a pictorial illustration showing the use of a
redistribution layer to connect area I/O to edge pads;
[0077] FIG. 4 is a detail drawing illustration of the area
pads;
[0078] FIG. 5 is a drawing illustration of a wafer level borderless
logic array;
[0079] FIG. 6 is a drawing illustration of a wafer shared between
two applications utilizing reticle sharing;
[0080] FIG. 7 is a drawing illustration of a wafer shared between
two applications;
[0081] FIG. 8 is a drawing illustration of a wafer shared between
three applications;
[0082] FIG. 9A is a drawing illustration of a reticle fabric;
[0083] FIG. 9B is a drawing illustration of a reticle fabric;
[0084] FIG. 9C is a drawing illustration of a reticle fabric;
[0085] FIG. 10A is a drawing illustration of a reticle fabric;
[0086] FIG. 10B is a drawing illustration of a reticle fabric;
[0087] FIG. 11 is a drawing illustration of a reticle fabric;
[0088] FIG. 12 is a drawing illustration of a wafer marked with
reticle projections;
[0089] FIG. 13 is a drawing illustration of a module;
[0090] FIG. 14 is a drawing illustration of a wafer comprise wafer
level borderless logic array covered with Area Pads;
[0091] FIG. 15 is a drawing illustration of via customizable
routing structure;
[0092] FIG. 16 is a drawing illustration of via customizable
I/O;
[0093] FIG. 17 is a drawing illustration of via customizable I/O
customized as input;
[0094] FIG. 18 is a drawing illustration of via customizable I/O
customized as output;
[0095] FIG. 19 is a layout drawing illustration of via customizable
I/O;
[0096] FIG. 20 is a layout drawing illustration of a small section
of via customizable I/O;
[0097] FIG. 21, consisting of FIGS. 21-1, 21-2, and 21-3, is a
drawing illustration of very long tracks over a core;
[0098] FIG. 22 is a drawing illustration of a configurable buffer
structure;
[0099] FIG. 23 is a drawing illustration of a simple "scramble
box;"
[0100] FIG. 24 is a drawing illustration of "scramble box" layout;
and
[0101] FIG. 25 is a drawing illustration of "scramble box: layout
for 24 lines.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0102] The present invention is now described with reference to
FIGS. 1-25, it being appreciated that the figures illustrate the
subjects matter not to scale or to measure.
[0103] The current method of semiconductor fabrication is on
lithography step for each layer. The dominating lithography
technique of submicron process is called step and repeat. The layer
pattern will be drawn into mask also called reticle. Such reticle
may be projected over an area of about 20 mm.times.20 mm by the
lithography tool called Stepper. Then the Stepper steps the wafer
so the reticle would be projecting the same pattern on area next to
it and so for. FIG. 1 illustrates a wafer 8 with marks 12 of
reticle projections 10. With an 8-inch wafer, over 50 copies of the
reticle will be typically stepped on one such wafer.
[0104] The current invention suggests the use of a much less common
lithography technique called direct-write using e-Beam. Such could
be done, for example, with direct-write e-Beam--Leica ZBA32 offered
by Leica Microsystems Lithography GmbH Jena, Germany or F5112
offered by Advantest, Japan. Direct-write e-beam allows direct
writing any pattern at any location over the wafer, without the use
of a physical mask. Direct-write e-beam is not used in commercial
fabrication of semiconductor devices due the low throughput and the
implication of such on a single wafer cost. The current invention
suggests the combination of reticle technique for the generic
portion of logic array and the use of direct-write e-beam for the
custom layers. A very good fit with this method is the logic array
invented by eASIC, as only it provides a logic array that could be
customized with single via layer. Via layer can be written much
faster than metal layer with direct-write e-beam and would make
such combination method commercially viable.
[0105] Such direct-write e-beam fabrication method are highly
attractive for custom designs as previously described. Since single
wafer may have room for hundreds of devices, the current invention
seeks to allow multiple designs to be placed on one wafer and
further, to allow each of these designs to be of different size
and, even further, to allow placing different quantities of such
designs on a single wafer, to support on one wafer the fabrication
needs of both prototype volumes for some design and pre-production
volumes for other designs.
[0106] While direct-write e-Beam is the most common technique,
other direct-write lithography could be used. A laser mask write
systems like Sigma 7000 from Micronic could be modified for such
usage.
[0107] The current invention suggests a new architecture of logic
array. This new architecture blends logic array with array of area
I/O and array of area pads. Therefore it provides a continuous
fabric instead of the master slice approach. Such fabric could
comprise of a repeating structure--repeating core--as is
illustrated in FIG. 2. The repeating core 28 comprises a set of
area I/O 26 and then logic array 24 which is constructed from array
of eCells 22. The area I/O may be constructed with thick oxide to
allow them to operate at higher voltage appropriate to interface
with the element outside the device, while the logic array might be
using thin oxide to operate at low voltage to reduce power
consumption and allow higher performance and packing density. The
area I/O might comprise elements that are common at boundary I/O
such as ESD protection and latch-up protection. The area I/O could
be configurable I/O that could be customized to the specific
function by the custom layers used to customize the logic. The area
I/O could include fixed function like input and output functions.
The power supply to the core 28 and to the area I/O 26 could be
supplied from the same group of area pads.
[0108] FIG. 3 is a drawing and pictorial illustration of the area
pads. FIG. 3A is a vertical cut drawing showing one area pad and
the associated bump 30, and the layers underneath it including a
thick layer 32 sometimes called redistribution layers and the
underlying layers such as Metal-1 34, Metal-2 36 and Metal-4 38.
FIG. 3B is a pictorial of section of the top surface of a device
according to the current invention, with a regular array of area
pads in the forms of bumps 39. FIG. 4 is a detailed drawing
illustration of an area pads and sample sizes for such bumps. To
maximize the number of pads per area, it is common to place the
area pads in a regular array as can be seen in FIG. 3B.
Consequently it is useful to have a top metal layer for pads
redistribution, to allow area pads placement to be independent from
area I/O placement.
[0109] This invention suggests a fabric of a repeating core which
include logic, area I/O, and area pads. The minimum size of such
core would be to fit single area pads like 3A. In most cases a
larger size core would be more practical. The core 28 of FIG. 2 is
about 1 mm.times.0.5 mm in 0.13 micron process. It would be quite
possible to provide 4.times.2 area pads and the appropriate number
of area I/O with it. Tilling such core to span a full wafer will
allow a fabric of borderless logic array of about 20.times.40 cores
28 in one reticle. If the accuracy of the stepper is high enough,
it would be conceivable that the borderless fabric could be
extended up to wafer level. In such case it may require somewhat
less dense lithography pitch for the routing structures, to allow
spanning across reticle boundaries. The wafer level borderless
fabric provides he highest level of flexibility and wafer
utilization effectiveness. For the ease of description, the
following detailed description of the additional preferred
embodiments of this invention assumes wafer level borderless logic
array. FIG. 5 is a drawing illustration of a wafer 50 comprising of
wafer level borderless logic array of continuous tilling of cores
52.
[0110] The redistribution layer may also be a custom layer. It
could therefore be custom designed to redistribute the area I/O to
the edge pads in a specific design and therefore allow such custom
design to be packaged using conventional bonding rather than
Flip-chip. FIG. 3C illustrates the use of redistribution layer 32
to connect area I/O 36 to edge pads 34 so wire bonding could be
used.
[0111] FIG. 6 is a drawing illustration of a wafer shared between
two designs utilizating reticle sharing. FIG. 6 illustrates the
existing art of reticle sharing wherein one reticle may include
design A' 62 which is placed and routed on the logic array and
occupies a large portion of the reticle, and design B' 64 that is
smaller and could be placed two times within the reticle, so
together with design A' the reticle is fully utilized. Design A'
edges are marked by marks 63 and 66 and design B' edges are marked
by marks 65, 66 and 67.
[0112] It might be highly desirable to have these edges 63, 65
marked by lithography and following process to allow proper dicing
of the wafer. Such marking would be best done at the top or very
close to the top layer and prior to the bump processing step. Such
marking step is not usually required for logic array where the
master slice are arranged for specific array size and the boundary
pads, together with the space between devices, make it very visible
where dicing should take place.
[0113] It is clear that conventional saw dicing would be proper for
dicing the wafer 60 from design A' point of view. Yet the edge 67
would be left to be diced at a later stage to separate the two dies
of design B'.
[0114] The current invention provides the ability to size each
design independently and to mix different designs on single wafer.
Constraining dicing along straight continuous lines places a strong
limitation on the ability to share one wafer with multiple-sized
designs. It is therefore suggested to use laser dicing for wafers
fabricated according to the current invention. Laser dicing is
being developed and offered by few companies such as DFL7160 made
by Disco Corporation Tokyo, Japan, and Multidice made by NanoVia,
LP of Londonderry, N.H. Thinning the back of the wafer may be
required so laser dicing would allow for a full cut rather than
just scribing.
[0115] In another embodiment of the current invention, a very
flexible wafer sharing is suggested. Such wafer sharing provides
much higher flexibility than reticle sharing. FIG. 7 is a drawing
illustration of a wafer shared between two applications taking
advantage of the borderless array, together with the use of
direct-write for wafer level lithography. It is therefore possible
to mix different designs at various quantities on such wafer. FIG.
7 illustrates design 72 placed for prototype stage, while another
design 74 is placed many more times. Unlike the case with reticle
sharing, the locations and the number of times one design is placed
on a wafer has little bearing on the other design. An important
advantage of this invention is that the location on the wafer in
which one design is placed, is independent to the location on the
wafer in which a second design is placed, other than the obvious
limitation that it can not be placed in location already taken by
the first design. More importantly, the number of times one design
is placed is independent to the number of times the other design is
placed.
[0116] FIG. 8 is a drawing illustration of a wafer 80 shared
between three applications. Design 82 has three sites on the wafer,
which represent prototype level. Designs 84 and 86 have tens of
locations assigned to them. It is clear that the location and the
number of sites for design 86 are independent on those of design
82. In addition it should be noted that many of the dicing lines 88
do not extend from one edge of the wafer 80 to the other edge. Dice
lines 88 do not fit saw dicing, but rather require the use of a
flexible dicing approach such as laser dicing.
[0117] Many logic arrays are now offering logic fabric with
additional functional blocks such as memory blocks, processors or
special elements like PLL. Typically the embedded memory takes the
second largest portion of the master slice area after the logic
array. In general embedded memories are constructed as a small
array of configurable memory blocks. The custom design may need
certain amount of memory or some number of PLL and so forth. It is
an increasing challenge to select the right master-slice
combination, since designs with similar amounts of logic may
require very different amounts of memory.
[0118] In yet another embodiment of the current invention, the
continuous logic array fabric is comprised of a continuous logic
array and continuous memory array of small memory blocks. It
therefore now possible that a specific design will be placed on a
section of such continuous fabric, sized to have exactly the
desired amount of logic and the desired amount of memory.
[0119] FIG. 9 is a drawing illustration of a reticle 90 fabric
comprising of continuous logic array 92 and memory array 94. FIG.
9A illustrates a custom design placed on such terrain as marked by
the rectangle 96 to have no memory. FIG. 9B illustrates a custom
design placed on such terrain as marked by the rectangle 97 to have
some memory. FIG. 9C illustrates a custom design placed on such
terrain as marked by the rectangle 98 to have a small amount of
logic and all the rest memory. FIG. 10A is a drawing illustration
of a reticle fabric 100 wherein the memory terrain 104 is shaped in
a staircase manner. FIG. 10B illustrates that such staircase
arrangement provides a higher level of flexibility with regards to
the amount of memory blended into the rectangular markings of the
custom design.
[0120] The advantage of continuous terrain is the ability to use
one set of generic masks to cover many variations of product
fabrics, with the ability to tailor the right amount of logic with
the right amount of memory. The additional advantage is the ability
to use one wafer run to make a flexible mix of custom products. It
is usually highly desirable to utilize the silicon area as
effectively as possible. Yet it may often happen that by tailoring
the amount of logic and memory to the need of a specific design,
the tiling efficiency is compromised. The number of devices on one
wafer would be at least the number of times the reticle is stepped
over the wafer. If high volume production is required then custom
masks could be fabricated so volume production would be done at
maximum silicon utilization.
[0121] FIG. 11 is a drawing illustration of a reticle 110 of a
logic array that in addition to array of logic fabric comprises
additional functional logic elements like processor blocks 112,
113, 114, 115 and memory array 118. FIG. 12 is a drawing
illustration of a wafer 120 marked with reticle 110 projections.
FIG. 12 illustrates the use of the wafer terrain to carve out
specific design 129 to include elements from four different reticle
projections 124--four processors--with a portion of the memory
array 128. By proper placing a specific design 129 on the wafer
terrain, it is possible to optimize the silicon area and yet
provide a different mix of elements from one generic fabric.
[0122] The construction of borderless logic array according to the
current invention should include consideration for wafer dicing.
The common way is to draw a scribe line indicating were the wafer
will be scribed, to allow the dicing of the wafer into many
individual dies. Typically a laser scribe can cut a 50 microns wide
width, but it may be preferred to plan for scribing width between
75 to 100 microns wide. Preferably the continuous array is
constructed as array of modules. A preferred module is rectangular
with each side sized between 0.5 to 2 mm. A module could be array
of logic or array of memory or combination thereof, which may
include other special function like PLL. A preferable location for
scribe lines is the edge of such module. The location for potential
scribe line may include transistors, which would not be powered if
that scribe line is used for dicing. Alternatively it could be
designed so only connectivity structures are placed in the scribe
lines designated areas. FIG. 13 is a drawing illustration of a
module 130 with designated area for scribe line 136 and
customizable connection 134 to the scribe line routing fabric (not
shown). The customizable connection 134 allows disconnection from
the routing fabric at the scribe lines area, if that potential
scribe line is designated for dicing. The repeating module 130
comprises of pads 132 for the I/Os that are included in the module
130 and pads 138 for the supply powering the circuits within the
module.
[0123] Yet another advantage of the current invention is the
possible use of single Probe Card for multiple designs. FIG. 14 is
a drawing illustration of a wafer comprised of wafer level
borderless logic array covered with Area Pads. The pads area of the
wafer is uniform and is independent of the specific design size and
placement. With such regularity, it is possible to construct single
probe card to allow testing of the wafer by stepping over it. Under
proper software control a single Probe Card could be used to test
any device on the wafer 140. Similarly, it is also contemplated
that a single Probe Card may be used to simultaneously test
multiple dies on the wafer, or with the proper test logic, test a
die with more area pads than probes on the Probe Card.
[0124] The current invention is not limited to products that
combine generic layers with custom layers. Rather it could be use
to build a borderless FPGA product. A borderless FPGA wafer could
than be diced to provide many options of gate count and block
memory size from one base mask-set.
[0125] Another use of the current invention is to yield a very
large device. Very large devices are subject to very low yield,
which make them economically unviable. Under the current invention
yield can be improved if the following procedure is applied: [0126]
(1) Test the substrate layers prior to the custom masks. This
implies that each module is independently tested. To do this there
need to be pads dedicated to some functions like clock, scan-in,
scan-out, and test control. Probe technology exists to probe pads
as small as 20.times.20 microns with minimal damage, though special
alignment equipment will probably need to be integrated into
existing standard Probers. [0127] (2) Place the specific design so
as to avoid faulty substrate cells. This requires a special
placement program, to make the best use of the available wafer area
given the outstanding orders of dies to manufacture. Presumably
this also controls the designation of the direct write of the
adapted for yield custom via patterns. [0128] (3) Dice the wafer
accordingly.
[0129] The resulting system should provide significant yield
improvement over existing techniques. Rough analysis suggests that
pre-testing and dynamic placement of die can double the revenue per
wafer over conventional techniques, if a sufficiently wide range of
die sizes are required for production. It should also be noted
that, as with the other techniques above, larger dies than are
currently possible with existing stepper technology could be
produced. In that case the described yield enhancement is
crucial.
[0130] It is further contemplated that the dedicated pads needed
for testing may or may not coincide with the area pads as shown in
FIG. 3c. It is also contemplated that the pads necessary for
testing may have the same configuration regardless of the type of
module, such that the probe card may be configured to
simultaneously probe any combinations of modules at a time.
[0131] In another embodiment, test, power, ground and clock logic
may be tied together at the wafer level, such that a single probe
of the wafer is sufficient to test all of the modules within the
wafer. Subsequent customization and scribing then isolates the
power, ground, test and clock logic to specific modules and dies,
to reduce the need for special pads, and pre-customization test
time.
[0132] FIG. 15 is a drawing illustration of via layer customizable
routing structure 150. In some fabrication processes a via layer
might have reduce yield. A variation of the structure 150, that
uses double via for the continuation bridges 154 instead of single
via 152, could be an effective solution. Via customizable routing
fabric increases the use of vias primarily in the form of same
direction connection utilizing small bridges. Therefore bridges
employing double vias are an effective solution. It should be
pointed out that double via bridges imply cost, by reducing the
number tracks available for routing.
[0133] An alternative solution could be employed for volume
production. It suggests that in addition to the custom via layer,
the two metal layers could use custom mask that connect the
segments 153, 155 with the same metal layer 156.
[0134] For volume production additional yield enhancement technique
could be employed. For example, a software routine can inspect the
custom design and replace any single via with a double via where
possible. Having most of the patterns in an array form with a
highly repetitive structure make it very friendly to employment of
yield enhancements. It is possible to keep track of yield loss in
production of specific designs that utilize the same logic array
fabric. Any failure mechanism could then be reviewed for yield
enhancement. The yield enhancement may involve changing the layout
of the generic logic array and therefore replacing some of the
generic masks.
[0135] Reference is now made to FIGS. 16, 17, and 18 which
illustrate another preferred embodiment of the current invention.
These figures illustrate via-configurable I/O. Preferably the area
I/O of the borderless logic array is configurable I/O. It is
advantageous to many users to have flexibility of the I/O
configuration, in addition to having flexibility of the logic. It
is the purpose of this invention to utilize the same custom mask to
configure both the core logic and the I/O. FIG. 16 illustrates a
simple via-configurable I/O 160, where the potential via are marked
by a circle 162. Few vias are arranged to connect a line used as a
jumper, and mark such as J4 164 to the crossing line, preferably
underneath 166 or 167 or 168. Different types of I/Os could be
constructed by selecting some of the potential vias. FIG. 17
presents a configuration of the configurable I/O of FIG. 16 as an
input cell 170. The selected vias are marked by black filled circle
172. FIG. 18 presents an alternative configuration as output cell
180.
[0136] FIG. 19 is a layout drawing illustration of via customizable
I/O 190. The I/O comprises the main elements pads 192, high drive
I/O section 194 and the I/O logic section 196 comprising the
pre-I/O circuits.
[0137] FIG. 20 is a layout drawing illustration of a small section
of the via customizable I/O. Illustrating a jumper 202 with via
activated 204 and via not activated 206
[0138] In another embodiment I/O may be comprised of many input
163, output 165 or pre-output 161 cells such that most I/O types
could be constructed by interconnecting to one or more of these
cells by providing additional segments between cells for via
programming. It is further contemplated that many more I/O cells 26
exist in each repeating core 28, FIG. 2, than area pads in each
repeating core, to allow flexible programming of each repeating
core's I/O pads.
[0139] In another embodiment of this current invention additional
routing channels, called very long tracks, are introduced.
Reference is now made to FIG. 21. FIG. 21 is a drawing illustration
of very long tracks 212, 214 across a module 210. The very long
tracks could go under or over the local routing fabric 150 to allow
segmented routing of more than 4 metal layers. When many modules
are tiled together to construct array of logic with over million
gates, more than 4 layers of routing might be required. The current
invention suggests the use of very long tracks in addition to the
short tracks and long tracks described in U.S. Pat. No. 6,331,733.
The very long tracks would have very few, or even no, contact
within the module. The router software could assign the very long
tracks to route between logic cells that are very far apart. At
every end point or contact point of the very long track, short
routing tracks would be used to connect it to the 4-metal routing
fabric. This approach allows extension of the segmented routing
architecture to as many metal layers as the fabrication process
supports. It is further contemplated that very long tracks will
include jumpers 154, an example of which is shown in FIG. 15,
between each repeating core, to allow for scribing between
repeating cores while maintaining reliable use of all segments. In
addition, it is contemplated that some of these long lines may be
used for power and ground distribution across modules within target
dies.
[0140] In another embodiment of the current invention a "scramble
box" is proposed for the routing connection between modules 190.
The objective of such "scramble box" is to reduce cross talk
between lines. By having such "scramble box" be part of the generic
fabric the solution is provided in the fabric rather than by
careful design of the customization layers. Preferably such a
"scramble box" would include buffers to further simplify the
customization. Reference is now made to FIG. 22. FIG. 22 is a
drawing illustration of a configurable buffer structure. Numeral
220 illustrates a via configurable buffer structure. It includes a
buffer 229 that has in the lower layers two Metal 7 jumpers 225,
226 and four Metal 6 connection lines. By selecting two or four
vias the structure could be configured for: [0141] (1) Buffer line
222 to line 224; [0142] (2) Buffer line 224 to line 222; [0143] (3)
Connect line 222 with line 224 with no buffer and tie off the
buffer; [0144] (4) Leave lines 222 and 224 unconnected and tie off
the buffer.
[0145] FIG. 23 is a drawing illustration of a simple "scramble box"
in which four lines are coming into the "scramble box" 230 to one
side 232 and coming out from the other side 234; each line is now
next to a new line.
[0146] FIG. 24 is a drawing illustration of a "scramble box"
layout. The four-lines "scramble box" 240 includes a configurable
buffer structure 242.
[0147] FIG. 25 is a drawing illustration of a "scramble box" layout
for 24 lines 250. It comprises six repetitions of the structure
240.
[0148] It will be appreciated by persons skilled in the art that
the present invention is not limited by what has been particularly
shown and described hereinabove. Rather, the scope of the present
invention includes both combinations and sub-combinations of
various features described hereinabove as well as modifications and
variations which would occur to persons skilled in the art upon
reading the foregoing description and which are not in the prior
art.
* * * * *