U.S. patent application number 10/431821 was filed with the patent office on 2004-11-11 for electrical fuse element test structure and method.
Invention is credited to Wu, Shien-Yang.
Application Number | 20040224431 10/431821 |
Document ID | / |
Family ID | 33131507 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040224431 |
Kind Code |
A1 |
Wu, Shien-Yang |
November 11, 2004 |
ELECTRICAL FUSE ELEMENT TEST STRUCTURE AND METHOD
Abstract
A method of monitoring heat dissipation behavior of a fuse
element formed in an integrated circuit structure is provided. A
fuse element is fabricated in an integrated circuit structure. A
plurality of resistors are formed adjacent the fuse element,
wherein a resistivity of the resistors is temperature dependent.
The fuse element is triggered, whereby heat is dissipated into the
integrated circuit structure. A resistance change in the resistors
is monitored to determine the heat dissipation behavior of the fuse
element during triggering.
Inventors: |
Wu, Shien-Yang; (Hsin-chu,
TW) |
Correspondence
Address: |
DUANE MORRIS, LLP
IP DEPARTMENT
ONE LIBERTY PLACE
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
33131507 |
Appl. No.: |
10/431821 |
Filed: |
May 8, 2003 |
Current U.S.
Class: |
438/17 ;
257/E23.149; 438/132 |
Current CPC
Class: |
H01L 22/34 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101; H01L 2924/0002
20130101; H01L 23/5256 20130101 |
Class at
Publication: |
438/017 ;
438/132 |
International
Class: |
H01L 021/66 |
Claims
What is claimed is:
1. A method of monitoring heat dissipation behavior of a fuse
element formed in an integrated circuit structure, comprising the
steps of: fabricating a fuse element in an integrated circuit
structure; forming a plurality of resistors adjacent said fuse
element, wherein a resistivity of said resistors is temperature
dependent; triggering said fuse element, whereby heat is dissipated
into said integrated circuit structure; and monitoring a resistance
change in said resistors to determine the heat dissipation behavior
of said fuse element during triggering.
2. The method of claim 1, wherein said fuse element is a
polysilicon fuse element.
3. The method of claim 1, wherein said fuse element is a silicided
polysilicon fuse element.
4. The method of claim 1, wherein said plurality of resistors
include a plurality of polysilicon resistors.
5. The method of claim 1, wherein said fuse element includes a pair
of contact regions and a body portion disposed therebetween, and
wherein said plurality of resistors includes a plurality of
resistors formed at respective locations spaced along at least one
lateral edge of said body portion, said method further comprising
the step of determining from said heat dissipation behavior a
location along said body portion where said fuse element has been
triggered.
6. The method of claim 5, wherein said resistors formed at said
respective locations include polysilicon resistors.
7. The method of claim 1, wherein said fuse element includes a pair
of contact regions and a body portion disposed therebetween, and
wherein said plurality of resistors includes a plurality of
resistors formed at respective locations spaced from at least one
lateral edge of said body portion.
8. The method of claim 7, wherein said resistors formed at said
respective locations include polysilicon resistors.
9. The method of claim 1, further comprising the step of forming an
insulating layer over said fuse element, wherein said plurality of
resistors include a plurality of resistors formed over said fuse
element and over or within said insulating layer.
10. The method of claim 9, wherein said resistors formed over said
fuse element include a plurality of metal resistors.
11. The method of claim 1, wherein said plurality of resistors
includes at least one well resistor.
12. The method of claim 1, wherein said fuse element is a
polysilicon fuse element including a pair of contact regions and a
body portion disposed therebetween, and wherein said plurality of
resistors includes a plurality of polysilicon resistors formed at
respective locations spaced along at least one lateral edge of said
body portion, and a plurality of polysilicon resistors formed at
respective locations spaced from at least one lateral edge of said
body portion said method further comprising the step of determining
from said heat dissipation behavior a location along said body
portion where said fuse element has been triggered.
13. A fuse element testing system, comprising: an integrated
circuit test structure, comprising: a fuse element formed over a
semiconductor substrate; and a plurality of resistors formed
adjacent to said fuse element, wherein a resistivity of said fuse
element is temperature dependent; and means for monitoring a
resistance change in said resistors to determine a heat dissipation
behavior of said fuse element during triggering.
14. The system of claim 13, wherein said fuse element is a
polysilicon fuse element.
15. The system of claim 13, wherein said fuse element is a
silicided polysilicon fuse element.
16. The system of claim 13, wherein said plurality of resistors
include a plurality of polysilicon resistors.
17. The system of claim 13, wherein said fuse element includes a
pair of contact regions and a body portion disposed therebetween,
and wherein said plurality of resistors includes a plurality of
resistors formed at respective locations spaced along at least one
lateral edge of said body portion.
18. The system of claim 17, wherein said resistors formed at said
respective locations include polysilicon resistors.
19. The system of claim 13, wherein said fuse element includes a
pair of contact regions and a body portion disposed therebetween,
and wherein said plurality of resistors includes a plurality of
resistors formed at respective locations spaced from at least one
lateral edge of said body portion.
20. The system of claim 13, wherein said resistors formed at said
respective locations include polysilicon resistors.
21. The system of claim 13, further comprising an insulating layer
formed over said fuse element, wherein said plurality of resistors
includes a plurality of resistors formed over said fuse element and
over or within said insulating layer.
22. The system of claim 19, wherein said resistors formed over said
fuse element include metal resistors.
23. The system of claim 13, wherein said plurality of resistors
includes at least one well resistor.
24. The system of claim 13, wherein said fuse element is a
polysilicon fuse element including a pair of contact regions and a
body portion disposed therebetween, and wherein said plurality of
resistors includes a plurality of polysilicon resistors formed at
respective locations spaced along at least one lateral edge of said
body portion, and a plurality of polysilicon resistors formed at
respective locations spaced from at least one lateral edge of said
body portion.
25. A method of monitoring heat dissipation behavior of a fuse
element formed in an integrated circuit structure, comprising the
steps of: fabricating a silicided polysilicon fuse element in an
integrated circuit structure, said polysilicon fuse element
including a pair of contacts and a body portion formed
therebetween; forming a plurality of resistors adjacent said fuse
element, wherein a resistivity of said resistors is temperature
dependent, said plurality of resistors including a plurality of
resistors formed over said fuse element, a plurality of resistors
formed proximate at least one lateral edge of said body portion, or
a plurality of resistors formed below said fuse element or a
combination thereof; triggering said fuse element, whereby heat is
dissipated into said integrated circuit structure; and monitoring a
resistance change in said resistors to determine the heat
dissipation behavior of said fuse element during triggering.
26. The method of claim 25, wherein said plurality of resistors
includes a plurality of polysilicon resistors formed proximate to a
lateral edge of said body portion and a plurality of metal
resistors formed in or over an insulating layer formed over said
fuse element.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to integrated
circuit fuse structures, and more particularly to methods and
systems for testing integrated circuit fuse element structure.
BACKGROUND OF THE INVENTION
[0002] Electrical fuses, particularly silicided and non-silicided
polysilicon fuses, have been widely adopted in integrated circuit
fabrication over conventional metal fuses because of their package
level reparability, field programming abilities, and built in
self-test/self-repair abilities. Fuse elements are commonly
utilized in field programmable, custom logic integrated circuits,
such as programmable read-only memory (PROM) and programmable logic
array circuits.
[0003] In the case of silicided polysilicon fuse elements,
programming occurs by applying a voltage or current stress that
results in a temperature high enough to cause agglomeration of the
silicided layer. Little is known, however, about the thermal
gradient or behavior of the fuse element with respect to its
integrated circuit environment during programming. Currently, the
thermal effect of programming cannot be understood without time
consuming and extensive physical examinations, such as top view SEM
(scanning electron microscopy) and cross-sectional SEM/TEM
(transmission electron microscopy) analysis.
[0004] Therefore, a new method and system of determining the
thermal behavior of a fuse element during programming are
desired.
SUMMARY OF THE INVENTION
[0005] A method of monitoring heat dissipation behavior of a fuse
element formed in an integrated circuit structure is provided. A
fuse element is fabricated in an integrated circuit structure. A
plurality of resistors are formed adjacent the fuse element,
wherein a resistivity of the resistors is temperature dependent.
The fuse element is triggered, whereby heat is dissipated into the
integrated circuit structure. A resistance change in the resistors
is monitored to determine the heat dissipation behavior of the fuse
element during triggering.
[0006] A fuse element testing system is also provided. The system
includes an integrated circuit test structure including a fuse
element formed over a semiconductor substrate and a plurality of
resistors formed adjacent to the fuse element, wherein a
resistivity of the fuse element is temperature dependent. The
system also includes means for monitoring a resistance change in
the resistors to determine a heat dissipation behavior of the fuse
element during triggering.
[0007] The above and other features of the present invention will
be better understood from the following detailed description of the
preferred embodiments of the invention that is provided in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The accompanying drawings illustrate preferred embodiments
of the invention, as well as other information pertinent to the
disclosure, in which:
[0009] FIG. 1 is a top plan view of a first embodiment of a test
structure having a fuse element and a plurality of sense resistors
formed adjacent thereto;
[0010] FIG. 2 is a top plan view of a second embodiment of a test
structure having a fuse element and a plurality of sense resistors
formed adjacent thereto;
[0011] FIG. 3 is a partial perspective view of a third embodiment
of a test structure having a fuse element and a plurality of sense
resistors formed adjacent thereto;
[0012] FIG. 4A is a plot of an expected resistance change against
resistor position for the test structure embodiment of FIG. 1;
and
[0013] FIG. 4B is a plot of a temperature behavior of the test
structure embodiment of FIG. 1 discerned form the resistance change
plot of FIG. 4A.
DETAILED DESCRIPTION
[0014] In connection with FIGS. 1-4B, a method and system are
provided for monitoring heat dissipation behavior of a fuse element
formed in an integrated circuit (IC) structure during triggering
thereof. Identifying the heat dissipation behavior of an old or new
fuse element design enables the circuit designer to safely locate
other circuit elements when the tested fuse design is incorporated
into an actual, functional integrated circuit design. For example,
the heat dissipation behavior can identify safe locations proximate
to the fuse element where heat sensitive elements, such as metal
resistors, well resistors and polysilicon resistors, can be located
in the integrated circuit design.
[0015] FIG. 1 is a top plan view of a fuse element test structure
formed in an integrated circuit. The test structure includes a fuse
element 10, which is preferably a silicided or non-silicided
polysilicon fuse element, as described in, for example, U.S. Pat.
No. 6,242,790 to Tsui et al., the entirety of which is hereby
incorporated by reference herein. The structure and operation of
these polysilicon fuse elements are familiar to those in the IC
fabrication art and are not repeated herein. Although described in
connection with polysilicon fuse elements, it should be understood
that the system and method described herein are not limited thereto
and apply equally to other fuse elements known in the art and that
may be developed that dissipate heat into a surrounding integrated
circuit environment.
[0016] Fuse element 10 includes a pair of contact regions 12 and a
body portion 14 disposed therebetween. A plurality of resistors are
formed adjacent to the fuse element 10. Each resistor has a
resistivity that is temperature dependent. In the embodiment of
FIG. 1, a plurality of polysilicon resistors 16 are formed adjacent
lateral edges 15 of the body portion 14 of the fuse element 10.
These resistors 16 are spaced along the lateral edges 15 so that
each resistor has a portion thereof proximate to a respective
portion of the body portion 14. In the embodiment of FIG. 1, the
resistors 16 are preferably polysilicon resistors formed in the
same plane or IC layer as the fuse element 10, thereby enabling a
polysilicon element 10 and resistors 16 to be formed in the same
process steps. Contacts to the resistors 16 may be silicided or
non-silicided. The change in resistance of the polysilicon heat
sensors is the result of the change in ambient temperature, since
no programming voltage or current is applied to the polysilicon
sensors.
[0017] A method of identifying the heat dissipation behavior of the
fuse element 10 is now described. Prior to triggering fuse element
10, the resistance of each resistor 16 is measured with general I-V
measurements. For example, a voltage of about 0.1V is applied and
the current is sensed with an appropriate tool, e.g. current meter,
oscilloscope, or ohm meter to obtain the resistance value, or a low
current of about 10-100 .mu.A is applied and the voltage is sensed
across the resistor with a voltage meter, oscilloscope or ohm meter
to obtain resistance value. It should be apparent that, although
not shown in the figures, contacts are made to the sensor resistors
to allow for testing and monitoring of initial resistance and
resistance change. After the initial resistance measurements are
made, an appropriate voltage or current pulse (1 .mu.s-1 ms) is
applied to the fuse element 10 via contact regions 12 in order to
trigger the fuse element 10 along body portion 14. The trigger
voltage pulse is typically between about 1.5-5.0 volts. As the
voltage or current is applied, the resistance of each resistor 16
is monitored using a measurement tool, such as an oscilloscope.
During triggering, the fuse element dissipates heat into the
integrated circuit structure. The resistance of a polysilicon
resistor is temperature dependent and increases with temperature.
Therefore, hot points can be identified by examining the change in
resistance at each resistor 16.
[0018] The accumulated data may be examined by plotting the data in
order to determine the heat dissipation behavior of the fuse
element. For example, referring to FIG. 4A, the change in
resistance (.DELTA.R) over original resistance (R.sub.O) is plotted
at a time t.sub.1 during the triggering step against the positions
of the various resistors 16 (R.sub.1-R.sub.6) spaced along a
selected lateral edge of the body portion 14 of the fuse element
10. The change in resistance (.DELTA.R) over original resistance
(R.sub.O) is plotted in order to account for variations in original
resistance between the various resistors R.sub.1-R.sub.6. As shown
in FIG. 1, each resistor R.sub.1-R.sub.6 has a portion that is
proximate to a different location of the body portion 16 for
sensing heat dissipated from the fuse element 10.
[0019] It is expected that a symmetrical fuse element 10 as shown
in FIG. 1 would have a symmetrical heat dissipation pattern along
body portion 14 as shown in FIG. 4A. This may not be the case for
non-symmetrical fuse elements. The methodology and system provide a
particularly powerful means of determining the thermal dissipation
behavior in the X direction of non-symmetrical elements. Because
resistance is temperature dependent, the relative temperature at
each resistor location along the body portion 14 may also be
plotted as shown in FIG. 4B and corresponds with the plot of FIG.
4A. It may be assumed, without performing time consuming and costly
SEM or TEM tests, that the fuse element "triggers" at the point of
highest temperature.
[0020] Referring to FIG. 2, a top plan view is provided of a second
embodiment of a fuse element test structure formed in an integrated
circuit. The test structure again includes a fuse element 10 and a
plurality of resistors formed adjacent to the fuse element 10. Each
resistor has a resistivity that is temperature dependent. In the
embodiment of FIG. 2, a plurality of polysilicon resistors 18 are
formed at different respective locations spaced off or apart from
the lateral edges 15 of body portion 14. This configuration allows
for determination of the thermal dissipation of the behavior of the
fuse element 10 by monitoring resistance changes in the resistors
18 as described above in connection with the embodiment of FIG. 1,
albeit in the Y direction rather than the X direction.
[0021] One would expect that the sensed temperature would be
greater in the resistors more proximate to the body portion (e.g.,
in R.sub.21 and R.sub.22 as compared to R.sub.23) of a symmetrical
fuse element 10 shown in FIG. 2. Monitoring the resistance changes,
however, can reveal the relative temperature experienced at each
location by a resistor 18. Further, the heat dissipation behavior
of a non-symmetrical element is not so easily determined by merely
viewing a schematic representation of the fuse element.
[0022] Referring now to FIG. 3, a structure is illustrated that
allows for the sensing of a heat dissipation behavior of the fuse
element in the vertical Z direction, i.e., above and/or below the
fuse element 10. In order to avoid overly complicating the figure,
the bottom portion of FIG. 3 is illustrated as a cross-section view
of the integrated circuit structure, and the top portion is
illustrated in perspective.
[0023] The fuse element test structure includes a semiconductor
substrate 20 including a field dielectric region, such as shallow
trench isolation region 28 formed in the substrate 20. A fuse
element 10 is formed over the isolation region 28. A N-type or
P-type well region 22 is formed by appropriate ion implantation
within the substrate 20 and may overlap N or P active regions 24.
Although only one well resistor is shown, one or more resistors can
be formed at different locations below the fuse. The resistance of
well resistors increases with temperature. Therefore, heat
diffusion downward to the substrate can be monitored.
[0024] A dielectric layer (shown generally as an insulation region
30) is formed over the fuse element 10. A plurality of resistors 26
are preferably formed over the fuse element 10 and over or within
the insulating layer 30. The change in resistance of the resistors
26 may be monitored in the same manner described above in
connection with the embodiments of FIGS. 1 and 2 in order to
determine the heat dissipation behavior of the fuse element 10
during triggering thereof, albeit in the vertical Z direction
rather than the horizontal X or Y direction.
[0025] In an exemplary embodiment, resistors 26 are metal
resistors, such as aluminum or copper resistors. Utilizing metal
resistors above a polysilicon fuse element 10, as opposed to
polysilicon resistors, allows the present structure to be
fabricated without introducing additional steps to the standard
integrated circuit fabrication process, i.e., the metal resistors
26 can be formed as part of a standard metallization step. The
resistance of metal resistors changes with ambient temperature due
to the heat generated and diffused from the programming of the
polysilicon fuse element. These changes can be monitored in real
time by general I-V measurements using, for example, an
oscilloscope
[0026] By utilizing sensing resistors above a fuse element, below a
fuse element, or adjacent the lateral edge or edges of a fuse
element, a detailed understanding of the heat dissipation
characteristics of a fuse element can be obtained. In testing an
old or new fuse element design, the fuse element can be fabricated
in an integrated circuit structure with all or one or a combination
of different adjacent resistor patterns. For example, a fuse
element may have a sensing well resistor formed below it, a
resistor pattern shown in FIG. 1 adjacent one lateral edge, a
resistor pattern shown in FIG. 2 adjacent a second lateral edge,
and metal resistors formed above it. In this manner, the detected
heat dissipation behavior can be determined from one fuse element.
Alternatively, several identical fuse element can be fabricated at
different locations in the integrated circuit. Each fuse element in
that case can have a different sensing resistor pattern as shown in
FIGS. 1-3 (or combination of patterns) formed adjacent thereto.
[0027] As mentioned above, once the heat dissipation behavior of a
fuse element is identified, the behavior can be used to aid the
circuit designer in locating heat sensitive elements within the
integrated circuit with respect to the fuse element. For example,
sensitive elements with low heat tolerances are not located
proximate to hot spots identified from the heat dissipation
behavior.
[0028] Although the invention has been described in terms of
exemplary embodiments, it is not limited thereto. Rather, the
appended claims should be construed broadly to include other
variants and embodiments of the invention that may be made by those
skilled in the art without departing from the scope and range of
equivalents of the invention
* * * * *