U.S. patent application number 13/413192 was filed with the patent office on 2012-06-28 for apparatus and method for programming an electronically programmable semiconductor fuse.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Gabriel Chiulli, Brian W. Messenger, Dan Moy, Edwin Soler, Peter Wang, Stephen Wu.
Application Number | 20120161855 13/413192 |
Document ID | / |
Family ID | 39302956 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120161855 |
Kind Code |
A1 |
Moy; Dan ; et al. |
June 28, 2012 |
APPARATUS AND METHOD FOR PROGRAMMING AN ELECTRONICALLY PROGRAMMABLE
SEMICONDUCTOR FUSE
Abstract
An apparatus for programming an electronically programmable
semiconductor fuse applies a programming current to a fuse link as
a series of multiple pulses. Application of the programming current
as a series of multiple short pulses provides a level of
programming current sufficiently high to ensure reliable and
effective electromigration while avoiding exceeding temperature
limits of the fuse link.
Inventors: |
Moy; Dan; (Bethel, CT)
; Wu; Stephen; (Poughkeepsie, NY) ; Wang;
Peter; (Austin, TX) ; Messenger; Brian W.;
(Newburgh, NY) ; Soler; Edwin; (Wallkill, NY)
; Chiulli; Gabriel; (Middlebury, CT) |
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
39302956 |
Appl. No.: |
13/413192 |
Filed: |
March 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11548482 |
Oct 11, 2006 |
|
|
|
13413192 |
|
|
|
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Current U.S.
Class: |
327/525 |
Current CPC
Class: |
H01L 2924/0002 20130101;
G11C 17/18 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101; H01L 23/5256 20130101 |
Class at
Publication: |
327/525 |
International
Class: |
H01H 37/76 20060101
H01H037/76 |
Claims
1. An apparatus for programming a semiconductor fuse structure
including a first conductive area and a second conductive area
coupled by a fuse link, the apparatus comprising: a current supply
including circuitry operatively coupled to the semiconductor fuse
to deliver a cyclic programming current as a series of pulses, each
pulse having an amplitude and a cycle duration, wherein programming
of the semiconductor fuse is completed upon application of the
programming current through the series of multiple pulses and
wherein the cycle duration is between about 0.01 and about 0.17
times a thermal time constant of the fuse link.
2. The apparatus of claim 1, wherein the cycle duration is less
than about 0.05 times the thermal time constant of the fuse
link.
3. An apparatus for programming a semiconductor fuse structure
including a first conductive area and a second conductive area
coupled by a fuse link, the apparatus comprising: a current supply
including a programmable pulse generator operatively coupled to the
semiconductor fuse and programmed to deliver a cyclic programming
current as a series of pulses, each pulse having an amplitude and a
cycle duration, wherein programming of the semiconductor fuse is
completed upon application of the programming current through the
series of multiple pulses and wherein continuous application of a
constant programming current having an amplitude equal to an
average of the maximum amplitudes of the series of pulses for a
time period equal to a sum of the cycle durations of each of the
series of pulses would cause heating of the fuse link to a
temperature exceeding a rupture temperature of the fuse link.
4. An apparatus for programming a semiconductor fuse structure
including a first conductive area and a second conductive area
coupled by a fuse link, the apparatus comprising: a current supply
including circuitry operatively coupled to the semiconductor fuse
to deliver a cyclic programming current as a series of pulses, each
pulse having an amplitude and a cycle duration, an amplitude, and a
duty cycle, wherein the current supply supplies current at an
amplitude to the semiconductor fuse greater than 120 percent of the
current required to initiate electromigration in the fuse link when
applied; wherein programming of the semiconductor fuse is completed
upon application of the programming current through the series of
multiple pulses, and wherein during programming, a fuse link
temperature does not exceed a rupture temperature.
5. The apparatus of claim 4, wherein the current supply includes a
programming FET and the step of applying the programming current
includes applying a programming voltage and a gate voltage to the
programming FET, wherein the programming voltage and gate voltage
are selected to maintain operation of the FET in a saturation
operating region of the programming FET.
6. The apparatus of claim 4, wherein the duty cycle of each pulse
is substantially equal.
7. The apparatus of claim 4, wherein the cycle duration of each
pulse is substantially equal.
8. The apparatus of claim 4, wherein the amplitude of each of the
multiple pulses is substantially equal.
9. The apparatus of claim 4, wherein the duty cycle of each pulse
is in the range of 0.62 to 0.69.
10. The apparatus of claim 4, wherein the duty cycle of an initial
pulse is different from the duty cycle of a final pulse.
11. The apparatus of claim 10, wherein the duty cycle of the
initial pulse is less than the duty cycle of the final pulse.
12. The apparatus of claim 10, wherein the duty cycle of the
initial pulse is greater than the duty cycle of the final
pulse.
13. The apparatus of claim 4, wherein the amplitude of an initial
pulse is different from the amplitude of a final pulse.
14. The apparatus of claim 12, wherein the amplitude of the initial
pulse is less than the amplitude of the final pulse.
15. The apparatus of claim 4, wherein the amplitude of each
programming current pulse is in the range of about four to about
ten milliamps.
16. The apparatus of claim 4, wherein the cycle duration is about
five nanoseconds to about one hundred nanoseconds.
17. The apparatus of claim 4, wherein the cycle time is less than
30 nanoseconds.
18. The apparatus of claim 4, wherein the cycle duration is between
about 0.01 and about 0.17 times a thermal time constant of the fuse
link.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 11/548,482, filed Oct. 11, 2006, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates generally to electronically
programmable semiconductor fuses, and more particularly to an
apparatus and method of programming an electronically programmable
semiconductor fuse.
[0003] Programmable semiconductor fuse devices are known in the
art. For example, with reference to FIGS. 1-5, and initially to
FIGS. 1 and 2, U.S. Patent Application Publication Nos.
2006/0087001 (Kothandaraman et al., the "'001 reference") and
2006/0108662 (Kothandaraman et al., the "'662 reference"), both of
which are assigned to the same assignee as the present application,
disclose an electronically programmable semiconductor fuse assembly
(or "eFuse") 10 including a first conductive area 12 and a second
conductive area 14 coupled by a fuse link 16. The '001 reference
and the '662 reference are incorporated herein by reference in
their entirety. The first and second conductive areas 12 and 14, as
well as the fuse link 16 are formed from a polysilicon layer 24 and
a metallic silicide layer 26 deposited over an insulating layer 22.
As discussed in the '001 reference, the polysilicon layer 24
preferably includes a dopant. The insulating layer 22 may be
formed, for example, from silicon oxide. The insulating,
polysilicon, and silicide layers 22, 24, and 26, respectively, are
formed on a semiconductor substrate 20. A capping barrier layer
(not shown) formed, for example, from silicon nitride, may be
provided over the insulating, polysilicon, and metallic silicide
layers 22, 24, 26, respectively. The first and second conductive
areas 12 and 14 are provided with contacts 18. The contacts are
preferably formed from a metal such as tungsten.
[0004] An eFuse 10 programmed by an electromigration process
changes from having a first resistance in an unprogrammed state to
a second resistance, significantly higher than the first
resistance, in a programmed state. To program the eFuse 10, a
potential is applied across the fuse link 16 generating a
programming current and raising the temperature of the fuse link
16. The electromigration process is affected by both the resultant
current density within the fuse link 16, as well as by the
temperature generated as a result of Joule heating generated by the
current flow within the fuse link 16. With application of
sufficient programming current, electromigration of metal within
the silicide layer 26 occurs, with migration of the metal toward
the anodic conductive area. Also, the dopant in the polysilicon
layer 24 migrates toward the anodic conductive area. With migration
of metal in the silicide layer 26 and of dopant in the polysilicon
layer 24, the resistance of the fuse link 16 increases.
[0005] Programming an eFuse 10 requires providing a programming
current of sufficient magnitude to reliably cause the desired
degree of electromigration within the fuse link 16. However,
exceeding the desired level of programming current can lead to
excessive fuse link temperatures T.sub.FL. Specifically, the fuse
link 16 has a rupture temperature T.sub.R at which the fuse link 16
is physically ruptured. Such rupture (uncontrolled explosion) of
the fuse link 16 is undesirable as it can damage both the fuse link
16 as well as surrounding portions of the semiconductor device,
rendering the eFuse 10 unsuitable for use. There is thus a
relatively narrow range within which the programming current is
both sufficiently large to cause an effective level of
electromigration and sufficiently small to avoid heating the fuse
link 16 beyond the rupture temperature T.sub.R.
[0006] The artisan will appreciate that variations inherent in the
semiconductor manufacturing process can affect the range of
acceptable programming current. For example, variations in the
geometry or material composition of the fuse link 16 can decrease
the range of acceptable programming current.
[0007] With reference now to FIG. 3, it is known to control the
programming process of the programmable fuse 10 using a prior art
current supply 40 comprising a programming field effect transistor
(FET) 30 operatively coupled to control circuitry 32. The control
circuitry 32 may include, for example, a pulse generator, one or
more logic gates, or other conventional electrical components. The
control circuitry is used to generate a pulse of voltage Vgs
delivered to the gate of the programming FET 30. The eFuse 10
designer selects set points for programming FET gate voltage Vgs
and programming voltage V.sub.FS corresponding to a programming
current within the desired range of programming currents. For
example, it is known in the art to generate a voltage pulse Vgs,
typically having a magnitude in the range of 1.5 to 3.3 V, for a
duration typically in the range of 5 to 250 microseconds, while
simultaneously applying a programming voltage V.sub.FS, typically
in the range of 1.0 to 3.5 V. With reference to FIG. 4, in one
example of a prior art current supply 40, assuming application of a
programming FET gate voltage Vgs of 2.0 V, in combination with a
programming voltage V.sub.FS of 2.0 V, a programming current of
roughly 15 mA is generated.
[0008] With continued reference to FIG. 4, it is noted that
operation of the programming FET 30 in the transistor's saturation
region, rather than in the linear region, is desirable, as in the
saturation region, the programming current is relatively stable and
insensitive to variations in the programming voltage. In the linear
region, the programming current is substantially more sensitive to
variation in the programming voltage. As discussed above, given
that it is necessary to control the programming current within a
specific range, additional variability in the programming current
resulting from operating in the linear region is undesirable.
[0009] With reference to FIG. 5, the set points chosen for Vgs and
V.sub.FS result in a theoretically satisfactory programming current
(that is, a programming current sufficient to generate the desired
degree of electromigration, without inducing a temperature in the
fuse link 16 which exceeds the rupture temperature T.sub.R).
However, given variability in the characteristics of the eFuse 10
device (including both the current supply 40 and the fuse link 16
itself), it is difficult to obtain a one hundred percent yield in
the programming process. That is, some eFuse 10 devices programmed
in the conventional manner will have either incomplete
electromigration or will rupture due to excessive temperature.
[0010] A need exists, therefore, for an apparatus and method of
programming an electronically programmable fuse which allows the
eFuse 10 to be reliably programmed while also avoiding application
of excessive programming current and the consequent potential for
exceeding the rupture temperature of the fuse link 16.
BRIEF SUMMARY OF THE INVENTION
[0011] Briefly stated, in a first aspect the invention is a method
of programming an electronically programmable semiconductor fuse.
The method comprises a step of providing a semiconductor fuse
structure including a first conductive area and a second conductive
area coupled by a fuse link. A current supply operatively coupled
to the semiconductor fuse is provided, wherein the current supply
is capable of supplying more current to the semiconductor fuse than
is required to initiate electromigration in the fuse link. A
programming current from the current supply to the semiconductor
fuse is applied as series of multiple pulses, each pulse having a
pulse duration, a cycle duration, an amplitude, and a duty cycle.
Programming of the semiconductor fuse is completed upon application
of the programming current through the series of multiple
pulses.
[0012] In a second aspect, the invention is an apparatus for
programming a semiconductor fuse structure including a first
conductive area and a second conductive area coupled by a fuse
link. The apparatus comprises a current supply including circuitry
operatively coupled to the semiconductor fuse to deliver a cyclic
programming current as a series of pulses. Each pulse has an
amplitude and a cycle duration. Programming of the semiconductor
fuse is completed upon application of the programming current
through the series of multiple pulses. The cycle duration is
between about 0.01 and about 0.17 times a thermal time constant of
the fuse link.
[0013] In a third aspect, the invention is an apparatus for
programming a semiconductor fuse structure including a first
conductive area and a second conductive area coupled by a fuse
link. The apparatus comprises a current supply including a
programmable pulse generator operatively coupled to the
semiconductor fuse and programmed to deliver a cyclic programming
current as a series of pulses, each pulse having an amplitude and a
cycle duration. Programming of the semiconductor fuse is completed
upon application of the programming current through the series of
multiple pulses. Continuous application of a constant programming
current having an amplitude equal to an average of the maximum
amplitudes of the series of pulses for a time period equal to a sum
of the cycle durations of each of the series of pulses would cause
heating of the fuse link to a temperature exceeding a rupture
temperature of the fuse link.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0014] The following detailed description of preferred embodiments
of the invention will be better understood when read in conjunction
with the appended drawings. For the purpose of illustrating the
invention, there is shown in the drawings embodiments which are
presently preferred. It should be understood, however, that the
invention is not limited to the precise arrangements and
instrumentalities shown.
[0015] FIG. 1 is a top plan view of an electronically programmable
semiconductor fuse device know in the prior art;
[0016] FIG. 2 is a cross-sectional view of the fuse device of FIG.
1, taken along line 2-2 of FIG. 1;
[0017] FIG. 3 is a schematic diagram of a known apparatus used to
program the fuse device of FIG. 1;
[0018] FIG. 4 is a graphical representation of variation of a
programming current with a gate voltage and a programming voltage
applied to a field effect transistor component of the known
apparatus of FIG. 3;
[0019] FIG. 5 is a graphical representation of variation of gate
voltage in the known apparatus of FIG. 3 and a fuse link
temperature in the fuse device of FIG. 1 with time;
[0020] FIG. 6 is a diagram of steps of a method of programming the
fuse device of FIG. 1 in accordance with the present invention;
[0021] FIG. 7 is a schematic diagram of an apparatus in accordance
with the present invention for practicing the method of FIG. 6;
[0022] FIG. 8 is a graphical representation of variation of gate
voltage generated by the apparatus of FIG. 7 and resulting fuse
link temperature in the fuse device of FIG. 1 with time; and
[0023] FIG. 9 is a graphical representation of variation of failure
rate as a function of a duty cycle of the method of FIG. 6.
DETAILED DESCRIPTION OF THE INVENTION
[0024] As used herein, when introducing elements of the present
invention or the preferred embodiments thereof, the articles "a",
"an", "the" and "said" are intended to mean that there are one or
more of the elements. Throughout the drawings, the same reference
numerals or letters are used to designate like or equivalent
elements. Detailed descriptions of known functions and
constructions unnecessarily obscuring the subject matter of the
present invention have been omitted for clarity. The drawings are
not necessarily drawn to scale.
[0025] Referring to FIGS. 6-9, there are shown preferred
embodiments of a current supply apparatus, generally designated 50,
and a method, generally designated 100, in accordance with the
present invention.
[0026] With particular reference to FIGS. 6-8, the method 100 of
programming the electronically programmable semiconductor fuse or
eFuse 10 comprises a step 110 of providing a semiconductor fuse
structure including first conductive area 12 and second conductive
area 14 coupled by fuse link 16. In a step 120, a current supply 50
operatively coupled to the semiconductor fuse 10 is provided,
wherein the current supply 50 is capable of supplying more current
to the semiconductor fuse than is required to initiate
electromigration in the fuse link. In a step 130, a programming
current from the current supply 50 is applied to the semiconductor
fuse 10 as series of multiple pulses, each pulse having a pulse
duration t.sub.on, a cycle duration t.sub.cycle, an amplitude A,
and a duty cycle. The duty cycle is defined as the ratio of the
pulse duration to the cycle duration (or period of the cycle). The
programming of the semiconductor fuse 10 is completed only upon
application of the programming current through the series of
multiple pulses.
[0027] With particular reference now to FIG. 7, the current supply
50 used in conjunction with the programming method 100 includes
circuitry 34 (for example, a programmable pulse generator or other
circuitry capable of producing gate voltage Vgs as a series of
pulses) operatively coupled to the fuse device 10 to deliver the
series of multiple pulses. The programming FET 30 used in the
current supply 50 is conventional, and operates in the manner
discussed above relative to the programming FET 30 of the prior art
current supply 40.
[0028] The current supply 50 is capable of supplying at least 120
percent of the current required to initiate electromigration in the
fuse link 16. If the current supply were capable of producing only
100 percent of the current required to initiate electromigration,
use of the method 100 would result in underprogramming. With a
current supply capable of supplying between 100 and 120 percent of
the current required to initiate elecgromigration, the duty cycle
would be limited to a value greater than 83 percent, providing very
little benefit over prior art techniques.
[0029] Preferably, in the step 130 of applying the programming
current, the programming voltage V.sub.FS and the gate voltage Vgs
applied to the programming FET 30 are selected to maintain
operation of the FET 30 in a saturation operating region of the
programming FET 30.
[0030] With particular reference now to FIG. 8, the duty cycles of
the series of multiple pulses may either be substantially equal as
illustrated, or may vary from one pulse cycle to the next. The duty
cycle of an initial pulse may be less than that of a final pulse,
or vice versa. Similarly, the pulse duration t.sub.on, cycle
duration t.sub.cycle (or period), and/or pulse amplitude A of each
of the multiple pulses may be substantially equal, or may vary from
one cycle to the next. For example, the pulse duration, cycle
duration and/or pulse amplitude of an initial pulse may be less
than that of a final pulse, or vice versa.
[0031] With reference now to FIG. 9, preferably, the duty cycle,
whether constant or variable from one pulse cycle to the next, is
within the range of 0.62 to 0.69. FIG. 9 plots an eFuse programming
failure rate as a function of duty cycle. In the illustrated
application, the programming voltage V.sub.FS was 2.9V, the gate
voltage Vgs was 2.6V, for operation of the programming FET 30 in
saturation. 350 pulses were employed. The duty cycle was varied by
varying the pulse duration (from 9 to 30 nano-seconds) and the
cycle duration (from 19 to 40 nanoseconds). The pulse off time was
held constant at 10 nanoseconds. For a duty cycle less than
approximately 0.55, the failure rate is 100 percent, as the
programming current was insufficient to cause electromigration. For
a duty cycle between 0.62 and 0.69, the failure rate dropped to
zero percent, as within this range the programming current was both
sufficient to cause electromigration while also insufficient to
cause the fuse link 16 to heat to the rupture temperature T.sub.R.
For a duty cycle greater than approximately 0.70, the failure rate
increased above 0 percent, due to excessive heating of the fuse
link 16.
[0032] Preferably, the amplitude of each programming current pulse
is in the range of about four to about ten milliamps. The cycle
duration t.sub.cycle (or, alternatively, corresponding frequency)
of the programming current pulse is preferably in the range of 5 to
100 nanoseconds. A thermal time constant of a preferred embodiment
of the fuse link 16 (that is, the time required for the fuse link
16 to reach 63.2% of it's final temperature when subjected to a
step input (such as a programming current) causing a change in
temperature) was experimentally determined to be in the range of
about 600 to 700 nanoseconds. Thus, the preferred range of cycle
durations corresponds to about 0.01 and 0.17 times a thermal time
constant. Most preferably, the cycle duration is less than about 30
nanoseconds, corresponding to about 0.05 times the thermal time
constant of the fuse link 16, or less.
[0033] The artisan will note that the experimentally determined
preferred 30 nanosecond limit is influenced not only by the thermal
characteristics of the fuse link 16, but also by parasitic
capacitances and inductances in other elements of the current
supply 50.
[0034] The benefit of a cycle duration which is substantially less
than the fuse link thermal time constant results from the fact that
the electroprogramming process is aided by higher temperatures.
With a relatively short cycle duration (relative to the fuse link
thermal time constant), the fuse link temperature does not decay
significantly between pulses.
[0035] The programming method 100 and associated current supply 50
provide the benefits of a relatively high programming current and a
relatively constant fuse link temperature (both of which result in
reliable initiation of the electromigration process), while
mitigating the potential for overheating the fuse link 16. As
suggested by the data of FIG. 9, if the programming current were
applied continuously for a period of time equal to a sum of the
cycle durations of each of the series of pulses, at an amplitude
equal to an average of the maximum amplitudes of the series of
pulses, the fuse link temperature T.sub.FL would reach a level
exceeding the rupture temperature T.sub.R.
[0036] From the foregoing it can be seen that the present invention
provides an apparatus and method for programming an electronically
programmable fuse providing a high level of programming current
necessary to reliably and effectively cause electromigration while
also avoiding excessive temperature in the fuse link.
[0037] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is to be
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *