U.S. patent application number 11/602378 was filed with the patent office on 2007-03-22 for manufacturable single-chip hydrogen sensor.
This patent application is currently assigned to Honeywell International Inc.. Invention is credited to James M. O'Connor.
Application Number | 20070065345 11/602378 |
Document ID | / |
Family ID | 32179393 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070065345 |
Kind Code |
A1 |
O'Connor; James M. |
March 22, 2007 |
Manufacturable single-chip hydrogen sensor
Abstract
A robust single-chip hydrogen sensor and a method for
fabricating such a sensor. By utilizing an interconnect
metallization material that is the same or similar to the material
used to sense hydrogen, or that is capable of withstanding an
etchant used to pattern a hydrogen sensing portion, device yields
are improved over prior techniques.
Inventors: |
O'Connor; James M.;
(Ellicott City, MD) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Assignee: |
Honeywell International
Inc.
Morristown
NJ
|
Family ID: |
32179393 |
Appl. No.: |
11/602378 |
Filed: |
November 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10838718 |
May 3, 2004 |
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11602378 |
Nov 17, 2006 |
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09788781 |
Feb 20, 2001 |
6730270 |
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10838718 |
May 3, 2004 |
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60183602 |
Feb 18, 2000 |
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Current U.S.
Class: |
422/88 |
Current CPC
Class: |
Y10S 438/975 20130101;
Y10T 29/49002 20150115; Y10T 436/22 20150115; Y10T 436/11 20150115;
G01N 27/125 20130101; G01N 33/005 20130101; Y10T 436/21
20150115 |
Class at
Publication: |
422/088 |
International
Class: |
G01N 30/96 20060101
G01N030/96 |
Claims
1. A method for fabricating a silicon-based hydrogen sensor,
comprising providing an interconnect metallization and a hydrogen
sensing portion, wherein the interconnect metallization and the
hydrogen sensing portion are both composed of a first material.
2. The method of claim 1, wherein the first material is a palladium
nickel alloy.
3. The method of claim 1, further comprising covering the
interconnect metallization with a material selected from the group
consisting of an oxide and a nitride.
4. The method of claim 1, wherein the silicon-based hydrogen sensor
is a single chip sensor comprising a bulk silicon substrate,
temperature control means, at least one sense transistor, and at
least one sense resistor.
5. The method of claim 1, further comprising providing a silicided
contact between the interconnect metallization and an underlying
base portion.
6. The method of claim 5, wherein providing a silicided contact
comprises: masking the underlying base portion; etching a contact
portion through the masked underlying base portion; depositing a
contact material; sintering the contact material; and removing any
unreacted contact material.
7. The method of claim 6, wherein the contact material is selected
from the group consisting of cobalt, titanium, tungsten, platinum,
tantalum, and molybdenum.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of, claims priority to, and
hereby incorporates by reference in its entirety U.S. patent
application Ser. No. 10/838,718, filed on May 3, 2004, which is a
divisional of and claims priority to U.S. patent application Ser.
No. 09/788,781, filed on Feb. 20, 2001, which application claims
priority to and incorporates by reference U.S. Provisional Patent
Application No. 60/183,602, titled "Robust PdNi Hydrogen Sensor,"
filed on Feb. 18, 2000, and naming James M. O'Connor as an
inventor.
FIELD
[0002] The present invention is related to hydrogen sensors, and
more particularly, to a robust single-chip hydrogen sensor and
method for manufacturing the same.
BACKGROUND
[0003] During the early 1990s, Sandia National Laboratory developed
a single-chip hydrogen sensor that utilized Palladium-Nickel (PdNi)
metal films as hydrogen gas sensors. U.S. Pat. No. 5,279,795,
naming Robert C. Hughes and W. Kent Schubert as inventors, assigned
to the United States as represented by the U.S. Department of
Energy, describes such a sensor and is incorporated by reference
herein.
[0004] One of the key benefits of the sensor described in the '795
patent is its ability to detect a dynamic range of hydrogen
concentrations over at least six orders of magnitude. Prior
solutions to the problem of detecting hydrogen concentrations had
been generally limited to detecting low concentrations of hydrogen.
These solutions include such technologies as
metal-insulator-semiconductor (MIS) or metal-oxide-semiconductor
(MOS) capacitors and field-effect-transistors (FET), as well as
palladium-gated diodes.
[0005] The hydrogen sensor described in the '795 patent was a
notable advance in hydrogen-sensing technology. It was, however,
primarily limited to an experimental laboratory environment due to
the difficulties encountered in manufacturing such a sensor.
[0006] In typical silicon fabrication facilities, metal films are
first blanket-deposited across the entire wafer, and are
subsequently patterned by an etch process. However, conventional
etchants for PdNi also attack aluminum, which is normally present
on the wafer surface as an interconnect metal before the PdNi film
is deposited. Patterning the PDNI by etching would also attack the
unprotected aluminum, destroying the sensor. Other non-conventional
semiconductor fabrication techniques involving the use of a
photoresistive material applied before the PdNi in a
"lift-off"process have produced very low yields in tests performed
by the assignee of the present invention. Low yields in the
production of semiconductor devices typically translates to
difficulties in producing a commercializable product.
[0007] One solution to the above problems is described in U.S.
patent application Ser. No. 09/729,147, titled "Robust Single-Chip
Hydrogen Sensor," assigned to Honeywell International Inc., and
incorporated by reference herein. The technique disclosed is a
lift-off process, in which an adhesion promoting layer, such as
chromium, is provided to cause a sense-resistive layer, such as a
PdNi layer, to adhere to an underlying base layer. As a result,
during the lift-off process, there is a reduced likelihood of
sensor portions being lifted off in conjunction with the portions
actually intended to be removed. However, the use of chromium has
been discovered to be prone to at least one disadvantage. The
chromium has a tendency to affect the operation of hydrogen sensing
transistors on the sensing chip. As a result, accuracy and/or
sensing range may be affected.
[0008] It would thus be desirable to provide a robust single-chip
hydrogen sensor that is capable of sensing hydrogen concentrations
over a broad range, such as from approximately 1% to approximately
100% concentrations.
[0009] It would also be desirable for such a sensor to be
efficiently manufacturable, so that costs are reduced and the
sensor is producible in high enough yields to enable
commercialization.
[0010] It would be desirable for such a sensor to provide
measurement results that approximate or improve on the results from
previous hydrogen sensors.
[0011] It would additionally be desirable to minimize sensor drift
and to improve device-to-device and wafer-to-wafer
repeatability.
SUMMARY
[0012] In accordance with an illustrative embodiment of the present
invention, some of the problems associated with manufacturing a
robust hydrogen sensor are addressed.
[0013] According to a first embodiment, a silicon-based hydrogen
sensor is provided. The sensor includes at least one hydrogen
sensing portion composed of a first material and at least one
interconnect metallization also composed of the first material. The
first material is preferably, but need not be, a palladium nickel
alloy. The interconnect metallization is preferably covered with an
oxide or nitride to make the interconnect metallization inert. In a
first aspect of this embodiment, the hydrogen sensing portion and
the interconnect metallization are formed concurrently with one
another. In a second aspect of the invention, the sensor further
includes an underlying layer and at least one contact between the
interconnect metallization and the underlying layer. The underlying
layer may, for example, be composed primarily of silicon, and the
contact may be a silicided contact.
[0014] In a second embodiment, a silicon-based hydrogen sensor
includes at least one hydrogen-sensing portion and at least one
interconnect metallization. The hydrogen-sensing portion is
patterned by a deposition, mask, and etch process, and the at least
one interconnect metallization is composed of a material that is
resistant to the deposition, mask, and etch process used to pattern
the hydrogen-sensing portion. For example, the at least one
hydrogen sensing portion may be composed of a palladium nickel
alloy and the at least one interconnect metallization may be
composed of a material that is relatively impervious to the
hydrogen-sensing etch process, such as gold.
[0015] In a third embodiment, a method for fabricating a
silicon-based hydrogen sensor is provided. The method includes
providing an interconnect metallization and a hydrogen sensing
portion made of the same material. The material is preferably a
palladium nickel alloy. The interconnect metallization is
preferably covered with an oxide or nitride to make the
interconnect metallization inert. In another aspect of the
invention, the method further includes providing a silicided
contact between the interconnect metallization and an underlying
base portion. The silicided contact may be provided by masking the
underlying base portion, etching a contact portion from the masked
underlying base portion, depositing a contact material, masking the
contact material, and sintering the contact material. Exemplary
materials that may be used to provide the contact include cobalt,
titanium, tungsten, platinum, tantalum, and molybdenum.
[0016] In a fourth embodiment, a method for fabricating a
single-chip hydrogen sensing-device is provided. The method
includes forming a silicided contact on an underlying base portion,
depositing a hydrogen sensing material over the silicided contact
and the underlying base portion, masking a pattern in the hydrogen
sensing material, and etching the hydrogen sensing material to form
a hydrogen sensing portion and an interconnect metallization
portion. In another aspect, the method may further include
annealing the hydrogen sensing material. The interconnect
metallization is preferably covered with an oxide or nitride to
make the interconnect metallization inert. Forming the silicided
contact may include depositing, etching, and sintering a first
material, such as cobalt, titanium, tungsten, platinum, tantalum,
and molybdenum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Presently preferred embodiments of the invention are
described below in conjunction with the appended drawing figures,
wherein like reference numerals refer to like elements in the
various figures, and wherein:
[0018] FIG. 1 is a simplified block diagram illustrating a robust
single-chip hydrogen sensor according to an embodiment of the
present invention;
[0019] FIG. 2 is a block diagram illustrating a top view of a
robust single-chip hydrogen sensor device according to a preferred
embodiment of the present invention;
[0020] FIG. 3 is a flow diagram illustrating a method for
fabricating a robust single-chip hydrogen sensor according to an
embodiment of the present invention;
[0021] FIG. 4 is a flow diagram illustrating a method for
fabricating a robust single-chip hydrogen sensor according to an
embodiment of the present invention;
[0022] FIG. 5 is a flow diagram illustrating a method for
fabricating a robust single-chip hydrogen sensor according to an
embodiment of the present invention; and
[0023] FIG. 6 is a flow diagram illustrating a method for
fabricating a single-chip hydrogen sensor, according to an
embodiment of the present invention.
DETAILED DESCRIPTION
[0024] FIG. 1 is a simplified block diagram illustrating a top view
of a robust single-chip hydrogen sensor in accordance with an
embodiment of the present invention. The sensor 100 includes at
least one sense resistor 102, at least one sense transistor 104, at
least one temperature sensor 106, and at least one temperature
control module 108 located in or on a substrate 110. On-chip and/or
external circuitry (not shown) may be included to assist in
precisely regulating the temperature of the chip 100 using the
temperature sensor 106 and the temperature control module 108.
Similarly, the same external circuitry, or other external
circuitry, may be used to obtain outputs from the sense resistor
102 and/or the sense transistor 104.
[0025] The substrate 110 preferably is a bulk silicon substrate.
Silicon enables the use of many common silicon semiconductor
processing techniques, such as masks, implants, etchings, dopings,
and others.
[0026] The temperature control module 108 preferably includes one
or more heater Field-Effect-Transistors (FETs) or other heating
devices (for example, resistive heating elements) formed in or on
the substrate 110. One or more cooling mechanisms may additionally
or alternatively be included as part of the temperature control
module 108. The temperature control module 108 adjusts the
temperature of the sensor 100 in response to temperature
measurements received from the temperature sensor 106 or associated
external circuitry.
[0027] The temperature sensor 106 is preferably a temperature
sensing diode formed in or on the substrate 110. Other methods for
sensing temperature may also be used. The sense transistor 104 is
used to sense hydrogen concentration levels in an environment in
which the sensor 100 is placed. The sense transistor 104 is
preferably a PdNi-gate sense transistor that is fabricated in or on
the substrate 110. Other types of sense transistors may also be
used. The sense transistor 104 may utilize
Metal-Oxide-Semiconductor (MOS) or Metal-Insulator-Semiconductor
(MIS) technology. In an alternative embodiment, the sense
transistor 104 may instead be a sensing element, such as a sense
capacitor. (In such a case, alternating current measurement
techniques may need to be employed.) The sense transistor 104
senses hydrogen concentration levels ranging from a first minimum
concentration to a first maximum concentration. Typical values for
the first minimum concentration and first maximum concentration are
one part per million (ppm) and 1,000 ppm, respectively. Other
minimum and maximum concentrations may also be possible for the
sense transistor 104.
[0028] The sense resistor 102 is preferably a PdNi film arrayed in
a serpentine pattern fabricated in or on the sensor 100. Other
materials besides PdNi may be used, such as various palladium
silicides and polymeric sensing elements. The resistance of the
sense resistor 102 changes in the presence of hydrogen, enabling
detection of hydrogen concentration in a particular environment.
The sense resistor 102 is preferably operable to sense hydrogen
levels ranging from a second minimum concentration to a second
maximum concentration. Exemplary values for the second minimum
concentration and second maximum concentration are 100 ppm and
1,000,000 ppm, respectively. Other minimums and maximums may also
be possible.
[0029] For purposes of illustration and to maintain generality, no
connections are shown, and no external circuitry is shown in FIG.
1. Connections are likely to exist between the resistor 102, the
sense transistor 104, the temperature sensor 106, the temperature
control module 108, and/or any external circuitry. Such connections
may be made by a network of interconnect metallizations, for
example. In the preferred embodiment, the interconnect
metallizations are formed of the same material as the sense
transistor and/or the sense resistor. Thus, if the sense resistor
and sensor transistor are composed of a PdNi alloy, an interconnect
metallization is also composed of a PdNi alloy. When the
interconnect metallization and hydrogen sensing portion are
composed of the same material, the interconnect metallization is
preferably covered with an oxide or nitride to render the
interconnect metallization resistance unchanged in the presence of
hydrogen. In another embodiment, the interconnect metallization is
formed of any material that is capable of surviving a subtractive
etch process. For example, gold or various alloys including gold,
may be a suitable interconnect material for a hydrogen sensor.
Further details on preferred connection layouts are shown in FIG.
2, described in further detail below.
[0030] Silicided contacts are preferably used to provide contacts
to various components, such as the sources and drains of the sense
transistor and the heater FET used in the temperature control
module. Ideally, each silicided contact serves as an ohmic contact,
such- that the potential difference across the contact is
proportional to the current passing through. Metals such as cobalt,
titanium, tungsten, platinum, tantalum, and molybdenum, may be used
to make silicided contacts. In an alternative embodiment, a
silicide is also or alternatively used to implement all or a
portion of the interconnect metallizations described above.
[0031] Also not shown in FIG. 1 is an underlying, non-conductive
layer that may be used to isolate the sense resistor 102, the sense
transistor 104, the temperature sensor 106, and/or the temperature
control module 108 from the substrate 110. The non-conductive layer
may, for example, be a silicon nitride or oxide layer. As used
throughout this description, the term "non-conductive" is intended
to describe conductive characteristics when compared to a
conductive material, such as aluminum, or a semiconductive
material, such as silicon. "Non-conductive" is not intended to
imply an actual inability to conduct electricity regardless of
applied conditions. Also, as used herein, the term "interconnect
metallization" will typically refer to a material that is
conductive with respect to any non-conductive layers.
[0032] Operation of the sensor 100 will now be briefly described.
The temperature sensor 106 and temperature control module 108 are
used to regulate the operating temperature of the sensor 100 when
sensing hydrogen. The temperature of the sensor 100 may, for
example, be held at a constant sense temperature. The temperature
sensor 106 and temperature control module 108 may also be used to
purge hydrogen and/or other gases, etc. after measurements are
taken, by heating the chip to a purge temperature. In the preferred
embodiment, the temperature control module 108 heats the chip to
approximately 80 degrees Celsius, as measured at the temperature
sensor 106. The purge temperature is preferably approximately 100
degrees Celsius. One or more feedback loops may be used to assist
in accurately regulating the temperature using the temperature
sensor 106 and the temperature control module 108. Such feedback
loop(s) may be included in external circuitry, for example. When
the sensor 100 is in a hydrogen-sensing mode, then the sense
resistor 102 and the sense transistor 104 preferably sense hydrogen
levels at overlapping ranges. This enables the combination of the
sense resistor 102 and the sense transistor 104 to provide
measurements of hydrogen concentration over a larger range than a
single sense element might otherwise provide. The determination as
to when to purge may be made by examining measurement outputs from
the sense resistor 102 and/or the sense transistor 104. In the case
of the sense resistor 102, the measurement output may be a
particular resistance corresponding to the concentration of
hydrogen gas in the environment of the sensor 100. Such a
determination may be made by external circuitry and may be used to
control the temperature control module 108.
[0033] FIG. 2 is a block diagram illustrating a top view of a
single-chip hydrogen-sensing device 300, according to a preferred
embodiment of the present invention. The device 300 includes a
first sense resistor 302a, a second sense resistor 302b, and a
third sense resistor 302c, to sense hydrogen concentrations at
approximate first minimum concentrations and approximate first
maximum concentrations. A first sense transistor 304a, a second
sense transistor 304b, and a third sense transistor 304c may be
used to sense hydrogen levels at second minimum concentrations and
second maximum concentrations.
[0034] A temperature sensing diode 306 is used to determine the
temperature of the device 300. A first heater Field Effect
Transistor (FET) 308a and a second heater FET 308b are used to
control the temperature of the device 300, so that the approximate
temperature is 80 degrees Celsius during a hydrogen-sensing period
and approximately 100 degrees Celsius during a purge period. The
temperature sensing diode 306 and the heater FETs 308a-b are used
in conjunction with external circuitry (not shown) to provide
temperature regulation. The sense resistors 302a-c, the sense
transistors 304a-c, the temperature sensing diode 306, and the
heater FETs 308a-b are located in and/or on a bulk semiconductor
substrate 310. Additional layers may be present on the substrate
310, and are not shown in FIG. 2. For example, conductive and/or
non-conductive layers may be deposited on one or more portions of
the substrate 310. A series of left-side contacts 312 extend
generally down the left side of the device and may be used to
provide power, to receive measurements, and/or to control device
operation. Similarly, right-side contacts 314 may be used to
provide these same operations. In addition, the left-side contacts
312 and the right-side contacts 314 may be used for other
functions, such as for testing the device 300. Special test
elements, such as the test element 316 (and others resembling test
element 316), may be located in or on the device 300 to enable
verification that the device 300 is operating properly. An
interconnection network 318 connects various components within the
device 300. Most of the unreferenced components shown in FIG. 2 are
test elements and/or interconnections between various referenced
and unreferenced components.
[0035] The device 300 includes multiple sense resistors 302a-c,
sense transistors 304a-c, and heater FETs 308a-b in order to
provide redundancy. This enables the device 300 to operate in case
one of the sensing mechanisms fails, and also enables improved
accuracy due to more than one sensing element providing
measurements and the ability to cross-check measurements. Other
quantities of components within the device 300 may also be used
without departing from the scope of the present invention.
[0036] The sense resistors 302a-c and the gates of the sense
transistors 304a-c preferably include an alloy that resists the
formation of a hydride phase of a catalytic metal contained in the
alloy. The preferred alloy is a nickel and palladium alloy (PdNi).
For example, an alloy of about 8% to 20% (by atom percentage)
nickel (with the balance being palladium) may be used. Other alloy
compositions and/or materials may also be used.
[0037] PdNi is not typically used in semiconductor manufacturing.
In typical silicon fabrication facilities, metal films are first
blanket-deposited across the entire wafer and are subsequently
patterned by an etch process. Conventional etchants for PdNi,
however, also attack various interconnect metals, such as aluminum,
which would likely destroy the sensor. Likewise, use of an adhesion
promoting layer (such as chromium) under the sense-resistive layer,
to prevent problems during a lift-off process, may affect the sense
transistors 304a-c. Thus, instead of using aluminum (or other
similar metals) for an interconnect, and instead of using a
lift-off process with an adhesion-promoting layer, the present
invention uses a blanket-deposition and etching process. To avoid
the undesirable effects caused by etchants on aluminum
interconnects, an interconnect material capable of surviving
subtractive etching is used. According to various embodiments of
the present invention, the interconnect material is the same
material used for hydrogen sensing. Thus, if a PdNi alloy is used
for the sense resistors 302a-c, then a similar or identical
material may be used for the interconnect metallizations. The alloy
composition may be varied to improve conductivity and/or other
characteristics. Use of an identical alloy, may, however have
economic and efficiency advantages. The interconnect metallization
is preferably covered with an oxide or nitride to make the
interconnect metallization inert. Alternatively, any other material
that is impervious to the etchant used may also serve as the
interconnect metallization material. Gold, for example, may be used
for the interconnect metallization material. Advantages in cost and
yield might be realizable through the use of the hydrogen sensing
material (PdNi) for the interconnect metallizations, since it is
possible to use a single patterning process for both the sensing
elements and the interconnect metallizations.
[0038] Silicided contacts are preferably used to provide contacts
between the interconnect metallizations and various components,
such as to the sources and drains of the sense transistor and the
heater FET used in the temperature control module. Ideally, each
silicided contact serves as an ohmic contact, such that the
potential difference across the contact is proportional to the
current passing through. As was described above with reference to
FIG. 1, metals such as cobalt, titanium, tungsten, platinum,
tantalum, and molybdenum, may be used to make silicided contacts.
Other silicides may also be used. As an alternative, other
materials providing a low resistance contact between a base layer
(such as doped silicon) and an interconnect metallization may also
be used. In another alternative embodiment, a silicide is also or
alternatively used to implement all or a portion of the
interconnect metallizations.
[0039] FIG. 3 is a flow diagram illustrating a method 400 for
fabricating a robust single-chip hydrogen sensor, according to an
embodiment of the present invention. In step 402, an interconnect
metallization composed of a first material is provided. In step
404, a hydrogen sensing portion, also composed of the first
material, is provided. The first material is preferably a PdNi
alloy. The interconnect metallization is preferably covered with an
oxide or nitride to make the interconnect metallization inert. The
hydrogen sensor itself is preferably a single-chip sensor
comprising a bulk silicon substrate, temperature control means, at
least one sense transistor, and at least one sense resistor. FIG. 4
is a flow diagram illustrating a method 450 for fabricating a
robust single-chip hydrogen sensor, according to an embodiment of
the present invention. Steps 452 and 454 correspond to steps 402
and 404 of the method 400. In step 456, a silicided contact is
provided between the interconnect metallization and an underlying
base portion. As was the case for the method 400, the interconnect
metallization is preferably covered with an oxide or nitride to
make the interconnect metallization inert. Preferably, the
silicided contact may be provided by masking the underlying base
portion, etching a contact portion from the masked underlying base
portion, depositing a contact material, masking the contact
material, and centering the contact material. The contact material
is preferably one of the following: cobalt, titanium, tungsten,
platinum, tantalum, and molybdenum.
[0040] FIG. 5 is a flow diagram illustrating a method 500 for
fabricating a robust single-chip hydrogen sensor, according to an
embodiment of the present invention. In step 502, a silicided
contact is formed on an underlying base portion. In step 504, a
hydrogen sensing material is deposited over the silicided contact
and the underlying base portion. In step 506, a pattern is masked
in the hydrogen sensing material. In step 508, the hydrogen sensing
material is etched to form a hydrogen sensing portion and an
interconnect metallization portion. Forming the silicided contact
preferably involves depositing, etching, and centering one of the
following materials: cobalt, titanium, tungsten, platinum,
tantalum, and molybdenum. The interconnect metallization is
preferably covered with an oxide or nitride to make the
interconnect metallization inert. The underlying base portion
preferably is one of the following: a semiconductor substrate, a
conductive layer, a semiconductor layer, or a non-conductive layer.
FIG. 6 is a flow diagram illustrating a method 600 for fabricating
a robust single-chip hydrogen sensor, according to an embodiment of
the present invention. Steps 602-608 correspond respectively to
steps 502-508 in the method 500. In step 610, the hydrogen sensing
material is annealed, using any well known annealing process. As
was the case for the method 500, the interconnect metallization is
preferably covered with an oxide or nitride to make the
interconnect metallization inert.
[0041] TABLE 1 illustrates process steps that may be used to
produce the single-chip hydrogen-sensing device 300, according to a
preferred embodiment of the present invention. The steps are
preferably performed in order, from top-to-bottom, starting with
the left column. The abbreviations correspond primarily to
semiconductor processing steps. Such abbreviations should be
readily apparent to those having skill in the relevant technology
field. TABLE-US-00001 TABLE 1 Phos. Implant poly etch nitride 2
mask initial ox spacer ox nitride dry etch diff mask n+ mask BPSG
diff etch n+ imp BPSG reflow p-well mask s/d implant contact mask
p-well imp poly re-ox contact etch chan-stop imp p+ mask Co dep
p-well drive p+ implant Co sinter nitride strip BF2 implant Co etch
threshold imp h-gate mask Alloy gate ox h-gate implant split NiPd
dep poly dep boe etchback NiPd mask poly dope h-gate oxidation 200A
NiPd etch poly mask R&D nitride dep 200A Anneal
[0042] In Table 1, the last few steps (involving Co and NiPd) refer
to making silicided contacts (cobalt silicide) and a combination
NiPd interconnect metallization and sensing structure. The mask and
etch steps performed prior to the cobalt deposition serve to
confine the cobalt (and the cobalt silicide resulting after
sintering) to the desired contact location. Other silicides (or
other contact materials) may be formed in a similar manner. It
should be noted that although Table 1 describes using only one NiPd
deposition, mask, and etch process to form both the interconnect
metallization and the sensing structure, a separate deposition,
mask, and etch process could also be performed. For example, a
separate deposition, mask, and etch process would be required if
the interconnect metallization material was different from the
hydrogen sensing material.
[0043] In view of the wide variety of embodiments to which the
principles of the present invention can be applied, it should be
understood that the illustrated embodiments are exemplary only, and
should not be taken as limiting the scope of the present invention.
For example, the steps of the flow diagrams may be taken in
sequences other than those described, and more or fewer elements
may be used in the block diagrams.
[0044] The claims should not be read as limited to the described
order or elements unless stated to that effect. In addition, use of
the term "means" in any claim is intended to invoke 35 U.S.C.
.sctn.112, paragraph 6, and any claim without the word "means" is
not so intended. Therefore, all embodiments that come within the
scope and spirit of the following claims and equivalents thereto
are claimed as the invention.
* * * * *