U.S. patent application number 14/042955 was filed with the patent office on 2015-04-02 for anisotropic magnetoresistive (amr) sensors and techniques for fabricating same.
This patent application is currently assigned to ALLEGRO MICROSYSTEMS, LLC. The applicant listed for this patent is ALLEGRO MICROSYSTEMS, LLC. Invention is credited to Joseph Burkhardt, David G. Erie, Steven Kosier.
Application Number | 20150091559 14/042955 |
Document ID | / |
Family ID | 52739484 |
Filed Date | 2015-04-02 |
United States Patent
Application |
20150091559 |
Kind Code |
A1 |
Erie; David G. ; et
al. |
April 2, 2015 |
ANISOTROPIC MAGNETORESISTIVE (AMR) SENSORS AND TECHNIQUES FOR
FABRICATING SAME
Abstract
Novel anisotropic magneto-resistive (AMR) sensor architectures
and techniques for fabricating same are described. In at least one
embodiment, an AMR sensor is provided that includes barber pole
structures having upper and low metal layers that are formed of
different materials. The metal material closer to the AMR element
is formed of a material that can be etched using an etching process
that does not attack the AMR material. In some other embodiments,
AMR sensors having segmented AMR sensing elements are
described.
Inventors: |
Erie; David G.; (Cottage
Grove, MN) ; Burkhardt; Joseph; (Minneapolis, MN)
; Kosier; Steven; (Lakeville, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALLEGRO MICROSYSTEMS, LLC |
Worcester |
MA |
US |
|
|
Assignee: |
ALLEGRO MICROSYSTEMS, LLC
Worcester
MA
|
Family ID: |
52739484 |
Appl. No.: |
14/042955 |
Filed: |
October 1, 2013 |
Current U.S.
Class: |
324/252 ; 216/13;
29/602.1 |
Current CPC
Class: |
C23F 1/12 20130101; C23F
1/14 20130101; Y10T 29/4902 20150115; G01R 33/096 20130101; G01R
33/0052 20130101; G11B 5/33 20130101 |
Class at
Publication: |
324/252 ; 216/13;
29/602.1 |
International
Class: |
G01R 33/00 20060101
G01R033/00; C23F 1/12 20060101 C23F001/12; C23F 1/14 20060101
C23F001/14; G01R 33/09 20060101 G01R033/09 |
Claims
1. An anisotropic magneto-resistive (AMR) sensor comprising: an
inter layer dielectric (ILD) surface; an AMR element above the ILD
surface, the AMR element being at least partially formed of an AMR
material; and a plurality of barber poles above and conductively
coupled to the AMR element, wherein each of the barber poles
includes a lower portion formed of a first metal material and an
upper portion formed of a second metal material, wherein the first
metal material is at least partially etched using an etching
process that does not attack the AMR material of the AMR
element.
2. The AMR sensor of claim 1, wherein: the first metal material
includes a titanium compound and the second metal material includes
an aluminum compound.
3. The AMR sensor of claim 1, wherein: the first metal material
includes titanium-tungsten (TiW) and the second metal material
includes aluminum-copper (AlCu).
4. A method for fabricating an anisotropic magneto-resistive (AMR)
sensor, comprising: providing an inter layer dielectric (ILD)
surface; forming a stack over the ILD surface, the stack having an
AMR element formed of an AMR material, a first metal layer above
the AMR element, and a second metal layer above the first metal
layer, wherein the first and second metal layers are formed of
different metal materials; applying a mask over the stack to define
barber poles; etching the stack using a first etching process and
stopping before reaching the AMR element; and etching the stack
using a second etching process, after etching the stack using the
first etching process, wherein etching the stack using the second
etching process includes stopping upon or after reaching the AMR
element.
5. The method of claim 4, wherein: the second etching process is
less damaging to the AMR material of the AMR element than is the
first etching process.
6. The method of claim 4, wherein: the first metal layer comprises
a titanium compound and the second metal layer comprises an
aluminum compound.
7. The method of claim 4, wherein: the first metal layer comprises
titanium-tungsten (TiW) and the second metal layer comprises
aluminum-copper (AlCu).
8. The method of claim 4, wherein: the first etching process
includes a dry etch using a chlorinated chemistry and the second
etching process includes a dry etch using a fluorinated
chemistry.
9. The method of claim 8, wherein: the first etching process uses a
solution including at least one of: BCl3, CL2, and CCl4; and the
second etching process uses a solution including at least one of:
CF4, CHF3, and NF3.
10. The method of claim 4, wherein: the first etching process
includes a dry etch using a chlorinated chemistry and the second
etching process includes a wet etch using a solution including
hydrogen peroxide (H.sub.2O.sub.2) and water (H.sub.2O).
11. The method of claim 4, wherein: etching the stack using the
first etching process is stopped upon or after reaching the first
metal layer.
12. An anisotropic magneto-resistive (AMR) sensor comprising: a
plurality of metallic elements on a first layer; and a plurality of
separate anisotropic magneto-resistive (AMR) element segments on a
second layer; wherein the plurality of metallic elements are
conductively coupled to the plurality of AMR element segments so
that a current applied to the AMR sensor will flow through the
plurality of metallic elements and the plurality of AMR element
segments in an alternating fashion.
13. The AMR sensor of claim 12, wherein: the first and second
layers are separated from one another by at least one layer of
dielectric material; and the plurality of metallic elements are
conductively coupled to the plurality of AMR element segments using
via connections.
14. The AMR sensor of claim 13, wherein: the AMR sensor has a
longitudinal direction; and the via connections are located so
that, during sensor operation, current will flow within the
plurality of AMR element segments in a direction that is at an
acute angle to the longitudinal direction of the AMR sensor.
15. The AMR sensor of claim 12, wherein: the first and second
layers are abutting; and the plurality of metallic elements are
conductively coupled to the plurality of AMR element segments by
direct conductive contact.
16. The AMR sensor of claim 12, wherein: the plurality of metallic
elements are disposed above an inter layer dielectric (ILD) surface
of the AMR sensor; and the plurality of AMR element segments are
disposed above the plurality of metallic elements; wherein the AMR
sensor further includes a passivation layer above the plurality of
AMR element segments to protect the AMR sensor from external
environmental conditions.
17. A method for fabricating an anisotropic magneto-resistive (AMR)
sensor, comprising: forming a plurality of metallic elements on a
first layer to serve as barber poles for the AMR sensor; forming a
plurality of separate AMR element segments on a second layer; and
providing conductive connections between the plurality of metallic
elements and the plurality of separate AMR element segments so that
a current applied to the AMR sensor will flow through the plurality
of metallic elements and the plurality of AMR element segments in
an alternating fashion during sensor operation.
18. The method of claim 17, wherein: providing conductive
connections between the plurality of metallic elements and the
plurality of separate AMR element segments includes forming via
connections between the plurality of AMR element segments and the
plurality of metallic elements.
19. The method of claim 18, wherein: forming via connections
includes forming groups of via connections in an orientation that
supports current flow at a desired angle within the separate AMR
element segments during sensor operation.
20. The method of claim 17, wherein: forming the plurality of AMR
element segments is performed before forming the plurality of
metallic elements.
Description
FIELD
[0001] Subject matter disclosed herein relates generally to sensors
and, more particularly, to sensors that include magnetoresistive
(MR) elements.
BACKGROUND
[0002] Magnetoresistance is the ability of a material to change its
electrical resistance when exposed to an external magnetic field.
This ability may be taken advantage of to provide, among other
things, sensors for detecting magnetic field intensity. Anisotropic
magnetoresistance (AMR) is a form of magnetoresistance where the
change in resistance of a material depends upon the angle between
the direction of magnetization and the direction of current flow in
the material. Typically, the resistance of an AMR material will be
a maximum when the magnetization of the material is in the same
direction as the current. To achieve linear operation in an AMR
sensor, an angle may need to be maintained between the direction of
magnetization with no external magnetic field applied (i.e., the
easy angle) and the current in the AMR element. Most modern AMR
sensors use "barber pole" structures to provide the desired current
angle. Typically, an angle of around 45 degrees is used.
[0003] As with any electrical device, there is a need for new and
improved AMR sensor architectures. There is also a need for new
techniques for efficiently and/or inexpensively fabricating AMR
sensors. Techniques are also needed for producing AMR sensors that
are capable of high performance operation.
SUMMARY
[0004] In accordance with one aspect of the concepts, systems,
circuits, and techniques described herein, an anisotropic
magneto-resistive (AMR) sensor comprises: an inter layer dielectric
(ILD) surface; an AMR element above the ILD surface, the AMR
element being at least partially formed of an AMR material; and a
plurality of barber poles above and conductively coupled to the AMR
element, wherein each of the barber poles includes a lower portion
formed of a first metal material and an upper portion formed of a
second metal material, wherein the first metal material is a
material that can be etched using an etching process that does not
attack the AMR material of the AMR element.
[0005] In one embodiment, the first metal material includes a
titanium compound and the second metal material includes an
aluminum compound.
[0006] In one embodiment, the first metal material includes
titanium-tungsten (TiW) and the second metal material includes
aluminum-copper (AlCu).
[0007] In accordance with another aspect of the concepts, systems,
circuits, and techniques described herein, a method for fabricating
an anisotropic magneto-resistive (AMR) sensor, comprises: providing
an inter layer dielectric (ILD) surface; forming a stack over the
ILD surface, the stack having an AMR element formed of an AMR
material, a first metal layer above the AMR element, and a second
metal layer above the first metal layer, wherein the first and
second metal layers are formed of different metal materials;
applying a mask over the stack to define barber poles; etching the
stack using a first etching process and stopping before reaching
the AMR element; and etching the stack using a second etching
process, after etching the stack using the first etching process,
wherein etching the stack using the second etching process includes
stopping upon or after reaching the AMR element.
[0008] In one embodiment, the second etching process is less
damaging to the AMR material of the AMR element than is the first
etching process.
[0009] In one embodiment, the first metal layer comprises a
titanium compound and the second metal layer comprises an aluminum
compound.
[0010] In one embodiment, the first metal layer comprises
titanium-tungsten (TiW) and the second metal layer comprises
aluminum-copper (AlCu).
[0011] In one embodiment, the first etching process includes a dry
etch using a chlorinated chemistry and the second etching process
includes a dry etch using a fluorinated chemistry.
[0012] In one embodiment, the first etching process uses a solution
including at least one of BCl3, CL2, and CCl4; and the second
etching process uses a solution including at least one of CF4,
CHF3, and NF3.
[0013] In one embodiment, the first etching process includes a dry
etch using a chlorinated chemistry and the second etching process
includes a wet etch using a solution including hydrogen peroxide
(H.sub.2O.sub.2) and water (H.sub.2O).
[0014] In one embodiment, etching the stack using the first etching
process is stopped upon or after reaching the first metal
layer.
[0015] In accordance with a further aspect of the concepts,
systems, circuits, and techniques described herein, an anisotropic
magneto-resistive (AMR) sensor comprises: a plurality of metallic
elements on a first layer; and a plurality of separate anisotropic
magneto-resistive (AMR) element segments on a second layer; wherein
the plurality of metallic elements are conductively coupled to the
plurality of AMR element segments so that a current applied to the
AMR sensor will flow through the plurality of metallic elements and
the plurality of AMR element segments in an alternating
fashion.
[0016] In one embodiment, the first and second layers are separated
from one another by at least one layer of dielectric material; and
the plurality of metallic elements are conductively coupled to the
plurality of AMR element segments using via connections.
[0017] In one embodiment, the AMR sensor has a longitudinal
direction; and the via connections are located so that, during
sensor operation, current will flow within the plurality of AMR
element segments in a direction that is at an acute angle to the
longitudinal direction of the AMR sensor.
[0018] In one embodiment, the via connections are arranged in
groups having orientations that are different from the longitudinal
direction of the AMR sensor.
[0019] In one embodiment, the first and second layers are abutting;
and the plurality of metallic elements are conductively coupled to
the plurality of AMR element segments by direct conductive
contact.
[0020] In one embodiment, the plurality of metallic elements are
disposed above an inter layer dielectric (ILD) surface of the AMR
sensor, and the plurality of AMR element segments are disposed
above the plurality of metallic elements; wherein the AMR sensor
further includes a passivation layer above the plurality of AMR
element segments to protect the AMR sensor from external
environmental conditions.
[0021] In accordance with still another aspect of the concepts,
systems, circuits, and techniques described herein, a method for
fabricating an anisotropic magneto-resistive (AMR) sensor,
comprises: forming a plurality of metallic elements on a first
layer to serve as barber poles for the AMR sensor, forming a
plurality of separate AMR element segments on a second layer; and
providing conductive connections between the plurality of metallic
elements and the plurality of separate AMR element segments so that
a current applied to the AMR sensor will flow through the plurality
of metallic elements and the plurality of AMR element segments in
an alternating fashion during sensor operation.
[0022] In one embodiment, providing conductive connections between
the plurality of metallic elements and the plurality of separate
AMR element segments includes forming via connections between the
plurality of AMR element segments and the plurality of metallic
elements.
[0023] In one embodiment, forming via connections includes forming
groups of via connections in an orientation that supports current
flow at a desired angle within the separate AMR element segments
during sensor operation.
[0024] In one embodiment, forming via connections is performed
after forming the plurality of metallic elements and forming the
plurality of separate AMR element segments.
[0025] In one embodiment, forming the plurality of AMR element
segments is performed after forming the plurality of metallic
elements.
[0026] In one embodiment, forming the plurality of AMR element
segments is performed before forming the plurality of metallic
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The foregoing features may be more fully understood from the
following description of the drawings in which:
[0028] FIG. 1 is a top view of a conventional anisotropic
magnetoresistive (AMR) sensor having metallic barber poles disposed
on top of an underlying film of AMR material;
[0029] FIGS. 2 and 3 are sectional side views of exemplary AMR
sensor architectures having AMR elements disposed above barber pole
elements in accordance with various embodiments;
[0030] FIG. 4 is a sectional side view of an exemplary AMR sensor
architecture having an AMR element disposed above barber pole
elements that does not use planarization in accordance with an
embodiment;
[0031] FIG. 5 is a flowchart illustrating an exemplary method for
fabricating an AMR sensor having an AMR element disposed above
barber pole elements in accordance with an embodiment;
[0032] FIG. 6 is a sectional side view of an exemplary AMR sensor
that includes multiple capping layers in accordance with an
embodiment;
[0033] FIG. 7 is a sectional side view of an exemplary AMR sensor
that includes a single capping layer in accordance with an
embodiment;
[0034] FIG. 8 is a flowchart illustrating an exemplary method for
use in fabricating an AMR sensor having at least one capping layer
in accordance with an embodiment;
[0035] FIGS. 9A-9E are sectional side views illustrating various
stages in an exemplary process for fabricating an AMR sensor in
accordance with an embodiment;
[0036] FIG. 10 is a flowchart illustrating a method for fabricating
an AMR sensor using two different etching processes in accordance
with an embodiment;
[0037] FIGS. 11 and 12 are a top view and a sectional side view,
respectively, of an AMR sensor that uses a segmented AMR element in
accordance with an embodiment; and
[0038] FIG. 13 is a flowchart illustrating a method for fabricating
an AMR sensor having a segmented AMR element in accordance with an
embodiment.
DETAILED DESCRIPTION
[0039] FIG. 1 is a top view of an anisotropic magnetoresistive
(AMR) sensor 10 having metallic barber poles 12, 14, 16, 18, 20
disposed on top of an underlying film 22 of a magnetic material
having the AMR property (which will be referred to hereinafter as
an AMR material). The barber poles 12, 14, 16, 18, 20 are formed of
aluminum or other suitable conductor and are oriented at an angle
of 45 degrees with respect to a longitudinal direction 24 of the
sensor. During sensor operation, a test current I.sub.r is applied
to the sensor 10 to measure changes in an electrical resistance of
the film 22 of AMR material to sense an external magnetic field.
Typically, a number of AMR sensor elements may be implemented in a
bridge configuration to facilitate the measurement of the
resistance changes. In other embodiments, the segments of the
barber poles 12 and 20 are not included and contact is made to the
AMR layer in those areas.
[0040] The current I.sub.r may be applied to a first barber pole 12
of the sensor 10. Because of the resistivity of the barber poles
12, 14, 16, 18, 20 is much lower than that of the AMR material, the
current will flow through the barber poles 12, 14, 16, 18, 20 when
it can, and will flow through the underlying AMR material 22 in the
gaps between the barber poles 12, 14, 16, 18, 20. In addition, the
differences in resistivity between the materials will cause the
current in the gap regions to flow through the AMR material at an
angle dictated by the angle of the barber poles 12, 14, 16, 18, 20.
This is because the current will take the shortest route through
the higher resistivity material (i.e., perpendicular to the edges
of the barber poles 12, 14, 16, 18, 20). It is due to the magnetic
field being measured that the route is changed and thus the
resistance is increased. As shown in FIG. 1, the current I through
the AMR material flows at a 45 degree angle to the longitudinal
direction 24 of the sensor. The current eventually exits the sensor
10 at the last barber pole 20. In general, the barber poles need to
be made of a material with low enough resistance (or resistivity)
to effectively redistribute the current flow.
[0041] In a typical implementation, the underlying film 22 of AMR
material may be formed so that a magnetization vector with no
applied magnetic field (i.e., the easy axis) is in a longitudinal
direction with respect to the sensor 10 (i.e., along a long axis of
the sensor 10 or the AMR element). The sensor may then be used, for
example, to sense changing magnetic fields in a transverse
direction. Other arrangements may alternatively be used.
[0042] In conventional AMR sensors, the barber poles are
implemented on top of the AMR element, as described above. It was
found that this approach presented a potential for contamination in
some fabrication process flows. For example, in some conventional
process flows, etches performed during fabrication are required to
stop on the AMR material (e.g., permalloy (NiFe), etc.) of the AMR
element, which exposes the etching tool to NiFe contamination. In
conceiving some of the features, techniques, and structures
described herein, it was determined that fabrication efficiencies
and cost reductions could be achieved by forming the AMR element
above (or after) the barber poles during sensor fabrication. As
indicated above, the AMR elements of AMR sensors are often formed
from a material known as permalloy, which is an alloy of nickel and
iron. In general, iron is a material that is not easy to deal with
in a clean room fabrication environment. By forming the AMR element
above the barber pole structures, the lower portion of the AMR
sensor can be generated using a standard device fabrication process
(e.g., a CMOS, BiCMOS, or similar standardized process). The AMR
element can then be added using a different process (e.g., in a
different fabrication environment, equipment, or clean room)
without having to expose the original fabrication environment to
NiFe or another AMR material.
[0043] FIG. 2 is a sectional side view of an exemplary AMR sensor
30 in accordance with an embodiment. It should be appreciated that
the structures illustrated in FIG. 2, and in other figures
described herein, may not be to scale. That is, one or more
dimensions within the various figures may be exaggerated to
increase clarity and facilitate understanding. As shown, the AMR
sensor 30 may be formed on top of an inter layer dielectric (ILD)
32 or substrate. As used herein, the terms "ILD," "ILD layer," and
"ILD surface" encompass any surface of dielectric material within a
device including a substrate of dielectric material or layers
higher than the substrate. The ILD layer may be formed of any of a
variety of different dielectric materials including, for example,
SiO.sub.2, Si.sub.xN.sub.y (nitride), Al.sub.2O.sub.3 (or other
aluminum oxide compounds), and many others. A metal layer 34 may be
deposited on the ILD surface and formed into metal elements to
serve as barber poles 36a, 36b, 36c, 36d, 36e. Any of a variety of
different techniques may be used to shape the barber poles 36a,
36b, 36c, 36d, 36e including, for example, deposition,
photolithography, and etch; or seed layer deposition, patterning
(photolithography), and electroplating, and/or others. Although
illustrated in FIG. 2 with 5 barber pole elements 36a, 36b, 36c,
36d, 36e, it should be appreciated that any number of elements
greater than 2 may be used in different implementations. The metal
layer 34 may be formed of aluminum, copper, gold, or any other
metal or metal alloy having the desired characteristics to serve as
barber pole elements.
[0044] Although not shown in FIG. 2, the barber poles 36a, 36b,
36c, 36d, 36e may be oriented at a fixed angle (e.g., 45 degrees,
etc.) with respect to a longitudinal direction (x) of the sensor 30
(as viewed from above). Alternatively, the barber poles 36a, 36b,
36c, 36d, 36e may be oriented at a variable angle, where the edge
of the barber pole changes angle across the AMR width. In some
embodiments, the regions 38a, 38b, 38c, 38d between the barber
poles 36a, 36b, 36c, 36d, 36e may be filled with a dielectric
material after the barber poles are formed. An upper surface of
metal layer 34 with the dielectric material in the regions may then
be planarized using any of a variety of planarization
techniques.
[0045] After the barber poles 36a, 36b, 36c, 36d, 36e have been
formed, an AMR element 40 may next be formed above metal layer 34.
The AMR element 40 may be formed of any of variety of AMR
materials, the most common of which is NiFe. As described
previously, in some implementations, the formation of the AMR
element 40 (as well as subsequent processing steps) may be
performed in a different processing environment or clean room from
the above described fabrication steps. In one approach, a film of
AMR material may first be deposited as a sheet or layer over an
upper surface of metal layer 34. A mask may then be applied to the
AMR film and the film may be etched into the desired shape of AMR
element 40. In some cases, the mask may be a photoresist mask,
while in other cases a hard mask such as an oxide or a nitride may
be deposited and then patterned with a photoresist or similar
material. After the AMR element 40 has been formed, a layer of
passivation 42 may be applied over the top and sides of the AMR
element 40 to, among other things, protect the AMR element 40 from
an external environment. Metallic contacts 44a, 44b may be formed
to provide external connection points on the AMR sensor 30 to, for
example, allow measurement circuitry to be coupled thereto. In
other embodiments, these contacts connect to other areas of the
integrated circuit. As shown, the metallic contacts 44a, 44b may
each be conductively coupled to corresponding ones of the barber
pole elements 36a, 36e. In other embodiments, alternative
structures may be provided to permit connection to the sensor
(e.g., tungsten plugs to provide connection from below, etc.). In
still other embodiments, the pads for bonding may be provided
elsewhere in the integrated circuit.
[0046] In the AMR sensor 30 of FIG. 2, some or all of the barber
pole elements 36a, 36b, 36c, 36d, 36e may be arranged in an
orientation that will result in a desired current flow direction
within the AMR element 40 during sensor operation. In some
embodiments, this current flow direction may within a range of
approximately 30 to 60 degrees with respect to the long axis (or
the longitudinal axis) of the AMR element 40. In at least one
embodiment, this current flow direction is nominally 45 degrees
with respect to the long axis of the AMR element 40.
[0047] FIG. 3 is a sectional side view of an exemplary AMR sensor
50 in accordance with an embodiment. AMR sensor 50 is similar to
AMR sensor 30 of FIG. 2, except one or more additional layers 48
exist between metal layer 34 and AMR element 40. For example, in
one implementation, layer 48 may include a layer of hard metal
(e.g., tungsten (W), titanium (Ti), titanium nitride (TiN), etc.)
on top of metal layer 34 to facilitate subsequent planarization
(e.g., polishing, etc.). If used, the hard metal layer may be
applied before the barber pole elements are patterned on metal
layer 34. The material used for the hard metal layer must have an
appropriate conductivity for use between the barber pole elements
of metal layer 34 and AMR element 40.
[0048] In addition to, or as an alternative to, the hard metal
layer, layer 48 may also include a seed layer to facilitate uniform
growth of the AMR film above metal layer 34. The seed layer may be
formed from any of variety of different materials including, for
example, copper (Cu), gold (Au), and/or others. If used, the seed
layer would preferably be applied after planarization. In some
embodiments, an adhesion layer may precede the seed layer to
improve the mechanical adhesion of the seed layer to the underlying
layer. The adhesion layer may include, but is not limited to, a
titanium or chromium layer having a thickness in the range of
approximately 10 to 500 Angstroms.
[0049] Layer 48 may also, or alternatively, include a diffusion
barrier to prevent diffusion of material between metal layer 34 and
AMR element 40 (e.g., diffusion between an aluminum layer and a
NiFe layer, etc.). In some embodiments, a single metal layer may be
used that serves as both a diffusion barrier and a hard metal
layer. The material that is used in these layers will typically
depend on the materials used in metal layer 34 and AMR element 40.
When aluminum is used in the metal layer 34 and NiFe is used in AMR
element 40, materials such as tungsten (W), titanium (Ti), titanium
nitride (TiN), etc. may be used as both a diffusion barrier and a
hard metal layer.
[0050] In some embodiments, non-metallic materials may be used as a
hard/diffusion barrier. For example, in at least one embodiment, a
very thin layer of alumina (Al.sub.20.sub.3) or a similar
dielectric material may be used. The alumina layer must be thin
enough to allow electron tunneling between the barber poles and the
AMR element (e.g., less than 3 to 8 Angstroms in thickness, and
maybe less than 1 Angstrom). Such layers may provide an increased
level of hardness to facilitate planarization.
[0051] FIG. 4 is a sectional side view of an exemplary AMR sensor
60 in accordance with still another embodiment. The AMR sensor 60
of FIG. 3 may be easier to construct than the previously described
embodiments as one or more processing steps associated with those
embodiments have been eliminated. As before, barber poles 36a, 36b,
36c, 36d, 36e are formed on a metal layer 34 above an ILD layer 32.
However, instead of filling in the regions between the barber pole
elements 36a, 36b, 36c, 36d, 36e with dielectric material and then
planarizing, the AMR material may be deposited over the barber pole
elements 36a, 36b, 36c, 36d, 36e and allowed to fill the regions.
The resulting AMR film may then be patterned to a desired size and
shape. This technique may require the AMR film layer to be thicker
than the metal layer 34 associated with the barber poles. As shown,
because the AMR film was allowed to fill in the regions, an upper
surface 64 of the AMR element 62 may not be smooth (e.g., it may
have depressions or other distortions corresponding to the regions
below). In some embodiments, the upper surface 64 of the AMR
element 62 may be planarized at this point. However, in other
embodiments, as shown in FIG. 4, the upper surface 64 of the AMR
element 62 may be left unplanarized and a passivation layer 42 may
be applied to the unplanarized element. Contact pads 44a, 44b may
then be added to the sensor 60 as described previously.
[0052] In some embodiments, one or more capping layers may be used
within an AMR sensor to protect some materials within the sensor
from other materials. One or more capping layers may also serve as
an etch stop during sensor fabrication to avoid the need to etch
down to one or more materials that may be problematic during sensor
fabrication. As will be described in greater detail, in at least
one embodiment, an AMR sensor having one or more capping layers may
be fabricated using a simplified process whereby all layers of the
sensor element and the barber poles are deposited before any
patterning is performed. Patterning may then be performed in two
successive stages: a first stage to form the shape of the AMR
element and a second stage to form the shape of the barber pole
elements.
[0053] FIG. 5 is a flowchart illustrating an exemplary method 90
for fabricating an AMR sensor in accordance with an embodiment. The
method 90 may be used to fabricate sensors such as, for example,
those illustrated in FIGS. 2, 3, and 4, as well as other AMR
sensors. An inter layer dielectric (ILD) surface is first provided
upon which the AMR sensor will be built (block 92). A plurality of
metallic elements may next be formed above the ILD surface to serve
as barber pole conductors for the AMR sensor (block 94). In some
embodiments, the formation of the metallic elements may include the
deposition of one or more of a hard metal layer, a diffusion
barrier, or a seed layer above the metallic elements. One or more
layers of metal may be deposited on the ILD surface and the layers
may then be masked and etched to form the metallic elements. As
described previously, the metallic elements may be oriented at an
angle (e.g., 45 degrees) to a longitudinal direction associated
with the sensor being fabricated.
[0054] An AMR element may next be formed above the plurality of
metallic elements (block 96). In some embodiments, the regions
between the metallic elements may be filled with a dielectric
material and a planarization process may then be used to planarize
an upper surface of the metallic elements before the AMR element is
formed. In other embodiments, the AMR element may be formed without
first filling in the regions and planarizing. In these embodiments,
the AMR element may extend down to the ILD surface below. To form
the AMR element, a film of AMR material may first be deposited over
the metallic elements. Patterning may then be used to shape the AMR
film into the desired element shape.
[0055] After the AMR element has been formed, a passivation process
may be used to enclose the AMR element, and possibly the metallic
elements, to protect them from an external environment (block 98).
In embodiments where the regions between the metallic elements were
not filled in with dielectric material, the upper layer of the AMR
element may be uneven. In some embodiments, the passivation may be
applied directly to the uneven AMR element without first
planarizing the upper surface thereof. In other embodiments, the
upper surface of the AMR element may be planarized before the
passivation is applied.
[0056] In some embodiments, metallic contact pads may next be
formed to provide external connection points for the AMR sensor
(block 100). These contact pads may be used, for example, to
connect external measurement circuitry to the AMR sensor. The
metallic contact pads may be formed through the passivation
material to contact corresponding ones of the metallic elements. In
other embodiments, other techniques may be used to provide external
connection to the AMR element.
[0057] FIG. 6 is a sectional side view of an exemplary AMR sensor
70 that includes multiple capping layers in accordance with an
embodiment. As shown, the AMR sensor 70 may be formed above, for
example, an ILD layer 72. In some embodiments, tungsten plugs 74a,
74b may be provided in the ILD layer 72 to allow connection to the
sensor 70 from below. The AMR sensor 70 may have an AMR element 78
formed above the ILD layer 72. The AMR element 78 may have a seed
layer 76 below it. The seed layer 76 may be provided to, for
example, facilitate growth of an AMR film from which the AMR
element 78 is formed. In some implementations, a seed layer may not
be present.
[0058] A first capping layer 80 may be formed over the AMR element
78. One purpose for the first capping layer 80 may be to protect
other materials within the AMR sensor 70 from the AMR material of
the AMR element 78. Another possible purpose may be to serve as an
etch stop during formation of the barber poles of the sensor 70 so
that the etch does not extend through to the AMR material (which
can cause contamination). The first capping layer 80 may be formed
of any material that is capable of protecting other materials in
the AMR sensor 70, at least to some extent, from the AMR material
of AMR sensor 78. Capping materials that may be used include, for
example, tantalum (Ta), tungsten (W), titanium (Ti), titanium
nitride (TiN), and others. If used, the capping layer 80 should be
thin so that it does not increase the resistance to the barber pole
structures and thereby prevent a significant portion of the total
current in the AMR layer 78 from flowing into the barber poles.
Alternatively, a more conductive capping layer 80 can be used such
as ruthenium (Ru), where the conductivity is high enough as not to
pose the same restriction of thinness as noted above. As shown in
FIG. 6, even with capping layer 80, there may be some exposure to
the AMR material of element 78 on the sides of the element.
However, this exposure will typically only be a small percentage of
the exposure that would exist without the capping layer 80.
[0059] With reference to FIG. 6, barber poles 88 may be formed over
the AMR element 78. The barber poles 88 may each have a lower
portion 82 formed of a metal material such as, for example, copper,
copper-aluminum, aluminum, or some other metal. The barber poles 88
may each also have an upper portion to serve as a second capping
layer 84 to protect other materials in the sensor 70 from the metal
of lower portion 82. The second capping layer 84 may be formed of
the same material as, or a different material from, the first
capping layer 80 (e.g., tantalum (Ta), tungsten (W), titanium (Ti),
titanium nitride (TiN), and/or others).
[0060] In at least one embodiment, to form the AMR sensor 70 of
FIG. 6, the seed layer 76, a layer of AMR material, the first
capping layer 80, a metal layer, and the second capping layer 84
may all be deposited before any patterning is done. The patterning
may then be performed in two steps. In at least one embodiment, ion
beam etching may be used to perform the patterning in both steps,
although other techniques or combinations of techniques may
alternatively be used. The first patterning step is performed to
form the desired shape of the AMR element 78. The second patterning
step is performed to form the desired shape of the barber poles 88.
During sensor fabrication, the first patterning step may stop on
the ILD layer 72 or some other dielectric layer. The second
patterning step may stop at or within the first capping layer 80.
In this manner, the AMR material is not exposed from above, thereby
reducing the risk of contamination. Masks may be formed for each
patterning step and then stripped after each patterning is
complete. In some cases, masks may remain if they do not interfere
with a subsequent step in the process and then mask materials may
be etched at the same time if appropriate before moving on to a
subsequent process step.
[0061] After the barber poles 88 have been formed, a passivation
material 86 may be applied over the AMR sensor 70 to protect the
sensor from external environmental conditions. In some embodiments,
as shown in FIG. 7, an AMR sensor similar to that of FIG. 6 may be
fabricated without the first capping layer 80. In such embodiments,
the etch process to form the barber poles will extend down to the
AMR material of the AMR sensor 78.
[0062] FIG. 8 is a flowchart illustrating an exemplary method 110
for use in fabricating an AMR sensor in accordance with an
embodiment. The method 110 may be used to fabricate, for example,
the sensor 70 of FIG. 6 or similar sensors. As illustrated, an ILD
surface may first be provided (block 112). An optional adhesion
and/or seed layer may then be formed on the ILD surface to
facilitate the deposition of an AMR film (block 114). An AMR film
may then be formed on the seed layer (or the ILD surface if a seed
layer is not provided) (block 116). A first capping layer may next
be deposited over the AMR film (block 118). In some embodiments, a
first capping layer is not provided.
[0063] A metal layer (e.g., a layer of copper or another metal or
metal alloy) may next be formed above the layer of AMR material
(block 120). A second capping layer may then be formed above the
metal layer (block 122). A first patterning step may then be
performed to form the desired shape of the AMR element (block 124).
A second patterning step may then be performed to form the barber
poles over the AMR element (block 126). The first and second
patterning steps may use the same patterning process or different
processes. In at least one implementation, photolithography and
then ion beam etching is used for both steps. An optional hard mask
may be deposited before photolithography and then patterned after
photolithography before the ion beam etch step. If a first capping
layer is used, the second patterning step to form the barber poles
may be stopped within the first capping layer before it reaches the
AMR element. If a first capping layer is not used, the second
patterning step may extend down to the AMR element. After the
barber poles have been formed, a passivation process may be used to
cover the barber poles and the AMR material with a passivation
material (block 128). Metallic contacts may then be formed through
the passivation material to provide an electrical connection to the
AMR sensor or some other connection technique may be used (e.g., a
connection from below using tungsten plugs, etc.).
[0064] FIGS. 9A-9E are sectional side views illustrating various
stages in an exemplary process for fabricating an AMR sensor in
accordance with an embodiment. With reference to FIG. 9A, the
process may begin with an ILD layer 130 with or without tungsten
plugs 132, 134. A layer of AMR material 136 (e.g., NiFe, etc.) may
then be deposited upon the ILD layer 130 using any known deposition
process. In some embodiments, a seed layer may first be formed on
the ILD layer 130 before the AMR layer 136 is deposited (although
this is not performed in every embodiment). A first metal layer 138
and a second metal layer 140 may then be deposited over the layer
of AMR material 136. As will be described in greater detail, the
materials used for the first and second metal layers 138, 140 may
be selected based upon the etching processes and chemistries that
work well with the two materials. In some embodiments, the first
metal layer 138 may be formed from titanium tungsten (TiW), or some
other titanium based compound, and the second metal layer 140 may
be formed from aluminum copper (AlCu), or some other aluminum based
compound (e.g., Al, AlSi, etc.). Other materials may be used for
the first and second metal layers 138, 140 in other embodiments. In
some embodiments, an adhesion layer and/or diffusion barrier may be
deposited between the layer of AMR material 136 and the first metal
layer 138 to improve adhesion and/or reduce diffusion (although
these layers are not used in every embodiment).
[0065] Referring now to FIG. 9B, the AMR layer 136 and the first
and second metal layers 138, 140 may next be patterned into an AMR
element 136 having first and second metal layers 138, 140 above.
Any of a variety of different patterning techniques may be used to
form the AMR element 136. With reference to FIG. 9C, a layer of
photo-resist 142 or other mask material may be formed over the AMR
element 136 and the first and second metal layers 138, 140. The
photo-resist layer 142 may then be formed into a mask having the
pattern of the barber poles of the AMR sensor being fabricated. A
first etching process and process chemistry may then be used to
etch through the second metal layer 140 to a point at a top
boundary of or within (but not all the way through) the first metal
layer 138, as shown in FIG. 9C. A second etching process and
process chemistry may then be used to etch the rest of the way
through the first metal layer 138 (and any intervening layers) to
the AMR element 136.
[0066] In at least one embodiment, the second etching process will
be a process that does not significantly attack the AMR material of
the AMR element 136 such that the AMR film will not function as the
desired magnetic field sensor. As such, the material used for the
first metal layer 138 may be a material that works well with the
selected etching process. As described above, in some embodiments,
titanium tungsten (TiW) or some other titanium based compound may
be used for the first metal layer 138. In these embodiments, a dry
etch process using a fluorinated chemistry such as, for example,
CF.sub.4, CHF.sub.3, SF.sub.6, or others may be used for the second
etching process as these chemistries do not attack magnetic films,
such as NiFe. As an alternative, in some embodiments, a wet etch
process may be used for the second etching process using a
chemistry such as, for example, hydrogen peroxide/water
(H.sub.2O.sub.2/H.sub.2O) or phosphoric acetic nitric (PAN). Other
processes are also possible for the second etching process. The
first etching process used to etch through the second metal layer
140 can be a process that does attack the AMR material as this
process will not reach the AMR element 136 during fabrication. This
process may include, for example, a dry etch process using a
chlorinated chemistry such as, for example, BCl.sub.3 or Cl.sub.2.
These chemistries work well with aluminum and aluminum compounds as
well as other metals. Other processes may alternatively be used for
the first etching process.
[0067] After the second etching process has completed, the
photo-resist 142 may be stripped to compete the formation of the
barber poles. FIG. 9D shows the resulting sensor with barber poles
146 after the photo-resist 142 has been stripped. In some cases, it
may be desirable to deposit a hard mask and pattern the hard mask
(e.g., if a wet etching process is used for the second etching
process), and it may be desirable to strip the photo-resist 142
before the second etching process. As shown in FIG. 9E, after the
barber poles 146 have been formed, a coating of passivation 148 may
be applied to the sensor to protect it from, for example, an
exterior environment. Any of various techniques may be used to
provide an external electrical connection to the sensor.
[0068] FIG. 10 is a flowchart illustrating a method 160 for
fabricating an AMR sensor in accordance with an embodiment. The
method 160 may be used to fabricate, for example, the sensor shown
in FIG. 9E as well as other AMR sensors. An ILD surface may first
be provided upon which the sensor will be formed (block 162). A
seed layer may then be formed on the ILD surface (block 164). In
some embodiments, a seed layer may not be used. An AMR element
having first and second metal layers above it may then be formed
over the ILD surface (block 166). The first and second metal layers
will be used to form the barber poles of the AMR sensor. In at
least one embodiment, the first metal layer is formed of
titanium-tungsten (TiW) or another titanium compound and the second
metal layer is formed of aluminum-copper (AlCu) or another aluminum
compound. Other metal materials may alternatively be used. In one
approach, the AMR element with the first and second metal layers
may be formed by first depositing a layer of AMR material over the
ILD surface and then depositing first and second metal layers over
the layer of AMR material. The three layers may then be patterned
together into the desired shape of the AMR element. Other
techniques may alternatively be used to form the AMR element.
[0069] A mask may next be applied over the second metal layer to
form the barber poles of the sensor (block 168). A first etching
process is then used to etch through the second metal layer (block
170). The first etching process may be stopped once the first metal
layer is reached, or somewhere within the first metal layer, but
will not be permitted to proceed all the way through to the AMR
material of the AMR element. A second etching process may then be
used to finish the etch through to the AMR material of the AMR
element (block 172). The second etching process will be a process
that is less deleterious to the AMR material than the first etching
process would be. In at least one embodiment, the first etching
process is a dry etch using a chlorinated chemistry and the second
etching process is a dry process using a fluorinated chemistry. In
another approach, the first etching process is a dry etch using a
chlorinated chemistry and the second process is a wet etching
process using, for example, a hydrogen peroxide-water chemistry.
Other process combinations may alternatively be used.
[0070] In conventional AMR sensors, barber pole structures are
typically formed in abutting conductive relation to an underlying
AMR element. In some embodiments described below, separation exists
between barber pole conductors and AMR material. In these
embodiments, via connections or other structures for providing
interlayer conductive coupling may be used to couple the barber
poles to the AMR material. In addition, in some embodiments,
instead of using a single continuous AMR element as in conventional
sensors, a segmented element is used that has multiple separate AMR
element sections that are interconnected with one another through
the barber pole conductors.
[0071] FIGS. 11 and 12 are a top view and a sectional side view,
respectively, of an AMR sensor 190 that uses a segmented AMR
element in accordance with an embodiment. As shown in FIGS. 11 and
12, the AMR sensor 190 includes a number of barber pole conductor
elements 192a, 192b, 192c, 192d, 192e on a first layer and a number
of AMR element segments 194a, 194b, 194c, 194d on a second layer
that is above the first layer. The barber pole conductor elements
192a, 192b, 192c, 192d, 192e may be formed on an ILD layer 200. In
the illustrated embodiment, the first and second layers are
separated from one another by one or more intervening dielectric
layers 196. Via connections 198 are used to provide conductive
coupling between the barber pole conductor elements 192a, 192b,
192c, 192d, 192e and the AMR element segments 194a, 194b, 194c,
194d. Techniques for forming via connections between conductive
layers are known in the art. Although illustrated with four AMR
element segments 194a, 194b, 194c, 194d in FIGS. 11 and 12, it
should be appreciated that any number of AMR element segments
(i.e., two or more) may be used in other segmented AMR element
embodiments. In addition, in at least one implementation, the
finished sensor 190 may include a passivation layer 202 covering
the AMR element segments 194a, 194b, 194c, 194d and dielectric
layer 196.
[0072] As shown in FIG. 12, the barber pole conductor elements
192a, 192b, 192c, 192d, 192e and the AMR element segments 194a,
194b, 194c, 194d may be interconnected so that a current applied to
a barber pole element at one end of the sensor (e.g., element 192a)
will flow through all of the barber pole conductor elements 192a,
192b, 192c, 192d, 192e and all of the AMR element segments 194a,
194b, 194c, 194d in an alternating fashion (i.e., barber pole
element, AMR element segment, barber pole element, AMR element
segment, and so on) before emerging from a barber pole element at
an opposite end of the sensor (e.g., element 192e). In addition,
the locations and orientation of the via connections 198 and the
conductivities of the associated materials, may be selected so that
the current I will flow through the AMR element segments 194a,
194b, 194c, 194d at an angle to the easy axis thereof (e.g., a 45
degree angle in the illustrated embodiment). The AMR element
segments 194a, 194b, 194c, 194d may be magnetized so that the easy
axis of each of the segments aligns with the longitudinal direction
of the sensor (although this might not be the case in some
embodiments).
[0073] With reference to FIG. 11, the via connections 198 may be
formed within groups (e.g., in rows, etc.) that form a 45 degree
angle with respect to a longitudinal direction of the sensor 190.
If the combined resistance of the barber pole elements 192a, 192b,
192c, 192d, 192e and the corresponding via connections 198 is low
enough with respect to the resistance of the AMR element segments
194a, 194b, 194c, 194d, then the current (1) will flow within the
AMR element segments 194a, 194b, 194c, 194d at a 45 degree angle,
as shown in FIG. 11. For example, in one possible implementation,
the resistance of each AMR element segment may be around 20 Ohms,
the resistance of each barber pole element may be around 0.1 Ohms,
and the resistance of each group of via connections may be around
0.05 Ohms. Thus, the combined resistance of one barber pole element
and two via groups will be substantially less than the resistance
of one corresponding AMR element segment. In this scenario, the
current flow will occur within the AMR element segments at the
desired angle. Other resistance scenarios may be used in other
embodiments. It should be appreciated that both the number and the
size of the via connections used in a particular implementation may
be selected so that an appropriate via resistance is achieved to
support current flow at the desired angle in the AMR element
segments. In some alternative embodiments, the AMR material layer
194 is not cut between the via connection areas.
[0074] In the embodiment illustrated in FIGS. 11 and 12, the barber
pole elements 192a, 192b, 192c, 192d, 192e are implemented below
the AMR element segments 194a, 194b, 194c, 194d. As described
previously, this arrangement may provide various benefits related
to, for example, the prevention of contamination during the
fabrication process. In some embodiments, however, an AMR sensor
having a segmented AMR element may be provided with the barber pole
elements located above the AMR element segments.
[0075] In the embodiment of FIG. 11, the barber pole elements 192a,
192b, 192c, 192d, 192e and the AMR element segments 194a, 194b,
194c, 194d are shown as having edges that also form 45 degree
angles to the longitudinal direction of the sensor 190. However,
this is not the case in every embodiment. That is, it is the angle
associated with the via connections that will establish the current
angle within the AMR element segments 194a, 194b, 194c, 194d and
not the outer shape of the barber pole elements 192a, 192b, 192c,
192d, 192e and the AMR element segments 194a, 194b, 194c, 194d. The
edges of these elements may be angled, however, so that a more
compact sensor can be achieved. It should be appreciated that the
density of the vias may have to be adjusted in a particular design
to achieve a viable resistance scenario in the sensor 190.
[0076] In at least one embodiment, an AMR sensor is provided that
uses a segmented AMR element, but does not use via connections
between the AMR sensor segments and the corresponding barber pole
elements. That is, the AMR sensor segments and the barber pole
elements are formed in an abutting, conductively coupled relation
to one another with no intervening dielectric layer (although there
could be one or more intervening conductive layers, such as a seed
layer, a diffusion barrier, etc.). For example, with reference to
FIG. 12, in one alternative arrangement, the AMR element segments
194a, 194b, 194c, 194d may be disposed directly above the barber
pole elements 192a, 192b, 192c, 192d, 192e, with no dielectric
layer 196 in between. As described previous, the regions between
the barber pole elements 192a, 192b, 192c, 192d, 192e may, in some
embodiments, be partially or fully filled with dielectric material
before the AMR element segments 194a, 194b, 194c, 194d are formed.
Planarization may also be performed before the AMR element segments
194a, 194b, 194c, 194d are formed in some implementations. In the
above-described arrangement, the current flow within the AMR
element segments 194a, 194b, 194c, 194d will still be at the
desired angle with respect to the easy axis. The shapes of the
barber pole elements 192a, 192b, 192c, 192d, 192e and the AMR
element segments 194a, 194b, 194c, 194d will be more important in
this arrangement, however. That is, the edges of these structures
will have to be angled to provide the desired current
direction.
[0077] FIG. 13 is a flowchart illustrating a method 210 for
fabricating an AMR sensor having a segmented AMR element in
accordance with an embodiment. A plurality of metallic elements are
formed on a first layer to serve as barber pole elements for the
AMR sensor (block 212). A plurality of separate AMR element
segments are provided on a second layer (block 214). Conductive
coupling is provided between the plurality of metallic elements and
the plurality of AMR element segments so that a current applied to
the AMR sensor will flow through the plurality of metallic elements
and the plurality of AMR element segments in an alternating fashion
during sensor operation. In different embodiments, the metallic
elements may be formed either before or after the AMR element
segments. In some embodiments, the first layer and the second layer
may be separated from one another by at least one dielectric layer.
In these embodiments, via connections may be used to provide the
conductive coupling between the elements. In other embodiments, the
conductive coupling may be provided by forming the plurality of
metallic elements and the plurality of AMR element segments in an
abutting, conductive relationship to one another.
[0078] In some embodiments, the via connections that are used to
provide the conductive coupling between the elements are arranged
in groups having an orientation that supports current flow at a
desired angle within the AMR element segments, during sensor
operation. The angle may be, for example, an angle of 45 degrees
(or approximately 45 degrees) with respect to an easy angle of the
AMR element segments (although other angles may be used in other
implementations). The via connections will typically be formed
after the formation of the plurality of metallic elements and the
formation of the plurality of AMR element segments. In one
implementation, for example, the plurality of metallic elements may
first be formed on an ILD layer. One or more other dielectric
layers may then be deposited over the plurality of metallic
elements. The AMR element segments may then be formed over the
intervening dielectric layer(s). The via connections may then be
formed to conductively couple the metallic elements to the AMR
element segments. Techniques for forming via connections in desired
locations are well known in the art. In at least one
implementation, after the metallic elements have been conductively
coupled to the AMR element segments, a passivation layer may be
applied over the AMR sensor to protect the sensor from external
environmental conditions.
[0079] In the discussion above, various exemplary embodiments have
been described. It will be apparent to those of ordinary skill in
the art that modifications and variations may be made to these
exemplary embodiments without departing from the spirit and scope
of the invention. These modifications and variations are considered
to be within the purview and scope of the invention and the
appended claims. It will also be apparent to those of ordinary
skill in the art that the disclosed embodiments, although
different, are not necessarily mutually exclusive. That is, one or
more features, structures, or characteristics described herein in
connection with one embodiment may be incorporated into one or more
other embodiments to form new embodiments without departing from
the spirit and scope of the invention. Similarly, the location or
arrangement of individual elements within each disclosed embodiment
may be modified without departing from the spirit and scope of the
invention. All publications and references cited herein are
expressly incorporated herein by reference in their entirety.
* * * * *