U.S. patent application number 12/835768 was filed with the patent office on 2011-01-20 for semiconductor device and method.
This patent application is currently assigned to NXP B.V.. Invention is credited to Matthias Merz, Youri Victorovitch Ponomarev, Marcus Johannes Henricus van Dal.
Application Number | 20110012211 12/835768 |
Document ID | / |
Family ID | 41506471 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110012211 |
Kind Code |
A1 |
Merz; Matthias ; et
al. |
January 20, 2011 |
SEMICONDUCTOR DEVICE AND METHOD
Abstract
Disclosed is a semiconductor device comprising a stack of
patterned metal layers (12) separated by dielectric layers (14),
said stack comprising a first conductive support structure (20) and
a second conductive support structure (21) and a cavity (42) in
which an inertial mass element (22) comprising at least one metal
portion is conductively coupled to the first support structure and
the second support structure by respective conductive connection
portions (24), at least one of said conductive connection portions
being designed to break upon the inertial mass element being
exposed to an acceleration force exceeding a threshold defined by
the dimensions of the conductive connection portions. A method of
manufacturing such a semiconductor device is also disclosed.
Inventors: |
Merz; Matthias; (Leuven,
BE) ; Ponomarev; Youri Victorovitch; (Leuven, BE)
; van Dal; Marcus Johannes Henricus; (Heverlee,
BE) |
Correspondence
Address: |
NXP, B.V.;NXP INTELLECTUAL PROPERTY & LICENSING
M/S41-SJ, 1109 MCKAY DRIVE
SAN JOSE
CA
95131
US
|
Assignee: |
NXP B.V.
Eindhoven
NL
|
Family ID: |
41506471 |
Appl. No.: |
12/835768 |
Filed: |
July 14, 2010 |
Current U.S.
Class: |
257/415 ;
257/E21.002; 257/E29.324; 438/50 |
Current CPC
Class: |
B81B 2203/0315 20130101;
H01L 21/768 20130101; B81C 1/00246 20130101; G01P 15/0802 20130101;
H01L 23/564 20130101; B81B 2201/0235 20130101; B81C 2201/013
20130101; G01P 2015/0877 20130101; B81B 2207/015 20130101; B81C
2203/0714 20130101; B81B 7/0006 20130101; H01L 23/5226 20130101;
H01L 23/528 20130101; B81C 2203/0136 20130101; G01P 2015/0862
20130101; H01L 23/5256 20130101; G01P 15/06 20130101; B81C 99/005
20130101 |
Class at
Publication: |
257/415 ; 438/50;
257/E29.324; 257/E21.002 |
International
Class: |
H01L 29/84 20060101
H01L029/84; H01L 21/02 20060101 H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2009 |
EP |
09165533.2 |
Claims
1. A semiconductor device comprising: a stack of patterned metal
layers separated by dielectric layers, said stack comprising: a
first conductive support structure and a second conductive support
structure; and a cavity in which an inertial mass element
comprising at least one metal portion is conductively coupled to
the first support structure and the second support structure by
respective conductive connection portions having dimensions, at
least one of said conductive connection portions being designed to
break upon the inertial mass element being exposed to an
acceleration force exceeding a threshold defined by the dimensions
of the conductive connection portions.
2. The semiconductor device of claim 1, further comprising a
detector for detecting a disruption in said conductive coupling of
the metal portion and the first support structure and the second
support structure.
3. The semiconductor device of claim 1, wherein the respective
conductive connection portions are metal portions from the same
metal layer as the metal portion of the inertial mass element,
wherein at least one of the respective conductive connection
portions has at least one of a reduced width and a reduced
thickness compared to the metal portion of the inertial mass
element.
4. The semiconductor device of claim 1, wherein the inertial mass
element has a plurality of perforations extending through the
inertial mass element.
5. The semiconductor device of claim 1, wherein one of the metal
layers of the stack below the inertial mass element comprises a
first further metal portion extending from the first to the second
conductive support structure and a second further metal portion
extending from the second to the first conductive support
structure, said first and said second further metal portions being
separated from each other by a gap preventing said further metal
portions becoming conductively connected, said first and said
second further metal portions defining an etch barrier for
preventing formation of said cavity beyond said further metal
portions.
6. The semiconductor device of claim 1, wherein the inertial mass
element comprises a stack of metal layer portions separated by
dielectric layer portions, each of said dielectric layer portions
comprising a plurality of vias for conductively interconnecting the
metal layer portions.
7. The semiconductor device of claim 1, wherein the metal portion
of the inertial mass element is coupled to respective metal
portions of the first and second conductive support structures,
said respective metal portions belonging to a different metal layer
of the stack than the metal portion of the inertial mass element,
and wherein each of the respective conductive connection portions
comprises at least one via
8. The semiconductor device of claim 7, wherein the inertial mass
element is sandwiched between the metal portion of the first
conductive support structure and the metal portion of the second
conductive support structure.
9. The semiconductor device of claim 7, wherein the inertial mass
element is suspended from the respective metal portions of the
first and second conductive support structures by the respective
conductive connection portions.
10. The semiconductor device of claim 1, wherein the inertial mass
element extends in a lateral direction, and wherein the respective
conductive connection portions are connected to the same lateral
end portion of the inertial mass element such that the inertial
mass element acts as a lever.
11. The semiconductor device of claim 10, wherein one of said
conductive connection portions is a metal portion and the other of
said conductive connections portions comprises at least one
via.
12. The semiconductor device of claim 1, wherein the stack further
comprises a perforated metal portion extending over the inertial
mass element and at least partially extending over the first and
the second conductive support structures.
13. The semiconductor device of claim 1, wherein the stack
comprises a plurality of cavities each comprising an inertial mass
element conductively coupled to a first conductive support
structure and a second conductive support structure by respective
conductive connection portions, wherein at least one of the
conductive connection portions in each cavity is designed to break
upon the inertial mass element being exposed to an acceleration
force exceeding a threshold that is unique to that cavity.
14. A method of manufacturing a semiconductor device, comprising:
forming a stack of patterned metal layers separated by dielectric
layers, said stack comprising a first conductive support structure
and a second conductive support structure and an inertial mass
element comprising at least one metal portion conductively coupled
to the first support structure and the second support structure by
respective conductive connection portions each having dimensions,
at least one of said conductive connection portions being designed
to break upon the inertial mass element being exposed to an
acceleration force exceeding a threshold defined by the dimensions
of the conductive connection portions; forming a passivation layer
over said stack; selectively removing the passivation layer over an
area comprising the inertial mass element to form an exposed area;
and etching the exposed area to form a cavity around the inertial
mass element.
15. The method of claim 14, wherein said stack comprises a
perforated metal portion extending over the inertial mass element
and at least partially extending over the first and second
conductive support structures, wherein said etching step is
performed through said perforations.
Description
[0001] This application claims the priority under 35 U.S.C. .sctn.
119 of European patent application no. 09165533.2, filed on Jul.
15, 2009, the contents of which are incorporated by reference
herein.
FIELD OF INVENTION
[0002] The present invention relates to a semiconductor device
comprising a stack of patterned metal layers separated by
dielectric layers.
[0003] The present invention further relates to a method of
manufacturing such a semiconductor device.
BACKGROUND OF THE INVENTION
[0004] Nowadays, semiconductor devices such as integrated circuits
(ICs) routinely comprise patterned metallization layers for
interconnecting circuit elements, e.g. transistor terminals in the
substrate or to provide external access, e.g. bond pads, to the
circuit elements that are embedded in the semiconductor device.
Typically, the metallization layers are formed by stacking and
patterning dielectric layers and metal layers to obtain the
required interconnections. The dielectric and metal layers
themselves may contain sub-layers. The dielectric layers typically
comprise vias to conductively connect metal portions in the
different metal layers with each other.
[0005] Typically, significant efforts are made to ensure that
defective semiconductor devices are removed from a batch of
manufactured semiconductor devices to avoid field returns of such
devices as much as possible. Field returns inconvenience the
customer, and can lead to a loss of business because of the
customer losing faith in the product. Nevertheless, it is very
difficult to capture all defective semiconductor devices such that
it cannot be avoided that some defective devices enter the market.
On the other hand, a returned faulty device may have entered the
market functioning correctly, where it is possible that the fault
has developed through misuse of the semiconductor device, e.g. by
the customer exposing the device to excessive mechanical impacts.
Obviously, in such a case, the manufacturer cannot be held
responsible for the failure of the device.
[0006] It is difficult to establish why a semiconductor device
returned from the field has failed. Re-engineering the device to
determine the cause of failure is not always successful and is
cost-prohibitive for single devices. It is possible to embed a
micro-electromechanical sensor (MEMS) device in the metallization
stack of the semiconductor device to monitor the acceleration
forces to which the device has been subjected with such forces
exceeding certain threshold values being indicative of the device
having been subjected to sudden impacts. This approach has the
drawback that active monitoring of the MEMS sensor is required
during the lifetime of the semiconductor device, which adds to the
energy consumption of the device as well as to its cost because
some memory element and logic circuitry must be provided for
continuous sensor read out and to store the maximum acceleration
force to which the MEMS device has been exposed.
SUMMARY OF THE INVENTION
[0007] The present invention seeks to provide a semiconductor
device for which exposure to mechanical shocks can be more easily
detected.
[0008] The present invention further seeks to provide a method of
manufacturing such a semiconductor device.
[0009] According to a first aspect of the present invention, there
is provided a semiconductor device comprising a stack of patterned
metal layers separated by dielectric layers, said stack comprising
a first conductive support structure and a second conductive
support structure; and a cavity in which an inertial mass element
comprising at least one metal portion is conductively coupled to
the first support structure and the second support structure by
respective conductive connection portions, at least one of said
conductive connection portions being designed to break upon the
inertial mass element being exposed to an acceleration force
exceeding a threshold defined by the dimensions of the conductive
connection portions.
[0010] Hence, the present invention provides a mechanical fuse-type
shock sensor where the fuse element is formed by at least one of
the connection portions that connect the inertial mass element to
the conductive support structures. Due to the fact that the
inertial mass element is surrounded by a cavity, the acceleration
forces experienced by the inertial mass element cause the formation
of counter force on the connection portions. At least one of the
connection portions may be dimensioned such that the counter
portion material loses its structural integrity, i.e. breaks, upon
this counter force exceeding a certain value. Hence, the
dimensioning of the connection portions may be used to set the
acceleration force value at which the connection portion breaks.
This has the advantage that no permanent monitoring of the sensor
is required. Since the inertial mass element and the connection
portions define a conductive path between the first and second
conductive support structures, upon return of the device it may
simply be established if this conductive path is still intact, e.g.
by measuring the resistance of this path.
[0011] The first and second conductive support structures may be
externally accessible, e.g. connected to contact pads or pins of
the electronic device in order to establish if this conductive path
is still intact. Alternatively, the electronic device may further
comprise a detector for detecting a disruption in said conductive
coupling. This has advantage that the pin count of the
semiconductor device may be reduced.
[0012] In an embodiment, the respective conductive connection
portions are metal portions from the same metal layer as the metal
portion of the inertial mass element, wherein at least one of the
respective conductive connection portions has a reduced width
and/or thickness compared to the metal portion of the inertial mass
element. In case of the conductive portion(s) having a reduced
thickness, this may be established by selectively exposing the
appropriate portion(s) to a selective etching step. A reduced width
has the advantage that no additional processing steps are required
because this may be achieved by the provision of an appropriate
metal patterning mask.
[0013] In a further embodiment, the inertial mass element comprises
a plurality of perforations extending through the inertial mass
element. This has the advantage that the formation of the cavity
can be better controlled because at least part of the etchant for
forming the cavity can penetrate the stack through these
perforations.
[0014] Advantageously, one of the metal layers of the stack below
the inertial mass element further comprises a first further metal
portion extending from the first to the second conductive support
structure and a second further metal portion extending from the
second to the first conductive support structure, said first and
second further metal portions being separated from each other by a
gap preventing said further metal portions becoming conductively
connected, said first and second further metal portions defining an
etch barrier for preventing the formation of said cavity extending
beyond said further metal portions. This prevents the cavity from
extending into the stack too deeply, thus protecting the structural
integrity of the stack in general and the first and second
conductive support structures in particular.
[0015] It is also advantageous if the stack further comprises a
perforated metal portion extending over the inertial mass element
and at least partially extending over the first and second
conductive support structures. The presence of such a perforated
metal portion allows capping of the shock sensor cavity, e.g. by
deposition of SiN, SiO2 or another metal layer. The advantage of
using a perforated metal portion rather than a perforated
passivation layer is that the perforations in the metal typically
can be kept smaller, such that these perforations are rapidly
sealed by the sealant, thus reducing the amount of sealant
contaminating the cavity.
[0016] In an embodiment, the inertial mass element comprises a
stack of metal layer portions separated by dielectric layer
portions, each of said dielectric layer portions comprising a
plurality of vias for conductively interconnecting the metal layer
portions. This increases the weight of the inertial mass element,
such that the fracturing of the conductive connection portions can
be more easily achieved.
[0017] The metal portion of the inertial mass element may be
coupled to respective metal portions of the first and second
conductive support structures, said respective metal portions
belonging to a different metal layer of the stack than the metal
portion of the inertial mass element, and wherein each of the
respective conductive connection portions comprises at least one
via. In this embodiment, the support structures are vertically
displaced compared to the metal portion of the inertial mass
element to which the vias are connected. This overcomes a potential
problem with shock sensors in which the support structures are
laterally displaced with respect to the inertial mass element,
where elastically deformable conductive connection portions can
deform to such an extent that the inertial mass element is
displaced such that it becomes supported by the cavity wall, in
which case the conductive connection portions may fracture at an
inaccurate force or may not fracture at all.
[0018] In an embodiment, the inertial mass element is sandwiched
between the metal portion of the first conductive support structure
and the metal portion of the second conductive support structure.
This shock sensor is particularly suitable for detecting
acceleration forces having a substantial lateral (horizontal)
component.
[0019] In an alternative embodiment, the inertial mass element is
suspended from the respective metal portions of the first and
second conductive support structures by the respective conductive
connection portions. This shock sensor is particularly suitable for
detecting acceleration forces having a substantial longitudinal
(vertical) component.
[0020] The inertial mass element may extend in a lateral direction,
and wherein the respective conductive connection portions are
connected to the same lateral end portion of the inertial mass
element such that the inertial mass element acts as a lever. This
has the advantage that smaller forces are required to fracture at
least one of the conductive coupling elements.
[0021] In an embodiment, one of said conductive connection portions
is a metal portion and the other of said conductive connections
portions comprises at least one via. This has the advantage that
the shock sensor is sensitive to acceleration forces in both the
lateral and the vertical direction.
[0022] Advantageously, the stack comprises a plurality of cavities
each comprising an inertial mass element conductively coupled to a
first support structure and a second support structure by
respective conductive connection portions, wherein at least one of
the conductive connection portions in each cavity is designed to
break upon the inertial mass element being exposed to an
acceleration force exceeding a threshold that is unique to that
cavity. This has the advantage that the acceleration force to which
the electronic device has been subjected can be more accurately
determined.
[0023] According to another aspect of the present invention, there
is provided a method of manufacturing a semiconductor device,
comprising forming a stack of patterned metal layers separated by
dielectric layers, said stack comprising a first conductive support
structure and a second conductive support structure and an inertial
mass element comprising at least one metal portion conductively
coupled to the first support structure and the second support
structure by respective conductive connection portions, at least
one of said conductive connection portions being designed to break
upon the inertial mass element being exposed to an acceleration
force exceeding a threshold defined by the dimensions of the
conductive connection portions; forming a passivation layer over
said stack; selectively removing the passivation layer over the
area comprising the inertial mass element; and etching the exposed
area to form a cavity around the inertial mass element. This method
has the advantage that it can easily be realized in existing
semiconductor manufacturing processes, in particular CMOS
processes. Preferably, said stack comprises a perforated metal
portion extending over the inertial mass element and at least
partially extending over the first and second conductive support
structures, wherein said etching step is performed through said
perforations. As previously explained, this facilitates the
deposition of a capping layer to seal the cavity without
significantly contaminating the cavity in the sealing step.
BRIEF DESCRIPTION OF THE EMBODIMENTS
[0024] Embodiments of the invention are described in more detail
and by way of non-limiting examples with reference to the
accompanying drawings, wherein
[0025] FIG. 1 schematically depicts an example embodiment of the
method of the present invention;
[0026] FIG. 2 schematically depicts an aspect of an electronic
device in accordance with an embodiment of the present
invention;
[0027] FIG. 3 schematically depicts an aspect of an electronic
device in accordance with another embodiment of the present
invention;
[0028] FIGS. 4-7 schematically depict various further embodiments
of an electronic device of the present invention;
[0029] FIG. 8 schematically depicts an aspect of an electronic
device in accordance with yet another embodiment of the present
invention;
[0030] FIGS. 9-12 schematically depict various further embodiments
of an electronic device of the present invention;
[0031] FIGS. 13 and 14 schematically depict the operation principle
of respective parts of yet further embodiments of the electronic
device of the present invention; and
[0032] FIG. 15 schematically depicts another example embodiment of
the method of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0033] It should be understood that the Figures are merely
schematic and are not drawn to scale. It should also be understood
that the same reference numerals are used throughout the Figures to
indicate the same or similar parts. In the following detailed
description, the principles of the present invention will be
explained in further detail using complementary metal oxide silicon
(CMOS) devices and processes. CMOS has been chosen because it is
the most commonly used semiconductor technology. It is pointed out
that this choice has been made by way of non-limiting example only
and that the present invention may be applied in any suitable
semiconductor technology, e.g. silicon-on-insulator and SiGe
technologies.
[0034] FIG. 1 depicts the main steps for a CMOS compatible
manufacturing process of an electronic device comprising a
fuse-like passive shock sensor. As shown in step (a), on a
substrate 10, a stack of patterned metal layers 12 separated by
dielectric layers 14 is provided. In FIG. 1, an electronic device
having five metal layers is shown by way of non-limiting example
only. The device may have any suitable number of metal layers. The
dielectric layers 14 in between the metal layers 12 comprise vias
16 for conductively connecting vertically displaced metal layer
portions. Such via-comprising dielectric layers 14 will also be
referred to as via layers. Further via layers, e.g. between the
bottom metal layer 12 and the substrate 10 may also be
provided.
[0035] Each metal layer 12 and each dielectric layer 14 is depicted
as a single layer in FIG. 1 for the sake of clarity only. It should
be appreciated that such layers may consist of a number of stacked
sub-layers, for instance in a CMOS 14 process, stacks of Ti, TiN,
AlCu, TiN may be used to define a single metal layer in the
metallization stack. Similarly, it will be apparent that the vias
16 may be formed from more than a single material. For instance, in
the aforementioned CMOS 14 technology, a via 16 may be formed by a
TiN liner and a W plug. Other semiconductor processes may use
different materials, e.g. Cu for the metal layers 12 and vias
16.
[0036] Each of the dielectric layers 14 may also comprise more than
a single layer. For instance, such a dielectric layer may be a
stack comprising FSG (fluorosilicate glass), SiO.sub.2 and HDP
oxide (High Density Plasma) any other suitable dielectric material
combination. Other suitable materials may also be used. In step
(a), a cross-section of a partially processed semiconductor device
structure is shown in which the deposition of the metallization
stack has been completed. This has not been explained in further
detail for reasons of brevity because this structure may be
obtained using existing processing steps. The metallization stack
typically comprises a plurality of interconnect structures for
interconnecting circuit elements, e.g. transistor terminals, in the
substrate 10 or for connecting such circuit elements to external
contacts, e.g. bond pads or pins, of the semiconductor device, e.g.
chip.
[0037] The shown cross-section comprises structures for a shock
sensor on the left and a conventional bond pad 30 on the right. The
entire die is capped by layers of oxide and nitride, the so-called
passivation stack 18 or scratch protection, which protects the chip
from external influences such as humidity or mechanical damage,
e.g. scratches. The shock sensor is implemented as an inertial mass
element 22 suspended by conductive connecting portions 24, which
are connected to support structures 20 and 21 in FIG. 1 (comprising
all of the metal layers 12 and the via layers 14 of the
metallization stack). It is emphasized that this is shown by way of
non-limiting example only; it should be understood that the support
structures 20 and 21 may be formed using only selected layers of
the metallization stack as will be explained in more detail later.
In FIG. 1, the inertial mass element 22 is formed as a patterned
metal portion of the metallization stack. The conductive connection
portions 24 will have an elastic modulus defined by the materials
chosen to form these portions, which in FIG. 1 are typically formed
as part of the metal layer 12 to which they belong. Because of this
elastic modulus, the conductive connection portions 24 act as
springs when the inertial mass element 22 is suspended in air, as
will be explained in more detail below.
[0038] In FIG. 1, the conductive connection portions 24 are
recessed with respect to the surrounding metal layer. This may be
achieved by subjecting these portions to an additional etching step
during the formation of the metallization stack. For instance, in
case of multi-layered conductive connection portions 24, the metal
stack of the portions can be reduced, e.g. etching away the top TiN
and AlCu metal layer, leaving only a Ti/TiN stack. An advantage of
this approach is that such a thin stack breaks more easily compared
to a metal stack having its full thickness, thus allowing a
reduction of the size of the inertial mass to achieve the same
detection characteristics, i.e. the detection of the same
acceleration force threshold being exceeded, which translates to a
reduction in overall sensor size and cost.
[0039] Alternatively, the conductive connection portions 24 may
consist of relatively narrow lines involving the same metal stack
as the inertial mass element 22. In this embodiment, the entire
shock sensor can be fully realized using conventional metallization
stack processing followed by one additional process step.
[0040] In order to create a void or cavity around the inertial mass
element 22, the passivation layer 18 is removed from over the
inertial mass element 22 by means of a conventional passivation
etch, e.g. a bond pad opening etch as shown in step (b). Openings
40 are shown over the inertial mass element 22 and the bond pad 30
by way of non-limiting example only.
[0041] The only step required in addition to conventional back end
processing steps is the step in which the inertial mass element 22
is released from the surrounding dielectric 14 (in steps (b) and
(c), the dielectric layers 14 are shown as a single structure for
reasons of clarity only), which for instance may be implemented by
means of an isotropic wet etch or HF (hydrofluoric acid) vapor etch
for example. This is shown in step (c), in which the etching step
has resulted in the inertial mass element 22 being suspended in a
cavity 42. It is important that the etchant removes the dielectric
materials but does not attack the conductive structures including
inertial mass element 22 and the conductive connection portions 24
such that a `free floating` inertial mass element 22 is
obtained.
[0042] As shown in FIG. 1(c), the dielectric etching step can
result in an under etch of the support structures 20, 21 to which
the conductive connection portions 24 are connected. This however
is not a cause for concern because these structures 20, 21 are
stabilized by the lower via layers 16 and metal layers 12. The
under etch at bond pads 30 should not be critical for the same
reason. However, in order to avoid potential problems with the
structural integrity of the bond pads 30, the bond pad openings 40
may be protected using an additional mask (not shown) during the
release etch of the inertial mass element 22.
[0043] The principle of the fuse-like shock sensor of the present
invention is now explained in more detail. The conductive
connection portions 24 of the shock sensor are dimensioned to break
at a critical force F.sub.c, exerted by the inertial mass element
22 having a mass m. In accordance with Newton's laws, F=m.a, such
that the critical force Fc=F when acceleration a reaches the
critical value. Depending on the material properties the conductive
connection portions 24, the dimensions of these elements, e.g.
thickness, width, number of conductive connection portions 24, mass
of the inertial mass element 22 and so on, may be chosen by design
to predefine the critical value of the acceleration according to
the following formula for defining the fracture force of a single
beam:
Fx=S*W*H.sup.2/(6*L)
[0044] Wherein L is the beam length, W is the beam width, H is the
beam height and S fracture strength. From F=m.a, the critical
acceleration a at which n beams having a combined mass M fracture
may be expressed as follows:
a=n*S*W*H.sup.2/(6*L*m)
[0045] Since the acceleration to which the inertial mass element 22
is subjected is directly related to an impact force, e.g. shock,
the dimensions of the conductive connection portions 24 may be
chosen such that the inertial mass element is (partially) released
by breaking at least one of the conductive connection portions 24
when the acceleration has reached a value that is indicative of the
electronic device having been subjected to an impact expected to
damage the device.
[0046] The conductive connection portions 24 and the inertial mass
element 22 define a conductive path between the first conductive
support structure 20 and the second conductive support structure
21. In order to detect whether this conductive path is still
intact, the electronic device may further comprise a detection
circuit (not shown) connected to the first conductive support
structure 20 and the second conductive support structure 21 for
measuring the conductivity or resistance of the conductive path.
Since such a detection circuit may be implemented by the skilled
person using routine skill, this circuit will not be further
explained for reasons of brevity only.
[0047] In an embodiment, the detection circuit is coupled to a test
arrangement such as a IEEE 1149.1 or IEEE 1500 compliant test
access port, which allows investigation of the shock sensor by
re-using test facilities that are already present in the electronic
device. This for instance may reduce the pin count of the
electronic device. Alternatively, the detection circuit may be
connected to dedicated bond pads for external access.
Alternatively, the detection circuit may be connected to a wireless
transceiver for allowing wireless access to the detection circuit.
In yet another embodiment, the first conductive support structure
20 and the second conductive support structure 21 are connected to
dedicated bond pads such that the detection circuit may be external
to the electronic device. Other suitable detection arrangements
will be apparent to the skilled person.
[0048] FIG. 2 schematically depicts a top view of the shock sensor
of FIG. 1, in which the inertial mass elements 22 is fixed to the
conductive connection portions 24, which are attached to the first
conductive support structure 20 and the second conductive support
structure 21. Perforations 23, which may be defined in the mask
used for etching the inertial mass element 22, are present in the
inertial mass element 22 to facilitate the release of the inertial
mass element 22 from the surrounding dielectric 14. The
perforations 23 provide better access to the dielectric layers 14
underneath the inertial mass element 22 during the etching step of
FIG. 1(c), thereby allowing a reduction of the duration of this
etching step, which reduces the under etching of the first
conductive support structure 20 and the second conductive support
structure 21, thereby improving the structural integrity of these
support elements.
[0049] In FIG. 2, the support frame formed by the first conductive
support structure 20 and the second conductive support structure 21
almost fully encloses the inertial mass element 22, thus reducing
lateral etch in the release etching step and restricting the size
of the cavity 42 to the area of the shock sensor. The frame must be
interrupted as indicated by gap 25 such that it does not form a
conductive path in parallel with the conductive path formed by the
conductive connection portions 24 and the inertial mass element 22.
Otherwise the fracture of at least one of the conductive connection
portions 24 cannot be detected by electrical measurements. FIG. 3
depicts a simplified support structure in which the first
conductive support structure 20 and the second conductive support
structure 21 are formed by respective pillars, one on either side
of the inertial mass element 22. Additional support pillars may be
provided if required, e.g. if the inertial mass element 22 is
suspended by more than two conductive connection portions 24.
[0050] In an embodiment as shown in FIG. 4, an additional etch
barrier formed in a metal layer 12 below the inertial mass element
22 may be provided. The additional etch barrier in FIG. 4 is formed
by two non-contacting metal portions 26, which extend from the
first conductive support structure 20 to the second conductive
support structure 21 and vice versa. A gap 27 separates the two
metal portions 26 to ensure that these portions do not provide an
additional conductive path parallel to the conductive path of the
fuse-like shock sensor. By the provision of this additional etch
barrier, the depth of the cavity 42 can be limited and the
potential under etch of the entire support structures can be
avoided, thus preventing the lift-off of the shock sensor.
[0051] In the above embodiments, the inertial mass element 22 is
formed of a single metal layer 12 (which may comprise a stack of
sub-layers as previously explained). As previously explained, since
the force at which the conductive connection portions 24 fracture
is correlated to the mass m of the inertial mass element 22,
relatively large area metal portions may be required in case of
limited thickness of the metal layer 12 from which the inertial
mass element 22 is formed, which may increase the footprint of the
electronic device.
[0052] This may be overcome by the embodiment of the electronic
device of the present invention as shown in FIG. 5, in which the
inertial mass element 22 is formed by a plurality of metal layer
portions 12 interconnected by vias 16 to increase the mass M of the
inertial mass element 22. In FIG. 5, the inertial mass element 22
comprises three metal layers 12 interconnected by two via layers by
way of non-limiting example only. Any suitable number of metal
layers may be chosen.
[0053] Any metal layer of the inertial mass element 22 may be
connected to the first conductive support structure 20 and the
second conductive support structure 21 via the conductive
connection portions 24. In FIG. 5, the bottom metal layer of the
inertial mass element 22 is connected to the respective top metal
layers of the first conductive support structure 20 and the second
conductive support structure 21, in FIG. 6 the top metal layer of
the inertial mass element 22 is connected to the respective top
metal layers of the first conductive support structure 20 and the
second conductive support structure 21 and in FIG. 7 an
intermediate metal layer of the inertial mass element 22 is
connected to respective intermediate metal layers of the first
conductive support structure 20 and the second conductive support
structure 21.
[0054] The first conductive support structure 20 and the second
conductive support structure 21 may have the same heights or may
have different heights, i.e. the same or different number of
interconnected metal layers 12. The inertial mass element 22 may be
connected to metal portions of the first conductive support
structure 20 and the second conductive support structure 21 at the
same metal layer level or at different metal layer levels. Each
side of the inertial mass element 22 may be connected by more than
conductive connection portion 24 to the corresponding support
structure 20 or 21, and the respective conductive connection
portions 24 may be connected to different metal layers 12 of the
support structure 20 or 21.
[0055] It should be recognized that the different embodiments of
the electronic device as shown in FIGS. 5-7 may be realized using
conventional CMOS processing steps with the addition of the release
etching step as explained in more detail in FIG. 1. Because both
the metal layers 12 as well as the interconnect vias 16 between
adjacent metal layers 12 contribute to the overall mass of the
inertial mass element 14, it is preferable that the via density is
as possible to minimize the required area of the inertial mass
element 22. For instance, in a CMOS 14 technology using Al for the
metal layers 12 and W vias 16, the mass of a via layer is as high
as the mass of a metal layer 12 due to the high specific density of
tungsten.
[0056] FIG. 8 shows a top view of a part of a shock sensor in
accordance with the embodiments shown in FIGS. 5-7, in which the
inertial mass element 22 comprises the perforations 23 as well as
the vias 16. The perforations 23 are vertically aligned in the
various metal layers 12 of the inertial mass element to aid the
formation of the cavity 42 in the release etching step as
previously explained. The conductive connection portions 24 connect
the inertial mass element 22 to the conductive support structures
(not shown).
[0057] In the above embodiments, the conductive connection portions
24 are formed in one of the metal layers 12 of the metallization
stack of the electronic device of the present invention. This,
however may not always be suitable, for instance when the elastic
deformability of the conductive connection portions 24 exceeds the
gap size between the mass element 22 and the walls of the cavity
42. Upon acceleration of the inertial mass element 22, this elastic
deformability will elongate the conductive connection portions 24,
thereby allowing the inertial mass element 22 to contact the cavity
walls. This may prevent the conductive connection portions 24 from
fracturing or may cause the conductive connection portions 24 to
fracture at acceleration values that deviate from the predefined
critical acceleration such that the fuse-like shock sensor can
produce inaccurate readings.
[0058] This may be prevented by using different, e.g. more brittle
materials for the conductive connection portions 24, e.g. TiN, but
this has the disadvantage that additional process steps may be
required, which adds to the cost of the electronic device. In case
of such small gap sizes, another embodiment of the shock sensor of
the present invention as depicted in FIGS. 9-11 may be used. In
these embodiments, the conductive connection portions 24 are formed
of vias such that the respective metal layers of first and second
conductive support structures 20, 21 are vertically displaced with
respect to the metal layer of the inertial mass element 22 to which
they are connected via the conductive connection portions 24.
[0059] In FIG. 9, the first conductive support structure 20 has two
conductive pillars surrounding the inertial mass element 22. The
conductive support structure 20 further has a metal layer portion
12 that interconnects the aforementioned pillars, and which extends
over the inertial mass element 22. The inertial mass element 22 is
connected to this bridging metal portion 12 by a conductive
connection portion 24 comprising a plurality of vias. The second
conductive support structure 21 is located underneath the inertial
mass element 22, with the inertial mass element 22 being connected
to the top metal layer of the second conductive support structure
21 via a further plurality of vias such that the inertial mass
element 22 is suspended (sandwiched) between the first and second
conductive support structures 20, 21, with the conductive path for
detecting the fracturing of the shock sensor being formed by the
inertial mass element 22 and the vias connecting the inertial mass
element 22 to these support structures.
[0060] It is emphasized that for any of the embodiments in FIGS.
9-11, any suitable number of vias may connect the inertial mass
element 22 to one of the conductive support structures. In FIG. 9,
a plurality of vias is shown by way of non-limiting example only.
It should further be understood that the critical acceleration
force at which the sensor is released is defined by the number of
vias; more vias per conductive connection structure 24 implies a
higher critical acceleration force, via geometry, e.g. length and
cross section area, the mass of the inertial mass element 22, with
a higher mass translating into a smaller critical acceleration
force and the adhesion force of the interface between the via(s) of
the conductive connection portions 24 and the metal layer of the
inertial mass element 22. Also, it is pointed out that the
embodiments shown in FIGS. 9-11 may be realized using the
manufacturing method depicted in FIG. 1, such that these
embodiments may be realized in existing processing technologies
without modification of the processing steps apart from the
formation of the cavity 42 as previously explained.
[0061] By connecting the shock sensor of electronic device of the
present invention to its support frame using vias, an additional
advantage is that the sensor can be made sensitive to acceleration
forces having different directional components by design. For
instance, the shock sensor of FIG. 9, in which the inertial mass
element 22 is vertically sandwiched between the first conductive
support structure 20 and the second conductive support structure 21
is sensitive to in-plane acceleration forces as indicated by the
force vectors (arrows) labeled `F` in FIG. 9.
[0062] In FIG. 10, the inertial mass element 22 is suspended
(dangling) from the first conductive support structure 20 and the
second conductive support structure 21 such that the shock sensor
is sensitive to in-plane acceleration forced as well as an
acceleration in a downward vertical direction, i.e. towards the
plane of the substrate 10, as indicated by the arrows `F`.
[0063] In FIG. 11, the inertial mass element 22 is resting on the
first conductive support structure 20 and the second conductive
support structure 21 such that the shock sensor is sensitive to
in-plane acceleration forced as well as an acceleration in a upward
vertical direction, i.e. away from the plane of the substrate 10,
as indicated by the arrows `F`. In the embodiments shown in FIGS.
10 and 11, the conductive support structures 20, 21 each comprise
at least one metal layer that laterally protrudes into the cavity
42 such that the inertial mass element 22 may be suspended from
these protruding metal layers.
[0064] It will be clear to the skilled person that depending on the
number and arrangement of vias comprised in the conductive
connection portions 24, as well as on the overall sensor geometry
and rupture characteristics of the interface, the critical
acceleration values at which the inertial mass element 22 is
released may vary for different directions. In case this is
unwanted, care has to be taken in the sensor design stage to ensure
that the same release value for all three directions in space is
achieved.
[0065] In the thus far described embodiments of the electronic
device of the present invention, opposite ends of the inertial mass
element 22 are typically connected to the conductive support
structures 20, 21. This however is not essential for the present
invention, as is demonstrated in FIG. 12 in which the inertial mass
element 22 is connected to the first conductive support structure
20 and the second conductive support structure 21 by respective
vias at the same end portion of the inertial mass element 22 such
that the inertial mass element 22 acts as a lever. The inertial
mass element 22 is shown to have perforations to aid the formation
of the cavity 42 as previously explained by way of non-limiting
example.
[0066] Upon exposure of the inertial mass element 22 to an
acceleration force, the lever design amplifies the forces exerted
on the conductive connection portions 24, e.g. vias. This has the
advantage that for the inertial mass element 22 to release from its
support structures 20, 21, a smaller mass per unit force is
required. In other words, the lever design allows for a reduced
size inertial mass element 22, thereby reducing the overall size
and cost of the electronic device of the present invention.
[0067] Although the theory of how levers work is well-known, the
lever principle is briefly discussed in FIG. 13, in which the total
length of the inertial mass element 22 is defined by 1+d, with 1
being the lever length and d being the distance between the centers
of the support structures 20, 21. For 1>>d, the leverage
ration may be approximated by 1/2 d, with lever ratios of 100 and
more being readily achievable in most semiconductor technologies
such as CMOS. For instance, in existing CMOS 14 technologies, the
minimum distance between the centers of the first conductive
support structure 20 and the second conductive support structure 21
is 0.512 micron, which requires a length 1 of 102.4 micron to
achieve a lever ratio of 100.
[0068] As indicated in the pane of FIG. 13 labeled `a`, forces in
the y and z direction exceeding the critical acceleration force
will cause a release of the inertial mass element 22 as shown in
pane `b` for a force in the z-direction. The lever-based embodiment
of the present invention is not limited to the arrangement shown in
FIGS. 12 and 13 where the inertial mass element 22 is mounted on
the conductive support structures 20, 21 using vias. Exemplary
alternative embodiments are schematically depicted in FIG. 14.
[0069] In pane a, opposite sides of the metal layer of the inertial
mass element 22 are connected to respective metal layers of the
conductive support structures 20, 21 (not shown) from the same
metal layer of the metallization stack by conductive connection
portions 24 from this same metal layer, such that the lever is
released upon being exposed to forces exceeding the critical
acceleration in the z-direction (i.e. the vertical direction).
[0070] In pane b, the same side of the metal layer of the inertial
mass element 22 is connected to respective metal layers of the
conductive support structures 20, 21 from the same metal layer of
the metallization stack by conductive connection portions 24 from
this same metal layer, such that the lever is released upon being
exposed to forces exceeding the critical acceleration in the
y-direction (i.e. a horizontal direction perpendicular to the
length 1 of the lever).
[0071] In pane c, an inertial mass element 22 being connected to
the conductive support structures 20, 21 through a combination of a
via-based conductive connection portion 24 and a metal layer
portion-based conductive connection portion 24' is shown. In this
embodiment, the lever is released upon being exposed to forces
exceeding the critical acceleration in the z-direction.
[0072] In pane d, an alternative to the embodiment shown in FIG. 12
is depicted. In this alternative embodiment, the conductive support
structures 20, 21 are arranged in a row (e.g. running from front to
back) with a small gap in between the two structures. Vias 16 are
placed in a single line on top of the support structures 20, 21
thereby minimizing d (given by fixed VIA diameter) and maximize
overall leverage ratio for a given lever length 1. The lever-based
shock sensor in pane d is released upon being exposed to forces
exceeding the critical acceleration in the z-direction as well as
in the y-direction.
[0073] The embodiments shown in FIG. 14 are shown by way of
non-limiting example only. Other arrangements, e.g. in which the
inertial mass element 22 hangs suspended from at least one of the
conductive support structures 20, 21 are equally feasible. It is
further pointed out that different embodiments of the present
invention may be advantageously combined. For instance, the
embodiments shown in FIGS. 5-14 may be combined with the etch stop
formed by the metal portions 26 as shown in FIG. 4, and so on.
[0074] The electronic device of the present invention may further
comprise a plurality of the above described fuse-like shock
sensors, which may have been designed to fracture at different
critical acceleration forces to allow accurate determination of the
force of the impact to which the electronic device has been
exposed. The plurality of fuse-like shock sensors may comprise
sensors according to the same embodiment of the present invention
in which the dimensions of the inertial mass element 22 and the
conductive connection portions 24 have been varied, as well as one
or more sensors of different embodiments of the present
invention.
[0075] FIG. 15 shows another embodiment of a method of
manufacturing an electronic device of the present invention, in
which a top metal layer portion 44 is provided over the cavity 42
to be formed. The top metal portion 44 comprises perforations 23 to
facilitate the packaging of the electronic device by sealing the
cavity 42 with a capping layer following its formation.
[0076] A known way of controlling the contamination of an etched
cavity in a capping process is by patterning the passivation stack
over the area to be etched, thereby forming a plurality of
(equidistant) openings, i.e. release holes, in the passivation
stack to provide limited access to the area to be etched. Such
release holes must be kept small enough to avoid that upon
re-sealing the electronic device, sealant enters the etched cavity
42, because this can leave the shock sensor unreliable or even
inoperable. Typically, release holes having a diameter of 1 micron
or less are acceptable if the capping layer deposition process is
highly non-conformal, e.g. a sputter process. However, such hole
sizes may not be easily achievable in a passivation layer without
the inclusion of additional process steps such as an additional
etching step. The etching step for opening the bond pads is
unsuitable for defining such perforations because this step
typically creates openings that are an order of a magnitude
larger.
[0077] For this reason, in step (a), the metallization stack of the
electronic device further comprises a top metal layer portion 44
over the cavity to be formed in which perforations 23 have been
provided. Such perforations may be defined in the etch step of this
metal portion, such that no additional processing steps are
required. The top metal layer portion 44, which at least partially
extends over the conductive support structures 20, 21, acts as a
capping structure for the cavity to be formed. As previously
explained, the top metal layer portion 44 may be a stacked layer
structure comprising a plurality of stacked sub-layers. Preferably,
no perforations 23 are provided in the parts of the top metal layer
portion 44 directly over the conductive connection portions 24
because any contamination of the conductive connection portions 24
portions by the sealant, i.e. the capping material 46, could alter
the critical acceleration at which the inertial mass element 22 is
released.
[0078] Upon exposing the top metal layer portion 44 (and the other
structures such as bond pad 30) by removing selective portions of
the passivation stack, thereby forming openings 40 as shown in step
(b), the perforations in the top metal layer portion 44 act as the
release holes for the release etching step in which the cavity 42
is formed, as shown in step (c). Next, in step (d), the openings 40
are sealed again using any suitable capping layer 46, e.g. a SiN,
SiO.sub.2 or metal layer, after which in step (e) the bond pads 30
are exposed again by selective removal of the capping layer 46 in
any suitable manner, thus creating opening 48. Alternatively, only
the shock sensor area is opened in step (b), in which case the bond
pads are only opened during step (e). It will be appreciated that
this embodiment is particularly suitable for packaging the
electronic device containing the shock sensor of the present
invention.
[0079] In summary, an electronic device comprising an embodiment of
the shock sensor of the present invention is capable of detecting
misuse of the electronic device without requiring continuous
monitoring of the electronic device. The electronic device be a
single chip or may comprise multiple components mounted on a
carrier such as a multi-chip module, system-in-package or printed
circuit board, in which at least one of the components may comprise
the shock sensor of the present invention. This shock sensor is
capable of monitoring the misuse of the electronic device as a
whole. Non-limiting examples of an electronic device of the present
invention include wireless communication devices such as mobile
phones and personal digital assistants, portable computers such as
laptops or notebooks, consumer electronics devices such as digital
cameras, MP3 players, digital radios and so on. The present
invention may be applied to any electronic device that can be
damaged by excessive impacts or mechanical shocks.
[0080] It should be noted that the above-mentioned embodiments
illustrate rather than limit the invention, and that those skilled
in the art will be able to design many alternative embodiments
without departing from the scope of the appended claims. In the
claims, any reference signs placed between parentheses shall not be
construed as limiting the claim. The word "comprising" does not
exclude the presence of elements or steps other than those listed
in a claim. The word "a" or "an" preceding an element does not
exclude the presence of a plurality of such elements. The invention
can be implemented by means of hardware comprising several distinct
elements. In the device claim enumerating several means, several of
these means can be embodied by one and the same item of hardware.
The mere fact that certain measures are recited in mutually
different dependent claims does not indicate that a combination of
these measures cannot be used to advantage.
* * * * *