U.S. patent application number 12/001567 was filed with the patent office on 2008-04-24 for mem switching device and method for making same.
This patent application is currently assigned to Cabot Microelectronics Corporation. Invention is credited to Heinz H. Busta.
Application Number | 20080093691 12/001567 |
Document ID | / |
Family ID | 34198897 |
Filed Date | 2008-04-24 |
United States Patent
Application |
20080093691 |
Kind Code |
A1 |
Busta; Heinz H. |
April 24, 2008 |
MEM switching device and method for making same
Abstract
A MEM device and method for fabricating a MEM device. A MEM
device comprising a lever mechanism residing along a substrate is
disclosed. A contact material is deposited on a first surface of
the lever mechanism. In one arrangement, the first surface is
disposed towards the substrate. A first contact region may be
deposited on the substrate. The first contact region attracts the
lever mechanism towards the substrate such that the contact
material becomes operationally coupled to a second contact region.
The MEM device may also comprise a first anchor portion and a
second anchor portion. The first and second anchor portions may be
integral to a top surface of the substrate. Aspects of the
invention are also particularly useful in providing an encapsulated
MEM switching device.
Inventors: |
Busta; Heinz H.; (Park
Ridge, IL) |
Correspondence
Address: |
STEVEN WESEMAN;ASSOCIATE GENERAL COUNSEL, I.P.
CABOT MICROELECTRONICS CORPORATION
870 NORTH COMMONS DRIVE
AURORA
IL
60504
US
|
Assignee: |
Cabot Microelectronics
Corporation
|
Family ID: |
34198897 |
Appl. No.: |
12/001567 |
Filed: |
December 12, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10689167 |
Oct 20, 2003 |
7317232 |
|
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12001567 |
Dec 12, 2007 |
|
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60420280 |
Oct 22, 2002 |
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60449994 |
Feb 25, 2003 |
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Current U.S.
Class: |
257/415 ;
257/E21.001; 257/E29.324; 438/51 |
Current CPC
Class: |
H01H 2001/0063 20130101;
H01H 2001/0089 20130101; H01H 1/0036 20130101; H01H 2001/0084
20130101 |
Class at
Publication: |
257/415 ;
438/051; 257/E29.324; 257/E21.001 |
International
Class: |
H01L 29/84 20060101
H01L029/84; H01L 21/50 20060101 H01L021/50 |
Claims
1. A MEM switching device comprising: (a) a rib enforced lever
mechanism residing along a surface of a substrate, said lever
mechanism having at least one anchor lever mechanism portion
extending from said surface; (b) a first contact region deposited
on said substrate, said first contact energized for attracting said
lever mechanism towards said substrate such that said lever
mechanism becomes electrically coupled to a third contact region;
and (c) a second contact region that pulls back said lever
mechanism from being electrically coupled to said third contact
region.
2. The invention of claim 1 wherein said rib enforced lever
mechanism comprises a rib that is integral to said lever
mechanism.
3. The invention of claim 2 wherein said rib comprises a conductive
layer.
4. The invention of claim 2 wherein said conductive layer comprises
Copper.
5. The invention of claim 3 wherein said conductive layer comprises
Diamond.
6. The invention of claim 3 wherein said conductive layer comprises
a conductive composition.
7. The invention of claim 1 wherein said switching device comprises
a planarized surface.
8. The invention of claim 5 wherein said planarized surface is
planarized by a Chemical Mechanical Planarization process.
9. The invention of claim 1 further comprising an integral
enclosure, said integral enclosure used to enclose said MEM
device.
10. The invention of claim 1 wherein said third contact region
comprises a first and a second micro-strip line.
11. A micro-machined structure for enclosing at least one MEM
device, said structure comprising: (a) a structure extending from a
substrate and at least partially enclosing said at least one MEM
device; and (b) a cover structure residing on a portion of said
substrate structure, wherein said micro-machined structure defines
at least one tortuous path.
12. The invention of claim 11 wherein said tortuous path provides
for a removal of material residing along said surface.
13. The invention of claim 11 further comprising a contact region,
said contact region provided on said cover substrate structure,
said contact region acting as a pull-back contact for a MEM device
residing on said substrate.
14. The invention of claim 13 wherein said contact region comprises
a shielding member, said shielding member preventing passage of
electromagnetic radiation.
15. A method of fabricating a micro-machined apparatus, said method
comprising the steps of: (a) providing a substrate; (b) fabricating
a substrate structure, said substrate structure extending from said
substrate; and (c) fabricating a cover substrate structure residing
on a portion of said substrate structure, said cover structure
defining at least one tortuous channel.
Description
RELATED CASES
[0001] The present patent application is a continuation of U.S.
patent application Ser. No. 10/689,167, filed on Oct. 20, 2003,
which is related to U.S. Provisional Patent Application Ser. Nos.
60/420,280 filed on Oct. 22, 2002, and 60/449,994 filed on Feb. 22,
2003, the full disclosures of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention is generally directed to a method and
apparatus for fabricating a micro-electro-mechanical (MEM) device.
More particularly, the present invention is generally directed to a
method and apparatus for providing an encapsulated MEM device.
Aspects of the invention are also particularly useful in providing
a MEM apparatus comprising a two arm lever mechanism having
increased rigidity. Such a lever mechanism may be used with a MEM
switch, relay, sensor, actuator, accelerometer, and other like MEM
device. Other aspects of the invention are also particularly useful
in providing a MEM apparatus comprising an abrasion resistive
contact that is preferably deposited along a contact area of the
MEM device. However, certain aspects of the invention may be
equally applicable in other scenarios as well.
DESCRIPTION OF RELATED TECHNOLOGY
[0003] Micro-electro-mechanical devices (MEM devices) generally
involve the integration of mechanical elements, actuators, sensors,
and electronics on a common substrate. Ordinarily, such integration
can occur through the use of micro-fabrication techniques. MEM
devices can range in size from as small as a few microns to as
large as a few millimeters. While the electronics that these MEM
devices utilize are fabricated using Integrated Circuit (IC)
process sequences (e.g., CMOS, Bipolar, or BiCMOS processes),
micro-mechanical components can be fabricated using compatible
"micro-machining" processes that selectively etch away portions of
materials deposited on a substrate. Alternatively, the
micro-machining process adds additional structural layers to form
mechanical and electromechanical devices.
[0004] MEM devices bring together silicon-based microelectronics
with micro-machining technology, thereby making possible the
realization of a complete system-on-a-single substrate. MEM devices
augment the computational ability of microelectronics with the
perception and control capabilities of microsensors and/or
microactuators. Examples of such electrical and mechanical
combinations are gyroscopes, accelerometers, micro-motors, and
sensors of micrometric size, all of which may need to be left free
to move after some type of encapsulation and/or packaging. MEM
devices may be used within digital to analog converters, air bag
sensors, logic, memory, microcontrollers, and video controllers.
Example applications of MEM devices are military electronics,
commercial electronics, automotive electronics, and
telecommunications.
[0005] MEM devices are essentially a technology used to create
micro-miniature mechanical devices (such devices can be
manufactured out of silicon or, alternatively, other materials).
Ordinarily, these MEM devices are designed to respond to external
stimuli. For example, where certain MEM devices are used for
sensing applications, they can be fabricated so as to respond to
the stimuli, and move (or actuate) mechanical structures. Known MEM
technology is being applied to accelerometers in automobile
airbags, pressure sensors, flow rate sensors, and other such like
applications. Micro-mechanical micro arrays have also been
developed for projection display applications. As will be discussed
with respect to FIG. 1, MEM devices may sometimes be based on
integrated circuit fabrication technologies such as those
technologies similar to CMOS, with the added ability to incorporate
moving and mechanical structures. Known MEM devices can typically
range in size from one micron to several hundreds microns.
[0006] Certain known problems exist with existing MEM devices. MEM
device are known to suffer from several types of problems. For
example, one such problem involves the fabrication of MEM devices
on top of a CMOS type device. An example of a known MEM device 10
is illustrated in FIG. 1. FIG. 1 illustrates a cantilever beam 12
designed over a CMOS device 16. As can be seen in FIG. 1, this MEM
10 includes a cantilevered beam 12 that generally follows the
contour 14 of the underlying CMOS device 16. Therefore, the design
and orientation of cantilever beam is not one that can be
customized based on the specifics of the application. Rather, the
cantilever beam shape will be generally dictated by the topology of
the substrate layers residing underneath the cantilever beam.
[0007] In addition, with cantilevers residing over a CMOS
topography, the shape of the cantilever will naturally be defined
by the underlying topography of the substrate unless it is
planarized before MEM fabrication. Consequently, such contoured
beams will have a tendency to possess a non-uniform intrinsic
stress distribution because of the device structure topography. In
addition, such non-uniform cantilevers have different zero-load
deflections.
[0008] One method that attempts to reduce these concerns with MEM
devices designed over CMOS has been to design the substrate such
that the MEM devices are located in a substrate location where no
CMOS processing takes place. However, isolating these MEM devices
to only a restricted substrate area can pose certain fabrication
issues. One such issue relates to limiting the number of MEM
devices per substrate. Isolating these MEM devices to a specific
substrate area can also place certain restrictions on the
applications for such a substrate.
[0009] There are other concerns arising from other known MEM
devices. For example, with other known MEM devices, such devices
often comprise a uniform or uni-planar cantilever beam. For
example, one such known problem that arises in the fabrication of
MEM devices from surface micromachining is that the cantilever does
not have enough rigidity to return to the "off" position. This
issue may be amplified where "stiction" occurs. Stiction usually
arises when surface adhesion forces are higher than the mechanical
restoring force of the micro-structure: the cantilever.
[0010] Stiction can also arise during the fabrication process. For
example, when a MEM device is removed from an aqueous solution
after wet etching of an underlying sacrificial layer, the liquid
meniscus formed on hydrophilic surfaces can pull the microstructure
towards the substrate. This pulling action results in what is known
in the art as stiction.
[0011] In use, stiction may be caused by capillary forces,
electrostatic attraction, and direct chemical bonding.
[0012] Another known approach to resolving the stiction issue
relates to applying an anti-stiction coating to the MEM device.
However, using anti-stiction coatings has other related issues. For
example, these known anti-stiction coating approaches eventually
degrade, particularly while the device is operating at high
temperatures. In addition, certain anti-stiction coatings also have
a limited service life.
[0013] MEM devices can find application as switches and relays in
RF and microwave communication circuit such as transmit/receive
switches, reconfigurable antennas, multiband switches, and signal
routers. These types of switching devices may also find application
in low frequency logic circuits. When a MEM device operates as a
switch, the signal circuit is directly coupled with the activation
circuit. In a MEM device operating as a relay, the two circuits are
decoupled. For frequencies below about 2 GHz, the switches and
relays are usually of a contact type. However, above 2 GHz, the
switches and relays can be indirect switches since at these
frequencies the impedance is rather small when coupling through a
thin insulator layer. The impedance is given by Z=1/2.pi.fC with f
the frequency of the signal and C the capacitance of the swith
contact.
[0014] Reliability issues often arise with such switches/relays.
For example, contacts having increased reliability should be
abrasion resistant. In addition, switches/relays having increased
reliability should have contacts that do not deform from micro-arcs
at high current densities, such as densities on the order of
1.times.10.sup.6 A/cm.sup.2. These switches/relays should also
operate at currents of up to 100 milli-Amps. For example, where a
MEM device has a relay contact area on the order of 20.times.20
.mu.m this corresponds to a current density of 2.5.times.10.sup.4
A/cm.sup.2. However, since the surface of the switch/relay contact
is not entirely smooth, local current densities at certain "hot"
spots can be significantly higher. Consequently, there is a general
need to provide a method and apparatus for reducing such current
hot spots and for providing a contact system that increases the
operating reliability of the switch/relay.
[0015] Another issue that is often faced by MEM device
manufacturers that affects product yields is the potential
contamination of MEM devices. For example, under ordinary
operation, MEM devices are often placed in operating environments
that have a certain amount of air-born contaminants, such as dust.
Consequently, as a result of the micron-size of typical MEM devices
(and therefore the micron-size movable components of such devices),
dust, various processing fluids, etchants, or other fluid and/or
air-born contaminants pose a threat to the efficient operation of
the MEM devices.
[0016] Another problem that may be associated with failure rates
relates to MEM lever mechanism beam rigidity. Consequently, there
may also be a general need for a MEM device having increased
rigidity. Based in part on these forgoing issues, there is,
therefore, a general need to be able to increase the production
yield of MEM devices deposited on a substrate. There is also a
general need to reduce the amount of contamination that a MEM
device may experience, either during device design, device
fabrication, device operation, device packaging, or otherwise.
There is also a general need to decrease the failure rate of a MEM
device caused in part by contamination, stiction, or other
operating concerns. These and other general needs should also be
met while fabricating a MEM device having uniform mechanical lever
stress for switching purposes.
SUMMARY
[0017] According to one exemplary arrangement, a MEM device
includes a lever mechanism residing along a substrate. A contact
material is deposited on a first surface of the lever mechanism.
The first surface is disposed towards the substrate. A first
contact region is deposited on the substrate. The first contact
region is energized to thereby attract the lever mechanism towards
the substrate such that the contact material becomes electrically
coupled to a second contact region.
[0018] According to another exemplary arrangement, a method of
fabricating a MEM device is provided. This method comprises the
steps of providing a lever mechanism along a substrate. The lever
mechanism is provided with a first contact material, the first
contact material provided along a surface of the lever mechanism. A
first contact layer is provided on the substrate, the first contact
layer capable of being energized so as to attract the lever
mechanism towards the substrate.
[0019] These as well as other advantages of various aspects of
applicant's present arrangements will become apparent to those of
ordinary skill in the art by reading the following detailed
description, with appropriate reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Exemplary arrangements described herein with reference to
the drawings, in which:
[0021] FIG. 1 illustrates a known cantilevered CMOS MEM device;
[0022] FIG. 2 provides a perspective view of a MEM device
fabricated according to one aspect of the present invention;
[0023] FIG. 3 illustrates a flow chart identifying certain
processing steps that may be used for fabricating the MEM device
illustrated in FIG. 2;
[0024] FIGS. 4-12 illustrate various processing steps for
fabricating the MEM device illustrated in FIG. 2;
[0025] FIGS. 13(a) and (b) illustrate alternative processing steps
for fabricating the MEM device illustrated in FIG. 2;
[0026] FIG. 14(a) illustrates a profile view of a two arm lever
mechanism fabricated according to one aspect of the present
invention;
[0027] FIG. 14(b) illustrates a profile view of a portion of a two
arm lever mechanism anchor fabricated according to one aspect of
the present invention;
[0028] FIGS. 15(a) and (b) illustrate alternative processing steps
for fabricating the MEM device illustrated in FIG. 2;
[0029] FIG. 16 illustrates a profile view of a two arm lever
mechanism fabricated according to an alternative aspect of the
present invention;
[0030] FIG. 17 illustrates a profile view of a portion of a two arm
lever mechanism anchor portion fabricated according to an
alternative aspect of the present invention;
[0031] FIG. 18 illustrates a flow chart identifying certain
processing steps that may be used for fabricating the MEM enclosure
structure illustrated in FIG. 2;
[0032] FIG. 19 illustrates an initial processing step for
fabricating the MEM enclosure structure illustrated in FIG. 2;
[0033] FIGS. 20-22 illustrate various processing steps for
fabricating the MEM enclosure structure illustrated in FIG. 2;
[0034] FIG. 23 illustrates a top view of the MEM enclosure
structure shown in FIG. 2;
[0035] FIGS. 24 and 25 illustrate alternative top views of the MEM
enclosure structure shown in FIG. 22;
[0036] FIG. 26 illustrates another processing step for fabricating
an integral enclosure for a MEM device illustrated in FIG. 2;
[0037] FIGS. 27-33 illustrate various processing steps for
fabricating an integral enclosure for a MEM device illustrated in
FIG. 2;
[0038] FIG. 34 illustrates a top view of the MEM enclosure
structure illustrated in FIG. 33;
[0039] FIG. 35 illustrates an alternative integral MEM device
enclosure fabricated according to one aspect of the present
invention;
[0040] FIG. 36 illustrates an alternative integral MEM device
enclosure fabricated according to one aspect of the present
invention;
[0041] FIG. 37 illustrates a flow chart identifying certain
processing steps that may be used for fabricating the MEM device
with abrasion resistive contact;
[0042] FIGS. 38-50 illustrate various processing steps for
fabricating a MEM relay device with abrasion resistant
contacts;
[0043] FIG. 51 illustrates a perspective view of a MEM device
fabricated in accordance with the process 400 illustrated in FIG.
37; and
[0044] FIG. 52 provides a profile view of an alternative embodiment
comprising a mechanical lever that includes a rib.
DETAILED DESCRIPTION
[0045] One known MEM device 10 is illustrated FIG. 1. MEM device 10
has been manufactured over a CMOS device. As can be seen from FIG.
1, the MEM device 10 includes a cantilever 12 that resides or is
positioned over a substrate 16. The substrate 16 has a top surface
and this top surface has a contour or topology that is dictated by
CMOS manufacturing. As a result, the cantilever 12 does not have a
uni-planar shape. Rather, the cantilever topology or contour 18
resembles the contour of the underlying substrate 16.
[0046] MEM cantilevers, aside from MEM CMOS devices, are also
generally known. For example, MEM cantilevers are typically
fabricated so that they are uniform. That is, the cantilever beam
will be fabricated such that the beam will have a constant width
for the entire length of the beam.
[0047] FIG. 2 illustrates a perspective view of an integral MEM
enclosure 20 fabricated in accordance with one aspect of the
present invention. MEM enclosure 20 provides protection to a MEM
device 25 that resides internally to enclosure 20. MEM device 25
comprises a two arm lever mechanism 21. This lever mechanism has a
first anchor portion 23(a) and a second anchor portion 23(b). Both
of these anchor portions 23(a) and (b) are positioned along a top
surface of a substrate 22 and anchored to this substrate 22. Apart
from the anchor portions 23(a) and (b), the remainder of the two
arm lever mechanism extends along the surface of substrate 22 over
various contact regions. Preferably, the remainder of the two arm
lever mechanism comprises a first extending portion 21(a) and a
second extending portion 21(b) and both of these portions extend
away from the anchor portions 23(a) and (b) while also residing
over a plurality of contact regions. More specifically, first
extending portion 21(a) extends over contact region 28 and second
extending portion 21(b) extends over contact region 26 and contact
region 24.
[0048] In the arrangement provided in FIG. 2, the lever mechanism
21 resides over a pull-in contact region 26, a switching contact
region 24, and a pull-back contact region 28. As can be seen from
FIG. 2, these contact regions extend along the substrate surface,
and eventually exit the integral enclosure 20. The two arm lever
mechanism also includes common contact 29 which functions as a
common reference for the pull-in and pull-out contact regions as
well as part of the switch. Alternatively, a pull-out contact
region could also be deposited on top of enclosure 20.
[0049] As can be seen from this perspective view given in FIG. 2,
the two arm lever mechanism does not have a topography of the
illustrated MEM CMOS device 10 illustrated in FIG. 1. Rather, the
MEM device 20 has a lever mechanism that has a top surface that is
essentially uni-planar. In other words, the contour of the top
surface of the lever mechanism 21 is not dictated by the underlying
substrate topography. As will be described in further detail below,
the lever mechanism 21 also has a bottom surface that is preferably
not uni-planar but rather contains a structure that tends to
increase lever mechanism rigidity. For example, in one arrangement,
the lever mechanism 21 is provided with a contoured surface such as
the ribbed surface 27(a). In such an arrangement, the contoured
surface can comprise a metallic layer which extends the length of
the lever mechanism.
[0050] Alternatively, the lever mechanism may be provided with a
metallic contact region. Such a metallic contact could be deposited
along an end of the first portion of the lever mechanism,
preferably near the switch contact region. Similarly, a metallic
contact region could be provided along an end of the second portion
of the lever mechanism, preferably near the second contact
region.
[0051] The pull-in contact region 26 functions by applying an
electric field between the lever structure and the pull-in contact
that drive the lever structure and the contact region 26 together.
An anchor lever mechanism arm 29 allows a potential voltage to be
applied to the lever mechanism 21. The pull-out contact region 28,
in this arrangement located at an opposite end of the lever
mechanism as the pull-in contact region 26, functions to separate
the switching function, either to turn off the device or in the
event of a false turn-on. Such a false turn-on could arise due to
stiction or MEM device contamination as previously discussed
herein.
[0052] The contact region 24 comprises two micro-strip lines 24(a)
and (b) wherein these strip lines are separated by a gap. This gap
resides under the lever mechanism and is not shown in FIG. 2
because it is obstructed by the lever mechanism. This MEM device
can operate as a switch when the gap between the strip lines is
shorted. Preferably, where the lever mechanism comprises a
conductive material such as copper, the MEM device is operated when
the ribbed portion 27(a) of the lever mechanism is pulled-in so
that the ribbed portion 27(a) connects or shorts the 24(a) and
24(b) strip lines together.
[0053] The two arm lever mechanism illustrated in FIG. 2 may be
fabricated utilizing different fabrication methods according to
aspects of the present invention. One such preferred fabrication
method, that of a switch using CMP, involves the MEM device
fabricating process 30 illustrated in FIG. 3. A second preferred
fabrication method, that of a relay using standard etching
techniques, involves a MEM device fabricating process 400
illustrated in FIG. 37. This second fabrication process involves
fabricating a MEM relay device with an abrasion resistive
contact.
[0054] As will be described in greater detail below, process 30
illustrated in FIG. 3 is particularly useful in fabricating MEM
devices where the lever mechanism includes a contoured surface,
preferably this contoured surface is a ribbed, metallic surface
comprising copper. A ribbed surface lever mechanism has increased
rigidity over a lever mechanism having a uni-planar surface.
Greater rigidity provides certain advantages such as reduced
stiction and easier pull-back. Process 30 of FIG. 3 will be
generally described in reference to the MEM device illustrated in
FIG. 2 and the various processing steps illustrated in the
following figures. Process 400 of FIG. 37 will be generally
described in reference to the device illustrated in FIGS.
38-52.
[0055] As will be described in greater detail below, process 400
illustrated in FIG. 37 is particularly useful in fabricating a MEM
device comprising an abrasion resistive contact area. The MEM
device may or may not be a two arm cantilever mechanism. A lever
mechanism having such an abrasion resistive contact area results in
certain advantages such as a device having increased contact
reliability, while also generally reducing high current density
induced "hot" spots.
[0056] Referring now to the process 30 illustrated in FIG. 3,
first, at step 32 a substrate is first provided. In one preferred
embodiment, this substrate is an insulator such as an oxidized
silicon substrate. FIG. 4 illustrates an initial processing step
for fabricating the MEM device illustrated in FIG. 2 and
incorporates aspects of the present invention. In one preferred
arrangement, and as will be explained in greater detail below, the
MEM device is fabricated in part by a planarization process,
preferably Chemical Mechanical Planarization ("CMP") process. More
preferably, in one arrangement, the MEM device is fabricated by way
of a triple damascene process.
[0057] The CMP process was initially developed to enable
next-generation Integrated Circuits (ICs) by ensuring each
interconnect level in a semiconductor chip be as flat and smooth as
possible before the next level is built. CMP is a preferred
manufacturing process since this process offers a sophisticated,
reproducible process that has vital characteristics to
state-of-the-art Integrated Chip manufacturing. CMP has had a
substantial impact in the fabrication of complex, multilevel, and
3-D metal interconnects.
[0058] By planarizing certain substrate surfaces during the MEM
fabrication process, MEM devices can be produced with certain novel
performance and reliability characteristics.
[0059] In one preferred arrangement, the MEM device is fabricated
by way of a triple copper damascene process. In this process, three
indentations are etched into a sacrificial layer. These
indentations are then filled with at least one metallic layer (such
as copper) and this metallic layer is then planarized down to a
level of the sacrificial layer. Before the metallic layer is
deposited, an adhesion layer may also be provided. Naturally, such
an adhesion layer would also be planarized down to the level of the
sacrificial layer during the planarization process.
[0060] As shown in FIG. 4, an insulator 42 is provided. Such an
insulator may comprise quartz (SiO.sub.2), or alternatively,
sapphire (Al.sub.2O.sub.3), or oxidized silicon or a layer of
silicon nitride on top of silicon or a layer of polyimide on
silicon.
[0061] Along a top surface 44 of insulator 42, a photo-resistive
layer 46 is provided. Such a photoresist could be Shipley 1818
which may be deposited onto the substrate by spin coating. In one
arrangement, the photoresist layer 46 is used to define a plurality
of etching areas. These etching areas along the substrate surface
may be etched to form a plurality of substrate wells. In one
arrangement, the depth of these substrate wells are all generally
similar and are approximately 1-2 microns deep.
[0062] FIG. 5 illustrates various process steps for defining the
substrate contact wells. As shown in FIG. 5, the substrate
structure 50 has been etched to define three contact regions 52,
54, and 56. These regions have been etched into the top surface 44
of the substrate 42. These etched regions or etched areas will then
be used to eventually define various contact regions for the MEM
device. For example, where the MEM device is fabricated as a MEM RF
switch (such as the MEM device in FIG. 2), the various contact
regions would define a pull-in contact, a pull-out contact, and an
RF contact. In the arrangement illustrated in FIG. 5, the
photoresist 46 has been masked so that the etching step defines
three contact wells 52, 54, and 56. However, as those of skill in
the art will recognize, alternative contact point arrangements may
also be used. Such as, for example, locating one of the contact
points on a top portion of a MEM enclosure.
[0063] In one arrangement, each contact well 52, 54, and 56 has a
width of approximately 15 to 100 microns. Once the substrate has
been etched, the next step in the flowchart 30 of FIG. 3 is the
step of providing an adhesion layer and then a metallic layer to
the contact wells. The process of providing the adhesion layer and
the metallic layer is illustrated in FIG. 6. Preferably, before a
metallic layer is provided and the various contact points
planarized, the contact wells may be provided with an adhesion
layer.
[0064] An adhesion layer can be provided so as to increase the
adhesion properties of the metallic layer to the insulator. For
example, where certain insulator substrates are selected, the
substrate and metallic composition adhesion characteristics may
need to be enhanced. For example, in one arrangement, a 200
Angstrom layer of Ta, TaN, TiW, or Cr and other like materials may
be used for such an adhesion layer. This adhesion layer may be
applied by either sputtering or electron-beaming the adhesion
material along the surface of the well and along the top of the
substrate.
[0065] As shown in FIG. 6, the substrate structure 60 is provided
with an adhesion layer 62. After this adhesion layer 62 is
deposited along the top surface, a metallic layer 64 is deposited
along a top surface 66 of the adhesion layer 62. This metallic
layer 64 may comprise aluminum (Al), copper (Cu), gold (Au), or
other such metals having desired conductive characteristics.
Preferably, this metallic layer 64 comprises copper. Copper may be
a preferred metallic layer material because of copper's conductive
properties. Copper may also be preferred because it may be desired
to utilize certain processing steps, such as CMP.
[0066] In one arrangement, the layer of copper could be on the
order of 2 to 4 microns in depth. After the metallic layer 64 has
been sputtered onto the adhesion layer 62, the next step involves
eliminating excess adhesion material and excess metallic material.
This elimination step could take place by way of a chemical
planarization process at step 36 or take place by way of
photolithography at step 35. Preferably, such an elimination step
occurs by way of chemical planarization that is used to planarize
the top surface of the substrate. Returning to FIG. 3, this CMP
planarization processing step 36 occurs after the adhesion and
metallic layer fabrication step 33. In this manner, the planarizing
process step removes excess metal residing on the substrate
surface. Alternatively, if planarization is not used, conventional
photolithography methods may be used at step 35 to remove the
excess adhesion and contact material.
[0067] FIG. 7(a) illustrates a substrate structure 70 after the
planarization process step 36 has been completed. As can be seen
from FIG. 7(a), the substrate structure 70 is provided with a top
surface 72 that is generally smooth. The planarization process also
results in the three contact regions 74, 76, and 78 having smooth
surfaces. What has been omitted in these drawings is the exact
nature of the RF strip. These are either fabricated in a co-planar
fashion, ground-signal-ground, or with a ground plane below the RF
lines device. These have to be included in the design, but are not
shown in these figures for ease of illustration. After completing
the planarization step 36 in FIG. 3, a sacrificial layer is
provided in step 38. Preferably, this sacrificial layer is
SiO.sub.2 and is deposited along the top surface of the substrate
at a depth of 5 to 7 microns. Other sacrificial layers such as
polyimides or metals can also be chosen. In selecting the material,
care should be exercised, when removing the sacrificial layer at
the end of the process, such that the contacts and the substrate
are not being attacked and/or damaged.
[0068] Alternatively, before adding a sacrificial layer at step 38,
a dielectric layer could be provided over the top surface 72 of the
substrate structure 70 (FIG. 7(a)). This dielectric layer would act
as an insulator. This process step is illustrated in FIG. 7(b). As
shown in FIG. 7(b), a substrate structure 77 is provided wherein
the substrate structure of FIG. 7(a) now comprises a dielectric
layer 73 deposited over top surface 72 of substrate 42. Such a
dielectric layer could comprise approximately 1000 Angstroms of an
insulator, such as silicon nitrite, or nanocrystalline diamond or
other like materials. One advantage of providing such a dielectric
layer is that the resulting MEM switch fabricated from the
structure illustrated in FIG. 7(b) would be able to operate at
certain higher frequencies, such as above 2 Giga-Hertz without
having to make direct metal-to-metal contact. Since the switch
impedance is given by 1/2.pi.fC, low values of several Ohms may be
obtained for a 20 micrometer by 20 micrometer contact region at an
RF frequency of 2 Giga-hertz and above. In the above equation, f is
the frequency of the RF signal and C is the capacitance of the
contact region. Such a dielectric layer may be added during step 38
in FIG. 3 before the sacrificial layer is deposited. For ease of
reference and illustration, dielectric layer 73 has been omitted
from the following figures.
[0069] FIG. 8 illustrates another processing step for fabricating
the two arm lever mechanism illustrated in FIG. 2. FIG. 8 includes
a substrate structure 80 that includes a patterned photoresist
layer 84. Photoresist layer 84 is patterned along a top surface 83
of the sacrificial layer 82. Specifically, FIG. 8 illustrates the
substrate structure 70 from FIG. 7(a) after a sacrificial layer 82
has been deposited. Preferably, this sacrificial layer comprises
SiO.sub.2. Alternatively, the sacrificial layer could be deposited
along the dielectric layer 73 illustrated in FIG. 7(b).
[0070] FIG. 10(a) illustrates a top view of a preferred pattern 100
that may be used for performing the etch patterning step 40
illustrated in FIG. 3. FIG. 10(a) may be used for providing and
therefore outlining the two arm lever mechanism portion as well as
the two arm lever mechanism anchor portions. Alternatively, two
patterns may be used: a first pattern defining the two arm lever
mechanism and a second pattern defining the two arm lever mechanism
anchor portion. Other patterning processes may also be used.
[0071] FIG. 10(a) provides a lever mechanism pattern portion 102.
As can be seen from FIG. 10(a), this pattern portion 102 will
define both the two arm mechanism as well as both the first and the
second two arm anchor portions illustrated in FIG. 2 residing over
the pull-back contact 106, and the pull-in contact region 108. The
pattern portion 102 also resides over the switch contact region:
both the first contact zone 110(a) and the second contact zone
110(b). A first portion of the arm lever mechanism 105 will be
patterned so as to extend past the first and second contact zones
110(a) and (b). In addition, a first and a second lever mechanism
anchor portion 104(a) and (b) are pre-patterned.
[0072] FIG. 9 illustrates a substrate structure 90 that has been
etched according to the preferred photoresist pattern 100
illustrated in FIG. 10(a). In one arrangement, the sacrificial
layer 82 has been etched to a depth of approximately 1-2
microns.
[0073] The photoresist layer 84 patterned along the top surface of
the sacrificial layer 82 in FIGS. 8 and 9 is pattered so as to
define various aspects of a MEM device. For example, the
photoresist layer 84 may be patterned to define the two arm lever
mechanism 25 illustrated in FIG. 2. Preferably, the sacrificial
layer 82 is etched to define both a lever mechanism substrate
portion 21 and the lever mechanism anchor substrate portions 23(a)
and (b) (See FIG. 2).
[0074] In a next processing step 41, a contoured surface 116 is
formed along the length of the two arm lever mechanism. This
contoured surface, in this arrangement a rib, provides certain
operating advantages such as increased lever mechanism rigidity.
Before this rib is etched along the length of the two arm lever
mechanism, a photoresist is patterned along the substrate surface.
FIG. 10(b) illustrates a second preferred pattern 109 for providing
and therefore outlining the two arm lever mechanism rib. FIG. 10(b)
provides an illustration of the pattern illustrated in FIG. 10
superimposed along the top surface of the substrate structure
illustrated in FIG. 9. FIG. 10(b) includes the pull-back contact
106, the pull-in contact 108, and the switching contact region 110
in FIG. 2. The RF contact region comprises two RF contacts 110(a)
and (b).
[0075] FIG. 11 illustrates a side view 111 along the B-B' cut of
FIG. 10(b) prior to rib etching. In FIG. 11, a photoresist layer
112 is provided along a top surface 114 of the sacrificial layer
82. Next, the sacrificial layer 82 is then etched so as to define a
rib 118 along the length of the cantilever. Preferably, this rib
118 has a depth of approximately 1-2 microns. The photoresist layer
112 is then striped away.
[0076] FIG. 12 provides a side view 120 taken along the C-C' cut of
FIG. 10(b) and illustrates the anchor etching step. In FIG. 12, the
substrate 42, the sacrificial layer 82, and a photoresist 122 are
shown. The photoresist 122 resides on a top surface 124 of the
sacrificial layer 82. In this arrangement, the sacrificial layer 82
has been deposited along the top surface of the substrate 42 to an
approximate height of 5 microns. Etching the sacrificial layer 82
defines a lever mechanism anchor cavity 126. Preferably, this lever
mechanism cavity 126 extends all the way to the top surface 128 of
the insulator 42. As illustrated by the second preferred pattern
109 illustrated in FIG. 10(b), for each two arm lever mechanism, a
first and a second lever mechanism anchor cavity is formed. After
both anchor cavities have been etched, the photoresist 122 is
stripped away so that the two arm lever mechanism and lever
mechanism anchor portions may be further fabricated.
[0077] Returning to FIG. 3, after etching the two arm lever
mechanism portion with the rib and both the first and the second
anchor portions at step 41, it is determined whether a planarizing
process will be utilized for defining both the two arm lever
mechanism and the anchor surfaces. This determination is made at
step 44. Consequently, a preferred process for fabricating the MEMS
device illustrated in FIG. 2 can include a chemical planarization
process (such as a triple copper damascene) step or an etching
process step.
[0078] If at step 44 it is determined that chemical planarization
will be used, the process proceeds to step 45. Step 45 involves
depositing an adhesion layer and after the adhesion layer is
deposited, a metallic layer is provided. Process step 45 will be
explained with reference to FIGS. 13(a-b) and FIGS. 14(a-b).
Alternatively, if at step 44 it is determined that chemical
planarization will not be used, the process proceeds to step 42.
Process step 46, which involves a photolithography step, will be
explained with reference to FIGS. 15(a-b) and FIGS. 16(a-b).
[0079] FIG. 13(a) illustrates another processing step for
fabricating the MEM device illustrated in FIG. 2. FIG. 13(a)
represents a side view of the two arm lever mechanism after the rib
118 has been etched. Preferably, rib 118 has been etched along the
entire length of the lever mechanism as illustrated in FIG. 11 but
this is not necessary. Shorter rib lengths may also be used. FIG.
13(a) includes a substrate structure 130 wherein an adhesion layer
132 is deposited over the top surface of the sacrificial layer 82.
Preferably, this adhesion layer 132 comprises 100 to 200 Angstroms
of Ta, Cr, TiW, or other like adhesion layer component. After
depositing the adhesion layer 132, approximately 7 microns of a
metallic layer 134 is deposited along this etched out cantilever
rib. Preferably, this metallic layer 134 comprises copper, gold, or
other like metal. Alternatively, this metallic layer 134 comprises
a metallic composition that includes a combination such as Cu/TaN,
Cu/Diamond, or Diamond/Cu.
[0080] Where the process includes chemical planarization, both the
first and the second lever mechanism anchor regions are chemically
planarized in a similar manner as the two arm lever mechanism. For
example, FIG. 13(b) represents a side view of a lever mechanism
anchor portion after the anchor cavity 126 has been etched. As
discussed previously, two anchor cavities are etched, a first
cavity for the first lever mechanism anchor portion and a second
cavity for the second lever mechanism anchor portion. FIG. 13(b)
includes a substrate structure 136 wherein an adhesion layer 138 is
provided over the sacrificial layer 82 and along a top portion 43
of the substrate 42. By completely etching the cavity to the top
surface 72 of insulator 42, an anchor bottom portion 137 of the
anchor provides stability for the two arm level mechanism and
allows the lever mechanism to move according to the bias potential
applied among the various contact regions. This lever motion is
facilitated by a torqueing of the two arms which are supported by
the lever mechanism anchors along the top surface 72 of the
insulator 42. Preferably, this adhesion layer 138 comprises 100 to
200 Angstroms of Ta, Cr, TiW, or other like adhesion layer
component and is deposited at the same time as the lever mechanism
adhesion layer 132. After depositing the adhesion layer 138,
approximately 7 microns of a metallic layer 139 is used to fill out
the anchor cavity. Preferably, this metallic layer 139 comprises
copper, gold, or other like metal or a combination such as Cu/TaN,
Cu/Diamond, or Diamond/Cu.
[0081] FIG. 14(a) illustrates a side view 140 of the two arm lever
mechanism 142. After completing the planarization process at step
45 (FIG. 3), the top surface of the two arm lever mechanism has
been planarized. FIG. 14(a) also illustrates a sacrificial layer 82
having a uniformly planar top surface 145.
[0082] Similarly, FIG. 14(b) illustrates a side view of the lever
mechanism anchor portion 146 after the planarization process. The
sacrificial layer 82 in both FIGS. 14(a) and (b) is etched away,
thereby providing a lever mechanism and lever mechanism anchor
configuration as shown in the MEMS device illustrated in FIG.
2.
[0083] Returning to the fabrication process 30 illustrated in FIG.
3, if the process does not involve planarization after step 45, an
adhesion layer and a metallic layer are deposited. These layers are
provided over both the etched lever mechanism and lever mechanism
anchor portion and then the substrate undergoes photolithography at
step 46. These process steps may be illustrated with reference to
FIGS. 15(a) and (b). As illustrated in FIG. 15(a), a substrate
structure 150 includes the insulator 42 and the sacrificial layer
82. An adhesion layer 152 is provided and on top of this adhesion
layer, a metallic layer 154 is deposited. Preferably, the thickness
of this metallic layer 154 is not as great as the thickness of the
metallic layer 134 deposited in FIG. 13(a). Next, a photoresist
layer 155 is then deposited. After the photoresist is deposited,
exposed, developed, and baked, the metallic layer 154 and the
adhesion layer 152 are etched away.
[0084] The substrate structure 156 illustrated in FIG. 15(b) is
processed in a similar manner as structure 150 in FIG. 15(a) and is
preferably deposited at the same time. As illustrated in FIG.
15(b), a substrate structure 156 includes the insulator 42 and the
sacrificial layer 82. An adhesion layer 157 is provided and on top
of this adhesion layer, a metallic layer 158 is deposited.
Preferably, the thickness of this metallic layer 158 is not as
great as the thickness of the metallic layer 139 deposited in FIG.
13(b). Next, a photoresist layer 159 is then deposited. After the
photoresist is deposited, the metallic layer 158 and then the
adhesion layer 157 are etched away.
[0085] FIG. 16 provides a profile view 160 of the mechanical lever
161 including rib 163. In FIG. 16, the mechanical lever is now
defined except that the sacrificial layer 82 is still shown
underlying the lever 161 and still residing along the substrate 42.
And FIG. 17 provides a profile view of an anchor portion 170. After
the sacrificial extraction step 48 in FIG. 3, the sacrificial layer
82 is etched away. In this manner, an alternative arrangement of
the two lever mechanical lever and the mechanical lever anchor
configuration shown in the MEM device illustrated in FIG. 2 may be
provided.
[0086] In operation, the MEM, rib-enforced lever arm pivots around
the torque arms, these torque arms are preferably fabricated in a
metal such as copper. One aspect of the reliability of the device,
typically measured in millions of switching cycles, depends on the
fatigue and creep properties of the metal. As those skilled in the
art will realize, copper might not be the ideal material. To
provide a higher degree of device reliability, a two material
system can be employed. For example, in one such two material
system, after deposition of the adhesion layer, a layer of about
half the thickness of the final torque arms of Cu can be deposited,
followed by a material of proven fatigue and creep resistance such
as doped nanocrystalline diamond, TaN, Ta, W, or a non-conductive
material such as silicon nitride, silicon carbide, etc. CMP is then
performed in the same fashion as described above. If a
non-conductive material is used, an additional photolithographic
step has to be used to open a contact window over one of the anchor
regions, thus providing electrical contact necessary to the
underlying conductive region for activating the pull-in and
pull-back contacts.
[0087] Once the MEM device has been fabricated, such as the MEM
device illustrated in FIG. 2, the MEM device may be encapsulated.
For example, FIG. 2 illustrates a perspective view of one aspect of
the present invention wherein a single MEM device has been
encapsulated into a micro-chamber of a unitary enclosure 170. As
can be seen from FIG. 2, the MEM device is entirely encapsulated in
a substrate material. The integral enclosure includes various
contact portions extending externally to the enclosure. For
example, in the enclosure 20, a first contact region 26, a second
contact region 28, and a third contact region 24 is provided along
the surface of the substrate 22. In one preferred arrangement,
these contact regions extend to other integral enclosures provided
on the substrate surface 22. The first contact region 28 can
comprise a pull-back contact, the second contact region 26 can
comprise a pull-in contact. Where the integral enclosure contains a
MEM device operating as a switch (such as an RF switch) internally
in a micro-chamber, the third contact region 24 can comprise an RF
contact.
[0088] The enclosure also includes a side wall structure residing
along the substrate surface. Coupled to this side wall structure is
an enclosure top portion. This top portion preferably includes a
first and a second aperture. As will be described in detail below,
these apertures provide a means by which material may escape the
enclosure micro-chamber during enclosure fabrication.
[0089] Encapsulating the resulting MEM device, such as
encapsulating the device illustrated in FIG. 2 in the enclosure 20
illustrated in FIG. 2, results in a number of advantages. For
example, encapsulation provides a clean environment for the device
to operate. Another advantage of an encapsulated MEM device is that
encapsulation can provide for the chamber of the encapsulation to
be filled with a type of filler and then sealed. For example, such
a filler could include an inert gas such as argon. Further aspects
of such a sealing method are provided in detail below.
[0090] FIG. 18 illustrates a processing step 180 for fabricating an
integral MEM enclosure according to one aspect of the present
invention. At a first step 181, a non-released MEM device is
provided along with a substrate. After the MEM device is provided,
an additional sacrificial layer is provided at step 182. This
sacrificial layer allows the next step of defining an enclosure
wall structure at step 183. After the enclosure wall has been
defined at step 183, an enclosure ceiling structure is defined at
step 184 is provided. After this enclosure ceiling structure is
defined at step 184, a tortuous path in the ceiling structure is
defined at step 186. At step 188, the chamber material is removed
through the tortuous path and the chamber may then be sealed at
step 190. These processes are further illustrated in the following
figures.
[0091] Preferably, the enclosure is fabricated using a
planarization process. For example, the first step 181 in process
180 in forming a MEM enclosure cavity is providing a MEM device
structure on a substrate. This first step (step 181 in FIG. 18) is
depicted in FIG. 19. FIG. 19 provides a substrate structure 190
that includes the MEM device structure 194 residing on a first
surface 195 of an insulator 192. The MEM device structure 194
includes both sacrificial material as well as a MEM device. This
device can resemble the MEM device fabricated in accordance with
the processing steps outlined in FIG. 3 but with one distinction.
That distinction being the MEM device 194 will be provided without
extracting the sacrificial layer 82 in step 48 from FIG. 3.
Consequently, the MEM device provided on the surface 195 of
substrate 192 will still include the sacrificial layer 82.
[0092] A second sacrificial layer 193 will then be deposited on top
of the initial sacrificial layer 82 along with the MEM device
structure 194. This is step 182 in FIG. 18. For ease of
illustration, both the initial sacrificial layer 82 and second
sacrificial layer 193 will be designated as sacrificial layer 196
in the subsequent figures. A photo-resist layer 198 is deposited
along a top surface 197 of the sacrificial layer 196. In the
arrangement illustrated in FIG. 19, the MEM device structure 194
may be the two arm mechanical lever device illustrated in FIG. 2.
Alternatively, MEM devices other then the device illustrated in
FIG. 2 may also be used with the arrangement illustrated in FIG.
19. For ease of description and illustration, the control circuitry
and activation lines of the MEM device structure are not
illustrated in the subsequent figures.
[0093] Returning to FIG. 19, preferably, the sacrificial layer 196
has a height of approximately 7 to 15 microns so as to further
encapsulate the MEM device structure 194. A photoresist layer 198
is then deposited along a top surface 197 of this sacrificial layer
196. Preferably, the photoresist layer 198 is deposited along
certain portions of this sacrificial layer 196. More preferably,
the photoresist layer provides for two areas that will be etched
using a wet chemical or plasma etching processes generally know to
those of skilled in the art. These two etching areas are identified
in FIG. 19 as etching area 191(a) and 191(b). Preferably, etching
areas 191(a) and 191(b) are approximately 20 to 100 microns in
width.
[0094] After etching the substrate structure 190 illustrated in
FIG. 19, the etched substrate structure resembles the illustration
provided in FIG. 20. FIG. 20 provides a substrate structure 200
that includes a first substrate cavity 202 and a second substrate
cavity 204. The first and second cavities 202, 204 extend from the
top surface 197 of the sacrificial layer 196 and extends to the top
surface 195 of the insulator 192.
[0095] After stripping away the photoresist layer 198 in FIG. 20,
the next processing step for fabricating a MEM enclosure involves
depositing a layer of poly-crystalline silicon or polyimide on the
sacrificial layer top surface and into areas 202 and 204 in FIG.
20. For example, as can be seen from FIG. 21, the substrate
structure 210 includes additional layer 212 wherein this additional
layer 212 now forms a first wall structure 214 and a second wall
structure 216. The first and second wall structures 214, 216
essentially surround the MEM device structure 194. As will be
discussed in further detail below, the first and second wall
structure defines an enclosure wall structure that surrounds the
MEM device structure 194. In a next processing step that is
illustrated in FIG. 22, the additional layer 212 is planarized.
Preferably, this additional layer 212 is planarized by way of
CMP.
[0096] Planarization of the additional layer 212 results in the
substrate structure 220 illustrated in FIG. 22. As illustrated in
FIG. 22, the substrate structure 220 includes the MEM device
structure 194 now residing internal to the sacrificial layer 196
while also being surrounded by the sacrificial material. The
sacrificial material residing above the insulator surface 195 and
between the first side enclosure 222 and the second side enclosure
224 defines a micro-chamber 221.
[0097] FIG. 23 provides a top view 230 of the substrate structure
220 illustrated in FIG. 22. As can be seen from FIG. 23, after the
planarization of the top layer 212 (FIGS. 21 and 22), there is now
a surrounding wall structure 232 that is positioned around the
micro-chamber 221 that envelopes the MEM device structure 194. One
advantage of structure 232 is that each fabricated MEM device that
resides on the substrate surfaced 192 is now physically isolated
from an adjacent MEM devices by an independent surrounding wall
structure, such as structure 232.
[0098] One advantage of isolating each MEM device in a separate
insulation chamber is that if one MEM device has been contaminated,
another adjacent device will not be contaminated. Another advantage
is that the MEM structure device will be less susceptible to
mechanical failure due to external contamination. Yet another
advantage is that each enclosure may be individualized. For
example, where one enclosure has been hermetically sealed and
includes one type of gas, an adjacent enclosure could have
different types of gases. Details on the encapsulation and sealing
methods are provided below.
[0099] FIG. 24 provides an alternative illustration as to the MEM
configuration provided in FIG. 23. The MEM substrate configuration
240 illustrated in FIG. 24 provides a top view of one arrangement
of an array of MEM devices. The substrate configuration 240
includes an array of MEM devices reproduced along the surface of
substrate 192. Each MEM device in the array is enclosed by a
surrounding structure. For example, MEM device 241 is surrounded by
surrounding enclosure 245. Enclosure 245 comprises four walls:
244(a), 244(b), 244(c), and 244(d). Each of the four walls 244(a-d)
can have a thickness of from 20 to 100 microns. As those of skill
in the art will recognize, other MEM device arrays are also
possible.
[0100] For example, the MEM device layout 240 illustrated in FIG.
24 could be revised so that more than one MEM device is included in
each surrounding wall enclosure, such as enclosure 245. For
example, FIG. 25 illustrates one such alternative arrangement. FIG.
25 includes a MEM layout 250 that resides on a substrate layer 192.
The MEM layout 250 can be fabricated in a similar manner as the
layout shown in FIG. 18. However, each MEM surrounding structure of
FIG. 25 provides isolation to at least two MEM devices residing
within a surrounding structure. Some of the MEM surrounding
structures of FIG. 25 provide isolation to more than two MEM
devices. For example, the MEM device array 252 in FIG. 25 includes
an array of MEM devices fabricates on the surface of substrate 192.
In a first portion of MEM layout structure 252, two MEM devices
256(a) and 256(b) are provided in enclosure 254. Enclosure 254
comprises four walls: 254(a), 254(b), 254(c), and 254(d). Each of
the four walls 254(a-d) can have a thickness ranging from 20 to 100
microns. Alternatively, on the same structure, a variety of layouts
could be fabricated. For example, as those of skill in the art will
recognize, such an alternative construction may depend on the
various types of MEM devices to be included on the same chip such
as switches, variable capacitors, oscillators, and other like MEM
devices.
[0101] Another advantage of the MEM arrangement is the ability to
isolate defective devices. For example, as previously discussed,
MEM devices have certain operating flaws that may arise during
fabrication, device processing, device cleaning, device separation,
etc. For example, stiction is a concern that often arises when
investigating the failure rate of MEM devices. If a failing MEM
device were to be contaminated with, for example, liquid, such a
contamination would be limited to the encapsulated or enclosed MEM
device and would not contaminate an adjacent MEM device.
[0102] Another advantage of this arrangement is that a certain
amount of mechanical isolation and/or protection is provided to
each individual MEM device. Another advantage relates to the
containment of contamination. For example, if a MEM has been
contaminated with some type of fluid or contaminated with some type
of air-born contaminant, MEM devices adjacent such a contamination
would not be contaminated. For example, returning to FIGS. 22 and
23, if the MEM structure device 194 included in enclosure 232 was
contaminated, this contamination would not affect the operability
of adjacent MEM devices. Similarly, turning to FIG. 25, if the two
MEM devices located in MEM device array 252 were contaminated, the
three MEMS devices located in adjacent array 256 would not be
affected. After the top layer 212 in FIG. 21 has been planarized as
shown in FIGS. 22 and 23, an additional layer of material is
deposited along the top surface of the sacrificial layer. FIG. 26
illustrates this next processing step which is step 184 in the
process provided in FIG. 18.
[0103] As can be seen from FIG. 26, an additional layer 262 is
deposited along the now planarized top surface of the sacrificial
layer 196. A photoresist layer 264 is also deposited on top of
layer 262. In one arrangement, this additional layer 262 comprises
a material that is similar to the material making up the two side
wall structures 222 and 224. However, in an alternative
arrangement, the additional layer 262 comprises a material that may
be different than the side wall material. For example, the
additional layer material could comprise a material having certain
desired optical properties. For example, in one arrangement the
layer 262 comprises a transparent material or may have other
desired optical properties such as being transparent to ultra
violet or infrared rays.
[0104] FIG. 26 provides a substrate structure 260 that includes a
photoresist 264 deposited on top of the sacrificial layer 196. In
one arrangement, the photoresist 264 is masked to define a
plurality of enclosure apertures: In FIG. 26, the photoresist 264
defines a first aperture 266(a) and a second aperture 266(b). Both
the first and the second aperture 266(a) and (b) are preferably
positioned so that both the first and second aperture reside over
the MEM device cavern as defined in part by the first cavern wall
and the second cavern wall 222, 224. Alternative aperture locations
may also be used.
[0105] In a next processing step, the substrate structure 260 is
then etched and the photoresist 264 is stripped away. The resulting
substrate configuration is illustrated in FIG. 27.
[0106] FIG. 27 illustrates a substrate structure 270 that includes
a top layer 272 that now defines two apertures: a first aperture
274(a) and a second aperture 274(b). Each aperture extends from a
top surface 278 of additional layer 272 to a bottom surface 276 of
the additional layer 272.
[0107] In a next processing step that is illustrated in FIG. 28,
another layer is deposed over the substrate configuration
illustrated in FIG. 27. As shown in FIG. 28, the additional layer
282. This additional layer 282 includes material that defines the
top most layer and also is deposited into both the first aperture
274(a) and second aperture 274(b). In one arrangement, this top
most layer material is a sacrificial substance and comprises
essentially the same material as the sacrificial substance that is
used to form the MEM enclosure micro-chamber 221.
[0108] After the depositing of the top most layer 282 illustrated
in FIG. 28, another photoresist layer is provided. This additional
photoresist layer will be used to help define a tortuous path
extending into the cavern containing the MEM device 194. As will be
explained in greater detail below, the tortuous paths will enable
the sacrificial material that resides within the enclosure cavern
to be etched away. In this manner, the tortuous paths will allow
the process to still have an enclosure surrounding the MEM device
while also releasing the MEM device to thereby allow operation.
[0109] The process step of providing an additional photoresist
layer is illustrated in FIG. 29. As with other processing steps
providing a photoresist layer, the photoresist layer provided in
FIG. 24 is patterned to cover only a portion of the top surface.
Preferably, the photoresist layer is patterned over the top surface
of material 282 so as to create at least two photoresist pads: a
first pad 292 and a second pad 294. More preferably, the first pad
292 is positioned over the first aperture 274(a) and the second pad
294 is positioned over the second aperture 274(b). FIG. 30
illustrates the substrate shown in FIG. 29 after etching layer 282
and before removal of the photoresist pads 292, 294.
[0110] FIG. 31 illustrates yet another processing step. As shown in
FIG. 31, the substrate structure 310 now includes an additional
layer 312. Layer 312 is deposited over the top surface of layer 272
and the edge layer 282. Preferably, layer 312 comprises a material
similar to the material used for the wall material 222 and 224 or
the top layer 272. A photoresist layer 314 is also provided.
Photoresist layer 314 is used to define two labyrinth hole openings
318 and 316. The substrate structure 310 is then etched.
[0111] FIG. 32 illustrates a substrate structure that results after
etching structure 310 illustrated in FIG. 31 and after photoresist
removal. As shown in FIG. 32, a substrate structure 320 is provided
wherein the top most layer 312 has been etched so as to create a
first tortuous path entrance 322 and a second tortuous path
entrance 324. Path entrances 322 and 324 enter into or extend from
the top layer 312 to the bottom surface of layer 272.
[0112] FIG. 33 illustrates a released MEM device 331 residing on
the substrate 192. As can be seen from FIG. 33, both tortuous path
openings 332, 334 are provided over the MEM device cavity. Now that
the tortuous paths 336, 338 have been defined, which in FIG. 18 is
step 186, the sacrificial layer material 196 (including both the
first sacrificial material 82 and the second sacrificial material
193 (FIG. 19)) deposited in the micro-chamber 221 may be removed.
Removing sacrificial layer 196 internally to the enclosure releases
the MEM device for operation. Extracting the sacrificial material
from the enclosure chamber is step 188 in FIG. 18.
[0113] Preferably, this sacrificial material is removed by
supplying an etchant(s) by way of the tortuous paths 336, 338 and
the etchant(s) will then be removed by these same paths as well.
The MEM device is also released during this process. After removing
the chamber sacrificial material 196, the substrate structure 330
and released MEM device 331 in FIG. 33 resembles that integral MEM
device enclosure illustrated in FIG. 2 and the MEM device resembles
the two arm lever mechanism illustrated in FIG. 2.
[0114] FIG. 34 provides a top view of the MEM device enclosure
illustrated in FIG. 33. As can be seen from this top view
illustration 340, the MEM device structure 194 resides on substrate
192 and has a surrounding enclosure 342. This surrounding enclosure
342 has an inner enclosure wall 344 that is illustrated as a dotted
line extending around a circumference of the substrate. Centered
near the MEM device structure 194 are both the first and the second
tortuous path openings 332 and 334. These path openings 332, 334 do
not extend directly into the chamber but rather extend in a
labyrinth fashion into the micro-chamber 339. Path openings 333,
337, extend into the micro-chamber 339. Providing such a non-linear
path structure has certain advantages. For example, such a
non-linear structure decreases the susceptibility of contamination.
Such a non-linear path also facilitates the ability to hermetically
seal the device enclosure without damaging the MEM device.
[0115] FIG. 35 provides one arrangement for sealing the integral
enclosure 330 illustrated in FIG. 33. FIG. 35 illustrates only a
top portion 350 of the enclosure 330 illustrated in FIG. 33. This
top portion 350 includes the surface layer 272 and upper surface
layer 312. A sealing layer 354 is provided on top of this upper
surface layer 312. Preferably, such a sealing layer comprises a
metallic layer such as tungsten, aluminum, copper, or other like
metal.
[0116] As can be seen from FIG. 35, one advantage of tortuous path
336 is that the deposited sealant will not extend into to the
chamber containing the MEM device structure and therefore will not
effect the operation of the MEM device. Rather, because of the
labyrinth nature of the tortuous path, the deposited sealant will
not progress past the tortuous chamber opening 337. After the
sealing layer 354 is provided, a photoresist layer 352 may be
deposited. The substrate structure 350 may then be etched and the
photoresist layer 352 may then be removed.
[0117] One advantage of being able to seal enclosure 330 is that
this sealing process allows the enclosure to be hermitically
sealed. Other advantages include the possibility of being able to
manipulate the operating environment of the MEM device. For
example, a MEM device may be fabricated to operate in sealed
enclosure containing an inert gas. Those of ordinary skill in the
art will recognize that other operating media may also be used.
[0118] As discussed in general detail above, providing an
encapsulated MEM device results in a number of advantages. For
example, encapsulating a MEM device could result in a MEM device
operating in a hermetically sealed environment. FIG. 35 illustrates
one such environment. For example, FIG. 35 includes a MEM device
residing along a top surface of a substrate, preferably an
insulator. The MEM device is residing inside of an encapsulating
enclosure that is fabricated according to the process illustrated
in FIG. 3 and described in detail above. In this illustration, the
enclosure chamber has been vacuum sealed and a metallic plug has
been provided in one of the tortuous paths. In this manner, the MEM
enclosure can be used to hermetically seal the MEM device.
Providing an inert gas inside such a hermetically sealed device
would be advantageous. For example, during normal operation, when
the contacts of such a device switch and micro-arcs occur, air
could possibly oxidize the Copper and degrade switching
performance. By providing an inert gas such as Argon, or Nitrogen,
such contact oxidation could be reduced. Alternatively, an arc
prevention medium such as SF.sub.6 may be provided prior to sealing
the enclosure.
[0119] FIG. 36 illustrates yet another alternative arrangement for
a top enclosure 360 of an encapsulated MEM device, such as the top
enclosure illustrated in FIGS. 33 and 34. For example, the MEM
encapsulating structure provided in FIGS. 33 and 34 may be further
modified to include a fabrication layer 362. This additional
fabrication layer 362 may be deposited along the top surface of the
enclosure and may be deposited along with layer 354 in FIG. 35 or
could be a separate layer. In one preferred arrangement, this top
material includes Aluminum, Copper, or other like metal. The top
enclosure 360 also includes a plurality of tortuous paths 364(a),
(b), (c), and (d).
[0120] In one arrangement, this additional fabrication layer 362
could be an electromagnetic shield shielding electromagnetic
radiation (such as RF, infra red, etc. radiation). Providing such
an electromagnetic shield has certain advantages. For example,
where the underlying MEM device is an RF switch, providing an RF
shield would confine the RF signal in close proximity to the
switching area of the MEM device. This would tend to limit
propagation of the signal to interfere with other signal lines or
adjacent MEM devices or other electronic devices. Alternatively,
this additional fabrication layer 362 could be a pull-back contact.
Where this layer 362 is used as a pull-back contact, such a contact
would operate in a similar manner as the pull-back contact 28
illustrated in FIG. 2.
[0121] A second preferred fabrication method for fabricating a MEM
device involves the MEM device fabricating process 400 illustrated
in FIG. 37. This process 400 is generally directed to a process for
fabricating a MEM device comprising an abrasion resistive contact.
More particularly, this process 400 is generally directed to a
process for fabricating a MEM relay comprising an abrasion
resistive contact wherein the resistive contact is deposited along
an underside of a two arm ribbed lever mechanism.
[0122] Referring now to the alternative fabrication process 400
illustrated in FIG. 37, at Step 402 a substrate is provided. The
substrates are generally identical to the substrates provided in
process 30 illustrated in FIG. 3. Where the MEM device is used for
microwave applications, a ceramic substrate may be appropriate such
as alumina.
[0123] FIG. 38 illustrates a substrate structure processed in
accordance with an initial processing step of process 400 and
incorporates aspects of the present invention.
[0124] As shown in FIG. 38, a substrate structure 440 includes an
insulator 442. Along a top surface 444 of insulator 442, an
adhesion layer 446 is deposited. Adhesion layer 446 may be utilized
where increased adhesion properties are required between a metallic
layer and an insulator, such as insulator 442. For example, where
certain insulator substrates are selected, the substrate and
metallic composition adhesion characteristics may need to be
enhanced. In one exemplary arrangement, the adhesion layer 446
comprises a 200 Angstrom layer of Ta, TaN, TiW or Cr. Such an
adhesion layer may be applied by either sputtering or
electron-beaming.
[0125] After the adhesion layer 446 has been defined, a metallic
stripline layer 448 is provided. Such a stripline layer 448 could
comprise copper, copper coated with gold, or a gold plated
substrate. Copper may be a preferred stripline layer material
because of copper's excellent conductive properties.
[0126] As a next processing step, it might be desirable to coat the
top surface of the stripline layer 448 with an appropriate contact
material 450. Providing such a contact material may result in
certain advantages. For example, providing such a contact material
may improve certain reliability aspects of the MEM device such as
increasing device reliability while also reducing contact surface
hot spots.
[0127] Contact material 450 may comprise TaN, conductive
nanocrystalline diamond, or another suitable type of switching
material. The contact material 450 can be provided so as to improve
contact performance by minimizing stiction, minimizing abrasion,
while also reducing device and/or contact degradation due to local
high current density regions. This material may also comprise
carbon nanotubes dispersed in an appropriate matrix. Providing the
adhesion layer, the stripline layer, and the contact material is
illustrated as Step 404 in FIG. 37.
[0128] As shown in FIG. 37, after Step 404, the next processing
Step 406 includes providing a photoresist layer, photoshaping the
photoresist, and then etching. FIG. 39(a) illustrates a substrate
structure 455 after this etching step. As can be seen from FIG.
39(a), the substrate structure 455 includes a first contact area
456, a second contact area 454, and a third contact area 452. Each
of these contact areas 456, 454, and 452 comprise three layers: an
adhesion layer 446, a metallic layer 448, and a contact material
layer 450.
[0129] FIG. 39(a) is a side view taken along the A-A' axis of FIG.
39(b). As illustrated in FIG. 39(b), the substrate structure
includes a first contact region 459, a second contact region 463,
and a third contact region 461. The first contact region 459
defines both an RF input contact 464(a) and an RF output contact
464(b). As will be described in detail below, a preferred MEM
device is fabricated to include a contact material disposed along a
bottom surface of a lever mechanism portion. Providing such a
contact material results in certain operational advantages such as
increasing the operational life of the contacts.
[0130] In the arrangement illustrated in FIG. 38, the photoresist
451 has been masked and photoshaped so that the etching step
defines three contact zones 452, 454, and 456 (FIG. 39(a)).
However, as those of skill in the art will recognize, alternative
contact zone arrangements may also be used. For example, one such
alternative arrangement could include locating one of the contact
zones on a top portion of a MEM enclosure. In one arrangement, each
contact region 452, 454, and 456 has a width of approximately 15 to
100 microns.
[0131] Once the substrate structure has been etched, the next step
in the process 400 of FIG. 37 is Step 408. Step 408 comprises
providing a first sacrificial layer to the substrate structure.
Such a first sacrificial layer could comprise aluminum. After this
first sacrificial layer is provided, a second sacrificial layer is
deposited over the first sacrificial layer. The process of
providing the first and the second sacrificial layer is illustrated
in FIG. 40.
[0132] FIG. 40 illustrates a substrate structure 465 having a first
sacrificial layer 467 and a second sacrificial layer 469.
Preferably this first sacrificial layer 467 is aluminum. The first
sacrificial layer 467 may be deposited by sputtering or e-beam
evaporation. As will be described in greater detail below, this
first sacrificial layer protects the contact regions 452, 454, and
456 from further processing during subsequent MEM device processing
steps. For instance, it would protect copper from oxidation if the
second sacrificial layer 469 was SiO.sub.2.
[0133] The second sacrificial layer 469 may comprise SiO.sub.2. As
can be seen from FIG. 40, the top surface 468 of the second
sacrificial layer 469 has a non-planar shape. Consequently, to
simplify certain subsequent processing steps, the top surface of
the second sacrificial layer 469 is planarized. Such a planarizing
processing step, represented as Step 410 in process 400 of FIG. 37,
may occur by way of CMP.
[0134] After the planarization process occurs at Step 410, the
resulting substrate structure 475 will have a planarized substrate
surface. Such a planarized substrate surface is illustrated in FIG.
41. As can be seen from FIG. 41, a substrate structure 475 is
provided wherein the second sacrificial layer 469 comprises a
planarized top surface 477.
[0135] Returning now to the processing steps of FIG. 37, the
planarization processing Step 410 occurs after the addition of the
second sacrificial layer at processing Step 408. In this manner,
the planarizing process step removes excess sacrificial layer
material residing on the substrate surface.
[0136] After completing the planarization Step 410 in FIG. 37, a
recess will be defined along the top surface 477 of the second
sacrificial layer 469. An initial step in defining the recess is
established by first providing a photoresist layer at Step 412
along the top surface of the second sacrificial layer. The
photoresist layer is then photoshaped so as to define a recess
along the top surface of the second sacrificial layer and generally
above the contact zone.
[0137] FIG. 42 illustrates the substrate structure 485 including
the photoresist layer 482 after the substrate structure 485 of FIG.
42 has been etched. As can be seen in FIG. 42, etching the
substrate structure results in a substrate structure 485 having a
recess 480. Preferably, the photoresist 482 is shaped so that the
resulting recess 480 is defined to reside above the third contact
zone 456. Preferably, the recess 480 is formed so that it has a
depth of approximately 0.5-2.0 .mu.m and extends to a width of
several microns extending past the third contact zone 456 and
extends to applicably compensate for certain process variabilities
(e.g., several microns). Then, at Step 413 in FIG. 37, the
photoresist layer 482 is removed.
[0138] FIG. 43 illustrates another processing step for fabricating
a MEM device. FIG. 43 includes a substrate structure 495 comprising
a substrate contact material layer 497. A contact material layer
497 is deposited along the generally planar top surface 477 of the
second sacrificial layer 469. Preferably, this contact material
layer 497 comprises conductive diamond deposited by chemical means.
Alternatively, this contact material layer 497 comprises a diamond
layer expressed in a polymer matrix, TaN, or other suitable
abrasion resistive material. More preferably, layer 497 comprises a
contact material similar to the contact material 450 deposited on
the top portion of the third contact zone 456. In other words, the
contact material used in layer 497 is preferably similar to the
contact material used for contact areas 452, 454, and 456.
[0139] As a next process step, Step 416 in FIG. 37, the contact
material layer 497 is planarized. Preferably, this contact layer is
planarized via CMP but as will be recognized by those skilled in
the art, other planarization methods may also be used. FIG. 44(a)
illustrates the substrate structure after the planarization of the
contact material layer. As can be seen from FIG. 44(a), the recess
is now filled with a contact material 506 that resides above the
third contact zone area 456. FIG. 44(b) provides a top view of the
substrate structure 510 illustrated in FIG. 44(a). In FIG. 44(b), a
substrate structure 510 is provided wherein the contact material
514 defines a recessed area filled with contact material 514.
Contact material 514 resides over the RF contact region 465 defined
by both the RF input and the RF output contacts 464(a) and (b).
More particularly, the contact area 514 resides over a portion of
both the RF input contacts 464(a) and the RF output contact zone
464(b).
[0140] Returning to the flow chart 400 illustrated in FIG. 37 and
the substrate structure 525 illustrated in FIG. 45, in a next
processing step, an etch stop layer 525 is provided at Step 418.
This etch stop layer 525 is provided along the top surface of the
second sacrificial layer 469 and also along the top surface of the
contact material area 506. Preferably, this etch stop layer 525 is
Aluminum and is deposited to a height of approximately 0.1
micrometer.
[0141] At a next processing Step 420 (FIG. 37), another sacrificial
layer 527 is provided along a top surface 526 of the metallic layer
525. Preferably, this layer comprises SiO.sub.2 and is deposited at
a height of approximately 1 to 4 microns. FIG. 45 also illustrates
the RF contact region 465 comprising both RF contacts 464(a) and
464(b) (see also FIGS. 44(a) and (b)). The RF contacts 464(a) and
(b) are separated by an RF contact gap 523.
[0142] Returning now to FIG. 45, after the sacrificial layer 527 is
provided, a photoresist layer 529 is deposited and photoshaped
along the top surface 528 of the sacrificial layer 527. Preferably,
this photoresist layer 529 is photoshaped to define a photoresist
void 530. This photoresist void extends by several microns over the
previously deposited and planarized contact material 506. The layer
527 is then etched. This etching step removes layer 527 down to
layer 525. Another etching step is performed to remove 525 where
not protected by 529. The resulting substrate structure, after
photoresist removal which is structure 535, is illustrated in FIG.
46.
[0143] As shown in FIG. 46, this etching step defines an enlarged
cavity 537. This enlarged cavity 537 extends through the
sacrificial layer 541 and through the metallic layer 539 to a top
surface 507 of previously deposited and planarized contact material
506. This enlarged cavity 537 helps define a ribbed lever mechanism
in the processing steps described below.
[0144] Next, at Step 423 and similar to the process described in
FIG. 3 and other related figures, the anchor portions are formed.
This step comprises the depositing, baking, masking, and exposure
of a photoresists layer and etching the two anchor cavities down to
the substrate through the sacrificial layers.
[0145] FIG. 47 illustrates an additional processing step for
fabricating a preferred MEM device. This processing step is
represented as Step 424 in FIG. 37. In Step 424, and referring to
FIG. 47, an insulating layer of Si.sub.3N.sub.4, Al.sub.2O.sub.3,
SiC, or nanocrystalline diamond 547 is deposited along the top
surface of the substrate structure 545. Preferably, this layer 547
is provided at a depth of approximately 1 to 4 micrometers.
[0146] Next, and as illustrated at Step 426 of FIG. 37, along the
top surface of the substrate structure illustrated in FIG. 47, a
photoresist layer 549 is provided. Preferably, this photoresist
layer 549 is photoshaped so as to essentially cover the enlarged
cavity 537 and photoshaped so as to define at least one aperture.
More preferably, this photoresist layer 549 is photoshaped so as to
define both a first and a second aperture 551, 553, respectively.
Defining the apertures 551 and 553 ocurrs at Step 426 in FIG. 37.
Aperture 551 and 553 extend from a top surface 550 of the
photoresist layer 549 to a top surface 548 of the layer 547. The
first and the second apertures 551, 553 are illustrated in FIG. 47.
The substrate structure 545 is then etched at Step 426 to form the
outline of the lever mechanism in material 547 and to etch
apertures into this mechanism.
[0147] FIG. 48 illustrates a substrate structure 560. Substrate
structure 560 illustrates a resulting structure after the structure
545 illustrated in FIG. 47 has been etched and the photoresist
layer 549 removed. As illustrated in FIG. 48, the substrate
structure 560 includes a layer 566 residing essentially over the
contact material 506. This layer 566 now includes two etched
apertures 562, and 564. Both etched apertures 562, 564 extend from
a top surface 567 of the layer 566 to a top surface 507 of the
contact area 506. Etching and defining apertures 562 and 564 is
represented by Step 426 in the flowchart illustrated in FIG. 37. As
those of skill in the art will recognize, alternate etched
apertures arrangements may be utilized, such as, for example, an
etched apertures arrangement comprising more than two
apertures.
[0148] FIG. 49 illustrates yet another substrate structure after
the apertures 562 and 564 have been etched and the outline of the
lever mechanism has been etched at Step 426 and includes additional
processing steps.
[0149] FIG. 49 illustrates a substrate structure wherein these
processing steps are used. As shown in FIG. 49, the substrate
structure 580 includes an adhesion layer 582 deposited over the
surface of the substrate structure 580. This adhesion layer may
comprise Ta or other like materials such as TiN, chrome, etc. One
reason for providing adhesion layer 582 is to increase certain
adhesion qualities of a metal layer to the MEM device. After this
adhesion layer 582 is deposited, a metallic layer 584 such as
copper is provided (Steps 430 and 432 in FIG. 37).
[0150] Importantly, during the adhesion layer and metallic layer
depositing, these process steps allow for the adhesion layer
material and to a certain extent the metallic material, to
propagate through the etched apertures and to thereby come into
contact with contact material 506. By having the adhesion material
and the metallic material join with the contact material 506,
certain operating advantages are realized. For example, this type
of channeling or riveting action increases the adhesion of the
contact material to the MEM device lever mechanism.
[0151] At a next processing step, Step 434, the substrate structure
580 is provided with a photoresist layer 586. This layer 586 is
then photoshaped over the contact material area 506 as illustrated
in FIG. 49. The substrate structure 580 is then etched. After this
etching step and removal of the photoresist, the substrate
structure resembles the structure illustrated in FIG. 50.
[0152] FIG. 50 illustrates a substrate structure 590 wherein the
etched adhesion layer 582 is shown as residing only over a portion
of the substrate surface. Preferably, this etched adhesion layer
582 resides over the material layer 506 and extends into both of
the cavities, thereby contacting with the material layer 506. In
addition, the etched metallic layer 584 is shown as residing over
the etched adhesion layer 582. As can be seen from FIG. 51, this
lever mechanism defines a ribbed shape. Providing such a ribbed
shaped lever mechanism provides certain operational and structural
advantages as previously described.
[0153] After etching the photoresist and removing the photoresist
586 from the substrate 580 in FIG. 49, this substrate structure is
then ready for release etching. This release etching step may be
accomplished by using buffered HF for the silicon dioxide and an
aluminum etchant such as phosphoric acid for the removal of the
aluminum. The buffered HF might also be sufficient to remove the
aluminum. The resulting substrate structure is illustrated in FIGS.
51 and 52.
[0154] FIG. 51 illustrates a partial perspective view of a MEM
device fabricated in accordance with the process 400 illustrated in
FIG. 37 and discussed with reference to FIGS. 38-50. FIG. 51
illustrates a MEM device 602 that resides along a surface of a
substrate 604. MEM device 602 comprises a two arm lever mechanism
606. This lever mechanism comprises pull-in signal contact areas
613(a) and 613(b), pull-back signal contact areas to the left of
the lever (not shown in FIG. 51 but see FIG. 44(b)), and an RF
contact area 624. The lever mechanism also includes a first anchor
portion 608(a) and a second anchor portion 608(b). Both of these
anchor portions 608(a) and (b) are positioned along a top surface
610 of a substrate 604 and anchored to this substrate 604. Apart
from the anchor portions 608(a) and (b), the two arm lever
mechanism extends along the surface of substrate 604 over certain
contact regions. Preferably, the two arm lever mechanism comprises
a first extending portion 611 and a second extending portion 612.
Both of these portions extend away from the anchor portions 608(a)
and (b) while also residing over the surface 610 of the substrate
604. More specifically, in this arrangemeent, the first extending
portion 611 resides over the pull-in contact region 613(b) and the
second extending portion extend portion 612 resides over an RF
contact region 624. More specifically, first extending portion 611
extends over contact region 613(b) and second extending portion
612.
[0155] As can be seen from this perspective view given in FIG. 51,
the two arm lever mechanism does not have a topography of the
illustrated MEM CMOS device 10 illustrated in FIG. 1. As described
in further detail above, the lever mechanism 606 also has a bottom
surface 632. Bottom surface 632 is preferably not uniplanar but
rather contains a structure that tends to increase lever mechanism
rigidity. For example, in one arrangement, the lever mechanism 606
is provided with a contoured surface such as a ribbed surface 620.
In such an arrangement, the contoured surface comprises an
insulating layer extending a length of the lever mechanism 606.
[0156] The pull-in contact region functions by applying an electric
field between the pull-in contact 613(a) on top of the lever
mechanism and the pull-in contact 613(b) residing along the surface
610 of the substrate 604 to drive the lever structure and the
contact region 624 together.
[0157] The contact region 624 comprises two micro-strip lines 626
and 628 wherein these strip lines are separated by a gap 630. This
gap resides under the lever mechanism 606 and is partially shown in
FIG. 51. This MEM device can operate as a relay when the gap
between the strip lines is shorted. Preferably, where the lever
mechanism 606 comprises an abrasion resistive material such as
diamond, the MEM device is operated when the ribbed portion 620 of
the lever mechanism 606 is pulled-in so that the ribbed portion 621
connects or shorts the 626 and 628 strip lines.
[0158] FIG. 52 provides a profile view 640 of a mechanical lever
660 that includes a rib 644. In FIG. 52, mechanical lever 660
comprises a top conductor 654, a rib enforced insulator 658, and a
contact material 652. (Not shown is an adhesion layer 582
illustrated in FIG. 50). As shown, the mechanical lever resides
over a surface 649 of substrate 642. When the MEM device 602
operates as a relay, the lever mechanism 660 is energized via pull
in contact (such as pull-in contacts 613(a) and (b) illustrated
FIG. 51), so that the contact material 652 of the mechanical lever
660 is operatively coupled to the contact material disposed along
both the first strip line 644 and the second strip line 646. By
using such contact material on both the lever mechanism 660 and the
strip lines 648 and 650, the MEM relay results in a number of
advantages such as those advantages described above. It might also
be possible to include the abrasion resistive material on only one
contact surface, such as on the movable member 660 or on the
stationary strip lines.
[0159] Once the MEM device has been fabricated in accordance with
the process steps identified in FIG. 37, the MEM device may be
encapsulated. The MEM device illustrated in FIGS. 51 and 52 may be
encapsulated in a similar manner as described in detail above with
reference to the process 180 of FIG. 18 and described with respect
to FIGS. 19 through 36.
[0160] Exemplary embodiments of the present invention have been
described. Those skilled in the art will understand, however, that
changes and modifications may be made to these embodiments without
departing from the true scope and spirit of the present invention,
which is defined by the claims.
* * * * *