U.S. patent application number 13/032334 was filed with the patent office on 2012-08-23 for cavity structures for mems devices.
Invention is credited to Stefan Kolb, Klemens Pruegl, Bernhard Winkler, Andreas Zankl.
Application Number | 20120211805 13/032334 |
Document ID | / |
Family ID | 46652034 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120211805 |
Kind Code |
A1 |
Winkler; Bernhard ; et
al. |
August 23, 2012 |
CAVITY STRUCTURES FOR MEMS DEVICES
Abstract
Embodiments relate to MEMS devices, particularly MEMS devices
integrated with related electrical devices on a single wafer.
Embodiments utilize a modular process flow concept as part of a
MEMS-first approach, enabling use of a novel cavity sealing
process. The impact and potential detrimental effects on the
electrical devices by the MEMS processing are thereby reduced or
eliminated. At the same time, a highly flexible solution is
provided that enables implementation of a variety of measurement
principles, including capacitive and piezoresistive. A variety of
sensor applications can therefore be addressed with improved
performance and quality while remaining cost-effective.
Inventors: |
Winkler; Bernhard;
(Regensburg, DE) ; Zankl; Andreas; (Wiesent,
DE) ; Pruegl; Klemens; (Regensburg, DE) ;
Kolb; Stefan; (Unterschleissheim, DE) |
Family ID: |
46652034 |
Appl. No.: |
13/032334 |
Filed: |
February 22, 2011 |
Current U.S.
Class: |
257/254 ;
257/E21.002; 257/E29.324; 438/50 |
Current CPC
Class: |
B81C 2203/0735 20130101;
B81C 2203/0714 20130101; B81B 2203/0315 20130101; B81B 2201/0264
20130101; B81C 1/00246 20130101; B81C 1/00158 20130101; H01L
27/0611 20130101; B81C 2203/0707 20130101; B81B 2207/015 20130101;
B81B 7/008 20130101; B81C 2203/0771 20130101 |
Class at
Publication: |
257/254 ; 438/50;
257/E21.002; 257/E29.324 |
International
Class: |
H01L 29/84 20060101
H01L029/84; H01L 21/02 20060101 H01L021/02 |
Claims
1. A method comprising: forming a microelectromechanical system
(MEMS) device on a substrate by: forming a sacrificial layer on the
substrate, depositing a first silicon layer on the sacrificial
layer, the first silicon layer comprising at least one release
aperture, forming a cavity in the sacrificial layer via the at
least one release aperture, and sealing the cavity by depositing a
second silicon layer; and forming an electrical device on the
substrate.
2. The method of claim 1, further comprising depositing a cavity
passivation layer in the cavity.
3. The method of claim 1, wherein forming the sacrificial layer
comprises patterning the sacrificial layer.
4. The method of claim 1, wherein forming the sacrificial layer
comprises forming a monocrystalline sacrificial layer.
5. The method of claim 1, wherein forming the electrical device
further comprises utilizing the monocrystalline sacrificial
layer.
6. The method of claim 1, wherein sealing the cavity further
comprises depositing a second silicon layer comprises
monocrystalline silicon.
7. The method of claim 1, wherein forming a MEMS device comprises
forming a sensor device.
8. The method of claim 7, wherein forming a sensor device comprises
forming at least one of a capacitive sensor device or a
piezoresistive sensor device.
9. The method of claim 1, wherein forming an electrical device
comprises forming at least one transistor.
10. The method of claim 1, wherein forming an electrical device
comprises utilizing one of a CMOS or BICMOS process.
11. The method of claim 1, wherein forming a MEMS device further
comprises filling a portion of the cavity via at least one release
aperture.
12. The method of claim 1, further comprising forming an isolation
trench between the MEMS device and the electrical device.
13. A monolithic integrated sensor device comprising: a
microelectromechanical system (MEMS) sensor formed on a substrate,
the MEMS sensor comprising a cavity formed in a sacrificial layer
via at least one release aperture and sealed by a silicon layer;
and an electrical device formed on the substrate.
14. The device of claim 13, wherein the silicon layer comprises a
monocrystalline silicon layer.
15. The device of claim 14, wherein the monocrystalline silicon
layer forms a part of the electrical device.
16. The device of claim 13, further comprising an isolation trench
formed between the MEMS sensor and the electrical device.
17. The device of claim 13, wherein the MEMS sensor is one of a
capacitive sensor or a piezoresistive sensor.
18. The device of claim 13, wherein the electrical device comprises
a transistor.
19. The device of claim 13, further comprising a cavity passivation
layer inside the cavity.
20. The device of claim 13, wherein the silicon layer comprises a
membrane.
21. A method comprising: obtaining a silicon substrate; forming an
implanted layer on the silicon substrate; patterning a
monocrystalline sacrificial layer on the implanted layer;
depositing a first silicon layer on the sacrificial layer, the
first silicon layer having at least one release aperture; etching
the sacrificial layer through the release aperture to form a
cavity; and sealing the cavity by depositing a second silicon layer
on the first silicon layer.
22. The method of claim 21, further comprising forming a
microelectromechanical system (MEMS) sensor by carrying out the
obtaining, forming, patterning, depositing, etching and
sealing.
23. The method of claim 22, further comprising forming a monolithic
integrated sensor device by forming an electrical device on the
substrate.
24. The method of claim 23, wherein forming an electrical device
further comprises utilizing the second silicon layer.
25. The method of claim 23, wherein forming a MEMS sensor further
comprises forming at least one of a capacitive MEMS sensor or a
piezoresistive MEMS sensor, and wherein forming an electrical
device further comprises forming a transistor.
Description
TECHNICAL FIELD
[0001] The invention relates generally to microelectromechanical
systems (MEMS) devices and more particularly to MEMS devices and
electrical devices on a single wafer.
BACKGROUND
[0002] MEMS devices, such as sensors, and related electrical
devices, such as an application-specific integrated circuit (ASIC),
are typically implemented on separate chips because the fabrication
processes for each are incompatible with the other. For example, in
modern CMOS technologies it can be critical to avoid high
temperatures in order to preserve doping profiles, whereas high
temperature steps may be necessary in steps of the electrical
device fabrication. There are many disadvantages associated with
two-chip solutions, including more complex and expensive packaging
and the inability to implement applications requiring processing of
very small signals.
[0003] More recently, so-called "MEMS first" processes have been
developed for integrating MEMS and electrical devices on a single
chip. Such processes, however, still present drawbacks and
disadvantages, leaving room for improvement.
[0004] Therefore, there is a need for improved systems and methods
that enable MEMS and electrical devices to be implemented on a
single wafer.
SUMMARY
[0005] Embodiments are directed to monolithic integrated MEMS
sensor devices and electrical devices and method related
thereto.
[0006] In an embodiment, a method comprises forming a
microelectromechanical system (MEMS) device on a substrate by
forming a sacrificial layer on the substrate, depositing a first
silicon layer on the sacrificial layer, the first silicon layer
comprising at least one release aperture, forming a cavity in the
sacrificial layer via the at least one release aperture, and
sealing the cavity by depositing a second silicon layer; and
forming an electrical device on the substrate.
[0007] In an embodiment, a monolithic integrated sensor device
comprises a microelectromechanical system (MEMS) sensor formed on a
substrate, the MEMS sensor comprising a cavity formed in a
sacrificial layer via at least one release aperture and sealed by a
silicon layer; and an electrical device formed on the
substrate.
[0008] In an embodiment, a method comprises obtaining a silicon
substrate; forming an implanted layer on the silicon substrate;
patterning a monocrystalline sacrificial layer on the implanted
layer; depositing a first silicon layer on the sacrificial layer,
the first silicon layer having at least one release aperture;
etching the sacrificial layer through the release aperture to form
a cavity; and sealing the cavity by depositing a second silicon
layer on the first silicon layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0010] FIGS. 1A-1E depict stages in the fabrication of a capacitive
MEMS device integrated with an electrical device according to an
embodiment.
[0011] FIGS. 2A-2D depict stages in the fabrication of a capacitive
MEMS device integrated with an electrical device according to an
embodiment.
[0012] FIG. 3 depicts a piezoresistive MEMS device integrated with
an electrical device according to an embodiment.
[0013] FIGS. 4A-4G depict stages in the fabrication of a capacitive
MEMS device integrated with an electrical device according to an
embodiment.
[0014] FIG. 5 depicts a piezoresistive MEMS device integrated with
an electrical device according to an embodiment.
[0015] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0016] Embodiments relate to MEMS devices, particularly MEMS
devices integrated with related electrical devices on a single
wafer. Embodiments utilize a modular process flow concept as part
of a MEMS-first approach, enabling use of a novel cavity sealing
process. The impact and potential detrimental effects on the
electrical devices by the MEMS processing are thereby reduced or
eliminated. At the same time, a highly flexible solution is
provided that enables implementation of a variety of measurement
principles, including capacitive and piezoresistive. A variety of
sensor applications can therefore be addressed with improved
performance and quality while remaining cost-effective.
[0017] FIG. 1 depicts stages in the fabrication of a capacitive
MEMS device 100 with a local sacrificial layer, such as oxide. FIG.
1A depicts a silicon substrate 102 having an implanted layer 104.
In one embodiment, substrate 102 is a p-type substrate, and layer
104 is an n-type implanted layer, forming a pn-junction. A
patterned sacrificial layer 106 is formed on layer 104. In one
embodiment, sacrificial layer 106 comprises oxide.
[0018] In FIG. 1B, a silicon layer 108 has been deposited, for
example by epitaxial growth in an embodiment. Silicon layer 108
comprises release apertures 110 through which a cavity 112 is
formed by sacrificial layer etching. In embodiments, cavity 112 is
about 50 nanometers (nm) to about 100 nm high (with respect to the
orientation of the drawing on the page). An optional cavity
passivation layer 114, such as silicon oxide or silicon nitride, is
deposited and etched back to assist with later cavity sealing.
[0019] In FIG. 1C, a silicon layer 116 deposited by epitaxial
growth seals cavity 112. Optional cavity passivation layer 114, if
implemented in embodiments, can help to avoid silicon growth in
cavity 112 under certain process conditions. As depicted in FIG.
1C, the result is a polycrystalline silicon sealed membrane 116 on
top of cavity 112, with remaining sacrificial layer 108 and a
monocrystalline silicon 118 on the other areas of the surface of
substrate 102.
[0020] In FIG. 1D, because of the monocrystalline silicon formed
next to membrane structure 116, electrical devices such as a MOS
transistor 120 can be processed in common CMOS or BICMOS processes
on the same wafer 102. Lateral electrical isolation can be achieved
by isolation trenches 122, and electrical contact to top and bottom
electrodes can be carried out by contacts structures 124.
[0021] In FIG. 1E, a common wafer finishing process with intermetal
oxide 126, electrical contacts 128 and metallization 130 can be
applied. After sensor release at 132 and passivation 134, a
capacitive sensor device 136, such as a pressure sensor in an
embodiment, is formed next to electrical devices, such as
transistor 120, on the same wafer 102. In other embodiments, sensor
device 136 can comprise another sensor technology, such as a
piezoresistive sensor, and transistor 120 can comprise some other
electrical device. While FIG. 1 is an example for monolithic
integrated sensor technology, the concept also has the flexibility
to create a discrete sensor device without electrical devices if
necessary or desired in specific applications.
[0022] FIG. 2 depicts stages in the fabrication of a capacitive
MEMS device 200 with a local monocrystalline sacrificial layer,
such as silicon germanium (SiGe) or doped silicon in embodiments.
In FIG. 2A, a silicon substrate 202 has an implanted layer 204. In
an embodiment, substrate 202 is a p-type substrate, and layer 204
n-type, such that a vertical pn-junction is formed. A
monocrystalline sacrificial layer 206 is patterned on layer 104.
Sacrificial layer 206 can comprise SiGe or doped silicon with a
different dopant type or doping concentration than the silicon
material 204 interfacing layer 206.
[0023] Referring to FIG. 2B, the monocrystalline nature of
sacrificial layer 206 permits formation of a monocrystalline layer
208 by epitaxial growth next to and on top of sacrificial layer
206. Through release apertures 210, a portion sacrificial layer 206
is removed to form cavity 212. Embodiments of this process sequence
are discussed in DE 19700290, which is incorporated herein by
reference in its entirety. In embodiments, cavity 212 is about 50
nm to about 100 nm high (with respect to the orientation of the
drawing on the page).
[0024] Referring to FIG. 2C, cavity 212 and release apertures 210
are filled with a filling material 214, such as oxide, for
isolation and removed from the wafer surface. Through release
apertures 216 formed over remaining sacrificial layer 206, a cavity
218 is formed by another sacrificial layer etch. An optional cavity
passivation layer 220, such a silicon oxide or silicon nitride, is
deposited and etched back on the wafer surface to assist with later
cavity sealing.
[0025] Referring to FIG. 2D, a silicon layer 222 deposted by
epitaxial growth seals cavity 218. Cavity passivation layer 220 can
help to avoid silicon growth inside cavity 218 under certain
process conditions. The result is a monocrystalline silicon sealed
membrane 224 on top of cavity 218 and a monocrystalline silicon 226
on other areas of the wafer surface.
[0026] Because of the monocrystalline silicon 226, electrical
devices like a MOS transistor 228 can be formed on the same wafer
202 in common CMOS or BICMOS processes. Lateral electrical
isolation can be provided by isolation trenches 230, with
electrical contact to the bottom and top electrodes of the
capacitive sensor device provided by contact structures 232.
[0027] A common wafer finishing process with intermetal oxide 234,
electrical contacts 236 and metallization 238 can be applied. After
sensor release 240 and passivation 242, a capacitive sensor device
244, such as a pressure sensor, has been formed with an electrical
device, such as transistor 228, on the same wafer 202. In other
embodiments, sensor device 244 can comprise another sensor
technology and transistor 228 can comprise some other electrical
device. While FIG. 2, like FIG. 1, is an example for monolithic
integrated sensor technology, the concept also has the flexibility
to create a discrete sensor device without electrical devices if
necessary or desired in specific applications.
[0028] FIG. 3 depicts a piezoresistive MEMS device 300 with a
monocrystalline sacrificial layer, such as silicon germanium (SiGe)
or doped silicon in embodiments. In the embodiment of FIG. 3, in
contrast with those of FIGS. 1 and 2, a monocrystalline sacrificial
layer need not be patterned because isolation is not needed in this
piezoresistive sensing embodiment as it was in the aforementioned
capacitive sensing embodiments.
[0029] Device 300 comprises a silicon substrate 302 with an
implanted layer 304. In an embodiment, substrate 302 is a p-type
substrate, and layer 304 is an n-type implanted layer. A
monocrystalline sacrificial layer 306 is formed on layer 304.
Sacrificial layer 306 can comprise, for example, SiGe or doped
silicon having a different dopant type and/or concentration than
the silicon material at the interface of layers 304 and 306.
[0030] Monocrystalline sacrificial layer 306 enables formation of a
monocrystalline layer 308 on layer 306 by epitaxial growth. Through
release apertures 310, a cavity 312 can be formed by sacrificial
etch, such as is described in DE19700290, which is incorporated
herein by reference in its entirety. In embodiments, cavity 312 is
about 50 nm to about 100 nm high (with respect to the orientation
of the drawing on the page). An optional cavity passivation layer
314, such as silicon oxide or silicon nitride or some other
suitable material, is deposited and etched back on the wafer
surface to assist with later cavity sealing. A silicon layer 316
deposited by epitaxial growth seals cavity 312, with cavity
passivation layer 314, if present, assisting to avoid silicon
growth inside cavity 312 under certain process conditions. The
result thus far is a monocrystalline silicon sealed membrane 316 on
top of a cavity 312, with the monocrystalline silicon also on all
other areas of the wafer surface. Implantation of piezoresistors
318 on monocrystalline membrane 316 provides a piezoresistive
sensor device 320.
[0031] The monocrystalline silicon 316 enables electrical devices
such as a MOS transistor 322 to be processed in common CMOS or
BICMOS processing concepts on the same wafer 302. A common wafer
finishing process with intermetal oxide 324, electrical contacts
326 and metallization 328 can be applied. After sensor release 330
and passivation 332, a piezoresistive sensor device 334, such as a
pressure sensor, has been formed next an electrical device, such as
a transistor 322, on the same wafer 302. In other embodiments,
sensor device 334 can comprise another sensor technology and
transistor 322 can comprise some other electrical device. While
FIG. 3, like FIGS. 1 and 2, is an example for monolithic integrated
sensor technology, the concept also has the flexibility to create a
discrete sensor device without electrical devices and/or both
capacitive and piezoresistive sensor devices on the same wafer if
necessary or desired in specific applications.
[0032] FIG. 4 depicts stages in the fabrication of a capacitive
MEMS device 400 formed on a silicon on insulator (SOI) substrate.
While SOI can be more expensive than other technologies, it can
provide a simplified process flow in embodiments.
[0033] Referring to FIG. 4A, an SOI substrate comprises a silicon
substrate 402, a box oxide layer 404 and a thin silicon device
layer 406. In embodiments, layer 406 is about 100 nm to about 400
nm thick.
[0034] In FIG. 4B, a doped layer 408 below box oxide layer 404 is
formed by high-energy implantation. Layer 408 thus can form a
bottom electrode for MEMS devices.
[0035] In FIG. 4C, a monocrystalline silicon layer 410 is formed by
epitaxial growth.
[0036] In FIG. 4D, a cavity 412 is formed by sacrificial layer etch
through release apertures 414. In embodiments, cavity 412 is about
50 nm to about 100 nm high (with respect to the orientation of the
drawing on the page). An optional cavity passivation layer 416,
such as silicon oxide, silicon nitride or some other suitable
material, is deposited and etched back on the wafer surface and can
later assist with cavity sealing.
[0037] In FIG. 4E, a silicon layer 418 is deposited by epitaxial
growth and seals cavity 412. Cavity passivation layer 416 can help
to prevent silicon growth inside cavity 412 under certain process
conditions. What results is a monocrystalline silicon sealed
membrane 418 on top of cavity 412 with a monocrystalline silicon
(418) also on all other areas of the wafer surface.
[0038] In FIG. 4F, a MOS transistor 420 or another electrical
device is formed in common CMOS or BICMOS processing on the same
wafer 402, enabled by the monocrystalline silicon 418. Lateral
electrical isolation between the MEMS device and transistor 420 can
be accomplished by isolation trenches 422. Electrical contact with
the top and bottom electrodes of the sensor device can be
established by contact structures 424.
[0039] In FIG. 4G, a common wafer finishing process with intermetal
oxide 426, electrical contacts 428 and metallization 430 can be
applied. After sensor release 432 and passivation 434, a capacitive
sensor device 436, such as a pressure sensor, is created beside and
on the same wafer as electrical devices, such as transistor 420. In
other embodiments, sensor device 436 can comprise another sensor
technology, and transistor 420 can comprise some other electrical
device. While FIG. 4, like FIGS. 1-3, is an example for monolithic
integrated sensor technology, the concept also has the flexibility
to create a discrete sensor device without electrical devices on
the same wafer if necessary or desired in specific
applications.
[0040] FIG. 5 depicts stages a piezoresistive MEMS device 500
formed on a SOI substrate. While SOI can be more expensive than
other technologies, it can provide a simplified process flow in
embodiments. An SOI substrate 502 has a box oxide layer 504 and a
silicon device layer 506 formed thereon. In embodiments, layer 506
is about 100 nm to about 400 nm thick. A monocrystalline silicon
layer 508 is formed on layer 504 by epitaxial growth. Through
release apertures 510, a cavity 512 is formed by sacrificial layer
etch. In embodiments, cavity 512 is about 50 nm to about 100 nm
high (with respect to the orientation of the drawing on the page).
An optional cavity passivation layer 514, such as silicon oxide,
silicon nitride or some other suitable material, is deposited and
etched back on the wafer surface to assist with later cavity
sealing.
[0041] A silicon layer 516 is then deposited by epitaxial growth,
sealing cavity 512. Cavity passivation layer 514 can help to avoid
silicon growth inside cavity 512 under certain process conditions.
The result is thus a monocrystalline silicon sealed membrane 516 on
cavity 512, with monocrystalline silicon on all other areas of the
wafer surface.
[0042] Implantation of piezoresistors 518 on the monocrystalline
membrane 516 forms a piezoresistive sensor device 520.
[0043] Monocrystalline layer 516 enables electrical devices, such
as a MOS transistor 522, to be processed in common CMOS or BICMOS
on the same wafer 502. A common wafer finishing process with
intermetal oxide 524, electrical contacts 526 and metallization 528
can be applied. After sensor release 530 and passivation 532, a
piezoresistive sensor device 520, such as a pressure sensor, is
formed next to an electrical device, such as transistor 522 or some
other device, on the same wafer 502. In other embodiments, sensor
device 520 can comprise another sensor technology, and transistor
522 can comprise some other electrical device. While FIG. 5, like
FIGS. 1-4, is an example for monolithic integrated sensor
technology, the concept also has the flexibility to create a
discrete sensor device without electrical devices and/or both
capacitive and piezoresistive sensor devices on the same wafer if
necessary or desired in specific applications.
[0044] Embodiments thereby provide cost-efficient, flexible
solutions for monolithic integration of MEMS structures in modern
CMOS and BICMOS technologies. Negative interactions between MEMS
and electrical processing steps are avoided, at least in part by
utilizing a novel cavity sealing process. The smaller dimensions of
the cavity that can be implemented in embodiments also improve the
robustness of the device, reducing the risk of over-stress.
Further, advantages in test stages of manufacturing can also be
provided in embodiments by enabling use of an applied voltage
rather than a physical pressure or acceleration load, thereby
reducing test complexity and efforts. This is enabled at least in
part by the narrower cavity. High flexibility for a variety of
sensing principles, such as capacitive and piezoresistive, is
provided based on the same MEMS technology platform.
[0045] Various embodiments of systems, devices and methods have
been described herein. These embodiments are given only by way of
example and are not intended to limit the scope of the invention.
It should be appreciated, moreover, that the various features of
the embodiments that have been described may be combined in various
ways to produce numerous additional embodiments. Moreover, while
various materials, dimensions, shapes, configurations and
locations, etc. have been described for use with disclosed
embodiments, others besides those disclosed may be utilized without
exceeding the scope of the invention.
[0046] Persons of ordinary skill in the relevant arts will
recognize that the invention may comprise fewer features than
illustrated in any individual embodiment described above. The
embodiments described herein are not meant to be an exhaustive
presentation of the ways in which the various features of the
invention may be combined. Accordingly, the embodiments are not
mutually exclusive combinations of features; rather, the invention
may comprise a combination of different individual features
selected from different individual embodiments, as understood by
persons of ordinary skill in the art.
[0047] Any incorporation by reference of documents above is limited
such that no subject matter is incorporated that is contrary to the
explicit disclosure herein. Any incorporation by reference of
documents above is further limited such that no claims included in
the documents are incorporated by reference herein. Any
incorporation by reference of documents above is yet further
limited such that any definitions provided in the documents are not
incorporated by reference herein unless expressly included
herein.
[0048] For purposes of interpreting the claims for the present
invention, it is expressly intended that the provisions of Section
112, sixth paragraph of 35 U.S.C. are not to be invoked unless the
specific terms "means for" or "step for" are recited in a
claim.
* * * * *