U.S. patent application number 11/278758 was filed with the patent office on 2006-07-27 for system and method for direct-bonding of substrates.
Invention is credited to Chien-Hua Chen, Charles C. Haluzak.
Application Number | 20060163712 11/278758 |
Document ID | / |
Family ID | 34964255 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060163712 |
Kind Code |
A1 |
Chen; Chien-Hua ; et
al. |
July 27, 2006 |
SYSTEM AND METHOD FOR DIRECT-BONDING OF SUBSTRATES
Abstract
A MEMS package includes a first substrate having a bonding
surface and a second substrate having a polished bonding surface
facing the bonding surface of the first substrate. The MEMS package
further includes a polished layer of bonding substrate material
deposited onto the bonding surface of the first substrate and
fusion bonded to the polished bonding surface of the second
substrate.
Inventors: |
Chen; Chien-Hua; (Corvallis,
OR) ; Haluzak; Charles C.; (Corvallis, OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD
INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Family ID: |
34964255 |
Appl. No.: |
11/278758 |
Filed: |
April 5, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10816509 |
Mar 31, 2004 |
|
|
|
11278758 |
Apr 5, 2006 |
|
|
|
Current U.S.
Class: |
257/680 ;
257/687 |
Current CPC
Class: |
B81C 2203/036 20130101;
B81B 7/0067 20130101 |
Class at
Publication: |
257/680 ;
257/687 |
International
Class: |
H01L 23/02 20060101
H01L023/02 |
Claims
1. A MEMS package, comprising: a first substrate having a bonding
surface; a second substrate having a polished bonding surface
facing the bonding surface of the first substrate; and a polished
layer of bonding substrate material deposited onto the bonding
surface of the first substrate and fusion bonded to the polished
bonding surface of the second substrate.
2. A MEMS package according to claim 1, wherein the polished
bonding surface of the second substrate and the polished layer of
bonding substrate material have Angstrom-level flatness.
3. A MEMS package according to claim 1, wherein the first
substrate, the second substrate and the bonding substrate material
each have a substantially identical refractive index.
4. A MEMS package according to claim 1, wherein the first
substrate, the second substrate and the bonding substrate material
form a hermetic seal around a MEMS device.
5. A digital projector, comprising: a MEMS package, wherein the
package comprises: a first substrate having a bonding surface; a
second substrate having a polished bonding surface facing the
bonding surface of the first substrate; and a polished layer of
bonding substrate material deposited onto the bonding surface of
the first substrate and fusion bonded to the polished bonding
surface of the second substrate.
6. A digital projector according to claim 5, wherein the polished
bonding surface of the second substrate and the polished layer of
bonding substrate material have Angstrom-level flatness.
7. A digital projector according to claim 5, wherein the first
substrate, the second substrate and the bonding substrate material
each have a substantially identical refractive index.
8. A digital projector according to claim 5, wherein the first
substrate, the second substrate and the bonding substrate material
form a hermetic seal around a MEMS device.
9. A MEMS package, comprising: a first substrate having a bonding
surface; a second substrate having a polished bonding surface
facing the bonding surface of the first substrate; and means for
bonding deposited onto the bonding surface of the first substrate
and fusion bonded to the polished bonding surface of the second
substrate.
10. A MEMS package formed by a method comprising the steps of:
depositing a layer of bonding substrate material onto a bonding
surface of a first substrate; increasing a bonding site density of
at least one of either the layer of bonding substrate material on
said first substrate or a bonding surface of a second substrate;
and bonding the bonding surface of the first substrate having the
layer of bonding substrate material to the bonding surface of the
second substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
10/816,509, filed Mar. 31, 2004, hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the field of
bonding of substrates. In particular, the invention relates to
methods of bonding substrates in MEMS and other devices to reduce
the reflection loss of light.
[0003] MEMS and other devices often include two or more substrates
either in close proximity or bonded together. For example, in
optical systems such as digital projectors, a device may include an
interference-based digital light display (DLD) package which
includes two or more substrates to direct light to and from the
DLD. Similar to a CRT in a rear-projection television, a DLD can be
used in digital projectors for processing or generating an image
from a source light.
[0004] One such DLD package is illustrated in FIG. 1. The package
100 includes a base substrate 120 with a driving electrode 122, a
pixel plate 110 which can move vertically, and a thin protective
substrate or membrane 130. A reflective coating may be provided on
the pixel plate 110, and a partial reflective coating may be
provided on the bottom surface of the membrane 130. The protective
membrane 130 encloses a cavity in which the DLD pixel plate 110 is
enclosed and allows some light to pass therethrough. In some cases,
such as in the case of the package 100 illustrated in FIG. 1, a
second substrate 140, which may be made of thick glass, is provided
in close proximity to the protective membrane 130 for processing
the light, for example. The protective membrane 130 and the second
substrate 140 are separated by a bond ring 150 positioned at the
perimeter of the protective membrane 130 and the second substrate
140. Thus, light 160 from a source (not shown) can pass through the
second substrate 140 and the protective membrane 130 to reach the
pixel plate 110. By moving the pixel plate vertically, different
light colors are generated as a result of light interference. As
the gap between the pixel plate 110 and the protective membrane 130
changes, the processed light 170 (image) goes through the second
substrate 140 to additional light processing components such as
lenses, for example.
[0005] As the light 160, 170 passes through the protective membrane
130 and the second substrate 140, it passes through regions of
differing refractive indices (RI's). For example, the protective
membrane 130 and the second substrate 140 may each have a different
RI, while the space between the protective membrane 130 and the
second substrate 140 may have a third different RI. This change in
RI along the path of the light causes a portion of the light 160,
170 to be lost as reflected light 180, thereby reducing the quality
of the image generated by the DLD package 100. To counter the
reflection, the various surfaces of the protective membrane 130 and
the second substrate 140 may be provided with anti-reflective
coating. Such coating can be expensive and difficult to implement,
particularly for certain internal surfaces. Further, the package
may not be hermetically sealed, as moisture or gas molecules may
penetrate the bond ring 150.
SUMMARY OF THE INVENTION
[0006] One embodiment of the invention relates to a method of
bonding substrates. The method includes depositing a layer of
bonding substrate material onto a bonding surface of a first
substrate. A bonding site density of at least one of the layer of
bonding substrate material on the first substrate and a bonding
surface of a second substrate is increased, and the bonding surface
of the first substrate having the layer of bonding substrate
material is bonded to the bonding surface of the second
substrate.
[0007] Another embodiment of the invention relates to a MEMS
package. The package includes a first substrate having a bonding
surface, a second substrate having a polished bonding surface
facing the bonding surface of the first substrate, and a polished
layer of bonding substrate material deposited onto the bonding
surface of the first substrate and fusion bonded to the polished
bonding surface of the second substrate.
[0008] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and exemplary only, and are not restrictive of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross-sectional view of a prior art MEMS
device;
[0010] FIG. 2 is a cross-sectional view of a MEMS device according
to an embodiment of the invention;
[0011] FIG. 3 is a cross-sectional view of the MEMS device of FIG.
2 prior to bonding of the substrates; and
[0012] FIG. 4 is a flow chart illustrating a method of bonding
substrates according to an embodiment of the invention.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0013] Referring to FIG. 2, a cross-sectional view of a package
according to an embodiment of the invention is illustrated. In one
embodiment, the package 200 includes an image processing device for
use in a digital projector. The package 200 includes an exemplary
digital light display (DLD) device with a pixel plate 210 mounted
on a support base 220 with a driving electrode 222. Of course,
other optical devices may be used, such as a liquid crystal display
(LCD) or liquid crystal on silicon (LCOS), for example. Such
optical devices are well known to those skilled in the art and do
not require further discussion for purposes of this application.
While the package 200 in the illustrated embodiment is an optical
device, it will be understood by those skilled in the art that the
invention is not limited to optical devices and may include other
devices having two or more substrates.
[0014] The support base 220 may be made of a variety of materials,
such as a semiconductor or a non-conductive substrate, and may have
a thickness selected to provide sufficient strength to support the
DLD pixel plate 210. The material and thickness of the support base
220 is not limiting on the invention.
[0015] The pixel plate 210 is encased by a protective membrane 230
mounted on the support base 220. The substrate 230 can be made of a
variety of materials. In one embodiment, the protective membrane
230 is made of tetraethoxysilane (TEOS). The protective membrane
230 may have a partial reflective coating on its bottom surface and
can allow portion of an incoming light to pass therethrough. The
light is reflected back from the pixel plate 210 to generate the
desirable interference color effect based on the gap between the
pixel plate 210 and the protective membrane 230. The protective
membrane 230 may have a known refractive index (RI). In the case of
TEOS, the protective membrane 230 has an RI of approximately 1.5.
In one embodiment, the protective membrane 230 has a thickness of
between 0.5 and 2.0 microns at least in the region above the pixel
plate 210.
[0016] A lid 240 is positioned above the protective membrane 230.
For an optical device, the lid 240 is adapted to allow light to
pass therethrough. In a particular embodiment, the lid 240 is made
of a substrate material, such as glass, and has a thickness of
between 0.5 and 3 mm. The thickness of the lid 240 may be selected
according to various system requirements, such as gas permeability,
for example. The lid 240 may have an RI that is similar or
different from the RI of the substrate 230. In one embodiment, the
lid 240 is formed of glass and has an RI of approximately 1.5,
similar to the RI of the protective membrane 230.
[0017] The lid 240 and the protective membrane 230 are bonded
together with a thin layer 250 of a bonding substrate material
therebetween. The layer of bonding substrate material 250 is
positioned between the protective membrane 230 and the lid 240 and
has a thickness on the order of a few microns. In a particular
embodiment, the layer 250 is formed of a material having an RI that
is similar to the RI at least one of the protective membrane 230
and the lid 240. The bonding substrate material may include any or
a variety of materials. For example, the bonding substrate material
may be a semiconductor, a dielectric or an insulator material. The
bonding substrate material may be formed of polysilicone, TEOS,
silicon nitride, or glass frit material, for example. In one
embodiment, the bonding substrate material is formed of TEOS that
has been deposited onto a bonding surface of the lid 240, as
described below with reference to FIGS. 3 and 4.
[0018] In this arrangement, the need for an anti-reflective (AR)
coating is eliminated on the bonding surfaces of the lid 240 and
the protective membrane 230. Since the RI of each of the protective
membrane 230, lid 240 and the layer 250 may be selected to be
similar to each other, the undesired reflection of light from the
bonding surfaces is eliminated or substantially reduced. Thus, in
one embodiment, the protective membrane 230 and the layer 250 may
be formed of TEOS, and the lid 240 may be formed of glass, each
having an RI of approximately 1.5.
[0019] An embodiment of a process of forming the package of FIG. 2
will now be described with reference to FIGS. 3 and 4. The method
400 includes depositing a layer of bonding substrate material 250,
such as TEOS, amorphous silicon, phosphosilicate glass (PSG), glass
frit, or silicon nitride to a bonding surface 242 of the lid 240,
which may be formed of glass (block 410). The bonding substrate
material 250 may be deposited through a variety of methods such as
sputtering, chemical vapor deposition (CVD), or screen print, for
example. The layer of bonding substrate material 250 is a
relatively thin layer having a thickness on the order of between
tens of an angstrom and tenths of a micron. In one embodiment, an
AR coating is applied to the opposite surface of the lid 240.
[0020] The bonding surfaces may be polished for smoothness. In this
regard, the bonding surface 232 of the protective membrane 230 and
the layer of bonding substrate material 250 on the bonding surface
242 of the lid 240 may be polished to Angstrom-level flatness via
chemical-mechanical polishing (CMP), for example.
[0021] At block 420, the bonding site (silanol group) density of at
least one of the bonding surfaces is increased to provide a more
secure bonding of the substrates. The bonding site density may be
increased through, for example, plasma treatment and an optional
wet treatment with either de-ionized water or SC1 (Standard Clean
1) chemistry. In this regard, the bond density of the bonding
surface 232 of the protective membrane 230 or the layer of bonding
substrate material 250 on the bonding surface 242 of the lid 240
may be increased through any of a variety of methods including
plasma treatment, ion implant and physical sputtering. In a
particular embodiment, the bonding site density is increased for
both surfaces. The increase in bonding site density effectively
increases the bond strength of the samples.
[0022] In one embodiment, the bonding site density is increased by
plasma treating the bonding surfaces. This may be accomplished
through, for example, an ion beam sputtering process, a reactive
ion etcher, striking plasma onto the bonding surface, ion
implantation or ion bombardment. The plasma treatment may use
O.sub.2, N.sub.2 or Ar plasma, for example.
[0023] Following the plasma treatment, the bonding surfaces may be
dipped in de-ionized water or SC1 chemistry for a period of time.
In this regard, a minute or less is generally sufficient to
increase the silanol group (Si--OH) density of the surfaces. For
example, dipping for five minutes may be sufficient. The surfaces
may then be dried using, for example, a spin-rinse drier. Other
methods of increasing bonding site density are well known to those
skilled in the art and are contemplated within the scope of the
invention.
[0024] At block 430, the bonding surfaces are fusion bonded at room
temperature. The fusion bonding may be accomplished by holding the
bonding surfaces together while applying a compression force. The
increased bonding site density allows the fusion bonding to be
performed at substantially room temperature, rather than typical
fusion bonding processes which may require annealing temperatures
as high as 900 .degree. C. "Room temperature," as used herein,
includes temperatures ranging between approximately 15 and
approximately 40.degree. C.
[0025] In one embodiment, the package 200 is annealed. In one
embodiment, the lid 240 formed of glass with a thin layer 250 of
TEOS is bonded to a protective membrane 230 formed of TEOS, and the
package 200 is annealed at approximately 200.degree. C. for
approximately two hours.
[0026] Thus, the protective membrane 230 and the lid 240 are bonded
to each other with no need for AR coating on the bonding surfaces
232, 242. The increasing of the silanol-group density through
plasma treatment and post-bond annealing provide a bond of
sufficient strength to secure the protective membrane 230 and the
lid 240 to each other. Further, the package 200 may be made
hermetically sealed by assuring that the lid 240 is sufficiently
thick to prevent moisture or gas molecules to penetrate
therethrough. In this regard, a lid 240 formed of glass and having
a thickness between 0.5 and 3 mm is sufficient.
[0027] The foregoing description of embodiments of the invention
have been presented for purposes of illustration and description.
It is not intended to be exhaustive or to limit the invention to
the precise form disclosed, and modifications and variation are
possible in light of the above teachings or may be acquired from
practice of the invention. The embodiment was chosen and described
in order to explain the principles of the invention and its
practical application to enable one skilled in the art to utilize
the invention in various embodiments and with various modification
as are suited to the particular use contemplated. It is intended
that the scope of the invention be defined by the claims appended
hereto and their equivalents.
* * * * *