U.S. patent application number 11/117155 was filed with the patent office on 2006-11-02 for micromirrors for micro-electro-mechanical systems and methods of fabricating the same.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Co., Ltd.. Invention is credited to Chia-Chiang Chen, Alan Lee, Shen-Ping Wang.
Application Number | 20060245029 11/117155 |
Document ID | / |
Family ID | 37234156 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060245029 |
Kind Code |
A1 |
Wang; Shen-Ping ; et
al. |
November 2, 2006 |
MICROMIRRORS FOR MICRO-ELECTRO-MECHANICAL SYSTEMS AND METHODS OF
FABRICATING THE SAME
Abstract
A micromirror for micro-electro-mechanical systems. The
micromirror comprises a pad layer, a doped aluminum layer
containing 0.002 wt % to 0.3 wt % of silicon overlying the pad
layer and a protective layer overlying the doped aluminum
layer.
Inventors: |
Wang; Shen-Ping; (Keelung
City, TW) ; Lee; Alan; (Taipei City, TW) ;
Chen; Chia-Chiang; (ShinChu City, TW) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
100 GALLERIA PARKWAY, NW
STE 1750
ATLANTA
GA
30339-5948
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Co., Ltd.
|
Family ID: |
37234156 |
Appl. No.: |
11/117155 |
Filed: |
April 28, 2005 |
Current U.S.
Class: |
359/290 |
Current CPC
Class: |
G02B 26/0833 20130101;
G02B 5/0808 20130101 |
Class at
Publication: |
359/290 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. A micromirror for micro-electro-mechanical systems, comprising:
a pad layer; a doped aluminum layer containing 0.002 wt % to 0.3 wt
% of silicon overlying the pad layer; and a protective layer
overlying the doped aluminum layer.
2. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, further comprising a pure aluminum layer under the
doped aluminum layer.
3. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, further comprising a pure aluminum layer overlying the
doped aluminum layer.
4. The micromirror for micro-electro-mechanical systems as claimed
in claim 3, wherein the pure aluminum layer is contacted with the
doped aluminum layer.
5. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, further comprising two pure aluminum layers so that the
doped aluminum layer is interposed between the pure aluminum
layers.
6. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the doped aluminum layer has a thickness of
about 2000 angstroms to 3000 angstroms.
7. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the doped aluminum layer contains 0.1 wt % to
0.25 wt % of silicon.
8. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the protective layer is a titanium layer or a
titanium nitride layer, or a composite layer comprising titanium
and titanium nitride.
9. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the protective layer has a thickness of about
100 angstroms to 800 angstroms.
10. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the pad layer comprises an oxide layer and has
a thickness of about 300 angstroms to 500 angstroms.
11. The micromirror for micro-electro-mechanical systems as claimed
in claim 1, wherein the doped aluminum layer is a copper-free
aluminum layer.
12. A micromirror for micro-electro-mechanical systems, comprising:
a pad layer; a dopant-containing aluminum layer overlying the pad
layer, the dopant being selected from a group consisting of
neodymium, tantalum, cobalt, nickel, chromium, molybdenum, and
titanium or combination thereof, and having a concentration of 0.01
wt % to 2 wt %; and a protective layer overlying the
dopant-containing aluminum layer.
13. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, further comprising a pure aluminum layer under the
dopant-containing aluminum layer.
14. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, further comprising a pure aluminum layer overlying the
doped aluminum layer.
15. The micromirror for micro-electro-mechanical systems as claimed
in claim 14, wherein the pure aluminum layer is contacted with the
dopant-containing aluminum layer.
16. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, further comprising two pure aluminum layers so that
the dopant-containing aluminum layer is interposed between the pure
aluminum layers.
17. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, wherein the dopant-containing aluminum layer has a
thickness of about 2000 angstroms to 3000 angstroms.
18. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, wherein the protective layer is a titanium layer or a
titanium nitride layer, or a composite layer comprising titanium
and titanium nitride.
19. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, wherein the protective layer has a thickness of about
100 angstroms to 800 angstroms.
20. The micromirror for micro-electro-mechanical systems as claimed
in claim 12, wherein the pad layer comprises an oxide layer and has
a thickness of about 300 angstroms to 500 angstroms.
Description
BACKGROUND
[0001] The present invention relates to micromirrors for
micro-electro-mechanical systems (MEMSs). More particularly, the
present invention relates to micromirrors using doped aluminum
layer and methods of fabricating the same.
[0002] New advancements in projection systems utilize an optical
semiconductor known as a digital micromirror device. A digital
micromirror device chip is one of the most sophisticated light
switches in the field. It contains an array of 750,000 to 1.3
million pivotally-mounted microscopic mirrors. Each mirror may
measure less than 1/5 of the width of a human hair and corresponds
to one pixel in a projected image. The digital micromirror device
chip can be combined with a digital video or graphic signal, a
light source and projector lens so that the micromirrors reflect an
all-digital image onto a screen or other surface.
[0003] US patent publication number 2004/0223240 discloses
micromirror arrays having a reflective layer comprising gold,
silver, titanium, or aluminum. The micromirror optimizes the
contrast ratio of the micromirror array so that when the
micromirrors are in their `off` state they send minimal light to
the spatial region where light is directed when micromirrors are in
their `on` state.
[0004] U.S. Pat. No. 6,778,315 discloses a Micro mirror structure
with flat reflective coating. Each mirror includes a substrate, a
diffusion barrier layer located above the substrate, and a
reflective layer located above the diffusion barrier layer. The
reflective layer comprises gold, silver or aluminum.
[0005] U.S. Pat. No. 6,800,210 discloses a method for making a
micromechanical device by removing a sacrificial layer with
multiple sequential etchants. The micromechanical device uses metal
such as gold, silver or aluminum as reflective layer.
[0006] Conventional micromirrors often include hillocks (raised
feature or bumps) or voids in the reflective layer. The hillocks or
voids may however cause artifacts or distortions in the projected
image. Conventional micromirrors also tend to have unstable
light-reflecting characteristics, possibly resulting from large
surface roughness of the reflective layer.
SUMMARY
[0007] Accordingly, an object of the invention is to provide a
micromirror having improved light-reflecting characteristics.
[0008] Another object of the invention is to provide a micromirror
to reduce surface roughness.
[0009] Still another object of the invention is to provide a
micromirror having a reflective layer which is substantially devoid
of precipitates.
[0010] In accordance with the objects, an embodiment of micromirror
for micro-electro-mechanical systems comprises a pad layer; a doped
aluminum layer containing 0.002 wt % to 0.3 wt % of silicon
overlying the pad layer; and a protective layer overlying the doped
aluminum layer.
[0011] Another embodiment of micromirror for
micro-electro-mechanical systems comprises a pad layer; a
dopant-containing aluminum layer overlying the pad layer, the
dopant is selected from a group consisting of silicon, neodymium,
tantalum, cobalt, nickel, chromium, molybdenum, and titanium or
combination thereof; and a protective layer overlying the
dopant-containing aluminum layer. The dopant may have a
concentration of about 0.01 wt % to 2 wt %.
[0012] In accordance with the objects, one embodiment of a method
of fabricating a micromirror for micro-electro-mechanical systems
is provided. A pad layer is formed followed by forming a
dopant-containing aluminum layer on the pad layer, the dopant is
selected from a group consisting of silicon, neodymium, tantalum,
cobalt, nickel, chromium, molybdenum, and titanium or combination
thereof. A protective layer is then deposited overlying the
dopant-containing aluminum layer.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0014] FIG. 2 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0015] FIG. 3 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0016] FIG. 4 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0017] FIG. 5 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0018] FIG. 6 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems.
[0019] FIG. 7 is a schematic diagram of an embodiment of a pair of
micromirrors attached to a transparent substrate.
[0020] FIG. 8 is a schematic diagram of an embodiment of multiple
micromirrors mounted in a digital mirror device.
[0021] FIG. 9 is a flowchart of an embodiment of a method of
fabricating a micromirror for micro-electro-mechanical systems.
DESCRIPTION
[0022] FIG. 1 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems. The micromirror 1 comprises a
pad layer 10, a doped aluminum layer 12 overlying the pad layer and
a protective layer 20 consisting of a titanium layer 14 and a
titanium nitride layer 16. The pad layer 10 may comprise silicon
oxide such as plasma enhanced silicon oxide (PEOX) and have a
thickness between about 300 angstroms and 500 angstroms. The pad
layer 10 protects the doped aluminum layer 12 from oxidation or
damage. Doping a dopant, for example silicon, into aluminum, may
reduce the surface roughness of the doped aluminum layer 12. It is
likely that the higher the concentration of silicon, the smaller
the surface roughness of the doped aluminum layer 12, thereby
improving light-reflecting characteristics. The silicon doped
concentration, however, exceeds its solubility at an operational
temperature of, for example 0.degree. C. to 200.degree.0 C., in a
micro-electro-mechanical system, thus, silicon particles may
precipitate on the surface of the doped aluminum layer 12,
potentially resulting in undesirable roughness problems. In one
embodiment, the doped aluminum layer may contain 0.002 wt % to 0.3
wt %, preferably 0.1 wt % to 0.25 wt %, of silicon at room
temperature about 25.degree. C. The doped aluminum layer 12 may
have a thickness of about 2000 angstroms to 3000 angstroms. In one
embodiment of the invention, the doped aluminum layer 12 is
preferably a copper-free aluminum layer.
[0023] The protective layer 20 comprises, but is not limited to, a
composite layer of the mentioned titanium layer 14 and titanium
nitride layer 16. An embodiment of protective layer 20 may
alternately comprise a single titanium layer or a single titanium
nitride layer. Moreover, the protective layer 20 may have a
thickness of about 100 angstroms to 800 angstroms. An embodiment of
the mirror may alternately comprises a doped aluminum layer
containing a dopant selected from a group consisting of neodymium,
tantalum, cobalt, nickel, chromium, molybdenum, and titanium or
combination thereof. That is, at least neodymium, tantalum, cobalt,
nickel, chromium, molybdenum, or titanium may replace silicon as a
dopant of the doped aluminum layer. The doped concentration of
neodymium, tantalum, cobalt, nickel, chromium, molybdenum, or
titanium is about 0.01 wt % to 2 wt %.
[0024] Alternately, an embodiment of a micromirror for
micro-electro-mechanical systems is shown in FIG. 2. The
micromirror 2 comprises pad layer 10 and protective layer 20 being
the same as those in FIG. 1. The micromirror 2 further comprises a
composite reflective layer consisting of the doped aluminum layer
12a and a pure aluminum layer 18 thereunder. The reflective layer
may have a thickness of about 2000 angstroms to 3000 angstroms. The
pure aluminum layer 18 may substantially reduce or eliminate the
formation of pits in the reflective layer.
[0025] FIG. 3 is a cross section of another embodiment of a
micromirror for micro-electro-mechanical systems. The micromirror 3
comprises pad layer 10 and protective layer 20 being the same as
those in FIG. 1. The micromirror 3 further comprises a composite
reflective layer consisting of the doped aluminum layer 12b and a
pure aluminum layer 18 thereon. The reflective layer may have a
thickness of about 2000 angstroms to 3000 angstroms.
[0026] FIG. 4 is a cross section of an embodiment of a micromirror
for micro-electro-mechanical systems. The micromirror 4 comprises
pad layer 10 and protective layer 20 being the same as those in
FIG. 1. The micromirror 4 further comprises a composite reflective
layer consisting of two pure aluminum layers 18a and 18b and the
doped aluminum layer 12c interposed therebetween.
[0027] Alternately, an embodiment of a micromirror for
micro-electro-mechanical systems is shown in FIG. 5. The
micromirror 5 comprises pad layer 10, protective layer 20 being the
same as those in FIG. 1. The micromirror 5 further comprises a
composite reflective layer consisting of pure aluminum layers 18b
and 18c and doped aluminum layers 12d and 12e. The pure aluminum
layer 18c, doped aluminum layer 12d, pure aluminum layer 18d, and
doped aluminum layer 12e are sequentially formed on the pad layer
10 by physical vapor deposition.
[0028] FIG. 6 is a cross section of another embodiment of a
micromirror for micro-electro-mechanical systems. The micromirror 6
comprises pad layer 10 and protective layer 20 being the same as
those in FIG. 1. The micromirror further comprises a composite
reflective layer consisting of doped aluminum layers 12f and 12g
and pure aluminum layers 18e and 18f. The doped aluminum layer 12f,
pure aluminum layer 18e, doped aluminum layer 12g, and pure
aluminum layer 18f are sequentially formed on the pad layer 10 by
physical vapor deposition.
[0029] The pure aluminum layers mentioned above may substantially
reduce or eliminate the formation of pits in the reflective
layer.
[0030] FIG. 7 is a schematic diagram of an embodiment of a pair of
micromirrors attached to a transparent substrate. Each of the
micromirrors contains a reflective layer comprising a doped
aluminum layer mentioned above.
[0031] The assembly 94 may comprise a transparent substrate 86. A
hinge 84 is formed on the transparent substrate 86. Each
micromirror 72 is secured to the transparent substrate 86 for
pivotal movement with respect to the corresponding hinge 84 and the
transparent substrate 86 by a hinge support 84a. Fabrication of the
assembly 94 can be carried out using conventional techniques known
to those skilled in the art.
[0032] FIG. 8 is a schematic diagram of an embodiment of multiple
micromirrors mounted in a digital mirror device 98. An assembly 96
may comprise a semiconductor device such as, but not limited to, a
complementary metal-oxide semiconductor (CMOS) device. Multiple
electrodes 90, one for each micromirror 72 of the assembly 94, are
formed on the semiconductor device 88. Each of the electrodes 90
communicates with electronic circuitry (not shown) on the
semiconductor device 88 so that each electrode 90 may be
selectively activated in response to a video or graphic signal.
Fabrication of the assembly 96 can be carried out using
conventional techniques known to those skilled in the art.
[0033] As further shown in FIG. 8, the digital mirror device 98
typically comprises the assembly 94 flipped over and overlying the
assembly 96 so the micromirrors 82 of the assembly 94 face and are
closet to the respective electrodes 90 of the assembly 96. Spacers
85 are provided so that the micromirrors 72 are set apart the
respective electrode so that each micromirror 72 can freely pivot
on the corresponding hinge 84 respective to activation of an
associated electrode 90.
[0034] In operation of the digital mirror device 98, as light 92 is
directed onto the micromirrors 72, electrode 90 associated with
each micromirror 72 may be activated to cause the micromirror 72 to
pivotally move about the corresponding hinge 84. Therefore,
depending on whether or not the electrode 90 associated with any
particular micromirror 72 has been activated, the light 92 may or
may not be reflected from that micromirror 72. Depending on how
fast and how often a particular micromirror 72 is deflected by the
corresponding electrode 90, the image (pixel) projected by the
mirror 72 will appear light or dark on a projection screen (not
shown) or other surface. It will be appreciated by those skilled in
the art that, due to the reduced surface roughness of the doped
aluminum layer in each micromirror 72 as well as the absence
precipitates, hillocks, pits, or voids thereof, the micromirrors 72
may project a high-quality image from the digital mirror device 98
onto the projection screen (not shown) or other surface.
[0035] FIG. 9 is a flowchart of an embodiment of a method of
fabricating a micromirror for micro-electro-mechanical systems.
This method comprises steps S10 to S14. First, in step S10 a pad
layer is formed. The pad layer may comprise silicon oxide and is
formed on a substrate having an amorphous silicon layer
(sacrificial layer) thereon by plasma enhanced chemical vapor
deposition. In step S12 a doped aluminum layer is formed on the pad
layer. The doped aluminum layer is preferably formed by physical
vapor deposition (PVD) or sputtering using a doped aluminum or an
aluminum alloy target. Alternately, a pure aluminum layer is
deposited followed by doping at least one dopant into the pure
aluminum layer. The doping method includes ion implantation,
chemical reaction or ion diffusion at a thermal ambient of about
20.degree. C. to 560.degree. C.
[0036] The dopant is preferably silicon and the doped aluminum
layer may contain 0.002 wt % to 0.3 wt %, preferably 0.1 wt % to
0.25 wt %, of silicon at room temperature of about 25.degree. C.
The dopant may alternately be selected from a metallic group
consisting of neodymium, tantalum, cobalt, nickel, chromium,
molybdenum, and titanium or combination thereof. The doped aluminum
layer may contain 0.01 wt % to 2 wt % of metal mentioned above.
[0037] Next, in step S14 a protective layer is deposited on the
doped aluminum layer. The protective layer comprises but not
limited to a composite layer of titanium layer and titanium nitride
layer. An embodiment of protective may alternately comprise a
single titanium layer or titanium nitride layer.
[0038] One embodiment of the method further comprises a step of
forming a pure aluminum layer overlying the doped aluminum layer
after step S12. The pure aluminum layer may contacts with the pad
layer. Another embodiment of the method further comprises a step of
forming a pure aluminum layer under the doped aluminum layer before
step S12. Alternately, one embodiment of the method comprises the
steps of forming pure aluminum layers before and after step S12
respectively so that the doped aluminum layer is interposed between
the pure aluminum layers.
[0039] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. To the contrary, it is intended
to cover various modifications and similar arrangements (as would
be apparent to those skilled in the art). Therefore, the scope of
the appended claims should be accorded the broadest interpretation
so as to encompass all such modifications and similar
arrangements.
* * * * *