U.S. patent application number 11/363846 was filed with the patent office on 2007-08-30 for method of manufacturing mirror support post of micromirror device using electro-plating process.
Invention is credited to Jin-Wan Jeon, Dae-Hyun Kim, Koeng Su Lim, Jun-Bo Yoon.
Application Number | 20070199823 11/363846 |
Document ID | / |
Family ID | 38442963 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070199823 |
Kind Code |
A1 |
Jeon; Jin-Wan ; et
al. |
August 30, 2007 |
Method of manufacturing mirror support post of micromirror device
using electro-plating process
Abstract
An embodiment of the present invention relates to a digital
micromirror device. More particularly, an embodiment of the present
invention relates to a method of manufacturing a digital
micromirror device having a perfectly flat mirror surface, wherein
a hole of a mirror surface from which light is reflected is
obviated by forming a mirror support post portion using an
electro-plating process, unlike the related art digital micromirror
device in which the hole is formed at the center of the mirror
surface, thereby degrading the reflection efficiency of light.
Inventors: |
Jeon; Jin-Wan; (Seoul,
KR) ; Kim; Dae-Hyun; (Imsil-gun, KR) ; Yoon;
Jun-Bo; (Yuseong-gu, KR) ; Lim; Koeng Su;
(Yuseong-gu, KR) |
Correspondence
Address: |
Klaus P. Stoffel;Wolff & Samson, PC
One Boland Drive
West Orange
NJ
07052
US
|
Family ID: |
38442963 |
Appl. No.: |
11/363846 |
Filed: |
February 28, 2006 |
Current U.S.
Class: |
205/70 |
Current CPC
Class: |
C25D 5/48 20130101; C25D
7/08 20130101; C25D 5/022 20130101 |
Class at
Publication: |
205/070 |
International
Class: |
C25D 1/10 20060101
C25D001/10 |
Claims
1. A method of manufacturing a mirror support post of a micromirror
device using a plating process, the method comprising the steps of:
forming a seed electrode on a substrate; forming a lower electrode,
a driving unit of a micromirror, and a sacrificial layer comprising
a mirror support post formation region on the seed electrode; and
forming a mirror support post in the mirror support post formation
region using an electro-plating process.
2. The method as claimed in claim 1, wherein in the step of forming
the mirror support post, the mirror support post has the same
height as the sacrificial layer.
3. The method as claimed in claim 1, wherein in the step of forming
the mirror support post, the mirror support post has a flat
surface.
4. A method of manufacturing a mirror support post of a micromirror
device using a plating process, the method comprising the steps of:
forming a lower electrode, a sacrificial layer and a cantilever
support post of a driving unit of a micromirror on a substrate;
forming a seed electrode on the cantilever support post of the
driving unit of the micromirror; forming a cantilever of the
micromirror and a sacrificial layer comprising a mirror support
post formation region on the seed electrode; and forming the mirror
support post in the mirror support post formation region using an
electro-plating process.
5. The method as claimed in claim 4, wherein in the step of forming
the mirror support post, the mirror support post has the same
height as the sacrificial layer.
6. The method as claimed in claim 4, wherein in the step of forming
the mirror support post, the mirror support post has a flat
surface.
7. A method of manufacturing a mirror support post of a micromirror
device using a plating process, the method comprising the steps of:
forming a conducting layer on a substrate; forming a lower
sacrificial layer, a hinge and a yoke on the conducting layer;
forming an upper sacrificial layer comprising a mirror support post
formation region on the yoke and the hinge; and forming a mirror
support post in the mirror support post formation region by an
electro-plating process.
8. The method as claimed in claim 7, wherein in the step of forming
the mirror support post, the mirror support post has the same
height as the upper sacrificial layer.
9. The method as claimed in claim 7, wherein in the step of forming
the mirror support post, the mirror support post has a flat
surface.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital micromirror
device, and more particularly, to a method of manufacturing a
digital micromirror device having a perfectly flat mirror surface,
in which the hole of a mirror surface from which light is reflected
is obviated by forming a mirror support post portion using an
electro-plating process, unlike the related art digital micromirror
device in which a hole is formed at the center of the mirror
surface so that the reflection efficiency of light is degraded.
[0003] 2. Background of the Related Art
[0004] FIG. 1 is a cross-sectional view of a micromirror device in
the related art, which is cut on a center line.
[0005] As shown in FIG. 1, the digital micromirror device was first
developed by Texas Instruments Incorporated (U.S.). An example of
the prior art micromirror device is disclosed in U.S. Pat. No.
5,535,047 (issued on Jul. 09, 1996 entitled "Active Yoke Hidden
Hinge Digital Micromirror Device" granted to Larry J. Hornbeck. The
micromirror device is driven by electrostatic force and adopts a
method in which the path of incident light is changed by reflecting
the light according to a driving angle. The micromirror device is
generally used in cantilever display fields.
[0006] Referring to FIG. 1, the related art micromirror device
compises a mirror 11 for reflecting incident light, a mirror
support post 13 for supporting the mirror surface, a twisting hinge
14 to operate the bi-directional tilting of the micromirror device,
a conducting layer 15 for electrical connection, and a yoke 16 that
connects the twisting hinge 14, the mirror support post 13 and so
on.
[0007] A hole 12 exists at the center of the mirror surface due to
the structure of the mirror 11 that reflects the incident light and
the support post 13 that supports the mirror surface. The mirror 11
and the mirror support post 13 are simultaneously fabricated using
a deposition method such as sputtering. As a result, the hole 12 is
inevitably formed at the center of the mirror surface. Reflected
light is lost due to the hole 12 of the mirror surface, which
results in a reduction in the contrast ratio when displaying
images. Furthermore, a central portion within one pixel is always
dark.
[0008] It is therefore necessary to form a perfectly flat mirror
surface by removing the concave hole 12 existing at the center of
the mirror surface to enhance the light use efficiency and the
contrast ratio, to remove a dark region in an image, to save power
consumption when displaying images and to implement images with a
high quality.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention has been made in view of
the above problems, and it is an object of the present invention to
enhance light reflection efficiency and the contrast ratio by
forming a perfectly flat mirror surface by fabricating mirror
support posts of a micromirror device using a plating process.
[0010] To achieve the above object, a method of manufacturing a
mirror support post of a micromirror device using a plating process
according to an embodiment of the present invention compises the
steps of forming a seed electrode on a substrate, forming a lower
electrode, a driving unit of a micromirror and a sacrificial layer
comprising a mirror support post formation region on the seed
electrode, and forming a mirror support post in the mirror support
post formation region using an electro-plating process.
[0011] In the step of forming the mirror support post, the mirror
support post may have the same height as the sacrificial layer.
[0012] In the step of forming the mirror support post, the mirror
support post may have a flat surface.
[0013] To achieve the above object, a method of manufacturing a
mirror support post of a micromirror device using a plating process
according to another embodiment of the present invention comprises
the steps of forming a lower electrode, a sacrificial layer and a
cantilever support post of a driving unit of a micromirror on a
substrate, forming a seed electrode on the cantilever support post
of the driving unit of the micromirror, forming a cantilever of the
micromirror and forming a sacrificial layer comprising a mirror
support post formation region on the seed electrode, and forming
the mirror support post in the mirror support post formation region
using an electro-plating process.
[0014] In the step of forming the mirror support post, the mirror
support post may have the same height as the sacrificial layer.
[0015] In the step of forming the mirror support post, the mirror
support post may have a flat surface.
[0016] To achieve the above object, a method of manufacturing a
mirror support post of a micromirror device using a plating process
according to still another embodiment of the present invention
comprises the steps of forming a conducting layer on a substrate,
forming a lower sacrificial layer, a hinge and a yoke on the
conducting layer, forming an upper sacrificial layer comprising a
mirror support post formation region on the yoke and the hinge, and
forming a mirror support post in the mirror support post formation
region by an electro-plating process.
[0017] In the step of forming the mirror support post, the mirror
support post may have the same height as the upper sacrificial
layer.
[0018] In the step of forming the mirror support post, the mirror
support post may have a flat surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Further objects and advantages of the invention can be more
completely understood from the following detailed description taken
in conjunction with the accompanying drawings in which:
[0020] FIG. 1 is a cross-sectional view of a micromirror device in
the related art, which is cut on a center line;
[0021] FIG. 2 is a dismantled perspective view schematically
showing the construction of a micromirror device according to the
present invention;
[0022] FIG. 3 is a plan view of the micromirror device shown in
FIG. 2, which is vertically viewed downward from the substrate
after the mirror is removed according to the present invention;
[0023] FIG. 4 is a flowchart schematically illustrating a plating
process of a mirror support post of a micromirror device according
to the present invention;
[0024] FIG. 5 is a flowchart illustrating an electro-plating
process of a mirror support post portion of a micromirror device
according to an embodiment of the present invention;
[0025] FIG. 6 is a flowchart illustrating an electroplating process
of a mirror support post portion of a micromirror device according
to another embodiment of the present invention;
[0026] FIG. 7 is a flowchart illustrating an electro-plating
process of a mirror support post portion of a micromirror device
according to still another embodiment of the present invention;
and
[0027] FIG. 8 shows a Scanning Electron Microscope (SEM) photograph
of micromirror devices that are actually fabricated according to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] These and other objects of the present application will
become more readily apparent from the detailed description given
hereinafter. However, it should be understood that the detailed
description and specific examples, while indicating preferred
embodiments of the invention, are given by way of illustration
only, since various changes and modifications within the spirit and
scope of the invention will become apparent to those skilled in the
art from this detailed description.
[0029] The present invention will now be described in detail in
connection with preferred embodiments with reference to the
accompanying drawings.
[0030] FIG. 2 is a dismantled perspective view schematically
showing the construction of a micromirror device according to the
present invention.
[0031] As shown in FIG. 2, the micromirror device compises a mirror
20, a substrate 21, a plurality of electrodes 22, a plurality of
cantilever support posts 23, a plurality of cantilevers 25 and a
plurality of mirror support posts 24.
[0032] In the micromirror device, an addressing circuit (not shown)
is formed in the substrate 21. The electrodes 22 are formed on the
substrate 21. Each of the three cantilever support posts 23 is
attached to the substrate 21. Each of three cantilevers 25 has a
flat plate and has its one end attached on each of the three
cantilever support posts 23. The mirror 20 is disposed on the
mirror support posts 24, each attached on the other end of each of
the cantilevers 25.
[0033] The cantilever support posts 23 that support the neighboring
cantilevers 25 intersect each other on the substrate 21. The three
mirror support posts 24 are adhered to the mirror 20 at locations
opposite to that of the cantilever support posts 23 of the
cantilevers 25.
[0034] The cantilever 25 that connects the cantilever support
post23 and the mirror support post24 is bent up and down under
expansion and contraction stress by electrostatic force generated
by a voltage applied to the electrodes 22 on the substrate 21 and
thus rotates the mirror 20.
[0035] In the three mirror support posts 24 that support the mirror
20, a location at which the substrate 21 is fixed and a location at
which the mirror 20 is attached intersect each other. Therefore,
the mirror 20 has two kinds of rotation states where it is inclined
either right or left at a predetermined angle depending on a
direction in which electrostatic force is applied. The rotation
angle of the mirror can also be controlled according to an amount
of applied electrostatic force.
[0036] A pair of the electrodes 22 for driving the mirror 20 is
connected to an addressing circuit (not shown).
[0037] FIG. 3 is a plan view of the micromirror device shown in
FIG. 2, which is vertically viewed downward from the substrate
after the mirror is removed according to the present invention.
[0038] Referring to FIG. 3, the cantilever support posts 23 for
supporting the cantilevers 25 and the mirror support posts 24 for
supporting the mirror 20 are symmetrical to each other on the basis
of the horizontal center line (a-a') of the substrate. The
electrodes 22 for addressing the mirror are symmetrical to each
other on the basis of the vertical center line (b-b') of the
substrate.
[0039] It has been shown in FIG. 3 that the electrodes 22 are not
overlapped with the cantilever support posts 22. However, the
present invention can be implemented even if the electrodes 22 and
the cantilever support posts 23 do not overlap.
[0040] Through the above structure, the mirror is applied with some
degree of force in two directions along which the mirror is
rotated. Therefore, the mirror can have the two kinds of rotation
states.
[0041] FIG. 4 is a flowchart schematically illustrating a plating
process of a mirror support post of the micromirror device
according to the present invention.
[0042] The plating process applied to the present invention
comprises a general electro-plating method.
[0043] In the general electro-plating method, if a sample 31
becoming a conducting layer and an electrode 33 are dipped into a
plating solution 30 and are then applied with a voltage, metal ions
32 within the plating solution 30 form the conducting layer in the
sample 31 according to a pattern shape of a pattern layer 34.
[0044] In the plating process of forming the mirror support posts
according to the present invention using the electro-plating
method, a seed metal 35, i.e., the conducting layer is previously
formed on the substrate 36 so that electricity can conduct on the
surface of the substrate 36.
[0045] For such electro-plating to be performed only in a selected
region of the surface of the substrate 36, it is necessary to block
a non-conductive material using the pattern layer 34. A photoresist
film used in the pattern layer 34 can be formed of an organic
material such as polymer. The organic material is not conductive
and can be thus used as an electro-plating mask. After the
completion of the electro-plating, the photoresist film that is no
longer necessary is removed using an organic solvent such as
acetone. The photoresist film can be removed easily using an
organic solvent since it is an organic material.
[0046] Where the electro-plating metal (refers to the mirror
support posts of the present invention) is used without being
separated from the substrate 36, it is preferred that the seed
metal 35 of the selective region be removed to prevent the entire
substrate from being electrically by the seed metal 35.
[0047] In this case, the seed metal 35 below the electro-plating
metal is not removed, but only the seed metal 35 in the region
where the electro-plating metal is not formed is removed.
[0048] Therefore, the plating process can deposit the conducting
layer without limitation in height using an external power supply
source that is electrically connected and the plating solution.
[0049] If the method is used, a metal pole with a high vertical
ratio can be formed in fully filled form. It is therefore possible
to fabricate the mirror support posts that support the mirror in
fully filled form in the micromirror manufacturing method of the
present invention.
[0050] The present applicant proposed Korean Patent Publication No.
2003-0023300 entitled "Micromirror Device Using Interdigitated
Cantilevers and Its Applications." A formation method of mirror
support posts will be described based on the structure disclosed in
the above patent.
[0051] FIG. 5 is a flowchart illustrating an electro-plating
process of a mirror support post portion of a micromirror device
according to an embodiment of the present invention. FIG. 5 is a
cross-sectional view of the micromirror device taken along line
a-a' in FIG. 3.
[0052] As shown in FIG. 5, to fabricate mirror support posts, a
mirror support post formation region 41 is required.
[0053] As shown in FIG. 5(a), the mirror support post formation
region 41 is formed using a photolithography process.
[0054] A seed electrode 44 is first formed on a substrate 45.
[0055] A lower electrode 48 for applying a voltage to rotate the
mirror, a driver 43 having a cantilever and a cantilever support
post, for driving the micromirror device, and a sacrificial layer
42 comprising the mirror support post formation region 41 are
formed on the seed electrode 44 by means of a photolithography
process.
[0056] The photolithography process is a process that has been
widely known to those skilled in the art. Therefore, description
thereof will be omitted. The region 41 in which the mirror support
post will be formed is patterned by the process.
[0057] Referring to FIG. 5(b), the region 41 formed in FIG. 5(a) is
filled with metal by means of the electro-plating method described
with reference to FIG. 4. In this case, the metal 46 becomes the
mirror support post.
[0058] In this case, it is preferred that the metal 46 filled by
electro-plating has the same height as the sacrificial layer
42.
[0059] Referring to FIG. 5(c), after the mirror support post 46 is
formed, a mirror 47 is formed by a deposition process and a
photolithography process.
[0060] In this case, if the mirror support post 46 is formed to
have the same height as the sacrificial layer 42 by the
electro-plating process, the region to be used as the mirror
support post 46 is completely filled with a metal material.
[0061] If the mirror 47 is formed by a method, such as the
deposition method, by forming the mirror support post 46 whose hole
is fully filled, a region on which the mirror 47 will be deposited
when forming the mirror 47 becomes perfectly flat. Therefore, the
mirror 47 having a perfectly flat can be formed.
[0062] Therefore, it is preferred that the mirror support post be
formed to have the same height as the sacrificial layer and to have
a perfectly flat surface, by accurately controlling the plating
method.
[0063] Thereafter, the sacrificial layer 42 is removed and the seed
electrode 44 formed for the plating process is removed, if needed,
for the purpose of avoiding an electrical short circuit.
[0064] FIG. 6 is a flowchart illustrating an electro-plating
process of a mirror support post portion of a micromirror device
according to another embodiment of the present invention. FIG. 6 is
a cross-sectional view of the micromirror device taken along line
a-a' in FIG. 3.
[0065] The mirror support post portion shown in FIG. 6 is different
from that of FIG. 5 in that a seed electrode 54 for electrical
connection of an electro-plating process is formed not on a
substrate 56, but formed in a sacrificial layer 52.
[0066] Referring to FIG. 6(a), a mirror support post formation
region 51 is formed using a photolithography process.
[0067] A lower electrode 55 to which a voltage is applied to rotate
the mirror, the seed electrode 54 formed in the sacrificial layer
52 and a cantilever support post of a driving unit 53 of the
micromirror, the driving unit 53 of the micromirror having a
cantilever and a cantilever support post, and a sacrificial layer
52 comprising the mirror support post formation region 51 are
formed by a photolithography process.
[0068] In the same manner as FIG. 5, the photolithography process
is a process that has been widely known to those skilled in the
art. Therefore, description thereof will be omitted. The region 51
in which a mirror support post will be formed is patterned by the
process.
[0069] Referring to FIG. 6(b), the region 51 formed in FIG. 6(a) is
filled with metal by means of the electro-plating method that has
been described with reference to FIG. 4. The mirror support post 57
that is fully filled can be formed without limitation in height. In
this case, the metal 57 filled by electro-plating becomes the
mirror support post.
[0070] In this case, it is preferred that the electroplated region
51 is formed to have the same height as the sacrificial layer
52.
[0071] Referring to FIG. 6(c), after the mirror support post 57 is
formed, a mirror 58 is deposited on the mirror support post 57.
[0072] If the mirror 58 is formed by a method, such as the
deposition method, by forming the mirror support post 57 as
described above, the mirror 57 having a perfectly flat surface can
be fabricated.
[0073] The region 51 that is previously defined by a
photolithography process, which is one of processes of forming a
semiconductor pattern, is filled using a plating process.
[0074] The conducting layer 54 for electrical connection of the
electro-plating process can be formed between-the-sacrificial layer
52. The micromirror structure comprises a conductive material such
as metal for the purpose of voltage application.
[0075] In the electro-plating process, since deposition is
performed beginning from an electrically connected portion, the
hole is sequentially filled. The mirror support post 57 that is
fully filled can be formed without limitation in height.
[0076] The plated region can be formed to have the same height as
the sacrificial layer 52.
[0077] By forming the mirror support post 57 as described above,
the mirror 58 with a perfectly flat surface can be formed if the
mirror 58 is formed using a method such as the deposition
method.
[0078] Thereafter, the sacrificial layer 52 is removed and the
metal layer 54 formed for the plating process is then removed, as
necessary, for the purpose of avoiding an electrical short
circuit.
[0079] FIG. 7 is a flowchart illustrating an electro-plating
process of a mirror support post portion of a micromirror device
according to still another embodiment of the present invention.
FIG. 7 is a flowchart illustrating an electro-plating process of
the mirror support post portion of the micromirror device shown in
FIG. 1.
[0080] FIG. 7(a) is a cross-sectional view of the micromirror
device in which an upper sacrificial layer 61 and a lower
sacrificial layer 62 are formed to form a conducting layer 65, a
hinge 64, a yoke 66 and a mirror support post 63. The conducting
layer 65 for electrical connection is first formed on a substrate
70. The lower sacrificial layer 62 for forming the hinge 64 is then
formed. The lower sacrificial layer 62 is removed by a subsequent
process. A space from which the lower sacrificial layer 62 is
removed remains as an air gap. The hinge 64 is formed on the lower
sacrificial layer 62.
[0081] The yoke 66 is then formed on the hinge 64. The upper
sacrificial layer 61 comprising a mirror support post formation
region 60 is formed on the yoke 66 and the hinge 64.
[0082] Referring to FIG. 7(b), the mirror support post 63 is formed
in the mirror support post formation region 60 by an
electro-plating process as described above. The mirror support post
63 may have the same height as the upper sacrificial layer 61 and
may have a perfectly flat surface.
[0083] Referring next to FIG. 7(c), the mirror 64 is deposited on
the upper sacrificial layer 61 and the mirror support post 63. As
shown in FIG. 7(d), the upper sacrificial layer 61 and the lower
sacrificial layer 62 are removed.
[0084] In this case, if the micromirror device of FIG. 1 is
fabricated by completely filling the mirror support post 63 using
the electro-plating process, a perfectly flat mirror surface cam be
formed as described above.
[0085] At this time, the conducting layer 65 may be used as a seed
electrode (refers to 44 in FIG. 5) for electrical connection for
the purpose of the electro-plating process. Alternatively, the
conducting layer 65 may be formed on the hinge 64 and may be used
as the seed electrode, as shown in FIG. 6. On the other hand, after
the upper sacrificial layer 61 and the lower sacrificial layer 62
are removed, the conducting layer 65 may be removed, if necessary,
for avoiding an electrical short circuit.
[0086] FIG. 8 is a SEM photograph of micromirror devices that are
actually fabricated according to the present invention.
[0087] As described above, according to the present invention, a
pole that supports a mirror surface is formed by a plating method.
Therefore, a hole of a mirror surface that reflects light can be
obviated. Therefore, the present invention is advantageous in that
a micromirror device can have a perfectly flat mirror surface.
[0088] Furthermore, a perfectly flat mirror surface can be formed.
Therefore, the present invention is advantageous in that it can
improve the reflection efficiency of light, obtain a high contrast
ratio of display images with a high quality and save power
consumption.
[0089] While the present invention has been described with
reference to the particular illustrative embodiments, it is not to
be restricted by the embodiments but only by the appended claims.
It is to be appreciated that those skilled in the art can change or
modify the embodiments without departing from the scope and spirit
of the present invention.
* * * * *