Method of manufacturing a microstructure

Details Method of manufacturing a microstructure Method of manufacturing a microstructure

2001-11-29

2003-06-24

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S291000, C359S221200, C438S052000

Reexamination Certificate

active

06583920

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2000-72123, filed Nov. 30, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a micromirror actuator, and more particularly, to a method of manufacturing a micromirror actuator that increases a flatness of a micromirror through the lamination of a film-type organic layer and a simplified process of planarizing the micromirror.
2. Description of the Related Art
A micro optical cross connector (MOXC) as used in optical communications is a device that selects an optical path to allow an optical signal to be transmitted from a certain input terminal to a certain output terminal. The core element of the MOXC in optical communications is a micromirror. Thus, the optical communication efficiency and performance of the MOXC is strongly dependent on the reflectivity of the micromirror and the ability of the micromirror to stand erect.
Referring to
FIG. 1
, a conventional micromirror actuator includes a substrate
100
, a trench
105
formed in the substrate
100
, lower and side electrodes
110
and
113
formed at a corresponding bottom and side of the trench
105
, posts
115
that protrude from the substrate
100
in an area outside the trench
105
, torsion springs
120
supported by the posts
115
, and a micromirror
125
elastically supported by the torsion springs
120
to be capable of rotating.
The micromirror
125
can be rotated by electrostatic forces generated through an interaction with the lower electrode
110
. The micromirror
125
can stand erect due to an interaction with the side electrode
113
. The micromirror
125
can also maintain its parallel state when voltage is turned off. A micromirror actuator having the above structure can select an optical path by reflecting optical signals when the micromirror
125
stands erect over the substrate
100
, and also allows the optical signals to directly pass over the surface of the micromirror
125
when the micromirror
125
is parallel with the surface of the substrate
100
.
When the micromirror actuator has the trench
105
, it is necessary therefore to planarize the micromirror
125
to increase its reflectivity.
FIGS. 2A through 2C
are cross-sectional views illustrating a conventional method of manufacturing the micromirror actuator as viewed along line V—V of FIG.
1
. The conventional process of planarizing the micromirror actuator includes forming the trench
105
by etching a portion of a silicon wafer
130
to a predetermined depth (shown in FIG.
2
A), thickly depositing a photoresist
135
by spin coating (shown in FIG.
2
B), and planarizing the photoresist
135
by chemical mechanical polishing (CMP) (shown in FIG.
2
C).
However, when the photoresist
135
is planarized by CMP, a cushion phenomenon occurs causing the surface of the photoresist
135
to become irregular as shown in FIG.
3
. In other words, the planarization of the photoresist
135
is performed while applying weight to the photoresist
135
in a lapping device (not shown). However, when the silicon wafer
130
is taken out from the lapping device after completing the planarization of the photoresist
135
, the cushion phenomenon occurs at the photoresist
135
. The cushion phenomenon occurs when a predetermined portion of the silicon wafer
130
to which weight has been applied swells up. The reason the cushion phenomenon occurs will be described in the following.
In
FIG. 2B
, the photoresist
135
deposited to a predetermined thickness h on the silicon wafer
130
is soft. In addition, the height of the photoresist
135
deposited over the trench
105
is less than the height of the photoresist
135
deposited outside the trench
105
by as much as a height difference of h′. Accordingly, the photoresist
135
deposited over the trench
105
is slightly recessed when the photoresist
135
is polished by CMP to planarize its surface.
After polishing of the photoresist
135
, the hardness of the resulting structure in a trench region becomes different from the hardness of the resulting structure outside the trench region. In other words, the lengthwise hardness of the structure including the photoresist
135
and the silicon wafer
130
in the trench region is equal to the sum of the hardness of photoresist
135
t
1
remaining over the trench
105
after the CMP, the hardness of photoresist
135
t
2
filling the trench
105
, and the hardness of a lower wafer
130
t
under the photoresist
135
t
2
. On the other hand, the lengthwise hardness of the structure outside the trench region is equal to the sum of the hardness of photoresist
135
n
remaining on the silicon wafer
130
outside the trench
105
after the CMP and the hardness of a lower silicon wafer
130
n
under the photoresist
135
n
. Here, since the hardness of the silicon wafer
130
is greater than the hardness of the photoresist
135
, the lengthwise hardness of the structure including the photoresist
135
and the silicon wafer
130
is greater outside the trench region than in the trench region. Accordingly, the photoresist
135
expands more in the region of the trench
105
than in the region around the trench
105
, producing a swell C on the surface of the photoresist
135
as shown in FIG.
3
. This swelling effect is referred to as the cushion phenomenon.
As described above, if the CMP that is usually applied to silicon is directly performed on the photoresist
135
deposited over the trench
105
, the photoresist
135
cannot be planarized because of the cushion phenomenon. In order to properly planarize the photoresist
135
, the CMP must therefore be performed twice. Accordingly, the costs of the planarization increases, the reflectivity of the micromirror may deteriorate, and an optical loss may increase.
SUMMARY OF THE INVENTION
To solve the above and other problems, it is an object of the present invention to provide a method of manufacturing a micromirror actuator that increases a flatness of a micromirror by laminating a film-type polyimide layer, enhances a reflectivity of the micromirror, and simplifies a process of planarizing the micromirror.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, a method of manufacturing a micromirror actuator according to an embodiment of the invention includes forming a trench on a substrate by etching, laminating a film-type organic layer on the substrate to cover but not fill the trench so that the trench remains hollow, depositing and patterning a metal layer on the film-type organic layer, and removing the film-type organic layer.
According to another embodiment of the invention, the method further includes forming a lower electrode and a side electrode by depositing and patterning an insulating layer and a metal layer on the substrate after forming the trench region, forming post holes by patterning the film-type organic layer after laminating the film-type organic layer, and forming a micromirror, torsion springs, and posts by patterning the metal layer on the film-type organic layer, and removing the film-type organic layer.


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patent: 402117115 (1990-05-01), None

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