U.S. patent application number 09/976316 was filed with the patent office on 2004-11-11 for method of fabricating anti-stiction micromachined structures.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Bae, Ki-deok, Yoon, Yong-seop.
Application Number | 20040224523 09/976316 |
Document ID | / |
Family ID | 19710174 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040224523 |
Kind Code |
A1 |
Bae, Ki-deok ; et
al. |
November 11, 2004 |
METHOD OF FABRICATING ANTI-STICTION MICROMACHINED STRUCTURES
Abstract
A method of fabricating micro-electromechanical system (MEMS)
structures that can prevent stiction between a microstructure and a
substrate or adjacent structures after etching for releasing the
microstructure is provided. In a micromaching process for
fabricating a microstructure suspended above a substrate using a
sacrificial layer, the fabricating method includes stacking an
anti-stiction layer, which can be removed by dry etching, before or
after stacking a sacrificial layer.
Inventors: |
Bae, Ki-deok; (Kyungki-do,
KR) ; Yoon, Yong-seop; (Seoul, KR) |
Correspondence
Address: |
SUGHRUE, MION, ZINN,
MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washingon
DC
20037-3202
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
|
Family ID: |
19710174 |
Appl. No.: |
09/976316 |
Filed: |
October 15, 2001 |
Current U.S.
Class: |
438/706 |
Current CPC
Class: |
B81B 3/0005
20130101 |
Class at
Publication: |
438/706 |
International
Class: |
H01L 021/302; H01L
021/461 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2001 |
KR |
2001-30085 |
Claims
1-8. (canceled).
9. A method for fabricating microstructures, the method comprising:
preparing a substrate; forming an anti-stiction layer on the
substrate; forming a sacrificial layer on the anti-stiction layer;
forming at least one structure layer for creating at least one
microstructure on the sacrificial layer; and removing the
sacrificial layer by wet etching and removing the anti-stiction
layer by dry etching in order to release the at least one
microstructure while preventing stiction.
10. The method of claim 9, wherein the anti-stiction layer is
formed of one of polymer and polycrystalline silicon.
11. The method of claim 9, wherein the anti-stiction layer is
formed of photoresist.
12. The method of claim 9, wherein the sacrificial layer is formed
of one selected from the group consisting of phosphosilicate glass
(PSG), silicon oxide, low temperature oxide, copper, iron,
molybdenum, nickel, chrome, and tetraethylorthosilicate glass
(TEOS).
13-14. (canceled).
15. A method of fabricating microstructures, the method comprising:
preparing a substrate; forming a sacrificial layer on the
substrate; forming an anti-stiction layer on the sacrificial layer;
and forming at least one structure layer for forming at least one
microstructure on the anti-stiction layer and removing the
sacrificial layer by wet etching while removing the anti-stiction
layer by dry etching in order to release the at least one
microstructure while preventing stiction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of fabricating
micro-electromechanical system (MEMS) structures and, more
particularly, to a microstructure fabricating method for preventing
stiction between a micromachined structure and a substrate or
adjacent structures after an etching process for releasing the
micromachined structure.
[0003] 2. Description of the Related Art
[0004] As shown in FIG. 1, an MEMS structure commonly referred to
as a "microstructure" is fabricated by wet etching for releasing a
portion of a microstructure 106 from a substrate 100 and creating a
"suspended" microstructure having a space or gap 110 between a
released portion 104 and the substrate 100 and one or more posts
102 attached to the substrate 100. The microstructure 106 including
the released portion 104 takes the form of a beam or plate having
top and bottom surfaces which are suspended to be substantially
parallel with the surface of the substrate 100. Examples of a
device having the suspended microstructure 106 may include
accelerometers, pressure sensors, flow sensors, transducers, and
microactuators. The term microstructure in this specification
collectively refers to a structure fabricated by an MEMS
fabrication technology including but not limited to
photolithography, thin film deposition, bulk micromachining,
surface micromachining, and etching.
[0005] A release etching method has two types of processes: a
process to create a cavity in the substrate 100 ("bulk
micromachining") and a process to remove a sacrificial layer at an
intermediate portion of the microstructure 106 and the substrate
100 ("surface micromachining"). In both micromachining processes,
the released portion 104 of the microstructure 106 often
permanently sticks to the substrate 100 or adjacent structures
during post-etch cleaning and drying steps as shown in 108 of FIG.
1.
[0006] More specifically, in the surface micromachining technique
for creating the released portion 104 of the microstructure 106, a
sacrificial layer is removed by common wet etching. In this case,
the substrate 100 is exposed to a chemical etching solution for
decomposing only the sacrificial layer not affecting a material of
the microstructure 106 and then cleaned with a cleaning solution.
When removing the cleaning solution, the surface tension of the
solution affects the released portion 104 of the suspended
microstructure 106 to adhere the bottom surface of the released
portion 104 to the substrate 100 or adjacent other structures as
shown in 108 of FIG. 1. The adhesion is called "stiction." This
stiction degrades the sensitivity of a sensor. Furthermore, severe
stiction results in failure in device fabrication and consequently
drops a micromachining process yield rate.
[0007] A variety of techniques have been developed to avoid
stiction. One technique is to reduce the contact area between a
released portion and a substrate as much as possible. Another
technique is to solidify and sublimate an etching cleaning solution
which is the cause of the surface tension between the released
portion of the microstructure and the substrate. Similar to this
technique, as disclosed in G. T. Mulhern et al., Proc. Int. Conf.
Solid State Sensors & Actuators (Transducers '93), Yokohama,
1993 (IEEJ, Tokyo, 1993) p. 296, a pressure-controlled and
temperature-controlled chamber is used to sublimate a cleaning
solution in its supercritical state.
[0008] The above methods for preventing stiction suffer from drops
in a yield rate and require additional fabrication steps and
expensive equipment. Furthermore, the stiction due to surface
tension forces may be basically removed by dry etching, but use of
the dry etching may damage the material of a suspended
microstructure such as polycrystalline silicon. Furthermore, none
of the above methods prevents stiction due to an elastic force
other than surface tension.
SUMMARY OF THE INVENTION
[0009] To solve the above problems, it is an aspect of the present
invention to provide a method for fabricating a microstructure that
can prevent stiction of a microstructure to a substrate during a
microstructure fabrication process in a simple way.
[0010] Accordingly, the present invention provides a method of
fabricating a micromachined structure suspended above a substrate
using a sacrificial layer. The method includes the step of stacking
an anti-stiction layer that can be removed by dry etching before or
after stacking the sacrificial layer.
[0011] The anti-stiction layer, which may be formed of polymer,
polycrystalline silicon or photoresist that can be removed by dry
etching, is formed on the substrate. However, the anti-stiction
layer may be formed after stacking the sacrificial layer.
[0012] If the anti-stiction layer is formed on the substrate before
stacking the sacrificial layer, the sacrificial layer and the
microstructure are sequentially formed on the anti-stiction layer.
The sacrificial layer is removed by wet etching. In this case, the
anti-stiction layer is removed by dry etching, thus providing a
microstructure without stiction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above aspects and advantages of the present invention
will become more apparent by describing in detail an exemplary
embodiment thereof with reference to the attached drawings, in
which:
[0014] FIG. 1 shows stiction of a micromachined structure;
[0015] FIGS. 2A-2E show process steps of a method of fabricating an
anti-stiction micromachined structure according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring to FIG. 2A, a substrate 100 having a predetermined
shape formed of an appropriate material such as silicon is
prepared. Then, a dry-etchable material such as polymer or
polycrystalline silicon ("polysilicon") is deposited on the
substrate to a thickness of about 3 .mu.m to form an anti-stiction
layer 101. For example, the anti-stiction layer may be Accuflo,
SOG, or photoresist. In this embodiment, the photoresist 101 is
used as the dry-etchable material.
[0017] Subsequently, as shown in FIG. 2B, phosphosilicate glass
(PSG), silicon oxide, low temperature oxide, copper, iron,
molybdenum, nickel, chrome, or tetraethylorthosilicate glass (TEOS)
is deposited on the photoresist 101 in order to form a sacrificial
layer 103. Then, as shown in FIG. 2C, using Al as an etch mask 105,
the anti-stiction layer such as photoresist 101 and the sacrificial
layer 103 stacked on the substrate 100 are etched to form a hole
107 for a post. Then, as shown in FIG. 2D, polysilicon 109, which
will be a micromachined structure ("microstructure"), is deposited
over the resulting structure from which the mask 105 has been
removed.
[0018] Referring to FIG. 2E, the sacrificial layer 103 is removed
by an etching solution such as a hydrogen fluoric (HF) solution in
order to form a released portion of a suspended microstructure 109.
The photoresist 101 deposited on the substrate 100 is removed by
isotropic dry etching, thereby fabricating the suspended
microstructure 109 having the release portion without stiction to
the substrate 100.
[0019] As described above, the fabricating method according to the
present invention is able to prevent stiction that may occur in
removing the sacrificial layer 103 through wet etching.
Furthermore, dry etching is used to remove the anti-stiction layer
101 while the inexpensive wet etching is used to remove the
sacrificial layer 103, thereby manufacturing the microstructure 109
in a cost-effective way.
[0020] While this invention has been particularly shown and
described with reference to an exemplary embodiment thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made therein without departing from the
spirit and scope of the invention as defined by the appended
claims.
[0021] For example, although stiction may occur between a
microstructure and a substrate or any adjacent structure, the
embodiment of the present invention has been described only with
respect to stiction occurring between a microstructure and a
substrate. It will be understood by those skilled in the art that
the present invention is applicable to stiction which may occur
between a microstructure and an adjacent microstructure other than
a substrate.
[0022] Furthermore, while an anti-stiction layer and a sacrificial
layer are sequentially deposited on a substrate in the exemplary
embodiment of the present invention, the anti-stiction layer may be
deposited on the sacrifical layer in order to manufacture a
suspended microstructure.
[0023] Thus, it is contemplated that numerous modifications may be
made to the method of the present invention without departing from
the spirit and scope of the invention as defined in the following
claims.
* * * * *