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JP2012040619

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DESCRIPTION JP2012040619
The present invention provides a capacitive MEMS sensor that does not require an additional
step of forming a protrusion and a method of manufacturing the same. A sacrificial layer 14 and
a fixed electrode 15 are laminated and formed on a diaphragm film 13 constituting a movable
portion. A through hole 17 is formed in the fixed electrode, and isotropic etching is performed
from this through hole. As a result, a part of the sacrificial layer can be left on the diaphragm
membrane farthest from the through hole. A part of this sacrificial layer is used as the protrusion
21 to prevent the movable part and the fixed electrode from sticking. [Selected figure] Figure 1
Capacitive MEMS sensor and method of manufacturing the same
[0001]
The present invention relates to a capacitive MEMS sensor in which a hollow structure is formed
by removing a sacrificial layer, and relates to a capacitive MEMS sensor including a protrusion
that prevents the movable part and the fixed electrode from sticking to each other, and a method
of manufacturing the same.
[0002]
In recent years, MEMS sensors formed using a manufacturing process of a semiconductor device
have been widely used.
In the structure of a general capacitive MEMS sensor, one of the electrodes is a movable
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structure (referred to as a movable portion or a movable electrode), and a fixed electrode is
formed so as to face it. A hollow structure is formed between the movable part and the fixed
electrode, and the movable part is displaced by the action of a mechanical quantity such as
pressure, and the amount of displacement is regarded as displacement of a capacitance value,
converted into an electrical signal and output Is configured to
[0003]
When forming a hollow structure of a capacitive MEMS sensor having such a structure, it is
general to form a film called a sacrificial layer between the movable portion and the fixed
electrode and etch away this sacrificial layer. is there.
[0004]
As etching for forming the hollow structure, a wet etching method using a hydrofluoric acid
solution or a dry etching method using a hydrofluoric acid gas is employed.
In general, it is preferable to use the wet etching method because the wet etching method is less
expensive than the dry etching method.
[0005]
In the wet etching method, after the etching of the sacrificial layer is completed, in order to
remove the hydrofluoric acid solution, it is necessary to immerse in a replacement solution such
as pure water or alcohol and to dry it. However, there is a problem that the movable portion and
the fixed electrode are stuck due to the surface tension of the substitution solution used at this
time.
[0006]
In order to solve such a problem, Patent Document 1 proposes a method of forming a protrusion
on the movable portion. FIG. 2 is an explanatory view of a manufacturing method of a capacitive
MEMS sensor according to a conventional method. First, the fixed electrode 2 is formed on the
silicon substrate 1, and the sacrificial layer 3 is laminated on the portion where the hollow
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portion is to be formed (FIG. 2a).
[0007]
Thereafter, the recess 4 is formed in the sacrificial layer 3 in the portion where the protrusion of
the movable portion is to be formed. The recess 4 is formed by a normal photolithographic
method. That is, the photoresist film is patterned so as to open the formation planned region of
the recess 4, and a part of the sacrificial layer 3 exposed in the opening of the photoresist film is
etched to form the recess 4. Formed by removing the membrane (Figure 2b).
[0008]
Thereafter, a film 5 to be a movable electrode is laminated on the sacrificial layer 3 in which the
concave portion 4 is formed, and patterned into a desired shape. Here, as shown in FIG. 2C, the
film 5 to be the movable electrode is also filled in the recess 4 formed previously. Thereafter, by
removing the sacrificial layer 3, the movable portion 5 having the hollow portion 6 and the
projection 7 can be formed (FIG. 2d).
[0009]
When the projections 7 are formed in this way, even when the sacrificial layer 3 is removed by
wet etching, only the tips of the projections 7 stick to the fixed electrode due to the surface
tension of the substitution liquid, and they are easily separated. It is possible to solve the problem
that the movable part and the fixed electrode stick.
[0010]
As another method, it is also known to form a projection on the fixed electrode by forming a
small LOCOS oxide film on a silicon substrate before forming the fixed electrode and forming the
fixed electrode on the convex portion. It is done.
[0011]
Japanese Patent Application Laid-Open No. 9-18021
[0012]
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As described above, in order to solve the problem that the movable part and the fixed electrode
stick, the method of forming the protrusion proposed in the prior art forms a recess in the
manufacturing process of a normal capacitive MEMS sensor It is necessary to add a process for
forming the LOCOS film and a process for forming the LOCOS oxide film, which causes a problem
that the number of manufacturing processes is increased.
[0013]
An object of the present invention is to solve the above-mentioned problems, and to provide a
capacitive MEMS sensor capable of forming a protrusion only by the manufacturing process of a
normal capacitive MEMS sensor and a method of manufacturing the same.
[0014]
In order to achieve the above object, according to the first invention of the present application,
the movable portion and the fixed electrode have a hollow structure formed by removing a
sacrificial layer, and the displacement of the movable portion is included in the movable portion.
In a capacitive MEMS sensor that outputs as a change in capacitance between a movable
electrode and the fixed electrode, a plurality of through holes are formed in the fixed electrode,
and a position between the through hole and another through hole A protrusion is formed on the
movable portion opposite to the other, leaving a part of the sacrificial layer removed when
forming the hollow structure.
[0015]
In a method of manufacturing a capacitive MEMS sensor according to a second aspect of the
present invention, there is provided a method of forming a first film to be a film constituting a
movable portion or a film constituting a fixed electrode on a silicon substrate; A step of forming a
sacrificial layer on the upper side, a step of forming a second film to be a film constituting the
fixed electrode or a film constituting the movable portion on the sacrificial layer, and a film
constituting the fixed electrode In the second film or the first film, the distance between one
through hole arranged in the projection formation planned area and another through hole is
arranged in the area where the projection is not formed Forming a film constituting a fixed
electrode having a plurality of through holes arranged to have a distance larger than the distance
between the first and the other through holes, and removing a part of the silicon substrate to
form a back chamber And the sacrificial layer from the through hole. The first film or the second
film to be a film constituting the movable portion located between the through hole and another
through hole which are widely spaced apart from each other. A part of the layer is left, and a
hollow structure and a step of forming a protrusion are provided.
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[0016]
According to the method of manufacturing a capacitive MEMS sensor of the present invention, a
protrusion can be formed without an additional process for forming a protrusion, and a
capacitive MEMS sensor with reduced manufacturing cost can be provided.
[0017]
Further, the size and height of the projections can be formed with good controllability only by
controlling the arrangement of the through holes and the etching of the sacrificial layer.
[0018]
In the capacitive MEMS sensor of the present invention, since the tip of the protrusion can be
sharpened, the protrusion itself does not stick to the fixed electrode.
In addition, since a very small protrusion can be formed as compared with the conventional
protrusion and the LOCOS oxide film, the protrusion does not affect the sensor sensitivity.
[0019]
It is a figure explaining the manufacturing process of the capacitive MEMS sensor of the present
invention.
It is a figure explaining the manufacturing process of the conventional capacitive MEMS sensor.
[0020]
According to the method of manufacturing a capacitive MEMS sensor of the present invention, it
is possible to form a capacitive MEMS sensor including a movable portion having a protrusion
without adding an additional manufacturing step to the manufacturing step of a conventional
capacitive MEMS sensor. Is possible.
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Hereinafter, examples of the present invention will be described in detail according to the
manufacturing process.
[0021]
First, a silicon substrate 11 with a crystal orientation of (100) on the surface is prepared, and a
thermal oxide film 12 with a thickness of 0.3 μm is formed on the surface and the back as a first
insulating film.
Further, a polysilicon film having a thickness of 0.1 μm is formed on the surface side thermal
oxide film 12 by the CVD (Chemical Vapor Deposition) method, and patterning is performed by
the normal photolithography method to obtain the diaphragm film 13 to be a movable portion.
Form (Figure 1a).
[0022]
Thereafter, a 2 μm thick USG (Undoped Silicate Glass) film 14 is laminated and formed as a
second insulating film on the entire surface.
This USG film corresponds to a sacrificial layer.
Further, a polysilicon film 15 of 1.0 μm in thickness to be a fixed electrode is formed on the USG
film 14, and then a silicon nitrogen film 16 of 0.2 μm in thickness is formed over the entire
surface (FIG. 1b).
[0023]
Next, in order to remove the USG film 14 corresponding to the previously formed sacrificial layer
in a later step, a plurality of through holes 17 are formed to expose a part of the surface of the
USG film 14 (FIG. 1C).
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Further, in the present invention, in order to form a protrusion, the through hole 17 is disposed
at a desired position described later.
The through hole 17 also functions as a sound hole for transmitting sound to the diaphragm film
13 of the movable part, for example, when the capacitive MEMS sensor is used as a microphone,
so that desired characteristics can be obtained. It is necessary to set the size, number and
arrangement of diameters.
[0024]
Wiring portions 18 respectively connecting the diaphragm film 13 of the movable portion and
the polysilicon film 15 to be a fixed electrode are formed (FIG. 1d).
Thereafter, a part of the thermal oxide film 12 on the back surface side of the silicon substrate
11 is etched away to expose the silicon substrate 11. Then, using the thermal oxide film 12 as an
etching mask, the silicon substrate 11 is etched using a reaction limited etching solution such as
tetra methyl ammonium hydroxide (TMAH). At this time, the surface of the silicon substrate 11 is
protected by the etching protective film 19. Since the silicon substrate 11 uses a substrate having
a predetermined plane orientation, etching in which the (111) plane appears is performed, and a
back chamber 20 as shown in FIG. 1E can be formed.
[0025]
Thereafter, the protective film 19 is removed, and the USG film 14 is etched from the through
hole 17 in order to form a hollow structure between the movable portion and the fixed electrode.
The etching solution used here has a high etching selectivity with the wiring material constituting
the wiring portion 18 and uses a hydrofluoric acid mixed acid aqueous solution capable of
performing isotropic etching. Specifically, a mixture of ammonium fluoride and acetic acid is
used.
[0026]
In the case of the above structure, this etching solution has an etching rate of 4.2 μm / h in the
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lateral direction in the vicinity of the through hole 17 near the surface, and in the vicinity of the
diaphragm film 13. Then, the etching rate in the lateral direction is 3.7 μm / h. Therefore, in the
portion where it is desired to form a protrusion, the mutual spacing of at least three through
holes 17 is set larger than the mutual spacing of all through holes 17 in the portion where it is
desired to remove all USG films 14.
[0027]
Then, by controlling the etching time advancing isotropically from each through hole, it is
possible to leave a portion which is not etched in the portion farthest from the through hole. A
portion of the sacrificial layer remaining without being etched is a protrusion. Since the shape of
the projection thus formed is by isotropic etching, the tip can have a sharp tip.
[0028]
Specifically, in the portion where the protrusion is formed, the distance between the center of the
through hole and the center of another through hole is 3.6 μm, and in the portion where the
protrusion is not formed, the distance is 3.1 μm. As a result, when etching is performed for 1
hour using the etching solution having the above etching rate, the protrusion 21 with a tip of 0.6
μm on one side of the bottom and a height of 0.6 μm is formed on the diaphragm film 13.
Could be formed (FIG. 1f).
[0029]
Thus, in the present invention, the protrusions 21 can be formed simultaneously with the
conventional removal process of the sacrificial layer, and no special process for forming the
protrusions 21 is required. In the present invention, it is only necessary to change the
arrangement of the through holes 17 in order to form the projections.
[0030]
The size and height of the protrusions can also be adjusted by appropriately setting the thickness
of the sacrificial layer, the arrangement of the through holes, the etching rate, the etching time,
and the like.
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[0031]
As described above, according to the present invention, the protrusions can be formed easily.
In the capacitive MEMS sensor formed according to the present invention, since the sharp
projections are formed by the wet etching method when the sacrificial layer is etched away, the
movable portion and the fixed electrode do not stick.
[0032]
In the above embodiment, the case where the diaphragm film 13 is formed on the silicon
substrate 11 has been described, but it is also possible to form a fixed electrode on the silicon
substrate 11. In that case, after the back chamber 20 is formed, the USG film 14 to be a sacrificial
layer may be removed by etching from the back chamber 20 side. The protrusions 21 can be
formed on the diaphragm film 13 also by such a manufacturing process.
[0033]
11: Silicon substrate, 12: thermal oxide film, 13: diaphragm film, 14: USG film, 15: polysilicon
film, 16: silicon nitrogen film, 17: through hole, 18: wiring portion, 19: etching protective film,
20 : Back chamber, 21: projection
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