JP5708290B2 - Manufacturing method of MEMS device, MEMS device, pressure sensor, and ultrasonic transducer - Google Patents

Description

  The present invention relates to a MEMS device manufacturing method for manufacturing a MEMS device having a uniform functional film, a MEMS device manufactured by the manufacturing method, and an ultrasonic transducer.

2. Description of the Related Art Conventionally, a MEMS (Micro Electro Mechanical Systems) device including a functional film (membrane) having a uniform film thickness is known (see, for example, Patent Document 1).
This patent document 1 is an ultrasonic sensor in which a piezoelectric body is laminated on a diaphragm. This ultrasonic sensor applies a voltage to the piezoelectric body and vibrates the diaphragm (functional film) to output ultrasonic waves, or converts the displacement of the diaphragm that is vibrated by receiving ultrasonic waves into an electrical signal using the piezoelectric body. It is a sensor that outputs. In such an ultrasonic sensor, one surface (first surface) of the Si substrate on the flat plate is oxidized to form a SiO ₂ film, and the surface opposite to the surface on which the SiO ₂ film is formed (second surface). ), A mask having a hole at the position where the diaphragm is formed is formed. Then, by etching the second surface side of the Si substrate, a portion corresponding to the hole of the mask is etched using the SiO ₂ film as an etching stopper, and a diaphragm of the SiO ₂ film is formed.

JP 2010-147658 A

By the way, in the ultrasonic sensor described in Patent Document 1, a hole portion of the mask is provided corresponding to the entire region of the diaphragm formation region, and the portion exposed from the hole portion is etched up to the diaphragm.
Here, in order to form the diaphragm with a uniform film thickness, it is necessary to ensure that the etching solution reaches the SiO ₂ film as an etching stopper. However, it is difficult to make the etching rate the same at each etching position, the position where the etching process is completed up to the SiO ₂ film which is an etching stopper, and Si remains, and the film thickness of the diaphragm increases. Part occurs. In such a case, there is a problem that the film thickness of the diaphragm becomes non-uniform.

  The objective of this invention is providing the manufacturing method of a MEMS device, a MEMS device, and an ultrasonic transducer which manufacture a MEMS device provided with the functional film which has a uniform thickness dimension.

The manufacturing method of the MEMS device of the present invention includes a convex portion forming step of forming a convex portion having a flat front end surface and a side surface portion on the first surface of the substrate, and covering at least the convex portion on the first surface. A film forming step for forming a functional film, a mask layer for forming a mask layer on the second surface opposite to the first surface of the substrate, and forming a hole in the mask layer; An etching step of etching the substrate using the functional film as an etching stopper, wherein the film forming step includes a main film portion in contact with the tip surface of the convex portion, and a side wall portion in contact with the side surface portion of the convex portion. And forming the functional film,
In the mask process, the hole having an area smaller than the area of the front end surface is formed at a position overlapping the front end surface in a plan view of the substrate viewed from the thickness direction of the substrate. The main film is etched from the second surface side to the main film part of the functional film in the thickness direction of the substrate, and then etched to the side wall part along the surface of the main film part. And an opening space including a region surrounded by the side wall portion.

According to the present invention, the convex portion is formed on the first surface of the substrate by the convex portion forming step, and the functional film is formed on the substrate by the film forming step. Thereby, a functional film including a main film part in contact with the front end surface of the convex part and a side wall part in contact with the side part of the convex part is formed corresponding to the surface shape of the convex part.
Thereafter, in the mask process, a mask layer is formed on the second surface side of the substrate to form holes in the mask layer, and in the etching process, the substrate is etched from the holes. At this time, the formation position of the hole is within the formation region of the tip surface of the convex portion in plan view of the sensor, and the opening area of the hole is made smaller than the tip surface. Thus, in the etching process, for example, by performing anisotropic etching such as cycle etching, the etching progresses along the substrate thickness direction from the hole portion to the main film portion as an etching stopper. In the etching step, the etching process is further continued to etch the side wall portion along the surface of the main film portion. Accordingly, the substrate is etched to the side wall portion along the surface of the main film portion by the etching gas, so that the opening having the cylindrical cavity portion having the main film portion as the bottom surface and the side wall portion as the cylinder inner peripheral surface. A space is formed.
In such a MEMS device manufacturing method, the etching process continues until the side wall portion is exposed along the main film portion by over-etching after the etching gas reaches the main film portion. The constituent components of the substrate remaining on the substrate can be removed by etching. Therefore, variation in the thickness of the main film portion due to the etching rate can be suppressed, and a MEMS device having a functional film (main film portion) with a uniform thickness can be manufactured.

  By the way, in order to remove the substrate component remaining on the support film, when the overetching process is performed, in the case where there is no side wall, the etching proceeds along the support film. There is also a problem that the desired film performance cannot be obtained because the area is exceeded. On the other hand, in the present invention, since the side wall portion is provided along the outer peripheral edge of the main film portion, even when etching proceeds along the main film portion, the side wall portion is formed by etching using the etching stopper. Increase of the open space forming area (the area of the open space in plan view when the substrate is viewed from the thickness direction) can be suppressed. That is, in a plan view of the substrate viewed from the thickness direction, the cavity formation region and the main film part formation region can be made the same, and therefore, a MEMS device having a functional film having a desired film performance is manufactured. Can do.

In the MEMS device manufacturing method of the present invention, a region where the hole is projected onto the tip surface is defined as a hole projection region, and a point located on the outer periphery of the tip surface to the outer periphery of the hole projection region. When the shortest distance is the alignment set value, the mask process forms the hole so that the difference value between the maximum value and the minimum value of the alignment set value is smaller than the height dimension of the convex portion. Is preferred.
Here, the height dimension of a convex part refers to the distance along the substrate thickness dimension from the lower end position (position which touches a 1st surface) of the side part of a convex part to the front end surface of a convex part.

According to the present invention, the formation position of the hole is set so that the difference value between the maximum value and the minimum value of the alignment setting value is smaller than the protruding dimension of the convex portion.
Here, when the alignment setting value varies, such as when a mask layer having a rectangular hole is formed on the circular protruding tip surface, the point on the outer peripheral edge of the protruding tip surface Among these, a point with a small alignment set value is etched first, and a time until etching of a point with a large alignment set value is completed becomes long. Here, in order to surely remove the substrate component on the front end surface in contact with the main film portion, the maximum alignment set point at which the alignment set value becomes the maximum value needs to be etched, and this maximum alignment set point is adjusted. It is necessary to set the etching time, and within this etching time, the minimum alignment set point at which the alignment set value becomes the minimum value is not etched beyond the side wall portion. Sizing) and alignment setting values need to be set.
Here, when the difference value between the maximum value and the minimum value of the alignment set value is larger than the protruding dimension of the convex portion, the etching may proceed beyond the side wall portion of the functional film at the minimum alignment set point. In this case, the cavity formation region does not fall within the desired range, and the film performance of the functional film deteriorates.
On the other hand, as described above, when the difference value between the maximum value and the minimum value of the alignment set value is smaller than the protruding dimension of the convex portion, the etching is performed so that the entire main film portion is in contact with the cavity. Even in the case where etching is performed, etching does not proceed beyond the side wall portion of the functional film, and a cavity can be formed in a formation region having a desired area. Therefore, a functional film having a desired film performance can be formed. For example, when a diaphragm is formed by a main film portion as a functional film, a diaphragm having a desired area and capable of stable film vibration can be accurately formed. Can do.

  In the MEMS device manufacturing method of the present invention, a region where the hole is projected onto the tip surface is defined as a hole projection region, and a point located on the outer periphery of the tip surface to the outer periphery of the hole projection region. In the case where the shortest distance is set as the alignment setting value, the protrusion forming step forms the protrusion so that the protruding dimension of the protrusion is larger than the difference value between the maximum value and the minimum value of the alignment setting value. It is preferable to do.

  In this invention, in the convex portion forming step, the convex portion is formed so that the protruding dimension of the convex portion is larger than the difference value between the maximum value and the minimum value of the alignment set value. Thus, as in the above-described invention, even when etching is performed so that the entire main film portion is in contact with the opening space in the etching step, the etching does not proceed beyond the side wall portion of the functional film. A cavity can be formed in the area region.

Further, when forming the hole in the mask process, it is usually preferable to form the hole having the same shape as the tip surface so that the center of gravity of the tip surface and the center of gravity of the hole overlap in plan view. . That is, it is preferable that the alignment setting value is the same value at each hole outer peripheral point. However, it is difficult to completely match these barycentric positions. Actually, a slight misalignment occurs, and the alignment setting values vary as described above.
When such an alignment shift occurs, the maximum value and the minimum value of the alignment setting value can be obtained in advance, for example, by simulation. Therefore, by setting the projecting dimension of the convex part according to the maximum value of such an alignment error, even when an alignment error occurs, the main film part and the opening space are formed in the same formation region in plan view. And a functional film having desired film performance can be formed.
For example, when the hole is displaced by a predetermined alignment error value in one direction, the difference value between the maximum value and the minimum value of the alignment setting value is twice the alignment error value. Therefore, it is preferable to form a convex part having a protruding dimension that is twice or more the alignment error value in the convex part forming step, so that a functional film with good film performance can be obtained even when misalignment occurs. it can.

  In the MEMS device manufacturing method of the present invention, it is preferable that the alignment setting values at the respective points on the outer peripheral edge of the tip end face have the same value.

  In this invention, the alignment setting values at the respective points on the outer peripheral edge of the front end surface of the convex portion are the same value. In this case, in the etching process, the etching gas reaches each point on the outer peripheral edge of the front end surface almost simultaneously, so that the processing time in the etching process can be shortened and the production efficiency can be improved.

  The MEMS device of the present invention is a MEMS device including a substrate and a functional film provided on the first surface of the substrate, wherein the functional film includes a planar main film portion and a main film portion. A cavity forming part that forms a cavity together with the main film part and the side wall part, the side wall part rising from a peripheral edge in a direction intersecting the main film part, And a communication hole that is provided from the second surface opposite to the first surface of the substrate toward the cavity forming portion, and that communicates the cavity and a space outside the second surface. It is a characteristic.

In this invention, the area of the main film part can be set to the area surrounded by the side wall part by forming the cavity by the main film part, the side wall part and the cavity forming part. In addition, since the main film part is surrounded by the side wall part, by using the main film part and the side wall part as an etching stopper and forming a cavity by etching, as described above, the substrate component remaining on the main film part can be reduced. It can be removed reliably, and the main film portion can be formed with a uniform thickness. Therefore, for example, when the main film part is used as a diaphragm, the diaphragm can be formed in a desired area region and the thickness of the diaphragm can be made uniform. Therefore, the vibration amount (displacement amount) of the diaphragm is changed to each position on the diaphragm. Will not vary.
Further, the cavity formed by the main film part, the side wall part and the cavity forming part of the substrate communicates with the outside of the second surface of the substrate through the communication hole, so that the pressure inside the cavity is made equal to the external pressure. be able to. Therefore, for example, even when the main film part is used as a diaphragm, the displacement amount of the diaphragm does not vary due to the internal pressure of the cavity.

In the MEMS device according to the aspect of the invention, it is preferable that the cavity forming portion has an inner wall surface whose opening area increases in a direction from the communication hole side toward the main film portion.
According to the present invention, the cavity forming portion is provided with the inner wall surface (tapered surface) in which the opening area in the plane orthogonal to the thickness direction of the substrate increases from the communication hole side toward the main film portion. In such a configuration, the air in the cavity can be smoothly flowed out and sucked from the communication hole, and the vibration of the outside air can be uniformly transmitted to the functional film. For example, when the main film part is displaced toward the cavity with respect to the film thickness direction, the air in the cavity is pushed out by the main film part and flows out to the outside air from the communication hole. At this time, the air in the cavity is inclined. It flows smoothly into the communication hole along the surface, and is discharged to the outside through the communication hole. For this reason, the fluctuation of the pressure in the cavity becomes minute and does not hinder the inhibition of the displacement of the main film portion, so that the displacement of the main film portion can be made uniform.

  The ultrasonic transducer of the present invention is an ultrasonic transducer comprising a substrate, a functional film provided on the first surface of the substrate, and a piezoelectric body provided on the functional film, wherein the function The film has a planar main film part and a side wall part rising in a direction intersecting the main film part from an outer peripheral edge of the main film part, and the substrate is in contact with the side wall part, A cavity forming part that forms a cavity together with the main film part and the side wall part, and provided from the second surface opposite to the first surface of the substrate toward the cavity forming part, the cavity and the second surface The piezoelectric body has a lower electrode layer, a piezoelectric layer, and a piezoelectric layer on a surface opposite to a surface of the main film portion on which the cavity forming portion is provided. And an upper electrode layer in order. Preferred.

In the present invention, an ultrasonic transducer is configured by providing a piezoelectric body on the main film portion. Here, similarly to the above-described invention, in the ultrasonic transducer, the film thickness of the main film portion can be formed to a uniform thickness, so that the stress balance of the main film portion is uniform and can be vibrated stably. it can. In addition, since the side wall portion is present, the cavity formation region and the main film portion formation region are the same region in plan view, and the main film portion having a desired area can be formed.
Therefore, when ultrasonic waves are transmitted by the ultrasonic transducer, ultrasonic waves of a desired frequency can be stably transmitted, and when receiving ultrasonic waves by the ultrasonic transducer, the reception sensitivity is stable. Can be made.

BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing and top view which show schematic structure of the ultrasonic transducer (MEMS device) of 1st embodiment which concerns on this invention. The flowchart which shows the manufacturing process of the ultrasonic transducer of 1st embodiment. It is sectional drawing of the ultrasonic transducer in each process of FIG. 2, (A) is sectional drawing in a convex part formation process, (B) is sectional drawing in a film-forming process. It is sectional drawing of the ultrasonic transducer in each process of FIG. 2, (A) is sectional drawing in a piezoelectric material formation process, (B) is sectional drawing in a grinding process. It is sectional drawing of the ultrasonic transducer in each process of FIG. 2, (A) is sectional drawing in a mask process, (B) is sectional drawing in an etching process. Sectional drawing of the ultrasonic transducer manufactured by each process of FIG. Sectional drawing which shows schematic structure of the ultrasonic transducer of 2nd embodiment which concerns on this invention. The flowchart which shows the manufacturing process of the ultrasonic transducer of 2nd embodiment. It is sectional drawing of the ultrasonic transducer in each process of FIG. 8, (A) is sectional drawing in a convex part formation process, (B) is sectional drawing in a 1st film-forming process, (C) is 2nd Sectional drawing in a film-forming process. FIG. 9 is a cross-sectional view of the ultrasonic transducer in each step of FIG. 8, (A) is a cross-sectional view after the grinding step, (B) is a cross-sectional view in the etching step, and (C) further proceeds the etching step. FIG. Sectional drawing which shows schematic structure in the etching process of the ultrasonic transducer of 3rd embodiment which concerns on this invention. Sectional drawing which shows schematic structure of the pressure sensor which is a MEMS device of 4th embodiment which concerns on this invention. The flowchart which shows the manufacturing process of the pressure sensor of 4th embodiment. FIG. 14 is a cross-sectional view showing a state in each step of FIG. 13, (A) is a cross-sectional view in a lower substrate forming step, (B) is a cross-sectional view in a lower support film forming step, and (C) is a lower electrode forming step. FIG. FIG. 14 is a cross-sectional view showing a state in each step of FIG. 13, (A) is a cross-sectional view in a lower grinding step, (B) is a cross-sectional view in a mask step, and (C) is a cross-sectional view in an etching step. FIG. 14 is a cross-sectional view showing a state in each step of FIG. 13, (A) is a cross-sectional view in the upper support film forming step, (B) is a cross-sectional view in the upper electrode forming step, and (C) is in the upper grinding step. Sectional drawing.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described based on the drawings.

[Configuration of ultrasonic transducer]
FIG. 1 is a cross-sectional view and a plan view showing a schematic configuration of an ultrasonic transducer (MEMS device) according to a first embodiment of the present invention.
As shown in FIG. 1, the ultrasonic transducer 10 includes a substrate 11 having an opening 111, a support film 12 (functional film) formed on one surface side (first surface 11 </ b> A) of the substrate 11, and a support film 12. And a piezoelectric body 20 formed thereon. The ultrasonic transducer 10 is a device that outputs ultrasonic waves by vibrating the support film 12 by applying a voltage to the piezoelectric body 20.
In the present embodiment, the ultrasonic transducer 10 is exemplified as the MEMS device, but is not limited thereto. As the MEMS device of the present invention, an ultrasonic transducer for receiving ultrasonic waves by the support film 12 and outputting an electric signal corresponding to vibration from the piezoelectric body 20, and both transmission and reception of ultrasonic waves are performed. It can also be applied to possible ultrasonic transducers. As the MEMS device, in addition to the ultrasonic transducer, for example, a stress detection element that detects the stress applied to the support film 12 based on the piezoelectric body 20, or the piezoelectric film 20 is driven to contact the support film 12. It can be used as a driving force generating element that applies a driving force to the target object.
Further, in this embodiment, only the configuration of one ultrasonic transducer 10 is illustrated, but actually, a plurality of ultrasonic transducers 10 are arranged in an array to form an ultrasonic transducer group. .

The substrate 11 is formed of a semiconductor forming material such as silicon (Si) that can be easily processed by etching or the like. Moreover, it is preferable that the opening part 111 formed in the board | substrate 11 is formed in circular shape by the planar view (sensor planar view) which looked at the said board | substrate 11 from the thickness direction. Thereby, in the membrane 122 (main film portion) of the support film 12 that closes the opening 111, the stress with respect to the bending of the membrane 122 can be made uniform. In the present embodiment, an example in which the opening 111 is circular in the sensor plan view is shown, but the present invention is not limited to this. For example, it may be formed in a strip shape (rectangular shape).
More specifically, the opening 111 of the substrate 11 has a tapered shape that inclines in a direction away from the membrane 122 from the inner peripheral surface of a side wall 121 described later of the support film 12 toward the central axis of the opening 111. Along the central axis of the cavity forming portion 112 and the opening 111, the cavity forming portion 112 extends toward the second surface 11B, which is the side surface opposite to the first surface 11A on which the support film 12 of the substrate 11 is provided. A communication hole 113 is provided. That is, the cavity forming portion 112 includes an inner wall surface whose opening area increases in a direction orthogonal to the thickness direction of the substrate 11 in the direction from the communication hole 113 side toward the membrane 122.

The support film 12 is formed on the substrate 11 so as to close the opening 111. The support film 12 has a two-layer structure of a first support film 12A formed of a SiO ₂ film and a second support film 12B formed of a ZrO ₂ layer. Here, when the substrate 11 is a Si substrate, the first support film 12A layer can be formed by thermally oxidizing the substrate surface. Further, the second support film 12B is formed by a technique such as thermal oxidation after sputtering on the SiO ₂ layer. Here, the ZrO ₂ layer is used to prevent Pb constituting PZT from diffusing into the SiO ₂ layer (first support film 12A) when, for example, PZT is used as the piezoelectric layer 22 constituting the piezoelectric body 20. Is a layer. The ZrO ₂ layer (second support film 12B) also has an effect of improving the bending efficiency with respect to the distortion of the piezoelectric layer 22.

The support film 12 includes an element configuration unit 120 corresponding to the position where the opening 111 of the substrate 11 is formed. The element component 120 includes a cylindrical side wall 121 protruding in a direction away from the substrate 11, and a membrane 122 formed continuously from the protruding tip of the side wall 121 and blocking the protruding tip of the side wall 121. It is equipped with.
The side wall part 121 is a part for determining the effective diameter of the membrane 122. Further, the side wall 121 is formed to rise from the substrate 11 in the thickness direction of the substrate 11. For this reason, the side wall 121 is strongly stressed in the thickness direction of the substrate 11 (film thickness direction of the membrane 122), and the side wall 121 does not expand or contract in the substrate thickness direction even when the membrane 122 vibrates.
In FIG. 1, the dimension in the thickness direction of the side wall portion 121 is shown large for the sake of explanation, but in actuality, it is formed to have a thickness of about 3 μm, for example. The diameter of the membrane 122 in the sensor plan view is, for example, 20 to 100 μm.

The membrane 122 is a portion that outputs ultrasonic waves by vibrating in the film thickness direction by driving the piezoelectric body 20 by laminating the piezoelectric bodies 20. As described above, the effective diameter of the membrane 122 is determined by the cylindrical inner diameter of the side wall 121 and outputs ultrasonic waves having a frequency corresponding to the effective diameter.
Further, the cavity forming portion 112 of the substrate 11 is connected to the cylindrical inner peripheral surface of the side wall portion 121 as described above. Thus, a cavity C is formed in a region surrounded by the side wall 121 of the element component 120, the membrane 122, and the cavity forming portion 112 of the substrate 11, and the cavity C and the hole internal space of the communication hole 113 are used to form the cavity C. The opening space of the invention is constructed.

The piezoelectric body 20 is formed on the surface opposite to the surface on which the cavity C is formed in the membrane 122 of the support film 12. The piezoelectric body 20 includes a lower electrode layer 21, a piezoelectric layer 22, and an upper electrode layer 23.
The lower electrode layer 21 is formed in an inner region of the membrane 122 in the sensor plan view, and the piezoelectric layer 22 is laminated on the upper layer. Further, a lower electrode line 211 is connected from the outer peripheral edge of the lower electrode layer 21, and the lower electrode line 211 is connected to a lower electrode terminal (not shown) provided on the outer peripheral edge of the support film 12. .

The piezoelectric layer 22 is laminated on the lower electrode layer 21. The piezoelectric layer 22 is formed by, for example, forming a film of PZT (lead zirconate titanate). In the present embodiment, PZT is used as the piezoelectric layer 22. However, any material can be used as long as it can be contracted in the in-plane direction by applying a voltage, for example, lead titanate. (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), lead lanthanum titanate ((Pb, La) TiO ₃ ), or the like may be used.
The piezoelectric layer 22 expands and contracts in the in-plane direction when a voltage is applied to the lower electrode layer 21 and the upper electrode layer 23. At this time, one surface of the piezoelectric layer 22 is joined to the membrane 122 of the support film 12 via the lower electrode layer 21, while the upper electrode layer 23 is formed on the other surface, but this upper electrode Since no other layers are laminated on the layer 23, the support film 12 side of the piezoelectric layer 22 is less likely to expand and contract, and the upper electrode layer 23 side easily expands and contracts. For this reason, when a voltage is applied to the piezoelectric layer 22, a convex bending toward the cavity C occurs, and the membrane 122 is bent. Therefore, when an AC voltage is applied to the piezoelectric layer 22, the membrane 122 vibrates in the film thickness direction, and ultrasonic waves are output by the vibration of the membrane 122.
The upper electrode layer 23 is laminated on the piezoelectric layer 22 and patterned at an arrangement position that is insulated from the lower electrode layer 21 in the sensor plan view. Further, an upper electrode line 231 is connected from the outer peripheral edge of the upper electrode layer 23, and the upper electrode line 231 is connected to an upper electrode terminal provided on the outer peripheral edge of the support film 12.

[Method of manufacturing ultrasonic transducer]
Next, a method for manufacturing the ultrasonic transducer 10 as described above will be described with reference to the drawings.
FIG. 2 is a flowchart showing the manufacturing process of the ultrasonic transducer 10. 3 to 7 are cross-sectional views showing states in each step of FIG.
In order to manufacture the ultrasonic transducer 10, as shown in FIG. 2, first, for example, the first surface 11A of the substrate 11 (Si) having a thickness dimension set to 625 μm is patterned, and FIG. As shown in the drawing, a columnar convex portion 114 is formed at a position where the element constituent portion 120 is formed (convex portion forming step S1).
In this convex portion forming step S1, for example, a resist layer is formed at the formation position of the element constituent portion 120 on the flat substrate 11, and the convex portion 114 is formed at the formation position of the element constituent portion 120 by etching.

Thereafter, film formation step S2 is performed.
In the film forming step S2, the substrate 11 is thermally oxidized to form a SiO ₂ layer (first support film 12A) on the first surface 11A of the substrate 11. Further, a Zr layer is formed on the first support film 12A by sputtering, and the second support film 12B is formed by oxidizing the Zr layer. Thereby, as shown in FIG. 3B, for example, the support film 12 having a thickness of 3 μm is formed. At this time, the projecting tip portion of the convex portion 114 and the second support film 12B laminated on the projecting tip portion serve as the membrane 122 of the element constituting portion 120, and the convex portion outer peripheral surface of the convex portion 114 and the convex portion outer peripheral surface thereof. The laminated second support film 12 </ b> B becomes the side wall 121 of the element constituting unit 120. In addition, a portion corresponding to the membrane 122 of the first support film 12A formed by the thermal oxidation process and the front end surface 114A having a flat boundary with the convex part 114 become a side wall of the first support film 12A formed by the thermal oxidation process. A portion corresponding to the portion 121 and a side portion 114B whose boundary between the convex portion 114 and the convex portion is the outer peripheral surface of the convex portion. At this time, the diameter dimension (L _w ) of the tip surface 114 A of the convex part 114 becomes the diameter dimension of the membrane 122, and the protruding dimension (height dimension H) of the side surface part 114 B becomes the height dimension of the side wall part 121. Here, the protrusion dimension H of the protrusion 114 in the protrusion formation process S1 and the protrusion dimension H of the film formation process S2 are set so that the protrusion dimension H of the protrusion 114 is about 2 μm, which is twice the maximum alignment error (about 1 μm). It is preferable to set a treatment time for the thermal oxidation treatment.
In the present embodiment, the first support film 12A is formed by oxidizing the surface of the convex portion 114, but the first support film 12A may be laminated on the surface of the convex portion 114 by sputtering or the like. .

Thereafter, the piezoelectric body forming step S3 is performed. In the piezoelectric body forming step S3, first, a conductive layer is formed uniformly by, for example, sputtering, and the lower electrode layer 21 is formed by patterning using, for example, a photolithography method. The conductive layer for forming the lower electrode layer 21 is not particularly limited as long as it is a conductive film, but in this embodiment, a Ti / Ir / Pt / Ti laminated structure film is used, and a piezoelectric film is formed. For example, the body layer is formed to have a film thickness of 0.2 μm after firing.
Thereafter, a PZT film is formed on the first surface 11A of the substrate 11, and the piezoelectric layer 22 is formed by patterning using, for example, a photolithography method. The piezoelectric layer 22 is formed by using a MOD (Metal Organic Decomposition) method with a film of the support film 12 so that the total thickness becomes 1.4 μm, for example.
Thereafter, a conductive layer is uniformly formed on the first surface 11A of the substrate 11 by, for example, sputtering, and the upper electrode layer 23 is formed by using, for example, a photolithography method. As the conductive film for forming the upper electrode layer 23, as in the lower electrode layer 21, any conductive material may be used. In the present embodiment, an Ir film is used and the thickness dimension is, for example, 50 nm.
In this way, as shown in FIG. 4A, the piezoelectric body 20 that is a laminate of the lower electrode layer 21, the piezoelectric layer 22, and the upper electrode layer 23 is formed on the membrane 122.

After the piezoelectric body forming step S3, as shown in FIG. 4B, a grinding step S4 for grinding the second surface 11B of the substrate 11 is performed. Thereby, the thickness dimension of the board | substrate 11 is formed in the set dimension, for example, 200 micrometers. And mask process S5 is implemented after this grinding process S4.
In the mask process S5, first, the mask layer 30 is formed on the second surface 11B of the substrate 11, and the hole 31 is formed in the mask layer 30 as shown in FIG. At this time, in the mask process S5, the sensor plan view, the central axis of the hole portion 31 becomes the center axis P coaxial with the convex portion 114, a circular hole 31 having a diameter L ₀ whose diameter than the distal end face 114A Form.
Further, at the time of forming the hole portion 31, it is preferable that the central axis of the hole portion 31 coincides with the central axis P of the convex portion 114, but actually, an alignment shift occurs. The alignment error due to this misalignment is about 1 μm at the maximum as described above, although it depends on the method of forming the hole 31 and the like. Therefore, even when an alignment deviation occurs, in order to form the hole 31 in the region of the tip surface 114A in the sensor plan view, the distance L ₁ (from the outer periphery of the hole 31 to the outer periphery of the tip surface 114A) The distance L ₁ from the predetermined hole outer peripheral point 31 on the outer peripheral edge 31 to the outer peripheral edge of the tip surface 114A closest to the hole outer peripheral point is set to be twice or more (for example, 2 μm) of the maximum alignment error. It is preferable to do.

Thereafter, an etching step S6 is performed.
In the etching step S6, the opening 111 is formed in the substrate 11 from the second surface 11B side.
Here, in the etching step S6, first, a so-called Bosch process in which an etching process using an etching gas such as SF ₆ and a deposition process using a deposition gas such as C ₄ F ₈ are repeatedly performed. A so-called cycle etching process is performed. As a result, as shown in FIG. 5B, the membrane 122 of the support film 12 is used as an etching stopper, and the inner peripheral cylindrical communication hole 113 having a uniform diameter from the hole portion 31 to the membrane 122 of the mask layer 30 is used. Is formed. Note that the region of the membrane 122 exposed in the communication hole 113 is the hole projection region A of the present invention.

In the etching step S6, an overetching process using an etching gas is further performed thereafter, and the substrate 11 is etched along the tip surface 114A of the convex portion 114. Here, the protrusion 114 is removed by etching so that the side wall 121 having a height of about H / 2 is exposed by the over-etching process. As a result, the tip surface 114A of the convex portion 114 is completely removed, and the Si component of the substrate 11 does not remain on the membrane 122 of the support film 12, and is formed to have a uniform thickness.
Further, by the over-etching process, a tapered cavity forming portion 112 is formed on the substrate 11, and a cavity C is formed by the cavity forming portion 112, the side wall portion 121, and the membrane 122, and an ultrasonic wave as shown in FIG. The transducer 10 is manufactured.

In general, the etching amount (dimension) when etching proceeds along the membrane 122 is approximately the same in the dimension perpendicular to the substrate thickness direction and the dimension along the substrate thickness direction. Therefore, when the distance L ₁ from the outer peripheral edge of the hole portion 31 to the outer peripheral edge of the tip end surface 114A is over-etched, the connection point between the cavity forming portion 112 and the communication hole 113 is a position where the distance L ₁ is from the membrane 122. Formed. In the present embodiment, by over-etching, etching is performed up to half the height (H / 2) of the side surface portion 114B, so that the connection point between the cavity forming portion 112 and the communication hole 113 is a distance (L ₁ + H / 2).

[Operational effects of the first embodiment]
As described above, the ultrasonic transducer 10 of the first embodiment is manufactured by the convex portion forming step S1, the film forming step S2, the piezoelectric body forming step S3, the grinding step S4, the masking step S5, and the etching step S6. At this time, in the mask process S5, the hole 31 is formed in the inner peripheral region of the tip surface 114A in the sensor plan view. In the etching process S6, the membrane 122 of the support film 12 is used as an etching stopper from the hole 31. A cycle etching process is performed. For this reason, the communication hole 113 can be formed in the inner peripheral side region of the tip surface 114A in the sensor plan view.

  Further, in the over-etching process of the etching step S6, the side wall 121 is etched by further performing an etching process on the communication hole 113 formed from the second surface 11B of the substrate 11 to the membrane 122 of the support film 12. As a stopper, the substrate 11 can be side-etched along the membrane 122. Thereby, the substrate 11 in contact with the membrane 122 can be reliably removed by etching, and the thickness dimension of the membrane 122 is determined by the first support film 12A and the second support film 12B. Further, the first support film 12A can be formed to have a uniform thickness by thermal oxidation treatment, and the second support film 12B can be formed to have a uniform thickness dimension by thermal oxidation after sputtering. The thickness dimension of the support film 12 constituted by the first support film 12A and the second support film 12B can be made uniform. Therefore, in the ultrasonic transducer 10 manufactured by the manufacturing method as described above, when the membrane 122 is driven by the piezoelectric body 20, the membrane 122 can be vibrated stably, and the ultrasonic wave is stably output. Can be made.

  Further, since the side etching is regulated using the side wall 121 as an etching stopper, the outer region of the side wall 121 is not etched. Therefore, the driving portion for transmitting ultrasonic waves in the ultrasonic transducer 10 is in the region where the membrane 122 is formed. In other words, by forming the membrane 122 with an appropriate diameter according to the transmission frequency, the ultrasonic transducer 10 can output the ultrasonic wave of the transmission frequency with high accuracy.

Further, in the ultrasonic transducer 10 manufactured by such a manufacturing method, since the cavity C communicates with the external space through the communication hole 113 as described above, the vibration of the membrane 122 is inhibited by the internal pressure of the cavity C. The ultrasonic wave with a large sound pressure can be output.
In addition to this, the cavity forming portion 112 is formed in a tapered shape that is inclined in a direction approaching the membrane 122 toward the side wall portion 121 from the connection position between the cavity forming portion 112 and the communication hole 113. For this reason, when the membrane 122 is vibrated, the air inside the cavity C can smoothly move to the communication hole 113 along the tapered surface of the cavity forming portion 112.

Further, in the mask process S5, the hole 31 is formed so that the central axis of the circular hole 31 is coaxial with the central axis P of the cylindrical convex 114. That is, when the shortest distance from each point on the outer peripheral edge of the tip surface 114A to the outer peripheral edge of the hole projection region A is used as the alignment setting value, in this embodiment, the alignment setting value at each point is the same value. .
In such a case, in the overetching process of the etching step S6, the time required for etching from the hole projection region A to the outer peripheral edge of the tip surface 114A is substantially the same, so the etching time can be shortened, Contributes to improved production efficiency.
Actually, if an alignment deviation occurs during the formation of the hole portion 31, it is conceivable that the center axis of the hole portion 31 is shifted from the center axis P of the convex portion 114 by a minute dimension by an error due to the alignment deviation. However, in the overetching process of the etching step S6, the etching region does not extend beyond the side wall portion 121 due to such a small dimensional deviation.

  The protrusion dimension H of the convex portion 114 is set to be twice or more the maximum alignment error that occurs in the formation of the hole portion 31. For this reason, even when an alignment error occurs in the hole 31 and the region to be etched is biased in one direction, the over-etching process can be restricted using the side wall 121 as an etching stopper. That is, it is possible to avoid the inconvenience that the effective area of the membrane 122 is increased due to over-etching beyond the side wall portion 121 to the outer region of the element constituent portion 120.

[Second Embodiment]
Next, 2nd embodiment which concerns on this invention is described based on drawing.
The ultrasonic transducer (MEMS device) according to the present embodiment has substantially the same configuration and function as the ultrasonic transducer 10 of the first embodiment. Here, the ultrasonic transducer 10 described above has a configuration in which the element component 120 having the side wall 121 and the membrane 122 protrudes from the first surface 11 </ b> A of the substrate 11. On the other hand, the ultrasonic transducer according to the second embodiment has a configuration in which the element component does not protrude from the substrate and the first surface side of the substrate is a flat surface. In this respect, the ultrasonic transducer according to this embodiment is different from the ultrasonic transducer 10 of the first embodiment described above. In the following description, parts that are the same as or substantially the same as those already described are given the same reference numerals and description thereof is omitted.

[Configuration of ultrasonic transducer]
FIG. 7 is a cross-sectional view showing a schematic configuration of an ultrasonic transducer 10A according to the second embodiment of the present invention.
As shown in FIG. 7, the ultrasonic transducer 10 </ b> A of this embodiment includes a substrate 11, a support film 13 (functional film), and a piezoelectric body 20.
The support film 13 is formed on the substrate 11 so as to close the opening 111. The support film 13 has a two-layer structure of a first support film 13A formed of a SiO ₂ film and a second support film 13B formed of a ZrO ₂ layer.

The support film 13 includes an element component 130 corresponding to the position where the opening 111 of the substrate 11 is formed. This element component 130 is configured by forming an inner circumferential cylindrical concave groove in a direction in which a part of the first support film 13A is separated from the first surface 11A of the substrate 11. In other words, the element constituent part 130 includes a membrane 132 constituted by the bottom part of the concave groove and a side wall part 131 constituted by the inner peripheral side surface of the concave groove.
Further, the surface of the first support film 13A opposite to the substrate 11 is a flat surface, and the second support film 13B is laminated on the flat surface. As a result, the surface of the second support film 13B becomes a flat surface, and the ultrasonic transducer 10A is configured by laminating the piezoelectric body 20 on the second support film 13B of the element constituting unit 130.

[Method of manufacturing ultrasonic transducer]
Next, a method for manufacturing the ultrasonic transducer 10A as described above will be described with reference to the drawings.
FIG. 8 is a flowchart showing a manufacturing process of the ultrasonic transducer 10A. 9 to 10 are cross-sectional views of the ultrasonic transducer 10A showing the state in each step of FIG.
As shown in FIG. 9, the ultrasonic transducer 10A includes a convex portion forming step S1, a first film forming step S21, a film polishing step S22, a second film forming step S23, a piezoelectric body forming step S3, a grinding step S4, and a mask. It is manufactured by each step of step S5 and etching step S6. Here, the convex portion forming step S1, the piezoelectric body forming step S3, the grinding step S4, and the mask step S5 are the same steps as the manufacturing of the ultrasonic transducer 10 in the first embodiment. In addition, the film-forming process of this invention is implemented by 1st film-forming process S21, film | membrane polishing process S22, and 2nd film-forming process S23.

That is, in the manufacture of the ultrasonic transducer 10A, first, the first surface 11A of the substrate 11 (Si) is patterned by the convex portion forming step S1, and as shown in FIG. A convex portion 114 having a cylindrical shape (diameter _Lw , height H) is formed.
Here, similarly to the manufacture of the ultrasonic transducer 10 described above, the protrusion dimension (height) H of the protrusion 114 is preferably set to about 2 μm, which is twice the maximum alignment error.

Thereafter, in the first film forming step S21, the substrate 11 is thermally oxidized to form a SiO ₂ layer (13A) on the first surface 11A of the substrate 11. At this time, as shown in FIG. 9B, the processing time of the thermal oxidation process is controlled so that the film thickness dimension of the first support film 13A is larger than the projecting dimension of the protrusion 114.
Next, by the film polishing step S22, the surface of the first support film 13A is ground to remove the protruding portion of the first support film 13A, and is processed into a flat surface. Here, as described above, since the film thickness dimension of the first support film 13A is formed larger than the projecting dimension of the convex part 114, even if the projecting part of the first support film 13A is removed, the convex part is formed. 114 is not exposed.
Thereafter, in the second film formation step S23, as shown in FIG. 9C, the second support film 13B is laminated on the first support film 13A. Thereby, the support film 13 having a flat surface is formed.

Thereafter, the ultrasonic transducer 10A is manufactured by performing the same process as in the first embodiment.
That is, in the piezoelectric body forming step S3, as shown in FIG. 10A, the piezoelectric body 20 that is a laminate of the lower electrode layer 21, the piezoelectric layer 22, and the upper electrode layer 23 on the second support film 13B of the membrane 132. Form. And by implementing grinding process S4, the 2nd surface 11B of the board | substrate 11 is ground and the thickness of the board | substrate 11 is 200 micrometers, for example.

And masking process S5 is implemented, the mask layer 30 is formed in the 2nd surface 11B of the board | substrate 11, and the hole part 31 is formed. In addition, by performing the cycle etching process of the etching step S6, the inner peripheral cylindrical communication hole 113 having a uniform diameter is formed from the hole 31 to the membrane 132. Thereafter, by performing an over-etching process in the etching step S6, the substrate 11 is etched along the tip surface 114A of the convex portion 114, and the Si component on the tip surface 114A is surely removed, and the cavity forming portion 112 is etched. Form.
Thus, the ultrasonic transducer 10A is manufactured.

[Operational effects of the second embodiment]
The ultrasonic transducer 10A of the second embodiment includes a convex portion forming step S1, a first film forming step S21, a film polishing step S22, a second film forming step S23, a piezoelectric body forming step S3, a grinding step S4, and a mask step S5. , Manufactured by the etching step S6. Therefore, as in the first embodiment, in the overetching process of the etching step S6, the etching process is further performed on the communication hole 113 formed from the second surface 11B of the substrate 11 to the membrane 132 of the support film 13. By doing so, the substrate 11 can be etched along the membrane 132 using the side wall 131 as an etching stopper. Thereby, the substrate 11 in contact with the membrane 132 can be reliably removed by etching, and the thickness dimension of the membrane 132 is determined only by the first support film 13A and the second support film 13B. Therefore, when the membrane 132 is driven by the piezoelectric body 20, the membrane 132 can be vibrated stably, and ultrasonic waves can be output stably.

  Further, since the etching in the lateral direction perpendicular to the substrate thickness direction is regulated using the side wall portion 131 as an etching stopper, the outer region of the side wall portion 131 is not etched. Therefore, by forming the membrane 132 with an appropriate diameter according to the transmission frequency, it is possible to accurately output ultrasonic waves of the transmission frequency from the ultrasonic transducer 10A.

Further, in the present embodiment, since the element component 130 does not protrude from the first surface 11A of the substrate 11 and is a flat surface as in the first embodiment, it is strong against vibration and external stress.
In the ultrasonic transducer 10 described above, the side wall 121 protrudes from the substrate 11. However, the side wall 121 has an extremely small protruding dimension, for example, 2 μm, and therefore the side wall 121 is affected by external stress or vibration. There is almost no deformation. However, since the element component portion 120 is slightly protruded, the protruding portion receives a slight stress, which may be an obstructive factor for stable ultrasonic waves. On the other hand, in the present embodiment, since the surface of the second support film 13B is a flat surface, the membrane 132 of the element constituent unit 130 can be driven stably without receiving the external stress as described above. .

[Third embodiment]
Next, a third embodiment according to the present invention will be described based on the drawings.
The ultrasonic transducer (MEMS device) according to the present embodiment has substantially the same configuration and function as the ultrasonic transducer 10 of the first embodiment. Here, in the manufacture of the ultrasonic transducer 10 described above, in the mask process S5, the hole 31 is formed so that the center axis of the hole 31 is coaxial with the center axis P of the protrusion 114, thereby forming a cavity. The part 112 was formed along the central axis P of the element constituent part 130. On the other hand, in the manufacture of the ultrasonic transducer of the third embodiment, the hole formed in the mask layer is formed decentered from the central axis of the convex portion. In this respect, the method for manufacturing the ultrasonic transducer according to this embodiment is different from the method for manufacturing the ultrasonic transducer 10 of the first embodiment described above. In the following description, parts that are the same as or substantially the same as those already described are given the same reference numerals and description thereof is omitted.

FIG. 11 is a cross-sectional view showing a schematic configuration in the etching step S6 of the ultrasonic transducer 10B of the third embodiment.
In such an ultrasonic transducer 10 </ b> B, in the mask process S <b> 5, the hole portion 31 is formed such that the central axis Q of the hole portion 31 is slightly decentered from the central axis P of the convex portion 114. Here, the amount of eccentricity of the central axis Q is ΔL. Further, in the sensor plan view, an area overlapping the hole 31 on the membrane 122 is defined as a hole projection area A, and the shortest distance from each point on the outer peripheral edge of the tip surface 114A to the hole projection area A is set as an alignment setting value. A point where the alignment setting value is the minimum value is a minimum alignment point A1, and a hole outer peripheral point where the alignment setting value is the maximum value is a maximum alignment point A2.
At this time, the alignment setting value _{L 1} at the minimum alignment points A1 _{'is L} 1 -Delta L, and the alignment setting value _{L 1''} at the maximum alignment point A2 becomes _{L 1} + [Delta] L.

Here, in the etching step S6, after performing etching along the thickness direction of the substrate 11 from the hole 31 to the membrane 122 by the cycle etching process, the etching is performed along the membrane 122 from the hole projection area A by the overetching process. Then, the substrate 11 is etched in the lateral direction. At this time, the etching gas reaches the minimum alignment point A1 before the maximum alignment point A2, and is etched. Therefore, in order to form the cavity C in the region of the element component 120, it is necessary that the etching region at the minimum alignment point A1 does not exceed the side wall 121 when the maximum alignment point A2 is reached.
That, L _1'' <must meet the L 1 '+ _H conditional expression, the projecting dimension H of the projection 114, and the alignment setting value, it is necessary to satisfy the following equation (1).

[Equation 1]
L _{1 ″} −L ₁ ′ <H
(Or ΔL <H / 2) (1)

  Therefore, in the present embodiment, when the projection 114 is formed in the projection formation step S1 or when the hole 31 is formed in the mask step S5, the protrusion dimension H of the projection 114 is appropriately set so as to satisfy the above relational expression. The maximum alignment setting value and the minimum alignment setting value (or eccentricity ΔL) are set.

In the ultrasonic transducer 10B according to the third embodiment as described above, the hole 31 is formed eccentrically from the central axis P in the mask process S5, and the cavity forming portion 112 is formed at a position eccentric from the central axis P. Even so, by satisfying the relational expression (1) described above, it is possible to achieve the same effect as the ultrasonic transducer 10 of the first embodiment.
That is, in the over-etching process in the etching step S6, the side wall 121 is etched by further performing an etching process on the communication hole 113 formed from the second surface 11B of the substrate 11 to the membrane 122 of the support film 12. As a stopper, the substrate 11 can be etched laterally along the membrane 122. Thereby, the substrate 11 in contact with the membrane 122 can be reliably removed by etching, and the thickness dimension of the membrane 122 can be made uniform. Therefore, when the membrane 122 is driven by the piezoelectric body 20, the membrane 122 can be vibrated stably, and ultrasonic waves can be output stably.
Further, since lateral etching is restricted using the side wall 121 as an etching stopper, the outer region of the side wall 121 is not etched. Therefore, by forming the membrane 122 with an appropriate diameter according to the transmission frequency, it is possible to accurately output ultrasonic waves of the transmission frequency from the ultrasonic transducer 10B.

  In the mask process S5, an error due to misalignment (alignment error) occurs when the hole 31 is formed. Since the maximum value of such an alignment error can be obtained in advance by, for example, simulation or the like, the projection dimension H of the convex portion 114 and the alignment set value are set on the assumption that such an alignment shift occurs. Thus, the influence of the misalignment can be eliminated, and the ultrasonic transducer 10B including the membrane 122 having a uniform film thickness in the same region as the formation region of the cavity C can be manufactured.

In the present embodiment, the case where the circular hole portion 31 is decentered with respect to the circular convex portion 114 in the sensor plan view is exemplified. However, for example, the planar shape of the membrane 122 is rectangular. Even when the distance from the central axis P to the outer peripheral edge is different, such as the case, it is preferable to set the protrusion dimension H of the protrusion 114 and the alignment setting value so as to satisfy the conditional expression (1). The component 120 can be formed.
For example, when the rectangular hole portion 31 having the center of gravity set to the center axis P is formed on the rectangular membrane 122 having the center of gravity set to the center axis P, and the etching step S6 is performed, the membrane 122 The alignment setting value at the corner is larger than the alignment setting value at a point located in the middle of the side of the membrane 122. In this case, by forming the hole 31 and the protrusion 114 so as to satisfy the above (1), side etching is spread over the entire region of the membrane 122, and the membrane 122 having a uniform film thickness can be formed. . Further, in the sensor plan view, the formation region of the membrane 122 and the formation region of the cavity C can be made the same region, and the membrane performance of the membrane 122 can be prevented from being deteriorated.

[Fourth embodiment]
Next, 4th embodiment which concerns on this invention is described based on drawing.
In the first to third embodiments, the ultrasonic transducer 10, the ultrasonic transducer 10A, and the ultrasonic transducer 10B are illustrated as the MEMS devices. On the other hand, in this embodiment, the structure of a pressure sensor and its manufacturing method are demonstrated as another example of a MEMS device.

[Configuration of pressure sensor]
FIG. 12 is a cross-sectional view illustrating a schematic configuration of a pressure sensor that is the MEMS device according to the fourth embodiment.
The pressure sensor 40 includes a lower substrate 41 having a lower opening 411, an upper substrate 42, a lower support film 43 that closes the lower opening 411, an upper support film 44, and a lower portion provided on the lower support film 43. An electrode 45 and an upper electrode 46 provided on the upper support film 44 are provided.

The lower substrate 41 is formed of a semiconductor forming material such as silicon (Si) that can be easily processed by etching or the like. Further, a concave groove 412 that is concave in a direction away from the upper substrate 42 is provided on the surface (first surface) of the lower substrate 41 that faces the upper substrate 42. Further, on the first surface of the lower substrate 41 facing the upper substrate 42, the outer region of the concave groove 412 constitutes a bonding portion 413 bonded to the upper substrate 42, and a lower portion formed on the bonding portion 413 in a stacked manner. The support film 43 is bonded to the upper support film 44 laminated on the upper substrate 42, so that the lower substrate 41 and the upper substrate 42 are bonded.
The lower opening 411 is formed in a circular shape at the bottom of the groove 412, for example, in a sensor plan view when the lower substrate 41 is viewed from the thickness direction. The lower opening 411 has the same configuration as the opening 111 in the ultrasonic transducer 10 described above, and includes a cavity forming portion 411A and a communication hole 411B.

The lower support film 43 is formed on the first surface side of the lower substrate 41 so as to close the lower opening 411. The lower support film 43 is formed, for example, by subjecting the first surface of the lower substrate 41, which is a Si substrate, to a thermal oxidation process.
The lower support film 43 has substantially the same configuration as the support film 12 in the ultrasonic transducer 10 described above, and corresponds to the position where the lower opening 411 of the lower substrate 41 is formed. It has. The lower element component 430 is formed continuously with a cylindrical lower side wall portion 431 protruding in a direction away from the lower substrate 41 and a protruding tip portion of the lower side wall portion 431. A lower membrane 432 for closing.
Further, a cavity forming portion 411 </ b> A of the lower substrate 41 is connected to the cylindrical inner peripheral surface of the lower side wall portion 431. As a result, a cavity C1 is formed in a region surrounded by the lower sidewall portion 431 of the lower element component 430, the lower membrane 432, and the cavity forming portion 411A of the lower substrate 41.
The lower support film 43 is formed by laminating the lower electrode 45 on the surface facing the upper substrate 42.

  The upper substrate 42 is formed of, for example, Si. In addition, in the surface of the upper substrate 42 facing the lower substrate 41, the region corresponding to the bonding portion 413 constitutes the bonding portion 423, and the upper support film 44 formed by lamination on the bonding portion 423 includes the bonding portion 423. By bonding to the lower support film 43 on 413, the lower substrate 41 and the upper substrate 42 are bonded as described above.

The upper support film 44 is formed of an oxide film, for example. The upper support film 44 forms a closed space C2 between the upper support film 44 and the lower support film 43 at a portion facing the concave groove 412 of the lower substrate 41.
The upper substrate 42 and the upper support film 44 are provided with through holes (not shown) that connect the closed space C <b> 2 and the space outside the upper substrate 42. Thereby, the pressure in the closed space C2 and the space outside the upper substrate 42 becomes the same pressure.
An upper electrode 46 is laminated on the surface of the upper support film 44 facing the lower support film 43.

  In such a pressure sensor 40, the upper opening 421 is communicated with a reference space set to a reference pressure such as atmospheric pressure, for example, and a pressure medium to be a pressure measurement target is introduced into the lower opening 411. The lower membrane 432 is displaced. The amount of displacement is measured by measuring the fluctuation value of the amount of charge held between the lower electrode 45 and the upper electrode 46, and the pressure value is calculated from the measured amount of displacement.

[Method of manufacturing pressure sensor]
Next, the manufacturing method of the above pressure sensors 40 is demonstrated based on drawing.
FIG. 13 is a flowchart showing the manufacturing process of the pressure sensor 40. 14 and 15 are cross-sectional views showing the state of each step in the lower portion forming step, and FIG. 16 is a cross-sectional view showing the state of each step in the upper portion forming step.
As shown in FIG. 13, the pressure sensor 40 is manufactured by a lower formation process (S31 to 36), an upper formation process (S37 to S39), and a bonding process S40.

The lower portion forming step includes a lower substrate forming step S31 (projection portion forming step), a lower support film forming step S32 (film forming step), a lower electrode forming step S33, a lower grinding step S34, a mask step S35, and an etching step S36. .
In the lower substrate forming step S31, for example, one surface side of the lower substrate 41, which is a 500 μm Si substrate, is etched to form the concave grooves 412 and the convex portions 414 as shown in FIG.
In the lower support film forming step S32, as in the film forming step S2 of the first embodiment, the one surface side of the lower substrate 41 is thermally oxidized, and the surface of the lower substrate 41 is uniformly formed as shown in FIG. A lower support film 43 having a thickness is formed.
In the lower electrode forming step S33, a conductive layer for forming the lower electrode 45 is formed on the lower membrane 432 of the lower support film 43, and is patterned by using, for example, a photolithography method, and the process shown in FIG. As shown, a lower electrode 45 is formed.

  In the lower grinding step S34, the mask step S35, and the etching step S36, the same processes as the grinding step S4, the mask step S5, and the etching step S6 of the first embodiment are performed. That is, in the lower grinding step S34, as shown in FIG. 15A, the lower substrate 41 is ground to have a thickness of about 200 μm, for example. In the mask process S35, as shown in FIG. 15B, the mask layer 30 having the hole 31 is formed on the surface of the lower substrate 41 opposite to the surface bonded to the upper substrate 42. In the etching step S36, the lower substrate 41 is subjected to a cycle etching process and an over-etching process from the hole 31 to form a lower membrane 432 having a uniform thickness as shown in FIG.

In the upper formation process, processing is performed on the upper substrate 42 which is, for example, a 500 μm Si substrate by the upper support film formation process S37, the upper electrode formation process S38, and the upper grinding process S39.
In the upper support film forming step S37, as in the film forming step S2 of the first embodiment, one surface side of the upper substrate 42 bonded to the lower substrate 51 is thermally oxidized, and as shown in FIG. An upper support film 44 having a uniform thickness is formed on the surface of the substrate 42.
In the upper electrode formation step S38, a conductive layer for forming the upper electrode 46 is formed on the upper support film 44, and is patterned by using, for example, a photolithography method. As shown in FIG. An electrode 46 is formed.
The upper grinding step S39 is the same processing as the grinding step S4 of the first embodiment, and as shown in FIG. 16C, the upper substrate 41 is ground to have a thickness of about 200 μm, for example.

  In the bonding step S <b> 40, the lower substrate 41 and the upper substrate 42 are bonded via the lower support film 43 and the upper support film 44. Here, as a joining method in joining process S40, various joining methods, such as adhesive joining by an adhesive material, resin, etc., and anodic joining, for example can be used. Thus, the pressure sensor 40 as shown in FIG. 12 is manufactured.

In the pressure sensor 40 as described above, the same effect as that of the ultrasonic transducer 10 of the first embodiment can be obtained.
That is, the pressure sensor 40 is manufactured by each process of S31-S40. Therefore, in the etching step S36, an opening is formed across the lower membrane 432 of the lower support film 43 from the surface opposite to the upper substrate 42 of the lower substrate 41 by a cycle etching process, and further by an over-etching process. The lower substrate 41 can be etched laterally along the lower membrane 432 using the lower side wall portion 431 as an etching stopper. Thereby, the lower substrate 41 in contact with the lower membrane 432 can be reliably removed by etching, and the thickness dimension of the lower membrane 432 can be formed uniformly. Further, since the etching in the lateral direction is restricted using the lower side wall portion 431 as an etching stopper, the outer region of the lower side wall portion 431 is not etched, and the lower membrane 432 can be formed in a desired area. .

[Modification]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

  For example, as the MEMS device, the ultrasonic transducer 10 for transmitting ultrasonic waves, the ultrasonic transducer 10A, the ultrasonic transducer 10B, and the pressure sensor 40 are illustrated, but the MEMS device is not limited thereto. As the ultrasonic transducer, the present invention may be applied to an ultrasonic transducer for ultrasonic reception or an ultrasonic transducer capable of performing both ultrasonic transmission and reception. Further, the present invention is not limited to such ultrasonic transducers and pressure sensors, and can be applied to any MEMS device having a diaphragm-shaped main film portion.

In each of the above embodiments, the side walls 121, 131, 431 rise in a direction orthogonal to the substrates 11, 41, and the rising direction of the side walls 121, 131, 431 is relative to the membranes 122, 132, 432. Although an orthogonal configuration is illustrated, the present invention is not limited to this.
The side wall portions 121, 131, and 431 may be formed at an angle that intersects the membranes 122, 132, and 432 as long as they function as etching stoppers for the overetching process in the etching process. In particular, when the angle between the side wall portions 121, 131, and 431 and the membrane 122, 132, and 432 is an acute angle, the etching progress rate along the side wall portions 121, 131, and 431 decreases in the overetching process. Therefore, the inconvenience of being etched beyond the side walls 121, 131, 431 can be prevented more reliably.

  Although the best configuration for carrying out the present invention has been specifically described above, the present invention is not limited to this. That is, the present invention has been illustrated and described primarily with respect to particular embodiments, but the present invention is not limited to the embodiments described above without departing from the scope of the technical idea and object of the present invention. Various modifications and improvements can be made by a trader.

  DESCRIPTION OF SYMBOLS 10, 10A, 10B ... Ultrasonic transducer (MEMS device), 11 ... Board | substrate, 111 ... Opening part, 112, 411A ... Cavity formation part, 113, 411B ... Communication hole, 114, 414 ... Convex part, 114A ... Tip surface , 114B ... side face part, 11A ... first face, 11B ... second face, 12, 13 ... support film (functional film), 121, 131, 431 ... side wall part, 122, 132, 432 ... membrane (main film part) 20 ... piezoelectric body, 21 ... lower electrode layer, 22 ... piezoelectric layer, 23 ... upper electrode layer, 30 ... mask layer, 31 ... hole, 41 ... lower substrate (substrate), 411A ... cavity forming portion, C, C1 ... cavity, S1 ... convex forming process, S2 ... film forming process, S5, S35 ... mask process, S6, S36 ... etching process, S21 ... first film forming process (film forming process), S22 ... film polishing process Film-forming step), S23 ... second film process (film formation step), S31 ... lower substrate formation step (convex forming step), S32 ... lower supporting film forming step (deposition step).

Claims (8)

A convex portion forming step of forming a convex portion having a flat front end surface and a side surface portion on the first surface of the substrate,
Forming a functional film covering at least the convex portion on the first surface; and
Forming a mask layer on the second surface opposite to the first surface of the substrate, and forming a hole in the mask layer; and
An etching step of etching the substrate using the functional film as an etching stopper through the hole, and
The film forming step forms the functional film having a main film portion that contacts the tip end surface of the convex portion, and a side wall portion that contacts the side surface portion of the convex portion,
In the mask process, in the plan view of the substrate viewed from the substrate thickness direction, the hole portion having an area smaller than the area of the tip surface is formed at a position overlapping the tip surface;
In the etching step, after etching from the second surface side of the substrate to the main film portion of the functional film in the thickness direction of the substrate, the side wall portion along the surface of the main film portion is sided. Etching forms an opening space including a region surrounded by the main film part and the side wall part. A method for manufacturing a MEMS device, comprising: In the manufacturing method of the MEMS device of Claim 1,
When the area where the hole is projected on the tip surface is a hole projection region, and the shortest distance from the point located on the outer periphery of the tip surface to the outer periphery of the hole projection region is an alignment setting value,
In the mask process, the hole is formed so that a difference value between a maximum value and a minimum value of alignment setting values is smaller than a height dimension of the convex portion. In the manufacturing method of the MEMS device of Claim 1 or Claim 2,
When the area where the hole is projected on the tip surface is a hole projection region, and the shortest distance from the point located on the outer periphery of the tip surface to the outer periphery of the hole projection region is an alignment setting value,
The convex part forming step forms the convex part so that a protruding dimension of the convex part is larger than a difference value between a maximum value and a minimum value of the alignment setting value. Method. In the manufacturing method of the MEMS device of Claim 2 or Claim 3,
The method for manufacturing a MEMS device, wherein the alignment setting values at each point on the outer peripheral edge of the tip surface are the same value. A MEMS device comprising a substrate and a functional film provided on the first surface of the substrate,
The functional film has a planar main film part and a side wall part extending in a direction intersecting the main film part from an outer peripheral edge of the main film part,
The substrate is
A cavity forming part that is in contact with the side wall part and forms a cavity together with the main film part and the side wall part;
A communication hole that is provided from the second surface opposite to the first surface of the substrate toward the cavity forming portion and communicates the cavity and a space outside the second surface. MEMS device. The MEMS device according to claim 5, wherein
The said cavity formation part has an inner wall surface from which the opening area increases in the direction which goes to the said main film part from the said communicating hole side. The MEMS device characterized by the above-mentioned. An ultrasonic transducer comprising a substrate, a functional film provided on the first surface of the substrate, and a piezoelectric body provided on the functional film,
The functional film has a planar main film part and a side wall part extending in a direction intersecting the main film part from an outer peripheral edge of the main film part,
The substrate is
A cavity forming part that is in contact with the side wall part and forms a cavity together with the main film part and the side wall part;
A communication hole provided from the second surface opposite to the first surface of the substrate toward the cavity forming portion, and communicating the cavity and a space outside the second surface;
Have
The piezoelectric body is configured by sequentially laminating a lower electrode layer, a piezoelectric layer, and an upper electrode layer on a surface opposite to a surface of the main film portion on which the cavity forming portion is provided. Ultrasonic transducer.   A substrate, a functional film provided on the first surface of the substrate, a first electrode provided on the functional film, and a second electrode supported at a position facing the first electrode through a space A pressure sensor comprising:
  The functional film has a planar main film part and a side wall part extending in a direction intersecting the main film part from an outer peripheral edge of the main film part,
  The substrate is
  A cavity forming part that is in contact with the side wall part and forms a cavity together with the main film part and the side wall part;
  A communication hole provided from the second surface opposite to the first surface of the substrate toward the cavity forming portion, and communicating the cavity and a space outside the second surface;
  Have
  The first electrode is provided on a surface of the main film portion opposite to the surface on which the cavity forming portion is provided.
  A pressure sensor characterized by that.

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