JP2014030878A - Mems element, electronic apparatus and manufacturing method for mems element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MEMS element in which a depressurized state of a cavity portion disposed with an MEMS structure is maintained and deterioration of characteristics is suppressed, and further to provide a manufacturing method therefor.SOLUTION: An MEMS element 100 provided with an MEMS vibrator 3 disposed in a cavity portion 2 formed by a sacrifice layer laminated on a principal surface of a wafer substrate 1 being subjected to etching comprises: a side wall portion 20 for implementing the cavity portion 2; a first coating layer 30 that covers the side wall portion 20 and the cavity portion 2, is laminated thereon and has one or more openings 31 passing therethrough into the cavity portion 2; and a second coating layer 32 that is laminated on the first coating layer 30 and seals the openings 31. The side wall portion 20 is configured so as to include a wiring layer 21 of the MEMS element 100. The side wall portion 20 and the openings 31 are formed at positions where a maximum length from the side wall portion 20 to the nearest opening 31 thereto is less than a length obtained on the basis of a product obtained by multiplying an etching speed by a predetermined period of time for performing etching.

Description

  The present invention relates to a MEMS element, an electronic device, and a method for manufacturing the MEMS element.

  In general, an electromechanical structure having a mechanically movable structure called a MEMS (Micro Electro Mechanical System) device formed by utilizing a microfabrication technique is known. For example, Patent Document 1 describes a MEMS element having a vibrator formed of a fixed electrode and a movable electrode formed on a semiconductor substrate. In the case of a MEMS device that uses such vibration of the movable part, the MEMS structure part is hermetically sealed in a reduced-pressure atmosphere in order to reduce air resistance during vibration of the movable part and to obtain excellent vibration characteristics. However, it is necessary to maintain a reduced pressure state. In the MEMS element described in Patent Document 1, the fixed electrode and the movable electrode are accommodated in a cavity (hereinafter also referred to as a cavity) hermetically sealed in a reduced pressure state. The cavity and the movable space of the movable electrode are formed by removing (release etching) a sacrificial layer such as an oxide film layer formed around the movable electrode by etching. After cleaning, an etching solution is introduced in a reduced-pressure atmosphere. The reduced pressure state is maintained by sealing the opened portion with a metal layer or the like.

Japanese Patent Laid-Open No. 2007-2222956

  However, after the sealing, when the laminated part where outgas is generated is exposed in the cavity or there is a residue where outgas is generated, the inside of the cavity is not maintained in a reduced pressure state, and the MEMS device There was a problem that the characteristics deteriorated. In particular, since an SOG (Spin on Glass) film for improving the step coverage of the electric wiring layer tends to generate outgas, it is necessary to avoid exposure and residual in the cavity. Therefore, when an SOG film is formed around the cavity, the etching time is managed so that the SOG film is not exposed by excessive etching. On the other hand, when the etching is insufficient, the sacrificial layer remains, and the dimensional accuracy of the MEMS structure may be lowered. For this reason, it is necessary to accurately set the etching time and etching conditions and to strictly manage the variation in etching. In recent years, as the size of MEMS devices has been further reduced, this management width (margin) has decreased, and there has been a problem that yield may be reduced.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following application examples or forms.

  Application Example 1 A MEMS element according to this application example is a MEMS element including a MEMS structure disposed in a cavity formed by etching a sacrificial layer stacked on a main surface of a substrate, A side wall part defining the cavity part, a first covering layer that covers and laminates the side wall part and the cavity part, and has one or more openings penetrating the cavity part; and laminated on the first covering layer; A second covering layer that seals the opening, and the side wall portion includes a wiring layer of the MEMS element, and the side wall portion and the opening are a maximum from the side wall portion to the opening closest to the side wall portion. Is formed at a position shorter than the length obtained based on the product of the etching speed and the predetermined time for performing the etching.

According to this application example, the sidewall portion includes the wiring layer of the MEMS element, and the sidewall portion and the opening have a maximum length from the sidewall portion to the nearest opening. It is formed at a position shorter than the length obtained based on the product with time. That is, the side wall portion and the opening are formed at a position where the sacrificial layer between the side wall portion and the opening is not etched and left in a predetermined time for etching the sacrificial layer.
Therefore, even if a material that generates outgas is used for part of the sacrificial layer, it can be removed by etching for a predetermined time. Specifically, for example, even when the SOG film for improving the step coverage is used for the wiring layer of the MEMS element constituting the side wall part, the side wall part and the opening including the SOG film are provided. As a result, the SOG film is not left in the cavity and the SOG film is not exposed in the cavity. As a result, the influence of outgas generated by the SOG film can be eliminated or reduced, so that the inside of the cavity can be maintained in a reduced pressure state. Or it becomes possible to maintain a pressure-reduced state for a longer period of time.
In addition, by using a wiring layer on the side wall, it can function as an etching stopper, so there is no need to strictly control the end timing of etching, and the management range (margin) of the etching process can be increased. It becomes.
That is, according to this application example, an excellent MEMS element in which characteristic deterioration does not occur due to outgas generated in the cavity or is suppressed, is provided by a process in which management is further simplified. be able to.

  Application Example 2 In the MEMS element according to the application example described above, the side wall portion includes the cavity portion in a polygonal shape when the main surface is viewed in plan.

  According to this application example, the side wall portion is provided with a hollow portion in a polygonal shape. Conventionally, the maximum length from the opening (etching hole) to the side wall portion of the conventional rectangular corner can be shortened by forming a polygonal shape with respect to the hollow portion that has been generally rectangular. As a result, in the step of forming the cavity by etching the sacrificial layer, the sacrificial layer can be stably removed without leaving the sacrificial layer without increasing the number of openings into which the etchant is introduced. Since the cavity is formed without increasing the opening, the reduced pressure state can be more reliably maintained.

  Application Example 3 In the MEMS element according to the application example, the side wall portion is provided with a circular or elliptical shape of the hollow portion when the main surface is viewed in plan. .

  According to this application example, the side wall portion is provided with a hollow portion in a circular shape or an elliptical shape. The maximum length from the opening to the side wall portion of the conventional rectangular corner can be shortened by making the hollow portion, which has been generally rectangular, conventionally circular or elliptical. As a result, in the step of forming the cavity by etching the sacrificial layer, the sacrificial layer can be stably removed without leaving the sacrificial layer without increasing the number of openings into which the etchant is introduced. Since the cavity is formed without increasing the opening, the reduced pressure state can be more reliably maintained. In addition, since the portion (first and second coating layers) that serves as the lid of the cavity is formed in a circular shape or an ellipse, the stress concentration with respect to the atmospheric pressure applied to the cavity is alleviated and dispersed throughout the sidewall. Thus, the airtight sealed state can be maintained more stably.

  Application Example 4 In the MEMS element according to the application example described above, the side wall portion defines the hollow portion in a rectangular shape when the main surface is viewed in plan, and the opening is provided in the rectangular shape. It is formed at a plurality of positions including a position penetrating the corner area of the hollow portion.

  According to this application example, the side wall portion is provided with a rectangular cavity portion, and the opening is formed at a plurality of positions including a position penetrating the corner region of the rectangular cavity portion. Yes. By forming the opening in this way, the sacrificial layer residue has been easily generated in the corner area of the hollow portion that has been conventionally drawn in a rectangular shape, whereas the corner area is etched more effectively, The etching can be stably removed without leaving the sacrificial layer.

  Application Example 5 A method of manufacturing a MEMS element according to this application example includes a step of forming a MEMS structure together with a sacrificial layer on a main surface of a substrate, and the sacrificial layer defined by a side wall portion including a wiring layer. A step of laminating a first covering layer having one or more openings penetrating the provided sacrificial layer so as to cover the side wall and the provided sacrificial layer; and And a step of etching the sacrificial layer provided by introducing an etching solution, and a step of laminating a second coating layer for sealing the opening on the first coating layer, and the sidewall portion and the The opening is formed at a position where a maximum length from the side wall portion to the nearest opening is shorter than a length obtained based on a product of the etching rate and a predetermined time for performing the etching. To do.

According to this application example, the side wall portion includes the wiring layer of the MEMS element, and the side wall portion and the opening have a maximum length from the side wall portion to the nearest opening, and the predetermined etching rate and etching are performed. It is formed at a position shorter than the length obtained based on the product with time. That is, the side wall portion and the opening are formed at a position where the sacrificial layer between the side wall portion and the opening is not removed and etched away during a predetermined time for etching the sacrificial layer.
Therefore, even when a material that generates outgas is used for part of the sacrificial layer, it can be removed by etching for a predetermined time. Specifically, for example, even when an SOG film for improving the step coverage is used for the wiring layer of the MEMS element constituting the side wall part, including the SOG film, between the side wall part and the opening. Since the sacrificial layer can be removed without etching, the SOG film does not remain in the cavity or the SOG film is not exposed in the cavity. As a result, the influence of outgas generated by the SOG film can be eliminated or reduced, so that the inside of the cavity can be maintained in a reduced pressure state. Or it becomes possible to maintain a pressure-reduced state for a longer period of time.
In addition, by using a wiring layer on the side wall, it can function as an etching stopper, so there is no need to strictly control the end timing of etching, and the management range (margin) of the etching process can be increased. It becomes.
That is, according to this application example, an excellent MEMS element in which characteristic deterioration does not occur due to outgas generated in the cavity or is suppressed, is provided by a process in which management is further simplified. be able to.

  Application Example 6 An electronic apparatus according to this application example includes the MEMS element according to the application example.

  According to this application example, it is possible to provide an electronic device in which predetermined characteristics can be obtained more stably.

(A) The top view which shows the MEMS element which concerns on Embodiment 1, (b) The AA cross section, (c) The enlarged side view of the side wall part and its peripheral part. (A) The top view which shows an example of the conventional MEMS element, (b) The AA sectional drawing, (c) The enlarged side view of the side wall part and its periphery part. (A)-(g) Process drawing which shows the manufacturing method of the MEMS element which concerns on Embodiment 1. FIG. (A) The top view which shows the MEMS element which concerns on Embodiment 2, The top view which shows the MEMS element which concerns on the modification 1. FIG. FIG. 4A is a perspective view illustrating a configuration of a mobile personal computer as an example of an electronic apparatus, and FIG. 5B is a perspective view illustrating a configuration of a mobile phone as an example of an electronic apparatus. The perspective view which shows the structure of the digital still camera as an example of an electronic device.

  DESCRIPTION OF EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention. In the following drawings, the scale may be different from the actual scale for easy understanding.

(Embodiment 1)
1A is a plan view showing the MEMS element 100 according to the first embodiment, FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A, and FIG. 1C is an enlarged side wall portion. It is sectional drawing.
The MEMS element 100 is a MEMS element that includes a MEMS structure disposed in a cavity formed by etching a sacrificial layer stacked on a main surface of a wafer substrate.
The MEMS element 100 includes a wafer substrate 1, a cavity 2, a MEMS vibrator 3 as a MEMS structure, a first oxide film 11, a nitride film 12, a first conductive layer 13, a second conductive layer 14, and a second oxide film 15. The third oxide film 16, the protective film 17, the side wall portion 20, the wiring layer 21, the first covering layer 30, the opening 31, the second covering layer 32, and the like.

The wafer substrate 1 is a silicon substrate, and the MEMS vibrator 3 is formed on the first oxide film 11 and the nitride film 12 stacked on the wafer substrate 1.
Here, the direction in which the first oxide film 11 and the nitride film 12 are sequentially laminated on the main surface of the wafer substrate 1 is described as an upward direction.

  The MEMS vibrator 3 includes a lower electrode 13 e and an upper electrode 14 e having a movable part, and is disposed in the cavity 2. The lower electrode 13e and the upper electrode 14e are formed by patterning the first conductive layer 13 and the second conductive layer 14 stacked on the nitride film 12 by photolithography. Although the 1st conductive layer 13 and the 2nd conductive layer 14 are comprised by the conductive polysilicon as a suitable example, respectively, it is not limited to this. Between the lower electrode 13e and the upper electrode 14e, a gap 13g that forms a movable space of the upper electrode 14e is formed. The cavity 2 and the cavity 13g are formed of a second oxide film 15 and a third oxide film 16 stacked on the MEMS vibrator 3, and a fourth oxide film 13f (described later) formed between the lower electrode 13e and the upper electrode 14e. It is formed by removing (release etching) by etching (shown in FIG. 3B). The second oxide film 15, the third oxide film 16, and the fourth oxide film 13f are so-called sacrificial layers, and the sacrificial layer is release-etched so that the upper electrode 14e is released from the lower electrode 13e. The movable electrode structure is formed.

FIG. 1C is an enlarged cross-sectional view of the side wall portion 20.
The right side of the figure shows a state in which the second oxide film 15 and the third oxide film 16 are removed by release etching and the cavity 2 is formed.
The second oxide film 15 is a CVD (Chemical Vapor Deposition) oxide film. In FIGS. 1B and 1C, a single-layer structure is shown, but a multi-layer structure may be used for planarization.
The third oxide film 16 has a three-layer structure for planarization. First, a CVD oxide film is stacked on the first layer among the three layers, and an SOG film is formed on the second layer above the CVD oxide film and planarized. FIG. 1C shows the residual SOG film 22 remaining after planarization. A CVD oxide film is again laminated on the third layer.

In the release etching, the sidewall portion 20 is formed as an etching stopper around the sacrificial layer composed of the second oxide film 15 and the third oxide film 16 laminated on the MEMS vibrator 3, and then the release etching is performed. Yes. That is, the cavity 2 formed by release etching is defined by the side wall 20.
The side wall portion 20 includes the second conductive layer 14 that forms the upper electrode 14e, the wiring layer 21 (the first wiring layer 21a and the second wiring layer 21b), and the like. As described above, the second conductive layer 14 is made of conductive polysilicon as a preferred example, and the wiring layer 21 is made of aluminum as a preferred example. These are resistant to buffered hydrofluoric acid as an etchant and function as an etching stopper. Note that the wiring material is not limited to these, and materials used in the semiconductor process can be utilized.

The second wiring layer 21 b constituting the uppermost part of the side wall part 20 is formed so as to cover the cavity part 2 and constitutes the first covering layer 30. In other words, the first coating layer 30 covers the side wall 20 and the cavity 2. The first covering layer 30 (the second wiring layer 21b) is provided with a plurality of openings 31 into which an etching solution is introduced when the sacrifice layer is subjected to release etching. That is, the opening 31 penetrates the cavity 2. The opening 31 is formed with a gap around the lower electrode 13e and the upper electrode 14e in order to remove the fourth oxide film 13f by the introduced etchant and to reliably form the MEMS vibrator 3.
A protective film 17 is laminated on the side wall portion 20. A second coating layer 32 is laminated on the first coating layer 30 and the protective film 17 after release etching and cleaning to seal the opening 31 from the outside air. A method for manufacturing the MEMS element 100 will be described later.

The electric wiring layer that electrically connects the lower electrode 13e and the upper electrode 14e and an external electric circuit (not shown) is formed by the second conductive layer 14, the wiring layer 21, etc., but is not shown. ing. Further, the external electric circuit can be configured integrally with the MEMS element 100 as a semiconductor circuit. That is, not only the second conductive layer 14 constituting the upper electrode 14e but also the first oxide film 11, the second oxide film 15, the third oxide film 16, the fourth oxide film 13f, and the protective film 17 can be an interlayer film or a protective film. The first wiring layer 21a and the second wiring layer 21b can be made of a material for integrally forming a semiconductor circuit as a circuit wiring layer. In other words, the MEMS element 100 can be formed in a semiconductor circuit manufacturing process.
In particular, in the case of a MEMS vibrator having a movable electrode formed of a semiconductor, it can be easily incorporated into a semiconductor process as compared with a vibrator such as a crystal.

Next, the planar configuration of the MEMS element 100 will be described.
FIG. 1A illustrates a plan view of the BB plane of FIG. Further, the opening 31 is indicated by a solid line for easy understanding.
As shown in the drawing, the side wall portion 20 defines the cavity portion 2 in an octagonal shape when viewed in plan. In FIG. 1A, a region indicated by an alternate long and short dash line indicates a release etching region 90. The release etching region 90 indicates a range where the sacrificial layer is removed in a predetermined release etching time when the side wall portion 20 is not formed. The release etching area 90 can be obtained from the position of the opening 31 and the length obtained based on the product of the release etching speed and the predetermined time for performing the release etching. The speed of release etching can be obtained in advance through experiments or the like. Therefore, the release etching region 90 can be obtained in advance by experiments.
Note that the predetermined etching time refers to a necessary and sufficient time for removing an unnecessary sacrificial layer and forming a predetermined cavity and a MEMS structure by etching.

  The side wall 20 is configured such that the inner wall that defines the cavity 2 is located inside the release etching region 90. In other words, the side wall 20 and the opening 31 have a maximum length from the side wall 20 to the nearest opening 31 shorter than the length obtained based on the product of the release etching speed and the predetermined time for performing the release etching. Formed in position. Therefore, in the present embodiment, the side wall portion 20 defines the cavity portion 2 in an octagonal shape. However, the side wall portion 20 does not necessarily have an octagonal shape, and the inner wall that defines the cavity portion 2 is a release etching region. Any polygon may be used as long as it is configured to be inside 90.

Next, a conventional MEMS device will be described with reference to FIGS.
2A is a plan view showing a MEMS element 99 as an example of a conventional configuration, FIG. 2B is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is an expanded sectional view of the peripheral part. FIG. 2A illustrates a plan view of the BB plane of FIG. Further, the opening 31 is indicated by a solid line for easy understanding.

The MEMS element 99 includes a side wall portion 20x. The MEMS element 99 is the same as the MEMS element 100 except that the shape of the side wall part 20x defining the cavity part 2 when viewed in plan is different from the shape of the side wall part 20.
As shown in FIG. 2A, the side wall portion 20x has a hollow portion 2 in a quadrangular shape when viewed in plan. In FIG. 2A, the portion indicated by the alternate long and short dash line indicates the sacrificial layer interface 90x remaining as a result of release etching. As described above, in the MEMS element 99 having the conventional configuration, the sacrificial layer provided by the side wall portion 20x has a quadrangular shape, and therefore, the sacrificial layer tends to remain in the corner portion away from the opening 31. In that case, as shown in FIG. 2C, when the sacrificial layer interface 90 x is in contact with the residual SOG film 22, the residual SOG film 22 is exposed to the cavity 2.
Since the SOG film generally tends to generate outgas, the outgas generated from the residual SOG film 22 exposed in the cavity 2 prevents the cavity 2 of the completed MEMS element 99 from maintaining a reduced pressure state. Therefore, conventionally, the release etching is managed so that the residual SOG film 22 is not exposed and the MEMS vibrator 3 is reliably formed. The MEMS device according to the present invention improves the complexity of management and the management margin due to the above-described configuration.

Next, a method for manufacturing the MEMS element 100 will be described.
3A to 3G are process diagrams sequentially illustrating a method for manufacturing the MEMS element 100.
The manufacturing method of the MEMS element 100 includes a step of forming the MEMS vibrator 3 as a MEMS structure together with a sacrificial layer on the main surface of the wafer substrate 1, and a sacrificial layer defined by the side wall portion 20 including the wiring layer 21. A step of laminating the first covering layer 30 having one or more openings 31 penetrating the provided sacrificial layer so as to cover the side wall portion 20 and the provided sacrificial layer; A step of etching the sacrificial layer provided by introducing an etching solution, and a step of laminating a second coating layer 32 for sealing the opening 31 on the first coating layer 30.
Further, the side wall portion 20 and the opening 31 are formed at positions where the maximum length from the side wall portion 20 to the nearest opening 31 is shorter than the length obtained based on the product of the etching rate and the predetermined time for etching. To do.

FIG. 3A: A wafer substrate 1 is prepared, and a first oxide film 11 is laminated on the main surface. As a preferred example, the first oxide film 11 is formed of a LOCOS (Local Oxidation of Silicon) oxide film, which is a general element isolation layer of a semiconductor process, but depending on the generation of the semiconductor process, for example, STI (Shallow Trench Isolation). ) Oxide film may be used.
Next, the nitride film 12 is laminated. The nitride film 12 is resistant to buffered hydrofluoric acid as an etchant and functions as an etching stopper.
Next, the first conductive layer 13 is stacked on the nitride film 12. The first conductive layer 13 is a polysilicon layer that constitutes the lower electrode 13e, and is ion-implanted after stacking to give predetermined conductivity.

  FIG. 3B: The first conductive layer 13 is patterned by photolithography to form the lower electrode 13e, and then thermally oxidized to form a fourth oxide film 13f. Formation of the oxide film by thermal oxidation is selectively performed on the polysilicon layer. The fourth oxide film 13f forms a gap with the upper electrode 14e as a sacrificial layer.

FIG. 3C: the second conductive layer 14 is laminated. The second conductive layer 14 is a polysilicon layer constituting the lowermost layer of the upper electrode 14 e and the side wall part 20. The second conductive layer 14 is patterned by photolithography to form the lowermost layer of the upper electrode 14e and the side wall 20. In the patterning of the side wall portion 20, the maximum length from the side wall portion 20 to the nearest opening 31 is based on the product of the etching speed in release etching and a predetermined time for performing etching, in accordance with the position where the opening 31 is disposed. Is formed at a position shorter than the length obtained.
The second conductive layer 14 constituting the upper electrode 14e is ion-implanted after stacking to have a predetermined conductivity.

FIG. 3D: a second oxide film 15 constituting a sacrificial layer is stacked. In the semiconductor process, the second oxide film 15 is formed as an interlayer film (IMD (Inter Metal Dielectric)), and is planarized using TEOS (Tetraethoxysilane) as a preferred example. Depending on the generation of the semiconductor process, planarization by CMP (Chemical Mechanical Polishing) or the like may be performed.
Next, prior to the lamination of the first wiring layer 21a, an exposed portion (hole) for electrically connecting the first wiring layer 21a and the second conductive layer 14 is formed in the second oxide film 15 by photolithography. . Next, the first wiring layer 21a is stacked and patterned by photolithography. As a suitable example, aluminum is laminated on the first wiring layer 21a by sputtering.
In FIG. 3D, since the illustration of the electric circuit is omitted, the first wiring layer 21a is shown only in the second layer portion constituting the side wall portion 20.

FIG. 3E: a third oxide film 16 is stacked as the second layer constituting the sacrificial layer. The third oxide film 16 has a three-layer structure for planarization. First, a CVD oxide film is stacked on the first layer among the three layers, and an SOG film is formed on the second layer above the CVD oxide film and planarized. FIG. 1C shows the residual SOG film 22 remaining after planarization. A CVD oxide film is again laminated on the third layer. In the semiconductor process, the third oxide film 16 is formed as an interlayer film (ILD (Inter Layer Dielectrics)). Depending on the generation of the semiconductor process, planarization by CMP or the like may be performed.
Next, prior to the lamination of the second wiring layer 21b, exposed portions (holes) for electrically connecting the first wiring layer 21a and the second wiring layer 21b are formed in the third oxide film 16 by photolithography. . Next, the second wiring layer 21b is stacked and patterned by photolithography. The second wiring layer 21 b constitutes the uppermost layer of the side wall portion 20, and includes an opening 31 for release etching the sacrificial layer of the MEMS element 100 and covers the sacrificial layer (third oxide film 16). The second wiring layer 21 b constitutes the first covering layer 30.
In addition, as a suitable example, aluminum is laminated on the second wiring layer 21b by sputtering.

FIG. 3F: A protective film 17 is laminated, an opening is provided so that the opening 31 is exposed, and patterning is performed by photolithography. The protective film 17 may be a general protective film (for example, a SiO ₂ film or a SiN two-layer film) in a semiconductor process, and may be a polyimide film or the like.
Next, the wafer substrate 1 is exposed to an etching solution, and the second oxide film 15, the third oxide film 16, and the fourth oxide film 13 f as sacrificial layers are release-etched, whereby the MEMS vibrator 3 as the MEMS structure. Form.

  FIG. 3G: After the end of the release etching, the second coating layer 32 is stacked after cleaning, and patterned by photolithography so that the portion not covered with the protective film 17 is sealed. The space where the opening 31 is sealed by the second covering layer 32 and the sacrificial layer is removed by release etching is maintained in a sealed state. As the second covering layer 32, aluminum is used as a preferred example, but the present invention is not limited to this, and other metal layers may be used.

As described above, according to the MEMS element and the method for manufacturing the MEMS element according to the present embodiment, the following effects can be obtained.
The side wall part 20 includes the wiring layer 21 of the MEMS element 100, and the side wall part 20 and the opening 31 have a maximum length from the side wall part 20 to the nearest opening 31 to a predetermined etching rate and etching. It is formed at a position shorter than the length obtained based on the product with time. That is, the side wall portion 20 and the opening 31 are formed at a position where the sacrificial layer between the side wall portion 20 and the opening 31 is not etched away during a predetermined time for etching the sacrificial layer.
Therefore, even when a material that generates outgas is used for part of the sacrificial layer, it can be removed by performing etching for a predetermined time. More specifically, the sacrificial layer between the side wall 20 and the opening 31 including the residual SOG film 22 of the wiring layer 21 constituting the side wall 20 is not etched away, so that the cavity 2 (cavity 2 ) And the residual SOG film 22 is not exposed in the cavity 2. As a result, the influence of the outgas generated by the residual SOG film 22 can be eliminated or reduced, so that the inside of the cavity 2 can be maintained in a reduced pressure state. Or it becomes possible to maintain a pressure-reduced state for a longer period of time.
Further, since the side wall portion 20 can function as an etching stopper, it is not necessary to strictly manage the end timing of etching, and a management width (margin) of the etching process can be increased.
In other words, according to the present embodiment, an excellent MEMS element in which characteristic deterioration does not occur due to outgas generated in the cavity or in which characteristic deterioration is suppressed is provided by a process in which management is further simplified. Can do.

  Moreover, the side wall part is provided with the cavity 2 in an octagonal shape. Conventionally, the cavity 2 having a generally rectangular shape is formed in an octagonal shape, whereby the maximum length from the opening 31 (etching hole) to the side wall 20x of the conventional rectangular corner can be shortened. . As a result, in the step of forming the cavity 2 by etching the sacrificial layer, the sacrificial layer can be stably removed without leaving the sacrificial layer without increasing the number of openings 31 into which the etchant is introduced. . Since the cavity 2 is formed without increasing the opening 31, the reduced pressure state can be more reliably maintained.

(Embodiment 2)
Next, the MEMS element 101 according to the second embodiment will be described. In the description, the same components as those in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.
FIG. 4A is a plan view of the MEMS element 101 according to the second embodiment.
The MEMS element 101 is formed at a plurality of positions including a position where the side wall portion has a rectangular hollow portion and the opening penetrates the corner region of the hollow portion having the rectangular shape. It is said.

The MEMS element 101 is the same as the MEMS element 99 except that a new opening 31x is provided. As described above, in the MEMS element 99 having the conventional configuration, the sacrificial layer provided by the side wall portion 20x has a quadrangular shape, so that the sacrificial layer is likely to remain in the corner portion away from the opening 31. In this case, as shown in FIG. 2C, when the sacrificial layer interface 90 x is in contact with the residual SOG film 22, the residual SOG film 22 is exposed to the cavity 2.
In order to improve this point, the opening 31x is formed at four corner portions away from the opening 31. As shown in FIG. 4A, a specific position where the opening 31x is formed is that the length Lx obtained based on the product of the etching speed in the release etching and the predetermined time for the etching is the radius. This is a position where the remaining sacrificial layer interface 90x is included in the etched region 91x. Therefore, the maximum length from the side wall portion 20x to the nearest opening 31 and the opening 31x is a position shorter than the length Lx obtained based on the product of the etching speed and the predetermined etching time, and as a result, The sacrificial layer is not removed by a predetermined release etching.
In the present embodiment, four openings 31x are newly formed at four corner portions, but the present invention is not limited to this. It suffices if the remaining sacrificial layer interface 90x is included in the etching region 91x with the length Lx as the radius centering on the newly formed opening. For example, the number may be two, or six as necessary.

According to the MEMS element 101 according to the present embodiment, in addition to the effects of the above-described embodiment, the following effects can be obtained.
The side wall portion 20x has a hollow cavity portion 2 provided in a rectangular shape, and the opening 31x is formed at a position penetrating a corner area of the hollow portion 2 provided in a rectangular shape. By forming the opening 31x in addition to the opening 31 in this way, the sacrificial layer remains easily generated in the corner area of the cavity 2 that is conventionally defined in a rectangular shape, whereas the corner area is more effective. Therefore, the etching can be stably removed without leaving the sacrificial layer.

  Note that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be added to the above-described embodiment. A modification will be described below. Here, the same components as those in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

(Modification 1)
FIG. 4B is a plan view of the MEMS element 102 according to the first modification.
In the first embodiment, as illustrated in FIG. 1A, the side wall portion 20 has been described as having the cavity portion 2 formed in an octagonal shape when viewed in plan, but the configuration is limited to this configuration. Instead, it suffices if the inner wall that defines the cavity 2 is configured to be inside the release etching region 90.
The MEMS element 102 includes a side wall portion 20w. The MEMS element 102 is the same as the MEMS element 100 except that the shape of the side wall portion 20 w that defines the cavity 2 when viewed in plan is different from the shape of the side wall portion 20.
As shown in FIG. 4B, the side wall portion 20w has an elliptical cavity portion 2 when viewed in plan. Further, the inner wall of the side wall portion 20 w that defines the cavity portion 2 is configured to be inside the release etching region 90.

  According to the present modification, the maximum length from the opening 31 to the side wall portion 20 of the conventional rectangular corner is made circular or elliptical with respect to the hollow portion 2 that has been generally rectangular. Can be further shortened. As a result, in the step of forming the cavity 2 by etching the sacrificial layer, the sacrificial layer can be stably removed without leaving the sacrificial layer without increasing the number of openings 31 into which the etchant is introduced. . Since the cavity 2 is formed without increasing the opening 31, the reduced pressure state can be more reliably maintained. In addition, since the portion (the first coating layer 30 and the second coating layer 32) serving as the lid of the cavity portion 2 is formed in a circular shape or an oval shape, stress concentration with respect to the atmospheric pressure applied to the cavity portion is alleviated, and the side wall Since it disperses | distributes to the whole part 20w, an airtight sealing state can be maintained more stably.

[Electronics]
Next, electronic devices to which the MEMS elements 100, 101, and 102 as electronic components according to an embodiment of the present invention are applied will be described with reference to FIGS. 5 (a), 5 (b), and 6. FIG. In the description, an example using the MEMS element 100 as an electronic component is shown.

  FIG. 5A is a perspective view schematically illustrating a configuration of a mobile (or notebook) personal computer as an electronic apparatus including an electronic component according to an embodiment of the present invention. In this figure, a personal computer 1100 includes a main body portion 1104 provided with a keyboard 1102 and a display unit 1106 provided with a display portion 1000. The display unit 1106 is rotated with respect to the main body portion 1104 via a hinge structure portion. It is supported movably. Such a personal computer 1100 includes a MEMS element 100 as an electronic component that functions as a filter, a resonator, a reference clock, and the like.

  FIG. 5B is a perspective view schematically showing a configuration of a mobile phone (including PHS) as an electronic apparatus including the electronic component according to the embodiment of the present invention. In this figure, a cellular phone 1200 is provided with a plurality of operation buttons 1202, an earpiece 1204 and a mouthpiece 1206, and a display unit 1000 is disposed between the operation buttons 1202 and the earpiece 1204. Such a cellular phone 1200 incorporates a MEMS element 100 as an electronic component (timing device) that functions as a filter, a resonator, an angular velocity sensor, or the like.

FIG. 6 is a perspective view schematically illustrating a configuration of a digital still camera as an electronic apparatus including the electronic component according to the embodiment of the present invention. In this figure, connection with an external device is also simply shown. The digital still camera 1300 generates an imaging signal (image signal) by photoelectrically converting an optical image of a subject using an imaging element such as a CCD (Charge Coupled Device).
A display unit 1000 is provided on the back surface of a case (body) 1302 in the digital still camera 1300, and is configured to display based on an imaging signal from the CCD. The display unit 1000 displays a subject as an electronic image. Functions as a viewfinder. A light receiving unit 1304 including an optical lens (imaging optical system), a CCD, and the like is provided on the front side (the back side in the drawing) of the case 1302.
When the photographer confirms the subject image displayed on the display unit 1000 and presses the shutter button 1306, the CCD image pickup signal at that time is transferred and stored in the memory 1308. In the digital still camera 1300, a video signal output terminal 1312 and an input / output terminal 1314 for data communication are provided on the side surface of the case 1302. As shown in the figure, a television monitor 1430 is connected to the video signal output terminal 1312 and a personal computer 1440 is connected to the input / output terminal 1314 for data communication as necessary. Further, the imaging signal stored in the memory 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation. Such a digital still camera 1300 incorporates a MEMS element 100 as an electronic component that functions as a filter, a resonator, an angular velocity sensor, or the like.

  Note that the MEMS element 100 as an electronic component according to an embodiment of the present invention includes the personal computer (mobile personal computer) in FIG. 5A, the mobile phone in FIG. 5B, and the digital still camera in FIG. In addition, for example, an ink jet discharge device (for example, an ink jet printer), a laptop personal computer, a television, a video camera, a car navigation device, a pager, an electronic notebook (including a communication function), an electronic dictionary, a calculator, an electronic game Equipment, workstations, videophones, security TV monitors, electronic binoculars, POS terminals, medical equipment (for example, electronic thermometers, blood pressure monitors, blood glucose meters, electrocardiogram measuring devices, ultrasonic diagnostic devices, electronic endoscopes), fish detectors , Various measuring instruments, instruments (for example, vehicles, aircraft, ships S), can be applied to electronic equipment such as a flight simulator.

  DESCRIPTION OF SYMBOLS 1 ... Wafer substrate, 2 ... Cavity, 3 ... MEMS vibrator, 11 ... 1st oxide film, 12 ... Nitride film, 13 ... 1st conductive layer, 13e ... Lower electrode, 13f ... 4th oxide film, 13g ... Gap 14, second conductive layer, 14 e, upper electrode, 15, second oxide film, 16, third oxide film, 17, protective film, 20, 20 x, 20 w, side wall, 21, wiring layer, 21 a, first. 1 wiring layer, 21b ... 2nd wiring layer, 22 ... residual SOG film, 30 ... 1st coating layer, 31, 31x ... opening, 32 ... 2nd coating layer, 90 ... release etching area | region, 90x ... sacrificial layer interface, 99 , 100, 101, 102 ... MEMS elements.

Claims (6)

A MEMS device comprising a MEMS structure disposed in a cavity formed by etching a sacrificial layer stacked on a main surface of a substrate,
A side wall portion defining the hollow portion;
A first covering layer that covers and laminates the side wall and the cavity, and has one or more openings penetrating the cavity;
A second covering layer laminated on the first covering layer and sealing the opening,
The side wall portion includes a wiring layer of the MEMS element,
The side wall and the opening are formed at positions where the maximum length from the side wall to the nearest opening is shorter than the length obtained based on the product of the etching speed and the predetermined time for performing the etching. A MEMS element characterized by being made.   The MEMS element according to claim 1, wherein the side wall portion has the cavity portion defined in a polygonal shape when the main surface is viewed in plan.   2. The MEMS element according to claim 1, wherein the side wall portion defines the cavity portion in a circular shape or an elliptical shape when the main surface is viewed in plan view. The side wall portion, when the main surface is viewed in plan, defines the hollow portion in a rectangular shape,
2. The MEMS element according to claim 1, wherein the opening is formed at a plurality of positions including a position penetrating a corner region of the hollow portion provided in the rectangular shape. Forming a MEMS structure together with a sacrificial layer on the main surface of the substrate;
A step of providing the sacrificial layer by a side wall portion including a wiring layer;
Laminating a first covering layer having one or more openings penetrating the provided sacrificial layer so as to cover the side wall and the provided sacrificial layer;
Etching the sacrificial layer provided by introducing an etchant from the opening;
Laminating a second coating layer for sealing the opening on the first coating layer,
The side wall and the opening are formed at a position where the maximum length from the side wall to the nearest opening is shorter than the length obtained based on the product of the etching speed and the predetermined time for performing the etching. A method for manufacturing a MEMS device, comprising:   An electronic apparatus comprising the MEMS element according to any one of claims 1 to 4.

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