MEMS device

A present MEMS device includes: a substrate; a functional element that is provided on a surface of the substrate; a structural member that is provided on the surface of the substrate and forms a cavity surrounding the functional element; a first lid portion that is provided with an opening and covers a part of the cavity in such a manner that a gap is present between the first lid portion and the functional element; a receiving portion that is provided between a plurality of electrodes or a plurality of units of wiring on the surface of the substrate and has a receiving face opposing the cozening of the first lid portion via a gap; and a second lid portion including an electrically conductive sealing portion that seals the opening of the first lid portion.

BACKGROUND

1. Technical Field

The present invention relates to, for example, a MEMS (Micro Electro Mechanical Systems) device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate.

2. Related Art

For example, in a MEMS device that includes a resonator with capacitance as a functional element, the resonator is airtightly sealed, in a vacuum state, in a cavity formed in a substrate. Also, even in the case of a functional element that does not require airtight vacuum seal, the functional element is airtightly sealed in a cavity so as to prevent the influences of dust, moisture, and the like.

In order to form a cavity in such a MEMS device, for example, a sacrificial film is formed in a cavity provided with a functional element, the cavity is covered by a first lid portion in which an opening (release hole) is formed in a predetermined position, and then the sacrificial film is removed through release etching. Furthermore, in order to seal the release hole, a second lid portion that includes a sealing portion is formed, through sputtering, on the first lid portion using a sealant of aluminum (Al) and the like.

However, when forming the sealing portion through sputtering, a part of the sealant enters the cavity via the release hole and attaches to a bottom surface of the cavity. Therefore, if a plurality of electrodes or units of wiring connected to different destinations are present on the bottom surface of the cavity immediately below the release hole, these electrodes or units of wiring could possibly be short-circuited. For this reason, traditionally, the plurality of electrodes or units of wiring connected to different destinations cannot be installed in proximity on the bottom surface of the cavity immediately below the release hole.

As related art, JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) discloses efficient execution of manufacturing processes of an electronic apparatus that is composed of an electronic circuit and a functional element installed in a hollow of a substrate, and that is intended to secure a manufacturing yield and reduce a manufacturing cost. This electronic apparatus has a substrate, a functional element formed on the substrate, and a covering structure that defines a hollow in which the functional element is installed. The covering structure has a layered structure made up of an inter-layer insulating film and a wiring layer that are formed on the substrate so as to surround the hollow. Out of the covering structure, at least apart of an upper covering portion, which covers the hollow from above, in a thickness direction includes a corrosion-resistant layer. The upper covering portion includes a first covering layer with a through-hole facing the hollow, and a second covering layer closing the through-hole.

On the other hand, JP-A-2010-223850 (paragraphs 0012 and 0013, FIG. 5) discloses a MEMS device that can be manufactured in simple processes, can be reduced in size, and has a highly reliable hollow space sealing structure. This MEMS device includes a substrate, a movable portion that is provided with a hole and formed on the substrate via a gap, a pillar that is formed on the substrate and penetrates into the hole without coming into contact with the movable portion, and a cap portion that is supported by the pillar and is formed on the movable portion via a gap.

JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) states that it is preferable that the through-hole (release hole) be formed in a position shifted from a position immediately above a MEMS structural member (functional element). This makes it possible to avoid an unfavorable situation in which the material of the second covering layer attaches to the MEMS structural member at the time of formation of the second covering layer. However, JP-A-2008-221435 (paragraphs 0007, 0008 and 0041, FIG. 8) does not disclose prevention of a short circuit that occurs due to the material of the second covering layer attaching to a plurality of electrodes or units of wiring provided on a bottom surface of a cavity. JP-A-2010-223850 (paragraphs 0012 and 0013, FIG. 5) does not disclose prevention of a short circuit of a plurality of electrodes or units of wiring provided on a bottom surface of a cavity, either.

SUMMARY

A first advantage of some aspects of the invention is that, in a MEMS device with a cavity in which a functional element is provided, a short circuit of electrodes or units of wiring provided on a bottom surface of the cavity is prevented, and the cavity is reduced in size. A second advantage of some aspects of the invention is that the strength of a structure of the cavity that houses the functional element is improved. A third advantage of some aspects of the invention is that a second lid portion including a sealing portion that seals a release hole is reduced in thickness. A fourth advantage of some aspects of the invention is that a diameter of the release hole formed in a first lid portion is increased to perform release etching efficiently.

A MEMS device according to a first aspect of the invention includes: a substrate; a functional element that is provided, either directly or via an insulating film, on a surface of the substrate; a structural member that is provided on the surface of the substrate or on a surface of the insulating film, and forms a cavity surrounding the functional element; a first lid portion that is provided with an opening and covers a part of the cavity in such a manner that a gap is present between the first lid portion and the functional element; a receiving portion that is provided between a plurality of electrodes or a plurality of units of wiring on the surface of the substrate or on the surface of the insulating film, and has a receiving face opposing the opening of the first lid portion via a gap; and a second lid portion including an electrically conductive sealing portion that seals the opening of the first lid portion.

According to the first aspect of the invention, the receiving portion with the receiving face opposing the opening of the first lid portion via a gap is provided between the plurality of electrodes or units of wiring. In this way, even if a part of an electrically conductive sealant enters the cavity via the release hole when forming, through sputtering, the sealing portion that seals the release hole, the receiving portion can prevent a short circuit of the plurality of electrodes or units of wiring. As a result, an interval between these electrodes or units of wiring can be reduced, and the cavity can be reduced in size. Furthermore, as the receiving portion opposes the opening of the first lid portion via a gap, it does not obstruct release etching.

Here, the sealing portion may extend to the receiving face of the receiving portion. In this way, together with the first lid portion, the second lid portion including the sealing portion is fixed to the receiving portion, thereby improving the strength of a structure of the cavity that houses the functional element.

Alternatively, the area of the receiving face of the receiving portion may be smaller than the area of the opening of the first lid portion. In this case, a part of the electrically conductive sealant attaches to a bottom surface of the cavity via the release hole when forming, through sputtering, the sealing portion that seals the release hole; however, as the receiving portion fulfills a role of a mask, a short circuit of the plurality of electrodes or units of wiring can be prevented. As a result, an interval between these electrodes or units of wiring can be reduced, and the cavity can be reduced in size.

A MEMS device according to a second aspect of the invention includes: a substrate; a functional element that is provided, either directly or via an insulating film, on a surface of the substrate; a structural member that is provided on the surface of the substrate or on a surface of the insulating film, and forms a cavity surrounding the functional element; a first lid portion that is provided with an opening and covers a part of the cavity in such a manner that a gap is present between the first lid portion and the functional element; an electrically conductive receiving portion that is provided on the surface of the substrate or on the surface of the insulating film, is electrically connected to the functional element, and has a receiving face opposing the opening of the first lid portion via a gap; and a second lid portion including an electrically conductive sealing portion that seals the opening of the first lid portion and extends to the receiving face of the receiving portion.

According to the second aspect of the invention, even if a part of the electrically conductive sealant enters the cavity via the release hole when forming, through sputtering, the sealing portion that seals the release hole, the receiving portion can prevent a short circuit of the electrodes or units of wiring. Moreover, as the electrically conductive receiving portion can be utilized as an external connection electrode, wiring for the functional element can be installed efficiently, and the cavity can be further reduced in size.

With regard to the first or second aspect of the invention, in a plan view, the receiving face of the receiving portion may overlap the opening of the first lid portion and a region surrounding the opening. In this way, even if a part of the sealant enters the cavity via the release hole when forming, through sputtering, the sealing portion that seals the release hole, the receiving face of the receiving portion can catch the sealant. Therefore, even if the second lid portion including the sealing portion is reduced in thickness, the release hole can be sealed. In addition, a diameter of the release hole formed in the first lid portion can be increased to perform release etching efficiently.

The above-referenced receiving portion may be formed of polysilicon doped with impurities. In this case, the receiving portion can be formed simultaneously when forming the functional element with polysilicon doped with impurities. Also, as the receiving portion has electrical conductivity, the receiving portion can be utilized as an external connection electrode.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following describes embodiments of the invention in detail with reference to the accompanying drawings. It should be noted that the same constituent element is assigned the same reference sign, and redundant descriptions are omitted.

A MEMS device according to the embodiments of the invention is a device in which a functional element, such as a resonator, a sensor and an actuator, and/or an electronic circuit are integrated on one substrate.

Below, as one example, a MEMS device will be described that includes a resonator with capacitance as a functional element, and also includes a MOS field-effect transistor as a semiconductor circuit element. The resonator is airtightly sealed in a cavity formed in a trench (a recessed portion in a surface) of a semiconductor substrate.

First Embodiment

FIG. 1is a plan view showing a structure of the inside of a trench of a MEMS device according to a first embodiment of the invention.FIG. 1shows the structure of the inside of trench before a cavity is covered by a lid portion.FIG. 2is a cross-sectional view, taken along the line A-A′ ofFIG. 1, showing major portions of the MEMS device. As shown inFIGS. 1 and 2, this MEMS device uses a semiconductor substrate10whose main surface (an upper surface inFIG. 2) has a first region (the right side inFIG. 2) in which a trench10ais formed and a second region (the left side inFIG. 2) in which impurity diffusion regions of a semiconductor circuit element are formed.

A resonator including a lower electrode31and an upper electrode32, external connection electrodes41and42, a receiving portion43, and a wall portion44are provided on a bottom surface of the trench10aof the semiconductor substrate via an insulating film20. Also, an insulating film51that reinforces the wall portion44is provided so as to surround the wall portion44. It should be noted that the receiving portion43and the wall portion44may be provided directly on the bottom surface of the trench10aof the semiconductor substrate. Also, in a case where a substrate with high insulating properties, such as a substrate of glass, ceramics, resin, or the like, is used, the lower electrode31, the upper electrode32and the external connection electrodes41and42may be provided directly on the substrate.

For example, the insulating film20includes an insulating film21of silicon dioxide (SiO2) and an insulating film22of silicon nitride (SiN). The lower electrode31, the upper electrode32and the external connection electrode41to the wall portion44are formed of, for example, polysilicon that has been doped with impurities and has electrical conductivity. The insulating film51is formed of silicon dioxide (SiO2) and the like.

The upper electrode32of the resonator includes a cantilever-like structural member that is fixed at one end and movable at the other end. The external connection electrodes41and42have, for example, a shape of a prism or a cylinder, and are used to electrically connect the lower electrode31and the upper electrode32of the resonator to the electronic circuit. The external connection electrode41is electrically connected to the lower electrode31, and may be constructed integrally with the lower electrode31. On the other hand, the external connection electrode42is electrically connected to the upper electrode32, and may be constructed integrally with the upper electrode32.

The receiving portion43has, for example, a shape of a prism or a cylinder, and is provided between a plurality of electrodes or units of wiring connected to different destinations so as to prevent a short circuit of these electrodes or units of wiring in a later-described sputtering process of a sealant. For example, in the examples shown inFIGS. 1 and 2, the receiving portion43is provided between the external connection electrode41and the external connection electrode42. The wall portion44is a structural member that forms the cavity surrounding the resonator and the external connection electrode41to the receiving portion43.

In the trench10aof the semiconductor substrate, a region surrounded by the wall portion44is the cavity. The space in the cavity is a high vacuum region. By applying an alternating current voltage between the lower electrode31and the upper electrode32in the resonator provided in the cavity, mechanical oscillation of the upper electrode32is excited by an electrostatic force, and a change in capacitance between the lower electrode31and the upper electrode32attributed to this mechanical oscillation is detected.

As shown inFIG. 2, the cavity is covered by a lid portion including a first lid portion60and a second lid portion70, in such a manner that a gap is present between the lid portion and the resonator. The first lid portion60includes, for example, an insulating film61of silicon nitride (SiN) and the like, and a polysilicon film62that has electrical conductivity. It should be noted that a surface of the polysilicon film62may be provided with a titanium nitride (TiN) film, a salicide film, or the like.

A part of the polysilicon film62is provided in a predetermined region of a main surface (an upper surface in the figure) of the external connection electrode41, and is electrically connected to the external connection electrode41. Another part of the polysilicon film62that is insulated from the above-referenced part is provided in a predetermined region of a main surface (an upper surface in the figure) of the external connection electrode42, and is electrically connected to the external connection electrode42.

An opening (release hole)60ais formed in a predetermined position of a face of the first lid portion60opposing the surface of the substrate or the insulating film20. The part of the first lid portion60other than the release hole60acovers the cavity. The release hole60ais used in removing, through release etching, a sacrificial film formed in the cavity. Thereafter, with the inside of the cavity placed in a decompressed state (vacuum state), the second lid portion70is formed, through sputtering (a high vacuum film formation technique), on a surface of the first lid portion60using an electrically conductive sealant of aluminum (Al) and the like.

The second lid portion70includes an intermediate conductive member71, an intermediate conductive member72and a sealing portion73. The intermediate conductive member71is electrically connected to the external connection electrode41via the polysilicon film62and insulated from the other part of the second lid portion70. The intermediate conductive member72is electrically connected to the external connection electrode42via the polysilicon film62and insulated from the other part of the second lid portion70. The sealing portion73seals the release hole60aof the first lid portion.

In a sputtering process for forming the second lid portion70, a part of the electrically conductive sealant enters the cavity via the release hole60a. In view of this, in the present embodiment, the receiving portion43is provided below the release hole60aso as to prevent a plurality of electrodes or units of wiring from getting short-circuited by the sealant that has entered the cavity.

FIGS. 3A to 3Care cross-sectional views showing the states of formation of the sealing portion in the sputtering process.FIG. 3Ashows the state of formation of the sealing portion in a MEMS device according to a comparative example. As shown inFIG. 3A, in the MEMS device according to the comparative example, when forming the sealing portion73on the surface of the first lid portion60through sputtering, a part of the electrically conductive sealant enters the cavity via the release hole60aand attaches to the bottom surface of the cavity. Therefore, a plurality of electrodes or units of wiring connected to different destinations cannot be installed in proximity on the bottom surface of the cavity immediately below the release hole60a.

Also, in the MEMS device according to the comparative example, as the release hole60ais sealed by forming an overhang in the sealing portion73above the release hole60a, a film thickness of the sealing portion73needs to be increased in proportion to a diameter of the release hole60a. Therefore, in order to reduce the sealing portion73in thickness, it is necessary to make the release hole60aminute by reducing the diameter of the release hole60a.

On the other hand,FIG. 3Bshows the state of formation of the sealing portion in the MEMS device according to the first embodiment of the invention. As shown inFIG. 3B, in the MEMS device according to the first embodiment of the invention, the receiving portion43is provided between a plurality of electrodes or units of wiring connected to different destinations. The receiving portion43has a receiving face43athat opposes the release hole60avia a gap.

In this way, even if a part of the electrically conductive sealant enters the cavity via the release hole60awhen forming, through sputtering, the sealing portion73that seals the release hole60a, the receiving portion43can prevent a short circuit of the plurality of electrodes or units of wiring. As a result, an interval between these electrodes or units of wiring can be reduced, and the cavity can be reduced in size. Also, as the receiving face43aof the receiving portion43opposes the release hole60avia the gap, it does not obstruct release etching.

As shown inFIG. 3B, the sealing portion73extends to the receiving face43aof the receiving portion43. In this way, together with the first lid portion60, the second lid portion including the sealing portion73is fixed to the receiving portion43, thereby improving the strength of a structure of the cavity that houses the functional element.

In addition, in a plan view, the receiving face43aof the receiving portion43overlaps the release hole60aand a region therearound. In this way, even if a part of the electrically conductive sealant enters the cavity via the release hole60awhen forming, through sputtering, the sealing portion73that seals the release hole60a, the receiving face43aof the receiving portion43can catch the sealant.

In this case, the release hole60acan be sealed if the film thickness of the sealing portion73on the receiving face43ais larger than a distance between the face of the first lid portion60opposing the surface of the substrate or the insulating film20and the receiving face43a. Therefore, even if the second lid portion including the sealing portion73is reduced in thickness, the release hole60acan be sealed. Accordingly, a shallow trench can be formed in the semiconductor substrate by reducing the second lid portion in thickness.

Furthermore, as the diameter of the release hole60ano longer depends on the film thickness of the sealing portion73, the diameter of the release hole60aformed in the first lid portion60can be increased to perform release etching efficiently.

FIG. 3Cshows the state of formation of the sealing portion in a MEMS device according to a modification example of the first embodiment according to the invention. As shown inFIG. 3C, in the MEMS device according to the modification example of the first embodiment of the invention, the area of the receiving face43aof the receiving portion43is smaller than the area of the release hole60a.

In this case, a part of the electrically conductive sealant attaches to the bottom surface of the cavity via the release hole60awhen forming, through sputtering, the sealing portion73that seals the release hole60a; however, as the receiving portion43fulfills a role of a mask, a short circuit of a plurality of electrodes or units of wiring can be prevented. As a result, an interval between these electrodes or units of wiring can be reduced, and the cavity can be reduced in size.

Referring back toFIG. 2, the semiconductor circuit element is provided in the second region of the main surface of the semiconductor substrate10. For example, impurity diffusion regions81and82, which serve as a source and a drain of a MOS field-effect transistor (MOSFET), are provided inside the semiconductor substrate10, and a gate electrode83is provided on the semiconductor substrate10via a gate insulating film.

A first insulating layer (inter-layer insulating film)91of silicon dioxide (SiO2), BPSG (Boron Phosphorus Silicon Glass), or the like is provided on the semiconductor substrate10provided with the lid portion and the semiconductor circuit element. The first insulating layer91covers the main surface of the semiconductor substrate10. The first insulating layer91is in contact with the insulating film61and insulates the intermediate conductive members71and72of the second lid portion70from the sealing portion73.

Contact plugs (electrodes)101and102of tungsten (W) and the like are provided in a first region of the first insulating layer91. The contact plugs101and102penetrate the first insulating layer91and are electrically connected to the intermediate conductive members71and72, respectively. Also, contact plugs (electrodes)103to105of tungsten (W) and the like are provided in a second region of the first insulating layer91. The contact plugs103to105penetrate the first insulating layer91and are electrically connected to the impurity diffusion region81, the impurity diffusion region82and the gate electrode83, respectively.

Electrical connection to the contact plugs101to105is implemented on a first wiring layer of aluminum (Al) and the like, which is provided on a surface of the first insulating layer91. Furthermore, where necessary, a second wiring layer is provided via a second insulating layer92, and a desired number of wiring layers are installed in a similar manner from then on. In addition, a protection film (not shown) is provided on a surface of a topmost wiring layer.

For example, wiring111provided on the first wiring layer brings the contact plug101and the contact plug103into electrical connection to each other. Also, wiring112provided on the second wiring layer brings the contact plug102and the contact plug104into electrical connection to each other via the first wiring layer. In this way, the resonator can be electrically connected to the semiconductor circuit element.

A description is now given of a method of manufacturing the MEMS device shown inFIGS. 1 and 2.

FIGS. 4A to 5Bare cross-sectional views pertaining to manufacturing processes of the MEMS device according to the first embodiment of the invention. First, for example, by providing a resist11using a photolithography technique and applying dry etching to a part of the main surface of the semiconductor substrate10constructed from a silicon monocrystal and the like, the deep trench10ais formed in the first region of the main surface of the semiconductor substrate10as shown inFIG. 4A. Thereafter, the resist11is removed.

Next, as shown inFIG. 4B, the insulating film20is formed on the bottom surface of the trench10aof the semiconductor substrate. For example, the insulating film20includes the insulating film21of silicon dioxide (SiO2) and the insulating film22of silicon nitride (SiN). The insulating film22of silicon nitride (SiN) withstands wet etching (release etching) for removing the later-described sacrificial film in the cavity.

Also, for example, polysilicon that has been doped with impurities and has electrical conductivity is formed on the bottom surface of the trench10aof the semiconductor substrate via the insulating film20, and patterning is applied through dry etching that uses a resist. Consequently, the lower electrode31of the resonator is formed. Furthermore, after forming a gap sacrificial film23on the lower electrode31, for example, polysilicon that has electrical conductivity is formed, and patterning is applied through dry etching that uses a resist. Consequently, the upper electrode32of the resonator, the external connection electrodes41and42, the receiving portion43, and the wall portion44are formed. Thereafter, the gap sacrificial film23is removed through wet etching.

In this way, the resonator including the lower electrode31and the upper electrode32, the external connection electrodes41and42that are electrically connected to the lower electrode31and the upper electrode32, respectively, the receiving portion43, and the wall portion44are formed on the bottom surface of the trench10aof the semiconductor substrate via the insulating film20. The wall portion44forms the cavity surrounding the resonator, the external connection electrodes41and42, and the receiving portion43.

Next, after an insulating film of silicon dioxide (SiO2) and the like is deposited, using a plasma CVD technique, on the surface of the semiconductor substrate10on which the resonator and the like are formed, the insulating film of silicon dioxide (SiO2) and the like is polished by CMP (Chemical Mechanical Polishing) and further etched. As a result, as shown inFIG. 5A, the insulating film51of silicon dioxide (SiO2) and the like is formed so as to surround the wall portion44in the trench of the semiconductor substrate10, and an insulating film52of silicon dioxide (SiO2) and the like is formed as a sacrificial film in the cavity.

Next, after an insulating film of silicon nitride (SiN) and the like is formed on the surface of the semiconductor substrate10on which the insulating films51and52and the like are formed, patterning is applied to the insulating film of silicon nitride (SiN) and the like through dry etching that uses a resist. As a result, the insulating film61of silicon nitride (SiN) and the like, which covers parts of the main surfaces of the external connection electrodes41and42and parts of the insulating films51and52, is formed.

Also, after a polysilicon film that has electrical conductivity is formed on the surface of the semiconductor substrate10on which the insulating film61and the like are formed, patterning is applied to the polysilicon film through dry etching that uses a resist. As a result, the first lid portion60including the insulating film61and the polysilicon film62is formed. The release hole60ais formed in the first lid portion60. The part of the first lid portion60other than the release hole60acovers the cavity.

Here, a part of the polysilicon film62is provided in the predetermined region of the main surface of the external connection electrode41, and is electrically connected to the external connection electrode41. Another part of the polysilicon film62that is insulated from the above-referenced part is provided in the predetermined region of the main surface of the external connection electrode42, and is electrically connected to the external connection electrode42.

Next, insulating film planarization and the like are applied to the surface of the semiconductor substrate10on which the first lid portion60and the like are formed. Thereafter, for example, a MOS field-effect transistor (MOSFET) is formed as a semiconductor circuit element in the second region of the main surface of the semiconductor substrate10as shown inFIG. 5B.

That is to say, the gate electrode83is formed on the semiconductor substrate10via the gate insulating film, and the impurity diffusion regions81and82that serve as the source and the drain are formed inside the semiconductor substrate10on both sides of the gate electrode83. Also, insulating side walls may be formed on side walls of the gate insulating film and the gate electrode83. Furthermore, an insulating film of a predetermined thickness may be formed in a region surrounding the insulating side walls.

Next, a resist24that has an opening24ain a position corresponding to the release hole60aof the first lid portion is provided, using a photolithography technique, on the surface of the semiconductor substrate10on which the MOS field-effect transistor and the like are formed. Furthermore, the insulating film of silicon dioxide (SiO2) and the like in the cavity, that is to say, the sacrificial film is removed through wet etching (release etching) that uses hydrofluoric acid and the like as an etchant. Thereafter, the resist24is removed through asking and the like.

Next, an electrically conductive sealant of aluminum (Al) and the like is deposited on the surface of the first lid portion60through sputtering (a high vacuum film formation technique) in a vacuum chamber, and patterning is applied to the deposited sealant through dry etching that uses a resist. In this way, as shown inFIG. 2, the second lid portion70is formed on the surface of the first lid portion60by the sealant.

The second lid portion70includes the intermediate conductive member71that is electrically connected to a predetermined region of the external connection electrode41via the polysilicon film62, the intermediate conductive member72that is electrically connected to a predetermined region of the external connection electrode42via the polysilicon film62, and the sealing portion73that seals the release hole60aof the first lid portion.

Next, the first insulating layer91is formed of silicon dioxide (SiO2), BPSG, or the like. The first insulating layer91covers the main surface of the semiconductor substrate10on which the first lid portion60, the second lid portion70and the semiconductor circuit element are formed. The first insulating layer91is in contact with the insulating film61and insulates the intermediate conductive members71and72of the second lid portion70from the sealing portion73.

Next, the contact plugs101to105of tungsten (W) and the like are simultaneously formed. The contact plugs101and102penetrate the first insulating layer91and are electrically connected to the intermediate conductive members71and72, respectively, whereas the contact plugs103to105penetrate the first insulating layer91and are electrically connected to the semiconductor circuit element.

Next, the first wiring layer is formed on the surface of the first insulating layer91by aluminum (Al) and the like. Electrical connection to the contact plugs101to105is implemented on the first wiring layer. For example, the wiring111provided on the first wiring layer brings the contact plug101and the contact plug103into electrical connection to each other.

Furthermore, where necessary, the second wiring layer is formed via the second insulating layer92, and a desired number of wiring layers are formed in a similar manner from then on. For example, the wiring112provided on the second wiring layer brings the contact plug102and the contact plug104into electrical connection to each other via the first wiring layer.

Accordingly, the external connection electrodes41and42can be electrically connected to the semiconductor circuit element. In this way, a necessary number of wiring layers can be installed, using a standard semiconductor wafer process, on a layer(s) above the cavity that houses the resonator, similarly to a layer(s) above the semiconductor circuit element. Thereafter, the protection film (not shown) is formed on the surface of a topmost wiring layer.

Second Embodiment

FIG. 6is a plan view showing a structure of the inside of a trench of a MEMS device according to a second embodiment of the invention.FIG. 6shows the structure of the inside of trench before a cavity is covered by a lid portion.FIG. 7is a cross-sectional view, taken along the line B-B′ ofFIG. 6, showing major portions of the MEMS device. In the second embodiment, an electrically conductive receiving portion43is electrically connected to a functional element and constitutes an external connection electrode. In other respects, the second embodiment is similar to the first embodiment.

A resonator including a lower electrode31and an upper electrode32, an external connection electrode42, the receiving portion43, and a wall portion44are provided on a bottom surface of a trench10aof a semiconductor substrate via an insulating film20. Also, an insulating film51that reinforces the wall portion44is provided so as to surround the wall portion44. It should be noted that the wall portion44may be provided directly on the bottom surface of the trench10aof the semiconductor substrate. Also, in a case where a substrate with high insulating properties, such as a substrate of glass, ceramics, resin, or the like, is used, the lower electrode31, the upper electrode32, the external connection electrode42and the receiving portion43may be provided directly on the substrate.

For example, the insulating film20includes an insulating film21of silicon dioxide (SiO2) and an insulating film22of silicon nitride (SiN). The lower electrode31, the upper electrode32and the external connection electrode42to the wall portion44may be formed of polysilicon that has been doped with impurities and has electrical conductivity. In this case, the receiving portion43can be formed simultaneously when forming the lower electrode31and the upper electrode32of the resonator and the like. Also, as the receiving portion43has electrical conductivity, the receiving portion43can be utilized as the external connection electrode. The insulating film51is formed of silicon dioxide (SiO2) and the like.

The receiving portion43and the external connection electrode42have, for example, a shape of a prism or a cylinder, and are used to electrically connect the lower electrode31and the upper electrode32of the resonator to an electronic circuit. The receiving portion43is electrically connected to the lower electrode31, and may be constructed integrally with the lower electrode31. On the other hand, the external connection electrode42is electrically connected to the upper electrode32, and may be constructed integrally with the upper electrode32.

As shown inFIG. 7, the cavity is covered by a lid portion including a first lid portion60and a second lid portion70, in such a manner that a gap is present between the lid portion and the resonator. The first lid portion60includes, for example, an insulating film61of silicon nitride (SiN) and the like, and a polysilicon film62that has electrical conductivity. It should be noted that a surface of the polysilicon film62may be provided with a titanium nitride (TiN) film, a salicide film, or the like. A part of the polysilicon film62is provided in a predetermined region of a main surface (an upper surface in the figure) of the external connection electrode42, and is electrically connected to the external connection electrode42.

An opening (release hole)60ais formed in the first lid portion60. The part of the first lid portion60other than the release hole60acovers the cavity. The release hole60ais used in removing, through release etching, a sacrificial film formed in the cavity. Thereafter, with the inside of the cavity placed in a decompressed state (vacuum state), the second lid portion70is formed, through sputtering (a high vacuum film formation technique), on a surface of the first lid portion60using an electrically conductive sealant of aluminum (Al) and the like.

In a sputtering process for forming the second lid portion70, a part of the electrically conductive sealant enters the cavity via the release hole60a. In view of this, in the present embodiment, the receiving portion43is provided below the release hole60aso as to catch the sealant that has entered the cavity.

The receiving portion43has a receiving face43athat opposes the release hole60avia a gap. In a plan view, the receiving face43aof the receiving portion43overlaps the release hole60aand a region therearound. In this way, even if a part of the electrically conductive sealant enters the cavity via the release hole60awhen forming, through sputtering, a sealing portion73that seals the release hole60a, the receiving face43aof the receiving portion43can catch the sealant.

The second lid portion70includes an intermediate conductive member72and the sealing portion73. The intermediate conductive member72is electrically connected to the external connection electrode42via the polysilicon film62and insulated from the other part of the second lid portion70. The sealing portion73, which is electrically conductive, seals the release hole60aof the first lid portion and extends to the receiving face43aof the receiving portion43. In this way, the sealing portion73is electrically connected to the receiving portion43that is electrically connected to the lower electrode31of the resonator and constitutes the external connection electrode.

A first insulating layer (inter-layer insulating film)91of silicon dioxide (SiO2), BPSG (Boron Phosphorus Silicon Glass), or the like is provided on the semiconductor substrate10provided with the lid portion and a semiconductor circuit element. The first insulating layer91covers a main surface of the semiconductor substrate10. The first insulating layer91is in contact with the insulating film61and insulates the intermediate conductive member72of the second lid portion70from the sealing portion73.

Contact plugs (electrodes)101and102of tungsten (W) and the like are provided in a first region of the first insulating layer91. The contact plugs101and102penetrate the first insulating layer91and are electrically connected to the sealing portion73and the intermediate conductive member72, respectively. Also, contact plugs (electrodes)103to105of tungsten (W) and the like are provided in a second region of the first insulating layer91. The contact plugs103to105penetrate the first insulating layer91and are electrically connected to an impurity diffusion region81, an impurity diffusion region82and a gate electrode83, respectively.

Electrical connection to the contact plugs101to105is implemented on a first wiring layer of aluminum (Al) and the like, which is provided on a surface of the first insulating layer91. Furthermore, where necessary, a second wiring layer is provided via a second insulating layer92, and a desired number of wiring layers are installed in a similar manner from then on. In addition, a protection film (not shown) is provided on a surface of a topmost wiring layer.

For example, wiring111provided on the first wiring layer brings the contact plug101and the contact plug103into electrical connection to each other. Also, wiring112provided on the second wiring layer brings the contact plug102and the contact plug104into electrical connection to each other via the first wiring layer. In this way, the resonator can be electrically connected to the semiconductor circuit element.

According to the second embodiment of the invention, even if a part of the electrically conductive sealant enters the cavity via the release hole60awhen forming, through sputtering, the sealing portion73that seals the release hole60a, the receiving portion43can prevent a short circuit of electrodes or units of wiring. Moreover, as the electrically conductive receiving portion43can be utilized as the external connection electrode, wiring for the functional element can be installed efficiently, and the cavity can be further reduced in size.

While the above-described embodiments have discussed a MEMS device with a cavity that is formed in a deep trench of a semiconductor substrate, the invention is by no means limited to the above-described embodiments. For example, the invention can be utilized in a MEMS device with a cavity that is formed in a shallow trench of a substrate or on the substrate, and can be modified in many ways by a person of ordinary skill in the art within the technical ideas of the invention.

The entire disclosure of Japanese Patent Application No. 2014-061566, filed Mar. 25, 2014 is expressly incorporated by reference herein.