JP2012127691A - Mems sensor and manufacturing method of the same, and mems package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MEMS sensor and a manufacturing method of the MEMS sensor that can facilitate the formation of a lower electrode directly below an upper electrode, prevents a short circuit between the upper electrode and the lower electrode, and can improve the detection accuracy of the sensor.SOLUTION: Driving electrodes 22 are selectively formed on a base substrate 7, and an electrode coating 23 made of SiOis formed so as to cover the driving electrodes 22. Then, a sacrificial polysilicon layer 52 and a sacrificial oxide film 53 are formed on the electrode coating 23 in this order. Then, a polysilicon layer 26 is formed on the sacrificial oxide film 53, and is etched into shapes of fixed electrodes 27, movable electrodes 28, and contact electrodes 29, while trenches 56 are concurrently formed between them. Then, the bottoms of the trenches 56 are further dug down to expose the sacrificial polysilicon layer 52 from the sacrificial oxide film 53. Finally, by completely removing the sacrificial polysilicon layer 52, a cavity 37 is formed directly below comb teeth parts 32 of the fixed electrodes 27 and comb teeth parts 39 of the movable electrodes 28.

Description

  The present invention relates to a manufacturing method of a MEMS sensor, a MEMS sensor manufactured by the manufacturing method, and a MEMS package including the MEMS sensor.

The capacitive acceleration sensor detects acceleration by detecting the amount of change in capacitance between the electrodes facing each other (between the fixed electrode and the movable electrode).
The acceleration sensor (100) disclosed in FIGS. 1a to 1g of Patent Document 1 includes, for example, two layers of an Si electrode (112) and a metal electrode (122) that are sequentially stacked via an insulating layer (132). The fixed portion (400) and the Si electrode (116) having the same shape as the Si electrode (112) of the fixed portion (400) and completely facing the Si electrode (112) in the reference posture (FIG. 1d of Patent Document 1) The movable part (300) which consists of a single layer. The acceleration sensor (100) measures the amount of change in capacitance between the Si electrode (116) of the movable part (300) that vibrates up and down by the action of acceleration and the Si electrode (112) of the fixed part (400). By detecting this, the acceleration in the Z-axis direction is detected.

U.S. Pat. No. 6,792,804

  By the way, in the acceleration sensor (100) of Patent Document 1, if an electrode can be provided in the cavity (640) (FIG. 6g of Patent Document 1) below the movable part (300), it cooperates with the movable part (300). Thus, the fixed electrode (lower electrode) for forming the capacitor can be formed along the surface of the Si substrate. If the lower electrode is formed along the surface of the Si substrate, the opposed area of the lower electrode to the movable part (300) can be easily increased. Therefore, the capacitance of the capacitor between the movable part (300) and the lower electrode can be increased, and thereby the detection accuracy of the sensor may be improved.

  However, in the invention of Patent Document 1, the movable portion (300) is formed by forming a plurality of trenches in the Si substrate and making the lower portions of the trenches continuous with each other by isotropic etching (Patent Document 1). 6a-6g). Therefore, it is difficult to form the lower electrode below the movable part (300) at any timing before and after the formation of the movable part (300).

Even if it can be formed, in the configuration in which the lower electrode is simply disposed in the cavity (640), when the movable part (300) approaches the lower electrode, the lower electrode and the movable part (300) come into contact with each other and short-circuit. There is a fear.
Therefore, an object of the present invention is to easily form a lower electrode directly below the upper electrode through a cavity, and further prevent a short circuit between the upper electrode and the lower electrode, thereby improving the detection accuracy of the sensor. It is providing the MEMS sensor which can be made, and its manufacturing method.

  Another object of the present invention is to provide a MEMS package including a MEMS sensor having excellent detection accuracy.

  The invention according to claim 1 for achieving the above object is characterized in that a step of selectively forming a lower electrode on a semiconductor substrate and a step of forming polysilicon on the semiconductor substrate so as to cover the lower electrode. A step of laminating an electrode coating film made of a material having an etching selectivity, a step of selectively forming a sacrificial polysilicon layer on the electrode coating film, and the sacrificial poly layer on the electrode coating film. A step of laminating a sacrificial oxide film so as to cover the silicon layer; a step of forming a polysilicon layer for electrodes on the sacrificial oxide film; and selectively etching the polysilicon layer for electrodes to form an upper portion Forming a protective film having an etching selectivity with respect to polysilicon so as to cover a sidewall of the upper electrode, removing a portion of the sacrificial oxide film, and forming the sacrificial poly A step of exposing the silicon layer by removing the sacrificial polysilicon layer exposed, and forming a cavity directly below the upper electrode, a manufacturing method of the MEMS sensor.

  According to this method, the upper electrode is formed on the semiconductor substrate by using the electrode polysilicon layer after the lower electrode is formed on the semiconductor substrate. Therefore, the lower electrode can be easily formed immediately below the upper electrode before the upper electrode is formed. Further, a sacrificial polysilicon layer is formed between the lower electrode and the electrode polysilicon layer. After the upper electrode is formed, the sacrificial polysilicon layer is removed. Therefore, a cavity can be easily formed between the upper electrode and the lower electrode. As a result, a MEMS sensor having a capacitor in which the upper electrode and the lower electrode face each other vertically with a cavity therebetween can be manufactured.

  Such a MEMS sensor includes, for example, a semiconductor substrate, a lower electrode selectively formed on the semiconductor substrate, and an insulating material, and covers the lower electrode so as to cover the lower electrode. A polysilicon layer having an electrode coating film formed on a semiconductor substrate and an upper electrode formed above the electrode coating film with a space therebetween and facing the lower electrode through the electrode coating film Including.

According to this configuration, the lower electrode is formed along the surface of the semiconductor substrate. Therefore, by adjusting the area of the lower electrode, the capacitor capacity of the upper electrode and the lower electrode can be controlled to an optimum size for the sensor operation.
Moreover, even after the cavity is formed by removing the sacrificial polysilicon layer, the lower electrode is covered with the electrode coating film. Therefore, even when the upper electrode approaches the lower electrode, contact between the upper electrode and the lower electrode can be prevented. As a result, a short circuit between the upper electrode and the lower electrode can be prevented. Therefore, malfunction of the sensor can be reduced.

As a result, according to the MEMS sensor of the present invention, the detection accuracy of the sensor can be improved.
According to a second aspect of the present invention, the step of forming the upper electrode includes a step of forming the electrode polysilicon layer into a comb-shaped fixed electrode and a movable electrode that are engaged with each other at an interval. A method for manufacturing the MEMS sensor according to Item 1.

The MEMS sensor according to claim 8, that is, the MEMS sensor according to claim 7, wherein the upper electrode includes a comb-shaped fixed electrode and a movable electrode that are engaged with each other with a space therebetween. it can.
In the MEMS sensor, a capacitor composed of a fixed electrode and a movable electrode can be used for sensor operation. As a result, the number of capacitors involved in the detection operation of the sensor can be increased, so that the detection accuracy of the sensor can be further improved.

The invention according to claim 3 further includes the step of removing the protective film from the side walls of the fixed electrode and the movable electrode after the removal of the sacrificial polysilicon layer. Is the method.
In the manufactured MEMS sensor, if the protective film remains on the side walls of the fixed electrode and the movable electrode, the fixed electrode and the movable electrode are easily charged as compared with the case where there is no protective film. Therefore, for example, when a voltage X (V) is applied between the fixed electrode and the movable electrode, a potential difference between the fixed electrode and the movable electrode caused by charging is applied between the fixed electrode and the movable electrode. There is a risk of causing a so-called memory effect that the sensor erroneously recognizes that the voltage is present. As a result, a voltage less than the voltage X (V) is applied between the fixed electrode and the movable electrode, and the detection performance as designed may not be exhibited.

Therefore, in the MEMS sensor manufactured by the manufacturing method according to claim 3, the side walls of the fixed electrode and the movable electrode are exposed. Therefore, the occurrence of the memory effect described above can be reduced. As a result, a necessary and sufficient voltage can be applied between the fixed electrode and the movable electrode, and the detection performance as designed can be reliably exhibited.
In addition, the invention of claim 4 further includes the step of forming an opening through the electrode coating film to selectively expose the lower electrode prior to the formation of the polysilicon layer for electrodes. In the step of forming the electrode polysilicon layer, the electrode polysilicon layer is formed on the sacrificial oxide film, and at the same time, a part of the electrode polysilicon layer is allowed to enter the opening of the electrode coating film. 4. The method according to claim 1, comprising a step of contacting the lower electrode, wherein the step of forming the upper electrode includes a step of forming a contact electrode separated from the upper electrode and in contact with the lower electrode. A method for manufacturing the MEMS sensor according to the item.

9. The MEMS sensor according to claim 9, wherein the polysilicon layer further includes a contact electrode that penetrates the electrode coating film and contacts the lower electrode. A sensor can be manufactured.
In the MEMS sensor, the contact electrode is formed in the same layer as the upper electrode by using a part of the polysilicon layer for the electrode that forms the upper electrode. Therefore, the contacts for the upper electrode and the lower electrode can be concentrated on the same layer (polysilicon layer).

As a result, for example, when the wiring is formed on the contact electrode, the contact wiring for the upper electrode can be formed in the same process. As a result, the number of manufacturing steps can be reduced and the cost can be reduced.
Then, the MEMS sensor according to claim 10, that is, the MEMS sensor according to claim 9, further including a wiring formed on the contact electrode, can be manufactured by the manufacturing method according to claim 5.

In addition, the step of forming the wiring on the contact electrode may include the step of simultaneously forming the wiring on the upper electrode as described in claim 6.
In addition, the MEMS sensor described above is an acceleration sensor that detects an acceleration acting on the MEMS sensor by detecting a change in capacitance between the lower electrode and the movable electrode. May be included.

In this configuration, acceleration can be detected by a plurality of capacitors including a capacitor composed of a lower electrode and a movable electrode and a capacitor composed of a fixed electrode and a movable electrode. Therefore, the acceleration acting on the sensor can be detected with high accuracy.
Further, as described in claim 12, the MEMS sensor described above drives the movable electrode in a direction toward and away from the lower electrode, and an angular velocity acting on the MEMS sensor at the time of driving is set to the movable electrode and the movable electrode. An angular velocity sensor that detects a change in electrostatic capacitance with the fixed electrode may be included.

  In this configuration, by adjusting the area of the lower electrode, the area of the lower electrode relative to the movable electrode can be made larger than the area of the fixed electrode relative to the movable electrode. Therefore, the movable electrode can be vibrated with a larger amplitude than when a driving voltage is applied between the fixed electrode and the movable electrode meshing in a comb shape. As a result, the angular velocity detection sensitivity can be improved.

Further, in the invention described in claim 13, the lower electrode is formed along a direction crossing each comb tooth of the movable electrode so as to face the entire comb-like movable electrode. It is a MEMS sensor as described in any one of Claims 9-12 concerning 8 or Claim 8.
In this configuration, since the lower electrode can be opposed to the movable electrode with a large area, the capacitor capacity between the lower electrode and the movable electrode can be increased. As a result, the detection accuracy of the sensor can be improved.

The electrode coating film may be made of SiO ₂ as described in claim 14. In addition, the side wall of the upper electrode may be covered with a protective thin film made of an insulating material.
The invention according to claim 16 is a MEMS package including the MEMS sensor according to any one of claims 7 to 15 and a resin package formed so as to cover the MEMS sensor.

  According to this configuration, the MEMS sensor of the present invention is used. Therefore, in the MEMS sensor, the capacitor capacitance between the upper electrode and the lower electrode can be controlled to an optimum size for the sensor operation, and a short circuit between the upper electrode and the lower electrode can be prevented. As a result, a MEMS package including a MEMS sensor having excellent detection accuracy can be provided.

  In addition, the MEMS package described above may further include an integrated circuit electrically connected to the MEMS sensor and covered with the same resin package together with the MEMS sensor. Moreover, when the substrate further includes a substrate having a front surface and a back surface and supporting the MEMS sensor on the front surface, the resin package covers the surface of the substrate and the substrate. The MEMS sensor may be sealed so as to expose the back surface.

It is a typical perspective view of the MEMS package which concerns on one Embodiment of this invention. It is typical sectional drawing of the Z-axis sensor shown in FIG. FIG. 3 is a cross-sectional view showing a part of the manufacturing process of the Z-axis sensor shown in FIG. 2, and shows a cut surface at the same position as FIG. 2. It is a figure which shows the next process of FIG. 3A. It is a figure which shows the next process of FIG. 3B. It is a figure which shows the next process of FIG. 3C. It is a figure which shows the next process of FIG. 3D. It is a figure which shows the next process of FIG. 3E. It is a figure which shows the next process of FIG. 3F. It is a figure which shows the next process of FIG. 3G. It is a figure which shows the next process of FIG. 3H. It is a figure which shows the next process of FIG. 3I. It is a figure which shows the next process of FIG. 3J. It is a figure which shows the next process of FIG. 3K. It is a top view which shows the form in the case of utilizing the Z-axis sensor shown in FIG. 2 for an acceleration sensor. It is a figure which shows the modification of the Z-axis sensor shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<Overall configuration of MEMS package>
FIG. 1 is a schematic perspective view of a MEMS package according to an embodiment of the present invention.
The MEMS package 1 is used for applications such as camera shake correction for video cameras and still cameras, car navigation position detection, and motion detection for robots and game machines, for example.

The MEMS package 1 includes a substrate 2, an angular velocity sensor 3 as a MEMS sensor, an external terminal 4, an integrated circuit 5 (ASIC: Application Specific Integrated Circuit), and a resin package 6.
The substrate 2 is formed in a rectangular plate shape having a front surface and a back surface.
The angular velocity sensor 3 is disposed at one end in the longitudinal direction on the surface side of the substrate 2. The angular velocity sensor 3 is disposed on a side of the base substrate 7 made of a square plate-shaped Si substrate, a sensor unit 8 provided at the center of the base substrate 7, and the sensor unit 8 on the base substrate 7. And an electrode pad 9 for supplying a voltage to.

The sensor unit 8 includes an X-axis sensor 10, a Y-axis sensor 11, and a Z-axis sensor 12 as sensors for detecting angular velocities around three axes that are orthogonal in a three-dimensional space. These three sensors 10 to 12 are covered and sealed with the lid substrate 13 by bonding a lid substrate 13 made of, for example, a Si substrate to the base substrate 7.
The X-axis sensor 10 uses the vibration Ux in the X-axis direction to generate a Coriolis force Fz in the Z-axis direction when the MEMS package 1 is tilted, and detects a change in capacitance due to the Coriolis force. The angular velocity ωy acting around the Y axis is detected. Further, the Y-axis sensor 11 uses the vibration Uy in the Y-axis direction to generate a Coriolis force Fx in the X-axis direction when the MEMS package 1 is tilted, and detects a change in capacitance due to the Coriolis force. Thus, the angular velocity ωz acting around the Z axis is detected. Further, the Z-axis sensor 12 uses the vibration Uz in the Z-axis direction to generate a Coriolis force Fy in the Y-axis direction when the MEMS package 1 is tilted, and detects a change in capacitance due to the Coriolis force. Thus, the angular velocity ωx acting around the X axis is detected.

A plurality (seven in FIG. 1) of electrode pads 9 are provided at equal intervals along the width direction orthogonal to the longitudinal direction of the substrate 2.
A plurality of external terminals 4 (12 in FIG. 1) are provided at the other end in the longitudinal direction of the substrate 2 (the end opposite to the angular velocity sensor 3) at equal intervals along the width direction of the substrate 2. Is provided. Each external terminal 4 is formed through the substrate 2 in the thickness direction, and is exposed as an internal pad 14 on the surface of the substrate 2 and as an external pad 15 on the back surface of the substrate 2.

  The integrated circuit 5 is disposed between the angular velocity sensor 3 and the external terminal 4 (internal pad 14) on the surface side of the substrate 2. The integrated circuit 5 is made of, for example, a rectangular plate-like Si substrate that is long in the width direction of the substrate 2. Inside the Si substrate, a charge amplifier that amplifies the electrical signal output from each of the sensors 10 to 12, a filter circuit (low pass filter: LPF, etc.) that extracts a specific frequency component of the electrical signal, and an electrical signal after filtering A logic circuit or the like that performs a logical operation of the above is formed. These circuits are constituted by, for example, CMOS devices. Further, the integrated circuit 5 includes a first electrode pad 16 and a second electrode pad 17.

A plurality of (seven in FIG. 1) first electrode pads 16 are provided at equal intervals along the width direction of the substrate 2 at the end portion on the side close to the angular velocity sensor 3 in the longitudinal direction of the substrate 2. Yes. The first electrode pads 16 are connected to the electrode pads 9 of the angular velocity sensor 3 on a one-to-one basis by bonding wires 18.
A plurality of (two in FIG. 1) second electrode pads 17 are provided at equal intervals along the width direction of the substrate 2 at the end portion on the side close to the external terminal 4 in the longitudinal direction of the substrate 2. Yes. The second electrode pads 17 are connected to the internal pads 14 of the external terminals 4 on a one-to-one basis by bonding wires 19.

The resin package 6 forms the outer shape of the MEMS package 1 in cooperation with the substrate 2 and is formed in a substantially rectangular parallelepiped shape. The resin package 6 is made of, for example, a known mold resin such as an epoxy resin, covers the bonding wires 18 and 19 and the internal pads 14 together with the angular velocity sensor 3 and the integrated circuit 5, and exposes the external pads 15. The integrated circuit 5 is sealed.
<Configuration of Z-axis sensor>
Next, the configuration of the Z-axis sensor 12 will be described with reference to FIG.

As described above, the angular velocity sensor 3 includes the base substrate 7 (for example, 625 μm thick).
A base insulating film 21 (for example, a thickness of 10,000 mm) is formed on the surface 20 of the base substrate 7. The base insulating film 21 is made of SiO ₂ (silicon oxide).
On the base insulating film 21, a drive electrode 22 (for example, a thickness of 5000 mm) is formed as a lower electrode. The drive electrode 22 is made of polysilicon.

On the base insulating film 21, an electrode coating film 23 (for example, having a thickness of 5000 mm) that covers the driving electrode 22 is formed. Electrode covering film 23 is made of SiO _2. In the electrode coating film 23, an opening 25 is formed for exposing a part of the driving electrode 22 as a pad 24.
A polysilicon layer 26 (for example, 10 μm thick) is formed on the electrode coating film 23. The polysilicon layer 26 includes a fixed electrode 27 and a movable electrode 28 as upper electrodes, and a contact electrode 29.

The fixed electrode 27 includes a plurality of contact portions 31 erected on the surface 30 of the electrode coating film 23, and a plurality of comb electrodes arranged along the surface 20 of the base substrate 7 above the electrode coating film 23. And a comb tooth portion 32 made of an electrode.
The contact portion 31 of the fixed electrode 27 is integrally connected to the base portion 33 (for example, 5 μm high) fixed to the surface 30 of the electrode coating film 23 and the top portion of the base portion 33, and the comb tooth portion 32. And a connecting portion 34 having the same thickness (described later).

The connecting portion 34 is formed so as to protrude outward from the side surface 35 of the base portion 33. Thereby, a step S <b> ₁ is formed between the side surface 36 of the connecting portion 34 and the side surface 35 of the base portion 33.
The comb tooth portion 32 of the fixed electrode 27 is formed integrally with the connecting portion 34 of the contact portion 31, and the connecting portion 34 forms a cavity 37 between the surface 30 of the electrode coating film 23. Cantilevered. That is, the comb tooth portion 32 is supported in a state of being lifted from the surface 30 of the electrode coating film 23 by the height of the base portion 33 of the contact portion 31. The thickness of the comb tooth portion 32 (height from the top of the base portion 33 to the surface of the polysilicon layer 26) is, for example, about 15 μm.

One movable electrode 28 is disposed between each contact portion 38 erected on the surface 30 of the electrode coating film 23 and each comb tooth portion 32 of the fixed electrode 27 above the electrode coating film 23. It includes a plurality of electrodes and a comb tooth portion 39 that meshes with the comb tooth portion 32 of the fixed electrode 27 as a whole. For example, a distance of about 2 μm (interelectrode distance d ₁ ) is provided between each of the comb teeth 39 and the comb teeth 32 of the fixed electrode 27.

  The contact portion 38 of the movable electrode 28 is provided on the opposite side of the comb tooth portion 32 of the fixed electrode 27 with respect to the contact portion 31 of the fixed electrode 27. The contact portion 38 is integrally connected to the base portion 40 (for example, 5 μm high) fixed to the surface 30 of the electrode coating film 23 and the top portion of the base portion 40, and has the same thickness as the comb tooth portion 39 ( And a connecting portion 41 having a later-described structure.

The connecting portion 41 is formed so as to protrude outward from the side surface 42 of the base portion 40. Thereby, a step S < _b > ₂ is formed between the side surface 43 of the connecting portion 41 and the side surface 42 of the base portion 40.
The comb-tooth portion 39 of the movable electrode 28 is formed integrally with the connection portion 41 of the contact portion 38, and the connection portion 41 of the electrode coating film 23 is similar to the comb-tooth portion 32 of the fixed electrode 27. Cantilevered so as to form a cavity 37 between the surface 30. That is, the comb-tooth portion 39 is supported in a state of being lifted from the surface 30 of the electrode coating film 23 by the height of the base portion 40 of the contact portion 38. Further, the thickness of the comb tooth portion 39 (height from the top of the base portion 40 to the surface of the polysilicon layer 26) is, for example, about 15 μm.

  In this embodiment, the driving electrode 22 has comb teeth at both ends so as to cross the comb teeth 32 and 39 of the fixed electrode 27 and the movable electrode 28 that mesh with each other just below the cavity 37 (FIG. 2). Then, it is formed across the comb tooth portion 32 closest to the contact electrode 29 and the comb tooth portion 39) closest to the contact portion 31 of the fixed electrode 27. Thus, one drive electrode 22 is opposed to the entire comb teeth 32 and 39 of the fixed electrode 27 and the movable electrode 28.

The contact electrode 29 includes a base portion 44 (for example, 5 μm high) connected to the driving electrode 22 through the opening 25 of the electrode coating film 23 and a connecting portion integrally connected to the top portion of the base portion 44. 45.
The connecting portion 45 is formed so as to protrude outward from the side surface 46 of the base portion 44. Thereby, a step S <b> ₃ is formed between the side surface 47 of the connecting portion 45 and the side surface 46 of the base portion 44.

On the polysilicon layer 26, a surface protective film 48 (for example, having a thickness of 3000 mm) made of SiO ₂ is formed. Accordingly, the comb teeth portions 32 and 39 of the fixed electrode 27 and the movable electrode 28, the contact portions 31 and 38 (connection portions 34 and 41), and the surfaces of the contact electrode 29 are covered with the surface protective film 48.
On the surface protective film 48, the first detection wiring 49, the second detection wiring 50, and the driving electrode are respectively provided on the contact portion 31 of the fixed electrode 27, the contact portion 38 of the movable electrode 28, and the portion facing the contact electrode 29. A wiring 51 is formed. Each wiring is made of Al (aluminum), penetrates the surface protective film 48, and is connected to the contact portion 31 of the fixed electrode 27, the contact portion 38 of the movable electrode 28, and the contact electrode 29, respectively.

In the Z-axis sensor 12 having the above-described structure, drive voltages having the same polarity / different polarities are alternately applied between the comb teeth 39 of the movable electrode 28 and the drive electrode 22. As a result, a Coulomb repulsive force / Coulomb attractive force is alternately generated between the comb tooth portion 39 of the movable electrode 28 and the driving electrode 22.
As a result, as if the comb-like movable electrode 28 is a pendulum, the same comb-tooth-like fixed electrode 27 vibrates up and down along the Z-axis direction with respect to the fixed electrode 27 (vibration). Uz).

In this state, when the movable electrode 28 rotates about the X axis as a central axis, a Coriolis force Fy is generated in the Y axis direction. Due to the Coriolis force Fy, the facing area and / or the inter-electrode distance d ₁ between the comb tooth portions 39 of the movable electrodes 28 adjacent to each other and the comb tooth portions 32 of the fixed electrode 27 change.
Then, by detecting the change in capacitance C between the movable electrode 28-the fixed electrode 27 due to a change in the opposing area and / or inter-electrode distance d _1, the angular velocity ωx about the X-axis is detected.
<Manufacturing method of angular velocity sensor>
Next, with reference to FIGS. 3A to 3L, the manufacturing process of the angular velocity sensor described above will be described in the order of steps. In this section, only the manufacturing process of the Z-axis sensor is illustrated and the manufacturing process of the X-axis sensor and the Y-axis sensor is omitted, but the manufacturing process of the X-axis sensor and the Y-axis sensor is the manufacturing process of the Z-axis sensor. In the same manner as described above, it is executed in parallel with the manufacturing process of the Z-axis sensor.

3A to 3L are schematic cross-sectional views showing a part of the manufacturing process of the Z-axis sensor shown in FIG. 2 in the order of steps, and show a cut surface at the same position as FIG.
In order to manufacture the Z-axis sensor 12, as shown in FIG. 3A, the surface 20 of the base substrate 7 made of conductive silicon is thermally oxidized (for example, temperature 1000 ° C. to 1200 ° C.). As a result, a base insulating film 21 made of SiO ₂ is formed on the surface 20 of the base substrate 7. Next, polysilicon is deposited over the entire surface of the base insulating film 21 by a CVD (Chemical Vapor Deposition) method. Subsequently, the polysilicon is selectively patterned by a known patterning technique to form the driving electrode 22.

Next, as shown in FIG. 3B, an electrode coating film 23 made of SiO ₂ having an etching selectivity with respect to polysilicon is formed over the entire surface of the base insulating film 21 by CVD. As a result, the driving electrode 22 is completely covered with the electrode covering film 23.
Here, the material having an etching selectivity with respect to polysilicon (in this paragraph, defined as material A) is, for example, the etching rate of polysilicon with respect to a certain etching medium and the material A with respect to the etching medium. (Etching selectivity) = (material A etching rate / polysilicon etching rate) ≠ 1. In particular, the material A is preferably a material that can make the etching selectivity close to 0 (zero) (etching selection ratio≈0), and specifically, it is SiO ₂ as in this embodiment. preferable. The electrode coating film 23 may be another material (for example, SiN) having an etching selectivity with respect to polysilicon.

Next, as shown in FIG. 3C, polysilicon (for example, a thickness of 5000 mm) is deposited over the entire surface 30 of the electrode coating film 23 by the CVD method. Subsequently, the polysilicon is selectively patterned by a known patterning technique to form a sacrificial polysilicon layer 52.
Next, as shown in FIG. 3D, a sacrificial oxide film 53 (for example, having a thickness of 5000 mm) made of SiO _{2 is} formed over the entire surface of the sacrificial polysilicon layer 52 by CVD.

Next, as shown in FIG. 3E, the sacrificial oxide film 53 is patterned by a well-known patterning technique, and portions of the sacrificial oxide film 53 where the base portions 33, 40, and 44 are to be formed are selectively removed. Openings 25, 54 and 55 are formed. As a result, a part of the driving electrode 22 is exposed from the opening 25 as the pad 24.
Next, a seed film made of polysilicon is formed on the sacrificial oxide film 53. Subsequently, polysilicon is epitaxially grown from the seed film. As a result, as shown in FIG. 3F, a polysilicon layer 26 (for example, 15 μm thick) is formed as the electrode polysilicon layer.

Next, as shown in FIG. 3G, CMP (Chemical Mechanical Polishing) is performed until the surface of the polysilicon layer 26 becomes flush. As a result, the thickness of the polysilicon layer 26 becomes, for example, 15 μm to 10 μm. Subsequently, a surface protective film 48 made of SiO ₂ is formed over the entire surface of the polysilicon layer 26 by CVD. Subsequently, the surface protective film 48 is selectively removed by a known patterning technique. Thereby, a contact hole is formed in the surface protective film 48. Subsequently, after a contact plug filling up the contact hole is formed, Al is deposited on the surface protective film 48 by sputtering, and the Al deposited layer is patterned. As a result, wirings 49 to 51 are simultaneously formed on the surface protective film 48.

Next, as shown in FIG. 3H, an opening is formed in the surface protective film 48 in a region other than the region where the fixed electrode 27, the movable electrode 28, and the contact electrode 29 are to be formed by a known patterning technique. Subsequently, the polysilicon layer 26 is dug down by anisotropic deep RIE using the remaining surface protective film 48 as a hard mask, specifically, by a Bosch process. In the Bosch process, there are a step of etching the polysilicon layer 26 using SF ₆ (sulfur hexafluoride) and a step of forming a protective film on the etching surface using C ₄ F ₈ (perfluorocyclobutane). Repeated alternately. As a result, the polysilicon layer 26 can be etched with a high aspect ratio, but wavy irregularities called scallops are formed on the etched surface (inner peripheral surface of the trench).

As a result, the polysilicon layer 26 is formed into the shape of the fixed electrode 27, the movable electrode 28, and the contact electrode 29, and a trench is formed between these parts (comb teeth 32, 39, contact parts 31, 38, etc.). 56 is formed. The surface of the sacrificial oxide film 53 is exposed at the bottom surface of the trench 56.
Next, as shown in FIG. 3I, SiO ₂ is applied to the entire surface of the fixed electrode 27, the movable electrode 28 and the contact electrode 29 and the entire inner surface of the trench 56 (that is, the side surface and the bottom surface defining the trench 56) by CVD. A protective thin film 57 made of is formed.

Next, as shown in FIG. 3J, the bottom surface of the trench 56 is further dug down by anisotropic deep RIE. As a result, the sacrificial polysilicon layer 52 is exposed as the bottom surface of the trench 56.
Subsequent to the anisotropic deep RIE, reactive ions and an etching gas (eg, SF ₆ gas) are supplied to the trench 56 by isotropic RIE. Then, as shown in FIG. 3K, the surface of the base substrate 7 is etched while the sacrificial polysilicon layer 52 is etched in the thickness direction of the base substrate 7 starting from the bottom of each trench 56 by the action of the reactive ions and the like. Etching is performed in a direction parallel to. As a result, the bottoms of all the trenches 56 adjacent to each other are integrated to form the cavity 37, and the fixed electrode 27 (comb tooth portion 32) and the movable electrode 28 (comb tooth portion 39) immediately above the cavity 37. Will be in a floating state.

Next, as shown in FIG. 3L, an etching gas (for example, HF (hydrofluoric acid) gas) is supplied to the trench 56. The protective thin film 57 and the sacrificial oxide film 53 made of SiO ₂ are removed by the action of the HF gas.
Through the above steps, the Z-axis sensor 12 shown in FIG. 2 is obtained.
According to the above method, the fixed electrode 27 and the movable electrode 28 for detecting the angular velocity in the Z-axis sensor 12 are formed on the base substrate 7 after the driving electrode 22 is formed on the base substrate 7 (step of FIG. 3A). 7 is formed using a polysilicon layer 26. Therefore, the drive electrode 22 can be easily formed immediately below the fixed electrode 27 and the movable electrode 28 before the fixed electrode 27 and the movable electrode 28 are formed.

  Further, in the manufacturing process of the Z-axis sensor 12, a sacrificial polysilicon layer 52 and a sacrificial oxide film 53 are formed between the drive electrode 22 and the polysilicon layer 26 (steps of FIGS. 3C and 3D). These sacrificial layers 52 and 53 are removed after forming the polysilicon layer 26 into the fixed electrode 27 and the movable electrode 28 (steps of FIGS. 3K and 3L). Therefore, the cavity 37 can be easily formed between the fixed electrode 27 (comb tooth portion 32) and the movable electrode 28 (comb tooth portion 39) and the driving electrode 22. Thus, the Z-axis sensor 12 having a capacitor in which the fixed electrode 27 (comb tooth portion 32) and the movable electrode 28 (comb tooth portion 39) and the driving electrode 22 face each other with the cavity 37 therebetween is manufactured. Can do.

Therefore, in the process shown in FIG. 3A, by adjusting the area of the drive electrode 22 to an appropriate size, the capacitor capacitance of the movable electrode 28 (comb portion 39) and the drive electrode 22 is optimal for the sensor operation. The size can be controlled.
Specifically, the drive electrode 22 is formed across the comb teeth at both ends so as to cross the comb teeth portions 32 and 39 of the fixed electrode 27 and the movable electrode 28. As a result, the area of the drive electrode 22 with respect to the movable electrode 28 (comb portion 39) can be made larger than the area of the fixed electrode 27 (comb portion 32) facing the movable electrode 28 (comb portion 39). . Therefore, the movable electrode 28 can be vibrated with a larger amplitude than when a drive voltage is applied between the fixed electrode 27 and the movable electrode 28 meshing in a comb shape. As a result, the angular velocity detection sensitivity can be improved.

  In addition, even after the cavity 37 is formed by removing the sacrificial polysilicon layer 52 and the sacrificial oxide film 53, the driving electrode 22 is covered with the electrode coating film 23. Therefore, even when the movable electrode 28 approaches the drive electrode 22 due to large vibrations, the contact between the movable electrode 28 (comb tooth portion 39) and the drive electrode 22 can be prevented. As a result, short circuit between the movable electrode 28 (comb portion 39) and the drive electrode 22 can be prevented. Therefore, malfunction of the sensor can be reduced.

As a result, according to the MEMS package 1, the detection accuracy of the Z-axis sensor 12 can be improved.
By the way, in the Z-axis sensor 12 after manufacture, if the protective thin film 57 remains on the side walls of the fixed electrode 27 and the movable electrode 28, the fixed electrode 27 and the movable electrode 27 are movable as compared to the case of the present embodiment in which the protective thin film 57 is not provided. The electrode 28 is easily charged. Therefore, for example, when a voltage X (V) is applied between the fixed electrode 27 and the movable electrode 28, the potential difference between the fixed electrode 27 and the movable electrode 28 caused by charging is expressed as the fixed electrode 27 and the movable electrode 28. There is a possibility that a so-called memory effect that the Z-axis sensor 12 erroneously recognizes that the voltage is applied during the period of time is generated. As a result, a voltage less than the voltage X (V) is applied between the fixed electrode 27 and the movable electrode 28, and the detection performance as designed may not be exhibited.

  Therefore, in the Z-axis sensor 12 of this embodiment, after forming the cavity 37, the protective thin film 57 is removed (step of FIG. 3L) to expose the side walls of the fixed electrode 27 and the movable electrode 28. Therefore, the occurrence of the memory effect described above can be reduced. As a result, a necessary and sufficient voltage can be applied between the fixed electrode 27 and the movable electrode 28, and detection performance as designed can be reliably exhibited.

  In the Z-axis sensor 12, the contact electrode 29 is formed in the same layer as the fixed electrode 27 and the movable electrode 28 using a part of the polysilicon layer 26 that forms the fixed electrode 27 and the movable electrode 28. Therefore, all the contacts to the fixed electrode 27, the movable electrode 28, and the driving electrode 22 can be concentrated on the wirings 49 to 51 formed on the same layer (polysilicon layer 26). As a result, since these wirings 49 to 51 can be formed in the same process, the number of manufacturing processes can be reduced. Therefore, cost can be reduced.

As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form.
For example, the MEMS package 1 may include an acceleration sensor instead of the angular velocity sensor 3 or together with the angular velocity sensor 3. The acceleration sensor can be manufactured, for example, by using a capacitor formed between the drive electrode 22 and the movable electrode 28 as an acceleration detection capacitor.

For example, as shown in FIG. 4, a Z-axis acceleration sensor 60 that detects acceleration acting in the Z-axis direction includes a fixed electrode 27 (comb portion 32) and a movable electrode 28 (comb portion 39). In addition to the capacitor, the movable electrode 28 (comb tooth portion 39) and the second fixed electrode 61 are opposed to each other across the cavity 37 and the electrode coating film 23 (inter-electrode spacing d ₂ ) along the Z-axis direction. The capacitor can be used for sensor operation. As a result, the number of capacitors involved in the acceleration detection operation of the sensor can be increased, so that the acceleration acting on the MEMS package 1 can be detected with high accuracy.

In the above-described embodiment, the protective thin film 57 and the sacrificial oxide film 53 are removed in the process of FIG. 3L. However, by omitting the process of FIG. 3L, as shown in FIG. The film 53 may be left.
In addition, various design changes can be made within the scope of matters described in the claims.

DESCRIPTION OF SYMBOLS 1 MEMS package 2 Substrate 3 Angular velocity sensor 5 Integrated circuit 6 Resin package 7 Base substrate 12 Z-axis sensor 22 Drive electrode 23 Electrode coating film 25 Opening 26 Polysilicon layer 27 Fixed electrode 28 Movable electrode 29 Contact electrode 32 (fixed electrode 32 ) Comb portion 37 Cavity 39 Comb portion 51 (movable electrode) 51 Driving wiring 52 Sacrificial polysilicon layer 53 Sacrificial oxide film 57 Protective thin film 60 Z-axis acceleration sensor 61 Second fixed electrode

Claims (18)

Selectively forming a lower electrode on a semiconductor substrate;
Laminating an electrode coating film made of a material having an etching selectivity with respect to polysilicon so as to cover the lower electrode on the semiconductor substrate;
Selectively forming a sacrificial polysilicon layer on the electrode coating film;
Laminating a sacrificial oxide film on the electrode coating film so as to cover the sacrificial polysilicon layer;
Forming a polysilicon layer for an electrode on the sacrificial oxide film;
Forming the upper electrode by selectively etching the electrode polysilicon layer;
Forming a protective film having an etching selectivity with respect to polysilicon so as to cover the sidewall of the upper electrode;
Removing a portion of the sacrificial oxide film to expose the sacrificial polysilicon layer;
Forming a cavity directly under the upper electrode by removing the exposed sacrificial polysilicon layer.   2. The method of manufacturing a MEMS sensor according to claim 1, wherein the step of forming the upper electrode includes a step of forming the electrode polysilicon layer into a comb-shaped fixed electrode and a movable electrode that are engaged with each other with a space therebetween. .   3. The method of manufacturing a MEMS sensor according to claim 2, further comprising a step of removing the protective film from a side wall of the fixed electrode and the movable electrode after the removal of the sacrificial polysilicon layer. Prior to the formation of the polysilicon layer for electrodes, further comprising the step of forming an opening through the electrode coating film to selectively expose the lower electrode,
In the step of forming the electrode polysilicon layer, the electrode polysilicon layer is formed on the sacrificial oxide film, and at the same time, a part of the electrode polysilicon layer is allowed to enter the opening of the electrode coating film. And contacting the lower electrode
The method of manufacturing the MEMS sensor according to claim 1, wherein the step of forming the upper electrode includes a step of forming a contact electrode that is separated from the upper electrode and is in contact with the lower electrode.   The method of manufacturing a MEMS sensor according to claim 4, further comprising a step of forming a wiring on the contact electrode.   The method of manufacturing a MEMS sensor according to claim 5, wherein the step of forming a wiring on the contact electrode includes a step of simultaneously forming a wiring on the upper electrode. A semiconductor substrate;
A lower electrode selectively formed on the semiconductor substrate;
An electrode covering film made of an insulating material and formed on the semiconductor substrate so as to cover the lower electrode;
A MEMS sensor, comprising: a polysilicon layer formed above the electrode coating film at an interval and having an upper electrode facing the lower electrode through the electrode coating film.   The MEMS sensor according to claim 7, wherein the upper electrode includes a comb-like fixed electrode and a movable electrode that mesh with each other with a space therebetween.   9. The MEMS sensor according to claim 7, wherein the polysilicon layer further includes a contact electrode that penetrates the electrode coating film and contacts the lower electrode.   The MEMS sensor according to claim 9, further comprising a wiring formed on the contact electrode.   The acceleration sensor which detects the acceleration which acted on the said MEMS sensor by detecting the change of the electrostatic capacitance between the said lower electrode and the said movable electrode, Claim 9 or Claim 9 which concerns on Claim 8 or 8 10. The MEMS sensor according to 10.   By driving the movable electrode in a direction approaching and moving away from the lower electrode, an angular velocity acting on the MEMS sensor during the driving is detected by detecting a change in capacitance between the movable electrode and the fixed electrode. The MEMS sensor according to any one of claims 9 to 11 according to claim 8 or claim 8, comprising an angular velocity sensor to be detected.   The said lower electrode is formed along the direction which crosses each comb tooth of the said movable electrode so that the whole said movable electrode of a comb-tooth shape may be opposed, The claim 9 which concerns on Claim 8 or Claim 8 characterized by the above-mentioned. The MEMS sensor as described in any one of -12. The MEMS sensor according to claim 7, wherein the electrode coating film is made of SiO ₂ .   The MEMS sensor according to any one of claims 7 to 14, further comprising a protective thin film made of an insulating material and covering a side wall of the upper electrode. The MEMS sensor according to any one of claims 7 to 15,
And a resin package formed so as to cover the MEMS sensor.   The MEMS package according to claim 16, further comprising an integrated circuit electrically connected to the MEMS sensor and covered with the same resin package as the MEMS sensor. Further comprising a substrate having a front surface and a back surface and supporting the MEMS sensor on the front surface;
The MEMS package according to claim 16 or 17, wherein the resin package seals the MEMS sensor so as to cover the front surface of the substrate and to expose the back surface of the substrate.

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