JPH07183543A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide a semiconductor capacity-type acceleration sensor which is free from the effect of dust and moisture, small in chip area, and less affected by a stray capacitance by a method wherein a gap between a movable electrode and a stationary electrode is hermetically sealed up, the movable electrode and the stationary electrode are formed simple in shape, and the movable electrode, the stationary electrode, and an electronic circuit are arranged on the same substrate. CONSTITUTION:An acceleration sensor is composed of a glass layer 101 and silicon layers 103 and 105, wherein the glass layer 101 and the silicon layer 103 are bonded together through the intermediary of a polysilicon 102, and the silicon layers 103 and 105 are bonded together through the intermediary of an oxide film 104. A movable electrode 107 which swings in the lengthwise direction of the sensor by acceleration and stationary electrodes 106 and 108 arranged confronting the movable electrode 107 are provided to the silicon layer 103 by cutting grooves in it vertical to its surface through an etching process. An electronic circuit 109 which detects an electrostatic capacity is formed in the silicon layer 103 of the same substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor formed on a semiconductor substrate, and more particularly to a capacitive acceleration sensor having a movable electrode which moves according to acceleration and a fixed electrode which is arranged opposite to the movable electrode.

[0002]

2. Description of the Related Art In addition to the conventional acceleration sensor,
There is a monolithic accelerometer described in 04003 publication. This is a thin film type capacitive acceleration sensor in which polysilicon deposited on the surface of a semiconductor substrate is etched to form a movable electrode and a fixed electrode. This type of acceleration sensor has good compatibility with the manufacturing process for forming an electronic circuit, and it is easy to integrate the movable electrode, the fixed electrode, and the electronic circuit on the same semiconductor substrate.

The acceleration sensor described in Japanese Patent Laid-Open No. 5-52867 is a laminated capacitive acceleration sensor in which a plurality of silicon substrates and glass substrates are bonded together.
Since the movable electrodes in the central layer are sandwiched and overlapped by the fixed electrodes in the upper and lower layers, it is relatively easy to form an airtight structure and is not affected by dust or water.

[0004]

In the former thin film type acceleration sensor of the prior art, the gap between the movable electrode that moves according to the acceleration and the fixed electrode that faces the movable electrode is very narrow. Is. Therefore, if dust or water enters the gap, the movable electrode may become immovable and may not operate as an acceleration sensor. In particular, a thin film type acceleration sensor in which a movable electrode and a fixed electrode are formed on the same semiconductor substrate is more difficult to have an airtight structure than a laminated type in which a plurality of substrates are attached, and is easily affected by dust and water. Met.

In the capacitive acceleration sensor, increasing the detection sensitivity is to increase the capacitance between the movable electrode and the fixed electrode, that is, the facing area between the movable electrode and the fixed electrode. However, since the movable electrode and the fixed electrode of the thin film type acceleration sensor are formed by processing the vapor-deposited polysilicon, the vertical length of the facing surface of the movable electrode and the fixed electrode (the thickness of the vapor-deposited polysilicon). ) Is very thin, about 5 μm or less. Therefore, as the thickness is thinner, the edge face distance, which is the length in the lateral direction, is increased to secure the necessary facing area. Therefore, the shapes of the movable electrode and the fixed electrode are
The comb shape having a large number of teeth is complicated, and accordingly, the beam shape for supporting the lead wiring from each electrode and the movable electrode is also complicated. Further, the structure of the movable electrode, the fixed electrode, the beam and the wiring has been complicated, resulting in an increase in the chip area. In other words, the former conventional technique lacks consideration for the influence of dust and water and consideration for increasing the chip area due to the complicated structure.

On the other hand, in the latter type of laminated acceleration sensor, the movable electrode in the central layer and the two fixed electrodes in the upper and lower layers are formed on different substrates, but not on the same substrate. Therefore, it is difficult to dispose an electronic circuit for detecting a change in capacitance near the movable electrode, and the sensor is easily affected by stray capacitance. Further, it is difficult to connect each electrode to the electronic circuit, which is a bottleneck for downsizing of this type of sensor. That is, the latter conventional technology lacks consideration for reducing the influence of stray capacitance and downsizing the sensor by arranging the movable electrode, the fixed electrode, and the electronic circuit in close proximity to each other on the same substrate. there were.

As described above, the conventional capacitive acceleration sensor has advantages and disadvantages.

An object of the present invention is to hermetically seal a gap between a movable electrode and a fixed electrode, to form the movable electrode and the fixed electrode in a simple shape, and to form the movable electrode, the fixed electrode and an electronic circuit on the same substrate. The purpose of the present invention is to provide an acceleration sensor arranged in the. In other words, it is to provide an acceleration sensor that is not affected by dust and water, has a small chip area, and is less affected by stray capacitance.

[0009]

The object is to provide a movable electrode which is supported by a beam having elasticity and moves by inertial force due to acceleration, and a fixed electrode which has a minute gap between the movable electrode and faces each other. In an acceleration sensor that measures an acceleration by detecting a change in electrostatic capacitance between the movable electrode and the fixed electrode, the movable electrode and the fixed electrode are vertically etched from the surface of the semiconductor substrate so that the movable electrode and the fixed electrode are separated from each other. It is formed by engraving a groove including a minute gap in the periphery and leaving a part of the semiconductor substrate without being etched,
Separately, a support body that is left unetched to insulate the movable electrode and the fixed electrode from each other and supports the movable electrode and the fixed electrode so as to hold the minute gap, and the movable electrode and the fixed electrode sandwich the minute gap from at least one direction in the vertical direction. It is achieved by providing a sealing body that seals the groove.

Further, the movable electrode and the fixed electrode are sandwiched from at least one vertical direction, and a support that is not etched separately and supports the movable electrode and the fixed electrode so as to insulate the movable electrode and the fixed electrode from each other and hold the minute gap. And a sealing body that seals a groove including a minute gap, and the movable electrode is a one-sided support body having a support shaft in a direction perpendicular to the wafer surface of the semiconductor substrate. Those that are suspended in a direction perpendicular to the wafer surface and move in a direction parallel to the wafer surface, or the movable electrode is located near the surface of the semiconductor substrate and has a support shaft in a direction parallel to the wafer surface of the semiconductor substrate. This can be achieved even by suspending in a direction perpendicular to the wafer surface by a supporting body, swinging about a support shaft as a rotation center, and moving in a direction parallel to the wafer surface.

[0011]

The structure of the acceleration sensor of the present invention is a combination of the thin film type and the laminated type. That is, a thick silicon substrate is adopted instead of the vapor-deposited polysilicon of the thin film type acceleration sensor in which the movable electrode and the fixed electrode are formed on the same substrate. Then, the facing minute gap between the movable electrode and the fixed electrode where the electrostatic capacitance is generated is formed by forming a groove in the thickness direction of the silicon substrate by an etching processing method. The vapor-deposited polysilicon has a thickness of 5 μm or less, while the silicon substrate has a thickness of approximately 100 to 200 μm. Therefore, as the thickness is larger, the edge distance is shortened, and the facing area between the movable electrode and the fixed electrode is secured with a simple electrode shape.

On a thick silicon substrate on which the movable electrode and the fixed electrode are formed, a support for supporting each electrode while insulating is formed by a diffusion method or an epitaxial growth method.

Further, the movable electrode, the fixed electrode, and the electronic circuit are arranged on the same surface side of the silicon substrate, and the movable electrode and the electronic circuit are arranged in close proximity to each other, and they are connected by vapor deposition aluminum wiring.

Then, the silicon substrate on which the movable electrode, the fixed electrode, the electronic circuit and the like are formed is laminated with another sealing body to form a laminated structure.

Therefore, the airtight sealing of the gap portion between the movable electrode and the fixed electrode is achieved by covering the silicon substrate forming the movable electrode and the fixed electrode with the sealing member from above and below to cover the silicon substrate. It

Further, forming the movable electrode and the fixed electrode in a simple shape makes it possible to increase the thickness of the facing surfaces between the movable electrode and the fixed electrode and to fix the movable electrode and the fixed electrode with a simple electrode shape with a short edge distance. This is achieved by ensuring the facing area between the electrodes.

Further, disposing the movable electrode, the fixed electrode, and the electronic circuit on the same substrate is achieved by providing a thick silicon substrate structure capable of disposing the movable electrode, the fixed electrode, and the electronic circuit on the same substrate. .

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An acceleration sensor according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view of the acceleration sensor of this embodiment. The configuration and operation will be described. This acceleration sensor is composed of three layers of a glass layer 101 and silicon layers 103 and 105 which are insulating materials. Then, the glass layer 101 and the silicon layer 103 are bonded to each other via the polysilicon 102, and the silicon layer 103 and the silicon layer 105 are bonded to each other via the oxide film 104 which is an insulating material. The silicon layer 103 has fixed electrodes 106, 108,
It is composed of a movable electrode 107 and an electronic circuit 109. When an acceleration in the detected acceleration direction acts on this acceleration sensor, the movable electrode 107 moves in the detected acceleration direction due to inertial force. When the movable electrode 107 moves in the detected acceleration direction, the distance between the fixed electrode 106 and the movable electrode 107 and the fixed electrode 1
The electrostatic capacitance between 08 and the movable electrode 107 changes. This change in capacitance is taken as a change in the output of the electronic circuit 109,
Detect acceleration.

FIG. 2 is a diagram showing a manufacturing process of the acceleration sensor of FIG.

In step 1, an oxide film 104 is formed on the silicon layer 105 in which a recess is formed in advance in order to avoid contact with the movable electrode 107.

In step 2, the silicon layer 105 and the silicon layer 103 are bonded via the oxide film 104.

In step 3, polysilicon 102 is deposited. Further, the electronic circuit 109 is formed along the wafer surface of the silicon layer 103. Movable electrode 107 and fixed electrode 10
Since 6 and 108 are formed on the same silicon layer 103, the electronic circuit 109 can also be formed on the same silicon layer 103 in this way. Therefore, in a later step, the movable electrode, the fixed electrode, the electronic circuit, the silicon layer 103
It is possible to dispose the movable electrode and the electronic circuit on the same surface side of, and close to each other, and to connect them by the vapor-deposited aluminum wiring.

In step 4, a groove is formed perpendicularly to the thickness direction from the wafer surface of the silicon layer 103 by etching to form the fixed electrodes 106 and 108 and the movable electrode 107. In this embodiment, the silicon layer 103 has a thickness of about 15
It is 0 μm. By forming the groove, a facing surface (a facing area) necessary for changing the electrostatic capacitance between the movable electrode and the fixed electrode is formed. In addition, the facing surface is a silicon layer 10
It can be said that the surface is parallel to the dicing surface of 3.

In the conventional thin film type acceleration sensor, the length in the vertical direction (thickness of vapor-deposited polysilicon) of the facing surfaces of the movable electrode and the fixed electrode is very thin, about 5 μm or less. This is thin because it is formed by a manufacturing method called vapor deposition. Although it is possible to make the thickness as thick as a silicon substrate by a vapor deposition manufacturing method, it takes a very long time (from several hours to several tens of hours), and the compatibility with the manufacturing process of the acceleration sensor is poor.

On the other hand, the present invention is a manufacturing process in which an off-the-shelf silicon substrate of about 150 μm is adopted and a groove is processed in the thickness direction of the substrate, which is suitable for line production. Then, as the thickness increases, the distance between the edge surfaces can be shortened, and the necessary facing area can be easily secured. As a result, the shapes of the movable electrode and the fixed electrode are simplified, and accordingly, the lead wiring from each electrode and the beam shape for supporting the movable electrode are also simplified. Further, the simple electrode shape has an effect of reducing the design man-hour.

In step 5, the glass layer 101, which is an insulating material, is used.
Is bonded via the polysilicon 102, and the fixed electrode 10
6, 108, the movable electrode 107, and the electronic circuit 109 are hermetically sealed. That is, the glass layer 101 is a sealing body and a lid. Therefore, the gap between the movable electrode and the fixed electrode can be hermetically sealed, and the influence of dust and water can be eliminated. Note that the glass layer 101 is provided with a recess so that the glass layer 101 and the movable electrode 107 do not contact with each other.

Further, it is possible to replace the polysilicon 102 with a low melting point glass and replace the glass layer 101 with a silicon layer. With this configuration, the electrodes and the sealing body (lid) can be electrically insulated and hermetically sealed. Since the sealing body is a silicon layer (electric conductor), the silicon layer is grounded (earth).
However, it is also possible to obtain an "electrostatic shield effect" that prevents malfunction of the movable electrode due to a disturbance called electrostatic induction.

Furthermore, since the electronic circuit 109 is also hermetically sealed, the electronic circuit 109 is prevented from being contaminated. Therefore, a simple package is sufficient for mounting the present acceleration sensor.

Since the dry etching method can be adopted for the etching in the step 4, the electronic circuit 109 is used.
Does not pollute. Therefore, in the acceleration sensor of this embodiment, it is easier to form the movable electrode, the fixed electrode, and the electronic circuit on the same semiconductor substrate.

FIG. 3 is a diagram showing a first arrangement example of the movable electrode and the fixed electrode.

The movable electrode 107 has a simple H shape. The movable electrode 107 has fixed portions 301, 3
It is fixed to the silicon layer 103 at 02, 307 and 310, and can be moved in the left and right directions in the figure by bending the beams 303, 304, 305 and 306. The movable electrode 107 swings in the longitudinal direction of the figure.

The fixed electrodes 106 and 108 are arranged to face the movable electrode 107, and the electrostatic capacitance is changed by the movement of the movable electrode.

Further, stoppers 308 and 309 are arranged facing the movable electrode 107. Stoppers 308, 3
09 and the movable electrode 107, the gap between the fixed electrode 10
The gap is smaller than the gap between the movable electrode 107 and the movable electrodes 107 and 108, so that even if the movable electrode largely moves, it does not contact the fixed electrode but contacts the stopper first. That is, the movement of the movable electrode is restricted.

Further, the stoppers 308 and 309 and the movable electrode 107 are connected by a vapor-deposited aluminum wiring or the like so that the stopper and the movable electrode have the same potential. This prevents sticking due to the electrostatic force generated by the potential difference between the two (the gap is zero at the time of contact, so an excessive electrostatic force is generated even with a slight potential difference).

Furthermore, the stoppers 308 and 309 are provided with protrusions to reduce the contact area between the stopper and the movable electrode as much as possible. As a result, even if the potentials are equal, sticking due to a slight potential difference that remains to some extent is prevented.

That is, when an excessive acceleration is applied to the acceleration sensor and the movable electrode 107 is largely moved, the movable electrode 107 is brought into contact with the stoppers 308 and 309 having the same potential as the movable electrode 107 and a small contact area. Thus, the movable electrode 107 is prevented from being welded or fixed.
Even if the protrusion is provided on the movable electrode 107, the stopper 3
08, 309 or stoppers 308, 3
You may provide a projection part in both 09 and the movable electrode 107.

The fixed portions 301, 302, 307, 31
0, fixed electrodes 106 and 108, stoppers 308 and 3
09 is supported by a support called “n diffusion layer capable of electrically insulating”, which is formed by the diffusion method of the silicon layer 103.

FIG. 4 is a diagram showing a second arrangement example of the movable electrode and the fixed electrode.

The movable electrode 107 has a simple cross shape and is fixed to the silicon layer 105 by fixing portions 401, 402, 407, 409, and the beams 403, 405, 406, 4 are provided.
The bend of 08 allows movement in the left-right direction in the drawing. Further, the fixed electrodes 106 and 108 are arranged so as to face the movable electrode 107, and the electrostatic capacity is changed by the movement of the movable electrode.

Further, a hole is provided in the movable electrode 107, and a stopper 404 is arranged inside this hole. Similar to the first arrangement example, the gap between the stopper 404 and the movable electrode 107 is narrower than the gap between the fixed electrodes 106 and 108 and the movable electrode 107, and the stopper 404 and the movable electrode 1 are arranged.
07 is the same potential, and the contact area with the movable electrode 107 is reduced as much as possible by the protrusion. Next, the electronic circuit 109 will be described with reference to FIGS.

FIG. 5 is a configuration diagram of the electronic circuit 109, and FIG. 6 is a diagram showing an output waveform of the pulse generator 516. The electrostatic capacitance between the movable electrode 107 and the "one fixed electrode 106" is
The electrostatic capacitance 508 and the electrostatic capacitance between the movable electrode 107 and the "other fixed electrode 108" are indicated by the electrostatic capacitance 514.

The electronic circuit 109 generates a pulse signal having the output waveform shown in FIG. 6 to operate the electronic circuit 109, and an inverter target 506 that applies a pulse voltage to the electrostatic capacitance 508. 507 and capacitance 5
A pulse voltage having a phase opposite to that of the pulse voltage applied to the capacitor 08 is applied to the capacitance 514, and a pulse whose phase is inverted according to the output of the inverter 512 to the capacitance 505. A phase inverter composed of inverter targets 501 and 504 and switches 502 and 503 for applying a signal, switches 509 and 515 for integrating charges charged and discharged to electrostatic capacitances 505, 508 and 514, and an inverter.
It is composed of a charge integrator composed of a target 511 and a capacitance 510, and an invert target 512 which binarizes the output of the invert target 511.

Therefore, the electronic circuit 109 includes the switch 50.
9, 515, Inverter Target 511, Capacitance 510
It operates so that the output of the charge integrator constituted by is a constant value. The output of the charge integrator is the capacitance 508.
Capacitance 50 determined by the difference between the charged charge of the capacitor and the discharge charge of the capacitor 514 and the output of the inverter target 512.
It is proportional to the integrated value of the charge or discharge charge of 5. That is, the electronic circuit 109 operates so that the integrated value of the sum of the charged charge of the electrostatic capacitance 508, the discharged charge of the electrostatic capacitance 514, and the charged or discharged charge of the electrostatic capacitance 505 becomes a constant value. In other words, the average value of the sum of the charged or discharged charges of the electrostatic capacitance 505 and the difference between the charged charges of the electrostatic capacitance 508 and the discharged charge of the electrostatic capacitance 514 is made equal. Here, the charged charge of the electrostatic capacitance 508 is proportional to the capacitance value of the electrostatic capacitance 508, and the discharged charge of the electrostatic capacitance 514 is proportional to the capacitance value of the electrostatic capacitance 514. That is, the difference between the charge charged in the capacitance 508 and the discharge charge in the capacitance 514 is proportional to the difference between the capacitance 508 and the capacitance 514. The discharge of the electrostatic capacitance 505 or the charge that is integrated into the charge integrator depends on the output of the inverter target 512. Therefore, the average value of the sum of the charge or discharge charges of the electrostatic capacitance 505 is proportional to the pulse density of the output of the inverter target 512.

That is, since the pulse density of the output of the invert target 512 changes according to the difference between the electrostatic capacitance 508 and the electrostatic capacitance 514, the electronic circuit 109 outputs this change in pulse density as a signal. . Then, the acceleration is detected from the output signal proportional to the difference between the capacitance values of the electrostatic capacitance 508 and the electrostatic capacitance 514.

Next, an acceleration sensor according to another embodiment of the present invention will be described with reference to FIGS.

FIG. 7 is a sectional view of an acceleration sensor which is a first embodiment of another embodiment, FIG. 8 is an external view of the movable electrode 709 shown in FIG. 7, and FIG. 9 is a view of the first embodiment. It is a figure which shows the manufacturing process of an acceleration sensor.

First, the structure and operation of this acceleration sensor are shown in FIG.
Will be described. This acceleration sensor has a silicon layer 701,
It is composed of two glass layers 702. Then, the fixed electrodes 708 and 710, the movable electrode 709, and the electronic circuit 707 are arranged on the silicon layer 701.
8, 710, "n diffusion capable of electrically insulating" between the movable electrodes 709, 703, 704, 705,
706 are arranged. Further, by fixing the glass layer 702 to the silicon layer 701, the fixed electrode 708,
710 and the movable electrode 709 are hermetically sealed. The fixed electrodes 708 and 710, the movable electrode 709, and the electronic circuit 707 are connected to each other by aluminum wiring from the upper surface of the silicon layer 701.

Further, it is possible to move the movable electrode 709 largely by acceleration, as shown in FIG.
This is achieved by increasing the mass by thickening the central portion of 9 and reducing the spring constant by thinning the beams 801 and 802 for fixing to the silicon layer 701.

As shown in FIGS. 7 and 8, the movable electrode 709 has a beam 801 which is a one-sided support beam having a support axis in a direction perpendicular to the wafer surface of the silicon layer 701 which is a semiconductor substrate. , 802 are suspended in a direction perpendicular to the wafer surface of the silicon layer 701. Then, it moves in the direction parallel to the wafer surface of the silicon layer 701 in the detected acceleration direction shown in the figure.

When an acceleration in the direction of detected acceleration acts on this acceleration sensor, the movable electrode 709 moves in the direction of detected acceleration due to inertial force. When the movable electrode 709 moves in the detected acceleration direction, the electrostatic capacitance between the movable electrode 709, the fixed electrode 708, and the fixed electrode 710 changes. Therefore, by detecting this change in capacitance with the electronic circuit 707,
An output corresponding to the acceleration can be obtained.

On the other hand, in this acceleration sensor, the movable electrode 70
The movable electrode 709 and the fixed electrode 7 are formed by making the vertical direction of 9 longer (in the direction of increasing the thickness of the semiconductor substrate).
It is intended to increase the facing area (capacitance) between 08 and 710 and further reduce the edge distance in the lateral direction. Therefore, the shapes of the movable electrode and the fixed electrode can be made simpler than those in the above-described embodiments. As the thickness is increased, the shape of the electrode is further simplified, and the silicon layer 70
Since the planar area of 1 is reduced, the overall shape of the sensor is downsized. This is an advantage of utilizing the thickness direction of the silicon layer 701. Specifically, the silicon layer 701
Has a thickness of approximately 300 to 400 μm. This is 2-3 times the thickness of the previous example.

Next, the manufacturing process of this acceleration sensor will be described with reference to FIG.

First, in step 1, n diffusions 703, 704, 705 and 70 are formed in the silicon layer 701 which is p-type silicon.
6, p + diffusion 901 and electronic circuit 707 are formed. The impurity concentration of the p + diffusion 901 is set sufficiently higher than that of the silicon layer 701.

In step 2, a recess is formed in the bottom of the silicon layer 701 by partial etching. This is the glass layer 7
02 so that the movable electrode 709 can move without coming into contact with the glass layer 702.
This is done in order to prevent stress from acting on the glass layers 702 on the layers 8 and 710.

In step 3, a groove is formed in the wafer surface of the silicon layer 701 in the vertical direction by an etching method to form original portions of the fixed electrodes 708 and 710 and the movable electrode 709, that is, a minute gap. . Here, in order to make it easier to vertically form a groove in the thickness direction from the wafer surface of the silicon layer 701, a silicon substrate having a wafer surface orthogonal to the “110 direction of the semiconductor crystal axis” is used.
As a result, a relatively deep etching groove is formed in the silicon layer 70.
One can be dug almost vertically from the wafer surface.

When digging a groove by the etching method, n
Diffusions 703, 704, 705, 706 and silicon layer 70
A reverse bias voltage is applied during 1 and the groove is n-diffused 70
It is designed to stop at the portions 3, 704, 705, 706. The n-diffusions 703, 704, 705, and 706 are bedrock-like ceiling lids that are struck by digging holes. Thereby, the upward direction is sealed and the electrode shape is stabilized.
In addition, the ceiling cover, the n diffusions 703, 704, 705, and 706 are the silicon layer 701, the fixed electrodes 708 and 710, and the movable electrode 70.
It plays an important role in insulating each of the nine. The former is n-polar and the latter is p-polar. By applying different voltages, it is possible to "electrically insulate" between the two. And again, the n diffusions 703, 704, 705, 706 are
It is a support body that supports the fixed electrodes 708 and 710 and the movable electrode 709 so as to hold a minute gap between them.

Further, in the case of this embodiment, the support body which is n-diffused is also the ceiling lid as described above, and is therefore one sealing body.

In step 4, the p + diffusion 901 is removed by etching with nitric acid. As a result, the shape of the movable electrode 709 is processed as shown in FIG. Beam 8 shown in FIG.
01 and 802 are the rest of the silicon layer 701.

In step 5, the glass layer 702 which is the other sealing body is bonded to the silicon layer 701 by anodic bonding, and the fixed electrodes 708 and 710 and the movable electrode 709 are hermetically sealed downward. As a result, the gap between the fixed electrode and the movable electrode is hermetically sealed by the above-described ceiling cover made of n diffusion and the glass layer 702, and is not affected by dust or water.

FIG. 10 is a schematic external view of a two-dimensional acceleration sensor of another embodiment. This is an application of the embodiment shown in FIG. 7, in which movable electrodes are arranged to detect two-dimensional accelerations in the front, rear, left and right directions. In this acceleration sensor, a movable electrode 1003 that reacts to acceleration in the first detected acceleration direction and a movable electrode 1002 that reacts to acceleration in the second detected acceleration direction are arranged on the silicon layer 1001. Therefore, the movable electrodes 1002 and 1003 as described in the acceleration sensor of the embodiment of FIG. 7 are arranged so as to oppose the respective fixed electrodes, and the electronic circuit is provided with the silicon layer 100.
The first detection acceleration direction and the second detection acceleration direction
It is possible to configure a two-dimensional acceleration sensor that can detect acceleration in the detected acceleration direction.

FIG. 11 is a diagram showing an acceleration sensor of a second embodiment of another embodiment. FIG. 11 is a sectional view of the acceleration sensor of the second embodiment. In this embodiment, a piezoresistive method different from the electrostatic capacity method is adopted. The acceleration sensor includes a silicon layer 1106 and a glass layer 1107. Then, the thin film portion 1103, the electronic circuit 1104, and the mass portion 1105 are arranged on the silicon layer 1106, and the thin film portion 1103 has a diffusion resistance 1101,
1102 is arranged.

When an acceleration in the detected acceleration direction acts on this acceleration sensor, the suspended portion of the mass portion 1105 moves in the detected acceleration direction due to inertial force. When the suspended portion of the mass portion 1105 moves in the detected acceleration direction, stress acts on the thin film portion 1103,
The resistance values of the diffused resistors 1101 and 1102 change. By detecting the change in the resistance value of the diffused resistors 1101 and 1102 with the electronic circuit 1104, an output according to the acceleration can be obtained. Also in this embodiment, the mass portion 1105 can be hermetically sealed by adhering the glass layer 1107 to the silicon layer 1106, so that the influence of water and dust can be eliminated.

FIG. 12, FIG. 13 and FIG. 14 are views showing the acceleration sensor of the third embodiment of the other embodiments. Figure 12
FIG. 13 is a cross-sectional view of the acceleration sensor of the third embodiment, FIG. 13 is a perspective view of the silicon layer 1201 of FIG. 12 turned upside down, and FIG. 14 is a diagram showing a manufacturing process of the acceleration sensor of the third embodiment.

First, the structure of the present acceleration sensor will be described with reference to FIGS. This acceleration sensor has a silicon layer 1
201 is etched and fixed electrodes 1203, 1205,
A movable electrode 1204 supported by the beam 1207 is formed, an electronic circuit 1206 is arranged on the upper surface of the silicon layer 1201, and a glass layer 1202 is laminated so as to hermetically seal the concave portion of the silicon layer 1201. Has been done.

When acceleration in the detected acceleration direction acts on this acceleration sensor, the movable electrode 1204 moves in the detected acceleration direction due to inertial force. When the movable electrode 1204 moves in the detected acceleration direction, the movable electrode 1204 and the fixed electrodes 1203, 120
The capacitance between 5 changes. An output according to the acceleration can be obtained by detecting the change in the electrostatic capacitance by the electronic circuit 1206. The fixed electrodes 1203, 12
05, wiring from the movable electrode 1204 to the electronic circuit 1206 is performed by aluminum wiring from the upper surface of the silicon layer 1201. The glass layer 12 is provided below the silicon layer 1201.
02 is adhered and the fixed electrodes 1203, 1205 and the movable electrode 1204 are hermetically sealed, so that the influence of dust and water can be eliminated.

Next, a method of manufacturing this acceleration sensor will be described with reference to FIG.
Will be described. First, in step 1, the p-type silicon layer 1
Diffuse phosphorus into 201 with high concentration and p + diffuse 140
1, 1402, 1403 are formed. In step 2, the p-type epi layer 1 is epitaxially grown on the silicon layer 1201.
404 is formed.

In step 3, an n-type epi layer 1405 having a polarity different from that of the silicon layer 1201 is formed by epitaxial growth. The n-type epi layer 1405 is the silicon layer 120.
1 and the fixed electrodes 1203, 1205 and the movable electrode 1204, respectively, and support them so as to hold them so as to hold a minute gap between the fixed electrode and the movable electrode.

In step 4, phosphorus diffusion is performed on the silicon layer 1201 and p + diffusions 1406 and 1407 and the electronic circuit 120 are performed.
6 is formed. In step 5, the silicon layer 1201 is vertically etched from the bottom to the top, and the p + diffusion 140
A groove is formed around 1, 1402, 1403, 1406, 1407. This etching forms a gap between the fixed electrode and the movable electrode. At this time, a reverse bias voltage is applied between the n-type epi layer 1405 and the silicon layer 1201 so that the etching stops at the n-type epi layer 1405 formed in the silicon layer 1201.

The n-type epi layer 1405 is a rock-like ceiling cover that abuts against a hole. In step 6, the etching in step 5 is further advanced. At this time, p + diffusion 1401, 1
The portions 402, 1403, 1406, and 1407 have a high diffusion concentration and therefore remain without being etched. This gives p
The portions left by the + diffusions 1401 and 1406 are formed on the fixed electrode 1203, the portions left by the p + diffusions 1403 and 1407 are formed on the fixed electrode 1205, and the portions left by the p + diffusion 1402 are formed on the movable electrode 1204. In step 7, the glass layer 1 is formed under the silicon layer 1201.
202 is adhered and the fixed electrodes 1203 and 1205 and the movable electrode 1204 are hermetically sealed.

FIGS. 15, 16 and 17 are views showing the acceleration sensor of the fourth embodiment. FIG. 15 is a sectional view of the acceleration sensor of the fourth embodiment, and FIG. 16 is a silicon layer 1502.
17 is a cross-sectional perspective view of FIG. 17, and FIG. 17 is a diagram showing a manufacturing process of the acceleration sensor of the fourth embodiment.

First, the structure of the present acceleration sensor will be described with reference to FIGS. This acceleration sensor has a glass layer 150.
1, 1503, and a silicon layer 1502. Then, the silicon layer 1502 forms the fixed electrode 150.
7, 1509, the beam 1701, the movable electrode 1508 suspended from the beam 1701, the silicon layer 1502, the fixed electrodes 1507 and 1509, and the n diffusions 1504 and 150 arranged to insulate the movable electrode 1508 from each other.
5, 1506.

Referring to FIG. 16, n diffusions 1504, 15
05 and 1506 are the silicon layer 1502 and the fixed electrode 15.
07 and 1509 are insulated from the movable electrode 1508,
In addition, it is a support body that supports the fixed electrode and the movable electrode so as to hold a minute gap between them. Further, the movable electrode 1508 has a silicon layer 1502 which is a semiconductor substrate.
Beam 1701 located near the surface of the silicon layer 1502 and having a support axis in a direction parallel to the wafer surface of the silicon layer 1502.
At, the silicon layer 1502 is hung in a direction perpendicular to the wafer surface. The movable electrode 1508 swings around the support shaft as a rotation center and moves in the direction of the detected acceleration shown in FIG. 15 in the direction parallel to the wafer surface.

When an acceleration in the detected acceleration direction acts on this acceleration sensor, the movable electrode 1508 receives an inertial force, the beam 1701 is twisted by the swing of the movable electrode 1508, and the movable electrode 1508 moves in the detected acceleration direction. This movement changes the electrostatic capacitance between the movable electrode 1508, the fixed electrode 1507, and the fixed electrode 1509. An output according to the acceleration can be obtained by detecting the change in the electrostatic capacitance. Although not shown in FIG. 15, an electronic circuit can be easily formed in the silicon layer 1502.

Next, a method of manufacturing this acceleration sensor will be described with reference to FIG.
Will be described. First, in step 1, the silicon layer 1502
Then, n diffusions 1504, 1505, and 1506 are formed. Here, the n diffusion 1505 is also a portion that becomes the beam 1701. In step 2, a recess is formed in the bottom of the silicon layer 1502 by etching. This is because even if the glass layer 1503 is adhered, the movable electrode 1508 can move without coming into contact with the glass layer 1503.
7, 1509 to prevent the glass layer 1502 from exerting a stress. In step 3, the silicon layer 1502 is vertically etched to form fixed electrodes 1507 and 1509, a movable electrode 1508, and a beam 1701. This time,
n diffusions 1504, 1505, 1506 and silicon layer 15
02 by applying a reverse bias to the n diffusions 1504, 150
The portions 5 and 1506 are left unetched.

In step 4, the glass layer 150 which is the sealing body.
1, 1503 are bonded to the silicon layer 1502 by anodic bonding, and fixed electrodes 1507 and 1509 and movable electrode 1508 are attached.
Is hermetically sealed.

18, 19, and 20 are views showing the acceleration sensor of the fifth embodiment. FIG. 18 is a sectional view of the acceleration sensor of the fifth embodiment, FIG. 19 is a diagram showing the first half of the manufacturing process of the acceleration sensor of the fifth embodiment, and FIG. 20 is a diagram of the second half of the manufacturing process.

First, the structure and operation of this acceleration sensor are shown in FIG.
8 will be described. This acceleration sensor has a silicon layer 180.
1 and the glass layer 1802. Fixed electrodes 1803 and 1805 and a movable electrode 1806 are arranged on the silicon layer 1801, and a p + diffusion 1804 is arranged to take out an electric signal of the movable electrode 1806 to the upper surface of the silicon layer 1801. The p + diffusion 1804 also plays the role of a beam for supporting the movable electrode 1806. Further, by bonding the glass layer 1802 to the silicon layer 1801, the gap portions of the fixed electrodes 1803 and 1805 and the movable electrode 1806 are hermetically sealed.

When an acceleration in the detected acceleration direction acts on this acceleration sensor, the movable electrode 1806 rotates in the detected acceleration direction due to the inertial force. When the movable electrode 1806 rotates in the detected acceleration direction, the electrostatic capacitance between the movable electrode 1806, the fixed electrode 1803, and the fixed electrode 1805 changes. Therefore,
The acceleration can be detected from this change in capacitance. Although not shown in FIG. 18, it is possible to easily form an electronic circuit on the silicon layer 1801.

Next, the manufacturing process of this acceleration sensor is shown in FIG.
9 and FIG. 20.

First, in step 1, an oxide film 1901 is partially formed on the silicon layer 1801 which is p-type silicon. The oxide film 1901 is formed on the fixed electrodes 1803 and 1805.
The gap between the fixed electrodes 1803 and 1805 and the movable electrode 1806 can be controlled by controlling the thickness of the oxide film 1901.

In step 2, the silicon layer 1801 is epitaxially grown to form an n-type epi layer 1902 having a polarity different from that of the silicon layer 1801. This n-type epi layer 1
902 is a silicon layer 1801 and fixed electrodes 1803, 1
805 and the movable electrode 1806 are insulated from each other, and a small gap between the fixed electrode and the movable electrode is maintained,
It is a support that supports these.

In step 3, the fixed electrode 18 is formed by p + diffusion.
03, 1805, the movable electrode 1806 and the n-type epi layer 1
P + diffusion 180 for electrically connecting the top surface of 902
4 is formed. As mentioned above, the p + diffusion 1804 is also a beam. The beam can also be formed of, for example, a single cylinder or prism.

In step 4, a recess is formed in the bottom of the silicon layer 1801 by etching.

In step 5, the etching is performed from the bottom of the silicon layer 1801 toward the ceiling to move the movable electrode 180.
6 is formed. The shape of the movable electrode 1806 can be, for example, a disc shape. And the one beer
The structure is supported by p + diffusion 1804 which is a pillar. In this case, the fixed electrode is divided into a large number. By doing so, it is possible to detect the acceleration in all directions in the longitudinal direction of the sensor chip.

In step 6, the oxide film 1901 is removed by etching to form a gap between the fixed electrodes 1803 and 1805 and the movable electrode 1806. Also in this case, the n-type epi layer 1902 is a rock-like ceiling lid. Also in the case of this embodiment, the support made of the n-type epi layer 1902 serves as a ceiling cover, which is one of the sealing bodies.

In step 7, the glass layer 1802, which is the other sealing body, is bonded and sealed to the silicon layer 1801.

[0088]

According to the present invention, the gap between the movable electrode and the fixed electrode is hermetically sealed, the movable electrode and the fixed electrode are formed in a simple shape, and the fixed electrode, the movable electrode and the electronic circuit are formed. Since they can be arranged on the same substrate, it is possible to provide an acceleration sensor that is not affected by dust or water, has a small chip area, and is less affected by stray capacitance.

[Brief description of drawings]

FIG. 1 is a sectional view of an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the acceleration sensor of FIG.

3 is a diagram showing a first arrangement example of movable electrodes and fixed electrodes of the acceleration sensor of FIG.

FIG. 4 is a diagram showing a second arrangement example of movable electrodes and fixed electrodes of the acceleration sensor of FIG.

5 is a configuration diagram of an electronic circuit 109. FIG.

FIG. 6 is a diagram showing an output waveform of a pulse generator 516.

FIG. 7 shows a sectional view of an acceleration sensor according to a first embodiment of another embodiment of the present invention.

FIG. 8 is an external view of a movable electrode 709 according to the first embodiment.

FIG. 9 is a diagram showing a manufacturing process of the acceleration sensor according to the first embodiment.

FIG. 10 is a schematic external view of a two-dimensional acceleration sensor according to another embodiment.

FIG. 11 shows a sectional view of an acceleration sensor according to a second embodiment of the other embodiments.

FIG. 12 is a sectional view of an acceleration sensor according to a third embodiment.

FIG. 13 is a perspective view of the silicon layer 1201 according to the third embodiment as seen inside out.

FIG. 14 is a diagram showing a manufacturing process of the acceleration sensor according to the third embodiment.

FIG. 15 is a sectional view of an acceleration sensor according to a fourth embodiment.

FIG. 16 is a sectional perspective view of a silicon layer 1502 according to a fourth embodiment.

FIG. 17 is a diagram showing a manufacturing process of the acceleration sensor according to the fourth embodiment.

FIG. 18 is a sectional view of an acceleration sensor according to a fifth embodiment.

FIG. 19 is a diagram showing a manufacturing process of the first half of the acceleration sensor according to the fifth embodiment.

FIG. 20 is a diagram showing a manufacturing process of the latter half of the acceleration sensor of the fifth embodiment.

[Explanation of symbols]

101 ... Glass layer, 102 ... Polysilicon, 103 ... Silicon layer, 104 ... Oxide film, 105 ... Silicon layer, 10
6 ... Fixed electrode, 107 ... Movable electrode, 108 ... Fixed electrode,
109 ... Electronic circuit, 301 ... Fixed part, 302 ... Fixed part,
303 ... Beam, 304 ... Beam, 305 ... Beam, 3
06 ... Beam, 307 ... Fixed part, 308 ... Stopper, 3
09 ... Stopper, 310 ... Fixed part, 401 ... Fixed part, 4
02: fixed part, 403: beam, 404: stopper, 4
05 ... beam, 406 ... beam, 407 ... fixing part, 40
8 ... Beam, 409 ... Fixed part, 501 ... Inverter target
502 ... Switch, 503 ... Switch, 504 ... Inverter target, 505 ... Electrostatic capacitance, 506 ... Inverter
Target, 507 ... Invert target, 508 ... Electrostatic capacity, 509 ... Switch, 510 ... Electrostatic capacity, 511 ... Invert target, 512 ... Invert target, 513 ...
Inverter target, 514 ... Electrostatic capacitance, 515 ... Switch, 516 ... Pulse generator, 701 ... Silicon layer, 70
2 ... glass layer, 703 ... n diffusion, 704 ... n diffusion, 70
5 ... n diffusion, 706 ... n diffusion, 707 ... electronic circuit, 70
8 ... Fixed electrode, 709 ... Movable electrode, 710 ... Fixed electrode,
801 ... beam, 802 ... beam, 901 ... p + diffusion,
1001 ... Silicon layer, 1002 ... Movable electrode, 1003
... movable electrode, 1101 ... diffusion resistance, 1102 ... diffusion resistance, 1103 ... thin film portion, 1104 ... electronic circuit, 1105
Mass part, 1106 ... Silicon layer, 1107 ... Glass layer, 1201 ... Silicon layer, 1202 ... Glass layer, 12
03 ... Fixed electrode, 1204 ... Movable electrode, 1205 ... Fixed electrode, 1206 ... Electronic circuit, 1207 ... Beam, 140
1 ... p + diffusion, 1402 ... p + diffusion, 1403 ... p + diffusion, 1404 ... p type epi layer, 1405 ... n type epi layer, 1
406 ... p + diffusion, 1407 ... p + diffusion, 1501 ... glass layer, 1502 ... silicon layer, 1503 ... glass layer,
1504 ... n diffusion, 1505 ... n diffusion, 1506 ... n diffusion, 1507 ... fixed electrode, 1508 ... movable electrode, 150
9 ... Fixed electrode, 1701 ... Beam, 1801 ... Silicon layer, 1802 ... Glass layer, 1803 ... Fixed electrode, 180
4 ... p + diffusion, 1805 ... fixed electrode, 1806 ... movable electrode, 1901 ... oxide film, 1902 ... epi layer,

Front Page Continuation (72) Inventor Seiichi Ukai 7-1 Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor, Akira Koide 502, Kamidate-cho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd.

Claims (10)

[Claims] 1. A movable electrode, which is supported by an elastic beam and moves by an inertial force due to acceleration, and a fixed electrode which has a minute gap between the movable electrode and faces each other, and the movable electrode and the fixed electrode. In an acceleration sensor that measures acceleration by detecting a change in electrostatic capacitance between electrodes, the movable electrode and the fixed electrode are vertically etched from the surface of a semiconductor substrate to surround the movable electrode and the fixed electrode. A groove including the minute gap is dug in to form a part of the semiconductor substrate without being etched, and the movable electrode and the fixed electrode are insulated from each other by being left without being etched. Before including the minute gap, the support body that supports the minute gap and the movable electrode and the fixed electrode are sandwiched from at least one of the vertical direction. An acceleration sensor, characterized in that a sealing member for sealing the groove. 2. The acceleration sensor according to claim 1, wherein the support comprises a diffusion layer formed by diffusing impurities in the semiconductor substrate or an insulating layer formed by epitaxial growth. 3. The acceleration sensor according to claim 1, wherein at least one of the sealing bodies that sandwich the movable electrode and the fixed electrode in the vertical direction is the same as the support body. 4. The sealing body according to claim 1, wherein at least one of the encapsulating bodies sandwiching the movable electrode and the fixed electrode from above and below is an electric conductor containing a semiconductor and is grounded. An acceleration sensor characterized by being present. 5. A movable electrode supported by a beam having elasticity and moved by an inertial force due to acceleration, and a fixed electrode facing each other with a minute gap between the movable electrode and the movable electrode, and the fixed electrode. In an acceleration sensor that measures acceleration by detecting a change in electrostatic capacitance between electrodes, the movable electrode and the fixed electrode are vertically etched from the surface of a semiconductor substrate to surround the movable electrode and the fixed electrode. A groove including the minute gap is dug in to form a part of the semiconductor substrate without being etched, and the movable electrode and the fixed electrode are insulated from each other by being left without being etched. Before including the minute gap, the support body that supports the minute gap and the movable electrode and the fixed electrode are sandwiched from at least one of the vertical direction. A sealing body for sealing the groove is provided, and the movable electrode is a wafer of the semiconductor substrate by the one-sided support body having a support axis in a direction perpendicular to a wafer surface of the semiconductor substrate. An acceleration sensor, which is suspended in a direction perpendicular to a surface of the wafer and is moved in a direction parallel to the wafer surface. 6. A movable electrode, which is supported by a beam having elasticity and moves by an inertial force due to acceleration, and a fixed electrode which has a minute gap between the movable electrode and faces each other, and the movable electrode and the fixed electrode. In an acceleration sensor that measures acceleration by detecting a change in electrostatic capacitance between electrodes, the movable electrode and the fixed electrode are vertically etched from the surface of a semiconductor substrate to surround the movable electrode and the fixed electrode. A groove including the minute gap is dug in to form a part of the semiconductor substrate without being etched, and the movable electrode and the fixed electrode are insulated from each other by being left without being etched. Before including the minute gap, the support body that supports the minute gap and the movable electrode and the fixed electrode are sandwiched from at least one of the vertical direction. A sealing body for sealing the groove is provided, wherein the movable electrode is located in the vicinity of the surface of the semiconductor substrate and has a supporting shaft in a direction parallel to the wafer surface of the semiconductor substrate. An acceleration sensor which is suspended in a direction perpendicular to the wafer surface, swings around the support shaft as a rotation center, and moves in a direction parallel to the wafer surface. 7. The acceleration sensor according to claim 1, 5 or 6, wherein the support is provided with an electronic circuit for detecting a change in the electrostatic capacitance. 8. The method according to claim 1, 5 or 6, wherein the groove is formed by engraving in a direction perpendicular to a wafer surface of the semiconductor substrate and in parallel with a semiconductor crystal axis 110 direction. Characteristic acceleration sensor. 9. The stopper according to claim 1, 5 or 6, wherein the semiconductor substrate is equipotential with the movable electrode and limits the movement of the movable electrode due to inertial force. An acceleration sensor characterized by being left in. 10. The acceleration sensor according to claim 9, wherein the stopper has a protrusion.