JP3326905B2 - Semiconductor acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor, and more particularly to an acceleration sensor suitable for vehicle body control, engine control, airbag control, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art The performance required of an acceleration sensor for an automobile is to detect a relatively low level of acceleration (0 to ± 1 G) at a low level of frequency (0 to 100 Hz) with high accuracy. Here, 1G is a unit of acceleration, which represents 9.8 m / sec ² .

Conventionally, as such an acceleration sensor, a piezoelectric type using a piezoelectric effect, a magnetic type using a differential transformer, a semiconductor strain gauge type using a semiconductor fine processing technology, and a static type have been conventionally used. The capacitance type and the like are widely known. Among them, the semiconductor type is considered to be the most promising as a system which can detect a low acceleration level and a low frequency level with high accuracy, is inexpensive and is suitable for mass production.

The capacitance type is compared with the strain gauge type,
It has the feature of high detection sensitivity. A conventional example of such a capacitive acceleration sensor is disclosed in
FIG. 66 shows one disclosed in Japanese Patent No. 4570.
In FIG. 66, the detection unit of the capacitance type acceleration sensor is formed by directly bonding three silicon substrates 300, 301 and 302 via a thermal oxide film 303 which is an insulating film and joining them. On the silicon substrate 300, a silicon beam (beam-like portion) 304 and a movable electrode 305 are formed in advance by etching before joining. Further, fixed electrodes 306 and 307 made of polysilicon are also formed on the silicon substrates 301 and 302 before bonding. The movable electrode 305 having the weight function is supported by the silicon beam 304, and the movable electrode 305 and the fixed electrodes 306, 3
The size of the gap between the gap and the gap changes from 07 to 07. That is, the capacitance of the gap changes in accordance with the acceleration acting on the detecting portion, and the change is taken out to an external electronic circuit through the bonding pad 308 to detect the acceleration.

[0005]

However, in the capacitance type acceleration sensor having such a configuration, a sophisticated processing technique required for forming a beam by processing the silicon substrate itself by about 100 to 200 μm is required. And the manufacturing cost increases.

That is, a total of three silicon substrates, one silicon substrate forming the movable electrode and two silicon substrates forming the fixed electrode, are required, and it is difficult to reduce the cost. Further, since the silicon substrates must be joined via the thermal oxide film, there is a thermal limitation in the process. Furthermore, since the detection of the acceleration is performed by the change of the capacitance, the area of the electrode forming the capacitance cannot be made smaller than the lower limit of the measurement, and the miniaturization cannot be expected.

It is an object of the present invention to provide a novel semiconductor acceleration sensor having a small number of substrates and a method for manufacturing the same.

[0008]

According to a first aspect of the present invention, there is provided a semiconductor substrate, a movable electrode having a beam structure disposed at a predetermined distance above the semiconductor substrate, and a movable electrode of the movable electrode on the semiconductor substrate. and a fixed electrode of the impurity diffused layers formed on both sides, so as to detect the acceleration in the change in current between the fixed electrode caused by the displacement of the movable electrode due to the action of the acceleration, the horizontal direction on the semiconductor substrate To
When acceleration is applied, the inversion layer area between the fixed electrodes
The current changes due to the change in the area of the
The semiconductor acceleration sensor so as to output as its gist.

According to a second aspect of the present invention, there is provided a semiconductor device, comprising:
Beam structure arranged at a predetermined interval above the conductor board
Of the movable electrode of the semiconductor substrate
Fixed electrodes consisting of impurity diffusion layers formed on both sides
The displacement of the movable electrode caused by the acceleration.
The acceleration is detected by the change in the current between the fixed electrodes.
Then, the semiconductor substrate is located at a portion facing the movable electrode.
The movable electrode in at least a region where there is no fixed electrode.
The gist is a semiconductor acceleration sensor having a lower electrode having the same potential as that of the semiconductor acceleration sensor .

[0010] The invention according to claim 3, in claim 2, prior
The gist of the present invention is a semiconductor acceleration sensor having an insulating film on a semiconductor substrate .

According to a fourth aspect of the present invention, a semiconductor substrate and the semiconductor substrate are provided.
Beam structure arranged at a predetermined interval above the conductor board
Of the movable electrode of the semiconductor substrate
Fixed electrodes consisting of impurity diffusion layers formed on both sides
The displacement of the movable electrode caused by the acceleration.
The acceleration is detected by the change in the current between the fixed electrodes.
And the movable electrode is arranged in two horizontal axes with respect to the semiconductor substrate.
And is located above the fixed electrodes.
Is oblique from one fixed electrode to the other.
In the opposite direction
The gist is a pair of semiconductor acceleration sensors.

According to a fifth aspect of the present invention, there is provided a semiconductor device, comprising:
Beam structure arranged at a predetermined interval above the conductor board
Of the movable electrode of the semiconductor substrate
Fixed electrodes consisting of impurity diffusion layers formed on both sides
The displacement of the movable electrode caused by the acceleration.
The acceleration is detected by the change in the current between the fixed electrodes.
The movable electrode is three-dimensionally movable;
And four electrode parts protruding in directions orthogonal to each other.
The fixed electrode is arranged corresponding to the electrode part.
The gist is a semiconductor acceleration sensor .

[0013]

According to a sixth aspect of the present invention, there is provided a semiconductor substrate, a gate oxide film disposed on the semiconductor substrate, a lower gate electrode disposed on the gate oxide film, and a lower gate electrode on the semiconductor substrate. A fixed electrode comprising an impurity diffusion layer formed on both sides in a self-aligned manner with respect to the lower gate electrode; and a movable upper gate electrode having a beam structure disposed above the semiconductor substrate at a predetermined distance from the lower gate electrode. And a portion of the semiconductor substrate facing the movable upper gate electrode , wherein the lower gate electrode is formed.
The movable upper gate electrode,
The gist of the present invention is a semiconductor acceleration sensor comprising: a lower electrode having an equal potential; and a sensor configured to detect an acceleration by a change in a current between the fixed electrodes caused by a displacement of the movable upper gate electrode caused by the action of acceleration.

[0015]

[0016]

[0017]

According to the semiconductor acceleration sensor of the present invention, when acceleration is applied to the semiconductor substrate in the horizontal direction,
The change in the area of the inversion layer region between the two fixed electrodes
The current changes and the acceleration is detected.

[0018]

[0019]

The invention of claim 2 is, the lower electrode is disposed at least without the fixed electrode area in the variable dynamic electrode facing portion. Since the potential of the lower electrode is equal to the potential of the movable electrode, the electrostatic force generated between the semiconductor substrate and the movable electrode can be minimized .

According to a third aspect of the present invention, in the second aspect , by providing an insulating film on the semiconductor substrate, even when the sensor function is checked, short-circuit due to discharge between the electrodes or contact between the electrodes does not occur.

[0022] A fourth aspect of the present invention, it is detected that the variable dynamic electrode is moved in the horizontal two-axis directions with respect to the substrate.

Claims5The invention of, PossibleThe moving electrode is three-dimensional
It moves and its movement is detected. In other words, with one element
Three-dimensional acceleration is detected. Claim6Invention is movable
A capacitor is composed of the upper gate electrode and the lower gate electrode.
Formed on the gate oxide film, lower gate electrode, and fixed electrode.
A field effect transistor is formed. And movable
The upper gate electrode is displaced by acceleration and the capacitor
The capacitance of the transistor changes and the inversion layer of the transistor is marked.
The applied electric field strength changes. As a result, the acceleration
Detected as a change in the drain current of the effect transistor
It will be. Also, the part facing the movable upper gate electrodeso
A region where the lower gate electrode is not formedTo
A lower electrode is disposed, and a lower electrode, a movable upper gate electrode,
To make the semiconductor substrate and the movable upper gate
Electrostatic force generated between the poles can be minimized.
Wear.

[0024]

[0025]

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a semiconductor acceleration sensor according to the present embodiment. FIG. 2 shows an AA cross section of FIG.
FIG. 3 shows a BB cross section of FIG. P-type silicon substrate 1
An insulating film 2 is formed thereon, and the insulating film 2 is made of SiO ₂ , Si
Consisting of ₃ N _4, and the like. On the P-type silicon substrate 1, a rectangular region without the insulating film 2, that is, a void 3 is formed (see FIG. 1). A movable electrode 4 having a double-supported beam structure is arranged on the insulating film 2 so as to bridge the gap 3. The movable electrode 4 is made of polysilicon extending linearly in a strip shape. The P-type silicon substrate 1 and the movable electrode 4 are insulated by the insulating film 2.

The gap 3 in the lower part of the movable electrode 4
Is formed by etching a part of the insulating film 2 as a sacrificial layer. In the etching of the sacrificial layer, an etchant that does not etch the movable electrode 4 but etches the insulating film 2 that is the sacrificial layer is used as an etchant.

An interlayer insulating film 5 is disposed on the insulating film 2, and a movable electrode 4 is formed on the interlayer insulating film 5 through a contact hole 7.
Aluminum wiring 6 is provided for electrical connection to the device. In FIG. 3, fixed electrodes 8 and 9 made of an impurity diffusion layer are provided on both sides of movable electrode 4 on P-type silicon substrate 1.
The fixed electrodes 8 and 9 are formed on the P-type silicon substrate 1.
Formed by introducing an N-type impurity into the substrate by ion implantation or the like.

The movable electrode (double-supported beam) 4 may be made of a heat-resistant metal such as tungsten in addition to polysilicon. As shown in FIG. 1, wirings 10 and 11 made of an impurity diffusion layer are formed on a P-type silicon
Numerals 0 and 11 indicate N by ion implantation or the like into the P-type silicon substrate 1.
It is formed by introducing a type impurity. The fixed electrode 8 and the wiring 10 are electrically connected to each other, and the fixed electrode 9 and the wiring 11 are electrically connected to each other.

Further, the wiring 10 is provided in the contact hole 12
And is electrically connected to the aluminum wiring 13 through.
The wiring 11 is electrically connected to the aluminum wiring 15 via the contact hole 14. The aluminum wirings 13, 15 and 6 are connected to an external electronic circuit.

As shown in FIG. 3, an inversion layer 16 is formed between the fixed electrodes 8 and 9 on the P-type silicon substrate 1, and the inversion layer 16 applies a voltage to the movable electrode (both-supported beam) 4. This is caused by the application.

Next, a manufacturing process of the semiconductor acceleration sensor thus configured will be described with reference to FIGS. Here, the left side of the drawing shows the sensor, and the right side shows the transistor steps required for the processing circuit.

As shown in FIG. 4, a P-type silicon substrate 17 is formed.
Are prepared and N-type diffusion layers 18, 19, 20, and 21 serving as source / drain wiring portions of a sensor or a transistor are formed by ion implantation or the like through a photolithography process.

Then, as shown in FIG. 5, an insulating film 22 part of which serves as a sacrificial layer is formed in the sensor fabrication portion. still,
At this time, after the insulating film 22 is formed over the entire substrate, the insulating film over the transistor formation portion may be removed.

Further, as shown in FIG. 6, a gate oxide film 23 is formed on the transistor fabrication portion by gate oxidation. Then, as shown in FIG. 7, a polysilicon film is formed, and the movable electrode 24 of the sensor and the gate electrode 25 of the transistor are patterned by a dry etching or the like through a photolithography process.

Subsequently, as shown in FIG. 8, in order to form a fixed electrode of the sensor comprising an N-type diffusion layer, the openings 26, 27 are formed. In addition, openings 29 and 30 are formed by a resist 28 through a photolithography process in order to form the source and drain of the transistor.

Further, impurities are introduced from the openings 26 and 27 of the insulating film 22 and the resist 28 and the openings 29 and 30 of the resist 28 to the movable electrode 24 and the gate electrode 25 in a self-aligned manner by ion implantation or the like. As shown in FIG. 9, fixed electrodes 31, 32 of a sensor comprising an N-type diffusion layer are provided.
Source / drain regions 33 and 34 of the transistor are formed.

Next, as shown in FIG.
4. An interlayer insulating film 35 for electrically insulating the gate electrode 25 and the aluminum wiring is formed. Then, as shown in FIG. 11, the wiring diffusion layers 18, 19, 2
Contact holes 36, 37, 38, 39 for electrically connecting 0, 21 to the aluminum wiring are formed through a photolithography process.

Further, as shown in FIG. 12, aluminum as an electrode material is formed into a film, and aluminum wirings 40, 41, 42, 43 and the like are formed through a photolithography process. Then, as shown in FIG. 13, a part of the interlayer insulating film 35 and a sacrifice layer which is a part of the insulating film 22 are etched.

Thus, the process of manufacturing the transistor type semiconductor acceleration sensor is completed. Next, the operation of the acceleration sensor will be described with reference to FIG. When a voltage is applied between the movable electrode 4 and the silicon substrate 1 and between the fixed electrodes 8 and 9,
An inversion layer 16 is formed, and a current flows between the fixed electrodes 8 and 9. When the acceleration sensor receives acceleration and the movable electrode 4 is displaced in the Z direction (perpendicular to the substrate) shown in the drawing, the carrier concentration of the inversion layer 16 increases due to the change in the electric field intensity, and the current increases. Thus, the acceleration sensor can detect the acceleration by increasing or decreasing the amount of current.

As described above, in this embodiment, the insulating film 22 (sacrifice layer) is formed on the main surface of the P-type silicon substrate 17 (semiconductor substrate).
Is formed (first step), and a beam-shaped movable electrode 24 is formed on the insulating film 22 (sacrifice layer) (second step). And absolute
On both sides of the movable electrode 24 in the edge film 22 (sacrifice layer),
After the openings are formed in a consistent manner, impurities are diffused into the P-type silicon substrate 17 (semiconductor substrate) in a self-aligned manner with respect to the movable electrode 24 from the openings to form fixed electrodes 31 and 32 on both sides of the movable electrode 24. (3rd step), movable electrode 2
The insulating film 22 (sacrificial layer) under No. 4 was removed by etching (fourth step).

As a result, as shown in FIGS. 1 to 3, the P-type silicon substrate 1 (semiconductor substrate) and the P-type silicon substrate 1
A movable electrode 4 having a beam structure disposed above the (semiconductor substrate) at a predetermined interval, and formed on both sides of the movable electrode 4 in the P-type silicon substrate 1 (semiconductor substrate) in a self-aligned manner with respect to the movable electrode 4. Fixed electrode 8 made of a doped impurity diffusion layer,
9, the acceleration is detected by a change (increase / decrease) in the current between the fixed electrodes 8, 9 caused by the displacement of the movable electrode 4 due to the action of the acceleration.

As described above, the silicon substrate is not used as a material for forming the beam, but a thin film formed on the silicon substrate, for example, a highly doped impurity such as polysilicon or a heat-resistant metal. Material used. Therefore, it is possible to reduce the variation in the thickness of the beam for forming the movable electrode. Generally, when a one-point load is applied to a cantilever beam or a doubly supported beam, the change is inversely proportional to the cube of the beam thickness and the cube of the beam width. For this reason, the processing of the beam thickness requires much higher precision than the processing of the beam width. In this embodiment, the thickness of the beam is not controlled by etching as in the prior art, but by the deposited film thickness of the thin film, and the thickness controllability by this method is significantly better than that by etching. Therefore, controllability of the value of the change of the movable electrode when acceleration is applied to the movable electrode can be significantly improved.

Further, in order to form the beam, the material of the beam after forming the sacrificial layer in advance was formed, and after forming the shape of the beam, the sacrificial layer was removed by etching. Here, the term “sacrifice layer” generally refers to a thin film layer that is formed in advance for the purpose of removing and eliminating the movable portion in order to form the movable portion.
Therefore, it is possible to reduce the variation in the gap between the fixed electrode and the movable electrode. Generally, the inversion layer carrier concentration of a transistor is inversely proportional to the size of the gap,
Similarly, the current is inversely proportional to the size of the air gap. In the present embodiment, the size of the void is controlled by the thickness of the sacrificial layer, and the controllability of the film thickness by the method is good, so that the controllability of the current value between the fixed electrodes can be significantly improved. .

Further, a transistor structure is provided in which a pair of fixed electrodes are provided on a silicon substrate opposed to a beam forming a movable electrode in a vertical direction, and a current is generated between the fixed electrodes and the current is changed by displacement of the movable electrode. And
Therefore, it is possible to detect the displacement of the movable electrode from the current change between the fixed electrodes and measure the acceleration. In a transistor, the drain current is usually changed by changing the gate (corresponding to a movable electrode in this case) voltage. However, changing the gap between the gate and the substrate also changes the carrier concentration in the inversion layer. Change. Therefore, in the present embodiment, a change in the movable electrode that has undergone acceleration can be detected by the amount of current between the fixed electrodes. Since the current can be detected, the large electrode area required in the capacitance detection method is not required, and the size of the sensor is significantly reduced.

Further, the two fixed electrodes are formed of a diffusion layer which is formed in a self-aligned manner after forming the shape of the beam serving as the movable electrode. In such a method, a beam shape to be a movable electrode is formed, a sacrificial layer on a portion to be a fixed electrode is opened on a silicon substrate, and impurities are introduced into a portion to be a fixed electrode by an ion implantation method. Can be easily achieved. Therefore, it is easy to always form the movable electrode at the center between the fixed electrodes, and it is possible to improve the alignment accuracy in the manufacturing process.

Further, since these are all used in the IC fabrication process itself and diverted, the sensor structure can be formed in the IC fabrication process, and integration with the circuit can be extremely easily performed. (Second Embodiment) Next, a second embodiment will be described focusing on differences from the first embodiment.

FIG. 14 is a plan view of the acceleration sensor of this embodiment, FIG. 15 is a cross-sectional view taken along the line CC of FIG. 14, FIG. 16 is a cross-sectional view taken along the line DD of FIG. The EE section is shown.

In the first embodiment shown in FIG. 1, one doubly supported beam has a function as an elastic body, a function as a weight, and a function as an electrode. The movable electrode 47 made of polysilicon is composed of one beam portion 44 having a function as an elastic body and a function as a weight, and two electrode portions 45 and 46 having a function as a weight and a function as an electrode. Is formed.

On the P-type silicon substrate 48 under the electrode portions 45 and 46, fixed electrodes 49, 50 and 5 made of N-type diffusion layers are provided on both sides of the electrode portions 45 and 46 of the movable electrode 47.
1, 52 are formed. Each fixed electrode 49,
Reference numerals 50, 51, 52 denote diffusion layers 53, 54, 55,
56, and contact holes 57, 58,
Aluminum wiring 61, 62, 63, 64 via 59, 60
Is connected to The movable electrode 47 is in the contact hole 6
5 and connected to the aluminum wiring 66.

The etching region 67 indicates a region to be etched as a sacrifice layer in an insulating film (not shown). By performing sacrifice layer etching, the movable electrode 47 (polysilicon) has two fixed ends 68 and 69. Fixed at
The electrode portions 45 and 46 have a movable structure.

FIG. 15 shows that the fixed electrodes 49, 50, 51, 52 are formed longer on both sides of the figure than the electrode portions 45, 46. 16 and 17, between the electrode portions 45 and 46 and the substrate 48, and between the electrode portions 45 and 46 and the fixed electrode 49.
Inverted layers 70 and 71 are formed between the fixed electrodes 52 and 51 and between 49 and 50 by applying a voltage between the fixed electrodes 49 and 50, and between the fixed electrodes 49 and 50, 51 and 52. And a current flows between them.

Next, the operation of the acceleration sensor capable of two-dimensional detection will be described with reference to FIGS. When the acceleration sensor receives acceleration and the electrode portions (movable electrodes) 45 and 46 are displaced in the X direction (horizontal direction of the substrate) shown in FIG. 15, the area of the inversion layer region between the fixed electrodes (transistor) Of the fixed electrode 4)
The current flowing through the electrodes 9 and 50 decreases, and the current flowing through the fixed electrodes 51 and 52 increases. On the other hand, when the acceleration sensor receives acceleration and the electrode portions 45 and 46 are displaced in the Z direction shown in the figure, the carrier concentration of the inversion layers 70 and 71 decreases, so that the current simultaneously decreases.

As described above, the present acceleration sensor can detect a two-dimensional acceleration by increasing or decreasing two current amounts. As described above, in this embodiment, a pair of the movable electrode and the two fixed electrodes is provided in a pair, and the inversion layer region between the fixed electrodes is provided by the horizontal displacement, that is, the gate width increases on one side and decreases on the other side (eg And a movable electrode (beam) to form a cross shape). Therefore, it is possible to detect the acceleration in the horizontal and vertical directions of the beam from the increase and decrease of the two current amounts. That is, if the two currents change in phase, the beam will be displaced vertically, and conversely, if the two currents change in opposite phase, the beam will be displaced in the horizontal direction and the acceleration will be increased. Can be detected. This makes it possible to have a two-dimensional detection direction with one acceleration detection configuration. (Third Embodiment) Next, a third embodiment will be described focusing on differences from the first embodiment.

FIG. 18 is a plan view of the acceleration sensor of this embodiment. FIG. 19 shows a cross section taken along line FF of FIG. In the first embodiment shown in FIG. 1, one doubly supported beam has a function as an elastic body, a function as a weight, and a function as an electrode,
In the second embodiment shown in FIG. 14, one doubly supported beam has a function as an elastic body and a function as a weight, and a pair of electrode portions has a function of a weight and a function of an electrode. In the present embodiment, a movable electrode 76 made of polysilicon is formed by two beam portions 72 having a function as an elastic body, a mass portion 73 having a function as a weight, and electrode portions 74 and 75 having an electrode function. Is formed.

In order to enhance the function as a weight, a material serving as a weight, such as a metal, may be placed on the mass portion 73. Similarly, in this embodiment, the electrode portions 74 and 75
The fixed electrodes 78, 79, 80, and 81 made of an N-type diffusion layer are formed on both sides of the P-type silicon substrate 77 underneath. Each fixed electrode (diffusion layer) 78, 79, 8
0, 81 are connected to diffusion layers 82, 83, 84, 85 for wiring, and contact holes 86, 87, 88, 8
9 are connected to aluminum wirings 90, 91, 92, 93.

The movable electrode (polysilicon) 76 is connected to an aluminum wiring 95 via a contact hole 94. The etching region 96 indicates a region to be etched as a sacrifice layer in an insulating film (not shown). By performing sacrifice layer etching, the movable electrode (polysilicon) 7 is etched.
6 are fixed at two fixed ends 97 and the electrode portions 74 and 75
Becomes a movable structure.

In this embodiment, since the mass portion 73 is provided, the displacement of the movable electrode can be made larger than in the second embodiment, and the detection sensitivity can be increased. (Fourth Embodiment) Next, a fourth embodiment will be described focusing on differences from the third embodiment.

FIG. 20 is a sectional view of the acceleration sensor of this embodiment. The first embodiment shown in FIG. 1 and the second embodiment shown in FIG.
In the embodiment, the third embodiment shown in FIG. 18, a voltage difference between the movable electrode and the substrate other than the electrode functioning, for example, a beam or a mass portion is generated, so that an electrostatic force is inevitably generated.
When this electrostatic force is estimated, for example, when the voltage difference between the movable electrode and the substrate is 10 V and the gap is 0.5 μm, the electrostatic force is 1771 N per 1 m 2. It is about 80,000 times the force received by acceleration. Therefore, since the movable electrode is attracted to the substrate by a strong force, it is necessary to make the beam structure strong so that the beam does not contact the substrate. However, on the contrary, the displacement amount of the beam, that is, the movable electrode when receiving the acceleration is remarkably reduced, and it becomes difficult to detect the acceleration. To reduce the influence of the electrostatic force, it is necessary to reduce the area where the electrostatic force is generated.

For this purpose, as shown in FIG. 20, a lower electrode 98 for equipotential with the movable electrode 76 is provided on a movable portion which does not function as a movable electrode, for example, a silicon substrate 77 facing a beam or a mass portion. . The lower electrode 98
Of the movable electrode (polysilicon) 76, a silicon substrate 77 facing a portion of the movable electrode (polysilicon) having no function as an electrode (the lower substrate has no fixed electrode) is provided electrically separated from the fixed electrodes 78 to 81. Can be The lower electrode 98 is formed simultaneously with the wiring diffusion layer. Then, when detecting acceleration, the lower electrode 98 and the movable electrode 96 are connected by an external switch (not shown) to make them equal potential. As a result, the area where the electrostatic force is generated can be minimized.

As shown in FIG. 21, a weight 99 such as a metal Au having a large specific gravity is used to increase the displacement of the movable portion.
W or the like may be added on the mass part. (Fifth Embodiment) Next, a fifth embodiment will be described focusing on differences from the fourth embodiment.

In the fourth embodiment, the lower electrode 98 is provided and the potential of the movable electrode 76 is set to be equal to that of the movable electrode 76 to suppress the generation of electrostatic force. In the present embodiment, a potential difference is provided between the lower electrode 98 and the movable electrode 76 to reduce the electrostatic force. generate. As a result, the movable electrode 76 is displaced to generate a virtual acceleration, and the sensor function can be easily checked. At the same time, when the movable part is displaced in the Z direction shown in FIG. 20 due to acceleration during the sensor operation and the current between the fixed electrodes changes, the movable electrode 76 and the lower electrode 98 are returned so that the current returns to the original value. If the potential difference is reduced, the electrostatic force is reduced, and the movable electrode 76 is displaced in the direction opposite to the Z direction and returns to the original position.
If the electrostatic force (the potential difference between the movable electrode 76 and the lower electrode 98) is adjusted so that the current value between the fixed electrodes is always constant, the displacement amount of the movable electrode 76 when receiving acceleration is
It can be made very small, and the impact resistance becomes extremely large. In this case, the acceleration may be detected by a voltage change between the movable electrode 76 and the lower electrode 98. (Sixth Embodiment) Next, a sixth embodiment will be described focusing on differences from the second embodiment.

FIG. 22 is a perspective view of the acceleration sensor of this embodiment. This embodiment is a three-dimensional transistor type semiconductor acceleration sensor for detecting three-dimensional acceleration. The sensor unit 101 is disposed on the silicon substrate 100 such that the longitudinal direction of the beam is in the Y direction in the figure. The sensor unit 102 is arranged on the silicon substrate 100 such that the longitudinal direction of the beam is in the X direction in the figure.

That is, the movable electrode 115 having the electrodes 103 and 104 and the movable electrode 1 having the electrodes 105 and 106
16 and the fixed electrodes 107, 10
8, 109, 110, 111, 112, 113, 114
Are formed. Other lower electrodes, insulating layers, aluminum wiring, contact holes and the like are omitted. As described above, the sensor unit 101 includes the electrodes 107 and 108 and 1
The acceleration in the X and Z directions can be detected by increasing or decreasing the amount of current between 09 and 110. Further, the sensor unit 10
Reference numeral 2 denotes an increase or decrease in the current value between the electrodes 111 and 112 and between the electrodes 113 and 114, and the acceleration in the Y direction and the Z direction can be detected.

Accordingly, a three-dimensional acceleration sensor can be realized by arranging the two transistor-type semiconductor acceleration sensors shown in the second to fifth embodiments so as to be orthogonal to each other on the same silicon substrate. Therefore, three-dimensional acceleration can be detected on one silicon chip. (Seventh Embodiment) Next, a seventh embodiment will be described with reference to the drawings.

FIG. 23 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 24 shows a GG section of FIG. As shown in FIG. 24, an insulating film 118 is formed on the entire surface of the main surface of the P-type silicon substrate 117, and an insulating film 119 is formed on the insulating film 118. The insulating film 118 is a gate insulating film of the transistor, which reduces a leakage current on the substrate surface and suppresses a temporal change in transistor characteristics. Insulating film 118 and insulating film 119
Is made of SiO ₂ , Si ₃ N ₄ or the like. On the P-type silicon substrate 117, a region where the insulating film 119 is not provided, that is,
A void 120 is formed (see FIG. 23). A movable electrode 121 having a double-supported beam structure is arranged on the insulating film 119 so as to bridge the gap 120. The movable electrode 121 is made of polysilicon. Also, this movable electrode 1
Reference numeral 21 functions as a gate electrode of the MISFET. Here, the movable electrode 121 has electrode portions 157 and 158 protruding in the Y direction in FIG. 23, and the tip portions of the electrode portions 157 and 158 are formed obliquely. And this electrode part 15
7 and 158 are inclined, so that 2
The acceleration in the axial direction can be detected (detailed operation will be described later). The movable electrode 121 has bent portions 286 and 287, and the movable electrode 121 is movable in two axial directions (X and Y directions in FIG. 23) that are horizontal to the substrate 117.

The gap 120 of the insulating film 119 below the movable electrode 121 is formed by etching as a sacrificial layer. In this sacrifice layer etching, the insulating film 118 for protecting the movable electrode 121 and the substrate surface is not etched, and the insulating layer 1 serving as the sacrifice layer is not etched.
An etching solution for etching 19 is used. For example, a Si ₃ N ₄ film can be used as the insulating film 118, a SiO ₂ film can be used as the insulating film 119, and an HF-based liquid can be used as an etching solution.

The fixed electrodes 122, 123, 124, and 12 made of an impurity diffusion layer are formed on the P-type silicon substrate 117.
5 are formed, and the fixed electrodes 122, 123, 124,
Reference numeral 125 is formed by introducing an N-type impurity into the P-type silicon substrate 117 by ion implantation or the like.

The movable electrode (double-supported beam) 121 may be made of a metal having a high melting point such as dangsten, in addition to polysilicon. Also, fixed electrodes 122, 123, 124, 125
Are electrically connected to aluminum wirings 130, 131, 132, 133 via contact holes 126, 127, 128, 129. And the aluminum wiring 130,1
Reference numerals 31, 132, and 133 are connected to an external electronic circuit.

The fixed electrodes 122, 123 or 12
4, 125, the movable electrode 121, the gate insulating film 118, and the gap 120, a field effect transistor (MIS)
FET).

Therefore, when a voltage is applied to the movable gate electrode 121, the fixed electrode 1 on the P-type silicon substrate 117
22, 123 or 124, 125, the inversion layer 13
4 are formed, and the fixed electrodes 122, 123 or 124,
A drain current flows between 125.

Further, as shown in FIG.
A lower electrode 135 is provided on a P-type silicon substrate 117 facing a region (beam portion) excluding the electrode portions 157 and 158. The lower electrode 135 has the same potential as the movable electrode 121 to suppress the generation of electrostatic force.

Next, a manufacturing process of the semiconductor acceleration sensor thus configured will be described with reference to FIGS. As shown in FIG. 25, a P-type silicon substrate 136 is prepared,
A gate insulating film 137 is formed by CVD or the like. This is an insulating film that is not etched by the sacrificial layer etching solution.

Next, as shown in FIG. 26, the fixed electrodes 138 and 139 of the sensor made of an N-type diffusion layer are formed by a photolithography process, ion implantation, and the like. Is formed, and the transistor formation region of the circuit portion is removed by etching through a photolithography process.

Further, as shown in FIG. 27, a polysilicon film is formed, and after a photolithography process, a movable gate electrode 141 and a gate electrode 142 of a transistor in a circuit portion are formed by dry etching or the like.

Subsequently, as shown in FIG. 28, an opening is formed on both sides of the gate electrode 142 by using a resist 143 through a photolithography process in order to form a source / drain region of a transistor in a circuit portion formed of an N-type diffusion layer. Part 14
4,145 are formed.

Further, impurities are introduced into the gate electrode 142 of the transistor by ion implantation or the like in a self-aligned manner from the openings 144 and 145 on both sides of the gate electrode 142, and as shown in FIG. The source / drain regions 146 and 147 of the transistor made of are formed.

Next, as shown in FIG.
1. An interlayer insulating film 148 for electrically insulating the aluminum wiring from the gate electrode 142, the fixed electrodes 138 and 139, the source / drain regions 146 and 147 is formed. Then, as shown in FIG. 31, fixed electrodes 138 and 139 and source / drain regions 146 and 147 are formed on the interlayer insulating film 148.
Contact holes 149, 150, 151, 152 for electrically connecting each of them to an aluminum wiring are formed through a photolithography process.

Further, as shown in FIG. 32, aluminum as an electrode material is formed, and aluminum wirings 153, 154, 155, 156 and the like are formed through a photolithography process. Then, as shown in FIG. 33, a part of the interlayer insulating film 148 and a sacrificial layer which is a part of the insulating film 140 are etched.

Thus, the manufacturing process of the transistor type semiconductor acceleration sensor is completed. Next, the operation of the semiconductor acceleration sensor will be described with reference to FIGS. The movable electrode 121, the gap 120, the gate insulating film 118,
The fixed electrodes 122, 123, 124, and 125 form a field effect transistor.

The drain current I of the field effect transistor
d is

[0083]

(Equation 1)

(1) Here, μ is the carrier mobility, L, W,
Vth indicates a channel length, a channel width, and a threshold voltage of the field-effect transistor element, respectively, and Vg is a gate voltage. Ci is a movable electrode (gate electrode) 121.
And the gap 120, the gate insulating film 118, and the capacitance of the capacitor formed by the P-type silicon substrate 117. The combined capacitance is obtained by connecting the capacitance Cox by the gate oxide film and the capacitance Cgap by the gap in series. And is represented by the following equation.

[0085]

(Equation 2)

(2) The operation of the acceleration sensor capable of two-dimensionally detecting in the plane of the substrate will be described with reference to FIGS. 23, 34, 35, and 36. FIG. 34 is an enlarged view of the transistor portion of FIG.

In FIG. 34, the electrode portion 15 of the movable electrode 121
7, 158 each has a beveled tip,
Both fixed electrodes (source / drain diffusion layers) 122, 123
The width Wo of the inversion layer region is between them and between 124 and 125.

When the semiconductor acceleration sensor receives acceleration,
In the X direction (horizontal direction of the substrate) shown in FIG.
In the case where 1 is displaced, as shown in FIG. 35, an inversion layer region formed by the electrode portion 157 of the movable electrode 121 and the fixed electrodes 122 and 123, and an inversion layer formed by the electrode portion 158 of the movable electrode 121 and the fixed electrodes 124 and 125. The area of both regions increases, and the gate width Wo of the field-effect transistor becomes ΔW
Increases to W1, the source (fixed electrode 12
2) The drain current flowing between the drain (fixed electrode 123) and between the source (fixed electrode 124) and drain (fixed electrode 125) increases.

Here, when the semiconductor acceleration sensor receives acceleration and the electrode portions 157 and 158 of the movable electrode 121 are displaced in the Y direction shown in FIG. 34, as shown in FIG. And the area of the inversion layer region formed by the fixed electrodes 122 and 123 increases, and the gate width Wo of the field-effect transistor increases by ΔW to W2, so that the current flowing between the fixed electrodes 122 and 123 increases. or,
The electrode portion 158 of the movable gate electrode 121 and the fixed electrode 12
4, 125, the area of the inversion layer region is reduced, and the gate width Wo of the field effect transistor is reduced by ΔW to W3, so that the current flowing between the fixed electrodes 124, 125 is reduced.

The length of each source / drain diffusion layer is
In order to provide the linearity of the change in the drain current due to the change in the gate width, the change in the X and Y directions with respect to the acceleration is
It should be long enough. Table 1 shows changes in the drain current of each field-effect transistor including the case where the displacement is reversed in the X direction and the Y direction.

[0091]

[Table 1]

As shown in Table 1, when the movable electrode 121 was displaced in the X and Y directions,
The combination of changes in the drain current on the 58 side gives X,
It is possible to detect acceleration in two axes of Y.

Next, considering a case where the semiconductor acceleration sensor receives acceleration and the movable electrode 121 is displaced in the Z direction in FIG. 24, the capacitance Cgap formed by the movable electrode 121 and the semiconductor substrate increases, Since Ci increases according to the equation (2), the drain current of the transistor-type acceleration sensor increases according to the equation (1). Thus, Z
It becomes possible to detect the displacement in the direction. Therefore, FIG.
As shown in FIG. 7, by adding one X, Y gate electrode (electrode portion 159 and its corresponding fixed electrode) to the acceleration sensor capable of detecting the X and Y directions in FIG.
It is possible to detect acceleration in three axes in the X, Y, and Z directions. The electrode portion 159 sufficiently overlaps with the fixed electrode thereunder, so that the area of the inversion layer region does not change even if the movable electrode 121 is displaced in the X and Y directions in FIG.

Table 2 shows changes in the drain current of each field-effect transistor at that time.

[0095]

[Table 2]

As shown in Table 2, the gate (the electrode portion 15 of the movable electrode 121) is displaced in the X, Y, and Z directions.
7) side, the gate (electrode portion 158 of the movable electrode 121) side, and the gate (electrode portion 159 of the movable electrode 121) side change of the drain current change, the three-axis acceleration of X, Y, Z is set to one acceleration. It is possible to detect with an acceleration sensor, and it is possible to significantly reduce the size of the semiconductor acceleration sensor.

As an application of this embodiment, the gate electrode (the electrode portion 15 of the movable gate electrode 121) added in FIG.
9) shows an example in which the tip is not machined obliquely so that the gate width does not change with respect to displacement in the X and Y directions. May be used. Further, although the present embodiment has been described with a double-supported beam, a cantilever beam may be used. Further, in the present embodiment, the drain current in the saturation region of the equation (1) has been described as the current to be detected, but the drain current in the linear region may be used for detection.

As described above, in this embodiment, the movable electrode 121
Are movable in two horizontal axis directions with respect to the P-type silicon substrate 117, and the movable electrode 121 is provided with electrode portions 157, 158 extending in opposite directions.
8 is formed obliquely from one fixed electrode to the other fixed electrode with respect to a portion located above between the fixed electrodes.
Therefore, it can be detected that the movable electrode 121 has moved in the biaxial directions with respect to the substrate. (Eighth Embodiment) Next, an eighth embodiment will be described focusing on differences from the third embodiment.

FIG. 38 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 39 shows an HH cross section of FIG. In the first embodiment shown in FIG. 1, one doubly supported beam has a function as an elastic body, a function as a weight, and a function as an electrode. In the second embodiment shown in FIG. 14, one doubly supported beam is used. Has a function as an elastic body and a function as a weight, and a pair of electrode portions has a function of a weight and a function of an electrode. Also, FIG.
In the third embodiment shown in FIG.
A movable electrode made of polysilicon is formed by the beam portion, the mass portion having a weight function, and the electrode portion having an electrode function.

Here, in this embodiment, like the third embodiment, two beam portions 160, 1 having a function as an elastic body are provided.
A movable electrode 165 made of polysilicon is formed by 61, a mass portion 162 having a weight function, and electrode portions 163 and 164 having an electrode function. Here, FIG.
As shown in FIG. 9, concave portions 166 and 167 are formed in the two beam portions 160 and 161 having a function as an elastic body.
The beams 160 and 161 are thinned. Due to this reduction in thickness, the functions of the beams 160 and 161 as elastic bodies are enhanced. Similarly, in this embodiment, the electrode portions 163, 16
The fixed electrodes 169, 170, 171, 17 made of N-type diffusion layers are formed on both sides of the P-type silicon substrate
2 are formed. Each fixed electrode (diffusion layer) 1
69, 170, 171 and 172 are diffusion layers 17 for wiring.
3, 174, 175, and 176, and aluminum wirings 181, 182, 183, and 184 via contact holes 177, 178, 179, and 180.

The movable electrode (polysilicon) 165 is connected to an aluminum wiring 186 via a contact hole 185. The etching region 187 indicates a region of the insulating film to be etched as a sacrifice layer. By performing sacrifice layer etching, the movable electrode (polysilicon) 165 is fixed at two fixed ends 188 and 189, and the electrode portion 163 is formed. ,
164 becomes a movable structure.

As described above, in this embodiment, the movable electrode 165
Since the beam portions 160 and 161 which are a part of are formed to have a thin structure, the spring constant of the beam portions 160 and 161 can be reduced and the displacement of the movable electrode 165 can be increased as compared with the third embodiment. It is possible to increase the detection sensitivity. (Ninth Embodiment) Next, a ninth embodiment will be described with reference to the drawings.

FIG. 40 is an overall view of a field effect transistor type three-dimensional semiconductor acceleration sensor (hereinafter, referred to as a semiconductor acceleration sensor) of the present embodiment. Also, FIG.
1 shows a II section of FIG. 40, and FIG. 42 shows a JJ section of FIG.

The semiconductor acceleration sensor shown in FIGS. 40 to 42 is manufactured according to the following process. SiO ₂ , Si ₃ on a semiconductor substrate, ie, a silicon substrate 190
An insulating film 191 made of N ₄ or the like is formed, and a film made of polysilicon, an oxide-based material, or another metal-based material is formed on the insulating film 191. This film on the insulating film 191 is formed by a wet or dry process on the gate electrode portion 1 corresponding to the gate of the field effect transistor.
92, 193, 194, 195, beams 196, 197,
198, 199, mass part 200, anchor part 201,
02, 203, 204 and bent portions 205, 20
Movable electrode 20 of doubly supported structure comprising 6,207,208
9 is formed. The insulating film 191 is etched leaving the lower portions of the anchor portions 201, 202, 203, and 204 provided at the ends of the movable electrode 209 as shown in FIGS. 41 and 42, so that the gap 210 is formed. Then, the movable electrode 209 is shaped like a bridge on the insulating film 191. Here, this etching is called sacrificial layer etching, and the movable electrode 209 is not etched as an etchant, and the insulating film 191 which is a sacrificial layer formed under the movable electrode 209 is selectively etched. An etchant is used.

As shown in FIGS. 40 and 42, a silicon substrate 190 has a fixed electrode 211 corresponding to a source and a drain of a field effect transistor formed of an impurity diffusion layer.
212,213,214,215,216,217,2
18 are formed. Therefore, the gate electrode portion 192 and the fixed electrodes 211 and 212, and the gate electrode portion 193 and the fixed electrode 2
13, 214, the gate electrode portion 194 and the fixed electrode 215,
216, gate electrode portion 195 and fixed electrodes 217, 218
Are acceleration detection units.

As shown in FIGS. 40 and 41, the beam portions (beam portions 196 to 199, bent portion 205) of movable electrode 209 are provided.
To 208), a lower electrode 219 is provided on the silicon substrate 190. The lower electrode 219 has the same potential as the movable electrode 209 to suppress the generation of electrostatic force.

Such semiconductor acceleration sensors are all
Since it is manufactured by the C manufacturing process itself and by diversion, the sensor structure can be formed in the IC manufacturing process, and integration with the circuit is significantly facilitated.

The semiconductor acceleration sensor manufactured as described above has the following configuration. That is, the movable electrode 209
Gate electrode sections 192, 194 and 1 in the acceleration detection section of FIG.
As shown in FIG. 40, 93 and 195 are arranged so as to be orthogonal to each other with the mass part 200 as the center.
The anchor portions 201 and 20 are formed by four beams as shown in FIG.
2,203,204. The anchor portions 201, 202, 203, and 204 are connected to an external electronic circuit via aluminum wiring (not shown). Each of the beam portions 196, 197, 198, and 199 is provided with bent portions 205, 206, 207, and 208 in the middle so that the mass portion 200 is given three-dimensional degrees of freedom. Thereby, one element (element) can provide degrees of freedom in the X-axis direction, the Y-axis direction, and the Z-axis direction,
It is possible to detect acceleration acting in three dimensions.

Therefore, the semiconductor acceleration sensor configured as shown in FIG. 40 operates as follows. That is, the beam 19
6, 197, 198, 199, when acceleration in the horizontal direction (X-axis direction, Y-axis direction) is applied to the semiconductor acceleration sensor, the mass portion 200 receives a force due to the horizontal acceleration, and displacement occurs. . Due to this displacement, two sets of gate electrode portions 192 (fixed electrodes 211 and 212) and gate electrode portions 194 (fixed electrodes 215 and 216) and a gate electrode portion 193 (fixed electrode 2
13, 214) and the gate electrode 195 (fixed electrode 21)
7, 218) causes a change in the gate width of each acceleration detection unit. as a result,
The horizontal acceleration acting on the semiconductor acceleration sensor is detected as a change in the drain current of the field effect transistor. Similarly, the mass part 200 is similar to the beam part 196,
Perpendicular to 197, 198, 199 (Z-axis direction)
When displacement occurs due to acceleration, the acceleration detection unit 2
Since the gap 210 between the pair of gate electrode portions 192, 194 and 193, 195 and the silicon substrate 190 changes,
The electric field strength changes. As a result, the vertical acceleration acting on the semiconductor acceleration sensor is detected as a change in the drain current of the field effect transistor. Each detected change in drain current is processed as an electric signal by an external circuit via an aluminum wiring (not shown) and calculated, whereby acceleration acting on three axes can be detected by one element (element). .

That is, if the acceleration detecting section is arranged as shown in FIG. 40, three-dimensional acceleration can be detected by one element. With respect to the method of detecting acceleration acting in three dimensions described in detail above, a theoretical analysis is performed according to FIG.

The drain current Id flowing through the acceleration detecting section constituted by the field effect transistor changes according to the above equation (1). Now, when acceleration acts on the semiconductor acceleration sensor of this embodiment and the mass part 200 is displaced in the X, Y, and Z directions as shown in FIG. 43, two sets of fixed electrodes 211 arranged orthogonally to each other. , 212 and between the fixed electrodes 215 and 216 and between the fixed electrodes 213 and 314 and between the fixed electrodes 217 and 218, the drain currents Id1, Id3, Id2 and Id4 are acceleration gx in the X direction and acceleration in the Y direction, respectively. The two sets of gate electrode portions 192 and 194 of the acceleration detection unit are obtained by the displacements Wgx and Wgy of the gate width of the acceleration detection unit due to gy and the acceleration gz in the Z direction.
And 193, 195 and the changed gap 210 (g = gz) between the silicon substrate 190 are expressed as follows.

[0112]

Id1 = (W-Wgy) α (g = gz) Id2 = (W-Wgx) α (g = gz) Id3 = (W + Wgy) α (g = gz) Id4 = (W + Wgx) α (g = gz) α (g = gz) = μCi (g = gz) (Vg−Vth (g = gz)) ² / 2L Here, Ci (g = gz) and Vth (g = gz) are the values of the acceleration detector. Two sets of gate electrode portions 192, 194 and 19
3, 195 and the capacitance of the field effect transistor which change in proportion to the gap 210 between the silicon substrate 190 and the threshold voltage, and α (g = gz) is Ci (g
= Gz) and Vth (g = gz).

Therefore, the following equation is derived from Equation 3.

[0114]

Wgx / W = − (Id2−Id4) / (Id2 + Id4) Wgy / W = + (Id1−Id3) / (Id1 + Id3) where the accelerations gx and gy in the X and Y directions are accelerations, respectively. Since the gate width displacements Wgz and Wgy of the detection unit are proportional to Wgz and Wgy, the acceleration gx in the X direction is calculated from Equation 4 by the drain currents Id2 and Id4 flowing through the fixed electrodes 213, 214 and 217 and 218 of the acceleration detection unit. The acceleration gy in the Y direction is proportional to the difference,
It can be seen that the difference is proportional to the difference between the drain currents Id1 and Id3 flowing through the respective elements 11, 212 and 215 and 216.

As described above, the acceleration in the X and Y directions can be easily separated from the acceleration in the Z direction. Further, when the acceleration in the Z direction is theoretically analyzed, the acceleration in the Z direction is different from the detection of the accelerations in the X and Y directions, and cannot be obtained from the ratio of the drain current Id flowing through the acceleration detection unit. By calculating the value of

[0116]

Id1 + Id2 + Id3 + Id4 = 4W.alpha. (G = gz) Table 3 shows the results of the above theoretical analysis.

[0117]

[Table 3]

Table 3 shows that when the acceleration acts on the semiconductor acceleration sensor of the present embodiment and the mass section 200 is displaced in the X, Y, and Z directions, the acceleration detection section 2 is arranged to be orthogonal to each other.
22, 223, 224, 225
It is an example showing how d changes. When the mass section 200 is displaced in the X direction, the acceleration detection section 223,
225, the drain current Id of the acceleration detectors 222 and 224 when displaced in the Y direction.
And the acceleration detection unit 22 when displaced in the Z direction
The increase and decrease of the drain current Id of 2,223,224,225 were shown. Here, if the acceleration acting on the semiconductor acceleration sensor acts in the opposite way to the above case, the increase / decrease of the drain current Id in the X, Y, Z directions is all reversed.

As described above, in this embodiment, two sets of the gate electrode portion and the fixed electrode of the acceleration detecting portion constituted by the field effect transistor are arranged so as to protrude in directions orthogonal to each other, and the movable electrode 209 is three-dimensionally arranged. It was made to move. Therefore, three-dimensional acceleration can be obtained with one element (element).

As an application example of the present embodiment, any support may be used for the beam structure as long as the mass portion 200 is three-dimensionally displaced. For this purpose, the balance of the movable portion of the movable electrode 209 is maintained in addition to the beam having the double-supported structure as in the present embodiment, the beam having the cantilever structure, or the two beams shown in the present embodiment. For this reason, more beams can be used. (Tenth Embodiment) Next, a tenth embodiment will be described focusing on differences from the first embodiment.

FIG. 44 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 45 shows a KK section of FIG. 44, FIG. 46 shows an LL section of FIG. 44, and FIG. 47 shows an MM section of FIG.

In this embodiment, fixed electrodes 8 and 9 are formed in a self-aligned manner on the P-type silicon substrate 1 at the center of the movable electrode 4 with respect to the movable electrode 4 having the double-supported beam structure. P below the movable electrode 4 without the electrodes 8 and 9
Lower electrodes 226 and 227 are formed on the silicon substrate 1. The diffusion electrodes 22 are provided on the lower electrodes 226 and 227.
8 and 229 are connected, and the diffusion electrodes 228 and 229 are connected to the aluminum wiring 23 through the contact holes 230 and 231.
2,233.

The lower electrodes 226 and 227 have the same potential as the movable electrode 4 to suppress the generation of electrostatic force. Other operations of the semiconductor acceleration sensor are the same as those of the first embodiment. (Eleventh Embodiment) Next, an eleventh embodiment will be described focusing on differences from the tenth embodiment.

FIG. 48 is a plan view of the semiconductor acceleration sensor of this embodiment. Also, FIG. 49 shows an NN section of FIG. 48, FIG. 50 shows an OO section of FIG. 48, and FIG. 51 shows a PP section of FIG.

In this embodiment, the P-type silicon substrate 1
An insulating film 234 is formed on the upper surface of the substrate. That is, the fixed electrodes 8 and 9 are formed in a self-aligned manner below the insulating film 234 in the central portion of the movable electrode 4, and the insulating film 23 below the movable electrode 4 without the fixed electrodes 8 and 9 is formed.
4, lower electrodes 226 and 227 are formed.
The lower electrodes 226 and 227 have diffusion electrodes 228 and 22 respectively.
9 are connected, and the diffusion electrodes 228 and 229 are connected to the aluminum wirings 232 and 233 through the contact holes 230 and 231.
Is connected to

The lower electrodes 226 and 227 have the same potential as the movable electrode 4 to suppress the generation of electrostatic force. or,
When a potential difference is applied between the lower electrodes 226 and 227 and the movable electrode 4 to generate a virtual acceleration by electrostatic force and perform a self-test of the sensor, the insulating film 234 causes a short circuit due to discharge between the electrodes or contact between the electrodes. Circuit damage,
Welding of the gate and the substrate can be prevented. (Twelfth Embodiment) Next, a twelfth embodiment will be described focusing on differences from the second embodiment.

FIG. 52 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 53 shows a QQ cross section of FIG. In this embodiment, the movable electrode 47 having a doubly supported structure is used.
A lower electrode 235 is formed on the P-type silicon substrate 48 below the beam portion 44. Diffusion electrode 236 is connected to lower electrode 235, and diffusion electrode 236 is connected to aluminum wiring 2 through contact hole 237.
38.

The lower electrode 235 is connected to the movable electrode 4
The generation of the electrostatic force is suppressed by making the potential equal to that of the beam portion 44 of FIG.
Other operations of the semiconductor acceleration sensor are the same as those of the second embodiment. (Thirteenth Embodiment) Next, a thirteenth embodiment will be described focusing on differences from the third embodiment.

FIG. 54 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 55 shows an RR cross section of FIG. In this embodiment, the movable electrode 76 having a double-supported beam structure is used.
A lower electrode 239 is formed on the P-type silicon substrate 77 below the beam portion 72 and the mass portion 73 of FIG. The diffusion electrode 240 is connected to the lower electrode 239,
0 is an aluminum wiring 242 through a contact hole 241
Is connected to

The lower electrode 239 is connected to the movable electrode 7.
The generation of electrostatic force is suppressed by making the beam portion 72 and the mass portion 73 of the sixth electric potential equal to each other. Other operations of the semiconductor acceleration sensor
This is the same as the third embodiment. (Fourteenth Embodiment) Next, a fourteenth embodiment will be described with reference to the drawings.

FIG. 56 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 57 shows an SS section of FIG. 56, FIG. 58 shows a TT section of FIG. 56, and FIG.
6 shows a U-U section.

As shown in FIGS. 57 to 59, a gate oxide film 244 is formed on a P-type silicon substrate 243. On the gate oxide film 244, a lower (fixed) gate electrode 245 is arranged.
45 is made of polysilicon. Further, the gate oxide film 2
An insulating film 246 and an insulating film 247 are formed on the gate electrode 44 and the lower gate electrode 245, and the insulating films 246 and 247
It is made of iO ₂ , Si ₃ N ₄ or the like. On the insulating film 246, a rectangular region without the insulating film 247, that is, a void 248 is formed (see FIG. 56). As shown in FIG. 56, the lower gate electrode 245 is
45a and the strip 24 extending from the rectangular portion 245a
5b, and a rectangular portion 2
45a are arranged, and the band-like portion 245b extends outside the gap portion 248. Further, a movable upper gate electrode 249 having a doubly supported structure is arranged on the insulating film 247 so as to bridge the gap 248. The movable upper gate electrode 249 is made of polysilicon.

The gap 248 of the insulating film 247 below the movable upper gate electrode 249 is formed by etching as a sacrificial layer. In etching the sacrificial layer, an etchant that does not etch the movable upper gate electrode 249 and the insulating film 246 but etches the insulating film 247 that is a sacrificial layer is used as an etchant. Here, in the case where the gate oxide film 244 is not etched by an etching solution for etching the insulating film 247 serving as a sacrificial layer,
The insulating film 246 may not be provided.

On the insulating film 247, an interlayer insulating film 250 is formed.
Is arranged thereon, and an aluminum wiring 252 for electrically connecting to the movable upper gate electrode 249 via the contact hole 251 is arranged thereon.

In FIG. 58, a P-type silicon substrate 243
Fixed electrodes 253 and 254 made of an impurity diffusion layer are formed on both sides of the band-like portion 245b of the lower gate electrode 245 on the upper side. The fixed electrodes 253 and 254 are formed by introducing an N-type impurity into the P-type silicon substrate 243 by ion implantation or the like in a self-aligned manner with respect to the band portion 245b of the lower gate electrode 245.
The lower gate electrode 245 and the movable upper gate electrode (double-supported beam) 249 may be made of a metal having a high melting point such as tungsten in addition to polysilicon.

Also, as shown in FIG.
3, 254 are electrically connected to aluminum wirings 257, 258 via contact holes 255, 256.
The aluminum wirings 257, 258 and 252 are connected to an external electronic circuit.

The fixed electrodes 253 and 254, the lower gate electrode 245, and the gate oxide film 244 constitute a field effect transistor. Therefore, as shown in FIG. 58, when a voltage is applied to lower gate electrode 245, inversion layer 259 is formed between fixed electrodes 253 and 254 on P-type silicon substrate 243, and fixed electrodes 253 and 254 are formed.
A drain current flows between them.

As shown in FIG. 56, lower electrodes 260 and 261 are formed on both sides of the rectangular portion 245a of the lower gate electrode 245 in the P-type silicon substrate 243 below the movable upper gate electrode 249. ing. Diffusion electrodes 262 and 263 are connected to lower electrodes 260 and 261, and diffusion electrodes 262 and 263 are connected to contact holes 2.
It is connected to aluminum wirings 266 and 267 via 64 and 265.

The lower electrodes 260 and 261 have the same potential as the movable upper gate electrode 249 to suppress the generation of electrostatic force. This semiconductor acceleration sensor detects a state in which the capacitance formed by the movable upper gate electrode 249 and the lower gate electrode 245 changes due to acceleration as an output change (drain current change) of the field effect transistor. I do. That is, the acceleration is detected by a change in output (drain current change) of the field-effect transistor caused by the displacement of the movable upper gate electrode 249 due to the action of the acceleration.

As described above, in this embodiment, the P-type silicon substrate 243 (semiconductor substrate), the gate oxide film 244 disposed on the P-type silicon substrate 243, and the gate oxide film 24
4, fixed electrodes 253 and 254 formed of impurity diffusion layers formed on both sides of the lower gate electrode 245 in the P-type silicon substrate 243 in a self-aligned manner with respect to the lower gate electrode 245. A movable upper gate electrode 2 having a beam structure, which is disposed above a P-type silicon substrate 243 with a predetermined distance from a lower gate electrode 245.
49 and lower electrodes 260 and 2 which are arranged in a portion of the P-type silicon substrate 243 facing the movable upper gate electrode 249 and have the same potential as the movable upper gate electrode 249.
61, and the acceleration is detected by a change in current between the fixed electrodes 253 and 254 caused by the displacement of the movable upper gate electrode 249 due to the action of the acceleration. That is,
The movable upper gate electrode 249 and the lower gate electrode 245 form a capacitor, and the gate oxide film 244, the lower gate electrode 245, and the fixed electrodes 253, 254 form a field effect transistor. Then, the movable upper gate electrode 249 is displaced by the acceleration, the capacitance of the capacitor changes, and the intensity of the electric field applied to the inversion layer of the transistor changes. As a result, the acceleration is detected as a change in the drain current of the field effect transistor. In addition, since the gate oxide film 244 is disposed on the inversion layer, the operation of the field effect transistor becomes stable. Further, lower electrodes 260 and 261 are disposed at portions facing movable upper gate electrode 249, and lower electrodes 260 and 261 are disposed.
And the movable upper gate electrode 249 are set at the same potential, so that the electrostatic force generated between the silicon substrate 243 and the movable upper gate electrode 249 can be minimized. (Fifteenth Embodiment) Next, a fifteenth embodiment will be described focusing on differences from the fourteenth embodiment.

FIG. 60 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 61 shows a cross section taken along line VV in FIG.
FIG. 62 shows a WW section in FIG. In this embodiment,
A lower electrode 268 extends on a P-type silicon substrate 243 below the movable upper gate electrode 249. Diffusion electrode 269 is connected to lower electrode 268, and diffusion electrode 269 is connected to aluminum wiring 271 via contact hole 270. (Sixteenth Embodiment) Next, a sixteenth embodiment will be described focusing on differences from the fourteenth embodiment.

FIG. 63 is a plan view of the semiconductor acceleration sensor of this embodiment. FIG. 64 shows a cross section taken along line XX of FIG. In this embodiment, the movable upper gate electrode 249 is
Two field effect transistors are arranged. The lower gate electrodes 272 and 273 are symmetrically arranged so as to partially overlap the movable upper gate electrode 249.

In FIG. 64, the movable upper gate electrode 24
9, a voltage determined according to the capacitance formed by the movable upper gate electrode 249 and the lower gate electrodes 272 and 273 and the gate oxide film capacitance is applied to the lower gate electrodes 272 and 273, The drain current of the effect transistor flows.

The present semiconductor acceleration sensor receives acceleration,
When the movable upper gate electrode 249 is displaced in the Z direction shown in FIG. 64, the gap between the movable upper gate electrode 249 and the lower gate electrodes 272 and 273 is reduced, so that the capacitance is increased. The drain current increases.

On the other hand, the present semiconductor acceleration sensor receives acceleration and moves in the X direction shown in FIG.
Is displaced, the overlap area between the lower gate electrodes 272 and 273 increases on one side and decreases on the other side. As a result, the movable upper gate electrode 249 and the lower gate electrode 27
The capacitance between 2,273 increases on the one hand and decreases on the other hand. Therefore, the drain current increases on one side and decreases on the other side. In this way, the present semiconductor acceleration sensor can detect a two-dimensional acceleration by increasing or decreasing two current amounts.

A lower electrode 274 extends from the P-type silicon substrate 243 below the movable upper gate electrode 249. Diffusion electrode 275 is connected to lower electrode 274, and diffusion electrode 275 is connected to aluminum wiring 277 via contact hole 276.

The lower electrode 274 has the same potential as the movable upper gate electrode 249 to suppress the generation of electrostatic force. (Seventeenth Embodiment) Next, a seventeenth embodiment will be described focusing on differences from the sixteenth embodiment.

FIG. 65 is a plan view of the semiconductor acceleration sensor of this embodiment. In this embodiment, the movable upper gate electrode 249
The lower electrodes 278, 2 are provided on both sides of the lower gate electrodes 272, 273 in the P-type silicon substrate 243 below the lower electrode.
79 are formed. Diffusion electrodes 280 and 281 are connected to the lower electrodes 278 and 279, respectively.
0, 281 are connected to aluminum wirings 284, 285 via contact holes 282, 283.

The lower electrodes 278 and 279 have the same potential as the movable upper gate electrode 249 to suppress the generation of electrostatic force. The present invention is not limited to the above embodiments. For example, each semiconductor acceleration sensor has been described for a P-type substrate. However, for an N-type substrate, the impurity of the diffusion layer may be P-type. Further, the description of the manufacturing process of the semiconductor acceleration sensor and the MOSFET for detection is simplified, and some steps (for example, an element isolation process) are omitted in the description so as not to obscure the properties of the entire process. It is clear that there is.

The beam may be a doubly supported beam or a cantilever beam. Further, in the third embodiment shown in FIG. 18, the number of beams is shown as two. However, more beams may be used in order to maintain the balance of the movable part.

[0151]

As described in detail above, according to the present invention,
An excellent effect of providing a novel semiconductor acceleration sensor having a small number of substrates and a method of manufacturing the same is exhibited.

[Brief description of the drawings]

FIG. 1 is a plan view of a semiconductor acceleration sensor according to a first embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 5 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 6 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 7 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 8 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 9 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 10 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 11 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 12 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 13 is a sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 14 is a plan view of a semiconductor acceleration sensor according to a second embodiment.

FIG. 15 is a sectional view taken along the line CC of FIG. 14;

FIG. 16 is a sectional view taken along line DD of FIG. 14;

FIG. 17 is a sectional view taken along line EE of FIG. 14;

FIG. 18 is a plan view of a semiconductor acceleration sensor according to a third embodiment.

FIG. 19 is a sectional view taken along line FF of FIG. 18;

FIG. 20 is a sectional view of a semiconductor acceleration sensor according to a fourth embodiment.

FIG. 21 is a sectional view showing an application example of the fourth embodiment.

FIG. 22 is a sectional view of a semiconductor acceleration sensor according to a sixth embodiment.

FIG. 23 is a plan view of a semiconductor acceleration sensor according to a seventh embodiment.

24 is a sectional view taken along line GG of FIG. 23.

FIG. 25 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 26 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 27 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 28 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 29 is a sectional view illustrating a manufacturing process of the semiconductor acceleration sensor.

FIG. 30 is a cross-sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 31 is a cross-sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 32 is a cross-sectional view showing a manufacturing process of the semiconductor acceleration sensor.

FIG. 33 is a cross-sectional view showing the manufacturing process of the semiconductor acceleration sensor.

FIG. 34 is a partially enlarged view of the semiconductor acceleration sensor.

FIG. 35 is a plan view for explaining the operation of the semiconductor acceleration sensor.

FIG. 36 is a plan view for explaining the operation of the semiconductor acceleration sensor.

FIG. 37 is a plan view of a semiconductor acceleration sensor.

FIG. 38 is a plan view of a semiconductor acceleration sensor according to an eighth embodiment.

FIG. 39 is a sectional view taken along line HH of FIG. 38;

FIG. 40 is a plan view of a semiconductor acceleration sensor according to a ninth embodiment.

FIG. 41 is a sectional view taken along the line II of FIG. 40;

FIG. 42 is a sectional view taken along the line JJ of FIG. 40;

FIG. 43 is a plan view for explaining the operation of the semiconductor acceleration sensor.

FIG. 44 is a plan view of a semiconductor acceleration sensor according to a tenth embodiment.

FIG. 45 is a sectional view taken along line KK of FIG. 44.

FIG. 46 is a sectional view taken along line LL of FIG. 44;

FIG. 47 is a sectional view taken along line MM of FIG. 44;

FIG. 48 is a plan view of a semiconductor acceleration sensor according to an eleventh embodiment.

FIG. 49 is a sectional view taken along line NN of FIG. 48;

FIG. 50 is a sectional view taken along line OO of FIG. 48;

FIG. 51 is a sectional view taken along line PP of FIG. 48;

FIG. 52 is a plan view of a semiconductor acceleration sensor according to a twelfth embodiment.

FIG. 53 is a sectional view taken along line QQ of FIG. 52;

FIG. 54 is a plan view of a semiconductor acceleration sensor according to a thirteenth embodiment.

FIG. 55 is a sectional view taken along line RR of FIG. 54;

FIG. 56 is a plan view of a semiconductor acceleration sensor according to a fourteenth embodiment.

FIG. 57 is a sectional view taken along the line SS in FIG. 56.

FIG. 58 is a sectional view taken along line TT of FIG. 56;

FIG. 59 is a U-U sectional view of FIG. 56.

FIG. 60 is a plan view of a semiconductor acceleration sensor according to a fifteenth embodiment.

61 is a sectional view taken along line VV of FIG. 60.

FIG. 62 is a sectional view taken along line WW of FIG. 60.

FIG. 63 is a plan view of a semiconductor acceleration sensor according to a sixteenth embodiment.

FIG. 64 is a sectional view taken along line XX of FIG. 63;

FIG. 65 is a plan view of a semiconductor acceleration sensor according to a seventeenth embodiment.

FIG. 66 is a cross-sectional view showing a conventional semiconductor acceleration sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... P-type silicon substrate as a semiconductor substrate, 4 ... movable electrode, 8 ... fixed electrode, 9 ... fixed electrode, 17 ... P-type silicon substrate as a semiconductor substrate, 22 ... insulating film as a sacrificial layer, 24 ... movable electrode Reference numeral 31, 31 fixed electrode, 32 fixed electrode, 98 lower electrode, 117 P-type silicon substrate as a semiconductor substrate, 121 movable electrode, 157 electrode part, 1
58 ... electrode part, 166 ... recess, 167 ... recess, 192 ...
Gate electrode portion, 193: gate electrode portion, 194: gate electrode portion, 195: gate electrode portion, 209: movable electrode, 2
11 fixed electrode, 212 fixed electrode, 213 fixed electrode, 214 fixed electrode, 215 fixed electrode, 216 fixed electrode, 217 fixed electrode, 218 fixed electrode, 243
... P-type silicon substrate as a semiconductor substrate, 244 ... gate oxide film, 245 ... lower gate electrode, 249 ... movable upper gate electrode, 253 ... fixed electrode, 254 ... fixed electrode, 2
60 lower electrode, 261 lower electrode

Continuation of the front page (72) Inventor Tadashi Hattori 1-1-1, Showa-cho, Kariya-shi, Aichi, Japan Denso Co., Ltd. (72) Inventor Toshimasa Yamamoto 1-1-1, Showa-cho, Kariya, Aichi, Japan 72) Inventor Kazuhiko Kano 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture, Japan Nippon Denso Co., Ltd. JP-A-4-278464 (JP, A) JP-A-4-25764 (JP, A) JP-A-59-74682 (JP, A) JP-B-48-14877 (JP, B1) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01L 29/84 G01P 15/125

Claims (6)

(57) [Claims] 1. A fixed structure comprising: a semiconductor substrate; a movable electrode having a beam structure disposed at a predetermined distance above the semiconductor substrate; and an impurity diffusion layer formed on both sides of the movable electrode in the semiconductor substrate. And an electrode, wherein the acceleration is detected by a change in current between the fixed electrodes caused by the displacement of the movable electrode accompanying the action of acceleration, and when acceleration is applied to the semiconductor substrate in a horizontal direction,
A semiconductor acceleration sensor wherein the acceleration is detected by changing the current when the area of the inversion layer region between the fixed electrodes changes. 2. A fixed structure comprising: a semiconductor substrate; a movable electrode having a beam structure disposed at a predetermined interval above the semiconductor substrate; and an impurity diffusion layer formed on both sides of the movable electrode in the semiconductor substrate. And an electrode, wherein the acceleration is detected by a change in current between the fixed electrodes caused by the displacement of the movable electrode accompanying the action of acceleration, the semiconductor substrate, at least the fixed electrode of the portion facing the movable electrode A semiconductor acceleration sensor having a lower electrode having the same potential as that of the movable electrode in an area where no movable electrode exists. 3. The semiconductor acceleration sensor according to claim 2, further comprising an insulating film on said semiconductor substrate. 4. A fixed structure comprising: a semiconductor substrate; a movable electrode having a beam structure disposed at a predetermined distance above the semiconductor substrate; and an impurity diffusion layer formed on both sides of the movable electrode in the semiconductor substrate. And an electrode, wherein acceleration is detected by a change in current between the fixed electrodes caused by displacement of the movable electrode accompanying the action of acceleration, wherein the movable electrode is movable in two horizontal axis directions with respect to the semiconductor substrate. A semiconductor acceleration sensor characterized in that a portion located above the two fixed electrodes is formed obliquely from one fixed electrode to the other fixed electrode, and that there is a pair in the opposite direction. . 5. A fixed structure comprising: a semiconductor substrate; a movable electrode having a beam structure disposed at a predetermined interval above the semiconductor substrate; and an impurity diffusion layer formed on both sides of the movable electrode in the semiconductor substrate. And an electrode, wherein the acceleration is detected by a change in current between the fixed electrodes caused by displacement of the movable electrode due to the action of acceleration. The movable electrodes are three-dimensionally movable, and are orthogonal to each other. A semiconductor acceleration sensor having four electrode portions protruding in a direction in which the fixed electrodes are arranged, the fixed electrodes being arranged corresponding to the electrode portions. 6. A semiconductor substrate, a gate oxide film disposed on the semiconductor substrate, a lower gate electrode disposed on the gate oxide film, and lower gate electrodes on both sides of the lower gate electrode in the semiconductor substrate. A fixed electrode made of an impurity diffusion layer formed in a self-aligned manner with respect to a movable upper gate electrode having a beam structure disposed above the semiconductor substrate at a predetermined distance from the lower gate electrode; A portion facing the movable upper gate electrode in the above, disposed in a region where the lower gate electrode is not formed, comprising a lower electrode having the same potential as the movable upper gate electrode, the above-mentioned accompanying the action of acceleration A semiconductor acceleration sensor wherein acceleration is detected by a change in current between the fixed electrodes caused by displacement of a movable upper gate electrode.