JPH06163934A - Semiconductor acceleration sensor and fabrication thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor acceleration sensor, and fabrication thereof, in which capacitances between a movable electrode and a pair of fixed electrodes can be equalized with reduced number of substrates. CONSTITUTION:A dielectric film is formed on the main surface o a P-type silicon substrate and a beam type movable electrode is formed thereon. Impurities are then diffused into the substrate while self-aligning with the movable electrode to form fixed electrodes on the opposite sides of the movable electrode and then the dielectric film underneath the fixed electrodes is removed by etching. The semiconductor acceleration sensor comprising the P-type silicon substrate 1, the movable electrode 4 of beam structure arranged above the substrate 1 through a predetermined gap, and the fixed electrodes 8, 9 formed of an impurity diffused layer on the opposite sides of the movable electrode 4 while being self-aligned therewith detects acceleration based on the variation (increase/ decrease) of capacitances between the movable electrode 4 and two fixed electrodes 8, 9 caused by displacement of the movable electrode 4 due to acceleration.

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 a semiconductor acceleration sensor suitable for vehicle body control, engine control, airbag control and the like and a method for manufacturing the same.

[0002]

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

By the way, as such an acceleration sensor, conventionally, a piezoelectric type utilizing a piezoelectric effect, a magnetic type utilizing a differential transformer, or a semiconductor type such as a semiconductor strain gauge type utilizing a fine processing technology of silicon or a static type is used. The capacitance type and the like are widely known. Among these, the semiconductor method is considered to be the most promising as a method that can detect the low acceleration level and the low frequency level with high accuracy and is inexpensive and suitable for mass production. In particular, the capacitance type has a feature that the detection sensitivity is large and the temperature characteristic is good as compared with the strain gauge type.

FIG. 16 shows a conventional example of such a capacitance type acceleration sensor disclosed in Japanese Patent Application Laid-Open No. 2-134570. In FIG. 16, the detection portion of the capacitance type acceleration sensor is composed of three silicon substrates 71, 72, 7
3 is directly bonded and joined through the thermal oxide film 74 which is an insulating film. A silicon beam (beam-shaped portion) is formed on the silicon substrate 71 by etching before joining.
75 and the movable electrode 76 are formed in advance. Further, fixed electrodes 77 and 78 made of polysilicon are formed in advance on the silicon substrates 72 and 73 before bonding. The movable electrode 76 having the function of a weight is supported by the silicon beam 75, and the gap between the movable electrode 76 and the fixed electrodes 77 and 78 is determined depending on the magnitude of the vertical acceleration acting on the silicon beam 75. The dimensions change. That is, the capacitance of the void changes according to the acceleration acting on the detection unit, and the change is taken out to the external electronic circuit via the bonding pad 79 to detect the acceleration.

[0005]

However, in the electrostatic capacitance type acceleration sensor having such a structure, there is a demand for advanced processing technology and an increase in manufacturing cost that are generated for processing the silicon substrate itself to form a beam. Was invited.

That is, a total of three silicon substrates, that is, one silicon substrate for forming the movable electrode and two silicon substrates for forming the fixed electrode are required, which makes it difficult to reduce the cost. Further, since the silicon substrates must be bonded to each other via the thermal oxide film, there is a problem that not only the thermal restrictions in the process are imposed but also the positioning accuracy of the movable electrode 76 and the fixed electrodes 77 and 78 is deteriorated. It was

Therefore, an object of the present invention is to provide a semiconductor acceleration sensor with a smaller number of substrates and capable of easily equalizing two electrostatic capacitances between a pair of a fixed electrode and a movable electrode, and a manufacturing method thereof. Especially.

[0008]

According to a first aspect of the present invention, a semiconductor substrate, a movable electrode having a beam structure which is arranged above the semiconductor substrate with a predetermined space therebetween, and both sides of the movable electrode in the semiconductor substrate. A fixed electrode composed of an impurity diffusion layer formed in self-alignment with the movable electrode, and two static electrodes between the movable electrode and the two fixed electrodes caused by displacement of the movable electrode due to the action of acceleration. The gist of the invention is a semiconductor acceleration sensor that detects acceleration based on a change in capacitance.

According to a second aspect of the invention, a first step of forming a sacrificial layer on a main surface of a semiconductor substrate, a second step of forming a beam-shaped movable electrode on the sacrificial layer, and a self-alignment with the movable electrode. A third step of diffusing impurities into a semiconductor substrate to form fixed electrodes on both sides of the movable electrode; and a change in two electrostatic capacitances between the movable electrode and the two fixed electrodes due to displacement of the movable electrode. A gist is a method of manufacturing a semiconductor acceleration sensor, which comprises a fourth step of etching and removing the sacrificial layer under the movable electrode so as to be detected.

[0010]

In the first aspect of the invention, when the acceleration acts, the movable electrode is displaced and the two capacitances between the movable electrode and the two fixed electrodes are changed. Acceleration is detected by the change in the capacitance.

In the second invention, the sacrificial layer is formed on the main surface of the semiconductor substrate in the first step, and the beam-shaped movable electrode is formed on the sacrificial layer in the second step. And the third
By the process, impurities are diffused in the semiconductor substrate in a self-aligning manner with respect to the movable electrode, and fixed electrodes are formed on both sides of the movable electrode. Further, in the fourth step, the sacrificial layer under the movable electrode is removed by etching, and it becomes possible to detect the change in the two electrostatic capacitances between the movable electrode and the two fixed electrodes due to the displacement of the movable electrode. As a result, the semiconductor acceleration sensor of the first invention is manufactured.

[0012]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a plan view of a semiconductor acceleration sensor. Further, FIG. 2 shows an AA cross section of FIG. 1, and FIG. 3 shows a BB cross section of FIG. An insulating film 2 is formed on the P-type silicon substrate 1, and the insulating film 2 is made of SiO ₂ , Si ₃ N _4, or the like. Further, a rectangular region without the insulating film 2, that is, a void portion 3 is formed on the P-type silicon substrate 1 (see FIG. 1). On the insulating film 2, a movable electrode 4 having a double-supported beam structure is arranged so as to bridge the void 3. The movable electrode 4 is made of rod-shaped polysilicon. Thus, the insulating film 2 insulates the P-type silicon substrate 1 and the movable electrode 4 from each other.

The void portion 3 of the insulating film 2 below the movable electrode 4 is formed by etching as a sacrificial layer. During the sacrifice layer etching, an etching solution that does not etch the movable electrode 4 but etches the insulating layer 2 that is the sacrifice layer is used as the etching solution.

An interlayer insulating film 5 is arranged on the insulating film 2, and a movable electrode 4 is formed on the interlayer insulating film 5 via a contact hole 7.
Aluminum wiring 6 for electrically connecting with is arranged. In FIG. 3, fixed electrodes 8 and 9 made of an impurity diffusion layer are formed on the P-type silicon substrate 1. The fixed electrodes 8 and 9 are formed by introducing N-type impurities into the P-type silicon substrate 1 by ion implantation or the like. It was formed.

The movable electrode (double-supported beam) 4 may be made of refractory metal such as tungsten instead of polysilicon. Further, as shown in FIG. 1, wirings 10 and 11 made of an impurity diffusion layer are formed on the P-type silicon substrate 1, and the wiring 1
0 and 11 are N by the ion implantation etc. to 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, and the fixed electrode 9 and the wiring 11 are electrically connected.

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

Next, a manufacturing process of such a semiconductor acceleration sensor will be described with reference to FIGS. First, FIG.
As shown in FIG. 5, a P-type silicon substrate 16 is prepared, and an N-type diffusion layer 17 which will be a wiring portion of a fixed electrode is formed by ion implantation or the like through a photolithography process. Then, as shown in FIG. 5, on the P-type silicon substrate 16, an insulating film 18 of which a part serves as a sacrifice layer is formed, and a polysilicon 19 is formed thereon.

Further, as shown in FIG. 6, the polysilicon 19 is processed through a photolithography process so as to form a movable electrode 20 having a doubly supported beam shape. Subsequently, as shown in FIG. 7, in order to form a fixed electrode made of an N-type diffusion layer, an opening 21 is formed in the insulating layer 18 in a self-aligned manner with respect to the movable electrode 20 through a photolithography process.

Then, as shown in FIG. 8, impurities are introduced into the opening 21 of the insulating layer 18 by self-aligned ion implantation or the like with respect to the movable electrode 20, and the fixed electrodes 22 and 23 made of N type diffusion layers. To form. Further, as shown in FIG. 9, an interlayer insulating film 24 for electrically insulating the movable electrode 20 and the aluminum wiring is formed on the P-type silicon substrate 16.

Next, as shown in FIG. 10, the interlayer insulating film 2
A contact hole 25 for electrically connecting the fixed electrodes 22 and 23 to the aluminum wiring is processed in 4 through a photolithography process. Then, as shown in FIG. 11, aluminum which is an electrode material is formed into a film, and an aluminum wiring 26 is formed through a photolithography process.

Then, as shown in FIG. 12, finally, a part of the interlayer insulating film 24 and a part of the insulating layer 18 are etched. As a result, the manufacturing process of the semiconductor acceleration sensor is completed.

Next, the operation of the semiconductor acceleration sensor will be described with reference to FIG. Movable electrode (double-supported beam) 4 and fixed electrode 8
Forms a capacitance C1. Further, the movable electrode 4 and the fixed electrode 9 form a capacitance C2.

When the present acceleration sensor receives acceleration and the movable electrode 4 is displaced in the X direction shown in the figure, the electrostatic capacitance C1 decreases and the electrostatic capacitance C2 increases conversely. On the other hand, when the movable electrode 4 is displaced in the Z direction shown in the figure due to the acceleration of this acceleration sensor, the capacitance C
1 and the capacitance C2 decrease at the same time. As described above, this acceleration sensor can detect a two-dimensional acceleration by increasing / decreasing the two electrostatic capacitances.

As described above, in this embodiment, the insulating film 18 (sacrificial layer) is formed on the main surface of the P-type silicon substrate 16 (semiconductor substrate).
Is formed (first step), the beam-shaped movable electrode 20 is formed on the insulating film 18 (sacrificial layer) (second step), and the movable electrode 20 is formed.
On the other hand, the fixed electrodes 22 and 23 are formed on both sides of the movable electrode 20 by diffusing impurities into the P-type silicon substrate 16 (semiconductor substrate) in a self-aligned manner (third step).
The insulating film 18 (sacrificial layer) under the layers 2 and 23 was removed by etching (fourth step).

As a result, as shown in FIGS. 1 to 3, a P-type silicon substrate 1 (semiconductor substrate) and a P-type silicon substrate 1 are used.
A movable electrode 4 having a beam structure, which is arranged above the (semiconductor substrate) with a predetermined gap, 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 consisting of a doped impurity diffusion layer,
9 is provided, and the acceleration is detected by the change (increase / decrease) in the two capacitances between the movable electrode 4 and the two fixed electrodes 8 and 9 caused by the displacement of the movable electrode 4 due to the action of the acceleration.

As described above, a silicon substrate is not used as a material for forming a beam, but a thin film formed on the silicon substrate, for example, polysilicon doped with impurities with high precision (or heat resistant metal Material) was 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 double-supported beam, the displacement is inversely proportional to the cube of the beam thickness and the beam width to the first power. Therefore, the processing of the thickness of the beam requires much higher accuracy than the processing of the width of the beam. In this embodiment, the thickness of the beam is not controlled by etching as in the past, but is controlled by the thickness of the deposited thin film, and the film thickness controllability by this method is significantly better than that by etching. Therefore, the controllability of the displacement value of the movable electrode when acceleration is applied to the movable electrode can be significantly improved.

In order to form the beam, a sacrificial layer was formed in advance, a beam material was formed, the beam shape was formed, and then the sacrificial layer was removed by etching. Here, the sacrificial layer generally refers to a thin film layer formed in advance for the purpose of finally removing and eliminating the sacrificial layer 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 capacitance of a parallel plate capacitor is inversely proportional to the size of the air gap. In this example, the size of the void is controlled by the film thickness of the sacrificial layer. Since the film thickness controllability by this method is good, the controllability of the capacitance value between the fixed electrode and the movable electrode can be improved. It can be significantly improved.

Further, a pair of fixed electrodes is provided on a silicon substrate facing in the direction perpendicular to the beam forming the movable electrode, and two electrostatic capacitances formed between one movable electrode and two fixed electrodes are formed. did. 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 capacitances. That is, if the two capacitances change in the same phase, the beam is displaced in the vertical direction, and if the two capacitances change in the opposite phase, the beam is displaced in the horizontal direction. Acceleration can be detected. This makes it possible to have a two-dimensional detection direction with one acceleration detection configuration.

Further, the two fixed electrodes are composed of a diffusion layer which is formed in a self-aligning manner after forming the shape of a beam to be a movable electrode. In such a method, a beam shape to be a movable electrode is formed, a sacrifice layer above a portion to be a fixed electrode on a silicon substrate is opened, and then an impurity is introduced into the portion to be a fixed electrode by ion implantation. Easily achieved with. Therefore, it is possible to easily match the two capacitances between the fixed electrode and the movable electrode when no acceleration is applied or when acceleration is not applied in the horizontal direction. This remarkably facilitates the design of an electronic circuit that detects a slight change in capacitance, and makes it possible to eliminate a compensation circuit such as an offset adjustment circuit. (Second Embodiment) Next, the second embodiment will be described focusing on the differences from the first embodiment.

In the first embodiment shown in FIG. 1, one double-supported beam has a function as an elastic body and a function as a weight. On the other hand, in the second embodiment shown in FIG. 13, a movable electrode 29 made of polysilicon is composed of four beam portions 27 having a function as an elastic body and three mass portions 28 having a function as a weight. Is formed. P at the bottom of the mass part 28
Fixed electrodes 31, 32 made of N-type diffusion layers are formed on both sides of the type silicon substrate 30 in a self-aligned manner with respect to the mass portion 28 of the movable electrode 29.

The fixed electrodes 31 and 32 are connected to wiring diffusion layers 33 and 34, and are connected to aluminum wirings 37 and 38 through contact holes 35 and 36. The movable electrode 29 is connected to the aluminum wiring 40 through the contact hole 39. The void portion 41 is a region of the insulating film (not shown) that is etched as a sacrificial layer. By performing the sacrificial layer etching, the movable electrode 2 is formed.
9 is fixed at four fixed ends 42, and the mass portion 28 has a movable structure.

In this embodiment, since the mass portion 28 is fixed at both ends, there is an effect that the warp of the movable electrode 29 after the sacrifice layer etching can be suppressed. (Third Embodiment) Next, the third embodiment will be described focusing on the differences from the first embodiment.

In FIG. 14, the movable electrode 45 made of polysilicon is formed by the two beam portions 43 that oscillate the function of the elastic body and the two mass portions 44 that have the function of the weight. In this case, the beam portion 43 also has a function as a weight at the same time. In this embodiment as well, the fixed electrodes 47 and 48 made of N type diffusion layers on both sides of the P type silicon substrate 46 below the mass portion 44 are similarly movable electrodes 45.
Is formed in a self-aligned manner with respect to the mass portion 44 of

The respective diffusion layers 47 and 48 are connected to wiring diffusion layers 49 and 50, and the contact holes 5 are formed.
It is connected to aluminum wirings 53 and 54 via 1, 52. The movable electrode 45 is connected to the aluminum wiring 56 through the contact hole 55.

The void 57 is a region of the insulating film (not shown) that is etched as a sacrificial layer. By performing the sacrificial layer etching, the movable electrode 45 is fixed at the two fixed ends 58, and the mass part 44 is formed. Becomes a movable structure. Although the mass portion 44 is fixed at one end in this embodiment, the lateral size of the movable electrode 45 after the sacrifice layer etching can be made smaller than that in the second embodiment. (Fourth Embodiment) Next, the fourth embodiment will be described focusing on the differences from the first embodiment.

As shown in FIG. 7, in this embodiment, a three-dimensional capacitance type semiconductor acceleration sensor for detecting three-dimensional acceleration is used. On the silicon substrate 59, the electrostatic capacity type semiconductor acceleration sensor of the first embodiment is arranged in a state of being extended in two orthogonal directions.

In other words, the first sensor section 60 has the silicon substrate 59 so that the longitudinal direction of the beam thereof becomes the Y direction in the figure.
The second sensor section 61 is arranged on the silicon substrate 59 so that the longitudinal direction of the beam thereof is the X direction in the drawing. That is, the movable electrodes 62 and 63 are arranged on the silicon substrate 59, and the fixed electrodes 64, 65, 66 and 67 are formed on the silicon substrate 59.
Other insulating films, aluminum wiring, contact holes, etc. are omitted.

As described above, the first sensor section 60 (semiconductor acceleration sensor) includes the movable electrode 62 and the fixed electrodes 64, 6.
Accelerations in the X and Z directions can be detected by increasing / decreasing the electrostatic capacitances C1 and C2 between 5. Furthermore, the second sensor unit 61 (semiconductor acceleration sensor) increases or decreases the electrostatic capacitances C3 and C4 between the movable electrode 63 and the fixed electrodes 66 and 67,
Accelerations in the Y and Z directions can be detected.

Therefore, a three-dimensional acceleration sensor can be realized by installing two semiconductor acceleration sensors on the same silicon substrate so as to be orthogonal to each other. The conventional acceleration sensor has a detection direction limited to one direction perpendicular to the silicon substrate, and in order to construct a three-dimensional acceleration sensor having a three-dimensional detection direction, three individual acceleration sensors have their respective axial directions mutually. Since it has to be arranged in three directions orthogonal to each other, that is, in the X, Y, and Z directions, the overall shape of the sensor is increased and the manufacturing cost is increased. However, in this embodiment, three-dimensional acceleration can be easily detected.

As described above, in this embodiment, two acceleration sensors are arranged on the same silicon substrate by rotating them by 90 degrees. Therefore, it is possible to detect three-dimensional acceleration on one silicon chip.

The present invention is not limited to the above-described embodiments. For example, although the semiconductor acceleration sensor has been described as a P-type substrate in each of the above-mentioned embodiments, the N-type substrate does not have impurities of P in the diffusion layer. Just make it into a mold.

Further, in the second embodiment shown in FIG. 13, three mass parts 28 which are a part of the movable electrode have been described. However, when the value of the electrostatic capacitance to be detected is increased, the number of the mass parts 28 is further increased. Just make it bigger. The same applies to the third embodiment shown in FIG.

[0044]

As described above in detail, according to the present invention,
An excellent effect that the two capacitances between the pair of fixed electrodes and the movable electrodes can be easily equalized with a smaller number of substrates is exerted.

[Brief description of 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.

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

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

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

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

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

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

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

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

FIG. 12 is a cross-sectional view showing the manufacturing process of the semiconductor acceleration sensor.

FIG. 13 is a plan view of a semiconductor acceleration sensor according to a second embodiment.

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

FIG. 15 is a perspective view of a semiconductor acceleration sensor according to a fourth embodiment.

FIG. 16 is a sectional view showing a semiconductor acceleration sensor according to a conventional technique.

[Explanation of symbols]

 1 P-type silicon substrate as a semiconductor substrate 4 Movable electrode 8 Fixed electrode 9 Fixed electrode 16 P-type silicon substrate as a semiconductor substrate 18 Insulating film as a sacrificial layer 20 Movable electrode 22 Fixed electrode 23 Fixed electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Kano 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd. (72) Inventor Shigeyuki Akita 1-1-1, Showa-cho, Kariya city, Aichi Nidec Incorporated (72) Inventor Masaru Hattori 1-1-1, Showa-cho, Kariya, Aichi Prefecture

Claims (2)

[Claims] 1. A semiconductor substrate, a movable electrode having a beam structure arranged above the semiconductor substrate at a predetermined distance, and formed on both sides of the movable electrode in the semiconductor substrate in a self-aligned manner with respect to the movable electrode. And a fixed electrode formed of an impurity diffusion layer, the acceleration being detected by a change in two capacitances between the movable electrode and the two fixed electrodes caused by displacement of the movable electrode due to the action of acceleration. A semiconductor acceleration sensor characterized in that 2. A first step of forming a sacrificial layer on the main surface of the semiconductor substrate, a second step of forming a beam-shaped movable electrode on the sacrificial layer, and a semiconductor substrate self-aligned with the movable electrode. A third step of diffusing impurities to form fixed electrodes on both sides of the movable electrode, and detecting changes in two electrostatic capacitances between the movable electrode and the two fixed electrodes due to displacement of the movable electrode. And a fourth step of etching away the sacrificial layer below the movable electrode.