JPH07174786A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To provide a semiconductor acceleration sensor with an improved yield. CONSTITUTION:An acceleration sensor substrate 1 is obtained by forming a surrounding fixed part 11 by machining silicon, an operation part 12 receiving force due to the acceleration at the center, and a thin flexible part 13 for connecting the fixed part 11 and the operation part 12, and by forming diffusion resistors Rx1-Rx4, Ry1-Ry4, and Rz1-Rz4 on the surface of the flexible part 13. A weight body 3 is connected to the operation part of the acceleration sensor substrate 1 and a pedestal 2 is joined to the fixed part 11 and further the pedestal 2 is joined to a bottom plate 4. A conductor film 31 is formed in advance on a surface opposing to the bottom plate 4 of the weight body 3 by metallization.

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.

[0002]

2. Description of the Related Art Acceleration sensors are used for acceleration detection in various applications such as collision detection of air bag systems of automobiles, attitude control of various devices, and industrial robots. Among accelerometers, diffusion resistance (gauge resistance) with piezoresistive effect using silicon single crystal substrate
The semiconductor acceleration sensor formed by forming can be mass-produced with excellent productivity by applying the manufacturing technology of the semiconductor sensor. In a semiconductor acceleration sensor chip, a semiconductor substrate is processed into a peripheral fixed portion, a central action portion that receives a force by acceleration, and a thin flexible portion that connects the fixed portion and the action portion. A plurality of diffusion resistors are formed in a predetermined pattern on the surface of the flexible portion.

A weight body is joined to the bottom surface of the working portion of the semiconductor acceleration sensor chip, and a pedestal is joined to the bottom surface of the peripheral fixing portion and is joined to the bottom plate through this pedestal. The weight body and the pedestal are obtained, for example, by processing one glass substrate. A groove is formed on the surface of the glass substrate in advance to separate the weight body part and the pedestal part, and this is joined to the bottom surface of the semiconductor acceleration sensor substrate and then cut from the back surface to form the weight body part and the pedestal part. Completely separated from each other (for example, Japanese Laid-Open Patent Publication No. 3-25535).
(See the official gazette).

In such a semiconductor acceleration sensor, when an acceleration is applied, an external force acts on the weight body and is transmitted to the acting portion, causing mechanical deformation of the flexible portion. Therefore, the weight body needs to be in a suspended state, and a predetermined gap is provided between the weight body and the bottom plate. The bottom plate also serves as a stopper when the weight body is displaced. Therefore, the width of the gap between the weight body and the bottom plate is set within a range in which the necessary movement of the weight body can be allowed and in which the sensor chip can be prevented from being destroyed by a large impact. For low gravitational acceleration measurements, those with small gaps, eg 10 μm or less, are desired.

[0005]

However, in the above-described conventional semiconductor acceleration sensor, when the gap between the weight body and the bottom plate becomes small, the weight of the acceleration sensor substrate is increased in the step of joining the acceleration sensor substrate to the bottom plate through the pedestal. At the same time, the bottom of the weight body is firmly joined to the bottom plate, which causes a defect. This is considered to be because the Coulomb force is generated in the joining process in addition to the small gap. That is, to join the acceleration sensor board to the bottom plate via the pedestal,
A so-called anodic bonding is used in which a DC voltage is applied between the sensor substrate and the bottom plate to apply temperature and pressure. In this anodic bonding process, an electrostatic charge is generated at the bottom of the weight body that is usually made of a glass substrate, and due to this electrostatic charge, the bottom of the weight body adheres to the bottom plate, and further temperature and pressure are applied. Therefore, they are fixedly joined. This is a major cause of reduction in manufacturing yield of semiconductor acceleration sensors for measuring small accelerations.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a semiconductor acceleration sensor capable of improving yield.

[0007]

In a semiconductor acceleration sensor according to the present invention, a semiconductor substrate has a peripheral fixed portion, a working portion that receives a force due to central acceleration, and a thin wall connecting the fixed portion and the working portion. And a bottom plate in which a bottom surface of a fixed portion of the acceleration sensor substrate is joined via a pedestal, and the acceleration sensor substrate. And a weight body having a conductor formed on the surface facing the bottom plate.

[0008]

According to the present invention, the conductor is formed on the surface of the weight body joined to the bottom surface of the working portion of the acceleration sensor substrate, the surface facing the bottom plate, so that the weight body is joined to the bottom plate in the step of anodic joining the pedestal. The problem of being fixed is prevented. It is considered that this is because the conductor provided on the bottom surface of the weight body acts as an antistatic film. Therefore, according to the present invention, it is possible to manufacture a sensor for low acceleration measurement, which has a small gap provided between the weight body and the bottom plate, with good yield.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are a plan view and a sectional view taken along the line AA 'of a semiconductor acceleration sensor according to an embodiment of the present invention. The acceleration sensor substrate 1 is formed by processing a silicon single crystal wafer, and has a thick fixing portion 11 in the periphery, a thick acting portion 12 in the center, and a thin flexible portion 13 between the fixing portion 11 and the acting portion 12. Are formed. The flexible portion 13 is the action portion 12
Is a part that undergoes mechanical deformation when it receives an external force due to acceleration.

On the surface of the flexible portion 13, diffusion resistances Rx1 to Rx4 for detecting a force component in the x direction, diffusion resistances Ry1 to Ry4 for detecting a force component in the y direction, and a force component in the z direction are provided. Diffusion resistors Rz1 to Rz4 for detection are arrayed in a pattern as shown. A three-dimensional acceleration can be detected by configuring a bridge circuit using these diffused resistors.

A pedestal 2 is joined to the bottom surface of the fixed portion 11 of the acceleration sensor substrate 1, and the pedestal 2 is further joined to the bottom plate 4. The weight body 3 is joined to the bottom surface of the acting portion 12 of the acceleration sensor substrate 1. The pedestal 2 and the weight 3 are preferably made of a material having the same thermal expansion coefficient as that of the acceleration sensor substrate 1, and a glass substrate is used, for example. In this embodiment, as will be described later, the pedestal 2 and the weight body 3 are originally formed by using integral borosilicate glass, and are separated after bonding. A silicon substrate is used for the bottom plate 4.

A conductor film 31 is formed on the bottom surface of the weight body 3, that is, the surface facing the bottom plate 4. The conductor film 31 is, for example, titanium or platinum metallized. Other metal films such as aluminum and gold may be used. A shallow groove 41 is formed on the surface of the bottom plate 4, and a width D (= several μm to 10 μm) that allows movement of the action portion 12 between the weight body 3 and the bottom plate 4.
) Is provided.

Next, a specific manufacturing process of the semiconductor acceleration sensor of this embodiment will be described with reference to FIGS. As shown in FIG. 2A, a diffusion resistance layer is formed on each surface of the silicon wafer 10 according to a normal process in each sensor chip region, and the back surface is etched by a wet etching method to form a ring-shaped flexible portion 13. To form. The alternate long and short dash line in FIG. 2 indicates a cutting position where a chip is separated later.

Separately from the silicon wafer 10, a glass substrate 20 having a separating groove 21 formed between a portion which becomes the weight body 3 and a portion which becomes the pedestal 2 is prepared. A conductor film 31 is formed by sputtering on the bottom surface of the portion of the glass substrate 20 that becomes the weight body 3. The glass substrate 20 is shown in FIG.
As shown in (a), the silicon wafer 10 is anodically bonded. Specific conditions for anodic bonding are, for example, a temperature of 300 to 5
00 ° C, applied voltage is 400 to 200 with the glass side being negative
Set to 0V. The conductor film 31 may be formed after the silicon wafer 10 and the glass substrate 20 are bonded together.

After that, the glass substrate 20 is cut from the back surface side along the groove 21 which is previously processed on the front surface, and the weight body 3 and the pedestal 2 are separated. This state is shown in chips.
When viewed from the bottom side of, it becomes as shown in FIG. As shown in the figure, a conductor film 31 is formed on the weight body 3. The pedestal 2 is divided into eight pedestal portions 21 to 28 by cutting. In this way, the sensor substrate in which the pedestal 2 and the weight body 3 are separated is shown in FIG.
As shown in (b), the silicon wafer 30 that will be the bottom plate 4 is anodically bonded. In the silicon wafer 30, a shallow groove 42 is previously formed in a portion of each sensor chip facing the weight body 3. The conditions for this anodic bonding are, for example, a temperature of 300 to 5
00 ° C., DC applied voltage 400 to 20 with glass side as negative
00V. Finally cut at the position indicated by the dashed line,
Separate each sensor chip.

According to this embodiment, even if the gap 42 between the weight body 3 of the sensor substrate and the bottom plate 4 is as small as several μm to 10 μm, the anodic bonding process for bonding the pedestal 2 to the bottom plate 4 is performed. The weight body 3 and the bottom plate 4 are not joined, and a high manufacturing yield can be obtained.

FIG. 4 is a cutaway perspective view of a semiconductor acceleration sensor according to another embodiment of the present invention. In the previous embodiment, the weight 3
While the conductor film 31 is formed on the bottom surface of the thin metal plate by metallization, the thin conductor plate 32 is formed on the bottom surface of the weight body 3 in this embodiment.
Is pasted. With this, the same effect as that of the previous embodiment can be obtained.

[0018]

As described above, according to the present invention, by providing the conductor on the surface of the weight body facing the bottom plate,
When the pedestal part is anodically bonded to the bottom plate, the weight body is not accidentally bonded to the bottom plate, and the yield of a particularly small semiconductor acceleration sensor can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a manufacturing process of the embodiment.

FIG. 3 is a drawing for explaining the manufacturing process of the embodiment.

FIG. 4 is a diagram showing a semiconductor acceleration sensor of another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor acceleration sensor substrate, 11 ... Fixed part, 12 ... Working part, 13 ... Flexible part, 2 ... Pedestal, 3 ... Weight body, 4 ... Bottom plate, 31 ... Conductor film, 42 ... Gap.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hitoshi Nishimura 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Ltd.

Claims (1)

[Claims] 1. A semiconductor substrate is processed into a peripheral fixed portion, a working portion that receives a force from a central acceleration, and a thin flexible portion that connects the fixed portion and the working portion, and the flexible portion is formed. An acceleration sensor substrate having a diffusion resistance formed on its surface, a bottom plate to which the bottom surface of the fixed portion of the acceleration sensor substrate is joined via a pedestal, and a small gap between the bottom surface of the action portion of the acceleration sensor substrate and the bottom plate. And a weight body having a conductor formed on a surface facing the bottom plate.