JPH06258164A - Semiconductor pressure sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an inexpensive and highly reliable semiconductor pressure sensor excellent in temperature and static pressure characteristics by providing an annular support portion at the same time as forming a diaphragm on a sensor substrate. [Constitution] Simultaneously with the formation of a diaphragm, a sensor substrate provided with an annular supporting portion is anodically bonded to a supporting member having a through hole. [Effect] By providing the sensor substrate with the annular supporting portion that can be formed simultaneously with the etching of the diaphragm, the influence of temperature and static pressure of the sensor can be reduced. Because of anodic bonding,
The reliability of the joint surface is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor, and more particularly to a semiconductor which is excellent in zero-point temperature characteristics, has a small temperature hysteresis, and is capable of obtaining a stable signal with a good S / N ratio even at low sensitivity output. Regarding a pressure sensor.

[0002]

2. Description of the Related Art Conventionally known semiconductor pressure sensors use a diaphragm that responds to a pressure difference applied to both sides of the diaphragm. This diaphragm is composed of a sensor substrate made of a single crystal semiconductor substrate having a stress sensor arranged on one surface thereof. And, widely used stress sensors for this purpose exhibit piezoresistive properties such that the resistance of the stress sensor changes with the stress experienced by the sensor as the stress in the sensor substrate changes. Also, a circular cavity is formed in the other surface of the sensor substrate to form the diaphragm. Then, a support member is joined to the other surface of the sensor substrate.

A sensor substrate made of a square single crystal semiconductor substrate having a circular thin diaphragm is usually used. This is because many of such square sensor substrates are easily obtained by cutting or slicing a crystal wafer. Further, when the chip is bonded to the supporting member, a material having the same thermal expansion coefficient as that of the sensor substrate is used. This supporting member also has a hole formed in the wafer and is cut after being bonded to the semiconductor (silicon) wafer. It depends on what you have obtained. Then, the entire thick portion of the bonded portion is joined to the support member.

However, in the conventional semiconductor pressure sensor, since the shape of the joining region with the supporting member does not have symmetry with the shape of the diaphragm, when the ambient temperature of the semiconductor pressure sensor changes, the supporting member and the sensor substrate are not changed. Due to the difference in the materials between and, thermal strain occurs in the diaphragm. In addition, the temperature non-uniformity due to heat generation of the stress itself changes the offset voltage of the sensor itself. Furthermore, when the static pressure (the pressure common to both sides of the diaphragm) changes, an erroneous or false signal with the content of zero shift is generated. Due to this zero shift phenomenon, the electric signal must be compensated for the measurement of the differential pressure that requires high accuracy. In particular, in Japanese Patent Laid-Open No. 54137/1990, in order to relieve such stress caused by temperature change or static pressure application, a diaphragm is enclosed on the surface where the sensor substrate and the support member are joined, and a concentric joint is formed. It has an annulus. This bonding loop is provided by a photolithography technique, and silicon of the portion other than the bonding loop is etched by 1 to 2 μm to increase the bonding portion.

[0005]

According to the above-mentioned conventional technique, in order to form the bonding loop provided on the sensor substrate, a portion other than the bonding loop is etched by several μm to raise the connection portion. . In the case of such a method, it is necessary to perform the process of forming the joining ring zone in addition to the process of the diaphragm, and this alone requires two steps. Also, 2
When performing two steps (etching twice), a step is always formed in the sensor substrate by one process, so that the photolithography work becomes difficult when performing the second process. As described above, the above-mentioned conventional technique has a problem that the workability is deteriorated as the number of work steps is increased.

An object of the present invention is to form an annular support portion provided on a sensor substrate at the same time as etching of the diaphragm and then to join it to the support member, thereby reducing the number of steps and improving workability and cost reduction. In addition to reducing the stress when static pressure changes and temperature changes, it is possible to perform high-sensitivity differential pressure measurement with high sensitivity and small zero shift amount. It is to provide a high-priced semiconductor pressure sensor, and to provide a large amount of inexpensive semiconductor pressure sensors by forming a sensor substrate and a supporting member in a wafer state and performing steps of etching and anodic bonding.

[0007]

In order to achieve the above object, the sensor substrate is provided with an etching mask shape capable of forming an annular supporting portion together with the etching of the diaphragm, and when the etching is performed, the diaphragm is formed. At the same time, an annular supporting portion is formed. This is anodically bonded to a supporting member having a through hole. At this time, the sensor substrate is held by the supporting member via the annular supporting portion. In order to form a large number of pressure sensors, the sensor substrate and the supporting member are provided with a plurality of strain sensitive gauge elements and through holes, respectively, and are formed in a wafer state.

[0008]

In the semiconductor pressure sensor according to the present invention, the annular support portion provided on the sensor substrate can be formed at the same time when the diaphragm is etched, so that the work steps can be reduced and the workability is improved. Further, since the annular support portion of the sensor substrate is held by the support member, the change in stress caused by the change in temperature or static pressure is caused by the reduction of the area of the joint portion between the sensor substrate and the support member and the symmetry. However, it has less effect on the stress sensor on the diaphragm, which minimizes the zero shift signal due to changes in temperature and static pressure.

Further, by forming the sensor substrate and the supporting member in a wafer state, a large number of pressure sensors can be formed at one time.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view and a sectional view showing an embodiment of a semiconductor pressure sensor according to the present invention. Reference numeral 1 is a sensor substrate on which the strain sensitive gauge element 4 is formed, and 2 is a supporting member having a through hole 6 which becomes an inlet for pressure and the like later. On the surface of the sensor substrate 1, the strain sensitive gauge element 4 is provided around the diaphragm 3.
Individually arranged, the stress applied to the diaphragm 3 is sensed. The strain sensitive gauge element 4 is formed by doping impurities by, for example, ion implantation or thermal diffusion. Further, the strain sensitive gauge element 4 exhibits a piezoresistive characteristic, and its resistance changes depending on the stress experienced by the sensor. Further, a circular or polygonal cavity 8 is formed in the surface opposite to the surface on which the strain sensitive gauge element 4 is arranged.

On the other hand, the supporting member 2 has a circular pressure introducing port 6 near the center thereof and is connected to the surface opposite to the surface on which the strain sensitive gauge element 4 is arranged. Further, a circular ring-shaped support portion 5 that surrounds the diaphragm 3 and is concentric with the diaphragm 3 is provided in a bonding region that is a surface of the thick portion 9 of the sensor substrate 1 that surrounds the diaphragm 3 and faces the support member 2. The annular support portion 5 is formed simultaneously with the etching of the diaphragm 3, and the annular support portion 5 is formed in the same thickness as the diaphragm 3. Annular support 5
In the formation of, since it can be processed simultaneously with the shape of the diaphragm, that is, in one step, workability is improved and the number of steps can be reduced. Here, the sensor substrate 1 is held by the support member 2 in order to maintain the characteristics of the pressure sensor. The supporting member 2 is made of a material having a thermal expansion coefficient that is the same as or similar to that of the sensor substrate 1 so as not to affect the characteristics of the pressure sensor itself, and to maintain electrical insulation from the sensor substrate 1. An insulating material is used for. The sensor substrate 1 and the support member 2 are aligned at a predetermined position and anodic bonding is performed. Since the sensor substrate 1 and the support member 2 that are joined together are mechanically strongly joined together, they have the effect of improving reliability.

Next, an embodiment in which the sensor substrate 1 and the supporting member 2 configured as described above are formed in a wafer state will be described with reference to FIG.

Reference numeral 11 is a wafer on which a plurality of strain sensitive gauge elements 4 are formed, and 22 is a wafer on which a plurality of through holes 6 are formed. Similarly, these also take steps of etching and anodic bonding. When the sensor substrate 1 becomes a wafer,
By etching the wafer 11 of the sensor substrate 1, a large number of diaphragms 3 and the annular supporting portion 5 can be easily processed at one time, and workability is further improved. If this is anodically bonded to the wafer 22 as a supporting member, a semiconductor pressure sensor having uniform characteristics can be obtained. A large number of pressure sensors can be manufactured at a high yield and at a low cost by cutting them into dices with a dicer or a wire saw later.

More specifically, the material of the wafer 11 of the sensor substrate 1 is silicon which can be used in the semiconductor process. By utilizing the advantage of the semiconductor process, a plurality of strain sensitive gauge elements 4 are provided on the surface of the wafer 11 of the sensor substrate 1. An etching mask for forming the diaphragm 3 and the annular support portion 5 is provided on the opposite surface. The etching mask is previously provided with a SiO ₂ film, a SiN film, or the like. The exposed Si of this surface is processed by etching. In the case of etching, for example, anisotropic etching allows deep processing to be performed at high speed and with high precision, so that it is possible to suppress variations in the thickness of the diaphragm 3 and improve the yield. Moreover, according to the isotropic etching, the diaphragm 3
Since the corners of the sensor are rounded, the pressure resistance of the sensor can be improved. By the etching process, the annular support portion 5 can be processed simultaneously with the processing of the diaphragm 3, so that the workability is improved. Borosilicate glass having a thermal expansion coefficient similar to that of silicon is used as the material of the wafer 22 of the supporting member 2. Anodic bonding is used for these bonding. In the case of anodic bonding, the wafer 11 of the sensor substrate 1 and the supporting member 2
The wafers 11 of the sensor substrate 1 are bonded to the positive electrode of the DC high voltage, and the wafer 22 of the supporting member 2 is bonded to the negative electrode, respectively. In a high temperature atmosphere, for example, at 250 to 400 ° C., a high voltage, for example,
When a voltage 500～1500V, which is the material sodium oxide borosilicate glass wafer 22 of the support member ₂ (Na 2 O) is, 2Na +, O ₂ ^- ionized to each cathode,
Move to the anode. The O ₂ ⁻ that has moved to the anode side combines with silicon (Si) that is the material of the wafer 11 of the sensor substrate 1 to generate a silicon oxide film, and the wafer 11 of the sensor substrate 1
And the wafer 22 of the support member 2 are firmly bonded. Na is deposited on the cathode side. In the case of anodic bonding, since the bonded portion can be bonded uniformly and airtightly, a highly reliable pressure sensor can be manufactured with high yield.

In the semiconductor pressure sensor constructed as described above, since the joint region of the diaphragm 3 of the sensor substrate 1 and the supporting member 2 is concentric and symmetrical, the stress caused by the change in temperature or static pressure is The change has less influence on the strain-sensitive gauge element 4 on the diaphragm 3, whereby the zero shift signal caused by the change in temperature or static pressure can be minimized. In addition, the bonding area between the diaphragm 3 of the sensor substrate 1 and the support member 2 can be optimized by patterning on the sensor substrate 1 side. Further, as a method of joining the diaphragm 3 of the sensor substrate 1 and the supporting member 2 to each other, a method of extremely strong adhesive strength called anodic bonding is used.
Can be securely fixed. Furthermore, since the anodic bonding is performed between the wafers, the bonding parts of the individual semiconductor pressure sensors can be bonded uniformly, and the bonding parts of the individual semiconductor pressure sensors after dicing can be made uniform throughout. In addition, the yield of hermetic sealing is improved.

More specifically, since the bonding area between the diaphragm 3 of the sensor substrate 1 and the supporting member 2 is small, the thermal strain hardly affects the circular or polygonal diaphragm 3 when the temperature and static pressure change. Not because
Zero shift amount decreases. Further, the generation of thermal stress is small, and the stress generation due to the change in static pressure due to the difference in material between the sensor substrate 1 and the supporting member 2 is alleviated at the joint portion, so that the zero shift characteristic can be improved. Furthermore, if the area of the adhesive portion due to excessive pressure is determined so that the diaphragm 3 has the strength until it breaks, a very small joining area, that is, an annular support portion 5 having a very small area can be provided. Furthermore, since wafer-to-wafer bonding is possible, the assembly process can be simplified. The steps described above make use of the advantages of the semiconductor process steps, and can contribute to improvement of reliability and cost reduction.

As described above, in the semiconductor pressure sensor of this embodiment, the diaphragm 3 is etched on the surface of the thick portion 9 of the sensor substrate 1 that surrounds the circular or polygonal diaphragm 3 facing the support member 2. Since the annular supporting portion 5 is formed to reduce the number of joints between the sensor substrate 1 and the supporting member 2 and the joining by anodic bonding is performed between the wafers, stress during static pressure change and temperature change during temperature change. The stress can be relieved, and it is possible to provide low-cost and uniform characteristics with a small amount of zero shift. Furthermore, since the zero shift characteristic which requires a compensating circuit for an electric signal, which has been difficult in the past, can be improved, it becomes possible to perform differential pressure measurement with higher sensitivity and higher accuracy.

[0019]

As is apparent from the above description, the present invention has the following effects.

Since the sensor substrate is provided with an annular support portion surrounding and concentric with the diaphragm on the surface facing the support member of the thick portion surrounding the diaphragm, the stress and temperature changes when the static pressure changes. It is possible to provide an inexpensive and highly reliable semiconductor pressure sensor that can relieve the stress of time and can perform high-sensitivity and high-precision differential pressure measurement with a small amount of zero shift. Further, since the annular support portion can be formed simultaneously with the etching of the diaphragm, the number of steps can be reduced and workability is improved. further,
Since the joining portion is formed by anodic joining, the joining surface is a uniform and airtight joining surface, so that a highly reliable pressure sensor can be obtained. If these sensor substrate and supporting member are formed in a wafer state, inexpensive and highly reliable yield sensors can be manufactured in large quantities. Further, by using materials having a thermal expansion coefficient close to each other for the sensor substrate and the supporting member, the temperature influence on the sensor can be further reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Sensor substrate, 2 ... Support member, 3 ... Diaphragm, 4
... strain-sensitive gauge element, 5 ... annular support portion, 6 ... through hole,
7 ... Dicing line, 8 ... Cavity, 9 ... Thick portion, 11 ...
Sensor substrate wafer, 22 ... Support member wafer.

Front page continuation (72) Inventor Yukio Takahashi 882, Ige, Katsuta-shi, Ibaraki Hitachi, Ltd. Measuring Instruments Division

Claims (3)

[Claims] 1. A semiconductor pressure sensor comprising a square sensor substrate having a strain-sensitive gauge element for detecting a differential pressure or pressure formed in a thin portion of a diaphragm, and a supporting member having a through hole and supporting the sensor substrate. The semiconductor pressure sensor is characterized in that an annular support portion is formed on the sensor substrate at the same time as the diaphragm is etched and is joined to a joint surface with the support member. 2. The semiconductor pressure sensor according to claim 1, wherein a wafer having a plurality of strain sensitive gauge elements formed thereon as the sensor substrate and a wafer having a plurality of through holes formed as the supporting member are used, and the diaphragm is formed by etching. A method for manufacturing a semiconductor pressure sensor, wherein a plurality of pressure sensors are obtained by simultaneously processing an annular supporting portion, collectively performing anodic bonding, and then collectively cutting. 3. The semiconductor pressure sensor according to claim 1, wherein silicon is used as a material of the sensor substrate and borosilicate glass is used as a material of the supporting member.