JPH0821774A - Semiconductor pressure sensor and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the working processes, improve the workability and cut the production cost by setting a ring-shaped supporting part at a supporting member and bonding the part with a sensor substrate. CONSTITUTION:Four strain-sensitive gauge elements 4 are arranged in the periphery of a diaphragm 3 on a surface of a sensor substrate 1. A stress to the diaphragm 3 is sensed by the elements 4. The strain-sensitive gauge element 4 shows a piezoelectric resistance characteristic, changing its resistance in accordance with the stress. A circular or polygonal hollow 8 is formed on the opposite side. A supporting member 2 has a through hole 6 as a circular pressure introduction port. A ring-shaped supporting part 5 is set concentrically with the diaphragm 3 to surround the diaphragm 3 in an area where the supporting member 2 is bonded with a thick part 9 of the sensor substrate 1. The supporting part 5 is formed by etching or sandblasting or the like manner, in other words, processed easily, so that a workability is improved. Since the sensor substrate 1 and the supporting member 2 are bonded mechanically rigidly in an anode process, a reliability is high.

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. The present invention relates to a pressure sensor and a manufacturing method thereof.

[0002]

2. Description of the Related Art
There is a publication of 2-54137.

Conventionally known semiconductor pressure sensors use a diaphragm that responds to the 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.

Usually, a sensor substrate made of a square single crystal semiconductor substrate having a circular thin diaphragm is 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 support member does not have symmetry with the shape of the diaphragm, when the ambient temperature of the semiconductor pressure sensor changes, the support member and the sensor substrate. 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 ring is provided by a photolithography technique, and has a structure in which the silicon in the portion other than the bonding ring is etched by 1 to 2 μm to increase the bonding portion.

[0006]

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 two processes are performed (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 not to provide an annular support portion on the sensor substrate, but to provide an annular support portion on the support member by a method such as etching and join the sensor substrate, thereby reducing the number of steps. It is possible to improve workability, reduce costs, reduce stress when static pressure changes and temperature change, and to measure differential pressure with small zero shift, high sensitivity and high accuracy. To provide a reliable and reliable semiconductor pressure sensor,
Further, it is 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.

[0008]

In order to achieve the above object, an annular supporting portion is formed on a supporting member by etching, sandblasting or the like, and a through hole is further formed. This is anodically bonded to the sensor substrate on which the diaphragm is formed. 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.

[0009]

In the semiconductor pressure sensor according to the present invention, since the annular support portion provided on the support member can be easily formed by etching or the like, the work steps can be reduced and the workability is improved. Further, since the sensor substrate is held by the annular supporting portion of the supporting member, the stress caused by the change in temperature or static pressure is reduced due to the reduction of the area of the joint portion between the sensor substrate and the supporting 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.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view and a bottom 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 support member 2 has a through hole 6 serving as a circular pressure inlet near the center thereof, and is connected to the surface opposite to the surface on which the strain sensitive gauge element 4 is arranged. There is.
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. This annular support portion 5 is formed by etching or
It is formed by a method such as sandblasting.
In forming the annular support portion 5, the workability can be improved because it can be easily processed by the above method.
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. These sensor boards 1
Then, the support member 2 is aligned with 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 and a plurality of annular supporting portions 5 are formed. Similarly, these also take steps of etching and anodic bonding. When the sensor substrate 1 is in the wafer state, a large number of diaphragms 3 can be easily processed at one time by etching the wafer 11 of the sensor substrate 1, so that workability is further improved. If this is anodically bonded to the wafer 22 of the supporting member 2, 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 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. Further, since the corners of the diaphragm 3 can be rounded by the isotropic etching, the pressure resistance of the sensor can be 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 wafer 22 of the supporting member 2 are set so as to be overlapped with each other, and the wafer 11 of the sensor substrate 1 is bonded to the positive electrode of DC high voltage and the wafer 22 of the supporting member 2 is bonded to the negative electrode, respectively. To do. In a high temperature atmosphere, for example, 250 to 4
When a high voltage, for example, a voltage of 500 to 1500 V is applied at 00 ° C., sodium oxide (Na ₂ O) in the borosilicate glass, which is the material of the wafer 22 of the supporting member 2, becomes 2Na +, O ₂
^- ionized to move each cathode, the anode. The O ₂ ⁻ that has moved to the anode side is combined with silicon (Si) that is the material of the wafer 11 of the sensor substrate 1 to form a silicon oxide film, and the wafer 11 of the sensor substrate 1 and the wafer 22 of the support member 2 are solidified. Bind to. 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 between the diaphragm 3 of the sensor substrate 1 and the annular support portion 5 of the support member 2 is concentric and symmetric, the temperature and static pressure are kept constant. A change in stress caused by a change in pressure has less influence on the strain-sensitive gauge element 4 on the diaphragm 3, whereby a zero shift signal caused by a change in temperature or static pressure can be minimized. Further, the bonding area between the diaphragm 3 of the sensor substrate 1 and the support member 2 can be set to an optimum area by patterning on the support member 2 side. Furthermore, since the method of bonding the diaphragm 3 of the sensor substrate 1 and the supporting member 2 to each other is anodic bonding, which has extremely high adhesive strength, the sensor substrate 1 can be reliably fixed even with a small bonding area. 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 sensor substrate 1 and the supporting member 2 is small, thermal strain hardly affects the circular or polygonal diaphragm 3 when the temperature and static pressure change. 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 above-mentioned steps take advantage of the semiconductor process steps to improve reliability,
It can contribute to lower prices. As described above, in the semiconductor pressure sensor of this embodiment, the annular support portion 5 is formed on the support member 2 on the surface facing the thick portion 9 of the sensor substrate 1 surrounding the circular or polygonal diaphragm 3. Since the bonding portion between the sensor substrate 1 and the supporting member 2 is reduced and the bonding by anodic bonding is performed between the wafers, the stress when the static pressure changes and the stress when the temperature changes can be relaxed. It is possible to provide uniform characteristics with a small amount of zero shift at low cost. 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.

[0018]

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

Since the support member is provided with an annular support portion that surrounds the diaphragm and is concentric with the diaphragm on the surface of the support substrate that is joined to the thick portion that surrounds the diaphragm of the sensor substrate, stress and temperature when the static pressure changes. It is possible to provide a semiconductor pressure sensor that is capable of relieving stress at the time of change, has a small amount of zero shift, can perform high-sensitivity and high-precision differential pressure measurement, and is inexpensive and extremely reliable.

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 gate element, 5 ... annular support portion, 6 ... through hole,
7 ... Dicing line, 8 ... Cavity, 9 ... Thick part, 11,
22 ... Wafer.

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 support member having a through hole and supporting the sensor substrate. A semiconductor pressure sensor, wherein the support member is provided with an annular support portion that is joined to a joint surface with the sensor substrate. 2. The semiconductor pressure sensor according to claim 1, wherein the sensor substrate is a wafer on which a plurality of strain sensitive gauge elements are formed, and the supporting member is a wafer on which a plurality of through holes and annular supporting portions are formed. A method for manufacturing a semiconductor pressure sensor, characterized in that a plurality of pressure sensors are obtained by 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.