JP2634172B2 - pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a pressure sensor having a reference pressure chamber.

(Prior Art) FIG. 8 shows a conventional structure of this type of pressure sensor. In the figure, 1 is an insulating substrate, 2 is a pedestal provided thereon,
A communication hole 2a is formed in the pedestal 2, and a pressure equalizing pipe 3 is connected to the communication hole 2a. Reference numeral 4 denotes a silicon substrate, which is formed into a container shape by etching so as to have a concave portion 4a to form a thin diaphragm portion 4b, and is fixed to the pedestal 2 so that the inside of the concave portion 4a is connected to the equalizing pipe 3. ing. 5
Is a seal cap, which is attached to the insulating substrate 1 so as to cover the silicon substrate 4, and a space inside the seal cap 5 outside the silicon substrate 4 is set as a reference pressure chamber 6 to be in a vacuum state. Then, the diaphragm portion of the silicon substrate 4
4b is provided with a strain sensor by a piezoresistive diffusion resistor, and the strain sensor is connected to the pin 8 via the bonding wire 7. Here, since the inside of the concave portion 4a of the silicon substrate 4 is made equal in pressure to the pressure measuring portion through the equalizing pipe 3, and the inside of the reference pressure chamber 5 is vacuum,
The diaphragm 4b of the silicon substrate 4 bends and deforms in accordance with the absolute pressure of the pressure measuring portion, and a signal corresponding to the amount of the deformation is obtained from the strain sensor.

(Problems to be Solved by the Invention) However, in the above configuration, even if the diaphragm 4b and the strain sensor of the silicon substrate 4 can be finely processed by a so-called semiconductor process, the silicon substrate 4 is fixed on the pedestal 2 and sealed. Since the pressure sensor is covered with the cap 5 and the pressure equalizing pipe 3 is led out, there is a limit to downsizing of the pressure sensor as a whole, and it is unavoidable that the assembly process is complicated and expensive.

Therefore, an object of the present invention is to provide a pressure sensor that can be manufactured at low cost while being able to reduce the overall size.

[Constitution of the Invention] (Means for Solving the Problems) The pressure sensor of the present invention has a hollow portion formed by a semiconductor process including an etching process effective only in a silicon dioxide region formed in a single crystal silicon substrate. A sealed reference pressure chamber, and a strain sensor mainly composed of a diffusion resistance formed by a semiconductor process on a surface of a partition wall that partitions the reference pressure chamber and an outer space of the silicon base among the silicon base. It has a characteristic in that it can be provided.

(Operation) Since the reference pressure chamber is formed in the silicon substrate,
In accordance with the pressure difference between the external space of the silicon substrate and the reference pressure chamber, the partition located between them is deformed, and a signal is obtained from a strain sensor provided in the partition. Therefore, a conventional seal cap or pressure equalizing pipe is not required by using the outer space of the silicon substrate as a pressure measuring portion, and the whole is significantly reduced in size. In addition, since the reference pressure chamber and the strain sensor can be manufactured by a semiconductor process, the manufacturing cost can be reduced by mass production.

(Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a completed form as a pressure sensor. In FIG. 1, reference numeral 11 denotes an insulating substrate, and 12 denotes a silicon substrate as a semiconductor substrate provided on the insulating substrate 11.
The detailed structure and manufacturing method of the 12 will be described later. Reference numeral 13 denotes a protective case fixed on the insulating substrate 11 so as to cover the silicon substrate 12. The protective case 13 has a communication hole 14 for communicating the inside and the outside of the case 13, and the protection case 13 is formed through the communication hole 14. Can be connected to the pressure measuring part. on the other hand,
A wiring conductive film 15 is formed on the insulating substrate 11, and a predetermined portion thereof is connected to a bonding pad 16 on the silicon substrate 12 by a bonding wire 17. Reference numeral 18 denotes a lead-out lead fixed to the wiring conductive film 15, and 19 denotes a sealing material for sealing a base end portion of the lead-out lead 18.

A reference pressure chamber 20 is hermetically formed inside the silicon substrate 12, and the inside of the silicon substrate 12 is substantially in a vacuum state. As shown in FIG. 3 (A), four piezos are provided on the upper partition wall 21 of the silicon substrate 12 which divides the reference pressure chamber 20 and the space outside the silicon substrate 12. The strain sensor 23 is formed by forming the resistive diffusion resistor 22 and connecting it in a bridge form. Here, a method of manufacturing the silicon substrate 12 will be described with reference to FIGS.
SiO ₂ inside for example, a disk-shaped silicon wafer 24 by implanting high-concentration oxygen ions by a known ion implantation method as shown in (1 shows only chips), for example, in Japanese Patent Publication 54-16716 Patent etc. A region 25 is formed (see FIG. 2). In this case, the depth at which oxygen ions reach the inside of the silicon wafer 24 can be controlled according to the acceleration voltage of the ion implantation apparatus.
By adjusting the acceleration voltage, the formation depth of the SiO ₂ region 25 can be set as desired. Next, the diffusion resistor 22, the wiring pattern 26 and the bonding pad 16 are formed on the surface of the silicon wafer 24 by diffusion of impurities by a known semiconductor process (FIG. 3). Thereafter, as shown in FIG. 4, an opening 27 reaching the SiO ₂ region 25 as a specific modified region is formed in the silicon wafer 24 by a dry etching method of silicon using an etching resist mask. Is used to etch the silicon wafer 24 with buffered hydrofluoric acid. Then, since the etching rate of SiO ₂ by hydrofluoric acid is much higher than that of silicon, the SiO ₂ region 25 is selectively removed by etching to form a hollow portion 28 (FIG. 5). Thereafter, in a vacuum (for example, about 1/100 atm), a passivation film 29 such as silicon nitride is formed on the entire silicon wafer 24 by a plasma CVD method to close the opening 27 (FIG. 6). As a result, the hollow portion 28 is sealed in a vacuum state to form the reference pressure chamber 20, so that the passivation film 29 on the bonding pad 16 is removed, inspected and diced, and the silicon substrate according to the present embodiment is removed. 12 is completed.

In the pressure sensor of the present embodiment in which the semiconductor substrate 12 is incorporated in the protective case 13, the partition 21 is bent and deformed in accordance with the difference between the pressure in the protective case 13 and the pressure in the reference pressure chamber 20, The resistance value of the diffusion resistor 22 formed in the partition 21 changes, and the resistance value of the strain sensor 23 changes. Here, particularly in this embodiment, since the inside of the reference pressure chamber 20 is in a substantially vacuum state,
The resistance value of the strain sensor 23 is a function of the absolute pressure in the protective case 13 and thus in the pressure measurement part.

According to this embodiment, since the reference pressure chamber 20 is integrally formed in the silicon base 12 by a semiconductor process, unlike the conventional pressure sensor shown in FIG. Thus, there is no need to configure the reference pressure chamber 5. As a result, the pressure sensor can be miniaturized, and can be manufactured by a semiconductor process suitable for mass production without complicated assembly steps, so that the manufacturing cost can be significantly reduced.

The method for forming the hollow portion 28 in the silicon substrate 12 is not limited to the method using the ion implantation method as shown in the present embodiment, but also uses the epitaxial growth of crystals as in the second embodiment described below. It may be what you did. In the second embodiment, for example, as shown in FIG.
An impurity is diffused at a high concentration in a predetermined region of the p-type silicon substrate 30 to form ap ⁺ region 31 as a specific modified region, and thereafter, an epitaxial growth layer 32 is formed on the p-type silicon substrate 30. As a result, p ⁺ region 31 is buried under epitaxial growth layer 32. Thereafter, impurities are diffused from the surface of the epitaxial growth layer 32 by using a mask (not shown) to form a vertical p ⁺ region 33 reaching the internal p ⁺ region 31 (FIG. 7C).
Thereafter, when anodizing is performed in hydrogen fluoride, for example,
According to the principle shown in JP-A-48-102988, the p ⁺ region
Only 31,33 becomes porous. Therefore, if this silicon wafer is subjected to, for example, thermal oxidation treatment, the porous silicon is easily oxidized into porous SiO _2, and this can be etched with a buffered hydrofluoric acid solution as in the first embodiment. Then, only the porous SiO ₂ is removed by selective etching to form a hollow portion similar to that shown in FIG.
Thereafter, if the processing is performed in the same manner as in the first embodiment, a silicon substrate 12 having a reference pressure chamber therein is formed, and the same operation and effect as in the first embodiment can be obtained.

When forming the SiO ₂ region 25 inside the semiconductor substrate 12 by ion implantation, by controlling the acceleration voltage of the ion implantation apparatus, also SiO ₂ using the epitaxial growth method
When the region 31 is formed, by controlling the thickness of the epitaxial growth layer 32, the depth of the partition can be freely set, so that the thickness of the partition 21 can be adjusted to the measurement pressure range. It is extremely easy to set.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings. For example, not only a silicon nitride film is used for sealing a hollow portion but also a phosphate glass is used as a passivation film. The opening may be closed by melting the passivation film of phosphate glass in a vacuum after the film is formed. Furthermore, the inside of the reference pressure chamber 20 is not limited to being kept at a vacuum, and an appropriate pressurization can be given according to the measurement pressure. Moreover, since the semiconductor substrate according to the present invention has a reference pressure chamber inside, a pressure sensor can be constituted only by the semiconductor substrate 12 without being covered by the protective case 13 as shown in the above embodiment. For example, the semiconductor substrate 12 is attached to the tip of a medical catheter.
It is possible to adapt to a wide range of applications by remarkably miniaturizing, for example, it is possible to incorporate the.

[Effect of the Invention] As described above, the pressure sensor of the present invention can be made extremely small as a whole because the silicon substrate itself has the reference pressure chamber inside, and the manufacturing cost is reduced by employing a semiconductor process. Has an excellent effect that the cost can be significantly reduced.

[Brief description of the drawings]

1 to 6 show a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view of a pressure sensor shown in a completed form, and FIGS. 2 to 6 are productions of a semiconductor substrate in the first embodiment. The steps are shown in order, with each figure (A) being an enlarged plan view and the same figure (B) being an enlarged longitudinal sectional view. FIG. 7 is a longitudinal sectional view showing a manufacturing process of a semiconductor substrate according to a second embodiment of the present invention halfway, and FIG. 8 is a longitudinal sectional view of a conventional pressure sensor. In the drawing, 12 is a silicon substrate (semiconductor substrate), 13 is a protective case, 20 is a reference pressure chamber, 21 is a partition, 22 is a diffusion resistor, 23
Is a strain sensor.

Claims (1)

(57) [Claims] A reference pressure chamber for sealing a hollow portion formed by a semiconductor process including an etching process effective only in a silicon dioxide region formed in a single crystal silicon substrate; A pressure sensor comprising: a strain sensor mainly formed by a diffusion resistance formed by a semiconductor process on a surface of a partition that divides a pressure chamber and an external space of a silicon substrate.