JPH0786619A - Strain gauge and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a strain gauge, a film of which can be thinned and which can be miniaturized and which can also be bonded with the front and rear surfaces of a body to be measured or a body to be measured having a non- planar shape, and manufacture thereof. CONSTITUTION:The strain gauge consists of an insulating film 1 having flexibility, a protective film 2 protecting the insulating film 1 at the time of electrochemical etching, a semiconductor resistor 3 composed of a semiconductor single crystal and an electrode 4 applying voltage to the semiconductor resistor 3 at the time of electrochemical etching and extracts an output signal from the semiconductor resistor 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain gauge in which a resistor and a gauge base which is a substrate to which the resistor is attached are integrally formed, and a method for manufacturing the strain gauge.

[0002]

2. Description of the Related Art Conventionally, as a simple method used to measure the strain on the surface of an object, there are a method using a resistance change of metal due to deformation and a method using a resistance change of a semiconductor. For example, the metal strain gauge utilizes the relationship that the resistance change of the metal wire due to elastic deformation is almost determined by the increase or decrease of the cross-sectional area of the metal wire, and the structure of the metal strain gauge is a plastic film using a thin metal wire as a gauge base. There is a foil gauge with a foil attached instead of a metal wire. Further, as the metal material, a material having a stable resistance value and a small temperature coefficient, such as copper, nickel-based alloy, or nichrome-based alloy, is used.

The semiconductor strain gauge uses a resistance change of a silicon semiconductor instead of a metal resistance wire, and has a characteristic that the gauge ratio is higher than that of metal.
The change in resistance due to strain is also large. This semiconductor strain gauge uses a bulk semiconductor gauge that is used by adhering to the object to be measured by using the piezoresistive effect of the semiconductor single crystal, or a gauge resistance by a diffusion process on the surface of a silicon single crystal as a strain element. There is a diffusion type semiconductor gauge with a structure to make.

Further, regarding the diffusion type semiconductor gauge,
As disclosed in Japanese Patent Laid-Open No. 3-112169, there is also one in which four semiconductor resistors obtained by diffusing impurities in a single crystal silicon substrate are provided on the same substrate to form a Wheatstone bridge.

On the other hand, when it is necessary to measure not only the strain but also the temperature at the same time, a technique relating to a sensor for measuring the strain detection and the temperature detection by one sensor without using a temperature detecting device dedicated to the temperature is disclosed in Japanese Patent Laid-Open Publication As disclosed in Japanese Patent Laid-Open No. 5-34182, a resistor material made of metal and amorphous or polycrystalline silicon by a CVD method or the like on the surface of glass, a polyimide film or the like, or a surface of a metal substrate having an insulating treatment applied thereto. And a ground / power supply terminal and a metal material such as a lead wire for electrically connecting the resistors to each other, and by patterning each of them by a photo-etching method, a "strain / temperature composite sensor" There is.

[0006]

However, in the strain gauge disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-112169, a high gauge factor is possible by using a resistor made of single crystal silicon. 100μ
Since it is integrated with a very thick silicon substrate such as m, it is difficult to measure the strain in a minute area. Since the silicon substrate has a large mechanical strength, it hinders the distortion of a minute object to be measured. Furthermore, even when the Wheatstone bridge is composed of four resistors, it is integrated with the silicon substrate. It is not flexible, and it is difficult to bond it simultaneously to the front and back of the object to be measured, and it is difficult to measure strains such as tensile strain, compressive strain, and bending strain separately.

On the other hand, in the "strain / temperature composite sensor" disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-34182,
Since all the functional elements are on the same plane due to the structure and the manufacturing method, the miniaturization is determined by the processing limit. Further, when the CVD method or the photo etching method is used, the thickness of the substrate needs to be several hundreds of μm or more due to the handling in the manufacturing process, and a large thickness of the substrate causes a large error in strain measurement. Furthermore, since the mechanical strength is lower than that of single crystal silicon due to the use of amorphous or polycrystalline silicon, the usable strain amount is limited, and when large strain is applied, the amorphous or polycrystalline silicon is destroyed. Will end up. Amorphous or polycrystalline silicon has a smaller gauge factor than single crystal silicon.

In any of the strain gauges, when the output signal from the strain gauge is amplified and taken out as the strain detection signal, it is necessary to connect an amplifier separately provided separately to the strain gauge by a lead wire. It was unsuitable for conversion.

The present invention has been made in view of the above problems, and it is an object of the present invention to form a thin film by integrally forming a semiconductor resistor made of a semiconductor single crystal on a flexible insulating film. A strain gauge that can be downsized and can be adhered to the front and back of the object to be measured or to the object to be measured having a shape other than a plane, and can form a metal thin film resistor that also functions as an electronic circuit or an electrothermal conversion element in the same insulating film. And to provide a manufacturing method thereof.

[0010]

In order to solve the above problems, the strain gauge of the present invention comprises a flexible insulating film, a protective film for protecting the insulating film during electrochemical etching, and a semiconductor single crystal. It is characterized in that it is provided with a semiconductor resistor and an electrode for applying a voltage to the semiconductor resistor during electrochemical etching and for extracting an output signal from the semiconductor resistor.

The method of manufacturing the strain gauge of the present invention is
A first step of forming an impurity diffusion region by diffusing an impurity in a region of the single crystal semiconductor substrate to be a semiconductor resistor; and a step of forming a stopper for electrochemical etching on the first plane side of the single crystal semiconductor substrate. 2 step, a third step of forming an electrochemical etching mask on the second flat surface side of the single crystal semiconductor substrate, and a flexible insulating film serving as a gauge base is formed on the single crystal semiconductor substrate. A fourth step of film formation, a fifth step of forming an electrode in electrical contact with the impurity diffusion region, and a single crystal semiconductor not protected by a mask except the impurity diffusion region by the electrochemical etching. Is removed, and a seventh step of separating the insulating film from the single crystal semiconductor substrate is performed.

[0012]

That is, in the strain gauge of the present invention, the flexible insulating film is protected by the protective film during the electrochemical etching, and the semiconductor resistor made of the semiconductor single crystal is protected by the electrodes by the voltage during the electrochemical etching. Is applied, and an output signal is taken out from the semiconductor resistor.

The method of manufacturing the strain gauge of the present invention is
In the first step, impurities are diffused into a region of the single crystal semiconductor substrate which will be a semiconductor resistor to form an impurity diffusion region. In the second step, electrochemical etching is performed on the first plane side of the single crystal semiconductor substrate. A stopper is formed, a mask for electrochemical etching is formed on the second plane side of the single crystal semiconductor substrate in the third step, and a flexible base serving as a gauge base is formed on the single crystal semiconductor substrate in the fourth step. An insulating film is formed, an electrode is formed in electrical contact with the impurity diffusion region in the fifth step, and protected by a mask excluding the impurity diffusion region by the electrochemical etching in the sixth step. The single crystal semiconductor which has not been removed is removed, and in the seventh step, the insulating film is separated from the single crystal semiconductor substrate.

[0014]

First, a first embodiment of the present invention will be described. FIG. 1A is a plan view showing the configuration of the strain gauge according to the first embodiment, and FIG. 1B is a sectional view thereof. As shown in the figure, the strained gate according to the first embodiment includes a flexible insulating film 1 such as a polyimide film and a silicon nitride film that protects the insulating film 1 during electrochemical etching. And the like, a resistor 3 in which N-type impurities are diffused in P-type single crystal silicon having both positions, and an electrode for applying a voltage to the resistor 3 during electrochemical etching. And an electrode 4 which also serves as an electrode for taking out an output signal from the resistor 3.

The method of manufacturing this strain gauge will be described. First, as shown in FIG. 2A, impurities are formed by ion-implanting the silicon single crystal substrate 5 with a resist mask or the like to open only a portion to be a semiconductor resistor. The diffusion region 3 is formed. Further, a silicon nitride film by a LPCVD method or a fluororesin (for example, CYTOP (trade name; Asahi Glass Co., Ltd.)) that can be formed by performing spin coating and volatilization treatment of an unnecessary solvent is formed into a film and an etching stopper is formed by photoetching Then, the protective film 2 and the mask 6 for etching silicon provided on the back surface side are formed.

Then, as shown in FIG. 2 (b), a resin solution such as polyimide is spin-coated on the surface side of the single crystal substrate 5 and unnecessary solvent is volatilized and sintered to form a film, which is then photo-etched. The insulating film 1 having the contact holes is formed. At this time, although not particularly shown, the surface of the insulating film 1 is protected by a fluorinated resin if necessary. Next, a metal thin film is formed by a sputter deposition method or the like, and the electrode 4 is formed by photoetching.

Then, as shown in FIG. 2C, the strain gauge shown in FIG. 1 can be manufactured by leaving the resistor 3 by electrochemical etching and then cutting the resistor 3 into an appropriate size. The separated strain gauge is the resistor 3
It is used by coating the insulating film 1 on the substrate or by adhering it to the object to be measured with an insulating adhesive.

Here, the electrochemical etching used in this embodiment will be described in detail with reference to FIG. FIG. 3 is a diagram showing a state in which a protective film 7 made of fluorinated resin or the like is formed to protect the insulating film 1 made of polyimide or the like and the electrode 4.

First, as shown in FIG. 3B, an alkaline etchant 9 such as an aqueous solution of potassium hydroxide or an aqueous solution of tetramethylammonium hydroxide is placed in the etching bath 8.
The sample and the electrode 1 as shown in FIG.
Set 0.

Then, in order to apply a voltage between the electrode 4 and the electrode 10, a voltage applying device 11 composed of wiring and a voltage source is connected, and etching is started. When this etching progresses to reach the resistor 3, the resistor 3 remains without being etched because an oxide film is formed on the bonding surface of the N-type diffusion layer by anodic oxidation.

Further, as shown in FIG. 4, since the strain gauges obtained in the first embodiment utilize the semiconductor manufacturing technology, the same strain gauges can be manufactured in an array, so that the strain gauges in a minute plane can be formed. It is also possible to measure the strain distribution.

As described above, in the first embodiment,
Since the resistor 3 is made of single crystal silicon in which impurities are diffused, it has excellent mechanical strength and has a very large gauge factor. Further, since the insulating film 1 serving as the gauge base, the resistor 3 and the electrode 4 can be integrally formed by using the semiconductor manufacturing technique, thinning, miniaturization and mass production by batch processing are possible.

Next, a strain gauge according to a second embodiment of the present invention will be described. FIG. 5 is a plan view showing the configuration of the strain gauge according to the second embodiment. As shown in the figure, the strain gauge according to the second embodiment constitutes a Wheatstone bridge circuit using four resistors 22 to 25 obtained according to the first embodiment. These are connected to electrodes 26 to 29 by gauge leads 30 as shown in FIG. Incidentally, the gauge lead 30 and the electrodes 26 to 29
Are formed by the same process as the electrode 4 shown in FIG.

FIG. 6 is a circuit diagram of the strain gauge shown in FIG. The resistor R1 shown in FIG. 6 is the resistor 22 in FIG. 5, and similarly the resistor R2 is the resistor 23 and the resistor R.
3 corresponds to the resistor 24, and resistor R4 corresponds to the resistor 25. When a voltage is applied between E1 and E3,
A strain output voltage proportional to the amount of temperature-compensated strain can be measured between E2 and E4.

FIG. 7A is a plan view showing a state in which the strain gauge of the second embodiment is mounted on the object 31 to be measured.
(B) is the side view. As shown in FIG. 7A, the strain gauge is adhered and fixed to the object 31 to be measured, but only the resistor portion is adhered in order to erase the change in the resistance value due to the strain of the gauge lead. Then, the object 31 to be measured is bent and deformed as shown in FIG. 7B, pulled by a strain gauge, and only the bending strain in which the compressive strain is eliminated can be measured.

In the second embodiment described above, since all the electrodes are formed on the upper surface, the external wiring can be easily attached. Further, although not particularly shown, by changing the installation direction of the resistors 22 to 25 in FIG. 5, it is possible to measure only the temperature-compensated tensile and compressive strains or only the torsional strains. For example, by installing the resistors 23 and 25 in a direction perpendicular to the resistors 22 and 24, only the temperature-compensated tensile compression strain can be measured.

Next, a strain gauge according to a third embodiment of the present invention will be described. FIG. 8A is a plan view showing the configuration of the strain gauge according to the third embodiment, and FIG. 8B is a sectional view thereof. In the third embodiment, an electronic circuit 43 is integrally formed on the strain gauge obtained in the first embodiment, and a resistor 42 is formed by diffusing impurities in a flexible insulating film 41 and a silicon single crystal. From a Wheatstone bridge circuit or resistor 42 configured by a gauge lead 44 connecting the resistor 42 and the electronic circuit 43, an electrode 45 for applying a voltage and detecting a strain output, and a resistor having a fixed resistance value. And an electronic circuit 43 including an amplifier and the like for amplifying the output signal of.

The electronic circuit 43 is formed by a known semiconductor manufacturing technique before the electrochemical etching, but it is necessary to leave the electronic circuit region during the electrochemical etching. Then, as a concrete means for leaving this electronic circuit area, a slightly larger area than the electronic circuit area is shown in FIG.
By providing a mask corresponding to the mask 6 on the back surface of the substrate, the silicon substrate only in the electronic circuit region remains in an integrated state with the insulating film. Alternatively, an electronic circuit is formed in a common N-type impurity diffusion region, and the impurity diffusion region is left by electrochemical etching.

FIG. 9 is a diagram showing a specific circuit example of the strain gauge according to the third embodiment, and the resistor 42 shown in FIG.
And the resistor R1 correspond to each other. The resistor R is a resistor formed in the electronic circuit and having a fixed resistance value, and the resistor R1 and the resistor R of the strain gauge form a Wheatstone bridge circuit. The amplifier A is for amplifying and extracting the distortion signal output from the Wheatstone bridge circuit. It should be noted that the well-known layout of gauges and gauge leads enables temperature compensation and strain measurement that is not affected by other strains. For example, it is composed of two strain gauge resistors and a resistor having a fixed resistance value formed in the electronic circuit region, and one resistor is provided on each of the front and back sides of the object to be measured.
By bonding the individual resistors, it is possible to measure only the temperature-compensated bending strain.

When the Wheatstone bridge circuit is composed of four resistors as shown in FIG. 5, only the amplifier is manufactured in the electronic circuit. Further, in the bonding of the third embodiment, it is not desirable that the electronic circuit region is subjected to strain, so it is desirable that only the periphery of the resistor of the strain gauge is bonded and the electronic circuit region is not bonded. .

As described above, according to the third embodiment, a Wheatstone bridge circuit and a strain gauge resistor and a resistor having a fixed resistance value are provided on the same flexible insulating substrate. Since an electronic circuit such as an amplifier for amplifying the output signal from the resistor is integrally formed, it is possible to miniaturize the entire system, and it is possible to measure the strain of a minute DUT or inside a microtube. .

Next, a strain gauge according to a fourth embodiment of the present invention will be described. FIG. 10A is a plan view showing the configuration of the strain gauge according to the fourth embodiment, and FIG. 10B is a sectional view thereof. As shown in the figure, this strain gauge has a flexible insulating film 51, a resistor 52 obtained by diffusing impurities in a silicon single crystal, a resistor 53 made of a metal thin film, and outputs from each resistor. Electrodes 5 and 5 for detecting
It is composed of 5 and 5.

As for a concrete method of manufacturing the strain gauge according to the fourth embodiment, the manufacturing process of the resistor 53 may be added to the method shown in FIG.
After forming, a flexible insulating film such as a first layer of polyimide film is formed, a metal material is formed by sputtering vapor deposition, and the metal thin film resistor 53 is formed by photoetching.

Next, a flexible insulating film such as a second layer of polyimide film is formed, and contact holes are formed in the single crystal silicon resistor 52 and the metal thin film resistor 53 for electrical connection. To do. After that, electrochemical etching is performed with the voltage applied to the electrode 54 to form the resistor 5
By allowing 2 to remain, the resistor 52 and the metal thin film resistor 53 made of single crystal silicon are formed on the flexible insulating film.
A strain gauge integrally formed with is obtained.

By using the strain gauges thus obtained, if the temperature and strain of the object to be measured change at the same time, the semiconductor resistor and the metal thin film resistor have known gauge factors and temperature resistance coefficients, respectively. Therefore, if you want to obtain the temperature-compensated strain, the temperature is kept constant and the output from the semiconductor resistor and the output from the metal thin-film resistor are connected simultaneously. Can be obtained by Similarly, the temperature can be obtained by keeping the strain constant.

As described above, in the fourth embodiment,
It is possible to detect the temperature-compensated strain and temperature of the surface of the measured object. In addition, the gauge factor of the metal thin film resistor is usually about 2, and the gauge factor of the semiconductor resistor is about two orders of magnitude higher than that of the metal thin film resistor. Therefore, by combining these two types of resistors, highly accurate strain and It becomes possible to measure the temperature.

Finally, the strain gauge according to the fifth embodiment will be described. The strain gauge according to the fifth embodiment is a strain gauge in which the semiconductor resistor and the metal thin film resistor obtained in the fourth embodiment are combined, and Joule heat is generated by applying a voltage to the metal thin film resistor made of a metal material. It is characterized in that the metal thin film resistor that utilizes the generation also serves as an electrothermal conversion element.

FIG. 11A is a plan view showing a structure in which the strain gauge according to the fifth embodiment is bonded to a thermodynamic conversion element 61 such as a shape memory alloy or bimetal with an insulating adhesive 62. 11B is a sectional view thereof. In FIG. 11A, Joule heat is generated by applying a voltage to the metal thin film resistor.
Bending deformation or expansion / contraction deformation can occur as indicated by the arrow in (b). The direction and size of deformation depend on the thermodynamic conversion element 61.

As described above, in the fifth embodiment, it is possible to measure the temperature-compensated strain and temperature of the thermodynamic element 61 deformed by Joule heat. Furthermore, since the strain gauge and the electrothermal conversion element are integrally formed on the flexible insulating film, a minute thermodynamic conversion element capable of measuring strain is possible, and is composed of a flexible film. Therefore, it does not hinder the deformation of the thermodynamic conversion element.

Further, it is of course possible to apply a voltage to the semiconductor resistor to generate Joule heat and use it as an electrothermal conversion element, or to integrate an electronic circuit as described in the third embodiment. is there.

As described above in detail, according to the strain gauge of the present invention and the method of manufacturing the same, a semiconductor resistor made of a semiconductor single crystal in which impurities are diffused is integrally formed in a flexible insulating film. Can be thinned and miniaturized,
The strain can be accurately measured with high accuracy, and it can be applied to a minute object to be measured or an object to be measured having a non-planar shape, and mass production by batch processing is also possible.

[0042]

According to the present invention, by integrally forming a semiconductor resistor made of a semiconductor single crystal on a flexible insulating film, it is possible to reduce the thickness and size of the semiconductor resistor, and A strain gauge capable of adhering to a measured object having a non-planar shape and capable of forming a metal thin film resistor capable of also serving as an electronic circuit or an electrothermal conversion element in the same insulating film, and a manufacturing method thereof. .

[Brief description of drawings]

1A is a plan view showing a configuration of a strain gauge according to a first embodiment, and FIG. 1B is a sectional view thereof.

FIG. 2 is a drawing for explaining the manufacturing method of the strain gauge according to the first embodiment.

FIG. 3 is a diagram for explaining electrochemical etching used in the first embodiment.

FIG. 4 is a diagram showing a state where the strain gauges according to the first example are manufactured in an array.

FIG. 5 is a plan view showing the outline of a strain gauge according to a second embodiment.

6 is a circuit diagram of the strain gauge shown in FIG.

7A is a plan view showing a state in which the strain gauge of the second embodiment is mounted on the device under test 31, and FIG. 7B is a side view thereof.

8A is a plan view showing the configuration of a strain gauge according to a third embodiment, and FIG. 8B is a sectional view thereof.

FIG. 9 is a diagram showing a specific circuit example of a strain gauge according to a third embodiment.

10A is a plan view showing the structure of a strain gauge according to a fourth embodiment, and FIG. 10B is a sectional view thereof.

FIG. 11A shows a strain gauge according to a fifth embodiment,
FIG. 11B is a plan view showing a structure in which a thermodynamic conversion element 61 such as a shape memory alloy or a bimetal is bonded with an insulating adhesive 62, and FIG. 11B is a sectional view thereof.

[Explanation of symbols]

1, 21, 41, 51 ... Insulating film, 2, 7 ... Protective film, 3,
22-25, 42, 52, 53 ... Resistors, 4, 10, 2
6 to 29, 45, 54, 55 ... Electrodes, 5 ..., 6 ... Mask, 8 ... Etching bath, 9 ... Alkaline etchant,
11 ... Voltage applying device, 30, 44 ... Gauge lead, 31
... object to be measured, 43 ... electronic circuit.

Claims (2)

[Claims] 1. A flexible insulating film, a protective film for protecting the insulating film during electrochemical etching, a semiconductor resistor made of a semiconductor single crystal, and the semiconductor resistor during electrochemical etching. An electrode for applying a voltage to the semiconductor resistor and taking out an output signal from the semiconductor resistor. 2. A first step of forming an impurity diffusion region by diffusing an impurity in a region of a single crystal semiconductor substrate, which is to be a semiconductor resistor, and electrochemical etching on the first flat surface side of the single crystal semiconductor substrate. A second step of forming a stopper, a third step of forming an electrochemical etching mask on the second flat surface side of the single crystal semiconductor substrate, and a flexible base serving as a gauge base on the single crystal semiconductor substrate. A fourth step of forming an insulating film, a fifth step of forming an electrode in electrical contact with the impurity diffusion region, and protection by the mask excluding the impurity diffusion region by the electrochemical etching. A method for manufacturing a strain gauge, comprising: a sixth step of removing a single crystal semiconductor that has not been formed; and a seventh step of separating the insulating film from the single crystal semiconductor substrate.