JPH03181179A - Stress conversion element and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a stress conversion element and a method of manufacturing the same, and particularly to a structure of a strain gauge thereof and a method of manufacturing the same.

(Prior Art) With advances in semiconductor technology, semiconductor sensors that utilize the piezoresistance effect of semiconductors such as silicon and germanium have attracted attention in recent years.

Such semiconductor sensors are equipped with a semiconductor strain gauge on a strain-generating part such as a cantilever or diaphragm, and detect the amount of strain generated in the strain-generating part with the semiconductor strain gauge and output it as an electrical signal. Used for loads, etc.

The sensitivity of this semiconductor strain gauge (i.e., the ratio of the linear change in resistance to the amount of strain) is determined by j, lj with good crystallinity.
It is said that viscous thin films or polycrystalline thin films are superior, and PU semiconductors or n-type semiconductors containing impurities are superior to intrinsic semiconductors. Therefore, a strain gauge is constructed by forming an impurity diffusion layer pattern of a desired conductivity type in a medium crystal substrate, or a strain gauge is constructed by forming a polycrystalline thin film pattern doped with a desired conductivity type. is used.

Among these, many sensors that measure low loads use single-crystal substrates. One typical example is one in which a strain gauge pattern made of an impurity diffusion layer is formed on the surface of a single crystal silicon substrate shaped into a diaphragm having a thin wall portion.

This diffusion type pressure sensor is implemented as follows.

First, as shown in Figure 7(a), a 350 μm thick l
j The surface of the crystalline silicon substrate 1 is oxidized to form a silicon oxide film 2.

Next, as shown in FIG. 7(b), a diffusion window W is formed in the silicon oxide film 2 by photolithography.

Thereafter, as shown in FIG. 7(c), impurity diffusion is performed through the diffusion window W to form an impurity diffusion layer as the strain gauge button 3.

After forming the strain gauge pattern 3 in this way, the seventh
As shown in Figure (d), after forming a silicon oxide film 2 again by thermal oxidation, the front and back surfaces are coated with resist, only the resist on the back side is selectively removed, and this is used as a mask to cover the back side of the substrate. The silicon oxide film 2 thus formed is patterned.

Further, as shown in FIG. 7(e), the silicon substrate 1 is etched from the back side to form a thin portion 4.

Thereafter, as shown in FIG. 7(f), a metal film 5 of aluminum or the like is formed by vapor deposition and patterned to form a wiring layer 5.

Finally, the silicon substrate 1 with the strain gauge formed thereon is fixed to the pedestal 6 to complete the pressure sensor as shown in FIG. 7(g).

In such a pressure sensor, when the thin part 4 of the silicon substrate 1 receives pressure from the back side of the strain gauge forming surface, the thin part 4
At the same time, the strain gauge is distorted, and the resulting change in the strain gauge resistance value is extracted as an electrical signal.

Furthermore, since a single crystal silicon substrate is used, the sensitivity is extremely high.

A typical sensor for measuring high loads is a strain gauge made of a thin polycrystalline silicon film pattern doped with impurities on a metal diaphragm made of stainless steel or the like.

This thin film pressure sensor is implemented as follows.

First, as shown in FIG. 8(a), a silicon oxide film 12 is formed as an insulating film on a stainless steel diaphragm 11 having a thin portion.

Next, as shown in FIG. 8(b), an n-type or p-type polycrystalline silicon thin film 13 is deposited on the silicon oxide film 12 by plasma CVD.

Thereafter, as shown in FIG. 8(C), the polycrystalline silicon thin film 13 is patterned to form a strain gauge pattern 14.

Finally, as shown in FIG. 8(d), a metal film such as aluminum is shaped and patterned by vapor deposition to form a wiring layer 15.

In this thin film pressure sensor, a stainless steel diaphragm 11
The thin portion of the strain-generating portion constitutes a strain-generating portion, and this strain is detected by a strain gauge pattern made of a polycrystalline silicon thin film.

In such a pressure sensor, each strain gauge pattern usually constitutes a bridge circuit as shown in Fig. 9.
Pressure is measured by detecting a voltage change between wiring layer patterns E2 and R5 caused by a change in the resistance value of the strain gauge due to strain caused by pressure.

That is, when there is no load (when there is no distortion), the resistance values of the strain gauge patterns R1 to R4 are all set to the same value R.

If pressure P is applied to the diaphragm 1 as shown in FIG. 10, the structure will be such that strain gauge patterns R1 and R3 are arranged at the periphery of the diaphragm, and strain gauge patterns R2 and R4 are arranged at the center. Therefore, strain gauge patterns R1 and R3 receive compressive stress and become R+ΔR, while strain gauge patterns R2 and R4 receive tensile stress and become RΔR.

Assuming that Vin is applied between the electrode wiring patterns El and E6, when no load is applied, the four strain gauge patterns R1,
Since R2, R3, and R4 are all equal, the electrode wiring pattern E2. The potential between E5 is equal and the voltage between them is V-0
It is.

Therefore, when a load such as the pressure P shown in FIG. 10 is applied, strain gauge patterns R1 and R3 become R+ΔR1, strain gauge patterns R2 and R4 become R−ΔR, and electrode wiring pattern E2. The voltage between E5 is V-2 (ΔR/R)·Vin.

In this way, a voltage corresponding to the load is output, subjected to processing such as amplification in an amplifier section (not shown), and output to an external circuit.

(Problems to be Solved by the Invention) When forming the former diffusion type pressure sensor, the diffusion process requires a high temperature process of about 1000° C., and therefore handling is extremely difficult.

Furthermore, after forming the strain gauge, etching is performed to form the thin part, but since a high temperature process (about 1000°C) is required to form a silicon oxide film as a protective film for this etching, the strain gauge is There is a problem that the constituent diffusion layer may elongate or undergo re-diffusion.

Therefore, a method of etching to form the thin part before forming the strain gauge may be considered, but the etching process requires exposing the substrate on which the thin part has already been formed to the high temperature during diffusion, which may cause breakage due to thermal strain. There is a possibility that
This method was also problematic.

Furthermore, in the latter thin film pressure sensor, the substrate temperature must be about 500° C. when forming the semiconductor thin film constituting the strain gauge. In addition, with such a sensor,
To improve detection accuracy, strain gauge patterns R1 to R4
All resistance values must be constant. For this reason, there was a problem in that a complicated process such as a photolithography process had to be performed during turning.

Therefore, the material constituting the strain-generating portion must be resistant to high temperatures and chemicals, such as metal, and there is a problem in that only a limited number of materials can be used. In addition, when the strain-generating part is made of a power failure material such as metal, the surface must be covered with an insulating film, but this insulating film must also be able to withstand high-temperature processes, so silicon oxide films, etc. Only limited items can be used.

To make matters worse, it takes a lot of time to stack the silicon oxide films to a required thickness, causing a rise in costs.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a stress converting element that is easy to manufacture, inexpensive, and highly accurate.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the stress conversion element of the present invention, a semiconductor base is disposed on the surface of the strain-generating part made of metal via an insulating layer formed by modifying the metal surface. Further, the strain gauge pattern is provided by selectively irradiating the semiconductor base surface with a laser under a condition where impurities are present on the semiconductor base surface.

For example, this insulating layer can be obtained by oxidizing the constituent metal of the strain-generating portion.

As an example of this, the strain-generating portion may be made of aluminum, and the insulating layer may be made of an alumite layer obtained by oxidizing the surface of the aluminum.

In addition, in the method for manufacturing a stress conversion element of the present invention, after forming a strain-generating part made of metal, an insulating layer is formed by modifying and insulating the surface of this strain-generating part, and further, on this insulating layer. A semiconductor base is formed, impurities are introduced into the surface of the semiconductor base, and laser irradiation is selectively performed to form a strain gauge consisting of an impurity region pattern in the laser irradiation area.

(Function) According to the above configuration, the strain-generating portion is made of metal, and the insulating layer is formed by modifying the metal surface, so it is possible to form the insulating layer extremely easily. be.

Further, the process of forming strain gauges by laser irradiation in the above configuration is as follows.

First, when the surface of a semiconductor substrate is irradiated with a laser, the irradiated region absorbs light from the surface according to the laser wavelength and the absorption coefficient of the semiconductor substrate material.

When energy from this light is applied to the semiconductor substrate,
It is converted into heat and the temperature rises. When the semiconductor substrate is heated above its melting point due to this temperature increase, it melts. (This dissolution depth is proportional to the irradiation energy and time.) At this time, if impurities are present on the surface of the semiconductor substrate,
Since this impurity is taken in and melted, high concentration doping becomes possible.

Then, when the laser irradiation is stopped, cooling begins, and the molten region resolidifies in a highly doped state.

At this time, if the semiconductor substrate is a single-crystal semiconductor, the crystal grows again with impurities taken in, and a strain gauge consisting of a highly doped impurity diffusion region in a crystal state different from that of the substrate is formed.

In addition, if the semiconductor substrate is a polycrystalline semiconductor at this time, the crystals will grow again with impurities incorporated, the crystal grain size will be large (sometimes it will become a single crystal), and the crystal state will be in a high concentration that is different from that of the substrate. A strain gauge is formed consisting of a doped impurity diffusion region.

Furthermore, if the semiconductor substrate is an amorphous semiconductor at this time, the crystal grows again with impurities incorporated therein, becomes polycrystalline, and a strain gauge consisting of a heavily doped impurity diffusion region is formed.

By the way, as this impurity introduction step, there are, for example, the following three methods.

The first method is to adsorb impurities onto the surface of a semiconductor substrate, and for example, laser irradiation is performed in an impurity-containing atmosphere to form an impurity diffusion pattern (strain gauge).

The second method is to form a film containing impurities on the surface of the semiconductor substrate, and use this film as a diffusion source to form an impurity diffusion pattern (
strain gauge).

The third method is to incorporate impurities into the semiconductor substrate at the time of forming the semiconductor substrate, by forming a semiconductor substrate doped with one of the conductivity types from the beginning and selectively irradiating the semiconductor substrate with a laser. Form a low resistance impurity diffusion pattern (strain gauge). For example, if the semiconductor substrate is a polycrystalline semiconductor or an amorphous semiconductor, only this region has a large crystal diameter and low resistance, as described above.

In either case, the strain gauge pattern can be formed at low temperature without going through a photolithography process, and manufacturing is easy.

In addition, especially when a semiconductor substrate is formed on the surface of a strain-generating part whose surface is insulated and a strain gauge pattern is formed on this semiconductor substrate, the strain gauge pattern can be formed at low temperature without going through a photolithography process. Since heat resistance or chemical resistance is not required, the strain-generating portion may be formed of any metal material, and the cost can be reduced.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The pressure sensor according to the embodiment of the present invention has a diaphragm made of an Al1-5i-Cu alloy molded by precision die casting, as shown in the manufacturing process diagrams in FIGS. 1(a) to 1(d). A strain gauge pattern is formed by irradiating a semiconductor substrate made of a semiconductor thin film containing impurities with a laser through an alumite layer 101 formed on the surface of 100 by surface oxidation.

That is, first, as shown in FIG. 1(a), <, Al-3
Forming i-Cu alloy by precision die casting,
After forming and cleaning the diaphragm 100, an alumite layer having a thickness of 10 μm is formed as an insulating film by anodizing using sulfuric acid.

After that, as shown in FIG. 1(b), sputtering is performed on the surface of the alumite layer 101 formed by surface oxidation using silicon containing B as a target.
A boron-bubbled amorphous silicon thin film 102 having a thickness of 6000 Å is deposited. Note that the deposition conditions at this time are that sintered polycrystalline silicon containing 0.1% B is used as a target, and sputtering is performed at an RF power of 300 W for 1 hour.

Next, as shown in FIG. 1C, the diaphragm 100 on which the boron-doped amorphous silicon thin film 101 has been formed is installed in a laser irradiation chamber, and after exhausting, the inside of the irradiation chamber main body 201 is filled with 50 Torr of inert gas. A laser beam 103 from a xenon chloride excimer laser with a wavelength of 308 nm is applied to the strain gauge forming area for 10 minutes.
A low-resistance strain gauge 104 made of boron-doped amorphous silicon is formed on a portion of the boron-doped amorphous silicon thin film 102 by shot irradiation. At this time, the depth of the strain gauge 104, that is, the diffusion depth is 0.4 to 0.8μ, and the sheet resistance is expressed as Ω/cd.
The resistivity was 10-■Ω mark. As shown in FIG. 2, this laser beam irradiation chamber includes a beam 71. It consists of a basic body 201, a pipe 202 for introducing and exhausting gas into the irradiation chamber, a quartz window 203 for introducing laser light, and a laser oscillator 204! ! (This is to selectively irradiate the surface of the sample 205 installed in the irradiation chamber with laser light. That is, by moving the laser light or the sample 205, a fine irradiation pattern can be drawn.

Finally, as shown in FIG. 1(d), a wiring pattern 105 made of an aluminum layer is formed by vapor deposition.

In this method, since impurities are added at the same time as the semiconductor substrate is deposited, the number of steps is reduced and a highly reliable horn conversion element can be easily obtained.

In addition, conventional amorphous semiconductors such as amorphous silicon thin films could not be used as strain gauges without heat treatment due to their poor crystallinity; Same■,′?
It is possible to improve crystallinity and improve sensitivity, and it is possible to obtain a stress conversion element that is easy to manufacture and has high reliability without going through a high temperature process or a photolithography process for patterning.

In addition, with metal materials, the strain-generating part and the pedestal can be integrally molded, but there are processing limitations in reducing the thickness of the strain-generating part, and there are limits to low-load measurements. For example, by using aluminum or aluminum alloy as the diaphragm, which has a lower deflection ratio of about 1/3 compared to stainless steel, the same amount of strain will be generated for the same pressure even if the wall thickness of the strain-generating part is about three times as large. , low load measurement is possible.

Furthermore, by using aluminum or aluminum alloy for the diaphragm, the insulating layer can be formed extremely easily and in a short time by anodic oxidation. Compared to forming, the number of man-hours is significantly reduced.

Further, since the substrate does not require heating and can be kept at about room temperature, distortion due to heat does not occur.

FIG. 3 shows the results of measuring the relationship between the gauge resistance and the boron concentration of the pressure sensor thus formed.

Further, FIG. 4 shows the results of measuring the relationship between the V span and the boron concentration. Here, V span means that the resistance of each strain gauge on the diaphragm is R1-R4, and the applied voltage is V1.
When the applied pressure is PO, Pl, R2 (P l)
R3(P+)Vspan(llV)-Vx
() R1 (PI) + R2 (Pi) R3 (Pi) + R4
(PI)R2(PO) R3(PO)-Vx
() R1 (PO) + R2 (PO) R3 (PO) + R4
(Po). In addition, here, V-
5000mV, applied pressure PO-Okg/crl, P1
= IQkg/c#, total 1111.

From the results shown in FIGS. 3 and 4, it can be seen that this pressure sensor has extremely good reproducibility of the resistance value depending on the boron concentration.

Furthermore, FIG. 5 shows the results of measuring the relationship between the rate of change in resistance of the strain gauge of this pressure sensor and the amount of compression. It can be seen from FIG. 5 that the strain gauge of this pressure sensor has linearity with respect to applied pressure both in compression and tension.

Furthermore, the results of measuring the heavy fatigue characteristics of this pressure sensor are shown in FIG. As is clear from FIG. 6, no change in the rate of change in resistance was observed even after the pressure application was repeated 106 times.

From the above results, it can be seen that the pressure sensor according to the embodiment of the present invention is extremely easy to manufacture and inexpensive, and has characteristics comparable to those of conventional pressure sensors.

In the above embodiment, the alumite layer was formed by sulfuric acid alumite treatment, but in addition to this, alumite treatment using hydrochloric acid, phosphoric acid, or the like may be used.

Further, in the above embodiment, a diaphragm made of an aluminum alloy was used, but other metals such as magnesium and titanium may also be used. For example, in the case of magnesium, magnesium oxide is used as the surface insulating film, and in the case of titanium, titanium oxide is used as the surface insulating film.

Furthermore, the insulating layer on the surface is not limited to an oxide film such as an alumite layer, but may be a nitride film or the like.

Furthermore, the formation of a semiconductor thin film containing impurities is not limited to the sputtering method, but also includes vacuum evaporation method, plasma CVD method, etc.
D method etc. may also be used. Here, when using the vacuum evaporation method, a target containing impurities such as B and P is used. In addition, when using the plasma CVD method, B2 H6
A method is used in which gas or PH3 gas is mixed with SiH4 or 5i2H6 and decomposed to form a film.

Furthermore, the semiconductor thin film serving as the substrate for the conductor (1) is not limited to amorphous silicon, and may be other semiconductor layers such as a single crystal silicon layer or a polycrystalline silicon layer.

Furthermore, without being limited to semiconductor thin films containing impurities, we can deposit an intrinsic semiconductor thin film and irradiate the surface of this semiconductor thin film with laser light in an atmosphere containing impurities such as B2 H6 gas!
! A strain gauge made of an impurity diffusion pattern may be formed by direct radiation.

In addition, by forming a diffusion source thin film on the surface of the semiconductor substrate, laser light! ! <(IN may be used to diffuse impurities from this diffusion source thin film to the surface of the semiconductor substrate to form a strain gauge made of an impurity diffusion button.

As a method for forming this diffusion source thin film, it is also possible to use a spin code method. In other words, this method is
N-type impurities such as phosphorus or p-type impurities such as boron caps and 5
This is a method in which a film-forming coating solution in which a glassy forming agent such as i02 is dissolved in an organic solvent such as alcohol is supplied to the surface of a semiconductor substrate and coated uniformly with a spinner, depending on the concentration of the coating solution and the rotation speed of the spinner. By changing , the film thickness can be easily controlled. Therefore, by controlling the film thickness of the diffusion source impurity, the impurity concentration of the strain gauge can be easily controlled.

In addition, as mentioned above, this impurity introduction step includes (1) a method of adsorbing impurities on the surface of the semiconductor substrate, and (2) a method of forming a film containing impurities (diffusion source film) on the surface of the semiconductor substrate. (3) There is a method of incorporating impurities into the semiconductor substrate at the time of forming the semiconductor substrate, and this method may be selected as appropriate depending on the constituent material of the strain generating portion and the constituent material of the strain gauge.

In addition, in the embodiments, a structure having a diaphragm-shaped strain-generating portion has been described, but it goes without saying that a shape such as a cantilever or the like may also be used.

[Effects of the Invention] As explained above, according to the stress converting element of the present invention, the diaphragm is made of a metal insulated by surface modification, and the strain gauge pattern is formed on the surface of the semiconductor base forming the strain-generating portion. Since it is composed of an impurity diffusion region formed by selective laser irradiation in the presence of impurities, it is low cost, easy to manufacture, and highly reliable.

[Brief explanation of drawings]

1(a) to 1(d) are diagrams showing the manufacturing process of a pressure V sensor according to an embodiment of the present invention, FIG. 2 is a diagram showing a laser irradiation chamber used in an embodiment of the present invention, and FIG. The figure shows the relationship between gauge resistance and boron concentration for the same pressure sensor at 1TFJ.
Figure 4 is a diagram showing the results of measuring the relationship between V span and boron concentration. Figure 5 is a diagram showing the relationship between the rate of change in resistance and the applied pressure of the pressure sensor.
The figure shows the heavy fatigue characteristics of the same pressure sensor, Figures 7 and 8 show conventional pressure sensors, Figure 9 is an equivalent circuit diagram of the pressure sensor, and Figure 10 is an explanation of &lIJ regular. It is a diagram. DESCRIPTION OF SYMBOLS 1... 11 Crystal silicon substrate, 2... Silicon oxide film W... Window, 3... Strain gauge pattern, 4... Thin wall part, 5... Wiring layer, 100... Aluminum diaphragm , 101... Alumite layer, 102... Boron-doped amorphous silicon thin M, 103...
...Laser light, 104...Strain gauge, 105...Wiring pattern 201...r! ((shooting chamber body, 202...
- Piping, 203...quartz window, 204...laser oscillator, 205...sample, wl...window. Figure Figure pressure 77 CkQ/Cm') Figure 5 Figure 10

Claims (4)

[Claims] (1) A strain-generating portion made of metal; an insulating layer formed on the surface of the strain-generating portion by modifying the metal surface; a semiconductor base disposed on the surface of the insulating layer; and a strain gauge pattern formed by selectively irradiating the surface of the semiconductor base with a laser in the presence of impurities. (2) Claim (1) characterized in that the insulating layer is a metal oxide film obtained by oxidizing the metal.
) described stress conversion element. (3) the metal is aluminum; The insulating layer is an alumite layer. The stress conversion element according to claim (1). (4) A method for manufacturing a stress converting element including a strain generating part and a strain gauge pattern disposed on the surface of the strain generating part, comprising: a strain generating part forming step of forming a strain generating part made of metal; an insulating step of forming an insulating layer by modifying and insulating the surface of the strained portion; a semiconductor base forming step of forming a semiconductor base on the insulating layer; and an impurity-containing step on the surface of the semiconductor base. and a laser irradiation step of irradiating the impurity-introduced semiconductor base with a laser to form a strain gauge consisting of an impurity region pattern. Production method.