JPH02100372A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To enable controlling correctly and easily the thickness of a pressure diaphragm by performing pressurization to a pressure at which the center of single-crystal silicon parts is detected as the pressure diaphragm and taking the detection signal from a distortion gauge. CONSTITUTION:A semiconductor pressure sensor consists of single-crystal silicon parts 1 and 2 comprising single-crystal thin plates of one conductivity type and having a distortion gauge formed in the center of one face thereof by diffusing an impurity of the other conductivity type, a silicon compound film 3 covering the other face of said single-crystal silicon parts, and a single-crystal silicon part 4 grown on said silicon compound film 3 and the part, corresponding to the center of the single-crystal silicon parts, of which is dug to the silicon compound film. The semiconductor pressure sensor is pressurized to a pressure at which the center of the single-crystal silicon parts 1 and 2 is detected as a pressure diaphragm and the detection signal is took from the distortion gauge. Thereby the thickness of the pressure diaphragm can be controlled correctly and easily.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a semiconductor pressure sensor using single-crystal silicon, that is, a thin single-crystal silicon is used as a highly elastic pressure-receiving diaphragm, and the deflection of this diaphragm is controlled by a high pressure sensor built into it. This relates to what is detected by a gauge factor semiconductor strain gauge.

[Conventional technology]

Single-crystal silicon is excellent as a semiconductor material for manufacturing various semiconductor devices, and as is well known, it also has almost ideal high elasticity with no history of mechanical strain and stress characteristics. Since the extremely high strain gauge of the gauge soactor can be easily fabricated by impurity diffusion, a compact and highly sensitive semiconductor pressure sensor can be constructed by using this single crystal silicon as both an elastic material and a semiconductor. can do. FIGS. 5 and 6 show conventional examples of such semiconductor pressure sensors, respectively.

In the example of FIG. 5, for example, an n-type single crystal silicon substrate 20
First, a plurality of strain gauges 7, which are a type of resistance layer, are formed from the upper surface by diffusion of p-type impurities, usually in an elongated strip pattern, and both ends of each strain gauge 7 are formed through a window of 115 oxide as shown in the figure. A connection 11910 made of aluminum or the like is connected to the part, and the entire surface is covered with a protective film 11 such as a nitride film as usual. In Figure 0, only two strain gauges 7 are shown.
In the five cases, four strain gauges are arranged so as to form, for example, a rectangle as a whole, and are bridge-connected via a connection film 10. As shown in the figure, a window is opened in the protective film 11 on the other end of the connection film IO, one end of which is connected to each vertex of this bridge, and used as a connection pad CP for connection with an external circuit. .

Next, a mask film 21 such as an oxide film or a photoresist film is attached to the lower surface of the substrate 20, and the substrate 20 is chemically etched through the window opened in the mask film 21, so that the strain gauge 7 is fabricated as shown in the figure. A hole 22 is deeply dug from the back side of the substrate Fi 20 in the area.The thinned part of the substrate 20 on the upper side of the figure of this person 22 is used as the pressure receiving diaphragm of the semiconductor pressure sensor, and the surrounding substrate that is not dug is [Part 20 is used for installation. The method of attachment is simply shown by the dashed line in the figure, and the semiconductor pressure sensor is attached to the base 16 at the periphery of the diaphragm by soldering or other means via the attachment base 15 made of silicon or the like. and cap 17 from above.
It is stored in a sealed container by covering it and sealing it.

The inside of the closed container is usually kept at a constant reference pressure Pr, for example, a vacuum, and the pressure P to be detected or measured is applied to the space inside the hole 22 through the holes 15a and 16a bored in the mount 15 and the base 16. introduced from outside. As a result, the detected pressure P,! A pressure difference between the diaphragm of the substrate 20 and the M' quasi-pressure Pr is applied to the diaphragm of the substrate 20, and a change in the resistance value of the strain gauge 7 due to the deflection is detected by the aforementioned bridge circuit.

In the conventional example shown in FIG.
As before, an n-type layer 31 with a high impurity concentration is used as before, and after first diffusing a p-type layer 31 with a high impurity concentration on its surface, an n-type epitaxial layer 32 is grown, and then an n-type epitaxial layer 32 is grown in it. In addition to fabricating the strain gauge, in this example, related electronic circuits including transistors and the like for amplifying the detection signal are fabricated in the same manner as in the case of an integrated circuit.

For this purpose, the p-type separation layer 6 is deeply diffused with high impurity concentration from the surface of the n-type epitaxial layer 32 so as to reach the p-type layer 31, thereby junction-separating it into a plurality of semiconductor regions. The strain gauge 7 is fabricated in one of these semiconductor areas in the same manner as before, and circuit elements for electronic circuits are fabricated in the other semiconductor areas as appropriate. An example of this circuit element is shown in Figure 0. , an epitaxial layer 3 separated into a semiconductor region
An npn transistor is shown having a collector region 2 with a p-type base layer 8 and an n-type emitter layer 9 diffused therein. A connection 11gl0 that makes conductive contact with each part as shown through the window of the oxide film 5 is connected to the strain gauge 7.
is connected to this transistor, etc., and the protection wA1
The end exposed in the window 1 is appropriately used as a connection pad CP.

Next, a mask 1933 is attached to the lower surface of the substrate 30, and a hole 34 is dug into the substrate 30 through the window opened in the mask 1933, thereby forming a pressure receiving diaphragm in the same manner as in the previous example. The procedure for attaching this semiconductor pressure sensor and detecting pressure using it is the same as in the case of FIG. 5. Of course, in this example, a constant voltage or current can be supplied to the bridge circuit of the strain gauge 7 via the electronic circuit, and a detection signal amplified by the electronic circuit can be taken out from the semiconductor pressure sensor.

[Problem to be solved by the invention]

In any of the above-mentioned semiconductor pressure sensors, pressure detection values with good reproducibility can be obtained due to the high elasticity of single crystal silicon, and pressure can be detected with high sensitivity due to the high gauge factor of semiconductor strain gauges. The conventional example shown in the figure has a problem in that its pressure detection characteristics tend to vary.

This is because it is difficult to accurately control the depth at which the holes 22 are chemically etched in the substrate 20 of FIG. 5, and therefore the thickness of the pressure receiving diaphragm tends to vary. As can be easily seen, this variation increases as the depth of the hole 22 is dug, so if the board 20 is made thinner and the depth of the hole 22 is made shallower, this variation can be reduced. Due to the difference in thermal expansion coefficient between the silicon substrate 20 and the base 16, which is usually a metal, thermal stress is likely to be applied to the pressure receiving diaphragm, increasing the temperature dependence of the pressure detection characteristics.

In the example of FIG. 5, this thermal stress is absorbed by the silicon mounting base 15, but it is originally most desirable to increase the thickness of the substrate 20 so that it can be mounted directly to the base 16. In terms of manufacturing, the thickness of the substrate 20 is thin, for example, 20 mm.
When the diameter is less than about 0 μm, the wafer becomes easily bent and becomes extremely difficult to handle, so a small-diameter wafer must be used, which reduces the number of semiconductor pressure sensors that can be produced from one wafer and increases production costs. There's a problem.

In the conventional example shown in FIG. 6, the above-mentioned problem can be solved by using electrolytic etching to dig the hole 34 into the substrate 30. When digging this hole 34, first, the substrate 30 is etched by chemical etching using, for example, a caustic potash solution.
By digging to most of the thickness of the p-type layer 31 and finally performing electrolytic etching using an acid-based solution, the digging can be automatically stopped at the lower surface of the p-type layer 31 as shown in the figure.

That is, the substrate 30 is placed on the positive side of the low voltage power supply for electrolysis.

By performing electrolytic etching with the electrolyte connected to each negative side, when the digging reaches the lower surface of the p-type layer 31, the p-type layer 3 is removed by the p-n junction with the n-type substrate 30.
No current flows through the hole 1, and the digging stops automatically.

In this way, in the conventional example shown in FIG. 6, even if the substrate 30 is thick, the digging of the hole 34 is automatically stopped at the p-type layer 31, and the thickness of the pressure receiving diaphragm can be controlled with precision. However, in terms of manufacturing, there remains the problem that two steps are required to dig into the substrate to form the diaphragm, and electrolytic etching takes a considerable amount of time. Furthermore, crystal defects are likely to occur in the epitaxial layer 32 grown on the p-type layer 31 with a high impurity concentration, and the strain gauge 7
When a semiconductor pressure sensor is fabricated, its gauge factor tends to decrease due to leakage current due to crystal defects, which poses a problem of lowering the production yield of semiconductor pressure sensors. Further, the same applies when related electronic circuits are incorporated therein as described above, and the withstand voltage value and current amplification factor of transistors etc. are likely to decrease due to crystal defects.

The present invention solves the problems of the prior art and provides a semiconductor pressure sensor in which the thickness of the pressure-receiving diaphragm can be precisely controlled and easily controlled, and the strain gauge can have a high gauge factor. With the goal.

[Means for solving CRB] According to the present invention, this purpose is achieved by forming a thin plate of single crystal silicon having one conductivity type, and forming a strain gauge on one side of the central part by diffusing impurities of the other conductivity type. a silicon compound film that covers the other side of the single crystal silicon part; and a silicon compound film that is grown on the silicon compound film and covers the central part of the single crystal silicon part. This is achieved by a semiconductor pressure sensor comprising a polycrystalline silicon portion that is dug up to a depth of .

The wafer used to fabricate this semiconductor pressure sensor is made by attaching a silicon compound film such as a silicon oxide film to one side of a single crystal silicon substrate, growing polycrystalline silicon on top of it, and then attaching the single crystal silicon substrate to a pressure-receiving diaphragm. It is possible to use a material that has been ground to a suitable thickness and finished by lapping or other means. Although the polycrystalline silicon portion can be etched by electrolytic etching, it is more practical to use chemical etching, and this chemical etching process can be divided into two steps: high-speed etching at the beginning and slow etching at the end. It is desirable to separate them in order to shorten etching time and improve etching accuracy.

[Effect]

As can be seen from the above structure, the present invention takes advantage of the fact that polycrystalline silicon and silicon compound films are fundamentally different in etching speed or presence, and etches into a polycrystalline silicon portion to form a pressure receiving diaphragm. By automatically stopping at the boundary with the silicon compound film, the thickness of the pressure receiving diaphragm can be accurately and easily controlled, and the single crystal silicon part has far fewer crystal defects than conventional epitaxial layers. By constructing a thin plate or substrate of single-crystal silicon and fabricating a strain gauge from its surface, we succeeded in giving it a high gauge factor.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same parts as in Figs. 5 and 6 explained before Fig. That's it. 1 to 3 show different embodiments of the present invention, and FIG. 4 shows the manufacturing process of the embodiment of FIG. 1.

Hereinafter, in order to facilitate understanding, the manufacturing process will be explained starting from the manufacturing process shown in FIG. 4.

First, in the first step shown in FIG. 4(a), a single crystal silicon substrate 1 is used as a starting point. This substrate 1 is of n-type in this example, and has an impurity concentration of, for example, 1Qlfi~
A material with a density of 1Q16 atoms/cd and a thickness of approximately 500 nm is used. In the figure of this single crystal silicon substrate l, on the bottom surface,
First, the p-type layer 2 is diffused to a depth of, for example, 5 to 10 .mu.m with a high impurity concentration of 10@11 atoms/C@- or more. This p-type layer 2
As in the case of the previous FIG. If only the gauge needs to be formed on the substrate 1, it is not necessary to provide this p-type layer 2. Next, a silicon compound film 3, for example, a silicon oxide film, is formed on the surface of this wafer to a thickness of approximately lp- by thermal oxidation or CVD. This silicon compound film 3 is normally applied to both sides of the wafer as shown, but in the present invention, the lower side is more important.

In the step shown in FIG. 4(c), polycrystalline silicon 4 is deposited, for example, on the silicon compound film 3 on which the p-type layer 2 is diffused.
In the step of FIG. 4(C) of the 0th order, which is grown to a thickness of 00 to 500 nm to form the polycrystalline silicon part referred to in the present invention,
The single-crystal silicon substrate l is ground from its top surface to the desired thickness for the pressure-receiving diaphragm, and then polished to a mirror finish by lapping. Although this thickness varies depending on the pressure to be detected by the semiconductor pressure sensor, it is usually 20 to 100 pm including the p-type layer 2. As shown in Figure 1,
This ground single-crystal silicon substrate 1 including the P-type layer 2 constitutes a single-crystal silicon portion according to the present invention. It should be noted that since the surface of the polycrystalline silicon portion 4 tends to have some unevenness during its growth, it is desirable to flatten the surface at the same time by using the above-mentioned roughing process.

In the step shown in FIG. 4(d), the separation layer 6 is first diffused from the mirror-finished surface of the quasi-crystalline silicon portion as described above in the same manner as in FIG. After separating the junctions into a plurality of semiconductor regions, a strain gauge 7, a base layer 8 for a transistor, and an emitter layer 9 are formed in the semiconductor region, and oxidation 1! After completing the specified connection with the connection film lO on II5, connect the connection pad cp with the protective film 11.
The strain gauge 7 is a relatively high-resistance resistance layer diffused as a p-type in an n-type semiconductor region of a single-crystal silicon substrate l. The concentration is 1014 to 101?atoms/cd, and the diffusion depth is 2 to 5 pm.Then, for example, CV
By method D, an oxide film 12 having a dense structure is grown on the entire surface to a thickness of 1 to 3 nm as shown in the figure.

In this embodiment, the engraving of the polycrystalline silicon 4 is carried out in a two-step process of high-speed etching and low-speed etching, and FIG. 4(e) shows the high-speed etching process. After opening the window, the hole 13 is dug by chemically etching the polycrystalline silicon part 4 using, for example, a mixed acid of butic acid and nitric acid as an etching solution. However, in this process, as shown in the figure, polycrystalline silicon 4
For example, a thickness of about 20 nm is always left on part 1.

FIG. 1 shows the completed state in which the semiconductor pressure sensor is separated from the wafer after the low-speed etching process has been completed. Using a highly selective solution 8, for example, a mixed solution of butic acid, nitric acid, and sodium nitrite, the digging of the hole 14 into the polycrystalline silicon portion 4 is automatically stopped at the boundary with the silicon compound film. The etching rate at this time is, for example, about 1 nm per minute.

After completing the digging of the hole 14, the oxide 11112 is removed and the semiconductor pressure sensor is separated from the wafer at the separation layer 6 in the usual manner, resulting in the completed state shown in FIG.

This semiconductor pressure sensor is used while being housed in a sealed container as previously shown in FIG. By allowing it to absorb thermal stresses, the installation of FIG. 5 allows the mount 15 to be omitted from the structure.

In the embodiment shown in FIG. 2, instead of junction-isolating the single-crystal silicon substrate 1, a groove 18 separates the semiconductor region from the substrate. Therefore, as shown in FIG. 1, the p-type layer 2
The silicon compound 111J is directly applied to the surface of the substrate 1 without providing a silicon compound 111J! 3 and after growing a polycrystalline silicon portion 4 thereon, the surface of the substrate 1 is ground to a desired thickness and lapped to a mirror surface. To cut a trench-like groove 18 deeply from the surface of the substrate l as shown in the figure,
For example, by using an anisotropic dry etching method, silicon oxide is grown by a CVD method so as to fill this groove, so as to be continuous with the oxide film 5. The procedure for forming the semiconductor layer such as the strain gauge 7 on the substrate l and the procedure for digging the hole 14 in the polycrystalline silicon portion 4 for forming the pressure receiving diaphragm are the same as in the previous embodiment.

In the embodiment shown in FIG. 3, the single crystal silicon base FX1
A dielectric separation method is used to divide the semiconductor region into semiconductor regions. For this purpose, first, a ■-shaped groove 1b is cut on the lower surface of the substrate l by chemical etching, and the inner surface of this groove tb and the group F are etched.
After covering the lower surface of i1 with a silicon compound film 3 that also serves as a dielectric film and growing a polycrystalline silicon portion 4 thereon, the upper surface of the substrate l is ground until the bottom of the groove 1b is exposed. a 4iii1 is dielectrically separated into a dish-shaped semiconductor region as shown. After forming the strain gauges 7 and the like in each semiconductor region, holes 14 are made in the polycrystalline silicon portion 4 under the flat bottom surface of the semiconductor region in which the strain gauges are formed in the same manner as before. to form a pressure receiving diaphragm. Thereby, even if the V-shaped groove 18 is cut in the substrate 1, the pressure receiving diaphragm portion in which the strain gauge 7 is formed can have the high elasticity of single crystal silicon.

As can be seen from the embodiments described above, the present invention can be implemented in various ways within the above-mentioned gist, but the strain gauge is always fabricated by diffusion from the surface of single crystal silicon, and the strain gauge is The engraving of polycrystalline silicon to form the pressure receiving diaphragm part that is built in reaches the silicon compound film surface by taking advantage of the essentially different etching properties of polycrystalline silicon and silicon compound films. Therefore, the pressure-receiving diaphragm is always composed of highly elastic single-crystal silicon.

〔Effect of the invention〕

As explained above, in the present invention, a single crystal silicon part is made of a thin plate of single crystal silicon of one conductivity type, and a strain gauge is built into one side of the central part by diffusion of impurities of the other conductivity type. , a silicon compound film that covers the other side of this single crystal silicon part, and a multilayer film that is grown on this silicon compound film and is dug until the area corresponding to the central part of the single crystal silicon part reaches the silicon compound waist. A semiconductor pressure sensor is constructed with the crystalline silicon part, and the central part of the single crystal silicon part is connected to the pressure receiving diaphragm L7 to apply the pressure to be detected and extract the detection signal from the strain gauge. (a) Pressure receiving diaphragm It is possible to automatically stop the digging of the polycrystalline silicon portion to form a polycrystalline silicon layer at the boundary between the polycrystalline silicon and the silicon compound film by taking advantage of the fact that the etching speed or presence is essentially different between the two. As a result, it is possible to provide a semiconductor pressure sensor with less variation in pressure detection characteristics while accurately and easily controlling the thickness of the pressure receiving diaphragm. (b) The resistance layer for the strain gauge is made of single crystal silicon with few crystal defects. To provide a semiconductor pressure sensor with high detection sensitivity by reducing leakage current that does not contribute to pressure detection to the minimum and giving the strain gauge a high gauge factor by fabricating it from the surface of the part. Can be done.

Furthermore, the present invention has the following advantages.

(C) When incorporating related electronic circuits in addition to strain gauges into semiconductor pressure sensors, leakage current can be reduced because the circuit elements for these can be built into a single-crystal silicon part with far fewer crystal defects than in the past. As a result, the withstand voltage value of the circuit element and the current amplification factor of the transistor can be improved.

(d) Since it is possible to use a single-crystal silicon substrate with the most suitable crystal plane for fabricating strain gauges in single-crystal silicon parts, it is possible to fabricate strain gauges from the surface of the epitaxial layer, regardless of the problem of crystal defects. It is possible to fabricate a strain gauge with an essentially higher gauge factor than when the strain gauge is fabricated using a conventional method.

The present invention, which has these features, is particularly suitable for manufacturing small, inexpensive, general-purpose semiconductor pressure sensors, reduces variations in its pressure detection characteristics, improves its pressure detection sensitivity, and improves its economic efficiency. It is expected that this improvement will contribute to the further spread and development of this type of semiconductor pressure sensor.

[Brief explanation of the drawing]

1 to 4 relate to the present invention, and FIG. 1 to 3 relate to the present invention.
The figures up to the figures are sectional views showing different embodiments of the semiconductor pressure sensor according to the present invention, and FIG. 4 is a sectional view of a wafer for a semiconductor pressure sensor showing the manufacturing process of the embodiment of FIG. 1. FIGS. 5 and 6 are cross-sectional views of semiconductor pressure sensors according to different conventional techniques, respectively, in FIG. 0, l: a single crystal silicon substrate constituting a single crystal silicon portion;
1a double trench groove, lb: V-shaped groove, 2: p-type layer of single crystal silicon part, 3: silicon compound film or silicon oxide film, 4: polycrystalline silicon part, 5I oxide film, 6: min am
, 7: strain gauge or resistance layer for it, 8: base layer,
9: Emitter layer, 10: Connection film, 117 IMS12:
Mask film or oxide film, 13, 14: Drilled hole for polycrystalline silicon part, 15 + silicon mounting base, 16
: base of sealed container, 15a, 16b + detection pressure introduction hole, 17 + cap of sealed container, 20 + single crystal silicon substrate, 21: mask film, 22: dug hole, 30: single crystal silicon substrate, 31: p-type layer , 32: epitaxial layer, 33: mask film, 34: dug hole, CP: connection pad, P: detected pressure, I'r: &heavy pressure. Figure 5 Figure 6

Claims (1)

[Claims] A single-crystal silicon part is made of a thin plate of single-crystal silicon of one conductivity type, and a strain gauge is built into one side of the central part by diffusion of impurities of the other conductivity type, and the other part of this single-crystal silicon part is made of a thin plate of single-crystal silicon having one conductivity type. comprising a silicon compound film covering the surface side, and a polycrystalline silicon part grown on the silicon compound film and dug until a range corresponding to the central part of the single crystal silicon part reaches the silicon compound film, A semiconductor pressure sensor characterized in that the central part of a single crystal silicon part is used as a pressure receiving diaphragm to apply pressure to be detected and to extract a detection signal from a strain gauge.