JPH0368829A - Pressure detector and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to achieve high sealing property and to improve the accuracy of a pressure receiving diaphragm by employing an oxide based single crystal substrate as a pressure detector for high temperature. CONSTITUTION:A pressure receiving diaphragm 1a is composed of the junction of an oxide-based single crystal substrate 12 such as sapphire having a through- hole 12a and a planar oxide-based single crystal substrate 11. Therefore, the dimensional accuracy of the diaphragm 1a is determined only by the machining accuracy of the hole 12a in the substrate 12. Thus the dimensional accuracy can be constituted highly accurately. Therefore, dispersion in stress which is applied on semiconductor strain gages 13 arranged on the surface of the diaphragm can be suppressed, and the accuracy is improved. Furthermore, the detector can be rigidly fixed to a metallic housing by using high temperature treatment or a bonding agent, and high sealing property is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detector, and particularly to a pressure detector suitable for measuring the pressure of high-temperature fluid, for example, the combustion pressure of an internal combustion engine.

[Conventional technology]

Conventionally, in this type of device, the sensing section has a so-called SO2 structure in which a semiconductor strain gauge element made of single crystal or polycrystalline silicon is formed on an insulating substrate. This one is P like the diffusion gauge type one.
Since it does not have an N junction, there is no leakage current at high temperatures, making it possible to detect pressure in a high temperature atmosphere of 200''C or higher.

As a sensing section having a Sol structure, one is known in which a semiconductor strain gauge element made of single crystal silicon or polycrystalline silicon is formed on a single crystal silicon substrate with an insulating layer interposed therebetween.

[Problem to be solved by the invention]

However, in high-temperature pressure detectors, metal is used for the housing, etc., and in those using the silicon substrate described above, the bonding of the silicon substrate to the metal housing is limited to glass bonding, where the adhesive strength is not very strong. However, there is a problem in that high sealing performance cannot be achieved.

Therefore, the present inventors adopted an oxide single crystal substrate of sapphire, spinel, magnesia, etc., which can be firmly adhesively fixed to a metal housing by brazing, as the insulating substrate.

However, the problem with oxide single crystal substrates is that chemical etching, which is used to process single crystal silicon substrates, cannot be applied, and the processing must rely on mechanical processing.

If we were to process a pressure sensor using this new substrate using the same concept as before, we would have to perform cutting from the back side of the substrate using a drill or the like to form a thin pressure-receiving diaphragm. As shown in Figure 12, it is inevitable that the shape accuracy will deteriorate significantly, and as a result, the stress value applied to the semiconductor strain gauge element 13 formed on the diaphragm surface will vary greatly, and furthermore, the output value as a pressure detector will vary. will occur.

The present invention was made in view of the above problems, and uses an oxide single crystal substrate that can be firmly fixed to a metal housing as a pressure detector for high temperatures. Based on this idea, we provide a pressure detector that can suppress variations in output values by configuring the shape of a pressure receiving diaphragm with high accuracy, and a manufacturing method that allows the pressure receiving diaphragm to be configured with high shape accuracy. .

[Means to solve the problem]

In order to achieve the above object, the present invention has the following features: As shown in the basic configuration diagram of FIG. a second oxide-based single-crystal substrate that is bonded onto the first oxide-based single-crystal substrate and forms a pressure-receiving diaphragm at the predetermined position; 4. A structure characterized in that a semiconductor strain gauge element is disposed on an end surface of the second oxide single crystal substrate opposite to the bonding surface with the first oxide single crystal substrate. The described invention includes a hole processing step of opening a through hole at a predetermined position of the first oxide single crystal substrate in the first and second oxide single crystal substrates; Substrate bonding in which the mirror surfaces of the first oxide single crystal substrate and the flat second oxide single crystal substrate are bonded to form a bonded substrate having a pressure receiving diaphragm at the predetermined position. In this bonded substrate, a semiconductor strain gauge element is provided on the pressure-receiving diaphragm surface of the end surface of the second oxide-based single-crystal substrate opposite to the bonded surface with the first oxide-based single-crystal substrate. Provided is a method for manufacturing a pressure sensor, characterized in that the method includes a step of forming an element.

[Action/Effect]

As shown in FIG. 1, the pressure receiving diaphragm 1a includes a first oxide single crystal substrate 12 having a through hole 12a opened at a predetermined position, and a second oxide single crystal substrate 11 having a flat plate shape.
It is constructed by joining with.

Therefore, the dimensional accuracy on the pressure receiving diaphragm surface is determined only by the processing accuracy of the through hole 12a of the first oxide single crystal substrate 12 and the thickness accuracy of the second oxide single crystal substrate 11. can be configured with high precision. Therefore, variations in the stress applied to the semiconductor strain gauge element 13 disposed on the diaphragm surface can be suppressed, which has the excellent effect of suppressing variations in the output value from the semiconductor strain gauge element 13.

Furthermore, as described above, since the oxide single crystal substrate is used, it can be firmly fixed to the metal housing and high sealing performance can be achieved.

Furthermore, the invention as set forth in claim 4 has an excellent effect in that a pressure detector having the above-mentioned effects can be manufactured.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

FIG. 2 shows the main structure of a pressure detector to which an embodiment of the present invention is applied. Cylindrical housing 3 with a large diameter at the right end
A mounting screw portion 3a is formed on the outer periphery of the main body, and an element holder 2 made of a cylinder with one end closed is inserted through the left end opening and is tightly fixed by welding.

The element holder 2 is made of Fe-Ni- which has a small coefficient of thermal expansion.
It is made of a Co-based alloy, and there is no pressure introduction port inside the element holder 2. Furthermore, an opening 2a is provided in the side wall of the pressure introduction boat.

The element holder 2 includes a sensing element 1 made of a sapphire substrate which is an oxide single crystal substrate.
However, in order to close the opening 2a, it is firmly bonded and covered by brazing from above the opening 2a, as will be described later. In addition,
A thin recess is provided in the sensing element 1 directly above the center of the opening 2a, and serves as a pressure receiving diaphragm 1a. The details of sensing element 1 are shown in Figure 3 (a
).

Shown in (b). Note that FIG. 3(a) is an AA sectional view of what is shown in FIG. 3(b), and FIG. 3(b) is a plan view (however, the surface protective film is shown in the illustration).

The sensing element 1 is a processed sapphire substrate, and a thin pressure-receiving diaphragm 1a is constructed by bonding a flat sapphire substrate 11 onto a sapphire substrate 12 that has been processed with through holes. Note that the pressure receiving diaphragm 1a is formed at one end of the rectangular parallelepiped-shaped sensing element 1 in the vertical direction. The other end is a pad portion 15 which will be described later as a lead extraction head area. An IC circuit chip 5 and the like are configured.

Moreover, the sensing element 1 is shown in FIGS. 3(a) and (b).
), a semiconductor strain gauge element 13a is made of a p-type wheel crystalline silicon thin film doped with impurities by vapor phase growth of silicon at four locations on the surface of the bonded sapphire substrate;
13b is formed.

The plane orientation of the semiconductor is (100), and the longitudinal direction of the semiconductor strain gauge element is the [110] direction of the (100) plane, which is the longitudinal direction of the sensing element 1 in FIG. 3(b). Moreover, the semiconductor strain gauge element 13a,
13b are arranged directly above the peripheral edge of the pressure receiving diaphragm 1a, and are connected to each other by lead electrodes 14 made of a metal thin film or a semiconductor thin film also formed on a sapphire substrate. This lead electrode 14 is wired in parallel to the other end of the sensing element 1 constituting the above-mentioned readout region, and a pad portion 15 made of a metal electrode is provided at the end of the wire.

A surface protection film 16 for passivation is deposited on the surface of the sensing element 1.

In FIG. 2, a lead extraction area is formed at the right end of the surface of the sensing element 1, and the signal processing IC is bonded to the pad portion 15 and the wire line 4 described above.
A circuit chip 5 is fixed with adhesive. IC circuit chip 5
is composed of an amplifier circuit and a temperature compensation circuit, and is connected to the outside via a lead wire 6. Note that the temperature compensation circuit compensates for the resistance value characteristic of the semiconductor strain gauge element that changes with the temperature change of the pressure receiving diaphragm 1a.

Furthermore, in FIG. 2, a cylindrical cover 7 is welded and fixed to the housing 3, and the housing element 1 is supported at its right end by a holder member 8 that is adhesively fixed to the cover 7 and the housing 3.

In the above configuration, when the fluid pressure of the high temperature fluid acts on the pressure receiving diaphragm 1a provided in the sensing element 1, stress corresponding to this fluid pressure acts on the pressure receiving diaphragm 1a, deforming it, and causing deformation strain, that is, the applied stress. An output signal corresponding to the value is emitted from the semiconductor strain gauge element. Here, the sensing element l is a bonded substrate made of a substrate 12 with a through hole formed therein and a flat substrate 11 as described above, and the pressure receiving diaphragm 1a is constructed with high dimensional accuracy as shown in the detailed view of FIG. Therefore, the semiconductor strain gauge element 1 formed on the surface of the pressure receiving diaphragm 1a
Variations in the stress values applied to 3a and 13b become extremely small. Therefore, variations in the output signal generated by the semiconductor strain gauge element are also extremely small.

Next, the principle of generation of the output signal of this embodiment will be explained using FIG. FIG. 4 shows the semiconductor strain gauge element 1 of this example.
FIG. 3 is a layout diagram of 3a and 13b. In FIG. 4, a stress σ- in the tangential direction of the diaphragm 1a acts on the semiconductor strain gauge element 13a in the longitudinal direction of the gauge element 13a, and a stress σ- in the radial direction of the diaphragm 1a acts on the semiconductor strain gauge element 13a in a direction perpendicular to the longitudinal direction. □ works. On the other hand, semiconductor strain gauge element 1
3b, a stress σl is applied in the longitudinal direction of the gauge element 13b, and a stress σ− is applied in a direction perpendicular to the elongated direction. The piezoresistance coefficient πo, π in the (110) direction of the (100) plane of p-type wheel crystal silicon.

(πl is a vertical coefficient, π is a horizontal coefficient), there is a relationship of πlz−π, and the semiconductor strain gauge elements 13a and 13b
The rate of resistance change according to stress is expressed as follows. Note that Ra and Rb are resistance values of the semiconductor strain gauge elements 13a and 13b, respectively.

That is, the resistance changes of semiconductor strain gauge elements 13a and 13b are in opposite directions, and when a bridge circuit (not shown) is configured, the balance of this bridge circuit is balanced by the resistance change of the semiconductor strain gauge elements in response to the applied stress. Change. A constant current or constant voltage is applied to the bridge circuit, and this resistance change is generated as an output signal.

The output signal, that is, the pressure signal detected in this manner is amplified by the signal processing IC circuit chip 5, temperature compensated, and taken out to the outside via the lead wire 6.

Note that the pressure receiving diaphragm 1a is exposed to high temperatures due to the heat of the high-temperature fluid, but the pad portion 15. Since the sensing element 1 is configured in an elongated rectangular parallelepiped shape, the lead extraction area of the IC circuit chip 5 can suppress the influence of heat from the high temperature fluid, and the reliability of the lead extraction area against high temperatures is high. It becomes.

Furthermore, the coefficient of thermal expansion of sapphire is close to that of the Fe-Ni-Co alloy used for the element holder 2, and the so-called bimetallic effect caused by the difference in coefficient of thermal expansion can be suppressed.

In addition, as shown in FIG. 11, the back surface of the sensing element 1 excluding the diaphragm 1a, that is, the end surface of the sapphire substrate 12 having a through-hole in contact with the element holder 2, has a Ti metallized layer 9a, a Mo metallized layer 9b.

A Ni plating M9c is formed, and the Ag paste is brazed to the element holder 2 through a layer 9d. Incidentally, Ni plating 1i2b is also formed on the brazed portions of the element holder 2, making the joint by brazing strong. That is,
Even if high pressure acts on the sensing element, the sealing performance between the element holder 2 and the sensing element 1 is ensured, and pressure measurement can be performed accurately in a high temperature and high pressure environment.

Next, the manufacturing procedure of the sensing element 1 shown in FIGS. 3(a) and 3(b) will be explained using FIGS. 5 and 6(a) to (8). Figure 5 shows the process flow, Figure 6 (
a) to (g) are cross-sectional views in the order of manufacturing steps.

(Oxide-based single-crystal substrate hole processing step) In this example, a sapphire substrate is used as the oxide-based single-crystal substrate. A through hole 12a is opened in a predetermined position of the sapphire substrate 12 by mechanical polishing using a drill or the like (see FIG.
a)).

(Mirror finish process) Next, the sapphire substrate 12 with this through hole 12a opened.
By lapping and polishing the surface of each unprocessed sapphire substrate 11,
Finish to a mirror finish (as shown).

(Substrate bonding process) Next, the mirror-finished sapphire substrates 11 and 12 are bonded together to form a bonded substrate (see Figure 6(b)).
. Note that the joining method will be explained in detail later.

(Substrate thinning process) As shown in FIG. 6(C), the sapphire substrate 11 on the upper side of the bonded substrate is polished to a predetermined thickness, and then the surface is mirror-finished by lapping and polishing. As a result, a thin pressure receiving diaphragm 1a is formed.

(Semiconductor strain gauge element forming process) Next, as shown in FIG. 6(d), a semiconductor thin film, for example, a single crystal silicon thin film 13'' is deposited on the surface of the bonded substrate by vapor phase growth or the like. An impurity is added to make the conductivity type of the semiconductor thin film p-type. Methods for adding this impurity include a method of introducing an impurity gas during film formation of the semiconductor thin film, and a method of forming a film by introducing an impurity gas during film formation, and a method of forming a film by ion implantation etc. after film formation. There is a method of doping with impurities.

Next, the p-type crystal silicon thin film 1 added with this impurity is
By finely processing 3' by etching, a semiconductor strain gauge element 13 is formed at a predetermined position on the surface of the bonded substrate, as shown in FIG. 6(e).

(Lead electrode wiring step) Next, as shown in FIG. 6(f), a lead electrode 14 made of a metal thin film such as PT is wired. The thin gold film is formed by CVD, sputtering, vapor deposition, etc., and then microfabricated to form the lead electrode 14. At this time, a pad portion 15 made of a metal electrode is also formed (as shown in the figure).

(Protective film forming step) Then, as shown in FIG. 6(8), a surface protective film 16 for passivation is formed by CVD, sputtering, vapor deposition, etc.
form.

(Dicing process) Then, step dicing is performed to a predetermined size as shown in Figure 3 (
Sensing elements 1 shown in a) and (b) were manufactured.

In the above manufacturing method, the dimensional accuracy of the thinned pressure receiving diaphragm is determined by the processing accuracy of through-hole drilling during the oxide single crystal substrate hole processing process and the thickness control of the flat plate during the substrate thinning process. , it is possible to easily construct a pressure receiving diaphragm with high dimensional accuracy.

Note that in the above manufacturing process, the lead electrode 14 made of a metal thin film is wired during the lead electrode wiring process, but the lead electrode 14 may be made of the same semiconductor as the semiconductor strain gauge element 13. In that case, It can be formed simultaneously with the semiconductor strain gauge element 13 during the semiconductor strain gauge element forming process.

In addition, in the above manufacturing process, the pressure receiving diaphragm 1a is constructed by joining the substrates 11 and 12 and then thinning the substrate 11. However, the substrate 12 with through-holes formed therein and the substrate 11 which has been thinned in advance or after thinning. The substrate 11 having the semiconductor thin film 13' may be bonded thereto. However, when the thickness of the thin portion is as thin as 100 μm or less, care must be taken in handling.

Next, the substrate bonding process shown in FIG. 5 will be explained using FIGS. 7 to 10. In addition, Fig. 7.

8(a) to 8(d) are diagrams showing the direct bonding method of sapphire substrates, FIG. 7 is a process flow diagram, and FIG. 8(a)
-(d) are configuration diagrams showing the state of bonding at the atomic level. 9, 10(a) and 10(b) are diagrams showing a method of bonding using a bonding agent, FIG. 9 is a process flow diagram, and FIGS. 10(a) and 10(b) are It is a sectional view of process order.

First, as a first substrate bonding method, FIGS. 7 and 8 (a
) to (d), a method for directly bonding sapphire substrates will be explained. This is an application of direct bonding, which is normally used for bonding silicon wafers together, to bonding sapphire substrates.

(a Water treatment step) First, two mirror-finished sapphire substrates are immersed in an acidic solution such as CAROS (a mixture of sulfuric acid and hydrogen peroxide), and as shown in FIG. 8(a), the sapphire substrates are Adds hydroxyl groups (-OH) to the surface.

(Substrate bonding step) When the mirror surfaces of the substrates to which hydroxyl groups have been added are bonded together, the two substrates are brought into close contact by hydrogen bonding force as shown in FIG. 8(b).

(Dehydration Process) Next, a dehydration process is performed at a temperature of 200 to 400°C to remove excess water present at the bonding interface, as shown in FIG. 8(C).

(High-temperature treatment step) After that, heat treatment is applied at a high temperature of 1000 to 1400''C for about 1 hour, whereby hydroxyl groups are released in the form of water (H2O), and the two substrates are firmly bonded at the atomic level. In addition, in the bonding strength test of the prepared bonded substrates, all fractures occurred outside the bonded areas, and the strength of the bonded areas was equivalent to the substrate strength.In addition, according to this bonding method, the bonding interface is extremely thin, so there is no heat resistance. Almost no distortion occurs.

Next, as a second substrate bonding method, a method using a bonding agent will be explained using FIGS. 9, 10(a), and (b). This bonding method uses a metal alkoxide solution as a bonding agent, and when a sapphire substrate is used as the oxide single crystal substrate, stable oxide Affi is used on the bonding surface.
, O, + can be formed in aluminum triethoxide (A
ffi (C,H,0)ff), aluminum triisopropoxide (,1!(○CzHt),) solution, etc. are used.

(Metal alkoxide solution coating step) First, as shown in FIG. 10(a), a metal alkoxide solution 17 is coated on the mirror surface side of the substrate 11.12 using a spinner or the like.

(Substrate Bonding Step) Next, as shown in FIG. 10(b), the mirror surfaces of the two substrates 11 and 12 coated with the metal alkoxide solution 17 are bonded together.

(Dehydration Process) In the same manner as the dehydration process shown in FIG. 7, excess moisture present at the bonding interface is removed by dehydration.

(High-temperature treatment step) Thereafter, a high-temperature treatment of 1000° C. or more is applied to form a stable oxide Al z○ at the bonding interface, and the substrates are firmly bonded to each other by this oxide.

By the first and second substrate bonding methods described above, it is possible to firmly bond oxide single crystal substrates (sapphire substrates in the example) to each other, and as described above, a pressure receiving diaphragm having high dimensional accuracy can be obtained. A sensing element can be easily formed.

Note that in the above series of examples, sapphire was used as the oxide single crystal substrate, but the present invention is not limited to this, and can also be applied to spinel, magnesia, etc., for example.

Alternatively, different types of oxide single crystal substrates may be bonded. In addition, especially when the first substrate bonding method described above is applied, hydrogen bonds may be broken due to stress due to the difference in thermal expansion coefficient during the high-temperature treatment process, and the substrate may peel off. It is a good idea to choose the one that has.

Further, the metal alkoxide solution shown in the second substrate bonding method above was applied to the bonding surface at 1! ! However, the present invention is not limited to this, and may also include, for example, s t(OCzl(s)a), S t(OCHs), which forms Sin on the bonding surface.
)4 solution etc. may be used.

The present invention relates to a thin-walled diaphragm made of an oxide single crystal substrate that can be used at high temperatures, and a method for manufacturing the same, and is not limited to the high-temperature pressure detector shown in the above embodiment, but is also applicable to high-temperature acceleration sensors, for example. It can also be applied to detectors, high-temperature magnetic detectors, etc.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a pressure receiving diaphragm section showing the basic configuration of the present invention, Fig. 2 is a cross-sectional view showing the main structure of a pressure detector to which an embodiment of the present invention is applied, Fig. 3 (a), b) is a detailed view of the sensing element 1 in Fig. 2, (a) is a sectional view taken along line AA in Fig. 2 (b), Fig. 4 (b) is a plan view, and Fig. 4 is Fig. 3 (b). 5 is a process flow diagram showing an example of the manufacturing process of the sensing element shown in FIGS. 3(a) and (b), and FIG. 6(a)
~(8) are cross-sectional views of the main parts of the sensing element in the order of manufacturing steps corresponding to FIG. 5, FIG. 7 is a process flow diagram of the substrate bonding process showing the first substrate bonding method, and FIG. 8(a) ~(d) is a structural diagram showing the state of bonding at the substrate bonding interface corresponding to FIG. 7, FIG. 9 is a process flow diagram of the substrate bonding process showing the second substrate bonding method, FIG. 10(a), (b) is a sectional view of the substrate in the process order corresponding to FIG. 9, FIG. 11 is an enlarged sectional view showing the bonded state of the sensing element and element holder, and FIG. 12 is a reference pressure receiving diaphragm section for explaining the present invention. This is a cross-sectional view of . l... Sensing element, la... Pressure receiving diaphragm, 11... Flat oxide single crystal (sapphire) substrate, 12... Oxide single crystal (sapphire) substrate with through hole processing. , 12a... through hole, 13.1
3a, 13b--Semiconductor strain gauge element, 13°...
Semiconductor thin film, 14... Lead electrode, 17... Metal alkoxide) liquid.

Claims (7)

[Claims] (1) a first oxide single crystal substrate having a through hole opened at a predetermined position; and a pressure receiving diaphragm bonded onto the first oxide single crystal substrate to form a pressure receiving diaphragm at the predetermined position. a flat second oxide single crystal substrate; and an end face of the second oxide single crystal substrate opposite to the bonding surface of the first oxide single crystal substrate of the pressure receiving diaphragm. , a pressure detector characterized in that a semiconductor strain gauge element is provided. (2) Claim 1, wherein the first and second oxide-based single crystal substrates are bonded via an oxide layer.
Pressure detector as described. (3) The pressure sensor according to claim 1 or 2, wherein the first and second oxide single crystal substrates are sapphire, spinel, or magnesia. (4) In the first and second oxide-based single crystal substrates,
a hole processing step of opening a through hole in a predetermined position of a first oxide single crystal substrate; the first oxide single crystal substrate having the through hole opened; and the flat second oxide substrate. a substrate bonding step of bonding the mirror surfaces of the oxide-based single crystal substrates to form a bonded substrate having a pressure-receiving diaphragm at the predetermined position; A method for manufacturing a pressure sensor, comprising the step of forming a semiconductor strain gauge element on the pressure-receiving diaphragm surface on the opposite end surface to the bonding surface with the oxide-based single crystal substrate. (5) In the substrate bonding step, hydroxyl groups are added to each mirror surface of the first and second oxide single crystal substrates, and the mirror surfaces to which the hydroxyl groups are added are brought into close contact with each other by the hydrogen bonding force of the hydroxyl groups. 4. Then, the first and second oxide single crystal substrates are directly bonded by releasing the hydroxyl groups as water by heating.
A method of manufacturing the pressure detector described. (6) In the substrate bonding step, the mirror surfaces of the first and second oxide single crystal substrates are brought into close contact with each other via a bonding agent layer made of metal alkoxide, and then heat treatment is performed to bond the mirror surfaces of the first and second oxide single crystal substrates together. 5. The method according to claim 4, wherein an oxide layer is formed on the bonding surface of the oxide single crystal substrate, and the first and second oxide single crystal substrates are bonded via this oxide layer. A method of manufacturing a pressure detector. (7) The method for manufacturing a pressure sensor according to any one of claims 4 to 6, wherein the first and second oxide single crystal substrates are sapphire, spinel, or magnesia.