JP2003329642A - Gas sensor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-power-consumption gas sensor in which a gas detection part can be effectively heated by curbing heat radiation from a substrate, and which is low in power consumption so as to be able to use batteries as a power source. <P>SOLUTION: The gas sensor is provided with a silicon substrate 1 which is a n-type single crystal having a (1 0 0) plane, a heater 2 formed on the silicon substrate 1, a diaphragm 7 formed by removing the silicon substrate under the heater 2 using anisotropic etching, an insulating film 1a formed on the heater 2, a solid electrolyte 3 formed on the insulating film 1a, and a pair of electrodes 4 and 5 formed on the solid electrolyte 3. Since heat radiation from the substrate is curbed, a gas detection part is effectively heated, and the sensor requires less electricity. Therefore, the sensor can utilize batteries as a power source. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor for detecting combustible gas contained in the atmosphere or exhaust gas of a combustion device or an internal combustion engine, particularly carbon monoxide which is a harmful substance to the human body.

[0002]

2. Description of the Related Art Conventionally, as this type of gas sensor, for example, there has been one described in JP-A-10-31003. FIG. 10 shows the conventional gas sensor described in the above publication.

In FIG. 10, 1 is an insulating substrate made of electrically insulating alumina or the like, 2 is a heater made of platinum or the like formed on the surface thereof, and 3 is a flat plate yttria-stabilizing material having oxygen ion conductivity. Solid electrolytes such as zirconia, 4 and 5 are a pair of electrodes such as platinum, and 6 is a porous oxidation catalyst.

In order to extract the sensor output from the gas sensor having the above structure, a potential difference detecting means is connected between the pair of electrodes 4 and 5 and the pair of electrodes 4 corresponding to the concentration of the gas to be detected.
The potential difference generated between and was detected.

Next, the principle of the conventional gas sensor will be briefly described.

First, the conventional gas sensor is held in a gas to be detected which does not contain combustible gas such as carbon monoxide,
When the solid electrolyte 3 is heated to a predetermined operating temperature by the heater 2, the amounts of oxygen reaching the pair of electrodes 4 and 5 are equal, so that no potential difference is generated between the pair of electrodes 4-5. At this time, the electrode reactions represented by the formula (1) occur on the pair of electrodes 4 and 5, respectively, and the equilibrium is maintained.

Oad + 2e- ← → O2 -... (1) Here, Oad represents an oxygen atom adsorbed on the surfaces of the pair of electrodes 4 and 5.

Next, when carbon monoxide, which is a flammable gas, is introduced into the gas to be detected, on the electrode 5 on which the porous oxidation catalyst 6 is not formed, in addition to the electrode reaction represented by the formula (1), The electrode reaction represented by the formula (2) occurs.

CO + Oad → CO2 (2) On the other hand, on the electrode 4 on which the porous oxidation catalyst 6 is formed,
Carbon monoxide is oxidized to carbon dioxide by the oxidation catalyst 6, carbon monoxide cannot reach the surface of the electrode 4, and only the electrode reaction represented by the formula (1) occurs.

Therefore, the balance of the amount of oxygen adsorbed between the pair of electrodes 4 and 5 is lost, and a difference in density occurs in the oxygen concentration, and the adsorbed oxygen becomes oxygen ions from the electrode 4 having a high oxygen concentration to the electrode 5 having a low oxygen concentration. It moves in the solid electrolyte 3 which is an oxygen ion conductor, and a potential difference is generated between the pair of electrodes 4-5. The relationship between this potential difference and the concentration of carbon monoxide follows the Nernst equation, and as the concentration increases, the potential difference also increases, so by detecting this potential difference with the potential difference detection means, the concentration of flammable gas such as carbon monoxide I was asking.

[0011]

However, in the above-mentioned conventional structure, when the thermal conductivity of the insulating substrate 1 is alumina, it is as large as about 20 W / m · K, so that the heat radiation from the insulating substrate 1 becomes large and the efficiency is high. There was a problem that the solid electrolyte 3 could not be heated well and the power consumption increased.

The present invention solves the above-mentioned problems of the prior art by suppressing heat dissipation from the substrate, efficiently heating the solid electrolyte, and using a power source such as a battery with low power consumption. An object is to provide a gas sensor with stable detection performance.

[0013]

In order to solve the above-mentioned conventional problems, the gas sensor of the present invention is an n-type (100)
A single crystal silicon substrate of a surface, a heater formed on the silicon substrate, a diaphragm formed by removing the silicon substrate under the heater from the back surface of the silicon substrate by anisotropic etching, and a heater An insulating film made of silicon oxide formed above, a solid electrolyte formed on the insulating film, and a pair of electrodes formed on the solid electrolyte, to suppress heat dissipation from the substrate, Since the solid electrolyte is efficiently heated, the power consumption becomes low and a power source such as a battery can be used.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is one in which an n-type (100) -plane single crystal silicon substrate, a heater formed on the silicon substrate, and a silicon substrate below the heater are made of silicon. A diaphragm formed by anisotropic etching from the back surface of the substrate, an insulating film made of silicon oxide formed on the heater, a solid electrolyte formed on the insulating film, and a pair formed on the solid electrolyte. Since it is provided with the electrode of (1), heat dissipation from the substrate is suppressed, and the solid electrolyte is efficiently heated, the power consumption is low and a power source such as a battery can be used.

According to a second aspect of the present invention, in particular, the heater according to the first aspect is p-type silicon obtained by adding a Group III element to a silicon substrate, which is expensive like platinum as in the prior art. Since it is formed of the same material as the substrate without using a different material, it is not only economical, but because the thermal expansion coefficient is the same, physical damage such as peeling or floating does not occur,
The durability as a heater is improved.

Silicon, which is not valence-controlled, exhibits a slight electric conductivity due to thermal energy.
Since a valence-controlled silicon semiconductor is used, a heater that is p-type silicon is a base material of an n-type silicon substrate due to the rectifying action of passing a current from p-type to n-type but not the other way. Is sufficiently insulated, and it is not necessary to form an insulator between the substrate and the heater.

In the anisotropic etching using the anisotropic etching solution, the n-type silicon is well etched, but the p-type silicon is hardly etched. Therefore, only the heater portion can be anisotropically etched. Therefore, by removing the n-type silicon having good thermal conductivity, the heat capacity of the substrate can be greatly reduced, the power consumption becomes low, and a power source such as a battery can be used.

The invention described in claim 3 is an n-type (10
The (0) plane single crystal silicon substrate is thermally oxidized to form an oxide film made of silicon oxide, the oxide film in the portion to be ion-implanted is removed by photolithography, and a group III element is ion-implanted to form a heater. After that, thermal oxidation is performed in oxygen to form an insulating film made of silicon oxide, a contact hole for a heater electrode is formed in the insulating film by photolithography, and a heater electrode is formed on the contact hole. The oxide film on the back surface that is to be anisotropically etched is removed by photolithography, the silicon substrate is anisotropically etched from the back surface to form a diaphragm, a solid electrolyte is formed on the insulating film, and a solid electrolyte is formed on the solid electrolyte. It forms a pair of electrodes, suppresses heat radiation from the substrate, and efficiently heats the solid electrolyte, resulting in low power consumption, battery, etc. Power can be used.

According to a fourth aspect of the present invention, a resist film is formed not only on the back surface of the silicon substrate according to the third aspect, which is not subjected to anisotropic etching, but also on the front surface of the silicon substrate. By protecting the front surface, anisotropic etching from the front surface of the silicon substrate can be prevented, and the productivity becomes good.

According to a fifth aspect of the present invention, in particular, the solid electrolyte according to the third aspect is formed by sputtering using a metal mask to form anisotropically etched p-type silicon on the diaphragm. Since the solid electrolyte can be formed without applying load or impact to the heater, the yield is improved and the productivity is improved.

According to a sixth aspect of the present invention, in particular, the solid electrolyte according to the third aspect is sputtered in oxygen of 10 to 50% so that the sputtering target containing the raw material of the solid electrolyte is blackened by reduction. It is possible to form a solid electrolyte membrane having a stable composition, and to obtain a gas sensor with stable sensor output.

According to the invention described in claim 7, in particular, the crystal of the solid electrolyte membrane formed on the silicon substrate grows by sputtering the solid electrolyte described in claim 3 at a substrate temperature of 500 to 900 ° C. However, the crystal structure has a good oxygen ion conductivity, and a high-output gas sensor can be obtained.

In the invention described in claim 8, a pair of electrodes is formed on the solid electrolyte according to claim 3 by using platinum, and then a porous electrode is formed on one of the pair of electrodes. By forming an oxidation catalyst, carbon monoxide is oxidized to carbon dioxide by the oxidation catalyst, and carbon monoxide cannot reach the surface of the electrode made of platinum on which the oxidation catalyst is formed. A density difference occurs in the oxygen concentration, and a potential difference occurs, and by detecting this potential difference, the concentration of flammable gas such as carbon monoxide can be obtained.

The invention according to claim 9 is formed by anisotropic etching without using a dicing device by forming a break groove by anisotropic etching on the silicon substrate according to claim 3 in particular. Since the silicon substrate can be divided into the bridge-shaped heater made of p-type silicon on the cavity without applying a load or shock, the yield is improved and the productivity is improved.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the configuration of a gas sensor according to an embodiment of the present invention.

In FIG. 1, 1 is an n-type (1 0 0)
The surface is a single crystal silicon substrate. This silicon substrate 1
The silicon atoms that make up the are covalently bonded, and the electrons are strongly bound to the silicon atoms, but due to thermal energy, a small number of electrons move around the binding of the atoms, and at room temperature, there is a slight electric charge. Shows conductivity. n
Type silicon is obtained by adding atoms such as phosphorus, arsenic, and antimony, which are group V elements, into silicon by ion implantation, and the group V atoms have five bonding hands. More than one electron is generated that is not bound to the atom, and n-type silicon exhibits electrical conductivity due to the electron.

An insulating film 1a and an oxide film 1b made of amorphous silicon oxide are formed on the surface of the silicon substrate 1, and a heater 2 made of p-type silicon is formed on a part of the surface. ing. p-type silicon is
Atoms such as boron (boron) and indium, which are Group III elements, are added to silicon by ion implantation, etc. Since Group III atoms have only three bond hands, they have only one bond. Not enough holes, holes (electrons)
(Hole) is generated, and an electron adjoining this hole can move to move the electron, thus exhibiting electric conductivity. Also,
Between the p-type silicon formed on the n-type silicon, p
The heater 2 made of p-type silicon is sufficiently insulated from the silicon substrate 1 made of n-type silicon, because it has a rectifying function of passing a current from the mold to the n-type, but vice versa.

Further, an insulating film 1a made of electrically insulating silicon oxide is formed on the heater 2 by heat-treating the silicon substrate. And the insulating film 1
A solid electrolyte 3 made of yttria-stabilized zirconia is formed on a.

Then, electrodes 4 and 5 made of platinum are formed on the solid electrolyte 3 as a pair of electrodes. A porous oxidation catalyst 6 is formed on the one electrode 4. According to this configuration, carbon monoxide is oxidized to carbon dioxide by the oxidation catalyst 6, and carbon monoxide cannot reach the surface of the electrode 4 made of platinum on which the oxidation catalyst 6 is formed. A density difference occurs between the oxygen concentration and the oxygen concentration, and a potential difference occurs, and by detecting this potential difference, the concentration of flammable gas such as carbon monoxide can be obtained.

Further, since the diaphragm 7 is formed on the silicon substrate 1 under the heater 2 by anisotropic etching to remove the silicon having good thermal conductivity, the heat capacity and the thermal diffusion can be greatly reduced. it can. (10
Anisotropic etching in the (0) plane is performed in an inverted pyramid shape along the (1 1 1) plane whose angle is 55 degrees with respect to the (1 1 0) plane in the <1 1 0> direction circumscribing the pattern. Grooves or through holes can be formed,
Since the insulating film 1a made of silicon oxide is not etched, the diaphragm 7 made of the insulating film 1a and the heater 2 is formed.

Next, a method of manufacturing the gas sensor according to the embodiment of the present invention will be described.

2 to 7 show a method of manufacturing a gas sensor according to an embodiment of the present invention. In the present invention, the diaphragm type micro-heater 2 is manufactured in a clean room by using the silicon bulk micro-machining technique, and the solid electrolyte type gas detection part is formed on the micro-heater 2. According to the configuration of the present invention, heat dissipation from the substrate 1 is suppressed and the solid electrolyte 3 is efficiently heated, resulting in low power consumption and a power source such as a battery can be used. First, in FIG. 2 (1), reference numeral 1 denotes an n-type single crystal silicon substrate having a plate thickness of (500) plane of about 500 μm.

Next, as shown in FIG. 2 (2), the silicon substrate 1 was thermally oxidized in a quartz tube using steam to form an oxide film 1b made of silicon oxide and having a thickness of about 8,000 Å. . Since the oxide film 1b is formed in water vapor having a high film formation rate, it can be formed earlier than in the atmosphere or in oxygen, and the productivity is improved.

Then, a mixed solution of sulfuric acid and hydrogen peroxide was used for washing at 50 to 70 ° C., washing with water and drying to completely remove stains and impurities existing on the surface. Since the dirt and impurities existing on the surface are completely removed, the state of film formation becomes good and the yield can be improved.

Next, before forming a pattern, a small mustache-like scratch is made on the oxide film 1b with a sharp tip such as tweezers on an arbitrary irrelevant end of the silicon substrate 1,
Anisotropic etching was performed by immersing in an anisotropic etching solution. The n-type silicon existing under the scratch circumscribes the scratch <1
Since a cavity is formed by anisotropically etching in a reverse pyramid shape in the 10> direction, the portion to be the heater 2 can be accurately arranged in the <110> direction of the silicon substrate 1 and the yield can be improved. It improves and productivity becomes good.

If a silicon wafer having an orientation flat in the <1 1 0> direction is used in advance, this step can be omitted.

Next, as shown in FIG. 2A, the silicon substrate 1 was set on a spinner, a few drops of the primer were dropped, and spin coating was performed. The primer removes water and the like attached to the surface of the oxide film 1b, and the resist film 8 and the substrate 1 are removed.
The adhesion of can be improved. Then, a few drops of positive type resist solution were dropped, spin coated, and then 5 ° C. at 5 ° C.
Pre-bake for minutes, dry the solvent in the resist solution,
A resist film 8 having a film thickness of about 0.5 μm was formed.

Next, as shown in FIG. 2 (2), the silicon substrate 1 is set on a mask aligner (exposure device), the photomask 9 and the silicon substrate 1 are brought into close contact with each other, and the light of an ultrahigh pressure mercury lamp is irradiated. .

After that, as shown in FIG. 2C, the silicon substrate 1 is immersed in a developing solution, developed for 1 to 3 minutes, and thoroughly washed with pure water to ensure adhesion and resistance of the resist film 8. Post-baking was performed at 120 ° C. for 10 minutes in order to improve chemical properties. Further, the resist solution is applied not only on the front surface of the silicon substrate 1 which is not subjected to ion implantation but also on the oxide film 1b on the back surface of the silicon substrate 1 to form a resist film 8 so that the oxide film 1b is not etched. Protected. The silicon substrate 1 is protected by protecting the oxide film 1b on the back surface.
It is possible to prevent anisotropic etching from the back surface of the and the productivity is improved.

Next, as shown in FIG. 2 (4), the silicon substrate 1 is immersed in a mixed solution (1: 6) of hydrofluoric acid and an aqueous solution of ammonium fluoride in a Teflon (registered trademark) beaker, The oxide film 1b made of silicon oxide was etched at the portion of the heater that was used for ion implantation.

Then, as shown in FIG. 2 (5), the resist film 8 was peeled off with acetone, washed with 2-propanol, further washed with pure water, and dried with an air gun.
The release agent may be sulfuric acid / hydrogen peroxide or the like. Further, when the resist film 8 is solidified and difficult to remove, it can be removed by ashing with oxygen plasma.

Next, as shown in FIG. 3 (6), boron (boron), which is a group III element, is applied to the portion where the oxide film 1b is removed at an acceleration voltage of 50 keV at 5 × using an ion implantation apparatus. 10 ¹⁶ / cm ^{2 was} injected to form the heater 2 made of p-type silicon.

Further, as shown in FIG. 3 (7), after ion implantation of boron, heat treatment was performed in nitrogen at 1,000 ° C. to 1,200 ° C. for 1 to 2 hours to damage by ion implantation. The crystallinity of silicon was recovered, and at the same time boron atoms were diffused into n-type silicon to form a heater 2 having a stable structure of p-type silicon. By heat treatment,
The heater 2 made of p-type silicon becomes thicker.

Continuing, as shown in FIG. 3 (8), 30 minutes to 1 hour in oxygen at 1,000 ° C. to 1,200 ° C.
Heat treated for about 1,500Å on the surface of silicon substrate 1
The insulating film 1a was formed. This insulating film 1a is economical because it insulates the heater 2 and the solid electrolyte formed thereon and it is not necessary to newly form an insulating film by vapor deposition or the like.

Next, as shown in FIG. 3 (9), the silicon substrate 1 is set again on the spinner in order to form a contact hole for a heater electrode in the insulating film 1a formed by thermal oxidation. A few drops of primer were applied and spin coated. Then, several drops of a positive resist solution were dropped, spin-coated, and prebaked at 90 ° C. for 5 minutes to form a resist film 10 having a film thickness of about 0.5 μm.

Next, as shown in FIG. 3 (10), the silicon substrate 1 is set on a mask aligner, and the pattern on the photomask 11 and the pattern on the silicon substrate 1 are aligned with each other by using a microscope to form the photomask 11 and The substrate 1 was brought into close contact with the substrate and irradiated with light from an ultra-high pressure mercury lamp.

Then, as shown in FIG. 4 (11), the silicon substrate 1 is immersed in a developing solution, developed for 1 to 3 minutes, thoroughly washed with pure water, and post-baked at 120 ° C. for 10 minutes. went. Further, the oxide film 1b on the back surface of the silicon substrate 1
Also, a resist solution was applied to form a resist film 10 and protect the oxide film 1b from being etched. By protecting the oxide film 1b, the back surface of the silicon substrate 1 can be prevented from being etched, and the productivity is improved.

Next, as shown in FIG. 4 (12), the silicon substrate 1 is dipped in a mixed solution of hydrofluoric acid and an aqueous solution of ammonium fluoride to insulate the portion of the contact hole 1c made of silicon oxide. The film 1a was etched.

Then, as shown in FIG. 4 (13), after removing the resist film 10 with sulfuric acid / hydrogen peroxide or acetone, 2-
It was washed with propanol, further washed with pure water, and dried with an air gun.

Next, as shown in FIGS. 4 (14) and (15), a multilayer film of chromium 12 and gold 13 was continuously formed as an electrode for the heater 2 by vacuum evaporation. When chromium is heated in a vacuum, it does not melt and sublimes, so a tungsten basket was used to form 200 to 300 Å. On the other hand, a tungsten boat is used for gold,
00-3,000 Å formed. Since the anisotropic etching liquid used in the subsequent step is a strong alkali, gold which can withstand anisotropic etching was used for the electrode for the heater 2. Also,
Gold 13 has very weak adhesion to the silicon substrate 1, so
Chromium 12 having good adhesion was used as a base. Further, once the chrome 12 is formed, if it is exposed to the atmosphere, the chrome 12 may be oxidized or water vapor may be adsorbed on the surface, resulting in poor adhesion and peeling between the gold 13 and the chrome 12. Therefore, the chromium 12 and the gold 13 must be continuously formed without breaking the vacuum.

Then, in order to improve the denseness and the adhesion of the multilayer film of chromium 12 and gold 13, the temperature is kept at 300 ° C. in nitrogen for 3
Heat treatment was performed for 0 minutes.

Next, as shown in FIG. 5 (16), in order to etch the multilayer film of chromium 12 and gold 13, the silicon substrate 1 was set on a spinner, a few drops of primer were dropped, and spin coating was performed. Then, a few drops of a positive resist solution were dropped, spin-coated and then prebaked at 90 ° C. for 5 minutes to form a resist film 14 having a film thickness of about 0.5 μm.

Next, as shown in FIG. 5 (17), the silicon substrate 1 is set on a mask aligner, and the pattern on the photomask 15 and the pattern on the silicon substrate 1 are aligned with each other by using a microscope to form the photomask 15 The silicon substrate 1 was brought into close contact and irradiated with light from an ultra-high pressure mercury lamp.

After that, as shown in FIG. 5 (18), the silicon substrate 1 is dipped in a developing solution, developed for 1 to 3 minutes, and thoroughly washed with pure water to ensure the adhesion and resistance of the resist film 14. Post-baking was performed at 120 ° C. for 10 minutes in order to improve chemical properties.

Next, as shown in FIG. 5 (19), 100 g of iodine, 100 g of potassium iodide, and 400 of pure water.
Gold 13 was etched using a mixed aqueous solution of cc while being careful not to cause over-etching, and gold electrode 13a for heater 2 was formed.

Further, as shown in FIG. 5 (20), the chromium 12 was similarly etched using an aqueous solution of dicerium ammonium nitrate, and the chromium electrode 12 for the heater 2 was used.
a was formed.

Then, as shown in FIG. 6 (21), after removing the resist film 14 with sulfuric acid / hydrogen peroxide or acetone, 2-
It was washed with propanol, further washed with pure water, and dried with an air gun.

Next, as shown in FIG. 6 (22), in order to form a pattern of the opening on the back surface for anisotropic etching, the back surface of the silicon substrate 1 was set on a spinner and a few drops of a primer were set. Spinned and spin-coated. Then, a few drops of positive type resist solution are dropped, spin-coated, and then prebaked at 90 ° C. for 5 minutes to give a film thickness of about 0.5.
A μm resist film 16 was formed.

Next, as shown in FIG. 6 (23), the silicon substrate 1 is set on a mask aligner, and the pattern on the photomask 17 and the pattern on the silicon substrate 1 are aligned with each other by using a microscope. The silicon substrate 1 was brought into close contact and irradiated with light from an ultra-high pressure mercury lamp.

After that, as shown in FIG. 6 (24), the silicon substrate 1 is immersed in a developing solution, developed for 1 to 3 minutes, and thoroughly washed with pure water to ensure the adhesion and resistance of the resist film 16. Post-baking was performed at 120 ° C. for 10 minutes in order to improve chemical properties. Further, a resist solution was applied to the surface of the silicon substrate 1 to form a resist film 16 so as to prevent the oxide film 1b from being etched and protected. By protecting the surface, anisotropic etching from the front surface of the silicon substrate 1 can be prevented and the productivity becomes good.

Next, as shown in FIG. 6 (25), the silicon substrate 1 is dipped in a mixed solution of hydrofluoric acid and an aqueous solution of ammonium fluoride to etch the oxide film 1 b at the portion to be the opening 1 d. Removed by.

Next, as shown in FIG. 7 (26), a hot plate was used to prepare 1 by using a mixed aqueous solution of 75 cc of ethylenediamine, 12 g of pyrocatechol and 24 cc of pure water.
Anisotropic etching was performed in a draft for 2 hours while heating at 16 ° C. The boiling point of the mixed aqueous solution is about 116 ° C.,
It is necessary to heat at 105 to 125 ° C. By using this anisotropic etching solution, an aqueous solution of an alkali metal hydroxide, which is considered to be a factor of variation in characteristics, is not used, so that the yield is improved and the productivity is improved. Further, since the p-type silicon that is the heater 2 is hardly anisotropically etched as compared with the n-type silicon of the substrate 1, the diaphragm-type micro-heater 2 can be formed.
By removing the n-type silicon having good thermal conductivity, the heat capacity of the silicon substrate 1 can be greatly reduced, the power consumption becomes low, and a power source such as a battery can be used.

If anisotropic etching is performed after a lapse of time after removing the oxide film 1b in the opening 1d, a natural oxide film is formed on the surface of the silicon substrate 1 and anisotropic etching cannot be performed. Therefore, anisotropic etching must be performed immediately after removing the oxide film 1b in the opening 1f. The resist film 16 formed simultaneously with the anisotropic etching is peeled off. Immediately after anisotropic etching,
It was washed with pure water, further washed with 2-propanol, and dried. Since the diaphragm 7 etc. may be broken when the water is blown off with an air gun etc., it was dried in an oven.
Further, in order to avoid the destruction of the diaphragm 7 due to the surface tension of water, it was washed with water, replaced with 2-propanol, and dried.

Further, a 15% to 25% aqueous solution of tetramethylammonium hydroxide is used as the anisotropic etching solution instead of a mixed solution of ethylenediamine and pyrocatechol.
When anisotropic etching is performed at 70 ° C. to 90 ° C., anisotropic etching can be performed without using a carcinogenic substance, and safety is improved.

In this way, the diaphragm 7 is formed under the heater 2 of the silicon substrate 1 by anisotropic etching, silicon having good thermal conductivity is removed, and the heater 2 having the diaphragm type structure is formed. The heat capacity and heat diffusion can be greatly reduced. Further, since the heater 2 made of p-type silicon forms a pn junction with the silicon substrate 1 made of n-type silicon, it is possible to pass a current only to the heater portion, which consumes less power and is excellent in high-speed response. The micro heater 2 is obtained.

Next, as shown in FIG. 7 (27), in order to form the solid electrolyte 3 on the insulating film 1a, yttria-stabilized zirconia was formed to a thickness of about 2 μm by sputtering using a metal mask. By forming by sputtering using a metal mask, without applying load or impact to the heater 2 made of p-type silicon on the diaphragm 7 formed by anisotropic etching,
Since the solid electrolyte 3 can be formed, the yield is improved and the productivity is improved.

The sputtering was carried out in oxygen of 10 to 50%, and the silicon substrate 1 was sputtered at a substrate temperature of 500 to 900.degree. By adding oxygen at the time of sputtering, the solid electrolyte 3 having a stable composition without blackening the sputtering target 3
Can be formed into a thin film. Further, by raising the substrate temperature, the crystallinity of the solid electrolyte 1 is improved and the oxygen ion conductivity can be increased.

Next, as shown in FIGS. 7 (28) and (29), a pair of electrodes 4 and 5 made of platinum are formed on the solid electrolyte 3 by sputtering using a metal mask. A porous oxidation catalyst 6 was formed on the electrode 4 by sputtering using a metal mask. By forming by sputtering using a metal mask, the heater 2 made of p-type silicon on the diaphragm 7 formed by anisotropic etching,
Since the electrodes 4 and 5 and the oxidation catalyst 6 can be formed without applying load or impact, the yield is improved and the productivity is improved.

Further, as shown in FIG. 8, when the silicon substrate is anisotropically etched and the break groove 18 is formed by anisotropic etching at the same time, it is formed by anisotropic etching without using a dicing device or the like. Since the silicon substrate 1 can be divided without applying load or impact to the heater 2 made of p-type silicon on the diaphragm 7, the yield is improved and the productivity is improved.

In order to examine the characteristics of the gas sensor obtained as described above, the silicon substrate 1 is divided and lead wires are bonded to the electrodes 4, 5 and 13a, and a direct current such as a battery is placed between the heater electrodes 13a. A power source was connected, and a DC voltage was applied in a pulsed manner to the heater 2 to maintain the operating temperature of the solid electrolyte 3 at about 450 ° C. Further, the sensor output of the gas sensor when various concentrations of carbon monoxide (CO) were supplied at 5 liters per minute was measured by the pair of electrodes 4.
It was measured using a potential difference detection means connected between -5. The measurement result is shown in FIG. It can be seen from FIG. 9 that the relationship between the sensor output and the CO concentration follows the Nernst equation, and the output also increases as the concentration increases, and if the gas sensor of the embodiment of the present invention is used, the accurate concentration of carbon monoxide You can ask.

[0072]

As described above, according to the present invention, the n-type (100) plane single crystal silicon substrate, the heater formed on the silicon substrate, and the silicon substrate below the heater are different. A diaphragm formed by removing by means of isotropic etching, an insulating film formed on the heater, a solid electrolyte formed on the insulating film, and a pair of electrodes formed on the solid electrolyte, Since the heat radiation from the substrate is suppressed and the gas detection unit is efficiently heated, the power consumption is low and a power source such as a battery can be used.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a gas sensor according to an embodiment of the present invention.

FIG. 2 is an upper configuration diagram showing a method of manufacturing the gas sensor and FIG.
-A sectional view

FIG. 3 is an upper configuration diagram showing a method of manufacturing the gas sensor and FIG.
-A sectional view

FIG. 4 is an upper configuration diagram showing a method of manufacturing the gas sensor and FIG.
-A sectional view

FIG. 5 is an upper configuration diagram and A showing a method for manufacturing the gas sensor.
-A sectional view

FIG. 6 is an upper configuration diagram showing a method of manufacturing the gas sensor and FIG.
-A sectional view

FIG. 7 is an upper configuration diagram showing a method of manufacturing the gas sensor and FIG.
-A sectional view

FIG. 8 is a top view showing a break groove of the gas sensor.

FIG. 9 is a characteristic diagram showing the relationship between the carbon monoxide concentration and the sensor output of the gas sensor.

FIG. 10 is an assembly configuration diagram of a conventional gas sensor.

[Explanation of symbols]

1 Silicon substrate 1a insulating film 1b oxide film 1c contact hole 2 heater 3 Solid electrolyte 4, 5 electrodes 6 Oxidation catalyst 7 diaphragm 8 Resist film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuhiko Uno             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Takashi Niwa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Kunihiro Tsuruta             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 2G004 BB04 BD02 BE12 BE22 BF07                       BJ02 BJ10 BM07

Claims (9)

[Claims] 1. Anisotropy of an n-type (100) plane single crystal silicon substrate, a heater formed on the silicon substrate, and the silicon substrate under the heater from the back surface of the silicon substrate. A diaphragm formed by etching, an insulating film made of silicon oxide formed on the heater, a solid electrolyte formed on the insulating film, and a pair of electrodes formed on the solid electrolyte. Gas sensor. 2. The gas sensor according to claim 1, wherein the heater is p-type silicon obtained by adding a Group III element to a silicon substrate. 3. An n-type (100) plane single crystal silicon substrate is thermally oxidized to form an oxide film made of silicon oxide, and the oxide film in a portion to be ion-implanted is removed by photolithography. After forming a heater by ion-implanting a group III element, it is thermally oxidized in oxygen to form an insulating film made of silicon oxide, and a contact hole for a heater electrode is formed in the insulating film by photolithography, A heater electrode is formed on the contact hole, the oxide film in the anisotropically etched portion of the back surface of the silicon substrate is removed by photolithography, and the silicon substrate is anisotropically etched from the back surface to form a diaphragm. A method for manufacturing a gas sensor, comprising forming a solid electrolyte on the insulating film and forming a pair of electrodes on the solid electrolyte. 4. The method according to claim 3, wherein a resist film is formed not only on the back surface of the silicon substrate that is not subjected to anisotropic etching but also on the front surface of the silicon substrate to protect the front surface. Gas sensor manufacturing method. 5. The method for manufacturing a gas sensor according to claim 3, wherein the solid electrolyte is formed by sputtering using a metal mask. 6. The method for manufacturing a gas sensor according to claim 3, wherein the solid electrolyte is sputtered in 10 to 50% oxygen. 7. The method for producing a gas sensor according to claim 3, wherein the solid electrolyte is sputtered at a substrate temperature of 500 to 900 ° C. 8. The gas sensor according to claim 3, wherein after forming a pair of electrodes using platinum on the solid electrolyte, a porous oxidation catalyst is formed on one electrode of the pair of electrodes. Production method. 9. The method of manufacturing a gas sensor according to claim 3, wherein the break groove is formed in the silicon substrate by anisotropic etching.