JP2005315873A - Method of manufacturing gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing gas sensors, in which a metal oxide semiconductor film used for the gas sensors is a uniform membrane and has fine particle diameters by means of a wet method advantageous in terms of costs. <P>SOLUTION: The method of manufacturing gas sensor is provided with a process for bringing a substrate 12 into contact with a processing liquid 22, containing both metallic fluoro complexes and capturing agents for chemically capturing fluorine ions from the metal fluoro complexes or the processing liquid 22, containing only the capturing agent and making the metal oxide semiconductor film deposit onto the substrate 12, while adding the metallic fluoro complexes to the processing liquid 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a gas sensor that can be used for detection and quantification of various gases. Specifically, the present invention relates to a manufacturing method capable of forming a metal oxide semiconductor functioning as a gas detection unit of a gas sensor with a thin film having a uniform small particle diameter.

  A gas sensor is used to detect a trace amount of gas components contained in the gas. This gas sensor detects the gas by utilizing a difference in chemical characteristics such as adsorption of a gas to be detected, a chemical reaction, and an electrode reaction.

  As one of such gas sensors, there is a semiconductor gas sensor using semiconductor electrical resistance, transistor action and rectification action. Among these, the electrical resistance type utilizes, for example, the detection of gas in a porous metal oxide semiconductor in which the electrical resistance changes depending on the gas atmosphere. This electric resistance type gas sensor is more general than a gas sensor using semiconductor transistor action or rectification action, and has a wider application range (for example, see the thin film fabrication application handbook).

  An apparatus using this electrical resistance type metal oxide semiconductor gas sensor is widely used for detecting various combustible gases and oxidizing gases, for example, with a combustible gas leak alarm as a representative example. Furthermore, the range of use is expanding for continuous monitoring of ppb level environmental pollutant gases and highly sensitive detection of volatile organic compound (VOC) gases in living environments.

  The gas sensor includes a metal oxide semiconductor film formed on a substrate, an electrode formed in contact with the metal oxide semiconductor film, and a heater for heating the metal oxide semiconductor film. Yes.

As a material of a metal oxide semiconductor that functions as a gas sensor, many n-type semiconductor oxides such as SnO ₂ , ZnO, Fe ₃ O ₄ , In ₂ O ₃ , TiO ₂ , and WO ₃ are used. Of these, the materials most widely used is SnO _2. As the manufacturing method, a dry method includes a sputtering method, a CVD method, a vapor deposition method, a laser ablation method, and the like, and a wet method includes a sol-gel method and the like.

  As metal oxide semiconductor gas sensors that have been put to practical use, a sintered body or a thick film having a thickness of several tens of μm or more has been often used. The main reason for this is thought to be that the thin film gas sensor did not necessarily have sufficient characteristics stable for use at high temperatures.

  By the way, Japanese Patent Application Laid-Open No. 5-149907 discloses a film type gas sensor. This publication states that the metal oxide semiconductor film may be a thick film having a thickness of 5 to 100 μm or a thin film having a thickness of 0.1 to 1 μm.

Japanese Patent Application Laid-Open No. 7-197237 discloses a moisture sensitive element using a SnO ₂ thin film. This SnO ₂ thin film has an average particle diameter of 10 to 200 nm. The film thickness of the SnO ₂ thin film in the examples is 300 nm and is produced by a vapor deposition method.

  Now, in the ceramics magazine [38 (2003), No. 6, p407-420], it is shown that a high gas sensitivity can be obtained when a sensor is made of a metal oxide semiconductor having a fine particle size. This is called the particle size effect of the sensor material.

Further, a technique for adding or supporting, for example, a noble metal or a metal oxide on the SnO ₂ film is also disclosed.
For example, Japanese Patent Laid-Open No. 5-087762 discloses "In a gas sensor manufacturing method including a step of supporting a noble metal catalyst on a support, an organic noble metal compound is added after the formation of the support and decomposed to form a noble metal catalyst. A gas sensor manufacturing method ”is disclosed, and specifically,“ Pd is supported on a SnO ₂ film ”.

Japanese Patent Laid-Open No. 10-246714 discloses "a gas sensor material used for a gas sensor using VOC and formaldehyde as a gas to be detected, and a gas sensitive material made of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. A gas sensor material characterized by adding approximately 0.2 to approximately 50 atomic percent of one of Gd, Y, La, Nd, Ca, Mg, and Ba as an additive is disclosed.

  One of the applicants of the present application is Japanese Patent Application Laid-Open No. 2000-32230, which is a odor detecting element including a noble metal wire and a sensitive layer formed of a semiconductor mainly composed of tin oxide, An odor detecting element is disclosed in which a rare earth metal oxide is added as a first component to a sensitive layer, and further gold is added as a second component.

  Japanese Patent Application Laid-Open No. 2001-074681 discloses that, in a semiconductor gas sensor including a gas sensitive body mainly composed of tin oxide, the gas sensitive body is obtained by adding or supporting manganese oxide on tin oxide. A semiconductor gas sensor characterized by the above is disclosed.

Shunichi Hamada Supervision: 21st Century Thin Film Fabrication Application Handbook (NTS Corporation, 2003), p1038-1050 Ceramics, 38 (2003), no. 6, p407-420 JP-A-5-149907 JP-A-7-197237 JP-A-5-087762 Japanese Patent Laid-Open No. 10-246714 JP 2000-32230 A JP 2001-074681 A

  In order to obtain the particle size effect of the sensor material described above, it is necessary to produce a metal oxide semiconductor having a fine particle size. However, it has been difficult to stably produce a metal oxide semiconductor having a fine particle size in the form of a sintered body or a thick film of several tens of μm or more.

  If a metal oxide semiconductor can be formed as a thin film, it is difficult for the particle diameter to grow, so that a fine particle diameter can be obtained.

  Note that a method for manufacturing a thin metal oxide semiconductor film is not mentioned at all in the above-mentioned Japanese Patent Application Laid-Open No. 5-149907. Furthermore, in Japanese Patent Laid-Open No. 7-197237, it was based on a vapor deposition method.

  In general, the dry process requires high energy and expensive equipment under high temperature and low pressure, whereas the wet process is advantageous in that it does not require large energy and is low in cost.

  By the way, even in the wet method which is advantageous in terms of cost, the production of a metal oxide semiconductor film as a sensor has been studied only focusing on the sol-gel method.

  Specific coating methods in the sol-gel method include a spin coating method and a dip coating method. In these methods, the thickness of the film formed easily varies depending on the portion of the substrate. For example, when a large number of chip-shaped sensors are cut out from a single substrate, the manufacturing method based on the sol-gel method has a problem that the characteristics are different because the film thickness is different among the cut out sensors.

Accordingly, an object of the present invention is to provide a method for manufacturing a gas sensor which is a wet method that is advantageous in terms of cost and that has a uniform thin film and a fine particle size.
Furthermore, an object of the present invention is to provide a method for manufacturing a gas sensor in which a Sn oxide semiconductor film and a metal oxide different from Sn are combined.

  The first characteristic means of the gas sensor manufacturing method according to the present invention is a treatment liquid containing a metal fluoro complex and a capture agent that chemically captures fluorine ions from the metal fluoro complex, or a process containing only the capture agent. There is a step of depositing the metal oxide semiconductor film on the substrate while bringing the substrate into contact with the solution and further adding the metal fluoro complex to the treatment solution.

  The second characteristic means of the method for producing a gas sensor according to the present invention is that the addition of the metal fluoro-complex is performed intermittently or continuously.

  The third characteristic means of the method for producing a gas sensor according to the present invention is that the addition amount of the metal fluoro complex is adjusted according to the amount captured by the scavenger.

  The fourth characteristic means of the gas sensor manufacturing method according to the present invention is that the substrate brought into contact with the processing liquid is swung.

  A fifth characteristic means of the method for producing a gas sensor according to the present invention is that the rocking is performed at least when the fluoro complex of the metal is added.

  A sixth characteristic means of the method for producing a gas sensor according to the present invention is that the scavenger is boric acid.

  The seventh characteristic means of the method for producing a gas sensor according to the present invention is that the metal fluoro complex is a Sn fluoro complex.

  According to an eighth feature of the gas sensor manufacturing method of the present invention, an Sn oxide semiconductor film is formed on the substrate, and then Sn is formed on the Sn oxide semiconductor film by liquid phase deposition. Has a step of depositing oxides of different metals.

  The ninth characteristic means of the method for producing a gas sensor according to the present invention is that the substrate is formed by depositing a metal oxide different from Sn by a liquid phase deposition method.

Tenth feature means of a method of manufacturing a gas sensor according to the present invention is that an oxide of a different metal is WO ₃ and the Sn.

  In the present invention, the above-described oxide of the n-type semiconductor metal used for the gas sensor can be deposited by a liquid phase deposition method.

  In the liquid phase deposition method, a substance that forms a more stable fluoro complex by utilizing the hydrolysis equilibrium reaction of a metal fluoro complex with an oxide or oxyhydroxide from the treatment liquid regardless of the base material or shape ( In this technique, the equilibrium is shifted to the oxide side in accordance with the law of mass action by adding a scavenger or an initiator), so that a stable metal oxide is deposited and grown uniformly on the substrate. Such a reaction is represented by the following chemical formula 1 and chemical formula 2, where M is this metal.

(Chemical formula 1)
[MF _6-x (OH) _x ] ² + (6-x) H ₂ O ⇔ [M (OH) ₆ ] ² + (6-x) HF
However, x is an integer of 0-5.
(Chemical formula 2)
[M (OH) ₆ ] ^2- ⇒ MO ₂

In the liquid phase deposition method, in Formula 1, hydrogen fluoride is consumed when a scavenger is added. Therefore, the equilibrium reaction formula of Formula 1 is shifted to the direction in which [M (OH) ₆ ] ²⁻ is generated. Become. Then, this [M (OH) ₆ ] ²⁻ causes a dehydration condensation reaction, and a metal oxide represented by MO ₂ is deposited as shown in Chemical Formula 2.

As this scavenger, boric acid (H ₃ BO ₃ ), FeCl ₂ , FeCl ₃ , NaOH, NH ₃ , Al, Ti, Fe, Ni, Mg, Cu, Zn, Si, SiO ₂ , CaO, B ₂ O ₃ , Al ₂ O ₃ , MgO and the like are known. Even if any of the above-mentioned scavengers is used, a stable fluoro complex compound or fluoride is generated in the treatment liquid, so that precipitation is not hindered. In particular, boric acid is known not to precipitate impurities. In this method, the equilibrium reaction can be controlled by the addition amount (concentration) of the scavenger, and various metal oxides can be deposited (see, for example, JP-A-4-338136).

  By the way, in the above-described metal oxide semiconductor, a considerable amount of precipitates are generated in the liquid due to the inherent properties of the material. If such a material is applied to the continuous film formation process shown in the prior art, a large amount of precipitates are generated not only on the substrate but also in the liquid. In some cases, it is difficult to continuously form films over a long period of time.

  Therefore, in the liquid phase precipitation method, if a metal fluoro complex is added to the treatment liquid instead of adding a scavenger to the treatment liquid, the film formation rate can be kept as constant as possible. It can suppress that an oxide precipitates.

  As described above, if the precipitation of the metal oxide in the liquid can be suppressed, the metal oxide semiconductor can be deposited as a thin film, and a uniform film can be obtained.

As a method for adding this scavenger, it has been common to add boric acid to the treatment solution as disclosed in Japanese Patent Laid-Open No. 58-161944 by the applicant. In this method, in the case of an oxide of a metal other than SiO ₂ , it was not possible to suppress the precipitation of the metal oxide in the liquid.

Although the details are unknown as the reason, it is considered as follows.
First, when a metal fluoro complex and a scavenger coexist, intermediates of metal fluoro complexes in which x of [MF _6-x (OH) _x ] ²⁻ has various values exist. Once this intermediate is in the form of an oxyhydroxide represented by [M (OH) ₆ ] ²⁻ , the reaction of Formula 2 described above becomes dominant. In this case, it is presumed that not only on the target substrate but also in the treatment liquid, a large amount of metal oxide precipitates and becomes a precipitate.

The generation mechanism of this precipitate will be discussed in detail from the viewpoint of chemical reaction.
・ Method of adding scavenger (boric acid) At the beginning of adding boric acid to the treatment liquid, the amount of boric acid added was small, and the reaction of capturing fluorine ions from the metal fluorocomplex was not performed sufficiently. A large number of fluoro complexes of metal are present in the treatment liquid. When the amount of boric acid added reaches a certain level, a large amount of oxyhydroxide is generated. As a result, a large amount of metal oxide is deposited, resulting in a precipitate.

In contrast to this, in the method of adding a metal fluoro complex solution to the treatment liquid of the present invention, a reaction for sufficiently capturing fluorine ions from the metal fluoro complex is performed from the initial stage of the addition. Oxyhydroxide begins to be produced quickly. As a result, it is considered that the metal oxides are deposited constantly and no precipitate is generated.
In addition, since there exists a possibility that a precipitate may generate | occur | produce when a large amount of metal fluoro complex solutions are added at once, it is preferable to adjust the addition amount of a metal fluoro complex.

  In the present invention, the addition method of the metal fluoro complex solution may be intermittent or continuous. In addition, for example, at the initial stage of production, intermittent addition and continuous addition may be arbitrarily selected in the production process, such as intermittent addition of a metal fluoro complex solution followed by continuous addition. it can.

  Furthermore, in order to improve the precipitation amount and uniformity of the metal oxide, the addition amount may be temporarily increased while adding a constant amount of the metal fluoro complex solution continuously. Moreover, the timing and amount of addition may be set as appropriate.

  As a specific method of adding a metal fluoro complex solution, it may be added continuously using a tubing pump or the like, or intermittently at regular intervals using a tubing pump and a timer. You may add to.

  The metal fluoro-complex used as the raw material of the treatment liquid is not particularly limited as long as it is a material that exists stably in the treatment liquid and can be precipitated by the presence of the scavenger. For example, metal hydrofluoric acid, metal ammonium fluoride salt, or a mixture thereof can be used.

  The initial treatment liquid in the present invention may be a mixture of a metal fluoro complex and a scavenger, or only a scavenger.

The substrate used in the present invention is not particularly limited as long as it is a material that can withstand high temperatures when applied as a gas sensor and can precipitate an oxide semiconductor that functions as a gas sensor, for example, SnO ₂ , such as Si, glass, and ceramics. What is necessary is just to select suitably from materials according to a use.

  Before the substrate is immersed in the treatment liquid, it is preferable to perform cleaning in order to remove impurities such as organic substances on the surface. For example, when glass is used as the substrate, it is preferable to perform pure water cleaning after alkali cleaning.

  As a means for keeping the substrate in contact with the processing liquid, a jig having durability against the processing liquid may be used to fix the substrate directly to the reaction vessel or to hang it from the top. Examples of the material having durability include fluorine resin, polyethylene, polypropylene, polycarbonate, or methylpentene resin.

  In order to deposit a metal oxide having a more uniform film thickness, the substrate may be swung in the processing solution. At this time, the swing time, distance, and speed are not particularly limited. The rocking time may be adjusted in accordance with the timing of adding the metal fluoro complex solution.

  Furthermore, in order to make the treatment liquid concentration uniform, stirring or ultrasonic irradiation may be performed. The treatment liquid is preferably stirred while avoiding a region where the precipitate is deposited so that the precipitate does not approach the substrate. For example, there is a method of stirring the upper part of the treatment liquid with a propeller.

  In the present specification, a thin film means a film having a thickness of several μm, and particularly a film having a thickness of 1 μm or less.

  Here, the gas sensor is generally operated in a temperature range of 400 ° C. or higher. Therefore, the obtained metal oxide semiconductor thin film is preferably baked in advance at or above the temperature in order to be thermally stabilized in the operating temperature range of the gas sensor.

SnO ₂ is most widely used as an oxide semiconductor material that functions as a gas sensor. According to the present invention, since this SnO ₂ film can be densely deposited, it is easy to take electrical continuity and can be preferably used as a gas sensor.

Furthermore, the SnO ₂ film formed by the gas sensor manufacturing method according to the present invention can be combined with an oxide of a metal different from Sn. The order of deposition on the substrate is not particularly limited.

The metal oxide combined with the SnO ₂ film may be formed by a liquid phase deposition method, and examples thereof include WO ₃ , ZnO, Fe ₃ O ₄ , In ₂ O ₃ , and TiO _2. . For example, WO ₃ obtained by the liquid phase precipitation method is in the form of particles at the initial stage of precipitation, and this particle group continuously forms a film as the precipitation proceeds. The form of WO ₃ combined with the SnO ₂ film may be in the form of particles or film. The liquid phase deposition method applied to the formation of the metal oxide combined with the SnO ₂ film may be an ordinary liquid phase deposition method, and is particularly limited to the method of adding a metal fluoro complex as in the present invention. I can't.

A schematic diagram of a configuration example of the SnO ₂ film and another metal oxide in the present invention is shown in FIG. FIG. 4A shows an example in which the SnO ₂ film 53 is first formed on the substrate 52 and the particulate metal oxide 54 is formed thereon to form the sensor element unit 51. Similarly, (b) is an example in which a SnO ₂ film 53 is first formed on a substrate 52 and a metal oxide 55 in the form of a film is formed thereon to form a sensor element unit 51.

FIG. 4C shows an example in which a sensor element 51 is formed by first forming a particulate metal oxide 54 on a substrate 52 and forming an SnO ₂ film 53 so as to cover the oxide. In (d), the sensor element 51 is formed by first forming a film-like metal oxide 55 on the substrate 52 and forming an SnO ₂ film 53 so as to cover it.

For example, when a particle-like oxide such as WO ₃ is combined with a SnO ₂ film, good sensitivity and selectivity can be obtained for various VOC gases. This is because WO ₃ has a particle property, so that the surface area of the sensor increases, and the adsorption site of the detection gas increases, thereby improving the sensitivity of the gas sensor. WO ₃ is known to exhibit a specific catalytic action for VOC and produce an intermediate product by partial oxidation. The effect of combining SnO ₂ and WO _{3 is} considered to be that the intermediate product produced by the catalytic action of WO ₃ is adsorbed on SnO ₂ and, as a result, the characteristic of specifically responding to VOC is developed. It is done.

In addition, since the SnO ₂ film is dense and uniform and has good conductivity, it is considered that the sensitivity is prevented from being lowered due to an increase in electric resistance by combining oxides having particle properties.

  According to the present invention, a gas sensor having a uniform thin film and a fine particle diameter can be provided. In addition, a dense and uniform metal oxide semiconductor thin film can be formed on the substrate, so that a gas sensor with uniform characteristics can be obtained.

  Furthermore, by making the gas sensor a thin film type, it is easy to make elements microscopic and integrated, which is suitable for mass production.

Hereinafter, the manufacturing method of the metal oxide semiconductor sensor by this invention is demonstrated using an Example.
FIG. 1 is a schematic cross-sectional view illustrating a configuration example of the gas sensor 10. The apparatus 10 includes a substrate 12, electrodes 13 and 13 formed on the substrate, a metal oxide semiconductor film 11, and a heater 14 below the substrate.

  In this example, the electrodes 13 and 13 are buried under the metal oxide semiconductor film 11. However, the electrodes 13 and 13 may be in any form as long as they are in contact with the metal oxide semiconductor film 11. The electrodes 13 and 13 are connected to a circuit for detecting an electric current and a voltage and calculating an electric resistance by a lead wire (not shown). The heater 14 for heating the metal oxide semiconductor film 11 is connected to a power source by a lead wire (not shown). In this way, the gas sensor 10 is configured.

[Example 1]
Example 1 is an example in which a SnO ₂ film is formed on a Si substrate as a metal oxide semiconductor film 11 of a gas sensor. FIG. 2 is a diagram for explaining a manufacturing process of the gas sensor.

In FIG. 2, first, a Si substrate 12 is prepared (a).
Next, Pt is formed on the surface of the Si substrate 12 by vapor deposition or paste. Thereafter, the electrodes 13 and 13 having a desired pattern shape are formed by patterning (b).
Further, Pt or the like is formed on the back surface of the Si substrate 12 by vapor deposition or paste. Thereafter, a heater 14 having a desired pattern shape is formed by patterning (c).
Then, an SnO ₂ film as the metal oxide semiconductor film 11 is formed on the Si substrate 12 on which the electrodes 13 and 13 and the heater 14 are formed (d).

Hereinafter, the step of forming the SnO ₂ film will be described in detail.
1. 1. Preparation of treatment solution 2. Preparation of substrate 3. Preparation of initial treatment solution 4. Immerse the substrate in the processing solution 5. Addition of metal fluorocomplex to treatment solution 6. Picking up the substrate Substrate cleaning / drying

First, a metal fluorocomplex for forming a SnO ₂ film was prepared by the following procedure. The tin fluoride powder was dissolved in hydrogen fluoride water to prepare a metal fluorocomplex solution so that the Sn concentration was 1.5 mol / L. As the fluorine ion scavenger, an aqueous boric acid solution prepared at a concentration of 0.5 mol / L was used.

The prepared metal fluorocomplex solution and boric acid aqueous solution were diluted with an appropriate amount of water to prepare a Sn concentration of 0.01 mol / L and a boric acid concentration of 0.48 mol / L as an initial treatment solution. An SnO ₂ film to be the metal oxide semiconductor film 11 was formed on the substrate 12 using the manufacturing apparatus 21 shown in FIG.

After immersing the Si substrate 12 in the initial treatment liquid 21, the metal fluoro complex solution 26 was sucked up by the tubing pump 24, and added in a certain amount through the pipe 25 every 2 hours. After the substrate 12 was immersed for a predetermined time, it was pulled up, washed with pure water and dried to obtain a Si substrate 12 on which an SnO ₂ film was formed.

In Example 1, as shown in FIG. 2D, the SnO ₂ film, which is the metal oxide semiconductor film 11, is also formed on the heater on the back side of the substrate. However, there is no problem as a gas sensor. . If not necessary, the SnO ₂ film may be formed by masking the back side of the substrate.

(Surface observation)
SEM observation of the obtained SnO ₂ film was performed. The observation conditions were tilted 15 degrees from the fracture surface, the acceleration voltage was 10 kV, the irradiation current was 10 μA, and the imaging magnification was 50,000 times. The obtained SEM photographs are shown in FIGS.

  As can be seen from FIGS. 5 to 7, it was confirmed that a metal oxide semiconductor film having a uniform film thickness of 1 μm or less can be obtained.

(Measurement of particle diameter)
Furthermore, the particle diameter of the obtained SnO ₂ film was measured by TEM observation. In consideration of the actual usage of the sensor, the sample for observation was first baked at 600 ° C. for 2 hours, and then a sample for TEM observation was prepared. The observation conditions were an acceleration voltage of 200 kV and an imaging magnification of 170,000 times. Note that the lattice spacing of the (111) plane of the Si sample was used as a reference for correction when determining the actual particle size from the photograph.

  As a result of obtaining the particle size of the obtained metal oxide semiconductor film from a photograph obtained by TEM observation, it was found that the particle size was sufficiently small because it was distributed in a region of 6 to 8 nm. In the above-mentioned ceramics magazine, it is shown that the sensitivity increases when the particle diameter is 10 nm or less.

(Adhesion)
Furthermore, when the adhesiveness was evaluated by a method of peeling off vigorously after applying a transparent adhesive tape (5 mm width) to the obtained SnO ₂ film, the film has an adhesiveness that does not peel off. It was confirmed.

  In the above description, the method and material for forming the electrode and the heater are Pt. However, the present invention is not limited to this, and a metal material such as Au can be used. Moreover, the formation method is not particularly limited.

  Further, the metal oxide semiconductor film may be formed either before or after the electrodes and the heater are formed on the substrate. However, when a metal oxide semiconductor film is formed after forming an electrode on a substrate, formation by a liquid phase deposition method is advantageous. In the vapor deposition method or the like, the electrode part may become a shadow and a space may be formed between the electrode part and a non-uniform film may be formed. On the other hand, the liquid phase deposition method is a film formation method from the liquid phase, and a relatively uniform film can be easily obtained as long as it is in contact with the treatment liquid.

The substrate material is not limited to Si, and may be Al ₂ O ₃ or the like.

[Example 2]
The second embodiment is an example in which the substrate is swung during the formation of the metal oxide semiconductor film. A metal fluoro complex solution and an aqueous boric acid solution were prepared in the same manner as in Example 1.

  The metal oxide semiconductor film 11 of Example 2 was manufactured by the following procedure (see FIG. 8). The initial treatment liquid was the same as in Example 1, and after the Si substrate 12 was immersed in the treatment liquid 21, it was swung in the vertical direction by the vertical movement mechanism 27. The Si substrate 12 is connected to the shaft 28 of the vertical movement mechanism 27 by a clamp 29.

While the substrate 12 was immersed, the metal fluoro complex solution 26 was sucked up by the tubing pump 24 and added through the pipe 25 at a constant rate every 2 hours. After being immersed for a certain period of time, this was pulled up, washed with pure water and dried to obtain a Si substrate 12 on which a SnO ₂ film was formed.

Further, the film thickness of the obtained SnO ₂ film was measured in the same manner as in Example 1. The obtained film thickness is shown in Table 1 together with the results of Example 1. From Table 1, it was confirmed that in-plane variation was further reduced and a uniform film was obtained in the case of rocking as compared to the case without rocking.

  Therefore, even if a large number of sensors are cut out from a single substrate, the film thickness is uniform between the cut out sensors, and the characteristics are well aligned.

  When the adhesion was evaluated by a method of peeling off vigorously after applying a transparent adhesive tape (5 mm width) to the obtained metal oxide semiconductor film, the metal oxide semiconductor film has adhesiveness that does not peel off. I confirmed.

[Example 3]
In the same manner as in Example 1, after forming a SnO ₂ film on the substrate, WO ₃ was formed by the following method.
Tungstic acid (WO ₃ .H ₂ O) was dissolved in hydrogen fluoride water to prepare a fluoro complex of tungsten. An aqueous boric acid solution was used as the fluorine ion scavenger. WO ₃ was formed by a normal liquid phase precipitation method using a treatment solution prepared by adjusting the tungsten concentration in the treatment solution to 0.005 mol / L and the boric acid concentration to 0.15 mol / L. After formation, the substrate was baked at 600 ° C.

SEM observation of the obtained gas sensor was performed. The observation conditions were an acceleration voltage of 20 kV, an irradiation current of 10 μA, and an imaging magnification of 10,000 times. The obtained SEM photograph is shown in FIG. From FIG. 9, it was found that WO ₃ was precipitated in the form of particles. As a result, the gas sensor has a large surface area.

[Example 4]
First, WO ₃ was formed on a substrate by the method of forming WO ₃ shown in Example 3. Next, on the substrate on which WO ₃ is formed by a method of forming a SnO ₂ film shown in Example 1 to form a SnO ₂ film. After formation, the substrate was baked at 600 ° C.

  SEM observation similar to Example 3 was implemented for the obtained gas sensor. The result is shown in FIG. Also in Example 4, irregularities were observed on the surface, and the gas sensor had a large surface area.

Cross-sectional schematic diagram showing a configuration example of a gas sensor The figure explaining the manufacturing process of a gas sensor Schematic diagram schematically illustrating an example of a manufacturing apparatus that can be used in the present invention In the present invention, schematic diagram illustrating a configuration example of the SnO ₂ film and the other metal oxides SEM photograph of Sn oxide semiconductor film (film thickness 100 nm) obtained in Example 1 SEM photograph of Sn oxide semiconductor film (film thickness 300 nm) obtained in Example 1 SEM photograph of Sn oxide semiconductor film (film thickness 900 nm) obtained in Example 1 The figure which illustrates typically a mode that the board | substrate is rock | fluctuated with the manufacturing apparatus which can be used for Example 2. FIG. In Example 3, an SEM photograph of a gas sensor in which WO ₃ is formed on a SnO ₂ film In Example 4, an SEM photograph of a gas sensor in which a SnO ₂ film was formed on WO ₃

Explanation of symbols

10: Gas sensor 11: Metal oxide semiconductor film 12: Substrate 13: Electrode 14: Heater 21: Manufacturing apparatus 22: Treatment liquid 23: Container 24: Pump 25: Pipe 26: Metal fluoro complex solution 27: Vertical movement mechanism 28 : Shaft 29: Clamp 51: Sensor element part 52: Substrate 53: SnO ₂ film 54: Metal oxide (particulate)
55: Metal oxide (film-like)

Claims (10)

  A substrate is brought into contact with a treatment liquid containing a metal fluoro complex and a capture agent that chemically captures fluorine ions from the metal fluoro complex, or a treatment liquid containing only the capture agent, and the metal is then contacted with the treatment liquid. A method for producing a gas sensor, comprising the step of depositing the metal oxide semiconductor film on the substrate while adding the fluoro complex.   The method of manufacturing a gas sensor according to claim 1, wherein the addition of the metal fluoro complex is performed intermittently or continuously.   The method for producing a gas sensor according to claim 1 or 2, wherein an addition amount of the metal fluoro complex is adjusted according to an amount captured by the capturing agent.   The manufacturing method of the gas sensor as described in any one of Claims 1-3 which rocks | fluctuates the said board | substrate made to contact the said process liquid.   The method of manufacturing a gas sensor according to claim 4, wherein the rocking is performed at least when a fluoro complex of the metal is added.   The method for producing a gas sensor according to claim 1, wherein the scavenger is boric acid.   The method for producing a gas sensor according to claim 1, wherein the metal fluoro complex is a Sn fluoro complex.   8. The method comprising: forming a Sn oxide semiconductor film on the substrate; and depositing a metal oxide different from Sn on the Sn oxide semiconductor film by liquid phase deposition. A method for producing the gas sensor according to 1.   The method for producing a gas sensor according to claim 7, wherein the substrate is formed by depositing a metal oxide different from Sn by a liquid phase deposition method. Method for producing a gas sensor according to claim 8 or 9 oxide of different metals is WO ₃ and the Sn.