JPH053907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting gaseous hydrides.
Specifically, the present invention relates to a method of detecting gaseous hydrides based on changes in electrical resistance of a tin oxide element obtained by a specific method.

[Conventional technology]

With recent advances in the semiconductor industry, the usage of epitaxial gases such as silane and disilane, and doping gases such as diborane, phosphine, alumin, and germane has increased significantly.

These gaseous hydrides are flammable, natural, and toxic, and if even a trace amount of these gaseous hydrides leak out, they pose a health and safety problem, so it is desired to develop a method for detecting trace amounts of gaseous hydrides.

In contrast, known methods include constant potential electrolysis, galvanic cell method, IR method, UV method, and chemiluminescence method, but all of them are expensive, require complicated and costly maintenance, and have large detection units. Moreover, there is the problem of vulnerability. On the other hand, semiconductor sensing elements such as tin oxide have good sensitivity to flammable gases such as methane, propane, ethanol, and acetone, but have poor sensitivity to the above-mentioned gaseous hydrides. To deal with this, a sensing element is known that utilizes the fact that tin oxide, which has been subjected to a specific treatment, causes a change in thermal conductivity due to the presence of gaseous hydrides (New Cosmos Electric Co., Ltd. Technical Data No. .SK−2011).

[Problem that the invention seeks to solve]

The above-mentioned method using a semiconductor detection element has a simple detection device and excellent durability, but the sensitivity is insufficient with a normal detection element for combustible gas, and the method using thermal conduction has a simple detection device and excellent durability. There was a problem in that the sensing element was difficult to manufacture because it used the resistance of the heater for heating.

As a result of intensive studies by the present inventors on ways to solve the above problems, it was found that the detection element for combustible gas, which was deemed unsuitable for detecting gaseous hydrides, uses tin oxide made by a specific manufacturing method. It was discovered that if the device is made into an element using a specific method, it can be used as a detection element for gaseous hydrides with high sensitivity and selectivity, and has excellent properties such as improved mechanical strength. The invention has been completed.

[Object of the Invention] An object of the present invention is to provide a method for detecting gaseous hydrides with high sensitivity.

[Means for solving problems]

That is, the present invention uses a precipitated product obtained by neutralizing an aqueous solution of tin tetrachloride (SnCl ₄ ) with ammonia (NH ₃ ) in the coexistence of ammonium nitrate (NH ₄ NO ₃ ).
Calcining at 700°C to obtain powder, contacting the powder with hydrochloric acid, forming it into an element shape, heating and sintering at 500 to 700°C, and detecting changes in electrical resistance of the obtained element. A method for detecting gaseous hydrides is characterized by:

The gaseous hydrides targeted in the present invention include hydrides of silicon, boron, phosphorus, germanium, and arsenic, which are diluted with not only mono- and di-forms such as monosilane, disilane, borane, and diborane, but also other gases. Furthermore, if it is in a gaseous state, it may also contain a larger amount of poly.

One of the features of the present invention is that the calcined tin oxide powder is further contacted with hydrochloric acid. This operation greatly improves the detection sensitivity of gaseous hydrides. For example, a method of treating powder made of tin oxide with hydrochloric acid is disclosed in Japanese Patent Publication No. 50-26239.
This method is already known and can be applied as is.

In the method of the present invention, the question is how to form the tin oxide powder to be brought into contact with hydrochloric acid.

For example, even if ordinary tin oxide, such as that obtained by neutralizing tin tetrachloride with ammonia, is treated by contacting it with hydrochloric acid, the hardness, which is a measure of the mechanical strength of an element, does not improve much. In the case of tin oxide obtained by neutralizing tin tetrachloride with ammonia in the presence of ammonium nitrate as in the present invention, surprisingly, an unexpected improvement in hardness occurs when brought into contact with hydrochloric acid. It is.

The present invention will be explained in detail below.

The device of the present invention is manufactured through the following four steps.

(a) a step of neutralizing an aqueous tin tetrachloride solution with ammonia in the coexistence of ammonium nitrate to obtain a precipitated product; (b) a step of calcining the precipitated product at 400 to 700°C; (c) a step of calcining the precipitated product. (iv) After contacting with hydrochloric acid, the powder is molded into an element shape and heated and sintered at 500 to 700°C to produce a sensing element.

In the step (a), a SnCl ₄ aqueous solution is neutralized with NH ₃ in the coexistence of ammonium nitrate to form β-stannic acid ([H ₂ SnO ₃ ] ₅ ).
This is a process to produce a white precipitate whose main component is

Note that ammonia may be blown into the SnCl ₄ aqueous solution as a gas or may be supplied as a liquid solution, but from the viewpoint of ease of operation, it is preferable to supply it in the form of an aqueous solution.

The concentration of SnCl ₄ aqueous solution used here is 20~40wt
%, for aqueous solution the concentration of _NH3 aqueous solution is 10 ~
The concentration of the NH ₄ NO ₃ aqueous solution is preferably 30 wt% and 5 to 30 wt%, respectively.

The NH ₃ aqueous solution and the NH ₄ NO ₃ aqueous solution may be mixed in advance and added, or may be added separately. However, in that case, it is necessary to add the NH ₄ NO ₃ aqueous solution first and then add the NH ₃ aqueous solution.

The pH of the neutralization point is 6.5 to 7.5, more preferably 6.8 to 7.0.

In step (b), the white precipitate produced in step (b) is
This is the process of producing SnO ₂ by calcining.

This calcination temperature is preferably 400 to 700°C.

Below 400°C, the residual rate of SnCl ₄ is high, hygroscopicity is large, and the properties are unstable. Also, if the temperature exceeds 700℃, the active sites disappear, so the normal
The performance is not much different from that of SnO ₂ .

In Special Publication No. 51-25159, the calcination temperature was set at 500 to 700.
℃, but for the purposes of this invention, 500
The temperature does not need to be higher than 400°C, and a sufficiently good element can be produced at a temperature of 400°C or higher.

The SnO ₂ produced in step (b) is never pure SnO ₂
Rather, Cl atoms, hydroxyl groups, etc. remain, and the surface structure such as specific surface area and pores is also unique _. It seems to be given.

Step (c) is a step in which the calcined powder obtained in step (b) is brought into contact with hydrochloric acid.

The concentration of hydrochloric acid is preferably 10 wt% to 30 wt% aqueous solution.

The temperature of hydrochloric acid is preferably in the range of room temperature to 60°C.

The method for contacting the calcined powder with hydrochloric acid may be any commonly used method for contacting solids and liquids. Typical examples include mixing and adding calcined powder to hydrochloric acid while stirring, leaving it for a certain period of time and using it in step (d), or air-drying it and using it in the next step (d). do.

Another example is using an appropriate amount of hydrochloric acid, mixing it with the calcined powder to make a paste, and leaving it as is.
It may be used in the step (d).

This contact treatment with hydrochloric acid causes the _SnO2 surface to
It is thought that changes in the surface structure and composition caused by HCl occur, resulting in improved detection sensitivity for gaseous hydrides and improved hardness of the device due to sintering during the device fabrication process.

Step (d) is a step of manufacturing an element.

The SnO ₂ produced in (b) above is molded into an element shape of an appropriate size.

In this case, the shape and size of the element can be arbitrary, but
The preferred size is about 1 mm square to 5 mm square.

The device is equipped with a pair of electrodes for measuring changes in current flowing in response to changes in electrical resistance of the element, and a heater for heating the element. One electrode may also serve as a heater. The material used for the electrodes is Pt, Pd-Ir, or the like.

In order to manufacture the element, a liquid binder such as water or an aqueous polyvinyl alcohol solution, or a sintering aid that remains in the molded body and maintains its shape after heating is added to the SnO ₂ in (b), such as silica sol or glass frit. be done. Furthermore, in some cases, inorganic auxiliaries such as alumina, milica alumina, and magnesia are added to maintain the strength of the element and improve response characteristics to changes in gas concentration.

If necessary, platinum (Pt), palladium (Pd),
Metal oxides and halides such as gold (Au) and antimony (Sb) are added.

The preferable addition amounts of these are as follows.

The liquid binder may be used in an amount necessary to achieve sufficient mixing and to facilitate device molding.

If the sintering aid is too small, it will be ineffective, and if it is too large, it will cover the SnO ₂ particles and prevent the development of properties, so it is generally 0.01-5wt%, preferably 0.1-5wt%.
It is 1wt%.

If the amount of inorganic auxiliary agent is too large, it will actually become difficult to mold, so a range of 0 to 10 wt% is preferable.

The catalyst is preferably 0.001 to 1 wt% since it is ineffective if it is too small and expensive if it is too large.

Next, the sintering temperature is preferably 500 to 700°C.

If it is less than 500, the liquid binder remains or the sintering effect is not sufficient, which is not preferable. Furthermore, if the temperature exceeds 700°C, the properties obtained in steps (b) and (c) will be lost.

Now, when carrying out the present invention, (a), (b), and (c)
It is essential to manufacture the gas detection element through each of the steps (d).

For example, using the white powder obtained by neutralizing without adding NH ₄ NO ₃ in step (a), (b) (c) (d)
Even if the device is manufactured through the above process, only a low detection sensitivity for gaseous hydrides can be obtained.

Also, in step (a), instead of _NH3 , NaOH,
Neutralize using hydroxides of alkali metals and alkaline earth metals such as KOH and CaOH, and use the resulting white powder to manufacture devices through steps (b), (c), and (d). However, the detection sensitivity for combustible gases is also extremely poor.

In addition, we obtained commercially available SnO ₂ that omitted steps (a) and (b),
Even if a gas detection element is produced by finely pulverizing it and going through the steps (c) and (d), the detection sensitivity of gaseous hydrides is very low.

Now, when the gas detection element manufactured through the steps (a), (b), (c), and (d) is used for gaseous hydride detection,
Used at temperatures ranging from 100 to 500°C.

In semiconductor factories, monosilane, a gaseous hydride, is often used together with a diluent gas, hydrogen. It is very important to selectively detect only monosilane under such conditions.

In such a case, the element temperature may be set at 100 to 200°C. Sensing elements using oxide semiconductors such as _SnO2 have higher detection sensitivity for flammable gases such as _H2ethyl alcohol and propane, and the higher the element temperature, the higher the detection sensitivity.Conversely, the lower the element temperature, the lower the detection sensitivity. The sensing element of the present invention has a property that this property is low, and the sensing element of the present invention has this property particularly strongly.
This is because when the element temperature becomes low, there is no detection sensitivity at all. On the other hand, surprisingly, for gaseous hydrides such as monosilane, there is a detection sensitivity peak in the low element temperature range.

Monosilane can also be used with inert gases such as N ₂ ,
Used in gases other than O ₂ such as Ar ₂ and H ₂ . Therefore, it is also important to detect monosilane in inert gas.

Normally, sensing elements using oxide semiconductors such as _SnO2 are
The detection sensitivity for combustible gases is high in air, that is, in the presence of O ₂ , but the detection sensitivity is low in inert gases.

However, the sensing element of the present invention surprisingly exhibits high detection sensitivity for gaseous hydrides even in an inert gas at the same level as in air.

In the sensing element of the present invention, the electrical resistance of the element changes depending on the concentration of gaseous hydride. Therefore, by utilizing this change, a circuit including an element, a power source, and an alarm means or a control circuit is configured to detect gaseous hydride.

An example of specifically configuring a detection device using the detection element of the present invention will be shown.

Connect the element, power supply, and fixed resistor in series, and
Load a constant voltage such as 10V. Apply an appropriate voltage to the element heater to keep the element temperature constant.
The output from both ends of the fixed resistor is taken out and connected to an amplifier to operate alarm means such as a bell or light emitting diode, or to operate a control circuit such as a relay.

The limits for gaseous hydrides are, for example, SiH ₄ (monosilane) 5ppm, B ₂ H ₆ 0.1ppm, PH ₃ 0.3ppm,
_AsH3 is 0.05ppm.

As mentioned above, oxide semiconductors such as SnO ₂ , which are popular for flammable gas detection, are fabricated using conventional methods in detection methods that utilize the property of causing resistance value changes in response to gas concentration. In Motoko,
It has been impossible to obtain a detection sensitivity that satisfies the above-mentioned limit, or even close to it.

However, surprisingly, when using the device manufactured by the method of the present invention, it is possible to obtain extremely high sensitivity that exceeds the limit or is sufficient for practical use.

By adding a step of contacting with hydrochloric acid to the method already proposed by the present inventors, the device of the present invention not only further improves the detection sensitivity of gaseous hydrides, but also has a An incredibly large improvement in element hardness occurs. As a result, the mechanical strength and durability of the device have been significantly improved.

In the method of the present invention, the detection element used can be manufactured at a very low cost, is durable, and easy to maintain. It also has a high detection sensitivity for gaseous hydrides that is not found in conventional production methods.

Since the circuit using the gas detection element can be easily constructed, the entire device can be manufactured at a much lower cost than conventional methods.

The method of the present invention can be applied to continuous monitoring and spot detection of waxy gaseous hydrides in work environments and high pressure gas equipment. It is also possible to measure the amount of gaseous hydride remaining in waste gas from semiconductor manufacturing equipment.

Examples will be described in detail below, but the scope of the present invention is not limited thereto.

Example 1 300 g of SnCl ₄ and 5 g of aluminum nitrate were added to 1 part of water.
dissolve in

On the other hand, prepare an aqueous solution in which 150 g of NH ₄ NO ₃ and 170 g of NH ₃ are dissolved per 1 portion of water, and add dropwise to the solution while stirring until the pH reaches 7.0. A large amount of white precipitate is separated, washed once with water, and then calcined at 400°C.

Mix the calcined powder with 27% hydrochloric acid while stirring,
Continue stirring for 30 minutes to form a paste.

Add palladium chloride (PdCl ₂ ) to the resulting paste.
Add 0.1 wt% silica sol, 0.1 wt% silica sol, and an appropriate amount of a 2% polyvinyl alcohol aqueous solution, and stir thoroughly to mix.

This paste is applied to an alumina carrier with electrodes at both ends and air-dried overnight.

Afterwards, it is baked at 600℃ for 2 hours to make the element.

A circuit is constructed in which this element, a power supply, and a fixed resistor are connected in series, and the output is taken out from both ends of the fixed resistor.

Monosilane was detected with the element temperature set at 170°C. The result is the resistance of the element in air (Va)
and the resistance (Vg) when monosilane is detected,
Displayed as resistance change rate (Va/Vg).

The results are shown in Figure 1.

It can be seen that concentrations lower than the monosilane limit of 5 ppm can be detected satisfactorily.

The hardness was 200g when measured using a Kiya hardness tester.

Comparative Example 1 During the operation of Example 1, except for the operation of contacting the calcined powder with 27% hydrochloric acid, the other steps were as in Example 1.
I went in the same way.

That is, the powder after calcination was made into a paste with an appropriate amount of 2% aqueous polyvinyl alcohol solution, and additives were added thereto, and the same procedure as in Example 1 was carried out.

As a result, the resistance change rate was 7 at a SiH ₄ concentration of 10 ppm.

Moreover, the hardness measured with a Kiya type hardness meter was 20 g.

Comparative Example 2 NH ₄ NO ₃ was added to the ammonia aqueous solution used for neutralization.
The same procedure as in Example 1 was carried out except for the addition of .

As a result, the resistance change rate was 1.4 at a SiH ₄ concentration of 10 ppm.

The hardness measured using a Kiya hardness tester was 40g.

Example 2 300 g of SnCl ₄ and 5 g of aluminum nitrate were added to 1 part of water.
dissolve in

On the other hand, prepare an aqueous solution in which 100 g of NH ₄ NO ₃ and 150 g of NH ₃ are dissolved per 1 portion of water, and add dropwise to the solution while stirring until the pH reaches 7.0. A large amount of white precipitate is separated, washed once with water, and then calcined at 500°C.

Mix the calcined powder with 25% hydrochloric acid while stirring,
Continue stirring for 1 hour and then age.

Add palladium chloride (PdCl ₂ ) to the resulting cake
Add 0.5wt% glass frit, 0.1wt% glass frit, and an appropriate amount of 2% polyvinyl alcohol aqueous solution, stir thoroughly and mix to form a paste.

This paste is applied to an alumina support having electrodes at both ends and air-dried overnight.

Afterwards, it is baked at 600℃ for 2 hours to make the element.

Thereafter, a circuit was constructed in the same manner as in Example 1, and the monosilane gas in the chitso was tested.

The element temperature was set at 250°C.

The results are shown in Figure 2.

It can measure concentrations well below the 5ppm limit for monosilane.

The hardness measured using a Kiya hardness tester was 250g.

[Effect]

The reason why the method of the present invention is extremely sensitive as a method for detecting gaseous hydrides is unknown, but it is highly sensitive even under conditions where substantially no oxygen exists, so gaseous hydrides may be detected in some form in the element. It is presumed that this is because it adsorbs and/or reacts and changes the electrical conductivity of the element with good sensitivity.

[Industrial applicability]

By employing the method of the present invention, gaseous hydrides can be detected at low cost and with high sensitivity, making it extremely valuable industrially.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the relationship between resistance change rate and gas concentration.

Claims (1)

[Claims] 1. A precipitated product obtained by neutralizing a tin tetrachloride aqueous solution with ammonia in the coexistence of ammonium nitrate is 400 to 700
It is characterized by detecting changes in the electrical resistance of the obtained element by calcining it at ℃ to obtain a powder, contacting the powder with hydrochloric acid, molding it into an element shape, and heating and sintering it at 500 to 700 ℃. A method for detecting gaseous hydrides.