JPH053906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting gaseous hydrides.
In particular, the present invention relates to a method for detecting gaseous hydrides by a change in the electrical resistance of a participating tin element obtained by a specific method.

[Conventional technology]

With the progress of the semiconductor industry in recent years, the usage of epitaxial gases such as silane and disilane, and doping gases such as diborane, phosphine, aluminium, 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 heatable gases such as methane, propane, ethanol, and acetone, but have poor sensitivity to the above-mentioned gaseous hydrides. For this purpose, a detection 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 hot gas, and the method using thermal conduction has a simple detection device. 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. The present invention was completed by discovering that if the device is made into an element using the specific method used, it has the excellent properties of being able to detect gaseous hydrides with high sensitivity and selectivity. .

[Purpose of the invention]

It is an object of the present invention to provide a method for detecting gaseous hydrides with high purity.

[Means for solving problems]

That is, in the present invention, a precipitated product obtained by neutralizing an aqueous tin tetrachloride solution with ammonia in the coexistence of nitric acid and ammonium is calcined at 400 to 700°C, then formed into an element shape, and heated and sintered at 500 to 700°C. This is a method for detecting gaseous hydrides, which is characterized by detecting a change in electrical resistance of an element obtained by the method.

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 with other gases. Furthermore, as long as it is gaseous, it may be a higher polyester.

The method for manufacturing the sensing element used in the present invention will be described in detail below.

The device of the present invention is manufactured through the following three 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. The powder was molded into an element shape, and 500
This is the process of creating a sensing element by heating and sintering at ~700°C.

Step (a) is a step in which a tin tetrachloride aqueous solution is neutralized with ammonia in the coexistence of ammonium nitrate to produce a white precipitate containing β-stannic acid ([H ₂ SnO ₃ ] ₅ ) as a main component.

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
%, the concentration of the NH ₃ working solution when added as an aqueous solution is:
10~ _30wt %, concentration of _NH4NO3 used liquid is 5~30wt
% is preferable.

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 tin oxide (SnO ₂ ) by calcining.

This calcination temperature is preferably 400 to 700°C.

At temperatures below 400°C, the residual rate of tin tetrachloride (SnCl ₄ ) is high, hygroscopicity is large, and the properties are unstable. Furthermore, when the temperature exceeds 700°C, the performance is not much different from that of normal SnO ₂ , probably because there are no active sites.

In addition, in the known technology (Japanese Patent Publication No. 51-25159), the calcination temperature is set at 500 to 700°C, but for the purpose of the present invention, the temperature does not need to be 500°C or higher, and 400°C or higher is sufficient. Good elements can be made.

The SnO ₂ produced in step (b) is never pure.
Instead of _SnO2 , 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 to ₂ .

The step (c) 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 approximately 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, (b) SnO ₂ must be combined with a liquid binder such as water or polyvinyl alcohol aqueous solution, or a sintering aid that remains in the molded body and maintains its shape after heating, such as silica sol or glass frit. is added.
Furthermore, in some cases, inorganic auxiliaries such as alumina, silica 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.

The sintering aid is generally 0.01 to 5wt%, preferably 0.01 to 5wt%, because if it 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.
It is 0.1-1wt%.

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°C, the liquid binder may remain or the sintering effect will not be sufficient, which is not preferable. Furthermore, if the temperature exceeds 700°C, the properties obtained in step (b) will be lost.

When carrying out the present invention, it is essential to manufacture a gas detection element through the steps (a), (b), and (c), respectively.

For example, it is possible to omit the addition of NH ₄ NO ₃ in step (a) and use the white powder obtained by neutralization to manufacture an element through steps (b) and (c). , only very poor detection sensitivity for gaseous hydrogen compounds can be obtained.

Also, in step (a), instead of _NH3 , NaOH,
Even if an element is manufactured through steps (B) and (C) using the white powder obtained by neutralization using hydroxides of alkali metals and alkaline earth metals such as KOH and CaOH, it is still flammable. The detection sensitivity for sexual 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 pulverizing it and going through the step (c), there is almost no detection sensitivity for gaseous hydrides.

Now, when the gas detection element manufactured through the steps (a), (b), and (c) is used for gaseous hydride detection, it is used at a temperature in the range of 100 to 500°C.

In semiconductor factories, monosilane, a gaseous hydride, is often used in conjunction with diluent gas and hydrogen. It is very important to selectively detect only monosilane in such a state, but selective detection has been difficult with conventional elements.

In such a case, the element of the present invention may be used by setting the element temperature to 100 to 200°C. Sensing elements using oxide semiconductors such as SnO ₂ have higher detection sensitivity for flammable gases such as H ₂ ethyl alcohol and propane, and the higher the element temperature, the higher the detection sensitivity. This is because the sensing element of the present invention has a property of decreasing sensitivity, and this property is particularly strong, and 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 peak in detection sensitivity in the range of low element temperatures.

Monosilane can also be used with inert gases such as N ₂ ,
Used in gases other than O ₂ such as Ar, H ₂ etc. 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 a high detection sensitivity for gaseous hydrides even in 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 hydrides.

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, in a detection method that utilizes the property of SnO ₂ oxide semiconductor, which is widely used for combustible gas detection, to cause a change in resistance value in response to gas concentration, elements manufactured using conventional methods are used. In this case, it has been impossible to obtain a detection sensitivity that satisfies the above-mentioned limit, let alone a detection sensitivity that is close to it.

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

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. Moreover, it has a high detection sensitivity for gaseous hydrides that is not found in conventional production methods.

Furthermore, 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 suitably applied to continuous monitoring and spot detection of leaked gaseous hydrides in work environments and high-pressure gas equipment. It is also possible to measure the amount of gaseous hydrides remaining in waste gas from semiconductor manufacturing equipment.

The present invention will be described in detail below with reference to Examples, but these are merely illustrative and the technical scope of the present invention is not restricted thereto.

Example 1 300g of tin tetrachloride and 5g of aluminum nitrate in 1 part of water
dissolve in

On the other hand, prepare an aqueous solution in which 150 g of ammonia nitrate and 150 g of ammonia are dissolved per 1 water, and add dropwise to the solution while stirring until the pH reaches 6.8. A large amount of white precipitate is separated, washed once with water, and then calcined at 400°C.

Palladium chloride (PdCl ₂ ) is added to the resulting calcined product.
Add 0.1wt% silica sol, 0.1wt% silica sol, 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 carrier with electrodes at both ends and air-dried overnight.

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

One of the electrodes at both ends of the carrier also serves as a heater, and a circuit is formed in which this element, a power source, 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 results are the resistance of the element in air (Va) and the resistance when monosilane is detected (Vg).
Displayed as the rate of change in specific resistance (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.

Example 2 300 g of tin tetrachloride and 5 g of aluminum nitrate are dissolved in 1 part of water.

On the other hand, prepare an aqueous solution in which 100 g of ammonia nitrate and 150 g of ammonia are dissolved per 1 water, and add dropwise while stirring until the pH reaches 6.5. A large amount of white precipitate is separated, washed once with water, and then calcined at 500°C.

Palladium chloride (PdCl ₂ ) is added to the resulting calcined product.
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 with electrodes at both ends and air-dried overnight.

Afterwards, it is baked at 650℃ for 2 hours to make the element.

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

The element temperature was set at 250°C.

The results are shown in Figure 2.

It can be seen that it is possible to measure concentrations well below the 5 ppm limit for monosilane.

[Function and effect]

The reason why the method of the present invention is extremely sensitive as a method for detecting gaseous hydrides is unknown, but since it is highly sensitive even under conditions where substantially no oxygen exists, It is presumed that this is because the hydride adsorbs and/or reacts and changes the electrical conductivity of the element with high 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 drawings]

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 an aqueous solution of tin tetrachloride with ammonia in the coexistence of ammonium nitrate,
Calcinate at 700℃ and then form into an element shape with a temperature of 500 to 700℃.
A method for detecting gaseous hydrides characterized by detecting changes in electrical resistance of an element obtained by heating and sintering at °C.