KR100481744B1 - How to reduce metal impurities in ozone gas piping - Google Patents

Abstract

Prevent generation of metallic impurities from the piping, which is a problem when generating ozone gas through stainless steel piping.

In order to prevent a decrease over time of the ozone density, the density of nitrogen gas added as a catalyst gas to a raw material gas composed of high purity oxygen gas is limited to 1.0 vol%.

Description

How to reduce metal impurities in ozone gas piping

The present invention relates to an ozone gas pipe for preventing metal impurities from being generated from an ozone gas supply pipe, which is a problem when the ozone gas generated by the ozone generator is provided through a stainless pipe using high purity oxygen. A method for reducing metal impurities.

In the manufacture of semiconductors, ozone gas has begun to be used for the formation of oxide films, ashing of resists and cleaning of silicon wafers. Since ozone gas for semiconductor manufacture requires a high density gas with few impurities, the one which generate | occur | produced 99.95% or more of what is called high purity oxygen by raw discharge as a raw material gas is normally used. The generated high purity-high density ozone gas is supplied to the place of use via a pipe made of stainless steel such as SUS316L to prevent its contamination.

However, when high purity oxygen is used as a raw material gas, there exists a problem that the density of ozone gas falls with time. In order to solve this problem, some have added a small amount of catalyst gas to high-purity oxygen (see Japanese Patent Laid-Open Nos. Hei 1-282104, Hei 1-298003 and Hei 3). -218905]. High purity nitrogen gas (99.99% or more) as the catalyst gas is often used because of its availability in the semiconductor manufacturing process.

However, when high purity-high density ozone gas generated by using high purity oxygen is supplied to the use place, the ozone gas obtained at the supply point contains metal impurities, and there is a risk that the metal impurities adversely affect semiconductor manufacturing. This has recently been revealed. Since ozone gas generated in the ozone generator contains almost no metal impurities, it is considered that the metal impurities detected at the supply point are generated from a supply pipe made of stainless steel. High quality plumbing materials are costly.

It is an object of the present invention to provide a method of reducing metal impurities in an ozone gas piping which can economically reduce metal impurities in ozone gas supplied through stainless steel piping without changing the piping material.

In order to achieve the above object, according to the inventors' investigation into the cause of the occurrence of metal impurities in the case of supplying high purity-high density ozone gas while using stainless steel piping, the density decrease over time of the ozone gas is prevented It has been found that a trace amount of nitrogen gas must be added as a catalyst to high purity oxygen.

That is, when nitrogen gas is added to high purity oxygen to generate ozone gas, nitrogen oxide is present as a by-product in the generated ozone gas, thereby deteriorating or corroding the inner surface of the stainless steel pipe. As a result, the metallic impurities produced from the stainless steel tubing are separated at the point of use.

Nitrogen oxides are not considered harmful enough to corrode stainless steel piping because the dew point of high purity oxygen used for semiconductor manufacturing is low enough. Generally, since the dew point of the raw material gas used when generating ozone using an ozone generator is low, nitrogen oxide generation as a by-product is not suppressed.

As a result of further investigation of these unexpected results, the amount of metal impurities even when a sufficient amount of catalyst gas is added, as long as the nitrogen density in the feed gas is limited to 1.0 vol% or less, especially 0.25 vol% or less. It has been clearly shown that this can be suppressed to a negligible extent.

On the basis of this fact, the present invention, when generating ozone gas with an ozone generator and supplying the ozone gas to the stainless steel pipe, the high purity oxygen gas to one of nitrogen gas, helium gas, argon gas, carbon dioxide gas and carbon monoxide gas A mixed gas containing at least 0.025% by volume or more of total species is used as a source gas, and the density of nitrogen gas in the source gas is 1.0% by volume or less, and a method for reducing metal impurities in an ozone gas pipe is provided. .

In the metal impurity reduction method of the present invention, a catalyst gas is added in view of preventing a decrease in ozone density over time. As the catalyst gas, at least one of nitrogen gas, helium gas, argon gas, carbon dioxide gas and carbon monoxide gas is used. Even when any catalyst gas is used, the density of nitrogen gas is 1.0 vol% or less, preferably 0.5 vol% or less, more preferably 0.25 vol% or less, in order to suppress the generation of metal oxides from the stainless steel piping. .

As the upper limit of the amount of the catalyst gas, when the total amount exceeds 10% by volume, the effect of adding the catalyst gas is saturated and economic efficiency is deteriorated, so 10% by volume or less is preferable. However, helium gas, argon gas, carbon dioxide gas and carbon monoxide gas are preferably added at 1.0 volume% of the total amount because a sufficient addition effect is obtained even at a small amount of 1.0 volume% or less. Therefore, although nitrogen gas is not allowed to be added in an amount of 1.0 vol% or more, addition of helium gas, argon gas, carbon dioxide gas and carbon monoxide gas in an amount of 1.0 vol% or more is also allowed in view of reduction of metal oxide.

In addition, the regulatory effect on the economic lowering of the ozone density is greater in nitrogen gas. Therefore, it is also effective to mix trace amounts of nitrogen gas with at least one of helium gas, argon gas, carbon dioxide gas and carbon monoxide gas.

The metal impurity reduction method of the present invention can be applied to an ozone gas supply system particularly used in a semiconductor manufacturing process, and also to an ozone gas supply system in a liquid crystal display manufacturing process. The purity of the high purity oxygen gas is preferably 99.99% or more, and the purity of the catalyst gas is preferably 99.999% or more.

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

1 is a schematic view of a film forming apparatus showing an application example of the present invention. This is also called TEOS-CVD. The silicon substrate 1 is heated by the heater 2, and the raw material gas for film formation is sprayed on the surface of the silicon substrate 1 by the branch plate nozzle 3.

The raw material gas for film-forming is TEOS and ozone gas. TEOS or Si (OC ₂ H ₅ ) ₄ is heated and vaporized in the liquid state and supplied to the nozzle 3 through the stainless steel pipe 4 together with nitrogen gas as the carrier gas. (7) is a heater. In the ozone gas, high purity oxygen gas as a raw material gas, nitrogen gas as a catalyst gas, and the like are supplied to the ozone generator 5. The generated ozone gas is supplied to the nozzle 3 through the stainless steel pipe 6. A silicon oxide film is formed on the surface by spraying each gas from the nozzle 3 onto the surface of the silicon substrate 1.

At this time, the metal oxide generated in the stainless steel pipe 6 for supplying the oxygen gas becomes a problem. Therefore, when the catalyst gas is nitrogen gas, the density of the raw material gas is 0.025% by volume or more and 1.0% by volume or less (preferably 0.5% by volume or less, more preferably 0.25% by volume or less). When the catalyst gas is helium gas, the density is from 0.025 to 10 vol%. If the catalyst gas is argon gas, carbon dioxide gas and carbon monoxide gas, it is from 0.025 to 10% by volume. When these mixed gases are used, the total amount is 0.025 to 10% by volume. The nitrogen gas amount here is 1.0 vol% or less (preferably 0.5 vol% or less, more preferably 0.25 vol% or less).

Embodiments of the present invention are described below to clearly describe the effects through comparison with the comparative examples.

The silent discharge ozone generator (Table 1) feeds ozone gas through stainless steel piping. The content of metal impurities, nitrogen oxide content and ozone density in the feed gas are measured.

As a raw material, high purity oxygen gas (purity of 99.99% or more) and 0.020 to 1.5% by volume of nitrogen gas (purity of 99.999% or more) and 0.020 to 12 volume% of argon gas (purity of 99.999% or more) respectively added to such high purity oxygen gas ), 0.018 to 11 vol% helium gas (purity 99.999% or more), 0.010 to 15 vol% carbon dioxide gas (purity 99.999% or more), 0.020 to 14 vol% carbon monoxide gas (purity 99.999% or more), 0.2 vol% Of a mixture of nitrogen gas and 0.28% to 9.0% argon gas, and 0.2% by volume nitrogen gas and 0.6% to 5.3% by volume helium gas are used.

For stainless steel piping, SUS 316L-EP with an outer diameter of ¼ in (6.35mm), a thickness of 1mm, and a length of 4m is used. The composition of SUS 316L (JIS G3459) is shown in Table 2. EP stands for electrical polishing and means electropolishing.

The method of quantitatively analyzing metal impurities includes spraying ozone gas having an ozone density of 120 g / m 3 onto the surface of a silicon wafer under conditions of 15 minutes x 6 l / min, and vapor phase decomposition (VPD) of the surface. Decomposing to fluoric acid vapor and analyzing the recovered decomposition liquid by ICP-MS (Coupled Plasma Mass Spectrometer).

The measurement of nitrogen oxides is carried out by checking whether the reduction of metal impurities is caused by the influence of nitrogen oxides, and in a jar containing pure water, ozone gas under conditions of 12 hours x 6 l / min in 120 g / m 3 ozone gas Absorbing or harvesting the nitrogen oxides in the solution and analyzing the solution with ion chromatography.

The measurement of the ozone density is to observe the stability of the ozone density by an ozone monitor of ultraviolet absorption type.

The measurement results are shown in Tables 3 to 8. The content of metal impurities required for the gas used in the semiconductor manufacturing process is generally 10 ¹¹ atoms / cm 2 or less on the silicon wafer. The effect of reducing the metal impurity content, the stability and economy of the ozone density is evaluated by the following criteria.

(Reduction effect of metal impurity content)

Measure the maximum amount of metal element.

X: 10 ¹² atoms / cm 2

△: 10 ¹¹ atoms / cm 2

○: 10 ¹⁰ atoms / cm 2

◎: 10 ⁹ atoms / cm 2

(Ozone Density Stability)

The stability of the ozone density is measured for 1 hour continuously.

X: 120g / ㎥ ± 10% or more

○: 120 g / ㎥ ± 10% or less

(Economics)

The addition amount of catalyst gas is measured.

X: 10% or more

Δ: 1% to 10%

○: 1% or less

As can be seen from Table 3, the content of Cr, Fe and Ni can all be made up to 10 ¹¹ atoms / cm 2 or less by adjusting the density of nitrogen gas to 1.0 vol% or less. However, when the nitrogen gas density is 0.025% by volume or less, the stability of the ozone density is lowered.

When the catalyst gas is argon gas, helium gas, carbon dioxide gas and carbon monoxide gas, the generation of metal impurities is prevented to a negligible level. However, this effect does not affect gas density. 10 volume% or less is enough. There is no problem even when the catalyst gas is 1.0 vol% or less. Therefore, 1.0 vol% or less is preferable. However, when the gas density is 0.025% by volume or less, the stability of the ozone density is lowered.

As is apparent from Table 6, nitrogen gas can be mixed with other gases when their content is trace. Even in such a case, it is not necessary to specifically add more than 1.0% by volume of other gases.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

TABLE 8

As described above, the impurity reduction method of the present invention can be used in a semiconductor manufacturing process while preventing the occurrence of metal impurities from piping without manipulating the quality of the piping material by operating the catalyst gas added to the raw material gas. To the metal impurity level (10 ¹¹ atoms / cm 2 or less) normally required in the gas to be obtained.

1 is a schematic diagram of a film forming apparatus showing an application example of the present invention, wherein (1) represents a silicon substrate, (3) a nozzle, (5) an ozone generator, and (6) a stainless steel pipe.

2 is a schematic diagram showing a discharge cell structure.

Claims (6)

When ozone gas is generated by the ozone generator and the ozone gas is supplied to the stainless steel pipe, at least 0.025% by volume of at least one of nitrogen gas, helium gas, argon gas, carbon dioxide gas, and carbon monoxide gas is added to the high purity oxygen gas. A method for reducing metal impurities in an ozone gas pipe, characterized in that a mixed gas is used as a source gas. The method of claim 1, wherein the density of nitrogen gas in the source gas is limited to 1.0 vol% or less. The method for reducing metal impurities in an ozone gas piping according to claim 2, wherein the raw material gas is a mixed gas obtained by adding 0.025 to 0.25% by volume of nitrogen gas to high-purity oxygen gas. The ozone according to claim 2, wherein the raw material gas is a mixed gas in which 0.025 to 0.25% by volume of nitrogen gas and at least one of 0.025 to 1.0% by volume of helium gas, argon gas, carbon dioxide gas, and carbon monoxide gas are added to the high purity oxygen gas. Method for reducing metal impurities in gas pipelines. The method for reducing metal impurities in an ozone gas pipe according to claim 1 or 2, wherein the purity of the high purity oxygen gas is 99.99% or more. The method for reducing metal impurities in an ozone gas piping according to claim 1 or 2, wherein the added gas has a purity of 99.999% or more.