JP3279608B2 - Steam purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying steam, and more particularly to a method for purifying steam capable of removing oxygen contained as impurities in steam to an extremely low concentration. Water vapor is used in the manufacture of semiconductors, such as formation of oxide films of silicon and aluminum. However, with the progress of film forming technology, those having extremely few impurities are being demanded.

[0002]

2. Description of the Related Art Usually, as a method for supplying steam used in semiconductor manufacturing, purified water such as distilled water or deionized water is put into a bottle having an open end, and the bottle is immersed in a thermostat to control the temperature to an appropriate temperature. Then, a method of supplying steam to the reactor by controlling the generated steam by a mass flow controller, a method of supplying purified water to a bubbler and bubbling with H ₂ , N ₂ , He or the like to supply the reactor to the reactor are used. In the steam thus generated, oxygen and the like mixed in when the raw material purified water is charged into a bottle or a bubbler are present. These water vapors usually contain 10 pp
m of oxygen is contained, and these oxygens are removed to a low concentration of 0.1 ppm or less by only a reduced pressure purge performed before the use of water vapor or a purge using an inert gas in the raw material liquid. It is difficult.

[0003]

Recently, a gas such as silane used together with water vapor in the production of a compound semiconductor can be purified to a high purity. For example, oxygen contained as an impurity is removed to 0.01 ppm or less. It is possible to do. For this reason, it is strongly desired that the oxygen content of the water vapor be 0.01 ppm or less. In addition, since these water vapors may be contaminated by impurities such as air during the supply process to the semiconductor device such as when connecting a bottle or switching pipes, it is desirable to finally remove the impurities immediately before the device. However, there is almost no known technique for efficiently removing oxygen contained in steam and supplying high-purity steam to a semiconductor manufacturing process or the like.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to efficiently remove oxygen contained in steam to an extremely low concentration, and as a result, have found that steam is converted to metallic nickel or
The present inventors have found that the oxygen concentration can be reduced to 0.1 ppm or less and further to 0.01 ppm or less by contacting with a refining agent mainly containing a nickel compound which has been subjected to a primary treatment , and the present invention has been completed. That is, the present invention provides a method for purifying steam comprising contacting a crude steam with a purifying agent mainly containing metallic nickel or a reduced nickel compound to remove oxygen contained in the crude steam. is there. The present invention uses water vapor alone, hydrogen (based on hydrogen gas)
It is also applied to the removal of oxygen contained in steam (hereinafter referred to as crude steam) diluted with an inert gas (inert gas base) such as nitrogen or argon.

[0005] The refining agent used in the present invention is a refining agent mainly composed of a nickel compound which is easily reduced, such as nickel metal or a nickel oxide, subjected to a reduction treatment . Further, a metal component other than nickel may contain a small amount of heavy metals such as chromium, iron, cobalt, and copper. These nickels may be used alone, or may be used in a form supported on a carrier or the like, but may be used on a carrier or the like for the purpose of increasing the contact efficiency between the nickel surface and gas. It is preferable to use them. As a method of supporting nickel on a carrier,
For example, a carrier powder such as diatomaceous earth, alumina, silica alumina, aluminosilicate and calcium silicate is dispersed in an aqueous solution of a nickel salt, and an alkali is added to precipitate a nickel component on the carrier powder, followed by filtration and filtration. 120 to 1 cake obtained by washing with water
After drying at 50 ° C., it is fired at 300 ° C. or more, and the fired product is pulverized, or NiCO ₃ , Ni (OH) ₂ , Ni
Inorganic salts such as (NO ₃ ) ₂ , NiC ₂ O ₄ , Ni (CH
₃ COO) calcining the organic salts such as _2, after grinding, which was mixed with refractory cement, and the like fired. These are usually formed into a molded product by extrusion molding, tablet molding, or the like, and are used as they are, or crushed to an appropriate size as needed. As a molding method, a dry method or a wet method can be used, and in that case, a small amount of water, a lubricant, or the like may be used. Further, as the nickel-based catalyst, for example, a steam conversion catalyst, C11-2-03 (NiO-cement), C11-2-06 (NiO-refractory), C1
1-2 (Ni-calcium aluminate), C11-9
(Ni-alumina); hydrogenation catalyst, C46-7 (Ni-
Diatomaceous earth), C46-8 (Ni-silica), C36 (Ni
-Co-Cr-alumina); gasification catalyst, XC99 (N
iO); hydrotransformation catalyst, C20-7 (Ni-Mo-alumina) [all, manufactured by Toyo CCI Co., Ltd.] and hydrogenation catalyst, N-111 (Ni-diatomaceous earth); gasification transformation catalyst, N
-174 (NiO); gasification catalyst, N-185 (Ni
O) There are various types such as [the above, manufactured by JGC Corporation], and those selected from them may be used. In short, it is sufficient if reduced nickel, nickel oxide, and the like are finely dispersed and have a large surface area and high contact efficiency with gas.

[0006] The specific surface area of the purifying agent is usually BET.
In the range of 10 to 300 m ² / g, preferably 3
It is in the range of 0 to 250 m ² / g. The content of nickel is usually 5 to 95 wt% in terms of metallic nickel.
%, Preferably 20 to 95 wt%. If the content of nickel is less than 5 wt%, the deoxidizing ability is reduced. If the content is more than 95 wt%, sintering may occur during reduction with hydrogen, and the activity may be reduced.
In order to activate the purifying agent , hydrogen reduction is usually performed. Hydrogen can be reduced, for example, by passing a mixed gas of hydrogen and nitrogen at a cylinder linear velocity (LV) of about 5 cm / sec at about 350 ° C. or less. is necessary.

[0007] Purification of steam is usually carried out by passing crude steam through a purifying cylinder filled with a purifying agent mainly composed of a reduced nickel compound.
By contact with the purifying agent , oxygen contained as impurities in the crude steam is removed. The oxygen concentration in the crude steam applied to the present invention is usually 100 ppm or less. If the oxygen concentration is higher than this, the calorific value increases, so a heat removal means is required depending on the conditions. The filling length of the purifying agent filled in the purifying cylinder is usually 50 to 150 in practice.
0 mm. If the filling length is shorter than 50 mm, the oxygen removal rate may decrease. If the filling length is longer than 1500 mm, the pressure loss may become too large. The linear velocity (LV) of the crude steam at the time of refining differs depending on the oxygen concentration in the supplied steam and the operating conditions and cannot be specified unconditionally, but is usually 100 cm / sec or less, preferably 30 cm / sec or less. With steam
The contact temperature of the purifying agent is usually 200 ° C. or lower, preferably 1 ° C.
When the partial pressure of water vapor is low, the temperature may be room temperature when the partial pressure of water vapor is low.Heating is not particularly required, but when the partial pressure is high and there is a risk of dew condensation, the refining cylinder is heated to an appropriate temperature. It is preferable that the contact be made. The pressure of the gas at the time of contact is not particularly limited, and the treatment can be performed at any of normal pressure, reduced pressure, and increased pressure, but is usually 20 kg / cm ² abs or less.
Preferably it is 0.1 to 10 kg / cm ² abs.

[0008]

【Example】

Example 1 (Reduction treatment of nickel) A commercially available nickel catalyst [N-111, manufactured by JGC Corporation] was used. Its composition is N
In the form of i + NiO, 45 to 47 wt% as Ni,
Cr 2-3 wt%, Cu 2-3 wt%, diatomaceous earth 27-2
9 wt% and graphite 4-5 wt%, specific surface area 150 m
² / g, a molded body having a diameter of 5 mm and a height of 4.5 mm. 63 ml of this nickel catalyst crushed to 8 to 10 mesh was packed in a stainless steel purification cylinder having an inner diameter of 16.4 mm and a length of 400 mm, and a filling length of 300 mm (filling density:
1.0 g / ml). Hydrogen was added thereto at normal pressure at a temperature of 150 ° C. and a flow rate of 595 ml / min (LV = 3.6 cm).
/ Sec) for 3 hours, and then cooled to room temperature. (Purification of steam) Subsequently, purification of steam was performed. About 50 ml of distilled water inside diameter 50mm, height 1
A 75 mm stainless steel bubbler is immersed in a thermostat set at 40 ° C. to control the steam pressure, and bubbling the steam with nitrogen to about 7.3 v on a nitrogen base.
A gas containing ol% steam was generated. Next, while heating the pipe to 60 ° C. so as to prevent condensation, the above gas was used for 3 hours.
After purging the pipe for 0 minutes, the oxygen concentration in the gas containing water vapor was measured using a yellow phosphorus emission type oxygen analyzer (measurement lower limit concentration: 0.01 ppm).
ppm. As a result of flowing this gas through a purification cylinder heated to 40 ° C. at 0.633 L / min (LV = 5 cm / sec) and measuring the oxygen concentration in the outlet gas, 0.01 pp
m or less. Even after 100 minutes from the start of the purification, the oxygen concentration of the outlet gas was 0.01 ppm or less.

Example 2 (Purification of steam) Steam was purified using the same purification cylinder as used in Example 1. A stainless steel bubbler having an inner diameter of 50 mm and a height of 175 mm containing about 50 ml of distilled water is immersed in a thermostat set at 40 ° C. to control the steam pressure, and bubbling the steam with hydrogen to about 7.3 vol on a hydrogen basis. A gas containing% steam was generated. After purging the inside of the pipe with the above gas for 30 minutes while heating in the same manner as in Example 1, the oxygen concentration in the gas containing the water vapor was measured using a yellow phosphorus emission type oxygen analyzer. there were. 40 ℃
0.633 L / min (LV = 5c)
m / sec), and the oxygen concentration in the outlet gas was measured. The result was 0.01 ppm or less. Even after 100 minutes from the start of the purification, the oxygen concentration of the outlet gas is 0.01 p.
pm or less.

Example 3 (Purification of steam) Steam was purified using the same purification cylinder as used in Example 1. A stainless steel bubbler having an inner diameter of 50 mm and a height of 175 mm containing about 50 ml of distilled water was immersed in a thermostat set at 60 ° C. to control the steam pressure, and the mass flow controller controlled the steam flow rate to 0.1 L / min. At that time, a differential pressure for flow rate control was obtained by installing a vacuum pump downstream of the mass flow controller. After purging for 30 minutes while heating the pipe in the same manner as in Example 1, a gas containing this water vapor was added to this water vapor stream while adding nitrogen, which was confirmed to have an oxygen concentration of 0.01 ppm or less, at 0.4 L / min. The oxygen concentration in the flow was measured using a yellow phosphorus emission type oxygen analyzer and was found to be about 0.06 ppm. 0.1 L / min of the steam before nitrogen dilution was passed through a purification cylinder heated to 60 ° C., and the oxygen concentration in the gas obtained by adding 0.4 L / min of nitrogen having an oxygen concentration of 0.01 ppm or less to the outlet gas was measured. , And 0.01 ppm or less. Even after 100 minutes from the start of the purification, the oxygen concentration of the outlet gas is 0.01 p.
pm or less.

[0011] Example 4 Al (NO ₃₎ in water (nickel Preparation of Catalyst) 3L ₃ 9
454 g of H ₂ O were dissolved and cooled to 5-10 ° C. in an ice bath. While stirring vigorously, a solution of 200 g of NaOH dissolved in 1 L of water and cooled to 5 to 10 ° C. was added dropwise over 2 hours to obtain sodium aluminate. Next, N
101 g of i (NO ₃ ) ₂ .6H ₂ O was dissolved in 600 ml of water, 45 ml of concentrated nitric acid was added thereto, and the mixture was cooled to 5 to 10 ° C. and added to the sodium aluminate solution over 1 hour with vigorous stirring. Was. The resulting precipitate was filtered, and the obtained precipitate was stirred six times in 2 L of water for 15 minutes and washed to make the precipitate neutral. The obtained precipitate was subdivided, dried in an air bath at 105 ° C. for 16 hours, and then pulverized, and sieved to collect 12 to 24 mesh. This is 29.5 wt% nickel oxide (N
iO). (Reduction treatment of nickel) 63 ml of this was packed in the same purification cylinder as used in Example 1 (packing density: 0.77 g)
/ Ml) and hydrogen at normal pressure at a temperature of 350 ° C and a flow rate of 16
After performing a reduction treatment by flowing at 5 cc / min (LV = 1 cm / sec) for 16 hours, the mixture was cooled to room temperature. (Purification of steam) Subsequently, purification of steam was performed. 0.633 L / min (LV = 5 cm / sec) was added to a purification cylinder heated at 40 ° C. with 7.3 vol% steam (nitrogen base) containing about 0.14 ppm of oxygen used in Example 1.
As a result of measuring the oxygen concentration in the outlet gas flowing in c),
It was 0.01 ppm or less. 100 since the start of purification
Even after minutes, the oxygen concentration of the outlet gas was 0.01 ppm or less.

Comparative Example 48 g of activated carbon (coconut shell charcoal) crushed to 8 to 24 mesh was placed in the same purification cylinder as in Example 1 at 300 mm.
(Filling density: 0.57 g / ml), the mixture was heated in a helium stream at 270 to 290 ° C. for an hour, and then cooled to room temperature. About 0.14p same as that used in Example 1
7.3 vol% water vapor containing pm oxygen (nitrogen base)
0.633 L / min (L
(V = 5 cm / sec), and the oxygen concentration in the outlet gas was measured. The result was 0.14 ppm. In this state, the gas continued to flow for 2 hours, but no change in the oxygen concentration was observed.

[0013]

According to the present invention, oxygen in water vapor, which has been difficult to remove in the past, is reduced to 0.1 ppm or less, and more preferably to 0.1 ppm or less.
It can be removed to an extremely low concentration of not more than 01 ppm, and it has become possible to obtain ultra-high-purity steam.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-188407 (JP, A) JP-A-2-188408 (JP, A) JP-A-2-188409 (JP, A) JP-A-2-188 204304 (JP, A) JP-A-2-204305 (JP, A) JP-A-2-204306 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/14 B01J 21 / 00-38/74 C01B 5/00

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the crude steam is treated with metallic nickel or a reducing process.
A steam purification method comprising: contacting a purified nickel compound as a main component with a purification agent to remove oxygen contained in the crude steam. 2. The refining agent contains nickel of 5 to 95% by weight in terms of metal and has a specific surface area of 10 to 3 by a BET method.
The method for purifying steam according to claim 1, wherein the water purification rate is 00 m ² / g. 3. The contact temperature between steam and a purifying agent is 200 ° C.
The method for purifying steam according to claim 1, which is as follows.