JPH0753571B2 - Disilane purification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying disilane by removing phosphine (PH ₃ ) contained in a small amount in disilane (Si ₂ H ₆ ).

BACKGROUND ART In recent years, with the development of the electronics industry, demand for semiconductor silicon such as polycrystalline silicon or amorphous silicon has rapidly increased.

Si ₂ H ₆ has recently been particularly spotlighted as a new raw material for the production of silicon for semiconductors together with monosilane (SiH ₄ ), and it is expected that demand will increase in the future.

As a method for producing Si ₂ H ₆ , several methods are known as exemplified below, but whichever method is adopted, the disilane gas normally synthesized contains a trace amount of PH _3. . In particular, in silicon hydride produced by the method according to PH ₃ is contained at a concentration of around 100 ppm. The effect of PH ₃ as an impurity in silicon hydride used as a semiconductor gas is large, and its content is usually 10 ^-9 or less (ppb or less).
Need to

Prior art There is a limit to the distillation separation of PH ₃ (bp-88 ° C) in Si ₂ H ₆ (bp-15 ° C), and it is practical to reduce the PH ₃ content to 10 ^-9 or less by distillation. It is impossible.

SiH ₄ is known as a number of conventional methods for removing PH ₃ in silicon hydride using an adsorbent.
Little is reported about ₂ H ₆ .

That is, with regard to SiH ₄ , for example, the exchangeable cation in zeolite having a uniform pore size that hardly adsorbs SiH ₄ is exchanged with a divalent cation (Japanese Patent Publication No. 48-41437, 4).
8-41439), sodium ion in synthetic zeolite 4A exchanged with divalent cation or silver ion (JP-A-48-75475, JP-A-59-30711), activated carbon and synthetic zeolite-4A in combination What does (Japanese Patent Laid-Open No. 58-69715, 58
-172220), a method using a metal material for hydrogen storage or a metal hydride (JP-A-58-120511), and the like.

On the other hand, as for Si ₂ H ₆ , Japanese Patent Application Laid-Open No. 58-172 filed by the present applicant.
In 220, a method of treating with activated carbon and synthetic zeolite has been proposed, but this method only removes by-product silicon halide compound and low-fluoride-point aliphatic hydrocarbon. When the mixture gas of Si ₂ H ₆ and PH ₃ is to be separated by an adsorption method, it should be a substance to be adsorbed between the two.
PH ₃ has a lower boiling point than Si ₂ H ₆ , so Si ₂ H
Removal of PH ₃ in ₆ is expected to be considerably more difficult than in the case of SiH ₄ . That SiH _4, Si ₂ boiling point of H _6, PH _3, respectively -112 ° C., -14.5 ° C., a -87 ° C., adsorption of Si ₂ H ₄ has priority, in Si ₂ H ₆ by principle adsorbent PH ₃ of is adsorbed and removed for PH ₃ is higher boiling components is relatively easy, in the case of PH ₃ in Si ₂ H _6, the temperature relationship is reversed, than the PH ₃ Si ₂ H ₆ adsorption has priority. Therefore, selective adsorption of PH ₃ was considered to be difficult. Furthermore, since the molecular diameters of these molecules are almost the same, it has been difficult to adsorb and separate PH ₃ .

Contrary to these conventional expectations, the present inventors have found that PH _{3 in} Si ₂ H ₆
As a result of earnest studies on the development of a new adsorbent capable of selectively removing carbon dioxide, the present invention has been achieved.

That is, according to the present invention, although Si ₂ H ₆ has almost no polarity,
Paying attention to the fact that H ₃ has a very slight polarity (basicity), and using a strongly polar (acidic) adsorbent, PH ₃
It is intended to selectively adsorb PH ₃ in Si ₂ H ₆ by increasing the adsorption energy of.

SUMMARY OF THE INVENTION That is, the present invention is characterized in that disilane containing phosphine is treated with 4A type synthetic zeolite in which a part or all of the exchangeable cations are exchanged with divalent cations. Method of purification.

Detailed Disclosure of the Invention Hereinafter, the present invention will be described in detail.

The adsorbent used in the present invention is one in which a part or all of the exchangeable cations of the 4A type synthetic zeolite are exchanged with divalent cations. The 4A type synthetic zeolite is
"Lynde Molecular Sieves" from Linde, USA
It is marketed under the trademark of
₁₂ [(AlO ₂ ) ₁₂ (SiO ₂ ) ₁₂ ] · 27H ₂ O 4A type zeolite represented by ordinary commercial products can be used. The effective pore size is about 4Å. The divalent cation referred to in the present invention is an element ion of Group (II) of the periodic table,
For example, magnesium, calcium, strontium, zinc, cadmium; element ion of Group (VIII) of the periodic table,
For example, iron, cobalt, nickel; and other group elemental ions such as manganese, lead, tin, and the like. Among these, manganese, calcium, zinc and lead ions are particularly preferable.

There is no particular limitation on the method for exchanging cations in the present invention. For example, 4A type zeolite is simply immersed in an aqueous solution of a water-soluble salt such as a metal salt of a divalent cation or a nitrate mentioned above. This can be done by a general method. The exchange rate is 20 to 100%, preferably 40 to 90%. In addition, activation prior to use is usually carried out in the range of 200 to 500 ° C. under reduced pressure and in an inert gas.

The purification treatment of Si ₂ H _{6 with} an adsorbent in the present invention can be carried out under reduced pressure or under pressure, and Si ₂ H ₆ may be in a gas phase or a liquid phase, but it is preferable to carry out in a gas phase. . The temperature of the adsorption treatment is not particularly limited, but it is preferably -50 to 50 ° C. At temperatures below this range Si ₂ H ₆
By condensation of (bp-14.5 ℃), not preferred adsorption rate of PH ₃ is decreased, undesirably adsorption capacity of PH ₃ than the range that it high temperature decreases. Of course, it is also possible to use it together with other adsorbents. Further, Si ₂ H ₆ may contain a gas other than PH ₃ (for example, hydrogen, nitrogen, rare gas, methane, silane, etc.).

Hereinafter, the present invention will be described with reference to examples.

<Example 1> molecular sieves -4A the (Nishio Kogyo Co., 30 to 60 mesh) 50g, Mn (NO ₃₎ solution 2 obtained by dissolving ₂ 191 g
It was immersed in it for 2 days. Then, filtration and washing were performed, and the obtained zeolite was calcined in air at 400 ° C. for 1 hour. According to the results of chemical analysis, the exchange rate with manganese ion is 70%.
Met.

An adsorption tube having an inner diameter of 3 mm and a length of 42 mm was filled with 0.25 g of the above zeolite. After treatment in helium at 400 ° C for 1 hour and further under reduced pressure (0.2 mmHg) for 2 hours, the temperature of the adsorption tube was-
5 ℃, mixed gas of Si ₂ H ₆ and H ₂ containing 120 ppm of PH ₃ (Si ₂ H
₆ 35 vol%, H ₂ 65 vol%) was passed at a flow rate of 115 ml / min to purify Si ₂ H ₆ .

The results are shown in Fig. 1. From FIG. 1, it was found that the adsorption capacity of the adsorbent (the point where the PH ₃ concentration at the adsorption tube outlet was 10 ppb, the same applies hereinafter) was about 5 mg PH ₃ / g adsorbent. The PH ₃ concentration in the outlet gas was analyzed by gas chromatography using FPD as a detector.

<Examples 2 to 5> 50 g of the molecular sieve-4A used in Example 1 was immersed for 2 days in a dilute hydrochloric acid solution 2 in which ZnCl ₂ 93 g, MgCl ₂ 65 g, CaCl ₂ 28 g and CoCl ₂ 40 g were dissolved. . After that, filtration and washing are performed, and each obtained zeolite is placed in air.
It was baked at 400 ° C. for 1 hour. According to the results of chemical analysis, the exchange rates of the respective ions were 71%, 52%, 46% and 43%, respectively.

An experiment was conducted in the same manner as in Example 1 using these zeolites.

The adsorption capacities in these cases were as shown in Table 1, respectively.

<Examples 6 and 7> In Example 2, the amount of ZnCl ₂ used was 46 g or 104 g, and cation exchange rates of 59% and 87% were obtained.

An experiment was conducted in the same manner as in Example 2 using this zeolite as an adsorbent.

The results are shown in Table 1.

<Examples 8 and 9> An experiment was performed in the same manner as in Example 1 except that the adsorption temperature was changed to -10 ° C and 20 ° C.

The results are shown in Table 1.

<Example 10> An adsorption tube having an inner diameter of 6 mm and a length of 100 mm was filled with 1.8 g of the same zinc-exchanged zeolite as used in Example 2. The temperature of the adsorption tube is 0 ℃, the pressure in the adsorption tube is 5.3Kg / cm ² abs, PH ₃
Si ₂ H ₆ containing 120 ppm of was purified in a liquid phase. The supply rate of Si ₂ H ₆ was 0.2 g / min.

The adsorption capacity in this case was as shown in Table 1.

Example 11 By reacting magnesium silicide (Mg ₂ Si) with a hydrochloric acid aqueous solution having a concentration of 20 wt%, PH ₃ 90 ppm, SiH ₄ 77%, Si ₂ H
₆ 23% mixed gas was obtained. This mixed gas is -20 to 50
Distilled using a 50-stage distillation column under the conditions of ℃ and 7 atm, PH ₃ 1
Si ₂ H ₆ containing 1 ppm was obtained.

An adsorption tube having an inner diameter of 8 mm and a length of 1000 mm was filled with 32 g of the same zinc-exchanged molecular sieve-4A as that used in Example 2. After the temperature of the adsorption tube was set to -5 ° C, the synthesized Si ₂ H ₆ gas was flown at a flow rate of 30 ml / min x velocity (linear velocity 1.0 cm / se
c, contact time 1.67 min), and purified Si ₂ H ₆ was collected in a cylinder cooled at dry ice temperature. After 495 hours from the beginning of distribution, the distribution is stopped and PH ₃ in the collected gas is
When analyzed by gas chromatography using D as a detector, PH ₃ was not detected (detection limit of about 10 ppb, PH ₃ adsorption amount at this point was 6.5 mg PH ₃ / g adsorbent). Furthermore, an epitaxial film was formed using this purified SiH ₄ , and its specific resistance was measured and found to be 1105 Ωcm.

<Comparative Example 1> An experiment was conducted in the same manner as in Example 1 except that the molecular sieve-4A that did not undergo ion exchange was used as the adsorbent.

The adsorption capacity in this case was extremely small as shown in Table 1, and almost no adsorption of PH ₃ was observed.

Effect of the Invention According to the adsorbent in the method of the present invention, PH ₃ can be selectively adsorbed and removed without being inhibited by Si ₂ H ₆ for adsorption. The method of adsorption and removal of PH ₃ in Si ₂ H ₆ , which is the subject of the present invention, was first proposed by the present invention.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the PH ₃ concentration in the adsorption tube outlet gas and the PH ₃ adsorption amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page Examiner Koji Amamiya (56) References JP-A-61-53106 (JP, A)

Claims (2)

[Claims] 1. A method for purifying disilane, which comprises treating a disilane containing phosphine with 4A type synthetic zeolite in which a part or all of the exchangeable cations are exchanged with divalent cations. 2. The method according to claim 1, wherein the divalent cation is manganese ion or zinc ion.