JPH0329003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for purifying silicon hydride by removing trace amounts of phosphine (PH ₃ ) contained in silicon hydride.

BACKGROUND ART In recent years, with the development of the electronics industry, the demand for silicon for semiconductors such as polycrystalline silicon or amorphous silicon has increased rapidly.
Silicon hydrides such as SiH ₄ and Si ₂ H ₆ have recently become increasingly important as raw materials for producing silicon for semiconductors, and demand is expected to increase in the future.

There are several known methods for producing these silicon hydrides, such as those exemplified below, but regardless of which method is used, trace amounts of Mg ₂ Si + 4HClaq are usually present in the synthesized silicon hydride gas. .→2MgCl ₂ +n/1 Si _o H _2o+2 +(1
−1/n) H ₂ Mg ₂ Si+4NH ₄ Br−33℃ ――――――――――→ in ig.NH ₃ 2MgBr ₂ +4NH ₃ +1/nSi _o H _2o+2 +(1−1/n )H ₂ SiCl ₄ +LiAlH ₄ ――――――――→ in etharLiCl+AlCl ₃ +SiH ₄ Si+SiCl ₄ +2H ₂ →SiHCl ₃ +SiH ₃ Cl 2SiHCl ₃ →SiCl ₄ +SiH ₂ Cl ₂ 2SiH ₂ Cl ₂ →SiHCl ₃ +SiH ₃ Cl ₂ 2SiH ₃ Cl→SiH ₄ +SiH ₄ Cl ₂ PH ₃ is included. The content of PH ₃ varies depending on the production method, but for example, silicon hydride produced by the method described above contains PH ₃ at a concentration of about 100 ppm. The influence of PH ₃ as an impurity in silicon hydride used as a semiconductor gas is large, and its content usually needs to be kept at 10 ^-9 or less (ppb or less).

Prior Art Silicon hydride, such as _SiH4 , contains trace amounts of
As a method for removing PH ₃ , it is common to use an adsorbent, and for example, the following methods are known. That is, those that use synthetic zeolite A or synthetic zeolite Synthetic zeolites, in which ions are exchanged with divalent cations, especially zinc and lead (Special Publications No. 48-41437, 48-41439)
4A in which the sodium ions are exchanged with divalent cations or silver ions (Japanese Patent Laid-Open No. 1973-
75475, JP-A-59-30711), a combination of activated carbon and synthetic zeolite-4A (JP-A-58-30711)
69715, 58-172220), those using metal materials or metal hydrides for hydrogen storage (JP-A-58-
120511) have been reported. However, these adsorbents have various problems such as a small adsorption capacity, a large silane adsorption loss, and an inability to regenerate.

The present inventors investigated adsorbents that can remove phosphine (PH ₃ ) from these silicon hydrides, and found that type 5A zeolite has excellent adsorption ability for PH ₃ in a certain temperature range. The present invention was completed based on the discovery that this shows the following.

That is, the present invention is a method for purifying silicon hydride, which is characterized by treating silicon hydride containing phosphine with a type 5A zeolite adsorbent maintained at -80°C to 0°C.

DETAILED DISCLOSURE OF THE INVENTION The adsorbent used in the present invention is a type 5A synthetic or natural zeolite with the composition formula Na ₁₂
At least 10% of the sodium ions in type 4A zeolite expressed as [(AlO ₂ ) ₁₂ (SiO ₂ ) ₁₂ ]・27H ₂ O
or more, preferably 20% or more, more preferably 30%
The above is exchanged with calcium ions.
These can be easily manufactured according to known methods, and those with 30% or more replacement are commercially available, for example, from Linde in the United States under the trade name "Linde Molecular Sheaves", and are easily available. The effective pore size is approximately 5 Å.

The adsorption treatment can be carried out under reduced pressure or increased pressure, but is preferably at normal pressure or higher. The silicon hydride may be in either a gas phase or a liquid phase, but it is usually preferable to use the gas phase.

The silicon hydride targeted by the present invention includes monosilane, disilane, trisilane, etc., but monosilane is most preferred.

The adsorption treatment temperature in the present invention is -80℃ to 0℃
It is particularly preferably between -80 and -20°C. At temperatures below this range, silicon hydride, especially
Adsorption of SiH ₄ becomes noticeable, which is undesirable, and at higher temperatures than this range, the adsorption capacity of PH ₃ decreases dramatically, which is undesirable.

The content of PH ₃ in silicon hydride is not particularly limited, but is usually 1% or less, particularly 0.1% or less.
In addition, silicon hydride contains gases other than PH ₃ (e.g.
Hydrogen, nitrogen, rare gas, methane, disilane, etc.) may be included. It is also possible to use adsorbents other than 5A type zeolite in combination.

Furthermore, as described later, the adsorbent in the present invention is
It is characterized in that it has a larger adsorption capacity than conventionally known adsorbents and can be regenerated. Incidentally, the fact that type 5A zeolite can be reused by being regenerated under the following conditions was revealed for the first time by the present invention. Being able to regenerate the adsorbent not only reduces the amount of adsorbent used, but also eliminates the need to replace the adsorbent with a purification column, which has enormous benefits in the industrialization process. Type 5A zeolite is regenerated in an inert gas atmosphere or under reduced pressure.
The treatment is carried out at a temperature in the range of 500°C to 500°C, preferably 100 to 300°C. If the temperature is below this temperature, a considerable amount of adsorbed PH ₃ still remains, which is undesirable; if the temperature exceeds this temperature range, PH ₃ will be removed due to sintering of the zeolite.
This is not preferable because the effective adsorption sites of

Type 5A zeolite is also unique in that it can be regenerated at extremely low temperatures, and even when regenerated at a lower temperature range of 100 to 200°C, it still exhibits more than 80% of its original adsorption capacity. Type 4A zeolite exchanged with cations other than calcium ions, such as magnesium ions, strontium ions, zinc ions, lead ions, and manganese ions, has a small adsorption capacity, requires high temperatures for regeneration, and has a poor recovery rate.

Hereinafter, the present invention will be explained with reference to Examples.

Example 1 An adsorption tube with an inner diameter of 3 mm and a length of 42 mm was filled with 0.25 g of Molecular Sieves-5A (manufactured by Nishio Kogyo Co., Ltd., exchange rate 75%, 30 to 60 mesh). After treatment in helium at 400℃ for 1 hour and under reduced pressure (0.2mmHg) for 2 hours, the temperature of the adsorption tube was set to -20℃, and the PH ₃ was
SiH ₄ gas containing 279 ppm was passed at a flow rate of 36 ml/min (linear velocity 8.5 cm/sec, contact time 0.49 sec). The _PH3 concentration in the outlet gas from the adsorption tube is sequentially
It was analyzed by gas chromatography using FPD as a detector. Note that analysis of low concentration PH ₃ was performed using the concentration analysis method proposed by the present inventors.

The results are shown in Figure 1. From FIG. 1, it was found that the adsorption capacity of the adsorbent (the point at which the PH ₃ concentration at the outlet of the adsorption tube is 10 ppb, the same applies hereinafter) was approximately 6 mg PH ₃ /g adsorbent.

Examples 2 and 3 The same procedure as in Example 1 was carried out except that the temperature of the adsorption tube was set to -50°C or -78°C. The adsorption capacity in this case is approximately 19
mg·PH ₃ /g adsorbent, and 26 mg·PH ₃ /g adsorbent.

Example 4 In Example 2, the molecular sieves-5A after the adsorption test was heat-treated at 400° C. under reduced pressure (0.1 mmHg) for 2 hours. Thereafter, the regenerated adsorbent was set at -50°C and an experiment was conducted in the same manner as in Example 1.

In this case, the adsorption capacity is approximately 18mg・PH ₃ /g
The adsorbent had almost the same value as Example 2.

The same regeneration operation was repeated and the adsorption capacity was determined to be 17 mg.PH ₃ /g adsorbent. The same operation was repeated three more times, but it was found that there was no substantial change in the adsorption capacity and that the product could be recycled many times.

Example 5 Magnesium silicide (Mg ₂ Si) at a concentration of 20 wt%
By reacting with an aqueous solution of hydrochloric acid, the PH
_{3. SiH4} gas containing 75 ppm was obtained.

The same molecular sieves used in Example 1 for an adsorption tube with an inner diameter of 8 mm and a length of 100 mm - 5A 32 g
was filled with. After setting the temperature of the adsorption tube to -50℃, the pressure in the system was set to 5Kg/ ^cm2・abs, and the SiH ₄ gas synthesized above was pumped at a flow rate of 30Nml/min (linear velocity).
The purified SiH ₄ was collected in a cylinder cooled at the temperature of liquid nitrogen. 593 hours after the start of the flow, the flow was stopped and the amount of _PH3 in the collected gas was analyzed by gas chromatography using an FPD as a detector.
₃ was not detected (detection limit was about 0.1 ppb, the amount of PH ₃ adsorbed at this point was 3.8 mg·PH ₃ /g adsorbent).
Furthermore, an epitaxial film was prepared using this purified SiH ₄ and its specific resistance was measured and found to be 1024 Ωcm.

Comparative Example 1 According to the example of Japanese Patent Publication No. 48-41437, 50 g of Molecular Sieve 3A (manufactured by Nishio Kogyo Co., Ltd., 30 to 60 mesh) was immersed for 2 days in a dilute hydrochloric acid aqueous solution 2 in which 10 g of ZnCl ₂ was dissolved. This was followed by filtration and washing to obtain a molecular sieve with a cation exchange rate of 44%. An experiment was carried out in the same manner as in Example 2, except that the above zinc-exchanged molecular sieve was used instead of the molecular sieve 5A.

In this case, the adsorption capacity is approximately 12mg・PH ₃ /g
It was an adsorbent.

Next, after completing this adsorption test, regeneration treatment was carried out in the same manner as in Example 4, and then an adsorption experiment was conducted at -50°C.

In this case, the adsorption capacity is approximately 3 mg・PH ₃ /g
It was found that the adsorption capacity of the adsorbent was drastically reduced by regeneration. Furthermore, when we regenerated it again using the same procedure and conducted an adsorption experiment, we found that the pH _{was 3} .
was hardly adsorbed.

As described above, this adsorbent is virtually impossible to reproduce or reuse.

[Brief explanation of drawings]

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

Claims (1)

[Claims] 1. Silicon hydride containing phosphine is heated to -80°C.
A method for purifying silicon hydride, characterized by treating it with a type 5A zeolite adsorbent maintained at a temperature of 0 to 0°C. 2. The 5A type zeolite used for adsorption treatment is heated to
The method according to claim 1, wherein the material is recycled at a temperature range of 500°C and reused.