JPH0812678A - Method for purifying organometallic compound - Google Patents

Abstract

PURPOSE:To industrially and readily obtain a high purity organometallic compound suitable as a raw material for compound semiconductor fields by bringing a heated liquid organometallic compound into contact with a cooling material and solidifying and depositing the compound on the surface of the cooling material. CONSTITUTION:A liquid organometallic compound (containing an oxygen- containing compound, etc., as impurity) such as trimethylaluminum, trimmethylgallium, trymethylindium, triisobutylaluminum, dimethylaluminum hydride, t-butylphosphine or t-butylarsine is brought into contact with a cooling material such as a cooling tube kept to a melting point or above of the compound under stirring to solidify and deposit the organometallic compound on the surface of the cooling material. Then, the deposited compound is separated from the residual organometallic compound kept in a liquid state to recover the solidified and deposited purified compound. Furthermore, the deposition rate is preferably controlled so that the thickness of the deposited compound becomes about 1-5mm.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for purifying an organometallic compound. More specifically, the present invention relates to a method for purifying an organometallic compound that is preferably used as a raw material in the field of compound semiconductors.

[0002]

2. Description of the Related Art Organometallic compounds are gas phase pyrolyzed (hereinafter referred to as M
It is used as a raw material for forming a compound semiconductor thin film by OCVD. These thin films are expected to be used in light emitting diodes, laser diodes, microwave devices, ultra high speed ICs, optical ICs, and the like. Alkyl aluminum has been studied for application as a wiring material for LSI.

Oxygen-containing compounds are present as impurities in organometallic compounds due to reaction with air or moisture mixed in during production or handling. When an organometallic compound containing such an oxygen-containing component is used as the above-mentioned MOCVD raw material, oxygen atoms are incorporated into the semiconductor thin film, and as a result, electrical and optical characteristics are significantly impaired and Problems such as that only a resistive film or a film having low luminous efficiency can be obtained, and even if a target thin film is obtained, the life of the device is short, etc. arise.

Therefore, many methods for removing oxygen, silicon and the like contained in these organometallic compounds have been introduced so far. For example, a method of distilling an organometallic compound has been adopted as a simple and effective means, but in the case of impurities having similar boiling points, it is extremely difficult to lower the ppm level and cannot be adopted. Therefore, various chemical purification methods have been proposed. For example, JP-A-2-672
No. 30 discloses a method of treating with a metal hydride corresponding to 0.1 to 50% by weight, and JP-A No. 3-112991 discloses treating with an aluminum halide for removing oxygen compounds in alkylaluminum. The method of doing is proposed.

However, it is of course necessary to newly add a reaction agent to the organometallic compound to be treated, and as a result, the additive and the organometallic compound must be separated after the treatment. , Many complicated treatments such as considering the purity of the additive to be used, and in some cases, a new side reaction is caused by the additive and a step of separating and refining the by-product and the organometallic compound must be provided. In addition, there is a drawback that a sufficient effect cannot be obtained.

[0006]

In view of such a situation, the present inventors have aimed to remove a compound containing oxygen from an organometallic compound, and substantially eliminate the use of additives and have a large purification effect. As a result of intensive studies to find a method that can easily obtain a high-purity organometallic compound industrially, surprisingly, after coagulating and precipitating a part of the organometallic compound, the remaining liquid phase It was found that all the above objects can be achieved by adopting an extremely simple means of removing a part, and completed the present invention.

[0007]

That is, according to the present invention, a liquid organometallic compound held at a melting point temperature or higher in a container is brought into contact with a coolant adjusted to a temperature lower than the melting point of the organometallic compound under stirring, An organometallic compound characterized by solidifying and precipitating an organometallic compound on the surface of the coolant, separating it from the remaining organometallic compound in a liquid state, and collecting the organometallic compound solidified and deposited on the surface of the coolant. In order to provide a purification method.

The present invention will be described in detail below. The organometallic compound targeted by the method of the present invention is a compound used for MOCVD, particularly in the field of semiconductors, and includes metal alkyls and hydrogens thereof, halogen derivatives and ethers thereof, amine complexes and the like. A substance having a melting point of −20 ° C. or higher is suitable from the viewpoint of being industrially easily implemented, but is not limited thereto.

Organometallic compounds to which the method of the present invention can be applied include trimethylaluminum, triisobutylaluminum, dimethylaluminum hydride, dimethylaluminum hydride trimethylamine, trimethylamine alane, trimethylgallium, dimethylgallium chloride, triisobutylgallium, trimethylamine. Galan, trimethylindium, ethyldimethylindium, tert-butylarsine, tert-butylphosphine and the like can be mentioned.

The purpose of these organometallic compounds can be usually achieved by directly applying them to the method of the present invention, but if necessary, those which have been subjected to a distillation treatment in advance may be used, and they are removed by each operation. Since the target of possible impurities is different, the treatment may be performed in combination with a known impurity removal method. Further, if necessary, it is possible to use a small amount of a solvent which is essentially inert to an organic metal such as hydrocarbon, but basically it is more effective and economical to carry out without a solvent. .

Hereinafter, the method of the present invention will be described in detail with reference to FIG. 1. FIG. 1 shows one embodiment of an organometallic compound refining apparatus for carrying out the method of the present invention, which limits the method of the present invention. is not. In FIG. 1, 1 is a container, 2 is an inert gas inlet, 3 is a vacuum pump connection port, 4 is an organometallic compound supply port, 5 is an organometallic compound extraction port, 6 is an organometallic compound, and 7 is cooling. A tube, 8 is a medium inlet, 9 is a medium outlet, 10 is a rotor, 11 is a thermostat, 12 is a magnetic stirrer, and 13 is a solidified and precipitated crystal of an organometallic compound. In order to remove the oxygen-containing compound, which is an impurity of the organometallic compound, the present device should be constructed so that the sealing property of the entire device is emphasized, and the sealing property of the connection part must be carefully considered.

In the refining operation, the container 1 is first evacuated by a vacuum pump (not shown) connected to the vacuum pump connection port 3 and then the high purity nitrogen is introduced from the inert gas introduction port 2. The system is replaced with nitrogen. This operation is repeated a plurality of times as necessary to completely replace nitrogen in the system.

Next, an organometallic compound for purification is introduced through a supply port 4 from an organometallic compound vessel (not shown) which is connected in advance to the vessel 1 after nitrogen substitution. The container 1 is heated and adjusted by the constant temperature bath 11 so that the temperature of the organometallic compound in the container 1 is slightly higher than the melting point (2 to 3 ° C.), and the organometallic compound supplied into the container 1 is heated. The organometallic compound 6 is slowly stirred by the rotor 10 and the magnetic stirrer 12 so that the temperature of the compound 6 becomes constant. At the center of the container 1, a cooling pipe 7 is arranged from the upper part of the container 1 so as to be immersed in the melted liquid organometallic compound 6 from the tip to the center. Cooling pipe 7
Has a double tube structure, and the medium introduced from the medium inlet 8 cools or heats the cooling pipe wall from the inside and is led out from the medium outlet 9. As the medium, a cooling medium is used when the organometallic compound is solidified on the surface of the cooling pipe 7, and a heating medium having a temperature higher than the melting point of the organometallic compound is used when the solidified organometallic compound is dissolved and recovered. When refining the organometallic compound, a cooling medium is introduced into the cooling pipe 7, and the cooling pipe 7 is gradually cooled. The temperature of the medium is first set to be approximately the same as the melting point of the organometallic compound, and then gradually lowered, whereby the medium temperature is set while observing the growth state of the crystal 13 of the organometallic compound which solidifies and precipitates on the surface of the cooling pipe 7. It may be adjusted to control the deposition rate.

When the temperature of the medium is rapidly lowered, the precipitation rate of the crystal 13 is high, but it is not preferable because solidification and cracks occur on the precipitation surface, and the liquid phase organometallic compound containing impurities is easily included therein. The appropriate growth (coagulation, precipitation) rate is not unique depending on the type of the target organometallic compound, the structure of the container used for purification, etc., but usually the precipitation thickness is preferably about 1 mm to about 5 mm per hour. , These can be easily determined by preliminary experiments. However, the crystals to be precipitated first serve as the nuclei for the subsequent precipitation, so it is better to slowly precipitate from a state that is close to thermal equilibrium.

When solidifying and depositing the organometallic compound on the cooling pipe 7, it is preferable to continue stirring in order to obtain a higher purity organometallic compound. The stirring strength is not particularly limited as long as the entire liquid phase portion flows gently and the temperature distribution of the entire liquid phase portion becomes relatively uniform. Without stirring, high-purity crystals may not be obtained, probably due to insufficient diffusion of impurities from the crystal surface of the cooling pipe 7 into the liquid phase. Amorphous crystals are easily formed. On the contrary, if the stirring is too strong, problems such as separation of the precipitated crystals are likely to occur.

When the crystal 13 of the organometallic compound deposited on the cooling pipe 7 has grown to a desired amount, the stirring operation is stopped and immediately the molten organometallic compound in the container 1 is not shown in the figure through the supply port 3. Transfer to an organometallic compound container. After discharging the residual molten organometallic from the container 1 in this manner, a medium having a melting point of the organometallic compound or higher is conducted to the cooling pipe 7 to remove the crystals of the organometallic compound deposited on the surface of the cooling pipe 7. After melting, it is transferred to another organometallic compound container (not shown) through the extraction port 5 and recovered as a purified organometallic compound.

Although the amount of the organometallic compound crystal to be deposited by this method varies depending on the initial impurity concentration, it can be grown up to just before the crystal comes into contact with the vessel wall. The ratio varies depending on the shape of the purification container, but this operation 1
It is 40 to 70% by weight of the organometallic compound initially supplied per time, and in this case, the precipitated crystal is the target high-purity organometallic compound.

The method of the present invention has been described above with the refining apparatus having the structure shown in FIG. 1. However, the apparatus structure is not limited by this. In addition to the method of circulating an organometallic compound in a solution state and a cooling pipe structure arranged in the center of the container as a cooling material as shown in FIG. 1, crystals are deposited toward the inside of the container with the wall surface of the container as a cooling surface. It is also possible to adopt a cooling material such as a cooling type.

In designing such a refining apparatus, considering the efficiency of the apparatus and the time efficiency, the shape of the apparatus is preferably such that the thickness of the crystal to be precipitated is small and the crystallization rate is high. In the case of the refining device of the type shown, it is preferable that the surface area per volume of the cooling pipe is relatively large and the height-to-diameter ratio (height / diameter) of the container is about 2 to 3 times.

The material of the refining device is not particularly limited, but when a metal material such as stainless steel is used, a temperature sensor is attached to a key portion to control the state of the entire system, or the state of internal crystals. For example, a peep window can be installed everywhere to observe, or an ultrasonic transmitter is attached to the outer wall of the refiner to monitor the distance between the crystal wall and the crystal surface in order to grasp the degree of crystal growth. Can be easily implemented even on an industrial scale by appropriately adopting.

[0021]

According to the method of the invention described in detail above, the oxygen-containing compound can be removed only by a very simple method of solidifying and precipitating a part of the organometallic compound and then removing the remaining liquid phase part. As well as organic silicon and hydrocarbons,
Impurities other than oxygen-containing compounds can be removed and purified at the same time, and when the treatment operation is repeatedly carried out, a high-purity organometallic compound having a purity of substantially 100% can be obtained. The utility value of is enormous.

[0022]

The present invention will be described in more detail with reference to the following examples. The concentration of impurities shown in the examples was measured by the following method. Oxygen-containing compound concentration: The organometallic compound was diluted with hydrocarbon and then hydrolyzed, and the alcohol extracted in the aqueous phase was quantified by gas chromatography and expressed as an alkoxy content. Organosilicon: Organosilicon extracted in a hydrocarbon solvent was quantified by the inductively coupled plasma emission method, and the organosilicon was expressed as the concentration of silicon atoms.

Example 1 A Pyrex container having a capacity of 500 ml shown in FIG. 1 was replaced with vacuum nitrogen, 350 ml of trimethylaluminum was charged, and the temperature of the constant temperature bath was maintained at 17 ° C. while stirring. After about 30 minutes, a temperature of 15 ° C. was passed through the cooling pipe to gradually lower the temperature. When the temperature at the inlet of the cooling medium was 10 ° C., crystals began to precipitate on the surface of the cooling pipe. Then, the temperature of the cooling medium was further slowly lowered, and when it reached 1 ° C. after 6 hours, a trimethylaluminum crystal having a thickness of about 20 mm was deposited. Then, stirring was stopped, liquid trimethylaluminum that did not precipitate was extracted, and then the crystals were melted and transferred to a stainless steel container. The volume of this trimethylaluminum was 160 ml. This corresponds to about 46% of the charged trimethylaluminum before purification. The oxygen-containing compound (referred to as -OMe in the table) and organic silicon of this product were analyzed, and the results of comparison before and after purification are shown in Table 1.

[0024]

[Table 1]

Example 2 Purification was repeated twice in the same manner as in Example 1. The trimethylaluminum obtained by final crystallization was 28% by weight of the trimethylaluminum initially fed. The oxygen-containing compound of this product was analyzed and compared before and after purification. Table 2 shows the results.

[0026]

[Table 2]

[Brief description of drawings]

FIG. 1 is a schematic view of an organometallic compound purification apparatus used in the method of the present invention.

[Explanation of symbols]

1 is a container, 2 is an inert gas introduction port, 3 is a vacuum pump connection port, 4 is an organometallic compound supply port, 5 is an organometallic compound extraction port, 6 is an organometallic compound, 7 is a cooling pipe, 8 is a medium inlet , 9 is a medium outlet, 10 is a rotor, 11 is a constant temperature bath, 1
2 is a magnetic stirrer, and 13 is a crystal of an organometallic compound.

Claims (3)

[Claims] 1. A liquid organometallic compound maintained at a melting point temperature or higher in a container is brought into contact with a cooling material adjusted to a temperature lower than the melting point of the organometallic compound under stirring, and the organometallic compound is applied to the surface of the cooling material. A method for purifying an organometallic compound, comprising: solidifying and precipitating the metal, separating it from the remaining organometallic compound in a liquid state, and collecting the organometallic compound solidified and deposited on the surface of the coolant. 2. The organometallic compound according to claim 1, wherein the organometallic compound is trimethylaluminum, trimethylgallium, trimethylindium, triisobutylaluminum, dimethylaluminum hydride, tert-butylphosphine and tert-butylarsine. Purification method. 3. The method for purifying an organometallic compound according to claim 1, wherein an organometallic compound containing an oxygen-containing compound is used as an impurity.