JP3221237B2 - Purification method of organometallic compounds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 suitably used as a raw material in the field of compound semiconductor.

[0002]

2. Description of the Related Art Organometallic compounds are thermally decomposed in the gas phase (hereinafter referred to as M
OCVD). These thin films are expected to be used for light-emitting diodes, laser diodes, microwave devices, ultra-high-speed ICs, optical ICs, and the like. In addition, research on application of alkylaluminum as a wiring material for LSI has been conducted.

[0003] 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 organic metal compound containing such an oxygen-containing component is used as the MOCVD raw material, oxygen atoms are incorporated into the semiconductor thin film, and as a result, electrical and optical characteristics are significantly impaired, and Even if only a resistive film or a film with low luminous efficiency can be obtained, or even if a target thin film is obtained, problems such as a short life of the element occur.

Therefore, a number of methods for removing oxygen, silicon and the like contained in these organometallic compounds have been introduced. For example, a method of distilling an organometallic compound has been adopted as a simple and effective means. However, in the case of impurities having similar boiling points, it is extremely difficult to lower the impurity level to the ppm level and cannot be adopted. For this reason, 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 Japanese Patent Application Laid-Open No. Hei 3-112991 discloses a method of removing an oxygen compound in an alkyl aluminum by treating with an aluminum halide. A way to do that has been proposed.

However, all of these require the addition of a new reactant to the organometallic compound to be treated, and consequently the additive and the organometallic compound must be separated after the treatment. Many complicated processes, such as considering the purity of the additive used, and in some cases, generating a new side reaction depending on the additive and providing a step of separating and purifying the by-product and the organometallic compound. In addition, there is a disadvantage that a sufficient effect cannot be obtained.

[0006]

In view of such circumstances, an object of the present invention is to remove a compound containing oxygen from an organometallic compound. In order to find a method that can easily obtain a high-purity organometallic compound on an industrial scale, as a result of intensive studies, surprisingly, a part of the organometallic compound was coagulated and precipitated, and the remaining liquid phase It has been found that all of the above objects can be achieved by employing a very simple means of removing the part, and the present invention has been completed.

[0007]

That is, according to the present invention, a liquid organometallic compound containing an oxygen-containing compound held at a temperature not lower than the melting point temperature in a container is adjusted to a temperature lower than the melting point of the organometallic compound while stirring. After contacting with the cooled coolant and solidifying and precipitating the organometallic compound on the surface of the coolant, the organometallic compound is separated from the remaining organometallic compound in a liquid state, and the organometallic compound solidified and precipitated on the coolant surface is recovered. It is another object of the present invention to provide a method for purifying an organometallic compound containing an oxygen-containing compound .

Hereinafter, the present invention will be described in detail. 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 their hydrogens, halogen derivatives and their ethers and amine complexes. A material having a melting point of −20 ° C. or more is suitable from the viewpoint of industrially easy implementation, but is not limited thereto.

The 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, trimethyl indium, ethyl dimethyl indium, tertiary butyl arsine, tertiary butyl phosphine and the like can be mentioned.

The purpose of these organometallic compounds can usually be achieved by directly applying them to the process of the present invention. However, if necessary, those which have been subjected to a distillation treatment may be used. The treatment may be performed in combination with a known impurity removal method because the target of impurities that can be performed is different. It is also possible to use a small amount of a solvent essentially inert to organic metals such as hydrocarbons if necessary, but it is basically more effective and economical to carry out the reaction without a solvent. .

Hereinafter, the method of the present invention will be described in more detail with reference to FIG. 1. FIG. 1 shows an embodiment of an apparatus for purifying an organometallic compound 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 oxygen-containing compounds, which are impurities of the organometallic compound, the present device is configured to emphasize the hermeticity of the entire device, and sufficient consideration must be given to the sealability of the connection portion.

At the time of the purification operation, the vessel 1 is first evacuated to a vacuum pump (not shown) connected to the vacuum pump connection port 3, and then 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 purge the system with nitrogen.

Next, an organometallic compound to be purified is introduced through a supply port 4 from an organometallic compound container (not shown) previously connected to the container 1 after the nitrogen replacement. The container 1 is heated and adjusted by a thermostat 11 so that the temperature of the organometallic compound in the container 1 is slightly higher than the melting point (2 to 3 ° C.). 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 disposed from the top of the container 1 so as to be immersed in the molten liquid organometallic compound 6 from the tip to the center. Cooling pipe 7
Has a double pipe structure, in which the medium introduced from the medium inlet 8 cools or heats the cooling pipe wall from the inside, and is drawn out from the medium outlet 9. As the medium, a cooling medium is used when the organometallic compound is coagulated 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 coagulated and precipitated organometallic compound is dissolved and recovered. When purifying the organometallic compound, a cooling medium is introduced into the cooling pipe 7 and the cooling pipe 7 is gradually cooled. At first, the temperature of the medium is set to be approximately the same as the melting point of the organometallic compound, and then gradually decreased. By observing the growth state of the organometallic compound crystal 13 which solidifies and precipitates on the surface of the cooling pipe 7, the medium temperature is reduced. It may be adjusted to control the deposition rate.

When the temperature of the medium is rapidly lowered, the deposition rate of the crystals 13 is high, but it is not preferable because solidification and cracks occur on the deposition surface, and the liquid organic metal compound containing impurities is easily contained therein. The appropriate growth (solidification, precipitation) rate is not unique depending on the type of the target organometallic compound, the container structure used for purification, etc., but usually, the thickness of the precipitation is preferably about 1 mm to about 5 mm per hour. Can be easily determined by preliminary experiments. However, since the crystal to be deposited first becomes a nucleus for subsequent deposition, the purification effect is better if the crystal is slowly deposited from a state close to thermal equilibrium.

During the solidification and precipitation of the organometallic compound in the cooling pipe 7, it is preferable to keep stirring to obtain a higher-purity organometallic compound. The stirring intensity is not particularly limited, and may be any degree as long as the entire liquid phase portion flows slowly and the temperature distribution of the entire liquid phase portion becomes relatively uniform. Without stirring, high-purity crystals may not be obtained, possibly due to insufficient diffusion of impurities from the crystal surface of the cooling tube 7 into the liquid phase, and this may be due to uneven temperature. Amorphous crystals are easily formed. Conversely, if the stirring is too strong, problems such as separation of precipitated crystals are likely to occur.

When the organic metal compound crystals 13 deposited on the cooling pipe 7 have grown to a desired amount, the stirring operation is stopped, and the molten organic metal compound in the container 1 is not immediately shown through the supply port 3. Transfer to an organometallic compound container. After discharging the residual molten organic metal from the container 1 in this manner, a medium having a melting point of the organometallic compound or higher is passed through the cooling pipe 7 so that the crystal of the organometallic compound precipitated on the surface of the cooling pipe 7 is removed. After being melted, it is transferred to another organometallic compound container (not shown) through the extraction port 5 and collected as a purified organometallic compound.

Although the amount of the organometallic compound crystal deposited by the present 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 vessel.
The amount is from 40% to 70% by weight of the initially supplied organometallic compound, and in this case, the precipitated crystal is the desired high-purity organometallic compound.

Although the method of the present invention has been described with reference to the purification apparatus having the structure shown in FIG. 1, the structure of the apparatus is not limited by this. In addition to the method of circulating the organometallic compound in a solution state and the cooling pipe structure provided in the center of the vessel as a coolant as shown in FIG. 1, a crystal is deposited toward the inside of the vessel using the vessel wall as a cooling surface. It is also possible to employ a cooling material of such a type as to be made.

In designing such a refining device, in consideration of the efficiency of the device and the time efficiency, it is preferable that the shape of the device is such that the thickness of the crystal to be precipitated is small and the crystallization ratio is high. In the case of a purifying apparatus 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 vessel is about two to three times.

The material of the refining device is not particularly limited. For example, when a metal material such as stainless steel is used, a temperature sensor may be attached to a key point to control the state of the entire system, or the state of the internal crystal. Such as installing a viewing window everywhere so that the observer can observe it, or installing an ultrasonic transmitter on 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 carried out even on an industrial scale by appropriately employing.

[0021]

According to the invention method described in detail above, the oxygen-containing compound is removed only by a very simple method of solidifying and depositing a part of the organometallic compound and then removing the remaining liquid phase. 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 performed, a high-purity organometallic compound having a purity of substantially 100% can be obtained. The utility value of is very large.

[0022]

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

Example 1 After 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 thermostat was maintained at 17 ° C. while stirring. After about 30 minutes, the temperature of the cooling pipe was gradually lowered by passing a refrigerant of 15 ° C. through the cooling pipe. When the inlet temperature of the refrigerant was 10 ° C., crystals began to precipitate on the surface of the cooling pipe. Thereafter, the temperature of the refrigerant was lowered more slowly, and when the temperature reached 1 ° C. after 6 hours, trimethylaluminum crystals having a thickness of about 20 mm were deposited. Then, the stirring was stopped, and liquid trimethylaluminum that did not precipitate was drawn out, and then the crystals were melted and transferred to a stainless steel container. The volume of this trimethylaluminum was 160 ml. This represents about 46% of the charged trimethylaluminum before purification. This product was analyzed for oxygen-containing compounds (denoted by -OMe in the table) and organic silicon, 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 final crystallized trimethylaluminum was 28% by weight of the initially supplied trimethylaluminum. 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 the drawings]

FIG. 1 is a schematic view of an apparatus for purifying an organometallic compound 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, and 8 is a medium inlet. , 9 is a medium outlet, 10 is a rotor, 11 is a thermostat, 1
2 denotes a magnetic stirrer, and 13 denotes a crystal of an organometallic compound.

Claims (2)

(57) [Claims] 1. Oxygen containing material maintained at a temperature equal to or higher than the melting point of the container.
While stirring the liquid organometallic compound containing the compound,
After bringing the organometallic compound into contact with a coolant adjusted to a temperature lower than the melting point of the organometallic compound to solidify and precipitate the organometallic compound on the surface of the coolant, it is separated from the remaining organometallic compound in a liquid state, Contains oxygenated compounds characterized by recovering organometallic compounds solidified and precipitated on the surface
And purification method of the organometallic compound has. 2. The organometallic compound according to claim 1, wherein the organometallic compound is trimethylaluminum, trimethylgallium, trimethylindium, triisobutylaluminum, dimethylaluminum hydride, tertiarybutylphosphine and tertiarybutylarsine. Purification method.