JPH11124386A - Stabilization of trimethoxysilane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of stabilizing trimethoxysilane that can be stored for a long period of time in on need of an additive and is useful as a silica membrane-forming material through the CVD process. SOLUTION: Trimethoxysilane is stabilized by subjecting the trimethoxysilane to be purified to heat treatment, distillation treatment, and filtration treatment in an inert gas atmosphere, charging the resultant purified product into a metallic vessel having surface roughness (Rmzx ) at the parts contacting with the liquid and possibly contacting therewith of <=5 μm for storage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing trimethoxysilane as a silica film forming material by CVD, which is used for an insulating film of a semiconductor.

[0002]

2. Description of the Related Art Organosilicon compounds have a wider variety of types and uses than ever before, but new applications have recently been developed in the field of electronics. For example, tetraethoxysilane (TEOS: Si (OC ₂ H ₅ ) ₄ )
Has been widely used as a raw material of a CVD process in VLSI manufacturing.

Further, trimethoxysilane (HSi (O
CH _{3) 3} organosilicon compounds having Si-H bonds such as) have been published as being effective in similar applications (Society of Applied Physics ('95)). Trimethoxysilane is a film-forming material for CVD that has recently attracted attention because it can form a silica film at a lower temperature than TEOS and can provide excellent film quality with excellent water resistance and a small amount of carbon.

In the field of electronics such as VLSI, such a film forming material for CVD is a high-purity product containing extremely small amounts of impurities because a small amount of impurities causes deterioration of film forming characteristics. In recent years, the degree of integration of LSIs has been increasing, and there is an increasing demand for higher purity.

[0005] However, trimethoxysilane is a very unstable substance and is liable to decompose during storage, so that long-term storage after synthesis has been difficult. For example, methanol contaminated from the synthesis route of trimethoxysilane,
It reacts slowly with trimethoxysilane at room temperature to generate hydrogen or to generate tetramethoxysilane (Si (OCH ₃ ) ₄ ). Trimethoxysilane is also hydrolyzed by a small amount of moisture to produce methanol, and this methanol also causes the above-described reaction.

Further, trimethoxysilane causes a disproportionation reaction due to a catalytic effect of a trace amount of metal contamination, an alkali source, a halide, and the like, thereby producing tetramethoxysilane and monosilane (SiH ₄ ) having a low boiling point and spontaneous combustion. It has the property of generating.

For these reasons, a stabilization technique for making trimethoxysilane storable for a long period of time has been studied, and a method for preventing the reaction with methanol by adding an amine (Japanese Patent Laid-Open No. 57-1185).
No. 92) and those obtained by adding an organic phosphorus or an amino acid (JP-A-53-146343). However, in a CVD film forming material which requires strict control of vapor pressure and purity, there is a problem that the additive itself acts as an impurity and adversely affects film forming characteristics.

[0008] Therefore, there is no conventional technique for preserving trimethoxysilane, which is a very unstable substance, stably for a long period of time. That is, a reproducible and stable CVD film formation using trimethoxysilane has been required. It was difficult.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems without adding an additive, and to provide a trimethoxysilane which can be used as a material for forming a silica film by CVD even when stored for a long time. It is to provide a stabilization method for

[0010]

That is, the present invention provides a method for treating trimethoxysilane to be purified by subjecting it to a heat treatment, a distillation treatment and a filtration treatment under an inert gas atmosphere. An object of the present invention is to provide a method for stabilizing trimethoxysilane, which comprises filling and storing a metal container having a surface roughness ( _Rmax ) of 5 μm or less in a portion which may come into contact with a liquid.

According to the present invention, the content of methanol in trimethoxysilane is set to 1 for each of methanol and water.
0 ppm or less, chlorine content 1 ppm or less, metal content 1 pp
m or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. First, the trimethoxysilane to be purified in the present invention may be any of trimethoxysilane obtained according to a general synthesis route, and there is no particular limitation on the synthesis method.

The trimethoxysilane to be purified is subjected to a heat treatment, a distillation treatment and a filtration treatment, all of which are performed under an inert gas atmosphere. Examples of the inert gas include nitrogen, argon, and helium having a dew point of −70 ° C. or less, and the treatment operation is to completely avoid contact with the atmosphere.

First, trimethoxysilane to be purified,
For example, untreated trimethoxysilane immediately after synthesis is subjected to heat treatment. The heating temperature is preferably from 50 to 80C, and the heating time is preferably from 30 to 60 minutes. Hydrogen generated by this heat treatment is removed out of the system.

The subsequent distillation treatment is not particularly limited, and is carried out by a conventional method.

The next filtration is performed, for example, with a pore size of 0.5 μm.
Hereafter, it is desirable to pass through a filter of preferably 0.3 μm or less. The material of the filter may be any material as long as it is inert to trimethoxysilane, and examples thereof include a membrane filter made of polytetrafluoroethylene.

The purified product obtained by such a series of purification treatments is filled and stored in a metal container under specific conditions.
That is, the obtained purified product is filled in a metal container having a surface roughness (R _max ) of 5 μm or less in the liquid contact portion and the portion which may be in contact with the liquid. The metal container includes a valve serving as an outlet for taking out the trimethoxysilane liquid. The liquid-contacting portion and the liquid-contacting portion on the inner surface of the container body and the valve inner surface have an R _max of 5 μm. It is preferable that the film has a smoothness of 1 μm or less. Note that the R _max in the present invention means a surface roughness as defined in JIS-B-0601.

The material of the metal container is not particularly limited, but stainless steel, which is generally advanced in polishing technique, is preferable. For stainless steel intended to acid cleaning was carried out after the conventional atmospheric annealing, since R _{ma x} is about 50 [mu] m, it is necessary to perform processing to further specially smooth surface.

Examples of surface treatment techniques include mechanical polishing such as buffing, electrolytic polishing, and the like. Fine pinholes and foreign substances on the inner surface of a metal container exhibit trimethoxysilane decomposition catalytic activity. In order to realize the cleaning and smoothing without the problem, a method of further performing electrolytic polishing after mechanical polishing, or a method of combined electrolytic polishing in which mechanical polishing and electrolytic polishing are performed simultaneously is preferable.

The metal container after polishing is used in a clean state when filling with trimethoxysilane. For example, the metal content is reduced to 1 ppm or less and dust having a diameter of 0.2 μm or more is reduced to 50 particles / ml or less. After cleaning with a cleaning agent such as pure water, the substrate is dried at 120 ° C. to 200 ° C. for 3 to 7 hours, and then subjected to vacuum degassing and inert gas replacement, and then to a metal container for storage. Is preferred.

The form of the metal container is not particularly limited, and examples thereof include a cylindrical shape used for a cylinder or the like, and a shape without corners is preferable.

[0022]

The present invention will be further described below with reference to examples and comparative examples. (Example) Untreated trimethoxysilane immediately after synthesis was charged into a usual distillation apparatus, and subjected to heat treatment at 70 ° C for 40 minutes in a nitrogen atmosphere having a dew point of -72 ° C, followed by fractional distillation. The trimethoxysilane obtained by distillation was passed through a polytetrafluoroethylene membrane filter having a pore diameter of 0.2 μm under nitrogen pressure to fill 1500 ml into a metal container.
The inside of the metal container was kept under a normal pressure of a nitrogen atmosphere. The metal container was made of stainless steel, and the entire inner surface of the container and the inner surface of the valve at the liquid outlet were subjected to composite electrolytic polishing to set R _max to 0.8 μm. The shape of the metal container is cylindrical and the volume is 2000 ml. Further, inside the metal container, metal impurities are 2 ppb and dust having a diameter of 0.2 μm or more is 13 ppb.
Washed with pure water at a temperature of 150 ° C
For 6 hours, vacuum treated and purged with nitrogen.

The purity of the purified trimethoxysilane was measured immediately after filling the metal container and after 6 months. Table 1 shows the results.

[0024]

[Table 1] Table 1 Untreated product Immediately after filling 6 months after filling ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Trimethoxysilane pure 98.36% 99.99% 99.99% Impurities: methanol 0.16% <2 ppm <2 ppm water 71 ppm <10 ppm <10 ppm chlorine 6.3 ppm <0.5 ppm <0.5 ppm metal 46 ppm <10 ppb <10 ppb Container pressure (gauge pressure)-0 g / cm ² 0 g / cm ² ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━

As can be seen from Table 1, the impurities were all below the detection limit. At this time, there was no change in purity during storage, and no alteration of trimethoxysilane occurred. From the data on the internal pressure of the container, it was found that no low-boiling substances such as hydrogen and monosilane were formed.

The analysis was carried out by gas chromatography for pure trimethoxysilane, methanol and water, coulometric titration for chlorine, and flameless atomic absorption spectrometry for metal.

(Comparative Example) A stainless steel container (R _ma ) having the same shape and capacity as in the above-mentioned Example 1 and having been subjected to the same washing, drying and nitrogen purging treatments as in Example 1, but not subjected to polishing. _x = 58 μm) was filled with 1500 ml of untreated trimethoxysilane immediately after synthesis, and the pressure was reduced to normal pressure in a nitrogen atmosphere.

The purity of the untreated trimethoxysilane was measured immediately after filling the metal container and after 6 months. Table 2 shows the results.

[0029]

[Table 2] Table 2 Immediately after filling 6 months after filling 純 Pure trimethoxysilane 98.27% 97.1 % Impurity: Methanol O.16% 0.02% Water content 76 ppm <10 ppm Chlorine content 6.3 ppm 6.3 ppm Metal content 54 ppm 89 ppm Container pressure (gauge pressure) 0 g / cm ² 0.8 kg / cm ² ━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━

From the results shown in Table 2, it was suggested that the internal pressure of the container was increased and that a low-boiling substance was formed. In addition, it can be seen that the contents of pure trimethoxysilane, methanol and water decreased, and the mutual reaction proceeded. Furthermore, since the metal content has increased, the metal has been dispersed from the container, and the effect of the difference in the presence or absence of polishing has become clear.

[0031]

The effect of the present invention is to solve the conventional problems without adding an additive and to provide a method for stabilizing trimethoxysilane which can be used as a material for forming a silica film by CVD. That is, according to the present invention, by applying trimethoxysilane to a specific purification step and storing the purified product in a metal container under specific conditions, high purity is maintained for a long time, and as a silica film forming material in a CVD process. Can be provided. In particular, the present invention can be applied to semiconductor manufacturing in which strict quality and high purity of materials are required.

Claims (3)

[Claims] 1. A method for producing a purified product, comprising subjecting trimethoxysilane to be purified to a heat treatment, a distillation treatment, and a filtration treatment under an inert gas atmosphere. A method for stabilizing trimethoxysilane, comprising filling and storing in a metal container having a surface roughness ( _Rmax ) of 5 μm or less. 2. The method for stabilizing trimethoxysilane according to claim 1, wherein a metal container having a surface roughness (R _max ) of 1 μm or less is used. 3. The method for stabilizing trimethoxysilane according to claim 1, wherein the metal container is made of stainless steel.