Method for purifying alkyl alkoxy silane

Abstract

The invention discloses a purification method of alkyl alkoxy silane. The purification method comprises the following steps: providing an alkyl alkoxy silane crude product; mixing the alkyl alkoxy silane crude product with sodium alkoxide to form a purification reaction system, and carrying out chemical reaction on the sodium alkoxide and water in the alkyl alkoxy silane crude product; and purifying in the purified reaction system after the reaction through rectification to obtain an alkyl alkoxy silane refined product with low water content. According to the purification method provided by the invention, the sodium alkoxide is adopted as a water removal agent to react with the crude product of the alkyl alkoxy silane, and then the water removal purpose is achieved through reactive distillation, so that the reactive distillation water removal method combines the reaction and distillation effects of the sodium alkoxide and the water; according to the method, water impurities with the magnitude of dozens of ppm in the alkyl alkoxy silane can be simply and effectively removed, new impurities are not introduced, reaction products are easy to separate, and the alkyl alkoxy silane with high purity and extremely low water content can be efficiently and cheaply obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and particularly to a purification method for alkylalkoxysilanes. Background Art

[0002] Low dielectric constant (k) thin films are key materials for constructing semiconductor chips, which can reduce the resistance capacitance (RC) delay and interconnect delay, thereby improving the performance of semiconductor devices and increasing the circuit speed. Currently, the commonly used low-k thin film material SiCO:H is composed of Si, C, O, and H elements, and is prepared by the chemical vapor deposition reaction of organosilanes and oxygen through a plasma-enhanced chemical vapor deposition (PECVD) process. One type of organosilane suitable for this application is alkylalkoxysilanes, including dimethyldimethoxysilane (DMDMOS), etc. Compared with other alkylalkoxysilanes, DMDMOS has obvious application cost advantages due to its low production cost, and is widely used as a low-k thin film precursor for PECVD.

[0003] DMDMOS is industrially prepared by the methanolysis of dimethyldichlorosilane and purified by rectification. The main chemical reactions involved are:

[0004] (CH 3 ) 2 SiCl 2 +2CH 3 OH=(CH 3 )2Si(OCH 3 ) 2 +2HCl

[0005] Although the DMDMOS produced in this way has a high organic purity, it contains a certain amount of water. The impurity water can enter the production and purification system through various channels and ultimately contaminate the product. The sources of water include impurities in the methanol raw material, or through incompletely dried equipment, or from a humid environment. For example, industrially produced DMDMOS analyzed by GC-FID has an organic purity of 99.29%, but contains 48 ppm of water. It is very difficult to reduce the water content to <1 ppm of the coating precursor requirement only by rectification.

[0006] The impurity water in DMDMOS will interfere with the effect of the PECVD coating process. Therefore, DMDMOS used for depositing low-k thin films needs to meet the requirement of extremely low water content. Based on this situation, the industry urgently needs to find a simple and feasible reactive distillation method that can efficiently and inexpensively remove the low amount of water in industrially produced pure DMDMOS, so that the product obtained after reactive distillation meets the quality requirements for semiconductor chip manufacturing. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the object of the present invention is to provide a method for purifying alkylalkoxysilanes.

[0008] To achieve the foregoing object of the invention, the technical solutions adopted by the present invention include:

[0009] In a first aspect, the present invention provides a method for purifying alkylalkoxysilanes, which includes:

[0010] Providing a crude alkylalkoxysilane;

[0011] Mixing the crude alkylalkoxysilane with sodium alkoxide to form a purification reaction system, and causing the sodium alkoxide to chemically react with the water in the crude alkylalkoxysilane;

[0012] Purifying the reaction product of the purification reaction system by rectification to obtain a refined alkylalkoxysilane with a low water content.

[0013] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0014] The purification method provided by the present invention uses sodium alkoxide as a water remover, reacts with the crude alkylalkoxysilane, and then achieves the purpose of water removal through reactive distillation. This reactive distillation water removal method combines the reactions of sodium alkoxide and water and the function of distillation, can simply and effectively remove water impurities in the alkylalkoxysilane in the order of dozens of ppm, does not introduce new impurities, the reaction products are easy to separate, and can efficiently and inexpensively obtain high-purity alkylalkoxysilane with an extremely low water content.

[0015] The above description is only an overview of the technical solutions of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it in accordance with the content of the specification, the following is described by way of preferred embodiments of the present invention. Detailed Embodiments

[0016] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solutions of the present invention through long-term research and a large number of practices. The following will further explain the technical solutions, their implementation processes and principles.

[0017] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0018] An embodiment of the present invention provides a method for purifying alkylalkoxysilanes, which includes the following steps:

[0019] Providing a crude alkylalkoxysilane.

[0020] Mix the crude alkylalkoxysilane with sodium alkoxide to form a purification reaction system, and cause the sodium alkoxide to chemically react with the water in the crude alkylalkoxysilane.

[0021] Purify the reaction product of the purification reaction system by distillation to obtain a refined alkylalkoxysilane product with a low water content.

[0022] In the above technical solution, the addition method of sodium alkoxide is powder addition, and the purification reaction system is constructed by mixing sodium alkoxide powder and crude alkylalkoxysilane. This is mainly for two considerations: 1) Compared with the addition of sodium alkoxide solution, the reactivity of sodium alkoxide in powder state is stronger than that in solution state, and it is more suitable for reacting with water in ppm level; 2) The powder is pure sodium alkoxide without solvents such as methanol, and does not introduce additional and unnecessary solvent impurities into the distillation system. Although sodium alkoxide reacts with water to generate alcohol, since the water content in the crude DMDMOS is only dozens of ppm, the generated methanol content is still in ppm level and will not have a significant impact on the final distillation purity. However, once sodium alkoxide is added in solution form, due to the large amount of solvent added, it will have an adverse effect on the final distillation.

[0023] In addition, in the preferred embodiment of the present invention, sodium alkoxide and water react during the distillation process. Under the action of high temperature and reflux, the water removal effect is better, and the method is easier to implement, belonging to the category of reactive distillation technology. And by accurately controlling the dosage of sodium methoxide powder, it is ensured that sodium methoxide is completely dissolved in the crude DMDMOS at the distillation temperature, achieving the maximum water removal effect.

[0024] Theoretically, all water scavengers that can react with water can remove water impurities, but in practical applications, not all water scavengers are applicable to the purification of alkylalkoxysilane. This is because on the one hand, the water content is relatively low, and it is difficult to remove water impurities in the ppm level if the reaction activity is insufficient. On the other hand, the boiling point of alkylalkoxysilane is similar to that of most liquid substances, and it has a high reaction activity. Many water scavengers may produce new impurities that are difficult to separate, or react with alkylalkoxysilane, resulting in the inability to carry out distillation purification. Based on a large amount of research and practice by the inventors of the present invention, the preferred sodium alkoxide used as a water scavenger in the present invention is considered based on five factors: 1) High reactivity with water; 2) Does not react with alkylalkoxysilane; 3) The products generated after reacting with water are easy to remove (i.e., methanol and sodium hydroxide); 4) Does not introduce new impurities; 5) Low cost. Therefore, considering and screening comprehensively, sodium alkoxide is a better choice as a water scavenger for alkylalkoxysilane. In contrast, general water scavengers, whether based on physical or chemical water removal mechanisms, cannot meet these requirements simultaneously.

[0025] In some more specific embodiments, the construction process of the purification reaction system includes:

[0026] Provide an organic solution of sodium alkoxide.

[0027] Remove the organic solvent from the organic solution to obtain sodium alkoxide powder, which is used to directly mix with the crude alkylalkoxysilane to form the purification reaction system.

[0028] In some embodiments, the construction process may specifically include:

[0029] Add the organic solution to a distillation device.

[0030] Remove the organic solvent by vacuum pumping to form the sodium alkoxide powder in the distillation device.

[0031] Add the crude alkylalkoxysilane to the distillation device containing the sodium alkoxide powder to form the purification reaction system.

[0032] The present invention preferably introduces sodium alkoxide powder by the solution method, and after introduction, the solvent is removed by various feasible methods, not limited to the vacuum pumping method exemplified above, and other methods such as heating can also be used. Such embodiments have the following advantages: 1) Easy to operate, relatively easy to transfer liquids, and there is a standard operation process; 2) It is easier to avoid contamination by water vapor in the environment; 3) Due to better quality assurance, the reaction activity of the solid powder obtained by on-site evaporation / drying under vacuum is higher.

[0033] In the above preferred scheme, powdered sodium alkoxide is not directly added to the reaction system. There are at least the following considerations: 1) Sodium alkoxide solid is highly sensitive to water in the environment. Transferring solid materials is already difficult in industrial production, and it is even more difficult to transfer air-sensitive solid materials; 2) It is very difficult to avoid contact with water vapor in the environment during the transfer of solids. Reacting with water not only reduces the reactivity of the solid but also introduces additional impurities. Once the powder is contaminated with moisture during the transfer process, it is extremely easy to cause the water content in the reaction system to double, bringing great difficulties to the complete removal of water; 3) The reactivity of solid powders may be unstable between batches due to the influence of the supplier's production process. These problems will affect the product quality, cost, and EHS of the purified alkylalkoxysilane (such as the health and protection of personnel during the transfer of highly reactive solids, etc.).

[0034] Regarding the specific reaction and distillation conditions, in some embodiments, the temperature of the chemical reaction is 0 - 100 °C, and the time is 0.1 - 24 h.

[0035] In some embodiments, to ensure the removal effect and the ease of product separation, the mass ratio of the crude alkylalkoxysilane to sodium alkoxide in the purification reaction system is preferably controlled at (50 - 10,000):1

[0036] In some embodiments, the rectification specifically includes:

[0037] During rectification, fractions are collected at preset time intervals, and the water content of the collected fractions is analyzed and tested.

[0038] Based on the results of the analysis and test, the corresponding fractions with a water content meeting the requirements are combined to obtain the refined alkylalkoxysilane.

[0039] Regarding the raw materials used before the reaction, in some embodiments, the purity of the crude alkylalkoxysilane is 90 - 99.99%, and the water content is 10 - 100 ppm.

[0040] After the reaction and rectification, in some embodiments, after the purification, the water content of the refined alkylalkoxysilane is below 1 ppm.

[0041] Regarding the specific material selection, in some embodiments, the crude alkylalkoxysilane includes any one or a combination of two or more of diethoxymethylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

[0042] In some embodiments, the sodium alkoxide includes sodium alkoxides with 1 - 5 carbon atoms.

[0043] In some embodiments, the sodium alkoxide is preferably sodium methoxide. The reason for preferably using sodium methoxide is that the methanol formed after its reaction with water has a low boiling point of only 65°C and is easily separated from DMDMOS with a boiling point of 81°C by rectification. If sodium ethoxide is used, ethanol is formed after the reaction with water, and its boiling point is 13°C higher than that of methanol, and the boiling point difference from DMDMOS is only 3°C, making it very difficult to separate ethanol, and it is difficult for the product to meet the requirements of electronic grade purity. However, this does not mean that sodium ethoxide and other sodium alkoxides cannot be applied to the present invention at all, but only that the final rectification purity may be slightly affected. During rectification, the generated sodium hydroxide remains in the rectification still bottom without volatility and is removed.

[0044] The technical solutions of the present invention are further described in detail below through several examples. However, the selected examples are only used to illustrate the present invention and do not limit the scope of the present invention.

[0045] Example 1

[0046] This example illustrates the purification process of diethoxymethylsilane, which is specifically as follows:

[0047] Take 2 kg of crude diethoxymethylsilane with a purity of 90% and a water content of 34 ppm. First, add 90 g of a 20% sodium ethoxide ethanol solution into the flask of the distillation device, and remove the ethanol by vacuum pumping, leaving behind solid sodium ethoxide powder. Then add diethoxymethylsilane and react at 70 °C for 3 h with stirring. After sufficient reaction, distill at atmospheric pressure, collect the fractions every 1 h, and conduct analysis and testing. Combine the qualified fractions to obtain a diethoxymethylsilane product with a water content of 0.1 ppm and a purity of 99.6%.

[0048] Example 2

[0049] This example is generally the same as Example 1, with the main difference being:

[0050] Replace the sodium ethoxide ethanol solution with a sodium methoxide methanol solution, and keep the other material ratios and reaction conditions unchanged.

[0051] Finally, this example obtains a diethoxymethylsilane product with a water content of 0.1 ppm and a purity of 99.9%.

[0052] Example 3:

[0053] This example illustrates the purification process of dimethyldimethoxysilane, which is specifically as follows:

[0054] Take 2 kg of crude dimethyldimethoxysilane with a purity of 98% and a water content of 48 ppm. First, add 40 g of a 30% sodium methoxide methanol solution into the flask of the distillation device, and remove the methanol by vacuum pumping, leaving behind solid sodium methoxide powder. Then add dimethyldimethoxysilane and react at 70 °C for 8 h with stirring. After sufficient reaction, distill at atmospheric pressure, collect the fractions every 1 h, and conduct analysis and testing. Combine the qualified fractions to obtain a dimethyldimethoxysilane product with a water content of 0.4 ppm and a purity of 99.8%.

[0055] Example 4:

[0056] This example illustrates the purification process of dimethyldimethoxysilane, which is specifically as follows:

[0057] Take 2 kg of crude dimethyldimethoxysilane with a purity of 99% and a water content of 53 ppm. First, add 20 g of a methanol solution of 30% sodium methoxide into the flask of the rectification device, and remove the methanol by vacuum pumping. The remaining solid powder of sodium methoxide is then added with dimethyldimethoxysilane, and the reaction is carried out at 70 °C for 2 h with stirring. After the reaction is complete, distillation is carried out at atmospheric pressure, and the fractions are collected every 1 h for analysis and testing. The qualified fractions are combined to obtain a dimethyldimethoxysilane product with a water content of 0.1 ppm and a purity of 99.98%.

[0058] Example 5:

[0059] This example demonstrates the purification process of dimethyldimethoxysilane, which is specifically as follows:

[0060] Take 2 kg of crude dimethyldimethoxysilane with a purity of 99% and a water content of 53 ppm. First, add 40 g of a methanol solution of 30% sodium methoxide into the flask of the rectification device, and remove the methanol by vacuum pumping. The remaining solid powder of sodium methoxide is then added with dimethyldimethoxy, and the reaction is carried out at 70 °C for 8 h with stirring. After the reaction is complete, distillation is carried out at atmospheric pressure, and the fractions are collected every 1 h for analysis and testing. The qualified fractions are combined to obtain a dimethyldimethoxysilane product with a water content of 0.4 ppm and a purity of 99.99%.

[0061] Example 6

[0062] This example is generally the same as Example 5, and the main difference lies in:

[0063] An equal amount of sodium methoxide powder is added to the rectification device to replace the addition method of the methanol solution of sodium methoxide, and the other material ratios and reaction conditions remain unchanged.

[0064] Finally, a dimethyldimethoxysilane product with a water content of 1.0 ppm and a purity of 99.8% is obtained. This is because during the addition of sodium methoxide powder, moisture in the air was contaminated, resulting in too high a water content and causing difficulty in removal.

[0065] Comparative Example 1

[0066] This comparative example is generally the same as Example 5, and the main difference lies in:

[0067] Instead of removing methanol by vacuum pumping, the methanol solution is directly combined with the crude dimethyldimethoxysilane, and the other material ratios and reaction conditions remain unchanged.

[0068] Finally, a dimethyldimethoxysilane product with a water content of 0.9ppm and a purity of 99.2% was obtained. This was because the large amount of methanol solvent added caused the reaction system to be transformed from a two-component system to a three-component miscible system of dimethyldimethoxysilane, sodium methoxide and methanol. A large amount of methanol affected the reactivity of sodium methoxide to trace amounts of water and caused difficulty in separating methanol. The water content of the final product was 0.9ppm and the purity was 99.2%.

[0069] Comparative Example 2

[0070] This comparative example is substantially the same as Example 5, except that:

[0071] The dehydrating agent sodium methoxide was replaced by molecular sieves, and the other material ratios and reaction conditions remained unchanged.

[0072] Finally, a dimethyldimethoxysilane product with a water content of 15 ppm and a purity of 99.8% was obtained, which shows that the molecular sieve in the alkylalkoxysilane system cannot effectively remove the water content of the ppm level.

[0073] Comparative Example 3

[0074] This comparative example is substantially the same as Example 5, except that:

[0075] The dehydrating agent sodium methoxide was replaced with solid phosphorus pentoxide. After adding crude dimethyldimethoxysilane, a sample was taken for GC analysis, and other new impurities with a recent boiling point were found to be formed, so distillation purification was no longer performed. This indicates that the use of phosphorus pentoxide introduces new impurities that are difficult to remove by distillation.

[0076] It can be seen from this that, specific to the alkyl alkoxysilane system and for water impurities in the order of tens of ppm, it is essential to use the specific water removal agent sodium alcohol provided by the present invention in combination with corresponding technical means. Replacing it with other water removal methods commonly used in other fields is often difficult to achieve better positive effects.

[0077] Based on the above embodiments and comparative examples, it can be clearly seen that the purification method provided by the present invention adopts sodium alcoholate as a dehydrating agent to react with the crude product of alkyl alkoxysilane, and then achieves the purpose of dehydration by reactive distillation. The reactive distillation dehydration method combines the reaction of sodium alcoholate and water with the effects of distillation, and can simply and effectively remove water impurities of tens of ppm in the alkyl alkoxysilane without introducing new impurities, and the reaction products are easy to separate, so that high-purity alkyl alkoxysilane with extremely low water content can be obtained efficiently and cheaply.

[0078] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it is not intended to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A purification method for alkylalkoxysilane, characterized in that, it includes: providing a crude alkylalkoxysilane; mixing the crude alkylalkoxysilane with sodium alkoxide to form a purification reaction system, and causing a chemical reaction between the sodium alkoxide and the water in the crude alkylalkoxysilane; performing purification on the post-reaction purification reaction system by distillation to obtain a refined alkylalkoxysilane product with a low water content.

2. The purification method according to claim 1, characterized in that, the construction process of the purification reaction system includes: providing an organic solution of sodium alkoxide; removing the organic solvent from the organic solution to obtain a sodium alkoxide powder, and the sodium alkoxide powder is used to directly mix with the crude alkylalkoxysilane to form the purification reaction system.

3. The purification method according to claim 2, characterized in that, specifically it includes: adding the organic solution to a distillation device; removing the organic solvent by vacuum pumping to form the sodium alkoxide powder in the distillation device; adding the crude alkylalkoxysilane to the distillation device containing the sodium alkoxide powder to form the purification reaction system.

4. The purification method according to claim 1, characterized in that, the temperature of the chemical reaction is 0 - 100 °C and the time is 0.1 - 24 h; and / or, the mass ratio of the crude alkylalkoxysilane to sodium alkoxide in the purification reaction system is (50 - 10000)∶1.

5. The purification method according to claim 1, characterized in that, the distillation specifically includes: collecting fractions at preset intervals during the distillation process, and analyzing and testing the water content of the collected fractions; based on the results of the analysis and testing, combining the corresponding fractions with a water content meeting the requirements to obtain the refined alkylalkoxysilane product.

6. The purification method according to claim 1, characterized in that, the purity of the crude alkylalkoxysilane is 90 - 99.999% and the water content is 10 - 100 ppm.

7. The purification method according to claim 1, characterized in that, after the purification, the water content of the refined alkylalkoxysilane product is below 1 ppm.

8. The purification method according to claim 1, characterized in that, the crude alkylalkoxysilane includes any one or a combination of two or more of diethoxymethylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

9. The purification method according to claim 1, characterized in that, the sodium alkoxide includes sodium alkoxides with 1 - 5 carbon atoms.

10. The purification method according to claim 9, characterized in that, the sodium alkoxide is selected from sodium methoxide.