CS261343B1 - Process for the preparation of high purity chlorsilanes - Google Patents

Abstract

Liquid and gaseous chlorosilanes, as well as mixtures of chlorosilanes with other gases, are purified before further use by microfiltration through a microfilter made of a material perfectly resistant to the action of the filtered medium, preferably from polyfluorocarbon polymers, with a pore size below 1 µm buS, alone or as a final refining stage after rectification of chlorosilanes or in combination with partial hydrolysis of the purified chlorosilanes carried out before microfiltration.

Description

The present invention relates to a process for the preparation of highly pure chlorosilanes which are used as sources of silicon in the production of starting materials for electronics and optoelectronics, which are semiconductor silicon, silicon oxide and nitride for realizing their own functional structures of microelectronic elements of high integration and silica for fiber waveguides with low attenuation of transmitted energy.

Extremely high purity is required in these chlorosilane applications, affecting the immediately critical parameters of the structures formed by the various refining processes applied to thousands of tons of these high energy-intensive substances. These procedures are mostly based on the refining effect of rectification supplemented by partial hydrolysis with water or other reagents. Partial hydrolysis also occurs in conventional handling of chlorosilanes by contact with air humidity.

partial hydrolysis always results in the formation of heterogeneous polysiloxane particles which are capable of adsorbing on their large surface impurities present in the form of metal oxides and chlorides, which are insoluble in this non-polar environment and are mostly products of corrosion of the inner surface of the process line. Heterogeneous particles of all kinds can penetrate into the distillate during rectification and therefore cannot be fully removed by rectification. The heterogeneous particles are then incorporated into the deposit, respectively. preforms where they increase the concentration of undesirable trace impurities, especially metals.

The above-mentioned disadvantages are eliminated by the process for preparing the highly pure chlorosilanes according to the invention, which consists in that liquid and gaseous chlorosilanes as well as mixtures of chlorosilanes with other gases are cleaned by microfiltration through a microfilter from a material perfectly resistant to the filtered medium, preferably polymers. polyfluorinated hydrocarbons having a pore size below 1 µm either alone or at its terminal refining stage after rectifying the chlorosilanes or in combination with partial hydrolysis of the purified chlorosilanes performed prior to microfiltration.

Microfiltration carried out just prior to the adjustment or application of chlorosilanes will significantly reduce the content of heterogeneous particles that are formed either by partial hydrolysis or as corrosion products and by order of magnitude reduce the trace contaminants present in the chlorosilanes. For some purposes, microfiltration can partially replace more energy-intensive refining processes, particularly multiple rectification, and can be used as the final refining stage of chlorosilanes used for electronics and optoelectronics in combination with processes that lead to the formation of heterogeneous particles, eg by partial hydrolysis.

The practical use of the process for preparing the highly pure chlorosilanes of the invention is illustrated by the following examples.

Example 1

The trichlorosilane used as the basic raw material in the production of semiconductor silicon, fed from the intermediate storage tank, after evaporation into a stream of hydrogen with oxygen contents below 5 ppm and water below 2 ppm, is filtered through a Teflon microfilter with porosity below 1 µm just before entering the deposition reactor. By this operation, the metal content of the produced silicon decreases in the order of magnitude. Compared to the standard procedure without microfiltration, the concentration of electroactive boron additive is also reduced to the order of 10 ⁴⁴ atoms / cm 2.

Example 2

Refined rectification to reduce trichlorosilane content below 10 ppm, hydrocarbons, organosilicon compounds and siloxanes below 1 ppm is filtered through a Teflon microfilter with porosity before being adjusted to specially cleaned shipping containers or directly before application in the production of fiber waveguide preforms. 1yum. The concentration of metallic trace impurities drops below 10 ppb, allowing the production of optical waveguides of both PCS and GI type with low energy loss.

Example 3

The dichlorosilane gas used in the electronics for the preparation of epitaxial, insulating and passivation layers, typically taken from a transfer cylinder, is filtered through a Teflon microfilter with a porosity below 1 µm just prior to entering the reactor to form epitaxial or LPCVD layers. Reducing the amount of heterogeneous particles results in a reduction in the number of failures on the board being processed and thus an increase in the yield of the produced semiconductor devices.

Example 4

Trichlorosilane for the production of semiconductor silicon containing 100 ppb boron is subjected to partial hydrolysis by water vapor contained in an inert gas at a dew point of - 30 ° C, dosed to trichlorosilane at a ratio of 1: 100. The resulting boron adsorbing heterogeneous polysiloxane particles are removed after 120 hours by filtration through a Teflon microfilter with a porosity below 1 µm. The boron concentration in trichlorosilane drops below 30 ppb and semiconductor silicon can be produced directly from such refined trichlorosilane without further energy-intensive rectification

Example 5

Silicon tetrachloride for the production of fiber waveguides having a metal impurity content above 50 ppb is partially hydrolysed by water vapor contained in an inert gas with a dew point of - 30 ° C. The resulting heterogeneous particles are removed by filtration through a Teflon microfilter with a porosity below 1 µm. Refined silica chloride is adjusted to specially cleaned shipping containers and used to produce silica fiber waveguides of the Gl type with energy attenuation at a wavelength of 0.8 / µm below 2 dB / km.

Example 6

The silicon tetrachloride, used as a silicon source for the preparation of epitaxial layers on monocrystalline silicon wafers, is prior to adjustment into shipping containers. before entry into the epitaxial reactor, it is purified by filtration through a Teflon microfilter with a porosity below 1 µm.

This decreases the concentration of metallic impurities reducing the lifetime of minor current carriers to below 10 ppb, resulting in improved epitaxial layer properties.

Claims (1)

SUBJECT OF THE INVENTION Process for the preparation of highly pure chlorosilanes, characterized in that the liquid and gaseous chlorosilanes as well as mixtures of chlorosilanes with other gases are cleaned by microfiltration through a microfilter 2 of a filter media resistant material, preferably polyfluorocarbon polymers having a pore size below 1 µm, either alone or as a final refining step after rectification of chlorosilanes, or in combination with partial hydrolysis of purified chlorosilanes, performed prior to microfiltration.