This invention relates to a method for selectively reducing hexachlorodisilane to produce 1,1,1-trichlorodisilane.

Reduction of hexachlorodisilane with tri-n-butyl tin hydride has been reported, e.g., in U. Herzog et al., /. Organometallic Chem. , 1978 (161) 165-169. However, the major product obtained in this reference differed with the catalyst used and was SiHCh, silane or disilane.

There is a challenge in making 1,1,1-trichlorodisilane (1,1,1-3CDS) with a high degree of selectivity for 1,1,1-3CDS over other disilanes including other isomers of trichlorodisilane as well as other chloro(di)silanes and alkyl(di)silane impurities.

Statement of the Invention

The present invention solves the problem of providing a method for making 1,1,1- 3CDS with a high degree of selectivity for 1,1,1-3CDS over other disilanes including other isomers of trichlorodisilane as well as other chloro(di)silanes and alkyl(di)silane impurities. In particular, the present invention provides a method for producing 1,1,1-3CDS with 99 weight-percent (wt%) selectivity over the 1,1,2-trichlorodisilane isomer relative to combined weight of the two trichlorodisilane isomers. Moreover, at the same time the method of the present invention produces 1,1,1-3CDS at 65 wt% or higher selectivity over other chlorodisilane byproducts. Wt% values for selectivity are determined by gas

chromatography using the method described hereinbelow.

The method of the present invention is a result of discovering that 1,1,1-3CDS can be made with a high level of selectivity by starting with tri-n-butyl tin hydride in a solvent to form a mixture and then adding to the mixture hexachlorodisilane (HCDS) at a temperature of 20 degrees Celsius (°C) or colder.

In a first aspect, the present invention is a method for producing 1,1,1- trichlorodisilane; said method comprising adding hexachlorodisilane to a mixture of tri-n- butyl tin hydride in a solvent at a temperature no greater than 20 °C.

Detailed Description

Percentages are weight percentage (wt%) and temperatures are in °C unless specified otherwise. Chloro(di)silane refers to both chlorosilanes and chlorodisilane. Alkyl(di)silane refers to both alkylsilane and alkyldisilane. Tri-n-butyl tin hydride (Bu3SnH) has CAS No. 688-73-3 and is also known as Tri-n-butylstannane. The method of the present invention requires forming a mixture of tri-n-butyl tin hydride (TBTH) in a solvent. TBTH can be added to solvent or solvent can be added to TBTH to form the mixture. Desirably, the solvent is a non-polar organic solvent. Preferred non-polar organic solvents include C4-C20 hydrocarbons and ethers; preferably C6-C20 linear or branched alkanes, C6-C20 aromatic hydrocarbons or C4-C20 ethers; preferably decane, isododecane, toluene, xylene, diisopropylbenzene, mesitylene, diethyl ether or dibutyl ether; preferably xylene, decane or isododecane. Mixtures of organic solvents mentioned herein may be used. The non-polar organic solvent can be aromatic or non-aromatic.

The solvent is generally present at a concentration of 1 to 99 wt%, based on the weight of the organic solvent and TBTH. Desirably, the solvent is present at a concentration of 10 wt% or more, preferably 20 wt% or more and can be 30 wt% or more, 40 wt% or more, 50 wt% or more while at the same time is preferably 90 wt% or less, preferably 80 wt% or less, preferably 70 wt% or less and can be 60 wt% or less, 50 wt% or less, 30 wt% or less, even 25 wt% or less with wt% relative to combined weight of solvent and TBTH.

Preferably, the mixture of organic solvent and tri-n-butyl tin hydride is substantially free of Lewis bases, which means the mixture has less than 5 wt% of Lewis bases (Lewis bases do not include ether solvents), preferably less than 2 wt%, preferably less than 1 wt%, preferably less than 0.5 wt%, preferably less than 0.1 wt%, as a percentage of the total amount of solvent and tri-n-butyl tin hydride.

The method requires addition of hexachlorodisilane (HCDS) to the mixture of organic solvent and TBTH. During the addition of HCDS, maintain a mixture temperature of 20°C or colder, preferably 15°C or colder, 10°C or colder, 5°C or colder, 0°C or colder, -5°C or colder, -10°C or colder, -12°C or colder, -14°C or colder and even -15°C or colder. At the same time, while the method may work better the colder the temperature, practically speaking the temperature is generally -30°C or warmer, -25 °C or warmer, -20°C or warmer and can be -15°C or warmer. The solvent is selected so as to remain liquid at the temperature maintained during the addition of HCDS.

Desirably, maintain the mixture within these same temperature values after addition of HCDS is complete for a time of 0.5 hours or more, preferably one hour or more, more preferably two hours or more, and can be 5 hours or more while at the same time for a period generally of 12 hours or less, preferably 8 hours or less, and can be 5 hours or less, and even 3 hours or less. Preferably, add enough HCDS so as to achieve a molar ratio of hexachlorodisilane (HCDS) to tri-n-butyl tin hydride that is from 1:3 to 1:2, preferably 1:2.8 to 1:2.2, and more preferably 1:2.7 to 1:2.3.

1,1,1-3CDS is formed by the reaction of HCDS and TBTH during the addition of HCDS and during the time after completion of HCDS addition. It is desirable to purify the 1,1,1-3CDS by distillation, preferably at a pressure below 760 millimeters mercury.

1,1,1-3CDS may be used to form a silicon-heteroatom film by known techniques, including, e.g., physical vapor deposition, atomic layer deposition (ALD), or chemical vapor deposition (CVD). The physical vapor deposition method may comprise sputtering. Suitable sputtering methods include direct current (DC) magnetron sputtering, ion-beam sputtering, reactive sputtering, and ion-assisted sputtering. Typically, the deposition method comprises ALD or CVD. Preferably, the heteroatoms are selected from carbon, oxygen and nitrogen.

Suitable ALD methods include plasma enhanced atomic layer deposition methods (PEALD), spatial atomic layer deposition (SALD) and thermal atomic layer deposition (TALD) methods. When PEALD methods are employed, the plasma may be any one of the foregoing plasmas. The plasma may optionally further contain a carrier gas such as molecular nitrogen or argon gas. Plasmas are formed from plasma-forming gases, which may comprise a mixture of molecular nitrogen and molecular hydrogen.

Suitable CVD methods include simple thermal vapor deposition, plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance (ECRCVD), atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), ultrahigh vacuum chemical vapor deposition (UHVCVD), aerosol-assisted chemical vapor deposition (AACVD), direct liquid injection chemical vapor deposition (DLICVD), microwave plasma-assisted chemical vapor deposition (MPCVD), remote plasma-enhanced chemical vapor deposition (RPECVD), atomic layer chemical vapor deposition (ALCVD), hot wire chemical vapor deposition (HWCVD), hybrid physical- chemical vapor deposition (HPCVD), rapid thermal chemical vapor deposition (RTCVD), and vapor-phase epitaxy chemical vapor deposition (VPECVD), photo-assisted chemical vapor disposition (PACVD), and flame assisted chemical vapor deposition (FACVD). Examples

Comparative Example 1 showing low selectivity for 1,1,1-3CDS over other chlorodisilanes by using Bu3SnH at room temperature in a solvent with a Lewis base catalyst (/. Organomet. Chem. 1995, 494, 143)

Reduction of HCDS by 2 eq of Bu3SnH in 38 wt% toluene at room temperature with PPI13 added as the Lewis base catalyst lead to a product distribution of 5 mole% 1,1,1-3CDS and 43 mole% combined other chlorodisilanes. It is clear from these mole percent values that 1,1,1- 3CDS is a minor component in the reaction product distribution.

Comparative Example 2 showing low selectivity for 1,1,1-3CDS over other chlorodisilanes by using Bu3SnH at room temperature and in a solvent absent of a Lewis base catalyst (Batch 27003-16-1) In a glovebox, tri-n-butyltin hydride (2.15 mL, 2.33 g, 2.0 eq) and toluene (0.75 mL, 0.65 g. 37 wt%) were loaded into a 250 mL 3-neck half -jacketed round bottom flask equipped with a glass thermowell and held at 23 °C. Dropwise, hexachlorodisilane (HCDS, 0.69 mL, 1.1 g, 1 eq) was added to the Bu3SnH solution over 6 min, followed by continued stirring for 50 min. The solution was analyzed by GC-TCD, showing a solution containing 16.5 wt% 1,1,1-3CDS, 53.1 wt% combined other chlorodisilanes, and no detectable alkyl(di)silane with wt% relative to all mono and disilanes present as determined by gas chromatography (GC) using the method described hereinbelow.

Inventive Example 1 showing high selectivity for 1,1,1-3CDS over other chlorodisilanes by using a low reaction temperature and in a solvent absent of Lewis base catalyst (Batch 27003- 16-Q)

In a glovebox, tri-n-butyltin hydride (3.75 mL, 4.06 g, 2.5 eq) and decane (1.69 mL, 1.23 g. 45 wt%) were loaded into a 250 mL 3-neck half -jacketed round bottom flask equipped with a glass thermowell and held at -14 °C. Dropwise, hexachlorodisilane (HCDS, 0.96 mL, 1.50 g, 1 eq) was added to the Bu3SnH solution over 5 min, followed by continued stirring for 165 min. The solution was analyzed by GC-TCD, showing a solution containing 43.4 wt% 1,1,1- 3CDS, 22.5 wt% combined other chlorodisilanes, and no detectable alkyl(di)silane with wt% relative to all mono and disilanes present as determined by gas chromatography (GC) using the method described herein below. Notably, no 1 , 1 ,2-trichlorodisilane was detected indicating greater than 99 wt% selectivity of 1,1,1-3CDS over the combination of 1,1,1 -and 1,1,2-trichlorodisilane isomers.

Gas Chromatography Selectivity Analysis

Determine the wt% selectivity of 1,1,1-3CDS relative to other products using gas chromatography with a thermal conductivity detector (GC-TCD). Use a capillary column with a 20 meter length, 0.32 millimeter inner diameter and containing a 0.25 micrometer thick stationary phase in the form of a coating on the inner surface of the capillary column, wherein the stationary phase is composed of phenyl methyl siloxane. Carrier gas is helium gas used at a flow rate of 105 millimeters per minute. The gas chromatography instrument can be an Agilent model 890A gas chromatograph. Inlet temperature is 200 degrees Celsius (°C). the temperature profile consists of soaking (holding) at 50°C for two minutes, ramping the temperature at a rate of 15°C per minute to 250°C and then soaking (holding) at 250°C for ten minutes.