TECHNICAL FIELD

Methods of selectively synthesizing n-tetrasilane are disclosed. N-tetrasilane is prepared by pyrolysis of silane (SiH4), disilane (Si2H6), trisilane (Si3H8), or mixtures thereof. More particularly, the disclosed synthesis methods tune and optimize the n-tetrasilane:i-tetrasilane isomer ratio. The isomer ratio may be optimized by selection of process parameters, such as temperature, residence time, and the relative amount of starting compounds. The disclosed synthesis methods allow facile preparation of n-tetrasilane.

BACKGROUND

Polysilanes have been used in a variety of industries.

Vapor deposition of silicon-containing films using polysilanes is disclosed by JP Pat No 3,185,817 to Seiko Epson Corp.; Kanoh et al., Japanese Journal of Applied Physics, Part 1: Regular Papers, Short Notes & Review Papers 1993, 32(6A), 2613-2619; JP Pat No 3,484,815 to Showa Denko KK; and JP Pat App Pub No 2000/031066 to Showa Denko KK, among others.

Epitaxial Si-containing films, such as Si, SiGe, SiC, SiN, and SiO, have been grown using polysilanes as disclosed by Hazbun et al.,Journal of Crystal Growth2016, 444, 21-27; US Pat App Pub No 2017/018427 to Yi-Chiau Huang et al.; US Pat App Pub No 2016/126093 to Dube et al.; and Hart et al.,Thin Solid Films2016, 604, 23-27]; among others.

Polysilanes have also been used to form larger polymers. See, e.g., US Pat App Pub No 2016/0297997 to Forschungzentrum Jülich Gmbh.

Converting lower silanes into higher silanes has been studied extensively both for research and for commercial purposes. Pyrolysis has been studied. See, e.g., Timms et al., J. Chem. Soc. 1964 pp. 1467-1475; Tebben et al., Inorg. Chem. Vol. 8, No. 8 Aug. 1969; Vanderwielen et al., JACS, v. 97 (1975) p. 993; Martin et al., J. of Chem. Kin., v. 22, p. 613 (1990); Yoshida et al., J. Phys. Chem. A, 2006, 110, 4726-4731; DE2139155 to Peter Plichta; U.S. Pat. No. 6,027,705 to Kitsuno et al.; U.S. Pat. No. 7,906,094 to Bourasseau et al.; U.S. Pat. No. 8,163,261 to Hazeltine: U.S. Pat. No. 8,969,610 to Wieber et al.; U.S. Pat. No. 9,034,292 to OCI Materials Co., Ltd.; WO2017/018771 to SK-Materials Co., Ltd.; and WO2017/018771 and WO2017/018772 to SK-Materials Co., Ltd.

All these disclosures notwithstanding, commercial use of polysilanes remains elusive.

SUMMARY

Methods of selectively synthesizing n-tetrasilane are disclosed. A n-Si4H10:i-Si4H10mixture having a ratio ranging from approximately 5:1 to approximately 15:1 is produced by heating Si2H6and optionally Si3H8in a reactor to a temperature ranging from approximately 250° C. to approximately 360° C. The disclosed processes may further include one or more of the following aspects:the method not utilizing H2;the method not utilizing a catalyst;the method not utilizing glass wool;the method not utilizing a vacuum;the method not producing any solid polysilane reaction products;the pressure of the reactor ranging from approximately atmospheric pressure to approximately 30 psig;the pressure of the reactor ranging from approximately atmospheric pressure to approximately 15 psig;the method further comprising pre-heating the Si2H6and optional Si3H8;the method further comprising cooling the n-Si4H10:i-Si4H10mixture;wherein the pre-heating and cooling occurs in the reactor;maintaining Si2H6and optional Si3H8at the temperature for a time period ranging from approximately 5 seconds to approximately 30 seconds;maintaining Si2H6and optional Si3H8at the temperature for a time period ranging from approximately 5 seconds to approximately 10 seconds when the temperature ranges from approximately 360° C. to approximately 380° C.;maintaining Si2H6and optional Si3H8at the temperature for a time period ranging from approximately 10 seconds to approximately 20 seconds when the temperature ranges from approximately 280° C. to approximately 360° C.;maintaining Si2H6and optional Si3H8at the temperature for a time period ranging from approximately 20 seconds to approximately 30 seconds when the temperature ranges from approximately 250° C. to approximately 280° C.;the mixture comprising between approximately 0.1% mol/mol to approximately 25% mol/mol Si3H8and between approximately 75% mol/mol and 99.9% mol/mol Si2H6;the mixture comprising between approximately 0.1% mol/mol to approximately 10% mol/mol Si3H8and between approximately 90% mol/mol and 99.9% mol/mol Si2H6;the mixture comprising 100% mol/mol Si2H6;recycling unreacted Si2H6;recycling unreacted Si2H6and Si3H8;the ratio of n-Si4H10:i-Si4H10ranging from approximately 8:1 to approximately 15:1;fractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 90% w/w to approximately 100% w/w n-Si4H10;fractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 95% w/w to approximately 100% w/w n-Si4H10;fractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 97% w/w to approximately 100% w/w n-Si4H10;fractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 0% w/w to approximately 10% w/w i-Si4H10;fractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 0% w/w to approximately 5% w/w i-Si4H10; orfractionally distilling the n-Si4H10:i-Si4H10mixture to produce a Si-containing film forming composition comprising approximately 0% w/w to approximately 3% w/w i-Si4H10.

Si-containing film forming composition produced by any of the methods disclosed above are also disclosed. The disclosed compositions may further include one or more of the following aspects:the Si-containing film forming composition comprising approximately 0 ppmw to approximately 100 ppmw halide contaminants;the Si-containing film forming composition comprising approximately 0 ppmw to approximately 25 ppmw halide contaminants;the Si-containing film forming composition comprising approximately 0 ppmw to approximately 5 ppmw halide contaminants;the Si-containing film forming composition comprising approximately 90% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 95% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 97% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 10% w/w i-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 5% w/w i-Si4H10; and/orthe Si-containing film forming composition comprising approximately 0% w/w to approximately 3% w/w i-Si4H10.

Methods of maintaining the vapor pressure of tetrasilane during vapor deposition processes are also disclosed. The vapor deposition processes use any of the Si-containing film forming composition disclosed above. The Si-containing film forming composition is maintained at a vaporizing temperature. The disclosed methods may further include one or more of the following aspects:the Si-containing film forming composition comprising approximately 90% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 95% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 97% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 10% w/w i-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 5% w/w i-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 3% w/w i-Si4H10;the Si-containing film forming composition having an initial vapor pressure at the vaporizing temperature;the vaporizing temperature ranging from approximately 0° C. to approximately 40° C.;the vaporizing temperature ranging from approximately 20° C. to approximately 25° C.;maintaining approximately 80% Pa/Pa of the initial vapor pressure of the Si-containing film forming composition at the vaporizing temperature until approximately 95% w/w of Si-containing film forming composition is consumed;maintaining approximately 90% Pa/Pa of the initial vapor pressure of the Si-containing film forming composition at the vaporizing temperature until approximately 95% w/w of Si-containing film forming composition is consumed; and/ormaintaining approximately 95% Pa/Pa of the initial vapor pressure of the Si-containing film forming composition at the vaporizing temperature until approximately 95% w/w of Si-containing film forming composition is consumed.

Methods of reducing the formation of branched polysilanes during polymerization are also disclosed. The polymerization processes use any of the Si-containing film forming compositions disclosed above. The disclosed methods may further include one or more of the following aspects:the Si-containing film forming composition comprising approximately 90% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 95% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 97% w/w to approximately 100% w/w n-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 10% w/w i-Si4H10;the Si-containing film forming composition comprising approximately 0% w/w to approximately 5% w/w i-Si4H10; and/orthe Si-containing film forming composition comprising approximately 0% w/w to approximately 5% w/w i-Si4H10.

Notation and Nomenclature

Certain abbreviations, symbols, and terms are used throughout the following description and claims, and include:

As used herein, the indefinite article “a” or “an” means one or more.

As used herein, the terms “approximately” or “about” mean±10% of the value stated.

As used herein, the term “comprising” is inclusive or open-ended and does not exclude additional, unrecited materials or method steps; the term “consisting essentially of” limits the scope of a claim to the specified materials or steps and additional materials or steps that do not materially affect the basic and novel characteristics of the claimed invention; and the term “consisting of” excludes any additional materials or method steps not specified in the claim.

As used herein, the term “higher silanes” means SinH2n+2, wherein n=4-100 and the term “lower silanes” means SinH2n+2with n=1-3. The higher silanes may be linear or branched.

The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviations (e.g., Si refers to silicon, C refers to carbon, H refers to hydrogen, etc.).

Any and all ranges recited herein are inclusive of their endpoints (i.e., x=1 to 4 or x ranges from 1 to 4 includes x=1, x=4, and x=any number in between), irrespective of whether the term “inclusively” is used.

As used herein, the term “anhydrous” means containing between approximately zero ppmv and approximately 100 ppmv moisture and preferably between approximately zero ppmv and approximately 10 ppmv moisture.

