The present invention relates generally to a process and purification method for making an aminosilane. More particularly, the present invention relates to a process and purification method for making the aminosilane, bis(tertiarybutylamino)silane.
Silicon-nitrogen based compounds are used as precursors for depositing, via chemical vapor deposition or similar means, silicon nitride, silicon carbonitride, and silicon oxynitride films that can be used in semiconductor device fabrication. For example, silicon nitride has many applications in device fabrication because of its superior barrier properties and oxidation resistance. Typically, NH3 and Cl2SiH2 mixtures are used to deposit silicon nitride via chemical vapor deposition at temperatures approaching 800° C. The volatile ammonium chloride (“NH4Cl”) and other chlorine by-products of this reaction can lead to particle formation and hazy films and can also deposit at the exhaust of the reactor tube. These deposits can cause wafer and pump damage.
The aminosilane, bis(tertiary-butylamino)silane, is a liquid chemical precursor for the chemical vapor deposition (CVD) of uniform silicon nitride, silicon oxynitride and silicon dioxide films. U.S. Pat. Nos. 5,874,368 and 5,976,991, which are assigned to the assignee of the present invention, describe CVD methods for preparing silicon and oxide containing films using the bis(tertiary-butylamino)silane (BTBAS). Bis(tertiary-butylamino)silane has the following chemical formula: (t-C4H9NH)2SiH2. The deposited films obtained using BTBAS as the precursor are free of ammonium chloride and chlorine contamination at relatively lower process temperatures, i.e., 500 to 800° C. Further, the BTBAS precursor does not contain direct Si—C bonds, and the resulting films are substantially free, or contain very low levels, of carbon. By contrast, analogous aminosilanes which contain ligands such as n-butylamines and tetrakis(dimethylamino)silane do not deposit carbon free films at the lower process temperature ranges and the film uniformities are relatively poorer.
The prior art is silent with regard to a process for the production of the aminosilane compound bis(tertiary-butylamino)silane. However, current production methods for aminosilane compounds typically involve one or more solvents. Prior to use, the solvent needs to be purified and dried to prevent the introduction of impurities in the end-product and dried to the prevent the newly-formed compound from hydrolyzing to siloxane and its respective amine. The articles, K. N. Radhamani et al., “High Yield Room Temperature Synthesis and Spectral Studies of Tri(amino)silanes: (R2N)3SiH”, Phosphorous, Sulfur, and Silicon, Vol. 66 (1992), pp. 297-300 (“Radhamani I”) and K. N. Radhamani et al., “A Convenient High Yield Room Temperature Synthesis of Mixed Tri(amino)silanes by Transamination of Tris(cyclohexylamino)silane and Their Characterization”, Phosphorous, Sulfur, and Silicon, Vol. 79 (1993), pp. 65-68 (“Radhamani II”), describe similar reactions for the synthesis of triaminosilanes and mixed aminosilanes, respectively. Radhamani I describes reacting a secondary amine (R2NH) with trichlorosilane to form (R2N)3SiH and 3R2NH.HCl salt. Similarly, Radhamani II describes reacting dicyclohexylamine with trichlorosilane to form tris(dicyclohexylamino)silane and dicyclohexyamine.HCl salt. Both reactions are conducted at a temperature near room temperature under a nitrogen atmosphere using a benzene/n-hexane mix as the solvent. The benzene and n-hexane solvents were purified via distillation and dried via sodium wire prior to use within the reaction.
Accordingly, there is a need in the art to provide a process for the production and for the purification of the aminosilane bis(tertiary-butylamino)silane. There is also a need in the art for a safe industrial and cost-effective process to make and purify the aminosilane compound bis(tertiary-butylamino)silane at a high yield, less cycle time, lower process temperatures, less volatility, and in a single reaction vessel. It is thus surprising and unexpected to produce the aminosilane compound bis(tertiary-butylamino)silane compounds at relatively high yields, lower process temperatures, and without the need for a solvent.
All references cited herein are incorporated herein by reference in their entirety.