Trisilylamine is a useful molecule for use in semiconductor manufacturing. It is stable once produced, but is susceptible to decomposition from excessive reaction conditions and synthesis by products. Dussarrat, et al. U.S. Pat. No. 7,192,626 demonstrated that a stable Silicon nitride film is formed on a substrate by feeding trisilylamine and ammonia into a CVD reaction chamber that contains a substrate.
Wells and Schaeffer (J. Am. Chem. Soc., 88:1, 37 (1996)) discuss a batch method of preparing trisilylamine by the reaction silyl chloride with ammonia. They report the yields of trisilylamine varied depending on the method of mixing and the purity of the reactants. Wells and Schaeffer allowed the reactants to mix in the gas phase by introducing the ammonia from below into a 1 liter bulb containing silylchloride. After introducing the gaseous ammonia very slowly, the reaction bulb and contents were allowed to remain at room temperature for 15 min. Copious amounts of white solid were precipitated on the walls of the bulb as soon as mixing occurred. The product was removed and the trisilylamine recovered. The process yield was about 77% of the theoretical amount of trisilylamine.
In the batch reactor process, all of monohalosilane is charged into the reactor vessel. Batch size is limited by this initial charge and the size of the vessel. Ammonia gas is then very slowly added into the flask. Reaction conditions will vary in the vessel depending on the initial concentrations of monohalosilane and ammonia and the efficiency of turbulent mixing in the vessel. The mixing is affected by vessel size as well as the efficiency of the mechanical mixing device if one is employed. In addition, during the batch process the silylamines produced are in contact with ammonium halide which is also a product of the reaction. Ammonium halides such as ammonium chloride are catalysts and will disproportionate TSA into silane and other degradation products thereby lowering the yield of TSA. The reaction of silyl halide and ammonia produces heat thereby exacerbating the degradation conditions in a closed reactor vessel.
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