UCLA

In semiconductor manufacturing, safety concerns regarding the use of highly reactive precursors, which are volatile and pyrophoric by nature, arise from potential energetic reactions in the downstream exhaust lines of deposition reactors. Mishaps have been reported in the recent decade when an excess of unreacted precursors or pyrophoric byproducts reacts among themselves or with other gases. In order to reduce risks and develop a mitigating strategy for a safe working environment, it is imperative to have a comprehensive understanding through monitoring of the reactions, formation, and accumulation of hazardous compounds in the utilized tools. This study evaluates silane chemistry for plasma-enhanced chemical vapor deposition (PECVD) and trimethyl aluminum and tetrakis (dimethyl amido) hafnium chemistries for atomic layer deposition (ALD) using in-situ and ex-situ Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) techniques to support safety measures during semiconductor processing. In the PECVD downstream exhaust line, the use of silane, nitrous oxide, and ammonia resulted in an averaged mass accumulation of 0.15 mg per hour of silane at a flow rate of 20 sccm. The FTIR analysis indicated O-H and Si-OH stretching vibrational nodes, and their signals intensified with the accumulated deposits. Combining with the Si-O bonds observed by XPS analysis, the formation of silanol, which is unstable, flammable, and toxic, is indicated. In the ALD downstream exhaust line, the use of trimethyl aluminum, tetrakis (dimethyl amido) hafnium, and water resulted in an averaged mass accumulation of 0.20 mg per hour of hafnium precursor gas with a 0.25 second pulse per cycle at 20 sccm. The FTIR analysis was unable to distinguish absorbance peaks of Al-OH and Hf-OH contributing to metallic hydroxide. However, the observed deposition is unlikely from aluminum precursor, based on XPS analysis, which showed the atomic composition of hafnium hydroxide and oxide increased with increasing processing time, but Al 2p features were not observed. Since metal hydroxides have highly exothermic reactions with low flash points and auto ignition temperatures, byproducts can act as unforeseen ignition sources, and their formation should be minimized. This study emphasizes the inherent safety problems in semiconductor fabrication, particularly those associated with the use of volatile and pyrophoric precursors in deposition reactors. A buildup of unstable, flammable, and toxic silanol was observed in the PECVD system, while metal hydroxides with exothermic properties formed in the downstream of the ALD tool. This monitoring result established insight into understanding compositions in the exhaust line, enabling prospects for designing ways to reduce safety hazards and provide a safe working environment.