Ammonia Byproduct Formation in H2/N2 RF Plasma Processes

Michael Gibbons

Ammonia (NH3) is a reactive, caustic compound that can cause operational impacts in semiconductor processing tool exhaust piping through the formation of solid-phase byproducts when mixed with acid gases. This paper identifies that mixtures of hydrogen (H2) and Nitrogen (N2) gases in Radio Frequency (RF) plasma environments could theoretically form ammonia byproducts using Gibbs Free Energy Minimization calculations. Field measurements confirm this theoretical prediction using mass spectrometry to detect the presence of NH3 in the exhaust stream of a processing tool. Tools that utilize RF plasma processes with H2 and N2 as the only input gases should be designed to address the hazards of ammonia in their exhaust system. Vacuum pump and exhaust piping seal materials should be evaluated to ensure appropriate compatibility with NH3. Systems where acid gases are also present may need safeguards for solids deposition and clogging such as pipe heaters or wet scrubbers. Systems that have a risk for nitrate compound formation should be considered carefully to prevent the buildup of energetic ammonium nitrate solids.

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