Reaction mechanisms of atomic layer deposition of TaNx from Ta(NMe2)5 precursor and H2-based plasmas

Abstract

The reaction mechanisms of plasma-assisted atomic layer deposition (ALD) of TaNx using Ta(NMe2)5 were studied using quadrupole mass spectrometry (QMS). The fact that molecule dissociation and formation in the plasma have to be considered for such ALD processes was illustrated by the observation of 4% NH3 in a H2-N2 (1:1) plasma. Using QMS measurements the reaction products during growth of conductive TaNx using a H2 plasma were determined. During the Ta(NMe2)5 exposure the reaction product HNMe2 was detected. The amount of adsorbed Ta(NMe2)5 and the amount of HNMe2 released were found to depend on the number of surface groups generated during the plasma step. At the beginning of the plasma exposure step the molecules HNMe2, CH4, HCN, and C2H2 were measured. After an extended period of plasma exposure, the reaction products CH4 and C2H2 were still present in the plasma. This change in the composition of the reaction products can be explained by an interplay of aspects including the plasma-surface interaction, the ALD surface reactions, and the reactions of products within the plasma. The species formed in the plasma (e.g., CHx radicals) can re-deposit on the surface and influence to a large extent the TaNx material composition and properties.