Rf discharge dissociative mode in NF₃ and SiH₄

This paper shows that the rf capacitive discharge in NF₃ and SiH₄ can burn in three possible modes: weak-current α-mode, strong-current γ-mode and dissociative δ-mode. This new dissociative δ-mode is characterized by a high dissociation degree of gas molecules (actually up to 100% in NF₃ and up to 70% in SiH₄), higher resistivity and a large discharge current. On increasing rf voltage first we may observe a weak-current α-mode (at low NF₃ pressure the α-mode is absent). At rather high rf voltage when a sufficiently large number of high energy electrons appear in the discharge, an intense dissociation of gas molecules via electron impact begins, and the discharge experiences a transition to the dissociative δ-mode. The dissociation products of NF₃ and SiH₄ molecules possess lower ionization potentials, and they form an easily ionized admixture to the main gas. At higher rf voltages when near-electrode sheaths are broken down, the discharge experiences a transition to the strong-current γ-mode.