Study on re-sputtering during CNx film deposition through spectroscopic diagnostics of plasma

A nitrogen-carbon plasma was generated during the deposition of carbon nitride (CNx) thin films by pulsed laser ablation of a graphite target in a discharge nitrogen plasma, and the optical emission of the generated nitrogen-carbon plasma was measured for the diagnostics of the plasma and the characterization of the process of CNx film deposition. The nitrogen-carbon plasma was recognized to contain various species including nitrogen molecules and molecular ions excited in the ambient N2 gas, carbon atoms and atomic ions ablated from the graphite target and CN radicals. The temporal evolution and spatial distribution of the CN emission and their dependence on the substrate bias voltage show two groups of CN radicals flying in opposite directions. One represents the CN radicals formed as the products of the reactions occurring in the nitrogen-carbon plasma, revealing the reactive deposition of CNx film due to the reactive expansion of the ablation carbon plasma in the discharge nitrogen plasma and the effective formation of gaseous CN radicals as precursors for CNx film growth. The other one represents the CN radicals re-sputtered from the growing CNx film by energetic plasma species, evidencing the re-sputtering of the growing film accompanying film growth. And, the re-sputtering presents ion-induced sputtering features.