Hydrocarbon layer formation and removal studies on SiN films etched in halogen/hydrofluorocarbon plasmas

Abstract

Plasma etch residue formation and its removal from silicon nitride (SiN) films deposited at 200°C, 480°C and 700°C is explored. X-Ray Photoelectron Spectroscopy (XPS) measurements showed that SiN contains more nitrogen (N) and less oxygen (O) with increasing deposition temperature. SiN films were etched in an Inductively Coupled Plasma (ICP) reactor in a halogen/hydrofluorocarbon (H:HFC) gas mixture; the carbon (C) containing species in the resulting residue films were studied as a function of the H:HFC ratio in the plasma. Post-plasma etch cleaning methods of the SiN surface were compared, these included: wet treatment with diluted hydrofluoric acid (dHF), sputtering with argon (Ar) plasma, and combined dHF and Ar plasma. After etch, Secondary Ion Mass Spectroscopy (SIMS) and XPS data showed formation of fluorocarbon (FC) films on SiN. FC film thickness after etch was estimated from XPS to reach up to 2 nm. Ultimately the SiN etch rate was shown to drop with increasing deposited C thickness while the lower nitrogen content in the SiN film (i.e. 200°C) led to higher etch rate, which is in good agreement with literature. Ar plasma sputter turned out to be the most effective way of cleaning C residues: C surface content after Ar sputter was reduced to or below the reference data (unetched sample). In terms of wet treatment, an optimized chemistry was identified (AltChem) and post-RIE cleaning was more efficient than dHF in reducing C surface concentrations.