Differences in HF Wet Etching Resistance of PECVD SiNx:H thin films

Hydrogenated silicon nitride (SiNx:H) thin films are deposited by plasma-enhanced chemical vapor deposition (PECVD) using different gas mixtures of SiH4+NH3+N2 or SiH4+N2 and plasmas conditions. Resulting differences in terms of overall film composition are herein associated with wet etch rate (WER) in hydrofluoric acid (HF). Different acid concentrations, as well as etching temperatures, have been investigated and it is demonstrated that not only hydrogen but also the oxygen content of nitride have a strong impact on film chemical resistivity. The role of annealing of nitride layers is also studied in terms of wet etching response and further elucidates the role of crystalline structure and chemical evolution of oxidized components on HF nucleophilic attack mechanism. Samples have been characterized by Field Emission-Scanning Electron Microscopy (FE-SEM), X-rays Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FT-IR), and X-Ray Diffraction (XRD). The WER is measured by implementing a fast and straightforward FT-IR data treatment.