Etching of High-k Dielectric HfO2 Films in BCl3-Containing Plasmas Enhanced with O2 Addition

Etching characteristics of high dielectric constant HfO2 films have been studied in high-density BCl3-containing plasmas without rf biasing. Emphasis was placed on plasma conditions and etch chemistries to achieve a high selectivity over Si and SiO2 and to enhance the etch rates. The HfO2 etch rate was ~5 nm/min at a pressure P0=10 mTorr in a BCl3 plasma, giving a selectivity of >10 over Si and SiO2. At lower P0 ≤6 mTorr in BCl3, the deposition of boron–chlorine compounds BxCly was observed on all sample surfaces of HfO2, Si, and SiO2 to inhibit etching. The addition of O2 to BCl3 was found to suppress the deposition and significantly enhance the HfO2 etch rate, which was ~50 nm/min at P0=5 mTorr in a BCl3/30%-O2 plasma; at higher O2 addition ≥40%, the heavy deposition of boron–oxygen compounds BxOy occurred on surfaces to inhibit etching. The mechanisms underlying the phenomena observed are discussed based on plasma and surface diagnostics.