Paper PS-MoA8
Comparative Study of ECR and ICP Plasma Etching of High-k Dielectric HfO₂ Films with BCl₃-Containing Gas Chemistries

Monday, October 15, 2007, 4:20 pm, Room 607

Etching of high-k materials is indispensable for their removal in integrating them into device fabrication. Moreover, the high-k etching is required for chamber cleaning of the deposition apparatuses in mass production. This paper presents a comparative study of the etching of high-k HfO₂ films in electron cyclotron resonance (ECR) plasma and inductively coupled plasma (ICP) reactors with BCl₃-containing chemistries, where emphasis is placed on a better understanding on the etching mechanisms concerned. The ECR reactor had a configuration of divergent magnetic fields, and the discharge was established by 2.45-GHz microwave powers of 600 W. The ICP reactor had a three-turn planar coil, and the discharge was established by 13.56 MHz rf powers of 300 W. Feedstock gases were BCl₃, Cl₂, O₂, and Ar at total pressures of 2-20 mTorr with a total flow rate of 40 sccm. The significant differences between ECR and ICP plasmas are: the etching of HfO₂ without rf biasing was obtained in ECR BCl₃-containing plasmas, while was not obtained in ICP; moreover, the etch selectivity HfO₂/Si was >> 1 with no bias in ECR, while was < 1 with bias in ICP. In ECR, the HfO₂ etch rate was increased in order of BCl₃, BCl₃/O₂, BCl₃/Cl₂, and BCl₃/Cl₂/O₂; typically, the HfO₂ etch rate in BCl₃/Cl₂ was ~100 nm/min at ~60% Cl₂ with a selectivity of ~10 over Si, and a high selectivity >50 was obtained at 40-50% Cl₂ with a HfO₂ etch rate of ~50 nm/min. The Langmuir probe measurements indicated that in ECR, the difference between the plasma and floating potentials was of the order of 10 V, which is lower than the threshold ion energy ~26 eV known for the HfO₂ etching in BCl₃ plasmas. In contrast, the HfO₂ etching in ICP occurred with additional rf biasing, where the threshold energy was estimated to be ~ 30 eV from the difference between the plasma potential and dc self-bias voltage; the etch rate increased with increasing rf bias power, being ~50 nm/min with a HfO₂/Si selectivity of ~0.5 at an ion energy of ~100 eV in BCl₃/Cl₂. The gas-phase and surface chemistries responsible for the HfO₂ etching is discussed based on several plasmas and surface diagnostics including OES, QMS, LIF, FTIR, and XPS, to achieve higher etch rate and selectivity under conditions of low ion energies and/or less ions.