Dry etching of TaN/HfO₂ gate-stack structure in BCl₃/Ar/O₂ inductively coupled plasmas

In this work, etching characteristics of TaN(200 nm)/HfO₂(80 nm) gate-stack structures on Si substrate were investigated by varying the process parameters such as BCl₃/(BCl₃+Ar+O₂) gas mixing ratio (Q), top-electrode power, dc self-bias voltage (V_dc), and overetch time in an inductively coupled plasma etcher. To understand the role of the etch gas chemistry, we measure the relative changes in the optical emission intensity of ions and radicals in the plasma as well as in the chemical binding states of the etched TaN surfaces. We used optical emission spectroscopy and x-ray photoelectron spectroscopy respectively. The results showed that BCl₃/Ar/O₂ plasma is more effective in etching the oxidized TaN than Cl₂/Ar/O₂ or HBr/Ar/O₂ plasma. It is believed that the B radical species removes the oxygen atoms on the oxidized TaN surface more effectively by forming volatile boron-oxygen-chlorine compounds, such as trichloroboroxin (BOCl)₃), boron oxychloride (BOCl), and boron dioxide. The measurement data also indicated that high etch selectivities of the TaN to the HfO₂ layer could be obtained at the low V_dc, high top-electrode power, and shorter overetch time.