Etching of high-$k$ HfO$_{2}$ films in high-density chlorine-containing plasmas without rf biasing

Plasma etching of high dielectric constant ($k)$ films is indispensable for the fabrication of high-$k$ gate stacks. This paper presents the etching of high-$k$ materials of HfO$_{2}$ in high-density chlorine-containing plasmas excited by electron cyclotron resonance. Experiments were performed with BCl$_{3}$/Cl$_{2}$ mixtures at a pressure of 5 mTorr in the absence of rf biasing; under these conditions, the difference between the plasma and floating potentials was of the order of 10 V. In pure BCl$_{3}$ plasma, some deposition was found to occur on HfO$_{2}$ surfaces to inhibit etching. By adding Cl$_{2}$ to BCl$_{3}$, the deposition was suppressed to result in the etching of HfO$_{2}$. The HfO$_{2}$ etch rate increased with increasing Cl$_{2}$ concentration, giving the maximum HfO$_{2}$ etch rate of about 100 nm/min at 60{\%} Cl$_{2}$. At lower Cl$_{2}$ concentrations of 25-50{\%}, the HfO$_{2}$ etch rate was $>$ 20 nm/min, while the Si etch rate remained almost zero, thus giving a high selectivity of $>>$ 50 over Si. Moreover, by adding a small amount of O$_{2}$ to BCl$_{3}$/60{\%}-Cl$_{2}$ plasma, the HfO$_{2}$ etch rate was found to increase to about 150 nm/min at 5{\%} O$_{2}$, while the Si etch rate was also increased to deteriorate the selectivity over Si down to 4. The addition of Cl$_{2}$ and/or O$_{2}$ to BCl$_{3}$ would increase the concentration of Cl and decrease that of inhibitors BCl$_{x}$ in the plasma. These results were compared with plasma and surface diagnostics, to understand plasma-surface interactions responsible for.