Threshold energy for plasma etching of high-$k$ dielectric HfO$_{2}$ films in BCl$_{3}$-containing plasmas

Plasma etching of high dielectric constant ($k)$ materials is indispensable for fabricating of future high performance ULSIs. This paper presents the dependence of HfO$_{2}$ etch rate on incident ion energy onto a wafer stage, with emphasis being placed on the threshold energy for HfO$_{2}$ etching in BCl$_{3}$-containing plasmas. Experiments were performed in both an electron cyclotron resonance (ECR) and an inductively coupled plasma (ICP) reactor by varying the rf bias power, indicating that the threshold in pure BCl$_{3}$ plasma was $E_{th}\approx $5-14 eV, which is lower than the known $E_{th}\approx $26 eV previously reported. In addition, the threshold was further lowered by adding O$_{2}$ to BCl$_{3}$, where the HfO$_{2}$ etch rate was found to increase more significantly with increasing substrate temperature. These imply that the etching was chemically enhanced by O$_{2}$ addition to lower the threshold, probably because a small amount of added O$_{2}$ reduced the concentration of surface inhibitor species BCl$_{x}$ and increased the concentration of atomic reactant Cl in the plasma [e.g., 2BCl$_{2}$ + O $\to $ BOCl + BCl + 2Cl]. We also investigated reactant and product species therein by using optical emission spectroscopy and quadrupole mass spectrometry, to discuss the etching mechanisms responsible for HfO$_{2}$ etching and their differences in ECR and ICP.