Mechanisms and selectivity for etching of HfO2 and Si in BCl3 plasmas

The authors have investigated plasma etching of HfO2, a high dielectric constant material, and poly-Si in BCl3 plasmas. Etching rates were measured as a function of substrate temperature (Ts) at several source powers. Activation energies range from 0.2to1.0kcal∕mol for HfO2 and from 0.8to1.8kcal∕mol for Si, with little or no dependence on source power (20–200W). These low activation energies suggest that product removal is limited by chemical sputtering of the chemisorbed Hf or Si-containing layer, with a higher Ts only modestly increasing the chemical sputtering rate. The slightly lower activation energy for HfO2 results in a small improvement in selectivity over Si at low temperature. The surface layers formed on HfO2 and Si after etching in BCl3 plasmas were also investigated by vacuum-transfer x-ray photoelectron spectroscopy. A thin boron-containing layer was observed on partially etched HfO2 and on poly-Si after etching through HfO2 films. For HfO2, a single B(1s) feature at 194eV was ascribed to a heavily oxidized species with bonding similar to B2O3. B(1s) features were observed for poly-Si surfaces at 187.6eV (B bound to Si), 189.8eV, and 193eV (both ascribed to BOxCly). In the presence of a deliberately added 0.5% air, the B-containing layer on HfO2 is largely unaffected, while that on Si converts to a thick layer with a single B(1s) peak at 194eV and an approximate stoichiometry of B3O4Cl.