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 (T-s) at several source powers. Activation energies range from 0.2 to 1.0 kcal/mol for HfO2 and from 0.8 to 1.8 kcal/mol for Si, with little or no dependence on source power (20-200 W). These low activation energies suggest that product removal is limited by chemical sputtering of the chemisorbed Hf or Si-containing layer, with a higher T-s 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 194 eV was ascribed to a heavily oxidized species with bonding similar to B2O3. B(1s) features were observed for poly-Si surfaces at 187.6 eV (B bound to Si), 189.8 eV, and 193 eV (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 194 eV and an approximate stoichiometry of B3O4Cl. (C) 2008 American Vacuum Society.