Reaction mechanisms in patterning hafnium-based metal oxide thin films in halogen-based plasma chemistries.

摘要

The development of an effective and selective plasma etching process is necessary to pattern new gate dielectric materials, such as hafnium-based oxides, for sub45-nm metal oxide semiconductor field effect transistors (MOSFET). As the introduction of new gate dielectric materials increases the complexity of the gate stack etch process, it is critical to formulate a more comprehensive kinetics model to predict the physical and chemical effects of plasma chemistries on these complex gate dielectric materials.;In this work, the reaction mechanism in patterning complex hafnium-based oxides (Hf1-xAlxOy and Hf1-xSi xOyNz) were determined, as they are promising materials for gate oxide replacement due to their high dielectric constant compared to that of SiO2, larger bandgap and higher recrystallization temperature compared to those of HfO2. An electron cyclotron resonance high density plasma reactor was used in this work to study the effect of plasma chemistry and ion energy on the etching rates of hafnium-based oxides with different compositions in chlorine-based chemistries. The electron temperature and ion/neutral compositions were shown to depend strongly on the pressure, power, and the chemistry of gases used in the plasma, and dictate the surface reactions in generating volatile etch products.;Hafnium oxides with varying Al, Si, and N contents were etched in Cl 2/BCl3 plasmas and, in general, the etch-rate scaled with the square-root of ion energy, though the addition of BCl3 significantly enhanced the etch-rate. This was attributed to a change in the dominant ion from Cl2+ to BCl2+ as determined by QMS, and the formation of BCl radicals. The composite oxides were found to etch faster than the hafnium dioxide, and had lower etching threshold energies. The dominant metal-containing etch products were mainly MCI, species, and increased with ion energy. Oxygen was detected removed as ClO and BOxCly in Cl2/BCl3 plasmas. Chlorine and boron were measured on the surface of all films etched in Cl 2/BCl3. At lower ion energies in BCl3, a BCl x deposition layer remained on the surface.;A model was formulated to accurately describe the etching of composite oxide films in complex plasma chemistries involving competing deposition and etching mechanisms. This site balance-based model explains the etch-rate dependence on key plasma parameters including plasma chemistry/condition, neutral-to-ion flux ratio, and ion energy, as well as the film composition. The model fits well to the experimental data demonstrating its validity and potential application to various plasma etching processes.