Nucleation and growth of atomic layer deposited HfO2 gate dielectric layers on chemical oxide (Si–O–H) and thermal oxide (SiO2 or Si–O–N) underlayers

A study was undertaken to determine the efficacy of various underlayers for the nucleation and growth of atomic layer deposited ${\mathrm{HfO}}_{\mathrm{2}}$ films. These were compared to films grown on hydrogen terminated Si. The use of a chemical oxide underlayer results in almost no barrier to film nucleation, enables linear and predictable growth at constant film density, and the most two-dimensionally continuous ${\mathrm{HfO}}_{\mathrm{2}}$ films. The ease of nucleation is due to the large concentration of OH groups in the hydrous, chemical oxide. ${\mathrm{HfO}}_{\mathrm{2}}$ grows on chemical oxide at a coverage rate of about 14% of a monolayer per cycle, and films are about 90% of the theoretical density of crystalline ${\mathrm{HfO}}_{\mathrm{2}}.$ Growth on hydrogen terminated Si is characterized by a large barrier to nucleation and growth, resulting in three-dimensional, rough, and nonlinear growth. Thermal oxide/oxynitride underlayers result in a small nucleation barrier, and nonlinear growth at low ${\mathrm{HfO}}_{\mathrm{2}}$ coverages. The use of chemical oxide underlayers clearly results in the best ${\mathrm{HfO}}_{\mathrm{2}}$ layers. Further, the potential to minimize the chemical oxide thickness provides an important research opportunity for high-κ gate dielectric scaling below 1.0 nm effective oxide thickness.