Atomic layer deposition of HfO_2: Effect of structure development on growth rate, morphology and optical properties of thin films

摘要

HfO_2 films were grown by atomic layer deposition from HfCl_4 and H_2O on Si(100), Si(111) and amorphous SiO_2 substrates at 180-750 ℃ and the effect of deposition temperature and film thickness on the growth rate and optical properties of the film material was studied. Crystallization, texture development and surface roughening were demonstrated to result in a noticeable growth rate increase with increasing film thickness. Highest surface roughness values were determined for the films deposited at 350-450 ℃ on all substrates used. The density of the film material increased with the concentration of crystalline phase but, within experimental uncertainty, was independent of orientation and sizes of crystallites in polycrystalline films. Refractive index increased with the material density. In addition, the refractive index values that were calculated from the transmission spectra depended on the surface roughness and crystallite sizes because the light scattering, which directly influenced the extinction coefficient, caused also a decrease of the refractive index determined in this way.