Transmission electron microscopy studies of HfO2 thin films grown by chloride-based atomic layer deposition
Detailed transmission electron microscopy characterization of Hf02 films deposited on Si(1 0 0) using atomic layer deposition has been carried out. The influence of deposition temperature has been investigated. At 226 oC, a predominantly quasi-amorphous film containing large grains of cubic Hf02 (a0 = 5.08 Ao) was formed. Grain morphology enabled the nucleation sites to be determined. Hot stage microscopy showed that both the cubic phase and the quasi-amorphous phase were very resistant to thermal modification up to 500 oC. These observations suggest that nucleation sites for the growth of the crystalline cubic phase form at the growing surface of the film, rather homogeneously within the film. The films grown at higher temperatures (300–750 oC) are crystalline and monoclinic. The principal effects of deposition temperature were on: grain size, which coarsens at the highest temperature; roughness with increases at the higher temperatures due to the prismatic faceting, and texture, with texturing being strongest at intermediate temperatures. Detailed interfacial characterization shows that interfacial layers of Si02 form at low and high temperatures. However, at intermediate temperatures, interfaces devoid of Si02 were formed.