Atomic layer deposition of thin hafnium oxide films using a carbon free precursor

Thin ${\mathrm{HfO}}_2$ films have been deposited on silicon via atomic layer deposition using anhydrous hafnium nitrate $[\mathrm{Hf}({\mathrm{NO}}_3{)}_4\mathrm{].}$ Properties of these films have been investigated using x-ray diffraction, x-ray reflectivity, spectroscopic ellipsometry, atomic force microscopy, x-ray photoelectron spectroscopy, and capacitance versus voltage measurements. Smooth and uniform initiation of film growth has been detected on H-terminated silicon surfaces. As-deposited films were amorphous, oxygen rich, and contained residual ${\mathrm{NO}}_3$ and ${\mathrm{NO}}_2$ moieties from the nitrate precursor. Residual nitrates were desorbed by anneals $\text{>400\hspace{0.05em}°}\mathrm{C},$ however, the films remained oxygen rich. Crystallization of thin films $\text{(<10\hspace{0.05em}}\mathrm{nm})$ occurred at roughly 700 °C. For films less than $\text{∼10\hspace{0.05em}}\mathrm{nm}$ thick, the effective dielectric constant of the film and any interfacial layer (neglecting quantum effects) was found to be in the range of $\text{k∼10−11.}$ From a plot of electrical thickness versus optical thickness, the dielectric constant of the ${\mathrm{HfO}}_2$ layer was estimated to be $k_{{\mathrm{HfO}}_2}\text{∼12−14.}$ Leakage current was lower than that of ${\mathrm{SiO}}_2$ films of comparable equivalent thickness. The lower than expected dielectric constant of the film stack is due in part to the presence of an interfacial layer (likely ${\mathrm{HfSiO}}_x\mathrm{).}$ Excess oxygen in the films may also play a role in the reduced dielectric constant of the ${\mathrm{HfO}}_2$ layer.