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

摘要

Thin HfO_(2) films have been deposited on silicon via atomic layer deposition using anhydrous hafnium nitrate Hf(NO_(3))_(4). 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 NO_(3) and NO_(2) moieties from the nitrate precursor. Residual nitrates were desorbed by anneals >400℃, however, the films remained oxygen rich. Crystallization of thin films (<10 nm) occurred at roughly 700℃. For films less than ～10 nm thick, the effective dielectric constant of the film and any interfacial layer (neglecting quantum effects) was found to be in the range of k～10-11. From a plot of electrical thickness versus optical thickness, the dielectric constant of the HfO_(2) layer was estimated to be k_(HfO_(2))～12 -14. Leakage current was lower than that of 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 HfSiO_(x)). Excess oxygen in the films may also play a role in the reduced dielectric constant of the HfO_(2) layer.