Tructure And Properties Of Ta Or La Doped HfO₂Thin Films

The materials with high dielectric constant (high k) play a vital role in different kinds of dielectric materials. HfO2probably substitutes SiO2and becomes the new type of high k gate dielectric due to the relatively high dielectric constant, relatively high band gap and excellent thermal stability. But the crystallization temperature of pure HfO2thin film is relatively low (range400-600℃). The crystallization of HfO2gate dielectric thin film is not good for the device properties. In recent years, in order to enhance the crystallization temperature of HfO2thin film, the study and research of gate dielectric thin films with multielement-HfO2based material are obtained more and more attention.In this work, both HfTaO and HfLaO thin films are prepared by reactive radio-frequency magnetron sputtering. The HfTaO thin films with different [Ta]/[Hf+Ta] atomic ratios (0-72%) are deposited through modulating powers of Ta target and fixing the power of Hf target. Meanwhile, the HfLaO thin films with different [La]/[Hf+La] atomic ratios (0-37%) are prepared through adjusting powers of La target and with a fixing power of Hf target. The component, structure, surface morphology, thermal stability and optical properties of all these thin films are characterized by X-ray fluorescence (XRF), Electron Probe X-ray Microanalysis (EPMA), X-ray diffraction (XRD), atomic force microscope (AFM) and ultraviolet-visible spectrophotometer. The results are as follows. For HfTaO thin films, when the amount of Ta doping increases, the film structure varies from monoclinic phase (Ta:0-3%) to amorphous phase (Ta:3-72%). After high-temperature annealing, the film structure varies from monoclinic phase (Ta:10%) via Hf6Ta2O17orthorhombic phase (Ta:26%and50%) to amorphous phase (Ta:72%). The crystallization temperature for HfTaO thin films with Ta content of10%,26%,50%is800℃,900℃and950℃, respectively. The thermal stability of HfTaO thin films is obviously better than that of pure HfO2thin films. The refractive index increases with the increase of Ta content. While the optical band gap decreases with the increase of Ta content. For HfLaO thin films, when the amount of La increases, the film structure varies from HfO2monoclinic phase (La:0%) via La2Hf2O7cubic phase (La:17%) to amorphous phase (La:25-37%). After high-temperature annealing, the structure of thin films is La2Hf2O7cubic phase (La:17-37%). The crystallization temperature for HfLaO thin films with La content of25%,33%,37%is850℃,900℃and950℃, respectively. The thermal stability of HfLaO thin films is also obviously better than that of pure HfO2thin films. With the increase of La content, both the average surface roughness and the optical band gap of thin films decrease. The optical band gap values are5.96eV (HfO2),5.90eV (La:17%),5.87eV (La:25%),5.80eV (La:33%) and5.77eV (La:37%), respectively.