| With the rapid development of semiconductor industry, the traditional SiO2 material has more and more can't meet the request of gate material by the MOS device. While because of its high dielectric constant (high-k) and the advantages of wide band gap of the HfO2 based film, HfO2 has become a hot research topic, and has been widely used in the semiconductor industry to replace SiO2 as a gate dielectric materials. In recent years, it has been reported that HfO2 nanometer film doped with proper elements (such as Al, Si, Y) can be observed significant ferroelectricity. Compared with the traditional perovskite-type ferroelectric material, HfO2 based film has good compatibility with the silicon-based semiconductors, which can be made for non-volatile ferroelectric memory with fast speed and low power consumption.In this paper, the property of hafnium oxide doped yttrium thin films by sol-gel method was researched. The influence of yttrium and film thickness on the phase transformation and electrical performance was main analyzed. Decomposition of the precursor when heating was researched by using thermal gravimetric analyzer (TGA) and differential scanning calorimetry (DSC). X-ray reflectivity measurement (XRR) was used to measure the thickness of the film, and analyze its density and surface roughness. X-ray photoelectron spectroscopy (XPS) measurements were carried out to probe the atomic ratio of yttrium and hafnium as well as the bonding features. With grazing incidence X-ray diffraction (GIXRD) phase analysis was carried out on the film. The polarization-electric field and leakage current density-electric field measurements were performed using the ferroelectric tester to get the dielectric constant of the film and analyze the quality of the film.The results show that for 12.9 nm-thickness film prepared by sol-gel method, yttrium doping amount at 1.75 mol% is a critical transition phase transition point. When yttrium doping amount is less than the critical transition point the film should be monoclinic phase, more than the critical point film transform to cubic phase, and yttrium doping amount is just about 1.75 mol% the film become two phase coexistence. HfC2 films doped 2.50 mol% yttrium exist critical thickness of phase transition phase, the thickness is about 18.4 nm, lower than the thickness thin film is cubic phase, higher than the thickness the thin film transform to monoclinic phase. It indicates that in the case of the film is very thin (reaching nanometer level) a small amount of yttrium doping amount, i.e. introducing a small amount of oxygen vacancy, together with interface energy can make the cubic phase of HfO2 stable at room temperature. The XPS analyses confirm the formation of Hf-O and Y-O bonds and prove that the theoretical and the actual content of yttrium in the film are almost accordant. Film deposited from different cycles has better electrical performance than film preparated from concentrated or diluted precursor. Dielectric constant depends on crystal structure of film. Measured at 1 MV/cm, the leakage current density of film deposited from different cycles is 10-6,10-7 A/cm2 orders of magnitude, further indicating high quality of the thin films derived from aqueous solution precursor. |
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