| Transistor number on integrated circuits doubles since 1965 as Moore’s Law predicted, in the past fifty years, researchers in different fields has been developing the performance of transistors while cutting down the price of a single component. However, the equivalent thickness of the gate dielectric of MOSFET is required to be scaled to around 10? when the technology node comes to 22 nm. At this time, the traditional silicon oxide gate dielectrics cannot meet the need of scaling. The introduction of high-K dielectrics was considered the most promising solution by the semiconductor industry. Higher dielectric constant enables the gate layer to have a thicker physical thickness when the high-k dielectrics was used, solving the problems caused by the traditional silicon oxide gate when it is too thin. In 2007, Hf O2 was introduced to the newest 45 nm product by Intel, and HKMG structure was employed by TSMC in its 28 nm products in the year of 2011. However, the dielectric constant of Hf O2 is still not high enough and it is not high temperature stable, limiting its continuous application in the further production. As this reason, this thesis studies the La2O3 and La-Al-O high-k dielectrics which was considered as the most promising gate dielectrics in the future production. By large amount of experimental and theoretical analysis, this article exhibit conclusions at follows:1. Systematic analysis on atomic layer deposited La2O3 gate dielectric and optimization of the preparation parameters of high quality dielectric was made. It was found that the precursor obtains excessive kinetic energy from the surface of the sample when the deposition temperature is greater than 320 ℃, thus the precursor cannot be effectively adsorbed on the reaction atom, thereby reducing the growth rate of La2O3 gate dielectric. When the deposition temperature is between 260 ℃ and 320 ℃, growth rate turns to be more stable which is chosen as the optimal growth temperature range. When the oxidant Purge Time is less than 5s, the growth rate is too low which decreased the efficient preparation of La2O3/Si O2 gate dielectric structure. When the oxidant Purge Time is greater than 10 s, the growth rate saturates gradually. After rapid thermal annealing for 30 seconds at 800 ℃ in a nitrogen atmosphere, the stairs and hysteresis of the capacitance- voltage characteristics disappeared because the high temperature nitrogen atmosphere eliminated defects at the interface.2. La-Al-O/Si O2 gate dielectric structures with various La/Al atomic ratio were fabricated and characteristics of these samples were studied. Chemical characteristics of La-Al-O/Si O2 gate dielectric structure with various La/Al atomic ratio was analyzed using X-ray photoelectron spectroscopy technology. The study found that the growth rate of La-Al-O/Si O2 increases evidently after the incorporation of Al2O3, higher than the growth rate of a single dielectric material. Using Atomic Force Microscopy technology, it was illustrated that surface roughness of La-Al-O/Si O2 gate structure decreases significantly when Al2O3 was incorporated. La 3d5/2 peak spectral intensity of the XPS results shows that La(OH)3 was generated after the incorporation of Al2O3 in the La-Al-O/Si O2 gate dielectric structures, and the change of growth rate can be also explained.3. Bandgaps of the La2O3 gate dielectric and the La-Al-O gate dielectrics with different La / Al atomic ratio were measured using spectroscopic ellipsometer. It was found that when the dielectric film thickness is larger than 8 nm, the bandgap of the La2O3 dielectric stables at around 5.5e V, the bandgap of the La2O3 dielectric increases as its thickness reduce due to the influence of quantum confinement effect. After high temperature rapid thermal annealing at 800 ℃ for 30 seconds in a nitrogen atmosphere, the bandgap of La2O3 increased slightly, while the influence of deposition temperature was negligible. Bandgap of the La-Al-O gate dielectrics with different La / Al atomic ratio all stabled at around 5.5e V. Finally, by comparing the bandgaps of gate dielectrics with different structure, it was found that small amounts of Al2O3 dielectric incorporation may also greatly increase the bandgap of the La-Al-O dielectrics. |
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