Fabrication And Properties Study Of Novel La_xAl_yO High-k Gate Dielectric Thin Films

Since the late 1980s,the semiconductor industry has been succeeding due to the complementary metal-oxide-semiconductor?CMOS?integrated circuit technology.The main reason for this success is due to the features of the complementary metal oxide semiconductor field effect transistor?CMOSFET?that are its low power consumption,high speed of operation and its performance enhancement over the past years following the Moore's Law of scaling.Gate dielectrics have traditionally been fabricated using SiO₂which acts as the insulator between the channel and the gate electrode.But as the scaling continues,Si O₂ has been reduced to only a few atomic layers.At this thinness,SiO₂ ceases to behave as an insulator and tends to leak current through it which is the direct tunneling of electrons through the dielectric layer.Hence it has become necessary to replace SiO₂with some other material.This is where the high-k materials come into play.In contrast to others techniques,atom layer deposition?ALD?is based on self-limiting film growth via alternate saturative surface reaction.Therefore,the films deposited by ALD have high purity,density and accurate thickness.Furthermore,compared to traditional techniques,the deposition temperature can be set between 200°C and 400°C by ALD.These qualities make the ALD method attractive for manufacturing of future generation integrated circuits especially,gate dielectric applications.In this dissertation,the optimized processing parameters of LaAlO₃ film deposited by ALD have been researched.Furthermore,La_xAl_yO films of different structures and oxidants have been discussed.1.The influence of deposit processing parameters such as precursor heating temperature,deposition temperature,pulse/purge time of precursor and pulse/purge time of oxidant on the growth rate of La₂O₃ and Al₂O₃ films are discussed.The growth rate of La₂O₃ film is0.07nm/cycle while H₂O is used as oxidant and precursor heating temperature set as 180^oC,pulse and purge time of precursor set as 0.3 and 4s,pulse and purge time of H₂O set as 0.3and 8s.Growth rate of La₂O₃ film is 0.1nm/cycle while O₃ is used as oxidant and pulse and purge time of precursor set as 0.5 and 8s,pulse and purge time of O₃ set as 0.5 and 10s.Growth rate of Al₂O₃ film is 0.1nm/cycle while H₂O is used as oxidant and pulse and purge time of precursor set as 0.1 and 3s,pulse and purge time of H₂O set as 0.1 and 4s.Growth rate of Al₂O₃ film is 0.1nm/cycle while O₃ is used as oxidant and pulse and purge time of precursor set as 0.1 and 3s,pulse and purge time of O₃ set as 0.5 and 4s.Furthermore,the best temperature window for deposition of LaAlO₃ obtained which between 270^oC and320^oC.2.La_xAl_yO films deposited by different pulse ratio of precursors are observed.The k value of film increases and EOT of film decreases with increasing the La/Al precursor pulse ratio.Due to the increasing content of La for film,the k value of film reached a maximum and EOT of film reached a minimum while the ratio of La and Al precursor is 3 to1.Under this circumstances,the La/Al/O ratio of sample fits the stoichiometric LaAlO₃ composition?1:1:3?better,and this result is close to the standard value.Moreover,the influences of RTA on the physical and electrical characteristics of different deposition sequences of La₂O₃/Al₂O₃/Si and Al₂O₃/La₂O₃/Si films are investigated.First of all,the content of C and N impurities is low and surface uniformity is perfect for La₂O₃/Al₂O₃/Si and Al₂O₃/La₂O₃/Si films deposited by ALD.Secondly,the dielectric constant,EOT,electrical properties,and stability of Al₂O₃/La₂O₃/Si films are enhanced during RTA process.Dues to the diffusion of La atoms and the hygroscopicity of La₂O₃ film,the EOT increased and the dielectric constant decreased of La₂O₃/Al₂O₃/Si film after annealing.Furthermore,the characteristics of La₂O₃/Al₂O₃/Si films are superior to characteristics of Al₂O₃\La₂O₃\Si before and after annealing according to the values of EOT and dielectric constant.Overall,the formation of complicated interfacial layer has had a bigger influence on the whole property of Al₂O₃/La₂O₃/Si films;the formation of La?OH?₃ that exposing to the air long time and during RTA process has had a bigger influence on the whole property of La₂O₃/Al₂O₃/Si film.3.La_xAl_yO nanolaminate films with different structures and oxidants were deposited on Si substrates by ALD.Dues to the kinetic and thermodynamic stability on Si,furthermore,Al₂O₃ barrier layers can restrain the interdiffusion of La,O and Si atoms and making films possess superior performances.The La_xAl_yO films that Al₂O₃ used as a barrier layer with H₂O and O₃ used as oxidants possessed the highest k value?18.90 and 20.83?and the smallest EOT?3.13 and 2.67?comparing to the films which the substrate treated with HF-diluted and SiO₂ used as barrier layer.Moreover,compare to the H₂O-based La_xAl_yO films,values of dielectric constant,EOT and hysteresis voltage showed better superiority that O₃ are used as oxidant.Furthermore,LaAlO₃ films with single and mixed oxidants deposited by ALD are observed.The changes of concentrations of C and N impurity are analyzed by XPS.In summary,the La_x Al_yO film grown with O₃ as the oxidant generates lower C impurity level and higher N impurity level than the films grown using H₂O.Thermal annealing reduces the C and N impurity concentrations and improves the characteristics of La_xAl_yO films,especially the refractive indexes and the dielectric constants and that the oxidants each have a small influence on the stoichiometry of La_xAl_yO film,except the C and N impurities.Contents of La?OH?₃ and La silicate from interface layer improved after annealing analyzed by XPS.In summary,films grown with mixed oxidants possess excellent property compare to the film that H₂O is used as oxidant.However,properties of films grown with O₃ oxidant are the best before and after annealing.