Studies On The Gate Dielectric And Resistance Switching Performances Of La-based High-k Materials Deposited By ALD

The semiconductor industry has been developing steadily as predicted by Moore's law in the past few decades.The traditional SiO₂ dielectric has been thinned to the thickness of several atomic layers,leading to high gate leakage current due to the direct tunneling effect.The large gate leakage current desity brings in unacceptable static power consumption and serious reliability problems.In this case,it is necessary to introduce insulating gate dielectric materials with higher dielectric constant than SiO₂ to the integrated circuit,to ensure that the gate oxides can obtain enough physical thickness to reduce gate leakage current and static power consumption with the scaling down of the equivalent oxide thickness?EOT?.Among most high-k dielectric materials for gate oxide applications,La-based high-k dielectric films are considered to be one of the most promising high-k dielectric materials for integrated circuits because of their large dielectric constant,large band gap and suitable band offsets with Si or Ge substrates.In the post-Moore era,the development of the integrated circuit technology tends to be application-driven.For the microelectronic devices used in different fields and directions,the requirements of semiconductor insustry are no longer to simply improve the integrated degree and dimension of chips.Recently,due to its simple structure,high storage density,high speed of reading/writing and good endurance,resistive random access memory?RRAM?devices have been becoming one of the alternatives for the next generation of the non-volatile memory.Similar to most high-k metal oxides,La-based high-k dielectrics exhibit resistance switching characteristics by changing the applied voltage of metal-insulator-metal?MIM?structure.In this dissertation,the physical,chemical and electrical properties of La-based high-k dielectrics deposited by atomic layer deposition?ALD?for the application of gate insulator film in MOSFETs and resistive switching layer in RRAM devices are investigated.The main contents and achievements of this dissertation are outlined as follows:1.Amorphous La_x Al_yO films were grown on n-type Ge substrates by ALD method using O₃ and H₂O as oxidant,respectively.A comparison of the XPS results indicate that a thicker interfacial layer with the component of LaGeO_x and GeO_x is formed at O₃-based La_xAl_yO/Ge interface,causing lower band gap value as well as the conduction band offset?CBO?value relative to Ge substrate for O₃-based La_xAl_yO film,with a concomitant degeneration in the interfacial properties.In contrast,for the O₃-based film,the leakage current of over one order of magnitude more than that of H₂O-based La_xAl_yO film is obtained.All the results indicated that H₂O is a more appropriate oxidant for improving the interfacial properties in the atomic-layer-deposited La_xAl_yO dielectric on Ge.However,as for the Si substrate,benefiting from the excellent performance of SiO₂/Si interface,the O₃-based La_xAl_yO film gains higher band offsets with Si substrate,causing lower gate leakage current density.2.The effects of different annealing ambients on the physical and electrical properties of La_xAl_yO films grown by atomic layer deposition are investigated.After the deposition of La_xAl_yO films,post-grown rapid thermal annealing?RTA?is carried out at 600°C for 60 s in N₂ and O₂,respectively.It is found from the X-ray photoelectron spectroscopy?XPS?results that the formation of interfacial layer with the component of LaGeO_x and GeO_x is enhanced during the RTA process.For the sample annealed at O₂ ambient,the oxygen-enriched conditions suppress the desorption from GeO₂ to volatile GeO,and the Ge sub-oxides are oxidized to GeO₂,improving the interfacial properties.The k values of LaGeO_x and GeO_x are much lower than that of La_xAl_yO,resulting in the decrease of the k value for La_xAl_yO film,especially in O₂ ambient.Besides,based on the capacitance-voltage?C-V?characteristics of Al/La_xAl_yO/Ge metal-insulator-semiconductor?MIS?capacitors,the negative flat band voltage(V_FB)shift is observed originating from the existence of effective positive oxide charges for the as-grown La_xAl_yO film.After the post-deposition annealing?PDA?process,benefiting from the decrease of defects,positive V_FB shifting tendency could be observed,and the gate leakage current and breakdown characteristics are improved.Compared with the as-grown sample,almost one order of magnitude decrease in the gate leakgate current density is achieved after annealing treatment in O₂ ambient.3.The impact of La₂O₃ passivation layers on the interfacial properties of Ge-based MIS structures is investigated.It is proven that the formation of a thermodynamically stable LaGeO_x component by incorporating a La₂O₃ interlayer into the interface of Al₂O₃and Ge substrate could effectively suppress desorption of the interfacial layer from GeO₂ to volatile GeO.The volatilization of GeO would bring in interface traps?such as defects and dangling bonds?.Thus,the suppression of GeO desorption contributes to the decrease in oxide trapped charges and interfacial traps in the bulk of the gate insulator,or the nearby interfacial regions in the Al₂O₃/La₂O₃/Ge structure.Consequently,the hysteretic behavior of the dual-swept C-V curves and the frequency dispersion of multi-frequency C-V curves are remarkably weakened.Besides,more than one order of magnitude decrease in the gate leakage current density and higher insulator breakdown electric field are obtained after inserting a La₂O₃ passivation layer.4.Effects of the La₂O₃ passivation layer thickness on the interfacial properties of high-k/Ge interface are investigated systematically.In a very thin range?0¹5 cycles,approximately 0¹.3 nm?,the increase of La₂O₃ passivation layer deposition cycles improves the surface smoothness of HfO₂/La₂O₃/Ge structures.The transmission electron microscope?TEM?results for the interfaces exhibit that the HfO₂ films show different crystallization behaviors for the HfO₂/Ge and HfO₂/1.3 nm La₂O₃/Ge structures,indicating that 15 ALD cycles of La₂O₃ passivation layer could effectively suppress the Ge outdiffusion to gate oxides.The C-V characteristics of Al/HfO₂/La₂O₃/Ge MIS capacitors show that the thickness of La₂O₃ passivation layer can affect the shift of V_FB,hysteretic behaviors,and the shapes of the dual-swept C-V curves.Moreover,the k values of HfO₂/La₂O₃ stacks increase with the increase of La₂O₃ passivation layer thickness.However,anomalous humps in the weak inversion region of C-V curves and the interface trap density(D_it)values extracted by conductance method and single-frequency approximation method indicate that a 5 ALD cycles of La₂O₃ passivation layer brings in extra defects at the interface,deteriorating the interfacial properties.With the further increase of La₂O₃ ALD cycles,the improvement of LaGeO_x component on the interfacial properties of MIS devices plays a more and more leading role,ameliorating the C-V,gate leakage current and breakdown characteristics of Ge-based MIS capacitors5.Resistive random access memory?RRAM?devices are designed using Al₂O₃/La₂O₃/Al₂O₃ multi-stacked films grown by atomic layer deposition as functional layers.The impact of Al⁺ions implantation on the resistive switching performances of the RRAM devices is investigated.Compared with the control sample without Al⁺implantation,forming-free operation,more concentrated switching threshold voltage distributions and larger ON/OFF resistance ratio are achieved in the Al⁺implanted RRAM device.Besides,the resistive switching stability and electrical uniformity of the implanted device are enhanced.The enhanced performances of the Al⁺implanted RRAM device are deduced by the improvement in the formation and disruption of conducting filaments in the Al₂O₃/La₂O₃/Al₂O₃ multi-stacked films.