Study On Key Technology Of Hafnium Oxide-based Ferroelectric Field Effect Transistors

With the development of Si-based CMOS integrated circuits,non-ideal effects such as drain induced barrier lowering and power consumption followed by feature size reduction have become the bottleneck restricting the further development of integrated circuits.In recent years,ferroelectric field effect transistors have attracted considerable interests due to its capability achieving sub-60 m V/decade subthreshold swing.The amazing ferroelectricity observed in hafnium oxide ferroelectric field effect transistors is due to the existence of non-centrosymmetric orthorhombic Pca2₁ phase in hafnium thin films.Besides,semiconductor germanium is considered as a potential channel material for high speed and high performance semiconductor devices for its higher carrier mobility than silicon channel.This dissertation studies the key technologies of hafnium oxide ferroelectric field effect transistors for the requirements of high performance and low power devices in the post-Moore era of integrated circuits.The effects of stress on hafnium oxide system,the surface passivation of germanium and the interface band alignments of hafnium oxide-germanium,the manufacture and characterization of hafnium oxide-based ferroelectric field effect transistor,which emphasize on hafnium zirconium oxygen（HZO）film manufacturing process parameters optimizing and the electrical characteristics characterization of germanium channel field effect transistor are studied.The main research contents and results of this paper are as follows:1.For the origin of ferroelectricity in hafnium oxide-based ferroelectric field effect transistor,the structures of strained orthogonal Pca2₁ phase hafnium are modeled,simulated and analyzed.The effects of different strain types and strains on lattice structure,electron band structure and ferroelectric polarization transition potential energy of ferroelectric hafnium oxide are studied and analyzed.The regulation laws of stress on lattice structure and band structure of hafnium oxide crystal are revealed.And the effects of different strain types and strains on transitions between different polarization states of hafnium oxide are revealed.The results showed that:（1）Orthotropic hafnium oxide crystals exhibit anisotropic Poisson’s ratio.The Poisson’s ratio of lattice constants b and c to elastic deformation due to strain of lattice constants a is 0.2846and 0.1752,respectively（2）The band gap value of hafnium oxide crystals can be modulated by adjusting the energy position of the conduction band by applying stress.From tensile strain to compressive strain,the band gap of hafnium oxide increases first and then decreases.（3）The transition barrier energy from the intrinsic orthotropic hafnium oxide towards the tetragonal phase is 91.2 me V/formula unit,while the reverse transition energy is only 2me V/formula unit.For a strained hafnium oxide crystal,the transition barrier between the two polarized ferroelectric phases decreases when the crystal x axis is subjected to compressive strain or the y axis is subjected to tensile strain.But strain in the direction of polarization increases the transition barrier.2.For the influence of the interface characteristics of germanium on the device performance,the germanium surface structures with different crystal orientation and passivation methods and the interface between hafnium oxide and germanium are modeled,simulated and analyzed.The reconstructed germanium surface structures with different crystal orientation are modeled.The reconstructed surface structures of germanium with different crystal orientation are established.On this basis,the passivation characteristics of different elements and groups on germanium surface are investigated.The interface band alignments between different germanium surfaces and ferroelectric phase hafnium oxide heterojunction are studied.The influence of different passivation methods and crystal orientation on the interface characteristics of germanium and the interface band alignment properties of hafnium-germanium interface are determined.The results show that:（1）Ge（100）surface reconstruction forms the surface dimer structure,and each surface germanium atom has one adsorption site.When the dimer structure is passivated,the germanium atoms on the surface undergo secondary reconstruction（2）The crystal orbital Hamilton population（COHP）analysis shows that the halogen family,hydroxyl and methyl groups form covalent bonds with surface germanium atoms,achieving passivation of germanium surface.（3）The Ge（100）surface reconstruction results in a reduction in the work function from 5.00e V to 4.56 e V.The surface work function of germanium increases with the increase of halogen coverage.The electronegativity difference between halogen and surface germanium and the surface reconfiguration result in the redistribution of the surface charge,thus realizing the modulation of germanium interface characteristics.（4）Both the valence band and conduction band offsets of the Ge（100）and（111）plane-orthotropic hafnium oxide heterojunction are above 2 e V,which can achieve effective carrier restriction3.For HZO thin film field effect transistor,manufacturing process parameters of HZO thin film and transistor are optimized.HZO thin film silicon channel field effect transistors are fabricated.The electrical characteristics of HZO thin film field effect transistor are revealed.The results show that:（1）10 nm HZO thin film devices annealed at 450℃exhibit steep subthreshold swing,negative differential resistance and obvious gate capacitance peak.（2）4 nm and 10 nm HZO field effect transistors achieve zero hysteresis transfer characteristic curve while maintaining a steep subthreshold swing.（3）After 1500 and 10000 direct current tests,HZO film field effect transistors still maintain steep subthreshold swing characteristics4.For the requirements of high performance and low power devices in the post-Moore era of integrated circuits,the negative capacitance characteristics of HZO thin film germanium channel field effect are studied.The metal-HZO film-metal（MFM）three-layer capacitance structure and germanium channel field effect transistors are fabricated and its electrical characteristics are analyzed.The ferroelectric characteristics of HZO thin film are further clarified,and the capacitance characteristics of HZO thin film ferroelectric transistor are revealed.The results show that:（1）The P-V curve and butterfly C-V curve of the counterclockwise loops are tested by the MFM capacitance annealed at 450℃,which confirmed the ferroelectric properties of HZO thin film.（2）The germanium channel field effect transistors annealed at 450℃show steep subthreshold swing,obvious negative differential resistance and capacitance peak,which exhibit typical negative capacitance characteristics.（3）Within the MHz operating range,germanium channel transistors annealed at 300℃,400℃and 450℃show capacitance peak phenomenon.The gate capacitance curve of the devices annealed at 450℃does not decrease with the increase of test frequency.