Fabrication And Synchrotron Radiation Study Of Hf-based High-k Gate Dielectrics On Novel Substrates

In recent decades,in order to continue the miniaturization of complementary metal-oxide-semiconductor?CMOS?devices,it has become an undoubted trend on the replacement of traditional SiO₂ gate dielectrics by high-k oxide.On the other side,a new requirement for channel materials with enhanced carrier mobility has been raised,with the rapid improvement of the device and integrated circuit?IC?performance.As the hole mobility is far lower than the electron mobility,Silicon channel materials are unsuitable for high speed devices with high performance.Therefore,novel substrates as the channel materials are required.Research on Hf-based high-k gate dielectrics,especially systematic study combined with novel channel materials,is of great significance and application prospects in microelectronics industry.Hafnium oxide?HfO₂?has been considered as one of the most promising candidates for an alternative gate insulator,due to its reasonably high dielectric constant,relatively large band gap,large band offsets on Si?1.5 and 3.4 eV in the conduction and valence bands,respectively?.However,some issues to resolve are known for HfO₂ thin films,such as the low crystallization temperature?⁴00??,the formation of the interfacial layer between Si substrates and the films,the instability of the threshold voltage(V_th)and increased gate leakage caused by the low carrier mobility.It is reported that the introduction of La into HfO₂ not only raises the crystallization temperature?>900??without lowering the permittivity?>20?,but also suppresses the Fermi level pinning.The use of a compressively strained Si₁-xGe_x surface channel may serve as a solution against the high-k material induced carrier mobility degradation because of its higher hole motility and electron motility values.Moreover,it has good compatibility with Silicon process.Thus,the strained Si₁-xGe_x based CMOS-FETs have attracted people's concern and attention in recent years.In this paper,the research is focused on the ULSIC?Ultra large scale integration circuit?key materials-high k gate dielectrics.Fabrication and Synchrotron Radiation study of Hf-based high-k gate dielectrics on novel substrates has been carried out.Based on the principle of combining preparation of materials/devices,microstructural characterization with performance test and analysis,this paper emphasizes on studying the interfacial properties and energy band alignment of Hf-based high k/semiconductor substrate interface.The aim of this study is to develop the new high k preparation technology with own intellectual property rights,and realize the control of doping elements and optimization of the material system.Furthermore,core devices based on high-k material system are developed.The electrical properties are evaluated and investigated,especially for the device reliability in aspects of constant voltage stress?CVS?and total ionizing dose?TID?radiation.The main research context is as follows:1.Based on the advantages of dual-ion energetic particle beam deposition and atomic layer deposition,the Hf-based high-k dielectric films?doped with La/N?are prepared on Si and SiGe substrates by DIBSD and PEALD techniques,respectively.The effect of the assisted ion bombardment on interfacial characteristics,surface roughness,dielectric property,and leakage current characteristics of HfLaON/Si are investigated.For the HfO₂and HfLaO prepared by ALD,systematic investigations are conducted on the surface roughness and microstructure,interfacial characteristics,electrical property and energy band alignment.In particular,the unique synchrotron based x-ray absorption fine structure?XAFS?technique is employed to probe the local structures?especially the average coordination of the oxygen?of HfO₂ and HfLaO films.Quantitative information such as the bond distance,coordination number of the neighboring atom round the Hf atom is extracted from the fitted spectra.2.The interfacial characteristics and energy band alignment of ultra-thin HfLaO/Si and HfLaO/SiGe with and without thermal annealing treatment,respectively,are studied.Systematic investigations are conducted on the surface roughness and microstructure,interfacial components and chemical states of HfLa O/Si and HfLaO/SiGe systems,by using TEM and XPS.The band alignments of HfLaO/Si and HfLaO/SiGe with and without annealing treatment are investigated by valence-band spectra for band offset properties using XPS.Parts of the annealed specimens are fabricated into Pt/HfLaO/SiGe/Si/Al MOS capacitors for the electrical characterization,in order to investigate the leakage current property of HfLaO/Si and HfLaO/SiGe systems.The results indicate that,high temperature annealing treatment can aggravate diffusion and interfacial reaction of HfLaO/Si and HfLaO/SiGe systems.For HfLaO/SiGe system,the VBO value is higher than that of the HfLaO/Si system,regardless of the annealing condition,which is good news for SiGe applications.3.The effect of NH₃ plasma passivation on the surface roughness and microstructure,interfacial components and chemical states between ultra thin HfLaO and strained SiGe substrate has been investigated,in terms of HRTEM,AES,XPS,and XAFS,respectively.The band alignments of HfLa O/Si Ge with and without NH₃ plasma passivation are investigated by valence-band spectra for band offset properties using XPS.A partial of the annealed specimens are further fabricated into Pt/HfLaO/SiGe/Si/Al MOS capacitors for the electrical characterization,in order to investigate the leakage current property of HfLaO/SiGe system.The results indicate that,the passivated interfacial layer with N-Hf,La-N,and N-Si/Si-O-N bonds acts as a barrier layer against interdiffusion of Ge,Si,O,Hf,and La,during annealing in some degree,thus improving the interfacial quality.Moreover,the nitrided capacitor after PDA shows a lower?by 2 factors?leakage current density,and larger VBO value than that of the un-nitrided capacitor,which would make HfLaO/SiGe with NH₃ plasma nitridation more suitable for the fabrication of p-channel MOSFETs.4.The electrical evaluation and characterization on Hf-based high-k related core devices are conducted focused on the device reliability under CVS and TID radiation.The characteristics of charge trapping during CVS in MOS capacitors with ultrathin HfO₂ gate dielectric have been investigated.The reliability characterization of stress-induced charge trapping is also studied.The results indicate that,the positive charges are induced in the insulator rather than charges originating due to a change in interface state densities under CVS.The dominant positive charge trapping mechanism in HfO₂ gate dielectric is hole trapping and anode hole injection?AHI?.At low field,charge conduction mechanism is considered as the direct tunneling compared to the trap-assisted tunneling?DT+TAT?.For high field region,the mechanism is the Fowler-Nordheim?FN?tunneling.On the other side,the ⁶⁰Co?-ray TID radiation effects are evaluated for PD SOI MOSFETs.T-gate Body contact?TB?and H-gate Body contact?HB?SOI MOSFETs are used here in the experiments,the two structures are designed to suppress the floating body effect in SOI devices.The results indicate that,there is nearly no dependence of TID-induced V_th shift on W/L of device.The radiation induced leakage current is clearly observed for TB NMOS after 1 Mrad radiation.For the devices with larger W/L,the radiation induced leakage current increases more greatly.Moreover,the large gate bias during radiation leads to more hole trapping in gate oxide and the enhanced leakage current.