Study And Fabrication Of Silicon-based Negative Capacitance Field-effect Transistors

With the development of Moore's law,the number of the transistors on the unit area increases with the device size reduction and process optimization,which makes the the power consumption becomes seriously.How to improve the performance of the device while ensuring the reliability of the device has encountered serious challenges.More and more people are working to obtain the Steep Subthreshold Swing,improve the switching speed of the device and reduce the power consumption of the device.In this context,a negative capacitance field effect transistor?NCFET?with a ferroelectric material as a gate dielectric was proposed.As the NCFET can break down the physical limit of the sub-threshold swing of the conventional MOS device to 60mV/decade,and can achieve a low working voltage?such as less than 0.5V?,good switching performance,high on state current,and compatibility with the CMOS technology,which has attracted wide attention.At present,the traditional ferroelectric materials such as BaTiO₃,P?Zr,Ti?O₃?PZT?,P?VDF-TrFE??PVDF?,etc.,are widely researched.But these ferroelectric material is not compatible with the traditional CMOS process,so they are still limited in the future applications.2011,T et al.,found that the doped HfO₂ materials exist ferroelectricity,this material can avoid process of incompatible problems,therefore received widespread attention.HfO₂ doped Zr element can show ferroelectricity in large scale,so the Hf_1-xZr_xO₂?HZO?materials in the field of ferroelectric memory and ferroelectric transistor has great application prospect.Therefore,with HZO ferroelectric thin film as the research object,we studied its material properties and the electrical properties of the corresponding NCFET devices in this paper.The details are as follows:?1?Hf_1-xZr_xO₂ thin film with different Zr composition were grown by PEALD.The XRD results show that the 10 nm Hf_0.5Zr_0.5O₂ film exist a peaks at 30.5°after annealing,and showing a mixed phase of tetragonal?011?/orthorhombic?111?/cubic?111?.The existence of orthorhombic evidence of the ferroelectricity of Hf_0.5Zr_0.5O₂.AFM test results show that the root mean square roughness of Hf_0.5Zr_0.5O₂ thin film increases with the annealing temperature,it can be seen that HZO starts to crystallize after annealing,and the grain size gradually becomes larger as the annealing temperature increases.In addition,the band alignment for Hf_1-xZr_xO₂/Si with different Zr composition of 0.3,0.4,0.5,0.6,0.7,1 were also analyzed by XPS.The results show that the band gap of Hf_1-xZr_xO₂ films increases with the increasing of Zr components,and the valence band offset increases with the increasing of Zr components,while the conduction band offset decrease with the decreasing of Zr component.Also,the band offset can both over than 1 eV,which could effectively inhibit the leakage current.?2?The electrical properties of the MFM?Metal/Ferroelectricity/Meta?structure and the MFS?Metal/Ferroelectricity/Si?structure with H_0.5Z_0.5O₂ thin film were studied.From the P-V characteristics curve of the MFM structure,it can be seen that the remanent polarization 2Pr of the HZO film increases first and then decreases with the increasing of the annealing temperature.At 550?,the 2Pr of the 20 nm,30nm samples is 31.3?C/cm²and 26.9?C/cm²,and the coercive electric field E_C increases monotonously with the increasing of the annealing temperature.At the same time,it was also found that both the2Pr and the E_C of the HZO film increased as the test voltage increased.The results of the C-V characteristics of the MFM structure show that the dielectric constant of the HZO film increases first and then decreases when the annealing temperature increase,and reaching a maximum value at 550?,the max dielectric constant of the 20 nm sample is 36.5,and 30nm sample is 28.3.The results of the MFS structures processed by different methods show that a high temperature RTP annealing can form a high performance SiO₂ passivation layer on the surface of the Si substrate,and a better interface between the Si and HZO films can be obtained.?3?Si NCFET device was fabricated with Hf_0.5Zr_0.5O₂ thin film as gate dielectric.A device with a channel length of 5?m achieves a sub-threshold swing of 61mV/decade after annealing,close to the physical limit of an ideal MOS device of 60mV/decade,and a negative differential resistance appears in the input and output characteristics of the Si NCFET.The characteristics of the negative capacitive device,compared with Si MOS,increase the output current of the Si NCFET by 38%,and a sudden increase in capacitance is observed in the C-V characteristic curve.These phenomena all prove that the HZO film has ferroelectric and negative capacitance effects.At the same time,we also summarized the performance of devices with different channel sizes.As a result,it was found that as the channel size increases,the gate leakage current density of the device increases,the output current decreases,and the switching performance decreases accordingly.