Laminated Gate Dielectrics Structure Design,interface And Electrical Performance Optimization Of MOS Devices

With the continuous miniaturization of the chip and integration,complementary metal-oxide-semiconductor field-effect transistor（CMOSFET）devices have been scaled down to the nanoscale,and the narrowing always follows the Moore’s Law.The thickness of the SiO₂ gate dielectric layer has been continuously reduced resulting in that the tunneling effect is enhanced and the leakage current is increased exponentially.It is inevitable to use high-k materials to replace SiO₂.The introduction of high-k materials can increase the physical thickness of the gate dielectric film resulting in the decrease in of leakage current.Among the many high-k materials,Hf-based gate dielectric materials are widely used due to their high dielectric constants,wide band gaps,excellent interfaces,and electrical properties.In particular,the rare earth element-doped Hf-based gate dielectrics（such as HfLaO_x,HfDyO_x,HfGdO_x,HfYbO_x）can make up for the defects of a single HfO₂.In addition,the introduction of Hf-based high-k materials will cause the decrease of the carrier concentration of the MOS devices and generating a low-k interfacial layer.To further optimize the device performance,another necessary mean is higher mobility semiconductor material（such as Ge and III-V group compounds）instead of Si.To solve the lattice matching problem between the substrate and the channel layer,the gate dielectric doping and the buffer layer structure were used to build devices of optimize performance.In this thesis,rare earth element Dy-doped HfO₂（HfDyO_x）became the research object of high-k gate dielectrics.The effects of doping concentration and annealing temperature on the interface and electrical characteristics of the HfDyO_x/Ge device are studied.The ALD buffer layer was used to optimize the HfDyO_x/Si device structure.The effects of the laminated gate dielectric structure on high-k/Ge MOS devices performance.The main research contents and innovations are as follows:（1）The effects of annealing temperatures on the microstructure,interface quality and electrical properties of the sputtered Dy₂O₃/Si MOS capacitors were systematically explored.The results show that the annealed Dy₂O₃ films have cubic crystal and the crystallinity of the film have enhanced as the increases of annealing temperature.The Dy-O content of the 600℃annealed sample has been increased and its silicate content was the lowest.It is means that the interface quality of the device was optimized.However,the silicate content at 700℃annealed has been increase suddenly resulted in the decrease of interface quality.The test results show that the proper annealing temperature can promote the self-diffusion of oxygen in gate dielectric film without increasing the interface interdiffusion resulted in the enhancement of interface performance.Electrical analysis shows that the device of the 600℃annealed has the optimizing electrical performance,included the smallest EOT,the largest dielectric constant and the smallest leakage current density.All the results show that the appropriate annealing temperature can promote the self-diffusion of oxygen in the film without increasing the interfacial interdiffusion,which indicates the optimized interface and the enhanced device performance of Dy₂O₃/Si MOS.（2）The effects of ALD HfO₂ and Al₂O₃ passivation layers on the interface chemistry and electrical characteristics of HfDyO_x/Si MOS capacitors were been systematically investigated.The results show that:compared with the ALD Al₂O₃,the ALD HfO₂ interface passivation layer can effectively suppress the HfDyO_x/Si interface diffusion,increased in the conduction band offset and decreased the leakage current.The C-V capacitance characteristics of the device without the passivation layer treatment are poor,and the optimized device after the passivation layer treatment shows a smaller flat-band voltage and hysteresis.The analysis of the leakage current mechanism shows that Schottky emission is dominant in the lower field,and P-F emission and F-N tunneling are in the middle or higher field.Since Schottky emission and P-F emission are related to ambient temperature,so that the F-N tunneling is mainly effective at low temperatures.The analysis shows that the HfO₂ passivation layer can effectively regulate the HfDyO_x/Si interface,improve device performance and reduce power consumption,which shows that is an effective method to promote the production and application of Hf-based gate dielectrics.（3）The effects of doping concentration and annealing temperature on the interface and electrical properties of TMA passivated HfDyO_x/Ge gate stack were systematically investigated.The research indicates that:crystallinity of the HfDyO_x films decrease as the increase of the Dy-doped concentration and increase as the increase of the annealing temperature.Sputtering power of 10 W,HfDyOx/Ge device interface is unstable low-state Ge oxide content is the lowest;Sputtering power of 15 W,HfDyO_x/Ge interface has a significant increase in content of germanate and a reduction in the content of Ge element,which indicates that too high Dy-doped concentration will promote interdiffusion in HfDyO_x/Ge interface and re-diffusion of Ge.The analysis of the annealing treatment shows that the HfDyO_x gate dielectric film（10 W）without annealed has the best capacitance characteristics and the smallest leakage current density.Although high temperature increases the film density to a certain extent,it also promotes the interfacial oxygen diffusion and leads to the formation of a large number of unstable oxides,thereby reducing the interface quality and electrical performance of the device.（4）Based on the ALD technology,the effects of different deposition sequences of HfO₂ and Al₂O₃ laminated gate dielectrics on the interface and electrical performance of Ge-MOS devices were investigated.The experimental results show that compared with the HfO₂/Al₂O₃/Ge double-layer structure,the gate dielectric of the three-layer structure introduces a large amount of oxygen vacancies and interface trap charges,which leads to the decrease in the interface and electrical properties.The HfO₂/Al₂O₃/Ge stack structure device has the best performance,mainly because Al replaces Ge combined with O during the deposition process of ALD Al₂O₃ on Ge substrate,thereby consuming substrate intrinsic oxide;On the other hand,due to the high thermal stability of Al₂O₃ will hinder the interdiffusion between Al₂O₃ and Ge interfaces,optimize the interface and improve performance of device.