Research On Ga Sb Mosfets And Its Stress Characteristics With High-k Dielectric And Metal Gate Stacks

Moore’s law has been promoting the rapid development of integrated circuit technology for half a century. The feature size of the silicon-based metal-oxide-semiconductor field effect transistors(MOSFETs) keeps scaling down. For nanoscale transistor, however, the power consumption, gate leakage current density and other factors will be bottlenecks of its further performance improvements. Compared to the silicon-based devices, gallium antimonide(GaSb) MOSFETs with high dielectric constant(k) gate dielectric and metal gate stacks can guarantee higher carrier mobility and lower gate leakage current, which helps transistors keep scaling down. In this dissertation, fabrication process, electrical and stress characteristics of GaSb MOSFETs with high-k dielectric and metal gate stacks are investigated systematically.High interface trap density(Dit) between the high-k gate dielectric and GaSb substrates is the bottleneck of the development of GaSb MOSFETs. In this dissertation, different methods to passivate GaSb MOS capacitors are studied. Ozone pretreatment, non-aqueous sulfur pretreatment, aluminum oxide(Al2O3) layer insertion method and self-cleaning method are proposed. Ammonium sulfide solution pretreatment method and the formation of hafnium aluminum oxide dielectric layer method are improved. These methods lower the gate leakage current and Dit of Al2O3/GaSb and hafnium oxide(HfO2)/GaSb MOS capacitors effectively.Based on the proposed passivation mechanism of ammonium sulfide solution on GaSb, process parameters such as concentration, passivation time and pH value of the solution are optimized. Equivalent oxide thickness of 1.67 nm, gate leakage current density of less than 10-7 A/cm2 and Dit of 4.8×1012 eV-1cm-2 have been achieved on HfO2/GaSb MOS capacitor. Gate leakage current density of 1.1×10-8 A/cm2 and Dit of 5.8×1012 eV-1cm-2 have been achieved on Al2O3/GaSb MOS capacitor using the proposed self-cleaning method.Schottky source/drain based and ion implantation source/drain based GaSb MOSFETs are also studied, respectively. A method using silicon nitride film to introduce stress is proposed to enhance the GaSb MOSFET mobility. By introducing compressive stress, a peak hole mobility of 638 cm2/V·s is achieved, an on-state(Ion) to off-state(Ioff) current ratio Ion/Ioff as large as 2526 is obtained, and the subthreshold swing(SS) is determined to be 568 mV/dec.Finally, the mechanism of stress to enhance the mobility of GaSb MOSFETs is studied. Based on density functional theory, the change of carrier effective mass of GaSb material before and after the introduction of stress is calculated by the first principle. Theoretical results show that the larger the deformation induced by the compressive stress is, the smaller the hole effective mass is. Consequently, according to the relationship between the effective mass and mobility, under compressive stress conditions, the larger the deformation is, the larger the hole mobility is. These results are in good agreement with experimental results in this dissertation. The study of this mechanism provides a reference for optimizing device structure and manufacturing process.