Investigation Of Hf Based High-k Materials

International Technology Roadmap for Semiconductors (ITRS) has declared the continuous scaling down of advanced CMOS (Complementary Metal-Oxide-Semiconductor) device dimensions. To continue the equivalent oxide thickness (EOT) of gate layer scaling below about 1.5nm, a suitable replacement must be found for SiO₂, the traditional material in the gate region, since any further reduction in thickness of gate would increase the operating current exponentially due to quantum mechanical tunneling. A material that has a higher dielectric constant (k) would allow a thicker thinness to reduce current. Meanwhile, since the threshold voltage is inversely proportional to dielectric constant, the high k material would also reduce the threshold voltage. However, the dielectric constant should not be too high, since the higher k value would generally also reduce the band width, which is harmful for the reduction of leakage current. Additionally, the thermal stability with Si is also a concern problem. Several possible replacements have been identified that form a thermodynamically stable interface with silicon dioxide, the most promising of which are hafnium dioxide (HfO₂). Hafnium-based dielectrics have been widely investigated as potential candidates for the gate dielectric application.The present dissertation basically focuses on the study of the electrical characteristics. Meanwhile, to further understand the Hf-based materials, it also sets foot in the photoluminesence and field emission properties of HfO₂ and HfON. We have brought forward a new HfON-HfO₂-HfON sandwich stack structure using sputtering method, which possesses excellent electrical characteristic comparing a pure HfON or HfO₂ film. Meanwhile, the photoluminescence characteristics of HfON/rare earth and HfON/porous Si were also investigated as well as HfON's field-emission characteristic. The details are presented below:1. The electrical property of Hf-based high k materials. Comparing with a pure HfON or HfO₂ film, the HfON-HfO₂-HfON sandwich-stack structure possesses better electrical characteristics as well as good ability to block oxygen diffusion. Since the fabrication of this sandwich stack is simple and not-introducing any new dopants, it is suitable for the application of semiconductor industry. Its shortcoming is the difficulty for the actual determination of individual layer thickness.Meanwhile, the charge trapping characteristics were identified as a primary issue preventing the introduction of Hf-based materials into CMOS technology, potentially causing the threshold voltage instability and the mobility degradation. Several measurement techniques can be used to study and quantify charge trapping: Capacitance-Voltage (C-V) hysteresis, alternating stress and sense V_FB/V_t instability measurements. By using these measurement approaches on varying physical thicknesses of Hf-based gate dielectric stacks, the impact of interfacial and bulk charge-trapping properties on device performance (i.e., mobility) was investigated.2. The photoluminescence and field-emission characteristics of Hf-based materials. As known, Hf-based material has been well used in many fields. In this dissertation, we also investigated the photoluminescence and field emission properties of Hf-based materials, as well as its high k application. From our experiments, HfON shows good field emission ability and great influence to the enhancement of porous Si and rare earth materials. These characteristics confirm the existence of HfN phase in high k film, which has been used to explain some phenomenon in high k electrical investigation. Furthermore, photoluminescence characteristic is strongly related to the electrical and thermal properties of HfON, to further understand this material, it is necessary to list this section in our thesis.