Dielectric Properties And Nanomagnetism Of Hfo2Films On Si83Ge17/Si Substrate

With the development of giga scale integration circuits (GSI), the channel length of complementary metal-oxide-semiconductor field effect transistors (CMOS-FETs) has reduced down to32nm, and is approaching to22nm. In order to retain large drive-current and sufficient gate capacitance, the thickness of SiO2/SiOxNy gate dielectric layer has reduced down to lnm and below. However, this causes a series of technological problems, such as excess direct leakage current, small drive current and degradation of device reliability caused by the tunneling of boron/phosphorus dopants. As a consequence, the SiO2/SiOxNy gate dielectric films cannot meet the requirement of the next generation of CMOS-FETs. One of the solutions is to find a new high-κ dielectric candidate which can replace the SiO2/SiOxNy gate dielectric film. In recent years, HfO2has been highlighted due to its excellent dielectric properties and good thermodynamic stability on Si-based semiconductors. On the other hand, the conventional Si semiconductor will be incapable for further higher-degree integrated circuit because its hole mobility is much lower than its electron mobility. So it is necessary to find another new semiconductor material. Considering the compatibility to the conventional Si-based semiconductor technology, strained Si, Ge, SiGe and their stacked structures are most attractive semiconductor candidates. Owing to the improvement of both electron and hole-mobility, which is attributed to the strain caused by the lattice mismatch between Ge and Si atoms, CMOS-FETs based on Si1-xGex/Si stacked structures are widely studied in recent years.In this paper, HfO2films are deposited on p-type Sig3Ge17/Si substrates by means of radio-frequency magnetron sputtering method. The films’ crystal structure are investigated by means of X-ray diffraction. It is demonstrated that the as-deposited HfO2film has monoclinic crystalline structure. Its dielectric properties before and after post-annealing treatments are measured with Agilent4294A precision impedance analyzer and Keithley2400digital multimeter, and then compared with the dielectric properties of HfO2films deposited on p-type Si substrate under the same condition. It is found that the measured relative permittivity shows no remarkable frequency dependence (-23.8at1MHz). Comparison experiment reveals that under the same optimized condition, dielectric properties of the HfO2films on Si83Ge17/Si(100) substrate are better than that on Si(100) substrate, such as relatively larger accumulation capacitance, lower leakage current density (2.51×10-5A-cm-2at-1V gate voltage), lower flat-band voltage (-0.06V), and smaller hysteresis of capacitance-voltage curves.On the other hand, the interfacial microstructures of HfO2films on Si83Ge17/Si or Si substrate have been studied by atomic force microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. According to the standard Gibbs free energy of formation, the possible kinetic processes of the interfacial reaction are studied. It is argued that as-deposited HfOx robs oxygen atoms from initial GeOx in compressively strained Si83Ge17buffer layer and becomes oxygen-stoichiometric HfO2. Moreover, it is GeOx that avoids the direct contact between HfO2and Si, depresses their reactions, and eventually reduces the formation of unstoichiometric HfSixOy and HfSix in interfacial layer. As a result, the dielectric properties of the HfO2films on Si83Ge17/Si substrate are improved.Moreover, we report the effects of working power and post annealing treatment on the nanomagnetism of HfO2films on compressively strained Si83Ge17/Si substrate, and discuss their possible origins. Magnetization curves of HfO2samples are characterized by means of vibrating-sample-magnetometer (VSM). Morphology and interfacial microstructures of HfO2samples are investigated using scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The compositions of film and interfacial layer for annealed samples are investigated using X-ray photoelectron spectroscopy (XPS) depth profiling technology. SEM images indicate that the RT-deposited HfO2film is crystallized with a dense and uniform surface. Post-annealing treatment at500℃results in an increased grain size as well as cracks in the film. HRTEM and XPS investigations reveal that the film annealed in oxygen is a mixture of stoichiometric HfO2and HfSiOx, while the film annealed in vacuum is a mixture of oxygen-defective HfOx<2and HfSiOx. An interfacial layer mixed with HfSiOx and HfSix is observed in the samples annealed either in oxygen or in vacuum, but the ratio of HfSix in the interfacial layer for the sample annealed in vacuum is higher than that annealed in oxygen. Room-temperature magnetization curves indicate a typical weak ferromagnetic behavior with a Curie temperature higher than400K, and show a visible anisotropy; but there is no magnetic hysteresis observed. Under the optimized conditions (room temperature growth in3Pa Ar ambient with working power of70W), HfO2films exhibit a magnetic moments of1.8emu/cm3. After annealing at below800℃, the saturated magnetic moments of samples annealed in oxygen atmosphere decrease as the annealing temperature increase; While on the contrary, the saturated magnetic moments of samples annealed in vacuum slightly increase. However, once the annealing temperature reaches800℃, the results are quite different. The saturated magnetic moments of samples annealed in vacuum greatly decrease, while for the samples annealed in oxygen atmosphere their saturated magnetic moments increase significantly. The above experimental results indicate that the ferromagnetism of HfO2film is strongly affected by the oxygen content of annealing ambient and temperature. We believe that oxygen vacancies in the HfO2films are the main origin of the observed weak ferromagnetism.