Dielectric Properties And Weak Ferromagenetism Of HfO₂ Films Deposited By RF Magnetron Sputtering

With the improved integration of Si-based integrate circuit (IC), the channel length of complementary metal-oxide-semiconductor field effect transistors (MOS-FETs) has been reduced down to 45nm now. And it will be reduced to 14nm in 2020, according to the prediction of latest international technology roadmap for semiconductors (ITRS). In order to keep sufficient gate capacitance, the thickness of traditional SiO2/SiOxNy gate dielectric layer should be reduced down to 1nm and below. As a result, a series of technological issues such as excess direct leakage current, small drive current and degradation of device reliability caused by the tunneling of boron (phosphor) dopants, make it inevitable to replace traditional SiO2/SiOxNy gate dielectrics with high-k dielectrics. Among many candidates, HfO2 is one of the most promising applied high-k materials due to its good physical properties and perfect dielectric performances.Dielectric properties of HfO2 films deposited by radiofrequency (RF) Magnetron Sputtering in different ambient have been investigated by Agilent 4294A Precision Impedance Analyzer. It is demonstrated that dielectric properties of HfO2 film deposited at room temperature (RT) in pure Ar ambient (effective dielectric constant is about 17.7; flat band voltage is 0.36 V and leakage current density is about 4.15×10-3 A cm-2 at 1 V gate voltage) are better than those of films deposited in Ar+N2 or Ar+O2 mixed ambient. Investigated by using high-resolution electron microscope and X-ray photoelectron spectroscopy, the unstoichiometric HfSixOy mixed with HfSix interfacial layers are found to exist between stoichiometric amorphous HfO2 films and Si(100) substrates. These unstoichiometric interfacial layers with low-k are responsible for the decrease of effective dielectric constant of HfO2 films and the clock-wise hysteresis of capacitance-voltage curves of MOS capacitor structures.On the other hand, the effects of deposition/annealing ambient and temperature on the unexpected weak ferromagnetism of HfO2 films deposited by RF Magnetron Sputtering have also been investigated. It is found that magnetic moments of HfO2 films deposited in oxygen-defective ambient (pure Ar and Ar+N2) are bigger than those of films deposited in oxygen-rich ambient (Ar+O2). Moreover, annealing treatments in oxygen-defective ambient induce its significant increase with annealing temperature. On the contrary, annealing treatments in pure oxygen atmosphere are responsible for its sharp decrease. X-ray photoelectron spectroscopy depth profiling investigation shows that HfO2 films deposited in oxygen-defective ambient (pure Ar and Ar+N2) are non-stoichometrical HfOx<2 films. The sensitivity of magnetic moments on deposition/annealing ambient rather than deposition/annealing temperature implies that oxygen vacancies may be one of dominating origins of the observed weak ferromagnetism.