Abstract
The mechanism of flat band voltage (VFB) shift for alternate La2O3/Al2O3 multilayer stack structures in different annealing condition is investigated. The samples were prepared for alternate multilayer structures, which were annealed in different conditions. The capacitance-voltage (C-V) measuring results indicate that the VFB of samples shift negatively for thinner bottom Al2O3 layer, increasing annealing temperature or longer annealing duration. Simultaneously, the diffusion of high-k material to interfaces in different multilayer structures and annealing conditions is observed by X-ray photoelectron spectroscopy (XPS). Based on the dipole theory, a correlation between the diffusion effect of La towards bottom Al2O3/Si interface and VFB shift is found. Without changing the dielectric constant k of films, VFB shift can be manipulated by controlling the single-layer cycles and annealing conditions of alternate high-k multilayer stack.
Highlights
High dielectric constant materials have been extensively used to substitute conventional SiO2 gate oxides for its prominent properties such as small equivalent oxide thickness (EOT) and low leakage current
The experiment in our work shows no relevance between the metal/high-k interface and the Flat band voltage (VFB) shift
The C-V curves and X-ray photoelectron spectroscopy (XPS) results of alternate La2O3/ Al2O3 multilayer stacks are investigated in the paper
Summary
High dielectric constant (high-k) materials have been extensively used to substitute conventional SiO2 gate oxides for its prominent properties such as small equivalent oxide thickness (EOT) and low leakage current. The properties of La2O3 and Al2O3 gate stacks have been studied by many researchers, and much promotion has been made in restraining leakage current and suppressing the formation of parasitic interface [3,4,5]. Earlier researchers claimed that the fixed charges are the main factor for flat band voltage (VFB) shift [6]. Researchers revealed that the main origin of VFB is the dipoles between high-k/interface layer [9, 10]. The atomic mechanism of VFB shifts for different high-k gate stacks is discussed by Lin and Robertson [11, 12]. Based on the theory of dipoles and diffusion effect, the mechanism of VFB shift was studied
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