Growth and characterization of UHV sputtering HfO2 film by plasma oxidation and low temperature annealing

Abstract

Ultra-thin (∼4.0 nm) HfO 2 films were fabricated by plasma oxidation of sputtered metallic Hf films with post low temperature annealing. Advantage of this fabrication process is that the pre-deposition of Hf metal can suppress the formation of interfacial layer between HfO 2 film and Si substrate. The as-deposited HfO 2 films were subsequently treated by rapid thermal annealing at different temperatures in N 2 to investigate the effects of thermal annealing on the physical and electrical properties of HfO 2 film. A SiO 2 -rich interface layer was observed after higher temperature rapid thermal annealing and the phase change of HfO 2 film from amorphous into crystalline occurred at about 700 • C. As a result of higher temperature annealing, effective dielectric constant and leakage current were significantly influenced by the formation of interface layer and the crystallization of HfO 2 film.complementary metal-oxide-semiconductor (CMOS) device. Several metal oxides with higher dielectric constant (k) in the range of 10-25, such as Al 2 O 3 (∼10) and La 2 O 3 (∼20), have been proposed as potential candidates for SiO 2 gate replacement. However, Hafnium Dioxide (HfO 2 ) is attractive due to its high dielectric constant (22-25), relatively large band gap (5.8 eV) and thermodynamic stability in direct contact with silicon [1, 2]. HfO 2 films prepared by sputtering, atomic layer deposition, pulse laser deposition, and electron beam evaporation had been widely studied [3-6]. However, the formation of interfacial layer, due to the oxidation of Si substrate during film fabrication and subsequent annealing, and the crystallization of HfO 2 films are still serious issues [7][8][9]. Recently, remote plasma oxidation has been performed to form the stoichiometric HfO 2 film, in which the oxygen radicals oxidize the Hf metal selectively other than Si substrate [10]. In comparison to rapid thermal annealing (RTA), plasma oxidation technique has advantages of suppressing the interfacial diffusion at the interface between HfO 2 film and Si substrate [11]. Plasma oxidation, using oxygen radicals to oxidize Hf metal at low temperatures, can maintain HfO 2 film in an amorphous phase with silicate interface, but it leads to both reduction of equivalent oxide thickness (EOT) and leakage current density (J g ) [12]. Rapid thermal annealing at elevated temperature can be used to densify the deposited oxide film and improve the properties of the films. However, uncontrolled formation of an interfacial oxide layer during annealing is undesirable and will increase the EOT.In this paper, we investigated the effects of post-deposition annealing of HfO 2 film (∼4 nm) on their interfacial, microstructural and electrical characteristics. As a result of higher temperature annealing, a SiO 2 -rich interface layer was observed. The phase transition of HfO 2 film from amorphous into crystalline occurred at about 700 • C. The formation of Springer

Hf-Based High-κ Dielectrics: A Review

“…Both thickness and band gap of the films decreased with increase of annealing temperature[54]. Li et al found as the highest dielectric constant of κ = 22 of HfO 2 when the film was annealed at 500 • C by plasma oxidation[67]. Yamamoto et al have analyzed the relation between leakage current density and EOT of HfO 2 films prepared by remote plasma oxidation.…”

“…of results of different coating methods[43,58,[62][63][64][65][66][67][68][69][70][71][72][73][74][75][76]. × 10 −8 A/cm 2 at 1 V EOT= 2.73 nm at 700 • C…”