Electrical characterization of hafnium oxide and hafnium-rich silicate films grown by atomic layer deposition

doi:10.1016/j.microrel.2004.11.052

Microelectronics Reliability

Volume 45, Issues 5–6, May–June 2005, Pages 949-952

https://doi.org/10.1016/j.microrel.2004.11.052 Get rights and content

Abstract

An electrical characterization comparative analysis between Al/HfO₂/n-Si and Al/Hf-Si-O/n-Si samples has been carried out. Hafnium-based dielectric films have been grown by means of atomic layer deposition (ALD). Interface quality have been determined by using capacitance–voltage (C–V), deep level transient spectroscopy (DLTS) and conductance transient (G-t) techniques. Our results show that silicate films exhibit less flat-band voltage shift and hysteresis effect, and so lower disordered induced gap states (DIGS) density than oxide films, but interfacial state density is greater in Hf–Si–O than in HfO₂. Moreover, a post-deposition annealing in vacuum under N₂ flow for 1 min, at temperatures between 600 and 730 °C diminishes interfacial state density of Hf–Si–O films to values measured in HfO₂ films, without degrade the interface quality in terms of DIGS.

Introduction

In the last years, HfO₂ and Hf silicates have attracted the attention of researchers who are looking for dielectric materials to replace SiO₂ in complementary metal-oxide-semiconductor (CMOS) transistors [1], [2]. The requirements for these materials are: high dielectric constant (k) value, chemical stability at high temperatures, large band gap, and structural homogeneity. HfO₂ exhibits a high-k value, and is nominally stable on Si, but crystallizes at relatively low temperature. However, by using thermodynamic arguments and ternary phase diagrams, the relative stability of the HfSi_xO_y three-component material system has been demonstrated [3]. Due to its higher dielectric constant (about 20–25), pure HfO₂ is considered to be more scalable than Hf-silicates. On the other hand, despite its lower permittivity, Hf-silicate can yield lower leakage current than HfO₂ at the same equivalent SiO₂ thickness (EOT), because of its larger band gap and heavier effective mass for electron tunnelling.

The aim of this work is to carry-out a comparative electrical characterization of some Al/HfO₂/n-Si and Al/Hf–Si–O/n-Si structures. Hafnium-based dielectric films have been grown by using atomic layer deposition (ALD) [4].

Section snippets

Experimental

Hf-based dielectric films were grown in a hot-wall horizontal flow-type ALD reactor [5] onto 〈1 0 0〉 oriented n-Si (14 Ω cm) single crystal substrates. Prior to the deposition, the silicon substrates were etched in 5% aqueous solution of hydrofluoric acid in order to remove the native SiO₂ layer and then rinsed in distilled water. In the HfO₂ cases, precursors used were HfCl₄ and water, and growth temperature varied between 300 and 600 °C. As for hafnium-rich silicate films, growth temperature was

Results and discussion

Fig. 1 shows capacitance-voltage curves obtained at liquid nitrogen (77 K) for as-deposited Al/HfO₂/n-Si and Al/Hf–Si–O/n-Si structures. The observed positive flat-band voltage shift means negative trapped charge in the insulator, the origin of which could be extrinsic defects, such as hydrogen [6]. Indeed, using water as oxidant in the ALD process leaves residual hydrogen species in the films. It has been pointed out [7] that residual OH⁻ ions can cause negative trapped charge in HfO₂ films. On

Conclusions

In summary, a comparative electrical characterization has shown that hafnium-rich silicate films exhibit less flat-band voltage shift and hysteresis effect, and so lower DIGS density than HfO₂ films, but interfacial state density is greater in Hf–Si–O than in HfO₂.

However, a post-deposition annealing in vacuum under N₂ flow for 1 min, at temperatures between 600 and 730 °C diminishes D_it of Hf–Si–O films to values measured in HfO₂ films, without degrade the interface quality in terms of DIGS.

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