Effects of an Al 2 O 3 capping layer on La 2 O 3 deposited by remote plasma atomic layer deposition
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Jaesang Lee Division of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791, Korea
Honggyu Kim, Hyerin Lee, and Hyeongtag Jeona) Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea (Received 24 December 2009; accepted 17 May 2010)
The physical and electrical properties of La2O3 with and without an Al2O3 capping layer deposited by remote plasma atomic layer deposition were investigated. The electrical properties of the La2O3 films degraded due to the formation of lanthanum hydroxide after being exposed to air. The results of x-ray photoemission spectroscopy showed that the quantity of OH groups absorbed increased after exposure to air. For La2O3 with an Al2O3 capping layer, however, the electrical properties of the film did not change substantially because the capping layer effectively suppressed the formation of lanthanum hydroxide. The capacitance of the La2O3 decreased more than 30% after exposure to air, while La2O3 with an Al2O3 capping layer decreased by only about 4%. The VFB value of the La2O3 with an Al2O3 capping layer was near zero, and the hysteresis was about 120 mV. The leakage current densities of the film were maintained below 5 10 7 A/cm2 up to 15 MV/cm and the effective breakdown field was about 23.5 MV/cm.
I. INTRODUCTION
As conventional gate dielectric films in complementary metal-oxide-semiconductor (CMOS) applications approach their physical and electrical property limits, the leakage current density through the gate dielectric layer rapidly increases and is expected to cause problems such as increased power dissipation or poor circuit reliability. Thus, high-dielectric constant materials such as HfO2, ZrO2, Al2O3, and La2O3 have been widely investigated as possible replacements for current gate dielectric materials, which include silicon oxide (SiO2) and silicon oxynitride (SiOxNy).1–3 Among the high-k gate dielectrics, La2O3 has been extensively studied due to its relatively high permittivity (27), large band gap (4.3 eV), high band offset (>2 eV), and thermal stability with Si.4–7 However, it has been reported that moisture absorption deteriorates the permittivity of La2O3 films on silicon. The main reasons for this are the formation of low permittivity lanthanum hydroxide and La-silicate grown at the interface, which generate charges in the gate dielectric and lead to a large flatband voltage shift.8,9 This undesirable large flatband voltage is due to the fixed oxide charge located at the interface a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0245
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 10, Oct 2010 Downloaded: 26 Mar 2015
between the oxide and Si, and the oxide trap charge located in the bulk oxide. Moisture absorption also leads to nonuniform volume expansion due to the density difference between lanthanum hydroxide and lanthanum oxide. Furthermore, nonuniform volume expansion results in changes in surface roughness and film density, causing degra
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