Memory effect in nanostructured Si-rich hafnia films
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Memory effect in nanostructured Si-rich hafnia films L. Khomenkova1, X. Portier2, F. Gourbilleau2, A.Slaoui3 1
V. Lashkaryov Institute of Semiconductor Physics, 45 Pr. Nauky, Kyiv 03028, Ukraine CIMAP, CEA/CNRS/ENSICAEN/UCBN, 6 Blvd. Maréchal Juin, 14050 Caen cedex 4, France 3 ICube, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France 2
ABSTRACT Microstructral and charge-trap properties of single Hf-silicate dielectric films are presented versus annealing treatment. The as-grown films were found to be homogeneous and amorphous. It is shown that annealing treatment results in the formation of alternated Hf-rich and Si-rich layers. The mechanism responsible for this phenomenon is found to be surface directed spinodal decomposition. The increase of annealing temperature up to 1000-1100°C resulted in the crystallization of Hf-rich phase. The stability of its tetragonal phase caused an enhancement of film permittivity was observed. The evolution of charge trapping properties of the films results in the memory effect which nature was discussed. INTRODUCTION Non-volatile memory devices (NVM) with discrete charge-trapping layers have drawn much attention due to their wide-spread applications and compatibility with standard CMOS processing [1,2]. Among NVM structures, silicon oxide layers with embedded semiconductor or metallic nanoclusters (NCs) have been widely investigated [2-7]. These structures demonstrated higher scalability, larger memory capacitance and good retention properties, operating under relatively lower voltage than conventional floating gate memories. High-k dielectrics are considered mostly to be used instead of conventional silicon oxide gate in NVM devices [2,8-10]. However, their charge-trap role is not often addressed. Meanwhile, the high-k layers with embedded discrete dielectric NCs offer promising properties as a charge-storage node in NVM devices. For example, an incorporation of RuO discrete NCs in amorphous ZrHfO layers led to a significant memory effect in comparison with NCs-free ZrHfO layers [11]. Furthermore, more interesting issue is the elaboration and investigation of NVM structures fully based on high-k dielectrics of the same nature. Recently, charge storage properties of NVM prototype fully-based on Zr-silicate with modulated composition were demonstrated in [12]. It was shown that the formation of ZrO2 NCs in Zr0.8Si0.2O4 layer upon annealing at 800°C allowed the memory effect to be achieved [12]. It is worth to note that Zrbased dielectrics were rather considered then Hf-based materials. However, the isovalent similarity of Hf and Zr ions as well as of their oxides and silicates opens the ways to wider application of Hf-based dielectrics for NVM devices. In this paper we demonstrate NVM properties of metal-insulator-semiconductor (MIS) structures based on single Hf-silicate layers with modulated composition. EXPERIMENT Radio frequency (RF) magnetron sputtering technique was used for layers fabrication, whereas an annealing treatment allowed their microstructure and electrica
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