Microstructural Investigations of Hafnium Aluminum Oxide Films
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Microstructural Investigations of Hafnium Aluminum Oxide Films Doina Craciun1, Gabriel Socol1, Emanuel Axente1, Aurelian-Catalin Galca2, Rajiv Singh3, and Valentin Craciun1,3 1 National Institute for Laser, Plasma and Radiation Physics, Bucharest, 077125, Romania 2 National Institute of Materials Physics, Bucharest, 077125, Romania 3 University of Florida, Gainesville, FL, 32611 ABSTRACT The crystalline structure, composition, chemical bonding and thermal stability of HfO2-Al2O3 mixtures deposited on Si using a combinatorial pulsed laser deposition technique were investigated. After deposition some films were annealed at temperatures from 850 to 950 oC for 6 or 12 minutes. Grazing incidence x-ray diffraction investigations were performed to asses the crystallinity and thermal stability of the annealed layers. Measurements of the Al to Hf ratios were performed using energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. From simulations of the x-ray reflectivity and spectroscopic ellipsometry spectra the phase composition and thickness of the films was calculated and then the Al to Hf ratios. Al/Hf values of 1 and 8 were found to be necessary to block the crystallization of the films after anneals at 850 and 950 oC, respectively. INTRODUCTION Recently, HfO2 has emerged as one of the best alternative high-k material to replace SiO2 gate oxides [1-2]. Unfortunately, HfO2 possesses a rather low crystallization temperature, the amorphous deposited film becoming polycrystalline after a mild thermal treatment at temperatures above 500 oC , which results in severe increase of the leakage current [3, 4]. It has been previously shown that by alloying HfO2 with Al2O3 or other oxides the crystallization temperature could be increased, the structure being able to withstand much higher temperature processes without the degradation of the dielectric properties [3-7]. However, since Al2O3 possesses a lower dielectric constant than HfO2, it is necessary to accurately determine the precise amount of Al2O3 that is required to prevent crystallization during a certain temperature cycle. Most of such studies were performed by depositing samples containing various fractions of HfO2 and Al2O3 oxides that were submitted to different thermal anneals and then their crystallinity was assessed [7-10]. A more effective way to determine the right Al concentration is to use the combinatorial approach, where films having gradients of concentration are deposited onto a substrate [11-13]. Analytical techniques with high lateral resolutions could therefore determine where exactly or for what concentrations the transition from amorphous to crystalline phase occurred and where it was blocked. In this paper we used a combinatorial pulsed laser deposition (C-PLD) technique to deposit films with a gradient of Al concentration and then determined their thermal stability.
EXPERIMENT We used the C-PLD technique, where two targets of HfO2 and Al2O3 located in two different positions were ablated sequentially. Each film will h
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