Modification of Si(001)/SiO 2 Interfaces by Nitric Oxide Treatments: An Electron Paramagnetic Resonance Study
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ABSTRACT The modification of the Si(001)/SiO 2 interface and the related interface defect reduction by thermal treatments in nitric oxide (NO) have been studied by Electron Paramagnetic Resonance spectroscopy for 630A thick and ultrathin (28A) oxides. The effects of annealing temperature, annealing time and rapid (RTN) or furnace annealing have been explored. Our results show that an appropriate NO treatment can drastically reduce the defect densities if, in addition to N incorporation in the transition layer near the interface, the thermal relaxation of the nitrided oxide is allowed. Our results indicate that NO treatment can lead to "defect free" Si/SiO 2 interfaces.
INTRODUCTION The requirement of ultrathin gate oxides with a thickness below 3nm necessitates a new approach to optimize its structural and physical properties [1]. The usual concepts to describe the growth process, i.e. separating the dielectric and its properties in surface, bulk and interface regions evidently no longer apply and a mixed system has to be treated, where oxygen exchange, oxygen incorporation and silicon injection take place within a few monolayers during the thermal oxidation. Whereas such thin oxides have been successfully grown, the problems of dopant diffusion in the dielectric during post growth thermal processing and of electrical degradation are becoming increasingly important and require a modification of the oxide [2]. One promising approach is the thermal treatment of the Si/SiO 2 interface in NH 3 , N 20 or NO atmospheres [3]. This treatment leads to nitrogen incorporation at the interface which has been shown to suppress the boron diffusion in the dielectric and to improve the electrical properties with a reduction in the interface state generation under current stress [4,5,6,7]. Most of the previous studies of nitrided oxides have focussed on the determination of the N profile in the oxide and its correlation with the new electrical properties. The main experimental techniques used in this context are Nuclear Reaction Analysis (NRA) [8,9], X-ray Photoemission Spectroscopy (XPS) [10,11 ], Fourier Transform Infrared spectroscopy, (FT-IR) [12,13], Atomic Force Microscopy [14], capacitance spectroscopy [5] and Electron Paramagnetic Resonance (EPR) [15]. However the microscopic structure of the nitrided oxide and the reactions leading to the nitrogen incorporation have not yet been established. To understand better the physical mechanisms responsible for the N induced modifications of the interface properties, we studied equally thick (>100 'A) oxides. This case is conceptually more simple as surface, bulk and interface reactions between the gas phase
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molecules and the dielectric can be well separated. It is therefore of interest to study this case in more detail before coming back to the ultrathin oxides. Among the different nitridation schemes explored, thermal treatments in nitric oxide (NO) have shown to be particularly interesting due to the sel
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