Abstract
In this paper, we report the plasma-enhanced atomic layer deposition (PEALD) of TiO2 and TiO2/Al2O3 nanolaminate films on p-Si(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. In the PEALD process, we used titanium tetraisopropoxide (TTIP) as a titanium precursor, trimethyl aluminum (TMA) as an aluminum precursor and O2 plasma as an oxidant, keeping the process temperature at 250 °C. The effects of PEALD process parameters, such as RF power, substrate exposure mode (direct or remote plasma exposure) and Al2O3 partial-monolayer insertion (generating a nanolaminate structure) on the physical and chemical properties of the TiO2 films were investigated by Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM) techniques. The MOS capacitor structures were fabricated by evaporation of Al gates through mechanical mask on PEALD TiO2 thin film, followed by evaporation of an Al layer on the back side of the Si substrate. The capacitors were characterized by current density-voltage (J-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Our results indicate that RF power and exposure mode promoted significant modifications on the characteristics of the PEALD TiO2 films, while the insertion of Al2O3 partial monolayers allows the synthesis of TiO2/Al2O3 nanolaminate with well-spaced crystalline TiO2 grains in an amorphous structure. The electrical characterization of the MOS structures evidenced a significant leakage current in the accumulation region in the PEALD TiO2 films, which could be reduced by the addition of partial-monolayers of Al2O3 in the bulk of TiO2 films or by reducing RF power.
Highlights
TiO2 thin films were deposited on p-type Si substrates under different conditions by plasma-enhanced atomic layer deposition (PEALD) technique
Structural, chemical and morphological properties of the as-grown films were studied as a function of the following deposition parameters: RF power, substrate exposure mode and Al2O3 partial-monolayer insertion
Chemical composition determined by Rutherford backscattering spectroscopy (RBS) analysis showed that the TiOx films have an excess of oxygen content, with x values ranging from 2.13 ± 0.01 to 2.33 ± 0.01, which can be related to the higher reactivity of O2 plasma
Summary
Titanium dioxide (TiO2) thin films and nanolaminates have a significant number of promising applications in different areas, such as microelectronics [1,2,3,4,5,6], photovoltaics [7,8], photocatalysis [9,10,11], fuel cells [12], sensors [13,14,15,16], anti-reflective coating applications [17], biomedical coatings [18,19] and food packaging applications [20]. PEALD requires lower substrate and process temperatures to obtain crystalline films [35] It is one of the most promising technologies for the growth of conformal coatings and nanolaminates in various structures and topographies [32,36] with layer thickness precisely defined by self-limited surface reactions [37]. Its high reactivity enhances surface chemical reactions, allowing the process to be carried out at lower temperature and, preventing the interlayer diffusion that is responsible for the degradation of nanoscale device properties [40]. J-V, C-V and G-V characteristics of the MOS capacitors at room temperature were investigated in function of the following PEALD process parameters: (i) RF power, (ii) plasma exposure mode and (iii) Al2O3 partial monolayer insertion (generating a nanolaminate structure). There is a lack of available literature on the electrical characteristics of MOS capacitors formed by PEALD TiO2-based films on p-type Si substrates grown under different conditions
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