Abstract
The crystallographic orientation of the substrate is an essential parameter in the kinetic mechanism for the oxidation process. Hence, the choice of substrate surface orientation is crucial in nanofabrication industries. In the present work, we have studied qualitatively the influence of substrate orientation in nanoelectrode lithography using ReaxFF reactive molecular dynamics simulation. We have investigated the oxidation processes on (100), (110) and (111) orientation surfaces of silicon at different electric field intensities. The simulation results show the thickness of the oxide film and the initial oxygen diffusion rate follow an order of (100) > (110) > (111) at lower electric field intensities. It also confirms that surfaces with higher surface energy are more reactive at lower electric field intensity. Crossovers occurred at a higher electric field intensity (7 V nm−1) under which the thickness of the oxide film yields an order of T(110) > T(100) > T(111). These types of anomalous characteristics have previously been observed for thermal oxidation of silicon surfaces. Experimental results show different orders for the (100) and (111) substrate, while (110) remains the largest for the oxide thickness. A good correlation has been found between the oxide growth and the orientation-dependent parameters where the oxide growth is proportional to the areal density of the surfaces. The oxide growth also follows the relative order of the activation energies, which could be another controlling factor for the oxide growth. Less activation energy of the surface allows more oxide growth and vice versa. However, the differences between simulation and experimental results probably relate to the empirical potential as well as different time and spatial scales of the process.
Highlights
Over the past decades, local oxidation-based nanolithography has been proved as an efficient lithographic tool where researchers used AFM tips [1,2,3,4] to fabricate the nanostructures on different substrates
Due to the slowness of the AFM based oxidation lithography, some researchers modified the local oxidation approaches by using other conductive stamps, which facilitates the large-area fabrication [5,6,7]. The principle of this method is shown in figure 1, which is commonly known as Nanoelectrode lithography (NEL)
We have applied an electric field of 7 V nm−1 (i.e. 7 V bias voltage) between the reflecting wall and the substrate for a Crystallographic orientations (1 0 0)
Summary
Local oxidation-based nanolithography has been proved as an efficient lithographic tool where researchers used AFM tips [1,2,3,4] to fabricate the nanostructures on different substrates. Due to the slowness of the AFM based oxidation lithography, some researchers modified the local oxidation approaches by using other conductive stamps, which facilitates the large-area fabrication [5,6,7] The principle of this method is shown, which is commonly known as Nanoelectrode lithography (NEL). We chose silicon substrates with low Miller indices, namely (100), (110) and (111), which are the dominant substrates and structural materials in Integrated Circuits (IC) and device fabrications They have been an excellent model to illustrate some of the fundamental aspects that are involved in the oxidation process. A reflecting wall was introduced on top of the system to confine the molecules, and an external electrical field was applied between the reflecting wall and the substrate to mimic the presence of a conductive stamp The details of these models are summarized in table 1. All the nanofabrication and observations were done in the AFM contact mode at room temperature and the relative humidity of 70%
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