A lattice constant of ‘a’ = 7.595 Å in the hexagonal (X-Y) plane whereas ‘c’ = 2.902 Å in the vertical (Z) direction are obtained. Various groups have already described the crystal structure of β-Si 3N 4 and for the bulk crystals. Although there were some contradiction about these two phases, finally it has been well accepted that the only stable phase is the β-Si 3N 4 phase whereas the α-Si 3N 4 phase is a meta-stable one and has a lattice constant along c-axis (0001) just double of the β-phase. Both the phases have space groups of P31 c and P6 3 for α- and β-Si 3N 4, respectively and the structures appeared with a hexagonal symmetry. Crystalline silicon nitride appears with two different phases, such as α-phase and β-phase of Si 3N 4. Usually the bulk Si 3N 4 has been produced by sintering method and structurally appeared as poly-crystalline ceramic. It is a semiconducting material with an energy band gap of about 4.7 eV, which is almost half of SiO 2 (9 eV). It shows a very high thermal stability, up to 1600☌ in air and also has a much larger dielectric constant (ε = 7.5) as compared to the conventional SiO 2 (ε = 3.8). It can also be useful because of its high fracture toughness. Silicon nitride is a structural ceramics, which exhibits high mechanical strength at room as well as elevated temperature. Therefore, better understanding of the initial Si 3N 4 films growth on Si, their structural and morphological evolution as well as chemical properties in a very local (atomic) scale are of high technological importance. Finally, crystalline Si 3N 4 on Si can also serve as a substrate for highly demanding GaN growth to integrate the opto-electronic devices to the well-established silicon based device technology. High thermal stability and refractive index of Si 3N 4 make it capable for high temperature structural ceramics and anti-reflective coating materials, respectively. Plasma assisted amorphous silicon nitride layer has recently been used as high performance gate dielectric. In this regard, crystalline silicon nitride (Si 3N 4) films received considerable attention to replace the existing SiO 2 gate dielectric materials, as it is compatible with existing Si processing technologies as well as larger dielectric constant and diffusion resistive materials properties. Hence, demand for new materials with a higher dielectric constant is of high priority which can replace the SiO 2 layer to overcome this issue. Very small fluctuations in thickness of the oxide layer may lead to the break-down due to the enhanced electron tunneling as this insulating barriers is extremely thin. Here, the homogeneity of the insulating film in terms of morphology and chemical purity becomes more pronounced. However, continuous miniaturization of device size now demands a thickness of this insulating layer down to a few atomic layers. Since last few decades, SiO 2 on silicon (Si) is found to be the most useful insulating material in VLSI device technology because of its high quality and superior homogeneity. This nanometer scale insulating films not only reduce the devices size, but also provide a platform for novel device fabrication such as resonant tunneling diodes or memory devices for magnetic tunnel junction. Due to the recent miniaturization in nanotechnology, insulating layer thickness needs to be precisely controlled down to a few nanometer ranges. In semiconductor technology, one of the most important parts is the formation of homogeneous insulating layers and are of high practical importance as it is an integral part all kinds of integrated circuits. All findings are explained in terms of thermally activated inter-diffusion of Si and N atoms as well as the surface adatom diffusion/mobility. The initial stage of N nucleation on Si(111), how the structure and morphology of the nitride films depend on thickness and temperature, surface atomic reconstructions and the nitride film chemical composition are discussed here. The substrate temperatures during the nitridation process were ranging from 600–1050☌ and the plasma exposure times were varied from 5 s for initial nucleation up to 45 min for saturation thickness. A radio frequency N2 plasma source from Epi Uni-bulb has been used for the nitridation of atomically clean Si(111) surfaces. A detailed investigation of the growth mechanism of ultra-thin silicon nitride (Si3N4) films on Si(111) substrates, their structure, morphology and surface chemistry down to atomic scale have been investigated using various surface analytical techniques such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and ESCA microscopy.
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