Crystallographically Determined Etching and Its Relevance to the Metal-Assisted Catalytic Etching (MACE) of Silicon Powders

Abstract

Metal-assisted catalytic etching (MACE) using Ag nanoparticles as catalysts and H2O2 as oxidant has been performed on single-crystal Si wafers, single-crystal electronics grade Si powders, and polycrystalline metallurgical grade Si powders. The temperature dependence of the etch kinetics has been measured over the range 5–37°C. Etching is found to proceed preferentially in a 〈001〉 direction with an activation energy of ~0.4 eV on substrates with (001), (110), and (111) orientations. A quantitative model to explain the preference for etching in the 〈001〉 direction is developed and found to be consistent with the measured activation energies. Etching of metallurgical grade powders produces particles, the surfaces of which are covered primarily with porous silicon (por-Si) in the form of interconnected ridges. Silicon nanowires (SiNW) and bundles of SiNW can be harvested from these porous particles by ultrasonic agitation. Analysis of the forces acting between the metal nanoparticle catalyst and the Si particle demonstrates that strongly attractive electrostatic and van der Waals interactions ensure that the metal nanoparticles remain in intimate contact with the Si particles throughout the etch process. These attractive forces draw the catalyst toward the interior of the particle and explain why the powder particles are etched equivalently on all the exposed faces.

Studying the wetting agent impact in the porous silicon production

“…So, the most stable surface of polycrystalline silicon element is Si (111), which has a rhombohedral unit cell with equal side lengths a and apex angle α = 60•. [9] So, at the differentiation of the wetting agent concentrations, the etching of the silicon planes is differentiated too, as shown in fig. 1.…”

“…Then, it controls the etching process in certain planes. Also, at the 25 Vol % NPA, the main plane is changed to (211) [9], as a result of a slow anisotropic etching process that change the rhombohedral plane (111) to the hexagonal plane (211). [11] [12].…”

High-Speed and Direction-Controlled Formation of Silicon Nanowire Arrays Assisted by Electric Field

“…Low-dimensional silicon (Si) nanostructures displayed remarkable electronic, mechanical, and optoelectronic properties that could act as building elements of functional devices and applications [1][2][3], such as field-effect transistors, biosensors, and photovoltaic cells [4][5][6][7][8][9]. To form the regular arrays of Si nanostructures, metalassisted chemical etching has been considered the prevailing strategy that even enabled to form Si nanowire (SiNW) arrays on planar substrates [10,11], powders [12,13], and pyramidal structures [14]. In the etching process, the hole injections across metal catalysts toward Si underneath and subsequently the dissolution of oxidized Si were continuously occurred, thus resulting in the long etching pores.…”

Curved Structure of Si by Improving Etching Direction Controllability in Magnetically Guided Metal-Assisted Chemical Etching

“…Ideally, MEMS structures such as Si cantilever and bridge arrays can be obtained via a simple MACE procedure, provided the etching direction can be easily manipulated during the etching process. However, similar to dry/wet etching methods, controlling the etching direction during MACE is difficult, as the etching direction can only be modulated via the crystalline orientation of the Si substrate [30][31][32] and the concentration of the etchant [33]. To fabricate complex Si structures such as cantilevers and bridges, a type of MEMS structure, the etching direction should be sequentially altered during the etching process.…”