Metal deposition and etching

Figure 15. Simplified process sequence for the fabrication of an NMOS transistor (a) substrate preparation, (b) selective exposure of substrate, (c) mask formation by differential solubility, (d) etching, (e) stripping of resist, (/) doping, (g) reoxidation of silicon surface, (h) formation of gate oxide, and (i) metal deposition and patterning. Abbreviations are defined as follows p-Si, p-type silicon PR, photoresist S, source G, gate and D, drain.

Theoretically, electrical patterning is one the simplest method to structure materials since they can be patterned directly on the surface of an electrode. Creating conducting microelectrodes is, nowadays, fast and simple using micro and nanotechnology tools. Deposition and etching, or deposition followed by lift-off, are the conventional methods [35], Other solutions based on electrodeposition of metals... 

No literature has been published in this area but, as a rule of thumb, metals which dissolve to give complexes that have linear or tetrahedral geometries, e.g. Cu, Ag, Zn, Sn, Pb, can be reversibly deposited and etched. Those with octahedral geometries, e.g. Fe, Ni, Co and Cr, are less reversible. The exceptions to this are the very electronegative metals, most notably A1 which is difficult to electrodeposit from some ionic liquids. The reversibility is also dependent upon the type of ionic liquid and the metal being deposited. Endres has shown that the adhesion of aluminum to mild steel is greatly enhanced by an anodic pulse prior to deposition. It has been shown that this alloy was formed between the steel substrate and the aluminum coating [1],... 

Processes that depend critically on these phenomena include energy storage and conversion, corrosion and corrosion control, membrane separations, deposition and etching by electrolytic and plasma processes, electrosynthesis of organic and inorganic chemicals, production and refining of metals, pollution detoxification and recovery, desalination, and many others. 

Huang et al. recently did a comprehensive and systematic review of metal-assisted ehemieal etehing mechanism and process parameters (Huang et al. 2011). The review by Ono is focused on combination of patterning methods of metal deposition and metal-assisted etching (Ono and Asoh 2012), whereas the review by Li is related to high aspect ratio structures with an emphasis on photovoltaic applications (Li 2012). Other papers contain a mini-review on metal-assisted etching (Kolasinski 2005 Qiu and Chu 2008 Korotcenkov and Cho 2010). 

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