Physical etching

Dry-etching techniques, in general, are methods by which a solid state surface is etched physically by ion bombardment or chemically by a chemical reaction with a reactive species at the surface or combined physical and chemical mechanisms. Under chemical methods, one distinguishes between wet etching (solvent, vapor, electrochemical) and dry etching in the gas phase. Depending on the mechanism, isotropic or anisotropic (directional) etch profiles are obtained. 

Kim, K. S., Hurtado, J. A. and Tan, H. (1999), Evolution of the surface-roughness spectrum caused by stress in nanometer scale chemical etching. Physical Review Letters 83, 3872-3875. 

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

The day that Wolfram s article appeared at ITP s library is forever etched in my mind as one of those proverbial milestone events in one s life. I knew instantly that cellular automata embodied a profound new approach to looking at physics and the world and that cellular automata were a subject about which I had to do a lot of thinking. I will forever be indebted to Max for allowing me to pursue musings that seemed-certainly to those making up the intellectual inner-circle of ITP at the time-comical, at best and childishly unphysics-like, at worst. So... 

An important recent trend is the tendency for the two processes, CVD andPVD, to merge. For instance, CVD now makes extensive use of plasma (a physical phenomenon) and reactive PVD (evaporation or sputtering) occurs in a chemical environment. Much ofthenew equipment reflects this process integration in the concept of cluster tools which may incorporate CVD, etching, sputtering, and ion implantation in one piece of equipment. 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

Khanna et al. [136] proposed a mechanism of the reactions of aluminum based clusters with O, which lends a physical interpretation as to why the HOMO-LUMO gap of the clusters successfully predicts the oxygen etching behaviors. The importance of the HOMO-LUMO gap strongly suggests that the reactions of the metal clusters belong to the pseudoexcitation band. 

Figure 1(a) shows the etch rates of niobium oxide pillar and Si film, and the etch selectivity of Si to niobium oxide as a function of CI2 concentration. The etch condition was fixed at coil rf power of 500 W, dc-bias to substrate to 300 V and gas pressure of 5 mTorr. As the CI2 concentration increased, the etch rate of niobium oxide pillar gradually decreased while Si etch rate increased. It indicates that the etch mechanism of niobium oxide in Cl2/Ar gas is mainly physical sputtering. As a result, the etch selectivity of Si film to niobium oxide monotonously increased. The effect of coil rf power on the etch rate and etch selectivity was examined as shown in Fig. 1(b). As the coil rf power increased, the etch rates of niobium oxide and Si increased but the etch rate of niobium oxide showed greater increase than that of Si. It is attributed to the increase of ion density with increasing coil rf power. Figure 1 (c)... 

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