Anisotropy etching techniques

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

In a follow up full publication to the work above, Harrison et al. showed that using porous thin films as described above, pattern transfer could be accomplished in both Si and Ge substrates as well [23]. While an entire three-inch Si wafer was patterned using this technique, practical limitations, such as in etch anisotropy, were reported. In this paper, an effective technique for confirming porosity in these films was demonstrated. After ozonolysis of these thin films, an overlayer of PS remained at the surface of these porous samples. By using a low power CF4 RIE followed by periodic SEM analysis, this layer could be slowly etched to reveal thus revealing the cylindrical pores (now observed as trenches). Also, the authors showed that the low power CF4 etch did not result in significant surface roughness. 

A planar substrate, such as silicon wafer, could be micromachined by a sequence of deposition and etching processes. This results in three-dimensional microstructures which can be implemented in cavities, grooves, holes, diaphragms, cantilever beams etc. The process referred to as silicon micromachining often employs anisotropic etchants such as potassium hydroxide and ethylene diamine pyrocatechol. The crystallographic orientation is important as the above-mentioned etchants show an etch-rate anisotropy. The ratio for the (100)-, (110)- and (111)- planes is typically 100 16 1. The technique of electrochemical etch stop could be applied for control of the microstructural dimensions. An alternative... 

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