Under-etching

Fig. 6.6 PS layer thickness inhomogeneities as a result of different kinds of masking layers and doping densities, (a) While underetching is minimal for a silicon nitride mask, (b) a resist mask shows severe under-etching.

Z. Irena and B. Irena, Silicon anisotropic etching in alkaline solutions. I. The geometric description of figures developed under etching Si(lOO) in various solutions. Sensors Actuators A70, 250, 1998. 

An ability to self-proximity corrections, i.e., unexposed areas can be recovered up to the desire dimensions, as a result of under etching in the course of subsequent isotropic wet etching. 

Constrained geometry insufficient or under etching higher than normal resistance... 

Internal conductor attributes including over- and under-etch, conductor cracks and voids, and foil thickness... 

In this approach, the bulk silicon substrate is not etched away, but only the sacrificial layer between the silicon substrate and the polysilicon microstructures is removed by lateral under-etching using the selective wet etchant of HE or BOE. Such etching solutions do not have any etching effect on the polysilicon film. Figure 6 illustrates the process steps to fabricate a polysilicon cantilever. 

A line disappears accordingly by under-etching when the etching depth reaches about 75% of the line width. The fineness of a structural image automatically limits the maximum etching depth. 

A num ber of different techniques have been used to study the surface preparation techniques used prior to anodic oxidation. For device fabrication, mechanical polishing Is usually necessary to insure a relatively flat surface. Some chemical treatment is necessary to remove the mechanical damage induced by grit polishing. Often etching or chem-mechanical polishing is used to remove this damaged layer. However, it has been shown that chemical treatments do not leave a stoichiometric surface (27-30)(63). A kinetic study of the reaction of 0.1N Br in methanol with (Hg,Cd)Te under etch conditions found the relative rates of reaction of the individual constituents to be ... 

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