Etching liquid plasma

One approach suitable for high-volume production is to stabilize the movable beam structure with pedestals of photoresist [19]. Rectangular openings are created in the sacrificial oxide layer and are isotropically underetched to create circular holes. These holes are filled with photoresist that is patterned to allow the etching liquid to enter the entire area under the movable beam structure. Subsequently the pedestals are removed in an oxygen plasma. Temperature control during this step is essential to avoid capillary forces due to low viscosity in the resist. 

Plasma etching has demonstrated viable solutions to essentially all the problems encountered with liquid etching. Adhesion does not appear to be critical with dry etching techniques. In addition, undercutting can be... 

Isotropic Profile No Overetch Liquid or Plasma Etching... 

Figure 1. Cross sections of films etched with liquid or plasma etchants. The isotropic profile represents no overetch, and can be generated with liquid or plasma etch techniques. The anisotropic profile requires plasma...

Last two decades were period of a transition from a liquid toward dry etching. That is why plasma resistance is among the most important properties of a photoresist. In the case of fluorine-containing plasmas, etch resistance... 

Figure 4.4 Comparison of the anisotropic etching process with liquid and gaseous (plasma) etching agents.

Plasma development derives its advantage over its liquid counterpart mainly from the anisotropic nature of the process, except when loss from the unexposed area is vanishingly small, in which case the isotropy comes from that already in the latent image. The resist must be tough to avoid being eroded completely while the substrate underneath is etched. To improve the plasma etch resistance, aromatic compounds have been added to PMMA (50, 51). Hence, for... 

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