Etching of Si Microchannels

Isotropic wet etch using HF-HN03, whose etch rate is independent of the etching direction, has been employed to produce approximately rectangular grooves, oriented in any direction on the Si 100 wafer, using thermal Si02 ( 1 pm thick) as the etch mask [1]. 

FIGURE 2.1 Process steps of a standard one-mask micromachining procedure to etch a channel structure into silicon [3]. Reprinted with permission from Elsevier Science. 

C-C )- But if the channel is perpendicular to the wafer flat (D-D ), a V-groove cross section will result due to the slanted 111 planes that define the stop-etch conditions [84]. 

Isopropyl alcohol (IPA) is sometimes added to KOH in order to reduce the etchant surface tension. This in turn assists in releasing H2 bubbles and in dissolving organic contaminants. So the addition of IPA avoids the micromask effect and produces smoothly etched channels [303]. 

Anisotropic etch on Si can also be achieved by reactive ion etching (RIE), which is a dry (plasma) etch process. In deep RIE, cyclic etch characteristics could be produced on the etched wall [85,86]. 

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