Isotropic Wet Chemical Etching of Silicon

Isotropic etching of silicon is done with an aqueous mixture of HF+HN03 + CH3COOH (hydrofluoric, nitric add and acetic add). Often the acetic add is omitted. The etch rates are very high at room temperature 940 pm/min with 20-46% HN03 (69% HNO3, 31% H20) complemented by HF (49% HF, 51% H20). The quality of the silicon surface produced will depend on the solution used. Smoother surfaces are achieved with a higher proportion of nitric acid and a lower proportion of acetic acid. 

The disadvantage, as far as silica is concerned, is the low degree of seledivity. For Si02 the etch rates are between 300 and 700nm/min. Silicon nitride and noble metals demonstrate better resistance to etching. Because of the isotropy, the asped 

Waiting for the natural etch stop means that L-, T-, or U -shaped V-troughs necessary for microreactors cannot be produced. For these, etching is intermpted. The etching is intermpted when the desired depth has been reached. These V ross-section troughs have convex 90° corners at any bends, and at those points, there is considerable undercutting of the mask. The remedy is comer compensation. Sacrificial surfaces are created at the convex comers, calculated in such a way that the etch time in the direction of the convex 90° corner will produce the correct shape. 

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Isotropic wet chemical etching of silicon (HF + HN03 + CH3COOH + H20). 

Isotropic Wet Chemical Etching of Silicon 67 Table 3.4 Configuration of photostructutable special glass. 

Silicon Micromachining, Fig.1 Schematic of cross-sectional view of isotropically etched silicon microchannels using wet chemical etchants of NHA... 

Silicon has a diamond cubic crystal structure. The Miller indices of the main crystallographic planes of silicon are (100), (110) and (111), respectively. In the wet bulk-micromachining, there are two silicon etching methods isotropic (direction-independent) and anisotropic (direction-dependent) etching. Wet chemical etching solutions are used in this bulk silicon micromachining technology. 

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