Hydrofluoric acid etch device

Next, the CdTe substrate is removed by dipping the device in an etching liquid comprising hydrofluoric acid (HF), nitric acid (HNO3), acetic acid (CH3COOH) and water (H2O) with a weight ratio of 2-5 3-5 6 6. 

Silicon oxides (SiOx) are the most widely used thin films in silicon microelectronic and micromechanical devices. Similar to silicon nitride (Section 5.5.4), these amorphous films exhibit dielectric properties. Silicon oxide is often utilized as part of a dielectric membrane, as a passivation or insulating layer, or as a sacrificial layer, which can be etched with hydrofluoric acid (HF)-containing etchants. Two different approaches to forming a silicon oxide thin film are... 

There are a number of materials used for the fabrication of pTAS devices. Perhaps the most common is glass due to its low cost, ease of machining, and suitability for electrophoresis and electroosmotic flow (EOF) applications without requiring surface modifications. It is also chemically inert to most reagents (apart from hydrofluoric acid and concentrated alkali). Silicon is also a valuable material that has similar chemical inermess and can easily be machined by chemical etching. While it is more expensive, it can be easily chemically etched to yield far higher aspect ratios than are possible with glass. Silicon is not suitable for electrophoresis or EOF applications without surface pretreatment. Devices fabricated from polymers such as polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) are also frequently used due to the low cost of the material (especially important for disposable devices) and the ease of fabrication. Perhaps one drawback with polymers is their incompatibility with solvents. They are suited to electrophoretic applications but frequently require surface modification to support EOF. Occasionally, metals are used however, these are far more frequently encountered in chemical microreactors. 

Concentrated acids also play an important role in the manufacturing of semiconductor devices. Hydrofluoric acid, for example, is used to remove oxide layers from wafer surfaces [239]. Glycolic acid is a major component of non-aqueous soldering agents [240], and concentrated orthophosphoric acid is used for etching silicon nitride on wafer surfeces [241]. 

The isotropic etching of glasses in hydrofluoric acid is used for contact holes in IC technologies [483] and for the production of microfluidic devices [495]. 

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