Profile control anisotropic etching

An interesting demonstration of profile control via alteration of the specific chemistry is that of silicon etching in C1F3 mixtures (86). Because a pure chemical (isotropic) etchant (F atoms) is combined with an ion-bombardment-controlled (anisotropic) etchant (Cl atoms), a continuous spectrum of profiles with varying anisotropies is generated by changing the gas composition. 

ICP is an important technology for micro- and nanoscale patterning process. High etch rate, high aspect ratio and anisotropic, good profile control, high uniformity, and RIE lag elimination are important issues in the development of MEMS... 

The limitations encountered with solution etching can be overcome by plasma-enhanced etching. Adhesion is not a major problem with dry-etch methods. Undercutting can be controlled by varying the plasma chemistry, gas pressure, and electrode potentials (2-6) and thereby generate directional or anisotropic profiles. 

Among the available anisotropic process schemes and recipes, the Bosch process which is named after the German company that developed and patented the technique is recognized as a standard process for ICP system. The Bosch approach is based on a variation of the Teflon-film sidewall passivation technique which avoids the recombination of active species in the gas phase. The deposition and etching steps are performed subsequently to control the sidewall profile of the 3D structures. In the deposition step, the precursor gas (CF4, C4Fg, CHF3, C2F6, or... 

---