Etching isotropic/anisotropic

The flux of F radicals to tire wafer is nearly isotropic. Anisotropic etching is due to ions tliat are incident on tire wafer essentially perjDendicular to tire surface (see above). 

Acidic silicon etchants are mainly used for two purposes for the delineation of crystal defects, as discussed in Section 2.5, or to remove silicon in an isotropic manner. Isotropic etching adds another degree of freedom to the design of micromechanical structures, because all alkaline etches are anisotropic. Most isotropic etchants for silicon were developed in the early days of silicon crystal technology and exhaustive reviews on this topic are available [Tu3, Rul]. A brief summary is given below. 

Figure 10.12 A microstructure after anisotropic, non-selective etching (left), anisotropic, selective etching (middle), and isotropic, selective etching (right).

Plasma etching. (PE) Physical-chemical etching with free radicals, supported by ions. Etching profile anisotropic-isotropic, good selectivity. 

Mesoporous dp = 2. .. 50 nm Carrier in liquid Affinity ligand in solid matrix anisotropic, isotropic track-etched immobilized in isotropic porous membrane isotropic, anisotropic Dialysis Carrier-mediated separation Ultrafiltration Electro- ultrafiltration... 

Aluminum, copper, diamond, gold, silicon Anisotropic etching, isotropic etching... 

Wet chemical etching (isotropic and anisotropic) Suspended membranes... 

Isotropic versus anisotropic etch Glass is always etched isotropically because the etchant etches all exposed surfaces at the same rate. This is independent of the etchant used and arises because glass does not have different planes. Depending on etchant, sihcon is either etched isotropically or anisotropically. Anisotropic etching occurs where material on one plane is removed at a greater rate than material on a different plane. The difference is most apparent in terms of channel shape and aspect ratio. Isotropic... 

Figure 3 The channel profiles for a channel etched isotropically and anisotropically into a silicon substrate. The same mask line width was used for both.

Anisotropic silicon etching Deep reactive ion silicon etching Electrochemical etching Isotropic silicon etching Selective sihcon etching Silicon etching Surface micro-... 

Figure C2.13.5. Schematic illustrations of isotropic etching by a neutral gas and anisotropic plasma etching.

Eig. 8. Schematic of etching directionaHty showing (a) isotropic etch, and (b) anisotropic etch. 

Fig. 2.72a-c Construction of buried micro-channels by combined anisotropic and isotropic etching. Reprinted from Kandlikar and Grande (2002) with permission... 

The high selectivity of wet etchants for different materials, e.g. Al, Si, SiOz and Si3N4, is indispensable in semiconductor manufacturing today. The combination of photolithographic patterning and anisotropic as well as isotropic etching of silicon led to a multitude of applications in the fabrication of microelectromechanical systems (MEMS). 

This arrangement changes drastically after inspection of the etched sample. The deep large voids designate the areas of isotropic phase (see Fig. 9.1 phase (b)). It further highlights that the anisotropic well-crystallized graphene layers adhere strongly only in a thin rim around the fiber axis. The immediate interface is also quite reactive to... 

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

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...

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