Etchants defect etching

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. 

Etchants for defect and junction delineation are usually composed of HF and an oxidizing agent such as HN03 [Dal, Gr4, Ka4, Nel], K2Cr207 [Se5] or Cr03 [Sil, Jel, Sc7, Ya4, Me5]. Alkaline solutions are rarely used for defect delineation [Mal2], An etch pit will form on a silicon surface if the dissolution rate is enhanced locally. Enhancement of the etch rate may occur for various reasons ... 

Etch pit formation as a result of the factors given in 1-4 above can be used to characterize silicon materials. A summary of common defect etchants for silicon is given in Table 2.1. 

Tab. 2.1 Composition and etch rates of common defect etchants for silicon. ...

Depending on surface termination and etchant, either plane etching or attack only at defects... 

The degree of differential etching at defects depends on the orientation of the crystal. In general, for diamond-type structures such as silicon it is much easier to reveal dislocations on the 111 planes than on other planes. Some etchants, such as Sirtl etch, reveal sharply the defects on (111) planes but are not satisfactory for (100) planes. 

KOH, is rather high compared to other organic etchants as shown in Fig. 26. Etch rate ratios are almost constant with respect to doping concentration up to the heavily doped levels where etch rate reduction occurs [45, 80, 92]. A highly defective surface, such as a saw-damaged surface, may not exhibit anisotropic etching rates [152],... 

Crystal defects impede domain wall movement by increasing Eo and To, the minimum field and stress needed to initiate motion. For this reason, studies of chemically etched surfaces of Gd2(Mo04)3 have been done to investigate the nature of these defects. Kashiwada and Kishino (1974) have used chemical etchants and X-ray transmission topography to identify flat helical dislocations and flat closed loop dislocations that have axes parallel [110] directions. Although these authors did not report on the interaction of these defects with... 

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