Chemistry Reference
In-Depth Information
(Fig. 7.57d), anisotropic dissolution (Fig. 7.57e), and formation of pores (Fig. 7.57f),
are associated with the structure and properties of the silicon crystal.
The surface of the silicon crystal, no matter how it is finished, will have a certain
number of lattice defects, which tend to dissolve preferentially resulting in formation
of etch pits and other features. Terraces and steps of various sizes are inevitable con-
sequences of anisotropic dissolution of the surfaces misoriented from the (111) surface.
Also, a silicon surface, whether initially smooth or not, in HF solutions, has an
intrinsic tendency to roughen and form micropores governed by sensitivity of the
electrochemical reactions on a semiconductor electrode to surface curvature.
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Furthermore, the two groups of factors shown in Fig. 7.57 may affect each other. For
example, the initial lattice inhomogeneities may provide the sites for deposition
whereas localized deposition may enhance the development of etch features such as
pits or hillocks.
7.8. APPLICATIONS
The applications of etching can be broadly classified into three categories: (1)
surface preparation, (2) structural characterization, and (3) device fabrication.
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In
category 1, etching is used to prepare suitable surfaces for subsequent physical and
chemical measurements or processing. Here etching is used as a tool for cleaning
or polishing, for removing the damaged or defective surface layer, or for surface sta-
bilization. In category 2, etching is used for the identification of defects such as dislo-
cations, for microstructrural studies, and for orientation examination, or for impurity
distribution. In category 3, etching is used for removing materials and for machining
structures in device fabrication.
