Chemistry Reference
In-Depth Information
4
Etching of Oxides
4.1. INTRODUCTION
Chemical etching is a process for removal of silicon dioxide films through dissolution
in solutions. Dissolution of silicon oxides, in the context of this topic, is related to the
anodic behavior of silicon electrodes. However, the dissolution of anodic oxides is not
well studied. In contrast, there is a wealth of information on the dissolution of other
types of oxides. Much of this information must also be applicable, at least the qualita-
tive and mechanistic nature, to that of anodic oxides. Also, because oxides of different
types are commonly used in device fabrication, compiling the etch rate data of these
oxides and those of silicon (presented in Chapter 7) in the same volume would be useful
in practice. Additionally, because silica-water interaction, which has been extensively
investigated in the geological field, is fundamental to the etching of silicon oxides, some
of the results from the investigations on the dissolution of rocks and sands are also
included.
4.2. GENERAL
Chemical etching of silicon oxides is a key processing step in practically all
silicon-based microfabrication technologies. The premier practical application of this
process is in the manufacture of integrated circuits, in wafer cleaning, and in pattern
delineation. It is the very first step in chip manufacturing and in many cases it is the
final cleaning after the final metal etch step. Also, etching of silicon oxide as a surface
micromachining process is utilized in the fabrication of precision quartz and silicon-
based micromechanical structures, where chemical etching provides a convenient
method for removing undesired surface layers, and for surface micromachining of the
desired microstructures.
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On the other hand, etching of silicon oxide is also impor-
tant in situations where the oxides are used as the masking material and etching of the
oxides can be detrimental.
Dissolution of silicon oxides is geographically important since silica is one of the
phases are
found in natural and engineered earth systems in the form of quartz, cristobalite,
most abundant minerals in the Earth's crust. At least nine different
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