Chemical etching etch rate

It has been speculated that there is a common origin of the reduced chemical etch rate for (111) oriented silicon substrates and for highly p-type doped substrates. But the electrochemical investigations discussed above indicate that the passivation of highly doped p-type Si can be ascribed to an oxide film already present at OCP, while no such oxide film is observed on (111) silicon below PP. This supports models that ascribe the reduced chemical etch rate on (111) planes to a retarded kinetic for Si surface atoms with three backbonds, present at (111) interfaces [Gil, A12], as discussed in Section 4.1. 

In the ion induced damage mechanism energetic ions break crystal bonds on the film surface thereby making the film more accessible and more reactive to the active chemical etchant. However, the side walls remain relatively unperturbed, and etching proceeds at the nominal chemical etch rate. Consequently, material removal proceeds far more rapidly in the ion flux direction, resulting in anisotropy. In actuality, the surfaces exposed to the plasma are likely to be composed of a chemisorbed coating of etchant... 

E. A. Irene, D. W. Dong, and R. J. Zeto, Residual stress, chemical etch rate, refractive index, and density measurements on SiO films prepared using high pressure oxygen, J. Electrochem. Soc. 127, 396, 1980. 

Y. Watanahe, Effects of annealing on oxygen depth profiles and chemical etching rates of thermally grown silicon oxides, J. Electrochem. Soc. 145(4), 1306, 1998. 

Silicon can be etched by chlorine atoms without any ion bombardment. Oxide is not etched by Cl and, therefore, a very high selectivity can be obtained. The chemical etch rate of -type single crystal Si or polysilicon is given by [216]... 

Chemical durability of materials is another research topic of importance. The tiny structures which are exposed to the harsh chemical environment inside the micro-TAS must be extremely stable chemically. Etching rates must be well below 1 A/h if 1 pm thick structures or a thin film coating are to be used for more than one year. The stability of the reagents used in the system must also be investigated if maintenance-free periods of a half year or more are to be achieved by the system. 

The energetic particle bombardment also improves the surface coverage and decreases the pinhole porosity in the deposited film. This increased density and better surface coverage is reflected in film properties such as better corrosion resistance, lower chemical etch rate, higher hardness,lowered electrical resistivity of metal films, lowered gaseous and water vapor permeation through the film, and increased index of refraction of dielectric films. 

Chemical etch rate - time for film removal/weight loss. 

Often, one characterization technique will yield results that depend on several properties of the material. For example, a chemical etch rate test will give an indication of density, surface area, porosity, and composition and is an excellent relative (comparative) test to determine if the product today is the same as it was yesterday. Often these simple observations provide the first clue to a problem or change in the processing, and often to the origin of the problem. Remember, properties should have been previously determined for a good product so that there is a baseline value with which to make a comparison. Property and compositional measurements often provide an average value and local property variations such as pinholes, stress, and thickness may be missed - are they important ... 

The chemical etch rate of a material by an etchant depends on the solution temperature, surface area (him morphology), residual him stress, him microstructure, stoichiometry, and the soluhon strength. It also dq)cnds on how fast the etch products arc removed from the surface and from the vicinity of the surface (i.e. agitahon). Gradahon of him properties through the thickness can also affect the etch rate. Chemical etch rates are primarily used as comparahve tests. Figure 11.7 shows a typical etch rate analysis and Table 3.11 Usts chemical etchants for a number of materials many more are to be found in the literature. 

Chemical etch-rate test (characterization) The rate (in angstroms per minute or mass per unit area per minute) at which material is removed by chemical etching. 

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