Materials can generally be etched in the RIEs as long as they form volatile byproducts, or products for which the vapor pressure (at the temperature of the etch) is higher than the pressure of the chamber. Etching is very complicated and this will be massive oversimplification...but generally volatile byproducts can be determined from literature, or as a fallback, the CRC Handbook of Chemistry and Physics Online, (4) Properties of the Elements & Inorganics, Physical Constants of Inorganic Compounds: https://hbcp.chemnetbase.com/faces/documents/04_02/04_02_0001.xhtml. From there, click "Go to Interactive Table", and find products that may be formed (i.e. chloride, fluorides, oxides, depending on the gasses). A compound is deemed volatile if it has a boiling point at a reasonable temperature range for the temperature and pressure of the system. Note that at lower pressures, boiling points decrease, so these are just a good staring point reference. As a VERY general rule of thumb, anything with a boiling point (tbp) < 185 C will be volatile in the ICP RIEs. As an example, aluminum chloride is volatile, and aluminum fluoride and aluminum are not.  Image Modified
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Neither Copper chloride or copper fluoride is volatile, which is why it is not allowed in any chamber:  Image Modified
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Byproducts of silicon are very volatile:  Image Modified
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Many times different fluorides/chlorides of the same material will have drastically different boiling points. It's important to research which will be formed in the plasma. Titanium is a good example of this, with TiCl2 and TiCl3 being non-volatile, and TiCl4 being volatile:  Image Modified
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