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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.
Neither Copper chloride or copper fluoride is volatile, which is why it is not allowed in any chamber:
Byproducts of silicon are very volatile:
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:
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A selection of potentially dry-etchable materials
Information from "Physical Constants of Organic Compounds," in CRC Handbook of Chemistry and Physics, 104th Edition (Internet Version 2023), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL. Link.
Note: The presence of a material here does not mean your etch will work or that you should etch this material in a particular system. It is only for reference.
Notable materials that can be deposited at Birck but not dry etched at Birck: Ag, Au, Co, Cu, Er, ITO (Indium), Mg, Mn, Ni, Pd, Sc
| Material | Gas Type | Volatile Etch Byproduct - Name | Volatile Etch Byproduct - Formula | CAS | Boiling Point (ºC) | Selected reaction and solubility notes |
|---|---|---|---|---|---|---|
| Ruthenium | Oxygen | Ruthenium tetroxide | RuO4 | 20427-56-9 | 40 | slightly soluble in H2O; reacts with ethanol |
| Boron | Fluorine | Trifluoroborane | BF3 | 7637-07-2 | -99.9 | soluble in H2O |
| Silicon | Fluorine | Silicon tetrafluoride | SiF4 | 7783-61-1 | -86 | reacts with H2O |
| Germanium | Fluorine | Germanium tetrafluoride | GeF4 | 7783-58-6 | -36.5 (sublimation point) | reacts with H2O |
| Tungsten | Fluorine | Tungsten hexafluoride | WF6 | 7783-82-6 | 17.1 | reacts with H2O; very soluble in cyclohexane |
| Rhenium | Fluorine | Rhenium hexafluoride | ReF6 | 10049-17-9 | 33.8 | soluble in HNO3 |
| Molybdenum | Fluorine | Molybdenum hexafluoride | MoF6 | 7783-77-9 | 34.0 | reacts with H2O; very soluble in hexane |
| Osmium | Fluorine | Osmium hexafluoride | OsF6 | 13768-38-2 | 47.5 | reacts with H2O |
| Vanadium | Fluorine | Vanadium pentafluoride | VF5 | 7783-72-4 | 48.3 | reacts with H2O |
| Iridium | Fluorine | Iridium hexafluoride | IrF6 | 7783-75-7 | 53.6 | reacts with H2O |
| Arsenic | Fluorine | Arsenic trifluoride | AsF3 | 7784-35-2 | 57.13 | reacts with H2O; soluble in ethanol |
| Platinum | Fluorine | Platinum hexafluoride | PtF6 | 13693-05-5 | 69.1 | |
| Rhenium | Fluorine | Rhenium heptafluoride | ReF7 | 17029-21-9 | 73.7 | |
| Selenium | Fluorine | Selenium tetrafluoride | SeF4 | 13465-66-2 | 101.6 | reacts with H2O; very soluble in ethanol |
| Tin | Fluorine | Stannic chloride | SnCl4 | 7646-78-8 | 114.15 | reacts with H2O; soluble in ethanol and acetone |
| Chromium | Fluorine | Chromium(V) fluoride | CrF5 | 14884-42-5 | 117 | reacts with H2O |
| Antimony | Fluorine | Antimony pentafluoride | SbF5 | 7783-70-2 | 141 | reacts with H2O |
| Tantalum | Fluorine | Tantalum pentafluoride | TaF5 | 7783-71-3 | 229.5 | soluble in H2O and ethanol |
| Niobium | Fluorine | Niobium pentafluoride | NbF5 | 7783-68-8 | 239 | reacts with H2O |
| Boron | Chlorine | Trichloroborane | BCl3 | 10294-34-5 | 12.5 | reacts with H2O and ethanol |
| Silicon | Chlorine | Silicon tetrachloride | SiCl4 | 10026-04-7 | 57.65 | reacts with H2O |
| Germanium | Chlorine | Germanium tetrachloride | GeCl4 | 10038-98-9 | 86.55 | reacts with H2O; soluble in ethanol |
| Arsenic | Chlorine | Arsenic trichloride | AsCl3 | 7784-34-1 | 130 | |
| Titanium | Chlorine | Titanium tetrachloride | TiCl4 | 7550-45-0 | 136.45 | reacts with H2O; soluble in ethanol |
| Vanadium | Chlorine | Vanadium tetrachloride | VCl4 | 7632-51-1 | 151 | reacts with H2O; soluble in ethanol |
| Aluminum | Chlorine | Aluminum trichloride | AlCl3 | 7446-70-0 | 180 (sublimation point) | |
| Gallium | Chlorine | Gallium trichloride | GaCl3 | 13450-90-3 | 201 | |
| Tantalum | Chlorine | Tantalum pentachloride | TaCl5 | 7721-01-9 | 239 | reacts with H2O; soluble in ethanol |
| Niobium | Chlorine | Niobium pentachloride | NbCl5 | 10026-12-7 | 247.4 | reacts with H2O |
| Iron (maybe) | Chlorine | Iron(III) chloride | FeCl3 | 7705-08-0 | 316 | soluble in ethanol and acetone |
A selection of likely non-dry-etchable materials
Notable materials that can be deposited at Birck but not chemically dry etched at Birck:
Ag, Au, Co, Cu, Er, ITO (Indium), Mg, Mn, Ni, Pd, Sc
All of these except Au may be etched (with ion milling, a physical process rather than chemical) in the AJA ICP Argon Ion Mill Etcher.
Specific Materials
Aluminum Oxide
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