Plasma etching

Plasma etching - мodern VLSI processes avoid wet etching, and use "plasma etching" instead. Plasma etchers can operate in several modes by adjusting the parameters of the plasma. Ordinary plasma etching operates between 0.1 and 5 Torr. (This unit of pressure, commonly used in vacuum engineering, equals approximately 133.3 pascals.) The plasma produces energetic free radicals, neutrally charged, that react at the surface of the wafer. Since neutral particles attack the wafer from all angles, this process is isotropic. The source gas for the plasma usually contains small molecules rich in chlorine or fluorine. For instance, carbon tetrachloride (CCl4) etches silicon and aluminium, and trifluoromethane etches silicon dioxide and silicon nitride. A plasma containing oxygen is used to oxidize ("ash") photoresist and facilitate its removal. "Ion milling", or "sputter etching", uses lower pressures, often as low as 10-4 Torr (10 mPa). It bombards the wafer with energetic ions of noble gases, often Ar+, which knock atoms from the substrate by transferring momentum. Because the etching is performed by ions, which approach the wafer approximately from one direction, this process is highly anisotropic. On the other hand, it tends to display poor selectivity. "Reactive-ion etching" (RIE) operates under conditions intermediate between sputter and plasma etching (between 10-3 and 10-1 Torr). "Deep reactive-ion etching" (DRIE) modifies the RIE technique to produce deep, narrow features.

Further information:

1. Wolf, S.; R.N. Tauber (1986). Silicon Processing for the VLSI Era: Volume 1 - Process Technology. Lattice Press. pp. 531–534
2. Wolf, S.; R.N. Tauber (1986). Silicon Processing for the VLSI Era: Volume 1 - Process Technology. Lattice Press. p. 546
3. Bahadur, Birendra (1990). Liquid Crystals: Applications and Uses. World Scientific. p. 183
4. Walker, Perrin; William H. Tarn (1991). CRC Handbook of Metal Etchants. pp. 287–291
5. Kohler, Michael (1999). Etching in Microsystem Technology. John Wiley & Son Ltd. p. 329
6. В. В. Усова, Т. П. Плотникова, С. А. Кушакевич. Травление титана и его сплавов
7. М. Беккерт, Х. Клемм. Способы металлографического травления. Справочник

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