Specific Process Knowledge/Etch/Etching of Silicon Oxide

Silicon oxide can be etched using either wet chemistry or dry etch equipment. Wet chemistry is mainly used to remove all the oxide on the surface (backside and front side) of a wafer or for isotrotropic etching. Dry etching etches anisotropic. It etches one side of the wafer at a time and can be used to etch structures with several masking materials.

Comparison of wet Silicon Oxide etch and dry etches (RIE and AOE) etch for etching of Silicon Oxide

	Wet Silicon Oxide etch (BHF)	RIE	AOE
What is it good for:	Isotropic etch	Anisotropic etch: vertical sidewalls	Anisotropic etch: vertical sidewalls, especially good for deep etch and high aspect ratio etch
Possible masking materials:		Photoresist (Poly)Silicon Aluminium Chromium (ONLY RIE2!) Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Photoresist (Poly)Silicon Aluminium
Etch rate		Typically 40-120 nm/min can be increased or decreased by using other recipe parameters.	Typically 200-600 nm/min can be increased or decreased by using other recipe parameters.
Process volume	25 wafers at a time	1 wafer at a time	1 wafer at a time
Size of substrate	4" wafers	4" wafers or smaller pieces	6" or 4" depending on the setup (smaller pieces if you have a carrier wafer)