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.

Etch of silicon oxide can be done by either wet etch or dry etch. The standard setups for this here at DANCHIP are:

Wet etches:

• Wet Silicon Oxide Etch

Dry etches:

• Dry etch using RIE1 or RIE2
• Dry etch using AOE
• IBE/IBSD Ionfab 300

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

	Wet Silicon Oxide etch (BHF, SIO Etch (wetting agent), 5%HF)	RIE	AOE
General description	Isotropic etch	Anisotropic etch: vertical sidewalls	Anisotropic etch: vertical sidewalls, especially good for deep etch and high aspect ratio etch
Possible masking materials	Photoresist Silicon nitride	Photoresist (Poly)Silicon Aluminium Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Photoresist (Poly)Silicon Aluminium Chromium (ONLY if the other masking materials can not be used!)
Etch rate	~75 nm/min (Thermal oxide) in BHF ~90 nm/min (Thermal oxide) in SIO Etch ~25 nm/min (Thermal oxide) in 5%HF	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.
Batch size	1-25 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)
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist Blue film Gold (Au) and Nickel (Ni) (but only in BHF2 (KOH)!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Chromium (ONLY as masking material if the other masking materials can not be used!)