Specific Process Knowledge/Etch/Etching of Silicon

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

Wet etches:

• KOH Etch
• Wet PolySilicon etch

Dry etches:

• Dry etch using RIE1 or RIE2
• ASE (Advanced Silicon Etch)

Comparison of KOH etch, wet PolySilicon etch, RIE etch and ASE etch for etching of Silicon

	KOH	PolySilicon etch	RIE	ASE
General description	Anisotropic etch in the (100)-plan High selectivity to the other plans	Isotropic etch in Silicon and Polysilicon	Can etch isotropic and anisotropic depending on the process parameters Anisotropic etch: vertical sidewalls independent on the crystal plans	As RIE but better for high aspect ratio etching and deep etches (higher etch rate) Good selectivity to photoresist
Possible masking materials	Silicon Nitride Silicon Oxide	Photoresist	Photoresist E-beam resist Silicon Oxide Silicon Nitride Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)	Photoresist Silicon Oxide Silicon Nitride Aluminium
Etch rate	Si(100) @80oC: 1.29+0.05 µm/min Si(100) @70oC: ~0.7 µm/min Si(100) @60oC: ~0.4 µm/min	~100-200 nm/min, highly dependent on doping level	<40nm/min to >600nm/min depending on recipe parameters and mask design	<130nm/min to >5.6 µm/min depending on recipe, mask design and aspect ratio.
Size of substrate	4" in our standard bath 4", 2" in "Fumehood KOH"	4" in our standard bath	4" (or smaller with carrier)	6" (when it is set up for 6") and 4" (or smaller if you have a carrier)
Batch size	25 wafers at a time 1-5 wafers in "Fumehood KOH"	25 wafers at a time	One wafer at a time	One wafer at a time
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Other materials (only in "Fumehood KOH")	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium