Specific Process Knowledge/Etch/Etching of Silicon Nitride

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

• Wet Silicon Nitride Etch
• Etch of Silicon Nitride using RIE

Comparison of wet Silicon Nitride etch and RIE etch for etching of Silicon Nitride

	Wet Silicon Nitride etch	Buffered HF (BHF)	RIE
General description	Isotropic etch Well suited for removing all nitride on a wafer surface (nitride strip) without a mask. High selectivity Si3N4/Si (>100) and Si3N4/SiO2 (>20) @ 180 C.	Isotropic etch Well suited for removing all PECVD nitride on a wafer surface (nitride strip) without a mask. Etches LPCVD nitride very slowly	Anisotropic etch: vertical sidewalls
Possible masking materials	Silicon Oxide PolySilicon	Photoresist PolySilicon Blue film	Photoresist Silicon Oxide Aluminium Chromium (ONLY RIE2!) Other metals if they cover less than 5% of the wafer area (ONLY RIE2!)
Etch rate	Si3N4 @ 180 oC: ~84 Å/min Si3N4 @ 160 oC: ~60 Å/min	PECVD nitride: ~400-1000 Å/min	Typically 40-50 nm/min can be increased or decreased by using other recipe parameters.
Batch size	1-25 wafers at a time	1-25 wafers at a time	1 wafer at a time
Size of substrate	4" wafers	4" wafers	4" wafers or smaller pieces
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist Blue film	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!)