Specific Process Knowledge/Etch/Wet Silicon Oxide Etch (BHF)

Wet Silicon Oxide Etch (BHF and SIO Etch (wetting agent))

Wet Silicon Oxide Etch (BHF): positioned in cleanroom 3

Silicon oxide can be etched using HF. At Danchip it is mainly used in a buffered version BHF (premixed). The BHF has a more stabil etch rate and has a high selectivty of oxide compared to photoresist which makes photoresist a good masking material for the oxide etch. However etching down to a silicon surface BHF leaves the siliocn surface slightly more rough than a pure HF solution.

SIO etch (BHF with wetting agent) can also be used for etching silicon oxide. This is mainly for etching small holes (~<?)

Silicon oxide etch data

	BHF	5% HF	SIO
General description	Etching of silicon oxide with a stabil etch rate	Mainly for removing native oxide
Chemical solution	6.5% HF and 30-40% NH$_{4}$F	5% HF	BHF with wetting agent
Process temperature	Room temperature	Room temperature	Room temperature
Possible masking materials	Photoresist Silicon nitride PolySi Blue film	Photoresist (in beaker) Silicon nitride (in beaker) PolySi (in beaker) Blue film (in beaker)	Photoresist Silicon nitride PolySi Blue film
Etch rate	Wet thermal oxide:~80nm/min PECVD1 (standard):~147nm/min TEOS:~265nm/min	Wet thermal oxide:~25nm/min PECVD1 (standard):~87nm/min TEOS:~153nm/min	Wet thermal oxide:~80nm/min PECVD1 (standard):~147nm/min TEOS:~265nm/min
Selectivity RSi3N4 / RSiO2	~21	<21
Batch size	1-25 wafers at a time	1-25 wafer at a time
Size of substrate	2-6" wafers	2-6" wafers
Allowed materials	Silicon Silicon nitrides Silicon oxides	Silicon Silicon nitrides Silicon oxides