Specific Process Knowledge/Etch/Wet Silicon Nitride Etch

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The 'Nitride etch' bath is placed inside 'Wet bench 02: Nitride ethc' in Cleanroom D-3

Wet Etching of silicon nitride - stoichiometric and Si-rich - is done in a dedicated wetbench with an integrated quartz tank. The quartz tank can take up to 25 6" wafers in dedicated carriers. The 'Wetbench 02: Nitride etch' is placed in cleanroom D-3. The process is mainly used to strip silicon nitride (maskless), but can also be used for masked etching of silicon nitride using some kind of silicon oxide as etch mask. However, the wet silicon nitride etch is isotropic - meaning that the under-etching (etch-bias) at least amounts to the thickness of the silicon nitride layer.

The etch solution is initially 85 wt% H₃PO₄ which is heated up to the boiling temperature - ca. 160°C the selectivity R_Si3N4 / R_SiO2.

NB: Great care has to be taken in this process due to risk of bumping. Therefore it is essential, that you stir thoroughly during heat up, before you start heating, at 50°C and finally at 100°C

The user manual, user APV and contact information can be found in LabManager:

Nitride etch info page in LabManager,

Wet Silicon Nitride Etch

	Nitride Etch @ 160oC
Generel description	Etch/strip of silicon nitride
Link to safety APV and KBA	see APV here see KBA here
Chemical solution	H3PO4 (85 wt%)
Process temperature	160 oC
Possible masking materials	Thermal oxide (converted si-rich surface) LPCVD-oxide (TEOS) PECVD-oxide
Etch rate	~26 Å/min (Si-rich Si3N4)
Selectivity RSi3N4 / RSiO2	The selectivity (sirich nitride:oxide) is higher at 160 oC than at 180 oC
Batch size	1-25 wafer at a time
Size of substrate	2-6" wafers
Allowed materials	Silicon Silicon nitrides Silicon oxides