Specific Process Knowledge/Etch/Etching of Silicon Nitride/Etch of Silicon Nitride using RIE

For a general introduction to RIE at Danchip see RIE (Reactive Ion Etch)

Etching of silicon nitride using RIE can be done with several recipes. It can be etched by our standard silicon etch recipe: OH_PolyA which is based on SF6. It can also be etched using the recipe 1Nitride which is based on CHF3. The difference of these two etches has not been investigate in details. Look in the table below to see what we know

Some RIE recipes for etching of silicon nitride:

Name	SF6 flow	O2 flow	CHF3 flow	N2 flow	Pressure	Power
OH_PolyA	32 sccm	8 sccm	.	.	80 mTorr	30 W
BGE-NITR	.	.	8 sccm	43 sccm	38 mTorr	50 W

Expected result using the above RIE recipes for etching of silicon nitride:

You should be aware that the result can deviate quit a lot from what is written here depending on ex. the mask loading.

Name	Tested with mask load:	Etch rate	Anisotropy	Selectivity to resist	Selectivity to oxide	Selectivity to silicon	Comments
OH_PolyA	10-20%	0.05 µm/min	?	~1:1	~1:2-3	~1:13	.
BGE-NITR	10-20%	0.04 µm/min	Expected to be very anisotropic - not verified	?	~1:1	~1:1	Especially good to remove nitride on one side of the wafer avoiding getting anything etched on the back side.

SEM picture shoving the etch profile for a wafer with 150 nm nitride that has been etched in RIE1. The wafer has been etched for 3.5 min with the recipe "BGE_NITR" (pressure increased to 42 mTorr), and most of the wafer (>99 %) has been etched. The structures are made with e-beam lithography, and the Al etch mask has been removed before the SEM inspection. Wafer tilted 45 degrees.