As with oxide etching, etching nitride with selectivity to silicon is
usually done by depositing fluorocarbon polymer on the wafer.
Suitable gases to deposit such a polymer are CHF3, C4F8, or more generally
C_xF_yH_z where (y-z)<=2x (which maximises the density of CF2 radicals in
the plasma)
The etchants (F) have to diffuse through this polymer film to attack the
substrate, so etch rate is very sensitive to film thickness.
Reaction with the nitrogen in the film reduces the polymer thickness, so
the nitride etches faster than the silicon, despite its stronger chemical
bonding.
See Schaepkens etc al, JVST A 17, 29 (1999) for a very clear experimental
study.

Regards,
Nick


Dr Nick Appleyard
Research Physicist
Etch Product Group, Trikon Technologies Ltd
Ringland Way, Newport, South Wales, NP18 2TA
Tel    (44) 01633 414187
Fax   (44) 01633 414180
Mob  (44) 0788 178 0727


Dear all:

I would like to find out a RIE recipe which performs a selective etching
between nitride and silicon.
I only know that CHF3 is one of the suitable etching gas.
Does anybody know the recipe, including gas types, flow rate, power,
pressure, and etching rate?
The RIE facility here only provides SF6, CF4, O2, N2, CHF3, etc.
The max power is 300W.
Please give me some advice if possible.
I really appreciate it.

Yi Chun

Dept. of Power Mechanical Engineering, National Tsing Hua University,
Taiwan.



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