Specific Process Knowledge/Etch/Etching of SU-8

Etching of SU-8

SU-8 can be etched by a oxygen plasma with a small amount of SF₆ to remove the antimony present from the photo initiator. Etching of SU-8 has been developed on the ASE and was tested as a mask less reduction of patterns defined by photo lithography. Two processes are available, a high and a low anisotropic etch for use as etching or thinning of structures.

• High anisotropic etch: etch rate ~400nm/min, anisotropy ~0.8
• Low anisotropic etch: etch rate ~170nm/min, anisotropy ~0.3

Recipes in ASE

SU8aniso

The anisotropic SU8aniso etch was design to etch structures in SU-8 with a low roughness of the etched surface, however it has not been tested with any mask material. For a polymeric mask a low selectivity is expected. The etch rate was measured to around 400 nm/min, but will depend on wafer coverage. The surface layer concentration of antimony (Sb) after etch is expected to be below 2%.

SU8aniso and SU8iso etches by khara@nanolab

Parameter	SU8aniso etch	SU8iso etch
O2 (sccm)	99	99
SF6 (sccm)	17	14
Pressure (mTorr)	40	20
Coil power (W)	800	800
Platen power (W)	30	0
Temperature (oC)	30	10
Etch rate (nm/min)	~400	~170
anisotropy	~0.8	~0.3
Sb in surface layer (%)	<2	<2.75

SU8iso

The SU8iso etch was developed for thinning of lithography defined structures to gain higher aspect ratio or thinner structures than possible with photo lithography.

Roughness and antimony effects in SU-8 etching

SU-8 lines by lithography	Oxygen etch	SU8aniso	SU8iso
No etching	Etch O2 flow [sccm]:99 SF6 flow [sccm]:0 Pressure [mTorr]:20 Coil power [W]:800 Platen power [W]:30 Temperature [°C]:10	Etch O2 flow [sccm]:99 SF6 flow [sccm]:17 Pressure [mTorr]:40 Coil power [W]:800 Platen power [W]:30 Temperature [°C]:30	Etch O2 flow [sccm]:99 SF6 flow [sccm]:14 Pressure [mTorr]:20 Coil power [W]:800 Platen power [W]:0 Temperature [°C]:10