Specific Process Knowledge/Etch/Etching of TOPAS

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Etching of TOPAS

TOPAS is etched by an oxygen plasma in the ASE. Masking of TOPAS was achieved by photo resist or a hard mask of aluminum or silicon. Photo resist is the preferred masking material, since hard masks tends to introduce local masking due to redeposition. TOPAS can be etched at rates up to 500 nm/min, with excellent uniformity over the wafer.

TOPAS by khara@anolab

Parameter	Slow TOPAS etch	Fast TOPAS etch
O2 (sccm)	50	99
CO2 (sccm) (not available anymore)	50	0
Pressure (mTorr)	40	40
Coil power (W)	800	720
Platen power (W)	60	60
Temperature (oC)	20	20
Etch rate (nm/min)	~350	~500
Center-Edge uniformity	0.98	0.95

Under etching and local masking

When etching TOPAS I have in general used a hard mask material underneath my layer of photoresist, to ensure that if the resist was completely removed, a mask was still present. It is however always recommended to have a photoresist as mask, as a hard mask material will introduce roughness in unmask areas of the polymer.

Silicon hard mask	Aluminum hard mask
Etch broke through the photoresist layer, and sputtered silicon have redeposited on the polymer surface, introducing local masking effects.	The aluminum hard mask has been etched in the resist developer introducing poor edge definition even though the resist was not completely removed by the etch.
Etch O2 flow [sccm]:50 CO2 flow [sccm]:50 Pressure [mTorr]:40 Coil power [W]:800 Platen power [W]:60 Temperature [°C]:20	Etch O2 flow [sccm]:50 CO2 flow [sccm]:50 Pressure [mTorr]:40 Coil power [W]:800 Platen power [W]:60 Temperature [°C]:20