Specific Process Knowledge/Etch/Wet Polysilicon Etch

Wet Poly Etch

Wet PolySilicon Etch (in the middle): positioned in cleanroom 4

The wet Poly Etch is an isotropic silicon etch. This holds for both a poly-silicon thin-film as well as single-crystalline material such as a Si(100) surface. The Poly Etch process is placed in a dedicated PP-tank in a laminar-flow bench in cleanroom 4.

The Poly Etch is typically used for opening holes in poly-silicon thin-films, using photoresist as an etch mask. Due to its isotropic nature the under-etching (etch-bias) at least amounts to the thickness of the poly-silicon layer. Another example of usage is etching of "circular-shaped" holes in silicon substrates.

The Poly Etch is based on the combined oxidation of silicon followed by dissolution of the silicon oxide. The etch solution consists of:

HNO₃ : BHF : H₂O 20 : 1 : 20

Poly Etch data

	Poly Etch @ room temperature
General description	Etch of poly-si/Si(100)
Chemical solution	H3PO4 (85 wt%)
Process temperature	180 oC
Possible masking materials:	Thermal oxide (converted si-rich surface) LPCVD-oxide (TEOS) PECVD-oxide
Etch rate	~85 Å/min (stoichiometric Si3N4) ~60 Å/min (si-rich Si3N4) ~30 Å/min (annealed si-rich Si3N4) ~4 Å/min (Thermal oxide)
Batch size	1-25 wafers at a time
Size of substrate	2-6" wafers