Specific Process Knowledge/Etch/Wet Polysilicon Etch

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Wet PolySi Etch

The 'Poly Si Etch' bath is placed inside Wet Bench 04 in cleanroom D-3

The wet PolySi 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 Si Etch bath is placed inside 'Wet Bench 04: Oxide and Poly etch' cleanroom D-3. For samples that are not allowed in this bath the polysilicon etch solution can also be mixed in a plastic beaker in Fume hood 01 or 02 (Acids/bases).

The PolySi Etch is typically used for opening holes in poly-silicon thin-films, using photoresist as an etch mask or to strip Poly silicon of a wafer. 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 PolySi Etch is based on the combined oxidation of silicon (by nitric acid) followed by an etch of the formed silicon oxide (by hydrofluoric acid). The etch solution consists of:

HNO₃ : BHF : H₂O - (20 : 1 : 20)

NB: The life time of the solution is a few days to 4 weeks.

The user manual and contact information can be found in LabManager:

Poly Si Etch info page in LabManager

PolySi Etch data

	PolySi Etch @ room temperature
General description	Etch of poly-si/Si(100)
Chemical solution	HNO3 : BHF : H2O (20 : 1 : 20)
Process temperature	Room temperature
Possible masking materials	Photoresist(min. 2.2 µm is recommended) LPCVD-oxide (TEOS)
Etch rate	RSi ~100-200 nm/min (depending on doping level) RSiO2 ~6 nm/min RSi3N4 ~0 nm/min Photoresist (2.2 µm) withstand ~20-30 min
Batch size	1-25 wafers at a time
Size of substrate	4-6" wafers