View source for Specific Process Knowledge/Etch/Wet Polysilicon Etch

==Wet Poly Etch==

[[Image:Wet_PolySi_etch.jpg|300x300px|thumb|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:

HNO<sub>3</sub> : BHF : H<sub>2</sub>O   (20 : 1 : 20)


===Poly Etch data===

{| border="1" cellspacing="0" cellpadding="4" align="left"
! 
! Poly Etch @ room temperature
|- 
|General description
|
Etch of poly-si/Si(100)
|-
|Chemical solution
|HNO<sub>3</sub> : BHF : H<sub>2</sub>O   (20 : 1 : 20)

|-
|Process temperature
|Room temperature
|-
|Possible masking materials:
|
*Photoresist(min. 2.2 µm is recommended)
*LPCVD-oxide (TEOS)
|-
|Etch rate
|
*~85 Å/min (stoichiometric Si<sub>3</sub>N<sub>4</sub>)
*~60 Å/min (si-rich Si<sub>3</sub>N<sub>4</sub>)
*~30 Å/min (annealed si-rich Si<sub>3</sub>N<sub>4</sub>)
*~4 Å/min (Thermal oxide)
|-
|Batch size
|
1-25 wafers at a time
|-
|Size of substrate
|
2-6" wafers
|-