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==Wet PolySi Etch==
==Wet PolySi Etch==


[[Image:BHF-PolySi-Al-etch.JPG|300x300px|right|thumb|Wet PolySilicon Etch (in the middle): positioned 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 PolySi Etch process is placed in a dedicated PP-tank in a laminar-flow bench in cleanroom D.


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 PolySi Etch process is placed in a dedicated PP-tank in a laminar-flow bench in cleanroom 4.
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 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 PolySi Etch is based on the combined oxidation of silicon followed by dissolution of the silicon oxide. The etch solution consists of:
The PolySi Etch is based on the combined oxidation of silicon followed by dissolution of the silicon oxide. The etch solution consists of:
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HNO<sub>3</sub> : BHF : H<sub>2</sub>O  - (20 : 1 : 20)
HNO<sub>3</sub> : BHF : H<sub>2</sub>O  - (20 : 1 : 20)


'''NB: The life time of the solution is only a few days.'''
'''NB: The life time of the solution is a few days to one week.'''


'''The user manual and contact information can be found in LabManager:'''
'''The user manual and contact information can be found in LabManager:'''
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[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=129 Isotropic Etch/Poly Etch info page in LabManager]
[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=379 Isotropic Etch/Poly Etch info page in LabManager]


===PolySi Etch data===
===PolySi Etch data===
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!Etch rate
!Etch rate
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*R<sub>Si</sub> ~1000-2000 Å/min (depending on doping level)
*R<sub>Si</sub> ~100-200 nm/min (depending on doping level)
*R<sub>SiO<sub>2</sub></sub> ~60 Å/min
*R<sub>SiO<sub>2</sub></sub> ~6 nm/min
*R<sub>Si<sub>3</sub>N<sub>4</sub></sub> ~0 nm/min
*Photoresist (2.2 µm) withstand ~20-30 min
*Photoresist (2.2 µm) withstand ~20-30 min
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!Size of substrate
!Size of substrate
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2-4" wafers
4-6" wafers
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