Specific Process Knowledge/Etch/Wet Polysilicon Etch: Difference between revisions

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==Wet PolySilicon Etch==
'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php/Specific_Process_Knowledge/Etch/Wet_Polysilicon_Etch click here]'''


[[Image:Wet_PolySi_etch.jpg|300x300px|thumb|Wet PolySilicon Etch (in the middle): positioned in cleanroom 4]]
'''Unless anything else is stated, everything on this page, text and pictures are made by DTU Nanolab.


Wet Etching of silicon nitride - stoichiometric and si-rich - is done in a dedicated laminar flow bench with an integrated quartz tank (Tiger Tank - TT-4). The quartz tank can take up to one 6" wafer carrier. The flow bench is placed in cleanroom 4. The process is mainly used to strip silicon nitride (maskless), but can also be used for masked etching of silicon nitride using some kind of silicon oxide as etch mask. However, the wet silicon nitride etch is isotropic meaning that the under-etching (etch-bias) at least amounts to the thickness of the silicon nitride layer.
'''All links to Kemibrug (SDS) and Labmanager Including APV requires login.'''


The etch solution is initially 85 wt% H<sub>3</sub>PO<sub>4</sub> which is heated up to the boiling temperature - ca. 157 <sup>o</sup>C. Water is allowed to boil off thus raising the concentration and the boiling temperature of the solution until a boiling temperature of 180 <sup>o</sup>C is reached. Thereafter, the wafers are submerged into the bath and the water-cooled lid is closed to maintain the concentration and the boiling temperature. In some cases a lower boiling temperature is chosen - typically 160 <sup>o</sup>C - which lowers the etch rate and improves the selectivity R<sub>Si<sub>3</sub>N<sub>4</sub></sub> / R<sub>SiO<sub>2</sub></sub>.
'''All measurements on this page has been made by Nanolab staff.'''


[[Category: Equipment|Etch Wet Polysilicon]]
[[Category: Etch (Wet) bath|Polysilicon]]


'''NB: Great care has to be taken in this process due to risk of "shock-boiling" '''
==Wet PolySi Etch==


[[Image:polyetch1.jpg|300x300px|thumb|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).


===Nitride etch - key facts===
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.


{| border="1" cellspacing="0" cellpadding="4" align="left"
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:
 
HNO<sub>3</sub> : BHF : H<sub>2</sub>O  - (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:'''
<!-- remember to remove the type of documents that are not present -->
 
[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=379 Poly Si Etch info page in LabManager]
 
===PolySi Etch data===
 
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;"
|-
|-style="background:silver; color:black"
!  
!  
! Nitride etch @ 180 <sup>o</sup>C
! PolySi Etch @ room temperature
! Nitride etch @ 160 <sup>o</sup>C
|-  
|-  
|General description
 
|-style="background:WhiteSmoke; color:black"
!General description
|
|
Etch/strip of silicon nitride
Etch of poly-si/Si(100)
|
Etch/strip of silicon nitride
|-
|-
|Chemical solution
 
|H<sub>3</sub>PO<sub>4</sub>    (85 wt%)
|-style="background:LightGrey; color:black"
|H<sub>3</sub>PO<sub>4</sub>     (85 wt%)
!Chemical solution
|HNO<sub>3</sub> : BHF : H<sub>2</sub>O  (20 : 1 : 20)


|-
|-
|Process temperature
|180 <sup>o</sup>C
|160 <sup>o</sup>C


|-style="background:WhiteSmoke; color:black"
!Process temperature
|Room temperature
|-
|-


|Possible masking materials:
|-style="background:LightGrey; color:black"
!Possible masking materials
|
|
*Thermal oxide (converted si-rich surface)
*Photoresist(min. 2.2 µm is recommended)
*LPCVD-oxide (TEOS)
*LPCVD-oxide (TEOS)
*PECVD-oxide
|
*Thermal oxide (converted si-rich surface)
*LPCVD-oxide (TEOS)
*PECVD-oxide
|-
|-
|Etch rate
 
|-style="background:WhiteSmoke; color:black"
!Etch rate
|
|
*~85 Å/min (stoichiometric Si<sub>3</sub>N<sub>4</sub>)
*R<sub>Si</sub> ~100-200 nm/min (depending on doping level)
*~60 Å/min (si-rich Si<sub>3</sub>N<sub>4</sub>)
*R<sub>SiO<sub>2</sub></sub> ~6 nm/min
*~30 Å/min (annealed si-rich Si<sub>3</sub>N<sub>4</sub>)
*R<sub>Si<sub>3</sub>N<sub>4</sub></sub> ~0 nm/min
*~4 Å/min (Thermal oxide)
*Photoresist (2.2 µm) withstand ~20-30 min
|
*~26 Å/min (si-rich Si<sub>3</sub>N<sub>4</sub>)
*~? Å/min (Thermal oxide)
|-
|-
|Batch size
 
|-style="background:LightGrey; color:black"
!Batch size
|
|
1-25 wafers at a time
1-25 wafers at a time
|
1-25 wafer at a time
|-
|-
|Size of substrate
 
|
|-style="background:WhiteSmoke; color:black"
2-6" wafers
!Size of substrate
|
|
2-6" wafers
4-6" wafers
|-
|-
|}

Latest revision as of 10:03, 7 February 2023

Feedback to this page: click here

Unless anything else is stated, everything on this page, text and pictures are made by DTU Nanolab.

All links to Kemibrug (SDS) and Labmanager Including APV requires login.

All measurements on this page has been made by Nanolab staff.

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

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