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


[[Category: Equipment|Etch Wet silicon nitride]]
'''Unless anything else is stated, everything on this page, text and pictures are made by DTU Nanolab.'''
[[Category: Etch (Wet) bath|Silicon Nitride]]
 
'''All links to Kemibrug (SDS) and Labmanager Including APV requires login.'''
 
'''All measurements on this page has been made by Nanolab staff.'''
 
 
 
[[index.php?title=Category:Equipment|Etch Wet silicon nitride]]
[[index.php?title=Category:Etch (Wet) bath|Silicon Nitride]]
 
[[Image:Nitrideetch.JPG|300x300px|thumb|The 'Nitride etch' bath is placed inside 'Wet bench 02: Nitride ethc' in Cleanroom D-3]]


==Wet Silicon Nitride Etch==
[[Image:Wet_nitride_etch.JPG|300x300px|thumb|Wet nitride etch: positioned in cleanroom D-3]]


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 D-3. 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.
Wet Etching of silicon nitride - stoichiometric and Si-rich - is done in a dedicated wetbench with an integrated quartz tank. The quartz tank can take up to 25 6" wafers in dedicated carriers. The 'Wetbench 02: Nitride etch' is placed in cleanroom D-3. 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.


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>.
The etch solution is initially 85 wt% H<sub>3</sub>PO<sub>4</sub> which is heated up to the boiling temperature - approx. 160°C.




'''NB: Great care has to be taken in this process due to risk of "shock-boiling" '''
'''NB: Great care has to be taken in this process due to risk of bumping. Therefore it is essential, that you stir thoroughly during heat up, before you start heating, at 50°C, 80°C and finally at 100°C'''




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[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=130 Nitride etch info page in LabManager],
[https://labmanager.dtu.dk/function.php?module=Machine&view=view&mach=377 Nitride etch info page in LabManager],


<br clear="all" />
<br clear="all" />


==Comparing Wet Silicon Nitride Etch==
==Wet Silicon Nitride Etch==


{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;"  
{|border="1" cellspacing="1" cellpadding="3" style="text-align:left;"  
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|-style="background:silver; color:black"
|-style="background:silver; color:black"
!
!
! Nitride Etch @ 180 <sup>o</sup>C
! Nitride Etch @ 160<sup>o</sup>C
! Nitride Etch @ 160 <sup>o</sup>C
|-
|-


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|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
!Generel description
!Generel description
|Etch/strip of silicon nitride
|Etch/strip of silicon nitride
|Etch/strip of silicon nitride
|-
|-
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|-
|-
|-style="background:LightGrey; color:black"
|-style="background:LightGrey; color:black"
!Link to safety APV and KBA
!Link to safety APV and SDS
|[http://labmanager.danchip.dtu.dk/d4Show.php?id=1892&mach=130 see APV here]
[http://kemibrug.dk/KBA/CAS/116297/?show_KBA=1&portaldesign=1 see KBA here]
|[http://labmanager.danchip.dtu.dk/d4Show.php?id=1892&mach=130 see APV here]  
|[http://labmanager.danchip.dtu.dk/d4Show.php?id=1892&mach=130 see APV here]  
[http://kemibrug.dk/KBA/CAS/116297/?show_KBA=1&portaldesign=1 see KBA here]  
[https://kemibrug.dk/Kemikalier/Action?id=RCU2MHolYzIlODIlN2UlYzIlODB2JWMyJTgxJTdleiVjMiU4N0RZeiVjMiU4OXYlN2UlYzIlODElYzIlODhESk1OTEZKTVRkJWMyJTg3JTdjdiVjMiU4MyU3ZSVjMiU4OHYlYzIlODklN2UlYzIlODQlYzIlODMlYzIlODglNWVZUkk=#K see SDS here (requires login)]  
|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
!Chemical solution
!Chemical solution
|H<sub>3</sub>PO<sub>4</sub>    (85 wt%)
|H<sub>3</sub>PO<sub>4</sub>    (85 wt%)
|H<sub>3</sub>PO<sub>4</sub>    (85 wt%)
|-
|-
|-style="background:LightGrey; color:black"
|-style="background:LightGrey; color:black"
!Process temperature
!Process temperature
|180 <sup>o</sup>C
|160 <sup>o</sup>C
|160 <sup>o</sup>C
|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|'''Possible masking materials'''
|'''Possible masking materials'''
|
*Thermal oxide (converted si-rich surface)
*LPCVD-oxide (TEOS)
*PECVD-oxide
|
|
*Thermal oxide (converted si-rich surface)
*Thermal oxide (converted si-rich surface)
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|-style="background:LightGrey; color:black"
|-style="background:LightGrey; color:black"
!Etch rate
!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)
|
|
*~26 Å/min (Si-rich Si<sub>3</sub>N<sub>4</sub>)
*~26 Å/min (Si-rich Si<sub>3</sub>N<sub>4</sub>)
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|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
!Selectivity R<sub>Si<sub>3</sub>N<sub>4</sub></sub> / R<sub>SiO<sub>2</sub></sub>
!Selectivity R<sub>Si<sub>3</sub>N<sub>4</sub></sub> / R<sub>SiO<sub>2</sub></sub>
|~20
|The selectivity (sirich nitride:oxide) is higher at 160 <sup>o</sup>C than at 180 <sup>o</sup>C
|The selectivity (sirich nitride:oxide) is higher at 160 <sup>o</sup>C than at 180 <sup>o</sup>C
|-
|-
|-style="background:LightGrey; color:black"
|-style="background:LightGrey; color:black"
!Batch size
!Batch size
|
1-25 wafers at a time
|
|
1-25 wafer at a time
1-25 wafer at a time
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|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
!Size of substrate
!Size of substrate
|
2-6" wafers
|
|
2-6" wafers
2-6" wafers
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|-style="background:LightGrey; color:black"
|-style="background:LightGrey; color:black"
!Allowed materials
!Allowed materials
|
*Silicon
*Silicon nitrides
*Silicon oxides
|
|
*Silicon
*Silicon
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