Specific Process Knowledge/Etch/Wet Silicon Nitride Etch: Difference between revisions

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! Nitride Etch @ 160 <sup>o</sup>C
! Nitride Etch @ 160 <sup>o</sup>C
|-  
|-  
|General description
|'''General description'''
|
|
Etch/strip of silicon nitride
Etch/strip of silicon nitride
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Etch/strip of silicon nitride
Etch/strip of silicon nitride
|-
|-
|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%)
|H<sub>3</sub>PO<sub>4</sub>    (85 wt%)
|-
|-
|Process temperature
|'''Process temperature'''
|180 <sup>o</sup>C
|180 <sup>o</sup>C
|160 <sup>o</sup>C
|160 <sup>o</sup>C
|-
|-
 
|'''Possible masking materials'''
|Possible masking materials:
|
|
*Thermal oxide (converted si-rich surface)
*Thermal oxide (converted si-rich surface)
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*PECVD-oxide
*PECVD-oxide
|-
|-
|Etch rate
|'''Etch rate'''
|
|
*~85 Å/min (stoichiometric Si<sub>3</sub>N<sub>4</sub>)
*~85 Å/min (stoichiometric Si<sub>3</sub>N<sub>4</sub>)
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*~? Å/min (Thermal oxide)
*~? Å/min (Thermal oxide)
|-
|-
|Batch size
|'''Batch size'''
|
|
1-25 wafers at a time
1-25 wafers at a time
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1-25 wafer at a time
1-25 wafer at a time
|-
|-
|Size of substrate
|'''Size of substrate'''
|
|
2-6" wafers
2-6" wafers
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2-6" wafers
2-6" wafers
|-
|-
|Allowed materials
|'''Allowed materials'''
|
|
*Silicon
*Silicon

Revision as of 13:19, 31 January 2008

Wet Silicon Nitride Etch

Wet nitride etch: positioned in cleanroom 4

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 (mask less), 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% H3PO4 which is heated up to the boiling temperature - ca. 157 oC. Water is allowed to boil off thus raising the concentration and the boiling temperature of the solution until a boiling temperature of 180 oC 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 oC - which lowers the etch rate and improves the selectivity RSi3N4 / RSiO2.


NB: Great care has to be taken in this process due to risk of "shock-boiling"



Nitride Etch data

Nitride Etch @ 180 oC Nitride Etch @ 160 oC
General description

Etch/strip of silicon nitride

Etch/strip of silicon nitride

Chemical solution H3PO4 (85 wt%) H3PO4 (85 wt%)
Process temperature 180 oC 160 oC
Possible masking materials
  • Thermal oxide (converted si-rich surface)
  • LPCVD-oxide (TEOS)
  • PECVD-oxide
  • Thermal oxide (converted si-rich surface)
  • LPCVD-oxide (TEOS)
  • PECVD-oxide
Etch rate
  • ~85 Å/min (stoichiometric Si3N4)
  • ~60 Å/min (Si-rich Si3N4)
  • ~30 Å/min (annealed Si-rich Si3N4)
  • ~4 Å/min (Thermal oxide)
  • ~26 Å/min (Si-rich Si3N4)
  • ~? Å/min (Thermal oxide)
Batch size

1-25 wafers at a time

1-25 wafer at a time

Size of substrate

2-6" wafers

2-6" wafers

Allowed materials
  • Silicon
  • Silicon nitrides
  • Silicon oxides
  • Silicon
  • Silicon nitrides
  • Silicon oxides
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