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<!--Checked for updates on 30/7-2018 - ok/jmli -->
<!--Page reviewed by jmli 9/8-2022  -->
<!--Page reviewed by bghe 31/3-2024  -->
==Etching of SU-8==
==Etching of SU-8==
SU-8 can be etched by a oxygen plasma with a small amount of SF<sub>6</sub> to remove the antimony present from the photo initiator. Etching of SU-8 has been developed on the ASE and was tested as a mask less reduction of pattern defined by photo lithography. Two processes are available, a high and a low anisotropic etch for use as etching or thinning of structures.
SU-8 can be etched by a oxygen plasma with a small amount of SF<sub>6</sub> to remove the antimony present from the photo initiator. Etching of SU-8 has been developed on the ASE and was tested as a mask less reduction of patterns defined by photo lithography. Two processes are available, a high and a low anisotropic etch for use as etching or thinning of structures.


* High anisotropic etch: etch rate ~400nm/min, anisotropy ~0.8
* High anisotropic etch: etch rate ~400nm/min, anisotropy ~0.8
* Low anisotropic etch: etch rate ~180nm/min, anisotropy ~0.3
* Low anisotropic etch: etch rate ~170nm/min, anisotropy ~0.3
 
==Recipes in ASE==
===SU8aniso===
The anisotropic SU8aniso etch was design to etch structures in SU-8 with a low roughness of the etched surface, however it has not been tested with any mask material. For a polymeric mask a low selectivity is expected. The etch rate was measured to around 400 nm/min, but will depend on wafer coverage. The surface layer concentration of antimony (Sb) after etch is expected to be below 2%.
 
{| border="2" cellpadding="2" cellspacing="1" style="text-align:center;"
|+ '''SU8aniso and SU8iso etches''' by khara@nanolab
|-
! Parameter
! SU8aniso etch
! SU8iso etch
|-
! O<sub>2</sub> (sccm)
| 99
| 99
|-
! SF<sub>6</sub> (sccm)
| 17
| 14
|-
! Pressure (mTorr)
| 40
| 20
|-
! Coil power (W)
| 800
| 800
|-
! Platen power (W)
| 30
| 0
|-
! Temperature (<sup>o</sup>C)
| 30
| 10
|-
! Etch rate (nm/min)
| ~400
| ~170
|-
!anisotropy
| ~0.8
| ~0.3
|-
!Sb in surface layer (%)
| <2
| <2.75
|}
 
===SU8iso===
The SU8iso etch was developed for thinning of lithography defined structures to gain higher aspect ratio or thinner structures than possible with photo lithography.
 
==Roughness and antimony effects in SU-8 etching==
 
{| border="1" cellspacing="1" cellpadding="2"  align="left"
! SU-8 lines by lithography
! Oxygen etch
! SU8aniso
! SU8iso
|-
|[[Image:SU8-noetch Q13.jpg|200x200px]]
|[[Image:SU8-oxygen-etch_Q12.jpg|200x200px]]
|[[Image:SU8-SU8aniso_R15.jpg|200x200px]]
|[[Image:SU8-SU8iso_R13.jpg|200x200px]]
|-
|No etching
|Etch
*O<sub>2</sub> flow [sccm]:99
*SF<sub>6</sub> flow [sccm]:0
*Pressure [mTorr]:20
*Coil power [W]:800
*Platen power [W]:30
*Temperature [°C]:10
|Etch
*O<sub>2</sub> flow [sccm]:99
*SF<sub>6</sub> flow [sccm]:17
*Pressure [mTorr]:40
*Coil power [W]:800
*Platen power [W]:30
*Temperature [°C]:30
|Etch
*O<sub>2</sub> flow [sccm]:99
*SF<sub>6</sub> flow [sccm]:14
*Pressure [mTorr]:20
*Coil power [W]:800
*Platen power [W]:0
*Temperature [°C]:10
|}
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