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==Substrate centring and flat alignment==
==Substrate centring and flat alignment==
<span style="color:red">New specs after the new writehead has been installed - section will be updated soon.</span>


During substrate detection, the sample is scanned along the X- and Y-axes, as well as diagonally. From these measurements, the size (diameter) of the substrate is calculated, as well as the stage position matching the center of the substrate. This stage position will be the default origin for the subsequent exposure.
During substrate detection, the sample is scanned along the X- and Y-axes, as well as diagonally. From these measurements, the size (diameter) of the substrate is calculated, as well as the stage position matching the center of the substrate. This stage position will be the default origin for the subsequent exposure.


At the end of substrate detection, the sample is scanned twice along the bottom edge (flat), in order to determine the substrate rotation. This angle will be presented in the exposure panel along with the option to expose the design rotated in order to compensate for this angle, i.e. aligned to the flat/edge of the substrate.
At the end of substrate detection, the sample is scanned twice along the bottom edge (flat), in order to determine the substrate rotation. This angle will be presented in the exposure panel along with the option to expose the design rotated in order to compensate for this angle, i.e. aligned to the flat/edge of the substrate.


'''Result of using "Expose with substrate angle" ("Expose with Global Angle"):'''
'''Result of using "Expose with substrate angle" ("Expose with Global Angle"):'''
*Rotation: 0.5±0.2°
*Rotation: 0 ±0.2°
*Centring:
*Centring:
** '''X''' 100±250µm
** '''X''' 0 ±100µm
** '''Y''' 200±250µm
** '''Y''' 0 ±100µm
Taran Mar 2019, average of 3 4" wafers.<br>
Taran Sep 2023, average of 3 4" wafers.<br>
The error on the flat alignment is surprising when compared to the 0±0.1° measured on Aligner: Maskless 01. The centring, on the other hand, is seen to be within a few hundred µm, without correcting for the flats.
 


'''Result of loading the same substrate ~10 times without removing it from the stage:'''
'''Result of loading the same substrate ~10 times without removing it from the stage:'''
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|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|Optical autofocus  
|Optical autofocus
(as installed)
| -4.7 mRad
| 3.7 mRad
| ±13.9 mRad
±0.8°
 
|-
|-style="background:WhiteSmoke; color:black"
|Pneumatic autofocus
(as installed)
| -3.1 mRad
| ±1.4 mRad
| ±1.4 mRad
±0.08°
(±0.08°)


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|Positioning a wafer repeatedly using the alignment tool
|Pneumatic autofocus
(measured using pneumatic autofocus)
| -2.8 mRad
| -1.7 mRad
| ±8.3 mRad
±0.5°
 
|-
|-style="background:WhiteSmoke; color:black"
|Optical autofocus
after hardware upgrade February 2020
| -0.3 mRad
| ±1.4 mRad
±0.08°
 
|-
|-style="background:WhiteSmoke; color:black"
|Pneumatic autofocus  
after hardware upgrade February 2020
| -0.6 mRad
| ±1.4 mRad
| ±1.4 mRad
±0.08°
(±0.08°)


|}
|}
 
Measured after conversion to write mode 2 in 2023 by Taran Sep 2023.
This shows that using optical autofocus (as installed) significantly increased the error on the flat measurement, while using pneumatic atuofocus performs similar to Aligner: Maskless 01. Initially, it was thus recommended to use pneumatic autofocus (or rely only on the alignment tool) for the first print if crystal alignment is important for subsequent processing. However, after the autofocus hardware and software upgrade in February 2020, the two methods yield equally good results.


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