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=Alignment=
=Alignment=
[[Image:section under construction.jpg|70px]]


The alignment accuracy of the Aligner: Maskless 01 is a combination of the position accuracy of the stage, the accuracy of the alignment mark detection (mostly determined by the offset between camera and stage), and the accuracy of the pattern already on the wafer (first print).
The alignment accuracy of the Aligner: Maskless 01 is a combination of the position accuracy of the stage, the accuracy of the alignment mark detection (mostly determined by the offset between camera and stage), and the accuracy of the pattern already on the wafer (first print).
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==Alignment tests==
==Alignment tests==
In the stitching test, the design consists of ±5µm and ±1µm verniers along the X and Y axis placed in a 3 by 3 matrix covering a 60mm by 60mm area centered on the wafer. The sample is loaded, and the first layer (the linear scales) is printed. Without unloading, the second layer (the vernier scales) is printed on top of the first, and then the sample is developed.


The results in the table below show that the errors are at or below the measurement uncertainty for the stitching tests using no flat alignment. In other words, the stage is accurate to within 100nm.
[[Image:section under construction.jpg|70px]]
<br/>When flat alignment is used, a rotation error of ~1.5ppm appears, along with a ~0.3µm misalignment and a -6ppm scaling of the Y axis. This level of accuracy (which corresponds to approximately half a pixel) is what we can expect when the rotation compensation is applied, i.e. when aligning to a previously printed layer.
 
After installation, multiple tests were conducted in order to assess the overlay accuracy of Aligner: Maskless 01. The conclusion to the early tests were that the stage accuracy is ±0.1µm, and the machine-to-self overlay accuracy is ±0.5µm. The machine-to-machine overlay accuracy was not determined (due to the lack of a suitable mask for the mask aligners). In 2019, efforts to establish regular QC of the equipment were started, and the accuracy of the alignment mark detection has been measured regularly since 2020. While both the average and the spread of the alignment errors for the x-axis (measured in 3x3 positions covering a 60x60mm<sup>2</sup> area) has consistently been within the ±1µm specification of the machine, the spread of the alignment errors for the y-axis is typically 3±1µm, despite the average error being in spec, due to negative offsets on the upper half of the wafer and positive offsets on the lower. In 2025, it was decided to investigate this problem further, in order to determine whether a specific alignment protocol could remedy the alignment error, or whether the acceptance limits for the QC would have to be changed.
 
The samples used for these tests are 100mm Si wafers coated with a 1.5µm layer of the positive tone resist AZ 5214E. The deviations (±) given for the results here are calculated as half the range of measurements. If the range is small, the measurement uncertainty is used in stead.
 
In the MLA1-MLA1 alignment tests, the design consists of ±5µm verniers with 0.1µm resolution along the X and Y axis placed in a 3 by 3 matrix covering a 60mm by 60mm area centered on the wafer. The sample is loaded, and the first layer with linear scales is printed (without global angle). Without unloading, the second layer with vernier scales is printed on top of the first, and then the sample is developed.


{|border="1" cellspacing="0" cellpadding="3" style="text-align:left;"  
{|border="1" cellspacing="0" cellpadding="3" style="text-align:center;"  
|-
|-


|-
|-
|-style="background:silver; color:black"
|-style="background:silver; color:black"
!colspan="2" align="center"|
!colspan="2"|MLA1-MLA1
!Misalignment [µm]
!Mark positions
!Translation [µm]
!Rotation [mRad]
!Run-out [ppm]
!Scaling [a.u.]
!Rotation [ppm]
!Shearing [mRad]
!Average error [µm]
!Deviation [µm]
|-
 
|-
|-style="background:WhiteSmoke; color:black"
|rowspan="2"|No alignment
(stage accuracy test)
|'''X'''
|rowspan="2" align="center"| -
|rowspan="2" align="center"| -
| -
|rowspan="2" align="center"| -
| 0.03
| ±0.05
 
|-
|-style="background:WhiteSmoke; color:black"
|'''Y'''
| -
| 0.10
| ±0.225
 
|-
|-style="background:WhiteSmoke; color:black"
|rowspan="2"|4 alignment marks
(like QC)
|'''X'''
|rowspan="2" align="center"|1: -37500; 0<br>2: 37500; 0<br>3: 0; 35000<br>4: 0; -35000
|rowspan="2" align="center"|0.000
| 1.000001
|rowspan="2" align="center"|0.0002
| 0.06
| ±0.05
 
|-
|-style="background:WhiteSmoke; color:black"
|'''Y'''
| 0.999960
| -0.31
| ±1.30
 
|-
|-style="background:WhiteSmoke; color:black"
|rowspan="2"|2 alignment marks
(on X-axis)
|'''X'''
|rowspan="2" align="center"|1: -37500; 0<br>2: 37500; 0
|rowspan="2" align="center"|0.003
| -
|rowspan="2" align="center"| -
| 0.01
| ±0.15
 
|-
|-
|-style="background:WhiteSmoke; color:black"
|'''Y'''
| -
| -0.26
| ±0.20


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|rowspan="2" align="center"|No flat alignment
|rowspan="2"|description
(two samples)
(comment)
|'''X'''
|'''X'''
| -0.03±0.08
|rowspan="2" align="center"|positions
| 0.00±0.05
|rowspan="2" align="center"|rotation
| -0.97±1.67
| x scaling
| 0.42±1.18
|rowspan="2" align="center"|shearing
| x error
| x deviation


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|'''Y'''
|'''Y'''
| -0.05±0.05
| y scaling
| -0.07±0.05
| y error
| -0.42±1.67
| y deviation
| 0.00±1.18
 
|}
 
 
{|border="1" cellspacing="0" cellpadding="3" style="text-align:center;"
|-
 
|-
|-style="background:silver; color:black"
!colspan="2"|MLA1-MLA1
!Mark positions
!Rotation [mRad]
!Scaling [a.u.]
!Shearing [mRad]
!Average error [µm]
!Deviation [µm]
|-


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|rowspan="2" align="center"|With flat alignment
|rowspan="2"|description
(comment)
|'''X'''
|'''X'''
| 0.05±0.10
|rowspan="2" align="center"|positions
| 0.05±0.05
|rowspan="2" align="center"|rotation
| 0.56±1.67
| x scaling
| -1.67±1.18
|rowspan="2" align="center"|shearing
| x error
| x deviation


|-
|-
|-style="background:WhiteSmoke; color:black"
|-style="background:WhiteSmoke; color:black"
|'''Y'''
|'''Y'''
| -0.25±0.35
| y scaling
| -0.29±0.16
| y error
| -6.39±1.67
| y deviation
| -1.39±1.18


|}
|}


<span style="color:red">OLD CONTENT:</span>


In the overlay test, two alignment accuracies are assessed: The machine-to-self overlay accuracy (MLA-MLA), and the machine-to-machine (MA6-MLA) overlay accuracy. Because alignment is possible using two marks or four marks, both are tested in each case. Exposing the first print with or without flat alignment was also tested, but no significant effect was observed.
In the overlay test, two alignment accuracies are assessed: The machine-to-self overlay accuracy (MLA-MLA), and the machine-to-machine (MA6-MLA) overlay accuracy. Because alignment is possible using two marks or four marks, both are tested in each case. Exposing the first print with or without flat alignment was also tested, but no significant effect was observed.
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