Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 01 processing: Difference between revisions

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 <br/>The samples used for these tests are 100mm Si wafers coated with a 1.5µm layer of the positive tone resist AZ 5214E.
 The conclusion to the tests are that the stitching accuracy of the Aligner: Maskless 01 is ±0.1µm. The machine-to-self overlay accuracy is ±0.5µm. The machine-to-machine overlay accuracy could not be determined.
+==Important note==
+The stage of Aligner: Maskless 01 has suffered some kind of damage (maybe during it's relocation to E-4 in 2019), which means the stage positioning is distorted. When aligning to a pattern exposed using a different machine, we typically see a shearing on the order of 0.1 rad, i.e. the axes are not orthogonal, but even when aligning to patterns exposed on Aligner: Maskless 01 itself, this distortion results in misalignment unless a specific procedure is followed.
+When aligning on Aligner: Maskless 01, one should either '''use only 2 alignment marks, or use four alignment marks and apply all the measured corrections (scaling and shearing)'''. Using only two alignment marks is usually fine for smaller chips, but when exposing full wafers there may be misalignment, especially if previous prints are made on a different machine. With 4 alignment marks and all corrections applied, the best alignment accuracy is obtained for all substrates.
+<br/>If four marks are measured but scaling and shearing is not applied, significant misalignment will be observed, even on chips. On a 4" wafer, the shift in Y can be several hundred µm.
 ==Stitching==