Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 01 processing: Difference between revisions
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<br>The alignment test with 4 alignment marks mimics the shift from the field alignment test, but the deviation on the Y-axis is very large, probably due to the surprising -40ppm scaling measured by the alignment routine. Keep in mind that the wafer has not been unloaded between the two exposures. Something is going on with the Y-axis. | <br>The alignment test with 4 alignment marks mimics the shift from the field alignment test, but the deviation on the Y-axis is very large, probably due to the surprising -40ppm scaling measured by the alignment routine. Keep in mind that the wafer has not been unloaded between the two exposures. Something is going on with the Y-axis. | ||
<br>Aligning with 2 marks on the X-axis seems to fix this problem, and shows an average error similar to the camera offset, with a tight distribution across the wafer. However, aligning using 2 marks on the Y-axis introduces a large shift in Y. This shift is repeated if 2 alignment marks along the X-axis on the top half of the wafer is used, but it is fixed if 2 marks along the X-axis on the bottom half are used, or if 2 marks on the Y-axis is used with the first mark on the bottom half of the wafer. Again, there seems to be something strange going on with the Y-axis. | <br>Aligning with 2 marks on the X-axis seems to fix this problem, and shows an average error similar to the camera offset, with a tight distribution across the wafer. However, aligning using 2 marks on the Y-axis introduces a large shift in Y. This shift is repeated if 2 alignment marks along the X-axis on the top half of the wafer is used, but it is fixed if 2 marks along the X-axis on the bottom half are used, or if 2 marks on the Y-axis is used with the first mark on the bottom half of the wafer. Again, there seems to be something strange going on with the Y-axis. | ||
<br>In an attempt to fix the large deviation on the Y-axis when using 4 alignment marks, a test was made adding an alignment mark in 0;0 as the first mark during alignment. This did not have any beneficial effect, as the deviation on the Y-axis values is similar to the deviation from the 4 mark test. Finally, inspired by the success of using two alignment marks on the bottom half of the wafer, a test using 3 alignment marks on the bottom half of the wafer was done. | <br>In an attempt to fix the large deviation on the Y-axis when using 4 alignment marks, a test was made adding an alignment mark in 0;0 as the first mark during alignment. This did not have any beneficial effect, as the deviation on the Y-axis values is similar to the deviation from the 4 mark test. Finally, inspired by the success of using two alignment marks on the bottom half of the wafer, a test using 3 alignment marks on the bottom half of the wafer was done. Strangely, this seems to fix the problem, showing no scaling of the Y-axis and yielding small shifts with reasonable deviation. | ||