Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 01 processing: Difference between revisions
| Line 151: | Line 151: | ||
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. | 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 | The result of these tests suggest that when aligning to a pattern exposed using MLA1, only 2 alignment marks on the X-axis should be used. If the first pattern was exposed using a different tool, 4 alignment marks must be used (with all corrections applied), but the alignment accuracy in Y-direction suffers. Most likely, the Y-shift will grow linearly with the distance from the center, so small samples will be ok, while full wafers will experience shifts that exceed the ±1µm specification. | ||
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. | |||
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. 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 instead. | |||
{|border="1" cellspacing="0" cellpadding="3" style="text-align:center;" | {|border="1" cellspacing="0" cellpadding="3" style="text-align:center;" | ||
| Line 328: | Line 329: | ||
<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. | ||
In the MLA3-MLA1 alignment tests, the design consists of ±5µm verniers with 0.25µm 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 first layer with linear scales was printed in MLA3 as QC test wafers a long time ago and subsequently patterned using lift-off of gold. These wafers are coated with resist, the second layer with vernier scales is printed in MLA1, and then the sample is developed. | |||
In the MLA3-MLA1 alignment tests, the design consists of ±5µm verniers with 0.25µm 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 first layer with linear scales was printed in MLA3 as QC test wafers a long time ago and subsequently patterned using lift-off of gold. These wafers are coated with resist, the second layer with vernier scales is printed in MLA1, and then the sample is developed. 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 instead. | |||
{|border="1" cellspacing="0" cellpadding="3" style="text-align:center;" | {|border="1" cellspacing="0" cellpadding="3" style="text-align:center;" | ||