Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 01 processing: Difference between revisions
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The easiest approach to mix-and-match is to use a (simple) positive tone resist, such as AZ 5214E, and develop the pattern after the first exposure. The remaining resist can be exposed using the same parameters as normal, and there is plenty of contrast for the alignment process. This process can also be used if the maskless aligner is used first. | The easiest approach to mix-and-match is to use a (simple) positive tone resist, such as AZ 5214E, and develop the pattern after the first exposure. The remaining resist can be exposed using the same parameters as normal, and there is plenty of contrast for the alignment process. This process can also be used if the maskless aligner is used first. | ||
Alternatively, the development after first exposure can be skipped. This enables the use of chemically amplified positive tone resists, such as AZ MiR 701, without the drop in sensitivity usually associated with the post-exposure bake. The contrast, however, is greatly reduced, making alignment more difficult. AZ MiR 701 shows more contrast than AZ 5214E, but in both cases the focus and brightness has to be optimized in order to make automatic alignment possible. The design may also have to be adapted, as the poor contrast makes navigation using the overview camera difficult. Also, a less reflective substrate than Si, e.g. oxidized Si, may complicate alignment further. | Alternatively, the development after first exposure can be skipped. This enables the use of chemically amplified positive tone resists, such as AZ MiR 701, without the drop in sensitivity usually associated with the post-exposure bake. The contrast of the alignment mark, however, is greatly reduced, making alignment more difficult. AZ MiR 701 shows more contrast than AZ 5214E, but in both cases the focus and brightness has to be optimized in order to make automatic alignment possible. The design may also have to be adapted, as the poor contrast makes navigation using the overview camera difficult. Also, a less reflective substrate than Si, e.g. oxidized Si, may complicate alignment further. | ||
In the case of negative tone resist, such as AZ nLOF 2020, there is no contrast after exposure, making alignment impossible. Performing post-exposure bake before the second exposure yields a slight contrast, but in the case of nLOF the automatic alignment failed. Manual alignment was possible, but the accuracy | In the case of negative tone resist, such as AZ nLOF 2020, there is no contrast after exposure, making alignment impossible. Performing post-exposure bake before the second exposure yields a slight contrast, but in the case of nLOF the automatic alignment failed. Manual alignment was possible, but the alignment accuracy is likely to suffer. | ||