Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 02 processing: Difference between revisions
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'''This section is under construction [[Image:section under construction.jpg|70px]]''' | '''This section is under construction [[Image:section under construction.jpg|70px]]''' | ||
The alignment accuracy of the Aligner: Maskless 02 is a combination of the position accuracy of the stage, the accuracy of the alignment mark detection, the accuracy of the pattern already on the wafer (first print), and the calibration of the machine (correction of offset between the exposure light axis and the center of the cameras). | |||
The calibration of the machine was performed during installation, but can also be corrected if systematic offsets are observed in alignment tests. This calibration also compensates errors in the detection of the alignment marks (at least on the standard samples used for calibration and alignment tests). By measuring the stitching accuracy between two layers printed on the same substrate (without unloading the substrate), we may be able to assess the stage accuracy. By aligning to a pattern previously exposed by the Aligner: Maskless 02, or ideally by another machine, we can assess the mask-less aligner's ability to compensate for any scaling and orthogonality errors between the two prints. | |||
The results reported here use printed verniers to assess the misalignment along the two axes at different points on the wafer using an optical microscope. Two different designs were used; a ±5µm vernier and a ±1µm vernier. Both consist of a scale of 4µm lines with 10µm pitch, and a vernier scale to enable subdivision of the 5µm or 1µm scale into tenths, i.e. 0.5µm or 0.1µm. During inspection, observation of the symmetry of neighboring lines enables the observer to read the shifts with ±0.25µm or ±0.05µm accuracy. | |||
The measurements are used to calculate the misalignment of the second layer with respect to the first print: The shift [µm] is the median of all measurement points in X or Y; the misplacement [µm] is the amount by which the image is shifted; the rotation [ppm] is the angle by which the image is rotated; and the run-out [ppm] is the amount of gain in the image. The unit of ppm (parts per million) is used as the rotation and run-out are generally small. A rotation of 1ppm corresponds to an angle of 0.2" (arcseconds) or a shift of 100nm across an entire 4" wafer, while a run-out of 1ppm corresponds to a shift of 50nm at the edge of a 4" wafer compared to the center. For comparison, the pixel size at the wafer surface is 160nm X 160nm, and the address grid size is 40nm. | |||
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. | |||
The samples used for these tests are 100mm Si wafers coated with a 1.5µm layer of positive tone resist (AZ 5214E or MiR 701). | |||
[[Image:MLA150_stitching.JPG|400x400px|thumb|Data from the stage stitching test, representing a 60x60mm<sup>2</sup> area.]] | [[Image:MLA150_stitching.JPG|400x400px|thumb|Data from the stage stitching test, representing a 60x60mm<sup>2</sup> area.]] | ||
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This test was performed by printing two layers on top of each other without unloading the substrate. There is no alignment performed, so it is a test of the stages ability to address the same spot twice. The first layer was a full 4" wafer, and was printed in ~½ hour. The second layer only consisted of alignment structures in a 5x5 grid, and printed in a few minutes. | This test was performed by printing two layers on top of each other without unloading the substrate. There is no alignment performed, so it is a test of the stages ability to address the same spot twice. The first layer was a full 4" wafer, and was printed in ~½ hour. The second layer only consisted of alignment structures in a 5x5 grid, and printed in a few minutes. | ||