Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 02 processing: Difference between revisions
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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 (gain) and shearing (orthogonality) errors between the two prints. | 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 (gain) and shearing (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 | 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 resolution. | ||
The measurement data is used to calculate the misalignment of the second layer with respect to the first print. The median of all measurement points in X or Y (reported as "Misalignment") is a measure of the average overall offset between the first and second print, as seen in the raw data. This alignment error has three contributions: The translational error ("Translation") is the amount by which the image is shifted; the run-in/run-out error ("Run-out") is the amount of gain in the image; and the rotational error ("Rotation") is the angle by which the image is rotated. The unit of ppm (parts per million) is used for run-out and rotation, as these errors are generally small. A run-out of 1ppm corresponds to a shift of 50nm at the edge of a 4" wafer compared to the center, while a rotation of 1ppm corresponds to an angle of 0.2" (arcseconds) or a shift of 100nm across an entire 4" wafer. For comparison, the pixel size at the wafer surface is 160nm X 160nm, and the address grid size is 40nm. | The measurement data is used to calculate the misalignment of the second layer with respect to the first print. The median of all measurement points in X or Y (reported as "Misalignment") is a measure of the average overall offset between the first and second print, as seen in the raw data. This alignment error has three contributions: The translational error ("Translation") is the amount by which the image is shifted; the run-in/run-out error ("Run-out") is the amount of gain in the image; and the rotational error ("Rotation") is the angle by which the image is rotated. The unit of ppm (parts per million) is used for run-out and rotation, as these errors are generally small. A run-out of 1ppm corresponds to a shift of 50nm at the edge of a 4" wafer compared to the center, while a rotation of 1ppm corresponds to an angle of 0.2" (arcseconds) or a shift of 100nm across an entire 4" wafer. For comparison, the pixel size at the wafer surface is 160nm X 160nm, and the address grid size is 40nm. | ||