Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 02 processing: Difference between revisions
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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 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 median of all measurement points in X or Y (reported as "Shift") is a measure for the average overall offset between the first and second print. At each point, this error | The measurements are 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 "Shift") is a measure for the average overall offset between the first and second print. At each point, this error has three contributions: The translational error ("Misplacement") 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. | ||
For back side alignment tests, only the alignment marks are printed in the first print. The alignment error is then assessed by first printing the scale aligned to these marks, then rotating the wafer 180° and printing the vernier scale, again aligned to the marks. The alignment error is half of the observed misalignment between the verniers. As this is an indirect measurement of the alignment error, and only a few points are generally printed, the alignment error is given as the "Offset". The run-out and rotation are believed to be similar to the ones observed for top side alignment. | |||
In advanced field alignment, the vernier scales in the second print are printed individually (as an array, rather than as one big image), and the position of each is corrected using local alignment to one mark. The rotation, scaling, and shearing is determined and set by global alignment marks, and is the same for each individual image. For these tests, run-out and rotation can not be assessed, and only the offset is reported. Any systematic error observed here is a measure of the offset between the exposure light axis and the center of the camera, and can be used to calibrate the machine. | |||
The deviations (±) given for the results here are calculated as half the range of measurements. If the range is smaller than the measurement uncertainty, the measurement uncertainty is used in stead. | The deviations (±) given for the results here are calculated as half the range of measurements. If the range is smaller than the measurement uncertainty, 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). | 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.]] | ||