Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 01 processing: Difference between revisions
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[[Category: Equipment|Lithography exposure]] | |||
[[Category: Lithography|Exposure]] | |||
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=Exposure technology= | =Exposure technology= | ||
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Aligner: Maskless 01 is not a direct writer. In the maskless aligner, the exposure light is passed through a spatial light modulator, much like in a video projector, and projected onto the substrate, thus exposing an area of the design at a time. The substrate is exposed by stepping the exposure field across the substrate. | Aligner: Maskless 01 is not a direct laser writer. In the maskless aligner, the exposure light is passed through a spatial light modulator, much like in a video projector, and projected onto the substrate, thus exposing an area of the design at a time. The substrate is exposed by stepping the exposure field across the substrate. | ||
The light source is a 10W 365nm LED with a FWHM of 8nm. The spacial light modulator is an 800 X 600 pixel digital micro-mirror device. The individual mirrors of the DMD are switched in order to represent the design, and are timed in order to yield the desired exposure dose, while taking into account illumination uniformity, soft-stitching, and possibly also sub-pixel features. This image is projected onto the substrate through a lens(system). The projected image yields a writing field of 400µm X 300µm, and thus a pixel size of 0.5µm X 0.5µm at wafer scale. This writing field is stepped across the substrate, in order to expose the entire design, each field overlapping slightly in order to minimize stitching errors. | The light source is a 10W 365nm LED with a FWHM of 8nm. The spacial light modulator is an 800 X 600 pixel digital micro-mirror device. The individual mirrors of the DMD are switched in order to represent the design, and are timed in order to yield the desired exposure dose, while taking into account illumination uniformity, soft-stitching, and possibly also sub-pixel features. This image is projected onto the substrate through a lens(system). The projected image yields a writing field of 400µm X 300µm, and thus a pixel size of 0.5µm X 0.5µm at wafer scale. This writing field is stepped across the substrate, in order to expose the entire design, each field overlapping slightly in order to minimize stitching errors. | ||
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==Exposure dose== | ==Exposure dose and defocus== | ||
[[Specific Process Knowledge/Lithography/Resist#Aligner:_Maskless_01|Information on UV exposure dose]] | |||
==Writing speed== | ==Writing speed== | ||
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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. | ||
<br/>The measurements are used to calculate the misalignment of the second layer with respect to the first print: The | <br/>The measurements are used to calculate the misalignment of the second layer with respect to the first print: The Misalignment [µm] is the median of all measurement points in X or Y; the Translation [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 500nm X 500nm, and the address grid size is 50nm. | ||
<br/>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. | <br/>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. | ||
<br/>The samples used for these tests are 100mm Si wafers coated with a 1.5µm layer of the positive tone resist AZ 5214E. | <br/>The samples used for these tests are 100mm Si wafers coated with a 1.5µm layer of the positive tone resist AZ 5214E. | ||
The conclusion to the tests are that the stitching accuracy of the Aligner: Maskless 01 is ±0.1µm. The machine-to-self overlay accuracy is ±0.5µm. The machine-to-machine overlay accuracy could not be determined. | The conclusion to the tests are that the stitching accuracy of the Aligner: Maskless 01 is ±0.1µm. The machine-to-self overlay accuracy is ±0.5µm. The machine-to-machine overlay accuracy could not be determined. | ||
==Important note about correction options== | |||
<span style="color:red">You must use all available alignment corrections!</span> | |||
* 2 point alignment can only correct for rotation | |||
* 3+ point alignment can correct for rotation, scaling and shearing - you must use all 3 alignment corrections! | |||
The stage of Aligner: Maskless 01 has suffered some kind of damage (maybe during it's relocation to E-4 in 2019), which means the stage positioning is distorted. When aligning to a pattern exposed using a different machine, we typically see a shearing on the order of 0.1 rad, i.e. the axes are not orthogonal, but even when aligning to patterns exposed on Aligner: Maskless 01 itself, this distortion results in misalignment unless a specific procedure is followed. | |||
When aligning on Aligner: Maskless 01, you should either: | |||
* Use only 2 alignment marks and apply rotation correction | |||
* Use 3+ alignment marks and apply all corrections (rotation, scaling and shearing) | |||
Using only two alignment marks is usually fine for smaller chips, but when exposing full wafers there may be misalignment, especially if previous prints are made on a different machine. With 4 alignment marks and all corrections applied, the best alignment accuracy is obtained for all substrates.<br/> | |||
<span style="color:red">If four marks are used, but scaling and shearing is not applied, ''significant'' misalignment will be observed, even on chips. On a 4" wafer the shift in Y can be several hundred µm.</span> | |||
==Stitching== | ==Stitching== | ||
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!colspan="2" align="center"| | !colspan="2" align="center"| | ||
! | !Misalignment [µm] | ||
! | !Translation [µm] | ||
!Run-out | !Run-out [ppm] | ||
!Rotation [ppm] | !Rotation [ppm] | ||
|- | |- | ||
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!Scaling [ppm] | !Scaling [ppm] | ||
!Shearing [mRad] | !Shearing [mRad] | ||
! | !Misalignment [µm] | ||
! | !Translation [µm] | ||
!Run-out | !Run-out [ppm] | ||
!Rotation [ppm] | !Rotation [ppm] | ||
|- | |- | ||
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!Scaling [ppm] | !Scaling [ppm] | ||
!Shearing [mRad] | !Shearing [mRad] | ||
! | !Misalignment [µm] | ||
! | !Translation [µm] | ||
!Run-out | !Run-out [ppm] | ||
!Rotation [ppm] | !Rotation [ppm] | ||
|- | |- | ||