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 and defocus | ==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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<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== | ||