Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 04 processing: Difference between revisions
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=Exposure technology= | =Exposure technology= | ||
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Aligner: Maskless 04 is both a direct writer and not a direct laser writer. In Raster mode, it works like | Aligner: Maskless 04 is both a direct laser writer and not a direct laser writer. In Raster mode, it works like MLA1, where an image is projected onto the substrate surface, and stepped across the substrate in order to produce the entire pattern. In Vector mode, it is a direct laser writer, where a focused laser beam is moved across the substrate surface in order to trace out the pattern. | ||
The writing head of the Aligner: Maskless 04 moves only in the z-direction. Using a focusing system, the maskless aligner is able to do real-time autofocus. The defocus process parameter is used to compensate offsets in the focusing mechanism, and to optimize printing quality in different resists and varying thicknesses. | The writing head of the Aligner: Maskless 04 moves only in the z-direction. Using a focusing system, the maskless aligner is able to do real-time autofocus. The defocus process parameter is used to compensate offsets in the focusing mechanism, and to optimize printing quality in different resists and varying thicknesses. | ||
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=Process Parameters= | =Process Parameters= | ||
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[[ | Control of the exposure dose differs between the two available exposure modes. In Raster mode, the dose is directly controlled by the on-time of the DMD mirrors during exposure, and the dose process parameter is thus simply given in units of mJ/cm<sup>2</sup>. As the intensity of the exposure light at the substrate surface cannot easily be measured, this dose is indirectly calibrated at the factory, by adjusting the optimal dose to match the known dose of a particular resist. | ||
<br>In Vector mode, however, the exposure dose is determined by combination of four different process parameters: | |||
*Pen [1, 2, 5, 10, or 25 µm]; the size of pinhole projected onto the substrate surface | |||
*Transmission [30, or 100 %]; the transparency of the filter in front of the pinhole | |||
*Laser Power [0-120 mW]; the output power of the diode laser | |||
*Exposure Velocity [0-200 mm/s]; the movement speed of the stage during exposure | |||
The Pen determines the size of the spot on the substrate surface and thus the ultimate resolution. It may also affect the intensity available at the substrate. For highly sensitive resists, the Transmission can be used to limit the available intensity at the substrate (lowering the required Exposure Velocity to a more reasonable value). The Laser Power directly affects the intensity available at the substrate. The Exposure Velocity determines the dwell time at each point on the substrate, and thus the effective dose received by the resist at the intensity determined by the three other parameters. | |||
Aligner: Maskless 04 offers not only two exposure modes, but also two autofocus modes; optical or pneumatic. The defocus process parameter is used to compensate for offsets between the autofocus mechanism and the focal point of the exposure light, and simultaneously optimize print quality in different resists and varying thicknesses. | Aligner: Maskless 04 offers not only two exposure modes, but also two autofocus modes; optical or pneumatic. The defocus process parameter is used to compensate for offsets between the autofocus mechanism and the focal point of the exposure light, and simultaneously optimize print quality in different resists and varying thicknesses. The "defoc" parameter us a unitless value, representing ±100% of the available correction available above and below the initial focus point established during loading of the substrate. One defoc step is approximately 0.25µm. Positive defoc is into the resist, i.e. writehead moves down when defoc is increased. | ||
'''Optical autofocus:''' Uses red laser light to focus on the substrate surface. Works for substrates down to 3x3 mm. | '''Optical autofocus:''' Uses red laser light to focus on the substrate surface. Works for substrates down to 3x3 mm. | ||
'''Pneumatic autofocus:''' Uses compressed air flowing through the nozzle of the writehead to focus on the substrate surface. Substrates must be at least 5x5 mm to be successfully loaded. The pneumatic AF fails at some distance from the substrate edge, which means that in order to have any useful area in the center of the sample when using the pneumatic AF, the substrate must likely be larger than 5x5 mm. When using the pneumatic autofocus, we recommend a substrate size of at least 10x10 mm. | '''Pneumatic autofocus:''' Uses compressed air flowing through the nozzle of the writehead to focus on the substrate surface. Substrates must be at least 5x5 mm to be successfully loaded. The pneumatic AF fails at some distance from the substrate edge, which means that in order to have any useful area in the center of the sample when using the pneumatic AF, the substrate must likely be larger than 5x5 mm. When using the pneumatic autofocus, we recommend a substrate size of at least 10x10 mm. | ||
==Exposure dose and defocus== | ==Exposure dose and defocus== | ||
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| 2024<br>FAT/SAT | | 2024<br>FAT/SAT | ||
| 0.5 µm | | 0.5 µm | ||
| Raster | | Raster<br>(365nm) | ||
| 80 mJ/cm<sup>2</sup> | | 80 mJ/cm<sup>2</sup> | ||
| 10 (optical) | | 10 (optical) | ||
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| 2024<br>During installation | | 2024<br>During installation | ||
| 1.5 µm | | 1.5 µm | ||
| Raster | | Raster<br>(365nm) | ||
| 85 mJ/cm<sup>2</sup> | | 85 mJ/cm<sup>2</sup> | ||
| 15 (optical) | | 15 (optical) | ||
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| 2025-??-??</span><br>elkh? | | 2025-??-??</span><br>elkh? | ||
| 15 µm | | 15 µm | ||
| Raster | | Raster<br>(365nm) | ||
| ? mJ/cm<sup>2</sup> | | ? mJ/cm<sup>2</sup> | ||
| ? (?) | | ? (?) | ||
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| 2024<br>FAT/SAT | | 2024<br>FAT/SAT | ||
| 0.5 µm | | 0.5 µm | ||
| Vector | | Vector<br>(405nm) | ||
| | | | ||
Pen: 1µm<br> | Pen: 1µm<br> | ||
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| 2025-??-??<br>taran? | | 2025-??-??<br>taran? | ||
| 1.5 µm | | 1.5 µm | ||
| Vector | | Vector<br>(405nm) | ||
| | | | ||
Pen: 1µm<br> | Pen: 1µm<br> | ||
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The site acceptance test performed during the installation of the Aligner: Maskless 04 showed an exposure speed of 47mm<sup>2</sup>/min, which is slightly higher than the 40mm<sup>2</sup>/min given in the specifications. At such speeds, a full 4" design would take 2:45-3:15 hours to expose. | The site acceptance test performed during the installation of the Aligner: Maskless 04 showed an exposure speed of 47mm<sup>2</sup>/min, which is slightly higher than the 40mm<sup>2</sup>/min given in the specifications. At such speeds, a full 4" design would take 2:45-3:15 hours to expose. | ||
The exposure time increases linearly with exposure dose and writing area. However, due to the stepped nature of the exposure, the exposure time as a function of fill factor is highly nonlinear. It takes the same time to expose a single pixel as the entire writing field, so the exposure time depends on the number of addressed writing fields, rather than on the fill factor of the design. In practice, there will probably not be much variation in exposure time with fill factor. Exposure tests have shown that the exposure speed is low for small areas, but reaches full speed at areas above 40x40mm<sup>2</sup>. The lower speed for small areas is probably due to the delay in exposure start caused by the generation of the data needed for the exposure (conversion). Exposure tests using a 25mm<sup>2</sup> design have shown that the exposure time increases linearly from 37s at 10mJ/cm<sup>2</sup> | The exposure time increases linearly with exposure dose and writing area. However, due to the stepped nature of the exposure, the exposure time as a function of fill factor is highly nonlinear. It takes the same time to expose a single pixel as the entire writing field, so the exposure time depends on the number of addressed writing fields, rather than on the fill factor of the design. In practice, there will probably not be much variation in exposure time with fill factor. Exposure tests have shown that the exposure speed is low for small areas, but reaches full speed at areas above 40x40mm<sup>2</sup>. The lower speed for small areas is probably due to the delay in exposure start caused by the generation of the data needed for the exposure (conversion). Exposure tests using a 25mm<sup>2</sup> design have shown that the exposure time increases linearly with dose, from 37s at 10mJ/cm<sup>2</sup> to 252s at 2000mJ/cm<sup>2</sup>. | ||
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The Vector mode will write structures line by line. Structures will have low edge roughness and there will be no stitching of long lines. However, write time of a given design will strongly depend on the number, shape, or size of structures. | The Vector mode will write structures line by line. Structures will have low edge roughness and there will be no stitching of long lines. However, write time of a given design will strongly depend on the number, shape, or size of structures. | ||
The exposure time is a function of the number of elements (lines) in the design and the stage velocity during exposure. While the maximum velocity of the stage is 200mm/s | The exposure time is a function of the number of elements (lines) in the design and the stage velocity during exposure. While a very low Exposure Velocity will of course slow down the exposure speed, a high velocity will also lower the exposure speed because the stage has to accelerate longer before the exposure of each element can start. The maximum velocity of the stage is 200mm/s but Heidelberg recommend not to exceed 120mm/s, in order to avoid distortions of the elements due to acceleration effects. | ||
<br>During exposure tests of different sizes of simple square designs, the optimal stage velocity (in terms of exposure time) increased linearly from 15mm/s for 0.5mm elements to 50mm/s for 5mm elements. The highest "exposure speed" was just below 4 elements per second, which was observed for the 0.5mm elements. In practice, exposure can't always be at the optimal Exposure Velocity, as it may be necessary to decrease the velocity in order to achieve the required dose. | |||
==Resolution== | ==Resolution== | ||
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=Substrate positioning= | =Substrate positioning= | ||
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During load, the machine will focus on the surface of the sample. Then, using the automatic focusing system, it will detect the edges of the sample (this function depends on the substrate template used) in order to determine the center and rotation of the sample. The following results rapport findings using the "Wafer (d=100 mm; Flat)" template on a standard 100mm Si substrate. | During load, the machine will focus on the surface of the sample. Then, using the automatic focusing system, it will detect the edges of the sample (this function depends on the substrate template used) in order to determine the center and rotation of the sample. The following results rapport findings using the "Wafer (d=100 mm; Flat)" template on a standard 100mm Si substrate. | ||
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=Alignment= | =Alignment= | ||
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The alignment accuracy of the Aligner: Maskless | The alignment accuracy of the Aligner: Maskless 04 is a combination of the position accuracy of the stage, the accuracy of the alignment mark detection, and the distortion of the pattern already on the wafer (first print). The alignment specification of the machine is 1µm for both raster and vector mode, which was demonstrated in the factory acceptance test and the site acceptance test after installation. | ||
<br>An alignment test performed shortly after installation, using a 3x3 array of structures with 30mm pitch, showed an alignment error of 0.29±0.18µm in X and -0.49±0.23µm in Y (Raster mode). | |||