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Optimization of an electron beam lithography instrument for fast, large area writing at 10 kV acceleration voltage
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Image of FIG. 1.
FIG. 1.

(Color online) Beam paths of the two different current modes. The numbers indicate the position of the different parts in the SEM column. 1. Filament, 2. Condenser lens, 3. Collimating aperture, 4−6. Additional lenses, and 7. Specimen. The focal length of the condenser lens is changed in the high current mode (b). This leads to a narrower beam with higher current density. Note that the angular spread of the focused beam on the sample is smaller in the high current mode, thus increasing the depth of field. Figures are reproduced with permission from Raith.

Image of FIG. 2.
FIG. 2.

(Color online) Figure illustrating the two different ways of moving the beam. In the line mode, the beam is blanked when moved between each line, and a dynamic compensation is enabled at the start and end of each line. The meander mode writes the full structure from top to bottom in one go, only blanking when passing areas not to be exposed and when stitching write-fields.

Image of FIG. 3.
FIG. 3.

(Color online) Black square is a pattern pixel: a single pixel in the reference pattern bitmap. The grid is the overlying step size defined grid pixels, where and represent the user-defined step sizes in x- and y-directions. The pixel area pointed to by the arrow indicates the first patterned grid pixel and thus represents the writing resolution. The beam will move in the direction indicated by the arrow. When passing over a grid pixel, the beam is moved in a sweeping pattern defined by Raith so that all of the grid pixel area is exposed evenly with the correct dose. The beam pattern movement over the grid pixel will add up to the dose and the dwell time defined in the software. When the beam is passing over the white area of the grid, the beam will be blanked by the beam blanker.

Image of FIG. 4.
FIG. 4.

(Color online) Stereo microscope image of our EBL-written chrome mask structure. The diameter of the pattern is 15.8 mm. A higher-magnification optical microscopy image of chrome mask structure details can be seen in Fig. 5(a) .

Image of FIG. 5.
FIG. 5.

(Color online) Comparison of the EBL-fabricated chrome mask (a) and a cut-out of the computer-generated bitmap used for writing the chrome mask (b). The images are approximately to-scale, and the resolution of the bitmap is 900 nm. It can be seen that the pixelation of the bitmap is reproduced in the EBL mask.

Image of FIG. 6.
FIG. 6.

Image showing the underlying chrome film (visible as a textured layer) taken using the fast write settings in Table I . The polystyrene beads are sitting on top of the PMMA, and the PMMA itself is transparent. This significantly improves the focus quality of the beam and the write-field alignment.

Image of FIG. 7.
FIG. 7.

(Color online) Optical microscopy image of a commercially produced chrome mask. The pattern is made using the same image file as for the ones fabricated using EBL [see Fig. 5(a) ]. The circles are drawn to show tapering lines, which have opened more than they should. The two circles in the middle show tapering lines, which have generated closed areas.


Generic image for table

Left column shows typical settings provided for writing with the Raith e_LiNE instrument. In the right column are the settings we used for fast, large-area writing. Note the beam current can vary considerably depending on the gun settings and the state of the filament.

Generic image for table

Patterning settings used for patterning the chrome mask structure (Ref. ). The beam speed and dwell time will vary depending on the measured beam current and the step size and dose set by the user.

Generic image for table

Time to expose a single grid pixel and the time to expose a full area (15 × 15 mm) is estimated for a beam current of 6.2 nA for a theoretical Fast Beam (FB) speed using the settings calculated in Eqs. (4) and (5) , and for the Actual Parameters (AP) we used in our experiment shown in Table II . The single grid pixel is the time for exposing one grid pixel and the full area is the time to expose a single pixel times the number of pixels extended over the full area. The actual writing time for our structure using AP settings was about 8 h and 45 min. Note that the reason the actual writing time is much shorter than the time listed for AP in the table is that less than half the full area is exposed when our structure is written.

Generic image for table

List of how much the write time was improved for each adjustment.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optimization of an electron beam lithography instrument for fast, large area writing at 10 kV acceleration voltage