Aperture-edge scattering in MeV ion-beam lithography. II. Scattering from a rectangular aperture
Programmable proximity aperture (PPA). (a) The PPA is defined in the GEANT4 simulation by four Ta sheets positioned in space to form an aperture with an opening ; (b) SEM image of two well-polished Ta sheets glued together to form an L-shaped blade.
Spatial distribution and energy of He ions passing through a aperture opening after impinging on the sample surface of behind the rear face of the fourth Ta blade. (a) The scattered flux is mainly located in the I and IV quadrants. (b) Zoomed central area from . (c) Zoomed central area from .
Angular distributions of He ions scattered from the edges of the programmable proximity aperture for different aperture openings: and , and , and and . The incident fluence is .
Scattered beam intensity on the sample from a aperture opening normalized to the incident fluence of of a perfectly parallel beam. The aperture-sample separation is .
Distribution of fluence of edge-scattered ions on the sample at and resulting from irradiation of opening of the PPA with incident fluence and beam divergence (uniform distribution of divergent angles within the beams is assumed).
Transmitted-beam intensity on the sample surface of behind the rear face of the fourth Ta plate. The beam with 0.28, 0.58, and divergences is incident on (X-opening) and (“Y-opening”) PPA openings.
Beam-spot broadening for different aperture openings, aperture-opening orientations, and beam divergences (0.28, 0.58, and ). “X” and “Y” in the figures stand for the vertical and horizontal orientations of the aperture opening, respectively (see text or Fig. 6). , where is the full width at half maximum of the simulated beam spot (e.g., such as those in Fig. 6) on the sample surface placed at the distance behind the rear face of sheet 4; and is the size of the aperture opening in the vertical or horizontal orientations. The bold text below the curves represents the slopes of the linear fits to the data. Note that is in micrometers and is in millimeters, hence the dimensionless slope should be multiplied by a factor of . (a) Beam-spot broadening for aperture opening. (b) Beam-spot broadening for aperture opening. (c) Beam-spot broadening for aperture openings.
SEM images of two different sizes of rectangular beam spots written in PMMA resist using ions from a Pelletron accelerator. The beam spots on the samples were shaped using the programmable proximity aperture. The samples were subsequently developed in a mixture of propan-2-ol and water 7:3 by volume. The shift of the center of the images was introduced during SEM imaging. The sample-aperture distance is varied between 1 and . (a) Structures exposed with a aperture opening. (b) Structures exposed with a aperture opening.
Maximum extent of the penumbra broadening and for an aperture opening in and directions for a beam divergence .
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