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This paper describes recent developments in three areas ofmasked ion beam lithography (MIBL). These are 1) fabrication
oflarge area, low distortion, silicon stencilmasks for demagnifying ion projection lithography, 2) fabrication ofstencil masks
with nanometer scale resolution for 1:1 proximity printing, and 3) development of a direct method of alignment using the
ion beam induced fluorescence of Si02. These topics are discussed below.
Demagnifying ion projection masks: We describe the fabrication of stencil masks in large area, low stress (10 MPa), n-type
silicon membranes. The projection masks have a silicon foil area 95 mm in diameter, thicknesses between 1.5-5 and
resolution of0.6um. Measured distortion (3a) in the IPL masks ranges between 0.23gm and 0.65,um, with an experimental
error of 0.20 1um.
Proximity printing masks: A process is described for fabricating stencil masks with 50 nm resolution in low stress, n-type
silicon membranes. Membranes less than 0.5 ,ttm thick are shown to be free of the sidewall taper that limits resolution in
thicker masks. These thin membranes show a slightly flared profile due to the imperfectly collimated etching ions.
Alignment: A direct method of alignment is being developed which uses the ion beam induced fluorescence of Si02 marks.
Fluorescence yield is characterized as a function of ion energy and resist coating thickness. The yield for Si02 is in the range
between 0.1-1.0 photons/proton, while the yields for Si, Al, and photoresist are negligibly small. Thus, a simple alignment
technique can be implemented where registration of a grating in the mask with a corresponding oxide pattern is detected
as a fluorescence maximum. A simple model predicts that 50 nm alignment can be accomplished, following a 1 im
prealignment, in 2 seconds.
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