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E-Beam Lithography
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Electron beam lithography is capable of writing resist patterns with accuracy and control down to about 10nm. These patterns are
then used as masks in further processing steps, such as etching, where the resist resists the etching and protects the covered
region. In other cases, material is deposited in such a way that it only remains on the samples in regions where the resist is
absent. We use resists such as poly(methyl methacrylate) (PMMA), a so-called positive resist that is removed wherever the beam
writes, as well as negative resists, such as hydrogen silsesquioxane (HSQ), which only remains on the sample where it was
exposed, as illustrated in Figure 1. Our VB6 tool has a 100keV electron beam, where the high energy helps to minimize indirect
exposure of the resist by electrons scattered forward as the beam passes through the resist or backwards to the resist from the
substrate.
Figure 1. Lithography processes. After coating a substrate with resist, a pattern is exposed on the sample with ebeam (or alternatively
with UV). In the case of a positive resist, after developing, the resist is removed from everywhere the beam wrote. For a
negative resist, it is removed from everywhere except where the beam wrote.
In recent
projects, we have created a wide range of nanodevices. Another important
aspect of our work is the layer-by-layer
alignment of nanofeatures. In addition to building devices, we are also exploring the
limits of electron beam lithography and developing and evaluating
new resists to allow us to continue to push the limits of nano-scale fabrication.
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