We are developing an electron beam (EB) stepper as one of the next-generation
lithography systems for feature sizes of less than 100 nm. As a reticle for the EB stepper
using a high-power EB (accelerating voltage:100 kV, current on reticle:100 µA), a scattering
stencil reticle with a grid-grillage structure is investigated. We evaluated the deformation
of a scattering stencil reticle, due to thermal expansion and bending by gravity. These
phenomena are computer simulated. Immediately after the EB is illuminated, the
temperature of the 2-µm-thick membrane of the reticle increases about 4 K. The induced
pattern distortion is about 2 nm and gravitational horizontal deformation is less than 1 nm.
Thermal and gravitational vertical deformations are about 3 nm and about 6 nm,
respectively. From these results, the induced image horizontal distortion is about 0.5 nm and
vertical distortion is about 0.4 nm on the wafer for a demagnification(1/4) system, due to
thermal expansion and bending by gravity. This shows that a scattering stencil reticle with a
2-µm-thick membrane is applicable to an EB stepper for high throughput and high
resolution, and has advantages compared with a conventional EB lithography mask from the
viewpoint of thermal problems.
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