Thermal Characteristics of Scattering Stencil Reticle for Electron Beam Stepper

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.