Electron Beam Block Exposure

A new exposure technique called block exposure was examined in order to increase the throughput of direct writing of memory LSI devices using an electron beam. With this technique, an electron beam is projected to a block of aperture patterns in the stencil mask to change the beam shape. Frequently used LSI pattern components are defined as blocks to be reused during the exposure. Patterns that are rarely used are exposed by using a variable-shape beam. With the demagnification ratio of one percent, masks are easy to fabricate and very reliable. The patterns with a 0.13-µm minimum feature size are well projected on a single-layer resist. With block exposure, any shape can be accurately transferred irrespective of the pattern shape or size. The throughput of about ten 8-in wafers per hour is estimated for several pattern layers of a 64-Mbit dynamic random-access memory (DRAM).