Electron-beam block exposure system for a 256 M dynamic random access memory

Abstract

A block exposure system is developed to expose a 256 M DRAM pattern. Four mask deflectors deflect beams to select one of 48 blocks of stencil patterns in a 5 mm region in diameter on a mask. Each mask pattern is extracted as a unit of repetitions from the dynamic random access memory (DRAM) pattern, which is demagnified to 1/100 on a wafer. In a 256 M DRAM contact hole layer, only two blocks are used to expose memory cell regions. Forty-six blocks are for sense amplifier and decoder regions. The total shot number of the layer is decreased to 21.5×106 with the block exposure system, which is about 1/8 of that with a conventional shaped beam system. One chip is exposed in 11.5 s. Throughput is 10 wafers (6 in.)/h for the contact hole layer.