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

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.