Electron image projection systems for microcircuit lithography

High-resolution electron-beam microfabrication requires long process times when using a single scanning beam to expose large-area integrated circuits. Exposure times for a 2-in wafer by a scanning beam system are typically between 30 min to 3 h, depending on the area and complexity of the circuit. This paper describes an electron projection system that projects the whole electron image of the integrated circuit mask onto the wafer at once, enabling exposure times of 1 s or less to be attained. The system incorporates a photocathode patterned into an integrated circuit mask. The pattern is projected and focused onto the wafer using axial magnetic and electrostatic fields. Described herein are factors affecting photocathode life and exposure times. A technique for automatic alignment of the mask to the wafer is also described which has achieved 0.25-µ alignment accuracies.