Design aspects of a scanning electron-beam-microfabrication instrument having 10×10 mm field coverage, normal substrate incidence, and high throughput

Abstract

A microfabrication instrument with a field size of 10×10 mm is being developed so that masks for large devices can be exposed without having to stitch together a number of small fields. A satisfactory probe size has already been achieved using a postlens deflection system which has written 10 000 lines per field. Normal substrate incidence will be incorporated in order to eliminate positional errors due to electron optical distortion and to maintain a high writing speed despite the large scanned area. It is proposed that the positional errors be reduced by the application of a polynomial correction function containing terms corresponding to each of the possible deflection distortions. These errors may either be precorrected by a digital computer during data handling for the vector scan generator, or corrected in ’’real time’’ during exposure by suitable analogue modification of the scan currents. The fundamental writing speed of the magnetic deflection system is limited by the self-inductance and self-capacitance of the scan coils. It is shown how the number of turns wound on the coils may be optimized to obtain the maximum writing speed, subject to the constraints imposed by the output characteristics of the scan amplifiers and the allowable power dissipation in the scan coils.