Variably shaped electron beam lithography system, EB55: I. System design

Abstract

The precision electron beam exposure system EB55 has been developed for direct wafer writing of submicron patterns. This paper describes the system architecture, design approach, and system specifications. The system utilizes a variably shaped beam column with a spot size ranging from 0.5 to 5.1 μm square, which is adjustable in 0.02 μm increments. Pattern data, compressed by a pattern data preparation software, is supplied to the high-speed digital control unit, where it is expanded to provide control data at a 320 ns shot rate to an analog unit. The analog unit provides deflection current and voltage to the electrostatic deflection plates and magnetic deflection coils with 0.02 μm resolution. Pattern accuracy is maintained by deflection distortion correction and overlay techniques. The deflection error is measured within 0.02 μm accuracy over a 2.6 mm square field with a mark detector and laser position sensor and corrected by a digital correction unit. Overlay accuracy is assured by registering to fiducial marks on the wafer and measuring wafer deformation to determine field adjustments. The exposure time per wafer is about 41 min with 0.5 μm minimum linewidth and ±0.1 μm overlay accuracy (3σ) using 20 μC/cm2 resist sensitivity and 8×108 shots per wafer. In this case, the writing time, the registration time, and the stage move time are 32, 3, and 6 min, respectively.