A high-speed patterning controller for the EB60 electron beam lithography system

Abstract

A high‐speed patterning controller consisting of a pattern generator, beam deflection circuits, and a mark signal processor has been developed for the EB60 electron beam lithography system. To achieve a throughput of 16M shots per second and high accuracy for pattern writing during continuous movement of the stage, three key developments are incorporated into the pattern generator: (1) a buffer memory of 128M bytes for storing an entire VLSI chip pattern and eliminating the need for the repetitious storing of the same pattern data; (2) six‐stage pipelining with a 400 MHz basic clock for performing dynamic corrections in under 60 ns (about five times faster than former systems); (3) feed‐forward control architecture for eliminating the beam position error caused by the data transmission system delay time. The major and minor deflection systems are equipped with the beam deflection circuits consisting of high‐accuracy digital to analogue converters (DACs) and high‐speed amplifiers. For the minor field deflection system (12 bit accuracy with ±50V output), GaAs FET current switches are used in the DAC to achieve a typical settling time of less than 60 ns. For the major field deflection system (18 bit accuracy with ±500V output), static induction transistors (SITs) are used in the final stage of the amplifiers and high‐stability feedback resistors with low temperature coefficients are also developed. As a result, a settling time of less than 4 μs is achieved for the minor field width step. To perform mark detection in under 50 ms per mark, a low noise electron detector and signal averaging hardware are developed for the mark signal processor. This patterning controller provides an electron beam lithography system with a high throughput and a high accuracy, which results in a shorter turn‐around time for the fabrication of VLSIs with submicron critical dimensions.