A NEW TYPE OF QUADRUPOLE CORRECTION LENS FOR ELECTRON-BEAM LITHOGRAPHY

A new type of quadrupole correction-lens system with lower aperture aberration coefficients has been developed for an electron-beam lithography system. The new lens is called a self-aligned quadrupole correction lens and consists of three-stage electrostatic quadrupoles, and aperture electrodes placed between quadrupoles. An octupole field for correction of aperture aberration is automatically created and aligned with a quadrupole field by supplying a voltage to the aperture electrode, and it has its peak near the edge portion of the quadrupole. A new mechanical construction of the quadrupole correction-lens system is developed for realizing high-precision alignment of the multistage lens electrodes. The optical properties of the new correction lens are exactly calculated by using simulated potential distributions. Aperture aberration coefficients of the new correction lens can be corrected to less than 0.1 mm. It is confirmed experimentally that the probe size is improved remarkably by excitations of the aperture electrodes. © 1990.