High Speed Beam Deflection and Blanking for Electron Lithography

Abstract

A fast magnetic deflection system and beam blanking unit have been incorporated into the electron optical column of a commercial SEM for application to electron lithography. The achieved response-time of the deflection system is about 1 μsec. Double deflection coils are located outside of a glass tube enclosing the electron beam. A thin silver film deposited on the inside surface of the tube serves to conduct charge to ground but does not significantly impede high-frequency deflection fields. A ferrite magnetic shield is placed between the deflection coils and the surrounding iron pole-piece of the objective lens. The function of the shield is to minimize the undesirable eddy currents induced in the iron by the deflection field. The response time of the beam blanking unit is about 10 nsec. The unit employs a pair of electrostatic plates which blank the beam by deflecting the latter against an aperture-stop. The center of deflection of the plates coincides with the crossover point produced by the first condenser lens. Under this condition the beam can be deflected and blanked without affecting the position of the writing spot. The spot position is also insensitive to unequal charging of the contaminated plates by stray electrons. The writing spot position drift, caused by electron charging of other surfaces in the column, has also been minimized by properly restricting the beam width in the column and centering the beam on the final aperture.