Electron Beam Apparatus Having Auto-Centering Dynamic Focus
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
In electron beam lithography it is important that the beam be centered in the rotationally symmetric field in order to obtain the best beam spot resolution. The present system uses a dynamic focus coil to automatically align the magnetic fields of the main focus coil to eliminate mechanical adjustments. Electron beam systems, which deflect a beam over an area of the target, require dynamic focusing with lens excitation changing as a function of beam deflection. Since only the center of the target is in the focal plane of the lens, all other locations require refocusing. With magnetic lenses, fast current changes cannot be made because of the high inductance of the focus coil. Because of this, a low inductance auxiliary focus coil is used.