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Browse Prior Art Database

Electron Beam Apparatus Having Auto-Centering Dynamic Focus

IP.com Disclosure Number: IPCOM000059663D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Pfeiffer, HC: AUTHOR [+3]

Abstract

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.

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Electron Beam Apparatus Having Auto-Centering Dynamic Focus

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. This coil has a small focusing power, but it is sufficient to compensate for beam focus changes over the desired deflection area. When the beam is centered in the rotationally symmetric lens field, it will not undergo sideways motion when lens excitation is changed. This is especially important in electron beam lithography systems where, in addition to resolution, beam positional accuracy and stability is critically important over large target areas and exposure times. To achieve this, the field of the dynamic focus coil, which is constantly changing as a function of beam position and target elevation, must be maintained concentric with the main focus coil. This is typi...