E-Beam Writing Techniques for Semiconductor Device Fabrication

Abstract

Electron-beam writing instruments for microcircuit fabrication are currently limited by total cycle time, field coverage, automatic registration, and reliability. A fully computer-controlled electron-beam pattern generator will be described which has been developed to advance the economic feasibility of electron beam writing. The instrument incorporates a fully automated mechanical stage and pattern registration system, computer designed deflection coils and a dynamic focusing system for correction of deflection introduced aberrations. Field coverage at the short working distance is variable, up to 0.120×0.120 in. with 60 000×60 000 addressable points in the field. Resolution over the field is 3500 lines at 8 mrad. Pattern distortion is within 1.0 μ over a 0.1 in. square field. The mechanical stage employs stepping motors driving lead screws to provide 3×3 in. movement in 250 μ in.steps. Additional travel of 7 in. is available in one axis for loading the wafer. The automatic pattern registration system employs four silicon etched “L” shaped fiducial marks located in the corners of each field. The electron beam is used to measure the position of the fiducial marks before each field exposure and position the pattern correctly on the wafer. Pattern position, size, rotation, and orthogonality are all typically set up by the automatic registration system in 300 msec. A vernier test pattern has been used to test the alignment system and shows registration better than ± 0.2 μ.