Variable spot shape control electronics

Publisher Website
Google Scholar
Abstract
The electronics, calibration, and registration techniques required to dynamically control electron beam spot size, position, and blanking on a spot‐by‐spot basis to write and overlay integrated circuit patterns are described in this paper. Pattern data which has been converted from a graphic language format to a compressed raster format is supplied to the Digital Control Unit (DCU) where it is expanded to provide control data at a 460 per spot rate to the Analog unit. The analog unit provides deflection voltages to the electron beam column which control retangular spot size and position to a resolution of 0.125 μm in X and Y over an 8 mm field, or 0.0625 μm over a 4 mm field. Pattern accuracy is assured by an automated deflection calibration system. A calibration grid placed underneath the beam is scanned using the same beam deflection pattern and field as that used for writing. Backscatter electrons from the grid are detected and the resultant signal processed to determine the deflection error at 900 points over the field. Corrections are applied to the deflection and the grid is rescanned. This process is repeated until the errors are within specified limits. Overlay of patterns is assured by registering to fiducial marks incorporated into the pattern to be overlayed. Four marks, one in each corner of the pattern, are scanned prior to writing. The resulting backscatter electron signals are processed to determine the errors in the four corners of the field. Corrections are claculated and applied as the pattern is written. Calibration techniques, registration techniques, and circuit performance criteria required to achieve 0.6 um pattern overlay over an 8 mm field are presented.

This publication has 0 references indexed in Scilit: