Variable spot-shaped <i>e</i>-beam lithographic tool

Abstract

The EL2 system was developed as a direct wafer writing e beam tool to be used for product and process development. EL2 is a high thruput, high resolution, fully automated tool that utilizes the variable spot shape technique as well as other design innovations. This paper will review the system architecture, design approach, system specifications, and results obtained with this system. The systems utilize a variable spot shaped column with a maximum spot size ranging from 2×2 μm to 4×4 μm adjustable in increments of 0.1 and 0.2 μm, respectively. Gun brightness and column alignment are maintained by a group of servos which maintain proper operating conditions. The spot is positioned via a raster deflection which can be up to 8 mm. A calibration technique is employed to insure deflection accuracy over long time periods. Overlay is achieved by scanning alignment marks in the four corners of fields and processing the backscattered electron signals to determine field adjustments. EL2 is capable of exposing over 10 wafers (2.25 in) per hour with 1.25-μm linewidths and 0.3-μm overlay (30). This is accomplished with 10-μC resist sensitivity and machine availability of about 80%.