High resolutionautomatic focus correction electronic subsystem for e-beam lithography.

摘要

This electronic signal processing system is a subsystem of an automatic focus system for an E-beam lithography tool. This subsystem allows the automatic focus system to achieve resolution of 0.25 microns. An automatic focus system is composed of several subsystems. The first is an optical subsystem which produces a focused image of a source aperture on a transducer, which is the second subsystem. This image moves across the transducer in response to variations of the z-position of the measured surface. The transducer, in this case a linear photodiode array, converts the optical position signal into an electronic signal similar to a television video signal. The signal processing subsystem produces multiple outputs from the electronic signal produced by the transducer. The analog correction output of this subsystem realizes a mathematical function of the measured z-height. This analog output is sent to the focus correction subsystem of the E-beam tool, thus achieving focus correction. A digital z-height measurement output is sent to the computer subsystem of the E-beam tool. The computer uses this value to compute deflection magnification corrections and rotation corrections.