Apparatus and method for inspection and testing of flat panel display substrates

Abstract

A charged particle optical system for testing, imaging or inspecting substrates comprises: a charged particle optical assembly configured to produce a line of charged particle beams equally spaced along a main scan axis, each beam being deflectable through a large angle along the main scan axis; and linear detector optics aligned along the main scan axis. The detector optics includes a linear secondary electron detector, a field free tube, voltage contrast plates and a linear backscattered electron detector. The large beam deflection is achieved using an electrostatic deflector for which the exit aperture is larger than the entrance aperture. One embodiment of the deflector includes: two parallel plates with chamfered inner surfaces disposed perpendicularly to the main scan axis; and a multiplicity of electrodes positioned peripherally in the gap between the plates, the electrodes being configured to maintain a uniform electric field transverse to the main scan axis.