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

A charged particle optical system for the production of a charged particle beam deflectable through a large angle in the direction of a main scan axis comprising:

• a charged particle optical assembly configured to produce a charged particle beam focused on a specimen plane, said charged particle optical assembly comprising:
• a charged particle source;
• a main lens;
• an accelerating region positioned between said source and said main lens;
• and
• a beam blanker positioned between said charged particle source and said main lens, for blanking said charged particle beam, wherein said beam blanker is a double-deflection beam blanker including upper blanker plates and lower blanker plates configured to deflect said charged particle beam in opposite directions;
• wherein said charged particle optical assembly is configured to project the effective blanking plane back to the position of the virtual source, and wherein there is no charged particle beam cross-over in said beam blanker;
• and
• an electrostatic deflector aligned on the optical axis of said optical assembly and positioned between said optical assembly and said specimen plane, said deflector having an exit aperture and an entrance aperture, wherein said exit aperture has a larger area than said entrance aperture.