Comparative study on variable axis lens systems based on tapered deflectors

A variable axis lens (VAL) concept has been demonstrated an effective method to reduce aberrations of electron beam machines and has been explored to several configurations. To implement the advantages of VAL fully, it is desirable to make the axial potential distribution of the objective lens match the deflection functions of deflectors well. To our knowledge, the electrostatic deflectors applied in electron-optical systems based on VAL concept are all constructed with a “cylindrical” shape. However, when a magnetic objective lens in the VAL configurations is constructed with different radii of upper and lower pole pieces, there is a mismatch between the asymmetric lens and cylindrical deflectors, which would lead to a significant increase in aberrations. With this in mind, we have developed tapered deflectors to address the foregoing problem. A comparative study on variable axis lens systems based on conventional cylindrical deflectors and the proposed tapered ones is undertaken. Simulation results demonstrate the validity and effectiveness of the proposed VALs to reduce aberrations and an electron beam landing angle.