| 摘要 |
PURPOSE:To reduce the diameter of the electron beam thus to improve the resolution, by setting the outermost incident angle of the electron beam in a main lens system to satisfy a specific formula. CONSTITUTION:The outermost incident angle theta in the main lens system 4 is set to satisfy the following formula: theta<=[4E*/3phii <k>sr*(a*)<3>] . Here EN*=emittance= Ro*thetaophio , ksr =inherent aberration constant= kso*(phiophii) , a*=the distance between the vertual object face 2 and the main lesn 4, kso*=spherical aberration factor at the object side=cso/fo*)<3>, phio=potential at the object side, phii=sceen potential, thetao=maximum radiation angle of the electron beam and Ro*=the size of the object. In other word the maximum incident angle theta is set to satisfy the formula theta/theta<a>=[-2.36X(phiophii)+ 1.45]X0.436(phii/phio) with reference to the outermost incident angle theta which will provide the minimum beam diameter in the proximity of the focus voltage ratio minimum beam diameter in the proximity of the focus voltage ratio phio/phii=19%. |
