Patent ID: 6246058
Filing Date: 2001-06-12
Classification: H01J

Abstract:
A particle-optical apparatus which includes,a particle source for producing a beam of electrically charged particles which travel along an optical axis of the apparatus in order to irradiate an object to be irradiated in the apparatus by means of the particle beam,a focusing lens for focusing the beam of electrically charged particles,and a correction device for correcting lens aberrations of the focusing lens,which correction device comprises pole faces for producing a uniform electrical field and a uniform magnetic field which extends perpendicularly thereto, both dipole fields also extending perpendicularly to the optical axis of the apparatus,which correction device also comprises pole faces for producing an electrical quadrupole field, which pole faces extend substantially parallel to the optical axis of the apparatus,the strengths of the electrical and the magnetic fields in the correction device are such that in the correction device the electrically charged particles travel along a sinusoidal trajectory which includes i full sine periods (i=0, 1, 2 . . . ) plus a sine line whose length does not deviate more than 10% from a full sine period,and that upstream as well as downstream from the correction device there is provided an n-pole where n=4, 6, . . . , which is arranged at a distance D.sub.1 and D.sub.2, respectively, from the correction device, D.sub.1 and D.sub.2 being smaller than (1/4) L, where L is the length of the pole faces governing the uniform fields in the direction of the optical axis.