Patent Number: 043307094
Section: summary

The invention relates to an electronic optical objective of use in microlithography. Objectives employed for this purpose comprise usually an electron lens and a deflecting system comprising coils which, depending on the intensity of the electric current therein, deflect the beam in a predetermined direction, the extent of this deflection being preferably a predetermined linear and increasing function of this intensity. Known objectives have certain drawbacks. In particular, they are the cause of aberrations and the eddy current increases the response time. Lastly, they are not linear. The objective according to the invention in large part avoids these drawbacks. According to the invention, there is provided an electronic optical objective comprising a magnetic lens of revolution which is capable of forming on its optical axis an axial magnetic field which varies from its input pupil to its output pupil, and at least one deflector formed by magnetic coils which create a magnetic field of variable intensity which is the cause of the deflection of the electron beam in a given direction, the objective further comprising two coil systems placed respectively close to the input pupil and close to the output pupil, the two systems being identical and angularly offset from each other by a certain angle .theta., the polepieces of the lens comprising an element of soft iron and an element of ferrite spaced apart by an airgap. According to another aspect of the invention, there is provided an objective wherein the first system is placed in a region where the axial field is of the order of one tenth of its maximum value, and the second system is placed in a region where it is of the order of one half of said value, the axial field increasing from the input pupil to the output pupil with a relatively small slope and reaching its maximum value in the immediate vicinity of the output pupil and being zero in the plane of said pupil.