such as an electron impact x ray tube there is obtained such a sectional shape of line pattern as shown in fig2 a in which the bottom of a resist 11 broadens about 0 1 u03bcm on the other hand according to this embodiment of the present invention there is obtained a good sectional shape of a resist 12 as shown in fig2 b fig3 shows how the resist broadening width changes with change of the angle u03b1 between a line pattern 13 of the diffraction grating and the electric vector direction 7 from which it is seen that the broadening with decreases as the angle u03b1 becomes smaller also when magnetic materials e g yig yhtrium iron garnet ggg gallium gadolinium iron garnet were used for the substrate there were obtained the same results in this embodiment there was used the same optical system as in the above first embodiment except that such a shape of a mask pattern as shown in fig4 was used this pattern corresponds to one used in the production of a gate of mos transistor it is necessary that the pattern formation be effected accurately on both side portions of a projection 14 of the pattern therefore the longitudinal direction of the pattern and the direction of the electric vector were brought into coincidence with each other and in this state there was performed exposure followed by development the pattern thus formed was good on both side portions of the projection 14 although broadening occured at both end sides 15 and 16 of the pattern in the above two embodiments the influence of photoelectrons in pattern formation was observed while in this embodiment 3 photoelectrons per se created at the time of pattern formation are counted more.