Patent Number: 
Section: description

Referring now to the accompanying drawings, some embodiments of the present invention will be described below. In any of the following embodiments, an electron beam exposure system for writing a pattern on a wafer using electron beams will be described as a charged particle beam exposure system. FIG. 1 is a schematic construction drawing showing an electron optical system of the first embodiment of a charged particle beam exposure system according to the present invention. As shown in this figure, this embodiment is characterized by the construction of electrostatic lenses and the construction of a reducing projecting optical system. That is, in an electron beam exposure system 10 shown in FIG. 1, all of electrostatic lenses except for illumination lenses 15a and 15b, i.e., a first shaping deflector 17, a second shaping deflector 21, electrostatic lenses 23Q1 through Q4 for controlling trajectories of electron beams independently in X and Y directions, a pre main deflector 25 and a sub deflector 31 comprise electrostatic multi-pole lenses. Each of these multi-pole lenses comprises eight electrodes which are arranged at angular intervals of 45 degrees. Referring to FIGS. 2A through 2C, the concrete shape of a multi-pole lens of the electron beam exposure system 10 in this embodiment will be described below. FIG. 2A shows a quadrupole lens with four electrodes. The electrodes Q11a through Q11d of a quadrupole lens in this figure are formed in a cylindrical shape respectively and arranged at angular intervals of 90 degrees. FIG. 2B shows an example of a quadrupole lens comprising eight electrodes, and shows eight cylindrical electrodes Q12a through Q12h which are arranged at angular intervals of 45 degrees. FIG. 2C is a plan view showing the construction of a multi-pole lens 23Q1 of the charged particle beam exposure system 10 in this embodiment, and typically shows the construction of electrostatic deflectors 17, 21, 25 and 31 and electrostatic lenses 23. The multi-pole lens 23 comprises eight electrodes Q13a through Q13h which are arranged at angular intervals of 45 degrees. Each of the electrodes is formed in a sector plane shape. In this embodiment, adjacent two of the eighth electrodes of the multi-pole lens 23 are used as a single quadrupole electrode so that the whole multi-pole lens 23 operates as a quadrupole lens. For example, a voltage of +V is applied to the electrodes Q13a and Q13b, so that these electrodes are controlled so as to function as the electrode Q11a shown in FIG. 2A. Then, in the following description the multi-pole lens 23 will be suitably described as the quadrupole lens 23. Referring to FIG. 1 again, the reducing projecting optical system of the charged particle beam exposure system 10 comprises: electrostatic quadrupole lenses 23Q1 through 23Q4, the quadrupole lenses 23Q1 and 23Q2 being provided upstream of the pre main deflectors 25a and 25b, and the quadrupole lenses 23Q3 and 23Q4 being provided downstream of the pre main deflectors 25a and 25b; a sub deflector 31 which is provided between Q4 of the fourth quadrupole lens 23 and a wafer 14; and shielding electrodes 36 and 39 which are arranged in the vicinity of the top and bottom faces of the first shaping deflector 17, the second shaping deflector 21, the pre main deflectors 25a and 25b, and the quadrupole lenses 23Q1 through Q4 in directions of the optical axis. The shielding electrode 36 is formed with an inside diameter "PHgr"1 of 5 mm and the shielding electrode 39 is formed with an inside diameter "PHgr"2 of 10 mm. These shielding electrodes 36 and 39 are connected to the ground to adequately eliminate the possibility that electrostatic fields formed by the respective lenses or deflectors interface with each other. As a result, as can be clearly seen from the comparison with FIG. 13, in this embodiment, all of the first shaping deflector 17, the second shaping deflector 21 and the first and second quadrupole lenses Q1 and Q2 are formed with the same inside diameter "PHgr"1 (5 mm) as the inside diameter of the shielding electrode 36. The third quadrupole lens Q3 and fourth quadrupole lens Q4 of the quadruple quadrupole lenses 23 are designed so that the diameters thereof are greater than those of the first and second quadrupole lenses Q1 and Q2. Specifically, the inside diameter of Q1 and Q2 is "PHgr"1=5 mm as shown in FIG. 3A and the inside diameter "PHgr"2 of Q3 and Q4 is 10 mm as shown in FIG. 3B. As will be described later, the quadrupole lenses Q3 and Q4 form a multi-pole lens field for independently controlling X and Y trajectories of electron beams 8, and also serve as a main deflector 27 for superimposing a deflecting electrostatic field on the multi-pole lens field. The shielding electrodes 36 and 39 are connected to the ground to prevent the leaching of the electrostatic field excited by the respective electrodes. Other constructions of the electron beam exposure system 10 are substantially the same as those of the electron beam lithography system 100 shown in FIG. 13. The operation of the electron beam exposure system shown in FIG. 1 is as follows. The electron beams 8 are emitted from the electron gun 11 to be accelerated and the first aperture 13 having the rectangular or circular opening is irradiated with the electron beams 8. The electron beams 8 passing through the first aperture 13 travel toward the second shaping aperture 19 in which a plurality of bulk exposure cell apertures are arranged. The beam diameter of the electron beams 8 is adjusted to such a size that it is sufficiently greater than an any one of the cell apertures and that the electron beams 8 do not interfere with adjacent cell patterns. The trajectories of the electron beams 8 are deflected and controlled by the first shaping deflector 17 so that a target aperture of the cell apertures formed in the second shaping aperture 19 is irradiated with the electron beams 8. The electron beams 8 passing through the second shaping aperture 19 start as cell pattern beams starting at the second shaping aperture 19 and are returned to the optical axis by means of the second shaping deflector 21 to illuminate the interior of the quadrupole 23. For example, assuming that the optical axis of the electron beams 8 extends in Z directions, a voltage is applied to the quadruple quadrupole lenses 23 so as to form such electrostatic fields in the X and Y directions, i.e., if the first through fourth electrostatic fields in the X directions are sequentially a divergent electrostatic field (Q1), a divergent electrostatic field (Q2), a convergent electrostatic field (Q3) and a divergent electrostatic field (Q4), the electrostatic fields in the Y directions are a convergent electrostatic field (Q1), a convergent electrostatic field (Q2), a divergent electrostatic field (Q3) and a convergent electrostatic field (Q4) by contraries. When the quadrupole lenses 23 are thus controlled, the trajectories of the electron beams 8 from the second shaping aperture 19 to the wafer 14 are shown in FIG. 4. As can be clearly seen from the comparison with FIG. 12, the electron beams 8 pass through different trajectories in the X and Y directions by means of Q1 through Q4 of the quadrupole lenses 23. This point is the same as the electron beam lithography system 100. However, in this embodiment, by means of Q1 and Q2 of the quadrupole lenses 23, the electron beam trajectory 8X in the X directions repeats divergence, and on the other hand, the electron beam trajectory 8Y in the Y directions repeats convergence, so that the electron beams 8 are condensed on the wafer 14 without forming any crossovers with a high electron density. As a result, in the low acceleration electron beam exposure, the influence of the space-charge effect can be substantially reduced. Furthermore, in this embodiment, only the pre main deflector 25a and 25b is used for controlling the beam trajectories. Referring to FIG. 1 again, a position of the region to be written (main field) on the wafer 14 illuminated with the electron beams 8 can controlled by the pre main deflector 25a and the main deflector 27 while referring to the position of the XY stage (not shown) on which the wafer 14 is mounted. The position of the range to be written which is obtained by finely dividing the interior of the stripe (sub field) is controlled by the sub deflector 31. In this embodiment, the quadrupole lenses Q3 and Q4 also serve as the main deflector 27. This is realized by superimposing a deflecting electrostatic field on an electrostatic field which serves to control the trajectories in the X and Y directions by Q3 and Q4 of the quadrupole lenses 23. FIGS. 5A through 7C show examples of electrostatic field superimposing methods. FIGS. 5A through 5C show voltage values which are applied to the respective electrodes of Q3 and Q4 of the quadrupole lenses 23 only for controlling the trajectories of the electron beams 8 in the X and Y directions. In this case, the voltage value applied to the pre main deflector 25a is 0. FIGS. 6A through 6C show the values of voltages which are applied to the pre main deflector 25a and the respective electrodes of Q3 and Q4 of the quadrupole lenses 23 only when the electron beams 8 are deflected in the X directions. FIGS. 7A through 7C show voltage values which are applied to the respective electrodes when the electrostatic field obtained by the voltage values shown in FIGS. 5A through 5C is superimposed on the electrostatic field obtained by the voltage values shown in FIGS. 6A through 6C respectively. The voltage values shown in FIGS. 7A through 7C are equal to voltage values which are obtained by adding the voltage values shown in FIGS. 5A through 5C to the voltage values shown in FIGS. 6A through 6C, respectively. By controlling such voltages, the deflection and control of the electron beams can be realized with the minimum construction. FIGS. 5A through 7C show the control methods for deflecting the electron beams in the X directions. The deflection and control in the Y directions can be realized by rotating the deflecting voltages of FIGS. 6B and 6C by 90 degrees, respectively, and setting all of the deflecting voltages V1 of the pre main deflector 25a to be zero. If a voltage obtained by adding the control voltage in the X directions to the control voltage in the Y directions is applied, it is possible to deflect the electron beams to a direction in which the electron beams are inclined at 45 degrees (diagonal direction). Thus, according to the electron beam exposure system 10 in this embodiment, the aberration components of the electron beams 8 can be minimized by adjusting the ratio of the deflecting voltage of the pre main deflector 25 to that of Q3 and Q4 of the quadrupole lenses 23 serving as the main deflector 27. The deflection of the electron beams can be independently carried out in the X and Y directions. For example, as shown in FIG. 8, the electron beams 48X in the X directions are deflected by means of the pre main deflector 25a, the main deflector 27 (Q3 and Q4 of the quadrupole lenses 23) and the sub deflector 31, and on the other hand, the electron beams 48Y in the Y directions are deflected only by means of the main deflector 27 (Q3 and Q4 of the quadrupole lenses 23) and the sub deflector 31, so that it is possible to further reduce deflection aberration. In this case, the aberration components of the electron beams 8 can be minimized by adjusting the deflecting voltage ratio between the pre main deflector 25, Q3 and Q4 of the quadrupole lenses 23 serving as the main deflector 27, and the sub deflector 31. If the wafer 14 is irradiated with the electron beams 8, secondary electrons and so forth are produced on the surface of the wafer 14. The secondary electron detector 33 provided below the quadrupole 23 is designed to detect these secondary electrons and so forth, and the electron beam exposure system 10 is designed to process the detection signals from the secondary electron detector 33 to detect a SEM image and to adjust the beams and the like. According to the electron beam exposure system 10 in this embodiment, the quadruple quadrupole lenses Q1 through Q4 are used for forming the multi-pole lens field, so that it is possible to avoid deceleration in lenses occurring in conventional rotation-symmetric decelerating electrostatic lenses. Since the beam trajectories of the low acceleration electron beams 8 passing through the second shaping deflector 21 are controlled independently in the X and Y directions respectively by means of the multi-pole lens field, the electron beams 8 can be condensed on the wafer 14 without forming any crossover with a high current density. Thus, it is possible to greatly remove the influence of the space-charge effect even at a low acceleration. Since the multi-pole lens with eight electrodes is operated as a quadrupole lens, it is possible to greatly reduce high-order aberration of deflection. Since the deflection electrostatic field is superimposed on the multi-pole lens field of the quadrupole lenses Q3 and Q4 to operate the quadrupole lenses Q3 and Q4 also as the main deflector, so that it is possible to reduce the optical length of the reducing projecting optical system. Since the inside diameters of the quadrupole lenses Q3 and Q4 are designed to be greater than those of Q1 and Q2, it is possible to form the trajectories of the electron beams in a region except for the vicinity of the electrodes. Thus, it is possible to further suppress deflection aberration. Moreover, since the shielding electrodes 36 and 39, which are ground electrodes, are arranged in close vicinity of both ends of the quadrupole lenses Q1 through Q4 in Z directions, it is possible to prevent the leaching of the electrostatic field from the respective electrodes. Thus, since the possibility of causing interference between the respective electrostatic fields is eliminated, it is possible to further shorten the optical length of the electron optical system, and it is possible to further improve deflection sensitivity. By using the optical system with the above described construction and the above described deflection control method, it was achieved to realize an electron beam exposure system wherein, for example, under a stigmatic condition of a reduction ratio of 1/10 in both of X and Y directions, the optical length between the second shaping aperture 19 and the wafer 14 is 101 mm (see FIG. 1) while the quadrupole lens length (length in Y directions) is 6 mm, the main deflection area is 1.5 mmxe2x96xa1 and the sub deflection function is 50 xcexcmxe2x96xa1. FIG. 9 is a schematic construction drawing showing an electron optical system of the second embodiment of a charged particle beam exposure system according to the present invention. As can be clearly seen from the comparison with FIG. 1, the charged particle beam exposure system 20 in this embodiment is characterized in that a shielding electrode 41 is provided upstream of the pre main deflector 25a, and a shielding electrode 38 is further provided between Q1 and Q2 of the quadrupole lenses 23 in place of the shielding electrode 36. Other constructions of the charged particle beam exposure system 20 are substantially the same as those of the charged particle beam exposure system 10 shown in FIG. 1. The inside diameter of the shielding electrode 38 is designed so as to be smaller than those of adjacent two shielding electrodes, i.e., the shielding electrodes 36 which are provided upstream of the quadrupole lens 23Q1 and downstream of the quadrupole lens 23Q2. For example, when the inside diameter "PHgr"1 of the shielding electrode 36 is 5 mm, the inside diameter "PHgr"3 of the shielding electrode 38 is designed to be 200 xcexcm. Thus, the shielding electrode 38 can be used as a beam aligning aperture for the illumination lenses 15a and 15b, the first shaping deflector 17, the second shaping deflector 21 and Q1 of the quadrupole lenses 23, or as a detector for the electron beams 8. Similar to the shielding electrode 38, the inside diameter of the shielding electrode 41 is smaller than that of each of other shielding electrodes 36 and 39, and for example, the inside diameter of the shielding electrode 41 is "PHgr"4=200 xcexcm. Due to such a small inside diameter, the shielding electrode 41 can be used as a beam aligning aperture for the illumination lenses 15a and 15b, the first shaping deflector 17, the second shaping deflector 21 and Q1 and Q2 of the quadrupole lenses 23, or a detector for the electron beams 8. Since the operation of the electron beam exposure system 20 is substantially the same as the operation of the electron beam exposure system 10 shown in FIG. 1, the detailed description thereof is omitted. While the embodiments of the present invention have been described above, the present invention should not be limited to these embodiments, and the invention can be embodied in various ways without departing from the scope thereof. For example, while all of the quadrupole lenses 23 comprise octpole electrodes to produce a quadrupole field in the above described embodiments, Q1 and Q2 of the quadrupole lenses 23 may comprise four electrodes, and only Q3 and Q4 of the quadrupole lenses 23 for superimposing deflection fields may comprise octpole electrodes as shown in FIG. 2B or 2C. In addition, Q3 and Q4 of the quadrupole lenses 23 should not be limited to octpole electrodes, but they may comprise a multi-pole wherein the number of poles is M (M=4N2, N2 is a natural number of 2 or more). If the multi-pole having the greater number of poles is thus used, it is possible to reduce high-order components in the deflection field and to minimize deflection aberration. While electron beams are used as charged particle beams in the above described embodiments, the present invention should not be limited thereto, but the invention may be generally applied to a charged particle beam exposure system using ion beams as charged particle beams.