Abstract:
A charged particle beam exposure system comprising: a charged particle beam emitting device which generates charged particle beams with which a substrate is irradiated, the charged particle beam emitting device generating the charged particle beams at an accelerating voltage which is lower than that at which an influence of a proximity effect occurs; an illumination optical system which adjusts a beam diameter of the charged particle beams so that density of the charged particle beams is uniform; an character aperture in which an aperture hole is formed in a shape corresponding to a desired pattern to be written; a first deflector which deflects the charged particle beams by an electrostatic field that the charged particle beams have a desired sectional shape and travel towards a desired aperture hole and which returns the charged particle beams passing through the aperture hole to an optical axis thereof; a reducing projecting optical system which forms a multi-pole lens field so that the charged particle beams passing through the character aperture substantially reduce at the same demagnification both in X and Y directions when the optical axis extends in Z directions and form an image on the substrate without forming any crossover between the character aperture and the substrate; and a second deflector which deflects the charged particle beams passing through the character aperture by means of an electrostatic field to scan the substrate with the charged particle beams.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims benefit of priority under 35USC §119 to Japanese patent application No.2000-237163, filed on Aug. 04, 2000, the contents of which are incorporated by reference herein.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to a charged particle beam exposure system, such as an ion or electron beam exposure system which is used in a process for fabricating semiconductors such as LSIs or VLSIs. More specifically, the invention relates to a low-accelerating-voltage charged particle beam exposure system.  
           [0004]    2. Description of the Prior Art  
           [0005]    Charged particle beam exposure systems have the function of being capable of forming a high resolution pattern since it is possible to write at a resolving power of a wavelength level of electrons (or ions) which is shorter than light wavelength. On the other hand, since a complete pattern is directly written with small divided pattern beams unlike a mask writing system based on light exposure, there is a problem in that charged particle beam exposure systems take a lot of time to write. However, in view of characteristics that accurate fine line patterns can be formed, the charged particle beam exposure technique has been developed as the next technique to the lithography technique of the light exposure system, or as an important tool to the fabrication of semiconductors in a multi-product small-lot production such as ASIC.  
           [0006]    A method for direct-writing a pattern with electron beams mainly uses two systems. That is, there is a system for writing a pattern by scanning the whole surface of a wafer while on-off-controlling small round beams, and a VSB writing system for writing a pattern with electron beams passing through a stencil aperture. As the electron beam writing technique developed from the VSB writing, there has been developed a bulk writing system for preparing a stencil on which repeated patterns are formed as one block and for selecting one of the patterns of the stencil to enable a high-speed writing.  
           [0007]    First, as a conventional charged particle beam exposure system, a typical example of an electron beam lithography system of a VSB writing system is shown in FIG. 10 (H. Sunaoshi et al.; Jpn. J. Appl. Phys. Vol. 34 (1995), pp. 6679-6683, Part 1, No. 128, December 1995). Furthermore, in the following drawings, the same reference numbers are given to the same portions to suitably omit the descriptions thereof.  
           [0008]    Electron beams  7  emitted and accelerated from an electron gun  11  are arranged as uniform electron beams by means of an illumination lens  15  and pass through a first forming aperture  85  to be formed as rectangular electron beams, and thereafter, projected on a second shaping aperture  89  of a rhombic or rectangular shape by means of a projection lens  87 . At this time, the beam irradiation position on the second shaping aperture  89  is controlled by a shaping deflector  21  so that the shape and the area of the second shaping aperture  89  is irradiated with the pattern beams in accordance with CAD data. The beams passing through the second shaping aperture  89  are reduced and projected by means of a reducing lens  64  and an objective lens  66 , and a position of the beams on a region of a wafer  14  to be written is controlled by means of a main deflector  95  and a sub deflector  93 . In this case, the main deflector  95  controls the interior of a stripe of an irradiation region to be written (main field) with respect to the wafer  14  referring to the position of an XY stage (not shown), and the sub deflector  93  controls the position of a range to be written which is obtained by finely dividing the interior of the stripe (sub-field). Below the objective lens  66 , there is an electron detector  33  for detecting secondary electrons and back-scattered electrons (which will be hereinafter referred to as secondary electrons and so forth) which are produced when the wafer  14  is irradiated with the electron beams  7 . By processing the detected signals acquired by the electron detector  33 , various control parts (not shown) detect an image of SEM, and controls such as adjustment of the trajectories of the beams based thereon are carried out.  
           [0009]    Since the electron optical system of an electron beam lithography system  120  shown in FIG. 10 comprises electromagnetic lenses and electrostatic deflectors, it is required to design the electron optical system while sufficiently taking account of the influence of the total optical characteristics of the lenses, the deflectors, the precision of mechanical assembly and contamination. In addition, in order to improve the resolution of beams, there has been widely adopted a system for driving highly accelerated electron beams  7  into a resist on the wafer  14 . For that reason, there is caused the proximity effect which is a phenomenon that the incident electron beams  7  reflect on various multilayer thin films deposited on the bottom face of the resist of the wafer  14  to travel above the resist again. This proximity effects causes blurring and deterioration of resolution on the written pattern. Therefore, in the design of the electron beam lithography system, it is essential that the control for correcting the proximity effect be carried out, so that it is required to provide a large-scale system in a control part in addition to the electron optical system. Thus, there is a problem in that the system is complicated and troubles are induced, so that precision is lowered. Moreover, since highly accelerated electrons are used, there is the possibility that the surface of the wafer may be damaged.  
           [0010]    In order to eliminate the above described problems in the VSB system of high-accelerating-voltage charged particle beams, an electron beam lithography system of an aperture system using low-accelerating-voltage electron beams has been proposed (Japanese Patent Application No. 10-363071, J. Vac. Sci. Technol. B14 (6), 1996, 3802). The electron beam lithography system proposed in Japanese Patent Application No. 10-363071 is shown in FIG. 11. A first aperture  13  having a rectangular or circular opening is irradiated with electron beams  67  which are emitted and accelerated from an electron gun  11 . The electron beams  67  passing through the first aperture  13  travel toward a second shaping aperture  19  comprising the arrangement of a plurality of bulk exposure cell apertures. The beam diameter of the electron beams  67  is adjusted by means of illumination lenses  15   a  and  15   b  to such a size which is sufficiently larger than that of any one of cell apertures and in which the electron beams  67  do not interfere with adjacent cell patterns. The illumination lenses  15   a  and  15   b  comprise two electrostatic lenses (Einzel lenses), and a negative voltage is applied to the central electrode to use the illumination lenses  15   a  and  15   b . The beams passing through the second illumination lens  15   b  are controlled to be deflected toward a target position by means of a first shaping deflector  17  so that a target cell aperture of the plurality of cell apertures formed in the second shaping aperture can be selected. The electron beams  67  passing through the second shaping aperture  19  start as cell pattern beams leaving the second shaping aperture  19 , and pass through a reducing lens  64  in a state that the beams are returned to an optical axis by a second shaping deflector  21 . Above the reducing lens  64 , a third shaping aperture  62  is provided for cutting undesired beams scattered by the second shaping aperture  19  and so forth. The electron beams reduced by the reducing lens  64  pass through a pre sub deflector  93 ′, a pre main deflector  95 ′, a sub deflector  93 , a main deflector  95  and an objective lens  66  to be reduced and projected on the top face of the wafer  14  which is mounted on an XY stage (not shown). The position irradiated with the beams with respect to the position of a pattern to be written on the wafer is controlled by means of the main deflector  95  and the sub deflector  93 . In addition, the control voltage of the pre main deflector  95 ′ with respect to the main deflector  95  is controlled in an addition direction, and the control voltage of the pre sub deflector  93 ′ is controlled in a subtraction direction, so that total aberration is minimized. The trajectories of the beams downstream of the second shaping aperture  19  are shown in FIG. 12.  
           [0011]    Since the electron optical system of the electron beam lithography system  110  shown in FIG. 11 uses the Einzel lenses in its reducing projecting optical system, the electron beams  67  pass through trajectories which are rotation-symmetric with respect to the optical axis as shown in FIG. 12. The pre main deflector  95 ′, the main deflector  95 , the pre sub deflector  93 ′ and the sub deflector  93  are then associated with each other for deflecting all of the trajectories of the electron beams  67  at the same deflection sensitivity and for causing the produced deflection aberration to be rotation-symmetric with respect to the optical axis. Therefore, the electron beam lithography system  110  is characterized in that it is possible to optimize deflection aberration characteristics in an arbitrary position of trajectories of electron beams to determine the positions of the main and sub deflectors.  
           [0012]    However, in the reducing projecting optical system of the electron beam lithography system  110 , crossovers  98  and  99  with a high current density are formed downstream of the second shaping aperture  19  as shown in FIG. 12. In addition, this projecting optical system adopts the rotation-symmetry type electrostatic lenses (Einzel lenses)  93  and  95  in a deceleration type focusing mode, the electron beams decelerate in the lenses. These two points cause the beams to blur in the electron beam lithography system  110  shown in FIG. 11 due to chromatic aberration and space-charge effect (particularly, Boersch effect) and the cell aperture image on the wafer to blur, so that there is a problem in that writing characteristics deteriorate.  
           [0013]    In order to eliminate the above described problems in the electron beam lithography system of the aperture system using low-accelerating-voltage electron beams, a charged particle beam lithography system having a reducing projecting optical system with a multiple multi-pole lens has been proposed (Japanese Patent laid open No. 2001-093825). An embodiment of the charged particle beam lithography system proposed in Japanese Patent laid open No. 2001-093825 is shown in FIG. 13. In comparison with the electron beam lithography system  100  shown in FIG. 11, the electron beam lithography system  100  shown in FIG. 13 is characterized in that the reducing projecting optical system downstream of the second shaping aperture  19  in the electron optical system is designed with an electrostatic quadrupole lens. A pre main deflector  25   a  is provided between Q 2  and Q 3  of an electrostatic quadrupole lens  73 .  
           [0014]    In the electron beam lithography system  100 , the operation after electrons are emitted and are accelerated at an electron gun  11  to be electron beams  68  and until the electron beams  68  pass through an illumination optical system is substantially the same as that of the electron beams  67  of the electron beam lithography system  110  shown in FIG. 11.  
           [0015]    After the electron beams pass through the second shaping aperture  19 , the interior of the electrostatic quadrupole lens  73  of the reducing projecting lens is irradiated with the electron beams. The quadrupole lens  73  comprises fourth cylindrical electrodes which are provided at angular intervals of 90 degrees. By the action of the quadrupole lens  73 , the electron beams pass through different trajectories in X and Y directions to be condensed on a wafer  14 . The trajectories of the electron beams between the second shaping aperture  19  and the wafer  14  at that time are shown in FIG. 14. By means of the deflector  25 , the incident position in a region to be written (a main field) on the wafer  14  mounted on an XY stage (not shown) is deflected and controlled while referring to the position of the XY stage, and the incident position of range to be written which is obtained by dividing the interior of a stripe (a sub field) is controlled. By adjusting the deflecting voltage ratio of the deflector  25 , aberration components produced by deflection are controlled so as to be minimized.  
           [0016]    However, if the multi-pole lens is applied to the electrostatic lens of the reducing projecting optical system as the electron beam lithography system  100  shown in FIG. 13 and if electron beams are deflected both in the X and Y directions by means of the same deflector, the electron beams in the X directions and the electron beams in the Y directions pass through asymmetric electron trajectories in a wide-range beam deflection over the wafer by the deflector. Therefore, deflection sensitivity and deflection aberration are greatly asymmetric. In such an optical system, the suppression of the deflection aberration in both of the X and Y directions and the realization of a wide range deflection with high sensitivity impose a great burden on design and fabrication, deteriorate aberration characteristics, and increase the influence of the space-charge effect due to an increase of the optical length.  
           [0017]    Moreover, in these optical systems, the electron beams passing through the second shaping aperture  19  form the crossover  98  with a high electron density. Therefore, the Coulomb interaction is conspicuous in this region, so that there is a problem in that the space-charge effect causes the blurring of the cell aperture image to deteriorate writing characteristics.  
         SUMMARY OF THE INVENTION  
         [0018]    According to the present invention, there is provided a charged particle beam exposure system comprising: a charged particle beam emitting device which generates charged particle beams with which a substrate is irradiated, the charged particle beam emitting device generating the charged particle beams at an accelerating voltage which is lower than that at which an influence of a proximity effect occurs, the proximity effect being a phenomenon in which a secondary charged particle and/or a reflected charged particle which is/are produced from the surface of the substrate irradiated with the charged particle beams influence(s) an exposure extent of a pattern which is adjacent to a pattern to be written; an illumination optical system which adjusts a beam diameter of the charged particle beams so that density of the charged particle beams is uniform; a character aperture in which an aperture hole is formed in a shape corresponding to a desired pattern to be written; a first deflector which deflects the charged particle beams by an electrostatic field that the charged particle beams have a desired sectional shape and travel towards a desired aperture hole and which returns the charged particle beams passing through the aperture hole to an optical axis thereof; a reducing projecting optical system which forms a multi-pole lens field so that the charged particle beams passing through the character aperture substantially reduce at the same demagnification both in X and Y directions when the optical axis extends in Z directions and form an image on the substrate without forming any crossover between the character aperture and the substrate; and a second deflector which deflects the charged particle beams passing through the character aperture by means of an electrostatic field to scan the substrate with the charged particle beams. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    In the drawings:  
         [0020]    [0020]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;  
         [0021]    [0021]FIGS. 2A through 2C are plan views for explaining the shape of the electrodes of a multi-pole lens of the charged particle beam exposure system shown in FIG. 1;  
         [0022]    [0022]FIGS. 3A and 3B are plan views for explaining the difference in inside diameter in multi-pole lenses of the charged particle beam exposure system shown in FIG. 1;  
         [0023]    [0023]FIG. 4 is an illustration showing the trajectories of electron beams in a reducing projecting optical system of the charged particle beam exposure system shown in FIG. 1;  
         [0024]    [0024]FIGS. 5A through 5C are illustrations for explaining a method for forming a lens electrostatic field with quadrupole lenses Q 3  and Q 4  shown in FIG. 1;  
         [0025]    [0025]FIGS. 6A through 6C are illustrations for explaining a method for forming a deflecting electrostatic field with quadrupole lenses Q 3  and Q 4  shown in FIG. 1;  
         [0026]    [0026]FIGS. 7A through 7C are illustrations for explaining a method for forming a deflecting electrostatic field with quadrupole lenses Q 3  and Q 4  shown in FIG. 1;  
         [0027]    [0027]FIG. 8 is a beam trajectory diagram for explaining a method for deflecting and controlling electron beams independently in X and Y directions in a reducing projecting optical system of the charged particle beam exposure system shown in FIG. 1;  
         [0028]    [0028]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;  
         [0029]    [0029]FIG. 10 is a schematic construction drawing showing a typical example of a conventional electron beam lithography system of a VSB writing system;  
         [0030]    [0030]FIG. 11 is a schematic construction drawing showing an example of a conventional electron beam lithography system of an aperture system using low-accelerating-voltage electron beams;  
         [0031]    [0031]FIG. 12 is an illustration showing trajectories of beams in the reducing projecting optical system of an electron beam lithography system shown in FIG. 11;  
         [0032]    [0032]FIG. 13 is a schematic construction drawing showing an embodiment of a conventional charged particle beam lithography system of an aperture system using low-accelerating-voltage electron beams; and  
         [0033]    [0033]FIG. 14 is an illustration showing the trajectories of electron beams in an electrostatic quadrupole lens optical system of the electron beam lithography system shown in FIG. 13. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    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.  
         [0035]    (1) First Embodiment  
         [0036]    [0036]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  15   a  and  15   b , i.e., a first shaping deflector  17 , a second shaping deflector  21 , electrostatic lenses  23 Q 1  through Q 4  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.  
         [0037]    [0037]FIG. 2A shows a quadrupole lens with four electrodes. The electrodes Q 1   1a  through Q 1   1d  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 Q 1   2a  through Q 1   2h  which are arranged at angular intervals of 45 degrees. FIG. 2C is a plan view showing the construction of a multi-pole lens  23 Q 1  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 Q 1   3a  through Q 1   3h  which are arranged at angular intervals of 45 degrees. Each of the electrodes is formed in a sector plane shape.  
         [0038]    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 Q 1   3a  and Q 1   3b , so that these electrodes are controlled so as to function as the electrode Q 1   1a  shown in FIG. 2A. Then, in the following description the multi-pole lens  23  will be suitably described as the quadrupole lens  23 .  
         [0039]    Referring to FIG. 1 again, the reducing projecting optical system of the charged particle beam exposure system  10  comprises: electrostatic quadrupole lenses  23 Q 1  through  23 Q 4 , the quadrupole lenses  23 Q 1  and  23 Q 2  being provided upstream of the pre main deflectors  25   a  and  25   b , and the quadrupole lenses  23 Q 3  and  23 Q 4  being provided downstream of the pre main deflectors  25   a  and  25   b ; a sub deflector  31  which is provided between Q 4  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  25   a  and  25   b , and the quadrupole lenses  23 Q 1  through Q 4  in directions of the optical axis.  
         [0040]    The shielding electrode  36  is formed with an inside diameter Φ1 of 5 mm and the shielding electrode  39  is formed with an inside diameter Φ2 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 Q 1  and Q 2  are formed with the same inside diameter Φ1 (5 mm) as the inside diameter of the shielding electrode  36 .  
         [0041]    The third quadrupole lens Q 3  and fourth quadrupole lens Q 4  of the quadruple quadrupole lenses  23  are designed so that the diameters thereof are greater than those of the first and second quadrupole lenses Q 1  and Q 2 . Specifically, the inside diameter of Q 1  and Q 2  is Φ 1 =5 mm as shown in FIG. 3A and the inside diameter Φ 2  of Q 3  and Q 4  is 10 mm as shown in FIG. 3B. As will be described later, the quadrupole lenses Q 3  and Q 4  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.  
         [0042]    The operation of the electron beam exposure system shown in FIG. 1 is as follows.  
         [0043]    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 .  
         [0044]    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 .  
         [0045]    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 (Q 1 ), a divergent electrostatic field (Q 2 ), a convergent electrostatic field (Q 3 ) and a divergent electrostatic field (Q 4 ), the electrostatic fields in the Y directions are a convergent electrostatic field (Q 1 ), a convergent electrostatic field (Q 2 ), a divergent electrostatic field (Q 3 ) and a convergent electrostatic field (Q 4 ) 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 Q 1  through Q 4  of the quadrupole lenses  23 . This point is the same as the electron beam lithography system  100 . However, in this embodiment, by means of Q 1  and Q 2  of the quadrupole lenses  23 , the electron beam trajectory  8 X in the X directions repeats divergence, and on the other hand, the electron beam trajectory  8 Y 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  25   a  and  25   b  is used for controlling the beam trajectories.  
         [0046]    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  25   a  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 Q 3  and Q 4  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 Q 3  and Q 4  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 Q 3  and Q 4  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  25   a  is 0. FIGS. 6A through 6C show the values of voltages which are applied to the pre main deflector  25   a  and the respective electrodes of Q 3  and Q 4  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 V 1  of the pre main deflector  25   a  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).  
         [0047]    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 Q 3  and Q 4  of the quadrupole lenses  23  serving as the main deflector  27 .  
         [0048]    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  48 X in the X directions are deflected by means of the pre main deflector  25   a , the main deflector  27  (Q 3  and Q 4  of the quadrupole lenses  23 ) and the sub deflector  31 , and on the other hand, the electron beams  48 Y in the Y directions are deflected only by means of the main deflector  27  (Q 3  and Q 4  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 , Q 3  and Q 4  of the quadrupole lenses  23  serving as the main deflector  27 , and the sub deflector  31 .  
         [0049]    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.  
         [0050]    According to the electron beam exposure system  10  in this embodiment, the quadruple quadrupole lenses Q 1  through Q 4  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 Q 3  and Q 4  to operate the quadrupole lenses Q 3  and Q 4  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 Q 3  and Q 4  are designed to be greater than those of Q 1  and Q 2 , 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.  
         [0051]    Moreover, since the shielding electrodes  36  and  39 , which are ground electrodes, are arranged in close vicinity of both ends of the quadrupole lenses Q 1  through Q 4  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 {fraction (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 mm□and the sub deflection function is 50 μm□.  
         [0052]    (2) Second Embodiment  
         [0053]    [0053]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  25   a , and a shielding electrode  38  is further provided between Q 1  and Q 2  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.  
         [0054]    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  23 Q 1  and downstream of the quadrupole lens  23 Q 2 . For example, when the inside diameter Φ 1  of the shielding electrode  36  is 5 mm, the inside diameter Φ 3  of the shielding electrode  38  is designed to be 200 μm. Thus, the shielding electrode  38  can be used as a beam aligning aperture for the illumination lenses  15   a  and  15   b , the first shaping deflector  17 , the second shaping deflector  21  and Q 1  of the quadrupole lenses  23 , or as a detector for the electron beams  8 .  
         [0055]    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 Φ 4 =200 μm. Due to such a small inside diameter, the shielding electrode  41  can be used as a beam aligning aperture for the illumination lenses  15   a  and  15   b , the first shaping deflector  17 , the second shaping deflector  21  and Q 1  and Q 2  of the quadrupole lenses  23 , or a detector for the electron beams  8 .  
         [0056]    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.  
         [0057]    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, Q 1  and Q 2  of the quadrupole lenses  23  may comprise four electrodes, and only Q 3  and Q 4  of the quadrupole lenses  23  for superimposing deflection fields may comprise octpole electrodes as shown in FIG. 2B or  2 C. In addition, Q 3  and Q 4  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=4N 2 , N 2  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.