Abstract:
A charged beam drawing apparatus deflects, by an electrostatic deflector, a charged beam generated from a charged beam source, and applies the charged beam to a desired position on a sample to draw a pattern. The electrostatic deflector includes a plurality of deflecting electrodes arranged symmetrically with respect to a point around an optical axis of the charged beam, a ground external cylinder which is disposed coaxially with the optical axis and which is provided to enclose the deflecting electrodes, a resistive film provided on an inner surface of the ground external cylinder, and a conductive film provided on a surface of the resistive film. A capacitance is formed between the deflecting electrodes and the conductive film, and a resistance is formed between the ground conductor and the conductive film.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-099133, filed Mar. 31, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a charged beam drawing apparatus for drawing an LSI pattern by use of a charged beam. 
     2. Description of the Related Art 
     In an electron beam drawing apparatus, various kinds of electrostatic deflectors are used, such as a blanking deflector, a shaping deflector and an objective deflector. The electrostatic deflector has a plurality of deflecting electrodes, and gives a potential generated by a deflection amplifier to each of the electrodes, thereby deflecting an electron beam by an electric field generated between the electrodes. 
     One end of a coaxial cable is connected to an output end of the deflection amplifier, and the other end of the coaxial cable is connected to the deflecting electrodes of the electrostatic deflector. In general, since the deflecting electrodes of the electrostatic deflector are electrically connected to the coaxial cable alone, it is possible to consider that a capacity load is added to the end of the coaxial cable in terms of an equivalent circuit. Thus, a signal input from the deflection amplifier is substantially totally reflected by the deflecting electrodes, and the input signal returns to the deflection amplifier with a delay of a given time corresponding to the length of the coaxial cable. In such a state, high-speed operation of the deflection amplifier is difficult. 
     On the other hand, if the deflecting electrodes are connected to a ground via a resistance equivalent to a characteristic impedance of the coaxial cable, the reflection of the signal by the deflecting electrodes is suppressed, such that a high-speed operation can be performed (JP-A 11-150055(KOKAI)). However, in this case, since there is a current running to the resistance even if a voltage is in a constant state, a load on the deflection amplifier is increased. Therefore, it is difficult to raise a driving voltage. For example, given that 50Ω is used in a terminating resistance and that a voltage of 50V is applied thereto, a current of 1 A steadily flows at the maximum in the terminating resistance. This is not realistic because loads on the amplifier, the cable and the terminating resistance are heavy. 
     Thus, in the conventional electron beam drawing apparatus, it has been difficult to achieve high-speed high-voltage operation of the electrostatic deflector without increasing the load on the deflection amplifier. Moreover, the problem described above is true with not only the electron beam drawing apparatus but also an ion beam drawing apparatus. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a charged beam drawing apparatus comprising: 
     a charged beam source which generates a charged beam; 
     an electrostatic deflector provided on a downstream side of the charged beam source to apply a charged beam to a desired position on a sample, the electrostatic deflector including a plurality of deflecting electrodes insulated from a ground plane with respect to a direct current to deflect the charged beam by an electric field and, a capacitance and an electric resistance arranged in series between the deflecting electrodes of the electrostatic deflector and the ground plane. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a schematic configuration diagram showing an electron beam drawing apparatus according to a first embodiment; 
         FIG. 2  is a sectional view showing a shaping deflector used in the first embodiment cut in a direction perpendicular to an optical axis direction; 
         FIG. 3  is a sectional view showing the shaping deflector used in the first embodiment cut along the optical axis direction; 
         FIG. 4  is an equivalent circuit diagram showing how the deflector in the first embodiment is connected to a deflection amplifier; 
         FIG. 5  is a sectional view showing a modification of the first embodiment; 
         FIGS. 6A and 6B  are schematic diagrams explaining a function of the first embodiment and showing a change of impedance in a lower frequency region and a high frequency region; 
         FIG. 7  is a sectional view showing a shaping deflector used in a second embodiment cut in a direction perpendicular to an optical axis direction; and 
         FIG. 8  is a sectional view showing a shaping deflector used in a third embodiment cut in a direction perpendicular to an optical axis direction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Details of the present invention will hereinafter be described in accordance with shown embodiments. 
     First Embodiment 
     There will be described an electron beam drawing apparatus according to a first embodiment referring to  FIG. 1 . 
     In the drawing,  11  denotes an electron gun (charged beam source) for generating an electron beam,  12  and  13  denote condenser lenses,  14  denotes a projection lens,  15  denotes a reducing lens,  16  denotes an objective lens,  21  denotes a first shaping aperture mask,  22  denotes a second shaping aperture mask,  31  denotes a blanking deflector for turning on/off the beam,  32  denotes a shaping deflector for varying the dimensions and shape of the beam,  33  denotes an objective deflector for scanning with the beam on a sample surface,  41  denotes a sample such as a mask or wafer, and  42  denotes a sample stage. In addition, although not shown in the drawing, the electron gun  11 , the various lenses  12  to  16 , the aperture masks  21  and  22 , and the various deflectors  31  to  33  are housed in an electronic optical column. 
     The electron beam emitted from the electron gun  11  at an accelerating voltage of 50 kV is focused by the condenser lenses  12  and  13  excited so that a crossover image coincides with a deflection fixed point of the shaping deflector  32 , and the electron beam is applied to the first shaping aperture mask  21 . The first shaping aperture mask  21  is provided with a rectangular opening, and the electron beam transmitted through this opening has a rectangular sectional shape. The electron beam formed into the rectangular shape by the first shaping aperture mask  21  is then focused by the projection lens  14  excited so that an image in the first shaping aperture mask  21  is formed on the second shaping aperture mask  22 , and the electron beam is applied to the second shaping aperture mask  22 . 
     Here, the position for the beam application on the second shaping aperture mask  22  can be changed by the shaping deflector  32 . Openings with various shapes are provided on the second shaping aperture mask  22 , and the beam can be transmitted through a desired position in the second shaping aperture mask  22  to obtain an electron beam having a desired sectional shape. 
     The electron beam transmitted through the second shaping aperture mask  22  is focused by the reducing lens  15  and the objective lens  16 , and reaches the surface of the sample  41  mounted on the stage  42 . At this moment, the electron beam is deflected by the objective deflector  33 , and thus reaches a desired position on the sample  41 . 
     Here, an electrostatic deflector comprising a plurality of deflecting electrodes is used for the deflector  31 ,  32 ,  33 . These deflectors apply a potential generated by a deflection amplifier to the deflecting electrodes to deflect the electron beam by an electric field generated between the electrodes. 
       FIGS. 2 and 3  are diagrams showing a specific configuration of the shaping deflector  32  used in the present embodiment.  FIG. 2  shows a section of the shaping deflector  32  cut vertically to a beam moving direction, and  FIG. 3  shows a section of the shaping deflector  32  cut along the beam moving direction. By way of example, the number of deflecting electrodes is four. Here, an example of the shaping deflector  32  is described as the electrostatic deflector, but the objective deflector  33  can be configured in the same manner. 
     The shaping deflector  32  comprises four deflecting electrodes  51  ( 51   a ,  51   b ,  51   c  and  51   d ). That is, the deflecting electrodes  51   a  and  51   c  are oppositely arranged across a beam axis, and, for example, a deflecting voltage in an x direction is applied across these deflecting electrodes. The deflecting electrodes  51   b  and  51   d  are oppositely arranged across the beam axis, and, for example, a deflecting voltage in a y direction is applied across these deflecting electrodes. 
     The four deflecting electrodes  51  are concentrically and circularly arranged inside a ground external cylinder  52  disposed coaxially with an optical axis. Each of the deflecting electrodes  51  is made of a plate member, and curved along a concentric circle around the beam axis. That is, a section in a direction perpendicular to the beam axis is formed into an arc shape. Further, portions of the deflecting electrodes  51  adjacent to each other are thin, so that the capacitance between the adjacent deflecting electrodes is small. Resistors  53  ( 53   a ,  53   b ,  53   c  and  53   d ) are arranged between the deflecting electrodes  51  and the ground external cylinder  52 . The resistors  53  are films of, for example, silicon carbide. 
     A deflection amplifier  54  is connected to each of the four deflecting electrodes  51  by a coaxial cable  55 , but one connection is only shown in  FIG. 2 , and two connections are only shown in  FIG. 3 . A characteristic impedance Zc of the coaxial cable  55  is 50Ω in the description. It is also possible to use a cable with a Zc of 75Ω or a higher value. The present drawings are schematic, and do not precisely reproduce an actual structure and dimensions. 
     The shaping deflector  32  is made up of, from the inside, the deflecting electrodes  51 , a space, the resistors  53  and the ground external cylinder  52 . Therefore, a capacitance and an electric resistance are connected in series between the deflecting electrodes  51  and the ground external cylinder  52 , and an equivalent circuit is as shown in  FIG. 4 . 
     The resistors  53  are desirably divided as many as the number of deflecting electrodes  51 , but may have an integral structure as shown in  FIG. 5  when a decrease in characteristics can be permitted. The resistors  53  are electrically insulated from the deflecting electrodes  51 . In order to maintain this insulating structure, the resistors  53  are actually insulated from by an insulator sufficiently smaller than the structure of the electrodes. Strictly speaking, a value of resistance between the deflecting electrodes  51  and the resistors  53  is limited even when they are connected by the insulator. However, anything can be regarded as an insulator as long as it has a value sufficiently greater than that of the resistance of the resistors  53 . For example, 1 MΩ or more is generally sufficient. In addition, although not shown in  FIG. 2 , insulators  56  are provided in parts between the resistors  53  and the deflecting electrodes  51  to mechanically hold the deflecting electrodes  51 . Moreover, inner surfaces of the resistors  53  are coated with good conductors  57  such as copper. 
     In this structure, a value R of resistance between the ground external cylinder  52  and the inner conductors  57  of the resistors  53  is substantially equal to the value of the characteristic impedance Zc of the coaxial cable  55 . In this example, the value is decided to be 50Ω. A length L of the deflecting electrodes  51  in an optical axis direction is 120 mm, an outside diameter 2 r of a cylinder made up of the four deflecting electrodes is 20 mm. Moreover, the distance between the deflecting electrodes  51  and the inner conductive surfaces of the resistors  53  is 0.6 mm. A capacitance C in this case is approximately as follows:
 
C˜∈0×2π×r×L/4d˜28pF
 
wherein ∈ 0  is a dielectric constant in a vacuum. This value is sufficiently greater than an interelectrode capacitance between the adjacent deflecting electrodes.
 
     At this point, when a value R of resistance between the inner conductors  57  of the resistors  53  and the ground external cylinder  52  is 50Ω, a time constant when viewed from the outside of the deflecting electrodes  51  is about 1.4 ns. A time constant of 1.4 ns is shorter than a beam setting time of an ordinary deflection amplifier, and therefore, no response delay is caused by this time constant. Since the insulators  56  between the resistors  53  and the deflecting electrodes  51  function to increase the capacitance, it is desirable that the outside diameter of the deflecting electrodes  51  be actually slightly decreased so that the capacity is not greater than the above-mentioned value. 
     Now, silicon carbide with a resistivity of 10 5  Ωcm is used as the resistors  53 , and the inside diameter thereof is set at 21.2 mm and the thickness thereof is set at 2 mm, such that a resistance value in the direction perpendicular to the beam axis can be about 50Ω. The resistors  53  are fixed in close contact with the ground external cylinder  52  to minimize a contact resistance. Proper holes are opened in the ground external cylinder  52  and the resistors  53  to apply a voltage to the deflecting electrodes  51 , and a core wire of the coaxial cable  55  is connected to the deflecting electrodes  51  through the holes. If the thickness at the end of the deflecting electrode  51  in a circumferential angle direction is 1 mm, the mutual capacitance between the adjacent electrodes is about 1 pF when the distance between the adjacent electrodes is 1 mm, so that the mutual capacitance can be sufficiently smaller than the capacitance between the deflecting electrodes  51  and the resistors  53 . 
       FIGS. 6A and 6B  are diagrams conceptually showing electric properties of the shaping deflector  32  when configured as described above. As shown in  FIG. 6A , an absolute value of a complex impedance ZL of the shaping deflector  32  is |−i/(C  ω )+R|=5.7 kΩ in a region at a comparatively low frequency of, for example, 1 MHz, so that a current can be held down to about 10 mA in amplitude with respect to a sinusoidal voltage having an amplitude of 50V. On the other hand, as shown in  FIG. 6B , the absolute value is about 50Ω in a region with a comparatively high frequency of, for example, 1 GHz, and a voltage reflectance in the shaping deflector  32  is 0.06 or less, which is low. That is, a state with little reflection can be achieved in the high frequency region. If the time constant is 1.4 ns, time to reach (1 to one ten-thousandth) X [v] from 0 [v] is about 13 ns with respect to a step input from 0 [v] to X [v]. That is, extremely rapid rising of the voltage is possible. 
     The lower limit of the time constant may be determined within a range that is permissible in light of the required accuracy. For example, when the time constant is 1/14 to 1/10 of the required rise time, the effect which the capacity may have on the pulse rise delay can be controlled to be 1 ppm to 50 ppm. 
     Thus, according to the present embodiment, the deflecting electrodes  51  of the shaping deflector  32  are connected with the ground external cylinder  52  via the electric resistance comprising the resistors  53  and via the capacitance, and the resistance value of the resistors  53  is substantially equal to the value of the characteristic impedance of the coaxial cable  55  connected to apply a voltage to the deflecting electrodes  51 . Thus, an impedance-matched state is approached in the high frequency region while a state insulated from a ground plane is maintained with regard to a direct current, such that the reflection of the signal can be suppressed. In this manner, influence of a reflected wave on the deflection amplifier  54  for driving the shaping deflector  32  is reduced in the high frequency region, and the shaping deflector  32  can be operated at a high speed and at a high voltage. That is, a high-speed high-voltage operation of the shaping deflector  32  can be achieved without increasing a load on the deflection amplifier  54 , such that a drawing speed can be improved. 
     Second Embodiment 
     There will be described an example of a shaping deflector used in an electron beam drawing apparatus according to a second embodiment in conjunction with  FIG. 7 . It is to be noted that the same numerals are assigned to the same parts as those in  FIG. 2 , and these parts are not described in detail. 
     The present embodiment is different from the first embodiment described above in that high dielectrics  71  ( 71   a ,  71   b ,  71   c  and  71   d ) which are insulators are inserted between deflecting electrodes  51  of a shaping deflector  32  and resistors  53 . For example, alumina can be used as the high dielectrics  71 . Here, strictly speaking, the resistance of the high dielectrics  71  is limited, but sufficiently greater than the resistance of the resistors  53 , so that the high dielectrics  71  can be regarded as insulators. By the provision of the high dielectrics  71 , the capacitance can be increased if the distance between the resistors  53  and the deflecting electrodes  51  is the same, and the distance between the resistors  53  and the deflecting electrodes  51  can be longer if the capacitance is the same. 
     In such a configuration, effects similar to those in the first embodiment described above can naturally be obtained, and the distance between the deflecting electrodes  51  and the resistors  53  can be wider than that in the example of  FIG. 2 , thereby providing an advantage of easier machining and assembly. 
     Third Embodiment 
     There will be described an example of a shaping deflector used in an electron beam drawing apparatus according to a third embodiment referring to  FIG. 8 . It is to be noted that the same numerals are assigned to the same parts as those in  FIG. 2 , and these parts are not described in detail. 
     The present embodiment is different from the first embodiment described above in that dielectrics  81  ( 81   a ,  81   b ,  81   c  and  81   d ) are inserted between deflecting electrodes  51  of a shaping deflector  32  and resistors  53 , and in that the dielectrics  81  and the resistors  53  are in an integral rod (rectangular parallelepiped) shape rather than a plate shape. Then, the resistors  53  and the dielectrics  81  integrally support the deflecting electrodes  51 . 
     In the present embodiment again, a material and a shape are decided so that a resistance value R of the resistors  53  may be 50Ω. For example, given a square whose section is 2 cm long on a side, a pipe-shaped material having therein a square hole 1 cm long on a side, and a resistivity of 100 Ωcm, the length necessary for the resistors  53  is 1.5 cm. Further, screws formed of an insulating material can be let through the holes in the rectangular parallelepiped material and the dielectric material to fix the deflecting electrodes  51  to a ground external cylinder  52 . 
     In such a configuration, effects similar to those in the first embodiment described above can naturally be obtained, and the deflecting electrodes  51  can simply be screwed to the ground external cylinder  52  through the holes in the dielectrics  81  and the resistors  53 , thereby providing an advantage of easier machining and assembly. 
     MODIFICATION 
     It is to be noted that the present invention is not limited to the embodiments described above. The deflecting electrodes are in a shape along the arc around the beam axis in the embodiments, but the deflecting electrodes do not necessarily have to be arc-shaped and may be plate-shaped electrodes. Moreover, the number of deflecting electrodes is not in the least limited to four, and may be two or eight. 
     Furthermore, the ground external cylinder is provided in the electronic optical column in the present embodiments, but the ground external cylinder can be omitted. In this case, the electronic optical column itself may be used as the ground plane. Moreover, the electron beam drawing apparatus has been described by way of example in the embodiments, but it should be understood that the present invention can also be applied to an ion beam drawing apparatus which electrostatically deflects a beam. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general invention concept as defined by the appended claims and their equivalents.