GB2369241A

GB2369241A - Charged particle beam exposure device with aberration correction

Info

Publication number: GB2369241A
Application number: GB0202656A
Authority: GB
Inventors: Kenichi Kawakami
Original assignee: Advantest Corp
Current assignee: Advantest Corp
Priority date: 1999-06-03
Filing date: 2000-06-02
Publication date: 2002-05-22
Also published as: GB0202656D0

Abstract

Charged particle beam exposure device including a lens 42, an aperture plate 50 to divide the beam into sub-beams and deflecting electrodes 51-56 to correct an aberration of the lens by deflecting the sub-beams. The aperture plate may comprise a first aperture through which the optical axis of the lens passes and a second aperture around the periphery of the first where only the sub-beam generated by the second aperture is deflected. The first aperture may be circular and the second aperture may be annular. The device may comprise an ozone supply unit.

Description

APPARATUS AND METHOD FOR IMAGE-FORMING CHARGED PARTICLE BEAMS AND CHARGED PARTICLE BEAM EXPOSURE APPARATUS This patent application claims priority based on a Japanese patent application, Hie-156940 filed on June 3,1999 and 2000-148417 filed on May 19,2000 the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam image forming method used in a charged particle beam exposure apparatus such as an electron beam exposure apparatus, an image forming apparatus and to a charged particle beam exposure apparatus using such the image forming apparatus. It particularly relates to the charged particle beam image forming method and the image forming apparatus where aberration is small even though a beam focusing angle is actually taken large, and to the charged particle beam exposure apparatus using such the image forming apparatus.

2. Description of the Related Art In recent years, the semiconductor technology has been further developed. It is expected to play a core technological role among a technology progress in the whole industry including a computer and a communication device control system. The IC technology achieves a high density (four times as much in two to three year period). For example, in

Dynamic Random Access Memory, its memory capacity increases at 1M, 4M, 16M, 256M and 1G. Such the IC high density is mainly due to the sub micron processing technology in the semiconductor manufacturing technology particularly an exposure technology.

The conventional photolithography technology used in a stepper and so on is soon expected to reach its limitation. The charged particle beam exposure technology such as the electron beam exposure technology possibly becomes a next generation sub micron processing replacing the photolithography technology. Though the description will be made using the electron beam exposure apparatus as an example, the present invention is not limited thereto.

In the electron beam exposure apparatus or the electron beam lithography, there are available a variable rectangular exposure method. a block exposure method, a multi-beam exposure method and so on. The electron beam exposure apparatus will be described briefly with the block exposure method taken as an example. In the block exposure method, a pattern serving repeatedly as a unit of a figure is placed on a transmission mask through which the electron beam is transmitted, so that the unit pattern is generated at a time and these are connected so as to repeatedly the figure.

Fig. 1 shows a structure of a beam irradiation system in the electron beam exposure apparatus implementing the block exposure method. The electron beam exposure apparatus includes: an electron gun 11 which generates the electron beams; the first focusing lens which makes the electron

beam from the electron gun 11 a parallel beam ; an aperture plate 13 which forms the transmitting parallel beam in a predetermined shape; a focusing lens 14 which focuses on the formed beam; a deflector 15 for use with formation ; the first mask deflector 16; a deflector 17 which dynamically corrects astigmatism due to the mask; the second mask deflector 18; a focusing coil 19 for with masking; the first forming lens 20; a block mask 21 which is moved by a state 21A ; the second forming lens 22; the third mask deflector 23; a blanking deflector 24 which controls the beam by switching on and off ; the

fourth mask deflector 25 ; the third lens 26 ; a circular aperture 27 ; a demagnification lens 28; a dynamic focus coil 29; an image forming lens 30; an electromagnetic main deflector 31; an electrostatic sub-field deflector 32; and a reflected electron detector 33 which outputs a reflected electron signal by detecting the electron beam irradiated to a sample 1.

The electron beam 10 is focused on the sample (wafer) 1 placed on the stage 2, by an imaging lens 30. The wafer 1 is placed on the stage 2 which moves along a two dimensional plane against the electron beam 10 in the perpendicular direction. Above elements are housed in an electric optical column, and the inside the column is vacuated and the exposure procedure is performed therein. The electron beam exposure apparatus further includes an exposure control unit which controls each element of the column in order to perform the exposure on a desired pattern. Detailed description therefore is omitted here.

The image forming lens 30 is generally made of the electromagnetic lens, and may be realized by an electrostatic lens or by combining the electromagnetic lens and the electrostatic lens. The electron beam is focused on the surface of the sample 1, by the image forming lens 30. The exposure position is changed by the main deflector 31 and the sub-field deflector 32 (referred to as a deflector collectively, hereafter); when the exposure position is changed in a large scale, the sample is moved by the stage 2. In the block exposure method too, a pattern moved by 1 shot is less than 10 um, and the pattern is exposed in a manner such that it is deflected so as to be adjacent to each other and then exposed in order.

The electron beam exposure method has extremely high resolution and depth of focus compared to the photolithography which is widely used in manufacturing LSI's at present. The electron beam exposure method can

write a high-resolution pattern which can not be achieved by the photolithography, however, a processing capacity, that is, its throughput is extremely low compared to the photolithography, thus not suitable for a mass production. Reasons for this will be described below. In order to expose the resist material having a particular sensitivity in a high speed, the current of the electron beam need be large at the sample surface. However, when the current increases, there is caused a problem where the resolution deteriorates due to repulsion between electrons. This is so called Coulomb interaction. In order to reduce this Coulomb interaction, the following three methods are considered: (1) acceleration voltage is increased; (2) a beam length from the beam reshaping is shortened; and (3) the convergence semi-angle is increased.

However, methods (1) and (2) include a factor which might deteriorate the deflection efficiency of the beam deflection. If the deflection efficiency is low, setting wait time becomes long, thus causing a problem where the throughput decreases. Thus, methods (1) and (2) are problematic and limited.

As for method (3), since the electromagnetic lens constituted by coils includes a spherical characteristic, the aberration increases when the convergence semi-angle a becomes larger than a certain amount. As a result, there is caused a problem where the resolution is deteriorated, so that method (3) is problematic and limited. These will be described with reference to drawings.

Fig. 2 illustrates to explain a principle where the aberration increase as the convergence semi-angle a increases. The aberrations dependent on a are the spherical aberration, coma-aberration, astigmatism, chromatic aberration.

The method of correcting the astigmatism is already known, the comaaberration can be sufficiently made small by the column design, and the chromatic aberration can be sufficiently made small by properly designing a light source and so on. Thus, the spherical aberration is usually a problem.

The spherical aberration is caused by the fact that the electromagnetic lens characteristic has a spherical lens characteristic which is called as such in the optical lens. Referring to Fig. 2, let a point 0 be a point on a material surface 41 so that the electron beam from the point 0 passes through a pupil plane of an image forming lens 42 and is image-formed on an image plane 44. Now a coordinate axis a where origin serves as an optical axis is provided on the pupil plane while a coordinate axis x where the optical axis serves as origin is provided on the image plane 44. Then, considering the spherical aberration of the image forming (spherical) lens 42. the electron beam that has emitted from origin 0 and has passed the position a=r on the pupil plane, is projected at the position x=cr3 on the pupil plane 44. Here, c is a constant. Thus, when the magnitude of the aperture 43 on the pupil plane is R, the

3 aberration of the image on the image plane 44 is approximately cR3. On the other hand, the convergence semi-angle a is directly proportional to R, so that the spherical aberration is directly proportional to the cube of the convergence semi-angle a.

In this manner, since the electromagnetic lens constituted by the coils exhibits the characteristics of the spherical lens, the spherical aberration directly proportional to the cube of the convergence semi-angle ex occurs. It is extremely difficult to manufacture a non-spherical and non-aberration lens by correcting this spherical aberration by designing the configuration of the coil and so on.

On the other hand, empirically or as a result of simulation, the image error (out-of-focus) due to Coulomb interaction is said to be in inverse proportion to the convergence semi-angle a if the current is kept constant.

When the current is kept constant and the convergence semi-angle ex is small,

the same amount of the electrons will be crowded into smaller space, thus causing to increase Coulomb interaction.

The actual image error or image displacement (out-of-focus) is a result of the image displacement due to Coulomb interaction and the image error due to the spherical aberration combined together, and is expressed in Fig. 3 as being a function of the convergence semi-angle a. Thus, a point of aberration at which the best resolution is attained in a predetermined current is P where the image error due to the Coulomb interaction and the image displacement due to the spherical aberration are equal. Under normal circumstances, the convergence semi-angle a is determined in this condition attaining the minimum value, so as to be designed keeping desirable resolution and throughput.

However, under the condition where sufficient resolution is obtained, the current density or the throughput is low. On the other hand, when trying to obtain sufficient current density, the resolution will be sacrificed. This trade-off unbalance shall be solved. If the spherical aberration can be corrected, the convergence semi-angle a can be taken large, so that further high resolution can be obtained at a desired current. On the other hand, if the beams have a desired resolution, further large current can be obtained.

Moreover, in apparatus utilizing the charged particle beams such as electron beams, contamination will be accumulated within the apparatus, thus causing a problem in that a drift occurs in the electron beams.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide apparatus and method for image-forming charged particle beams which

overcome the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.

According to an aspect of the present invention, there is provided apparatus for image-forming charged particle beams, comprising: an image forming lens which image-forms the charged particle beams and which has at least one of an electromagnetic lens and an electrostatic lens; an aperture plate including a plurality of charged particle beam passes which divide the charged particle beams into a plurality of sub-beams; and a correction deflector which deflects at least part of the sub-beams by correcting an aberration of said image forming lens.

An opening preferably serves as the charged particle beam pass.

Preferably, the correction deflector is arranged in the vicinity of a pupil plane, where the pupil plane is defined as a surface on which an aperture is placed.

Moreover, the aperture plate is preferably arranged in the vicinity of a pupil plane.

Moreover, the correction deflector may deflect the sub-beams in a direction toward or away from an optical axis of the image forming lens and wherein intensity of deflection depends on a distance between the sub-beams and the optical axis.

The apparatus may further comprise a deflector which deflects the subbeams in a direction toward or away from an optical axis of the image forming lens, and whose deflection intensity varies corresponding to a change of a deflection amount of the deflector.

The aperture plate preferably includes a first charged particle beam pass including an optical axis of the image forming lens, and at least one second charged particle beam pass in the periphery of the first charged particle beam pass, and the correction deflector preferably does not deflect the sub-beams having passed the first charged particle beam pass and deflects the sub-beams having passed at least one second charged particle beam pass, in a direction toward or away from the optical axis.

The first charged particle beam pass is preferably of a substantially circular shape about the optical axis of the image forming lens.

The first charged particle beam pass is preferably of a shape such that all charged particle beams are passed whose aberration by the image forming lens is within a predetermined allowable range.

Preferably, an electrode is provided and connected in the vicinity of the first charged particle beam pass.

Preferably, the second charged particle beam pass is of a substantially annular shape enclosed by two concentric circles whose center is the optical axis of the image forming lens.

Preferably, the second charged particle beam pass is of a substantially annular shape enclosed by two concentric circles whose center is the optical axis of the image forming lens, and a difference between radii of the two concentric circles enclosing the at least one second charged particle beam pass is less than a diameter of the first charged particle beam pass.

Moreover, the correction deflector may comprise a substantially circular-shaped deflection correcting electrode at both an optical axis center side of said image forming lens in the at least one second charged particle beam pass and at a side counter to the optical axis center, so that the

deflection correcting electrode deflects sub-beams which have passed the at least one second charged particle beam pass.

Preferably, the aperture plate has a plurality of the second charged particle beam passes so that difference of radii between the two concentric circles is small as the second charged particle beam pass is located far away from an optical axis center of the image forming leans.

Preferably, an area of the first charged particle beam pass is greater than that of the second charged particle beam pass.

Preferably, the aperture plate has a plurality of the second charged particle beam passes, and an area of the second beam pass becomes smaller as the second charged particle beam pass is located away from the optical axis.

Preferably, the correction deflector increases a deflection amount as the second charged particle beam pass locates away from the optical axis center of said image forming lens.

Moreover, the correction deflector may be provided in the aperture plate. The correction deflector may be provided in a plate which does not shield the sub-beams divided by the aperture plate. The apparatus may be further comprise an ozone supply unit which supplies ozone.

According to another aspect of the present invention, there is provided beam exposure apparatus for exposing a sample, comprising: a charged particle beam generator which generates a charged particle beam; a reshaping unit which reshapes the charged particle beam; a deflector which deflects the charged particle beam ; a sample stage which holds the sample ; at least one image forming lens which image-forms the charged particle beam on the sample, in which the image forming lens (es) has at least one of an electromagnetic lens and an electrostatic lens; and a correction deflector

which deflects at least part of the charged particle beams by correcting an aberration of the image forming lens.

The exposure apparatus may be further comprise a charged particle beam observing unit which observes the charged particle beam which is image-formed on the sample, and a deflection amount of the correction deflector is preferably determined so that the charged particle beam observed by the charged particle beam observing unit attains the maximum resolution.

According to still another aspect of the present invention, there is provided a method of image-forming charged particle beams by an image forming lens having at least one of an electromagnetic lens and an electrostatic lens, comprising: dividing the charged particle beams into subbeams by an aperture plate having a plurality of charged particle beam passes; and deflecting at least partially the sub-beams to be image-formed such that an aberration of the image forming lens is corrected.

Preferably, an opening serves as the beam pass.

Preferably, at least part of the plural sub-beams are deflected in the vicinity of a pupil plane.

According to still another aspect of the present invention, there is provided a method of image-forming charged particle beams by at least one image forming lens having at least one of an electromagnetic lens and an electrostatic lens, comprising: dividing the charged particle beams into subbeams by an aperture plate having a plurality of charged particle beam passes; and deflecting the sub-beams to be image-formed in an overlapped manner such that an aberration of the image forming lens is corrected.

According to still another aspect of the present invention, there is provided a method of image-forming charge particle beams by an image forming lens having at least one of an electromagnetic lens and an

electrostatic lens, comprising : dividing the charged particle beams into subbeams by an aperture plate having a plurality of charged particle beam passes ; and deflecting the sub-beams to be image-formed such that an aberration of the image forming lens is corrected individually.

This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a structure of an electron optical system in the electron beam exposure apparatus implementing the block exposure method.

Fig. 2 illustrates to explain a principle where the aberration increase as the convergence semi-angle a increases.

Fig. 3 shows relationship between the convergence semi-angle a and the image displacement (out-of-focus).

Fig. 4 illustrates the principle of the present invention.

Fig. 5 shows a cross sectional shape of an electron beam image forming apparatus according to the first embodiment of the present invention.

Fig. 6 is a plan view showing a structure of the aperture plate 50 used in the first embodiment.

Fig. 7 is a cross sectional shape of the electron beam image-forming apparatus according to the second embodiment.

Fig. 8 is a plan view showing the structure of the aperture plate 70 used in the electron beam image-forming apparatus shown in Fig. 7.

Fig. 9 is a cross sectional shape of the electron beam image forming apparatus according to the third embodiment.

Fig. 10 is a plan view showing the aperture plate of the electron beam image forming apparatus according to the fourth embodiment.

Fig. 11 shows a structure of an electron beam exposure apparatus using the electron beam image forming apparatus according to the present invention.

Fig. 12 shows a structure where a plurality of electron guns lIA-IIC are provided in Fig. 11 and the electron beam generated by each electron gun passes each opening of the aperture plate 100.

DETAILED DESCRIPTION OF THE INVENTION The invention will now be described based on the preferred embodiments, which do not intend to limit the scope of the present invention, but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.

Fig. 4 and Fig. 5 show image formation devices for explaining the principle of the present invention. As shown in Fig. 2, the displacement due to the spherical aberration a increases as the convergence semi-angle increases. Thus, as shown in Fig. 4, an aperture plate 45 is provided on a pupil plane of an image forming lens 42, so that a central opening 60 serving as an exemplary charged particle beam pass and a first charged particle beam pass is made such that a beam A having the convergence semi-angle a allowing the resolution can be generated. Moreover, provided is an opening 61, serving as an exemplary charged particle beam pass and second

charged particle beam pass, whose center is located R away from an optical axis of the pupil plane ; and provided in a position counter to the opening 61 is an opening 62, serving as an exemplary charged particle beam pass and second charged particle beam pass, so that a beam B and a beam C are generated, respectively. The width of the opening 61 and the opening 62 is less than that of the opening 60. Since the beam A passes the vicinity of a=0 on the pupil plane, the beam A is image-formed at a position of x=O on an image plane 44. This image contains a very small amount of displacement (image error) as little as cr3. The beam B and beam C pass through positions a = +R and a =-R, respectively, on a pupil plane, and are image-formed about the center displaced by-cR3 and +cR3, respectively. Here, the pupil plane is defined as a surface on which an aperture is placed. The error (out-of-focus) amount of the barn B and beam C is approximately c ( (R+r) -R).

Now, referring to Fig. 5, there are provided three sets of a pair of electrodes 51-52,53-54 and 55-56 located counter to the respective opening 60, opening 61 and opening 62, so as to form a correction deflector. A voltage is not applied to a pair of electrodes 51-52 so as to make it a ground level, so that the affect of the electric field from a surrounding area is shielded off. A voltage is applied to a pair of electrodes 53-54 so as to cause the electric field in an area of the opening 61, so that the position of the beam B on the image plane is displaced by +cR3. Namely, the beam B is imageformed on the image plane at the position of x=O. Similarly, a voltage is applied to the pair of electrodes 55-56, so that the beam C is image-formed on the image plane at the position x=O. Thereby, the three beams A, B and C are image-formed on the image plane at the position x=O. As a result, though the convergence semi-angle of the optical system becomes greater than a, the magnitude of the displacement due to the spherical aberration is in the range of the error amount of image by each beam length, that is, c ( (R+r)-R), and thus does not increase.

Thus, according to the charged particle beam image forming apparatus of the present invention, a straight line B shown in Fig. 3 is translated to the right, and the position of the point P moves to the right along a straight line A.

Thus, a state where the spherical aberration is small while the convergence semi-angle a is substantially rather large, namely, high resolution with high current density is obtained. Thereby, a limit set forth by a trade-off factor in the method and apparatus of the charged particle beam image formation is significantly improved, so that a throughput can be improved without deteriorating the resolution.

Next, various embodiments for the present invention will be described in detail. Fig. 5 shows a cross sectional shape of an electron beam image forming apparatus according to the first embodiment of the present invention.

Fig. 6 is a plan view showing a structure of the aperture plate 50 used in the first embodiment. A cross section along Q-Q'in Fig. 6 corresponds to the aperture plate 50. Referring to Fig. 6, the aperture plate 50 includes: (1) approximately circular shaped opening 60 serving as an exemplary charged particle beam pass and a first charged particle beam pass around the center of an optical axis of the image forming lens 42; and (2) openings 61 and 62 serving as an exemplary approximately annular shaped second charged particle beam pass enclosed by concentric circles around the optical axis of the image forming lens 42 as a center in the periphery of the above (1).

Namely, the opening 61 is integrally formed with the opening 62 in Fig. 5.

The width of the annular openings 61 and 62 is less than the diameter of the approximately circular opening 60. In part of the annular openings 61 and 62 there is provided a supporting portion 63 which supports the formation of the opening 60. In the periphery of the opening 60 the approximately circular

shaped electrodes 51 and 52 are provided so as to apply 0 V. In other words, the electrode 51 is integrally formed with the electrode 52 in Fig. 5. Moreover, in an optical axis center side of the image forming lens 42 (in the periphery of the inner side of the annular openings 61 and 62) there are provided approximately circular shaped electrodes 54 and 55; in the opposite of an optical axis center side of the image forming lens 42 (in the periphery of the outer side of the annular openings 61 and 62) there are provided approximately circular shaped electrodes 53 and 56. A negative voltage-VI

is applied to the electrodes 54 and 55, and a positive voltage +Vl is applied to p I the electrodes 53 and 56. Thereby, a uniform electric field directed toward the center of the pupil plane (optical axis) is formed in the annular openings 61 and 62. The electron beam having passed the opening is deflected in the direction away from the optical axis of the image-forming lens 42. If VI is set appropriately, the electron beam (beam B and beam C) having passed the openings 61 and 62 is irradiated at the position x=O on the image plane 44.

Moreover, VI which is once set will remain as such without being altered. The VI is set in a manner such that the most favourable resolution can be obtained, while observing a resolution state of the electron beam on the image plane.

Moreover, an optical system having further less aberration can be designed if a diameter of the opening 60 located near the optical axis is made large and radii (width) of the openings 61 and 62 located far from the optical axis (that is, the difference between radii of the two concentric circles surrounding the openings 61 and 62 are made small), so that the magnitude of the aberration caused by the electron beam having passed each opening in the image plane is made substantially equal to each other.

Fig. 7 is a cross sectional shape of the electron beam image-forming apparatus according to the second embodiment. Fig. 8 is a plan view showing the structure of the aperture plate 70 used in the electron beam image-forming apparatus shown in Fig. 7. The electron beam image forming apparatus according to this second embodiment has a similar construction to that of the first embodiment. The second embodiment differs from the first embodiment in that in the aperture plate 70 there are provided an opening 81 serving as an exemplary circular shaped first charged particle beam pass and openings 82 and 83 serving as exemplary double annular second charged particle beam passes. In part of the annular openings 82 and 83 there are provided supporting members 84,85 and 86 which support the inner side of the openings 82 and 83. The diameter of the opening 82 is greater than the width of the opening 82 while the width of the opening 82 is greater than that of the opening 83. An electrode 71 to which OV is applied is provided in the periphery of the opening 81. In the periphery of the inner side of the annular opening 83 there is provided an approximately circular electrode 72 while in the periphery of the outer side there is provided an approximately circular electrode 73. A negative voltage-VI is applied to the electrode 72 while a positive voltage +Vl is applied to the electrode 73. Moreover, in the periphery of the inner side of the annular opening 83 there is provided an approximately circular electrode 74 while in the periphery of outermost side there is provided an approximately circular electrode 75. A negative voltage - V2 is applied to the electrode 74 while a positive voltage +V2 is applied to the electrode 75. VI and V2 are so set that the electron beams having passed respective annular openings 82 and 83 are irradiated to the position x=O on the image plane 44. Thus, V2 is greater than VI.

Fig. 9 is a cross sectional shape of the electron beam image forming apparatus according to the third embodiment. In the third embodiment, the same aperture plate 50 as in the first embodiment where the electrodes are provided for correcting the deflection is used. The third embodiment differs in that an aperture plate 57 which includes openings that pass only the electron beam passing the openings of the aperture plate 50 is provided in an electron beam entering side and counter to the aperture plate 50. When the electron beam is irradiated to a front surface of the aperture plate 50 having the electrodes for correcting the deflection, the deflection correcting electrodes might be damaged. Since the provision of the aperture plate 57 reduces the amount of electron beam irradiated to the aperture plate 50, the occurrence frequency of the damage to the deflection correcting electros can be reduced.

In the first through third embodiments, the aperture openings are represented by the approximately circular shaped opening in the center and at least one annular opening. However, an opening of other shape is also possible.

Fig. 10 is a plan view showing the aperture plate of the electron beam image forming apparatus according to the fourth embodiment. The aperture plate according to the fourth embodiment includes a central opening 91 of hexagonal shape serving as a first charged particle beam pass with its center aligned with the optical center of the image forming lens, and six peripheral openings 92A, 92B, 92C, 92D, 92E and 92F, serving as a second beam pass, around the periphery of the central opening 91, each of which has less area than that of the central opening 91, the centers of the respective peripheral openings 92A-92F lie on the circular locus of which center is the center of the central opening 91. In the periphery of the central opening 91, there is

provided a shield electrode 93, corresponding to each side, to which 0 V is applied. Moreover, in the periphery of each peripheral opening 92A-92F there are provided deflection correcting electrodes 93 through 98 corresponding to each side. The negative voltage-V is applied to the electrode 96 provided in a side facing one of side of the central openings 91 while the positive voltage +V is applied to the deflection correcting electrode 93 of a corresponding side.-0. 5V is applied to two deflection correcting electrodes 94 and 98 located at both sides of the electrode 96 while +0. 5V is applied to two deflection correcting electrodes 94 and 98 located at both sides of the electrode 93. The deflection correcting electrodes corresponding to the peripheral openings 92A-92F are mutually connected and a voltage is applied.

The value of voltage applied is set so that the best resolution can be obtained while observing an image forming situation on the image plane in a similar manner to the first embodiment.

So far, the electron beam image forming apparatus according to first to fourth embodiments has been described in detail. Next, an electron beam exposure apparatus will be described using such electron beam image forming apparatus.

Fig. 11 shows a structure of an electron beam exposure apparatus using the electron beam image forming apparatus according to the present invention. Though this electron beam exposure apparatus shows a similar structure to that shown in Fig. 1, a portion related to a block mask and so on are omitted. The same element as in Fig. 1 is given the same reference number. The electron beam generated from the electron gun 11 is shaped to a rectangular shape by a first reshaping aperture 13 and converged to a position of a second reshaping aperture (diaphragm) 27 by an electromagnetic lens 14.

In part of the reshaping aperture 27, an electromagnetic lens 26 is also

provided. The electron beam having passed the aperture is once converged by the lens 28 and thereafter enlarged so as to enter an image forming lens to be converged on a sample 1. An aperture plate 100 having a deflection correcting electrode 101 is provided in an electron beam entering side near the image forming lens 30. The voltage applied to the deflection correcting

electrode 101 is set so that the best resolution can be obtained while observing the image forming situation of the electron beam on the image plane.

In this electron beam image forming apparatus, for example, when the electron beam is being irradiated, ozone is supplied from an ozone supply unit 33 to a chamber including an electron lens 14 and so on located downstream the aperture plate 13.

By implementing the electron beam image forming apparatus of the present embodiments, the spherical aberration does not increase though the convergence semi-angle a is actually increased. Since the convergence semiangle a increases, the image error (out-of-focus) due to the Coulomb interaction is small, and a high resolution can be obtained at a state where the spherical aberration is small, that is, at a high current density. In this manner, the throughput of the charged particle beam exposure apparatus can be improved without deteriorating the resolution. Moreover, since the ozone is supplied, contamination caused by the irradiation of the electron beam can be removed. Thereby, occurrence of a drift in the electron beam can be properly prevented and the aberration caused in the electron beam can be appropriately reduced.

Moreover, in the configuration shown in Fig. 11, the aperture structure shown in the electron beam image forming apparatus according to the fourth embodiment shown in Fig. 10 may be used as the aperture plate 100 having the deflection correcting electrode 101. In that case, the voltage applied to the deflection correcting electrode at each peripheral opening is such that it can be controlled independently. Thus, when the voltage applied to deflection

correcting electrode is varied according to a deflection amount of a deflector I (not shown), the coma-aberration can be corrected (reduced). As described above, the coma-aberration can be made sufficiently small by a column design. However, by reducing the coma-aberration by using the electron beam image forming apparatus of the fourth embodiment, the degree of freedom of the column design can be improved.

Fig. 12 shows a structure where a plurality of electron guns lIA-lIC are provided in Fig. 11 and the electron beam generated by each electron gun passes each opening of the aperture plate 100. In this manner such that a plurality of the electron guns are used, even though an convergence semiangle of the beam 10B and beam 10C (incident angle to the sample) is made large, each can have high beam intensity.

The present invention is not limited by the above present embodiments and various modifications are possible. For example though the openings are used as examples for the first charged particle beam pass and the second charged particle beam pass, the present invention is not limited thereto. For example, a silicon nitride film may serve as such. As a matter of fact, it could be anything that pass the charged particles.

Moreover, though in the third embodiment the electrodes are provided in the aperture plate 50, the present invention is not limited thereto, and for example, the electrodes may be provided in a base plate which does not shield off a beam having passed the aperture plate 57.

Moreover, we may add with slightly different language about the present embodiments as follows. The charged particle beams are divided into sub-beams by an aperture plate having a plurality of the charged particle beam passes. Then, the sub-beams to be image formed are deflected in an overlapped manner such that an aberration of the image forming lens is corrected. Moreover, the sub-beams to be image-formed may be deflected such that an aberration of the image forming lens is corrected individually.

As has been described, according to the present invention, if a constant current is supposed, desirable image characteristics can be obtained where the image error (out-of-focus) due to Coulomb interaction is small and the aberration of the optical system is small. Moreover, if a fixed amount of the

image error (out-of-focus) is supposed, an optical system having further large current can be designed, so that the throughput of the electron beam exposure apparatus can be improved. Moreover, by appropriately removing the contamination, the drift of the electron beam can be appropriately prevented, so that the aberration of the optical system can be effectively corrected.

Although the present invention has been described by way of exemplary embodiments, it should be understood that many changes and substitutions may be made by those skilled in the art without departing from the spirit and scope of the present invention which is defined only by the appended claims.

Claims

WHAT IS CLAIMED IS : 1. A charged particle beam image forming method by which to imageform charged particle beams by an image forming lens having at least one of an electromagnetic lens and an electrostatic lens, the method comprising: dividing the charged particle beams into sub-beams by an aperture plate having a plurality of charged particle beam passes; and deflecting at least partially the sub-beams to be image formed such that an aberration of the image forming lens is corrected.
2. A method of claim 1, wherein an opening serves as the charged particle beam pass.
3. A method of claim 1 or Claim 2, wherein at least part of the plural subbeams are deflected in the vicinity of a pupil plane, the pupil plane being a surface on which an aperture is placed.
4. A charged particle beam image forming method by which to imagez : l 9 form charged particle beams by an image forming lens having at least one of an electromagnetic lens and an electrostatic lens, the method comprising: dividing the charged particle beams into sub-beams by an aperture plate having a plurality of charged particle beam passes; and deflecting the sub-beams to be image-formed in an overlapped manner such that an aberration of the image forming lens is corrected.
5. A charged particle beam image forming method by which to imageform charged particle beams by an image forming lens having at least one of g t) an electromagnetic lens and an electrostatic lens, the method comprising: dividing the charged particle beams into sub-beams by an aperture plate having a plurality of charged particle beam passes; and deflecting the sub-beams to be image-formed such that an aberration of the image forming lens is corrected individually.
6. Charged particle beam image forming apparatus for image-forming charged particle beams, the apparatus comprising: an image forming lens which image-forms the charged particle beams and which has at least one of an electromagnetic lens and an electrostatic lens; an aperture plate including a plurality of charged particle beam passes which divide the charged particle beams into a plurality of sub-beams; and a correction deflector which deflects at least part of the sub-beams by correcting an aberration of said image forming lens.
7. Apparatus of claim 6, wherein an opening serves as the charged particle beam pass.
8. Apparatus of Claim 6 or Claim 7, wherein said correction deflector is arranged in the vicinity of a pupil plane, the pupil plane being a surface on which an aperture is placed.
9. Apparatus of Claim 6, Claim 7 or Claim 8, wherein said aperture plate is arranged in the vicinity of a pupil plane, the pupil surface being a surface on which an aperture is placed.
10. Apparatus of Claim 6, Claim 7, Claim 8 or Claim 9, wherein said correction deflector deflects the sub-beams in a direction toward or away from an optical axis of said image forming lens and wherein intensity of deflection depends on a distance between the sub-beams and the optical axis.
11. Apparatus of Claim 6, Claim 7, Claim 8, Claim 9 or Claim 10 further comprising a deflector which deflects the sub-beams in a direction toward or away from an optical axis of said image forming lens. and whose deflection intensity varies corresponding to a change of a deflection amount of said deflector.
12. Apparatus of Claim 6, Claim 7, Claim 8, Claim 9, Claim 10 or Claim 11, wherein said aperture plate includes a first charged particle beam pass including an optical axis of said image forming lens, and at least one second charged particle beam pass in the periphery of the first charged particle beam pass, wherein said correction deflector does not deflect the sub-beams having passed the first charged particle beam pass and deflects the sub-beams having passed at least one second charged particle beam pass, in a direction toward or away from the optical axis.

13. Apparatus of Claim 12, wherein the first charged particle beam pass is of a substantially circular shape about the optical axis of said image forming lens.

14. Apparatus of Claim 13, wherein the first charged particle beam pass is of a shape such that all charged particle beams are passed whose aberration by said image forming lens is within a predetermined allowable range.

15. Apparatus of Claim 13 or Claim 14, wherein an electrode is provided and connected in the vicinity of the first charged particle beam pass.

16. Apparatus of Claim 12, Claim 13, Claim 14 or Claim 15, wherein the second beam pass is of a substantially annular shape enclosed by two concentric circles whose center is the optical axis of said image forming lens.

17. Apparatus of Claim 13, wherein the second charged particle beam pass is of a substantially annular shape enclosed by two concentric circles whose center is the optical axis of said image forming lens, and a difference between radii of the two concentric circles enclosing the at least one second charged particle beam pass is less than a diameter of the first charged particle beam pass.

18. Apparatus of Claim 16 or Claim 17, wherein said correction deflector comprises: a substantially circular-shaped deflection correcting electrode at both an optical axis center side of said image forming lens in the at least one second charged particle beam pass and at a side counter to the optical axis center, so that the deflection correcting electrode deflects sub-beams which have passed the at least one second charged particle beam pass.

19. Apparatus of Claim 12, Claim 13, Claim 14, Claim 15, Claim 16, Claim 17 or Claim 18, wherein said aperture plate has a plurality of the second

charged particle beam pass so that difference of radii between the two concentric circles is small as the second charged particle beam pass is located far away from an optical axis center of said image forming leans.

20. Apparatus of Claim 12, wherein an area of the first charged particle beam pass is greater than that of the second charged particle beam pass.

21. Apparatus of Claim 12, wherein said aperture plate has a plurality of the second charged particle beam pass, and an area of the second charged particle beam pass becomes smaller as the second charged particle beam pass is located away from the optical axis.

22. Apparatus of Claim 19, Claim 20 or Claim 21, said correction deflector increases a deflection amount as the second charged particle beam pass locates away from the optical axis center of said image forming lens.

23. Apparatus of Claim 6, Claim 7, Claim 8, Claim 9, Claim 10, Claim 11, Claim 12, Claim 13, Claim 14, Claim 15, Claim 16, Claim 17, Claim 18, Claim 19, Claim 20, Claim 21 or Claim 22, wherein said correction deflector may be provided in said aperture plate.

24. Apparatus of Claim 6, Claim 7, Claim 8, Claim 9, Claim 10, Claim 11, Claim 12, Claim 13, Claim 14, Claim 15, Claim 16, Claim 17, Claim 18, Claim 19, Claim 20, Claim 21 or Claim 22, wherein said correction deflector is provided in a plate which does not shield the sub-beams divided by said aperture plate.

25. Apparatus of Claim 6, Claim 7, Claim 8, Claim 9, Claim 10, Claim 11, Claim 12, Claim 13, Claim 14, Claim 15, Claim 16, Claim 17, Claim 18, Claim 19, Claim 20, Claim 21 or Claim 22, further comprising an ozone supply unit which supplies ozone.

26. Charged particle beam exposure apparatus for exposing a sample, comprising : a charged particle beam generator which generates a charged particle beam; a reshaping unit which reshapes the charged particle beam; a deflector which deflects the charged particle beam; a sample stage which holds the sample; an image forming lens which image-forms the charged particle beam on the sample, said image forming lens having at least one of an electromagnetic lens and an electrostatic lens; and a correction deflector which deflects at least part of the charged particle beams by correcting an aberration of said image forming lens.

27. Exposure apparatus of Claim 26, further comprising a charged particle beam observing unit which observes the charged particle beam which is image-formed on the sample, wherein a deflection amount of said correction deflector is determined

so that the charged particle beam observed by said charged particle beam ZP observing unit attains a maximum resolution.

Amendments to the claims have been filed as follows

1. A method of focusing charged particle beams on a predetermined plane by an image forming lens having at least one of either an electromagnetic lens or an electrostatic lens the method comprising : dividing a charged particle beam into a first sub-beam and a plurality of second sub-beams radially spaced from the first sub-beam by an aperture plate formed with a first charged particle beam pass to have said first sub-beam pass therethrough, said first charged particle beam pass including an optical axis of said image forming lens, and at least a second charged particle beam pass spaced from a periphery of said first charged particle beam pass to have

al s said plurality of second sub-beams pass therethrough, said second charged particle beam pass being concentric with respect to said first charged particle beam pass, spacing between said first and said second charged particle beam pass extending radially with respect to said optical axis; and

deflecting at least one second sub-beam for correcting an aberration of 1- z : l the image forming lens so that the deflected at least one second sub-beam and ,, orm 'd f said first sub-beam substantially focus at the same place on said predetermined plane.

2. A method as claimed in claim 1, wherein the at least one second sub-beam is deflected in the vicinity of a pupil plane of the image forming lens.

3. A method as claimed in claim 1 or 2, comprising deflecting the first sub-beam and the at least one second sub-beam in an overlapped manner so that the aberration of the image forming lens is corrected.

4. A method as claimed in any preceding claim, individually deflecting the first sub-beam and the at least one second sub-beam so that the aberration of the image forming lens is corrected.

5. A charged particle beam image forming apparatus for imageforming charged particle beams for focusing charged particle beams on a 1. zn predetermined plane the apparatus comprising: an image forming lens having at least one of either an electromagnetic lens or an electrostatic lens through which the charged particle beams are arranged to pass; an aperture plate formed with a first charged particle beam pass including an optical axis of said image forming lens and a plurality of second charged particle beam passes provided concentrically with respect to said first

charged particle beam pass, spacing between said plurality of second charged I particle beam passes extending radially with respect to said first charged particle beam pass, said aperture plate dividing said charged particle beam into a first sub-beam arranged to pass through said first charged particle beam pass and a plurality of second sub-beams spaced outwardly from the first subbeam and arranged to pass through said second charged particle beam passes; and a correction deflector arranged to deflect at least one of the second subbeams for correcting an aberration of said image forming lens so that the at least one second sub-beam and the first sub-beam substantially focus at the same place on the predetermined plane.

6. An apparatus as claimed in claim 5, wherein said correction deflector is arranged in the vicinity of a pupil plane of said image-forming lens.

7. An apparatus as claimed in claim 5 or claim 6, wherein said aperture plate is arranged in the vicinity of a pupil plane of the image forming lens.

8. An apparatus as claimed in claim 5, 6 or 7, wherein said correction deflector is arranged to deflect the at least one of the second subbeams in a direction toward or away from the optical axis of said image I forming lens so that intensity of deflection varies in accordance with the distance between the second charged particle beam pass and the optical axis.

9. An apparatus as claimed in any of claims 5 to 8, further comprising a deflector for deflecting the charged particle beams, wherein said correction deflector is arranged to deflect the at least one of the second subbeams in a direction toward or away from the optical axis of said image forming lens so that intensity of deflection varies in accordance with a change in deflection of said deflector.

10. An apparatus as claimed in any of claims 5 to 9, wherein said correction deflector is arranged to deflect the at least one of the second subbeams in a direction towards or away from said optical axis of said image forming lens and wherein the intensity of deflection depends upon the distance from said at least one of the second sub-beams to said optical axis.

11. An apparatus as claimed in claim 10, wherein the first charged particle beam pass is of a substantially circular shape encircled by a first

electrode coaxial with the optical axis of the image forming lens.

1 12. An apparatus as claimed in claim 11, wherein the first electrode has a diameter such that aberrations of said first sub-beam arranged to pass I through the circular first charged particle beam pass caused by said image 117 11. 1 forming lens are within a predetermined allowable range.
13. An apparatus as claimed in claim 11 or claim 12, wherein the first electrode provided in the vicinity of the first charged particle beam pass is arranged to have a ground potential applied thereto.
14. An apparatus as claimed in any of claims 10 to 13, wherein the second charged particle beam pass is of a substantially annular shape encircled by second and third spaced concentric electrodes coaxial with the optical axis of said image forming lens.
15. An apparatus as claimed in claim 14, wherein the third electrode

is larger than the second electrode, and a difference between diameters of the ters of the second and third electrodes is smaller than the diameter of the first electrode.
16. An apparatus as claimed in claim 15, wherein said correction deflector comprises; a deflection correcting electrode including the first and second concentric substantially annular-shaped electrodes coaxial with the optical axis of the image forming lens, the diameter of said second electrode being greater than the diameter of said first electrode, and the diameter of said first electrode being greater than a diameter of said first charged particle beam pass, and a diameter of said second electrode being smaller than the diameter of said annular second charged particle beam pass, so that the deflection correcting electrode deflects the at least one second sub-beam passing through the annular second charged particle beam pass towards said first sub-beam.
17. An apparatus as claimed in any of claims 10 to 16, wherein the second charged particle beam pass comprises an annular inner second charged particle beam pass and an annular outer second charged particle beam pass spaced from a periphery of said annular inner second charged particle beam pass, said inner second charged particle beam pass is encircled by second and third electrodes concentric with said optical axis of said image forming lens and said annular outer second charged particle beam pass is encircled by fourth and fifth electrodes concentric with the optical axis of said image forming lens as a centre thereof, wherein a difference between diameters of

the fourth and fifth electrodes is smaller than the difference between diameters of the second and third electrodes.
18. An apparatus as claimed in any of claims 10 to 16, wherein the area of the first charged particle beam pass is larger than the area of the second charged particle beam passes.
19. An apparatus as claimed in claim 17, wherein an area of the outer second charged particle beam pass is smaller than the area of the inner second charged particle beam passes.
20. An apparatus as claimed in claim 17 or claim 19, wherein said correction deflector is arranged to deflect said at least one of the plurality of second sub-beams arranged to pass through said outer second charged particle beam pass more than said second sub-beams passing through said inner second charged particle beam passes.
21. An apparatus as claimed in any of claims 5 to 20 wherein said correction deflector is provided at said aperture plate.
22. An apparatus as claimed in any of claims 5 to 21, wherein said correction deflector is provided at a plate which does not shield the first and second sub-beams divided by said aperture plate.
23. An apparatus as claimed in any of claims 5 to 20, further comprising an ozone supply unit for supplying ozone.
24. An apparatus as claimed in any of claims 5 to 23, comprising a charged particle beam generator for generating charged particle beams; a reshaping unit for reshaping the charged particle beams; and a sample stage for holding a sample to be exposed to the charged particle beams.
25. A charged particle beam exposure apparatus for exposing a sample, comprising : a charged particle beam generator which generates a charged particle beam; an image forming lens for focusing said charged particle beam on said

sample, said image forming lens having at least one of an electromagnetic Z :) ic lens and an electrostatic lens so that said charged particle beam passes therethrough; an aperture plate formed with a first charged particle beam pass including an optical axis of said image forming lens and a plurality of second charged particle beam passes spaced from a periphery of said first charged particle beam pass and being concentric with respect to said first charged particle beam pass, spacing between said plurality of second charged particle beam passes extending radially with respect to said first charged particle beam pass, said aperture plate dividing said charged particle beam into a first subbeam arranged to pass through said first charged particle beam pass and a plurality of second sub-beams spaced outwardly from the first sub-beam and arranged to pass through said second charged particle beam passes; and a correction deflector which is arranged to deflect at least one of the second sub-beams for correcting an aberration of said image forming lens so that said at least one second sub-beam and said first sub-beam substantially focus at the same place on a predetermined plane on said sample.
26. An apparatus as claimed in claim 25, further comprising a charged particle beam observing unit for observing said charged particle beams which are focused on said sample, wherein the deflection of said correction deflector is determined so that said charged particle beams observed by said charged particle beam observing unit attains maximum resolution.
27. A method of focusing charged particle beams on a predetermined plane substantially as hereinbefore described, and as illustrated in Figures 4 to 6; or Figures 7 and 8; or Figure 9; or Figures 10 to 12 of the accompanying drawings.
28. A charged particle beam image forming apparatus substantially as hereinbefore described, and as illustrated in Figures 4 to 6; or Figures 7 and 8; or Figure 9; or Figures 10 to 12 of the accompanying drawings.