Electron beam exposure apparatus

Blurring of an electron beam image produced by the Coulomb effect upon forming a pattern on a substrate by exposure using a multi-electron beam exposure apparatus is corrected. The electron beam exposure apparatus has an elementary electron optical system array for generating a plurality of electron beams in accordance with the pattern to be exposed, a reduction electron optical system for imaging the electron beams coming from the elementary electron optical system array, a deflector for deflecting the electron beams, and a focal point/astigmatism control circuit for correcting the imaging positions of the electron beams in units of settling positions of the electron beams on the basis of correction data corresponding to the pattern to be exposed.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an electron beam exposure apparatus and,
 more particularly, to an electron beam exposure apparatus for drawing a
 pattern on a wafer or drawing a pattern on a mask or reticle using a
 plurality of electron beams.
 2. Description of the Related Art
 In an electron beam exposure apparatus which performs exposure by imaging
 an electron beam on a substrate, when the beam current is large, the
 electron beam image projected onto the substrate is blurred due to a
 Coulomb effect. Most of blurring caused by the Coulomb effect can be
 corrected by re-adjusting the focal point position of a reduction electron
 optical system for projecting an electron beam, but some blurring remains
 uncorrected. In a variable shaping exposure apparatus which shapes the
 sectional shape of an electron beam within a maximum range of about 10
 .mu.m.times.10 .mu.m, the blurring produced by the Coulomb effect is
 predicted from the area of the shaped beam, and apparatus parameters (beam
 current density, half beam incident angle, beam acceleration voltage, and
 optical length of the reduction electron optical system), and the focal
 point of the reduction electron optical system is adjusted in accordance
 with the prediction result.
 In a multi-electron beam exposure apparatus which irradiates an array of a
 plurality of electron beams in line onto a substrate, deflects these
 electron beams to scan the substrate, and draws a pattern by
 ON/OFF-controlling the electron beams to be irradiated in correspondence
 with the pattern to be drawn, since the electron beams are dispersed i.e.,
 since the effective current density per unit area on the substrate is low,
 blurring due to the Coulomb effect is small. This means that when the
 blurring due to the Coulomb effect is confined within a predetermined
 value, the multi-electron beam exposure apparatus can improve the exposure
 throughput by applying larger beam currents than the variable shaping
 exposure apparatus.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to allow high-resolution pattern
 drawing by appropriately correcting an electron beam image blurred due to
 the Coulomb effect.
 An electron beam exposure apparatus according to one aspect of the present
 invention is an electron beam exposure apparatus for forming a pattern on
 a substrate by exposure using a plurality of electron beams, comprising an
 electron beam source for generating a plurality of electron beams in
 accordance with a pattern to be exposed, a reduction electron optical
 system for imaging an electron beam group emitted by the electron beam
 source on the substrate, a scanning unit for scanning the electron beam
 group on the substrate, and a correction unit for correcting imaging
 positions of the electron beam group on the basis of correction data
 corresponding to the pattern to be exposed.
 In the electron beam exposure apparatus, the correction unit preferably
 corrects the imaging positions of the electron beam group on the basis of
 correction data corresponding to the number of electron beams that make up
 the electron beam group emitted by the electron beam source.
 In the electron beam exposure apparatus, the correction unit preferably
 corrects the imaging positions of the electron beam group on the basis of
 correction data corresponding to a distribution of electron beams that
 make up the electron beam group emitted by the electron beam source.
 In the electron beam exposure apparatus, the correction unit preferably
 adjusts a focal point position of the reduction electron optical system on
 the basis of the correction data.
 In the electron beam exposure apparatus, the electron beam source
 preferably comprises an electron source, a plurality of elementary
 electron optical systems for forming intermediate images of the electron
 source, and a control unit for controlling whether each of the plurality
 of elementary electron optical systems forms an intermediate image of the
 electron source.
 In the electron beam exposure apparatus, the correction unit preferably
 adjusts imaging positions of the intermediate images in an axial direction
 of the reduction electron optical system on the basis of the correction
 data.
 In the electron beam exposure apparatus, the correction unit preferably
 adjusts imaging positions of the intermediate images in an axial direction
 of the reduction electron optical system, and a focal point position of
 the reduction electron optical system on the basis of the correction data.
 In the electron beam exposure apparatus, preferably, a subarray is formed
 by a matrix of a plurality of elementary electron optical systems and an
 entire array is formed by a matrix of a plurality of subarrays.
 In the electron beam exposure apparatus, the correction unit preferably
 corrects imaging positions of the intermediate images in an axial
 direction of the reduction electron optical system in units of subarrays
 on the basis of the correction data.
 In the electron beam exposure apparatus, preferably, the correction unit
 commonly corrects imaging positions of electron beams coming from all the
 elementary electron optical systems of the entire array by adjusting a
 focal point position of the reduction electron optical system on the basis
 of the correction data, and adjusts imaging positions of the intermediate
 images in an axial direction of the reduction electron optical system in
 units of subarrays on the basis of differences between the common
 correction amount and appropriate correction amounts.
 In the electron beam exposure apparatus, preferably, the scanning unit
 comprises a main deflector and sub deflector for deflecting electron beams
 emitted by the electron beam source, the scanning unit divides an exposure
 region on the substrate into a plurality of fields, switches the field to
 be exposed by the main deflector, and scans the electron beam group in
 each field using the sub deflector, and a constant correction amount for
 imaging positions of the electron beam group is maintained while a pattern
 is drawn on each field.
 In the electron beam exposure apparatus, the correction unit preferably
 dynamically corrects imaging positions of the electron beam group emitted
 by the electron beam source on the basis of the correction data.
 In the electron beam exposure apparatus, the correction unit preferably
 corrects the imaging positions of the electron beam group on the basis of
 the correction data each time a positional relationship between the
 electron beam group emitted by the electron beam source and the substrate
 is settled.
 In the electron beam exposure apparatus, the correction data is preferably
 a function having, as variables, at least the number of electron beams
 coming from the subarray corresponding to an object to be corrected, a
 distance between the subarray corresponding to the object to be corrected,
 and another subarray that outputs the electron beams, and the number of
 electron beams coming from the other subarray.
 In the electron beam exposure apparatus, the correction data is preferably
 a function having, as a variable, at least a spacing of electron beams
 emitted by the electron source.
 The electron beam exposure apparatus preferably further comprises a
 calculation unit for generating correction data used for correcting
 imaging positions of the electron beam group on the basis of data that
 defines the pattern to be exposed on the substrate.
 An electron beam exposure method according to another aspect of the present
 invention is an electron beam exposure method for forming a pattern on a
 substrate by exposure using a plurality of electron beams, comprising the
 steps of: imaging a plurality of electron beams, which are emitted by an
 electron beam source in accordance with a pattern to be exposed, via a
 reduction electron optical system, and scanning the electron beam group on
 the substrate; and correcting imaging positions of the electron beam group
 on the basis of correction data corresponding to the pattern to be exposed
 in synchronism with the scan.
 In the electron beam exposure method, the correction step preferably
 includes the step of correcting the imaging positions of the electron beam
 group on the basis of correction data corresponding to the number of
 electron beams that make up the electron beam group emitted by the
 electron beam source.
 In the electron beam exposure method, the correction step preferably
 includes the step of correcting the imaging positions of the electron beam
 group on the basis of correction data corresponding to a distribution of
 electron beams that make up the electron beam group emitted by the
 electron beam source.
 In the electron beam exposure method, the correction step preferably
 includes the step of adjusting a focal point position of the reduction
 electron optical system on the basis of the correction data.
 In the electron beam exposure method, the electron beam source preferably
 comprises an electron source, a plurality of elementary electron optical
 systems for forming intermediate images of the electron source, and a
 control unit for controlling whether each of the plurality of elementary
 electron optical systems forms an intermediate image of the electron
 source.
 In the electron beam exposure method, the correction step preferably
 includes the step of adjusting imaging positions of the intermediate
 images in an axial direction of the reduction electron optical system on
 the basis of the correction data.
 In the electron beam exposure method, the correction step includes the step
 of adjusting imaging positions of the intermediate images in an axial
 direction of the reduction electron optical system, and a focal point
 position of the reduction electron optical system on the basis of the
 correction data.
 In the electron beam exposure method, preferably, a subarray is formed by a
 matrix of a plurality of elementary electron optical systems and an entire
 array is formed by a matrix of a plurality of subarrays.
 In the electron beam exposure method, the correction step preferably
 includes the step of correcting imaging positions of the intermediate
 images in an axial direction of the reduction electron optical system in
 units of subarrays on the basis of the correction data.
 In the electron beam exposure method, the correction step preferably
 includes the step of commonly correcting imaging positions of electron
 beams coming from all the elementary electron optical systems of the
 entire array by adjusting a focal point position of the reduction electron
 optical system on the basis of the correction data, and adjusting imaging
 positions of the intermediate images in an axial direction of the
 reduction electron optical system in units of subarrays on the basis of
 differences between the common correction amount and appropriate
 correction amounts.
 In the electron beam exposure method, preferably, an exposure region on the
 substrate is divided into a plurality of fields, the field to be exposed
 is switched by a main deflector, and the electron beam group in each field
 is scanned using a sub deflector, and a constant correction amount for
 imaging positions of the electron beam group is maintained while a pattern
 is drawn on each field.
 In the electron beam exposure method, the correction step preferably
 includes the step of dynamically correcting imaging positions of the
 electron beam group emitted by the electron beam source on the basis of
 the correction data.
 In the electron beam exposure method, the correction step preferably
 includes the step of correcting the imaging positions of the electron beam
 group on the basis of the correction data each time a positional
 relationship between the electron beam group emitted by the electron beam
 source and the substrate is settled.
 In the electron beam exposure method, the correction data is preferably a
 function having, as variables, at least the number of electron beams
 coming from the subarray corresponding to an object to be corrected, a
 distance between the subarray corresponding to the object to be corrected,
 and another subarray that outputs the electron beams, and the number of
 electron beams coming from the other subarray.
 In the electron beam exposure method, the correction data is preferably a
 function having, as a variable, at least a spacing of electron beams
 emitted by the electron beam source.
 The electron beam exposure method preferably further comprises the
 calculation step of generating correction data used for correcting imaging
 positions of the electron beam group on the basis of data that defines the
 pattern to be exposed on the substrate.
 A data generation method according to still another aspect of the present
 invention is a method of generating data for controlling the
 above-mentioned electron beam exposure apparatus, comprising the steps of:
 inputting data that defines a pattern to be exposed on a substrate; and
 generating correction data used for correcting imaging positions of an
 electron beam group on the basis of the input data.
 In the data generation method, the correction data generation step
 preferably includes the step of generating the correction data on the
 basis of the number of electron beams that make up the electron beam group
 emitted by an electron beam source.
 In the data generation method, the correction data generation step
 preferably includes the step of generating the correction data on the
 basis of a distribution of electron beams that make up the electron beam
 group emitted by an electron beam source.
 In the data generation method, the correction data generation step
 preferably includes the step of generating the correction data for
 correcting the imaging positions of the electron beam group when a
 positional relationship between the electron beam group and the substrate
 is settled.
 A computer readable program according to yet another aspect of the present
 invention is a computer readable program for generating data for
 controlling the above-mentioned electron beam exposure apparatus,
 comprising the steps of: inputting data that defines a pattern to be
 exposed on a substrate; and generating correction data used for correcting
 imaging positions of an electron beam group on the basis of the input
 data.
 In the computer readable program, the correction data generation step
 preferably includes the step of generating the correction data on the
 basis of the number of electron beams that make up the electron beam group
 emitted by an electron beam source.
 In the computer readable program, the correction data generation step
 preferably includes the step of generating the correction data on the
 basis of a distribution of electron beams that make up the electron beam
 group emitted by an electron beam source.
 In the computer readable program, the correction data generation step
 preferably includes the step of generating the correction data for
 correcting the imaging positions of the electron beam group when a
 positional relationship between the electron beam group and the substrate
 is settled.
 Further objects, features and advantages of the present invention will
 become apparent from the following detailed description of embodiments of
 the present invention with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 An exposure apparatus according to this embodiment is a multi-electron beam
 exposure apparatus which draws a desired pattern by irradiating a
 plurality of electron beams onto a substrate via an electron optical
 system, and adjusts the focal point of the electron optical system in
 correspondence with the number of electron beams irradiated onto the
 substrate, which sequentially changes in accordance with the pattern to be
 drawn. With this apparatus, an electron beam image blurred by the Coulomb
 effect can be corrected, and a pattern can be drawn at high resolution.
 In the multi-electron beam exposure apparatus, a plurality of electron
 beams irradiated onto the substrate are concentrated on a narrow range or
 uniformly distributed depending on the pattern to be drawn. Even when the
 number of electron beams irradiated onto the substrate remains the same,
 since the former case has a higher effective current density per unit area
 than the latter case, an electron beam image is blurred larger by the
 Coulomb effect.
 FIGS. 14A and 14B exemplify the patterns to be drawn on the substrate. In
 FIGS. 14A and 14B, the full circles indicate the actual irradiation
 positions of the electron beams, and the open circles indicate
 non-irradiation positions of the electron beams. The patterns shown in
 FIGS. 14A and 14B have the same number of electron beams to be irradiated
 onto the substrate (equivalent to the sum total of currents irradiated
 onto the substrate). However, in a region L in FIG. 14B, an electron beam
 image is blurred larger due to the Coulomb effect since a plurality of
 electron beams are concentrated within a narrower range than in FIG. 14A.
 On the other hand, in a region S in FIG. 14B, an electron beam image is
 blurred less due to the Coulomb effect since the electron beam density
 irradiated is smaller than that in FIG. 14A.
 The different degrees of blurring of an electron beam image due to the
 Coulomb effect arising from the distribution of electron beams irradiated
 onto the substrate also apply to, e.g., the patterns shown in FIGS. 15A
 and 15B.
 Hence, in order to accurately correct blurring of an electron beam due to
 the Coulomb effect, not only the number of electron beams to be irradiated
 onto the substrate (the sum total of currents irradiated onto the
 substrate) but also the distribution of electron beams are preferably
 taken into consideration.
 In the following description, an electron beam exposure apparatus which
 adjusts the focal point of an electron optical system in consideration of
 not only the number of electron beams to be irradiated onto the substrate
 but also the distribution of electron beams will be disclosed as a
 preferred embodiment of the present invention.
 (Explanation of Constituting Elements of Electron Beam Exposure Apparatus)
 FIG. 1 is a schematic view showing the principal part of an electron beam
 exposure apparatus according to the present invention.
 Referring to FIG. 1, reference numeral 1 denotes an electron gun made up of
 a cathode 1a, grid 1b, and anodes 1c. Electrons emitted by the cathode 1a
 form a crossover image between the grid 1b and anode 1c. The crossover
 image will be referred to as an electron source hereinafter.
 Electrons coming from this electron source are converted into nearly
 collimated electron beams by a condenser lens 2 whose front-side focal
 point position is located at the electron source position. The nearly
 collimated electron beams enter an elementary electron optical system
 array 3. The elementary electron optical system array 3 is formed by
 arranging a plurality of elementary electron optical systems, each
 consisting of an aperture, an electron optical system, and a blanking
 electrode, in directions perpendicular to an optical axis AX. The
 elementary electron optical system 3 will be explained in detail later.
 The elementary electron optical system array 3 forms a plurality of
 intermediate images of the electron source. These intermediate images are
 projected in a reduced scale by a reduction electron optical system 4 (to
 be described later), and form images of the electron source on a wafer 5.
 In this case, the individual elements of the elementary electron optical
 system array 3 are set so that the spacing between adjacent electron
 source images formed on the wafer 5 equals an integer multiple of the size
 of each electron source image. Furthermore, the elementary electron
 optical system array 3 makes the positions of the individual intermediate
 images differ in the optical axis direction in correspondence with the
 curvature of field of the reduction electron optical system 4, and
 corrects in advance any aberrations expected to be produced when the
 individual intermediate images are projected onto the wafer 5 in a reduced
 scale by the reduction electron optical system 4.
 The reduction electron optical system 4 comprises a symmetric magnetic
 doublet consisting of a first projection lens 41 (43) and second
 projection lens 42 (44). If f1 represents the focal length of the first
 projection lens 41 (43), and f2 represents the focal length of the second
 projection lens 42 (44), the distance between these two lenses is f1+f2.
 The object point on the optical axis AX is located at the focal point
 position of the first projection lens 41 (43), and its image point is
 formed at the focal point of the second projection lens 42 (44). This
 image is reduced to -f2/f1. Since two lens magnetic fields are determined
 to act in opposite directions, the Seidel aberrations and chromatic
 aberrations pertaining to rotation and magnification theoretically cancel
 each other, except for five aberrations, i.e., spherical aberration,
 isotropic astigmatism, isotropic coma, curvature of field, and on-axis
 chromatic aberration.
 Reference numeral 6 denotes a deflector for deflecting a plurality of
 electron beams coming from the elementary electron optical system array 3
 to displace a plurality of electron source images by nearly equal
 displacement amounts in the X- and Y-directions on the wafer 5. The
 deflector 6 comprises a main deflector 61 used when the deflection width
 is large, and a sub deflector 62 used when the deflection width is small.
 The main deflector 61 is an electromagnetic type deflector, and the sub
 deflector 62 is an electrostatic type deflector.
 Reference numeral 7 denotes a dynamic focus coil that corrects any
 deviations of the focus positions of the electron source images arising
 from deflection aberration produced upon operation of the deflector 6; and
 8, a dynamic stigmatic coil that corrects astigmatism of deflection
 aberration produced upon deflection as in the dynamic focus coil 7.
 Reference numeral 9 denotes a refocus coil for adjusting the focal point
 position of the reduction electron optical system 4 to correct blurring of
 electron beams due to the Coulomb effect produced when the number of a
 plurality of electron beams to be irradiated onto a wafer or the sum total
 of currents to be irradiated onto the wafer becomes large.
 Reference numeral 10 denotes a Faraday cup having two single knife edges
 respectively extending in the X- and Y-directions. The Faraday cup detects
 the charge amount of images formed by the electron beams coming from the
 elementary electron optical systems.
 Reference numeral 11 denotes a .theta.-Z stage that carries a wafer, and is
 movable in the direction of the optical axis AX (Z-axis) and in the
 direction of rotation about the Z-axis. A stage reference plate 13 and the
 Faraday cup 10 are fixed on the stage 11.
 Reference numeral 12 denotes an X-Y stage which carries the .theta.-Z stage
 and is movable in the X- and Y-directions perpendicular to the direction
 of the optical axis AX (Z-axis).
 The elementary electron optical system array 3 will be explained below with
 reference to FIG. 2.
 In the elementary electron optical system array 3, a plurality of
 elementary electron optical systems form a group (subarray), and a
 plurality of subarrays are formed. In this embodiment, five subarrays A1
 to A5 are formed. In each subarray, a plurality of elementary electron
 optical systems are two-dimensionally arranged, and 27 elementary electron
 optical systems (e.g., A3 (1,1) to A3 (3,9)) are formed in each subarray
 of this embodiment.
 FIG. 3 is a sectional view of each elementary electron optical system.
 Referring to FIG. 3, a substrate AP-P is irradiated with electron beams
 nearly collimated by the condenser lens 2. The substrate AP-P has an
 aperture (AP1) that defines the shape of electron beams to be transmitted,
 and is common to other elementary electron optical systems. That is, the
 substrate AP-P is a substrate having a plurality of apertures.
 Reference numeral 301 denotes a blanking electrode which is made up of a
 pair of electrodes and has a deflection function; and 302, a substrate
 which has an aperture (AP2) and is common to other elementary electron
 optical systems. On the substrate 302, the blanking electrode 301 and a
 wiring layer (W) for turning on/off the electrodes are formed. That is,
 the substrate 302 has a plurality of apertures and a plurality of blanking
 electrodes.
 Reference numeral 303 denotes an electron optical system, which uses two
 unipotential lenses 303a and 303b. Each unipotential lens is made up of
 three aperture electrodes, and has a convergence function by setting the
 upper and lower electrodes at the same potential as an acceleration
 potential V0, and keeping the intermediate electrode at another potential
 V1 or V2. The individual aperture electrodes are stacked on a substrate
 via insulating materials, and the substrate is common to other elementary
 electron optical systems. That is, the substrate has a plurality of
 electron optical systems 303.
 The upper, intermediate, and lower electrodes of the unipotential lens 303a
 and the upper and lower electrodes of the unipotential lens 303b have a
 shape shown in FIG. 4A, and the upper and lower electrodes of the
 unipotential lenses 303a and 303b are set at common potential in all the
 elementary electron optical systems by a first focal point/astigmatism
 control circuit 15 (to be described later).
 Since the potential of the intermediate electrode of the unipotential lens
 303a can be set by the first focal point/astigmatism control circuit 15 in
 units of elementary electron optical systems, the focal length of the
 unipotential lens 303a can be set in units of elementary electron optical
 systems.
 The intermediate electrode of the unipotential lens 303b is made up of four
 electrodes, as shown in FIG. 4B, and the potentials of these electrodes
 can be set independently and also individually in units of elementary
 electron optical systems by the first focal point/astigmatism control
 circuit 15. Hence, the unipotential lens 303b can have different focal
 lengths in a section perpendicular to its optical axis and can set them
 individually in units of elementary electron optical systems.
 As a consequence, by respectively controlling the potentials of the
 intermediate electrodes of the electron optical systems 303, the electron
 optical characteristics (the intermediate image forming positions and
 astigmatism) of the elementary electron optical systems can be controlled.
 Upon controlling the intermediate image forming positions, since the size
 of each intermediate image is determined by the ratio between the focal
 lengths of the condenser lens 2 and each electron optical system 303, the
 intermediate image forming position is moved by setting a constant focal
 length of each electron optical system 303 and moving its principal point
 position. With this control, the intermediate images formed by all the
 elementary electron optical systems can have nearly equal sizes and
 different positions in the optical axis direction.
 Each nearly collimated electron beam output from the condenser lens 2 forms
 an intermediate image of the electron source via the aperture (AP1) and
 electron optical system 303. Note that the aperture (AP1) is located at or
 in the vicinity of the front-side focal point position of the
 corresponding electron optical system 303, and the blanking electrode 301
 is located at or in the vicinity of the intermediate image forming
 position (rear-side focal point position) of the corresponding electron
 optical system 303. For this reason, if no electric field is applied
 across the electrodes of the blanking electrode 301, the electron beam is
 not deflected, as indicated by an electron beam 305 in FIG. 3. On the
 other hand, if an electric field is applied across the electrodes of the
 blanking electrode 301, the electron beam is deflected, as indicated by an
 electron beam 306 in FIG. 3. Since the electron beams 305 and 306 have
 different angle distributions on the object plane of the reduction
 electron optical system 4, they become incident on different regions at
 the pupil position (on a plane P in FIG. 1) of the reduction electron
 optical system 4. Hence, a blanking aperture BA that transmits the
 electron beam 305 alone is formed at the pupil position (on the plane P in
 FIG. 1) of the reduction electron optical system.
 The electron optical systems 303 of the elementary electron optical systems
 individually set the potentials of their two intermediate electrodes so as
 to correct the curvature of field and astigmatism produced when the
 intermediate images formed thereby are projected in a reduced scale onto
 the surface to be exposed by the reduction electron optical system 4,
 thereby making the electron optical characteristics (intermediate image
 forming positions and astigmatism) of the elementary electron optical
 systems different. However, in this embodiment, in order to decrease the
 number of wiring lines between the intermediate electrodes and the first
 focal point/astigmatism control circuit 15, the elementary electron
 optical systems included in a single subarray have identical electron
 optical characteristics, and the electron optical characteristics
 (intermediate image forming positions and astigmatism) of the elementary
 electron optical systems are controlled in units of subarrays.
 Furthermore, in order to correct distortion produced when a plurality of
 intermediate images are projected in a reduced scale onto the surface to
 be exposed by the reduction electron optical system 4, the distortion
 characteristics of the reduction electron optical system 4 are detected in
 advance, and the positions of the elementary electron optical systems in
 the direction perpendicular to the optical axis of the reduction electron
 optical system 4 are set based on the detected characteristics.
 FIG. 5 shows the system arrangement of this embodiment.
 A blanking control circuit 14 individually ON/OFF-controls the blanking
 electrodes of the elementary electron optical systems in the elementary
 electron optical system array 3, and the first focal point/astigmatism
 control circuit 15 individually controls the electron optical
 characteristics (intermediate image forming positions and astigmatism) of
 the elementary electron optical systems in the elementary electron optical
 system array 3.
 A second focal point/astigmatism control circuit 16 controls the focal
 point position and astigmatism of the reduction electron optical system 4
 by controlling the dynamic stigmatic coil 8 and dynamic focus coil 7. A
 deflection control circuit 17 controls the deflector 6. A magnification
 adjustment circuit 18 adjusts the magnification of the reduction electron
 optical system 4. A refocus control circuit 19 controls currents to be
 supplied to the refocus coil 9 to adjust the focal point position of the
 reduction electron optical system 4.
 A stage drive control circuit 20 controls driving of the .theta.-Z stage,
 and also controls driving of the X-Y stage 12 in collaboration with a
 laser interferometer 21 that detects the position of the X-Y stage 12.
 A control system 22 synchronously controls the plurality of control
 circuits described above and Faraday cup 10 to attain exposure and
 alignment based on exposure control data from a memory 23. The control
 system 22 is controlled by a CPU 25 for controlling the entire electron
 beam exposure apparatus via an interface 24.
 (Explanation of Operation)
 The operation of the electron beam exposure apparatus of this embodiment
 will be explained below with the aid of FIG. 5.
 Upon reception of pattern data to be formed on the wafer by exposure, the
 CPU 25 determines the minimum deflection amount the sub deflector 62 gives
 to the electron beams, on the basis of the minimum line width, types of
 line widths, and shapes of the pattern to be formed on the wafer by
 exposure. The CPU 25 divides the pattern data into those in units of
 exposure regions of the individual elementary electron optical systems,
 sets a common matrix made up of matrix elements FME using the minimum
 deflection amount as a matrix spacing, and converts the divided pattern
 data into those expressed on the common matrix in units of elementary
 electron optical systems. The processing pertaining to pattern data upon
 exposure using two elementary electron optical systems a and b will be
 described below for the sake of simplicity.
 FIGS. 6A and 6B show patterns Pa and Pb to be exposed by the neighboring
 elementary electron optical systems a and b on a common deflection matrix
 DM. More specifically, each elementary electron optical system irradiates
 an electron beam onto the wafer by turning off its blanking electrode at
 matrix positions denoted by hatched pattern portions.
 For this purpose, the CPU 25 determines first regions FF (solid black
 portions) consisting of the matrix positions corresponding to exposure
 positions of at least one of the elementary electron optical systems a and
 b, and second regions NN (blank portions) consisting of matrix positions
 where neither of the elementary electron optical systems a and b commonly
 perform exposure, as show in FIG. 6C, on the basis of the matrix position
 data to be exposed in units of elementary electron optical systems shown
 in FIGS. 6A and 6B.
 When a plurality of electron beams are located on the first region FF on
 the matrix, exposure is done by deflecting the electron beams by the sub
 deflector 62 in units of minimum deflection amounts (the matrix spacings),
 thus forming all the patterns to be drawn on the wafer by exposure. When a
 plurality of electron beams are located on the second region NN on the
 matrix, they are deflected without settling their positions, thereby
 attaining exposure while eliminating unnecessary deflection of the
 electron beams.
 Subsequently, the CPU 25 determines the matrix positions of matrix elements
 to be exposed on the basis of data pertaining to the regions FF and NN
 shown in FIG. 6C. Also, the CPU 25 determines the ON/OFF patterns of
 blanking electrodes corresponding to the matrix positions to be settled of
 the electron beams in units of elementary electron optical systems on the
 basis of data representing the patterns shown in FIGS. 6A and 6B.
 Consequently, the CPU 25 forms exposure data including, as elements, the
 matrix positions to be exposed by at least one beam, and ON/OFF states of
 blanking electrodes of each elementary electron optical system at the
 matrix positions, as shown in FIG. 7.
 Two examples that pertain to the method of correcting blurring produced by
 the Coulomb effect will be explained below.
 (First Correction Method)
 The CPU 25 executes evaluation shown in FIG. 8 on the basis of the formed
 exposure control data so as to correct blurring produced by the Coulomb
 effect.
 In the evaluation shown in FIG. 8, a distribution coefficient C for each
 subarray, which represents the distribution state of a plurality of
 electron beams irradiated onto the wafer, is calculated in the following
 sequence in units of matrix positions to be settled.
 (Step S101)
 The matrix position (x, y) to be settled is selected.
 (Step S102)
 The numbers N1 to N5 (the numbers of OFF blanking electrodes in subarrays)
 of electron beams that can reach the wafer without being intercepted in
 the subarrays A1 to A5 are checked. More specifically, the number of
 electron beams to be irradiated onto the wafer coming from each subarray,
 as an electron beam group made up of a plurality of electron beams, is
 checked.
 (Step S103)
 A distribution coefficient Ci for each subarray Ai is calculated by:
 ##EQU1##
 where Ni is the number of electron beams to be irradiated onto the wafer by
 the subarray Ai checked in step S102, K is a constant determined by, e.g.,
 the size of the subarray, and Di,j is the distance between the centers of
 subarrays Ai and Aj.
 With the above equation, even when the number of all electron beams to be
 irradiated onto the wafer remains the same, the distribution coefficient
 Ci of the subarray Ai becomes larger as the number of electron beams to be
 irradiated onto the wafer in the subarray Ai is larger. Even when the
 number of electron beams to be irradiated onto the wafer in the subarray
 Ai remains the same, the distribution coefficient Ai of the subarray Ci
 becomes larger if the number of electron beams in another subarray is
 large.
 (Step S104)
 The calculated distribution coefficients Ci in units of subarrays are
 stored as refocus control data.
 (Step S105)
 It is checked if the processing in steps S102 to S104 is complete for all
 the matrix positions (x, y) to be settled. If non-processed matrix
 positions (x, y) to be settled are found, the flow returns to step S101 to
 select the next non-processed matrix position (x, y).
 (Step S106)
 Upon completion of the above processing for all the matrix positions (x, y)
 to be settled, the evaluation shown in FIG. 8 ends, and refocus control
 data including distribution coefficients Ci in units of subarrays
 corresponding to the matrix positions to be settled is stored, as shown in
 FIG. 9.
 In this embodiment, these processing steps are executed by the CPU 25 of
 the electron beam exposure apparatus. Alternatively, the above steps may
 be executed by another processing device, and the obtained exposure
 control data and refocus control data may be transferred to the CPU 25 to
 achieve the above object and to obtain the same effects as above.
 The CPU 25 then instructs the control system 22 to "execute exposure" via
 the interface 24. In response to this instruction, the control system 22
 executes the following steps on the basis of the data on the memory 23
 that stores the exposure control data and refocus control data.
 (Step S201)
 The control system 22 directs the deflection control circuit 17 to deflect
 a plurality of electron beams coming from the elementary electron optical
 system array by the sub deflector 62 of the deflector 6 so as to settle
 their positions, on the basis of the exposure control data transferred
 from the memory 23 in synchronism with internal reference clocks.
 The control system 22 directs the first focal point/astigmatism control
 circuit 15 to control the intermediate image forming positions of the
 elementary electron optical systems, in units of sub arrays, on the basis
 of the refocus control data transferred in the same manner as the exposure
 control data. More specifically, the control system 22 sets, on the basis
 of the distribution coefficients Ci in units of subarrays, the
 intermediate image forming positions of the elementary electron optical
 system of each subarray to be closer to the electron gun 1 side as the
 distribution coefficient Ci is larger. As a result, the imaging position
 of an electron beam on the wafer, which moves to a position farther from
 the reduction electron optical system 4 owing to the Coulomb effect as the
 distribution coefficient Ci is larger, approaches the reduction electron
 optical system 4, thus correcting blurring produced by the Coulomb effect.
 The moving amount (correction amount) of the imaging position of each
 electron beam on the wafer is called a refocus amount. The relationship
 between the refocus amount and distribution coefficient C is obtained in
 advance by numerical simulations or experiments, and the electron optical
 characteristics of the elementary electron optical systems in units of
 subarrays are controlled to obtain desired refocus amounts on the basis of
 the distribution coefficients C.
 Furthermore, the control system 22 directs the blanking control circuit 14
 to turn on/off the blanking electrodes of the elementary electron optical
 systems in correspondence with the pattern to be exposed. At this time,
 the X-Y stage 12 is continuously moving in the X-direction, and the
 deflection control circuit 17 controls the deflection positions of the
 electron beams in consideration of the moving amount of the X-Y stage 12.
 As a result, an electron beam coming from one elementary electron optical
 system scans and exposes an exposure field (EF) on the wafer 5 to have a
 full square as a start point, as shown in FIG. 10A. Also, as shown in FIG.
 10B, the exposure fields (EF) of the plurality of elementary electron
 optical systems in each subarray are set adjacent to each other.
 Consequently, a subarray exposure field (SEF) including a plurality of
 exposure fields (EF) is exposed on the wafer 5. At the same time, a
 subfield made up of subarray exposure fields (SEF) respectively formed by
 the subarrays A1 to A5 is exposed on the wafer 5, as shown in FIG. 11A.
 (Step S202)
 The control system 22 directs the deflection control circuit 17 to deflect
 a plurality of electron beams coming from the elementary electron optical
 system array using the main deflector 61 of the deflector 6, so as to
 expose subfield 2 after subfield 1, as shown in FIG. 11B. At that time,
 the control system 22 directs the second focal point/astigmatism control
 circuit 16 to control the dynamic focus control 7 on the basis of dynamic
 focus correction data obtained in advance, and to control the dynamic
 stigmatic coil 8 on the basis of dynamic stigmatic correction data
 obtained in advance, thereby correcting astigmatism of the reduction
 electron optical system. Then, the control system 22 executes the
 operation in step S201 to expose subfield 2.
 By repeating steps S201 and S202 above, subfields are sequentially exposed
 like subfields 3, 4, . . . , as shown in FIG. 11B, thereby exposing the
 entire surface of the wafer.
 In the above-mentioned correction method, the refocus amount of electron
 beams for each subarray is set by adjusting the electron optical
 characteristics of the elementary electron optical systems of each
 subarray. Alternatively, the average value of the refocus amounts in units
 of subarrays may be calculated, the refocus amount corresponding to the
 calculated average value may be set by the refocus coil 6, and the
 elementary electron optical systems of respective subarrays may set
 refocus amounts as differences obtained by subtracting the average value
 from the refocus amounts to be set.
 In the above-mentioned correction method, every time the sub deflector 62
 deflects a plurality of electron beams coming from the elementary electron
 optical system array to settle their positions, the refocus amounts of
 electron beams in units of subarrays are changed. Alternatively, during
 exposure of one subfield, a constant refocus amount of the electron beams
 for each subarray may be used, and when the subfield to be exposed is
 switched to the next one, the refocus amount of electron beams for each
 subarray may be changed. In this case, the distribution coefficient C in
 units of subarrays can use the average value of the distribution
 coefficients C at the respective matrix positions in the subfield to be
 exposed. In other words, the imaging positions of the electron beams can
 be corrected in units of subarrays on the basis of the evaluation values
 in units of a plurality of subarray in each deflection region (subfield).
 (Second Correction Method)
 The CPU 25 executes evaluation shown in FIG. 16 on the basis of the formed
 exposure control data so as to correct blurring produced by the Coulomb
 effect.
 In the evaluation shown in FIG. 16, the distribution coefficient C
 representing the distribution state of a plurality of electron beams
 irradiated onto the wafer is calculated in the following procedure at each
 matrix position to be settled.
 (Step S301)
 The matrix position (x, y) to be settled is selected.
 (Step S302)
 The position, on the elementary electron optical system, of an elementary
 electron optical system that outputs an electron beam to be irradiated
 onto the wafer at the selected matrix position (x, y) is checked (the
 position, on the wafer, of that electron beam to be irradiated onto the
 wafer may be checked, as a matter of course).
 For example, if n represents the number of electron beams to be irradiated
 onto the wafer, a position Pi =(Xi, Yi) (for i=1 to n, Xi is the
 X-coordinate value on the elementary electron optical system array, and Yi
 is the Y-coordinate value on the elementary electron optical system array)
 of each beam is checked.
 (Step S303)
 The distribution coefficient C is calculated by:
 ##EQU2##
 As can be seen from the above equation, among all the different
 combinations of pairs of electron beams which are irradiated onto the
 wafer without being intercepted, the reciprocal value of the value
 obtained by calculating the square of the spacing between the pair of
 electron beams is calculated, and the sum total of the calculated values
 is the distribution coefficient C. Hence, as the number of electron beams
 irradiated onto the wafer is larger, the distribution coefficient C
 becomes larger. Even when the number of electron beams irradiated onto the
 wafer remains the same, if the electron beams are concentrated on a narrow
 range, the distribution coefficient C also becomes larger.
 (Step S304)
 The calculated distribution coefficient C is stored as refocus control
 data.
 (Step S305)
 It is checked if the processing in steps S302 to S304 is complete for all
 the matrix positions (x, y) to be settled. If non-processed matrix
 positions (x, y) to be settled are found, the flow returns to step S301 to
 select the next non-processed matrix position (x, y).
 (Step S306)
 Upon completion of the above processing for all the matrix positions (x, y)
 to be settled, the evaluation shown in FIG. 16 ends, and refocus control
 data including distribution coefficients C corresponding to the matrix
 positions to be settled is stored, as shown in FIG. 17.
 In this embodiment, these processing steps are executed by the CPU 25 of
 the electron beam exposure apparatus. Alternatively, the above steps may
 be executed by another processing device, and the obtained exposure
 control data and refocus control data may be transferred to the CPU 25 to
 achieve the above objective and to obtain the same effects as above.
 The CPU 25 then instructs the control system 22 to "execute exposure" via
 the interface 24. In response to this instruction, the control system 22
 executes the following steps on the basis of the data on the memory 23
 that stores the exposure control data and refocus control data.
 (Step S401)
 The control system 22 directs the deflection control circuit 17 to deflect
 a plurality of electron beams coming from the elementary electron optical
 system array by the sub deflector 62 of the deflector 6 so as to settle
 their positions, on the basis of the exposure control data transferred
 from the memory 23 in synchronism with internal reference clocks.
 The control system 22 directs the refocus control circuit 19 to control the
 focal point position of the reduction electron optical system 4 on the
 basis of the refocus control data transferred in the same manner as the
 exposure control data. More specifically, the control system 22 sets the
 focal point position of the reduction electron optical system 4 to be
 closer to the reduction electron optical system 4 as the distribution
 coefficient C is larger. As a result, the imaging position of an electron
 beam on the wafer, which moves to a position farther from the reduction
 electron optical system 4 owing to the Coulomb effect as the distribution
 coefficient C is larger, approaches the reduction electron optical system
 4, thus correcting blurring produced by the Coulomb effect. The moving
 amount of the imaging position of each electron beam on the wafer is
 called a refocus amount. The relationship between the refocus amount and
 distribution coefficient C is obtained in advance by numerical simulations
 or experiments, and the currents to be supplied to the refocus coil 9 are
 controlled to obtain desired refocus amounts on the basis of the
 distribution coefficient C.
 Furthermore, the control system 22 directs the blanking control circuit 14
 to turn on/off the blanking electrodes of the elementary electron optical
 systems in correspondence with the pattern to be exposed. At this time,
 the X-Y stage 12 is continuously moving in the X-direction, and the
 deflection control circuit 17 controls the deflection positions of the
 electron beams in consideration of the moving amount of the X-Y stage 12.
 As a result, an electron beam coming from one elementary electron optical
 system scans and exposes an exposure field (EF) on the wafer 5 to have a
 full square as a start point, as shown in FIG. 10A. Also, as shown in FIG.
 10B, the exposure fields (EF) of the plurality of elementary electron
 optical systems in each subarray are set adjacent to each other.
 Consequently, a subarray exposure field (SEF) including a plurality of
 exposure fields (EF) is exposed on the wafer 5. At the same time, a
 subfield made up of subarray exposure fields (SEF) respectively formed by
 the subarrays A1 to A5 is exposed on the wafer 5, as shown in FIG. 11A.
 (Step S402)
 The control system 22 directs the deflection control circuit 17 to deflect
 a plurality of electron beams coming from the elementary electron optical
 system array using the main deflector 61 of the deflector 6, so as to
 expose subfield 2 after subfield 1, as shown in FIG. 11B. At that time,
 the control system 22 directs the second focal point/astigmatism control
 circuit 16 to control the dynamic focus control 7 on the basis of dynamic
 focus correction data obtained in advance, and to control the dynamic
 stigmatic coil 8 on the basis of dynamic stigmatic correction data
 obtained in advance, thereby correcting astigmatism of the reduction
 electron optical system. Then, the control system 22 executes the
 operation in step S401 to expose subfield 2.
 By repeating steps S401 and S402 above, subfields are sequentially exposed
 like subfields 3, 4, . . . , as shown in FIG. 11B, thereby exposing the
 entire surface of the wafer.
 In the above correction method, every time the sub deflector 62 deflects a
 plurality of electron beams coming from the elementary electron optical
 system array to settle their positions, the refocus amount of each
 electron beam (the focal point position adjustment amount of the reduction
 electron optical system 4 by the refocus coil 9) is changed.
 Alternatively, during exposure of one subfield, a constant refocus amount
 of the electron beams for each subarray may be used, and when the subfield
 to be exposed is switched to the next one, the refocus amount of electron
 beam may be changed. In this case, the control system 22 can use, as the
 distribution coefficient C, the average value of the distribution
 coefficients C at the respective matrix positions in the subfield to be
 exposed. In other words, the focal point position of the reduction
 electron optical system 4 is adjusted on the basis of the evaluation
 values of the respective matrix positions in each deflection region
 (subfield).
 (Embodiment of Device Manufacturing Method)
 An embodiment of a device manufacturing method using the above-mentioned
 electron beam exposure apparatus will be explained below.
 FIG. 12 shows the flow in the manufacture of a microdevice (semiconductor
 chips such as ICs, LSIs, liquid crystal devices, CCDs, thin film magnetic
 heads, micromachines, and the like). In step 1 (circuit design), the
 circuit design of a semiconductor device is done. In step 2 (generate
 exposure control data), the exposure control data of the exposure
 apparatus is generated based on the designed circuit pattern. Separately,
 in step 3 (manufacture wafer), a wafer is manufactured using materials
 such as silicon and the like. Step 4 (wafer process) is called a
 pre-process, and an actual circuit is formed by lithography on the wafer
 using the exposure apparatus input with the prepared exposure control
 data, and the manufactured wafer. The next step 5 (assembly) is called a
 post-process, in which semiconductor chips are assembled using the wafer
 obtained in step 4, and includes an assembly process (dicing, bonding), a
 packaging process (encapsulating chips), and the like. In step 6
 (inspection), inspections such as operation tests, durability tests, and
 the like of semiconductor devices assembled in step 5 are conducted.
 Semiconductor devices are completed via these processes, and are delivered
 (step 7).
 FIG. 13 shows the detailed flow of the wafer process. In step 11
 (oxidation), the surface of the wafer is allowed to oxidize. In step 12
 (CVD), an insulating film is formed on the wafer surface. In step 13
 (electrode formation), electrodes are formed by deposition on the wafer.
 In step 14 (ion implantation), ions are implanted into the wafer. In step
 15 (resist process), a photosensitive agent is applied on the wafer. In
 step 16 (exposure), the circuit pattern on the mask is printed on the
 wafer by exposure using the above-mentioned exposure apparatus. In step 17
 (development), the exposed wafer is developed. In step 18 (etching), a
 portion other than the developed resist image is removed by etching. In
 step 19 (remove resist), the resist film which has become unnecessary
 after the etching is removed. By repetitively executing these steps,
 multiple circuit patterns are formed on the wafer.
 According to the manufacturing method of this embodiment, a highly
 integrated semiconductor device which is not easy to manufacture by the
 conventional method can be manufactured at low cost.
 According to the present invention, a pattern can be drawn at high
 resolution by correcting blurring of an electron beam image produced by
 the Coulomb effect in accordance with the pattern to be exposed.
 The present invention is not limited to the above embodiments and various
 changes and modifications can be made within the spirit and scope of the
 present invention. Therefore, to apprise the public of the scope of the
 present invention the following claims are made.