Patent Number: 063234998
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to an electron beam exposure apparatus and method, and a device manufacturing method and, more particularly, to an electron beam exposure apparatus and method in which exposure is performed by making a source emit an electron beam to form an image by the electron beam, and reducing and projecting the image on a target exposure surface by a reduction electron optical system, a stencil mask type electron beam exposure apparatus, and a device manufacturing method to which the above apparatus or method is applied. Examples of electron beam exposure apparatuses are apparatuses of a point beam type which uses a spot-like beam, a variable rectangular beam type which uses a beam variable in its size and having a rectangular section, and a stencil mask type which uses a stencil to form a beam having a desired sectional shape. The point beam type electron beam exposure apparatus is exclusively used for research and development purposes because of low throughput. The variable rectangular beam type electron beam exposure apparatus has a throughput higher than that of the point beam type apparatus by one to two orders, though the problem of throughput is still serious when forming an exposure pattern in which about 0.1 .mu.m fine patterns are highly integrated. The stencil mask type electron beam exposure apparatus uses a stencil mask having a portion corresponding to a variable rectangular aperture in which a plurality of repeated-pattern-through-holes are formed. The stencil mask type electron beam exposure apparatus can advantageously form repeated patterns by exposure, and its throughput is higher than that of the variable rectangular type electron beam exposure apparatus. FIG. 2 shows the arrangement of an electron beam exposure apparatus having a stencil mask. An electron beam from an electron gun 501 is irradiated on a first aperture 502 for defining the electron beam irradiation area of the stencil mask. The illumination electron beam defined by the first aperture irradiates the stencil mask on a second aperture 504 through a projection electron lens 503 so that the electron beam passing through repeated-pattern-through-holes which are formed in the stencil mask is reduced and projected on a wafer 506 by a reduction electron optical system 505. The images of the repeated-pattern-through-holes are moved on the wafer by a deflector 507 to sequentially expose the wafer. The stencil mask type electron beam exposure apparatus can form repeated patterns by a single exposure operation, so the exposure speed can be increased. However, although the stencil mask type electron beam exposure apparatus has a plurality of pattern through-holes, as shown in FIG. 3, the patterns must be formed in advance as the stencil mask in accordance with the exposure pattern. Because of the space charge effect and the aberrations of the reduction electron optical system, the exposure area which can be exposed at once is limited. If a semiconductor circuit needs so many transfer patterns that they cannot be formed in one stencil mask, a plurality of stencil masks must be prepared and used one by one. Time for exchanging the mask is required, resulting in a large decrease in throughput. When the stencil mask has patterns with different sizes, or when the pattern is a combination of patterns with different sizes, the blur of the exposure pattern caused by the space charge effect changes depending on the size of the pattern. Since the refocus amount changes depending on the size of the pattern accordingly, the blur cannot be corrected by refocusing. Therefore, such a pattern cannot be used as a stencil mask pattern. An apparatus for solving this problem is a multi-electron beam exposure apparatus which irradiates a plurality of electron beams on the sample surface along designed coordinates, deflects the plurality of electron beams along the designed coordinates to scan the sample surface, and at the same time, independently turns on/off the plurality of electron beams in correspondence with the pattern to be drawn, thereby drawing the pattern. The multi-electron beam exposure apparatus can draw an arbitrary pattern without using any stencil mask, so the throughput can be increased. FIG. 38A shows the arrangement of the multi-electron beam exposure apparatus. Reference numerals 501a, 501b, and 501c denote electron guns capable of independently turning on/off electron beams; 502, a reduction electron optical system for reducing and projecting the plurality of electron beams from the electron guns 501a, 501b, and 501c on a wafer 503; and 504, a deflector for deflecting the plurality of electron beams reduced and projected on the wafer 503. The plurality of electron beams from the electron guns 501a, 501b, and 501c are deflected by the same amount by the deflector 504. With reference to the beam reference position, each electron beam sequentially sets its position on the wafer and moves in accordance with an array defined by the deflector 504. The electron beams expose different exposure areas in exposure patterns to be formed. FIGS. 38B to 38D show a state in which the electron beams from the electron guns 501a, 501b, and 501c expose the corresponding exposure areas in exposure patterns to be formed in accordance with the same array. While setting and shifting the positions on the array in the order of (1,1), (1,2), . . . , (1,16), (2,1), (2,2), . . . , (2,16), (3,1), each electron beam is turned on at a position where an exposure pattern (P1, P2, P3) to be formed is present to expose the corresponding exposure area in the exposure pattern (P1, P2, P3) to be formed (i.e., a so-called raster scan is performed). However, in the multi-electron beam exposure apparatus using a raster scan, when the size of the exposure pattern to be formed is small, each electron beam must be turned on at a position defined by further finely dividing the exposure region of the electron beam (the array interval of the array defined by the deflector 504 decreases). As a result, with the same exposure area, the number of times of setting the position of the electron beam and exposing the area increases, resulting in a large decrease in throughput. FIG. 43 shows the main part of the multi-electron beam exposure apparatus. Reference numerals 501a, 501b, and 501c denote electron guns capable of independently turning on/off electron beams; 502, a reduction electron optical system for reducing and projecting the plurality of electron beams from the electron guns 501a, 501b, and 501c on a wafer 503; 504, a deflector for scanning the plurality of electron beams reduced and projected on the wafer 503; 505, a dynamic focus coil for correcting the focus position of the electron beam in accordance with any deflection errors generated in the electron beam passing through the reduction electron optical system 502 when the deflector 504 is actuated; and 506, a dynamic stigmatic coil for correcting the astigmatism of the electron beam in accordance with the deflection errors. With the above arrangement, the plurality of electron beams are scanned on the wafer to expose the wafer in which the exposure areas of the electron beams are adjacent to each other. However, the deflection errors generated in the plurality of electron beams passing through the reduction electron optical system 502 when the deflector 504 is actuated are different from each other. For this reason, even when the focus position and astigmatism of each electron beam are corrected by a dynamic focus coil and a dynamic stigmatic coil, optimum correction for each electron beam can hardly be performed. SUMMARY OF THE INVENTION It is the first object of the present invention to provide an electron beam exposure apparatus and method which minimize the influence of the space charge effect and aberrations of the reduction electron optical system and increase the area which can be exposed at once, thereby increasing the throughput. According to the present invention, the foregoing object is attained by providing an electron beam exposure apparatus having a source for emitting electron beams and a reduction electron optical system for reducing and projecting, on a target exposure surface, an image formed with the electron beam emitted from the source, comprising: a correction electron optical system arranged between the source and the reduction electron optical system to form a plurality of intermediate images of the source for correcting an aberration generated by the reduction electron optical system, the intermediate images being reduced and projected on the target exposure surface by the reduction electron optical system. According to another aspect of the present invention, the foregoing object is attained by providing an electron beam exposure method in which exposure is performed by making a source emit an electron beam to form an image, and reducing and projecting the image on a target exposure surface by a reduction electron optical system, comprising: the intermediate image formation step of forming a plurality of intermediate images of the source for correcting an aberration generated by the reduction electron optical system by a correction electron optical system arranged between the source and the reduction electron optical system. According to still another aspect of the present invention, the foregoing object is attained by providing an electron beam exposure method in which exposure is performed by independently shielding a plurality of electron beams in accordance with an exposure pattern to be formed on a target exposure surface while scanning the plurality of electron beams on the target exposure surface, comprising: the exposure procedure setting step of setting an exposure procedure in which the plurality of electron beams are scanned while skipping a portion where all the plurality of electron beams are shielded; and the control step of controlling exposure in accordance with the set exposure procedure. It is the second object of the present invention to provide an electron beam exposure apparatus which relaxes the limitation in patterns usable in a stencil mask. According to the present invention, the foregoing object is attained by providing an electron beam exposure apparatus having a source for emitting an electron beam and a reduction electron optical system for bringing the electron beam into a focus on a target exposure surface, comprising: electron density distribution adjustment means for adjusting electron density distribution of the electron beam when the electron beam passes through a pupil plane of the reduction electron optical system, in which density distribution of an electron density at a peripheral portion on the pupil plane becomes higher than that at a central portion. It is the third object of the present invention to provide an electron beam exposure apparatus and method which suppress a decrease in throughput for a fine pattern. According to the present invention, the foregoing object is attained by providing an electron beam exposure apparatus which has a deflector for deflecting a plurality of electron beams and exposes a target exposure surface by deflecting the plurality of electron beams, and simultaneously, independently controlling irradiation of the plurality of electron beams, comprising: control means for controlling an exposure operation such that a unit of deflection by the deflector is set to be small in a first area where a contour area of a pattern is formed by exposure with at least one of the plurality of electron beams, and the unit of deflection by the deflector is set to be large in a second area different from the first area, where an inner area of the pattern is formed by exposure with at least one of the plurality of electron beams. According to another aspect of the present invention, the foregoing object is attained by providing an electron beam exposure method in which a target exposure surface is exposed by deflecting a plurality of electron beams by a common deflector, and simultaneously, independently controlling irradiation of the plurality of electron beams, comprising: the control step of controlling an exposure operation to set a unit of deflection by the deflector to be small in a first area where a contour area of a pattern is formed by exposure with at least one of the plurality of electron beams, and the unit of deflection by the deflector is set to be large in a second area different from the first area, where an inner area of the pattern is formed by exposure with at least one of the plurality of electron beams. According to still another aspect of the present invention, the foregoing object is attained by providing an electron beam exposure method in which a target exposure surface is exposed by deflecting a plurality of electron beams by a common deflector, and simultaneously, independently controlling irradiation of the plurality of electron beams, comprising: the area determination step of determining, on the basis of an exposure pattern to be formed on the target exposure surface, a first area where a contour area of the pattern is formed by exposure with at least one of the plurality of electron beams and a second area different from the first area, where an inner area of the pattern is formed by exposure with at least one of the plurality of electron beams; and the control step of controlling an exposure operation to set a unit of deflection by the deflector to be small in the first area, and the unit of deflection by the deflector is set to be large in the second area. It is the fourth object of the present invention to provide an electron beam exposure apparatus and method which can independently correct aberrations generated in a plurality of electron beams. According to the present invention, the foregoing object is attained by providing an electron beam exposure apparatus having a source for emitting an electron beam, and a reduction electron optical system for reducing and projecting, on a target exposure surface, an image formed with the electron beam emitted from the source, comprising: an element electron optical system array constituted by arranging a plurality of subarrays each including at least one element electron optical system which forms an intermediate image of the source between the source and the reduction electron optical system with the electron beam emitted from the source; deflection means for deflecting an electron beam from the element electron optical system array to scan the target exposure surface; and correction means for correcting in units of subarrays a deflection error generated when the electron beam from the element electron optical system array is deflected by the deflection means. According to another aspect of the present invention, the foregoing object is attained by providing an electron beam exposure method in which exposure is performed by making a source emit an electron beam to form an image, and reducing and projecting the image on a target exposure surface by a reduction electron optical system, comprising: the correction step of correcting, in units of subarrays, a deflection error generated when an electron beam from an element electron optical system array constituted by arranging the plurality of subarrays each including at least one element electron optical system which forms an intermediate image between the source is deflected to scan the target exposure surface. It is the fifth object of the present invention to provide a method of manufacturing a device by using the above electron beam exposure apparatus and method. 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.