Electron beam exposure apparatus

Abstract: An electron beam exposure apparatus comprises an electron beam source (20), a holder (31) for supporting a semiconductor substrate (30), a beam patterning part (32) for patterning the electron beam, a beam focusing system (25 - 28) for focusing the patterned electron beam on the semiconductor substrate, and a beam deflector system (29) for deflecting the focused electron beam. The beam deflector comprises at least first, second and third coil assemblies (291 - 293) connected in series for producing first through third magnetic fields respectively such that the first through third magnetic fields (Bx1, By1) extend generally perpendicularly to the beam path of the electron beam at respective vertical levels on the beam path. The beam deflection means further comprises fourth and fifth coil assemblies (5a, 6a; 9a, 10a) for producing fourth and fifth magnetic fields respectively wherein the fourth coil assembly is disposed such that the fourth magnetic field (Bx2′) extends generally parallel to the second magnetic field (Bx2) for correcting the second magnetic field and the fifth coil means is disposed such that the fifth magnetic field (Bx3′) extends generally parallel to the third magnetic field (Bx3) for correcting the third magnetic field. Further, the electron beam exposing apparatus includes a driving system (41 - 45) for energizing the beam deflector by driving the fourth and fifth coil assemblies independently from the first through third coils, so that the electron beam is deflected by a desired deflection angle and hits the semiconductor substrate substantially vertically at a desired location without the coma aberration.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to fabrication of semiconductor devices and in particular to an electron beam exposure apparatus used in the fabrication of semiconductor devices. Electron beam exposure apparatuses are used in the fabrication of very large scale integrated circuits (VLSI) having an extremely large integration density because of the capability of writing semiconductor patterns with submicron- or even nanometric resolution. As the electron beam exposure apparatus in general has a relatively small throughput, efforts are made to increase the speed of exposure such that the efficiency of the production of the integrated circuit is improved. FIG.1 shows a typical prior art electron beam exposure apparatus. Referring to FIG.1, the electron beam exposure apparatus includes an electron gun 20 formed from a cathode 21, a grid 22 and an anode 23 for producing an electron beam B. The electron beam B thus produced is passed through an electron lens system including a conversion lens 25, demagnification lenses 26 and 27 and an objective lens 28 after a suitable shaping and are focused on a wafer 30 supported on a movable stage 31. Further, the electron beam B is moved over the wafer 30 by a deflector 29 to be described later. The wafer 30 is applied with an electron beam resist and in response to the irradiation of the electron beam, the part of the electron beam resist hit by the electron beam experiences a chemical reaction. Thereby, the wafer 30 is exposed according to a desired semiconductor pattern. The semiconductor pattern may be written on the wafer 30 by moving the sharply converged electron beam over the wafer 30 or by passing the electron beam B through a stencil mask to shape the electron beam according to a desired semiconductor pattern. For this purpose, the stencil mask is formed with the semiconductor pattern to be transferred on the wafer by the electron beam. Alternatively, the electron beam B may be passed through a blanking aperture array which selectively passes the electron beam B as an electron beam B1 under a control of an external control circuit to form an array of dots on the wafer 30 by the electron beam B1. In FIG.1, the blanking aperture array is shown schematically by a reference numeral 32. When passing through the blanking aperture array 32, a part of the electron beam B is deflected away as shown by a beam B2 and is thereby prevented from reaching the wafer 30. For this purpose, the blanking aperture array 32 has a number of deflection electrodes arranged in a row and column formation. Each of these electrodes are energized selectively under control of an external circuit. The foregoing deflector 29 may be an electromagnetic deflector using deflection coils and is provided below the lens 27. FIG.2 shows the deflector 29. As shown in FIG.2, the deflector 29 includes a first coil assembly 291 made of a pair of coils 1 and 2 connected in series for creating a magnetic field Bx1 extending from the coil 1 to the coil 2 in a plane generally perpendicular to the electron beam B, and another pair of coils 3 and 4 also connected in series for creating another magnetic field By1 in a direction perpendicular to the magnetic field Bx1 such that the magnetic field By1 extends from the coil 3 to the coil 4 in a plane generally perpendicular to the electron beam B. Similarly, the deflector 29 includes a second coil assembly 292 made of a pair of coils 5 and 6 connected in series for creating a magnetic field Bx2 extending from the coil 5 to the coil 6 in a plane generally perpendicular to the electron beam B, and another pair of coils 7 and 8 also connected in series for creating another magnetic field By2 such that the magnetic field By2 extends from the coil 7 to the coil 8 in a plane generally perpendicular to the electron beam B and in a direction perpendicular to the magnetic field Bx2. It should be noted that the second coil assembly 292 is disposed closer to the wafer 30 with respect to the first coil assembly 291. Further, the deflector 29 includes a third coil assembly 293 made of a pair of coils 9 and 10 for creating a magnetic field Bx3 extending from the coil 9 to the coil 10 in a plane generally perpendicular to the electron beam B, and another pair of coils 11 and 12 for creating another magnetic field By3 in a direction perpendicular to the magnetic field Bx3 such that the magnetic field By3 extends from the coil 11 to the coil 12 in a plane generally perpendicular to the electron beam B. The third coil assembly 293 is disposed further closer to the wafer 30 with respect to the second coil assembly 292. In response to the magnetic fields Bx1 - Bx3, the electron beam B is moved over the wafer 30 in the X-direction while in response to the magnetic fields By1 - By3, the electron beam B is moved over the wafer 30 in the Y-direction. Thus, by controlling the magnetic fields Bx1 - Bx3 and the magnetic fields By1 - By3 independently, the movement of the electron beam B on the wafer 30 is controlled in mutually perpendicular directions. Each of the magnetic fields created by the coils 1 - 11 shown in FIG.2 are substantially in a plane defined by X- and Y-axes of the coordinate system shown in FIG.2 wherein the coordinate system has its Z-axis chosen so as to coincide substantially with the general direction of the electron beam B exiting from the electron gun 20 and reaching the wafer 30 (FIG.1). In operation, the coils 1 and 2 are energized simultaneously and independently from other coils, the coils 3 and 4 are energized simultaneously and independently from other coils, the coils 5 and 6 are energized simultaneously and independently from other coils, the coils 7 and 8 are energized simultaneously and independently from other coils, the coils 9 and 10 are energized simultaneously and independently from other coils, and the coils 11 and 12 are energized simultaneously and independently from other coils. As a results the electron beam B is deflected in the X-Y plane independently in the X-direction and Y-direction. FIG.3 shows a drive circuit of the deflection system 29. In FIG.3, only the connection including the coils 1 and 2, the coils 5 and 6 and the coils 9 and 10 for deflecting the electron beam in the X-direction is shown. As shown in FIG.3, the coils 1, 2, 5, 6, 9 and 10 are connected in series and driven by a drive amplifier 41 which produces a drive current of about 2 - 3 amperes and about 10 volts in response to a semiconductor pattern data supplied to a deflection controller 43 which produces a digital deflection control data. The digital deflection control data is converted to an analog deflection control signal by a digital-to-analog converter 42 and in response thereto, the drive amplifier produces the drive current which is caused to flow through the coils 1, 2, 5, 6, 9 and 10. The same driving circuit is provided also for the coils 3 and 4, 7 and 8, and 11 and 12. Each of the coils shown in FIG.2 has a number of turns of about 5 - 20 and creates the foregoing magnetic field which act to deflect the electron beam B to a desired location on the wafer 30. In order to achieve the desired deflection with a satisfactory precision, the coils 1 - 11 are disposed with an exact geometrical relationship with each other and the drive current flowing through the coils are optimized. In the electron beam exposure apparatus in general, it is necessary to a) deflect the electron beam by a desired angle, b) deflect the deflected electron beam again so that the electron beam hits substantially vertically the substrate 30, and to c) minimize the coma aberration. With respect to the foregoing point a), it is desirable and essential that a large deflection angle is obtained for an efficient exposure of the semiconductor pattern. With respect to the foregoing point b), it should be noted that there occurs a lateral deviation in the beam spot on the top surface of the wafer if the electron beam does not hit the wafer vertically. Referring to FIG.4 showing an example of exposure of the wafer 30 by a deflected electron beam B, it will be understood that there occurs a lateral deviation of the electron beam B of ΔX in response to the variation ΔH which is a change in the level of the wafer surface with respect to the electron beam B when the electron beam B hits the wafer 30 obliquely. As shown therein, there holds a relation ΔX = ΔH.tan α where α represents the deviation of incidence angle from the vertical. When the angle α is zero and the beam hits the wafer 30 vertically, there occurs no deviation of the beam spot even when the level or height of the wafer 30 is changed because the angle α is zero. In the conventional electron beam exposure apparatus used currently, however, the parameter tan α usually takes a value of about 1/20. In this case, the variation of level of the wafer surface 30 of about 10 µm, which is quite common, induces a lateral variation of the electron beam B of about 0.5 µm. As it is required in the electron beam lithography that the semiconductor pattern can be written on the wafer 30 with the line width of less than about 0.5 µm preferably less than 0.01 µm, such a displacement of the electron beam on the wafer 30 is certainly not tolerable. The coma aberration in the foregoing point c) represents a deformation of the beam spot which cannot be compensated, unlike other aberrations, by the correction coils. In other words, this coma aberration has to be minimized by setting the relation between the coils forming the deflector 29 optimum on the basis of simulation. In order to satisfy the foregoing points a) - c), the conventional electron beam exposure apparatus of FIG.1 uses three coil assemblies 291 - 293, and the geometrical relationship as well as the drive current flowing therethrough are optimized to achieve the desired result with respect to the foregoing points a) - c). More specifically, the coils 1 - 4, 5 - 8 and 9 - 12 forming the coil assemblies 291 - 293 are adjusted with respect to their vertical positions measured along the path of the beam B as well as with respect to the direction of the magnetic field Bx1 - Bx3, By1 - By3 particularly the plane perpendicular to the path of the beam B. The geometrical relationship between the coils 1 - 11 as well as the construction of each of these coils are determined previously to the assembling of the electron beam exposure apparatus by conducting a simulation, and the coils are manufactured and mounted according to the geometrical relationship determined by the simulation as accurately as possible so that an ideal result is achieved with respect to the foregoing points a) - c). For example, the simulation indicates that a coma aberration of about 0.005 µm can be achieved in the ideal case. In the actual electron beam exposure apparatus, however, such an ideal state is not achieved. In addition to the commonly occuring variation of the level ΔH of the wafer surface of about 10 µm or more, there arises a problem of error in the mechanical setting of the coils forming the electromagnetic deflector 29. Further, there is an inevitable deviation in the number of turns of the coils forming the electromagnetic deflector since the optimized number of turns of the coils is usually a non-integral number while the actual number of turns has to be an integer. Because of the foregoing reasons one has to adjust the geometrical relationship by a trial and error process involving writing a test pattern repeatedly on the wafer 30. Such a trial and error process includes a process of breaking the vacuum and adjusting the position of the coils within the apparatus manually. Thus, the adjustment of the electron beam exposure apparatus is complex and needs considerable time. Although the optimization of the deflection of the electron beam may be achieved by changing the drive current independently by using independent driving systems for each of the coils 1 - 12, such an approach needs a number of large and bulky amplifiers capable of providing a drive current of several amperes. The power needed to drive the electromagnetic deflector likewise increases and the cost of the driving circuit increases steeply. Because of the foregoing reasons, the conventional electron beam exposure system had the problems that the electron beam could not be deflected accurately, vertical incidence of the electron beam to the wafer was not achieved, and a coma aberration of about 1.0 µm remained. Journal of Vacuum Science & Technology / Section B 6 (1988) Jan-Febr, No. 1, pages 204 to 208, discloses an electron beam exposure system in accordance with the preamble of claim 1. Accordingly, it is a general object of the present invention to provide an electron beam exposure apparatus wherein the foregoing problems are eliminated and wherein the electron beam is controlled accurately by simple means. It is particularly desirable to provide an electron beam exposure apparatus wherein the electron beam is deflected by an exactly controlled deflection angle, is controlled to be incident to a semiconductor wafer substantially vertically, and has a minimized or zero coma aberration. The invention proposes an electron beam exposure apparatus having an electromagnetic deflector, the electromagnetic deflector including primary deflection means for creating a primary magnetic field for deflecting an electron beam such that the electron beam hits a wafer as a desired position determined by a deflection control data, wherein there is provided secondary deflection means for creating a secondary magnetic field. According to the present invention, the electron beam is controlled exactly in such a way that the electron beam is deflected with an exactly controlled deflection angle, incident to the wafer vertically and is substantially free from coma aberration, by using the secondary or auxiliary deflection means in combination with a small power driving system for driving the secondary deflection means. According to the invention there is provided an electron beam exposure system according to claim 1. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which:- Fig. 1 is a diagram showing schematically the construction of a conventional electron beam exposure apparatus; Fig. 2 is a schematic perspective view showing the construction of the electromagnetic deflector used in the apparatus of Fig. 1; Fig. 3 is a block diagram showing the construction of a driving circuit for driving the electromagnetic deflector of FIG.2; FIG.4 is a diagram schematically showing the deflection of the electron beam and the deviation of the beam spot occuring in response to the deflection; FIG.5 is a diagram showing the principle of the present invention; FIG.6A is a perspective view showing a construction of the electromagnetic deflector according to a first embodiment of the present invention; FIG.6B is a plan view showing the electromagnetic deflector of FIG.6A; FIG.7 is a block diagram showing a driving circuit of the electromagnetic deflector of FIG.6; FIG.8 is a perspective view showing the electromagnetic deflector according to a second embodiment ot the present invention; FIG.9 is a block diagram showing a driving circuit of the electromagnetic deflector of FIG.8; and FIG.10 is a block diagram showing another driving circuit of the electromagnetic deflector of FIG.8. DETAILED DESCRIPTION FIG.5 shows the principle of the present invention. In the description hereinafter, it is assumed that the electron beam exposure apparatus has the general construction shown in FIG.1 except for the details of the electromagnetic deflector 29. Referring to FIG.5, this drawing shows the positional vector of the electron beam B focused on the wafer 30 after the deflection by the deflector 29. In FIG.5, the vector Pr designates the displacement of the beam spot caused by the first coil assembly 291 including the coils 1 - 4, the vector Por designates the displacement of the beam spot caused by the second coil assembly 292, and the vector Mor designates the displacement of the beam spot caused by the third coil assembly 293. In FIG.5, it should be noted that all the vectors Pr, Por and Mor are on an X-Y plane coincident to the top surface of the wafer 30 and the origin of FIG.5 coincides to the position which is hit by the undeflected electron beam B. In FIG.4, when it is desired to locate the beam spot of the electron beam B at a position represented by a vector Sum while satisfying the conditions wherein a large deflection angle is achieved, the vertical incidence of the electron beam to the wafer is realized and the coma aberration is eliminated, it is apparent that there needs some correction in the magnetic fields created by the coils 1 - 12. Note that the sum of the vectors Pr, Por and Mor does not give the vector Sum. In the present invention, additional, auxiliary coils are provided for creating additional, auxiliary magnetic fields so that the electron beam B is deflected additionally by a vector Ao and a vector Am such that the vector Por is changed to a vector Po and the vector Mor is changed to a vector Ma. It should be noted that the vectors Pr, Po and Ma are determined by the simulation so as to optimize the deflection of the beam with respect to the position of the beam spot on the wafer, the angle of incidence to the wafer and with respect to the minimized coma aberration. Thereby, the electron beam is deflected to the position defined by the vector Sum as a result of the sum of the vectors Pr, Po and Ma. When the vectors Por and Mor are defined generally in coincidence with the vectors Po and Ma, the deflection of the beam causing the displacement Ao and Am can be relatively small and thus, the additional coils and the driving system thereof may be designed compact. FIGS.6A and 6B show a first embodiment which realizes the concept of FIG.5. In the drawing, the parts constructed identically to the parts described with reference to the preceding drawings are given identical reference numerals and the description thereof will be omitted. Referring to FIG.6A, there are provided additional coils 5a and 6a respectively on the coils 5 and 6, additional coils 7a and 8a respectively on the coils 7 and 8, additional coils 9a and 10a respectively on the coils 9 and 10, and additional coils 11a and 12a respectively on the coils 11 and 12. Similarly to the case of the prior art electron beam exposure apparatus, the coils 1 and 2 are connected in series, the coils 3 and 4 are connected in series, the coils 5 and 6 are connected in series, the coils 7 and 8 are connected in series, the coils 9 and 10 are connected in series, and the coils 11 and 12 are connected in series. Further, the coils 1, 2, 5, 6, 9 and 10 are connected in series as shown in FIG.6A and the coils 3, 4, 7, 8, 11 and 12 are connected in series similarly although the series connection of the coils 3, 4, 7, 8, 11 and 12 is omitted from illustration for avoiding complexity of the drawings. Similarly to the conventional apparatus, the coils 1 - 4 create the magnetic field Bx1 and By1 which cause the displacement of the beam B which is now represented by the vector Por, and the coils 5 - 8 create the magnetic field Bx2 and By2 which cause the displacement of the beam B represented by the vector Mor shown in FIG.5. In the present embodiment, additional coils 5a - 8a are provided respectively adjacent to the coils 5 - 8 in generally the central part thereof for creating additional, auxiliary magnetic fields Bx2′ and By2′ as shown in FIG.6A. The auxiliary coils 5a - 8a are provided such that the direction of the auxiliary magnetic field Bx2′ substantially coincides to the direction of the magnetic field Bx2 created by the coils 5 and 6 and such that the direction of the auxiliary magnetic field By2′ substantially coincides the direction of the magnetic field By created by the coils 7 and 8. In one example, the auxiliary coils 5a - 8a may be provided such that the center of the magnetic field Bx2′ coincides substantially with the center of the magnetic field Bx2 and the center of the magnetic field By2′ coincides substantially with the center of the magnetic field By2. However, this requirement is not essential and the coils 5a - 8a may be offset upwards or downwards or to the left or to the right with respect to the coils 5 - 8. These magnetic fields Bx2′ and By2′ eventually cause the displacement of the electron beam B represented by the vector Ao. Similarly, additional coils 9a - 12a are provided respectively adjacent to the coils 9 - 12 for creating additional, auxiliary magnetic fields Bx3′ and By3′ shown in FIG.6A. Similarly to the case of the coils 5a - 8a, the coils 9a - 12a are provided such that the direction of the magnetic field Bx3′ coincides with the direction of the magnetic field Bx3 and the direction of the magnetic field By3′ coincides with the direction of the magnetic field By3. The coils 9a - 12a may be provided such that the center of the magnetic field Bx3′ coincides with the center of the magnetic field Bx3 and the center of the magnetic field By3′ coincides with the center of the magnetic field By3 similarly to the case of the coils 5a - 8a. However, this condition is not essential and the coils 9a - 12a may be offset upwards or downwards or to the right or to the left with respect to the center of the coils 9 - 12. As the setup of the coils 1 - 12 is already made at the time of assembling the electron beam exposure apparatus so that approximately the ideal deflection of the electron beam B is obtained, the magnetic fields Bx1′ - Bx3′ and the magnetic fields By1′ - By3′ may have a small strength and because of this, it is sufficient that each of the coils 5a - 12a has several turns or less. FIG.6B shows the arrangement of the coils shown in FIG.6A including the additional coils 5a - 12a in a plan view. As can be seen from FIG.6B, the coils are arranged concentrically about the electron beam B passing vertically to the plane of FIG.6B, wherein the additional coil 5a and 6a are provided slightly offset to the radially outward direction with respect to the coils 5 and 6 respectively, the coils 7a and 8a are provided slightly offset to the radially outward direction with respect to the coils 7 and 8 respectively, the coils 9a and 10a are provided slightly offset to the radially outward direction with respect to the coils 9 and 10 respectively, and the coils 11a and 12a are provided slightly offset to the radially outward direction with respect to the coils 11 and 12. FIG.7 shows an example of the driving circuit used in combination with the electromagnetic deflector 29 shown in FIG.6A. In FIG.7, the parts already described with reference to preceding drawings are given identical reference numerals and the description thereof will be omitted. Referring to FIG.7, the semiconductor pattern data is supplied to the deflection controller 43 which produces the deflection control data in the X-direction and Y-direction similarly to the foregoing conventional apparatus, and these deflection control data are converted to the deflection control signals by the digital-to-analog converter 42. In the construction of the driving circuit of FIG.6, the deflection control signal produced by the digital-to-analog converter 42 for deflecting the electron beam B in the X-direction is supplied on the one hand to the amplifier 41 similarly to the conventional apparatus and on the other hand to an amplifier 44 which drives the coils 5a and 6a and further to an amplifier 45 which drives the coils 9a and 10a. As already described, the coils 5a and 6a are connected in series and produce the additional magnetic fields Bx2′ and By2′ respectively. As the required magnitude of the magnetic fields Bx2′ and By2′ is small, the drive current flowing through the coils 5a and 6a may have the magnitude of a few hundred milliamperes (200 - 300 mA) and in correspondence to this, the driving power of the amplifier 44 may be small. Similarly, the amplifier 45 connected to the coils 9a and 10a may have a small driving power capable of providing only a few hundred milliamperes (200 - 300 mA) in correspondence to the relatively small magnitude of the magnetic fields Bx3′ and By3′. In a typical example, the voltage of the deflection control signal is chosen to be about 10 volts. An identical circuit construction is provided also for the deflection of the electron beam B in the Y-direction. In the driving circuit for this Y-deflection system, a deflection controller 43′ is provided in correspondence to the controller 43, a digital-to-analog converter 42′ is provided in correspondence to the digital-to-analog converter 42, and amplifiers 41′, 44′ and 45′ are provided respectively in correspondence to the amplifiers 41, 44 and 45. As the construction and operation of this Y-deflection system is identical to the foregoing X-deflection system, further description of the Y-deflection system will be omitted. In the present invention, the coarse adjustment for achieving the desired deflection, desired vertical incidence and the minimized coma aberration, is achieved similarly to the conventional electron beam exposure apparatus by driving the first through third coil assemblies 291 - 293 by flowing a drive current having a magnitude determined by the simulation. Further, the problem of deviation of the deflection angle from the desired deflection angle, the problem of deviation of the electron beam from the vertical incidence to the wafer, and the problem of not entirely minimized coma aberration are successfully eliminated by providing the auxiliary coils 5a - 12a. For example, the parameter tan α of FIG.4 indicating the deviation from the vertical incidence of the electron beam can be reduced to about 1/1000 or less. When this condition is satisfied, the lateral displacement of the beam spot due to the variation of the level of the wafer surface can be reduced to about 0.01 µm or less. Further, the coma aberration can be reduced below about 0.01 µm. As the adjustment made by the auxiliary coils 5a - 12a is minute, the size and number of turns of the auxiliary coils may be small. In correspondence thereto, one can use a compact driving system particularly the driving amplifiers 44 and 45 or 44′ and 45′ for energizing the auxiliary coils. Thereby, the setup of the electron beam exposure system can be made efficiently and the efficiency of production of the semiconductor device is improved. FIG.8 shows a construction of an electromagnetic deflector 29′ according to a second embodiment of the electron beam exposure apparatus of the present invention. In FIG.8, the parts described previously with reference to preceding drawings are given identical reference numerals and the description thereof will be omitted. In this embodiment, four pairs of auxiliary coils are provided in each of the coil assemblies 292 and 293. Thus, in the coil assembly 292, there are auxiliary coils 5a′ and 5b′ provided so as to be offset in the radially outward direction with respect to the coil 5 similarly to the coil 5a of FIG.5B such that the coil 5a′ is located relatively closer to the beam source of the electron beam B, i.e. the electron gun 20, and the coil 5b′ is located relatively closer to the wafer 30 (see Fig. 1). Further, there are auxiliary coils 6a' and 6b' provided so as to be offset in the radially outward direction with respect to the coil 6 similarly to the coil 6a shown in Fig. 6B and so that the coil 6a' is located closer to the source of the electron beam B so as to oppose the auxiliary coil 5a' with respect to the electron beam B, and the coil 6b' is located closer to the wafer 30 so as to oppose the auxiliary coil 5b' with respect to the electron beam B. Similarly, there are provided auxiliary coils 7a', 7b', 8a' and 8b' such that the coils 7a' and 7b' are offset in the radially outward direction with respect to the coil 7 similarly to the coil 7a shown in Fig. 6B, with the coil 7a' locating closer to the source of the electron beam B and the coil 7b' located closer to the wafer 30, and such that the coils 8a' and 8b' are offset in the radially outward direction with respect to the coil 8 similarly to the coil 8a shown in Fig. 6B, with the coil 8a' located closer to the source of the electron beam B and the coil 8b' located closer to the wafer 30. The coils 7a' and 8a' oppose each other and the coils 7b' and 8b' oppose each other with respect to the electron beam B similarly to the coils 5a', 6a', 5b' and 6b'. In the coil assembly 293 there are auxiliary coils 9a' and 9b' provided so as to offset in the radially outward direction with respect to the coil 9 similarly to the coil 9a of Fig. 6B with the coil 9a' located closer to the beam source of the electron beam B, i.e. the electron gun 20, and the coil 9b' located closer to the wafer 30 (see Fig. 1). Further, there are auxiliary coils 10a' and 10b' provided so as to be offset in the radially outward direction with respect to the coil 10 similarly to the coil 6a shown in Fig. 6B, the coil 10a' being located closer to the source of the electron beam B so as to oppose the auxiliary coil 9a' with respect to the electron beam B, the coil 10b' being located closer to the wafer 30 so as to oppose the auxiliary coil 9b' with respect to the electron beam B. Similarly, there are provided auxiliary coils 11a', 11b', 12a' and 12b' such that the coils lla' and 11b' are offset in the radially outward direction with respect to the coil 11 similarly to the coil lla shown in Fig. 6B, with the coil 11a' closer to the source of the electron beam B and the coil 11b' located closer to the wafer 30, and such that the coils 12a' and 12b' are offset in the radially outward direction with respect to the coil 12 similarly to the coil 12a shown in Fig. 6B with the coil 12a' closer to the source of the electron beam B and the coil 12b' closer to the wafer 30. Further, the coils 11a' and 12a' oppose each other, and the coils 11b' and 12a' oppose each other, and the coils 11b' and 12b' oppose each other with respect to the electron beam B. Fig. 9 shows the driving circuit of the electron magnetic deflector 29. Referring to Fig. 9, the drive circuit comprises a first deflection controller 43x supplied with semiconductor pattern data for producing first deflection control data which specify the deflection of the electron beam in the X-direction. The deflection control data are then converted by a digital-to-analog converter 42x into an analog deflection control signal, and this analog deflection control signal is supplied to a first main drive amplifier 41x to which the coils 1, 2, 5, 6, 9 and 10 are connected in series. This part of the connection is identical to the prior art connection shown in FIG.3. Further, the analog deflection control signal is supplied to a first auxiliary drive amplifier 44x to which the auxiliary coils 5a and 6a are connected in series and a second auxiliary drive amplifier 45x to which the auxiliary coils 9a and 10a are connected in series. Further, there is provided a second deflection controller 43y supplied with the semiconductor pattern data for producing a second deflection control data which specifies the deflection of the electron beam in the Y-direction. The second deflection control data is converted by a digital-to-analog converter 42y into a second analog deflection control signal which is supplied on the one hand to a second main drive amplifier 41y and on the other hand to third and fourth drive amplifies 44y and 45y. To the second main amplifier 41y, the coils 3, 4, 7, 8, 11 and 12 are connected in series in correspondence to the prior art connection shown in FIG.3. On the other hand, the third auxiliary drive amplifier 44y has its output connected to a series connection of the coil 7a and 8a and the fourth auxiliary drive amplifier 45y has its output connected to a series connection of the coils 11a and 12a. Further, the first and second auxiliary drive amplifiers 44x and 45x are supplied with the second deflection control signal from the second digital-to-analog converter 42y. Similarly, the third and fourth auxiliary drive amplifiers 44y and 45y are supplied with the first deflection control signal from the first digital-to-analog converter 42x. In response to the energization by the drive currents, the auxiliary coils 5a′ - 12a′ create respective auxiliary magnetic fields such that the direction of each of the created auxiliary magnetic fields coincides with the direction of the magnetic fields created by the coils 5 - 12. More specifically, the magnetic field created by the coils 5a′ and 6a′ enhances the magnetic filed Bx2 created by the coils 5 and 6 at the upper part thereof and thereby there is obtained an effect as if the coils 5 and 6 are displaced upwards as a whole towards the beam source 20. Similarly when the auxiliary coils 5b′ and 6b′ are energized, the magnetic filed Bx2 is enhanced in correspondence to the lower part thereof and thereby there is obtained an effect as if the coils 5 and 6 are displaced downwards as a whole towards the wafer 30 held on the stage 31. The effect of enhancing the magnetic field Bx2 in correspondence to the lower part thereof may also be achieved by reversing the direction of the drive current flowing through the coils 5a′ and 6a′. Similarly, the effect of enhancing the magnetic field Bx2 in correspondence to the upper part thereof may also be achieved by reversing the direction of the drive current flowing through the coils 5b′ and 6b′. A similar effect is obtained also for the magnetic field By2 created by the coils 7 and 8. Thus, the magnetic field created by the coils 7a′ and 8a′ enhances the magnetic filed By2 created by the coils 7 and 8 at the upper part thereof and thereby there is obtained an effect as if the coils 7 and 8 are displaced upwards as a whole towards the beam source 20. Similarly when the auxiliary coils 7b′ and 8b′ are energized, the magnetic filed By2 is enhanced in correspondence to the lower part thereof and thereby there is obtained an effect as if the coils 7 and 8 are displaced downwards as a whole towards the wafer 30 held on the stage 31. The effect of enhancing the magnetic field By2 in correspondence to the lower part thereof may also be achieved by reversing the direction of the drive current flowing through the coils 7a′ and 8a′. Similarly, the effect of enhancing the magnetic field By2 in correspondence to the upper part thereof may also be achieved by reversing the direction of the drive current flowing through the coils 7b′ and 8b′. As the effect of the coils 9a′ - 12b′ is substantially identical to the one described above, further description with regard to the effect of energization of the coils 9a′ - 12b' will be omitted. Similarly to the first embodiment, an effective compensation of deviation of the magnetic field as schematically illustrated in FIG.5 is achieved by the construction of FIG.9. FIG.10 shows another driving circuit used in cooperation with the electromagnetic deflector 29′ of FIG.8. In this circuit, the auxiliary coils 5a and 6a connected in series are driven by the amplifier 44x while the auxiliary coils 5b and 6b connected in series are driven by an amplifier 46x, wherein each of the amplifiers 44x and 46x is connected in parallel to the digital-to-analog converter 42x for receiving the deflection control signal specifying the deflection of the electron beam B in the X-direction. Further, the auxiliary coils 9a and 10a connected in series are driven by the amplifier 45x while the auxiliary coils 9b and 10b connected in series are driven by an amplifier 47x, wherein each of the amplifiers 45x and 47x is connected in parallel to the digital-to-analog converter 42x for receiving the deflection control signal specifying the deflection of the electron beam B in the X-direction. Similarly, the auxiliary coils 7a and 8a connected in series are driven by the amplifier 44y while the auxiliary coils 7b and 8b connected in series are driven by an amplifier 46y, wherein each of the amplifiers 44y and 46y is connected in parallel to the digital-to-analog converter 42y for receiving the deflection control signal specifying the deflection of the electron beam B in the Y-direction. Further, the auxiliary coils 11a and 12a connected in series are driven by the amplifier 45y while the auxiliary coils 11b and 12b connected in series are driven by an amplifier 47y, wherein each of the amplifiers 45y and 47y is connected in parallel to the digital-to-analog converter 42y for receiving the deflection control signal specifying the deflection of the electron beam B in the Y-direction. In this construction, too, the deviation of deflection of the electron beam B from the ideal deflection is compensated effectively. Similarly to the first embodiment, the number of turns of the auxiliary coils 5a - 12b may be only several turns and the driving current for creating the compensating magnetic field may be several hundred milliamperes.

Claims: An electron beam exposure system comprising; an electron beam source (20) for producing an electron beam and directing the beam toward an object according to a predetermined beam path (B); focusing means (26-28) for focusing the electron beam onto a surface of the object; deflection means (29) for deflecting the electron beam so as to move over the surface of the object, comprising at least first, second and third coil means (291-293) disposed at first, second and third positions respectively along the beam path , the first, second and third coil means being connected in series for simultaneous energisation so as to produce first, second and third magnetic fields respectively, the first second and third magnetic fields (Bx1, By1; Bx2, By2; Bx3, By3) each having an axis radially orientated in a plane perpendicular to the beam path (B); and a driving system (41) for energising said first, second and third coil means (291-293), having a relatively high power; characterised in that the deflection means further includes fourth coil means (5a, 6a; 7a, 8a) and fifth coil means (9a, 10a; 11a, 12a) disposed along the beam path at fourth and fifth locations respectively and associated respectively with and in the vicinity of the second and third coil means (292, 293), the fourth and fifth coil means being energised independently of said driving system (41) by an additional driving system (44-47) having a small power, so as to produce fourth and fifth magnetic fields (Bx2', By2'; Bx3', By3') respectively radially to and in planes substantially perpendicular to the beam path (B) for adjusting the effect of said first, second and third magnetic fields upon the electron beam in order that the electron beam (B) can be directed at an intended location on the object at an angle substantially perpendicular to the surface of the object and with minimized coma aberration. An electron beam exposure system according to claim 1 in which the fourth coil means includes a first additional coil pair (5a, 6a) and a second additional coil pair (7a, 8a) located radially outside the second coil means (292) with respect to the beam path (B) so as to produce the fourth magnetic field (Bx2', By2') between the first and second coil pairs; and the fifth coil means includes a third additional coil pair (9a, 10a) and a fourth additional coil pair (11a, 12a) located radially outside the third coil means (293) with respect to the beam path (B) so as to produce the fifth magnetic field extending between the third and fourth coil pairs. An electron beam exposure system according to claim 2 in which the first and second additional coil pairs (5a, 6a; 7a, 8a) forming the fourth coil means are located at a central part of the second coil means (292) when measured along the beam path (B), and the third and fourth additional coil pairs (9a, 10a; 11a, 12a) forming the fifth coil means (293) are located at a central part of the third coil means (293) when measured along the beam path (B). An electron beam exposure system according to claim 2 or 3 in which the fourth coil means further includes a fifth additional coil pair (5b', 6b') and a sixth additional coil pair (7b', 8b') provided radially outside the second coil means (292) with respect to the beam path (B), the fifth and sixth additional coil pairs being located along the beam path (B) closer to the object than the first and second additional coil pairs; and the fifth coil means further includes a seventh additional coil pair (9b', 10b') and an eighth additional coil pair (11b', 12b') provided radially outside the third coil means (293) with respect to the beam path (B), the seventh and eighth additional coil pairs being located along the beam path (B) closer to the object than the third and fourth additional coil pairs. An electron beam exposure system according to claim 2 or 3 in which the first and second additional coil pairs (5a, 6a; 7a, 8a) are connected in series, the third and fourth additional coil pairs (9a, 10a; 11a, 12a) are connected in series, and the drive system includes a first amplifier (44x, 44y) for driving the first and second additional coil pairs by supplying a first auxiliary drive current thereto, and a second amplifier (45x, 45y) for driving the third and fourth additional coil pairs by supplying a second auxiliary drive current thereto. An electron beam exposure system according to claim 4 in which the first and second additional coil pairs (5a, 6a; 7a, 8a) are connected in series, the third and fourth additional coil pairs (9a, 10a; 11a, 12a) are connected in series, the fifth and sixth additional coil pairs (5b', 6b'; 7b', 8b') are connected in series, and the seventh and eighth additional coil pairs (9b', 10b'; 11b', 12b') are connected in series, and the drive system includes a first amplifier (44x, 44y) for driving the first and second additional coil pairs, a second amplifier (45x, 45y) for driving the third and fourth additional coil pairs, a third amplifier (46x, 46y) for driving the fifth and sixth additional coil pairs and a fourth amplifier (47x, 47y) for driving the seventh and eighth additional coil pairs, the drive system driving these eight coils in such a way that the magnetic fields produced by the second and third coil means (292; 293) are moved towards and away from the object along the beam path (B) of the electron beam. An electron beam exposure system according to claim 4 in which each of the additional coil pairs (5a, 6a; 7a, 8a; 9a, 10a; 11a, 12a; 5b', 6b'; 7b', 8b'; 9b' 10b'; 11b' 12b') is driven independently by the driving system. An electron beam exposure system according to any one of claims 2 to 7 in which the first, second, third and fourth additional coil pairs of the fourth and fifth coil means respectively have a number of turns which is substantially smaller than the number of turns of the coils forming the first, second or third coil means (291-293).

Inventors: YAMADA AKIO, YASUTAKE NOBUYUKI, YAMADA, AKIO, YASUTAKE, NOBUYUKI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H01J37
IPC codes: H01L21, H01J37