Electron beam exposuring device and exposuring method using the same

Abstract: In an electron beam exposure device which comprises an electron gun (3), a mask plate (27) provided with a plurality of apertures of patterns, each having a predetermined shape for forming a cross-sectional shape of an electron beam composed of charged particles, deflecting means (5) provided both on a first side surface of a mask plate to which the beam is irradiated and on a second side surface thereof from which the beam is emitted, for deflecting the beam from an original axis thereof so as to pass to one of the apertures provided on the mask plate, and for deflecting again said beam so as to return to the original axis thereof, a sample holding means (26), a focus point adjusting means (28) provided between the mask plate and the sample holding means, and a control means for controlling the focus point adjusting means, wherein the focus point adjusting means is further provided with a processing means for processing a focus point adjusting condition data of each pattern having a certain shaped aperture utilizing a predetermined relationship between a cross-sectional area of an aperture of each pattern and a predetermined focus point adjusting value with respect to each of the patterns, and a supplying means for supplying information of said focus point adjusting condition data thus obtained to the focus point adjusting means.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam exposure device and an exposure method using the same in which fine patterns used for an integrated circuit are formed on a wafer utilizing a charged particle beam such as an electron beam. 2. Description of the Related Art In the recent times, along with the production of highly integrated circuits, the photolithographic system, which had been the main fine pattern forming method for a long time, has been replaced with a new exposure methods utilizing an electron beam. The conventional exposure device utilizing a charged particle such as an electron beam forms a pattern by deflecting and scanning an electron beam of having a variable rectangular cross-sectional shape on a sample wafer. This conventional device generally has a pattern generating function and forms a pattern utilizing pattern data software. In this device, a pattern is usually formed by assembling a plurality of rectangular shots configurations. As the pattern size becomes smaller, the number of shots of the electron beam in an unit area increases. Therefore, a problem arises in that the through-put is reduced. In order to overcome this problem, a block exposure system has been proposed. Generally speaking, most parts of an ultra fine pattern used in a semiconductor device such as a 64 MDRAM are formed by arranging certain basic patterns repeatedly and successively. Therefore, if a basic pattern of a certain complexity of pattern shape, i.e., a "block" can be generated in one operation and an electron beam having a certain cross-section shot to a wafer, a certain pattern can be exposed on a wafer with a predetermined constant through-put despite the fineness of the patterns. To obtain the overall pattern, several basic patterns, each having a different cross-section, are provided on a mask. The intended overall pattern is formed by exposing the basic patterns on the wafer repeatedly and combining them. Figure 1 shows a conventional block-exposuring system. In Fig. 1, an electron gun 3a is provided in a charged particle beam generating means 3. An electron beam emitted from the electron gun 3a is given a rectangular cross-section utilizing a plate 6. The plate 6 has an aperture which give the cross-section of the electron beam a first rectangular configuration. The electron beam thus formed is deflected from a center of the beam path by an aperture selecting deflector 5 and irradiated on a selected basic pattern formed on a stencil mask 27. The electron beam passing through the mask 27 is contracted by a contracting lens 14. Then irradiated on a wafer 25 through a projecting lens 24 and deflecting systems 21 and 23. Figure 2 shows one example of a conventional stencil mask 27. As shown, a pattern forming portion has a thin portion like a thin film. Several different kinds of basic patterns P 1 to P 3 are formed on the plate 27 utilizing an etching process. As a mask substrate, a semiconductor such as Si or a metal plate can be used. In this electron beam exposure device, the electron beam given the same cross-sectional configuration as a pattern on the pattern mask has a certain current value corresponding to the size of the cross-sectional configuration. The image-forming condition for the pattern image focused on the surface of the wafer slightly changes in response to the current value measured on the surface. Note that the size of an electron beam passing through any one of the apertures can be set by the patterns P 1 to P 3 . An electron beam passing through a pattern with a large aperture area generally has a large current while an electron beam passing through a pattern with a small aperture area has only a small current. When such an electron beam is irradiated on a wafer 25 mounted on a sample holder 26, the edge sharpness of the beam is sometimes lost due to a difference in electron scattering effect caused by a difference of the current, between a shot utilizing a large aperture pattern and one utilizing a small aperture pattern. Accordingly, a problem arises that sharp edge cannot be obtained. To resolve this, it has been proposed to provide a focus adjusting coil, i.e., a refocus coil 28, between the mask plate 27 and the sample holding device 26. In this system, however, the problem still remains as to how the focus adjusting value can be determined with respect to each of the block patterns P 1 to P 3 . That is, in the block-exposure device, when a plurality of block patterns having different aperture areas are used, since the beam size changes in accordance with the selected block pattern and the current, i.e., the detected electric current, passing through a surface of the sample may be changed when the beam is irradiated on the wafer, the conventional system required a focus adjusting operation utilizing a refocus coil. In this conventional focus adjusting system, however, while the sharpness of the beam edge can be relatively easily measured with a rectangular beams since a cross-sectional configuration of the beam obtained by the variable rectangular shape generating means is rectangular and thereby the focus adjusting value can be determined in response to the beam size (current flowing through surface of sample), it is very difficult to determine the focus adjusting value since it is not easy to measure the sharpness of a block pattern where the beam cross-sectional configuration is generally complicated. Another system can be considered in which exposure data representing aperture areas of each block patterns are previously stored in a suitable data storing means, a focus adjusting value is determined from the aperture area and the current density, and the focus adjusting value thus determined is applied to a refocus coil. In, this system, however, another problem arises in that the processing circuit and process control circuit for determining the focus adjusting value, i.e., adjusting data, are very complicated. EP-A-0-083 246 (Fujitsu Ltd) describes a known arrangement in which the problem of maintaining peripheral image shapeness is addressed. An auxiliary converging means is provided which refocusses the beam in accordance with its cross section, and to enhance throughput of the exposure system a facility is provided whereby a rectangular pattern can be divided into a plurality of patterns having the same size. The object of the present invention is to provide an electron beam exposure device and an exposure method in which the best focused image point of the exposure beam with respect to each of the block patterns to be used is formed on a surface of a sample wafer to form a sharp pattern thereof and the electron beam exposure operation is carried out effectively. According to a first aspect of the present invention, there is provided an electron beam exposure device including; an electron gun for generating an electron beam; a mask plate having a plurality of aperture patterns each for forming a predetermined cross-sectional shape of the electron beam; deflecting means provided on either side of the mask plate in relation to the beam path for deflecting the beam from its original axis so as to pass through one of the apertures, and for subsequently deflecting the beam back to its original axis; a sample holding means; a focus point adjusting means provided between the mask plate and the sample holding means; and control means for controlling the focus point adjusting means; characterised in that the device includes a discriminating means for determining whether the electron beam is deviated from the centre axis of the device and whether the focus point is optimum; the mask includes a variable rectangular shape generating means (R); and the control means for the focus point adjusting means includes: a processing means for processing focus point adjusting values for each pattern having a certain shaped aperture, using a predetermined relationship between the cross-sectional area of the aperture of each pattern and a predetermined focus point adjusting value for the pattern; a memory means for storing the predetermined focus point adjusting values for the aperture of each pattern provided on the mask plate; a supplying means for supplying the focus point adjusting values thus obtained to the focus point adjusting means; a measuring means for measuring the cross-sectional area of the aperture of a pattern provided on the mask plate; a cross-sectional area adjusting means for controlling a variable rectangular shape generating means to generate a cross-sectional area of a rectangular shaped aperture to coincide with that of the cross-sectional area of the pattern thus measured, and for supplying the data to the processing means for processing and determining focus point adjusting values with respect to the rectangular shaped aperture formed by the variable rectangular shape generating means; and a transferring means for transferring the focus point adjusting values thus obtained to the memory means. According to a second aspect of the present invention, there is provided a method for adjusting a focus point in the setting up of an electron beam exposure device comprising an electron gun, a mask plate having a plurality of apertures each having a predetermined shape for forming a cross-sectional shape of an electron beam and a variable rectangular aperture forming means with which the cross-sectional area of a rectangular aperture can be varied, deflecting means provided on either side of the mask plate in relation to the beam path respectively, for deflecting the beam from its original axis so as to pass through one of the apertures of the patterns provided on the mask plate, and for deflecting it back to its original axis, a sample holding means, a current measuring means for measuring the current flowing through a surface of the sample to be exposed by the electron beam, and a focus point adjusting means including a memory means for storing control data thereof and a control means for controlling the focus point adjusting means, said method including the steps of: selecting one of the patterns provided on the mask plate having a particular cross-sectional shape and a particular area; irradiating a beam through the pattern to form an image of the pattern on the sample holding means; characterised by the steps of measuring the value of a current representing the intensity of the beam, measured on a surface of the sample held on the sample holding means with respect to the selected pattern; storing the current values in a memory means; selecting a particular rectangular aperture having a cross-sectional area giving the same current value as that obtained from the selected pattern so as to make the cross-sectional area of the rectangular shaped aperture conform to the cross-sectional area of the pattern thus measured; irradiating the beam through the rectangular shaped aperture thus selected to form an image of the pattern on the sample holding means; determining focus point adjusting condition data for adjusting to the best focus point by means of the focus point adjusting means, using a discriminating means for determining whether the focus point is located at the best focus point or not and, if not, processing the focus point adjusting condition data to decide the best focus point; storing the data thus obtained in the memory means in the control means; and adjusting the focus point by operating the focus point adjusting means in response to the focus point adjusting condition data stored in the memory means. The invention will now be described with reference to the following drawings: Figure 1 shows one example of a conventional beam exposure device; Figure 2 shows a mask plate used for the electron beam exposure device on which a plurality of different types of apertures for patterns are provided; Figure 3 is a block diagram of an example of an electron beam exposure device of the present invention; Figure 4 is an enlarged cross-sectional view of an example of a focus point adjusting means of the present invention; Figs. 5 to 7 illustrate a process for determining a best focus point and a beam axis deviation from a centre axis of the deflecting means of an exposure device; Fig. 8 is a flow chart of a method for obtaining a best focus point; Fig. 9 is a graph illustrating the relationship between electric current and a focus adjusting value; and Fig. 10 is a flow chart for adjusting a focus point and directing an electron beam onto a sample. Preferred embodiments of the present invention will now be explained with reference to the attached drawings. Figure 3 is a schematic view of one embodiment of an electron beam exposure device and a diagram of a control circuit of the present invention, the basic construction thereof is the same as the conventional one shown in Fig. 1. An electron beam B composed of charged particles is irradiated from an electron gun 3a mounted on an electron beam generating means 3, and guided to an aperture means 6 having a rectangular cross-sectional shape to form a first rectangular shape, then irradiated onto a mask plate 27 through an optical system comprising lenses 7 and 10 and a beam deflector 9. The electron beam B then selectively passes through one of the apertures of the block patterns P 1 to P 3 , provided on the mask plate 27 to give a cross-sectional configuration the same as that of the pattern selected. Thereafter, the electron beam is irradiated on a sample water 25 mounted on a sample holder 26 through an electron beam deflecting means 13, a contracting lens 14, and a focus point adjusting means 28 comprising a focus point adjusting coil 30 and a focus adjusting lens. In this embodiment, the electron beam B is controlled to be exposed on the most suitable position of the sample by an electron beam deflecting means 31 comprising a lens 24 and deflectors 21 and 23. The electron beam deflecting means 31 also has separate functions not only to scan the electron beam B back and forth on the surface of the sample wafer but also to adjust an electron beam axis deviation from a center axis of the device, especially of the beam deflecting means 31, to make the deviated beam axis coincide with the center axis of the device. The mask plate 27 used in the present embodiment has the same construction as shown in Fig. 2. A plurality of patterns P 1 to P 3 having different shaped apertures are provided on the mask plate in a block condition. Note that the pattern P 1 has a rectangular shaped aperture. In the present embodiment, a plurality of the patterns P 1 having rectangular shaped apertures may be provided on the mask plate. Figure 2 shows four patterns P 1 provided on the mask plate. In Fig. 2, a plurality of patterns P 2 each having a key-hole like aperture and a plurality of patterns P 3 each having a hook-like aperture are also provided on the mask plate. In the present embodiment, the area of each aperture of each pattern may be different from the others even in the same pattern, if the case requires. The exposure device of the present invention also includes a variable rectangular shape generating means R having a rectangular shaped aperture Q. The area can be changed by changing the overlap of two plates each having a rectangular aperture. These plates allow any kind of rectangular aperture having any area to be obtained. As shown in Fig. 3, in the present embodiment, lenses 10 and 10' are provided respectively on the side of the mask plate to which the electron beam is irradiated, referred to as a first side, and on the side of the mask plate from which the beam is emitted, referred to as a second side. Further, there is provided a beam deflecting means 5 between the lens 10 and the mask plate 27, which deflects the incident electron beam B from a center axis of the device to pass through a selected necessary pattern provided on the mask plate 27. There is also provided a beam deflecting means 5' between the lens 10' and the mask plate 27 which deflects the deflected electron beam passed through the selected aperture of the pattern back to the original center axis of the device. The focus adjusting means 28 includes a focus adjusting lens 20 and a focus adjusting coil 30. It is important that the center axis of the focus adjusting means 28 coincide with the axis of the electron beam B. From the practical point of view, it is generally difficult to make all axes of the focus adjusting means 28, the focus adjusting lens 20, and the focus adjusting coil 30 coincide with each other, so there is naturally a slight deviation between the axis of the electron beam and the center axis of this device. Figure 4 is a cross-sectional view of a device including a focus adjusting means 28 and a beam deflecting means 31 serving as a beam axis deviation adjusting means. The focus adjusting means 28 comprises a spool 35 on which a focus adjusting coil 30 through which an adjusting current i flows is provided. The beam deflecting means 31 comprises a deflector 40, magnetic plate 41, and a coil for focusing lens 20. In this device, as explained above, the center axis X′ of the focus adjusting means 28 does not usually coincide with the axis Y of the electron beam B. Thus, the deviation should be adjusted utilizing the beam deflecting means 31. On the other hand, when the focus adjusting means 28 is operated to adjust the focus point to coincide with the best focus point, the beam axis is usually deviated from the center axis of the device and accordingly an operation for adjusting the deviation is again required. In the present embodiment, there is provided a control means comprising a circuit for controlling current to adjust a focus point in response to focus adjusting condition data generated from a pattern control means 102 connected to memories 120 and 121. These memories 120 and 121 store focus adjusting condition data and beam axis deviation adjusting data therein, respectively. In the present embodiment, a current detecting means 29 is provided on the sample holding means 26. This converts the intensity of the electron beam B striking the sample wafer 25 and the amount of charge into current (sample current) for measurement. The invention also includes a discriminating means 32 for determining whether the present focus point is set at a best focus point and whether the electron beam is deviated from the center axis of the device. This reports the results of the operation to the focus adjusting means or the beam axis deviation adjusting means. As shown in Fig. 5, the discriminating means 32 comprises a reference edge portion 33 and a secondary electron detector 34. The operation of the discriminating means 32 of the present embodiment will be explained hereunder with reference to Figs. 5 to 8. As explained above, when the pattern configuration or area of the aperture of a block pattern changes, the amount of an electron beam B passing through a selected aperture of a block pattern is naturally changed, therefore the current value of the electron beam B irradiated on the sample wafer changes depending upon the pattern configuration used. Thus, when the exposure operation is carried out with the same exposure conditions, the electron beam B cannot be focused on the surface of the sample wafer with the best focus point or the width of the beam diffuses to cause the pattern edge formed on the sample wafer to lose sharpness, making the pattern diffused. In the discriminating means 32, the reference edge portion 33 has a sharp edge 0 preferably formed at a right angle to a surface of the sample holding means 26. The secondary electron detector 34 detects the secondary electrons E emitted from the edge portion to which the electron beam B is irradiated. In actual operation, an electron beam B having a rectangular cross-sectional configuration strikes a surface of a sample wafer 25 and is scanned back and forth along the surface thereof by the beam deflecting means 31. When the beam B crosses the edge 0 of the reference edge portion 33, the secondary electrons E are emitted from the reference edge portion 33. The amount of the secondary electrons E is detected by the secondary electron detector 34 to give a voltage curve as shown in Fig. 5(b). According to the voltage curve as shown in Fig. 5(b), when the electron beam B is set at the best focus point on the sample wafer, a lot of secondary electrons are emitted, so when the electron beam B contacts to the edge 0 of the reference edge portion 33, a voltage curve (1) having a steep rising portion as shown in Fig. 5(b) is obtained. When the beam is not set at the best focus point but is diffused, the amount of the secondary electrons emitted from the reference edge portion 33 is rather smaller, so voltage curves (2) and (3) having inclined configurations are obtained Figure 6 is a plane view illustrating a scanning process of an electron beam B against the reference edge portion 33. In that figure, the electron beam B is scanned over the reference edge portion 33 in a direction L as indicated. When the electron beam is focused on a sample wafer without setting the best focus point, a voltage curve as shown in Fig. 7a is obtained in response to a data detected by the secondary electron detector 34. When it is set at the best focus point, a voltage curve as shown in Fig. 7b is obtained. Note that while the above explanation was made referring to an electron beam B having a rectangular cross-sectional configuration, any configuration may be used. An electron beam B having a rectangular cross-sectional configuration is preferably used, however, to obtain accurate data. As explained above, it is apparent that when the electron beam B is focused on the surface of the sample wafer, the steepest voltage curve can be obtained. By repeating the beam scanning operation as explained above changing the amount of current flowing through the focus adjusting coil 30 of the focus adjusting means 28 and observing the voltage curve obtained from each scanning operation, the best focus point can be determined. Note, that in these scanning operations, when the steepest voltage curve is obtained, it can be determined that the electron beam is set at the best focus point. The amount of the current used at this occasion is memorized in a suitable memory, explained later. Figure 8 is a flow-chart indicating an algorithm to carry an operation of the present invention by which the best focus point of the beam is discriminated. First, at step a, an electron beam B having a rectangular cross-sectional configuration is scanned over a reference edge portion 33 in a direction L. At step b, a voltage is detected by the secondary electron detector 34 and voltage waveform is output. At step c, the variation of the voltage thus obtained is differentiated to obtain the peak values and then a peak-to-peak value (p-p) is calculated. At step d, a decision is made whether the peak-to-peak value (p-p) thus obtained is maximum or not. If YES, this routine is finished, while if NOT, the process goes to step e to change the focus adjusting condition data, i.e., to change the amount of the current flowing through the focus adjusting coil 30, The control returns to step a. The same routine is repeated. Figure 9 shows the relationship between a necessary focus point adjusting value and the current flowing in the focus adjusting coil 30, as one of the focus adjusting condition data of the present invention. As apparent from the graph shown in Fig. 9, the necessary focus point adjusting value has a positive correlation with the amount of the current. It is clear that when the necessary amount of the focus point adjusting value is large, a large amount of current is required and vice versa. As explained above, when the focus point is adjusted by operating the focus adjusting means 28, the electron beam B is deviated from the center axis of the device, especially from the center axis of the focus adjusting means 28. Thus, a beam axis deviation adjusting operation is required to form an accurate pattern on the surface of the sample wafer by swinging back the beam to the center axis of the device to cancel the deviation. Toward this end, it is apparent that a discriminating means is also required for determining whether a deviation between the beam and the center axis of the device exists and if deviation exists, how far the beam is deviated from the center axis. Such a discriminating means can be provided separately from the means for discriminating the best focus point as explained above, but in this embodiment a single is used. When the best focus point is obtained in accordance with the discriminating operation as explained above, at least one of the steepest portions in the voltage curve, i.e., the curve portion indicating the position at which the rectangular beam B first contacts the edge 0 of the reference edge portion 33, shows the position of the axis of the beam B. Therefore, after this position is memorized by, for example, X, Y coordinate data in a suitable memory, the deviation can be easily processed by a suitable processor by other X, Y coordinate data representing a position of the center axis of the device. In this embodiment, when the data of the position representing the place at which the beam axis exists is memorized in a suitable memory means, information about the area of the rectangular cross-sectional aperture used is preferably memorized in the same memory means. The focus point adjusting process of the present invention utilizing the electron beam exposure device as explained above will be explained hereunder. The focus point adjusting process of the present invention comprises the following steps; Step 1: Selecting one of the block patterns P 1 to P 3 provided on a mask plate 27 utilizing a mask pattern deflecting means 5 and 5′ which is controlled by a mask deflector control circuit 103. The mask deflector control circuit 103 is further controlled by a pattern control circuit 102 controlled by a microcomputer 110 through an interface 108 and a data memory circuit 109. A beam deflecting means 9 is controlled by a beam deflecting means control circuit 111. At this step, one of the block patterns P 1 is selected. Step 2: Deflections the electron beam B so as to pass through an aperture of the selected block pattern P 1 to give the same cross-sectional configuration as that of the aperture and irradiating the beam on a surface of the sample wafer 25. Step 3: Measuring an amount of the current i 1 flowing on the surface of the sample wafer and generated by the charged particles composing the electron beam B striking the surface of the sample wafer by the current detecting means 29. (In step 3, the area of the aperture of the block pattern may previously be measured or it may still be unknown.) The measured current data i 1 is stored in a memory means 120 connected to the pattern control circuit 102 with the information representing the pattern identification no., for example, P 1 . Step 4: Deflecting the electron beam B to the variable rectangular shape generating means R pass through a rectangular aperture Q of the same. Step 5: Varying the area of the rectangular aperture of the variable rectangular shape generating means R by changing the overlap of two plates having rectangular apertures to obtain the same electrical current I 1 as obtained in step 3 and measuring the current i 1 in the same manner as in step 3. In an actual process, the current i is continuously detected during the operation in which the area of the rectangular aperture of the block pattern is changed. The current i 1 , which is the same current as obtained in the case utilizing a non-rectangular cross-sectional pattern P 1 , and the size of the aperture S 1 of the rectangular aperture Q by which the current i 1 is obtained are memorized in a memory means 120. The beam which passes through the rectangular aperture having the area S 1 may be referred to as the beam B 1 . In step 5, any kind of electron beam B having a specific cross-sectional configuration of a block pattern having a certain area can be converted into a beam B having a cross-sectional configuration of an area the same as that of the beam formed by the pattern P having a specific cross-sectional configuration other than a rectangular configuration. Step 6: Utilizing the beam B 1 thus obtained having a rectangular cross-sectional configuration with an area S the same as that of a beam B formed by passing through a block pattern P 1 having a non-rectangular cross-sectional aperture, the focus adjusting condition data D 1 is measured along the discriminating method as explained above. The focus adjusting condition data D 1 thus obtained seems to correspond to the same data if measured utilizing the block pattern P 1 . In Step 6, as explained above, the beam B 1 is repeatedly scanned varying the current I supplied to the focus adjusting means 28. In the discriminating means 32, the discriminating operation is continued until the voltage curve (1) having the steepest raising portion is obtained thereafter, the control current I 1 is supplied to the focus adjusting means 28. The voltage curve having the steepest raising portion is obtained and stored in a memory means 120 as the focus adjusting condition data D 1 . In the same manner, utilizing the beam B 2 , B 3 ... each having a cross-sectional configuration of an area the same as that of the beam formed by the pattern P 2 , P 3 ... each having a specific cross-sectional configuration other than a rectangular configuration, the current I 2 , I 3 ... is obtained respectively in the same manner as explained above. Finally, each current I 2 , I 3 ... is stored in a memory means 120 as the focus adjusting condition data D 2 , D 3 .... Step 7: Finally, the pattern configurations P 1 to P n and the focus adjusting condition data D 1 to D n which is required when each one of the patterns P 1 to P n is used are stored as a pair respectively in each address portion of the data memorizing region TB in a memory means 120 to form a first table. When information about the patterns is stored in the memory means 120, the configuration of the pattern per se may be stored therein or certain kind of identification number or symbol representing each of the patterns may be stored in the memory means. In Fig. 3, a memorizing condition of one example of the present invention is illustrated in which the data memorizing region TB is given address portions #P 1 to #P n corresponding to each one of the block pattern P 1 to P n , and each of the focus adjusting condition data D 1 to D n is stored in each addressed portion. The actual operation of the electron beam exposure device of the present invention will be explained hereunder. As shown in Fig. 3, when a desired block pattern P 1 is selected, a certain command signal is issued from the CPU 110 to the pattern control circuit 102, then the circuit 102 generates a control signal to the mask deflection control circuit 103 to deflect the beam B to the desired pattern P 1 by control the deflecting means 5 and 5′. Simultaneously, a command ordering that the pattern P 1 be selected is transferred to the memory circuit 120 from the pattern control circuit 102. The address #P 1 corresponding to the selected block pattern P 1 is confirmed and successively in accordance with the address #P 1 , the focus adjusting condition data D 1 stored in the address portion #P 1 is read out from the data storing region TB, then transferred to the focus point adjusting control circuit 100 including a digital-analog converter (DAC/AMP) to operate the focus point adjusting means 28. The focus point adjusting current I 1 corresponding to the focus point adjusting condition D 1 stored in the lookup table in the memory means is supplied to the focus point adjusting coil 30 to set the focus point at the best focus point as desired. After the focus point is set at the best focus point, the exposure operation is carried out to irradiate the beam B on the surface of the wafer 25. In Fig. 3, the deflection control circuit 106 is also used in the process for detecting the best focus point and measuring the focus adjusting condition data. In Fig. 3, a blanking circuit 112 is provided. The blanking circuit 112 controls a beam blanking means 13 so as to block beam passage during a time when a focus point should be moved from one place already exposed by the beam to a next place to be exposed by the beam. In the present embodiment as explained above, the focus adjusting condition data is stored in the memory means 120 as current values since the focus adjusting means 28 works by the coil 30 operated by current. When the focus adjusting means 28 works with a factor other than current, the focus adjusting condition data may be stored in the memory means in a form of another factor proportional to the current. In this embodiment, the area of the cross-sectional configuration of each block pattern P 1 to P 3 is converted to a rectangular cross-sectional pattern having the same area of each of the block patterns P 1 to P 3 by measuring the current I and adjusting the area of the variable rectangular shape generating means so as to obtain the same amount o current as obtained when the selected block pattern is used. But in the present invention, when the area of each of the block pattern P 1 to P 3 can be directly converted to a rectangular cross-sectional pattern having the same area of each of the block patterns P 1 to P 3 with certain function, for example, some mathematical equation, representing some relationship between the area of each block pattern and that of the pattern formed by the optional rectangular shape generating means, the rectangular cross-sectional configuration corresponding to that of each one of the block patterns P 1 to P 3 can be obtained more simply than the previously mentioned method. As explained above, in the present invention, there is another problem that the electron beam is sometimes deviated from a center axis of the electron beam exposure device, especially a focus adjusting means and beam deflecting means. Accordingly, it is necessary to correct this deviation by swinging back the deviated beam to the center axis. There is therefore provided a beam axis deviation adjusting means as explained above. One example of the correction of such deviation will be explained hereunder. Here, the beam axis deviation adjusting means is combined with the beam deflecting means 31 and works with the current detecting means 29. The operation of the beam axis adjusting method of the present embodiment comprises; steps 1 to 5 of the process for obtaining the focus adjusting condition data as explained above and an additional steps 6 and 7 as follows; Step 6: utilizing the beam B 1 having a rectangular cross-sectional configuration of an area S the same as that of a block pattern P 1 having a non-rectangular cross-sectional aperture, and measuring the beam axis deviation adjusting data L by the axis deviation discriminating means 32 (in this embodiment, the discriminating means for detecting the focus point adjusting condition data also has the function for detecting the beam axis deviation.) by the method as explained above. The beam axis deviation adjusting data L 1 corresponds to the same data which would be measured by the same method utilizing the block pattern P 1 . In step 6, as explained above, the beam B 1 is repeatedly scanned varying the current I supplied to the focus adjusting means 28 and the discriminating operation is continued until the voltage curve (1) having the steepest raising portion therein is obtained. Thereafter, the control current I 1 is supplied to the focus adjusting means 28, whereby the voltage curve having the steepest raising portion is stored in a memory means 120 as the focus adjusting condition data D 1 . As explained above, the beam axis deviation adjusting data is represented by the position in the voltage waveform where the steepest curve is obtained. Therefore, when the position thereof is memorized in the form of, for example, X-Y coordinate data in the memory means 121 and the position data of the center axis of the device is also stored in the memory means 121 in a form of X-Y coordinate data, the amount of a deviation thereof can be easily processed and determined. And thus, the beam axis deviation data L 1 indicating a corresponding deviation which would be obtained if the block pattern P 1 is used can be obtained. In order to deflect the deviated beam again to move back to the center axis of the device, a certain amount of an current ID or a voltage is supplied from the pattern control means 102 to the beam deflection control means 106. Practically, the beam axis deviation adjusting means is included in the pattern control means 102 and detects and measures continuously the deviation thereof by changing the supplied current or voltage to the beam deflection control means 106. When the deviation thereof thus detected is a minimum value, preferably zero, it is decided that the deviation is eliminated and the operation is stopped. The amount of the current ID 1 whereby the deviation thereof is corrected is stored in the data memorizing region TB in the memory means 121 as the beam axis deviation adjusting data with an address #P 1 representing a portion in which the area of the aperture equal to that of the block pattern P 1 is shown. Note, that in the memory means 121, the current data, i.e., beam axis deviation adjusting data ID 1 and the address #P 1 are stored as a pair. As the same manner, utilizing the beams B 2 , B 3 ... each having a rectangular cross-sectional configuration of an area the same as that of the beams formed by the pattern P 2 , P 3 ... each having a specific cross-sectional configuration other than a rectangular configuration respectively, the beam axis deviation adjusting data ID 2 , ID 3 ... is obtained in the same manner as explained above and finally each beam axis deviation adjusting data ID 2 , ID 3 ... is stored in a memory means 120. Step 7: Finally, the data memorizing region TB is given address portions #P 1 to #P n corresponding to each one of the block pattern P 1 to P n and each of the beam axis deviation adjusting data ID 1 to ID n is stored in each addressed portion respectively in the memory means 121 to form a second table. In actual operation, when the beam axis deviation adjusting means detects beam axis deviation with using the block pattern P 1 , for example, the beam axis deviation adjusting means first recognizes that the block pattern used is P 1 and then a beam axis deviation adjusting data ID 1 stored in the address #P 1 corresponding to the block pattern P 1 , is read out from the second memory means 121 through the pattern control means 102 and supplied to the beam deflection means 106 including a D/A converter to deflect the beam back to the center axis of the device. After the beam axis deviation is adjusted, the exposure operation is carried out to irradiate the beam B on the surface of the wafer 25. In the present embodiment as explained above, the focus point adjusting process and the beam axis deviation adjusting process are carried out separately, but these processes can be carried out simultaneously in one process. Since as explained above, the axis deviation of the electron beam is mainly caused by the focus point adjusting process, the beam axis deviation adjusting process may be carried out just after the focus point adjusting process. One example of a process flow in which both the focus point adjusting process and beam axis deviation adjusting process are simultaneously carried out is shown in Fig. 10. According to the present invention, no matter what block pattern is selected, the best exposure condition can be obtained since the focus adjusting condition data and the beam axis deviation adjusting data, both of which are necessary for setting the focus point of the beam formed by a selected block pattern on a sample wafer in the best condition, are previously stored in a memory means, the adjusting data as mentioned above is read out from the memory means in response to the selected pattern and supplied to one of the focus point adjusting means and the beam axis deviation adjusting means, and thereby the focus point thereof is suitably adjusted to be the best in response to the adjusting data thus supplied to obtain a fine and clear pattern image on the wafer efficiently.

Claims: An electron beam exposure device including; an electron gun (3a) for generating an electron beam (B); a mask plate (27) having a plurality of aperture patterns each for forming a predetermined cross-sectional shape of the electron beam (B); deflecting means (5, 5') provided on either side of the mask plate (27) in relation to the beam path for deflecting the beam (B) from its original axis so as to pass through one of the apertures, and for subsequently deflecting the beam (B) back to its original axis; a sample holding means (26); a focus point adjusting means (28) provided between the mask plate (27) and the sample holding means (26); and control means for controlling the focus point adjusting means (28); characterised in that the device includes a discriminating means (32) for determining whether the electron beam (B) is deviated from the centre axis of the device and whether the focus point is optimum; the mask includes a variable rectangular shape generating means (R) ; and the control means for the focus point adjusting means (28) includes: a processing means for processing focus point adjusting values for each pattern having a certain shaped aperture, using a predetermined relationship between the cross-sectional area of the aperture of each pattern and a predetermined focus point adjusting value for the pattern; a memory means (120) for storing the predetermined focus point adjusting values for the aperture of each pattern provided on the mask plate (27); a supplying means for supplying the focus point adjusting values thus obtained to the focus point adjusting means (28); a measuring means for measuring the cross-sectional area of the aperture of a pattern provided on the mask plate (27); a cross-sectional area adjusting means for controlling a variable rectangular shape generating means to generate a cross-sectional area of a rectangular shaped aperture to coincide with that of the cross-sectional area of the pattern thus measured, and for supplying the data to the processing means for processing and determining focus point adjusting values with respect to the rectangular shaped aperture formed by the variable rectangular shape generating means; and a transferring means for transferring the focus point adjusting values thus obtained to the memory means. An electron beam exposure device according to claim 1 in which the memory means (120) is adapted to store focus point adjusting values in accordance with the shape of the aperture of each pattern provided in the mask plate (27), and which includes a selecting means for selecting at least one of the predetermined focus point adjusting values from the memory means (120) in dependence on either the selected shape of the pattern or an identification number representing the selected shape of the pattern. An electron beam exposure device according to claim 1 or 2, in which the control means includes a function representing the relationship between the area of an aperture of each pattern on the mask plate (27) and the respective focus point adjusting value of each pattern. An electron beam exposure device according to claim 1, 2 or 3, in which the memory means (120) includes a table containing information on a plurality of apertures of each pattern provided on the mask plate (27) or identification symbols thereof, and the focus point adjusting values required for each one of the apertures of the patterns to be used. An electron beam exposure device according to any preceding claim including a discriminating means (32) for determining whether the focus point on a sample (25) held on the sample holding means (26) is at the best focus point or not. An electron beam exposure device according to any preceding claim, including a discriminating means (31) for determining the amount of deviation of the beam (B) from the centre of the device. An electron beam device according to any preceding claim including a beam axis deviation adjusting means (31) for measuring a deviation of the beam from the centre axis of the device and adjusting it to coincide with the centre axis of the device. An electron beam exposure device according to claim 7, including a control means for controlling the beam axis deviation adjusting means (31) which includes a memory means for storing predetermined adjusting data for adjusting the deviation of the beam (B), a measuring means for measuring the deviation from the axis of the device, and a processing means for processing the measured deviation data with stored adjusting data to generate control data used for the adjustment of the deviation of the beam (B) in the beam axis deviation adjusting means (31). An electron beam exposure device according to claim 8, in which the control data for adjusting the deviation of the beam (B) take into account the focus point adjusting values determined by the focus point adjusting means (28) for each one of a plurality of aperture patterns. An electron beam exposure device according to claim 8 or 9, including at least two separate memory means, one for storing information about the axis deviation adjusting data for each one of the patterns and another for storing information about the focus point adjusting values for each one of the said patterns. A method for adjusting a focus point in the setting up of an electron beam exposure device comprising an electron gun (3a), a mask plate (27) having a plurality of apertures each having a predetermined shape for forming a cross-sectional shape of an electron beam (B) and a variable rectangular aperture forming means with which the cross-sectional area of a rectangular aperture is varied, deflecting means (5, 5') provided on either side of the mask plate (27) in relation to the beam path (B) respectively, for deflecting the beam (B) from its original axis so as to pass through one of the aperture patterns provided on the mask plate (27), and for deflecting it back to its original axis, a sample holding means (26), a current measuring means for measuring the current flowing through a surface of the sample (25) to be exposed by the electron beam (B), and a focus point adjusting means (28) including a memory means for storing control data thereof and a control means (100) for controlling the focus point adjusting means (28), said method including the steps of: selecting one of the patterns provided on the mask plate having a particular cross-sectional shape and a particular area; irradiating a beam through the pattern to form an image of the pattern on the sample holding means (26); characterised by the steps of measuring the value of a current representing the intensity of the beam (B), measured on the surface of the sample (25) held on the sample holding means (26) with respect to the selected pattern; storing the values of the current in a memory means; selecting a particular rectangular shaped aperture having a cross-sectional area giving the same current value as that obtained from the selected pattern so as to make the cross-sectional area of the rectangular aperture conform to the cross-sectional area of the pattern thus measured; irradiating the beam through the rectangular shaped aperture thus selected to form an image of the pattern on the sample holding means (26); determining focus point adjusting values for adjusting to the best focus point by means of the focus point adjusting means (28), using a discriminating means (32) for determining whether the focus point is located at the best focus point or not and, if not, processing the focus point adjusting values to decide the best focus point; storing the data thus obtained in the memory means in the control means; and adjusting the focus point by operating the focus point adjusting means (28) in response to the focus point adjusting values stored in the memory means. A method for adjusting a focus point in an electron beam exposure device according to claim 11, further including the step of storing in a memory means a plurality of the focus point adjusting values obtained by measuring the same with respect to each one of the patterns provided on the mask plate (27); and selecting one of the values memorized in the memory means in response to the pattern used or pattern information corresponding to the pattern used. A method for adjusting a focus point in an electron beam exposure device according to claim 12, in which the focus point adjusting values thus obtained corresponding to a certain selected aperture on the mask plate (27) are stored with information corresponding to the selected pattern in a predetermined address portion of a table in the memory means. A method for adjusting a focus point in an electron beam exposure device according to claim 11, 12 or 13, the electron beam exposure device including a beam axis deviation adjusting means (31) provided between the mask plate (27) and sample holding means (26), and a control means for controlling the beam axis deviation adjusting means, including a memory means for controlling the beam axis deviation adjusting means (31), the method including the further steps of: measuring a beam axis deviation between the beam (B) and a centre axis of the deflecting means (5,5'); determining control data for adjusting the deviation to make the beam (B) coincide with the centre axis of the deflecting means (5,5') ; adjusting the deviation using a beam axis deviation adjusting means (31) in dependence on the control data thus determined. A method for adjusting a focus point in an electron beam exposure device according to claim 14 further including the steps of: storing in a memory means a plurality of the control data for adjusting the deviation with respect to each respective pattern used, and selecting any one of the data stored in the memory means in response to a particular pattern or pattern information input to the focus point adjusting means. A method for adjusting a focus point in an electron beam exposure device according to claim 13 or 15 in which the beam axis deviation control data corresponding to a particular selected aperture of the pattern from the mask plate (27) are stored with the information corresponding to the selected pattern in a predetermined address portion of a table in the memory means. A method for adjusting a focus point in an electron beam exposure device according to claim 11 and including the steps of: storing the focus point adjusting values in the control means with an address, adjusting the focus point by operating the focus point adjusting means (28) in response to the focus point adjusting values stored in the memory means; measuring a beam axis deviation between the axis of the focus point adjusting means and the beam (B); determining control data to make the beam (B) coincide with the axis of the focus point adjusting means (28); storing the beam axis deviation data thus obtained in the memory means with an address; adjusting the deviation using a beam axis deviation adjusting means (31) in accordance with the adjusting data stored in the memory. A method for adjusting a focus point in an electron beam exposure device according to claim 17, in which the focus point adjusting values and the beam axis deviation data are stored in separate memory means with the information corresponding to the selected pattern in a predetermined address portion of a table of each memory means. A method for adjusting a focus point in an electron beam exposure device according to any one of claims 12 to 18, in which when one of the apertures of the patterns provided on the mask plate (27) is selected, the control means reads out a predetermined focus point adjusting value stored in a predetermined address portion of the memory means in response to a selecting signal corresponding to the selected pattern and supplies the focus point adjusting value read by the control means to the focus point adjusting means (28). A method for adjusting a focus point in an electron beam exposure device according to claim 17, 18 or 19, in which when one of the apertures of the patterns provided on the mask plate (27) is selected, the control means reads out a predetermined beam axis deviation data stored in a predetermined address portion of the memory means in response to a selecting signal corresponding to the selected pattern and supplies the beam axis deviation data read by the control means to the beam axis deviation adjusting means (31). A method of exposing the surface of a sample (25) held on an electron beam exposure device to an electron beam (B), including the steps of adjusting the focus point for the setting up of the device according to any one of claims 11 to 19 and including the further step of: applying the electron beam (B) to a sample (25) through the selected pattern to form an image of the pattern on the sample (25). A method according to claim 21 when appendant to claim 14, including the step of determining a beam axis deviation from a centre axis of the device including generating beam axis deviation adjusting data to adjust the beam axis to coincide with the centre axis of the device, processing the beam axis deviation adjusting data utilizing a beam axis deviation detecting means, and storing the beam axis deviation adjusting data in the memory means, and the step of adjusting the beam axis deviation to coincide with the centre axis of the focus point adjusting means including operating a beam axis deviation adjusting means (31) in response to the beam axis deviation adjusting data stored in the memory means.

Inventors: SAKAMOTO KIICHI, YAMADA AKIO, SAKAMOTO, KIICHI, YAMADA, AKIO
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H01J37
IPC codes: H01J37, H01L21, G03F7