An exposure apparatus

Abstract: An exposure apparatus (fig 10) usable with synchrotron radiation source (201) wherein the synchrotron radiation (202,204) is generated by electron injection (210) into a ring (201). The exposure apparatus is to transfer a semiconductor element pattern of a mask (208) onto a semiconductor wafer (209) by the synchrotron radiation. The apparatus includes a shutter (207) for controlling the exposure of the wafer (209). The shutter (207) controls the exposure with the illuminance distribution on the wafer surface taken into account. The illuminance distribution is determined (206,211,216) in response to the electron injection (210), and thereafter, the illuminance distribution is corrected (216,215,213,207) in a predetermined manner. By this, the illuminance distribution data for controlling (213,215) the shutter (207) always correspond to the actual illuminance distribution. The entire shot areas of the semiconductor wafer (209) are exposed with high precision.

Description: The present invention relates to a mask pattern transferring exposure apparatus used in manufacturing semiconductor devices, more particularly to an exposure apparatus which uses as a radiation source a synchrotron radiation source. An exposure apparatus which uses synchrotron radiation emitted when high energy electron make circle orbit motion, is known. The synchrotron radiation has a wide and uniform intensity distribution in a horizontal plane that is in a plane including the circle orbit. However, the beam width measured in the vertical direction is very much limited. In order to expand the beam width in the vertical direction, there are proposed various method. In one method, a mirror is disposed in an optical path between the synchrotron radiation source to the member to be exposed to the radiation, and the mirror is swung to scan the member to be exposed (Japanese Laid-Open Patent Applications Nos. 45026/1981 and 113065/1986; "Investigation of X-ray exposure using plane scanning mirrors" J. Vac. Sci. Techol. vol. 31, (4) p.1271, 1983, by M. Bieber, H.U. Sheunemann, H. Betz, A. Heuberger). In another example, the electron orbit in the accumulation ring of the radiation source is vertically swung by application of a magnetic field ("stationary large area exposure in synchrotron radiation lithography utilizing a new arrangement of magnets applied to the storage ring", Jpn. Appl. Phys., 22; L718 - L720, 1983, H. Tanio, K. Hoh). A further example is that a fixed mirror is disposed in an optical path from the radiation source to the member to be exposed to provide a large exposure area having a uniform beam intensity (variation of the beam intensity is not more than ±5 % in the area of 3x3 cm 2 ) ("Design of Stationary Toroidal Mirror for Large Area Synchrotron Radiation Exposure", preprint for the 31th Applied Physics Meeting, 282, 1984, by Koji Tanino and Ohtori Koichiro, and Japanese Laid-Open Patent Application No. 84814/1985). Referring to Figure 1, an example of an exposure apparatus using synchrotron radiation is shown. In Figure 1, reference numerals 1, 5 and 6 are synchrotron radiation beam, a mask and a semiconductor wafer which is to be exposed to the radiation. The apparatus comprises a stationary or fixed mirror 2 for expanding the synchrotron beam, an exposure chamber 3 filled with helium gas or the like, a window 4 of the exposure chamber 3 made of beryllium, a wafer stage 7, a spring 8, a wafer stage driver 9 and a frame 10 The apparatus further comprises movable aperture blades 11 and 12, supporting members 13 and 14 for the movable aperture blades and drivers 15 and 16 for the movable aperture blades. The movable aperture blades 11 and 12, the supporting members 13 and 14 and the drivers 15 and 16 constitute an exposure control means. Designated by a reference 17 is an ultra-high vacuum chamber which is isolated from the exposure chamber 3, containing helium gas,by the window 4. In operation, light (radiation) 1 travels through the ultra-high vacuum chamber 17 and is expanded by the mirror 2, and is passed through the window 4. The exposure control means controlled by a shutter controller 20 limits the light 1, and the limited light is projected onto the semiconductor wafer 6 through the mask 5, by which the pattern of the mask is transferred onto the semiconductor wafer 6. In an exposure apparatus using a synchrotron radiation source, the strength or intensity distribution of the radiation beam is narrow in the direction perpendicular to the plane of the accumulation ring. Therefore, it is preferable to expand the intensity distribution in this direction by one method or another. For the purpose of this expansion, Japanese Laid-Open Patent Applications Nos. 141135/1986 and 59828/1986 disclose that the synchrotron radiation is passed through a monocrystal or a diffraction grating so as to expand the divergence angle measured in the vertical plane. The beam provided thereby, as it is, involves non-uniformity and variation in the spectral distribution in the vertical direction, so that it is still not possible to project the mask pattern onto the wafer with uniform exposure amount. Then, Japanese Laid-Open Patent Application No. 104438/1981 discloses that a shutter is driven with control to quake uniform the exposure amount over each shot area on the basis of exposure beam profiles predicted beforehand. However, in the conventional art, since there is no practical sequential operation for determining the profile of the synchrotron radiation incident on the mask, the data for determining the profile is not accurate. With the increase of the pattern density in integrated circuit devices, the line width of the pattern transferred by the exposure decreases, and the control of the line width in the resist becomes more severe. As is well known, the line width formed in the resist changes greatly depending on variation in the exposure amount. Therefore, it is important the the actual amount of exposure is to be controlled correctly to be the desired amount. As for the system for correctly controlling the amount of exposure, Japanese Laid-Open Applications Nos. 101839/1982 and 198726/1984 disclose that the intensity of the exposure radiation during the exposure operation is detected by a detector disposed adjacent to the mask, and upon the desired amount of exposure reached, a shutter is closed. In the conventional apparatus, the area in which the intensity of the exposure radiation is uniform is relatively wide, and therefore, a measurement at the marginal area of the mask is not much different from the intensity in the exposure area, but in the SOR exposure, the region in which the intensity of the SOR is uniform is narrow, so that the X-ray intensity is different at the marginal measuring position than at the exposure area. To obviate this problem, it is considered that a retractable X-ray detector is advanced into the exposure area when the exposure operation is not carried out, and it detects the X-ray intensity, whereas during the exposure, the detector is retracted so as not to block the X-rays. However, when X-ray intensity varies with time as in SOR, it is possible that the X-ray intensity is different at the time of the exposure to that at the time of measurement with the result of an additional error. The present invention is intended to provide an X-ray exposure apparatus which can determine X-ray intensity with high accuracy when SOR is used. Exposure apparatus in accordance with this invention is defined in claim 1 appended. In such apparatus, after an electron is injected into an SOR ring to generate the synchrotron radiation, the intensity of X-rays is measured, and the X-ray intensity during the exposure operation is determined on the basis of the measurement and an attenuation curve of the injected electron. The X-ray intensity during an exposure operation for a shot can be correctly predicted both from one or more X-ray measurements after the orbit electron injection and from the attenuation curve of the orbit electron amount. Other advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, wherein: Figure 1 schematically shows a conventional exposure apparatus; Figure 2 is a general arrangement of the exposure apparatus according to an embodiment of the present invention; Figure 3 shows one of major parts of the exposure apparatus shown in Figure 2; Figure 4 is a graph illustrating change, with time, of the intensity of synchrotron radiation; Figure 5 is a flow chart showing operations of the exposure apparatus shown in Figure 2; Figure 6 is a general arrangement of an X-ray exposure apparatus according to another embodiment of the present invention; Figure 7 is a graph showing change in X-ray intensity I with time t; Figure 8 is a flow chart illustrating operations of the apparatus of Figure 6; Figure 9 is a graph showing change, with time, of the X-ray intensity I with time t; Figure 10 shows an exposure apparatus to which the present invention is applicable; Figure 11 is a graph showing illuminance distribution in the direction of y axis on the surface to be illuminated on an optical axis of the synchrotron radiation; Figure 12 shows a driving profile for the shutter used in Figure 10 apparatus; Figures 13 and 14 show driving profiles in which the time axis is expanded or contracted in accordance with an embodiment of the present invention; Figure 15 is a graph showing the intensity change of the synchrotron radiation source; Figure 16 is a general arrangement of another exposure apparatus to which the present invention is applicable; Figures 17 and 18 show driving profiles for the mirror in which the time axis is expanded or contracted in accordance with the present invention; Figure 19 shows a system structure of an apparatus according to a further embodiment of the present invention; Figure 20 shows an actuator driving table in the apparatus of Figure 19 embodiment; Figure 21 is a general arrangement of an exposure apparatus according to a further embodiment of the present invention; Figure 22 shows a shutter driving curve according to an embodiment of the present invention; Figure 23 is a general arrangement of an apparatus according to a further embodiment of the present invention; Figure 24 is a perspective view of a shutter; and Figure 25 is a general arrangement according to a further embodiment of the present invention. Referring to Figure 2, there is shown an exposure apparatus according to an embodiment of the present invention. In this Figure, reference numerals 101 and 102 designate a linear accelerator and an accumulation ring, respectively. The linear accelerator 101 serves to inject electrons into the ring 102. The linear accelerator 101 and the ring 102 are connected to a controller 106 for controlling the synchrotron system through a control line 107, so that a synchrotron radiation generating apparatus is constituted. Since the controller 106 is connected to an exposure apparatus 109 through a communication line 108, the electron injection timing by the linear accelerator 101 is transmitted to the exposure apparatus 109, so that the exposure apparatus 109 can be synchronously operated in accordance with an output of the synchrotron. The synchrotron radiation 110 produced from the accumulation ring 102 is expanded in the divergence angle in a Y direction (vertical direction) by an X-ray reflecting mirror 103 into an expanded radiation 104, which is introduced into the exposure apparatus through a transmitting window 105. The window 105 is durable against a pressure difference between the synchrotron side and the exposure apparatus side, and is made of beryllium or the like. Figure 3 is a sectional view of an inside of the exposure apparatus 109 of Figure 2, seen from the positive side of the y axis. The exposure apparatus 109 is provided with a casing or frame 121. To the frame, a shutter 111 and a shutter controlling unit 112 are mounted to control the amount of synchrotron radiation 104 incident on the mask 114 and a wafer 113. To a stage 119 for supporting the wafer 113, an X-ray detector 118 for measuring the intensity of the incident X-ray is mounted, so that the X-ray intensity is detected through the mask 114 at any position in an exposure shot area by movement of the stage. A laser interferometer 115, its optical axis 116, a mirror 117 on the stage 119 and a guide 120 constitute a control system for positioning the stage 119 in an X-Y plane with high accuracy. Figure 4 is a graph showing change of the radiation intensity of the radiation produced by the synchrotron radiation generator with time. Once the linear accelerator 101 injects electrons into the ring 102, the intensity of the synchrotron radiation logarithmically decreases with time. The interval period of the electron injections is different depending on the individual synchrotron rings, but it is generally several hours. The hatched portion in a graph indicates the time period in which the profile (illuminance distribution) of the synchrotron radiation intensity incident on the exposure apparatus 109 is measured. As will be understood, the intensity measurement is performed when the intensity of the incident synchrotron radiation is substantially highest, by which the data has substantially the highest S/N ratio. In the case of the synchrotron radiation, as shown in Figure 4 even if the absolute level decreases, the profile itself for each of the electron injection does not change. The measuring step is applied to the time when the material covering the window 105 is exchanged. When the material is beryllium, it is contaminated more and more with normal exposure operation of the exposure apparatus 109 with the result of reduction of the transmissivity. Therefore, the profile is stored on the assumption that the contamination occurs uniformly over the entire area of the transmitting window 105. Figure 5 is a flow chart showing the process steps in the operation. At step 141, the exposure apparatus 109 is started. At step 142, the discrimination is made as to whether or not the window material 105 is exchanged. If it is exchanged, the electron injection into the ring 102 is waited for (step 145). After the injection, the X-ray detector 118 detects the profile (step 146). The measurement is performed for each of several positions predetermined within the exposure area, while the stage 119 carrying the X-ray detector 118 is moved on the X-Y plane, more particularly, along Y axis. On the basis of the data of the profile measurement, a shutter controlling table is produced (step 147). If the material covering the window 105 is not exchanged, the discrimination is made as to whether or not the electron injection into the ring 102 is carried out or not at step 143. If it is immediately after the electron injection, the sequence goes to step 146 where the X-ray detector 118 effects measurement to determine illuminance distribution. If the electron injection is not carried out, the normal exposure operation is performed (step 144). When the profile does not much change for the respective electron injections, it is possible to advance to the normal exposure operation (step 144) similarly to the case of no electron injection, even immediately after the electron injection. As described, according to this embodiment, the illuminance distribution of the synchrotron radiation adjacent the mask 114 or the wafer 113 is determined on the basis of the measurement immediately after the electron injection into the ring 102 after the exchange of the window 105 material, by which the profile data can be obtained with high S/N ratio. Figure 6 is a general arrangement of an X-ray exposure apparatus according to another embodiment of the present invention, wherein a fixed mirror is used. In this Figure, a reference numeral 201 designates an SOR ring. The apparatus comprises an X-ray mirror 203, an X-ray transmitting window made of beryllium (Be) or the like, a movable X-ray detector 206 and a shutter 207. Designated by reference numerals 208 and 209 are an X-ray mask and a wafer coated with a resist sensitive to the SOR radiation. The synchrotron radiation 202 is expanded by the X-ray mirror 203 into expanded radiation (X-ray) 204. The apparatus further comprises an electron injection 210, a signal processor 211, an X-ray detector driver 212, a shutter driver 213, an X-ray detector controller 214, a shutter controller 215 and a CPU (central processing unit) 216. Generally, an exposure operation using the SOR is started after low energy electrons are injected by the injector 210 into the SOR ring 201, and they are accelerated up to a predetermined energy level. However, the number of electrons injected gradually decreases due to the collision with gas molecules or the like remaining in the orbit in the SOR ring 201, with the result that the intensity of the radiation decreases. Therefore, when the number of orbit electrons or the intensity of the radiated X-rays becomes below a predetermined value, the electrons are stopped, and the exposure operation is interrupted. Thereafter, the electrons are injected again, and then the exposure operation is resumed. Referring to Figure 8 , the operation of the X-ray exposure apparatus of Figure 6 will be described. When the shutter 207 is closed (broken line in Figure 6 ), the electrons are injected by the injector 210 into the SOR ring 201 and are accelerated at step 221. At step 222, the CPU 216 instructs exposure intensity measurement to detect the X-ray intensity. In this detection process, the X-ray detector 206 is advanced into the exposure area by the X-ray detector driver 212 through the X-ray detector controller 214 (broken lines in Figure 6), by which the X-ray intensity is detected. The detected X-ray intensity is transmitted to the CPU 216 through the signal processor 211, and the X-ray detector 206 is retracted to outside the exposure area. At step 223, the CPU 216 calculates an X-ray intensity Ie during the exposure on the basis of the X-ray intensity detected. At step 224, the exposure time T is calculated from the set exposure amount D and the calculated level and it is set. Simultaneously, the alignment operation between the X-ray mask 208 and the wafer 209 is carried out. The exposure time T can be calculated by: T = D/Ie if the attenuation of the X-ray intensity is small during the exposure. Thereafter, at step 225, the CPU 216 instructs the shutter controller 215 to start exposure operation, in response to which the shutter driver 213 opens the shutter 207 to start the exposure. When the exposure period T elapses after the start of the exposure, the shutter 207 is closed. At step 225, the discrimination is made as to whether or not the intensity detection is performed. If so, the sequence goes to 222, and if not, it goes to step 223. The X-ray intensity Ie during the exposure is determined in consideration of the attenuation of the intensity in the following manner. Figure 7 is a graph showing the change of the X-ray intensity I with time t. The abscissa and ordinate represent time t and X-ray intensity I, respectively. It is assumed that the X-ray intensity is detected at the point of time tm, and the exposure operation is started at the point of time te. The X-ray intensity I(te) during the exposure is corrected in accordance with the intensity I(tm) during the detection by the following equation: I(te) = I(tm) exp(-(te-tm)/τ) where τ is a so-called electron beam life and can be calculated using the degree of vacuum of the apparatus and Touschek effect or the like or by measurement. "Accelerator Science", vol. 12, No. 2, P. 95, states that τ is given by: τ is 1x10 -27 x (1/p) x (1/σ T ) where p is a degree of vacuum, and σ T is a crosssectional area of collision. The equation for correction may be different from equation (1). For example, when (te-tm)/τ is sufficiently smaller than 1, the correction equation, taking into account up to the first order of the Taylor expansion, is as follows: I(te) = I(tm)[1 -(te-tm)/τ] As another example, the following equation is possible using the half-life th of the orbit electrons, as follows: te-tm/th I(te) = I(tm)(1/2) For example, if the X-ray intensity of 150 mw/cm 2 is detected at 30 sec under the conditions that the life of the electrons is 3600 sec in the SOR ring and that the target exposure illuminance is 50 mJ/cm 2 , the X-ray intensity Ie at the respective exposure times and the exposure period t is calculated as given in Table 1 below using the equation (1), where the transmissivity of the mask is assumed 50 %. TIME OF EXP. X-RAY INTENSITY (mw/cm 2 ) EXP. PERIOD 60 sec 148.8 0.67 sec 120 146.3 0.68 180 143.9 0.70 600 128.0 0.78 Since the X-ray intensity changes depending on the amount of injected electrons and the acceleration voltage, the X-ray intensities for the exposure operations can be determined by the equation (1) or another until the re-injection, if the X-ray intensity is detected once after the electron injection. If, in alternative to the present invention, the detections are performed at regular intervals, for example, immediately before the respective exposure operations, the X-ray intensity during the exposure can be determined more accurately. If the number of exposure operations is to be increased, it is possible to effect the detecting operation during the wafer exchanging operation. Referring to Figure 9, description according to the invention will be made as to determining the electron life τ on the basis of the intensity detection at the time of previous electron injection. Figure 9 shows the changes in the X-ray intensity I with time t when the electron injection is carried out plural times. The electrons are injected at the point of time ti, and the electrons are blocked at the point of time tc by which the orbit current becomes zero. The X-ray intensity is measured at the times t1 and t2, and the detected intensities are I(t1) and I(t2). The electron life τ is expressed as follows: τ = (t 2 -t 1 )/[ l n I(t 2 )/I(t 2 )] It is understood that the electron life is determined if the X-ray intensity is detected twice for one electron injection. However, in order to increase the accuracy of the determination of the electron life τ, it is preferable that three or more detections are performed at regular intervals for one electron injection, and the electron life is determined as an average or using least square approximation. In place of the detections at regular intervals, it is possible that the intensity is detected at such intervals that the X-ray intensity attenuates by a predetermined degree from the past data, and then the electron life τ is correctly determined with small number of detections. For example, assuming that the electron life determined on the basis of the past data is τ, and the detection is performed for every 5 % attenuation, the detection timing is 0.051τ, 0.105τ, 0.16τ and 0.22τ. Upon determination of the electron life τ, not only the data at the immediately previous injection, but also further previous data may be used. If two or more detecting operations are already carried out for the current injection, the data are usable. In this case, different weights may be placed on the data depending on the difference in the points of detection times. Where the degree of vacuum is different during the intensity detection for the determination of the electron life τ than during the exposure operation, the electron life τ may be corrected using the equation (2). For example, the electron life τe is expressed, τe = (Pm·τm)/Pe where Pm and τm are a degree of vacuum and the electron life during the detection, and Pe is the degree of vacuum during the exposure. Using the electron life τ and the detected intensity after the current injection, the X-ray intensity during the exposure period te can be determined on the basis of the equation (1). As described above, according to the X-ray exposure apparatus according to this embodiment, the X-ray intensity during the exposure operation is predicted from the X-ray intensity detected after the orbit electrons are injected and the attenuation curve of the X-ray intensity. Therefore, when the X-ray intensity during the exposure cannot always be measured, and when the X-ray detector is advanced into the exposure area during the non-exposure-operation to detect the X-ray intensity, the X-ray intensities during the exposure operation can still be determined with high accuracy. In addition, the difference between the detected intensity and the intensity during the exposure operation can be reduced when the attenuation of the radiation is large, or when the time interval between the X-ray intensity detection and the exposure operation is long. Figure 10 shows an exposure apparatus to which a further embodiment of the present invention is applicable, wherein reference numerals 501 and 502 designate a wafer and a mask, respectively, wherein the mask is disposed parallel to the wafer 501 with a gap of approximately 40 µm in a z direction. The apparatus comprises a mask stage 500 for supporting the mask 502, a wafer moving space 503 for supporting and moving the wafer 501. In this embodiment, the exposure apparatus is a so-called stepper exposure apparatus wherein the exposure areas sequentially stepped to expose all of the exposure areas of the wafer are exposed. The apparatus further comprises a sensor 504 mounted on the wafer moving stage 503 to detect the intensity of the illuminating radiation incident on the wafer 501 at a given point in the exposure area. A movable aperture stop 505 has an opening to constitute an exposure shutter together with an auxiliary shutter 506. Designated by a reference 507 is a thin film of beryllium. The space between the thin film 507 and the mask 502 contains pressure-reduced helium, and the space between the mask 502 and the radiation source is a ultra-high vacuum space. A radiation emitting point of the SOR ring which is an X-ray source is designated by a reference 508. The intensity of the synchrotron radiation is uniform in a direction parallel to a plane including the orbit of the electron beam, but the intensity is not uniform in the vertical direction, and is symmetrical. A convex cylindrical mirror 509 functions to expand the synchrotron radiation in the direction in which the radiation has the intensity distribution (y axis direction), so that the radiation can illuminate the exposure area required at the position of the mask 502 and the wafer 501 in the exposure apparatus. Generally, where a cylindrical mirror having a refraction surface of a single curvature, the illuminance intensity is a one-dimensional distribution having one peak in the exposure area. Figure 11 shows an example of calculated illuminance distribution weighed in consideration of the dependency, on the wavelength of the sensitivity of the resist applied on the wafer 501. Figure 12 schematically shows the appearance of the exposure shutter 505 and a driving profile. A belt 521 is stretched between the drums 528 and 529 and is made of stainless steel, for example, and the thickness is sufficient to block the X-rays. The aperture 524 is defined by a leading edge 526 and the trailing edge 527. The time period between the passage of the leading edge 526 at the view angle (exposure start) and the passage of the trailing edge 527 at the view angle (exposure end) is the time period of exposure. In the belt 521, another opening is formed so as not to block the exposure through the aperture 524 in the view angle. In the drive profile of the shutter 505 (in the graph of Figure 12) the area between Y1 - YN corresponds to the view angle to be exposed. In this region, an area of a small region ΔY defined by the leading edge 526 and the trailing edge 527 is an amount of exposure at a point in the view angle. The amount of exposure at each of such point, can be controlled one-dimensionally by moving the movable aperture 524 in a driving profile. In this example, the driving profile is so selected that the illuminance distribution of Figure 11 is uniformized. The intensity attenuation of the radiation provided by the synchrotron radiation source is logarithmic from the time of electron injection from linear accelerator, as shown in Figure 15. Therefore, it is preferable that the driving profile of the exposure shutter is changed for each of the exposure operations on the basis of the intensity detection from the radiation source, so that the desired amount of exposure can be provided for each of the shot areas. Alternatively to the present invention, in order to ease the correction operation, the intensity of the synchrotron radiation is detected by a detector 504 (Figure 10) in this embodiment. In response to the detected intensity, the driving profile is expanded or contracted in the direction of the time axis, thus providing the desired exposure amount. Figures 13 and 14 show an example. Figure 14 shows an expanded driving profile provided by expanding the Figure 12 driving profile only in the direction of the time axis (abscissa). This is applicable when the intensity of the synchrotron radiation by the radiation source is low. Figure 14 shows the opposite case. Figure 16 shows a system structure for accomplishing the above function. The system comprises driving motors 541 and 542 for driving the auxiliary shutter 506 and the main shutter 505 of Figure 10 The motors 541 and 542 are pulse motors or DC motors driven by motor drivers 543 and 544, respectively. Pulse generators 547 and 548 supply pulses to the motor driver 543 and 544, and in response to each of the pulses, the motor 541 or 542 is rotated by a predetermined angle accurately. The pulse generator 547 and 548 are provided with RAM which stores a table shown in Figure 20, for example. The contents of the table correspond to the pulse intervals produced from the pulse generators 547 and 548. A subordinate CPU (central processing unit) 550 controls the main shutter 505 and the auxiliary shutter 506 and controls the pulse generators 547 and 548 through a local bus line 556. A signal from the sensor 504 for the illuminance detection mounted on the stage 507 shown in Figure 11 is converted into a digital signal by a detector signal processing unit 550. The stage 503 is driven by a driving motor which is driven by a motor driver 545, and the positioning of the stage 503 is effected by a motor driver 546. A stage actuator controlling unit 551 controls the position of the stage 503. Designated by reference numerals 552 and 553 are a laser interferometer and a control unit for distance measurement, respectively. Those elements are effective to correctly measure the position of the wafer 501 carried on the wafer stage 503. The stage controlling unit 551 and the controlling unit 553 for the distance measuring system are controlled by the subordinate CPU 554. To a common bus 557, a detector signal processing unit 550 and the subordinate CPU 554 for the stage side are connected, and therefore, the illuminance of the exposure radiation can be effected at any point in the exposure area synchronously, and the detection can be stored in the memory 558 for the respective points in the exposure area by the instructions by the main controller 559. During the actual exposure operation (during the operation for transferring the pattern of the mask 502 to the wafer 501), a shutter driving table (Figure 20) for providing the desired exposure distribution from the contents stored in the memory 558, and the table data are supplied to the RAM of the pulse generators 547 and 548, and they drive the associated motors. Immediately before the shot exposure, the illuminance is detected by the sensor 504, and if the radiation intensity of the illumination source attenuates as compared with the previous shot, for example, the driving table of Figure 20 is corrected by mathematically by the main controller 559. The driving profile 29 is modified by changing the pulse intervals of the pulse generators 547 and 548 so as to provide the desired proper exposure amount distribution. The driving table first produced is stored as a source table together with the data of the illuminance of the exposure radiation when the data are obtained. Figure 16 shows another structure of the exposure apparatus to which an embodiment of the present invention is applicable. Since this embodiment is similar to Figure 10 embodiment, the same reference numerals as in Figure 10 are assigned to the elements having the corresponding functions, and the description thereof are omitted for simplicity. In Figure 10 exposure apparatus uses a movable aperture 505 to limit the exposure amount, but in the apparatus of this embodiment, the mirror 509 is swung to control the exposure amount. The mirror 509 expands the SOR in the direction of the Y axis to illuminate a part of the mask 502 and a part of the wafer 501. The mirror 509 is swung by an actuator mechanism 531. The actuator mechanism 531 swings the mirror 509 in the direction y and in the direction Wx (x axis rotational direction). By this, the reflected radiation is deflected in y direction, and therefore, the entire area of the mask 502 is illuminated by the exposure radiation. However, the spectral distribution and the intensity of the deflected radiation are different depending on the angle of incidence of the synchrotron radiation from the radiation source, and therefore, the exposure amount distribution is not uniform if the scanning is at constant speed in the Y direction. To obviate this problem, a mirror swinging profile as shown in Figure 16 is produced, and in accordance with this profile, the mirror 509 is swung to avoid the non-uniformity of the exposure. When the radiation source intensity changes similarly to the case of Figure 10 the profile is expanded or contracted in the direction of the time axis as shown in Figure 18 so as to provide a desired exposure amount. In Figure 18, an increase of the intensity of the radiation by the radiation source is compensated by contraction of the time axis of the profile, thus providing a desired amount of exposure. The system arrangement of Figure 16 embodiment is similar to Figure 10 embodiment. However, in Figure 19, the mechanical structures of the actuators 541 and 542 and the motor drivers 543 and 544 are modified to swing the mirror 509 in Figure 16. According to this embodiment, the necessity for producing the driving profile for driving the exposure amount controlling device of the exposure apparatus for each of the exposure shots is avoided, and simply by expanding and contracting the time axis of the profile once produced, the proper exposure distribution can be provided at all times quickly in response to the intensity change of the radiation by the radiation source. Therefore, the calculation process for repeatedly producing the profile has been greatly simplified. Figure 21 shows a further embodiment. In this Figure, the same reference numerals as in Figure 1 are assigned to the elements having the corresponding functions, and the detailed description of those elements are omitted for simplicity. In the present embodiment, the stage 7 is provided with an X-ray detector 622. Before the exposure operation, the wafer stage 7 is moved in the direction of y axis to detect the change of the beam intensity of the synchrotron radiation with time. The intensity of the synchrotron radiation attenuates with time. The change of the beam intensity I with time is expressed as follows: I = Io e -t/τ where Io is an initial beam intensity. The detector 622 detects the beam intensity of the synchrotron radiation for a necessary period of time, and the shutter controller determines a time constant τ (generally called as "electron life") of the attenuation using least square approximation. The time constant τ of the attenuation may be the one determined beforehand. If the attenuation characteristics are determined in this manner, the beam intensity of the synchrotron radiation can be calculated at any point of time. As an example, assuming that the time constant of the beam attenuation is 7600 sec, and that the beam intensity I at time T1 is 1 mW/cm 2 by calculation, and that the necessary amount of exposure Q is 120 mJ/cm 2 , the proper exposure period is The result is Q = 121 sec. The calculation is performed by the shutter controller 20. As shown in Figure 39 the aperture limiting or defining member 11 of the movable aperture stop 1 driven by the driver 15 for 121 sec from the time T1 to the time T2 at a speed of (Y2-Y1)/121 in the direction +Y, and thereafter, it is stopped. In Figure 22, (1) shows a relationship between a position of an edge surface 18 (Figure 3) of the opening limiting member 11 of the movable aperture and the time. The opening limiting member 12 of the movable aperture stop is moved from the time T2 in the direction +Y by the driver 16. As to the driving speed at this time, the shutter controller calculates the driving speed of the edge surface 19 to provide uniform amount of exposure within the angle of view 21 by the following equation: Where Y is a position of the edge surface 19 (Figure 3) of the opening limiting member 12 of the movable aperture stop at the time t. The speed v at which the limiting member 11 of the movable aperture stop moves in the direction +Y is: (Y2-Y1)/(T2-T1) The limiting member 12 of the movable aperture stop is moved from the time T2 at the following speed: v·e -t/τ /(e -t/τ + 1 - e -T2/τ ) where τ is a timing constant of the beam attenuation. This movement is in the direction +Y, and when it reaches the position Y2, opening limiting member 12 is stopped. In Figure 22, (2) shows a relationship between a position of the edge surface 19 of the opening limiting member 12 of the movable aperture and the time. By driving the movable aperture stop in this manner, the exposure amount within the view angle 21 is substantially uniformly 120 mJ/cm 2 , so that the mask pattern can be transferred onto the wafer with high resolution. Figure 23 shows a further embodiment. In this Figure, the same reference numerals as in Figure 21 are assigned to the corresponding elements, and detailed description of those elements are omitted for simplicity. A mirror 602 is disposed in the ultra-high vacuum ambience 17. The mirror 602 is supported by a supporting rod 623 for rotation about an axis 624. A driving rod 625 is connected to the mirror 602. The driving rod 625 is driven by a driver 626. The driver 626 is controlled by a mirror controller 620 which drives the driving rod 625 to swing the mirror 602 to scanningly illuminate the mask 5 and the wafer 6 with the SOR radiation reflected by the mirror 602. Similarly to Figure 21 embodiment, by the X-ray detector 622 mounted on the wafer stage 7, the change of the beam intensity of the synchrotron radiation is detected while the wafer stage 7 is being moved before the exposure operation. The beam intensity I is approximated as: I = Io e -t/τ where Io is the initial intensity, and the time constant τ is determined by least square approximation by the mirror controller 620. By this, the beam intensity of the synchrotron radiation at any point of time can be calculated. Figure 24 is an enlarged view of the shutter 627. The beam is indicated by hatched portion. The synchrotron radiation has a Gaussian distribution in the direction perpendicular to the beam, that is, in the plane z-y. The standard deviation is approximately 1 mm in the view angle 21, as an example. It is assumed that the beam strength at time T1 when the exposure starts is 100 mW/cm 2 , that the required amount of exposure Q is 100 mJ/cm 2 . If the beam intensity did not attenuate, it would suffice if the beam would sweep in the z direction on the view angle 21 at the speed of 2.5 mm/sec. However, since the beam intensity attenuates, the beam sweeping speed v is preferably calculated by the controller to compensate this. The sweeping speed v of the beam in the view angle 21 is obtained from the following equation: v = v o e -t/τ where v o is the sweeping speed at the time T1 of the exposure operation start. When the beam is swept at this compensated speed, the amount of exposure within the view angle 21 is substantially uniformly 100 mJ/cm 2 . Figure 25 shows a further embodiment. In the embodiment of Figure 23,the rotational speed of the mirror 602 is changed to compensate the attenuation, with time, of the beam intensity of the synchrotron radiation. However, in the present embodiment, the shutter 627 is fixed during the exposure operation, whereas the moving speed of the stage 7 is changed during the exposure for one view angle to compensate the beam intensity attenuation to provide a constant amount of exposure. The driving speed of the stage 7 is determined so that the relative positional relation between the beam and the view angle 21 is the same as that in Figure 23 embodiment. More particularly, the stage 7 is driven in the direction of -Y at a speed of v calculated by the stage controller 621 as follows: v = v o e -t/τ When the stage 7 is driven at this speed, the amount of exposure in the view angle 21 is substantially uniformly 100 mJ/cm 2 . As described in the foregoing, according to this embodiment, the cumulative amount of exposure in the view angle is substantially free from variation due to the attenuation, with time, of the beam intensity, so that the resolution of the exposure apparatus can be improved.

Claims: An exposure apparatus for exposing a substrate (113, 114; 208, 209; 501, 502; 5,6) to synchrotron radiation generated from a synchrotron radiation source (102; 201; 508), said exposure apparatus comprising: detecting means (118; 206; 604; 662) operable to detect intensity of the synchrotron radiation at a time immediately following electron injection into a ring of the synchrotron radiation source (102;201;508); exposure control means (111, 112; 207; 505,506; 11, 12, 16; 602) to be disposed in a radiation path between the synchrotron radiation source and the substrate (113, 114; 208, 209; 501, 502; 5,6) said exposure control means including a movable member (111; 207; 505, 506; 11, 12; 602; 707) for selectively limiting the synchrotron radiation to the substrate; determining means (106; 216; 559; 20) for determining a driving profile for driving said movable member so as to provide a constant amount of exposure of the substrate at each exposure operation despite attenuation, with time, of the intensity of the synchrotron radiation wherein said determining means (106; 216; 559; 20) is arranged to determine said driving profile from the intensity detected by said detecting means at said time immediately following electron injection into said ring by calculating intensity attenuation of the synchrotron radiation (104;204;532) on the basis of attenuation curve information for electrons injected into said ring; and driving means (213, 215; 543, 544, 555; 620) for driving said movable member (111; 207; 505, 506; 11, 12; 602) of said exposure control means (111, 112; 207; 505,506; 11, 12, 16; 602) in accordance with the driving profile determined by said determining means (106; 216; 559; 20). An apparatus according to claim 1, wherein said movable member comprises a movable shutter (111, 207, 505, 506; 11, 12). An apparatus according to claim 1, wherein said movable member (111; 207; 505, 506; 11, 12; 602) comprises a movable mirror (602). An apparatus according to claim 1, wherein said detecting means (118; 206; 604; 662) comprises an X-ray detector. An apparatus according to claim 4, wherein said X-ray detector is movable into and across an exposure area. Method of using the exposure apparatus as claimed in any of claims 1 to 5, with a synchrotron radiation source (102; 201; 508), wherein said exposure control means (111; 112; 207; 505; 506; 11, 12, 16; 602) is disposed in a radiation path between the synchrotron radiation source (102; 201; 508) and a substrate (113, 114; 208,209; 501, 502; 5, 6) that is to be exposed; and exposure of the substrate is controlled using said exposure control means (111, 112; 207; 505, 806; 11, 12, 16; 602) to selectively limit synchrotron radiation to the substrate. A method of producing a semiconductor circuit device in which a semiconductor wafer (6) is exposed to synchrotron radiation projected thereto through a mask (5), by using an exposure apparatus as claimed in any of claims 1 to 5 according to the method of claim 6.

Inventors: AMEMIYA MITSUAKI, KUROSAWA HIROSHI, SHIMODA ISAMU, TERASHIMA SHIGERU, UDA KOJI, UZAWA SHUNICHI, AMEMIYA, MITSUAKI, EBINUMA, RYUICHI, HARA, SHINICHI, KAWAKAMI, EIGO, KUROSAWA, HIROSHI, MIZUSAWA, NOBUTOSHI, MORI, MAKIKO, OZAWA, KUNITAKA, SHIMODA, ISAMU, TERASHIMA, SHIGERU, UDA, KOJI, UZAWA, SHUNICHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: G03F7
IPC codes: G03F7