Patent Number: 
Section: description

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the embodiments set forth below, an X-ray stepper in which a mask pattern is transferred to a wafer by a step-and-repeat operation will be described. However, the present invention is not limited to the following embodiments. First Embodiment Reference will be had to FIGS. 1 and 2 to describe an X-ray exposure apparatus according to first embodiment of the present invention. FIG. 1 is a schematic view illustrating an X-ray exposure apparatus according to a first embodiment of the present invention as seen from the side, and FIG. 2 is a schematic view illustrating the X-ray exposure apparatus according to this embodiment as seen from above. The apparatus includes a point-source X-ray source 101 that uses a solid metal target (not shown) and condenses laser light (not shown) to apply the laser light to the target in the form of pulses. The metal surface thus irradiated with the laser light is plasmatized and produces X-rays. The intensity and pulse width with respect to time of the laser light can be controlled by an intensity adjustment mechanism in the laser oscillator, not shown. By varying the intensity and pulse width with respect to time of the laser light using the intensity adjustment mechanism, the point-source X-ray source 101 is capable of controlling the intensity of the X-rays generated. In this X-ray exposure apparatus, the X-rays emitted by the point-source X-ray source 101 are introduced into a first collimator 110, second collimator 120 and third collimator 130. The centers of these three collimators 110 to 130 are disposed so as to have the same Z coordinate in the XYZ coordinate system of the drawings. The second collimator 120 uses X-rays in an area A as its input and the third collimator 130 uses X-rays in an area C as its input. Since the three collimator 110 to 130 in this case are disposed in a radial configuration with respect to the X-ray emission point of the point-source X-ray source 101, substantially the same design can be adopted for them. It is essential that the laser and target of the point-source X-ray source 101 be so disposed as not to interfere with an X-ray introduction chamber 102 and first, second and third exposure units 119, 129, 139, respectively. In the X-ray exposure apparatus of this embodiment, the first, second and third exposure units 119, 129, 139 are connected to the first, second and third collimators 110, 120, 130, respectively. In the first exposure unit 119, a first mask 113 and first wafer 114 are placed so that their angles will conform approximately to the emission angle of the first collimator 110. The same is true with regard to the second exposure unit 129 and third exposure unit 139. In each of the exposure units 119, 129, 139, precise angular and positional adjustments between the optical axis of exposure and the masks 113, 123, 133 and wafers 114, 124, 134 is carried out by moving the exposure units 119, 129, 139, per se, or the collimators 110,120, 130. In the first exposure unit 119, the first mask 113 is brought in and sent out between a mask introduction section (not shown) and the exterior of the first exposure unit 119 by means of the mask introduction selection. The first mask 113 introduced to the first exposure unit 119 is delivered to a mask stage (not shown) by a mask transport system (not shown). The same is true with regard to the second exposure unit 129 and third exposure unit 139. Further, in the first exposure unit 119, the first wafer 114 is brought in and seat out between a wafer introduction section (not shown) and the exterior of the first exposure unit 119, by means of the wafer introduction section. The first wafer 114 introduced to the first exposure unit 119 is delivered to a first wafer stage 16 by a wafer transport system (not shown). The same holds true for the second exposure unit 129 and third exposure unit 139. The first wafer stage 116, second wafer stage 126 and third wafer stage 136 are guided along respective ones of guides by gas bearings that employ helium gas. Position information concerning the wafer stages 116, 126, 136 is measured by laser interferometers (not shown) and the stages are driven by linear motors (not shown) based upon the measurements obtained. The first mask 113 is positioned with respect to a reference mark in the first exposure unit 119 by a position detector and mask stage, neither of which are shown. The first mask 113 and first wafer 114 are positioned relative to each other by the position detector and mask stage (not shown) and by the first wafer stage 116. The second mask 123 and third mask 133 are positioned in the same manner. A method of controlling the X-ray exposure apparatus according to this embodiment will now be described with reference to FIGS. 3 and 4, in which FIG. 3 is a control block diagram of the X-ray exposure apparatus according to this embodiment and FIG. 4 is a diagram of control timing of the X-ray exposure apparatus according to this embodiment. The emission timing of the laser in a point-source X-ray source 301, namely, the X-ray emission timing, is decided by an X-ray emission trigger signal. Further, the point-source X-ray source 301 is such that the intensity of the emitted laser is decided by an X-ray intensity control signal. It is preferred that the X-ray emission trigger signal and X-ray intensity control signal be signals of the kind shown in FIG. 4. Whether X-rays are capable of being emitted, and the internal device status, are constantly reported by the point-source X-ray source 301 to an exposure-apparatus total control unit 304 as a point-source X-ray source status signal. A target value of an amount of exposure by the first exposure unit is set in the total control unit 304. The set value is transmitted to a first exposure-amount controller 306. The same is true with regard to the second and third exposure units. The total control unit 304 calculates target values of X-ray intensity and emission pulse count based upon the set value of an amount of exposure. The total control unit 304 notifies an X-ray intensity control signal generator 303 of the X-ray intensity prevailing when the exposure is started, and the X-ray intensity control signal generator 303 sets the X-ray intensity control signal to a prescribed value. This control signal is set to prescribed values by the signal and timings shown in FIG. 4 and is output from the point-source X-ray source 301 to the X-ray intensity control signal generator 303. When preparations for exposure of a shot to be exposed are completed in the first exposure unit, the first exposure unit controller 306 so notifies the total control unit 304. Alternatively, if the first exposure unit is not scheduled to perform exposure for the time being, the first exposure unit controller 306 notifies the total control unit 304 that the first exposure unit is idle. Operation is the same with regard to the second and third exposure units. When all of the first to third exposure units are ready to perform exposure or are idle, the total control unit 304 sends a shutter controller 305 a command to open the shutter (first shutter 35, second shutter 36 or third shutter 317) corresponding to the exposure unit that is ready to perform exposure. In other words, a shutter corresponding to an exposure unit in the idle state is left closed. In this embodiment, the timings shown in FIG. 4 are adopted as an example of timings of the exposure states (exposure ON/exposure OFF) of the first to third exposure units and timings of the states (open/closed) of the first to third shutters. Since an exposure unit in the idle state does not undergo control of an amount of exposure, the description rendered below assumes that none of the exposure units are idle. The shutter controller 305 causes first, second and third shutter drive units 312, 313 and 314, respectively, to exercise control so as to open the first, second and third shutters 315, 316 and 317, respectively, whereby the shutters 315, 316, 317 are driven by the shutter driver units 313, 313, 314, respectively. Upon confirming that opening of the shutters 315, 316, 317 is completed, the first through third shutter drive units 312 to 314 so notify the shutter controller 305. Upon being so notified, the shutter controller 305 similarly notifies the exposure-apparatus total control unit 304. The exposure-apparatus total control unit 304 receives signals giving notification of the status of the point-source X-ray source, notification of completion of shutter opening and notification that the first to third exposure units are ready to perform exposure. Upon judging that exposure is possible based upon these notification signals, the total control unit 304 starts the exposure operation. At this time, the total control unit 304 issues a trigger generation command to an X-ray emission trigger generating unit 302. The latter outputs an X-ray emission trigger signal to the point-source X-ray source 301. The X-ray emission trigger signal is output as the pulsed signal and at the timings shown in FIG. 4, by way of example. The first exposure unit controller 306 measures the X-ray intensity by a first X-ray sensor 309, thereby obtaining an integrated value from the start of exposure of the first shot. The exposure-apparatus total control unit 304 reads the integrated value of X-ray intensity out of the first exposure unit controller 306 for every X-ray emission pulse. The total control unit 304 notifies the X-ray intensity control signal generator 303 to lower the X-ray intensity if the integrated value of X-ray intensity of the first exposure unit has approached the target value of the amount of exposure and the difference between them has fallen below a certain threshold value. As a result, the error between the target value of the amount of exposure and the actual amount of exposure of one shot in the first exposure unit diminished. These operations are the same with regard to the second exposure unit controller 307 and second X-ray sensor 310 and with regard to the third exposure unit controller 308 and third X-ray sensor 311. If X-ray intensity is controlled across the board in the above method, there is the possibility that an error in the amount of exposure will take on a large value because the target value has already been reached or because of the other exposure units whose integrated target values of the amount of exposure are nearly the same. In order to prevent this, the total control unit 304 has adjustment means for varying the threshold value, which is used in evaluating the error, in conformity with the target value of the amount of exposure of each exposure unit. With regard to the first exposure unit controller 306, the total control unit 304 judges the error in the amount of exposure in the first exposure unit from the target value of X-ray intensity of the next pulse and performs a calculation, pulse by pulse, to determine whether the error is the minimum error. If it is determined that the exposure error is minimum, then the exposure-apparatus total control unit 304 sends the shutter controller 305 a command to close the first shutter 315, thereby terminating exposure of one shot. These operations are the same with regard to the second exposure unit controller 307 and third exposure unit controller 308. In this embodiment, three exposure units are provided. However, the present invention is not limited to three exposure units. Two or more exposure units may be used and there is no limit upon the number of exposure units so long as this number of units can be installed. Second Embodiment A second embodiment of the present invention will now be described. FIG. 5 is a schematic view illustrating an X-ray exposure apparatus according to this embodiment, in which components identical with those shown in the FIGS. 1 and 2 are designated by like reference characters. As shown in FIG. 5, a fourth exposure unit 149, fourth collimator 140, fifth exposure unit 159 and fifth collimator 150 can be provided in addition to the first to third exposure units and first to third collimators of the first embodiment. These additional exposure units and collimators are disposed along the Z-axis. This embodiment makes it possible to raise the utilization efficiency of the X-ray source even further. Third Embodiment A third embodiment of the present invention will now be described. In this embodiment, all or part of the wafer transport system, which is for supplying wafers to each of the exposure units and ejecting wafers whose exposure has been completed, can be shared by each of the first to third exposure units of the first embodiment and by each of the first to fifth exposure units of the second embodiment. Further, all or part of the system for transporting masks or masks on which circuit patterns have been rendered for being burned into wafers can be shared by each of the first to third exposure units of the first embodiment and by each of the first to fifth exposure units of the second embodiment. Fourth Embodiment A fourth embodiment of the present invention will now be described. In each of the foregoing embodiments, the shots of n-number of exposure units start to be exposed simultaneously. An X-ray exposure apparatus using an exposure timing other than this will be described in this embodiment. In FIG. 3, the exposure-apparatus total control unit 304 can exercise control in such a manner that the exposure timings of the n exposure units are made to conform to particular objectives. Examples of these objectives are an improvement in the utilization efficiency of the X-ray source, a reduction in exposure processing time and suppression of a decline in precision caused by vibration between exposure units. In order to achieve the above, the X-ray exposure apparatus according to this embodiment sets a redundancy-allowance threshold value Tth of exposure processing time and redundancy-allowance threshold value of Pth of X-ray source pulses in the exposure apparatus total control unit 304 beforehand. In a range within which these two threshold values are not exceeded, the X-ray exposure apparatus of this embodiment is capable of tuning exposure timing in accordance with the above-objectives. In this embodiment, control of the amount of exposure of each shot is carried out by controlling both the number of exposure pulses and the X-ray intensity of the X-ray source in a manner similar to that described in the first embodiment. Further, the requirements concerning exposure processing time and the requirements concerning utilization efficiency of the X-ray source are decided depending upon the aim at the time the apparatus is utilized. These requirements need only be decided based upon the particular priority. Embodiment of a Semiconductor Production System Described next will be an example of a system for producing semiconductor devices (e.g., semiconductor chips such as IC and LSI chips, liquid crystal panels, CCDs, thin-film magnetic heads and micromachines, etc.) utilizing the X-ray exposure apparatus described above. This system utilizes a computer network outside the semiconductor manufacturing plant to provide troubleshooting and regular maintenance of manufacturing equipment installed at the manufacturing plant and to furnish maintenance service such as the provision of software. FIG. 6 illustrates the overall system as seen from a certain angle. As shown in FIG. 6, the system includes the business office 601 of the vendor (equipment supplier) that provides the equipment for manufacturing semiconductor devices. Semiconductor manufacturing apparatus for performing various processes used in a semiconductor manufacturing plant is assumed to be an actual example of the manufacturing apparatus. Examples of the apparatus are pre-treatment apparatus (e.g., lithographic apparatus such as exposure apparatus, resist treatment apparatus and etching apparatus, heat treatment apparatus, thin-film apparatus and smoothing apparatus, etc.) and post-treatment apparatus (e.g., assembly apparatus and inspection apparatus, etc.). The business office 601 includes a host management system 608 for providing a manufacturing-apparatus maintenance database, a plurality of control terminal computers 610, and a local-area network (LAN) 609 for connecting these components into an intranet. The host management system 608 has a gateway for connecting the LAN 609 to the Internet 605, which is a network external to the business office 601, and a security function for limiting access from the outside. Numerals 602 to 604 denote manufacturing plants of semiconductor makers (e.g., semiconductor device makers), which are the users of the manufacturing apparatus. The manufacturing plants 602 to 604 may be plants belonging to makers that differ from one another or plants belonging to the same maker (e.g., pre-treatment plants and post-treatment plants, etc.). Each of the plants 602 to 604 is provided with a plurality of manufacturing apparatus 606, a local-area network (LAN) 611, which connects apparatus to construct an intranet, and a host management system 607 serving as a monitoring unit for monitoring the status of operation of each manufacturing apparatus 606. The host management system 607 provided at each of the plants 602 to 604 has a gateway for connecting the LAN 611 in each plant to the Internet 605 serving as the external network of the plants. As a result, it is possible for the LAN of each plant to access the host management system 608 on the side of the vendor 610 via the Internet 605. By virtue of the security function of the host management system 608, users allowed to access the host management system 608 are limited. More specifically, status information (e.g., the condition of manufacturing apparatus that has malfunctioned), which indicates the status of operation of each manufacturing apparatus 606, can be reported from the plant side to the vendor side. In addition, information in response to such notification (e.g., information specifying how to troubleshoot the problem, troubleshooting software and data, etc.), as well as the latest software and maintenance information such as help information, can be acquired from the vendor side. A communication protocol (TCP/IP), which is used generally over the Internet, is employed for data communication between the plants 602xcx9c604 and the vendor 601 and for data communication over the LAN 611 within each plant. Instead of utilizing the Internet as the external network of a plant, it is also possible to utilize a highly secure leased-line network (e.g., an ISDN, for example) that cannot be accessed by a third party. Further, the host management system is not limited to that provided by a vendor, for an arrangement may be adopted in which the user constructs a database, places it on an external network and allows the database to be accessed from a number of plants that belong to the user. FIG. 7 is a conceptual view illustrating the overall system of this embodiment as seen from an angle different from that depicted in FIG. 6. In the earlier example, a plurality of user plants each having manufacturing apparatus are connected by an external network to the management system of the vendor that provided the manufacturing apparatus, and information concerning the production management of each plant and information concerning at least one manufacturing apparatus is communicated by data communication via the external network. In the example of FIG. 7, on the other hand, a plant having a manufacturing apparatus provided by a plurality of vendors is connected by an outside network to management systems of respective ones of the vendors of these plurality of manufacturing apparatus, and maintenance information for each manufacturing apparatus is communicated by data communication. As shown in the drawing, the system includes a manufacturing plant 701 of the user of the manufacturing apparatus, (e.g., the maker of semiconductor devices). The manufacturing line of this plant includes manufacturing apparatus for implementing a variety of processes. Examples of such apparatus are an exposure apparatus 702, a resist treatment apparatus 703 and a thin-film treatment apparatus 704. Though only one manufacturing plant 701 is shown in FIG. 7, in actuality, a plurality of these plants are networked in the same manner. The apparatus in the plant are interconnected by a LAN 706 to construct an intranet and the operation of the manufacturing line is managed by a host management system 705. The business offices of vendors (e.g., equipment suppliers) such as an exposure apparatus maker 710, a resist treatment apparatus maker 720 and a thin-film apparatus equipment maker 730 have host management systems 711, 721, 731, respectively, for remote maintenance of the apparatus they have supplied. These have maintenance databases and gateways to the outside network, as described earlier. The host management system 705 for managing each apparatus in the manufacturing plant of the user is connected to the management systems 711, 721, 731 of the vendors of these apparatus by the Internet or leased-line network serving as an external network 700. If any of the series of equipment in the manufacturing line malfunctions, the line ceases operating. However, this can be dealt with rapidly by receiving remote maintenance from the vendor of the faulty equipment via the Internet 700, thereby making it possible to minimize line downtime. Each manufacturing apparatus installed in the semiconductor manufacturing plant has a display, a network interface and a computer for executing network-access software and equipment operating software stored in a storage device. The storage device can be an internal memory or hard disk or a network file server. The software for network access includes a special-purpose or general-purpose Web browser and presents a user interface, which has a screen of the kind shown by way of example in FIG. 8, on the display. The operator managing the manufacturing equipment at each plant enters information at the input items on the screen while observing the screen. The information includes model 801 of the manufacturing apparatus, its serial number 802, subject matter 803 of the problem, its date of occurrence 804, degree of urgency 805, the particular condition 806, countermeasure method 807 and progress report 808. The entered information is transmitted to the maintenance database via the Internet. The resulting appropriate maintenance information is sent back from the maintenance database and is presented on the display screen. The user interface provided by the Web browser implements hyperlink functions 810, 811, 812 as illustrated and enables the operator to access more detailed information for each item, to extract the latest version of software, which is used for the manufacturing equipment, from a software library provided by the vendor, and to acquire an operating guide (help information) for reference by the plant operator. Accordingly, the maintenance information provided by the maintenance database also includes information relating to the present invention described above, and the software library also provides the latest software for implementing the present invention. A process for manufacturing a semiconductor device utilizing the production system set forth above will now be described. FIG. 9 illustrates the overall flow of a process for manufacturing semiconductor devices. The circuit for the device is designed at step 1 (circuit design). A mask on which the designed circuit pattern has been formed is fabricated at step 2 (mask fabrication). Meanwhile, a wafer is manufactured using a material such as silicon or glass at step 3 (wafer manufacture). The actual circuit is formed on the wafer by lithography, using the mask and wafer that have been prepared, at step 4 (wafer process), which is also referred to as xe2x80x9cpre-treatmentxe2x80x9d. A semiconductor chip is obtained, using the wafer fabricated at step 4, at step 5 (assembly), which is also referred to as xe2x80x9cpost-treatmentxe2x80x9d. This step includes steps such as actual assembly (dicing and bonding) and packaging (chip encapsulation). The semiconductor device fabricated at step 5 is subjected to inspections such as an operation verification test and a durability test, at step 6 (inspection). The semiconductor device is completed through these steps and then is shipped (step 7). The pre- and post-treatments are performed at separate special-purpose plants. Maintenance is carried out on an a per-plant basis by the above-described remote maintenance system. Further, information for production management and equipment maintenance is communicated by data communication between the pre- and post-treatment plants via the Internet or leased-line network. FIG. 10 is a flowchart illustrating the detailed flow of the wafer process mentioned above. The surface of the wafer is oxidized at step 11 (oxidation). An insulating film is formed on the wafer surface at step 12 (CVD), electrodes are formed on the wafer by vapor deposition at step 13 (electrode formation), and ions are implanted in the wafer at step 14 (ion implantation). The wafer is coated with a photoresist at step 15 (resist treatment), the wafer is exposed to the circuit pattern of the mark to print the pattern onto the wafer by the above-described exposure apparatus at step 16 (exposure), and the exposed wafer is developed at step 17 (development). Portions other than the developed photoresist are etched away at step 18 (etching), and unnecessary resist left after etching is performed is removed at step 19 (resist removal). Multiple circuit patterns are formed on the wafer by implementing these steps repeatedly. Since the manufacturing equipment used at each step is maintained by the remote maintenance system described above, malfunctions can be prevented and quick recovery is possible if a malfunction should happen to occur. As a result, the productivity of semiconductor device manufacture can be improved over the prior art. Thus, in accordance with the present invention as described above, it is possible to provide an X-ray exposure apparatus in which the energy of the X-rays emitted by an X-ray source can be utilized in a highly efficient manner. Further, the number of X-ray sources (light sources) can be reduced with respect to a plurality of collimators and plurality of exposure means disposed in the X-ray exposure apparatus of the present invention. This makes it possible to lower cost and reduce installation space. In addition, labor involved in maintaining the X-ray source can be reduced in comparison with the X-ray exposure apparatus of the prior art. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims.