Process for positioning of a mask relative to a workpiece and projection exposure apparatus for performing the process

Abstract: A process for positioning a mask (M) relative to a workpiece (W) which can be used for step and repeat exposure. A device for executing the process is also provided. The device includes a reflective component (4a) positioned on a workpiece carrier (4) in a position removed from the workpiece attachment site. Actinic light from an exposure light irradiation device (1) is projected onto the mask and alignment marks (MAM) provided on the mask are projected onto the reflective component. The alignment mark images are detected, their relative positions are stored, and emission of the actinic light terminated. The workpiece carrier, on which a workpiece is placed, is moved into a position in which the mask alignment marks are projected onto the workpiece. Furthermore, non-actinic light is emitted onto the alignment marks (WAM) of the workpiece, the workpiece alignment marks are detected and their relative positions are determined. Then the workpiece and/or the mask are/is moved such that the mask and workpiece alignment marks come to rest on top of one another.

Description: Background of the Invention Field of the Invention The invention relates to a process for positioning a mask relative to a workpiece and a device for executing the process in an exposure device which is used for production of a semiconductor device, a printed board, an LCD (liquid crystal display) and for similar purposes. Description of Related Art Production of electrical and electronic components and parts of various types in which processing of structures in the micron range is necessary includes an exposure process. These electronic parts are semiconductor components, liquid crystal displays, printer heads of the inkjet type, and multichip modules in which a host of different electronic components are produced on a substrate and thus a module is formed, and the like. In this exposure process, it is important, in the case of transmission of the mask pattern onto the workpiece, that a pattern to be subsequently transferred is positioned exactly to a pattern formed beforehand. The above described positioning is conventionally done such that the alignment marks of the mask and the workpiece come to lie on top of one another. As automated devices for transferring a mask pattern, exposure devices of the projection type are known wherein positioning is done using exposure light, for example of an i-line, an h-line or a g-line (i-line: 365 nm wavelength, h-line: 405 nm wavelength, g-line: 436 nm wavelength), or wherein positioning is done using nonexposure light, as, for example, an e-line, a d-line or a c-line (e-line: 546 nm wavelength, d-line: 588 nm wavelength, c-line: 656 nm wavelength). In the aforementioned devices, in the area used for positioning, a circuit pattern cannot be formed since the photoresist is exposed to the action of exposure light during positioning. In the case in which the yield from a workpiece is to be a host of chips, as in semiconductor components, the number of chips decreases according to the area used for positioning. Therefore, the disadvantage arises that production efficiency is impaired. On the other hand, in these devices, there is the advantage that the region of the circuit patterns is not limited by the positioning region, since the photoresist is not exposed to the action of exposure light during positioning. However, it is considered disadvantageous that, as a result of the different wavelengths of the exposure light and the nonexposure light, the mask pattern is not projected onto the same site. Figure 11 shows, schematically, an arrangement of the conventional exposure device in which positioning is done using the above described e-line. In the drawing reference number 1 indicates an exposure light irradiation device or a nonexposure light irradiation device; reference number 1a, a lamp; reference number 1b, a focussing mirror; reference number 1c, a shutter; reference number 1d, an optical filter; and reference number 1e, a condenser lens. Furthermore, reference number 2 indicates a mask carrier on which mask M is attached by means of a vacuum chuck or the like and which is driven by means of a drive device not shown in the drawing in the X-Y-Z- directions (X axis and Y axis being orthogonal axes on the plane parallel to one mask surface; Z axis being the axis in the vertical direction in Figure 11;  axis being the axis of rotation around the Z-axis). On mask M, a mask pattern and mask alignment marks MAM, hereinafter referenced to as mask marks, are recorded for purposes of positioning. Reference number 3 indicates a projection lens and reference letter W indicates a workpiece. Workpiece alignment marks WAM, hereinafter referenced to as workpiece marks, are recorded on workpiece W for purposes of positioning. Reference number 5 indicates an alignment mark detection unit which consists of lens 5a, objective lens 5b, half mirror 5c and image converter 5d which has a CCD camera. Workpiece mark WAM and mask mark MAM, which is projected onto the workpiece W, are detected via half mirror 5c, objective lens 5b and lens 5a by means of image converter 5d, and thus the positions of the two marks are observed. In Figure 11, alignment mark detection unit 5 is shown only once. However, there are several alignment units 5 (at least at two locations) since there are several mask marks MAM and several workpiece marks WAM (each at least at two locations) each on mask M and workpiece W, and because alignment unit 5 is assigned according to the respective alignment mark. Furthermore, alignment mark detection units 5 are ordinarily formed such that they can be removed in the direction of the arrow according to Figure 11. During exposure, alignment mark detection units 5 are removed when they extend within the exposure area. Alignment mark detection units 5 can be located in area B as shown. Moreover, they can also be located in additionally shown area A or area C. In Figure 11 when workpiece W is exposed, the e-line, as nonexposure light, is emitted first from exposure light (or nonexposure light) irradiation device 1 via optical filter 1d and, by means of alignment mark detection units 5, workpiece marks WAM and mask marks MAM, projected onto workpiece W, are detected. This method of determining mask marks MAM projected onto the workpiece by the projection lens is called TTL, i.e., the "through the lens", method. In the case of auto alignment, by means of a control device which is not shown in the drawing, based on the features of mask marks MAM and workpiece marks WAM, the respective marks are recognized and mask carrier 2 and/or a workpiece carrier 4 are automatically moved such that the positions of the two marks agree with one another. In the case of manual alignment, detected mask marks MAM and workpiece marks WAM are displayed on a monitor, which is not shown in the drawing, and by watching the monitor, an operator moves mask carrier 2 and/or a workpiece carrier 4 such that the two marks agree with one another. After completed positioning, optical filter 1d is removed from the optical path, the i-line, as exposure light, is then emitted from exposure light (or nonexposure light) irradiation device 1, the mask pattern is projected onto workpiece W, and exposure is effected. In the case of using the i-line as the exposure light and the e-line as the nonexposure light, as a result of the different wavelengths of the two lines, the following disadvantages arise in the above described positioning: 1) In a projection lens which is designed such that at exposure wavelengths no imaging error or aberration occurs, at nonexposure wavelengths, a deviation of the mask pattern projection surface takes place. This means that the mask pattern is not projected onto the same surface as is illustrated in Figure 11 wherein the pattern is projected on surfaces I and E. 2) The positions of mask marks MAM' on mask pattern projection surface E by the e-line, and the positions of mask marks MAM on mask pattern projection surface I by the i-line, do not agree with one another as a result of the chromatic aberration of the magnification factor. This means that the distance between projection lens 3 and mask pattern projection surface E by the e-line becomes greater than the distance between projection lens 3 and mask pattern projection surface I by the i-line, and distance Le of mask marks MAM' on mask pattern projectionsurface E by the e-line becomes greater than distance Li of mask marks MAM on mask pattern projection surface I by the i-line, as shown in Figure 11. Furthermore, the positions of the projection images of mask marks MAM' on mask pattern projection surface E are changed by the locations of the alignment marks. This means that different values are obtained for distances ΔL and ΔL' between the workpiece marks and projected mask marks, as illustrated in Figure 12. Conventionally, therefore, the deviation of the projection surfaces is corrected by inserting a parallel flat plate in the optical path of the projection optics system and, according to the wavelengths of the nonexposure light, by changing the plate thickness or adjusting the plate tilt (JP patent HEI 5-43168). In the above described prior art, the deviation of the projection images by the exposure light and the nonexposure light is corrected by inserting the parallel flat plate between the projection lens and the workpiece. The property being that, by inserting the parallel flat plate in the optical path, the focal position deviates by ΔS, as is illustrated in Figure 13. The above described prior art, however, has the following disadvantages: (1) As is shown in Figure 12, the positions of the projection images of the mask marks are changed by the nonexposure light depending on the positions of the alignment marks. It is therefore necessary to insert the parallel flat plate between the mask and the projection lens, to adjust its tilt and to correct the position deviation by the positions of the alignment marks, as is shown, for example, using the conventional device. (2) When the wavelength for exposure and the wavelength for alignment change, the amount of focal length correction changes. It is therefore necessary to make available the parallel flat plate according to a combination of the above described wavelengths. (3) To adjust the magnification factor, an optical component is used which consists of the parallel flat plate. It is therefore necessary to additionally use a retaining device for this purpose. Especially in the case in which the optical component is inserted and removed again, does the disadvantage arise that the device becomes complex and too large at the same time. (4) The disadvantage arises that the workpiece is contaminated by dust because directly above the workpiece is the insertion device of the parallel flat plate. As was described above, positioning using the nonexposure light has the advantage that the pattern can be formed in the vicinity of the alignment marks. But then it is necessary to correct the length of the optical path using the parallel flat plate and the like. This results in various disadvantages. Furthermore, in the conventional process in which the relative positions of the two alignment marks are determined in the state in which the mask mark is projected onto the workpiece provided with the workpiece marks, the disadvantage arises that when auto alignment is done, the control device only recognizes the workpiece marks with difficulty. To eliminate the above described disadvantages, the applicant has already proposed the device shown in Figure 14 (JP patent application HEI 6-294279 published 13 September 1996 as JP 8-233 529 A, not belonging to the prior art according to Article 54 EPC; corresponding U.S. Patent Application 08/564,005 published 7 July 1998 as US 5 777 747 A, not belonging to the prior art according to Article 54 EPC; and corresponding European application EP 0 715 214 A, published 5 June 1996 and belonging to the prior art according to Article 54(3)(4) EPC). In the drawing, the same parts as in Figure 11 are provided with the same reference numbers as in Figure 11. Reference number 1 indicates the exposure light (or nonexposure light) irradiation device, reference number 2 indicates the mask carrier, reference letter M indicates the mask on which a mask pattern and the mask alignment marks MAM are recorded for positioning. Reference number 3 indicates the projection lens and reference letter W indicates the workpiece on which workpiece marks WAM are recorded for purposes of positioning. Furthermore, reference number 4 indicates the workpiece carrier on which total reflection or half mirror 4a is installed and which is driven by means of a drive device which is not shown in the drawing in the X-Y-Z- directions. Reference symbol WAI indicates an alignment mark partial illumination system. The nonexposure light which is emitted from a light source not shown in the drawing is incident via optical fibers 6a, lens 6b and mirror 6c on half mirror 5e of alignment unit 5 and irradiates workpiece mark WAM on workpiece W. Exposure will now be described using the device shown in Figure 14; (1) Mask M is placed on mask carrier 2 and attached. Shutter 1c of exposure light (or nonexposure light) irradiation device 1 is opened in the state in which optical filter 1d in the optical path is removed. Exposure light is emitted onto mask M. In this process, step workpiece W is not placed on workpiece carrier 4. (2) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a installed in workpiece carrier 4 agrees with mask pattern projection surface Zo by the exposure light. (3) Alignment mark detection unit 5 is inserted. Alignment mark partial illumination-system WA1 is arranged integrally with alignment mark detection unit 5 and is inserted together with alignment mark detection unit 5. (4) By means of image converter 5d of alignment mark detection unit 5, mask mark-MAM, projected onto mirror 4a of workpiece carrier 4, is detected. An image processing part, not shown in the drawing, identifies mask mark MAM based on the detected image and stores the position coordinates thereof (XM, YM). (5) Shutter 1c of exposure light (or nonexposure light) irradiation device 1 is closed. In this way emission of exposure light onto mask M is stopped. (6) Workpiece W is placed on workpiece carrier 4 and attached. (7) Workpiece carrier 4 is moved in the Z-axis direction such that the surface of workpiece W agrees with mask pattern projection surface Zo. (8) Illumination light is supplied to alignment mark partial illumination-system WA1. Workpiece mark WAM on workpiece W is irradiated via optical fibers 6a, lens 6b, mirror 6c, half mirror 5e, lens 5b and half mirror 5c, and is detected by means of image converter 5d. The image of workpiece mark WAM, detected by means of image-converter 5d, is sent to the above described image processing part which identifies workpiece mark WAM and determines its position coordinates (XW, YW). (9) Emission of the illumination light of alignment mark partial illumination system WA1 is stopped. (10) The position deviation of workpiece W and mask M is determined on the basis of stored position coordinates (XM, YM) of mask mark MAM and determined position coordinates (XW, YW) of the workpiece mark. As a result of the above described position deviation, mask carrier 2 and/or workpiece carrier 4 is/are driven in the X-Y- directions and the position of mask mark MAM is brought into agreement with the position of workpiece mark WAM.With the above described agreement of the position of mask mark MAM with the position of workpiece mark WAM, alignment mark detection unit 5 is removed. Shutter 1c of exposure light (nonexposure light) irradiation device 1 is opened, the exposure light is emitted onto mask M, and thus exposure is effected.In the case of using the above described exposure for a step and repeat process in which each exposure zone on the workpiece is exposed in steps by moving the workpiece, according to above described process (10), the following processes are also performed, the processes of (8) through (15) are repeated, and exposure of the respective exposure zone is effected. (11) Alignment mark detection unit 5 is removed. 12) Shutter 1c of exposure light (nonexposure light) irradiation device 1 is opened, the exposure light is emitted onto mask M, and thus exposure (is effected. (13) Shutter 1c of exposure light (nonexposure light) irradiation device 1 is closed, and emission of exposure light is stopped. (14) Workpiece carrier 4 is moved in a certain amount in order that the next exposure zone is positioned in a stipulated exposure position. (15) Alignment mark detection unit 5 is inserted. There is a return to above described process (8). Processes (8) through (15) are repeated and the respective exposure zone on the workpiece undergoes step and repeat exposure. The above described technique suggested previously by the applicant does have the advantages that no parallel flat plate is used and that positioning of the mask to the workpiece can be done independently of the projection lens and with high precision. In the case of its use for the above described step and repeat exposure, however, the following disadvantage arises: In the case of using the previously suggested exposure process for step and repeat exposure, it is necessary to insert and remove alignment units 5 when each exposure is effected. As a result, the reproducibility of the insertion positions of alignment mark detection units 5 is important. Figure 15 schematically shows a case in which the stopping position of alignment mark detection unit 5 changes. When the stopping position of alignment mark detection unit 5 is identical to the position in Figure 15 by the broken line, the imaging position of mask mark MAM (or of workpiece mark WAM) on image converter 5d, changes accordingly. In the above described step and repeat cycle of processes (8) through (15), in step and repeat exposure, only the positions of workpiece marks WAM are, however, detected and stored starting the second time. Therefore, in this case, it is possible that deviations occur from the position of mask mark MAM which was stored the first time. In step and repeat exposure, the alignment accuracy is usually roughly ± 1 micron. A positioning accuracy of alignment mark detection unit 5 of roughly ± 0.1 microns (roughly 1/10 of the accuracy of alignment of mask M to workpiece W) is necessary in order that the deviations of workpiece marks WAM from the stored position of mask mark MAM lie within this range. It is difficult to do this mechanically with each insertion and removal of alignment mark detection unit 5. The above described disadvantage is, on the other hand, eliminated by the position of mask mark MAM being stored in each step and repeat cycle. However, in the above described case, the sequence of storing the position of mask mark MAM by emission of exposure light cannot be done because, beginning with the second step and repeat cycle, workpiece W is attached to workpiece carrier 4. In the document EP 0 509 797 A2 a projection exposure apparatus is disclosed. The apparatus comprises several detection optical systems in order to ensure proper alignment of the optical components. Also in US-A-4,962,318 an exposure apparatus is disclosed which is able to align a substrate to be exposed. However, none of the references mentions the problem of reproducibility in positioning of the detection unit. Summary of the Invention The invention was made in order to eliminate the above described disadvantages of the prior art and, specifically, the above described disadvantage with respect to the reproducibility of the insertion position of the alignment units. Therefore the first object of the invention is to provide a process, and a device for executing the process, which positions a mask relative to a workpiece in which the positioning of the mask can be done without using a parallel flat plate, regardless of the characteristic of the projection lens, and with high precision. Also, the process can be advantageously used for step and repeat exposure. A second object of the invention is to devise a process, and a device for executing the process, which positions a mask relative to a workpiece in which, even in the case of difficult identification of workpiece marks, as in the case of overlapping of mask marks with the workpiece marks or the like, the relative positions of the mask marks and the workpiece marks can be easily and automatically determined and positioning can be done with high precision within a short time. The above described objects are achieved according to independent claims 1 and 3. According to certain embodiments of the process of the present invention, positioning of the mask relative to the workpiece can be done without using a parallel flat plate and with high precision, regardless of the characteristic of the projection lens. Furthermore, the process by which the positions of the mask alignment marks and workpiece alignment marks are determined separately, makes it possible to prevent the identification of the workpiece alignment marks from becoming difficult due to the influence of the mask alignment marks or the mask pattern and the like, and the relative positions of the two alignment marks can be easily determined. In this way, positioning can be done in a short time with high precision auto alignment. According to other embodiments of the present process, by using the above described positioning step and repeat exposure, by which a reflection component is used, which is located in a position removed from the workpiece attachment area, and by which, thus, the relative positions of the mask alignment marks are determined/stored, the same effect is obtained as in the above solutions. Moreover, in this case, during exposure of each exposure zone on the workpiece, the projection images of the mask marks can be detected and the above described positions can be stored by the workpiece remaining attached to the workpiece carrier. Therefore alignment can be done with high accuracy without any effect being exerted by the accuracy of the insert positions of the alignment units. These and further objects, preferred features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention. Brief Description of the Drawings Figure 1 shows a schematic of a first embodiment of the invention; Figure 2 shows a schematic of the arrangement of a mirror on a workpiece carrier; Figure 3 shows a schematic of the arrangement of a system for control of the exposure device according to the invention; Figure 4 shows a schematic of the position of the workpiece carrier when mask alignment marks are detected; Figure 5 shows a schematic of the position of the workpiece carrier when workpiece alignment marks are detected; Figure 6 shows a schematic of a second embodiment of the invention; Figure 7 shows a schematic of an aperture which is used for the second embodiment; Figure 8 shows a schematic of the workpiece carrier according to a third embodiment of the invention; Figure 9 shows a schematic of the position of the workpiece carrier when the mask alignment marks are detected; Figure 10 shows a schematic of the position of the workpiece carrier when the workpiece alignment marks are detected; Figure 11 shows a schematic of an arrangement of a conventional exposure device; Figure 12 shows a schematic of the positions of the alignment marks on a mask pattern projection surface; Figure 13 shows a schematic of the deviation of the focal position by a parallel flat plate; Figure 14 shows a schematic of an arrangement of an exposure device which executes positions using a reflection component; and Figure 15 shows a schematic which reproduces the relation between the stopping positions of the alignment unit and the imaging positions. Detailed Description of the Preferred Embodiments Figure 1 is a schematic of a first embodiment of the invention. This embodiment relates to the execution of the above described step and repeat exposure. In the embodiment described below, step and repeat exposure is explained. However, the invention can be used not only for step and repeat exposure, but also for the exposure described above using the conventional example. In Figure 1, the same parts as in Figure 11 are provided with the same reference numbers as in Figure 11. Reference number 1 indicates the exposure light (respectively non-exposure light) irradiation device; reference number 1a, the lamp; reference number 1b, the focussing mirror; reference number 1c, the shutter; reference number 1d, the optical filter; and reference number 1e, the condenser lens. Reference number 2 indicates the mask carrier which is driven by means of a drive device (not shown in the drawing) in the X-Y-Z- directions. Reference letter M indicates the mask on which a mask pattern and mask alignment marks MAM are recorded for positioning purposes. Reference symbol MA1 labels a mask alignment mark partial illumination system for irradiating mask M with exposure light. Furthermore, reference number 7a indicates optical fibers for introducing the partial illumination light; reference number 7b, a lens; and reference number 7c, a mirror. Reference number 3 indicates the projection lens while reference letter W indicates the workpiece on which workpiece marks WAM are recorded for purposes of positioning. Reference number 4 furthermore indicates the workpiece carrier on which total reflection or half mirror 4a is installed. The workpiece carrier is driven by means of a drive device (not shown in the drawing) in the X-Y-Z- directions. It is desirable that mirror 4a be a half mirror as is described below. Figure 2 (a) illustrates workpiece carrier 4 as viewed from overhead in Figure 1. In the drawing, the site shown by the broken line designates the workpiece W attachment site. Above the workpiece attachment site, on workpiece carrier 4, is mirror 4a. On workpiece W are several exposure zones as is shown in the drawing. Furthermore, it is desirable that the height of mirror 4a be set to the normal height H of workpiece W as is shown in Figure 2 (b). As a result, workpiece carrier 4 can be moved in the Z-direction (vertically in Figure 1); the amount of movement in the Z-direction when the reflection surface of mirror 4a agrees with the mask pattern projection surface can be reduced; and the accuracy can be increased, as is described above. In Figure 1, reference number WA1 indicates the alignment mark partial illumination system. The nonexposure light which is emitted from a light source (not shown in the drawing) is incident, via optical fibers 6a, lens 6b and mirror 6c, on half mirror 5e of alignment unit 5 and irradiates workpiece mark WAM on workpiece W. Furthermore, the nonexposure light can be emitted from exposure light (or nonexposure light) irradiation device 1 via optical filter Id onto workpiece W without placing alignment-mark partial illumination system WA 1, as is described below. Reference number 5 indicates the alignment mark detection unit which consists of lens 5a, objective lens 5b, half mirrors 5c and 5e and image converter 5d which includes the CCD camera. Mask mark MAM, which is projected onto mirror 4a located on workpiece carrier 4, and workpiece mark WAM irradiated by the above described alignment mark partial illumination system WA1, are detected via half mirror 5c, objective lens 5b, half mirror 5e, and lens 5a by means of image converter 5d. Furthermore, as was described above, alignment mark detection unit 5 and partial illumination system WA1 are assigned according to the number of mask marks and workpiece marks, i.e., each are located at least at two sites. Figure 3 is a schematic of the arrangement of a system for controlling the exposure device according to the invention. In the drawing, reference number 11 indicates a control console; reference number 12, an arithmetic-logic unit for control of the projection exposure device shown in Figure 1; and reference number 13, a carrier control element which adjusts mask carrier 2 and workpiece carrier 4, which are shown in Figure 1 in the X-Y-Z- directions. Reference number 14 indicates an image processing part which recognizes mask mark MAM detected by means of image converter 5d of alignment mark detection unit 5, stores the position coordinates of the MAM, then recognizes workpiece mark WAM detected by means of image converter 5d of alignment mark detection unit 5 and determines the position coordinates of the WAM, as is described below. Furthermore, arithmetic-logic unit 12 determines the difference between the above described position coordinates of mask mark MAM and the above described position coordinates of workpiece mark WAM which have been determined in image processing part 14. Carrier control element 13 moves mask carrier 2 and/or workpiece carrier 4 such that the two agree with one another. Mask mark MAM and workpiece mark WAM, detected by alignment mark detection units 5, are displayed on monitor 15. In the following, exposure is described for this embodiment: (1) Mask M is placed on mask carrier 2 and attached. Mask alignment partial illumination system MA1 is inserted in a stipulated position. (2) Workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned at a location onto which mask mark MAM is projected. This means that workpiece carrier 4 is moved, for example, from the site shown in Figure 4 by the broken line as far as the site shown using the solid line, and the position of mirror 4a is brought into agreement with the projection site of mask mark MAM. (3) Exposure light is emitted onto mask M from mask alignment partial illumination system MA1. In this process step workpiece W is not placed on workpiece carrier 4. (4) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with mask pattern projection surface Zo caused by the exposure light. (5) Alignment mark detection unit 5 is inserted (in the case in which alignment unit 5 was removed). Alignment mark partial illumination system WA1 is arranged integrally with alignment mark detection unit 5 and inserted together with alignment mark detection unit 5. (6) By means of image converter 5d of alignment mark detection unit 5, mask mark MAM, projected onto mirror 4a of workpiece carrier 4, is detected and sent to image processing part 14. Image processing part 14 identifies mask mark MAM based on the detected image and stores the position coordinates thereof (XM, YM). The projection image of mask mark MAM conventionally has a greater contrast compared to workpiece mark WAM. When a total reflection mirror is used for the above described mirror 4a, there are cases in which the difference between the detected image of mask mark MAM and the detected image of workpiece mark WAM becomes great, and in which difficulties occur with respect to recognition of the alignment marks. It is therefore desirable to use a half mirror for above described mirror 4a and make the contrast the same as for workpiece mark WAM. (7) Emission of exposure light from mask alignment partial illumination system MA1 is stopped. (8) Workpiece W is placed on workpiece carrier 4 and attached in the position shown in Figure 2. (9) Workpiece carrier 4 is moved in the Z-direction such that the surface of workpiece W agrees with mask pattern projection surface Zo. (10) Workpiece carrier 4 is moved in the X-Y directions such thatwork-piece mark WAM agrees with the projection site of mask mark MAM. Thus, rough adjustment of the position of workpiece W is effected. This means that workpiece carrier 4 is moved, for example, from the position shown by the broken line to the position shown by the solid line, as shown in Figure 5. The position of workpiece mark WAM of the exposure zone as the article to be exposed on workpiece W, is brought essentially into agreement with projection site MAMT of mask mark MAM so that workpiece mark WAM extends into the visual field of alignment mark detection unit 5. (11) The illumination light is introduced into alignment mark partial illumination system WA1 as nonexposure light. This means that a shutter of a light source (not shown in the drawing) is opened for purposes of partial illumination and workpiece mark WAM on workpiece W is irradiated via optical fibers 6a, lens 6b, mirror 6c, half mirror 5e, lens 5b, and half mirror 5c. (12) Workpiece mark WAM is recorded by means of image converter 5d. The image of workpiece mark WAM detected by image converter 5d is sent to image processing part 14 which identifies workpiece mark WAM and determines its position coordinates (XW, YW). (13) Emission of nonexposure light from alignment mark partial illumination system WA1 is stopped. (14) Arithmetic-logic unit 12 determines the position deviation of workpiece W and mask M based on stored position coordinates (XM, YM) of mask mark MAM and determined position coordinates (XW, YW) of the workpiece mark WAM; the amount of the position deviations of workpiece carrier 4 being considered in above described steps (2) and (10). This means that the amount of position deviation of workpiece carrier 4 in above described steps (2) and (10) is known from values of an encoder count or the like, which is located in a workpiece carrier movement device (not shown in the drawing). The value of above described position coordinates (XW,YW) is corrected according to the value of the difference of ΔX, ΔY between the position of workpiece carrier 4 in step (2) and the position of workpiece carrier 4 in step (10). Thus, the position deviation between corrected position coordinates (XM + ΔX, YM + ΔY) and above described position coordinates (XW, YW) is determined. (15) Carrier control element 13, due to the above described position deviation, drives mask carrier 2 and/or workpiece carrier 4 in the X-Y- directions and brings the position of mask mark MAM into agreement with the position of workpiece mark WAM. (16) Alignment mark detection unit 5 and mask alignment partial illumination system MA1 are removed. (17) Shutter 1c of exposure light irradiation device 1 is opened. The exposure light is emitted onto mask M in the state in which optical filter 1d is removed from the optical path and thus exposure is effected. After completion of exposure, shutter 1c is closed. (18) Workpiece carrier 4 is moved a certain amount such that the next exposure zone is positioned in a stipulated exposure position. (19) Mask alignment partial illumination system MA1 is inserted in a stipulated position. (20) As in above described step (2), workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the projection site of mask mark MAM. (21) Exposure light is emitted onto mask M by mask alignment partial illumination system MA1. (22) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with mask pattern projection surface Zo by the exposure light. (23) Alignment mark detection unit 5 is inserted. Subsequently, there is a return to above described process (6), processes (6) through (23) are repeated, and the respective exposure zone of workpiece W is exposed. As was described above, in this embodiment, workpiece mark WAM can be irradiated by nonexposure light and the position coordinates of workpiece mark WAM can be determined, and positioning of the mask to the workpiece can be done without using the parallel flat plate, regardless of the characteristic of the projection lens, and with high precision. These advantages are achieved by the present process wherein mirror 4a is positioned on workpiece carrier 4, by which 1) workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the projection site of mask mark MAM; 2) the reflection surface of mirror 4a is brought into agreement with mask pattern projection surface Zo, by which, by emission of exposure light, mask mark MAM is projected onto mirror 4a and the position coordinates of mask mark MAM are stored; 3) then emission of the above described exposure light is stopped; 4) workpiece carrier 4 is moved such that the position of workpiece mark WAM in the exposure zone as the article to be exposed on workpiece W, is brought essentially into agreement with the projection site of mask mark MAM, and by which 5) the surface of workpiece W is brought into agreement with the mask pattern projection surface. Furthermore, by locating mirror 4a at a site which differs from the workpiece location on workpiece carrier 4, in each exposure of the respective exposure zone on workpiece W, the projection image of mask mark MAM can be detected and its position stored, while workpiece W remains attached on workpiece carrier 4. Therefore, in the above described position, the two alignment marks can be detected, even if the insertion position of alignment mark detection unit 5 differs upon each exposure. In this way, a reduction of alignment accuracy can be prevented. Furthermore, the process by which the positions of mask marks MAM and the positions of workpiece marks WAM are determined separately, prevents the identification of the workpiece marks from becoming difficult due to the influence of mask marks MAM or the mask pattern or the like. In this way, the relative positions of the mask marks and the workpiece marks can be easily determined and therefore positioning can be done with high precision within a short time by auto alignment. Figure 6 is a schematic of a second embodiment of the invention. In Figure 6, the same parts as in Figure 1 are provided with the same reference numbers as in Figure 1. In this embodiment, instead of the arrangement of mask alignment partial illumination system MA1 in Figure 1, there is aperture 8 which is inserted and removed on mask M. When the mask is aligned, exposure light is emitted from openings of the aperture onto the mask. Other arrangements are identical to the embodiment in Figure 1. Figure 7 is a view in which above described aperture 8 is viewed from overhead in Figure 6. As is shown in Figure 7, in aperture 8, there are openings which correspond to the sites provided with mask marks MAM. In the following, exposure is described according to this embodiment. (1) Mask M is placed on mask carrier 2 and attached. (2) Aperture 8 is inserted in a stipulated position on mask M, as shown in Figure 6. The openings of aperture 8 are essentially positioned directly above mask marks MAM. (3) As discussed above in relation to Figure 4, workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the position site of mask mark MAM so that the position of mirror 4a agrees with the projection site of mask mark MAM. (4) Shutter 1c of exposure light (or nonexposure) irradiation device 1 is opened in the state in which optical filter 1d is removed from the optical path, and the exposure light is emitted onto mask M. In this process, step workpiece W is not placed on workpiece carrier 4. (5) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with mask pattern projection surface Zo by the exposure light. (6) Alignment mark detection unit 5 is inserted. (7) Mask mark MAM projected onto mirror 4a of workpiece carrier 4 is detected by means of image converter 5d of alignment mark detection unit 5 and its position coordinates (XM, YM) are stored. (8) Shutter 1c of exposure light (or nonexposure) irradiation device 1 is closed. Emission of exposure light is stopped. (9) Workpiece W is placed on workpiece carrier 4 and attached. (10) Workpiece carrier 4 is moved in the Z-direction such that the surface of workpiece W agrees with mask pattern projection surface Zo. (11) Workpiece carrier 4 is moved in the X-Y directions such that workpiece mark WAM agrees with projection site MAMT of mask mark MAM, as illustrated in Figure 5. Thus rough adjustment of the position of workpiece W is effected. (12) Exposure light is introduced into alignment mark partial illumination system WA1 as nonexposure light. The nonexposure light is emitted onto workpiece mark WAM on workpiece W. (13) Workpiece mark WAM is detected by means of image converter 5d and its position coordinates (XW, YW) are determined. (14) Emission of nonexposure light from alignment mark partial illumination system WA1 is stopped. (15) The position deviation of workpiece W from mask M is determined on the basis of position coordinates (XM, YM) of mask mark MAM and position coordinates (XW, YW) of workpiece mark WAM; the amount of the position deviations of workpiece carrier 4 being considered in above described steps (3) and (11). As in the first embodiment, the amount of position deviations of workpiece carrier 4 in above described steps (3) and (11) is known from the values of an encoder count or the like, which is located in a workpiece carrier movement device which is not shown in the drawing. (16) Mask carrier (2) and/or workpiece carrier 4 is/are driven in the X-Y- directions and the position of mask mark MAM is brought into agreement with the position of workpiece mark WAM. (17) Aligment mark detection unit 5 and aperture 8 are removed. (18) Shutter 1c of exposure light irradiation device 1 is opened, exposure light is emitted onto mask M, and thus exposure is effected. After completion of exposure, shutter 1c is closed. (19) Workpiece carrier 4 is moved a certain amount such that the next exposure zone is positioned in a stipulated exposure position. (20) Aperture 8 is inserted in a stipulated position on mask M. (21) As in above described process (3), workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the projection site of mask mark MAM. (22) Exposure light is emitted onto mask M. (23) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with mask pattern projection surface Zo by the exposure light. (24) Alignment mark detection unit 5 is inserted. Subsequently, there is a return to above described process (7), processes (7) through (24) are repeated, and the respective exposure zone of workpiece W is exposed. As was described above, in this embodiment, a simpler arrangement of the device can be achieved with lower costs compared to the first embodiment as a result of the aperture being used instead of the mask alignment partial illumination system. Furthermore, it is desirable in this embodiment that the size of workpiece carrier 4 and its amount of movement in the X-Y directions is greater than in the first embodiment, and that the distance between the workpiece arrangement site and mirror 4a is greater than in the first embodiment. In this way, when the mask is aligned, it is possible to prevent workpiece W from being exposed by the exposure light which emerges from the openings of aperture 8. Figure 8 is a schematic of workpiece carrier 4 according to a third embodiment of the invention in which workpiece carrier 4 is viewed from overhead. In this embodiment, mirror 4a is located in a position which is completely removed from the workpiece arrangement site on workpiece carrier 4, as is shown in the drawing. This prevents exposure light from being emitted onto workpiece W when exposure light is emitted onto mask M in mask alignment from exposure light (or nonexposure light) irradiation device 1. The exposure process of this embodiment will now be described. In the exposure device in this embodiment, mask alignment partial illumination system MA1 is removed from the parts in Figure 1, or aperture 8 is removed from the parts in Figure 6. Furthermore, in this case, the size/arrangement of the mirror on workpiece carrier 4 is changed and the amount of movement of workpiece carrier 4 in the X-Y directions is increased, while other arrangements are identical to the arrangements in Figures 1 and 6. (1) Mask M is placed on mask carrier 2 and attached. (2) As is shown in Figure 9, workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the projection site of mask mark MAM so that the position of mirror 4a agrees with the projection site of mask mark MAM. (3) Shutter 1c of exposure light (or nonexposure) irradiation device 1 is opened in the state in which optical filter 1d is removed from the optical path, and the exposure light is emitted onto mask M. In this process step, workpiece W is not placed on workpiece carrier 4. (4) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with the mask pattern projection surface Zo by the exposure light. (5) Alignment mark detection unit 5 is inserted. (6) Mask mark MAM projected onto mirror 4a of workpiece carrier 4 is detected by means of image converter 5d of alignment mark detection unit 5 and its position coordinates (XM, YM) are stored. (7) Shutter 1c of exposure light (or nonexposure) irradiation device 1 is closed. Emission of exposure light is stopped. (8) Workpiece W is placed on workpiece carrier 4 and attached. (9) Workpiece carrier 4 is moved in the Z-direction such that the surface of workpiece W agrees with mask pattern projection surface Zo. (10) Workpiece carrier 4 is moved in the X-Y directions such that workpiece mark WAM agrees with projection site MAMT of mask mark MAM, as illustrated in Figure 10. Thus rough adjustment of the position of workpiece W is effected. (11) Illumination light as nonexposure light is introduced into alignment mark partial illumination system WA1. The nonexposure light is emitted onto workpiece mark WAM on workpiece W. (12) Workpiece mark WAM is detected by means of image converter 5d and its position coordinates (XW, YW) are determined. (13) Emission of nonexposure light from alignment mark partial illumination system WA1 is stopped. (14) The position deviation of workpiece W from mask M is determined on the basis of position coordinates (XM, YM) of mask mark MAM and determined position coordinates (XW, YW) of workpiece mark WAM; the amount of the position deviations of workpiece carrier 4 being considered in above described steps (2) and (10). As in the first embodiment, the amount of position deviation of workpiece carrier 4 in above described steps (2) and (10) is known from the values of an encoder count or the like, which is located in a workpiece carrier movement device which is not shown in the drawing. (15) Mask carrier 2 and/or workpiece carrier 4 is/are driven in the X-Y- directions and the position of mask mark MAM is brought into agreement with the position of workpiece mark WAM. (16) Alignment mark detection unit 5 is removed. (17) Shutter 1c of exposure light irradiation device 1 is opened, exposure light is emitted onto mask M, and thus exposure is effected. After completion of exposure, shutter 1c is closed. (18) Workpiece carrier 4 is moved a certain amount such that the next exposure zone is positioned in a stipulated exposure position. (19) As in above described process (2), workpiece carrier 4 is moved in the X-Y directions such that mirror 4a is positioned in the projection site of mask mark MAM. (20) Exposure light is emitted onto mask M. (21) The position of workpiece carrier 4 is shifted in the Z-direction such that the reflection surface of mirror 4a of workpiece carrier 4 agrees with mask pattern projection surface Zo by the exposure light. (22) Alignment mark detection unit 5 is inserted. Subsequently, there is a return to above described process step (6), process steps (6) through (22) are repeated and the respective exposure zone of workpiece W is exposed. In this embodiment, by the measure by which mirror 4a is located in a position which is completely removed from the workpiece arrangement site on workpiece carrier 4, without using the mask alignment partial illumination system in Figure 1 or the aperture 8 in Figure 6 during mask alignment, the exposure light can be emitted from exposure light (or nonexposure light) irradiation device 1, as was described above. Furthermore, the emission of nonexposure light in the respective embodiment can be done via optical filter 1d from exposure light (or nonexposure light) irradiation device 1, instead of using alignment mark partial illumination systems WA1. Furthermore, in all embodiments, it is desirable that, in the case in which the positions of mask marks MAM and the positions of workpiece marks WAM are brought into agreement with one another, only the workpiece carrier be driven in the X-Y- directions. The reason for this lies in the following: Generally, both the mask carrier and the workpiece carrier have certain inaccuracies in the amount of their movements. It is therefore necessary, after moving the carriers in the stipulated amount for purposes of positioning, to again confirm the position ratio between mask marks MAM and workpiece marks WAM and to repeat positioning if the amount of position deviation is not less than or equal to an allowable value. In the case in which only the workpiece carrier is driven, it is possible that nonexposure light is emitted again onto workpiece marks WAM and their position coordinates (XW, YW) stored and then compared to position coordinates (XM, YM) of the mask marks which were previously stored. On the other hand, in the case in which the mask carrier is driven, it is necessary that the exposure light is emitted onto mask marks MAM and that the positions of position coordinates (XM, YM) of its projection images are stored. In this case of repeated positioning, however, the above described projection images must be projected onto the workpiece with the resist on the workpiece being exposed to the action of exposure light. In the case of driving the mask carrier, it is therefore necessary, using a length measuring means such as an extra laser interferometer, or the like, to measure the amount of movement of the mask carrier, and based on this data, to execute readjustment, or to use a carrier with high accuracy of movement as the mask carrier. Ordinarily positioning is frequently accomplished only by driving the workpiece carrier. Action of the Invention As was described above, the following effects can be obtained by the process of the present invention by which, on the workpiece carrier in one position, there is a reflection component which is removed from the workpiece attachment site; by which the mask alignment marks are projected onto the reflection component; by which their relative positions are determined/stored; by which then the workpiece carrier provided with the workpiece is moved into a position in which the alignment marks on the mask are projected onto the above described workpiece; by which the nonexposure light is emitted onto the alignment marks of the workpiece; by which the relative positions of the workpiece alignment marks are determined/stored; by which the data of the relative positions of the mask alignment marks and the workpiece alignment marks are computed; and by which the workpiece and/or the mask is/are moved such that the two alignment marks come to rest on top of one another. (1) Positioning of the mask relative to the workpiece can be done with high precision and without using the parallel flat plate, regardless of the characteristic of the projection lens. Furthermore, by separately determining the positions of the mask marks MAM and workpiece marks WAM, the present process permits the relative positions of the mask marks and workpiece marks to be easily determined without identification of the workpiece alignment mask becoming difficult by the influence of mask marks MAM or by the mask pattern and the like. Therefore, positioning can be done in a short time with high precision by auto alignment. (2) By using the invention for step and repeat exposure and by determining/storing the relative positions of the alignment marks of the mask using the reflection component, which is located in the position removed from the workpiece attachment site, in the exposure of the respective exposure zone on the workpiece, the projection images of the mask marks can be detected and their positions stored, while the workpiece remains attached on the workpiece carrier. Therefore, alignment can be done with high precision without any influence being exerted by the accuracy of the insert positions of the alignment units. It is to be understood that although preferred embodiments of the invention have been described, various other embodiments and variations may occur to those skilled in the art. Any such other embodiments and variations which fall within the scope of the present invention as claimed are intended to be covered by the following claims.

Claims: A process for positioning a mask (M) relative to a workpiece in a projection exposure apparatus having a projection lens (3), comprising the steps of: positioning alignment mark detection units (5) between said projection lens (3) and a workpiece carrier (4); emitting exposure light from a first light irradiation device (MA1, 1, 8) onto alignment marks (MAM) of the mask (M); using said exposure light and said projection lens (3) to form projection images of said alignment marks (MAM) of the mask (M) onto a reflection component (4a) located on said workpiece carrier, said reflection component (4a) being in a position remote from a workpiece attachment site; detecting said projection images with said aligment mark detection units (5) and subjecting said projection images to image processing, determining and storing positions of said projection images; stopping emission of the exposure light from the first light irradiation device (MA1, 1, 8) in a state in which said alignment mark detection units (5) are positioned; moving the workpiece carrier (4) on which the workpiece (W) is positioned into a position in which the surface of said workpiece (W) agrees with the mask pattern projection surface; emitting non-exposure light from one of the first light irradiation device (MA1, 1, 8) and a second light irradiation device (WA1) onto alignment marks (WAM) of the workpiece (W); detecting the alignment marks (WAM) of the workpiece (W) with said alignment mark detection units (5) and subjecting the alignment marks (WAM) of the workpiece (W) to image processing; determining and storing the positions of the alignment marks (WAM) of the workpiece (W); computing data of the relative positions of the alignment marks (MAM, WAM) of the mask (M) and the workpiece (W); moving at least one of the workpiece (W) and the mask (M) such that the alignment marks (MAM, WAM) of the mask (M) and the workpiece (W) come to rest in agreement with one another; and removing said alignment mark detection units (5). A process for positioning a mask (M) relative to a workpiece (W) according to claim 1, comprising the steps of: moving the workpiece carrier (4) such that respective exposure zones on the workpiece (W) are successively moved to an exposure position; emitting exposure light onto said mask (M), thereby exposing the respective exposure zones on the workpiece (W) in steps. A projection exposure apparatus for performing a process according to claim 1, comprising a mask (M) including alignment marks (MAM); a mask carrier (2) for supporting the mask (M); a projection lens (3); a workpiece carrier (4) for supporting a workpiece (W) at a workpiece attachment site; a first light irradiation means (MA1, 1, 8) for irradiating one of the mask alignment marks (MAM) and a mask pattern with at least one of a non-exposure light and an exposure light, wherein projection images of the alignment marks (MAM) of the mask (M) are imaged by exposure light emitted from the first light irradiation means (MA1, 1, 8); a reflection component (4a) located on the workpiece carrier (4) in a position remote from the workpiece attachment site for reflecting said projection images ; a second light irradiation means (WA1) for emitting light, wherein the workpiece alignment marks (WAM) are illuminated by non-exposure light from one of said first light irradiation means (MA1, 1, 8) and said second light irradiation means (WA1); alignment mark detection units (5) for detecting the projection images of the mask alignment marks (MAM) and workpiece alignment marks (WAM); means (14) for subjecting the projection images of the mask alignment marks (MAM) and workpiece alignment marks (WAM) to image processing; means for determining and storing positions of the projection images of the mask alignment marks (MAM) and workpiece alignment marks (WAM); means (12) for computing data of the relative positions of the alignment marks (MAM, WAM) of the mask (M) and the workpiece (W); means (2, 4) for moving at least one of the workpiece (W) and mask (M) such that the alignment marks (MAM, WAM) of the mask (M) and workpiece (W) come to rest in agreement with each other; and means for controlling emission of the exposure light from the first light irradiation means (MA1, 1, 8), characterized in that the alignment mark detection units (5) for detecting the wafer alignment marks (WAM) are the same as the alignment mark detection units (5) for detecting the projection images of the mask alignment marks (MAM); and said alignment mark detection units (5) are movable between a position between said projection lens (3) and said workpiece carrier (4) and a removed position. A projection exposure apparatus according to claim 3, wherein: said workpiece carrier (4) is arranged to carry a workpiece (W) with several exposure zones, respective exposure zones being successively movable to an exposure position by moving the workpiece carrier (4).

Inventors: TANAKA YONETA, TANAKA, YONETA
Applicants: USHIO ELECTRIC INC, USHIODENKI KABUSHIKI KAISHA
Application year: 1996
Main classification: G03F9
IPC codes: G03F9, H01L21