Patent Number: 062122525
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described below. (Embodiment 1) An X-ray mask of an embodiment 1 of the invention will be described below with reference to FIG. 1. Referring to FIG. 1, the X-ray mask of the embodiment 1 of the invention includes a support ring 1, a substrate 2, a membrane 3 and an X-ray absorber 4. Membrane 3 is formed on substrate 2. X-ray absorber 4 is formed on membrane 3. Support ring 1 is arranged under substrate 2. Substrate 2 is provided with a window 11,. through which a rear surface of membrane 3 is exposed. X-ray absorber 4 includes a transfer circuit pattern 10, i.e., a circuit pattern for transfer in a region located above window 11. X-ray absorber 4 includes an opening 7, which functions as an alignment mark and is located in a region not overlapping with window 11 in a plan view, i.e., a region outside window 11. Since opening 7 functioning as the alignment mark is formed in X-ray absorber 4 as described above, it is not necessary to form a film of gold or the like functioning as the alignment mark on X-ray absorber 4 in contrast to the X-ray mask proposed in the prior art. Therefore, the X-ray mask provided with the alignment mark can be produced without an additional step of forming a film of gold or the like. In a process of manufacturing the X-ray mask which will be described later, a step of forming the transfer circuit pattern on X-ray absorber 4 can be performed using opening 7 for detecting the position on the X-ray mask. Therefore, the transfer circuit pattern having a high position accuracy can be formed. Opening 7 is situated in the region spaced from the region wherein transfer circuit pattern 10 is formed, and more specifically in a region, under which substrate 2 is present with membrane 3 therebetween. Therefore, significant change in position of opening 7 can be prevented in the step of writing the mask pattern for forming transfer circuit pattern 10, even when membrane 3 situated on window 11 vibrates or a distortion occurs due to resist stress relief or heat caused by the step of writing the mask pattern. Consequently, it is possible to prevent lowering of the accuracy of position detection of the X-ray mask, which may be caused by change in position of opening 7. Therefore, the transfer circuit pattern having a high position accuracy can be formed. A process of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIG. 1 will now be described below with reference to FIGS. 2 to 6. As shown in FIG. 2, membrane 3 of 1-3 .mu.m in thickness is first formed on substrate 2. X-ray absorber 4 is formed on membrane 3. A resist 5 is applied over X-ray absorber 4. Support ring 1 is disposed under substrate 2. Substrate 2 is partially removed by etching to form window 11 exposing the rear surface of membrane 3. As shown in FIG. 3, exposure with light and development are effected to form an alignment mark pattern 6, i.e., a pattern for the alignment mark in resist 5. In this step, alignment mark pattern 6 is formed in a region which does not overlap with window 11 in a plan view and, in other words, is located outside window 11. As described above, the step of forming alignment mark pattern 6 uses the light exposing method requiring a shorter exposure time than an exposing method with an electron beam, which is employed for forming the transfer circuit pattern to be described later. Therefore, the time required for manufacturing the X-ray mask can be reduced compared with the case where the electron beam writing method is used for writing both alignment mark pattern 6 and the transfer circuit pattern on the resist. The step of forming alignment mark pattern 6 may use the exposing method using the electron beam. Thereafter, X-ray absorber 4 masked with resist 5 is partially removed by etching to form opening 7 functioning as the alignment mark. Thereafter, resist 5 is removed. Through the above steps, the structure shown in FIG. 4 is formed. As described above, opening 7 functioning as the alignment mark is formed in X-ray absorber 4. Therefore, the process of manufacturing the X-ray mask can be simplified by eliminating a film forming step or deposition step required in the conventionally proposed method, in which a film of gold or the like is formed on X-ray absorber 4, and the alignment mark is formed by patterning this film of gold or the like by etching. Then, resist 8 is applied over X-ray absorber 4 as shown in FIG. 5. Then, the position of opening 7 functioning as the alignment mark is detected with an electron beam or the like emitted to opening 7. Based on this position information, the positions of X-ray absorber 4 and resist 8 are detected, and the transfer circuit pattern is written on resist 8 by the electron beam writing method while detecting the positions in this manner. By developing resist 8 thus written, transfer circuit pattern 9 is formed on resist 8 as shown in FIG. 6. As described above, transfer circuit pattern 9 is formed using opening 7, which functions as the alignment mark, for position detection of X-ray absorber 4 and resist 8. Therefore, the accuracies of position and size of the transfer circuit pattern 9 can be improved. Opening 7 is located in the region which is spaced from the region bearing transfer circuit pattern 9, and is situated over substrate 2 with membrane 3 therebetween. Therefore, significant change in position of opening 7 can be prevented in the step of writing the transfer circuit pattern, even when membrane 3 situated on window 11 vibrates or a distortion occurs due to resist stress relief or heat caused by the step of writing the transfer circuit pattern. Consequently, it is possible to prevent deterioration of the accuracy of position detection of the X-ray mask due to change in position of opening 7. Therefore, transfer circuit pattern 9 having a high position accuracy can be formed. Accordingly, the X-ray mask provided with the transfer circuit pattern having a high position accuracy can be manufactured. Then, X-ray absorber 4 masked with resist 8 is partially removed to form transfer circuit pattern 10 (see FIG. 1). Thereafter, resist 8 is removed. In this manner, the X-ray mask according to the embodiment 1 of the invention shown in FIG. 1 can be manufactured. (Embodiment 2) Referring to FIGS. 7 to 10, description will now be given on steps of manufacturing the X-ray mask of an embodiment 2 of the invention. First, a structure shown in FIG. 7 is produced through steps similar to those of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIG. 2. The X-ray mask in the first step of the process of manufacturing the X-ray mask according to the embodiment 2 of the invention shown in FIG. 7 basically has the same structure as the X-ray mask in the first step of the process of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIG. 2. In the step of manufacturing the X-ray mask of the embodiment 2 of the invention shown in FIG. 7, however, a resist 16 formed on X-ray absorber 4 is thicker than resist 5 in the step of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIG. 2. This is because resist 16 is used in both the step of forming opening 7 (see FIG. 9) functioning as the alignment mark and the step of forming transfer circuit pattern 10 (see FIG. 1), and therefore must endure the etching in these two steps. As shown in FIG. 8, light exposure is performed on resist 16 to form alignment mark pattern 6. In this step, alignment mark pattern 6 is formed in a region not overlapping with window 11, i.e., a region outside window 11, as is done also in the embodiment 1 of the invention. Since the light exposure is performed for forming alignment mark pattern 6, this can achieve an effect similar to that in the case where the light exposure is performed for forming alignment mark pattern 6 on resist 5 in the step of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIG. 3. Electron beam exposure may be employed for forming alignment mark pattern 6. Then, as shown in FIG. 9, X-ray absorber 4 masked with resist 16 is partially removed by etching to form opening 7 functioning as the alignment mark. Then, as shown in FIG. 10, the position of opening 7 functioning as the alignment mark is detected with an electron beam or the like emitted to opening 7. Based on this position information, the positions of X-ray absorber 4 and resist 16 are detected, and the transfer circuit pattern is written on resist 16 by the electron beam writing method while detecting the positions in this manner. By developing resist 16 after the above writing, transfer circuit pattern 9 is formed on resist 16. As described above, alignment mark pattern 6 for forming opening 7 and transfer circuit pattern 9 for forming transfer circuit pattern 10 (see FIG. 1) are written on the same resist 16. Therefore, one of the steps of forming the resists in the embodiment 1 of the invention can be eliminated. Accordingly, in addition to the effect achieved by the embodiment 1 of the invention, such an effect can be achieved that the X-ray mask provided with the transfer circuit pattern having a high position accuracy can be produced through further simplified steps. Thereafter, X-ray absorber 4 masked with resist 16 is partially removed by etching to form transfer circuit pattern 10 (see FIG. 1). By removing resist 16, the X-ray mask shown in FIG. 1 can be manufactured. (Embodiment 3) Referring to FIGS. 11 and 12, description will be given on the process of manufacturing an X-ray mask of an embodiment 3 of the invention. After performing the steps of manufacturing the X-ray mask of the embodiment 1 of the invention shown in FIGS. 2 to 4, resist 8 is formed only on a region of X-ray absorber 4 located above window 11 and, more specifically, a region where the transfer circuit pattern is to be formed. Thus, resist 8 exposing opening 7 is formed on X-ray absorber 4. Resist 8 may be formed in such a manner that a resist is first applied over an entire surface of X-ray absorber 4, and then the resist is removed from a peripheral portion covering opening 7. By removing the resist from an area on opening 7, opening 7 is exposed. As shown in FIG. 12, resist 8 formed only in the region over window 11 may have a circular form or may have a square form similar to the form of window 11. Instead of entirely removing the resist from the peripheral portion of X-ray absorber 4, the resist may be removed only from a region above and near opening 7, in which case a similar effect can be achieved. The position of opening 7 functioning as the alignment mark is detected with an electron beam or the like emitted to opening 7. Based on this position information, the positions of X-ray absorber 4 and resist 8 are detected, and the transfer circuit pattern is written on resist 8 by the electron beam writing method while detecting the positions in this manner. The resist is not present above opening 7 functioning as the alignment mark. Therefore, such a problem can be prevented that characteristics of the resist are deteriorated due to irradiation with the light or electron beam for detecting the alignment mark, and thereby detection of opening 7 is impeded. Consequently, the position of opening 7 functioning as the alignment mark can be performed accurately. Thereby, the transfer circuit pattern having a high accuracy can be formed. This embodiment 3 may be applied to the embodiment 2, in which case a similar effect can be achieved. (Embodiment 4) Referring to FIG. 13, the X-ray mask according to the embodiment 4 of the invention will now be described below. Referring to FIG. 13, the X-ray mask according to the embodiment 4 of the invention basically has the same structure as the X-ray mask of the embodiment 1 of the invention shown in FIG. 1. However, in the X-ray mask of the embodiment 4 of the invention shown in FIG. 13, an etching stopper 12, which is made of a material different in etching rate from X-ray absorber 4, is arranged between membrane 3 and X-ray absorber 4 for an etching step which is performed for forming opening 7 and transfer circuit pattern 10. Since etching stopper 12 is employed as described above, damage to membrane 3 by the etching can be prevented in the etching step for forming opening 7 functioning as the alignment mark and transfer circuit pattern 10. Since opening 7 is formed in the region not overlapping with window 11 in the plan view, this embodiment can achieve an effect similar to that by the X-ray mask of the embodiment 1 of the invention shown in FIG. 1. Referring to FIGS. 14 to 20, steps of manufacturing the X-ray mask of the embodiment 4 of the invention will be described below. As shown in FIG. 14, membrane 3 is formed on substrate 2. Window 11 exposing the rear surface of membrane 3 is formed in substrate 2. Support ring 1 is arranged under substrate 2. Etching stopper 12 is formed on membrane 3. X-ray absorber 4 is formed on etching stopper 12. An etching mask 13 is formed on X-ray absorber 4. Resist 5 is formed on etching mask 13. As shown in FIG. 15, alignment mark pattern 6 is formed in the region of resist 5 not overlapping with window 11 in the plan view by the light exposing method. In this step, alignment mark pattern 6 may be formed by an electron beam exposing method. Etching mask 13 masked with resist 5 is partially removed by etching to form an alignment mark pattern 14 in etching mask 13 (see FIG. 16). Thereafter, resist 5 is removed. In this manner, the structure shown in FIG. 16 is formed. Then, as shown in FIG. 17, X-ray absorber 4 masked with etching mask 13 is partially removed by etching to form opening 7 functioning as the alignment mark. As shown in FIG. 18, resist 8 is applied over etching mask 13. Then, as shown in FIG. 19, the position of opening 7 functioning as the alignment mark is detected with an electron beam or the like emitted to opening 7. Based on this position information, the positions of resist 8 and others are detected, and transfer circuit pattern 9 is formed on resist 8 by the electron beam writing method while detecting the positions in this manner. Etching mask 13 masked with resist 8 is partially removed to form a transfer circuit pattern 15 in etching mask 13 (see FIG. 20). Thereafter, resist 8 is removed. In this manner, the structure shown in FIG. 20 is formed. X-ray absorber 4 masked with etching mask 13 is partially removed by etching to form transfer circuit pattern 10 (see FIG. 13). Thereafter, etching mask 13 is removed so that the X-ray mask shown in FIG. 13 is formed. As shown in FIGS. 17 and 20, etching mask 13 and etching stopper 12 are subjected two times to the etching in the process of forming opening 7 and transfer circuit pattern 10 (see FIG. 13). Therefore, etching mask 13 and etching stopper 12 must have film thicknesses which can endure the etching performed two times. For example, it is now assumed that X-ray absorber 4 has a film thickness of 500 nm, the rate of overetching in the first etching process is 20%, and the selection ratio of X-ray absorber 4 with respect to etching mask 13 and etching stopper 12 is 10 when etching X-ray absorber 4. In this case, the required thicknesses of etching mask 13 and etching stopper 12 can be calculated as follows. Etching mask 13 is first discussed. In the etching step for forming opening 7 functioning as the alignment mark shown in FIG. 17, the thickness reduced by this etching is 600 nm when calculated based on X-ray absorber 4, because X-ray absorber 4 is 500 nm in thickness and the overetching rate thereof is 20%. Since the selection ratio of X-ray absorber 4 with respect to etching mask 13 is 10, the thickness of etching mask 13 removed in this etching step is 60 nm. In the etching step for forming transfer circuit pattern 10, the thickness of etching mask 13 reduced thereby is equal to the foregoing value, and thus is 60 nm. Therefore, etching mask 13 must have a thickness of 120 nm or more. Meanwhile, etching stopper 12 is etched as follows. In the etching step for forming opening 7 shown in FIG. 17, a portion of etching stopper 12 forming the bottom of opening 7 is subjected to the etching correspondingly to the overetching quantity. Therefore, the thickness of etching stopper 12 reduced in the first etching step is 10 nm. In the etching step for forming transfer circuit pattern 10, etching stopper 12 is subjected to the etching to remove its portion forming the bottom of transfer circuit pattern 10 correspondingly to the overetching quantity, similarly to the first etching step. Thus, the portion of etching stopper 12 forming the bottom of transfer circuit pattern 10 is removed by 10 nm. Meanwhile, etching stopper 12 is exposed at the bottom of opening 7 even at the start of the etching step for forming transfer circuit pattern 10. Therefore, etching stopper 12 is subjected to the etching similarly to etching mask 13. Accordingly, the thickness of etching stopper 12 removed by this etching step is 60 nm which is equal to the reduced thickness of etching mask 13. Therefore, the total thickness of etching stopper 12 reduced by the foregoing two etching steps is largest at the bottom of opening 7, and is equal to 70 nm. Thus, according to the process of manufacturing the X-ray mask of the embodiment 5 of the invention, etching stopper 12 must have a thickness of 70 nm or more. Further, in the etching step of forming opening 7 functioning as the alignment mark shown in FIG. 17, the etching conditions may be adjusted such that a selection ratio of X-ray absorber 4 with respect to etching mask 13 and etching stopper 12 is 100, whereby it is possible to reduce thicknesses of etching mask 13 and etching stopper 12 which are reduced in the above etching step. As a result, it is possible to reduce the required thicknesses of etching mask 13 and etching stopper 12. Under the above conditions, the etching step of forming opening 7 reduces the thickness of etching mask 13 by 6 nm, and also reduces the thickness of etching stopper 12 by 1 nm. If the foregoing conditions are employed in the etching step of forming transfer circuit pattern 10, the required minimum thickness of etching mask 13 is 66 nm, and the required minimum thickness of etching stopper 12 is 61 nm. If there is a difference between the size of opening 7 functioning as the alignment mark and the size of the interconnection pattern and others formed in transfer circuit pattern 10, the etching conditions for forming opening 7 may be determined depending on the size thereof, and thus may be independent of the etching conditions for forming transfer circuit pattern 10 which is determined depending of the size of the interconnection pattern and others. Thereby, both opening 7 and transfer circuit pattern 10 can be formed with high size accuracies. As a result, the X-ray mask provided with the transfer circuit pattern having a high position accuracy can be produced. The etching conditions for forming opening 7 may be adjusted such that the accuracy of the pattern configuration is not extremely high, but the selection ratio of X-ray absorber 4 with respect to etching mask 13 and etching stopper 12 is sufficiently large (e.g., 100). The etching conditions for forming transfer circuit pattern 10 may be adjusted such that the selection ratio of X-ray absorber 4 with respect to etching mask 13 and etching stopper 12 is not significantly high, but the accuracy of pattern configuration is sufficiently high. Thereby, it is possible to produce the X-ray mask provided with the transfer circuit pattern having a high position accuracy while reducing the required thicknesses of etching mask 13 and etching stopper 12. (Embodiment 5) Referring to FIGS. 21 to 26, description will now be given on a process of manufacturing an X-ray mask according to an embodiment 5 of the invention. The structure which is shown in FIG. 21 and is the same as that shown in FIG. 14 is formed through a manufacturing step similar to that for forming the structure of the X-ray mask shown in FIG. 14. However, in the process of manufacturing the X-ray mask of the embodiment 5 of the invention shown in FIG. 21, resist 16 is used in both the step of forming opening 7 functioning as the alignment mark and the step of forming transfer circuit pattern 10, as will be described later. Therefore, resist 16 is thicker than that in the manufacturing process of the embodiment 4 of the invention. As shown in FIG. 22, alignment mark pattern 6 is formed in resist 16 similarly to the process of manufacturing the X-ray mask of the embodiment 4 of the invention shown in FIG. 15. Etching mask 13 masked with resist 16 is partially removed to form alignment mark pattern 14 in etching mask 13. In this manner, the structure shown in FIG. 23 is formed. Then, as shown in FIG. 24, X-ray absorber 4 masked with resist 16 and etching mask 13 is partially removed by etching to form opening 7. As shown in FIG. 25, transfer circuit pattern 9 is formed on resist 16 by the electron beam writing. As described above, alignment mark pattern 6 and transfer circuit pattern 9 are formed in resist 16. Therefore, the manufacturing process can be simpler than that in the embodiment 4 of the invention which requires the step of forming the resist to be performed twice. Etching mask 13 masked with resist 16 is partially removed by etching to form transfer circuit pattern 15 in etching mask 13. Thereafter, resist 16 is removed to form the structure shown in FIG. 26. Thereafter, X-ray absorber 4 masked with etching mask 13 is partially removed by etching to form transfer circuit pattern 10 (see FIG. 13) in X-ray absorber 4. Thereafter, etching mask 13 is removed so that the X-ray mask shown in FIG. 13 is produced. If there is a difference between the size of opening 7 and the size of the interconnection pattern and others formed in transfer circuit pattern 10, the etching conditions for forming opening 7 may be determined depending on the size thereof, and thus may be independent of the etching conditions for forming transfer circuit pattern 10 which is determined depending of the size of the interconnection pattern and others. Thereby, an effect similar to that of the embodiment 4 of the invention can be achieved. The concept of the invention can be applied to the electron beam writing (EB writing) for directly writing a circuit pattern on a resist on a semiconductor substrate with an electron beam. The electron beam writing requires an alignment mark, which is prepared, in the prior art, by depositing a film on the semiconductor substrate and by forming the alignment mark from this film. However, this film forming process can be eliminated by employing the concept of the invention and forming the opening functioning as the alignment mark in the semiconductor substrate. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.