Patent Number: 055442137
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Preferred embodiments of the present invention will now be described. FIGS. 1(a) and 1(b) are structural views of a first embodiment. FIGS. 1(a) and 1(b) and 2(a) and 2(b) respectively show the structures of an X-ray mask and a mask chuck for holding the X-ray mask. A support frame 1 is shaped like a ring and provided with a rim, which is convenient to handle the mask during transportation, all around the outer periphery thereof. Although SiC is used as a material of the support frame 1 in this embodiment, other materials having a low coefficient of thermal expansion, for example, quartz glass, silicon, a ceramic material and the like, may be used. A silicon wafer 2 functioning as a mask substrate is adhesively fixed to the mask support frame 1, and its stiffness is provided by the mask support frame 1. The silicon wafer 2 may be fixed by anodic bonding or the like instead of adhesion. A mask membrane 3 made of a silicon nitride film is formed on the silicon wafer 2 by removing a portion of the silicon wafer 2, through which X-rays pass, by back etching. A transfer pattern such as a circuit pattern of a semiconductor device is drawn on the mask membrane 3 with an X-ray absorber of heavy metal, for example, gold. V-shaped linear grooves (referred to as "V-groove portions" hereinafter) 4 are formed to extend in the radial direction at three positions and at regular intervals (with 120.degree. pitches) on a periphery concentric with the ring-shaped support frame 1. Although the V-groove portions have the same shape and dimensions, the lengths thereof may be different for convenience of working. A notch 5 formed on the outer periphery of the ring-shaped mask support frame 1 is used to roughly determine the position (direction) of the mask support frame 1. Therefore, the notch 5 may be a cutout like an orientation flat. The relative positional relationship between the V-groove portions 4 and the notch 5 is controlled with high precision. FIG. 1(b) illustrates a mask chuck. Numerals 6 and 7 respectively denote a ring-shaped chuck base and projecting mounts. The mounts 7 are formed by embedding projecting members each having a spherical tip (rigid balls in this embodiment) at three positions on the chuck base 6. The mounts 7 are disposed at three positions to respectively engage with the V-groove portions formed on the mask support frame 1. When the X-ray mask is chucked, the V-groove portions 4 thereof respectively engage with the mounts 7 of the mask chuck. Clamp mechanisms 8 press the positioned X-ray mask against the mask chuck, and each of them is retreated by an actuator consisting of rotary and direct acting mechanisms to a position not to interfere with attachment and detachment of the X-ray mask. A cutout 9 formed on the chuck base 6 prevents interference between a transport unit 12 (FIGS. 2(a) and 2(b)) and the chuck base 6 when the X-ray mask is attached to and detached from the mask chuck. X-rays for exposure are radiated from the side opposite to the surface of the chuck base 6 on which the mounts 7 are formed. The procedure for attaching the X-ray mask to and detaching the X-ray mask from the mask chuck will be described with reference to FIGS. 2(a) and 2(b). FIG. 2(a) shows a state in which the X-ray mask taken out from an unillustrated mask housing device is being gripped and transported by the transport unit 12 to be attached to the mask chuck. Numerals 10 and 11 respectively denote a mask hand and clampers mounted in two positions at ends of the mask hand 10 and driven by an unillustrated actuator. It is better that the mask membrane 3 not lie under the clamp portion of the mask support frame 1 in order to prevent any dust, raised in contact portions of the clampers 11 and the mask support frame 1, from adhering onto the mask membrane 3 during transportation. On the other hand, the clamp mechanisms 8 of the mask chuck are retreated from the surface of the chuck base 6 in contact with the mask in preparation for attachment of the X-ray mask. FIG. 2(b) shows a state in which the X-ray mask carried by the mask transport unit 12 is attached to the mask chuck. The spherical portions of the mounts 7 respectively engage with the V-groove portions 4 of the mask support frame 1 at three positions. After positioning of the X-ray mask is completed, the clamp mechanisms 8 move to predetermined positions on the mask support frame 1 to press the mask support frame 1 as shown in FIG. 2(b). After that, the clampers 11 release the mask support frame 1 and retreat. The X-ray mask held by the mask chuck is detached in reverse order to that above. FIG. 3 is an enlarged view of an engaging portion between the V-groove portion 4 and the mount 7. In this embodiment, a rigid ball is embedded in the chuck base as the mount 7, thereby controlling the projection height. When the V-groove portion 4 and the mount 7 engage, the lower surface of the mask support frame 1 is not in contact with the upper surface of the chuck base 6. It is desirable that the force of the clamp mechanism 8 act on the center of the mount 7 through the mask support frame 1. For that purpose, the lower portion of the clamp mechanism 8 is curved as illustrated. The force acting on the mask support frame 1 thereby makes it more difficult for distortion of the mask pattern to occur. A preferable material of the clamp mechanism 8 is a non-metal, for example, resin in order to minimize the generation of dust. In a variation of the above embodiment, the V-groove portions 4 are disposed at four positions and at regular intervals with 90.degree. pitches on the periphery of the mask support frame 1 and the mounts 7 are disposed at four positions with 90.degree. pitches on the chuck base 6. It is thereby possible to bake the drawn pattern, whose phase is changed by 90.degree. and 180.degree. in exposure, using the same X-ray mask. Furthermore, it is easy to bake, for example, a vernier used to evaluate a wafer stage and an alignment system of an X-ray exposure apparatus. This embodiment has the following advantages: 1) Even if the mask support frame has a slight warp or the like in a natural state, since the mask can be held by the mask chuck while maintaining that state, the transfer pattern on the mask membrane is not distorted and a good pattern transfer precision can be obtained. PA1 2) The three points where the X-ray mask and the mask chuck are in contact with each other are disposed at regular intervals and have the same structure. Therefore, even if the mask support frame expands or contracts with heat change and the like, it is possible to let the expansion or contraction be relieved evenly in the three portions along the V-groove portions, and to restrict the influence of the expansion or contraction on the pattern transfer precision. PA1 3) Manufacture and inspection costs can be reduced only by forming simply shaped V-groove portions on the mask support frame of the X-ray mask or the chuck plane of the mask chuck. Embodiment 2 A second embodiment of the present invention will now be described. In FIGS. 4(a) and 4(b), the same numerals as those in the above embodiment denote the same components. FIG. 4(a) and 4(b) respectively illustrate the structures of an X-ray mask and a mask chuck in the second embodiment. The relationship between the V-groove portions and pins in this embodiment is opposite to the relationship between the V-groove portions and the mounts in the embodiment discussed above. Positioning pins 13 are disposed at three positions with 120.degree. pitches on a mask support frame 1, and both ends thereof project from both sides of a rim of the mask support frame 1. The projecting ends of the pins 13 are spherically shaped, and a material generating little dust (e.g., sapphire) is selected as the material of the pins 13. FIG. 4(b) illustrates a wafer chuck. V-groove portions 14 having the same shape as those in the above embodiment are formed at three positions with 120.degree. pitches, and respectively engage with the pins 13. FIG. 5 is an enlarged view of an engaging portion between the pin 13 and the V-groove portion 14. The pin 13 and the V-groove portion 14 are engaged and positioned in contact with each other at two points. Since a clamp mechanism 8 is nearly in point contact with the pin 13, a preferable material thereof is a relatively soft material, such as resin, so that an impression on the clamp mechanism 8 formed by the pin 13 functions as a seat for the pin 13. This is the same if projecting members are mounted on opposed surfaces in the engaging portions between the mask support frame 1 and the mounts 7 in the first embodiment. Since the operation procedure of the second embodiment is the same as that of the first embodiment, explanation thereof is omitted. According to this embodiment, since the mask support frame 1 is not directly in contact with the chuck base 6, but through the pins 13, it is possible to select a material in consideration of the dust raised when the X-ray mask is attached. Furthermore, since it is only necessary to apply drilling to the mask support frame 1 and fix the pins 13 into holes by adhesion, quality control is easy to implement. In particular, when a material, which is difficult to work, like SiC, is used as a material of the mask support frame 1, productivity is greatly enhanced from the viewpoint of manufacturing costs and yields. Embodiment 3 An embodiment of an exposure apparatus for producing a micro device (e.g., a semiconductor device, a thin-film magnetic head, a micromachine and the like) using the above-mentioned masks and mask chucks will now be described. FIG. 6 shows the structure of an X-ray exposure apparatus in this embodiment. Referring to FIG. 6, synchrotron orbital radiation 21 in the shape of a sheet beam radiated from an SOR source 20 is enlarged by a convex mirror 22 in the direction perpendicular to an orbital plane of the radiation 21. The radiation 21 reflected and enlarged by the convex mirror 22 is controlled by a shutter 23 so that the exposure amount in the radiation region is uniform, and led to an X-ray mask 24 through the shutter 23. The X-ray mask 24 is held by an unillustrated mask chuck in the above-mentioned mount method. An exposure pattern formed on the X-ray mask 24 is exposed and transferred onto a wafer 25 by a step and repeat method, a scanning method or the like. A device production method using the above exposure apparatus will now be described. FIG. 7 is a flow chart showing the procedure for producing a micro device (e.g., a semiconductor chip such as an IC, an LSI, a liquid crystal panel, a CCD, a thin-film magnetic head, and a micro-machine). A circuit of a semiconductor device is designed in Step S1 (circuit design). A mask on which a pattern of the designed circuit is formed is made in Step S2 (mask making). On the other hand, a wafer is made by using a material, such as silicon, in Step S3 (wafer making). In Step S4 (wafer process), referred to as a pre-process, an actual circuit is formed on the wafer using lithography technology by using the prepared mask and wafer. The next Step S5 (assembly), referred to as a post-process, produces a semiconductor chip by using the wafer made in Step S4, and includes an assembly step (dicing and bonding), a packaging step (chip encapsulation), and the like. In Step S6 (inspection), a performance test and a durability test are carried out on the semiconductor device made in Step S5. The semiconductor device is completed through the above steps and shipped in Step S7. FIG. 8 is a flow chart showing the above-mentioned wafer process in detail. The surface of the wafer is oxidized in Step S11 (oxidation), and an insulating film is formed on the surface of the wafer in Step S12 (CVD). An electrode is formed on the wafer by evaporation in Step S13 (electrode formation). Ions are implanted into the wafer in Step S14 (ion implantation). A sensitive material is applied on the wafer in Step S15 (resist process). The circuit pattern of the mask is baked on the wafer by exposure of the above-mentioned exposure apparatus in Step S16 (exposure). The exposed wafer is developed in Step S17 (development). Parts other than the developed resist image are cut off in Step S18 (etching). The resist which is unnecessary after etching is removed in Step S19 (resist stripping). The repetition of these steps forms circuit patterns on the wafer one on another. The use of the method in this embodiment makes it possible to produce a highly-integrated semiconductor device which has been previously difficult to produce. While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.