Patent Number: 060977906
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an X-ray extraction window E.sub.1 comprising a partition wall according to an embodiment of the present invention, as well as a portion of an X-ray exposure apparatus having the partition. The X-ray window E.sub.1 is disposed between an exposure chamber 1 and a beam duct 2. As will be described later, a beam of X-rays L.sub.1 such as synchrotron X-rays produced from a light source 3 (FIG. 3) such as a charged particle accumulation ring, for example, passes through the beam duct 2, being kept in a ultra-high vacuum, and it is introduced into the exposure chamber 1 through the X-ray window E.sub.1. The inside of the exposure chamber 1 is controlled to be occupied by a reduced pressure ambience of helium gas, for example, of about 0.2 Pa, for example. This is to prevent attenuation of X-rays and, with convection of helium gas, to facilitate heat radiation from a wafer W.sub.1, for example. The X-ray window E.sub.1 includes a beryllium film 11, comprising a thin film of several microns or several tens of microns in thickness, and a flange (supporting means) 12 for supporting the outside peripheral edge of the film. The outside peripheral edge of the beryllium film 11 is fixed to the flange 12 by means of a bonding ring 13. The flange 12 is fixedly mounted to a flange 2a, for example, of the beam duct 2 by means of an O-ring 14 and bolts 15. As described, the beryllium film 11 should have mechanical strength sufficient sufficient to bear a pressure difference AP between a pressure P.sub.1 of the beam duct 2, being kept in a high vacuum, and a pressure P.sub.2 of the exposure chamber, being kept in a reduced pressure ambience of helium gas. Additionally, it should have a high X-ray transmissivity. Thus, it is desirable to reduce the thickness of the beryllium film 11 as much as possible, within the limit of the required mechanical strength. Thus, the thickness T.sub.1 of the beryllium film 11 may be determined, from the tension stress .sigma..sub.1 to be produced at the central portion of the film 11 as flexure is produced in the film 11 in response to the tolerance value for the pressure difference .DELTA.P, that is, to a design pressure P.sub.0, and in accordance with equation (4) having been mentioned. However, there is a possibility that, even when the central tension stress .sigma..sub.1 does not exceed the breaking stress .sigma..sub.0, the outside peripheral portion of the beryllium film 11 is broken due to the stress concentration at the contact portion between the beryllium film 11 and the flange 12. In consideration of this, the flange 12 is provided at its inside peripheral edge with a curved portion (curvature support) 12a of a ring-like shape, having a predetermined curvature radius R. This curved portion 12a contacts the outside peripheral edge portion of the beryllium film 11 to bend it along the curved face of the curvature support. This effectively prevents stress concentration and, thus, breakage of the beryllium film 11. As the outside peripheral portion of the beryllium film is curved along the curvature portion 12a, a tension stress .sigma.f produced thereby is added to the tension stress .sigma..sub.2 to be produced by deflection caused by the pressure difference .DELTA.P between the exposure chamber 1 and the beam duct 2. Thus, the curvature radius R of the curvature portion 12a of the flange 12 may be determined as follows. When, as shown in FIG. 2, deflection is produced in the beryllium film 11 due to a pressure difference .DELTA.P and the outside peripheral edge portion of the beryllium film 11 is curved along the curvature portion 12a of the flange 12, the tension stress .sigma.t produced at the outside peripheral portion of the film 11 corresponds to the sum of (i) a tension stress .sigma..sub.2 produced by deflection resulting from the pressure difference .DELTA.P and (ii) a tension stress .sigma.f produced by flexure of the film along the curvature portion 12a of the flange 12. Namely: EQU .sigma.t=.sigma..sub.2 +.sigma.f (5) The tension stress .sigma.f can be calculated from the curvature radius R of the curved portion 12a and the thickness T.sub.1 of the beryllium film 11, in accordance with the following equation: EQU .sigma.f=0.5.multidot.E.multidot.T.sub.1 /R (6) From equations (6) and (2), it follows that: EQU .sigma.t=0.328(E.multidot..DELTA.P.sup.1/2 .multidot.a.sup.1/2 /T.sub.1.sup.2).sup.1/3 +0.5.multidot.E.multidot.T.sub.1 /R(7) In order to assure that the tension stress .sigma.t produced at the outside peripheral portion of the beryllium film 11 is smaller than the tension stress .sigma..sub.1 produced at the center of the film 11, on an occasion when the pressure difference .DELTA.P is equal to the design pressure P.sub.0, from equations (7) and (1) it follows that: EQU R&gt;5.263.multidot.(E.sup.2 .multidot.T.sub.1.sup.5 /P.sub.0.sup.2 /a.sup.2).sup.1/3 (8) Namely, the curvature radius R of the curvature portion 12a of the flange 12 may well be selected to satisfy equation (8). Practically, a larger tension stress is produced at a portion slightly inside the outside peripheral edge of the beryllium film, than at the outside peripheral edge, and preferably the curvature radius of the curvature portion 12a of the flange 12 may be gradually enlarged toward the inside edge thereof. When the outside peripheral portion of the beryllium film 11 is bent along the curvature portion having a curvature radius determined as described above, there is no possibility that a tension stress larger than that at the center of the beryllium film is produced in the outside peripheral portion thereof. Since breakage of the beryllium film can be avoided as the film thickness is designed on the basis of the tension stress at the central portion of the film, there is no necessity of using an unnecessarily enlarged safety factor as in the conventional example. Thus, the required beryllium film thickness can be reduced and the X-ray transmissivity of the film can be improved significantly. FIG. 3 shows a general structure of an X-ray exposure apparatus. Light source 3 projects a beam of X-rays L.sub.1, comprising sheet-beam-like synchrotron radiation, and it is expanded by a convex mirror 4 in a direction perpendicular to the orbital plane of the radiation light. The X-ray beam L.sub.1 being reflectively expanded by the convex mirror 4 passes through the X-ray window E.sub.1, and it is introduced into the exposure chamber 1. Then, by means of a shutter (not shown), the X-ray beam is adjusted to provide a uniform exposure amount within an exposure region. The X-ray beam L.sub.1 passing the unshown shutter is projected to a mask M.sub.1. A wafer (substrate) W.sub.1 is held vertically by a wafer chuck (substrate holding means) 5. An exposure pattern formed on the mask M.sub.1 is transferred, by exposure, onto the wafer W.sub.1 in accordance with a step-and-repeat procedure, for example. The wafer chuck 5 can be positioned precisely with respect to five directions, by means of a wafer stage 6, which comprises a fine-motion stage 6a and a rough-motion stage 6b. Next, an embodiment of a semiconductor device manufacturing method which uses an X-ray exposure apparatus such as described above, will be explained. FIG. 4 is a flow chart of a procedure for the manufacture of semiconductor devices such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels, CCDs, thin film magnetic heads or micro-machines, for example. Step S11 is a design process for designing a circuit of a semiconductor device. Step S12 is a process for making a mask on the basis of the circuit pattern design. Step S13 is a process for preparing a wafer by using a material such as silicon. Step S14 is a wafer process which is called a pre-process wherein, by using the so prepared mask and wafer, circuits are practically formed on the wafer through lithography. Step S15 subsequent to this is an assembling step which is called a post-process wherein the wafer having been processed by step S14 is formed into semiconductor chips. This step includes an assembling (dicing and bonding) process and a packaging (chip sealing) process. Step S16 is an inspection step wherein an operation check, a durability check and so on for the semiconductor devices provided by step S15, are carried out. With these processes, semiconductor devices are completed and they are shipped (step S17). FIG. 5 is a flow chart showing details of the wafer process. Step S21 is an oxidation process for oxidizing the surface of a wafer. Step S22 is a CVD process for forming an insulating film on the wafer surface. Step S23 is an electrode forming process for forming electrodes upon the wafer by vapor deposition. Step S24 is an ion implanting process for implanting ions to the wafer. Step S25 is a resist process for applying a resist (photosensitive material) to the wafer. Step S26 is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step S27 is a developing process for developing the exposed wafer. Step S28 is an etching process for removing portions other than the developed resist image. Step S29 is a resist separation process for separating the resist material remaining on the wafer after being subjected to the etching process. By repeating these processes, circuit patterns are superposedly formed on the wafer. With these processes, high density microdevices can be manufactured. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.