Optical arrangement for exposure apparatus

Abstract: Disclosed is an optical arrangement which includes an optical system (5a,6a) for transforming synchrotron radiation light emitted from an emission point (2) of a synchrotron ring (1) into a substantially parallel beam, with respect to a first direction (x) which is parallel to an orbit plane of the synchrotron ring and with respect to a second direction (y) which is perpendicular to the orbit plane, wherein an absolute value of a focal length of the optical system in the first direction is smaller than that in the second direction.

Description: This invention relates to an optical system according to the first part of claim 1, in particular to an optical arrangement suitably usable, for example, in an exposure apparatus such as an X-ray exposure apparatus which uses, as a light source, synchrotron radiation light produced by a charged particle accumulation ring (synchrotron ring). The invention relates further to a method of producing a semiconductor device. An example of exposure apparatus which uses synchrotron radiation light as a light source to transfer a fine mask pattern such as VLSI to a wafer, is illustrated in Figures 6A and 6B wherein synchrotron radiation light emitted from an emission point 12 of a synchrotron ring (SOR ring) 11 is reflected by a mirror 15, swinging in the direction of arrow, and thus it is expanded in a direction (Y direction) perpendicular to the orbit plane of the synchrotron ring 11. The expanded light illuminates a mask (original) 13 whereby a pattern of the mask is transferred to a wafer 14. In the illustrated example, the distance from the emission point 12 to the mirror 15 is, e.g., 5 m; the distance from the mirror 15 to the mask 13 is, e.g., about 5 m; the distance from the mask 13 to the wafer 14 (i.e. "proximity gap") is, e.g., about 30 microns; and the size of the transfer region is about 20 mm square. In this example, the acceptance angle (the angle of divergence of light, from a point light source, that can be accepted by an illumination system (mirror 15) for projection of light to a mask and a wafer) with respect to a direction (X direction) parallel to the orbit plane of the synchrotron ring is 2 mrad, and the tilt in the X direction of the synchrotron radiation light impinging on the mask 13 is 1 mrad (max.) while the tilt thereof in the Y direction is 2 mrad (max.). As a result, there occurs distortion (called "run-out error") in the mask pattern transferred to the wafer 14. The magnitude of this distortion in the Y direction is 0.06 micron (max.). Figures 7A and 7B show another example of radiation exposure apparatus by which the problem of run-out error such as described may be solved. In the apparatus of Figures 7A and 7B, for transferring a mask pattern of a mask 33 to a wafer 34, a beam emitted from an emission point 32 of a synchrotron ring 31 is reflected by a rotational hyperboloid reflecting mirror 35 and then by a rotational paraboloid reflecting mirror 36, whereby it is collimated with respect to the X and Y directions. In this structure, however, the system comprising the reflecting mirrors 35 and 36 has the same focal distance in the X and Y directions and, therefore, the angle of acceptance of the synchrotron radiation is the same with respect to both of the X and Y directions. However, since the synchrotron radiation light has a larger divergence angle in the X direction than that in the Y direction, with this system, only it is possible to retrieve or accept a very small portion of the light in the x direction. Namely, most of the light emitted from the synchrotron is not used and, naturally, the efficiency of using synchrotron radiation light is low. This consequently requires a prolonged exposure time. International Patent Application WO-A-8908920, features of which are recited in the preamble of claim 1 appended, describes an optical arrangement comprising an optical system for transforming synchrotron radiation light emitted from an emission point of a synchrotron ring into a substantially parallel beam, with respect to a first direction which is parallel to an orbit plane of the synchrotron ring and with respect to a second direction which is perpendicular to the orbit plane wherein an absolute value of a focal length of said optical system in the first direction is smaller than in the second direction. The optical system comprises a first mirror for collecting the synchrotron radiation light in the first direction and second mirror for collecting the synchrotron radiation light in the second direction. The first and second mirrors have each toroidal shape. Each mirror has a reflecting surface provided by a single-layer gold film or provided by a multilayered film. A synchrotron radiation beam is emitted from an emission point of the synchrotron ring into a substantially parallel beam, with respect to a first direction which is parallel to the orbit plane of the synchrotron ring and with respect to a second direction which is perpendicular to the orbit plane. The obtained parallel radiation beam is projected to a mask having a circuit pattern (lithographic mask) so that the circuit pattern of the mask is transferred to a wafer. International Patent Application WO-A-8911683 describes a synchrotron orbit radiation exposure apparatus usable with a synchrotron ring for transferring a pattern of an original onto a substrate. This apparatus comprises means for holding the original and the substrate in a predetermined positional relationship. These means form a position adjusting mechanism for adjusting the relative positional relationship between the original and the substrate. United States Patent US-A-5031199 describes a synchrotron orbit radiation exposure apparatus comprising an exposure adjusting mechanism for adjusting the amount of exposure for the pattern transfer (only the desired energy band). United States Patent US-A-4788698 describes a synchrotron orbit radiation exposure system with a plurality of exposure apparatuses. It is accordingly an object of the present invention to provide an optical arrangement by which synchrotron radiation light can be collimated in the X and Y directions and, additionally, by which the angle of acceptance of the synchrotron radiation light with respect to the X and Y directions can be enlarged. It is another object of the present invention to provide an improved semiconductor device manufacturing method which uses the optical arrangement described above. These and other objects, features and advantages of the present invention are achieved by the optical system according to claim 1 and the method according to claim 9 and will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. The dependent claims describe particular embodiments of the invention. Figures 1A and 1B show a first embodiment of the present invention, wherein Figure 1A is a side view and Figure 1B is a plan view; Figure 2A s a graph showing the wavelength vs. reflectivity characteristic of a multilayered film reflecting mirror; Figure 2B is a graph showing the wavelength vs. reflectivity characteristic of a single-layer film reflecting mirror; Figure 3 is a plane view of a second embodiment of the present invention; Figure 4 is a flow chart of a semiconductor device manufacturing process; Figure 5 is a flow chart showing details of a wafer process; Figures 6A and 6B show a known example of X-ray exposure apparatus, wherein Figure 6A is a side view and Figure 6B is a plan view; and Figures 7A and 7B show another known example of X-ray exposure apparatus, wherein Figure 7A is a side view and Figure 7B is a plan view. Preferred embodiments of the present invention will now be explained in conjunction with the drawings. Referring first to Figures 1A and lB showing the first embodiment of the present invention, synchrotron radiation light produced by a synchrotron ring (SOR ring) 1 emanates from an emission point 2. The emitted radiation light is collected and collimated by a first mirror 5 and a second mirror 6 Denoted at 9 is an exposure shutter for adjusting the amount of exposure. The radiation light then illuminates a mask (original) 3 by which the mask pattern is transferred to a resist applied to a wafer (substrate) 4. The wafer 4 can be displaced by a stage 8, for adjustment of the relative positional relationship between the mask 3 and the wafer 4. Here, each of the first and second mirrors 5 and 6 has formed on its reflection surface a multilayered film or a single-layer film, comprising SiC or Pt. The first mirror 5 has a toroidal shape having a curvature, concave in the X direction and convex in the Y direction. The second mirror 6a has a cylindrical shape having a curvature, infinite in the X direction and concave in the Y direction. The synchrotron radiation light is reflected by the first mirror 5 , by which it is collected with respect to the X direction. Thus, it is retrieved or accepted with a large angle and is collimated. Then, the synchrotron radiation light is reflected by the second mirror 6 , by which it is collimated with respect to the Y direction. The thus collimated synchrotron radiation light illuminates the mask 3, for transferring the mask pattern (circuit pattern) to the wafer 4. Table 1 below shows specifications of the first and second mirrors, of a first example of this embodiment. X DIRECTION Y DIRECTION MIRROR RADIUS OF CURVATURE FOCAL LENGTH RADIUS OF CURVATURE FOCAL LENGTH 1ST 0.279 4.0 -9.97 -0.174 2ND INFINITE INFINITE 238.4 4.167 Unit:meter (Primary Incidence Angle: 88 deg.) In Table 1, each positive curvature radius corresponds to a concave surface while the negative curvature radius corresponds to a convex surface. The distance from the emission point 2 to the first mirror 5a is 4 m; the distance from the first mirror 5 to the second mirror 6 is 4 m; and the primary incidence angle (angle with respect to the normal to the mirror) of the synchrotron radiation light to the mirror is 88 deg., in both of the cases of the first and second mirrors 5 and 6 . The synthetic focal length is 4 m in the X direction and 100 m in the Y direction. If the size of the exposure region on the mask is 20 mm square, the angle of acceptance of synchrotron radiation light is 0.29 deg. in the X direction and 0.011 deg. in the Y direction. Namely, in the X direction the light collection is 25 times as much as in the Y direction. As a consequence, the illuminance on the mask increases and it is possible to reduce the exposure time considerably. The reflectivity to the X-ray largely depends on the angle of incidence. In an ordinary reflecting mirror using metal or the like, a high reflectivity is attainable provided that the angle of incidence is slightly smaller than 90 deg. If the angle of incidence becomes small, the reflectivity decreases largely. Accordingly, the light has to be projected with an angle of grazing incidence. If a curved surface mirror is used with grazing light incidence and where the radius of curvature of the mirror is R and the angle of incidence is , then the focal length F in a plane defined by a straight line parallel to the projected light and the projection thereof onto the tangential plane to the mirror surface is given by: F = (R x cos)/2 On the other hand, in a plane perpendicular to that plane and containing a straight line parallel to the projected light, the focal length F is given by: F = R/(2 x cos) Also, if plural reflecting mirrors are used and where the focal length of a first mirror (5b) is F1 while the focal length of a second mirror (6b) is F2 and the distance from the first mirror to the second mirror is L, then the synthetic focal length FO of this system is given by: F0 = (F1 x F2)/(F1 + F2 -L) On the basis of these relations, it is possible to design a collimating optical system with different synthetic focal lengths in X and Y directions while using plural grazing incidence reflecting mirrors. Table 2 shows specifications of the first and second mirrors of a second example of this embodiment. X DIRECTION Y DIRECTION MIRROR RADIUS OF CURVATURE FOCAL LENGTH RADIUS OF CURVATURE FOCAL LENGTH 1ST 0.419 3.0 -2.75 -0.096 2ND INFINITE INFINITE 88.6 3.09 Unit:meter (Primary Incidence Angle: 86 deg.) Here, the distance from the emission point to the first mirror is 3 m; the distance from the first mirror to the second mirror is 3 m; and the primary incidence angle of the light to the mirror is 86 deg., in both of the cases of the first and second mirrors. The synthetic focal length is 3 m in the X direction and 100 m in the Y direction. In this second example, each of the mirrors 5 and 6 has formed thereon a multilayered film. More specifically, tungsten and carbon materials are accumulated alternately (each five layers) to provide a multilayered film. In an ordinary reflecting mirror using metal or the like, a high X-ray reflectivity is attainable provided that the angle of incidence (angle with respect to a normal) is about 90 deg. However, with decreasing incidence angle, the reflectivity reduces largely. To the contrary, if a multilayered film is provided on the surface of a reflecting mirror, it becomes possible to obtain a high reflectivity even with a small angle of incidence. Figures 2A and 2B are graphs each showing the wavelength vs. reflectivity characteristic of a reflector where the angle of incidence to the reflector is 86 deg. Figure 2A corresponds to a multilayered film mirror according to this embodiment wherein tungsten and carbon materials are accumulated alternately (each five layers). Figure 2B corresponds to a reflecting mirror with a single gold layer. It is seen that the reflecting mirror of this embodiment assures a high reflectivity, as compared with the reflecting mirror of single gold film. Using a multilayered film reflecting mirror in an exposure apparatus assures the following advantages: (1) The angle of incidence of X-ray can be made small and, therefore, it is possible to use a small size reflecting mirror for illuminating the exposure region. This facilitates reduction in size and cost of the exposure apparatus. (2) Since the angle of incidence of X-ray can be small, the surface precision of the reflecting mirror becomes less influential. This leads to improved parallelism of illuminating light and, thus, to improved precision of the exposure apparatus. Referring to Figure 3 showing a second embodiment of the present invention, like numerals as of those of Figures 1A and 1B are assigned to corresponding elements. Two flat reflecting mirrors 7 - 7 are provided to divide the synchrotron radiation light into three beams. For each of the three divided beams, there are provided two mirrors 5 and 6 so as to collect and collimate the corresponding beam. The three radiation beams each being collected and collimated are directed to three exposure units, respectively, for executing mask pattern transferring operations in these units, respectively. Each mirror 5 and 6 is of the same structure as that described with reference to either one of the first and second examples of the first embodiment of the present invention. In an arrangement according to this embodiment, a plurality of exposure units can operate simultaneously in conjunction with a single port and, therefore, the efficiency of utilization of synchrotron radiation light is high. Also, the area of floor necessary for the exposure apparatus as a whole can be made small. With the above-described structure of the present invention, various advantageous effects are obtainable. Examples are as follows: (a) A mask can be illuminated with substantially collimated (parallel) synchrotron radiation light. Thus, it is possible to avoid or reduce the run-out error. This assures improved positional precision of a transferred pattern. (b) Since the synchrotron radiation light can be accepted efficiently, the strength of illumination is high. This effectively reduces the exposure time and increases the throughput of the exposure apparatus. It is to be noted that the present invention is not limited to an exposure apparatus. The invention is applicable also to an X-ray microscope, an optical CVD apparatus, or an optical etching apparatus, for example. Referring now to Figures 4 and 5, description will now be made of a semiconductor device manufacturing method according to an embodiment of the present invention, which uses one of the exposure apparatuses of the first and second embodiments. Figure 4 is a flow chart of the sequence of manufacturing a semiconductor device such as a semiconductor chip (e.g. IC or LSI), a liquid crystal panel or a CCD, for example. Step 1 is a design process for designing the circuit of a semiconductor device. Step 2 is a process for manufacturing a mask on the basis of the circuit pattern design. Step 3 is a process for manufacturing a wafer by using a material such as silicon. Step 4 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 5 subsequent to this is an assembling step which is called a post-process wherein the wafer processed by step 4 is formed into semiconductor chips. This step includes assembling (dicing and bonding) and packaging (chip sealing). Step 6 is an inspection step wherein operability check, durability check and so on of the semiconductor devices produced by step 5 are carried out. With these processes, semiconductor devices are finished and they are shipped (step 7). Figure 7 is a flow chart showing details of the wafer process. Step 11 is an oxidation process for oxidizing the surface of a wafer. Step 12 is a CVD process for forming an insulating film on the wafer surface. Step 13 is an electrode forming process for forming electrodes on the wafer by vapor deposition. Step 14 is an ion implanting process for implanting ions to the wafer. Step 15 is a resist process for applying a resist (photosensitive material) to the wafer. Step 16 is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step 17 is a developing process for developing the exposed wafer. Step 18 is an etching process for removing portions other than the developed resist image. Step 19 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. The semiconductor device manufacturing method of this embodiment uses the optical arrangement described with reference to either one of the first and second embodiments of the present invention described hereinbefore. It is therefore possible to produce semiconductor devices of higher degree of integration. 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 scope of the following claims.

Claims: An optical system (5,6) for transforming synchrotron radiation light emitted from an emission point (2) of a synchrotron ring (1) into a substantially parallel beam, collimated with respect to a first direction (X) which is parallel to an orbit plane of the synchrotron ring (1) and collimated with respect to a second direction (Y) which is perpendicular to the orbit plane (1), said optical system comprising a first mirror (5), of toroidal shape for collecting and collimating the synchrotron radiation light in the first direction (X), and a second mirror (6) for collecting and collimating the synchrotron radiation light in the second direction (Y), wherein the absolute value of the focal length of said optical system in the first direction (S) is smaller than that in the second direction (Y); characterised in that: said second mirror (5) has a cylindrical shape. An optical system according to claim 1, wherein each of said first and second mirrors (5,6) has a reflecting surface provided by a single-layer film. An optical system according to claim 1, wherein each of said first and second mirrors (5,6) has a reflecting surface provided by a multilayered film. A synchrotron orbit radiation exposure apparatus usable with a synchrotron ring (1), for transferring a pattern of an original (3) onto a substrate (4), said apparatus (3-9) comprising: means (8) for holding the original (3) and the substrate (4) in a predetermined positional relationship; and an optical system (5,6) for collecting and collimating a synchrotron radiation beam for transferring the pattern of the original (3) onto the substrate (4), which optical system is as claimed in any preceding claim. An apparatus according to claim 4, further comprising an exposure adjusting mechanism (9) for adjusting the amount of exposure for the pattern transfer. An apparatus according to either claim 4 or claim 5, further comprising a position adjusting mechanism (8) for adjusting the relative positional relationship between the original (3) and the substrate (4). A synchrotron orbit radiation exposure system, comprising: a synchrotron ring (1); and one or a plurality of exposure apparatuses (5,6,8,9) each as claimed in any of claims 4 to 6. An exposure system according to claim 7 including a beam splitter comprised of first and second plane mirrors (7,7) arranged between said synchrotron ring (1) and the first mirror (5) of each of three exposure apparatuses as claimed such that each first mirror (5) collects x-radiation from a common point (2) in said ring (1). A method of producing a semiconductor device comprising steps of: illuminating a resist coated wafer substrate (4) with collimated x-radiation via a mask (3) having a circuit pattern defined therein, by collecting the x-radiation from a point (2) in the orbit of a synchrotron range (1) using a first mirror (5) of toroidal shape to collimate the radiation in a first direction (X) parallel to the orbital plane, and collecting and collimating x-radiation collected from said first mirror (5) in a second direction (Y) perpendicular to the orbit plane using a second mirror (6) of cylindrical shape, wherein the focal length of the two mirror arrangement (5,6) in the first direction (X) is smaller than in the second direction (Y); developing said resist and transferring the pattern of the developed resist to a metallisation layer of the wafer substrate (4) by etching thereby defining circuit wiring; producing further circuit wiring in subsequent metallisation layers by repeating the aforesaid steps; and completing manufacture of the semiconductor device by steps including dicing, bonding and packaging.

Inventors: MIYAKE AKIRA, WATANABE YUTAKA, MIYAKE, AKIRA, WATANABE, YUTAKA, MIYAKE, AKIRA, C/O CANON KABUSHIKI KAISHA, WATANABE, YUTAKA, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03F7
IPC codes: G03F7