Patent Number: 
Section: description

The present invention will be described in detail below in accordance with the embodiment shown in FIG. 1. A laser source 100 generates laser light having a wavelength from the infrared to the visible light regions. A YAG laser, for example, may be used for the laser source 100. Laser light generated by the laser source 100 is converged by a collecting optics 101 focusing at a focal point 3. An object (EUV light-generating object) dripped from an object source 2 is illuminated with high illuminance laser light at the focal point 3. The central portion of the object thereby becomes plasma, and a soft x-ray is then generated from this portion. The following objects may be used for the EUV light-generating object (target): water drops, ice particles, drops of any water solution, Xe gas, Kr gas, or tape or wire shaped Cu or Ta (Tantalum). For the wavelength of the soft x-ray, it is desirable to use a wavelength smaller than 50 nm, e.g. a radiation light source of 13 nm. Since the transmittance of soft x-rays relative to air is rather low, the whole apparatus is placed in a vacuum chamber 1. The soft x-ray generated at focal point 3 is directed to a field stop (aperture) 7, having an opening of a predetermined area, by the optics 4, 5, and 6, which is a combination of plane mirrors and concave mirrors. In this embodiment, a reflection-increasing film is applied to the reflecting surface of the optics 4, 5, and 6, increasing the reflectance in the soft x-ray region. For the reflection-increasing film, such combinations of materials as Mo and Si or Mo and Be, which are alternately applied in a number of layers, may be used. For the field stop 7, materials blocking soft x-rays are suitable. In this embodiment, although a laser plasma x-ray source is used for the light source, an undulator equipped with a synchrotron orbital radiation (SOR) may be used for the light source. In this embodiment, although a wavelength of 13 nm generated from a SOR is used, wavelengths such as 26 nm or 39 nm generated from a SOR as well as 1 nm of hard x-rays may also be used. The radiation light passing through the opening of the field stop 7 is then directed to a reflection mask 9 through a relay optical system 8 consisting of reflection optics. A pattern consisting of a portion reflecting, and a portion not reflecting, soft x-rays is formed on the surface of the reflection mask 9. The optical systems 4, 5, 6, and 8 compose an illumination optical system illuminating the reflection mask 9. The field stop 7 is optically conjugate with the reflection mask 9 with respect to the relay optical system 8, and an image of the field stop 7 is projected on the reflection mask 9. The image of the opening of the field stop 7 coincides with the illuminated area on the reflection mask 9. The radiation light selectively reflected by the reflection mask 9 is directed to a wafer 11 as an exposed substrate (work), placed on a substrate stage ST2 by a projection optical system 10 having a predetermined reduction magnification. The pattern in the illuminated area on the reflection mask 9 is then projected on the wafer 11. As shown in FIG. 2, an exposure area IE is formed on the wafer 11. The exposure area IE has a shape similar to the illuminated area on the reflection mask 9 which is also similar to the opening of the field stop 7. The image of the pattern in the illuminated area on the reflection mask 9 is formed in the exposure area IE. Returning to FIG. 1, a mask stage ST1 and the substrate stage ST2 are connected with drivers MT1 and MT2 respectively. These drivers MT1 and MT2 are connected with a main controller MCU. While performing the exposure, the reflection mask 9 and 20 wafer (exposed substrate) 11 are moved relative to the projection optical system 10 in the direction indicated by the arrow shown in FIG. 1 by means of the drivers MT1 and MT2. In this embodiment, since there is a vacuum inside the chamber 1, it is desirable to use a magnetic levitation type linear actuator or a differential exhaust type pneumatic bearing in combination with an actuator such as a linear motor for these drivers MT1 and MT2. It is also desirable to use an electrostatic chuck as a chucking mechanism for the mask stage ST1 and the substrate stage ST2. As shown in FIG. 2, the exposure area IE sweeps along the scanning direction, indicated by the arrow in the figure, on the wafer 11 as a work (exposed substrate). The exposure area on the wafer 11 consequently corresponds with the locus of the sweep of the exposure area IE, and the exposure area corresponds with the single shot area SA on the wafer 11. In this embodiment, the field stop 7 is optically conjugate with the reflection mask 9 with respect to the relay optical system 8. The field stop 7 is optically conjugate with the wafer 11 with respect to the relay optical system 8, the reflection mask 9 and the projection optical system 10. Since it is optically equivalent to placing the field stop 7 on the reflection mask 9, the illuminated area (or the exposure area) may be limited. In this configuration, because no field stop 7 exists in the vicinity of the reflection mask 9, there is no vignetting produced by the field stop 7 at any point in the exposure area, and good resolution may be obtained in the whole exposure area. If an intermediate image of the reflection mask 9 is formed in the projection optical system 10, the field stop 7 may be placed at the intermediate image position. It is desirable to compose the projection optical system 10 with a reflection optical system having less than six reflection surfaces. Although only one field stop 7 is used in the embodiment shown in FIG. 1, the field stop is not limited to one. It is possible to combine plural elements such as blades limiting the width in the direction perpendicular to the sweeping direction together with blades limiting the width in the sweeping direction. A modified example of the field stop is described with reference to FIG. 3. FIG. 3A represents a sectional view showing a field stop 70 consisting of a fixed field stop 71 and variable field stops 72A and 72B. FIG. 3B represents a plan view showing the relative position of the fixed field stop 71 and the variable field stops 72A and 72B. In FIGS. 3A and 3B, the field stop has the fixed field stop 71 and the movable field stop 72A and 72B, wherein the field stop has an arc shaped opening 71A and the movable field stop has two blades 72A, 72B defining the width in the sweeping direction of the illumination area (or exposure area) on the reflection mask 9 (or on the wafer 11). The fixed field stop 71 shown in FIGS. 3A, 3B is equivalent to the field stop 7 in FIG. 1. Each blade 72A, 72B defining the width in the sweeping direction of the movable field stop is movable such that each blade 72A, 72B has a driving unit 73A, 73B driving each blade in the sweeping direction independently. Here, the sweeping direction corresponds to the direction in which the projected image of the reflection mask 9 (or the wafer 11) on the field stop 7 by the relay optical system 8 (or by the relay optical system 8 in combination with the projection optical system 10) is swept. In the modified embodiment shown in FIG. 3, the radiation light illuminates the predetermined area defined by the movable field stop 72A, 72B, which is within the scope of the arc shaped illumination area on the reflection mask 9 (or the wafer 11) defined by the fixed field stop 71. Said main controller MCU controls the movable blade-driving unit 73A, 73B. An example of a control system will be described below with reference to FIGS. 3 and 4. FIGS. 4A through 4E represent plan views showing the relative position between the opening of the fixed field stop 71 and the blades 72A, 72B of the movable field stop. FIGS. 4F through 4J represent plan views showing the position of the exposure area IE relative to the single shot area on the wafer 11. FIG. 4F shows the relative position between the exposure area IE and the shot area SA where the position of the movable field stop is shown in FIG. 4A. In the same way, FIG. 4G corresponds to FIG. 4B, FIG. 4H to FIG. 4C, FIG. 4I to FIG. 4D, and FIG. 4J to FIG. 4E. In FIGS. 4F through 4J showing the relative position between the shot area SA and exposure area IE, the hatched area shows where the radiation light actually illuminates on the wafer 11. The main controller MCU shown in FIG. 3 drives the mask stage ST1 and the substrate stage ST2 by means of the drivers MT1, MT2, and places the exposure area IE at the left side of the shot area SA shown in FIG. 4F. At this time, since the blades 72A and 72B of the movable field stop are closed as shown in FIG. 4A, radiation light does not reach the exposure area IE (the exposure area IE is not formed). The main controller MCU then drives the mask stage ST1 and the substrate stage ST2 along the sweeping direction with velocities determined by the magnification of the projection optical system by means of the driving units MT1 and MT2. At the same time, the main controller MCU drives the blade 72B along the sweeping direction by means of the movable blade-driving unit 73B. At this time, in order that the edge image of the blade 72B substantially coincides with the edge of the shot area SA, the blade 72B is driven in accordance with the stages ST1 and ST2. When the blades 72A and 72B are opened as shown in FIG. 4C, radiation light passes through the whole area of the opening of the fixed field stop 71. As a result, the exposure area IE corresponding to the image of the opening of the fixed field stop 71 is formed in the shot area SA on the wafer 11 as shown in FIG. 4H. In this instance, since the stages ST1 and ST2 are still being driven along the sweeping direction, the exposure area IE sweeps the shot area SA. When the exposure area IE approaches the edge of the shot area SA as shown in FIG. 4I, the main controller MCU drives the blade 72A along the sweeping direction by means of the movable blade driving unit 73A, as shown in FIG. 4D. Therefore, radiation light overflowing from the shot area SA, which is directed to the exposure area IE, is blocked by the blade 72A. At this time, the blade 72A is driven in order that the image of the edge of the blade 72A substantially coincides with the edge of the shot area SA in accordance with the stages ST1 and ST2. When the exposure area IE goes beyond the shot area SA as shown in FIG. 4J, the blades 72A and 72B are then closed, and radiation light is no longer directed to the exposure area IE (the exposure area IE is no longer formed). From the series of movements described above, the pattern on the reflection mask 9 is projected in a single shot area on the wafer 11. The main controller MCU then drives the substrate stage ST2 by means of the driving unit MT2, and the exposure area IE is moved to another shot area (typically next to the former shot area SA). Then, the series of movements described above is repeated. Although the pattern is projected in a single shot area with a one stroke scanning exposure movement as described in FIGS. 3 and 4, a so called xe2x80x9cscan and stitch exposurexe2x80x9d may be used so that the pattern is projected in a single shot with a multi stroke scanning exposure movement. When the scan and stitch exposure is used, since a wide exposure area (in scanning direction) is not required for the projection optical system 10, it becomes simple to manufacture the projection optical system, and it has the merit of improving the imaging quality of the projection optical system. Suzuki discloses this type of scan and stitch exposure apparatus in U.S. patent application Ser. No. 08/654,747 filed on May 29, 1996. In the embodiment shown in FIG. 1, it is possible to use an illumination optical system disclosed in U.S. patent application Ser. No. 09/359,137 filed on Feb. 26, 1999 by Komatsuda, a coinventor of the present invention. It should be briefly explained that U.S. patent application Ser. No. 09/359,137 is applied to the present invention. In the illumination optical system disclosed in patent application Ser. No. 09/359,137, radiation light provided from light source 54 is directed to a reflection type optical integrator, forms a second source having a predetermined shape, and illuminates mask M through a condenser optical system 64. It is possible to replace the optical system 4, 5, and 6 shown in FIG. 1 of the present invention with the illumination optical system (54, 56, and 64) of patent application Ser. No. 09/359,137, so that the illumination optical system (54, 56, and 64) is used for illuminating the field stop 7, and the image of the field stop 7 is projected to the reflection mask 9 by the relay optical system 8 shown in FIG. 1. The illuminance distribution on the reflection mask 9 or on the wafer 11, may be varied by adjusting the position of at least one of the optical elements comprising the illumination optical system, or by inserting a reflecting element having a spatial distribution of reflectance into the illumination optical system. By means of varying the illuminance distribution on the reflection mask 9, or on the wafer 11 (exposed substrate as a work), it is possible to obtain a uniform (or other desired) illuminance distribution. In this case, it is desirable that the position of the optical element performing the adjustment be located in the optical path between the field stop 7 and the radiation source. In the illumination optical system shown in FIG. 1, it is possible to change distortion (isotropic or anisotropic) in the optical elements illuminating the field stop 7 by such procedures as changing the inclination of at least one of the plane mirrors 5, by changing the position of the concave mirror 6 along or perpendicular to the optical axis, or by changing the slight inclination of the concave mirror 6. As a result, the illuminance distribution on the field stop 7, on the reflection mask 9, or on the wafer 11, may be varied. It is likely that while moving one of the said optical elements, optical properties other than distortion (e.g., telecentricity) will change. In this case, moving the position of at least one other optical element may produce an adjustment. At this point, it is not desirable that an optical element between the field stop 7 and the reflection mask 9, which is an optical element consisting of the relay optical system 8, be moved to adjust the position. The reason is that it not only changes the luminance distribution of the radiation light but also changes the shape of the opening of the field stop 7. On the other hand, there is no limitation of position where a reflecting element having a spatial distribution of reflectance is inserted. In the embodiment described above, an arc shaped illumination area is formed on the reflection mask 9. However, the present invention is not limited to the arc shape. If the projection optical system is made for forming a rectangular shaped exposure area, the illumination optical system according to the present invention may easily be modified to illuminate the rectangular shaped area. This is accomplished by modifying the shape of the opening of the field stop from an arc shape to a rectangular shape. As for the projection optical system, a system having unit magnification and expansion magnification as well as reduction magnification may be used. The present invention may also be applied to a proximity type scanning exposure apparatus, such as an x-ray exposure apparatus where a mask and a wafer are moved in a body relative to the arc shaped illumination area illuminated with x-ray radiation. The present invention may be applied not only to a projection exposure apparatus for manufacturing semiconductor devices but also to a projection exposure apparatus for manufacturing display devices, including liquid crystal displays, by projecting device patterns onto a glass plate. It may also be applied to projection exposure apparatuses for manufacturing thin film magnetic heads by projecting a device pattern onto a ceramic wafer, for manufacturing image detectors (such as CCDs), or for manufacturing a reticle or mask by projecting a device pattern onto a glass substrate or silicon wafer. The foregoing description of the embodiment has been presented for the purpose of clarifying the technical content of the present invention. It is not intended to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.