Patent Number: 
Section: description

FIG. 1 is a schematic and perspective view for explaining reflection of parallel light impinging on a reflection type integrator having convex cylindrical surfaces. FIG. 2 is a schematic and sectional view of the reflection type integrator having cylindrical surfaces. FIG. 3 is a schematic view for explaining reflection of X-rays at a cylindrical surface of a reflection type integrator having convex cylindrical surfaces. FIG. 4 is a schematic view for explaining an angular distribution of X-rays reflected by a cylindrical surface of a reflection type integrator having cylindrical surfaces. In these drawings, denoted at 5 is a reflection type integrator having convex cylindrical surfaces. An X-ray beam of substantially parallel light emitted from an X-ray light source is projected on the reflection type integrator 5 having a plurality of cylindrical surfaces, and secondary light sources are defined by this integrator. The X-rays emitted from these secondary light sources have an angular distribution of a conical surface shape. A reflector having a focal point placed at the secondary light source position reflects the X-rays to illuminate a mask. For explanation of the function of such a reflection type integrator having cylindrical surfaces, first the action of reflection light in a case where parallel light impinges on one cylindrical surface reflector will be described with reference to FIG. 3. As shown, parallel light is incident on one cylindrical surface at an angle xcex8 with respect to a plane perpendicular to the central axis thereof. If the light ray vector of the projected parallel light is R1=(0, xe2x88x92cos xcex8, sin xcex8) and the vector of a normal to the reflection surface of the cylindrical surface shape is n=(xe2x88x92sin xcex1, cos xcex1, 0), then the light ray vector of the reflection light is R2=(cos xcex8xc3x97sin 2xcex1, cos xcex8xc3x97cos 2xcex1, sin xcex8). Here, if the light ray vector of the reflection light is plotted in a phase space, the result is a circle of a radius cos xcex8 on an X-Y plane as shown in FIG. 4. That is, the reflection light is formed into divergent light of a conical surface shape, and the secondary light source is located at the position of apex of this conical surface. If the cylindrical surface comprises a concave surface, the secondary light source is placed outside the reflection surface. If the cylindrical surface comprises a convex surface, the secondary light source is placed inside the reflection surface. Also, if the reflection surface is limitedly provided by a portion of a cylindrical surface and the central angle thereof is 2xc3x8, then as shown in FIG. 4 the light ray vector of reflection light is arcuate with a central angle 4xc3x8 upon the X-Y plane. Next, a case wherein parallel light is projected on a reflection mirror provided by a portion of a cylindrical surface, wherein a reflection mirror having a focal length f and a focal point placed at the position of this secondary light source, and wherein a mask is placed at the position away from this reflection mirror by a distance f, will be considered. The light emitted from the secondary light source is divergent light and, after it is reflected by the reflection mirror of a focal length f, it is transformed into parallel light. The reflection light here is formed into a sheet beam of an arcuate sectional shape with a central angle 4xc3x8, at a radius fxc3x97cos xcex8. Thus, only an arcuate region upon the mask, having a radius fxc3x97cos xcex8 and a central angle 4xc3x8 can be illuminated. While one cylindrical surface reflection mirror has been explained above, a cylindrical surface integrator such as shown in FIG. 1 will now be considered. That is, as shown, parallel light of a diameter D is projected on a reflection mirror of a wider area, having a number of cylindrical surfaces arrayed in parallel in a one-dimensional direction. If the reflection mirror and the mask are disposed in the same manner as in the foregoing example, the angular distribution of light reflected by the reflection mirror, with a number of cylindrical surfaces arrayed in parallel, is essentially the same as in the preceding case. Thus, an arcuate region on the mask with a radius fxc3x97cos xcex8 and a central angle 4xc3x8 is illuminated. Since the light which impinges on a single point on the mask comes from the whole illumination region on the reflection mirror provided by cylindrical surfaces arrayed in parallel, the angular extension of it is D/f. That is, the numerical aperture of the illumination optical system is D/(2f). If the mask-side numerical aperture of the projection optical system is NAp1, the coherence factor is "sgr"=D/(2fNAp1). Therefore, in accordance with the thickness (size) of the parallel light, an optimum coherence factor "sgr" can be set. Next, embodiments of the present invention which use a reflection type integrator with plural cylindrical surfaces will be explained with reference to some drawings. [Embodiment 1] FIG. 5 is a schematic view of an X-ray reduction projection exposure apparatus according to a first embodiment of the present invention. FIG. 6 is a schematic and perspective view of a reflection type integrator with convex cylindrical surfaces, usable in the first embodiment of the present invention. FIG. 7 is a schematic view for explaining an illumination region on the surface of a mask, in the first embodiment of the present invention. Denoted in these drawings at 1 is a light emission point for X-rays, and denoted at 2 is an X-ray beam. Denoted at 3 is a filter, and denoted at 4 is a first rotational parabolic surface mirror. Denotod at 5 is a reflection type convex cylindrical surface integrator, and denoted at 6 is a second rotatational parabolic surface mirror. Denoted at 7 is a mask, and denoted at 8 is a projection optical system. Denoted at 9 is a wafer, and denoted at 10 is a mask stage. Denoted at 11 is a wafer stage, and denoted at 12 is an arcuate aperture. Denoted at 13 is a laser plasma X-ray light source, and denoted at 14 is a laser collecting optical system. Denoted at 15 is an illumination region on the mask surface, and denoted at 16 is an arcuate region through which the exposure is to be performed. Denoted at 17 is a vacuum chamber. The X-ray reduction projection exposure apparatus of the first embodiment of the preset invention comprises a laser plasma X-ray light source 13, an illumination optical system, a mask 7, a projection optical system 8, a wafer 9, stages 10 and 11 on which the mask or wafer is placed, an alignment mechanism for precisely aligning the positions of the mask and wafer, a vacuum chamber 17 for keeping the optical arrangement as a whole in a vacuum to prevent X-ray attenuation, and an evacuation device, for example. The illumination optical system comprises a first rotational parabolic surface mirror 4, a reflection type convex cylindrical surface integrator 5, and a second rotational parabolic surface mirror 6. The mask 7 comprises a multilayered film reflection mirror on which a transfer pattern is defined by a non-reflective portion, provided by an X-ray absorptive material. The X-ray beam as reflected by the mask 7 is imaged by the projection optical system 8 upon the wafer 9 surface. The protection optical system 7 is so designed that good imaging performance is provided within a narrow arcuate region off the axis. For example, with a reduction magnification of 1:5, good imaging performance is assured with respect to a region on the mask 7 surface at 200 mm off the axis, and to a region on the wafer 9 surface at 40 mm off the axis, with a width of 1 mm. In order that the exposure process is performed only by use of this narrow arcuate region, an aperture 12 having an arcuate opening is disposed just before the wafer 9. For transfer of the pattern on the whole surface of the mask 7 having a rectangular shape, the mask 7 and the wafer 9 are scanningly moved simultaneously, at a predetermined speed ratio. The projection optical system 8 has two multilayered film reflection mirrors, and it serves to project the pattern of the mask 7 onto the wafer 9 in a reduced scale. The reduction magnification corresponds to the scan speed ratio between the mask and the wafer. The projection optical system 8 comprises a telecentric system. The X-ray beam 2 emitted from the light emission point 1 of the laser plasma X-ray source 13 passes a shield filter 3 of the target, for prevention of particle scattering, and it is reflected by the first rotational parabolic surface mirror 4, whereby it is transformed into a parallel beam. This beam is then reflected by the reflection type integrator 5 with convex cylindrical surfaces, whereby a number of secondary light sources are produced. The X-rays from these secondary light sources are reflected by the second rotational parabolic surface mirror 6, and they illuminate the mask 7. Both of the distance from the secondary light source to the second rotational parabolic surface mirror 6 and the distance from the second parabolic surface mirror 6 to the mask 7 are equal to the focal length of the second rotational parabolic surface mirror. Thus, the conditions for Koehler illumination are satisfied. The reflection type convex cylindrical surface integrator 5 comprises a total reflection mirror having a shape that a number of small convex cylindrical surfaces are arrayed one-dimensionally such as shown in FIG. 6. In the sectional shape of the integrator 5, each arcuate portion has a radius of 0.5 mm and a central angle of 30 deg. When parallel light impinges on it, on a plane inside the reflection surface at a distance of 0.25 mm, there is formed a virtual image of linear secondary light sources, arrayed in parallel, that is, of the laser plasma X-ray light source 13. In this embodiment, the parallel X-ray beam has a thickness of 20 mm, and the incidence angle of the parallel X-ray beam upon-the integrator 5 is 85 deg. The second rotational parabolic surface mirror 6, having a focal length f=2300 mm, has its focal point disposed at the position of the secondary light sources, as the linear secondary light sources arrayed in parallel are defined on a plane spaced by 0.25 mm from the reflection surface when parallel light is projected on the integrator 5. Also, the mask 7 is disposed at a distance 2300 mm from the second rotational parabolic surface mirror 6. Light emitted from one point on the secondary light source is divergent light having an angular distribution like a conical surface. It is reflected by the second rotational parabolic surface mirror 6 having a focal length f=2300 mm, and it is transformed into parallel light. Then, as shown in FIG. 7, an arcuate region 16 on the mask 7 having a radius 2300 mmxc3x97cos 85(deg)=200 mm and a central angle 30 deg.xc3x972=60 deg. is illuminated. Here, the numerical aperture of the illumination optical system is 20/(2xc3x972300)=0.0043. If the numerical aperture of the projection optical system is 0.01 on the mask side and 0.05 on the wafer side, the coherence factor is 0.43. On the mask 7 surface, an arcuate region 16 of a radius 200 mm and a central angle 60 deg. is illuminated, and the pattern within this region is projected in a reduced scale onto the resist surface of the wafer 9. If the reduction magnification is 1:5, an arcuate region on the wafer 9 having a radius 40 mm and central angle 60 deg. is illuminated at once. With the scan of the mask 7 and the wafer 9, a square region of 40 mm square, for example, can be exposed with good precision. As described, this embodiment uses a reflection type convex cylindrical surface integrator 5 having a reflection surface provided by a number of small convex cylindrical surfaces arrayed one-dimensionally, by which the region on the mask 7 to be illuminated can be defined with an arcuate shape and, simultaneously, an optimum value for a coherence factor of the illumination optical system can be set. Also, the shape of the illumination region 15 on the mask 7 surface is restricted to the vicinity of the arcuate region 16 with which the exposure process is performed actually. Wasteful illumination of X-rays to a wide area outside the exposure region, such as shown in FIG. 14, is prevented. Thus, the loss of light quantity is reduced, the exposure time can be shortened and throughput can be improved. [Embodiment 2] FIG. 8 is a schematic view of an X-ray reduction projection exposure apparatus according to a second embodiment of the present Invention. FIG. 9 is a schematic and perspective view of a reflection type integrator with concave cylindrical surfaces, usable in the second embodiment of the present invention. Denoted in these drawings at 801 is an undulator X-ray light source, and denoted at 802 is an X-ray beam. Denoted at 803 is a convex surface mirror, and denoted at 804 is a first concave surface mirror. Denoted at 805 is a reflection type integrator with concave cylindrical surfaces, and denoted at 806 is a second concave surface mirror Denoted at 807 is a mask, and denoted at 808 is a projection optical system. Denoted at 809 is a wafer. Denoted at 810 is a mask stage, and denoted at 811 is a wafer stage. Denoted at 812 is an arcuate aperture, and denoted at 817 is a vacuum chamber. The X-ray reduction projection exposure apparatus according to the second embodiment of the present invention comprises an undulator X-ray light source 801, an illumination optical system, a mask 807, a projection optical system 808, a wafer 809, stages 810 and 811 having the mask or wafer placed thereon, an alignment mechanism for precisely aligning the positions of the mask and wafer, a vacuum chamber for keeping the optical arrangement as a whole in a vacuum for prevention of X-ray attenuation, and an evacuation device, for example. The illumination optical system of this embodiment comprises an undulator X-ray light source 801, a convex surface mirror 803, a first concave surface mirror 804, a reflection type concave cylindrical surface integrator 805, and a second concave surface mirror 806. The mask 807 comprises a multilayered film reflection mirror on which a transfer pattern is defined by a non-reflective portion, provided by an X-ray absorptive material. The X-ray beam as reflected by the mask 807 is imaged by the projection optical system 808 upon the wafer 809 surface. The projection optical system 808 is so designed that good imaging performance is provided in a narrow arcuate region off the axis. In order that the exposure process is performed only by use of this narrow arcuate region, an aperture 812 having an arcuate opening is disposed just before the wafer 809. For transfer of the pattern on the whole surface of the mask 807 having a rectangular shape, the mask 807 and the wafer 809 are scanningly moved simultaneously. The projection optical system 808 has three multilayered film reflection mirrors, and it serves to project the pattern of the mask 807 onto the wafer 809 in a reduced scale. The X-ray beam 802 emitted from the light emission point of the undulator X-ray light source 801 is a narrow and substantially parallel beam. It is reflected by the convex surface mirror 803 and the first concave surface mirror 804, whereby it is transformed into a thick parallel beam. This beam is reflected by the reflection type concave cylindrical surface integrator 805 of the structure that concave cylindrical surfaces with multilayered films for increased X-ray reflectivity are arrayed in parallel. By this, a number of secondary light sources are produced. Light emitted from a single point on the secondary light source is divergent light of a conical surface shape and, after being reflected by the second concave surface mirror 806, it is transformed into parallel light. Then, an arcuate region on the mask 807 is illuminated. As described above, this embodiment uses a reflection type concave cylindrical surface integrator 805 having a number of small concave cylindrical surfaces arrayed one-dimensionally, by which the region on the mask 807 to be illuminated can be made arcuate and, additionally, an optimum value for the coherence factor of the illumination optical system can be set. Also, the shape of the illumination region on the mask 807 surface is restricted to an arcuate region with which the exposure is to be done actually. Wasteful X-ray illumination to those areas outside the exposure region is prevented. Thus, the loss of light quantity is reduced, the exposure time can be shortened and the throughput can be improved. The X-ray illumination optical system and X-ray reduction exposure apparatus described above assure, with use of a reflection type integrator having a reflection mirror of a wide area provided by a number of cylindrical surfaces arrayed in parallel, illumination of only an arcuate region on a mask. Also, it enables setting the numerical aperture of the illumination system to provide an optimum coherent factor "sgr". The shape of the illumination region on the mask is restricted to an arcuate region with which the exposure is to be done actually, and wasteful X-ray illumination to those areas other than the exposure region is prevented. Thus, loss of light quantity is reduced, the exposure time can be shortened and the throughput can be enhanced. The reflection surface of the reflection type integrator may be provided with a multilayered film, to provide higher X-ray reflectivity. [Embodiment of a Device Manufacturing Method] Next, an embodiment of a device manufacturing method for producing semiconductor devices, for example, which uses an exposure apparatus such as described above, will be explained. FIG. 10 is a flow chart of a procedure for the manufacture of microdevices such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels, and CCDs, for example. Step 1 is a design process for designing a circuit of a semiconductor device. Step 2 is a process for making a mask on the basis of the circuit pattern design. Step 3 is a process for preparing 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 having been processed by step 4 is formed into semiconductor chips. This step includes an assembling (dicing and bonding) process and a packaging (chip sealing) process. Step 6 is an inspection step wherein an operation check, a durability check and so on for the semiconductor devices provided by step 5, are carried out. With these processes, semiconductor devices are completed and they are shipped (step 7). FIG. 11 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 upon 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. 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.