Illumination apparatus

An illumination apparatus for illuminating an object with X-rays. The illumination apparatus has a high illumination efficiency, and the numerical aperture of the X-rays is nearly uniform over an arcuate area, and is independent of the illumination position. The apparatus comprises an excitation energy light generation unit for generating excitation energy light rays and a target member having a curved surface and plurality of X-ray sources formed thereon that emit X-rays when irradiated by the light rays. The apparatus further comprises an illumination optical system that images X-rays from said plurality of X-ray sources onto the object to be illuminated. The target member curved surface may be cylindrical. The target member may also be tape-shaped and provided along the curved surface. Further, the target member may be metallic, particulate, liquid or gas.

FIELD OF THE INVENTION 
The present invention relates to illumination apparatus and exposure 
apparatus, and in particular to illumination apparatus for use with soft 
X-ray projection exposure apparatus 
BACKGROUND OF THE INVENTION 
An exposure apparatus for semiconductor manufacturing is one that projects 
and transfers a circuit pattern formed on the surface of an object, such 
as a photomask (hereinafter, simply "mask"), onto a substrate, such as a 
wafer, through an image-forming apparatus, such as a projection lens. The 
substrate is coated with a light-sensitive material, such as photoresist. 
Upon exposure of the mask, a photoresist pattern is obtained on the 
substrate. To obtain a photoresist pattern over a desired area (i.e., 
exposure field), the mask must be illuminated by light having a uniform 
intensity and a uniform divergence angle. Accordingly, the illumination 
apparatus of such exposure apparatus have employed Kohler illumination to 
satisfy these conditions. 
If the exposure light is X-rays, then the image-forming apparatus comprises 
a reflector. An off-axis circular arc-shaped (i.e., arcuate) exposure 
field is used, so that only an arcuate area on the mask is projected and 
transferred onto the wafer in a static exposure. Accordingly, the transfer 
of the circuit pattern on the entire mask onto the wafer is performed by 
simultaneously scanning the mask and wafer in fixed directions. 
In a scanning-type exposure, it is desirable that the illumination optical 
system uniformly illuminate the entire arcuate area on the mask at a fixed 
numerical aperture. An illumination optical system that can accomplish 
this is disclosed in Japanese Patent Application Kokai No. Hei 7-235471, 
applied for by the present applicant. 
The optical system disclosed in the above-mentioned Japanese Patent 
Application is shown herein in FIG. 6 and FIG. 7. X-rays 120, comprising 
beams 121 and 122, are emitted from light source (or light source image) 
110 and are reflected by a special reflector 130, thereby forming 
convergent beams 124 and 125, respectively, which irradiate an arcuate 
area 140 on the mask (not shown). Arcuate area 140 is centered about a 
point 144 (see FIG. 6), and an X-Y-Z coordinate system is shown for 
reference. 
As an example of a method of forming a light source for an illumination 
optical apparatus, an illumination apparatus of high illumination 
intensity is disclosed in Japanese Patent Application Kokai No. Hei 
8-148414, applied for by the present applicant. With reference now to FIG. 
8, illumination optical system 100 comprises an excitation energy light 
generation unit 101, a target member 103, and an illumination optical 
system 104 as the principle components. Excitation energy light rays 102 
emitted from unit 101 irradiate a plurality of locations 110 on target 
member 103. X-rays 120 are respectively generated from locations 110, 
thereby forming a plurality of X-ray sources 110 (i.e., locations 110 
become X-ray sources 110). 
With reference now to FIGS. 9, 10a and 10b, parallel x-ray beams 121 and 
122 are emitted from sources 110 in the sagittal direction (i.e., in the 
plane of the paper). When the emission angle .theta. is 0 degrees, beam 
121 has a diameter p(.theta.)=q. When the emission angle is .theta., beam 
122 has a diameter p(.theta.)=q.multidot.cos .theta.. Light beam diameter 
p(.theta.) (in the plane of the paper) decreases as emission angle .theta. 
increases. Accordingly, with reference now to FIGS. 10a and 10b, the cross 
section of beam 121 when the emission angle is 0 degrees is nearly 
circular (see FIG. 10a). This is in contrast to the cross section of beam 
122, which cross section is elliptical when the emission angle is .theta. 
(see FIG. 10b). Beam 122 cross section (FIG. 10b) has a major axis p(0) in 
the meridional direction (i.e., perpendicular to the plane of the paper in 
FIG. 9) and a minor axis p(.theta.) in the sagittal direction. 
With reference now to FIG. 11, when parallel beam 121, having an emission 
angle of 0 degrees (see FIG. 9), is subject to the converging action of 
reflector 130 (see FIG. 7), convergent beam 124 is formed. Beam 124 is 
conical and constantly extends an equal angle with respect to convergence 
point P1 in an arcuate illumination area (field) BF formed on the object 
(not shown) to be irradiated. In contrast, when parallel light beam 122, 
having an emission angle of .theta. (see FIG. 9) is subject to the 
converging action of reflector 130 (see FIG. 7), convergent light beam 125 
is formed. Beam 125 converges in an elliptical spindle-shape at 
convergence point P2 in arcuate illumination area (field) BF on the object 
(not shown) to be irradiated. 
Consequently, in the radial direction R at convergence point P2, the angle 
that convergent beam 125 extends with respect to convergence point P2 is 
equal to that of parallel beam 121 mentioned above. However, in the 
tangential direction T at convergence point P2, the angle that convergent 
light beam 125 extends with respect to convergence point P2 is smaller 
than that in the radial direction R at convergence point P2 (a multiple of 
cos .theta.). In addition, this effect is pronounced for parallel light 
beams with a large emission angle .theta. with respect to the sagittal 
direction. Thus, if an object is illuminated by an illumination apparatus 
which forms convergent light beams of a different cross-sectional shape, 
and an image of the object is formed by an image-forming apparatus, then 
the resolution of the image thus formed is generally not uniform over the 
image plane (exposure field). This is because a portion of the object is 
illuminated under conditions that do not satisfy the numerical aperture 
required by the image-forming apparatus. 
Japanese Patent Application Kokai No. Hei 6-267894 discloses a method to 
solve the above-described problem by using a new image-forming optical 
system. However, since this optical system comprises a plurality of 
lenses, it is not useful in the X-ray region wherein lenses cannot be 
used. In addition, even the optical system disclosed therein comprised 
reflectors, the amount of X-rays obtained after reflection would be 
extremely small, since a plurality of reflectors would be necessary. 
SUMMARY OF THE INVENTION 
The present invention relates to illumination apparatus and exposure 
apparatus, and in particular to illumination apparatus for use with soft 
X-ray projection exposure apparatus. An objective of the present invention 
is to provide a high-performance illumination apparatus, wherein the 
illumination efficiency is markedly higher than in conventional apparatus, 
and the numerical aperture of the X-rays at the illumination area formed 
in a circular arc (i.e., an arcuate area) is nearly uniform, independent 
of the illumination position. 
A first aspect of the invention is an illumination apparatus for 
illuminating an object. The apparatus comprises an excitation energy light 
generation unit for generating excitation energy light rays, and a target 
member having a curved surface and plurality of X-ray sources provided 
thereon. The plurality of X-ray sources emit X-rays when irradiated by the 
light rays. The target member is positioned relative to the light 
generation unit so that at least some of the light rays intercept the 
curved surface. The illumination apparatus further includes an 
illumination optical system that images the X-rays from the plurality of 
X-ray sources onto the object to be illuminated. 
Since the plurality of X-ray sources is arranged on a curved surface, the 
numerical aperture at the illumination area formed in a circular arc is 
nearly uniform and independent of the illumination position. Consequently, 
the required numerical aperture of an image-forming optical system, used 
in combination with the illumination apparatus of the present invention, 
is met over the entire object. As a result, the imaging resolution is 
uniform over the entire image plane of the imaging-forming optical system. 
A second aspect of the invention is the illumination apparatus as described 
above, wherein the curved surface of the target member is a cylindrical 
surface. The cylindrical surface can be easily manufactured and, in 
addition, the numerical aperture of the X-rays at the illumination area 
formed in a circular arc can easily be made nearly uniform, independent of 
the illumination position. 
A third aspect of the invention is an illumination apparatus as described 
above, wherein the target member is tape-shaped and is provided along the 
curved surface. In so doing, the numerical aperture at the illumination 
area formed in a circular arc is nearly uniform, independent of the 
illumination position. In addition, the tape-shaped target member can be 
moved in accordance with the level of wear of the target member, and a new 
part can receive the excitation energy light rays. Thus, the illumination 
apparatus can be used over a long period of time. 
A fourth aspect of the invention is an illumination apparatus as described 
above, wherein a particulate target member is used in the first means or 
second means, and is constituted so that a plurality of target members is 
formed on a curved surface. In so doing, the numerical aperture at the 
illumination area formed in a circular arc is nearly uniform, independent 
of the illumination position. In addition, the target member can be 
supplied continuously and, moreover, the amount of dispersed matter from 
the target member can be reduced. 
A fifth aspect of the invention is an illumination apparatus as described 
above, wherein the target member is a liquid or a gas. As used herein, the 
phrase "liquid or a gas" means that it is a liquid or a gas at room 
temperature and room pressure. When used as a target member, it is 
possible that they may also be a solid or a liquid, respectively. 
A sixth aspect of the invention is a method of illuminating an object. The 
method comprises the steps of first, providing a target member having a 
curved surface, then irradiating the curved surface at a plurality of 
locations with excitation energy light rays. The next step is emitting 
X-rays from the plurality of locations. Then, the final step is imaging 
X-rays from the X-ray sources onto the object. In a preferred embodiment, 
the latter step involves providing an illumination optical system adjacent 
the target member, and then imaging the X-rays through the illumination 
optical system.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to illumination apparatus and exposure 
apparatus, and in particular to illumination apparatus for use with soft 
X-ray projection exposure apparatus. A soft X-ray projection exposure 
apparatus transfers the circuit pattern on a photomask (i.e., a mask or 
reticle) onto a substrate, such as a wafer, through a reflective-type 
image-forming apparatus by means of a mirror projection system, such as an 
X-ray optical system. The present invention has the objective to provide a 
high-performance illumination apparatus, wherein the illumination 
efficiency is markedly higher than is conventional, and the numerical 
aperture of the X-rays at the illumination area formed in a circular arc 
(i.e., an arcuate area) is nearly uniform, independent of the illumination 
position. 
With reference to FIG. 1, the illumination apparatus 5 of the present 
invention comprises an excitation energy light generation unit 10, a 
target member 12, and an illumination optical system 13. Excitation energy 
light rays 15 are emitted from unit 10 and irradiate a plurality of 
locations 16 on target member 12. Target number 12 is capable of 
generating X-rays upon being irradiated with light of the appropriate 
wavelength. X-rays 17 are generated from locations 16 on target member 12 
irradiated by excitation energy light rays 15. Thus, locations 16 become 
microscopic X-ray light sources 16. X-rays 17 emitted from sources 16 pass 
through illumination optical system 13 and irradiate a mask 14 as X-rays 
18. 
With reference now to FIG. 2, by arranging a plurality of sources 16 (i.e., 
individual sources 61-66) on target member 12 having a curved surface S, 
widths p1-p3 of X-ray beams 71-73, respectively, constituting X-rays 17 
can be controlled. For example, beam 71 includes X-rays emitted from 
sources 16, and in particular, includes X-rays emitted from sources 61 and 
64, as well as from sources 62 and 63 therebetween (sources outside of 
source 62 and light source 63 are not illustrated). Similarly, beam 72 
also includes the X-rays emitted from sources 16, and in particular, 
includes X-rays emitted from sources 62 and 65, as well as from sources 63 
and 64 therebetween (sources outside of sources 63 and 64 are not 
illustrated). Likewise, beam 73 also includes X-rays emitted from sources 
16, and in particular, includes X-rays emitted from sources 63 and 66, as 
well as from sources 64 and 65 therebetween (sources outside of sources 64 
and 65 are not illustrated). 
With continuing reference to FIG. 2, width p1 of beam 71 in the sagittal 
direction is determined by the space between sources 61 and 64. Likewise, 
width p2 of beam 72 in the sagittal direction is determined by the space 
between sources 62 and 65, and width p3 of beam 73 in the sagittal 
direction is determined by the space between sources 63 and 66. 
Accordingly, by forming sources 16 on the desired curved surface S of 
target member 12, widths p1-p3 of beams 71-73 emitted toward illumination 
optical system L13 can be made a desired width. 
In a preferred embodiment, curved surface S of target member 12 is shaped 
such that X-rays 18 illuminate mask 14 at a roughly uniform numerical 
aperture (see FIG. 1). In particular, if an optical system such as the one 
shown in FIGS. 6 and 7 is used as illumination optical system 13 in the 
present invention, it is preferable that curved surface S be made 
cylindrical. In so doing, widths p1-p3 of beams 71-73 emitted from light 
sources 16 are equal. Thus, arcuate illumination area 140 (see FIG. 7) can 
be illuminated at a uniform numerical aperture. 
With reference again to FIG. 2, target member 12 can be considered to have 
a cylindrically curved surface S. Accordingly, if light sources 61-66 are 
arranged on cylindrical surface S, then light beams 71-73 have the same 
widths p1-p3 (i.e., p1=p2=p3), since the spaces between light source 61 
and 64, between light source 62 and 65, and between light source 63 and 
66, respectively, are equal to the diameter of the circular cross section 
of target member 12. In other words, sources 16 form the shape of curved 
surface S such that widths p1-p3 of each beam 71-73 is equal, or nearly 
so. 
Thus, with reference now to FIGS. 7 and 11, beams 124 and 125 converging on 
arcuate illumination area (field) BF have a cone shape, while constantly 
extending an equal angle with respect to the convergent point at every 
part (i.e., have a uniform cross-section), and the numerical aperture at 
the illumination area is equal and is independent of the illumination 
position. 
With reference now to FIG. 3, target member 12 on which X-ray sources 16 
are formed can comprise a solid member 81 having curved surface S with a 
given shape, as shown. The shape in which sources 16 is arranged can be 
determined by the shape of curved surface S. Since member 81 can be 
designed to have curved surface S be of any desired shape, it is 
relatively straightforward to control the shape (i.e., curvature) of 
curved surface S on which light sources 16 are arranged. 
Generally, target member 12 tends to wear down when X-ray sources 16 are 
used over an extended period of time. Thus, with reference now to FIG. 4, 
it is preferable that a new target member be supplied. By providing a 
tape-shaped target member 82 moveable along curved surface S of a 
substrate 83, the target member can be continuously supplied. Tape-shaped 
target member 82 can be easily created in a desired curved surface shape 
by pressing or winding it onto substrate 83 having a desired shape of 
curved surface S, for example. 
With reference now to FIG. 5, a particulate target member 84 may also be 
employed. Particulate target member 84 is supplied by a particulate target 
member supply unit 85 (e.g., a nozzle). Further, particulate target member 
84 is preferably arranged to have a desired curved surface shape. Since 
the position of particulate target member 84, e.g., the nozzle position, 
can control the angle at which the particles are emitted from the nozzle, 
and can control the emission speed of the particles and the like, it is 
easy to arrange sources 16 to have a desired curved surface shape. This 
method also has advantage that particulate target member 84 can be 
supplied continuously. Moreover, the amount of dispersed matter from 
particulate target member 84 can be reduced. 
In addition, if a pulsed laser is included in excitation energy light 
generation unit 10 so that X-rays 17 are generated in pulses (see FIG. 1), 
the pulsed laser light can illuminate particulate target member 84, which 
is supplied continuously. X-rays can thus be generated by synchronizing 
the supply of particulate target member 84 from nozzle 85 with the timing 
of the generation of pulsed laser light. 
With reference again to FIG. 1, it is preferable that illumination optical 
system 13 illuminate mask 14 with X-rays 18 at a uniform intensity and at 
a uniform divergence angle. In particular, it is preferable to arrange 
target member 12 in the vicinity of the front focal position of 
illumination optical system 13. In this case, X-rays 17 emitted from each 
X-ray source 16 pass through illumination optical system 13, and then are 
transformed into parallel light and the like and irradiate mask 14. 
Further-more, X-rays 17 emitted from each light source 16 irradiate mask 
14 at various angles. Accordingly, mask 14 is illuminated by Kohler 
illumination or in a manner similar to Kohler illumination. 
In addition, it is preferable that illumination optical system 13 comprise 
a reflector (not shown), which preferably includes a multilayer film to 
increase the reflectance of the reflector surface. As previously 
discussed, excitation energy light rays 15 irradiate a plurality of 
locations 16 on target member 12, and X-rays 17 are generated from each of 
these locations, which become light sources 16. In this case, excitation 
energy light rays 15 can irradiate all locations (sources) 16 
simultaneously, or can irradiate them separately or sequentially. The 
locations (sources) 16 on target member 12 to be irradiated should take 
into consideration the specifications required by the illumination optical 
system, such as, the intensity and divergence angle of X-rays 18, which 
illuminate the mask, the uniformity thereof, and the like. 
With continued reference to FIG. 1, when performing static (i.e., 
non-scanning) illumination of the mask, as in conventional exposure 
apparatuses, light sources 16 should be arranged two-dimensionally. In 
addition, in the case of soft X-ray exposure apparatus M, a band-shaped or 
belt-shaped area (illumination field) may be scanned and exposed due to 
design limitations of the image-forming optical system. In this case, it 
is preferable to perform critical Kohler illumination, as described in 
Japanese Patent Application Kokai No. Hei 7-235470, and light sources 16 
should be arranged one-dimensionally. In other words, target member 12 
should be arranged one-dimensionally, or when target member 12 is arranged 
in a plane, it should be irradiated by a one-dimensional (line-shaped) 
excitation energy light rays 15. 
In another preferred embodiment of the present invention, it is preferable 
to use an excitation energy light generation unit 10 that can change the 
path of excitation energy light rays 15, that can split the excitation 
energy light rays into a plurality of paths or beams, or that a plurality 
of excitation energy light generation sources, and the like. Changing the 
ray path of the excitation energy light rays 15 may be achieved, for 
example, by moving (e.g., oscillating) an optical element. 
In another preferred embodiment of the present invention, the excitation 
energy light rays 15 may be split into a plurality of excitation energy 
light beams. This may be accomplished using, for example, an optical 
element, like a beam splitter or a micro-lens array. The intensity of 
X-rays emitted from sources 16 is determined principally by the intensity 
of excitation energy light rays 15. Accordingly, the intensity of each of 
sources 16 can be flexibly adjusted by controlling the intensity of each 
light beam. 
In an additional preferred embodiment of the present invention, excitation 
energy light generation unit 10 includes a laser as a light generation 
source. If a plurality of laser light generation sources is employed, the 
intensity of the laser light can be increased to each of sources 16. In 
this manner, the intensity of X-rays 17 generated from sources 16 can be 
increased. In other words, this method can be employed if it is desired to 
increase the throughput of the soft X-ray projection exposure apparatus. 
The present invention is not limited to light generation sources and 
optical arrangements as described above. Rather, these are just examples. 
Although there are cases wherein optical elements are needed when changing 
the path of laser light or splitting laser light, these do not reduce the 
intensity of the laser light. This is because the reflectance and 
transmittance of laser light through laser optical elements is generally 
nearly 100%. Accordingly, high-intensity X-rays are emitted from each of 
sources 16. 
Also, in the illumination apparatus of the present invention, the material 
comprising target member 12 varies according to the X-rays to be 
generated. Generally, it is preferable to use a material with a high X-ray 
generation efficiency. For example, to generate X-rays of a 13 nm 
wavelength, tin, antimony, lead, tungsten, tantalum, and gold and the like 
are preferred. In addition, materials with a low melting point and 
materials that are liquid or gas at room temperature may be used. 
Materials that are solidified or condensed by cooling and the like can 
also be used and, moreover, liquids or gases can be used as is. The latter 
case will often be preferable since the generation of dispersed matter 
(debris) can be reduced. 
With reference again to FIG. 1, if excitation energy light rays 15 
irradiate target member 12 to generate soft X-rays, it is preferable to 
use a laser plasma X-ray source as a light generation source in excitation 
energy light generation unit 10. In this regard, high-intensity soft 
X-rays can be generated by using laser light as the excitation energy 
light. Furthermore, in a preferred embodiment, a high-intensity laser may 
be used to provide laser light. For example, a YAG laser, excimer laser, 
glass laser or titanium sapphire laser, may be used to obtain a separate 
high-intensity X-ray source. 
In addition, excitation energy light rays 15 that illuminate target member 
12 are not limited to laser light rays. For instance, the excitation 
energy light rays 15 may be from a source that can generate soft X-rays, 
such as an electron beam from an electron beam unit, and the like. Soft 
X-ray optical systems are often placed in a vacuum, since the absorption 
of X-rays due to air and the like is large. Accordingly, such systems are 
well-suited to using an electron beam in illumination apparatus 5. 
The illumination apparatus according to the present invention can also form 
a light source equivalent to a secondary light source of a conventional 
illumination apparatus, without using an X-ray integrator. Moreover, such 
a light source is superior in that the widths of the light beams emitted 
from the light sources can be controlled. 
Since the loss in intensity of the laser light due to the optical system is 
extremely small, a high-intensity X-ray light source can be obtained. 
Furthermore, every illumination point on the mask can be illuminated at 
the desired numerical aperture. By using the exposure apparatus according 
to the present invention, it is possible to supply high-intensity uniform 
illumination light, and a soft X-ray exposure apparatus that can expose a 
large area at high throughput can be provided. 
WORKING EXAMPLES 
The present invention is now described in greater detail based on three 
Working Examples. With reference to FIGS. 1 and 2, in each of the Working 
Examples below, the relevant illumination apparatus 5 comprises three 
principal components: excitation energy light generation unit 10, target 
member 12 and illumination optical system 13. A plurality of excitation 
energy light rays 15 are emitted from excitation energy light generation 
unit 10, and irradiate a plurality of locations 16 on target member 12. A 
YAG laser light is included in light generation unit 10 as a light 
generation source and a beam splitter (not shown) is used to split the 
beam emanating therefrom, thereby generating excitation energy light rays 
15 as light beams. 
With reference to FIG. 1, in each of the Working Examples, X-rays 17 
emitted from light sources 16 pass through illumination optical system 13 
and irradiate mask 14 as X-rays 18. Illumination optical system 13 
comprises a reflector (not shown) provided with a molybdenum and silicon 
multilayer film on the surface, which reflects X-rays having a wavelength 
in the vicinity of 13 nm. Also, a portion of mask 14 spanning an area 120 
mm long and 5 mm wide is irradiated by X-rays 18 over an arcuate 
illumination area. At this point, mask 14 is Kohler illuminated by 
arranging target member 12 in the vicinity of the front focal position of 
illumination optical system 13. As a result, the entire arcuate 
illumination area (field) on mask 14 can be illuminated at a uniform 
numerical aperture. In addition, upon exposing a photoresist-coated 
substrate with an exposure apparatus provided with the illumination 
apparatus according to the present invention, a photo resist pattern of 
the desired shape can be obtained across the entire exposure area (field). 
However, a resist pattern of the desired shape could not be obtained over 
the entire exposure area with an exposure apparatus provided with a 
conventional illumination apparatus. 
Working Example 1 
In Working Example 1, target member 12 is cylindrical and is comprised of 
tin (see FIG. 3). X-rays with a wavelength of at least 13 nm are generated 
from the locations 16 irradiated by excitation energy light rays 15. 
X-rays 17 are generated from a plurality of locations (i.e., light 
sources) 16 on target member 12. 
Working Example 2 
In Working Example 2, target member 82 is a tape-shaped thin plate, as 
shown in FIG. 4. Target member (Plate) 82 is comprised of tungsten. Target 
member 82 is wound on cylindrical substrate 83 and arranged so that the 
shape of surface S forms a part of the cylinder shape. Furthermore, target 
member 82 is made so that it can be supplied continuously by offsetting 
its position in the longitudinal direction thereof. X-rays with a 
wavelength of at lease 13 nm are generated from the part irradiated by 
excitation energy light rays 15, and X-rays 17 are generated from a 
plurality of locations (i.e., light sources) 16 on target member 82. 
Working Example 3 
In Working Example 3, target member 84 is made of ice particles 
(particulates) 16 having diameter on the order of 100 .mu.m, as shown in 
FIG. 5. Particulate target member 84 is supplied from nozzle 85, and made 
so that a cylindrical surface is formed by plurality of ice particles 16. 
If excitation energy light rays 15 irradiate particles 16, X-rays with a 
wavelength of at least 13 nm are generated. X-rays 17 are generated from a 
plurality of "locations" (i.e., particulates) 16 on target member 84, 
thereby becoming sources 16, as discussed above. 
As explained above, illumination apparatus 5 according to the present 
invention includes an excitation energy light generation unit 10 that 
generates excitation energy light rays 15. Light rays 15 irradiate a 
plurality of locations on target member 12, thereby forming a plurality of 
X-ray sources 16 corresponding to the aforementioned plurality of 
locations. Illumination apparatus 5 further includes illumination optical 
system 13 that irradiates the object to be illuminated with X-rays from 
the plurality of X-ray sources. The object to be irradiated can be Kohler 
illuminated at a high illumination efficiency and uniform numerical 
aperture, since a plurality of sources 16 are arranged on a curved surface 
S. In other words, the object to be illuminated can be illuminated by 
X-rays having a uniform intensity and uniform divergence. 
In addition, since the illumination apparatus according to the present 
invention can form a light source equivalent to the two-dimensional light 
source of a conventional illumination apparatus without using an X-ray 
integrator, it has advantages in that the transmittance (utilization 
efficiency) of X-rays is high compared with conventional apparatus. 
Further, it is easy to manufacture. Consequently, the pattern of a mask 
can be transferred faithfully onto substrates at a high throughput. 
The above Working Examples are examples of the present invention, and do 
not limit the present invention. For instance, with regard to Working 
Example 2, which employs ice particles as the target member, the present 
invention is not so limited. For instance, gas can be discharged from a 
nozzle, and the discharged gas or clusters generated by adiabatic 
expansion may also be used as the target member. Indeed, it will be 
apparent to one skilled in the art that the number and arrangement of 
light sources 16 are also not limited to the ones shown in the Working 
Examples. Light sources 16 arranged one-dimensionally can also be easily 
created and used in the present invention. Accordingly, the present 
invention can also be applied to critical Kohler illumination. Thus, the 
present invention is intended to cover all alternatives, modifications and 
equivalents as may be included within the spirit and scope of the 
invention as defined in the appended claims.