JP3316699B2 - X-ray reflection optical element and X-ray optical system having the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray optical element constituting an X-ray (reduction) projection exposure apparatus used for X-ray lithography and an optical system having the same.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of semiconductor integrated circuit elements, X-rays having shorter wavelengths have been used in place of conventional ultraviolet rays in order to improve the resolution of an optical system limited by the diffraction limit of light. Reduced projection lithography technology has been developed. An X-ray exposure apparatus used in this technique mainly includes an X-ray source, an illumination optical system, a mask, an imaging optical system (reduction projection optical system), and a wafer stage. A radiation or laser plasma X-ray source is used as the X-ray source. The illumination optical system includes an oblique incidence mirror that reflects X-rays incident on the reflection surface from an oblique direction, a multilayer mirror whose reflection surface is formed by a multilayer film, a filter that reflects or transmits only X-rays of a predetermined wavelength, and the like. Consisting of
The mask is illuminated with X-rays of a desired wavelength. The mask includes a transmission mask and a reflection mask. The transmission mask is
The pattern is formed by providing a substance that absorbs X-rays in a desired shape on a thin membrane made of a substance that transmits X-rays well. On the other hand, the reflection type mask has a pattern formed by providing a portion having a low reflectance in a desired shape on a multilayer film that reflects X-rays, for example. The pattern formed on such a mask is imaged on a photoresist-coated wafer by a reduction projection optical system composed of a plurality of multilayer mirrors and the like, and is transferred to the resist. Note that X-rays are in the atmosphere (especially nitrogen in them)
Therefore, all the optical paths are maintained at a predetermined vacuum degree.

[0003]

In such an X-ray exposure apparatus, the illumination optical system needs to irradiate (illuminate) X-rays over a wide area of the mask. For example, if the reduction ratio is 1/5
In an X-ray reduction projection exposure apparatus provided with a reduction projection optical system, in order to expose a square area having a side length of 20 mm on a wafer by the reduction projection optical system, a square having a side length of 100 mm on a mask is required. The area needs to be illuminated. In this case, it is desired to use the entire numerical aperture of the reduction projection optical system in order to obtain a desired diffraction-limited resolution. To that end, exposure light (X) is simply applied to each point on the pattern surface on the mask.
In addition, it is necessary to irradiate each point with light having a divergence angle corresponding to the numerical aperture on the incident side of the exposure light of the reduction projection optical system.

[0004] Incidentally, since the radiation light or the laser plasma X-ray source used as the X-ray source has a considerably small size as a light source, the light beam of the emitted exposure light (X-ray) also has a small diameter. The size of the X-ray source is determined by the diameter of the electron beam in the case of radiation light, and is determined by the spot diameter of the laser light applied to the target in the case of a laser plasma X-ray source. However, in each case, the X-ray luminous flux obtained is only about 0.1 to 1 mm in diameter, and is very small as compared with the area to be irradiated on the mask.

[0005] Therefore, a curved mirror such as an oblique incidence mirror or a multilayer mirror or a conventional illumination optical system constituted by combining a plurality of these mirrors satisfies the above requirements as long as a small X-ray source as described above is used. Could not. For example, as shown in FIG. 2A, when the mask 4 is arranged near an image P of the light source 2 by the illumination optical system 3 (referred to as critical illumination), a sufficient divergence angle is formed on and near the optical axis A of the exposure light B. Exposure light B is applied. However, the area irradiated with the exposure light B here is about the size of the image of the light source 2 in a very narrow area near the optical axis A. The image of the light source 2 can be enlarged to some extent by increasing the magnification of the illumination optical system 3, but in this case, the spread angle of light is reduced.

When the image P of the light source 2 by the illumination optical system 3 is arranged on the entrance pupil 50 of the imaging optical system (referred to as Koehler illumination) as shown in FIG. It is possible to irradiate the exposure light B with the spread of the light. However, the spread angle of the light illuminating each point on the pattern surface on the mask 4 becomes extremely small, and it becomes difficult to obtain the diffraction-limited resolution of the imaging optical system. Also,
Even when the mask 4 is arranged at an intermediate position between FIGS. 2A and 2B, the size of the area where the exposure light B is irradiated on the mask 4 and the spread angle of the light that irradiates each point of the pattern of the mask 4 are compatible. I can't let that happen.

For the reasons described above, the conventional X-ray reduction projection exposure apparatus can only expose a very small area of the mask pattern when trying to obtain a diffraction-limited resolution, and will enlarge the exposure area. Then, there is a problem that a resolution limit of a diffraction limit cannot be obtained. An object of the present invention is to solve such a problem.

[0008]

In order to achieve the above object, the present invention provides an X-ray having a substrate provided with a plurality of projections or depressions and a multilayer film formed on the substrate for reflecting X-rays. Exposure is performed using a reflection optical element (claim 1). Further, an X-ray reflection optical element having a substrate provided with a plurality of fine projections or depressions and a multilayer film formed on the substrate and reflecting X-rays, a mask on which a desired pattern is formed, and An image forming optical system for forming an image of a pattern, wherein an image of the secondary light source when an X-ray reflected by the X-ray reflecting optical element is used as a secondary light source is formed on an entrance pupil of the image forming optical system. Alternatively, the X-ray optical system is configured so that an image is formed on the mask or at an arbitrary position between the entrance pupil and the mask. Using this optical system, X-rays are applied to an X-ray reflection optical element having a substrate provided with a plurality of fine projections or depressions and a multilayer film formed on the substrate and reflecting the X-rays. The X-ray radiated and reflected by the element is used as a secondary light source, and an image of the secondary light source is placed on an entrance pupil of an imaging optical system or on a mask or at any position between the entrance pupil and the mask. Exposure is performed by forming an image (claim 6).

[0009]

As shown in FIG. 3, the size of the light source 2 is
Since the light (exposure light B) is incident from various directions even at a point on the mask 4 away from the optical axis A, the resolution of the diffraction limit is reduced in a region covering the entire pattern of the mask 4. Obtainable. FIG. 3 shows the case of Koehler illumination, but also in the case of critical illumination, a large light source image is formed on the mask, so that the illumination area is enlarged. However, in reality, it is difficult to find such a large X-ray source. Therefore, in the present invention, a small light source (X-ray source) is converted into a secondary X-ray source having a sufficient size and divergence angle, and an image of this secondary X-ray source is placed on the entrance pupil of the reduction projection optical system or An image was formed on the mask or at a position between the two.

According to the present invention, as shown in FIG. 1, X-rays emitted from an X-ray source 2 are applied to an X-ray reflecting optical element 1 functioning as a secondary X-ray source. The surface (reflection surface) of the X-ray reflecting optical element 1 is provided with a large number of fine projections or depressions, and the incident X-ray does not simply reflect specularly.
The light is reflected so as to diffuse with a certain spread around the direction of specular reflection. Therefore, the surface (reflection surface) of the X-ray reflection optical element 1 serves as a secondary X-ray source having both a large area and a divergence angle.

FIG. 6 is a vertical sectional view schematically showing an example of the optical element 1 for X-ray reflection, and FIG. 7 is a perspective view schematically showing an example of the optical element 1. The optical element 1 for X-ray reflection includes a substrate 6
A fine convex portion 7 (FIG. 6a) or concave portion 8 (FIG. 6b)
Are provided, and a multilayer film 9 for reflecting X-rays is formed thereon. The dimensions of these projections and depressions need only be sufficiently smaller than the dimensions of the element itself, and their shapes are not particularly limited. Further, the convex portion 7 or the concave portion 8
May be formed individually in a circular shape in the X-ray reflection surface region as shown in FIG. 7A and closely contacted with each other, or may be formed continuously on the entire X-ray reflection surface as shown in FIG. 7B. You may.
However, it is preferable that the shape of the convex portion and the concave portion is a spherical shape as described below.

FIG. 4 shows how the reflected X-rays spread when the X-rays (represented by A, B, and C) enter the convex portion 10 of the spherical portion of the multilayer film that reflects the X-rays. FIG. The radius of curvature of the spherical surface is r, the diameter is d, the incident angle of X-rays at the top of the convex portion 10 is θ, and the angle at which a circular arc having a radius r and a chord length is d is 2φ. Since the distance from the light source (X-ray source) to the projection 10 is set to be much larger than d and r, the incident light may be considered as parallel light in this case. At this time, the X-ray B incident on the top of the convex portion 10 is reflected at an angle of θ with respect to the normal n from the top, but the X-ray incident on another point has its incident surface (reflection surface) inclined. Therefore, the light is reflected at an angle different from the reflected light at the top. For example,
As shown in FIG. 4, the X-ray A incident on one end of the projection 10 is reflected at an angle of (θ−2φ) with respect to the normal n, and the X-ray C incident on the other end is The light is reflected at an angle of (θ + 2φ). As a result, the parallel light beam incident on the convex portion 10 at an angle θ is 2φ around the direction of the specular reflection at the angle θ.
Diverging into a conical shape with a divergence angle of. Note that, as shown in FIG. 5, the same applies to the case where a parallel light beam is incident on the spherical recess 11. In this case, the reflected light diverges after being once focused. As described above, the surface of the X-ray reflection optical element 1 in which the individual projections or depressions are made sufficiently small and arranged in large numbers functions as a secondary light source having a divergence angle of 2φ. When φ is represented by r and d, 2r · sin φ = d is satisfied, and when φ is sufficiently small, 2φ = d / r.

The illumination optical system forms an image at the same magnification or an image magnified several times of the secondary X-ray source on the entrance pupil of the reduction projection optical system, on the mask, or at a position between the two. At this time, the luminous flux of the X-ray illuminating the mask must have a divergence angle sufficient to satisfy the entrance-side numerical aperture of the reduction projection optical system. Now, assuming that a light beam having a divergence angle of 2φ is incident on the illumination optical system, the incident side numerical aperture is sin2
φ to 2φ, and the exit-side numerical aperture is (sin 2φ) / m to 2φ / m = d / (rm) where m is the magnification of the optical system. To use the entire numerical aperture of the reduction projection optical system for the purpose of obtaining a desired diffraction-limited resolution, the exit-side numerical aperture of the illumination optical system is equal to or smaller than the entrance-side numerical aperture of the reduction projection optical system. A larger value may be used. However,
If the numerical aperture on the exit side is larger than the numerical aperture on the entrance side, the proportion of light rays that do not enter the reduction projection optical system will increase, and it will be necessary to lengthen the exposure time, and the throughput of the exposure apparatus will decrease. Therefore, it is preferable that the exit-side numerical aperture of the illumination optical system and the entrance-side numerical aperture of the reduction projection optical system have the same value.

The optical element for X-ray reflection used as a secondary X-ray source is composed of a substrate provided with fine irregularities and a multilayer film formed on the substrate to reflect X-rays.
The angle of incidence of X-rays on the multilayer film changes in the range of (θ ± φ) as shown in FIGS. Therefore, it is desired that the half width of the reflection peak of the multilayer film is about 2φ or more. In general, the peak half width of the multilayer film is sufficiently larger than this, but especially when it is desired to increase φ, the peak half width may be increased by reducing the number of layers of the multilayer film.

In the X-ray reflection optical element, it is not necessary to make the shape accuracy of the fine projections or depressions provided on the substrate particularly strict. However, the surface roughness is preferably small enough not to reduce the reflectivity of the multilayer film formed on the surface, and for example, it may be a smooth surface having a root mean square of several square inches or less. For this purpose, a method of applying a photosensitive material to a substrate and processing it by photolithography to form fine projections (first method);
A method of forming fine projections by screen printing a heat-resistant material on a substrate (second method), a method of forming fine depressions by etching a substrate (third method), and the like can be used. it can.

The photosensitive material used in the first method may be a photoresist used for lithography or a photosensitive polyimide. Polyimide is advantageous when irradiated with strong X-rays because of its excellent heat resistance. Since the cross section after development of a normal photoresist or photosensitive polyimide becomes rectangular, even if a gap is provided between this substrate and the mask to make this a gentle slope, even if the image blur due to diffraction is used. Good. Further, a method of applying a layer on a pattern having a rectangular cross section or a method of performing post-baking (baking of a resist after development) at a high temperature may be used. As the heat-resistant material used in the second method, for example, a heat-resistant resin such as polyimide can be used. In this case, a spherical convex portion is naturally formed by the surface tension of the resin. In addition, the etching step performed by the third method may be either dry etching or wet etching, and an appropriate method may be selected so that the etched surface maintains sufficient smoothness.

When a multilayer film is formed on the fine projections or depressions formed as described above, the same method as that for forming a normal multilayer film can be used. Examples include sputtering, vacuum deposition and CVD (Chemica
l Vapor Deposition). Examples of the material forming the multilayer film include a combination of Mo (molybdenum) and Si (silicon), but are not limited thereto.

[0018]

Embodiment 1 FIG. 10 is a diagram for explaining an outline of an embodiment of an X-ray reflecting optical element according to the present invention and a manufacturing process thereof. As shown in FIG. 10C, the X-ray reflection optical element 1
Is composed of a substrate 20 made of silicon, a photoresist layer 21 formed on the substrate 20 and provided with a plurality of substantially hemispherical projections, and a multilayer film 23 formed on the resist layer 21. I have.

In manufacturing the X-ray reflection optical element 1,
First, as shown in FIG. 10A, a mirror-polished silicon substrate 20 having a diameter of 3 inches and a thickness of 5 mm is prepared, and a photoresist is uniformly applied on the polished surface with a thickness of 0.2 μm. A photoresist layer 21 was formed. Then, the resist layer 21 was exposed by irradiating ultraviolet rays 81 through a mask 22 on which a predetermined pattern was formed. Mask 22
Is provided with a pattern in which circles having a diameter of 5 μm are arranged at a pitch of 10 μm. As the exposure method, the photoresist layer 21 and the mask 22 are not brought into close contact with each other, and the distance s is set between the two.
Was used. In this embodiment, the value of s is set to about 100 μm. Since the blurred image of the pattern on the mask 22 is transferred to the photoresist layer 21 by the diffraction of light due to this exposure, the cross section of the photoresist layer 21 after development has a gentle shape as shown in FIG. A substantially hemispherical convex portion was formed. Further, molybdenum and silicon are alternately laminated on the photoresist layer 21 by a sputtering method to form a multilayer film 23.
Was formed, an X-ray reflecting optical element 1 as shown in FIG. 10C was obtained.

In this embodiment, the projections are formed by photoresist, but other photosensitive materials such as photosensitive polyimide may be used.

[0021]

Embodiment 2 FIG. 11 is a view for explaining an outline of an embodiment of an X-ray reflecting optical element according to the present invention and a manufacturing process thereof. As shown in FIG. 11C, the X-ray reflection optical element 1
As in the first embodiment, a substrate 20 made of silicon, a photoresist layer 21 formed on the substrate and provided with a plurality of substantially hemispherical projections, and a resist layer 2
1 and a multilayer film 23 formed on the substrate 1.

In manufacturing the X-ray reflection optical element 1,
First, a mirror-polished silicon substrate 20 having a diameter of 3 inches and a thickness of 5 mm was prepared.
The coating was uniformly applied at a thickness of 2 μm. Then, the photoresist was patterned by a normal photolithography process. In this patterning, the photoresist layer 21 after development has a diameter of 6 μm as shown in FIG.
m, 0.2 μm high cylindrical photoresist with pitch 10
The pattern was set so as to be arranged in μm. After this patterning, the photoresist layer 21 was post-baked at a temperature higher than the glass transition point of the photoresist (200 ° C. in this embodiment). As a result, the photoresist layer 21 was softened to have a gentle shape as shown in FIG. 11B, and a substantially hemispherical convex portion was formed. Further, molybdenum and silicon are alternately laminated on the photoresist layer 21 by a sputtering method to form a multilayer film 23.
The X-ray reflection optical element 1 as shown in FIG.

[0023]

Embodiment 3 FIG. 12 is a view for explaining an outline of an embodiment of an X-ray reflecting optical element of the present invention and a process for manufacturing the same. As shown in FIG. 12C, the X-ray reflection optical element 1
Is composed of a substrate 20 made of silicon, a polyimide layer 24 formed on the substrate 20 and provided with a plurality of substantially hemispherical projections, and a multilayer film 23 formed on the polyimide layer 24. .

In manufacturing the X-ray reflection optical element 1,
First, a mirror-polished silicon substrate 20 having a diameter of 3 inches and a thickness of 5 mm was prepared, and a 1 μm-thick photosensitive polyimide resin was applied on the polished surface. Then, this polyimide resin is exposed, developed, and baked to obtain a structure shown in FIG.
A first polyimide layer 24a in which columnar polyimide resins having a diameter of 5 μm and a height of 1 μm are arranged at a pitch of 10 μm as shown in FIG. Next, the first polyimide layer 24a
A polyimide resin was applied thereon again so that the pattern portion was hidden (thickness: about 0.5 μm). Then, the second polyimide layer 24b was formed by performing baking as it was without performing exposure and development. This second polyimide layer 24
b is due to the viscosity of the polyimide resin.
As shown in FIG. 7, undulations corresponding to the shape of the first polyimide layer 24a serving as a base were generated, and a substantially hemispherical convex portion was formed. Further, molybdenum and silicon were alternately stacked on the second polyimide layer 24b by a sputtering method to form a multilayer film 23, thereby obtaining the X-ray reflection optical element 1 as shown in FIG. .

The second polyimide layer 24b does not necessarily need to use the same photosensitive polyimide resin as the first polyimide layer 24a, and may use a non-photosensitive polyimide resin. Also, the first polyimide layer 24
The manufacturing method of the present embodiment can be applied even if one or both of a and the second polyimide layer 24b are replaced with a photoresist layer.

[0026]

Fourth Embodiment FIG. 13 is a view for explaining the outline of an embodiment of the optical element for X-ray reflection according to the present invention and the manufacturing process thereof. As shown in FIG. 13C, the X-ray reflection optical element 1
Is composed of a substrate 20 made of silicon, a polyimide layer 24 formed on the substrate 20 and provided with a plurality of substantially hemispherical projections, and a multilayer film 23 formed on the polyimide layer 24. .

In manufacturing the X-ray reflecting optical element 1, first, a mirror-polished silicon substrate 20 having a diameter of 3 inches and a thickness of 5 mm is prepared, and a polyimide resin is screen-printed on the polished surface. As shown in FIG. 13A, a columnar pattern having a diameter of 5 μm and a height of 1 μm has a pitch of 10 μm.
The polyimide layers 24 arranged in m were formed. And
The pattern was left in a clean atmosphere for 30 minutes.
As a result, as shown in FIG. 13B, the patterned polyimide layer 24 spread on the substrate 20 by its own weight, and became substantially hemispherical due to the surface tension. Then, the polyimide layer 24 was baked to form hemispherical projections. Furthermore, this polyimide layer 2
13 is formed by alternately stacking molybdenum and silicon on the substrate 4 by sputtering to form a multilayer film 23.
An X-ray reflection optical element 1 as shown in FIG.

In this embodiment, the projections of the optical element are formed by using a polyimide resin. However, a ceramic such as alumina (Al ₂ O ₃ ), silicon carbide (SiC) or the like is used for the substrate 20, and the substrate is formed on the substrate. The projections may be formed by screen printing and firing a glass paste.

[0029]

Embodiment 5 FIG. 14 is a diagram for explaining the outline of an embodiment of the X-ray reflecting optical element of the present invention and the manufacturing process thereof. As shown in FIG. 14D, the optical element for X-ray reflection 1
Is a substrate 20 made of silicon provided with a plurality of concave portions.
And a multilayer film 23 formed on the substrate 20.

When manufacturing this X-ray reflecting optical element 1
First, a 3 inch diameter, 5 mm thick mirror polished silicon
14 is prepared and the polished surface is thermally oxidized.
0.5 μm thick SiO, as shown in FIG._TwoLayer 25
Formed. Then, a resist (not shown) is applied thereon.
Cloth and use the usual photolithography process
And then pattern the patterned resist.
CHF as a screen_Three, H _Two, O_TwoReaction of mixed gas
Perform Reactive Ion Etching
SiO_TwoHoles with a diameter of 2 μm are formed at a pitch of 10 μm in layer
FIG. 14 shows the state after the resist is removed.
(Shown in (b)). Thereafter, hydrofluoric acid (HF), nitric acid (HN)
O_Three), Acetic acid (CH_Three(COOH) mixed solution
Etching the silicon substrate 20 by immersing it in
Was. At this time, the etching solution is SiO 2_TwoShape on layer 25
Silicon substrate 20 isotropically etched through the formed hole
The etching solution after a certain period of time
When pulled up, the silicon substrate 20 is shown in FIG.
Such a hemispherical concave portion is formed. After etching, S
iO_TwoThe layer 25 is removed by dissolving it with hydrofluoric acid (HF).
Molybdenum on the substrate 20 by sputtering
Forming a multilayer film 23 by alternately stacking silicon
Thus, an X-ray reflecting optical element 1 as shown in FIG.
Was.

[0031]

[Embodiment 6] Fig. 15 is a view for explaining an outline of an embodiment of the X-ray reflecting optical element of the present invention and a manufacturing process thereof. As shown in FIG. 15D, the optical element for X-ray reflection 1
Is a substrate 20 made of silicon provided with a plurality of concave portions.
And a multilayer film 23 formed on the substrate 20.

In manufacturing the X-ray reflection optical element 1,
First, a mirror-polished silicon substrate 20 having a diameter of 3 inches and a thickness of 5 mm was prepared.
It was applied uniformly to a thickness of μm. Then, as in Example 2, the photoresist was patterned by a normal photolithography process. This patterning was set so that after development, a columnar photoresist having a diameter of 6 μm and a height of 0.2 μm was arranged at a pitch of 10 μm. After patterning, the photoresist layer 21 was post-baked at a temperature higher than the glass transition point of the photoresist (200 ° C. in this embodiment). This allows
The photoresist was softened to form a substantially hemispherical projection, and the photoresist layer 21 was formed in a pattern as shown in FIG. Next, using the patterned photoresist layer 21 as a mask, reactive ion etching was performed under conditions where the selectivity between resist and silicon was close to 1. At the time of etching, a mixed gas of CF ₄ and H ₂ was used as a reaction gas. FIG. 15B shows a state during the etching. Resist layer 21 and silicon substrate 20
Since the etching rates of the silicon substrate 20
Means that the thinner the patterned resist, the deeper it will be shaved. As a result, the shape of the resist layer 21 is transferred to the silicon substrate 20. Therefore, the silicon substrate 20 is subjected to the reactive ion etching as shown in FIG.
A substantially hemispherical convex portion as shown in FIG. After completion of the etching, molybdenum and silicon are alternately stacked on the silicon substrate 20 by a sputtering method to form a multilayer film 23, thereby obtaining the X-ray reflection optical element 1 as shown in FIG. .

Although silicon is used as the substrate material in this embodiment, ceramics such as silicon carbide (SiC) or glass may be used. The patterning of the resist layer 21 can be performed not only by the method used in the second embodiment but also by the method used in the first, third, and fourth embodiments.
Further, a resin such as polyimide may be used instead of the resist.

[0034]

Seventh Embodiment FIG. 8 is a schematic structural view of an X-ray optical system showing an embodiment of the present invention, which is used in an X-ray reduction projection exposure apparatus. This X-ray optical system includes an X-ray reflection optical element 1 functioning as a secondary X-ray source, Mo (molybdenum) /
An elliptical mirror 13, a mask 4, and a reduction projection optical system 14 having a multilayer film formed of a combination of Si (silicon) are provided, so that a reduced image of the pattern formed on the mask 4 is formed on the wafer 5. It has become. The X-rays 12 entering the X-ray optical system are emitted from an X-ray source (radiation light is used in this embodiment), and are transmitted by a front optical system (both not shown) including an oblique incidence mirror, a filter, and the like. After a wavelength around 130 ° is selected, a slit (not shown) is formed so that the shape of the X-ray light beam is about 30 mm square. Then, it enters the X-ray optical system as a substantially parallel light beam having a divergence angle of about 0.1 ° or less.

The X-ray reflecting optical element 1 has a reflecting surface (X
The surface on which the line 12 is incident is formed by a multilayer film made of a combination of Mo (molybdenum) / Si (silicon). Further, a plurality of hemispherical projections having a diameter d of about 10 μm and a radius of curvature r of the spherical surface of about 170 μm are formed on the reflecting surface.
It is formed in a square area of 30 mm on a side at a pitch of about 10 μm. The elliptical mirror 13 has one of two focal points X
It is arranged so as to be the installation position of the line reflection optical element 1. Although not shown in detail in the drawing, the reduction projection optical system 14 is composed of one mirror having a paraboloid and two mirrors having an elliptical surface, for a total of three mirrors. Each of these three mirrors has a multilayer film of Mo / Si combination formed on the reflection surface. The reduction projection optical system 14 of this embodiment has a reduction magnification of 1/5 and an image-side numerical aperture of 0.06 so that the resolution is 0.1 μm or more and the depth of focus is 1.8 μm or more. The number will be 0.012.

In the X-ray optical system having such a configuration,
As described above, the X-rays 12 incident as substantially parallel light beams having a divergence angle of about 0.1 ° or less are first reflected by the reflecting surface of the X-ray reflecting optical element 1. This optical element 1 functions as a secondary light source having a divergence angle of 2φ. The value of φ is calculated as 2φ = d / using the diameter d of the convex portion of the reflecting surface and the radius of curvature r of the spherical surface.
r, the divergence angle of the reflected X-ray is d
/R=10/170=0.06(rad)=3.4 ゜That is, X
The line reflection optical element 1 functions as a secondary X-ray source having a size of 30 mm square and a divergence angle of 3.4 °. The X-rays reflected by the X-ray reflecting optical element 1 are reflected by an elliptical mirror 13 to magnify the image of the secondary X-ray source by a factor of 5 to reduce the projection optical system 14.
At the entrance pupil. Therefore, the mask 4 illuminates a wide area of 150 mm square or more. At this time, the divergence angle of the X-rays decreases according to the magnification of the elliptical mirror 13, and is about 0.012 (rad) =
0.69 °, which is the same as the numerical aperture of the reduction projection optical system 14 on the mask side. The X-rays illuminating and transmitting the mask 4 pass through the reduction projection optical system 14 to form a reduced image of the pattern formed on the mask 4 on the wafer 5.

When a reduction projection exposure experiment was performed with the X-ray optical system of the present embodiment, a line-and-line of 0.1 μm was formed over an entire arc-shaped region having a length of 30 mm, a width of 0.2 mm and a radius of 17.5 mm.
Space could be resolved. On the other hand, when an exposure experiment was performed under the same conditions except that the X-ray reflection optical element 1 was replaced with a flat multilayer mirror, only a 0.2 μm line and space could be resolved. Was.

[0038]

[Embodiment 8] FIG. 9 is a schematic diagram of an X-ray optical system showing an embodiment of the present invention, which is used in an X-ray reduction projection exposure apparatus. In FIG. 9, components having the same configurations and functions as those in FIG. 8 are given the same reference numerals, and descriptions thereof will be omitted as appropriate. The X-ray optical system according to the present embodiment includes a laser plasma X-ray source 15, which is an X-ray source, a parabolic mirror 16, which reflects X-rays emitted from the X-ray source 15 so as to become substantially parallel light. An X-ray reflection optical element 1 functioning as a next X-ray source, a Schwarzschild mirror 17, a mask 4, and a reduction projection optical system 14 are provided, and a reduced image of a pattern formed on the mask 4 is formed on the wafer 5. It is supposed to be.

The parabolic mirror 16 has Mo / Mo on its reflection surface.
A multilayer film made of a combination of Si is coated, and the shape of the reflection surface (parabolic surface) is set so that the reflected X-rays 12 become substantially parallel light. The X-ray reflecting optical element 1 has a reflecting surface (a surface on which the X-rays 12 are incident) formed of a multilayer film made of a combination of Mo (molybdenum) / Si (silicon). Further, this reflecting surface has a diameter d of about 10 μm and a radius of curvature r of the spherical surface of about 80 μm.
m hemispherical projections with a pitch of approximately 10 μm and a diameter of 15
It is formed within a circular range of mm. The Schwarzschild mirror 17 has two spherical mirrors 17a sharing a central axis,
17b, the reflecting surface of each spherical mirror has M
A multilayer film made of a combination of o / Si is formed. In order to avoid interference between the spherical mirror (convex mirror) 17a installed near the optical axis of the Schwarzschild mirror 17 and the incident X-ray, the direction of the principal ray of the light reflected by the X-ray reflecting optical element 1 is changed by Schwarzschild. The mirror 17 is disposed so as to be inclined by about 10 ° with respect to the optical axis. The magnification of the Schwarzschild mirror 17 is set to 10 times. The reduction projection optical system 14 has the same configuration as that of the seventh embodiment. The reduction magnification is set to 1/5, the image-side numerical aperture is set to 0.06, and the mask-side numerical aperture is 0.012.

In the X-ray optical system having such a configuration,
As described above, the X-rays 12 incident as substantially parallel light beams having a divergence angle of about 0.1 ° or less are first reflected by the reflecting surface of the X-ray reflecting optical element 1. This optical element 1 functions as a secondary X-ray source having a divergence angle of 2φ. The value of φ is calculated as 2φ = d using the diameter d of the convex portion of the reflecting surface and the radius of curvature r of the spherical surface.
/ R, the divergence angle of the reflected X-rays is d / r = 10/80 = 0.12 (rad) = 6.9 °. That is,
The X-ray reflection optical element 1 has a diameter of 15 mm and a divergence angle of 6.9 °.
Functions as a secondary light source. The X-rays reflected by the X-ray reflecting optical element 1 are reflected by a Schwarzschild mirror 17 to magnify the image of the secondary X-ray source by a factor of 10 to form an image on the entrance pupil of the reduced projection optical system 14. Therefore, the mask 4 illuminates a wide area of about 150 mm. The divergence angle of the X-ray at this time decreases according to the magnification of the Schwarzschild mirror 17 and becomes 0.01
2 (rad) = 0.69 °, which coincides with the numerical aperture of the reduction projection optical system 14 on the mask side. The X-rays illuminating and transmitting the mask 4 pass through the reduction projection optical system 14 to form a reduced image of the pattern formed on the mask 4 on the wafer 5.

When a reduction projection exposure experiment was performed using the X-ray optical system of this embodiment, a line-and-line of 0.1 μm was formed over an entire arc-shaped region having a length of 30 mm, a width of 0.2 mm, and a radius of 17.5 mm.
Space could be resolved. On the other hand, when an exposure experiment was performed under the same conditions except that the X-ray reflection optical element 1 was replaced with a flat multilayer mirror, only a 0.2 μm line and space could be resolved. Was.

Incidentally, the optical element for X-ray reflection used as the secondary X-ray source in the present invention is placed at a position close to the X-ray source, so that it is exposed to relatively strong X-rays. Most of the unreflected X-rays are absorbed by this optical element, and the energy of the absorbed X-rays raises the temperature of the optical element.
Therefore, in this X-ray reflection optical element, heat resistance is important. The optical element for X-ray reflection in the present invention can be manufactured by various methods described in Examples 1 to 6. However, the manufacturing method of forming a convex portion on a reflection surface with a resist (Examples 1 and 2) is comparative. Although it is easy to achieve the target, it depends only on the heat resistance of the resist, and therefore has only a heat resistance of about 100 ° C. On the other hand, when polyimide (Examples 3 and 4) which is a heat-resistant resin is used, heat resistance of 300 ° C. or more can be obtained. In addition, high heat resistance of about 800 ° C in the method of printing and firing glass paste on the ceramics substrate and the method of etching the silicon substrate to form recesses, and more than 1000 ° C in the method of etching the ceramics substrate and forming recesses. It is possible to obtain The problem of heat resistance should be taken into consideration for a multilayer film that reflects X-rays. In each of the embodiments, a multilayer film made of a combination of Mo / Si is used, but this multilayer film has heat resistance of only about 300 ° C. Therefore, when higher heat resistance is required, a multilayer film having a high heat resistance itself (for example, a combination of Mo / SiC) may be used. As described above, the X-ray reflection optical element of the present invention can be applied to an X-ray source that emits X-rays of extremely high intensity,
It is possible to manufacture an element having the necessary heat resistance according to the strength of the wire.

[0043]

According to the present invention, X emitted from the light source
X-rays are reflected by an X-ray reflection optical element having a large number of fine projections or depressions on a substrate functioning as a secondary X-ray source having both a certain size and a divergence angle, and the reflected X-rays are used as a mask. Illuminate the mask by hundreds
A wide area of mm can be illuminated with a sufficient divergence angle. Therefore, it is possible to obtain a diffraction-limited resolution of the reduction projection optical system in a wide exposure area.

The convex or concave portion of the X-ray reflecting optical element has a substantially spherical shape, the outer diameter d, the radius of curvature r, and the magnification m of the illumination optical system for illuminating the mask.
Is set so that d / (rm) is substantially equal to the mask-side numerical aperture of the reduction projection optical system, most of the X-rays incident on the X-ray reflection optical element are imaged by the reduction projection optical system. , The efficiency of X-ray utilization can be increased, and the throughput of the X-ray reduction projection exposure apparatus can be greatly improved.

The present invention is not limited to use in an X-ray reduction projection exposure apparatus, but can be widely applied to other X-ray optical apparatuses utilizing X-ray imaging.
For example, if the present invention is applied to an illumination optical system of an X-ray microscope, the field of view of the microscope can be greatly expanded.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the principle of an X-ray optical system according to the present invention.

FIG. 2 is a schematic view showing an illumination optical system of a conventional X-ray reduction projection exposure apparatus.

FIG. 3 is a schematic view showing one method for solving the problem of the conventional illumination optical system.

FIG. 4 is a schematic diagram for explaining the operation of the optical element for X-ray reflection of the present invention.

FIG. 5 is a schematic diagram for explaining the operation of the optical element for X-ray reflection of the present invention.

FIG. 6 is a cross-sectional view showing an example of the optical element for X-ray reflection of the present invention.

FIG. 7 is a perspective view showing an example of the optical element for X-ray reflection of the present invention.

FIG. 8 is a schematic configuration diagram of an X-ray optical system according to one embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of an X-ray optical system according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating an outline of an embodiment of an optical element for X-ray reflection of the present invention and a manufacturing process thereof.

FIG. 11 is a diagram for explaining an outline of an embodiment of the optical element for X-ray reflection of the present invention and a manufacturing process thereof.

FIG. 12 is a diagram schematically illustrating an embodiment of an X-ray reflection optical element according to the present invention and a process for manufacturing the same.

FIG. 13 is a diagram schematically illustrating an embodiment of an X-ray reflecting optical element of the present invention and a process for manufacturing the same.

FIG. 14 is a diagram schematically illustrating an embodiment of an optical element for X-ray reflection according to the present invention and a manufacturing process thereof.

FIG. 15 is a diagram for explaining the outline of an embodiment of the optical element for X-ray reflection of the present invention and the manufacturing process thereof.

[Explanation of Signs of Main Parts]

DESCRIPTION OF SYMBOLS 1 X-ray reflection optical element 2 X-ray source 3 Illumination optical system 4 Mask 5 Wafer 6 Substrate 7 Convex part 8 Concave part 9 Multilayer film 10 Spherical convex part 11 Spherical concave part 12 Parallel X-ray 13 Elliptical mirror 14 Reduction projection Optical system 15 laser plasma X-ray source 16 parabolic mirror 17 Schwarzschild mirror 20 substrate 21 resist layer 22 mask 23 multilayer film 24 polyimide layer 25 SiO ₂ layer 50 entrance pupil of imaging optical system

Claims (9)

(57) [Claims] 1. A part of a spherical surface having a substantially constant radius of curvature.
An optical element for X-ray reflection , comprising: a substrate provided with a plurality of concave portions or convex portions; and a multilayer film formed on the substrate to reflect X-rays. 2. A step of forming a photosensitive material on a substrate, a step of transferring a blurred image of a pattern provided on a mask to the photosensitive material, and a step of developing a smooth convex portion on the surface of the photosensitive material. A method for manufacturing an optical element for X-ray reflection, comprising the steps of: providing; and forming a multilayer film that reflects X-rays on the photosensitive material. 3. A step of forming a photosensitive material on a substrate, a step of transferring an image of a pattern provided on a mask to the photosensitive material, and a step of developing, and post-baking the developed photosensitive material to soften it. Providing a gentle convex portion on the photosensitive material surface, transferring the gentle convex portion formed on the photosensitive material surface to the substrate by reactive ion etching, and X-rays on the photosensitive material. A method for producing an optical element for X-ray reflection, comprising a step of forming a multilayer film reflecting light. 4. A step of forming a photosensitive material on a substrate, a step of transferring an image of a pattern provided on a mask to the photosensitive material, and a step of developing, and further forming a photosensitive material on the developed pattern. An X-ray reflection optical element comprising: a step of providing gentle projections on the surface of the photosensitive material by baking the photosensitive material; and a step of forming a multilayer film that reflects X-rays on the photosensitive material. Manufacturing method. 5. A step of forming a pattern by screen-printing a heat-resistant material on a substrate, a step of providing a gentle convex by leaving the formed pattern in a clean atmosphere, Forming a multilayer film that reflects X-rays on the substrate. 6. A step of forming a layer serving as an etching mask on a substrate, a step of forming a predetermined pattern on the etching mask layer, and isotropically etching the substrate using the etching mask layer on which the pattern is formed as a mask. Forming a gentle concave portion in the substrate by forming a multilayer film that reflects X-rays on the etched substrate. 7. An X-ray reflection optical element having a substrate provided with a plurality of fine projections or depressions and a multilayer film formed on the substrate for reflecting X-rays, wherein a desired pattern is formed. A mask and an image forming optical system for forming an image of the pattern, wherein the image of the secondary light source when the X-ray reflected by the X-ray reflecting optical element is used as a secondary light source, An optical system for X-rays, which forms an image on an entrance pupil, on the mask, or on an arbitrary position between the entrance pupil and the mask. 8. An X-ray reflection optical element having a substrate provided with a plurality of fine projections or depressions and a multilayer film formed on the substrate for reflecting X-rays, wherein a desired pattern is formed. A mask, an illumination optical system disposed between the X-ray reflection optical element and the mask, and an imaging optical system for forming an image of the pattern, wherein a surface of each of the convex portions or the concave portions has substantially a curvature. Radius
When a part of a fixed spherical surface is formed, the radius of curvature of the spherical surface is r, the outer diameter is d, and the magnification of the illumination optical system is m, the value obtained by d / (rm) is the imaging optics. An optical system for X-rays, wherein the numerical aperture is equal to the numerical aperture on the side where the exposure light is incident in the system. 9. An X-ray reflecting optical element having a substrate provided with a plurality of fine projections or depressions and a multilayer film for reflecting X-rays formed on the substrate is irradiated with X-rays. X-rays reflected by the element are used as a secondary light source to form an image of the secondary light source either on the entrance pupil of the imaging optical system or on a mask or at an arbitrary position between the entrance pupil and the mask. Exposure method characterized by the above-mentioned.