JPH08264415A - X-ray reduction projection aligner - Google Patents

Abstract

PURPOSE: To obtain a lighting system satisfying NAo of a lighting system besides securing a practical exposure region. CONSTITUTION: An X-ray reduction projection exposure lighting optical system 24 is composed of a rotary mirror 30 and a fixed mirror 31. The rotary mirror 30 rotates on an axis 25 of a reduction projection exposure optical system 22. The fixed mirror 31 is arranged in parallel to an axis 25 of the reduction projection exposure optical system 22 besides matching a curvature center with the axis 25. When making an optical path length from a rotary mirror 30 to a fixed mirror 31 L1 and an optical path length from the fixed mirror 31 to a mask 4 L2 and an optical path length from the mask 4 to an entrance pupil 19 L3, a formula L1=L2+L3 can be satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray reduction projection exposure apparatus used for forming fine patterns in the manufacture of semiconductor integrated circuits. More specifically, the present invention is
The present invention relates to an optical system for illuminating a mask of a reduction projection exposure optical system by condensing X-rays generated by a synchrotron radiation light or a laser plasma X-ray source which is a light source in an X-ray reduction projection exposure apparatus. .

[0002]

2. Description of the Related Art X-ray reduction projection exposure has a wavelength of 5 to 20n.
It is a reduction projection exposure method using X-rays in the soft X-ray region of m,
Since conventional reduction projection exposure using light (ultraviolet light) cannot be applied to the manufacture of LSIs with line widths of 0.1 μm or less due to the resolution limit due to wavelength, future lithography technology for ultra-highly integrated LSIs of 1 Gbit and beyond Is expected as.

In the X-ray reduction projection exposure, the NA (numerical aperture) of the reduction projection optical system is much smaller than that of the light reduction projection exposure, and is about 0.1. In the Schwarzschild optical system, which is an optical system for reduction projection exposure currently used in experiments for verifying the principle, the reduction ratio is about several tens of minutes, so the NA _O on the illumination side is 0.01 or less. Small. Therefore, the divergence of the synchrotron radiation used as the light source or the laser plasma light source is larger than the NA _O on the illumination side, so that NA _O is combined using a diaphragm to realize incoherent or partial coherent illumination. .

However, since the Schwarzschild optical system is a rotationally symmetric optical system in which the exposure area is on the axis with few aberrations, the exposure area (field) is very small with a diameter of several tens of μm. Therefore, although it can be used for a principle verification experiment, it cannot be used for actual LSI manufacturing.
As a reduction optical system that enlarges the exposure area, the method of increasing the number of mirrors to secure the exposure area for one chip, and the optical system that has a ring-shaped exposure area with less aberration are used for synchronous scanning of the mask and the wafer. There is a method of securing an exposure area for one chip by using it. However, since a multilayer film reflecting mirror is used as a mirror, considering that the reflectance per sheet is about 60%, it is not desirable to increase the number of mirrors, and a ring field type reduction optical system that also uses synchronous scanning is effective. It is said that.

As an example of such an optical system, an X-ray projection exposure apparatus (hereinafter referred to as prior invention 1) disclosed in Japanese Patent Laid-Open No. 2-328766 is known. This prior invention 1 is designed to reduce aberrations off the axis in order to secure a practical exposure area, and a condenser mirror for condensing X-rays and illuminating a mask.
It is provided with a reflection mirror optical system in which either one or two aspherical mirrors or one of the two mirrors is a spherical mirror. A toroidal mirror is used as the condenser mirror. This condenser mirror illuminates the pattern on the mask so as to condense the X-ray toward one point (incident pupil) on the optical axis of the reflection mirror optical system. X reflected by the mask
The line is made incident on the surface of the sample substantially perpendicularly by the reflection mirror optical system, and projects the pattern on the mask in a reduced scale.

In the X-ray projection exposure apparatus according to Prior Art 1, the reduction ratio is considered to be about 1/5 due to the problems of the mask size and the achievable illumination area. Therefore, in order to realize incoherent illumination that satisfies the NA (= 0.1) of the reduction optical system, NA _O of the illumination system is 0.
About 02 is required. However, considering the divergence of the synchrotron radiation and the acceptance of the condenser mirror of the laser plasma X-ray source (the amount of the light emitted from the light source that the mirror receives), it is generally considered to be smaller than this value. Incoherent illumination cannot be realized without a focused illumination system. That is, when the original divergence of the light source is small, the NA of the reduction projection optical system cannot be satisfied, and partial coherent illumination is obtained. When the coherency of the illumination becomes high, the transfer pattern such as speckle (spot-like pattern degradation) will be deteriorated. Therefore, when considering practical X-ray reduction projection exposure, the converging illumination optical system becomes very important. Come on.

FIGS. 4 to 6 show examples of the illumination optical system proposed so far. In FIG. 4, the synchrotron radiation light is horizontally condensed by a single mirror. Here, 1 is a synchrotron radiation light source as a light source, 2 is synchrotron radiation light, 3 is a reflection mirror made of a spherical mirror, 4 is a transmissive mask, 5 is a reflection mirror optical system made of a Schwarzschild optical system, and 6 is A wafer as a sample surface. This illumination optical system collects synchrotron radiation light 2 horizontally radiated from a synchrotron radiation light source 1 on a mask 4 by one reflecting mirror 3,
The light transmitted through the mask 4 is imaged on the wafer 6 by the reflection mirror optical system 5. However, with this illumination optical system,
Since the mirror surface of the reflecting mirror 3 is spherical, it is a focusing system for focusing only in the horizontal direction. Therefore, rather than in the vertical direction NA _O is enough, there is a problem that reduction in resolution in the horizontal direction of the pattern occurs.

In order to avoid this problem, the illumination optical system shown in FIG. 4 has a full aperture illumination shown in FIG.
An optical system 7 called a system is provided with a reflection mirror 3 and a mask 4.
It is placed between and to collect two-dimensional light. The optical system 7 is composed of one spherical mirror 8 and two plane mirrors 9. However, even in this illumination optical system, since the light is condensed by one spherical mirror 8, there is a problem that it is not possible to control the difference between the divergence in the horizontal direction and the divergence in the vertical direction.

The illumination optical system shown in FIG. 6 has a critical illumination (an illumination system for converging the illumination light on a mask) in the vertical direction and an Koehler illumination (the illumination light is provided in the horizontal direction due to an off-axis spheroid. The illumination system for condensing on the entrance pupil) is performed. Here, 10 is a light source, 11 is an image forming optical system, 12 is its optical axis, 13 is a mirror composed of an off-axis spheroidal mirror, 14 is an exposure region of the mask 4, and 15 is off-axis in the yz plane. Cross section of the spheroidal mirror 13 (ellipse), 16
Is an exposure area on the wafer, 17 is the horizontal trajectory of the beam, 18 is the long axis of the spheroid 13, and 19 is the imaging optical system 1.
The entrance pupil is 1. The mask 4 and the light source 10 are spheroids 1
5 are arranged at respective focal positions. The light emitted from the light source 10 is reflected by the mirror 13. Mirror 13 is y-
Since the light source 10 and the mask 4 are arranged at the focal positions of the ellipse with the major axis of 18 with respect to the z plane, all the light reflected by the mirror 13 is collected on the mask 4. It Then, this light is vertically incident on the wafer by the imaging optical system 11 and projects the pattern of the mask 4. The exposure area 16 on the wafer is a rotation surface that rotates the mirror 13 with respect to the optical axis 12, and thus is a horizontally long arc-shaped area (ring field). However, this optical system is difficult to process because the shape of the mirror 13 is a very complicated aspherical surface called an off-axis spheroid, and the distance from the light source 10 to the mirror 13 is very short. It is not realistic when considering the design of the differential pumping system when using as the light source, and the measures against scattered particles when using the laser plasma as the light source.

[0010]

As described above, as shown in FIG.
None of the conventional optical systems shown in FIG. 6 satisfy a practical optical system. That is, in the conventional illuminating optical system shown in FIG. 4, since the horizontal body condensing, in the vertical direction of the NA _O insufficient resolution is lowered. Since the optical system shown in FIG. 5 uses one mirror 8, there is a problem that the difference in divergence in the horizontal and vertical directions cannot be controlled. Further, the optical system shown in FIG. 6 has a problem that the processing is difficult because the shape of the mirror 13 is an off-axis spheroid, which is a very complicated aspherical surface.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and its object is to:
With implementing an incoherent illumination, such as to satisfy the numerical aperture NA _O of the illumination side, it is to provide an X-ray reduction projection exposure apparatus that can secure practical exposure area.

[0012]

In order to achieve the above object, the present invention provides an X-ray reduction projection exposure illumination optical system for converging a parallel light beam from a light source on a mask, and a pattern on the mask on a sample surface. X equipped with a reduction projection exposure optical system for projecting and exposing
The line reduction projection exposure apparatus is characterized by including a rotating mirror for converting an optical path in an arc shape and a fixed mirror for condensing light reflected by the rotating mirror on a mask.
Further, the present invention is characterized in that the rotating mirror is a cylindrical mirror and the fixed mirror is a toroidal mirror. Further, the present invention is characterized in that the rotation axis of the rotating mirror coincides with the axis of the reduction projection exposure optical system. Also,
The present invention is characterized in that the fixed mirror is arranged parallel to the axis of the reduction projection exposure optical system, and the center of curvature in the direction orthogonal to the optical axis is aligned with the axis. Furthermore, the present invention is characterized in that the optical path length from the rotating mirror to the fixed mirror is made equal to the optical path length to the entrance pupil of the fixed mirror, the mask and the reduction projection exposure optical system.

[0013]

In the present invention, the rotating mirror converts the optical path into an arc by rotating about the axis of the reduction projection exposure optical system. The fixed mirror collects the light whose optical path is changed by the rotation of the rotating mirror on the mask. The irradiation area on the mask becomes a horizontally long arc-shaped area (ring field) as the rotating mirror rotates. The axis of rotation of the rotating mirror coincides with the axis of the reduction projection exposure optical system. The fixed mirror is arranged parallel to the axis of the reduction projection exposure optical system and with the center of curvature in the direction orthogonal to the optical axis aligned with the axis. The optical path length from the rotating mirror to the fixed mirror is equal to the optical path length from the fixed mirror to the entrance pupil of the reduction projection exposure optical system through the mask. With these, even if the rotating mirror rotates, the light illuminating the mask maintains the rotational symmetry with respect to the axis of the exposure optical system, and reaches all the entrance pupils.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an X-ray reduction projection exposure apparatus according to the present invention. The same components as those described in the related art are designated by the same reference numerals, and the description thereof will be omitted. Here, 22 is a reduction projection exposure optical system for image formation, 24 is an X-ray reduction projection exposure illumination optical system, 25 is an axis of the reduction projection exposure optical system 22, and 26 is a focusing optical system.

In the present embodiment, the reduction ratio is 1/5,
Vertical 20mm × horizontal 20mm as a practical exposure area, with NA = 0.1 the exposure optical system, an example of obtaining incoherent illumination that satisfies NA _O = 0.02 of the illumination system. Further, in the present embodiment, an example in which the two aspherical optical system according to the prior invention 1 described above is used as the reduction projection exposure optical system 22 will be shown. The exposure optical system 22 includes a concave mirror 2
7 and the convex mirror 28. However, as a reduction exposure optical system for image formation, a three-lens system or a four-lens system may be used as long as it is a ring-field scanning optical system. The effects of the present invention are not impaired by the difference in these optical systems.

The X-ray reduction projection exposure illumination optical system 24 collects X-rays having a parallel light flux on the mask 4 so as to satisfy the condition of critical illumination, and is composed of a rotating mirror 30 and a fixed mirror 31. Has been done. A cylindrical mirror is used as the rotating mirror 30. The rotating mirror 30 is arranged between the condensing optical system 26 and the entrance pupil 19 of the reduction projection exposure optical system 22, and is inclined by an angle φ with respect to the axis 25 of the reduction projection exposure optical system 22. . Further, the rotation axis of the rotating mirror 30 coincides with the axis 25. The fixed mirror 31 has the shaft 25 at the position of the concave mirror 27.
Is arranged in parallel with the center of curvature in the direction orthogonal to the optical axis with the axis 25 of the reduction projection exposure optical system 22. A toroidal mirror is used as the fixed mirror 31.

The condensing optical system 26 is for obtaining X-rays having a parallel light beam. In this embodiment, the X-ray condensing device previously proposed by the present inventors (Japanese Patent Application No. 6-82755).
No., hereinafter referred to as Prior Invention 2). This condensing optical system 26 is composed of a concave mirror 34 made of a concave toroidal mirror and a convex mirror 35 made of a convex toroidal mirror. By optimizing the distance between these mirrors, the parallelism is high and the shape distortion is reduced. Small parallel light flux 33
Synchrotron radiation with can be used. As the optimization conditions, the focal length of the concave mirror 34 in the direction orthogonal to the optical axis is set to approximately two-thirds of the distance between the concave mirror 34 and the light source, and the focal length in the direction parallel to the optical axis is set to the concave mirror 34 and the light source. It should be approximately twice the distance. FIG. 2 shows a beam shape of synchrotron radiation having a parallel light flux by the imaging optical system 26 obtained by the ray tracing program.

However, for example, two toroidal mirrors may be used without using the above-mentioned condensing optical system 26, or a parallel light flux may be obtained by using laser plasma as a light source. The effect of the present invention is not impaired by the difference in the means such as the light source and the condenser mirror for obtaining these parallel light fluxes.

Here, the following relationship is established between NA _O on the illumination optical system side, the distance L between the mirror and the mask, and the beam size D of the obtained parallel light beam. NA _O = D / 2 · L (1) Therefore, in order to satisfy NA _O (= 0.02) on the illumination optical system side, the beam size D of the obtained parallel light flux 33 is known. Then, the distance between the mirror and the mask 4, which is the focal point, is determined.

The collimated light beam 33 emitted from the synchrotron radiation light source 1 and condensed by the condensing optical system 26 is reflected by the rotating mirror 30, and the reduction projection exposure optical system 22.
Bent from the shaft 25 of the. Then, this parallel light flux 33
Illuminates the pattern area 4a on the mask 4 so that the light is reflected by the fixed mirror 31 and condensed on the entrance pupil 19 of the reduction projection exposure optical system 22. FIG. 3 shows the shape of the beam focused on the mask 4. Then, the image of the pattern on the mask 4 is projected onto the wafer 6 with a reduction ratio of 1/5 by the reduction projection exposure optical system 22. The irradiation region 36 on the mask 4 becomes an arc-shaped elongated irradiation region, that is, a ring field by the rotation of the rotating mirror 30. Since the irradiation area in the vertical direction is narrow, the irradiation area can be made large by scanning the mask 4 in the direction of arrow A. Further, in synchronization with this, by scanning the wafer 6 in the direction of arrow B, a practical exposure area can be obtained.

Here, interference between the mirrors (concave mirror 27 and convex mirror 28) of the reduction projection exposure optical system 22 and the optical axis 25 is avoided, and the distance between the mask 4 and the fixed mirror 31 is made as short as possible to increase divergence. The fixed mirror 31 is installed at the position of the concave mirror 27, as described above, so that it can be removed. In this embodiment, when the optical path length L2 between the fixed mirror 31 and the mask 4 and 283.46mm, NA _O of the illumination system
Since, is 0.02, incoherent illumination can be realized from the above formula (1) if the size of the parallel light flux in the vertical direction is 11.3 mm or more.

The rotation axis of the rotating mirror 30 coincides with the axis 25 of the reduction projection exposure optical system 22, and the fixed mirror 3
Since the center of curvature in the direction orthogonal to the optical axis of 1 coincides with the axis 25, the entire X-ray reduction projection exposure illumination optical system 24 is rotationally symmetrical with respect to the axis 25 of the reduction projection exposure optical system 22. There is. Therefore, the movement of the optical axis due to the rotation of the rotating mirror 30 is completely rotationally symmetrical with respect to the axis 25 of the reduction projection exposure optical system 22.

Further, the rotating mirror 30 and the fixed mirror 31.
Let L1 be the optical path length between the fixed mirror 31 and the mask 4, L2 be the distance between the fixed mirror 31 and the mask 4, and L3 be the optical path length between the mask 4 and the entrance pupil 19, then the rotating mirror 30 is L1 = L2 + L3.
Is placed in a position that satisfies By doing so, the light flux reflected by the rotating mirror 30 and condensed on the mask 4 maintains the rotational symmetry with respect to the axis 25 of the reduction projection exposure optical system 22 even if the rotating mirror 30 rotates, so that all of the entrance pupil 19 is illuminated. Will be reached.

Here, the radius of curvature R3 of the fixed mirror 31 for converging the vertical component of the synchrotron radiation on the mask 4 is the optical path length L2 between the fixed mirror 31 and the mask 4, and the fixed radius. When the oblique incidence angle φ3 of the mirror 31 is determined, it is uniquely determined. That is, when the radius of curvature in the optical axis direction is R, the distance from the mirror to the condensing point is a, the distance from the mirror to the light source point is b, and the oblique incidence angle of the mirror is φ, the following are generally given: Relationship is established. 1 / a + 1 / b = 2 / R · sin φ (2) Here, the incident light flux is parallel light, and b can be regarded as infinity. Therefore, the radius of curvature R3 of the fixed mirror 31 in the optical axis direction can be written as follows using the distance L2 between the fixed mirror 31 and the mask 4 and the oblique incidence angle φ3 of the fixed mirror 31. R3 = 2 · L2 / sin φ3 (3) Therefore, if the equation (3) is satisfied, the vertical component is focused on the mask 4. In the present embodiment, L2 = 2
83.46 mm, R3 = 6926.11 mm, φ3 =
It is 4.711 °.

In the horizontal direction, the fixed mirror 3
The radius of curvature r3 of the direction orthogonal to the optical axis of 1 (horizontal direction) is set to 85.86 mm so that the center of curvature coincides with the axis 25 of the reduction projection exposure optical system 22. As a result, the locus of the luminous flux due to the rotation of the rotary mirror 30 is the height of the mask 4 (62.
It is possible to illuminate a ring field having a radius of 5 mm and less aberration. However, with this curvature, the focus point in the horizontal direction is farther than the mask 4, so it is necessary to correct the aberration so as to focus the light on the mask 4. Therefore, the rotating mirror 30 is a cylindrical mirror having a radius of curvature r2 in the direction orthogonal to the optical axis of 137.22 mm. Further, here, the condition of the incoherent illumination of the formula (1) is also satisfied at the same time. With these configurations, light can be condensed on the mask 4 with equal divergence in both the horizontal and vertical directions. That is, the following relationship is generally established between the radius of curvature r in the direction orthogonal to the optical axis of the mirror, the distance a from the mirror to the condensing point, the distance b from the mirror to the light source point, and the oblique incidence angle φ of the mirror. Holds. 1 / a + 1 / b = 2 · sin φ / r (4) Here, the optical path length L2 from the fixed mirror 31 to the mask 4
, The optical path length L1 from the rotating mirror 30 to the fixed mirror 31
, The oblique incidence angle φ3 of the fixed mirror 31, the oblique incidence angle φ2 (φ3 / 2) of the rotating mirror 30, and the focus of the rotating mirror 30 to L
As 1 + L4, in equation (4), if b is infinite because of parallel light, the radius of curvature r3 in the direction orthogonal to the optical axis of the fixed mirror 31 and the radius of curvature in the direction orthogonal to the optical axis of the rotating mirror 30. r2 is expressed as follows. 1 / L2 + 1 / L4 = 2 · sin φ3 / r3 ··· (5) 1 / (L4 + L1) = 2 · sin φ2 / r2 ··· (6) Therefore, if r3 is determined, then r2 is given by equation (5) ), (6)
Can be obtained from

The rotating mirror 3 is used to obtain a practical exposure area.
A desired ring field length may be obtained with a rotation angle of 0. Due to the rotation, the focused spot moves along the ring field 36 on the mask 4. For example, the illumination area on the mask 4 is 100 mm (the lateral size of the chip is 20 mm).
To obtain, the rotation angle should be 106.26 °. Even if the rotating mirror 30 rotates, the incident angle on each mirror does not change, so that the exposure intensity basically does not change. Therefore, if the rotation speed is kept constant, uneven exposure on the circumference of the ring field 36 does not occur. Even if it occurs, it is possible to eliminate the unevenness by adjusting the speed.

Further, as described above, the exposure area in the width direction of the ring field 36 can be enlarged by scanning the mask 4 and the wafer 6 in synchronization with each other in the directions of arrows A and B, respectively. Therefore, by making the rotation speed of the rotating mirror 30 sufficiently faster than the scanning of the mask 4,
Exposure unevenness due to the rotation of the rotating mirror 30 does not occur. This enables exposure of a practical exposure area of 20 mm (horizontal) × 20 mm or more (vertical).

In this embodiment, since a reflection type mask is mainly used as a practical optical system,
Although the present invention is applied to a reflective mask, the effect of the invention is not lost even if a transmissive mask is used. Further, in this embodiment, the combination of the rotating cylindrical mirror and the fixed toroidal mirror is used to simplify the shape of the mirror as much as possible and improve the workability. It is also possible to use other aspherical mirrors such as a quadric surface.

[0029]

As described above, according to the X-ray reduction projection exposure apparatus according to the present invention, the X-ray reduction projection exposure illumination optical system is composed of the rotating mirror and the fixed mirror. The system can be illuminated incoherently and with a practical exposure area secured. Also,
Since the cylindrical mirror and the toroidal mirror are used as the rotating mirror and the fixed mirror, they can be manufactured inexpensively and accurately as compared with the aspherical mirror. Also,
If this illumination optical system is used, it is possible to manufacture an ultra-highly integrated LSI having a size of 0.1 μm or less by means of a reduction projection exposure optical system having a ring field.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an X-ray reduction projection exposure illumination optical system according to the present invention.

FIG. 2 is a diagram showing a beam shape of synchrotron radiation light having a parallel light flux.

FIG. 3 is a diagram showing a beam shape condensed on a mask.

FIG. 4 is a diagram showing a conventional example of an illumination system using synchrotron radiation light as a light source.

5 is a diagram showing a conventional example of an optical system in which an optical system called a full aperture illumination system is added to the optical system of FIG. 4 to perform two-dimensional light collection.

FIG. 6 is a diagram showing a conventional example of an optical system that performs critical illumination in the vertical direction and Koehler illumination in the horizontal direction by using an off-axis spheroid.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 4 ... Reflective mask, 6 ... Wafer, 19 ... Entrance pupil, 22 ... Reduction projection exposure optical system for image formation, 24 ... X-ray reduction projection exposure illumination optical system, 25 ... Reduction projection exposure optical system Axis, 26 ... Focusing optical system, 27 ... Concave mirror, 28 ... Convex mirror,
30 ... Rotating mirror, 31 ... Fixed mirror, 34 ... Concave toroidal mirror, 35 ... Convex toroidal mirror.

Claims (5)

[Claims] 1. An X-ray reduction projection exposure illumination optical system for converging a parallel light flux from a light source on a mask, and a reduction projection exposure optical system for projecting and exposing a pattern on the mask onto a sample surface.
In the line reduction projection exposure apparatus, the reduction projection exposure illumination optical system is configured by a rotating mirror that converts an optical path in an arc shape and a fixed mirror that collects light reflected by the rotating mirror on a mask. X-ray reduction projection exposure apparatus. 2. The X-ray reduction projection exposure apparatus according to claim 1, wherein the rotating mirror is a cylindrical mirror and the fixed mirror is a toroidal mirror. 3. The X-ray reduction projection exposure apparatus according to claim 1, wherein the rotation axis of the rotary mirror is aligned with the axis of the reduction projection exposure optical system. 4. The X-ray reduction projection exposure apparatus according to claim 1, wherein the fixed mirror is parallel to the axis of the reduction projection exposure optical system and orthogonal to the optical axis. An X-ray reduction projection exposure apparatus, wherein the center of curvature in the direction is arranged so as to coincide with the axis. 5. The X-ray reduction projection exposure apparatus according to claim 1, wherein the optical path length from the rotating mirror to the fixed mirror is set to the fixed mirror, the mask and the reduction projection exposure optical system. An X-ray reduction projection exposure apparatus characterized in that the optical path length between the entrance pupils is made equal.