JP2000114157A - Illuminator and projection aligner provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust the polarization ratio of a light source by direction to an arbitrary intensity ratio with respect to an arbitrary direction, by providing an condenser optical system and a double-diffracting member arranged in the optical path between a light source section and a wavefront dividing section, in such a way that the member can rotate around the advancing direction of luminous fluxes. SOLUTION: Luminous flux from a light source 1 is led to a fly-eye lens 4 through a first set of wedge-shaped prisms 200 and 201 and a second set of wedge-shaped prisms 202 and 203, and the wavefront of the luminous flux is divided through the lens 4, resulting in a plurality of light source images. The light rays from the light source images are reflected by 90 deg. with a reflecting mirror 8 after passing through lenses 6 and 9 and illuminate a mask 10 through a lens 9'. Here, a condenser optical system is constituted of the lenses 6, 9, and 9'. In addition, the crystal prism 200 and quartz prism 201 are constituted in such a way that the prisms 200 and 201 can be rotated integrally around the optical axis AX by means of a motor MT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus suitable for manufacturing a semiconductor integrated circuit and the like, and an illumination device mounted on the apparatus.

[0002]

2. Description of the Related Art In recent years, the light source wavelength of a projection exposure apparatus has been shortened with the increasing integration of semiconductor integrated circuits. For example, a projection exposure apparatus using a KrF excimer laser as a light source has already been put to practical use, and an apparatus using an ArF excimer laser is shifting from a research stage to a practical stage.
In a projection exposure apparatus using such a laser as a light source, the wavelength of the light source is short, so that glass materials usable as a transmission member are limited to quartz glass and fluorite. Therefore, when optically designing the projection lens of the projection exposure apparatus, it is extremely difficult to correct (achromatize) chromatic aberration. Further, in principle, the oscillation wavelength of the excimer laser has a half width and a wavelength width of about a few nanometers. For this reason, in order to alleviate various conditions of achromatism, the band is narrowed so that the oscillation wavelength is a half-value width and about several pm. Here, if the oscillation wavelength is narrowed using a diffraction grating or the like, only a specific polarization component is amplified in addition to amplification of a specific wavelength. When projection exposure is performed using a light beam having a large number of specific polarization components, the following problem occurs.

When exposure is performed using a polarized light beam as a light source, a phenomenon occurs that a finally formed image differs depending on the direction of a pattern. For example, when the light beam is polarized in the meridional direction, an image with a small NA is formed on the image plane as if in the direction. When the light is polarized in the sagittal direction, an image having a large NA is formed in the direction. Therefore, even if a pattern formed on a mask or the like is imaged by a projection optical system having a uniform NA, if the illuminating light beam is polarized, the image will be formed with a biased NA on the image plane. Causes a different resolution. Such a phenomenon is particularly remarkable in the case of high NA.
For details, see Hiroshi Oki: "Modern Optics for Freshman,
This is described in “Optics near Focus”, Optics, August 21 (1992).

On the other hand, the mainstream of semiconductor integrated circuits is shifting from memory circuits to logic circuits. A semiconductor integrated circuit for a logic circuit has an independent single pattern, and it is desirable that the pattern line width is uniform. If the resolution differs depending on the direction of the pattern in the semiconductor integrated circuit for the logic circuit, the processing speed of the logic circuit is undesirably reduced. For this reason, an ArF or KrF excimer laser is used as a light source.
The conventional projection exposure apparatus disclosed in Japanese Patent Publication No. 319 corresponds to the following method.

FIG. 6 is a diagram showing a schematic configuration of a conventional projection exposure apparatus. A light beam emitted from an excimer laser 1 having a rectangular cross-sectional shape is converted into a light beam having an appropriate shape and an aspect ratio by a shaping optical system 2. Fly-eye lens 4 which is an optical element in which lenses are arranged in high density in parallel
Incident on. FIG. 7 is a diagram in which the fly-eye lens is observed from the traveling direction of the light beam (x-axis direction). The light beam divided for each element lens by the fly-eye lens 4 passes through a lens 6, a field stop 7, and a lens 9, and then is reflected by a reflection mirror 8
Is bent 90 degrees and transmitted through the lens 9 ′.
It is focused on zero. Here, a condenser lens group is constituted by the lenses 6, 9, and 9 '. FIGS. 8A and 8B show the state of light rays from the incident surface of the fly-eye lens 4 to the mask 10. FIG. In FIG. 8, for convenience, the optical system from the lens 6 to the lens 9 is simply referred to as a lens LL. In FIG. 8A, the light beam a condensed on the incident surface of the fly-eye lens 4 is condensed at a position a ′ on the mask 10 by the condenser lens LL. That is, the entrance surface of each element lens of the fly-eye lens 4 and the mask 10 are conjugated. Further, as shown in FIG. 8B, the light beam b collected on the exit surface of the fly-eye lens 4 is
Is converted into parallel light, and the mask 10 is irradiated. As a result, the light beam incident on the fly-eye lens 4 is divided into wavefronts in units of element lenses, and is superimposed on the mask 10. Then, based on the illumination light supplied to the mask 10, the pattern on the mask 10 is changed by the projection optical system 11 to the wafer 15.
Is transferred to The projection optical system 11 includes lenses L1, L2,
It comprises an L3, mirrors 13 and 14, and a concave concave mirror M, and has an aperture stop 12. Here, the field stop 7
Is arranged at a position conjugate with the mask 10 in the condenser lens groups 6 to 9, and defines an illumination range. Also,
The exit surface of the fly-eye lens 4 is the aperture stop 1 of the projection lens.
2, an illumination system aperture stop 5 is provided on the exit surface of the fly-eye lens 4.

As described above, the shape of the light beam emitted from the excimer laser 1 is generally rectangular and polarized in parallel to the short side of the rectangle. In addition, in order to keep the illumination efficiency as high as possible, it is desirable to fit the rectangular laser emission light beam to the outer shape of the fly-eye lens 4 as much as possible by the shaping optical system 2 composed of a cylindrical lens or the like. FIG.
FIG. 4 is a diagram showing the relationship between the shaped laser emission light beam α and the fly-eye lens 4. The polarization direction po is parallel to the sides of the rectangle. Since the fly-eye element lens entrance surface is conjugate to the mask 10, the illumination range is defined by the outer diameter of the fly-eye element lens. For this reason, the mask 10 which is the surface to be illuminated
On the upper side, polarized light parallel to the sides of the rectangular illumination area is supplied, which causes a change in the NA of the imaging light beam due to the above-described polarization direction, which is not preferable.

[0007]

An arrangement for obtaining pseudo natural light in order to solve the problem caused by polarization will be described. Quartz member 100, which is a uniaxial crystal processed into a wedge shape
Is disposed between the light source 1 and the fly-eye lens 4. In addition, since the traveling direction of the light beam is bent by the refraction effect only by the quartz member 100, the quartz glass 1 processed into a wedge shape in the same manner as the quartz member 100 to correct the traveling direction.
01 is arranged as shown in FIG.

FIG. 10 shows the relationship between the direction of the optical axis of the quartz member (uniaxial crystal) 100, the polarization direction, and the fly-eye lens.
(A) to (c) are shown. 10A is a sectional view of a light beam α incident on the fly-eye lens 4, FIG. 10B is an optical axis opax of the quartz member, and FIG.
Are shown respectively. Opa axis of crystal member
x is set perpendicular to the traveling direction of the light beam and at an angle of 45 degrees with respect to the polarization direction po. According to this configuration, since the quartz member 100 is processed into a wedge shape, the thickness (transmission distance) of the light passing through the quartz member varies depending on the position where the light beam enters. For this reason, the polarization state of the emitted light beam differs depending on the position of incidence on the crystal. For example, when the polarization direction of the incident light incident on the quartz member 100 is as shown in FIG. 11A, the polarization of the emitted light is vertical linearly polarized light (FIG. 11B).
The light becomes horizontal linearly polarized light (FIG. 11D), intermediate circularly polarized light (FIGS. 11C and 11E), and furthermore, elliptically polarized light.
Then, since the wavefronts in various polarization states are divided and superimposed by transmitting through the fly-eye lens and the condenser lens, on the mask 10, a state in which polarized lights in various directions overlap, that is, pseudo natural light is obtained. be able to. By using the crystal member 100 in this way, it is possible to prevent unevenness in NA on the imaging plane (wafer 15) and variation in resolution of the formed pattern based on the light beam in a specific polarization state.

However, the projection exposure apparatus having the above configuration has the following problems. In an actual projection exposure apparatus, a plurality of reflection mirrors are used to bend the traveling direction of a light beam for reasons such as miniaturization of the apparatus. The projection exposure apparatus shown in FIG. 6 has four reflection mirrors 3, 8, 13, and 14. For example, if the optical systems are arranged in a straight line without bending the mirrors 3 and 4, the entire length of the optical system will be very long. Further, if the bending of the mirror 13 is eliminated, it is impossible to physically arrange the optical system.

Therefore, the reflection mirror is an indispensable optical element in the optical system of the projection exposure apparatus. However, it is not possible to manufacture a reflecting mirror having the same reflectance of P-wave and S-wave for short-wavelength light emitted from an ArF excimer laser or the like. For this reason, there is a problem that even if the mask is illuminated with natural light by bending the light beam by the reflection mirror, the light beam tends to be polarized on the surface to be exposed such as a wafer. Even if linearly polarized laser oscillation light is converted into pseudo natural light on the mask surface by transmitting through a quartz member as in the conventional apparatus, the p-component or The light beam has a specific polarization component such as the s component. Therefore, pattern resolution and line width variation due to non-uniform NA at the time of imaging on the wafer due to a specific polarization component occur.

Here, in order to prevent a change in the ratio of the polarization component due to the bending of the light beam in the conventional device, the laser light source and the shaping optical system are rotated to rotate the light beam incident on the quartz member itself. It is conceivable to change the ratio depending on the direction. However, when the incident light beam itself is rotated and the direction of the specific polarization is adjusted to the bending direction of the mirror, when the shape of the light beam and the direction of the polarization are fixed, the rectangular light beam is generated with respect to the rectangular fly-eye lens. It will rotate and enter. As a result, the rectangular area of the fly-eye lens does not coincide with the rectangular area of the light beam, and the light beam is blurred by the fly-eye lens, so that the light amount cannot be used effectively and the illumination efficiency is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an illumination device capable of easily adjusting the ratio of the direction of polarization of a light source to an arbitrary intensity ratio with respect to an arbitrary direction, and a projection including the illumination device. An object of the present invention is to provide an exposure apparatus.

[0013]

In order to solve the above problems, according to the first aspect of the present invention, a light source for supplying a light beam;
A wavefront splitting unit that splits a light beam from the light source into a wavefront, and forms a plurality of light source images based on the wavefront-divided light beam; and guides light from the plurality of light source images to a predetermined illumination area on a surface to be irradiated. It is characterized by comprising a condenser optical system, and a birefringent member disposed in an optical path between the light source unit and the wavefront splitting unit and rotatably provided around a traveling direction of a light beam.

Further, the invention according to claim 2 is characterized in that the birefringent member has a shape whose thickness in the traveling direction is different in a cross-sectional direction of the light beam.

[0015] In the invention described in claim 3, the birefringent member includes at least two birefringent elements, and at least one of the at least two birefringent elements rotates about the traveling direction. It is characterized by being possible.

In the invention according to claim 4, at least one of the birefringent elements is disposed such that the direction of the optical axis thereof is substantially perpendicular to the direction of travel of the light beam. It is characterized by.

In the invention described in claim 5, the predetermined illumination region is substantially rectangular, and at least one of the birefringent elements is fixed, and The direction of the optical axis is parallel to the direction of the side of the rectangular shape.

Further, in the invention according to claim 6, the fixed birefringent element is arranged between the rotatable birefringent element and the wavefront splitting portion.

According to a seventh aspect of the present invention, there is provided the illumination device according to any one of the first to sixth aspects, wherein the mask on which the predetermined pattern is formed is illuminated, and the pattern of the illuminated mask is exposed. A projection optical system for projecting and exposing on a substrate.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIG. 1 is a diagram showing a configuration of an illumination device according to a first embodiment of the present invention and a projection exposure apparatus having the illumination device. The light beam from the light source 1 such as an ArF excimer laser (wavelength λ = about 193 nm) is expanded in the light beam diameter and the aspect ratio is changed by a shaping optical system 2 including a cylindrical lens and the like. It is desirable that the light source 1 emits linearly polarized light parallel to the paper surface. Next, the shaped light beam is transmitted through the first pair of wedge prisms 200 and 201, and further guided to the fly-eye lens 4 via the second pair of wedge prisms 202 and 203. Prism 200 ~
Reference numeral 203 denotes a wedge shape in which the thickness in the traveling direction differs in the cross-sectional direction of the light beam. Prism 200-2
03 will be described later in detail. Next, the luminous flux from the light source is wavefront-divided by the fly-eye lens 4 to form a plurality of light source images. The exit surface of the fly-eye lens 4 is provided with an aperture stop 5 for determining the numerical aperture of illumination light on the wafer surface. Then, the light from the plurality of light source images passes through the lenses 6 and 9, is then bent by 90 degrees by the reflection mirror 8, passes through the lens 9 ′, and illuminates the mask 10 having a pattern. Here, a condenser optical system is constituted by the lens 6, the lens 9, and the lens 9 '. The field stop 7 is arranged at a position conjugate with the mask 10 in the condenser optical system. Then, the pattern on the mask 10 is transferred to the wafer 15 by the projection optical system 11 based on the illumination light supplied to the mask 10. The projection optical system 11 includes lenses L1, L2, L3, mirrors 13, 14, and a concave concave mirror M.
And the aperture stop 12 is provided. Thus, it is desirable that the projection optical system 11 of the present embodiment has a reflecting surface such as the mirror 13. Here, the field stop 7
Is arranged at a position conjugate with the mask 10 in the condenser optical systems 6 to 9 and defines an illumination range. The exit surface of the fly-eye lens 4 is located at the aperture stop 1 of the projection lens.
Conjugate to 2.

Next, the prisms 200 to 203 will be described. The prism 200 and the prism 202 are made of a quartz crystal processed into a wedge shape. As described in the above-described related art, since the optical path is bent by the refraction effect only with the quartz prism, the traveling direction of the light flux is corrected by combining the quartz glass 201 and 203 processed into the wedge shape. . Further, the angle of the wedge of each prism is set such that the light beam that has entered the prism vertically exits almost perpendicularly. The quartz prism 200 and the quartz prism 201 are integrally rotatable about the optical axis AX by a motor MT. On the other hand, the quartz prism 202 and the quartz prism 203 are fixed.

FIGS. 2A and 2B show the directions of the optical axes of the quartz prisms 200 and 202, respectively. Here, the direction of the optical axis is x, the direction perpendicular to the optical axis and in the plane of FIG. 1 is y, and the direction perpendicular to the plane of FIG. 1 is z. The angle between the optical axis opax of the quartz prism 200 and the y-axis is denoted by ψ. As shown in FIG. 2B, the direction of the optical axis opax of the fixed quartz prism 202 is parallel to the direction of the side of the rectangular area to be illuminated on the mask. However, when the light beam is bent by a mirror or the like, it is considered that there is no bending. Also, the quartz prism 200
And 202, it is desirable that the direction of the optical axis is substantially perpendicular to the traveling direction of the light beam.

In this embodiment, the reflection mirrors 8, 13,
The bending directions such as 14 are all directions of rotation with respect to an axis perpendicular to the paper surface of FIG. For this reason, in the light flux on the surface of the wafer 15, the polarization in the direction parallel to the paper of FIG. 1 is weak, and the polarization in the direction perpendicular to the paper is strong. For this reason, it is necessary that the intensity ratio of the polarization of the light beam formed by the prisms 200 and 202 is stronger in the y direction and weaker in the z direction, and that the ratio can be arbitrarily selected. After the linearly polarized light beam in the y direction passes through the prisms 200 and 201, it is converted into polarized light in various states. Focusing only on the linearly polarized light among them, as shown in FIG.
An intensity ratio of 1: 1 to polarized light having an angle of (ψ × 2) with the axis.
Separated by Further, when the light passes through the prisms 202 and 203, the linearly polarized light in the y direction passes through without any change, and the polarized light having an angle of (ψ × 2) with the y axis is y.
Polarized light having an angle of (ψ × 2) with respect to the axis and polarized light having an angle of − (ψ × 2) with respect to the y-axis are separated with an intensity of 1: 1. This is shown in FIG. That is, the prism 200
A: B = 1 + cos (2ｙ): sin (2ψ), where A is the polarization intensity in the y direction after transmission through 203, B is the polarization intensity in the z direction, and 回 転 is the rotation angle of the quartz prism 200.
Becomes From this, it is understood that in the present embodiment, it is possible to obtain polarized light with a large amount in the y direction and a small amount in the z direction. Further, since the rotation angle ψ is variable, the ratio between A and B can be arbitrarily selected. Preferably, while measuring the amount of polarization on the surface of the wafer 15, rotate the quartz prism 200 such that the ratio of the amount of polarization according to the direction is equal,
It is desirable to select ψ.

(Second Embodiment) The basic configuration of an illumination device and a projection exposure apparatus having the illumination device according to a second embodiment of the present invention is the same as that of the first embodiment, and is shown in FIG. Description is omitted. The difference from the first embodiment is that only the first pair of wedge prisms 200 and 201 are used instead of the prisms 200 to 203. FIGS. 5A to 5C show polarization states obtained by rotating the direction of the optical axis of the quartz prism 200 around the optical axis AX by the motor MT. In this case, only the linearly polarized light is shown because circularly polarized light does not matter. (A) shows the case where the angle between the optical axis and the polarization direction is 45 ° (the same figure as FIG. 11), (b) shows the case where it is 30 °, and (c) shows the case where it is 60 °. As is clear from the figure, this method can increase the polarization in a specific oblique direction (the direction of the optical axis).
As in the first embodiment, when the light beam is bent by the mirror, when the light beam is bent with respect to an axis parallel to any side of the rectangular illumination field, the intensity ratio of the polarized light is parallel to the rectangular side of the light beam. It is necessary that only the ratio in two directions (the y and z directions in FIG. 1) change. However, when there is no restriction on the bending direction by the mirror, the direction of the optical axis and the direction in which the intensity ratio of polarized light is desired to be changed can be matched by rotating the quartz prism 200. Therefore, by rotating one crystal prism 200, the intensity ratio in a desired direction can be changed.

In the above embodiment, an illumination system using only one fly-eye lens is used. However, a plurality of sets of a fly-eye lens and a condenser lens are provided in series, and a plurality of wavefront divisions and superposition of a light beam are performed. An illumination system which performs the rotation twice may be used. For example, a configuration in which two sets of a fly-eye lens and a condenser lens are arranged in series is generally called a double fly-eye system. In the case of such a configuration, it is desirable that the birefringent medium such as a crystal member be disposed closer to the light source than the first fly-eye lens, counted in order from the light source.

[0026]

As described above, according to the first aspect of the present invention, the intensity ratio of polarized light in a specific direction can be controlled by rotating the birefringent member. Therefore, it is possible to eliminate the influence of the polarization of the light that reaches the surface to be exposed (wafer) due to the manner in which the light beam is bent by the mirror.

According to the second aspect of the present invention, the birefringent member has a different thickness in the light beam traveling direction in the cross section direction of the light beam. Therefore, when linearly polarized light is incident, the distance of transmission through the birefringent member varies depending on the position of the light beam incident on the member, so that polarized light in various states can be obtained on the exit side.

According to the third aspect of the present invention, at least two birefringent elements are provided, one of which is rotatable. Therefore, the intensity ratio of polarized light in an arbitrary direction can be controlled.

According to the fourth aspect of the present invention, the direction of the optical axis is substantially perpendicular to the traveling direction of the light beam. Therefore, control of the amount of polarization is further facilitated.

According to the fifth aspect of the present invention, the illumination area on the mask has a substantially rectangular shape, and the direction of the optical axis of the fixed birefringent element is parallel to the direction of the side of the rectangular shape. . Therefore, even when the cross-sectional shape of the light beam emitted from the laser light source and shaped is a rectangular shape, illumination can be efficiently performed without loss of light amount, and the intensity ratio of polarized light can be controlled in accordance with the direction of the side of the illumination area. .

Further, in the invention according to claim 6, the fixed birefringent element is disposed between the rotatable birefringent element and the wavefront dividing portion. Therefore, since the drive rotation unit of the mirror is separated from the optical system such as the fly-eye lens, stable illumination can be performed.

According to the seventh aspect of the present invention, by using the illuminating device according to the present invention, it is possible to avoid the influence of polarization depending on the bending direction of the light beam, and to always project a good resolution pattern. Can be exposed

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an illumination device according to an embodiment of the present invention and a projection exposure apparatus including the same.

FIG. 2 is a diagram illustrating a direction of an optical axis of a quartz prism.

FIG. 3 is a diagram illustrating a state of polarized light after transmitting through a quartz prism 200;

FIG. 4 is a view for explaining the state of polarized light after passing through quartz crystal prisms 200 and 202.

FIG. 5 is a diagram illustrating a state of polarized light when a quartz prism 200 is rotated.

FIG. 6 is a diagram showing a configuration of a conventional projection exposure apparatus.

FIG. 7 is a diagram illustrating a configuration of a fly-eye lens.

FIGS. 8A and 8B are diagrams illustrating a system from a fly-eye lens to a mask.

FIG. 9 is a diagram showing a relationship between a shaped laser emission light beam α and a fly-eye lens 4;

FIGS. 10A to 10C are crystal members (uniaxial crystals) 1
FIG. 4 is a diagram illustrating a relationship among a direction of an optical axis of No. 00, a polarization direction, and a fly-eye lens.

FIGS. 11A to 11E are diagrams showing states of polarization of light emitted from the quartz member 100. FIGS.

[Explanation of symbols]

 Reference Signs List 1 light source 2 shaping optical system 3, 8, 13, 14 reflecting mirror 200, 202 quartz prism 201, 203 quartz prism 4 fly-eye lens 5 aperture stop 6, 9, 9 'condenser lens 7 field stop 10 mask L1, L2, L3 Lens 11 Projection optical system 12 Aperture stop 15 Wafer M Concave mirror

Claims (7)

[Claims] A light source that supplies a light beam; a wavefront dividing unit that divides a light beam from the light source into a wavefront, and forms a plurality of light source images based on the wavefront-divided light beam; A condenser optical system that guides light to a predetermined illumination area on a surface to be illuminated; and a condenser optical system that is disposed in an optical path between the light source unit and the wavefront splitting unit and that is rotatably provided around a traveling direction of a light beam. A lighting device, comprising: a refraction member. 2. The illuminating device according to claim 1, wherein the birefringent member has a shape having a different thickness in the traveling direction in a sectional direction of the light beam. 3. The birefringent member includes at least two birefringent elements, and at least one of the at least two birefringent elements is rotatable about the traveling direction. The lighting device according to claim 1. 4. The device according to claim 3, wherein at least one of the birefringent elements is disposed such that the direction of the optical axis thereof is substantially perpendicular to the direction of travel of the light beam.
The lighting device according to the above. 5. The predetermined illumination area has a substantially rectangular shape, at least one of the birefringent elements is fixed, and a direction of an optical axis of the fixed birefringent element is the rectangular shape. 4. The method according to claim 3, wherein the direction is parallel to the direction of the side of the shape.
The lighting device according to the above. 6. The lighting device according to claim 5, wherein the fixed birefringent element is disposed between the rotatable birefringent element and the wavefront splitting unit. 7. The illuminating device according to claim 1, which illuminates a mask on which a predetermined pattern is formed, and projection optics that projects and exposes the illuminated mask pattern onto a photosensitive substrate. And a projection exposure apparatus comprising: