JP4065923B2 - Illumination apparatus, projection exposure apparatus including the illumination apparatus, projection exposure method using the illumination apparatus, and adjustment method of the projection exposure apparatus - Google Patents

Description

[0001]
BACKGROUND 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 apparatus mounted on the apparatus.
[0002]
[Prior art]
In recent years, the light source wavelength of a projection exposure apparatus has been shortened along with the high integration of semiconductor integrated circuits. For example, a projection exposure apparatus using a KrF excimer laser as a light source has already been put into practical use, and an apparatus using an ArF excimer laser is shifting from a research stage to a practical stage. In the projection exposure apparatus using these lasers as the light source, the wavelength of the light source is short, so that the glass material that can be used as the transmission member is limited to quartz glass and meteorite. Therefore, when optically designing the projection lens of the projection exposure apparatus, it is extremely difficult to correct chromatic aberration (achromaticity). In principle, the excimer laser oscillation wavelength has a half width and a wavelength width of about several nanometers. For this reason, in order to alleviate the various conditions for achromaticity, the band is narrowed so that the oscillation wavelength has a half-value width of about a comma number pm. Here, when the band of the oscillation wavelength is narrowed using a diffraction grating or the like, only a specific polarization component is amplified in addition to the amplification of the specific wavelength. When projection exposure is performed using a light beam having a large amount of specific polarization components, the following problems occur.
[0003]
When exposure is performed using a polarized light beam as a light source, a phenomenon occurs in which the finally formed image differs depending on the pattern direction. For example, when the light beam is polarized in the meridional direction, an image having a small NA in the direction is formed on the image plane. When the light is polarized in the sagittal direction, an image having a large NA is formed in that 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 illumination light beam is polarized, an image is formed with an NA that is biased on the image plane. Depending on the resolution. Such a phenomenon is particularly remarkable when the NA is high. The details are described in Hiroshi Oki: “Contemporary optics for freshman, optics near the focal point”, Optics, 21 (1992) August issue.
[0004]
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 is different depending on the pattern direction in the semiconductor integrated circuit for the logic circuit, the processing speed of the logic circuit is lowered, which is not preferable. For this reason, the conventional projection exposure apparatus disclosed in, for example, Japanese Patent No. 2679319 using an ArF or KrF excimer laser as a light source, copes with the method described below.
[0005]
FIG. 6 is a diagram showing a schematic configuration of a conventional projection exposure apparatus. The light beam from the excimer laser 1 whose cross-sectional shape of the emitted light beam is rectangular is converted into a light beam having an appropriate shape and aspect ratio by the shaping optical system 2, and after passing through a quartz plate 100 and a quartz glass 101, which will be described later, The light enters the fly-eye lens 4 which is an optical element in which lenses are arranged in parallel at high density. FIG. 7 is a view of the fly-eye lens 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 the lens 6, the field stop 7 and the lens 9, is then bent 90 degrees by the reflection mirror 8, and passes through the lens 9 ′. Focused. Here, a condenser lens group is constituted by the lenses 6, 9, 9 '. 8A and 8B show the state of light rays from the entrance surface of the fly-eye lens 4 to the mask 10. For simplicity, in FIG. 8, the optical system from the lens 6 to the lens 9 is simply indicated 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 surface by the condenser lens LL. That is, the element lens entrance surface of the fly-eye lens 4 and the mask 10 are conjugated. Further, as shown in FIG. 8B, the light beam b condensed on the exit surface of the fly-eye lens 4 is converted into parallel light by the lens LL and irradiates the mask 10. As a result, the light beam incident on the fly-eye lens 4 is wavefront-divided into element lens units and superimposed on the mask 10. 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 L 1, L 2 and L 3, mirrors 13 and 14, and a reflective concave mirror M, and has an aperture stop 12. Here, the field stop 7 is disposed at a position conjugate with the mask 10 in the condenser lens groups 6 to 9 to define an illumination range. The exit surface of the fly eye lens 4 is conjugate with the aperture stop 12 of the projection lens, and the illumination system aperture stop 5 is disposed on the exit surface of the fly eye lens 4.
[0006]
As described above, the shape of the light beam emitted from the excimer laser 1 is generally rectangular, and is polarized parallel to the short side of the rectangle. Further, in order to keep the illumination efficiency as high as possible, it is desirable that the laser light beam having a rectangular shape is fitted to the outer shape of the fly-eye lens 4 as much as possible by the shaping optical system 2 constituted by a cylindrical lens or the like. FIG. 9 is a diagram showing the relationship between the shaped laser beam flux α and the fly-eye lens 4. The polarization direction po is parallel to the rectangular side. Since the entrance surface of the fly eye element lens is conjugate with the mask 10, the illumination range is defined by the outer diameter of the fly eye element lens. For this reason, since the polarized light parallel to the side of the rectangular illumination area is supplied onto the mask 10 which is the illuminated surface, the change in the NA of the imaging light beam due to the polarization direction as described above occurs. It is not preferable.
[0007]
[Problems to be solved by the invention]
In order to solve the problem caused by polarization, a configuration for obtaining pseudo natural light will be described. A 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. Then, since the traveling direction of the light beam is bent by the refraction action only with the quartz member 100, the quartz glass 101 processed into a wedge shape as in the quartz member 100 is disposed as shown in FIG. 6 in order to correct the traveling direction. .
[0008]
10A to 10C show the relationship between the direction of the optical axis of the quartz member (uniaxial crystal) 100, the polarization direction, and the fly-eye lens. 10A shows the cross-sectional shape of the light beam α incident on the fly-eye lens 4, FIG. 10B shows the optical axis opax of the quartz member, and FIG. 10C shows the shape of the fly-eye lens 4. The optical axis opax of the quartz member is set to be 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) that passes through the quartz member differs depending on the position where the light beam enters. For this reason, the polarization state of the emitted light beam differs depending on the incident position 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) and horizontal linearly polarized light (FIG. 11). (D)), circularly polarized light in the middle (FIGS. 11C and 11E), and elliptically polarized light. Then, by passing through the fly-eye lens and the condenser lens, the wavefronts of various polarization states are divided and superimposed, so that on the mask 10, the polarization of various directions overlaps, that is, pseudo natural light is obtained. be able to. By using the quartz member 100 in this way, it is possible to prevent non-uniformity of NA on the imaging surface (wafer 15) and variation in resolution of the imaged pattern based on a light beam in a specific polarization state.
[0009]
However, the projection exposure apparatus configured as described above has the following problems. In an actual projection exposure apparatus, a plurality of reflecting mirrors are used to bend the traveling direction of a light beam for reasons such as downsizing of the apparatus. The projection exposure apparatus shown in FIG. 6 has four reflecting mirrors 3, 8, 13, and 14. For example, if the optical system is arranged in a straight line without bending the mirrors 3 and 4, the optical system has a very long overall length. Further, if the mirror 13 is not bent, the optical system cannot be physically arranged.
[0010]
Therefore, the reflection mirror is an indispensable optical element in the optical system of the projection exposure apparatus. However, it is impossible to manufacture a reflection mirror having the same reflectivity for the P wave and the S wave for light having a short wavelength emitted from an ArF excimer laser or the like. For this reason, even if the mask is illuminated with natural light by bending the light beam with a reflecting mirror, there is a problem that the light beam becomes polarized on the exposed surface such as a wafer.
Even if linearly polarized laser oscillation light is converted into pseudo natural light on the mask surface by transmitting the crystal member as in the conventional apparatus, the p component or the optical component is bent by the reflection mirror in the subsequent optical system. The light beam has a specific polarization component such as the s component. Therefore, pattern resolution and line width variation due to non-uniformity of NA at the time of image formation on the wafer due to a specific polarization component occur.
[0011]
Here, in order to prevent the change in the ratio of the polarization component due to the bending of the light beam in the conventional apparatus, the laser light source and the shaping optical system are rotated, and the incident light beam itself to the quartz member is rotated to depend on the polarization direction. It is conceivable to change the ratio. However, if the incident light beam itself is rotated and the direction of the specific polarization is adjusted to the mirror bending direction, the rectangular light beam will be reflected to the rectangular fly-eye lens if the shape of the light beam and the direction of polarization are fixed. It will rotate and enter. As a result, the rectangular area of the fly-eye lens and the rectangular area of the light flux do not coincide with each other, and the light flux is generated by the fly-eye lens. Therefore, the amount of light cannot be used effectively, leading to a reduction in illumination efficiency.
[0012]
The present invention has been made in view of the above problems, and an illumination device that can easily adjust a ratio according to the direction of polarization of a light source to an arbitrary intensity ratio with respect to an arbitrary direction and a projection exposure apparatus including the illumination device. The purpose is to provide.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the invention according to claim 1, a wavefront splitting unit that wavefront-divides a light flux from a light source that supplies the light flux and forms a plurality of light source images based on the wavefront-divided light flux; In a lighting device including a condenser optical system that guides light from the plurality of light source images to a predetermined illumination region on an irradiated surface, a first compound disposed in an optical path between the light source and the wavefront splitting unit. and refracting element comprising a birefringent member comprising a second birefringent element, the first birefringent element, it relative to the second birefringent element is rotatable about the traveling direction of the light beam It is characterized by.
[0014]
According to a second aspect of the present invention, the birefringent member has a shape with a different thickness in the traveling direction in a cross-sectional direction of the light beam.
[0015]
The invention according to claim 3 is characterized in that at least one of the birefringent elements is arranged such that the direction of its optical axis is substantially perpendicular to the traveling direction of the light beam. To do.
[0016]
According to a fourth aspect of the present invention, the predetermined illumination area has a substantially rectangular shape, at least one of the birefringent elements is fixed, and the optical axis of the fixed birefringent element is fixed. The direction is parallel to the direction of the side of the rectangular shape.
[0017]
The invention according to claim 5 is characterized in that the fixed birefringent element is disposed between the rotatable birefringent element and the wavefront dividing portion.
[0018]
According to a sixth aspect of the present invention, the illumination device according to any one of the first to fifth aspects that illuminates a predetermined pattern, and a projection optical system that projects and exposes the illuminated pattern onto a photosensitive substrate It is characterized by having.
[0019]
According to a seventh aspect of the invention, there is provided a projection exposure apparatus adjusting method according to the sixth aspect,
A first step of measuring a polarization state of light reaching the surface on which the photosensitive substrate is set; and a second step of rotating the first birefringent element based on a measurement result in the first step. It is characterized by that.
According to an eighth aspect of the present invention, a step of illuminating a predetermined pattern using the illumination device according to any one of the first to fifth aspects, and projecting and exposing the illuminated pattern onto a photosensitive substrate. And a process.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram showing a configuration of an illumination apparatus according to a first embodiment of the present invention and a projection exposure apparatus including the illumination apparatus. The light beam from the light source 1 such as an ArF excimer laser (wavelength λ = about 193 nm) is enlarged in diameter and changed in aspect ratio by the shaping optical system 2 including a cylindrical lens. The light source 1 preferably emits linearly polarized light parallel to the paper surface. Next, the shaped light beam is transmitted through the first wedge-shaped prism set 200 and 201, and further guided through the second wedge-shaped prism set 202 and 203 to the fly-eye lens 4. The prisms 200 to 203 are processed into a wedge shape in which the thickness in the traveling direction differs in the cross-sectional direction of the light beam. Details of the prisms 200 to 203 will be described later. Next, the light 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. The light from the plurality of light source images passes through the lens 6 and the lens 9 and is then bent by 90 degrees by the reflecting mirror 8 to pass through the lens 9 ′ and illuminate the mask 10 having a pattern. Here, the condenser optical system is constituted by the lens 6, the lens 9, and the lens 9 ′. A field stop 7 is disposed at a position conjugate with the mask 10 in the condenser optical system. 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 L 1, L 2 and L 3, mirrors 13 and 14, and a reflective concave mirror M, and has an aperture stop 12. 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 disposed at a position conjugate with the mask 10 in the condenser optical systems 6 to 9 to define an illumination range. The exit surface of the fly-eye lens 4 is conjugate with the aperture stop 12 of the projection lens.
[0021]
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 prior art, since the optical path bends due to refraction when only a quartz prism is used, the traveling direction of the light beam is corrected by combining the quartz glass 201 and 203 processed into a wedge shape. . In addition, the angle of the wedge of each prism is set so that a light beam incident perpendicularly to the prism is emitted almost vertically. The quartz prism 200 and the quartz prism 201 are configured so as to be integrally rotated by the motor MT around the optical axis AX. On the other hand, the quartz prism 202 and the quartz prism 203 are fixed.
[0022]
The directions of the optical axes of the quartz prisms 200 and 202 are shown in FIGS. 2 (a) and 2 (b), 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. In addition, an angle formed by 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 crystal prism 202 is parallel to the direction of the side of the rectangular region 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. Further, it is desirable that at least one of the quartz prisms 200 and 202 is disposed so that the direction of the optical axis thereof is substantially perpendicular to the traveling direction of the light beam.
[0023]
In the present embodiment, the bending directions of the reflecting mirrors 8, 13, 14 and the like are all rotational directions with respect to an axis perpendicular to the paper surface of FIG. For this reason, the light flux on the surface of the wafer 15 is weakly polarized in the direction parallel to the paper surface of FIG. 1 and strong in the direction perpendicular to the paper surface. For this reason, it is necessary that the polarization intensity ratio of the light beams formed by the prisms 200 and 202 can be selected arbitrarily, with the y direction being strong and the z direction being weak. 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 on only the linearly polarized light, the intensity ratio is separated at 1: 1 as linearly polarized light in the y direction and polarized light having an angle of (ψ × 2) with respect to the y-axis as shown in FIG. Further, when passing 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 (ψ × 2) with respect to the y axis. And polarized light having an angle of − (ψ × 2) with respect to the y-axis at an intensity of 1: 1. This is shown in FIG. That is, if the polarization intensity in the y direction after passing through the prisms 200 to 203 is A, the polarization intensity in the z direction is B, and the rotation angle of the quartz prism 200 is ψ,
A: B = 1 + cos (2ψ): sin (2ψ)
It becomes. From this, it can be seen that in this embodiment, it is possible to obtain polarized light having a larger y direction and a smaller 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, it is desirable to rotate the quartz prism 200 so that the ratio of the amount of polarization depending on the direction becomes equal, and select ψ.
[0024]
(Second Embodiment)
Since the basic configuration of the illumination apparatus according to the second embodiment of the present invention and the projection exposure apparatus including the illumination apparatus is the same as that of the first embodiment, description thereof will be omitted. The difference from the first embodiment is that only the first wedge-shaped prism sets 200 and 201 are used instead of the prisms 200 to 203. FIGS. 5A to 5C show the 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, since circularly polarized light is not a problem, only linearly polarized light is shown. (A) is the case where the angle between the optical axis and the polarization direction is 45 ° (the same diagram as FIG. 11), (b) is the case of 30 °, and (c) is the case of 60 °. As is apparent from the figure, this method can increase the polarization in a specific oblique direction (the direction of the optical axis). When the light beam is bent by the mirror as in the first embodiment, when the bending is performed with respect to an axis parallel to any side of the rectangular illumination field, the polarization intensity ratio is parallel to the rectangular side of the light beam. Only the ratio of the two directions (y and z directions in FIG. 1) needs to change. However, when there is no restriction on the direction of bending by the mirror, the direction of the optical axis and the direction in which the polarization intensity ratio is desired to be changed can be made to coincide with each other by rotating the quartz prism 200. Therefore, by rotating one quartz prism 200, the intensity ratio in the desired direction can be changed.
[0025]
In the above-described embodiment, an illumination system using only one fly-eye lens is used. However, a plurality of pairs of fly-eye lenses and condenser lenses are provided in series, and the illumination is performed multiple times by dividing the wavefront and superimposing the light fluxes. A system may be used. For example, a configuration in which two pairs of fly-eye lenses and condenser lenses are arranged in series is generally called a double fly-eye system. In such a configuration, it is desirable that the birefringent medium such as a crystal member is arranged on the light source side with respect to the first fly-eye lens in order from the light source side.
[0026]
【The invention's effect】
As described above, in the first aspect of the 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 light reaching the exposed surface (wafer) due to the way the light beam is bent by the mirror.
[0027]
In the invention according to claim 2, the birefringent member has a different thickness in the traveling direction of the light beam in the cross-sectional direction of the light beam. Accordingly, when linearly polarized light is incident, since the distance transmitted through the member differs depending on the position of the light beam incident on the birefringent member, polarized light in various states can be obtained on the exit side.
[0028]
In the invention according to claim 3, 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.
[0029]
In the invention according to claim 4, the direction of the optical axis is substantially perpendicular to the traveling direction of the light beam. Therefore, it becomes easier to control the amount of polarization.
[0030]
In the invention described in claim 5, 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. Accordingly, even when the cross-sectional shape of the light beam emitted and shaped from the laser light source is rectangular, illumination can be performed efficiently without loss of light quantity, and the intensity ratio of polarized light can be controlled in accordance with the direction of the side of the illumination area. .
[0031]
In the invention according to claim 6, the fixed birefringent element is disposed between the rotatable birefringent element and the wavefront dividing portion. Accordingly, since the drive rotation unit of the mirror is away from the optical system such as the fly-eye lens, stable illumination can be performed.
[0032]
Further, in the invention described in claim 7, by using the illumination device according to the present invention, it is possible to avoid the influence of polarized light depending on the bending direction of the light beam, and always project and expose a good resolution pattern. [Short description of drawings]
FIG. 1 is a diagram showing a configuration of an illumination apparatus according to an embodiment of the present invention and a projection exposure apparatus including the illumination apparatus.
FIG. 2 is a diagram for explaining the direction of an optical axis of a quartz prism.
FIG. 3 is a diagram for explaining a state of polarized light after passing through a quartz prism 200;
FIG. 4 is a diagram for explaining the state of polarized light after passing through quartz prisms 200 and 202;
FIG. 5 is a diagram for explaining 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.
9 is a diagram showing the relationship between the shaped laser beam flux α and the fly-eye lens 4. FIG.
FIGS. 10A to 10C are diagrams showing the relationship between the direction of the optical axis of the crystal member (uniaxial crystal) 100, the polarization direction, and the fly-eye lens.
FIGS. 11A to 11E are diagrams showing polarization states of light emitted from the crystal member 100. FIGS.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Shaping optical system 3, 8, 13, 14 Reflection mirror 200, 202 Quartz prism 201, 203 Quartz prism 4 Fly eye lens 5 Aperture diaphragm 6, 9, 9 'Condenser lens 7 Field diaphragm 10 Mask L1, L2, L3 Lens 11 Projection optical system 12 Aperture stop 15 Wafer M Concave mirror

Claims (8)

A wavefront splitting unit that splits a wavefront of a light source from a light source that supplies the light flux, and forms a plurality of light source images based on the wavefront-divided light flux;
In an illuminating device comprising a condenser optical system that guides light from the plurality of light source images to a predetermined illumination region on the irradiated surface ,
A birefringent member including a first birefringent element disposed in an optical path between the light source and the wavefront splitting unit, and a second birefringent element;
It said first birefringent element, relative to the second birefringent element, the illumination device, characterized in that rotatable about the traveling direction of the light beam.   The lighting device according to claim 1, wherein the birefringent member has a shape in which a thickness in the traveling direction is different in a cross-sectional direction of the light beam. 3. The illumination according to claim 1, wherein at least one of the birefringent elements is disposed so that a direction of an optical axis thereof is substantially perpendicular to a traveling direction of a light beam. apparatus. The predetermined illumination area has a substantially rectangular shape,
At least one of the birefringent elements is fixed;
Direction of the optical axis of the fixed birefringence element lighting device according to any one of claims 1 3, characterized in that parallel to the direction of said rectangular sides.   The lighting device according to claim 4, wherein the fixed birefringent element is disposed between the rotatable birefringent element and the wavefront dividing unit. The illumination device according to any one of claims 1 to 5, which illuminates a predetermined pattern;
And a projection optical system for projecting and exposing the illuminated pattern onto a photosensitive substrate. An adjustment method for a projection exposure apparatus according to claim 6,
  A first step of measuring a polarization state of light reaching the surface on which the photosensitive substrate is set; and a second step of rotating the first birefringent element based on a measurement result in the first step. An adjustment method characterized by that. Illuminating a predetermined pattern using the illumination device according to any one of claims 1 to 5,
Projecting and exposing the illuminated pattern onto a photosensitive substrate.

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