US20090147234A1

US20090147234A1 - Beam transforming element, illumination optical apparatus, exposure apparatus, and exposure method with two optical elements having different thicknesses

Info

Publication number: US20090147234A1
Application number: US12320468
Authority: US
Inventors: Mitsunori Toyoda
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2003-11-20
Filing date: 2009-01-27
Publication date: 2009-06-11
Also published as: EP1693885B1; JP2011233911A; KR101220667B1; CN101685267A; JP2014003306A; KR20150103759A; US20110299055A1; EP2251896A1; KR101220616B1; KR101220636B1; EP3118890A2; JPWO2005050718A1; CN101685265B; KR101578310B1; CN101685266A; JP6160666B2; US20170351100A1; US20150338663A1; US20110273698A1; CN101685264A

Abstract

A beam transforming element for forming a predetermined light intensity distribution on a predetermined surface on the basis of an incident beam includes a first basic element made of an optical material with optical activity, for forming a first region distribution of the predetermined light intensity distribution on the basis of the incident beam; and a second basic element made of an optical material with optical activity, for forming a second region distribution of the predetermined light intensity distribution on the basis of the incident beam, wherein the first basic element and the second basic element have their respective thicknesses different from each other along a direction of transmission of light.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 11/319,057, filed Dec. 28, 2005, which is a continuation-in-part application of Application No. PCT/JP2004/016247 filed on Nov. 2, 2004. The disclosure of the prior application is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a beam transforming element, illumination optical apparatus, exposure apparatus, and exposure method and, more particularly, to an illumination optical apparatus suitably applicable to exposure apparatus used in production of microdevices such as semiconductor elements, image pickup elements, liquid crystal display elements, and thin-film magnetic heads by lithography.
2. Related Background Art
In the typical exposure apparatus of this type, a beam emitted from a light source travels through a fly's eye lens as an optical integrator to form a secondary light source as a substantial surface illuminant consisting of a number of light sources. Beams from the secondary light source (generally, an illumination pupil distribution formed on or near an illumination pupil of the illumination optical apparatus) are limited through an aperture stop disposed near the rear focal plane of the fly's eye lens and then enter a condenser lens.
The beams condensed by the condenser lens superposedly illuminate a mask on which a predetermined pattern is formed. The light passing through the pattern of the mask is focused on a wafer through a projection optical system. In this manner, the mask pattern is projected for exposure (or transcribed) onto the wafer. The pattern formed on the mask is a highly integrated pattern, and, in order to accurately transcribe this microscopic pattern onto the wafer, it is indispensable to obtain a uniform illuminance distribution on the wafer.
For example, Japanese Patent No. 3246615 owned by the same Applicant of the present application discloses the following technology for realizing the illumination condition suitable for faithful transcription of the microscopic pattern in arbitrary directions: the secondary light source is formed in an annular shape on the rear focal plane of the fly's eye lens and the beams passing the secondary light source of the annular shape are set to be in a linearly polarized state with a direction of polarization along the circumferential direction thereof (hereinafter referred to as a “azimuthal polarization state”).

SUMMARY OF THE INVENTION

An object of the present invention is to form an illumination pupil distribution of an annular shape in a azimuthal polarization state while well suppressing the loss of light quantity. Another object of the present invention is to transcribe a microscopic pattern in an arbitrary direction under an appropriate illumination condition faithfully and with high throughput, by forming an illumination pupil distribution of an annular shape in a azimuthal polarization state while well suppressing the loss of light quantity.
In order to achieve the above objects, a first aspect of the present embodiment is to provide a beam transforming element for forming a predetermined light intensity distribution on a predetermined surface on the basis of an incident beam, comprising:
a first basic element made of an optical material with optical activity, for forming a first region distribution of the predetermined light intensity distribution on the basis of the incident beam; and
a second basic element made of an optical material with optical activity, for forming a second region distribution of the predetermined light intensity distribution on the basis of the incident beam,
wherein the first basic element and the second basic element have their respective thicknesses different from each other along a direction of transmission of light.
A second aspect of the present embodiment is to provide a beam transforming element for, based on an incident beam, forming a predetermined light intensity distribution of a shape different from a sectional shape of the incident beam, on a predetermined surface, comprising:
a diffracting surface or a refracting surface for forming the predetermined light intensity distribution on the predetermined surface,
wherein the predetermined light intensity distribution is a distribution in at least a part of a predetermined annular region, which is a predetermined annular region centered around a predetermined point on the predetermined surface, and
wherein a beam from the beam transforming element passing through the predetermined annular region has a polarization state in which a principal component is linearly polarized light having a direction of polarization along a circumferential direction (azymuthally direction) of the predetermined annular region.
A third aspect of the present invention is to provide an illumination optical apparatus for illuminating a surface to be illuminated, based on a beam from a light source, comprising:
the beam transforming element of the first aspect or the second aspect for transforming the beam from the light source in order to form an illumination pupil distribution on or near an illumination pupil of the illumination optical apparatus.
A fourth aspect of the present embodiment is to provide an exposure apparatus comprising the illumination optical apparatus of the third aspect for illuminating a pattern,
the exposure apparatus being arranged to project the pattern onto a photosensitive substrate.
A fifth aspect of the present embodiment is to provide an exposure method comprising: an illumination step of illuminating a pattern by use of the illumination optical apparatus of the third aspect; and an exposure step of projecting the pattern onto a photosensitive substrate.
The illumination optical apparatus of the present embodiment, different from the conventional technology giving rise to the large loss of light quantity at the aperture stop, is able to form the illumination pupil distribution of the annular shape in the azimuthal polarization state, with no substantial loss of light quantity, by diffraction and optical rotating action of the diffractive optical element as the beam transforming element. Namely, the illumination optical apparatus of the present invention is able to form the illumination pupil distribution of the annular shape in the azimuthal polarization state while well suppressing the loss of light quantity.
Since the exposure apparatus and exposure method using the illumination optical apparatus of the present embodiment are arranged to use the illumination optical apparatus capable of forming the illumination pupil distribution of the annular shape in the azimuthal polarization state while well suppressing the loss of light quantity, they are able to transcribe a microscopic pattern in an arbitrary direction under an appropriate illumination condition faithfully and with high throughput and, in turn, to produce good devices with high throughput.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the embodiment.
Further scope of applicability of the embodiment will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration schematically showing a configuration of an exposure apparatus with an illumination optical apparatus according to an embodiment of the present invention.

FIG. 2 is an illustration showing a secondary light source of an annular shape formed in annular illumination.

FIG. 3 is an illustration schematically showing a configuration of a conical axicon system disposed in an optical path between a front lens unit and a rear lens unit of an afocal lens in FIG. 1.

FIG. 4 is an illustration to illustrate the action of the conical axicon system on the secondary light source of the annular shape.

FIG. 5 is an illustration to illustrate the action of a zoom lens on the secondary light source of the annular shape.

FIG. 6 is an illustration schematically showing a first cylindrical lens pair and a second cylindrical lens pair disposed in an optical path between the front lens unit and the rear lens unit of the afocal lens in FIG. 1.

FIG. 7 is a first drawing to illustrate the action of the first cylindrical lens pair and the second cylindrical lens pair on the secondary light source of the annular shape.

FIG. 8 is a second drawing to illustrate the action of the first cylindrical lens pair and the second cylindrical lens pair on the secondary light source of the annular shape.

FIG. 9 is a third drawing to illustrate the action of the first cylindrical lens pair and the second cylindrical lens pair on the secondary light source of the annular shape.

FIG. 10 is a perspective view schematically showing an internal configuration of a polarization monitor in FIG. 1.

FIG. 11 is an illustration schematically showing a configuration of a diffractive optical element for azimuthally polarized annular illumination according to an embodiment of the present invention.

FIG. 12 is an illustration schematically showing a secondary light source of an annular shape set in the azimuthal polarization state.

FIG. 13 is an illustration to illustrate the action of a first basic element.

FIG. 14 is an illustration to illustrate the action of a second basic element.

FIG. 15 is an illustration to illustrate the action of a third basic element.

FIG. 16 is an illustration to illustrate the action of a fourth basic element.

FIG. 17 is an illustration to illustrate the optical activity of crystalline quartz.

FIGS. 18A and 18B are illustrations showing octapole secondary light sources in the azimuthal polarization state consisting of eight arc regions spaced from each other along the circumferential direction and a quadrupole secondary light source in the azimuthal polarization state consisting of four arc regions spaced from each other along the circumferential direction.

FIG. 19 is an illustration showing a secondary light source of an annular shape in the azimuthal polarization state consisting of eight arc regions overlapping with each other along the circumferential direction.

FIGS. 20A and 20B are illustrations showing hexapole secondary light sources in the azimuthal polarization state consisting of six arc regions spaced from each other along the circumferential direction and a secondary light source in the azimuthal polarization state having a plurality of regions spaced from each other along the circumferential direction and a region on the optical axis.

FIG. 21 is an illustration showing an example in which an entrance-side surface of a diffractive optical element for azimuthally polarized annular illumination is planar.

FIG. 22 is a flowchart of a procedure of obtaining semiconductor devices as microdevices.

FIG. 23 is a flowchart of a procedure of obtaining a liquid crystal display element as a microdevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described based on the accompanying drawings.
FIG. 1 is an illustration schematically showing a configuration of an exposure apparatus with an illumination optical apparatus according to an embodiment of the present invention. In FIG. 1, the Z-axis is defined along a direction of a normal to a wafer W being a photosensitive substrate, the Y-axis along a direction parallel to the plane of FIG. 1 in the plane of the wafer W, and the X-axis along a direction of a normal to the plane of FIG. 1 in the plane of wafer W. The exposure apparatus of the present embodiment is provided with a light source 1 for supplying exposure light (illumination light).
The light source 1 can be, for example, a KrF excimer laser light source for supplying light with the wavelength of 248 nm, an ArF excimer laser light source for supplying light with the wavelength of 193 nm, or the like. A nearly parallel beam emitted along the Z-direction from the light source 1 has a cross section of a rectangular shape elongated along the X-direction, and is incident to a beam expander 2 consisting of a pair of lenses 2 a and 2 b. The lenses 2 a and 2 b have a negative refracting power and a positive refracting power, respectively, in the plane of FIG. 1 (or in the YZ plane). Therefore, the beam incident to the beam expander 2 is enlarged in the plane of FIG. 1 and shaped into a beam having a cross section of a predetermined rectangular shape.
The nearly parallel beam passing through the beam expander 2 as a beam shaping optical system is deflected into the Y-direction by a bending mirror 3, and then travels through a quarter wave plate 4 a, a half wave plate 4 b, a depolarizer (depolarizing element) 4 c, and a diffractive optical element 5 for annular illumination to enter an afocal lens 6. Here the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4 c constitute a polarization state converter 4, as described later. The afocal lens 6 is an afocal system (afocal optic) set so that the front focal position thereof approximately coincides with the position of the diffractive optical element 5 and so that the rear focal position thereof approximately coincides with the position of a predetermined plane 7 indicated by a dashed line in the drawing.
In general, a diffractive optical element is constructed by forming level differences with the pitch of approximately the wavelength of exposure light (illumination light) in a substrate and has the action of diffracting an incident beam at desired angles. Specifically, the diffractive optical element 5 for annular illumination has the following function: when a parallel beam having a rectangular cross section is incident thereto, it forms a light intensity distribution of an annular shape in its far field (or Fraunhofer diffraction region). Therefore, the nearly parallel beam incident to the diffractive optical element 5 as a beam transforming element forms a light intensity distribution of an annular shape on the pupil plane of the afocal lens 6 and then emerges as a nearly parallel beam from the afocal lens 6.
In an optical path between front lens unit 6 a and rear lens unit 6 b of the afocal lens 6 there are a conical axicon system 8, a first cylindrical lens pair 9, and a second cylindrical lens pair 10 arranged in order from the light source side on or near the pupil plane of the afocal lens, and the detailed configuration and action thereof will be described later. For easier description, the fundamental configuration and action will be described below, in disregard of the action of the conical axicon system 8, first cylindrical lens pair 9, and second cylindrical lens pair 10.
The beam through the afocal lens 6 travels through a zoom lens 11 for variation of σ-value and then enters a micro fly's eye lens (or fly's eye lens) 12 as an optical integrator. The micro fly's eye lens 12 is an optical element consisting of a number of micro lenses with a positive refracting power arranged lengthwise and breadthwise and densely. In general, a micro fly's eye lens is constructed, for example, by forming a micro lens group by etching of a plane-parallel plate.
Here each micro lens forming the micro fly's eye lens is much smaller than each lens element forming a fly's eye lens. The micro fly's eye lens is different from the fly's eye lens consisting of lens elements spaced from each other, in that a number of micro lenses (micro refracting surfaces) are integrally formed without being separated from each other. In the sense that lens elements with a positive refracting power are arranged lengthwise and breadthwise, however, the micro fly's eye lens is a wavefront splitting optical integrator of the same type as the fly's eye lens. Detailed explanation concerning the micro fly's eye lens capable of being used in the present invention is disclosed, for example, in U.S. Pat. No. 6,913,373 (B2) which is incorporated herein by reference in its entirety.
The position of the predetermined plane 7 is arranged near the front focal position of the zoom lens 11, and the entrance surface of the micro fly's eye lens 12 is arranged near the rear focal position of the zoom lens 11. In other words, the zoom lens 11 arranges the predetermined plane 7 and the entrance surface of the micro fly's eye lens 12 substantially in the relation of Fourier transform and eventually arranges the pupil plane of the afocal lens 6 and the entrance surface of the micro fly's eye lens 12 approximately optically conjugate with each other.
Accordingly, for example, an illumination field of an annular shape centered around the optical axis AX is formed on the entrance surface of the micro fly's eye lens 12, as on the pupil plane of the afocal lens 6. The entire shape of this annular illumination field similarly varies depending upon the focal length of the zoom lens 11. Each micro lens forming the micro fly's eye lens 12 has a rectangular cross section similar to a shape of an illumination field to be formed on a mask M (eventually, a shape of an exposure region to be formed on a wafer W).
The beam incident to the micro fly's eye lens 12 is two-dimensionally split by a number of micro lenses to form on its rear focal plane (eventually on the illumination pupil) a secondary light source having much the same light intensity distribution as the illumination field formed by the incident beam, i.e., a secondary light source consisting of a substantial surface illuminant of an annular shape centered around the optical axis AX, as shown in FIG. 2. Beams from the secondary light source formed on the rear focal plane of the micro fly's eye lens 12 (in general, an illumination pupil distribution formed on or near the pupil plane of the illumination optical apparatus) travel through beam splitter 13 a and condenser optical system 14 to superposedly illuminate a mask blind 15.
In this manner, an illumination field of a rectangular shape according to the shape and focal length of each micro lens forming the micro fly's eye lens 12 is formed on the mask blind 15 as an illumination field stop. The internal configuration and action of polarization monitor 13 incorporating a beam splitter 13 a will be described later. Beam through a rectangular aperture (light transmitting portion) of the mask blind 15 are subject to light condensing action of imaging optical system 16 and thereafter superposedly illuminate the mask M on which a predetermined pattern is formed.
Namely, the imaging optical system 16 forms an image of the rectangular aperture of the mask blind 15 on the mask M. A beam passing through the pattern of mask M travels through a projection optical system PL to form an image of the mask pattern on the wafer W being a photosensitive substrate. In this manner, the pattern of the mask M is sequentially printed in each exposure area on the wafer W through full-wafer exposure or scan exposure with two-dimensional drive control of the wafer W in the plane (XY plane) perpendicular to the optical axis AX of the projection optical system PL.
In the polarization state converter 4, the quarter wave plate 4 a is arranged so that its crystallographic axis is rotatable around the optical axis AX, and it transforms incident light of elliptical polarization into light of linear polarization. The half wave plate 4 b is arranged so that its crystallographic axis is rotatable around the optical axis AX, and it changes the plane of polarization of linearly polarized light incident thereto. The depolarizer 4 c is composed of a wedge-shaped crystalline quartz prism (not shown) and a wedge-shaped fused silica prism (not shown) having complementary shapes. The crystalline quartz prism and the fussed silica prism are constructed as an integral prism assembly so as to be set into and away from the illumination optical path.
Where the light source 1 is the KrF excimer laser light source or the ArF excimer laser light source, light emitted from these light sources typically has the degree of polarization of 95% or more and light of almost linear polarization is incident to the quarter wave plate 4 a. However, if a right-angle prism as a back-surface reflector is interposed in the optical path between the light source 1 and the polarization state converter 4, the linearly polarized light will be changed into elliptically polarized light by virtue of total reflection in the right-angle prism unless the plane of polarization of the incident, linearly polarized light agrees with the P-polarization plane or S-polarization plane.
In the case of the polarization state converter 4, for example, even if light of elliptical polarization is incident thereto because of the total reflection in the right-angle prism, light of linear polarization transformed by the action of the quarter wave plate 4 a will be incident to the half wave plate 4 b. Where the crystallographic axis of the half wave plate 4 b is set at an angle of 0° or 90° relative to the plane of polarization of the incident, linearly polarized light, the light of linear polarization incident to the half wave plate 4 b will pass as it is, without change in the plane of polarization.
Where the crystallographic axis of the half wave plate 4 b is set at an angle of 45° relative to the plane of polarization of the incident, linearly polarized light, the light of linear polarization incident to the half wave plate 4 b will be transformed into light of linear polarization with change of polarization plane of 90°. Furthermore, where the crystallographic axis of the crystalline quartz prism in the depolarizer 4 c is set at an angle of 45° relative to the polarization plane of the incident, linearly polarized light, the light of linear polarization incident to the crystalline quartz prism will be transformed (or depolarized) into light in an unpolarized state.
The polarization state converter 4 is arranged as follows: when the depolarizer 4 c is positioned in the illumination optical path, the crystallographic axis of the crystalline quartz prism makes the angle of 45° relative to the polarization plane of the incident, linearly polarized light. Incidentally, where the crystallographic axis of the crystalline quartz prism is set at the angle of 0° or 90° relative to the polarization plane of the incident, linearly polarized light, the light of linear polarization incident to the crystalline quartz prism will pass as it is, without change of the polarization plane. Where the crystallographic axis of the half wave plate 4 b is set at an angle of 22.5° relative to the polarization plane of incident, linearly polarized light, the light of linear polarization incident to the half wave plate 4 b will be transformed into light in an unpolarized state including a linear polarization component directly passing without change of the polarization plane and a linear polarization component with the polarization plane rotated by 90°.
The polarization state converter 4 is arranged so that light of linear polarization is incident to the half wave plate 4 b, as described above, and, for easier description hereinafter, it is assumed that light of linear polarization having the direction of polarization (direction of the electric field) along the Z-axis in FIG. 1 (hereinafter referred to as “Z-directionally polarized light”) is incident to the half wave plate 4 b. When the depolarizer 4 c is positioned in the illumination optical path and when the crystallographic axis of the half wave plate 4 b is set at the angle of 0° or 90° relative to the polarization plane (direction of polarization) of the Z-directionally polarized light incident thereto, the light of Z-directional polarization incident to the half wave plate 4 b passes as kept as Z-directionally polarized light without change of the polarization plane and enters the crystalline quartz prism in the depolarizer 4 c. Since the crystallographic axis of the crystalline quartz prism is set at the angle of 45° relative to the polarization plane of the Z-directionally polarized light incident thereto, the light of Z-directional polarization incident to the crystalline quartz prism is transformed into light in an unpolarized state.
The light depolarized through the crystalline quartz prism travels through the quartz prism as a compensator for compensating the traveling direction of the light and is incident into the diffractive optical element 5 while being in the depolarized state. On the other hand, if the crystallographic axis of the half wave plate 4 b is set at the angle of 45° relative to the polarization plane of the Z-directionally polarized light incident thereto, the light of Z-directional polarization incident to the half wave plate 4 b will be rotated in the polarization plane by 90° and transformed into light of linear polarization having the polarization direction (direction of the electric field) along the X-direction in FIG. 1 (hereinafter referred to as “X-directionally polarized light”) and the X-directionally polarized light will be incident to the crystalline quartz prism in the depolarizer 4 c. Since the crystallographic axis of the crystalline quartz prism is set at the angle of 45° relative to the polarization plane of the incident, X-directionally polarized light as well, the light of X-directional polarization incident to the crystalline quartz prism is transformed into light in the depolarized state, and the light travels through the quartz prism to be incident in the depolarized state into the diffractive optical element 5.
In contrast, when the depolarizer 4 c is set away from the illumination optical path, if the crystallographic axis of the half wave plate 4 b is set at the angle of 0° or 90° relative to the polarization plane of the Z-directionally polarized light incident thereto, the light of Z-directional polarization incident to the half wave plate 4 b will pass as kept as Z-directionally polarized light without change of the polarization plane, and will be incident in the Z-directionally polarized state into the diffractive optical element 5. If the crystallographic axis of the half wave plate 4 b is set at the angle of 45° relative to the polarization plane of the Z-directionally polarized light incident thereto on the other hand, the light of Z-directional polarization incident to the half wave plate 4 b will be transformed into light of X-directional polarization with the polarization plane rotated by 90°, and will be incident in the X-directionally polarized state into the diffractive optical element 5.
In the polarization state converter 4, as described above, the light in the depolarized state can be made incident to the diffractive optical element 5 when the depolarizer 4 c is set and positioned in the illumination optical path. When the depolarizer 4 c is set away from the illumination optical path and when the crystallographic axis of the half wave plate 4 b is set at the angle of 0° or 90° relative to the polarization plane of the Z-directionally polarized light incident thereto, the light in the Z-directionally polarized state can be made incident to the diffractive optical element 5. Furthermore, when the depolarizer 4 c is set away from the illumination optical path and when the crystallographic axis of the half wave plate 4 b is set at the angle of 45° relative to the polarization plane of the Z-directionally polarized light incident thereto, the light in the X-directionally polarized state can be made incident to the diffractive optical element 5.
In other words, the polarization state converter 4 is able to switch the polarization state of the incident light into the diffractive optical element 5 (a state of polarization of light to illuminate the mask M and wafer W in use of an ordinary diffractive optical element except for the diffractive optical element for azimuthally polarized annular illumination according to the present invention as will be described later) between the linearly polarized state and the unpolarized state through the action of the polarization state converter consisting of the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4 c, and, in the case of the linearly polarized state, it is able to switch between mutually orthogonal polarization states (between the Z-directional polarization and the X-directional polarization).
FIG. 3 is an illustration schematically showing the configuration of the conical axicon system disposed in the optical path between the front lens unit and the rear lens unit of the afocal lens in FIG. 1. The conical axicon system 8 is composed of a first prism member 8 a whose plane is kept toward the light source and whose refracting surface of a concave conical shape is kept toward the mask, and a second prism member 8 b whose plane is kept toward the mask and whose refracting surface of a convex conical shape is kept toward the light source, in order from the light source side.
The refracting surface of the concave conical shape of the first prism member 8 a and the refracting surface of the convex conical shape of the second prism member 8 b are formed in a complementary manner so as to be able to be brought into contact with each other. At least one of the first prism member 8 a and the second prism member 8 b is arranged movable along the optical axis AX, so that the spacing can be varied between the refracting surface of the concave conical shape of the first prism member 8 a and the refracting surface of the convex conical shape of the second prism member 8 b.
In a state in which the refracting surface of the concave conical shape of the first prism member 8 a and the refracting surface of the convex conical shape of the second prism member 8 b are in contact with each other, the conical axicon system 8 functions as a plane-parallel plate and has no effect on the secondary light source of the annular shape formed. However, when the refracting surface of the concave conical shape of the first prism member 8 a and the refracting surface of the convex conical shape of the second prism member 8 b are spaced from each other, the conical axicon system 8 functions a so-called beam expander. Therefore, the angle of the incident beam to the predetermined plane 7 varies according to change in the spacing of the conical axicon system 8.
FIG. 4 is an illustration to illustrate the action of the conical axicon system on the secondary light source of the annular shape. With reference to FIG. 4, the secondary light source 30 a of the minimum annular shape formed in a state where the spacing of the conical axicon system 8 is zero and where the focal length of the zoom lens 11 is set at the minimum (this state will be referred to hereinafter as a “standard state”) is changed into secondary light source 30 b of an annular shape with the outside diameter and inside diameter both enlarged and without change in the width (half of the difference between the inside diameter and the outside diameter: indicated by arrows in the drawing) when the spacing of the conical axicon system 8 is increased from zero to a predetermined value. In other words, an annular ratio (inside diameter/outside diameter) and size (outside diameter) both vary through the action of the conical axicon system 8, without change in the width of the secondary light source of the annular shape.
FIG. 5 is an illustration to illustrate the action of the zoom lens on the secondary light source of the annular shape. With reference to FIG. 5, the secondary light source 30 a of the annular shape formed in the standard state is changed into secondary light source 30 c of an annular shape whose entire shape is similarly enlarged by increasing the focal length of the zoom lens 11 from the minimum to a predetermined value. In other words, the width and size (outside diameter) both vary through the action of zoom lens 11, without change in the annular ratio of the secondary light source of the annular shape.
FIG. 6 is an illustration schematically showing the configuration of the first cylindrical lens pair and the second cylindrical lens pair disposed in the optical path between the front lens unit and the rear lens unit of the afocal lens in FIG. 1. In FIG. 6, the first cylindrical lens pair 9 and the second cylindrical lens pair 10 are arranged in order from the light source side. The first cylindrical lens pair 9 is composed, for example, of a first cylindrical negative lens 9 a with a negative refracting power in the YZ plane and with no refracting power in the XY plane, and a first cylindrical positive lens 9 b with a positive refracting power in the YZ plane and with no refracting power in the XY plane, which are arranged in order from the light source side.
On the other hand, the second cylindrical lens pair 10 is composed, for example, of a second cylindrical negative lens 10 a with a negative refracting power in the XY plane and with no refracting power in the YZ plane, and a second cylindrical positive lens 10 b with a positive refracting power in the XY plane and with no refracting power in the YZ plane, which are arranged in order from the light source side. The first cylindrical negative lens 9 a and the first cylindrical positive lens 9 b are arranged so as to integrally rotate around the optical axis AX. Similarly, the second cylindrical negative lens 10 a and the second cylindrical positive lens 10 b are arranged so as to integrally rotate around the optical axis AX.
In the state shown in FIG. 6, the first cylindrical lens pair 9 functions as a beam expander having a power in the Z-direction, and the second cylindrical lens pair 10 as a beam expander having a power in the X-direction. The power of the first cylindrical lens pair 9 and the power of the second cylindrical lens pair 10 are set to be equal to each other.
FIGS. 7 to 9 are illustrations to illustrate the action of the first cylindrical lens pair and the second cylindrical lens pair on the secondary light source of the annular shape. FIG. 7 shows such a setting that the direction of the power of the first cylindrical lens pair 9 makes the angle of +45° around the optical axis AX relative to the Z-axis and that the direction of the power of the second cylindrical lens pair 10 makes the angle of −45° around the optical axis AX relative to the Z-axis.
Therefore, the direction of the power of the first cylindrical lens pair 9 is perpendicular to the direction of the power of the second cylindrical lens pair 10, and the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10 has the Z-directional power and the X-directional power identical to each other. As a result, in a perfect circle state shown in FIG. 7, a beam passing through the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10 is subject to enlargement at the same power in the Z-direction and in the X-direction to form the secondary light source of a perfect-circle annular shape on the illumination pupil.
In contrast to it, FIG. 8 shows such a setting that the direction of the power of the first cylindrical lens pair 9 makes, for example, the angle of +80° around the optical axis AX relative to the Z-axis and that the direction of the power of the second cylindrical lens pair 10 makes, for example, the angle of −80° around the optical axis AX relative to the Z-axis. Therefore, the power in the X-direction is greater than the power in the Z-direction in the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10. As a result, in a horizontally elliptic state shown in FIG. 8, the beam passing through the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10 is subject to enlargement at the power greater in the X-direction than in the Z-direction, whereby the secondary light source of a horizontally long annular shape elongated in the X-direction is formed on the illumination pupil.
On the other hand, FIG. 9 shows such a setting that the direction of the power of the first cylindrical lens pair 9 makes, for example, the angle of +10° around the optical axis AX relative to the Z-axis and that the direction of the power of the second cylindrical lens pair 10 makes, for example, the angle of −10° around the optical axis AX relative to the Z-axis. Therefore, the power in the Z-direction is greater than the power in the X-direction in the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10. As a result, in a vertically elliptical state shown in FIG. 9, the beam passing through the composite system of the first cylindrical lens pair 9 and the second cylindrical lens pair 10 is subject to enlargement at the power greater in the Z-direction than in the X-direction, whereby the secondary light source of a vertically long annular shape elongated in the Z-direction is formed on the illumination pupil.
Furthermore, by setting the first cylindrical lens pair 9 and the second cylindrical lens pair 10 in an arbitrary state between the perfect circle state shown in FIG. 7 and the horizontally elliptical state shown in FIG. 8, the secondary light source can be formed in a horizontally long annular shape according to any one of various aspect ratios. By setting the first cylindrical lens pair 9 and the second cylindrical lens pair 10 in an arbitrary state between the perfect circle state shown in FIG. 7 and the vertically elliptical state shown in FIG. 9, the secondary light source can be formed in a vertically long annular shape according to any one of various aspect ratios.
FIG. 10 is a perspective view schematically showing the internal configuration of the polarization monitor shown in FIG. 1. With reference to FIG. 10, the polarization monitor 10 is provided with a first beam splitter 13 a disposed in the optical path between the micro fly's eye lens 12 and the condenser optical system 14. The first beam splitter 13 a has, for example, the form of a non-coated plane-parallel plate made of quartz glass (i.e., raw glass), and has a function of taking reflected light in a polarization state different from a polarization state of incident light, out of the optical path.
The light taken out of the optical path by the first beam splitter 13 a is incident to a second beam splitter 13 b. The second beam splitter 13 b has, for example, the form of a non-coated plane-parallel plate made of quartz glass as the first beam splitter 13 a does, and has a function of generating reflected light in a polarization state different from the polarization state of incident light. The polarization monitor is so set that the P-polarized light for the first beam splitter 13 a becomes the S-polarized light for the second beam splitter 13 b and that the S-polarized light for the first beam splitter 13 a becomes the P-polarized light for the second beam splitter 13 b.
Light transmitted by the second beam splitter 13 b is detected by first light intensity detector 13 c, while light reflected by the second beam splitter 13 b is detected by second light intensity detector 13 d. Outputs from the first light intensity detector 13 c and from the second light intensity detector 13 d are supplied each to a controller (not shown). The controller drives the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4 c constituting the polarization state converter 4, according to need.
As described above, the reflectance for the P-polarized light and the reflectance for the S-polarized light are substantially different in the first beam splitter 13 a and in the second beam splitter 13 b. In the polarization monitor 13, therefore, the reflected light from the first beam splitter 13 a includes the S-polarization component (i.e., the S-polarization component for the first beam splitter 13 a and P-polarization component for the second beam splitter 13 b), for example, which is approximately 10% of the incident light to the first beam splitter 13 a, and the P-polarization component (i.e., the P-polarization component for the first beam splitter 13 a and S-polarization component for the second beam splitter 13 b), for example, which is approximately 1% of the incident light to the first beam splitter 13 a.
The reflected light from the second beam splitter 13 b includes the P-polarization component (i.e., the P-polarization component for the first beam splitter 13 a and S-polarization component for the second beam splitter 13 b), for example, which is approximately 10%×1%=0.1% of the incident light to the first beam splitter 13 a, and the S-polarization component (i.e., the S-polarization component for the first beam splitter 13 a and P-polarization component for the second beam splitter 13 b), for example, which is approximately 1%×10%=0.1% of the incident light to the first beam splitter 13 a.
In the polarization monitor 13, as described above, the first beam splitter 13 a has the function of extracting the reflected light in the polarization state different from the polarization state of the incident light out of the optical path in accordance with its reflection characteristic. As a result, though there is slight influence of variation of polarization due to the polarization characteristic of the second beam splitter 13 b, it is feasible to detect the polarization state (degree of polarization) of the incident light to the first beam splitter 13 a and, therefore, the polarization state of the illumination light to the mask M, based on the output from the first light intensity detector 13 c (information about the intensity of transmitted light from the second beam splitter 13 b, i.e., information about the intensity of light virtually in the same polarization state as that of the reflected light from the first beam splitter 13 a).
The polarization monitor 13 is so set that the P-polarized light for the first beam splitter 13 a becomes the S-polarized light for the second beam splitter 13 b and that the S-polarized light for the first beam splitter 13 a becomes the P-polarized light for the second beam splitter 13 b. As a result, it is feasible to detect the light quantity (intensity) of the incident light to the first beam splitter 13 a and, therefore, the light quantity of the illumination light to the mask M, with no substantial effect of change in the polarization state of the incident light to the first beam splitter 13 a, based on the output from the second light intensity detector 13 d (information about the intensity of light successively reflected by the first beam splitter 13 a and the second beam splitter 13 b).
In this manner, it is feasible to detect the polarization state of the incident light to the first beam splitter 13 a and, therefore, to determine whether the illumination light to the mask M is in the desired unpolarized state or linearly polarized state, using the polarization monitor 13. When the controller determines that the illumination light to the mask M (eventually, to the wafer W) is not in the desired unpolarized state or linearly polarized state, based on the detection result of the polarization monitor 13, it drives and adjusts the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4 c constituting the polarization state converter 4 so that the state of the illumination light to the mask M can be adjusted into the desired unpolarized state or linearly polarized state.
Quadrupole illumination can be implemented by setting a diffractive optical element for quadrupole illumination (not shown) in the illumination optical path, instead of the diffractive optical element 5 for annular illumination. The diffractive optical element for quadrupole illumination has such a function that when a parallel beam having a rectangular cross section is incident thereto, it forms a light intensity distribution of a quadrupole shape in the far field thereof. Therefore, the beam passing through the diffractive optical element for quadrupole illumination forms an illumination field of a quadrupole shape consisting of four circular illumination fields centered around the optical axis AX, for example, on the entrance surface of the micro fly's eye lens 12. As a result, the secondary light source of the same quadrupole shape as the illumination field formed on the entrance surface is also formed on the rear focal plane of the micro fly's eye lens 12.
In addition, ordinary circular illumination can be implemented by setting a diffractive optical element for circular illumination (not shown) in the illumination optical path, instead of the diffractive optical element 5 for annular illumination. The diffractive optical element for circular illumination has such a function that when a parallel beam having a rectangular cross section is incident thereto, it forms a light intensity distribution of a circular shape in the far field. Therefore, a beam passing through the diffraction optical element for circular illumination forms a circular illumination field centered around the optical axis AX, for example, on the entrance plane of the micro fly's eye lens 12. As a result, the secondary light source of the same circular shape as the illumination field formed on the entrance surface is also formed on the rear focal plane of the micro fly's eye lens 12.
Furthermore, a variety of multipole illuminations (dipole illumination, octapole illumination, etc.) can be implemented by setting other diffractive optical elements for multipole illuminations (not shown), instead of the diffractive optical element 5 for annular illumination. Likewise, modified illuminations in various forms can be implemented by setting diffractive optical elements with appropriate characteristics (not shown) in the illumination optical path, instead of the diffractive optical element 5 for annular illumination.
In the present embodiment, a diffractive optical element 50 for so-called azimuthally polarized annular illumination can be set, instead of the diffractive optical element 5 for annular illumination, in the illumination optical path, so as to implement the modified illumination in which the beam passing through the secondary light source of the annular shape is set in the azimuthal polarization state, i.e., the azimuthally polarized annular illumination. FIG. 11 is an illustration schematically showing the configuration of the diffractive optical element for azimuthally polarized annular illumination according to the present embodiment. FIG. 12 is an illustration schematically showing the secondary light source of the annular shape set in the azimuthal polarization state.
With reference to FIGS. 11 and 12, the diffractive optical element 50 for azimuthally polarized annular illumination according to the present embodiment is constructed in such an arrangement that four types of basic elements 50A-50D having the same cross section of a rectangular shape and having their respective thicknesses different from each other along the direction of transmission of light (Y-direction) (i.e., lengths in the direction of the optical axis) are arranged lengthwise and breadthwise and densely. The thicknesses are set as follows: the thickness of the first basic elements 50A is the largest, the thickness of the fourth basic elements 50D the smallest, and the thickness of the second basic elements 50B is greater than the thickness of the third basic elements 50C.
The diffractive optical element 50 includes an approximately equal number of first basic elements 50A, second basic elements 50B, third basic elements 50C, and fourth basic elements 50D, and the four types of basic elements 50A-50D are arranged substantially at random. Furthermore, a diffracting surface (indicated by hatching in the drawing) is formed on the mask side of each basic element 50A-50D, and the diffracting surfaces of the respective basic elements 50A-50D are arrayed along one plane perpendicular to the optical axis AX (not shown in FIG. 11). As a result, the mask-side surface of the diffractive optical element 50 is planar, while the light-source-side surface of the diffractive optical element 50 is uneven due to the differences among the thicknesses of the respective basic elements 50A-50D.
The diffracting surface of each first basic element 50A is arranged to form a pair of arc regions (bow shape) 31A symmetric with respect to an axis line of the Z-direction passing the optical axis AX, in the secondary light source 31 of the annular shape shown in FIG. 12. Namely, as shown in FIG. 13, each first basic element 50A has a function of forming a pair of arc (bow shape) light intensity distributions 32A symmetric with respect to the axis line of the Z-direction passing the optical axis AX (corresponding to a pair of arc regions 31A) in the far field 50E of the diffractive optical element 50 (i.e., in the far field of each basic element 50A-50D).
The diffracting surface of each second basic element 50B is arranged so as to form a pair of arc (bow shape) regions 31B symmetric with respect to an axis line obtained by rotating the axis line of the Z-direction passing the optical axis AX, by −45° around the Y-axis (or obtained by rotating it by 45° counterclockwise in FIG. 12). Namely, as shown in FIG. 14, each second basic element 50B has a function of forming a pair of arc (bow shape) light intensity distributions 32B symmetric with respect to the axis line resulting from the −45° rotation around the Y-axis, of the axis line of the Z-direction passing the optical axis AX (corresponding to a pair of arc regions 31B), in the far field 50E.
The diffracting surface of each third basic element 50C is arranged to form a pair of arc (bow shape) regions 31C symmetric with respect to an axis line of the X-direction passing the optical axis AX. Namely, as shown in FIG. 15, each third basic element 50C has a function of forming a pair of arc (bow shape) light intensity distributions 32C symmetric with respect to the axis line of the X-direction passing the optical axis AX (corresponding to a pair of arc regions 31C), in the far field 50E.
The diffracting surface of each fourth basic element 50D is arranged so as to form a pair of arc (bow shape) regions 31D symmetric with respect to an axis line obtained by rotating the axis of the Z-direction passing the optical axis AX by +45° around the Y-axis (i.e., obtained by rotating it by 45° clockwise in FIG. 12). Namely, as shown in FIG. 16, each fourth basic element 50D has a function of forming a pair of arc (bow shape) light intensity distributions 32D symmetric with respect to the axis line resulting from the +45° rotation around the Y-axis, of the axis line of the Z-direction passing the optical axis AX (corresponding to a pair of arc regions 31D), in the far field 50E. The sizes of the respective arc regions 31A-31D are approximately equal to each other, and they form the secondary light source 31 of the annular shape centered around the optical axis AX, while the eight arc regions 31A-31D are not overlapping with each other and not spaced from each other.
In the present embodiment, each basic element 50A-50D is made of crystalline quartz being an optical material with optical activity, and the crystallographic axis of each basic element 50A-50D is set approximately to coincide with the optical axis AX. The optical activity of crystalline quartz will be briefly described below with reference to FIG. 17. With reference to FIG. 17, an optical member 35 of a plane-parallel plate shape made of crystalline quartz and in a thickness d is arranged so that its crystallographic axis coincides with the optical axis AX. In this case, by virtue of the optical activity of the optical member 35, incident, linearly polarized light emerges in a state in which its-polarization direction is rotated by θ around the optical axis AX.
At this time, the angle θ of rotation of the polarization direction due to the optical activity of the optical member 35 is represented by Eq (1) below, using the thickness d of the optical member 35 and the rotatory power ρ of crystalline quartz.
θ=d·ρ (1)
In general, the rotatory power ρ of crystalline quartz tends to increase with decrease in the wavelength of used light and, according to the description on page 167 in “Applied Optics II,” the rotatory power ρ of crystalline quartz for light having the wavelength of 250.3 nm is 153.9°/mm.
In the present embodiment the first basic elements 50A are designed in such a thickness dA that when light of linear polarization having the direction of polarization along the Z-direction is incident thereto, they output light of linear polarization having the polarization direction along a direction resulting from +180° rotation of the Z-direction around the Y-axis, i.e., along the Z-direction, as shown in FIG. 13. As a result, the polarization direction of beams passing through a pair of arc light intensity distributions 32A formed in the far field 50E is also the Z-direction, and the polarization direction of beams passing through a pair of arc regions 31A shown in FIG. 12 is also the Z-direction.
The second basic elements 50B are designed in such a thickness dB that when light of linear polarization having the polarization direction along the Z-direction is incident thereto, they output light of linear polarization having the polarization direction along a direction resulting from +135° rotation of the Z-direction around the Y-axis, i.e., along a direction resulting from −45° rotation of the Z-direction around the Y-axis, as shown in FIG. 14. As a result, the polarization direction of beams passing through a pair of arc light intensity distributions 32B formed in the far field 50E is also the direction obtained by rotating the Z-direction by −45° around the Y-axis, and the polarization direction of beams passing through a pair of arc regions 31A shown in FIG. 12 is also the direction obtained by rotating the Z-direction by −45° around the Y-axis.
The third basic elements 50C are designed in such a thickness dC that when light of linear polarization having the polarization direction along the Z-direction is incident thereto, they output light of linear polarization having the polarization direction along a direction resulting from +90° rotation of the Z-direction around the Y-axis, i.e., along the X-direction, as shown in FIG. 15. As a result, the polarization direction of beams passing through a pair of arc light intensity distributions 32C formed in the far field 50E is also the X-direction, and the polarization direction of beams passing through a pair of arc regions 31C shown in FIG. 12 is also the X-direction.
The fourth basic elements 50D are designed in such a thickness dD that when light of linear polarization having the polarization direction along the Z-direction is incident thereto, they output light of linear polarization having the polarization direction along a direction resulting from +45° rotation of the Z-direction around the Y-axis, as shown in FIG. 16. As a result, the polarization direction of beams passing through a pair of arc light intensity distributions 32D formed in the far field 50E is also the direction obtained by rotating the Z-direction by +45° around the Y-axis, and the polarization direction of beams passing through a pair of arc regions 31D shown in FIG. 12 is also the direction obtained by rotating the Z-direction by +45° around the Y-axis.
In the present embodiment, the diffractive optical element 50 for azimuthally polarized annular illumination is set in the illumination optical system on the occasion of effecting the azimuthally polarized annular illumination, whereby the light of linear polarization having the polarization direction along the Z-direction is made incident to the diffractive optical element 50. As a result, the secondary light source of the annular shape (illumination pupil distribution of annular shape) 31 is formed on the rear focal plane of the micro fly's eye lens 12 (i.e., on or near the illumination pupil), as shown in FIG. 12, and the beams passing through the secondary light source 31 of the annular shape are set in the azimuthal polarization state.
In the azimuthal polarization state, the beams passing through the respective arc regions 31A-31D constituting the secondary light source 31 of the annular shape turn into the linearly polarized state having the polarization direction substantially coincident with a tangent line to a circle centered around the optical axis AX, at the central position along the circumferential direction of each arc region 31A-31D.
In the present embodiment, as described above, the beam transforming element 50 for forming the predetermined light intensity distribution on the predetermined surface on the basis of the incident beam comprises the first basic element 50A made of the optical material with optical activity, for forming the first region distribution 32A of the predetermined light intensity distribution on the basis of the incident beam; and the second basic element 50B made of the optical material with optical activity, for forming the second region distribution 32B of the predetermined light intensity distribution on the basis of the incident beam, and the first basic element 50A and the second basic element 50B have their respective thicknesses different from each other along the direction of transmission of light.
Thanks to this configuration, the present embodiment is able to form the secondary light source 31 of the annular shape in the azimuthal polarization state, with no substantial loss of light quantity, through the diffracting action and optical rotating action of the diffractive optical element 50 as the beam transforming element, different from the conventional technology giving rise to the large loss of light quantity at the aperture stop.
In a preferred form of the present embodiment, the thickness of the first basic element 50A and the thickness of the second basic element 50B are so set that with incidence of linearly polarized light the polarization direction of the linearly polarized light forming the first region distribution 32A is different from the polarization direction of the linearly polarized light forming the second region distribution 32B. Preferably, the first region distribution 32A and the second region distribution 32B are positioned in at least a part of a predetermined annular region, which is a predetermined annular region centered around a predetermined point on the predetermined surface, and the beams passing through the first region distribution 32A and through the second region distribution 32B have a polarization state in which a principal component is linearly polarized light having the polarization direction along the circumferential direction of the predetermined annular region.
In this case, preferably, the predetermined light intensity distribution has a contour of virtually the same shape as the predetermined annular region, the polarization state of the beam passing through the first region distribution 32A has a linear polarization component substantially coincident with a tangential direction to a circle centered around a predetermined point at the central position along the circumferential direction of the first region distribution 32A, and the polarization state of the beam passing through the second region distribution 32B has a linear polarization component substantially coincident with a tangential direction to a circle centered around a predetermined point at the central position along the circumferential direction of the second region distribution 32B. In another preferred configuration, the predetermined light intensity distribution is a distribution of a multipole shape in the predetermined annular region, the polarization state of the beam passing through the first region distribution has a linear polarization component substantially coincident with a tangential direction to a circle centered around a predetermined point at the central position along the circumferential direction of the first region distribution, and the polarization state of the beam passing through the second region distribution has a linear polarization component substantially coincident with a tangential direction to a circle centered around a predetermined point at the central position along the circumferential direction of the second region distribution.
In a preferred form of the present embodiment, the first basic element and the second basic element are made of an optical material with an optical rotatory power of not less than 100°/mm for light of a wavelength used. Preferably, the first basic element and the second basic element are made of crystalline quartz. The beam transforming element preferably includes virtually the same number of first basic elements and second basic elements. The first basic element and the second basic element preferably have diffracting action or refracting action.
In another preferred form of the present embodiment, preferably, the first basic element forms at least two first region distributions on the predetermined surface on the basis of the incident beam, and the second basic element forms at least two second region distributions on the predetermined surface on the basis of the incident beam. In addition, preferably, the beam transforming element further comprises the third basic element 50C made of the optical material with optical activity, for forming the third region distribution 32C of the predetermined light intensity distribution on the basis of the incident beam, and the fourth basic element 50D made of the optical material with optical activity, for forming the fourth region distribution 32D of the predetermined light intensity distribution on the basis of the incident beam.
In the present embodiment, the beam transforming element 50 for forming the predetermined light intensity distribution of the shape different from the sectional shape of the incident beam, on the predetermined surface, has the diffracting surface or refracting surface for forming the predetermined light intensity distribution on the predetermined surface, the predetermined light intensity distribution is a distribution in at least a part of a predetermined annular region, which is a predetermined annular region centered around a predetermined point on the predetermined surface, and the beam from the beam transforming element passing through the predetermined annular region has a polarization state in which a principal component is linearly polarized light having the direction of polarization along the circumferential direction of the predetermined annular region.
In the configuration as described above, the present embodiment, different from the conventional technology giving rise to the large loss of light quantity at the aperture stop, is able to form the secondary light source 31 of the annular shape in the azimuthal polarization state, with no substantial loss of light quantity, through the diffracting action and optical rotating action of the diffractive optical element 50 as the beam transforming element.
In a preferred form of the present embodiment, the predetermined light intensity distribution has a contour of a multipole shape or annular shape. The beam transforming element is preferably made of an optical material with optical activity.
The illumination optical apparatus of the present embodiment is the illumination optical apparatus for illuminating the surface to be illuminated, based on the beam from the light source, and comprises the above-described beam transforming element for transforming the beam from the light source in order to form the illumination pupil distribution on or near the illumination pupil of the illumination optical apparatus. In this configuration, the illumination optical apparatus of the present embodiment is able to form the illumination pupil distribution of the annular shape in the azimuthal polarization state while well suppressing the loss of light quantity.
Here the beam transforming element is preferably arranged to be replaceable with another beam transforming element having a different characteristic. Preferably, the apparatus further comprises the wavefront splitting optical integrator disposed in the optical path between the beam transforming element and the surface to be illuminated, and the beam transforming element forms the predetermined light intensity distribution on the entrance surface of the optical integrator on the basis of the incident beam.
In a preferred form of the illumination optical apparatus of the present embodiment, at least one of the light intensity distribution on the predetermined surface and the polarization state of the beam from the beam transforming element passing through the predetermined annular region is set in consideration of the influence of an optical member disposed in the optical path between the light source and the surface to be illuminated. Preferably, the polarization state of the beam from the beam transforming element is so set that the light illuminating the surface to be illuminated is in a polarization state in which a principal component is S-polarized light.
The exposure apparatus of the present embodiment comprises the above-described illumination optical apparatus for illuminating the mask, and projects the pattern of the mask onto the photosensitive substrate. Preferably, at least one of the light intensity distribution on the predetermined surface and the polarization state of the beam from the beam transforming element passing through the predetermined annular region is set in consideration of the influence of an optical member disposed in the optical path between the light source and the photosensitive substrate. Preferably, the polarization state of the beam from the beam transforming element is so set that the light illuminating the photosensitive substrate is in a polarization state in which a principal component is S-polarized light.
The exposure method of the present embodiment comprises the illumination step of illuminating the mask by use of the above-described illumination optical apparatus, and the exposure step of projecting the pattern of the mask onto the photosensitive substrate. Preferably, at least one of the light intensity distribution on the predetermined surface and the polarization state of the beam from the beam transforming element passing through the predetermined annular region is set in consideration of the influence of an optical member disposed in the optical path between the light source and the photosensitive substrate. Preferably, the polarization state of the beam from the beam transforming element is so set that the light illuminating the photosensitive substrate is in a polarization state in which a principal component is S-polarized light.
In other words, the illumination optical apparatus of the present embodiment is able to form the illumination pupil distribution of the annular shape in the azimuthal polarization state while well suppressing the loss of light quantity. As a result, the exposure apparatus of the present embodiment is able to transcribe the microscopic pattern in an arbitrary direction under an appropriate illumination condition faithfully and with high throughput because it uses the illumination optical apparatus capable of forming the illumination pupil distribution of the annular shape in the azimuthal polarization state while well suppressing the loss of light quantity.
In the azimuthally polarized annular illumination based on the illumination pupil distribution of the annular shape in the azimuthal polarization state, the light illuminating the wafer W as a surface to be illuminated is in the polarization state in which the principal component is the S-polarized light. Here the S-polarized light is linearly polarized light having the direction of polarization along a direction normal to a plane of incidence (i.e., polarized light with the electric vector oscillating in the direction normal to the plane of incidence). The plane of incidence herein is defined as the following plane: when light arrives at a boundary surface of a medium (a surface to be illuminated: surface of wafer W), the plane includes the normal to the boundary plane at the arrival point and the direction of incidence of light.
In the above-described embodiment, the diffractive optical element 50 for azimuthally polarized annular illumination is constructed by randomly arranging virtually the same number of four types of basic elements 50A-50D with the same rectangular cross section lengthwise and breadthwise and densely. However, without having to be limited to this, a variety of modification examples can be contemplated as to the number of basic elements of each type, the sectional shape, the number of types, the arrangement, and so on.
In the above-described embodiment, the secondary light source 31 of the annular shape centered around the optical axis AX is composed of the eight arc regions 31A-31D arrayed without overlapping with each other and without being spaced from each other, using the diffractive optical element 50 consisting of the four types of basic elements 50A-50D. However, without having to be limited to this, a variety of modification examples can be contemplated as to the number of regions forming the secondary light source of the annular shape, the shape, the arrangement, and so on.
Specifically, as shown in FIG. 18A, it is also possible to form a secondary light source 33 a of an octapole shape in the azimuthal polarization state consisting of eight arc (bow shape) regions spaced from each other along the circumferential direction, for example, using the diffractive optical element consisting of four types of basic elements. In addition, as shown in FIG. 18B, it is also possible to form a secondary light source 33 b of a quadrupole shape in the azimuthal polarization state consisting of four arc (bow shape) regions spaced from each other along the circumferential direction, for example, using the diffractive optical element consisting of four types of basic elements. In the secondary light source of the octapole shape or the secondary light source of the quadrupole shape, the shape of each region is not limited to the arc shape, but it may be, for example, circular, elliptical, or sectorial. Furthermore, as shown in FIG. 19, it is also possible to form a secondary light source 33 c of an annular shape in the azimuthal polarization state consisting of eight arc regions overlapping with each other along the circumferential direction, for example, using the diffractive optical element consisting of four types of basic elements.
In addition to the quadrupole or octapole secondary light source in the azimuthal polarization state consisting of the four or eight regions spaced from each other along the circumferential direction, the secondary light source may be formed in a hexapole shape in the azimuthal polarization state and of six regions spaced from each other along the circumferential direction, as shown in FIG. 20A. In addition, as shown in FIG. 20B, the secondary light source may be formed as one having secondary light source of a multipole shape in the azimuthal polarization state consisting of a plurality of regions spaced from each other along the circumferential direction, and a secondary light source on the center pole in the unpolarized state or linearly polarized state consisting of a region on the optical axis. Furthermore, the secondary light source may also be formed in a dipole shape in the azimuthal polarization state and of two regions spaced from each other along the circumferential direction.
In the aforementioned embodiment, as shown in FIG. 11, the four types of basic elements 50A-50D are individually formed, and the diffractive optical element 50 is constructed by combining these elements. However, without having to be limited to this, the diffractive optical element 50 can also be integrally constructed in such a manner that a crystalline quartz substrate is subjected, for example, to etching to form the exit-side diffracting surfaces and the entrance-side uneven surfaces of the respective basic elements 50A-50D.
In the aforementioned embodiment each basic element 50A-50D (therefore, the diffractive optical element 50) is made of crystalline quartz. However, without having to be limited to this, each basic element can also be made of another appropriate optical material with optical activity. In this case, it is preferable to use an optical material with an optical rotatory power of not less than 100°/mm for light of a wavelength used. Specifically, use of an optical material with a low rotatory power is undesirable because the thickness necessary for achieving the required rotation angle of the polarization direction becomes too large, so as to cause the loss of light quantity.
The aforementioned embodiment is arranged to form the illumination pupil distribution of the annular shape (secondary light source), but, without having to be limited to this, the illumination pupil distribution of a circular shape can also be formed on or near the illumination pupil. In addition to the illumination pupil distribution of the annular shape and the illumination pupil distribution of the multipole shape, it is also possible to implement a so-called annular illumination with the center pole and a multipole illumination with the center pole, for example, by forming a center region distribution including the optical axis.
In the aforementioned embodiment, the illumination pupil distribution in the azimuthal polarization state is formed on or near the illumination pupil. However, the polarization direction can vary because of polarization aberration (retardation) of an optical system (the illumination optical system or the projection optical system) closer to the wafer than the diffractive optical element as the beam transforming element. In this case, it is necessary to properly set the polarization state of the beam passing through the illumination pupil distribution formed on or near the illumination pupil, with consideration to the influence of polarization aberration of these optical systems.
In connection with the foregoing polarization aberration, reflected light can have a phase difference in each polarization direction because of a polarization characteristic of a reflecting member disposed in the optical system (the illumination optical system or the projection optical system) closer to the wafer than the beam transforming element. In this case, it is also necessary to properly set the polarization state of the beam passing through the illumination pupil distribution formed on or near the illumination pupil, with consideration to the influence of the phase difference due to the polarization characteristic of the reflecting member.
The reflectance in the reflecting member can vary depending upon the polarization direction, because of a polarization characteristic of a reflecting member disposed in the optical system (the illumination optical system or the projection optical system) closer to the wafer than the beam transforming element. In this case, it is desirable to provide offsets on the light intensity distribution formed on or near the illumination pupil, i.e. to provide a distribution of numbers of respective basic elements, in consideration of the reflectance in each polarization direction. The same technique can also be similarly applied to cases where the transmittance in the optical system closer to the wafer than the beam transforming element varies depending upon the polarization direction.
In the foregoing embodiment, the light-source-side surface of the diffractive optical element 50 is of the uneven shape with level differences according to the differences among the thicknesses of respective basic elements 50A-50D. Then the surface on the light source side (entrance side) of the diffractive optical element 50 can also be formed in a planar shape, as shown in FIG. 21, by adding a compensation member 36 on the entrance side of the basic elements except for the first basic elements 50A with the largest thickness, i.e., on the entrance side of the second basic elements 50B, third basic elements 50C, and fourth basic elements 50D. In this case, the compensation member 36 is made of an optical material without optical activity.
The aforementioned embodiment shows the example wherein the beam passing through the illumination pupil distribution formed on or near the illumination pupil has only the linear polarization component along the circumferential direction. However, without having to be limited to this, the expected effect of the present invention can be achieved as long as the polarization state of the beam passing through the illumination pupil distribution is a state in which the principal component is linearly polarized light having the polarization direction along the circumferential direction.
The foregoing embodiment uses the diffractive optical element consisting of the plural types of basic elements having the diffracting action, as the beam transforming element for forming the light intensity distribution of the shape different from the sectional shape of the incident beam, on the predetermined plane, based on the incident beam. However, without having to be limited to this, it is also possible to use as the beam transforming element a refracting optical element, for example, consisting of plural types of basic elements having refracting surfaces virtually optically equivalent to the diffracting surfaces of the respective basic elements, i.e., consisting of plural types of basic elements having the refracting action.
The exposure apparatus according to the foregoing embodiment is able to produce microdevices (semiconductor elements, image pickup elements, liquid crystal display elements, thin-film magnetic heads, etc.) by illuminating a mask (reticle) by the illumination optical apparatus (illumination step) and projecting a pattern for transcription formed on the mask, onto a photosensitive substrate by use of the projection optical system (exposure step). The following will describe an example of a procedure of producing semiconductor devices as microdevices by forming a predetermined circuit pattern on a wafer or the like as a photosensitive substrate by means of the exposure apparatus of the foregoing embodiment, with reference to the flowchart of FIG. 22.
The first step 301 in FIG. 22 is to deposit a metal film on each of wafers in one lot. The next step 302 is to apply a photoresist onto the metal film on each wafer in the lot. Thereafter, step 303 is to sequentially transcribe an image of a pattern on a mask into each shot area on each wafer in the lot, through the projection optical system by use of the exposure apparatus of the foregoing embodiment. Subsequently, step 304 is to perform development of the photoresist on each wafer in the lot, and step 305 thereafter is to perform etching with the resist pattern as a mask on each wafer in the lot, thereby forming a circuit pattern corresponding to the pattern on the mask, in each shot area on each wafer. Thereafter, devices such as semiconductor elements are produced through execution of formation of circuit patterns in upper layers and others. The semiconductor device production method as described above permits us to produce the semiconductor devices with extremely fine circuit patterns at high throughput.
The exposure apparatus of the foregoing embodiment can also be applied to production of a liquid crystal display element as a microdevice in such a manner that predetermined patterns (a circuit pattern, an electrode pattern, etc.) are formed on a plate (glass substrate). An example of a procedure of this production will be described below with reference to the flowchart of FIG. 23. In FIG. 23, pattern forming step 401 is to execute a so-called photolithography step of transcribing a pattern on a mask onto a photosensitive substrate (a glass substrate coated with a resist or the like) by use of the exposure apparatus of the foregoing embodiment. In this photolithography step, the predetermined patterns including a number of electrodes and others are formed on the photosensitive substrate. Thereafter, the exposed substrate is subjected to steps such as a development step, an etching step, a resist removing step, etc., to form the predetermined patterns on the substrate, followed by next color filter forming step 402.
The next color filter forming step 402 is to form a color filter in which a number of sets of three dots corresponding to R (Red), G (Green), and B (Blue) are arrayed in a matrix, or in which a plurality of sets of filters of three stripes of R, G, and B are arrayed in the direction of horizontal scan lines. After the color filter forming step 402, cell assembly step 403 is carried out. The cell assembly step 403 is to assemble a liquid crystal panel (liquid crystal cell), using the substrate with the predetermined patterns obtained in the pattern forming step 401, the color filter obtained in the color filter forming step 402, and so on.
In the cell assembly step 403, for example, a liquid crystal is poured into the space between the substrate with the predetermined patterns obtained in the pattern forming step 401 and the color filter obtained in the color filter forming step 402 to produce the liquid crystal panel (liquid crystal cell). Thereafter, module assembly step 404 is carried out to attach such components as an electric circuit, a backlight, and so on for implementing the display operation of the assembled liquid crystal panel (liquid crystal cell), to complete the liquid crystal display element. The production method of the liquid crystal display element described above permits us to produce the liquid crystal display elements with extremely fine circuit patterns at high throughput.
The foregoing embodiment is arranged to use the KrF excimer laser light (wavelength: 248 nm) or the ArF excimer laser light (wavelength: 193 nm) as the exposure light, but, without having to be limited to this, the present invention can also be applied to other appropriate laser light sources, e.g., an F₂laser light source for supplying laser light of the wavelength of 157 nm. Furthermore, the foregoing embodiment described the present invention, using the exposure apparatus with the illumination optical apparatus as an example, but it is apparent that the present invention can be applied to ordinary illumination optical apparatus for illuminating the surface to be illuminated, except for the mask and wafer.
In the foregoing embodiment, it is also possible to apply the so-called liquid immersion method, which is a technique of filling a medium (typically, a liquid) with a refractive index larger than 1.1 in the optical path between the projection optical system and the photosensitive substrate. In this case, the technique of filling the liquid in the optical path between the projection optical system and the photosensitive substrate can be selected from the technique of locally filling the liquid as disclosed in PCT International Publication No. WO99/49504, the technique of moving a stage holding a substrate as an exposure target in a liquid bath as disclosed in Japanese Patent Application Laid-Open No. 6-124873, the technique of forming a liquid bath in a predetermined depth on a stage and holding the substrate therein as disclosed in Japanese Patent Application Laid-Open No. 10-303114, and so on. The PCT International Publication No. WO99/49504, Japanese Patent Application Laid-Open No. 6-124873, and Japanese Patent Application Laid-Open No. 10-303114 are incorporated herein by reference.
The liquid is preferably one that is transparent to the exposure light, that has the refractive index as high as possible, and that is stable against the projection optical system and the photoresist applied to the surface of the substrate; for example, where the exposure light is the KrF excimer laser light or the ArF excimer laser light, pure water or deionized water can be used as the liquid. Where the F₂laser light is used as the exposure light, the liquid can be a fluorinated liquid capable of transmitting the F₂laser light, e.g., fluorinated oil or perfluoropolyether (PFPE).
From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.

Claims

1. An apparatus which illuminates a surface to be illuminated with radiation from a radiation source, the apparatus comprising:
a polarization state converter arranged in an illumination path;

a first crystal optical element having a first thickness along an optical axis direction; and

a second crystal optical element having a second thickness along an optical axis direction;

wherein the first and second crystal optical elements are arranged in a plane disposed in an illumination path of the apparatus.
2. The apparatus according to claim 1, wherein the plane is arranged in the illumination path between the polarization state converter and the surface to be illuminated.
3. The apparatus according to claim 2, wherein the first and second crystal optical elements are made of an optical material with optical activity.
4. The apparatus according to claim 3, wherein optic axes of the optical material of the first and second crystal optical elements are aligned along the optical axis direction of the apparatus.
5. The apparatus according to claim 4, wherein the first and second thicknesses are different.
6. The apparatus according to claim 2, further comprising:
a diffractive surface arranged in an illumination path of the apparatus which generates a first diffracted radiation and a second diffracted radiation from the radiation from the radiation source, the first and second diffracted radiations reach different regions on an illumination pupil of the apparatus.
7. The apparatus according to claim 6, wherein the diffractive surface includes a first diffractive surface arranged between the first crystal optical element and the illumination pupil, and a second diffractive surface arranged between the second crystal optical element and the illumination pupil.
8. The apparatus according to claim 2, further comprising an optical integrator arranged between the first and second crystal optical elements and the surface to be illuminated.
9. The apparatus according to claim 2, further comprising:
a diffractive surface which is arranged in an illumination path of the apparatus, and which forms a first region distribution of the predetermined light intensity distribution and a second region distribution of the predetermined light intensity distribution on the basis of radiation from the radiation source,

the first crystal optical element provides a first rotation angle to an incident linearly polarized radiation, and the linearly polarized radiation from the first crystal optical element propagates to the first region distribution;

the second crystal optical element provides a second rotation angle to an incident linearly polarized radiation, the second thickness differs from the first thickness, and the linearly polarized radiation from the second crystal optical element propagates to the second region distribution.
10. The apparatus according to claim 9, further comprising an optical integrator arranged between the first and second crystal optical elements and the surface to be illuminated.
11. The apparatus according to claim 10, wherein the diffractive surface is arranged between the first and second crystal optical elements and the surface to be illuminated.
12. The apparatus according to claim 9, wherein the diffractive surface is arranged between the first and second crystal optical elements and the surface to be illuminated.
13. The apparatus according to claim 2, wherein the first crystal optical element and the second crystal optical element are integrally formed.
14. The apparatus according to claim 2, further comprising a polarization monitor arranged downstream of the first and second crystal optical elements.
15. The apparatus according to claim 1, wherein a polarization state of the beam from the first and second crystal optical elements is based on an influence of an optical member disposed in an illumination path between the light source and the surface to be illuminated.
16. The apparatus according to claim 15, wherein the optical member includes a reflective member.
17. An exposure apparatus comprising the apparatus as defined in claim 1, wherein the exposure apparatus illuminates a predetermined pattern, and projects an image of the predetermined pattern onto a photosensitive substrate on the surface to be illuminated.
18. The exposure apparatus according to claim 17, wherein an illumination pupil distribution on or near an illumination pupil of the apparatus is a distribution in at least a part of a predetermined annular region centered around an optical axis of the apparatus.
19. The exposure apparatus according to claim 17, wherein a polarization state of the beam from the first and second crystal optical elements is set based on an influence of an optical member disposed in an illumination path between the light source and the photosensitive substrate on the surface to be illuminated.
20. The exposure apparatus according to claim 19, wherein the optical member includes a reflective member.
21. The exposure apparatus according to claim 17, wherein a polarization state of the beam at an illumination pupil is set so that light illuminating the photosensitive substrate is in a polarization state in which a principal component is s-polarized light.
22. An exposure method comprising:
illuminating a predetermined pattern using the exposure apparatus as defined in claim 17, and

projecting an image of the predetermined pattern onto a photosensitive substrate.
23. A device manufacturing method comprising:
illuminating a predetermined pattern using the exposure apparatus as defined in claim 17;

projecting an image of the predetermined pattern onto a photosensitive substrate; and

developing the photosensitive substrate.
24. An exposure method comprising:
supplying radiation;

passing the supplied radiation through a polarization state converter,

passing the radiation from the polarization state converter through a first crystal optical element having a first thickness along a traveling direction of an incident radiation,

passing the radiation from the polarization state converter through a second crystal optical element having a second thickness along the traveling direction of an incident radiation, the first and second thicknesses being different from each other, the first and second crystal optical elements arranged in a plane crossing the traveling direction; and

projecting an image of a pattern illuminated with the radiation passed through the first and second crystal optical elements, onto a photosensitive substrate.
25. The method according to claim 24, wherein the first and second crystal optical elements are made of an optical material with optical activity.
26. The method according to claim 25, wherein optic axes of the optical material of the first and second crystal optical elements are aligned along the traveling direction of the radiation.
27. The method according to claim 26, further comprising:
generating a first diffracted radiation and a second diffracted radiation, the first and second diffracted radiations reach different regions on an illumination pupil;

optically rotating the first diffracted radiation with the first crystal optical element; and

optically rotating the second diffracted radiation with the second crystal optical element, wherein

the first and second crystal optical elements have thicknesses different from each other along a direction of transmission of the radiation.
28. The method according to claim 27, further comprising projecting the radiations from the first and second crystal optical elements through an optical integrator.
29. The method according to claim 28, wherein the first and second diffracted radiations are generated by radiations from the first and second crystal optical elements.
30. The method according to claim 24, wherein the first crystal optical element and the second crystal optical element are integrally formed.
31. The method according to claim 24, wherein polarization states of beams from the first and second crystal optical elements are set based on an influence of an optical member in an illumination path between a light source of the radiation and a substrate arranged on the surface to be illuminated.
32. The method according to claim 31, wherein the optical member is reflective.
33. A device manufacturing method comprising:
projecting an image of a pattern onto a photosensitive substrate using the exposure method according to claim 24; and

developing the photosensitive substrate.