JPH1079337A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress high-order spherical aberration fluctuation in the case of zonal illumination or irregular illumination. SOLUTION: A partially polarizing plate 10 which allows linear polarized components to pass through in a circular region 25 in the vicinity of a light axis AX, and which allows illumination light to pass through as it is in a zonal region 26 is provided on an illumination system pupil face PS2 conjugate with a pupil face PS1 of a projection optic system 13, and a polarizing plate 14 which allows linear polarized components orthogonal to a polarizing direction of the region 25 of the partially polarizing plate 10 to pass through is provided between the projection optic system 13 and a wafer 15, whereby high resolution similar to that with zonal illumination is obtained. In this case, since the linear polarized components which have passed through the zonal region at the center pass through in addition to a light flux which has passed through a zonal region of the partially polarizing plate 10 in the projection optic system 13, an illumination distribution in the projection optic system 13 can be leveled, so that the linear polarized components are shielded by the polarizing plate 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, a liquid crystal display device, an image pickup device (CCD or the like), a thin film magnetic head, or the like by using a photolithography process to form an image of a pattern on a mask on a photosensitive substrate. The present invention relates to a projection exposure apparatus that is used for performing exposure to an object, and is particularly suitable for application to a projection exposure apparatus that performs annular illumination or the like or uses a center-shielded pupil filter.

[0002]

2. Description of the Related Art Conventionally, for example, when manufacturing a semiconductor device, a wafer (or a photoresist (photosensitive substrate) coated with a photoresist as a photosensitive substrate via a projection optical system is used to project a pattern image of a reticle (or a photomask or the like) as a mask. A projection exposure apparatus such as a stepper for transferring onto a glass plate or the like is used. In these projection exposure apparatuses, in order to expose a pattern with the highest degree of integration onto a wafer, illumination light having the shortest possible wavelength is used as exposure light, and the numerical aperture (NA) of the projection optical system is increased. Efforts have been made to increase the resolution of.

However, if the numerical aperture of the projection optical system is simply increased, the depth of focus becomes too narrow. Therefore, a certain depth of focus or more is secured without depending on the numerical aperture, and high resolution is obtained. As a method, an illumination method of illuminating the reticle with the exposure light inclined has been developed. This illumination method includes an annular illumination in which the shape of a secondary light source of an illumination optical system is an annular shape and a shape of the secondary light source is a plurality (for example, four) of small light sources decentered from an optical axis, so-called deformation. There is lighting etc. According to such an illumination method, the resolution of the projection optical system is improved even with the same exposure wavelength and the same numerical aperture of the projection optical system. Also, a method has been developed in which a pupil filter having a ring shape or the like is arranged on the pupil plane of the projection optical system to improve the resolution by so-called “super-resolution”.

[0004]

In the above prior art, an illumination method for illuminating a reticle with exposure light which is uniformly distributed around a light beam perpendicularly incident on the reticle without using annular illumination or the like. According to the method, an image of the pattern is formed on a wafer mainly by three light beams of the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light that have passed through the reticle pattern. The lens is almost uniformly illuminated both at the center and at the periphery. In addition, even when an annular pupil filter that blocks a central portion is not arranged on the pupil plane of the projection optical system under a normal illumination method, the lens near the pupil plane of the projection optical system is uniformly illuminated. . In such an illuminated state, the temperature at the center of the lens mainly increases,
Thermal deformation and a change in the refractive index, which are functions of the second order or less with respect to the position, mainly occur, and only the movement of the Gaussian image plane occurs as the main aberration fluctuation near the optical axis. Therefore, there was little possibility that high-order spherical aberration fluctuation of the projection optical system would occur.

However, when illumination is performed by the annular illumination or the modified illumination method, when the illumination light for exposure that has passed through the pattern of the reticle is mainly the 0th-order diffracted light and the 1st-order diffracted light, the pattern is formed on the wafer. Therefore, when there are many patterns close to the critical line width of the resolution of the projection optical system, the amount of light transmitted near the optical axis of the projection optical system is extremely small as compared with the peripheral portion. Also, even if a pupil filter that shields the vicinity of the optical axis is arranged on the pupil plane of the projection optical system,
The amount of light rays passing near the optical axis of the lens disposed closer to the wafer than the pupil plane is extremely small as compared with the peripheral part.

[0006] When the distribution of the irradiation energy to the lens of the projection optical system becomes non-uniform as described above, a phenomenon occurs in which the peripheral portion of the lens mainly absorbs heat and the temperature rises, and the central portion does not rise. In proportion to such a temperature rise, the refractive index of the lens partially fluctuates or the lens is thermally deformed, so that a higher-order aspherical surface than the second-order and a corresponding refractive index distribution are newly added. It is formed. For this reason, in a portion close to the optical axis of the projection optical system, there is an inconvenience that not only the movement of the Gaussian image plane but also a new high-order spherical aberration fluctuation occurs due to the irradiation of the illumination light.

[0007] In view of the above, the present invention provides a high-order spherical surface of a projection optical system when performing exposure using annular illumination, modified illumination, or the like, or using a pupil filter that blocks light near the optical axis. It is an object of the present invention to provide a projection exposure apparatus capable of obtaining high resolution while suppressing aberration fluctuation.

[0008]

A projection exposure apparatus according to the present invention comprises a projection optical system (13) for projecting an image of a pattern on a mask (12) onto a photosensitive substrate (15) under exposure light (IL). ), And among the exposure light (IL), a light flux emitted obliquely from the mask (12) or a light flux obliquely incident on the mask (12) as an effective imaging light flux A projection exposure apparatus to be used, wherein an optical axis (AX) is substantially defined on a pupil plane (PS1) of the projection optical system (13), that is, a plane conjugate with an optical Fourier transform plane with respect to a pattern plane of the mask. An illumination optical system (7 to 9, which illuminates the mask (12) using the exposure light (IL) from the light source (6C) (including the secondary light source) uniformly distributed in the center circular region. 11) and the pupil plane (PS1) of the projection optical system (13), or On the pupil plane and a plane conjugate (PS2), a region (26 in which the effective imaging light beam passes; 27A
To 27D; region other than 26A) (25; 28; 25A)
A first polarizing member (10; 10A; 10C) for setting the polarization direction of the exposure light (IL) passing through the first direction to a predetermined direction, and disposed between the projection optical system (13) and the photosensitive substrate (15). And a second polarizing member (14) for shielding a light beam polarized in the predetermined direction from the exposure light (IL) having passed through the projection optical system (13).

According to the projection exposure apparatus of the present invention, when the light flux emitted obliquely from the mask (12) is used as an effective imaging light flux, the first polarizing member (10C) is used.
Are arranged on the pupil plane and function substantially as a pupil filter of a central light shielding type. On the other hand, when the light beam obliquely incident on the mask (12) is used as an effective image-forming light beam, the first polarizing member (10; 10A) is provided in the illumination optical system by the projection optical system. Arranged on a plane conjugate with the pupil plane, the illumination is performed substantially by the annular illumination or the modified illumination method.

The first polarizing member (10; 10A;
10C) and the second polarizing member (14), the effective image-forming light beam and the light beam polarized in a predetermined direction by the first polarizing member are combined and passed. Therefore, the illuminance distribution of the projection optical system (13) disposed between the first polarizing member (10; 10A; 10C) and the second polarizing member (14), particularly in the lens near the pupil plane (PS1), is reduced. Higher order thermal deformation and change in refractive index of the lens near the pupil plane (PS1) are suppressed, and as a result, higher order spherical aberration fluctuation of the projection optical system (13) is suppressed. Moreover,
The light beam other than the imaging light beam is transmitted to the second polarizing member (14).
As a result, high resolution can be obtained on the photosensitive substrate.

In this case, the first polarizing member (10; 10)
A; 10C) is an example of a region (25; 25A) inside a ring-shaped region around the optical axis (AX) or a region (28) excluding a plurality of regions (27A to 27D) eccentric from the optical axis. ) Is a member for setting the polarization direction of the exposure light (IL) passing through the predetermined direction. When the first polarizing member is a member (10; 10C) for setting the polarization direction in a region other than the region inside the annular region to the predetermined direction, an annular illumination or a center light shielding type pupil filter is used. It is equivalent to the case. On the other hand, when the first polarizing member is a member (10A) for setting the polarization direction in a region other than a plurality of regions decentered from the optical axis to the predetermined direction, it is equivalent to the case where the modified illumination method is used.

The first polarizing member (10; 10A;
10C) and the driving means (21 to 2) that rotate the second polarizing member (14) while maintaining a constant relative angular relationship.
Preferably, 3) is provided. During the exposure, the first polarizing member (10; 10A; 10C) and the second polarizing member (1
By rotating 4), the polarization direction of the exposure light incident on the photosensitive substrate (15) is rotated. Therefore, regardless of the periodic direction of the mask pattern, occurrence of line width abnormality of the image of the mask pattern formed on the photosensitive substrate (15) can be suppressed. Further, since the first polarizing member (10) and the second polarizing member (14) rotate while maintaining a constant relative angle relationship, the light beam polarized by the first polarizing member (10) is rotated by the first polarizing member (10). The light is reliably shielded by the two polarizing members (14).

Also, the driving means (21 to 23)
Instead of providing a third polarizing member (14) between the second polarizing member (14) and the photosensitive substrate (15) for converting the exposure light (IL) having passed through the second polarizing member (14) into circularly polarized light. A polarizing member (17) may be provided. As a result, the image-forming light beam that forms an image on the photosensitive substrate (15) becomes circularly polarized light, so that the line width abnormality due to the periodic direction of the mask pattern decreases.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a projection exposure apparatus according to the present invention will be described below with reference to FIGS.
This example is a stepper type projection exposure apparatus that projects a pattern on a reticle onto each shot area on a wafer via a projection optical system, and the present invention is applied when substantially annular illumination or deformed illumination is performed. Things.

FIG. 1 is a perspective view seen from the wafer side for explaining the configuration of the projection exposure apparatus of the present embodiment. In FIG. 1, at the time of exposure, a wafer 15 emitted from a light source 1 composed of a mercury lamp is shown. Illumination light IL photosensitive to the upper photoresist is condensed by the elliptical mirror 2, then enters the input lens 3 and an interference filter (not shown), and is irradiated with, for example, i-line (wavelength 365 nm) illumination light by the interference filter. The IL is extracted. As the illumination light IL, besides the i-line, a bright line such as a g-line, an ArF excimer laser beam, a KrF excimer laser beam, or a harmonic of a copper vapor laser or a YAG laser is used.

The illumination light IL is converted into a parallel light beam by the input lens 3 and is incident on a fly-eye lens 4 as an optical integrator. A secondary light source is formed on each exit surface of each lens element of the fly-eye lens 4, and these secondary light sources form a surface light source. On the exit surface of the fly-eye lens 4, one aperture stop selected from a plurality of aperture stops 6A to 6C (see FIG. 2A) is arranged to adjust the size of the surface light source. These aperture stops 6A to 6C are fixed to a turret-shaped disk 5, and a desired aperture stop can be set on the exit surface of the fly-eye lens 4 by rotating the disk 5 by a driving device (not shown).

FIG. 2A is a plan view for explaining a specific configuration of the aperture stop on the disk 5 of FIG. 1. In FIG. 2A, three aperture stops 6A to 6A are shown. 6C are fixed on the turret disk 5 at equal angular intervals. First
The aperture stop 6A has a circular aperture used for normal illumination, and the second aperture stop 6B has a small circular aperture used for illumination with a small coherence factor (σ value). The third aperture stop 6C has a large circular aperture. In this example, the third aperture stop 6C is set on the exit surface of the fly-eye lens 4 when performing annular illumination or deformed illumination. That is, during normal annular illumination, FIG.
An annular aperture stop 6D shown in (b) is used, and an aperture stop 6E having four (or two) small apertures arranged around the optical axis shown in FIG. Is done. However, in this example, the aperture stop 6D and the like are also used substantially by the partial polarizer 10 and the like described later. FIG.
In the figure, the third aperture stop 6C is arranged on the optical path of the illumination light IL.

The illumination light IL that has passed through the aperture stop 6C passes through the first relay lens 7, and the illumination range is defined by a field stop (reticle blind) 8. The illumination light IL whose illumination range is defined passes through the second relay lens 9 and enters the partial polarizer 10. The illumination light IL incident on the partial polarizer 10 is a so-called random polarized light beam composed of random polarized components similarly to natural light. The plane on which the aperture stop 6C is disposed and the plane on which the partial polarizer 10 is disposed (hereinafter referred to as "illumination pupil plane").
PS2) is conjugate.

FIG. 3A is a plan view of the partial polarizing plate 10. In FIG. 3A, the center of the partial polarizing plate 10 is arranged so as to substantially coincide with the optical axis AX of the illumination optical system. And a circular area 25 centered on the optical axis AX is
The polarizing plate transmits only a linearly polarized light component of which the polarization direction is the direction indicated by the arrow in the incident light beam. That is, of the illumination light IL incident on the region 25, only the linearly polarized light component indicated by the arrow passes through the region 25. The arrow indicates the direction of the electric vector (the same applies hereinafter). On the other hand, the illumination light IL that passes through the annular region 26 outside the outer periphery 25A of the circular region 25 passes through the partial polarizer 10 with random polarization. The outer periphery of the annular zone 26 is set to be larger than the outer periphery of the image of the aperture of the aperture stop 6C in FIG. As shown in FIG. 1, the partial polarizing plate 10 is configured to be rotatable by 180 ° about the optical axis AX of the illumination optical system, and is rotated by a rotation angle control system 22 via a rotation driver 21. The rotation angles of the ten optical axes AX are controlled. Further, the partial polarizing plate 10 is configured to be exchangeable with another partial polarizing plate for modified illumination via the rotary driver 21 and to be able to withdraw from the optical path of the illumination light IL at any time.

FIGS. 3 (b) and 3 (c) show a partial polarizing plate for modified illumination. In FIG. 3 (b), four circular plates are formed at equal angular intervals around the partial polarizing plate 10A. Opening 2
7A to 27D are provided, and the surrounding area 28 is a polarizing plate that passes a linearly polarized light component in the direction of the arrow. If the center of the partial polarizing plate 10A is arranged so as to coincide with the optical axis AX of the illumination optical system of FIG. 1, the illumination light IL of random polarization passes through the four circular openings 27A to 27D decentered from the optical axis AX. However, in the other area 28, only the linearly polarized light component passes.

Further, as shown in FIG.
A partial polarizing plate 10B is also used in which two openings 29A and 29B are provided, and a region 30 around the openings 29A and 29B is a polarizing plate that transmits a light beam that is linearly polarized in the direction of the arrow. The opening 29A, 2
The polarization state of the illumination light passing through 9B is also maintained at random polarization. Then, these partial polarizing plates 10A and 10B are also rotated by the rotation driver 21.

In FIG. 1, illumination light IL, which is composed of a randomly polarized light beam and a linearly polarized light beam that has passed through a partial polarizing plate 10, is irradiated onto a reticle 12 by a condenser lens 11. Illumination light IL irradiated on reticle 12
Passes through the pattern area on the reticle 12 and enters the polarizing plate 14 via the projection optical system 13. The polarization characteristics of the polarizing plate 14 are set so that, of the incident light flux, only a component that is linearly polarized in a direction orthogonal to the linearly polarized light component that passes through the circular region 25 of the partial polarizing plate 10 is passed.
The linearly polarized light component passing through the circular region 25 of the partial polarizing plate 10 is shielded by the polarizing plate 14, and the polarization direction of the polarizing plate 14 in the light beam of the randomly polarized light passing through the annular region 26 of the partial polarizing plate 10. Only the parallel linearly polarized light component passes through the polarizer 14 and irradiates the wafer 15. Illumination light IL
, The pattern surface of the reticle 12 and the surface of the wafer 15 are conjugate with respect to the projection optical system 13, and the polarizing plate 1
The image of the pattern on the reticle 12 is transferred onto the wafer 15 by the light beam having passed through the reticle 4.

Further, similarly to the partial polarizing plate 10, the polarizing plate 14 is configured to be rotatable by 180 ° about the optical axis AX, and the rotation angle control system 22 controls the rotation of the polarizing plate 10 via a rotation driver 23. The rotation angle about the optical axis AX is controlled. At this time, the partial polarizer 10 and the polarizer 14 are rotated synchronously in a state where the relative angle relationship is always constant, that is, in a state where the polarization directions of the region 25 of the partial polarizer 10 and the polarizer 14 are orthogonal. You. In this case, the pupil plane PS1 in the projection optical system 13, that is, the optical Fourier transform plane with respect to the pattern plane of the reticle 12, is the arrangement plane of the aperture stop 6C, and thus the partial polarizer 10
Is conjugate with the illumination system pupil plane PS2, which is the arrangement plane of. In FIG. 1, the optical axis AX of the illumination optical system coincides with the optical axis of the projection optical system 13. Hereinafter, the Z axis is taken in parallel with the optical axis AX, and the rectangular coordinates in a two-dimensional plane perpendicular to the Z axis will be described below. The system will be described as an X axis and a Y axis.

The reticle 12 is mounted on a reticle stage (not shown) that is finely movable in the X, Y, and rotation directions. The position of the reticle 12 is precisely measured by an external laser interferometer (not shown), and the position of the reticle 12 is controlled based on the measurement value of the laser interferometer. On the other hand, the wafer 15 is placed on a wafer stage 16 for positioning the wafer 15 in the X, Y and Z directions via a wafer holder (not shown), and the position of the wafer stage 16 in the X and Y directions is controlled by an external laser. It is precisely measured by an interferometer, and the position of the wafer stage 16 is controlled based on the measured value. The operation of moving the center of each shot area of the wafer 15 to the exposure center of the projection optical system 13 by the wafer stage 16 and the exposure operation are repeated in a step-and-repeat manner, so that the image of the pattern on the reticle 12 is The image is sequentially transferred to each upper shot area.

Next, the exposure operation of the projection exposure apparatus of this embodiment will be described. First, when performing annular illumination in this example,
As shown in FIG. 1, an aperture stop 6C having a large aperture is set on the exit surface of the fly-eye lens 4, and the rotation driver 21 sets the partial polarizer 10 on the optical path of the illumination light IL. In this case, the illumination light IL emitted from the fly-eye lens 4 is
It is a light beam containing all polarization components. Then, due to the partial polarizer 10 disposed on the illumination system pupil plane PS2, the light flux passing through the region 25 near the optical axis AX in the illumination light IL is only a linearly polarized light component. In addition, the illumination light IL passes through the annular zone 26 around the partial polarizer 10 with random polarization. As described above, the reticle 12 is irradiated with the illumination light IL such that the light flux smaller than a certain numerical aperture on the illumination system pupil plane PS2 is linearly polarized light and the peripheral light flux is random polarization.
Is illuminated, the lens near the optical axis AX of the lens near the pupil plane PS1 of the projection optical system 13 mainly transmits linearly polarized light. Therefore, not only the peripheral part but also the central part of the lens absorbs the irradiation energy and the temperature rises, so that the ratio of the second-order fluctuation component to the higher-order fluctuation component in the thermal deformation and the change in the refractive index of the lens increases. Higher order spherical aberration fluctuations are reduced.

The polarizing plate 14 whose polarization direction is orthogonal to the region 25 of the partial polarizing plate 10 is formed by the projection optical system 13 and the wafer 15.
The linearly polarized light component selected by the circular region 25 of the partial polarizer 10 is shielded by the polarizer 14 and does not contribute to the imaging of the wafer 15. However, of the illumination light IL that has passed through the annular region 26 of the partial polarizer 10, a polarized component parallel to the polarization direction of the polarizer 14 is involved in the image formation on the wafer 15, and as a result, FIG.
This is equivalent to a case where annular illumination is performed using an aperture stop 6D having an annular aperture whose center is shielded as shown in FIG.

In this case, since the illumination light IL related to the image formation on the wafer 15 is linearly polarized light, the pattern on the wafer 15 is determined by the angle difference between the polarization direction of the linearly polarized light and the periodic direction of the pattern of the reticle 12. There is a possibility that a line width abnormality that the line widths of the images are different will occur. Therefore, the partial polarization plate 10 and the polarization plate 14 are rotated by the rotation control system 22 during the exposure.
Rotational driving is performed synchronously via the rotary driving bodies 21 and 23 while keeping the polarization directions orthogonal to each other. That is, the partial polarizing plate 10 and the polarizing plate 14 are rotated by 180 ° during the exposure. Thus, occurrence of an abnormal line width of the image of the pattern on the wafer 15 is suppressed regardless of the periodic direction of the pattern of the reticle 12.

Instead of providing a mechanism for rotating the partial polarizer 10 and the polarizer 14 as described above, the line width abnormality caused by the angle difference between the polarization direction of the linearly polarized light and the periodic direction of the reticle pattern is eliminated. As shown by a two-dot chain line in FIG. 1, a １ ／ wavelength plate 1 for converting linearly polarized light to circularly polarized light is provided on the optical path of the illumination light IL between the polarizing plate 14 and the wafer 15.
7 may be arranged. As a result, the imaging light beam incident on the wafer 15 becomes circularly polarized light. Further, the 波長 wavelength plate 17
Alternatively, a half-wave plate may be provided, and the half-wave plate may be rotated. In these cases, the partial polarizer 10
And the rotation mechanism of the polarizing plate 14, that is, the rotation driver 2 of FIG.
1 and 23 and the rotation angle control system 22 can be omitted.

The polarizing plate 14 is provided between the projection optical system 13 and the wafer 15 so that all the lenses of the projection optical system 13 are irradiated with linearly polarized light components passing through the region 25 of the partial polarizing plate 10. It is most desirable to arrange them. However, thermal deformation and refractive index fluctuation due to non-uniform illuminance distribution on the lens near the pupil plane PS1 of the projection optical system 13 greatly contribute to the spherical aberration fluctuation. What is necessary is just to arrange | position at the position near the wafer 15 with respect to the pupil plane PS1.

Further, as shown in FIG.
Is arranged on the illumination system pupil plane PS2, the center of the lens near the pupil plane PS1 of the projection optical system 13 is mainly irradiated with linearly polarized light, and the peripheral part is mainly irradiated with random polarized light. The randomly polarized light is
It can be regarded as a light beam in which two mutually orthogonal linearly polarized light components are mixed by １ ／. Therefore, the center of the lens near the pupil plane PS1 is １ ／ of the periphery of the lens.
Irradiation energy density. For this reason, if the high-order spherical aberration fluctuation does not become sufficiently small, the illumination system pupil plane PS2
It is necessary to lower the illuminance in the annular zone 26 of the partial polarizing plate 10. For this purpose, an ND filter (Neutral Density filte) for weakening the light intensity in the annular zone 26 is used.
r) may be provided.

Next, in the case of performing the deformed illumination, the rotational drive 21 shown in FIG.
The partial polarizing plate 10A of FIG. 3B or the partial polarizing plate 10B of FIG. At this time, the partial polarizing plate 10A
The linearly polarized component of the illumination light IL that has passed through the region 28 other than the two openings 27A to 27D or the region 30 other than the two openings 29A and 29B of the partial polarizer 10B is the pupil plane of the projection optical system 13 in FIG. Since the light passes through the vicinity of the optical axis of the lens near PS1, fluctuations in high-order spherical aberration are suppressed. Further, since the linearly polarized light component is shielded by the polarizing plate 14, it is substantially equivalent to the case of performing deformed illumination, and a high resolution can be obtained for a predetermined periodic pattern.

In particular, when the partial polarizing plate 10B shown in FIG. 3C is used, the resolution may be improved as compared with the case where openings are provided in four localized portions as shown in FIG. 3B. That is, when the partial polarizing plate 10B is used, as a result, the wafer 15 is illuminated by linearly polarized light inclined in a direction perpendicular to the polarization direction. This partial polarizing plate 1
By providing a mechanism for rotating OB at least 180 ° during one exposure, the inclination direction and the polarization direction of the illumination become perpendicular to the periodic pattern in all directions. This is the same as that in which an annular polarizer that polarizes in a direction perpendicular to the radial direction (circumferential direction) is disposed in the illumination optical system, as disclosed in Japanese Patent Application Laid-Open No. 6-53120. There is an effect of improving the resolution. The effect of improving the resolving power is described in detail in Japanese Patent Application Laid-Open No. Hei 6-53120, and a description thereof will be omitted.

Next, when exposure is performed by a normal illumination method, the aperture stop 6A or 6B shown in FIG. 2A is set on the exit surface of the fly-eye lens 4 shown in FIG.
1 illuminates the partial polarizers 10, 10A, 10B with illumination light I
Retreat from the optical path of L. Further, the polarizing plate 14 may also be retracted. Thereby, normal exposure is performed. In the above-described embodiment, a polarizing beam splitter may be used instead of the partial polarizing plate 10 and the polarizing plate 14. When a polarization beam splitter is used instead of the circular area 25 of the partial polarizing plate 10, the surrounding area may be, for example, a transparent area.

Next, another embodiment of the projection exposure apparatus of the present invention will be described with reference to FIG. In this example,
The present invention is applied to a case where a pupil filter of a substantially central light shielding type is used. In FIG. 4, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.
FIG. 4 is a perspective view showing a schematic configuration of the projection exposure apparatus of the present embodiment. In FIG. 4, the reticle 12 is a light source 1 shown in FIG.
Illumination is performed by the same illumination optical system as the illumination optical system from to the condenser lens 11. However, in the illumination optical system (not shown) of this example, the partial polarizer 10 and the like in FIG. 1 are not provided. That is, the reticle 12 in FIG. 4 is illuminated by the randomly polarized illumination light IL. Hereinafter, for simplicity, the projection optical system 13 will be described by dividing it into an upper lens system 13A and a lower lens system 13B. As shown in FIG. 4, a partial polarizer 10C similar to the partial polarizer 10 of FIG. 1 is provided near the pupil plane PS1 of the projection optical system 13 of this example. The illumination light IL of random polarization incident on the upper lens system 13A from the reticle 12 is incident on the partial polarizer 10C. The partial polarizing plate 10C is a polarizing plate in which a circular region 25A centered on the optical axis AX passes a linearly polarized light component in the direction indicated by the arrow, and a ring-shaped region 26A around the circular region 25A allows a light beam of random polarization to pass as it is. It has become. Of the illumination light IL that has entered the partial polarizing plate 10C, the linearly polarized light component that has passed through the region 25A and the randomly polarized light beam that has passed through the region 26A are transmitted through the lower lens system 13B, and are in the region of the partial polarizing plate 10C. The light is incident on a polarizing plate 14 that passes a linearly polarized light component orthogonal to the polarization direction of 25A.
Then, the image of the pattern on the reticle 12 is transferred onto the wafer 15 by the linearly polarized light component that has passed through the polarizing plate 14. Note that, also in this example, the partial polarizing plate 10C has the optical axis A
The polarizing plate 14 is configured to be rotatable by 180 degrees around X, and the polarizing plate 14 is also driven to rotate in synchronization with the partial polarizing plate 10C and keeping the polarization directions orthogonal to each other.

According to the present embodiment, the circular area 25A of the partial polarizing plate 10C is included in the image forming light beam incident on the projection optical system 13.
Pass only the linearly polarized light component, and this linearly polarized light component is shielded by the polarizing plate 14. Therefore, the projection optical system 1
This is equivalent to a case where a pupil filter having a ring-shaped aperture is arranged on the third pupil plane PS1, and high resolution can be obtained.
In addition, since the central part of the lens of the lower lens system 13B is also irradiated with the linearly polarized light component, thermal deformation and change in the refractive index in the projection optical system 13 due to non-uniform illuminance distribution are suppressed. , The higher-order aberration fluctuation component decreases.

Further, since the partial polarizers 10C and the polarizers 14 are rotatable by 180 ° and are driven so as to maintain the same angular relationship in synchronization with each other, the two polarizers 10C and 14 are moved during exposure. For example, by rotating 180 degrees,
The occurrence of abnormal line width based on the periodic direction of the pattern of the reticle 12 is suppressed. In addition, similarly to the embodiment of FIG.
1/4 on the optical path between the polarizing plate 14 and the wafer 15 in FIG.
If a wavelength plate is installed and the light beam linearly polarized by the polarizing plate 14 is converted into circularly polarized light, the light is caused by the periodic direction of the pattern without providing a mechanism for rotating the partial polarizing plate 10C and the polarizing plate 14. No line width abnormality occurs.

Next, in the above-described embodiment, the fact that the illuminance distribution to the lens of the projection optical system 13 is made uniform and high-order aberration fluctuation is suppressed will be described based on a calculation example. First, the temperature distribution after the rise due to the illumination light irradiation is calculated. By approximating the lens to a cylindrical shape, heat does not flow out from the side of the lens through the surrounding air, and when the edge of the lens comes into contact with metal, heat flows out only from that edge and the absorbed energy density distribution in the lens changes to light. It is assumed that the angle is constant with respect to the angle around the axis AX. Assuming that a variable representing the radial distance of the lens is r, the temperature distribution after the rise is a variable r
Where T (r) is the heat absorption amount and thermal conductivity per unit volume of the lens, and a is the outer radius of the lens. In the cylindrical coordinate system in a thermal equilibrium state, The heat conduction equation can be expressed as the following equation.

[0038]

１ ² T / ∂r ² + (1 / r) ∂T / ∂r + ω
(R) / λ = 0 By solving this heat conduction equation, the following equation is obtained.

[0039]

(Equation 2)

Here, J _n (p _i · r) is a Bessel function of the n-th order (n = 0, 1, 2,...) Of the first kind.
p _i is a sequence satisfying J ₁ (p _i · a) = 0 (i =
1, 2, 3, ...). The coefficient B _i is obtained by the following equation.

[0041]

(Equation 3)

In particular, when the heat absorption ω (r) is represented by a step-like function within the irradiation diameter, that is, at a certain j (1 ≦ j ≦ N), the variable r becomes h _j ≦ r ≦ h in the section that satisfies _{j + 1,} when the heat absorption amount omega (r) takes a constant value omega _j, the following relation is established.

[0043]

(Equation 4)

[0044] Thus, equation (4) coefficient B _i is obtained by substituting the (number 3), the coefficients B _i (Equation 2)
To obtain the temperature distribution T (r) after the rise. Then, the increase after the temperature distribution T (r), r ¹⁰ to determine which order of aberration variation occurs more, the temperature distribution T after rise (r) with a minimum square method as follows
When the power series is expanded up to the term, the following equation is obtained.

[0045]

T (r) = T ₀ + C ₂ · r ² + C ₄ · r ⁴ + C
₆ · r ⁶ + C ₈ · r ⁸ + C ₁₀ · r ^{10 In} this case, the unit of the temperature distribution T (r) after the rise is ° C., and the unit of the variable r is mm. T ₀ is the optical axis AX, that is, the temperature distribution T (0) after the rise at the position where the variable r is 0.

Hereinafter, a calculation example based on actual numerical values will be described. The value (coherence factor) of the ratio of the numerical aperture on the exit side of the illumination optical system to the numerical aperture (NA) on the entrance side of the projection optical system is defined as a σ value, and this σ value is set to 0.75. An outer radius of 4 is obtained by an illumination system having a σ value of 0.75.
In a case where a lens made of quartz having a cylindrical shape of 0 mm is illuminated and the irradiation radius d on the lens is 30 mm, calculation is performed based on the solutions of the heat conduction equations of (Equation 2) to (Equation 4). The thermal conductivity of quartz is 0.0138 W / (cm ·
° C), and the absorptivity of the light energy of the lens to the illumination light sensitive to the photoresist on the wafer is 2% / cm.

In the first calculation example, first, for comparison, calculation is performed for a case where the total irradiation energy of the illumination light is 1 W and the lens is uniformly irradiated within a range of σ of 0.75. FIG. 5A shows the temperature distribution T (r) after the rise according to the first calculation example, where the horizontal axis represents the variable r and the vertical axis represents the temperature distribution T (r) after the rise. As shown by the solid curve 31A, the temperature distribution T (r) after the rise has a maximum value TA at the origin, that is, the optical axis AX, and shows a mountain-shaped change that is axially symmetric with respect to the optical axis AX. For reference, the irradiation energy density distribution P (r) of the illumination light is indicated by a dotted line 32A. In the irradiation energy density distribution P (r), the variable r is 0 to d (irradiation radius).
Is constant P1. Further, Table 1 shows coefficients C _{2 to} C ₁₀ when the temperature distribution T ₀ on the optical axis AX and the temperature distribution T (r) are expanded into a power series by (Equation 5).

[0048]

[Table 1]

Next, a second calculation example will be described. This calculation example is an example in the case where the annular illumination or the pupil filter is used, and is a calculation example for comparison as in the first calculation example. The σ value is 0.75 at the maximum, and the σ value inside the annular zone is 0.
5 The temperature distribution T (r) after the rise is calculated when the lens is uniformly illuminated when the σ value is in the range of 0.5 to 0.75 and the total irradiation energy amount is 1 W.

FIG. 5B shows the temperature distribution T (r) after the rise according to the second calculation example.
As shown by the solid line curve 31B, the temperature distribution T
(R) is a constant temperature TB when the variable r is substantially between 0 and e. Irradiation energy density distribution P (r) indicated by dotted line 32B
Indicates that the variable r has a constant value P2 between e and d, and the variable r
Is 0 between 0 and e. Similarly to the first calculation example, the coefficients C ₂ to C ₂ when the temperature distribution T ₀ after the rise on the optical axis AX and the temperature distribution T (r) after the rise are expanded into a power series by (Equation 5). Table ₁₀ shows Table ₁₀ .

[0051]

[Table 2]

Next, a third calculation example will be described. This calculation example is similar to the embodiment shown in FIG. 1 and FIG.
The temperature distribution T (r) after the rise when the lens is illuminated using the partial polarizer 10 or 10C is determined. In this case, when the σ value is in the range of 0.75 to 0.5, the lens is uniformly illuminated by the randomly polarized light at a total irradiation energy of 1 W, and the σ value is in the range of 0.5 to 0.0. In, it is assumed that the lens is illuminated by the illumination with the linearly polarized light component at an irradiation energy density of 1/2 of the σ value in the range of 0.75 to 0.5.

FIG. 5C shows the temperature distribution T (r) after the rise according to the third calculation example.
As shown by the solid curve 31C, the temperature distribution T
(R) has a maximum value TC at the origin, that is, the optical axis AX, and shows a mountain-shaped change that is axially symmetric with respect to the optical axis AX. Further, the irradiation energy density distribution P (r) changes in a stepped manner with a dotted line 32.
C, the variable r takes a constant value P2 between e and d, and a constant value P3 (= (1/1 /
2) and P2). Table 3 shows coefficients C _{2 to} C ₁₀ when the temperature distribution T ₀ and the temperature distribution T (r) on the optical axis AX are expanded into a power series by (Equation 5).

[0054]

[Table 3]

Note that in the first and second calculation examples,
The total irradiation energy amount is 1 W, and in the third calculation example, the irradiation energy amount is 1 W when the σ value is in the range of 0.75 to 0.5. In the third calculation example, the total irradiation energy exceeds 1 W when the irradiation energy in the range of 0.5 to 0.0 is added. In this case, the irradiation energy amounts of the photosensitive illumination light to the photoresist on the wafer 13 in the first to third calculation examples are set to be equal so that the exposure time (throughput) is equal.

The uniform illumination method shown in the first calculation example and the second
As shown in Tables 1 and 2, when comparing the annular illumination method or the pupil filter method (such as the annular illumination method) shown in the calculation example, the annular illumination method or the like is compared with the uniform illumination method. Thus, the temperature at the optical axis AX is low. Nevertheless, for example when comparing the coefficient C ₄ of the power series, the value of the coefficient C ₄ in the case of uniform illumination scheme, relative to 4.4000 × 10 ^-8, the coefficient in the case of such annular illumination method C ₄ is 2.73
It is 28 × 10 ^-7, which is larger for the ring illumination system and the like. That is, when comparing the uniform illumination method and the zonal illuminating method and the like, the absolute value of the coefficients of the power series other than the coefficient C ₂ is better for all such annular illumination system is large. Since the thermal deformation and the change in the refractive index are proportional to the temperature distribution T (r) after the rise, the aberration fluctuation is also proportional to the temperature distribution T (r) after the rise. That the coefficient of the high-order power series from the coefficient C ₂ is greater in all such annular illumination scheme means that people, such as annular illumination system is large higher order aberrations change.

Here, if the exposure method of the embodiment shown in FIGS. 1 and 4 is a "partial polarizing plate system", the vicinity of the optical axis is irradiated with a linearly polarized light component by this partial polarizing plate system.
As shown in the third calculation example, in spite of more than the total dose is uniform illumination method and annular illumination method, and the like, as shown in Table 3 and Table 2, the value of the coefficient C ₄ (= 1.7624 × 1
0 ^-7 ) is the value of the coefficient C ₄ (= 2.7) in the annular illumination system or the like.
328 × 10 ⁻⁷ ). Further, comparing the absolute values of the coefficients C ₆ , C ₈ , and C ₁₀ , the partial polarizing plate method is smaller than the annular illumination method or the like in any of the coefficients. This means that high-order aberration fluctuation is reduced by the partial polarizing plate method.

In the third calculation example, the σ value is 0
The irradiation energy density between 0.5 and 0.5 was の of the density distribution when the σ value was between 0.5 and 0.75. On the other hand, for example, an ND filter is used as described above so that the σ value is irradiated with a uniform irradiation energy distribution in the range of 0 to 0.75, or
Alternatively, as shown in FIGS. 3 (b) and 3 (c), the temperature distribution T when only randomly polarized light is transmitted using the modified illumination method and linearly polarized light components are transmitted in other portions. (R) is calculated and compared with the case of the annular illumination system shown in FIG. In this case, the total irradiation amount of the randomly polarized light transmitted through the poled portions in FIGS. 3B and 3C is set to 1 W.

In this case, the total irradiation amount T applied to the lens
P (W) is obtained by the following equation. TP = 1W ・ 0.75^Two /(0.75^Two -0.5^Two ) =
1.8W Therefore, in the partial polarizing plate method as shown in FIG.
Irradiation with a σ value within 0.5 is equal to the surrounding area
In the case of irradiation at the energy density, the uniformity shown in FIG.
In the illumination method, the irradiation energy density was 1.8 times
Equivalent to state. Therefore, all coefficients of the power series are shown in Table 1.
Is 1.8 times the value of_Four, C₆, C₈,
C_TenAre 7.9200 × 10^-8, -1.782
1 × 10 ^-Ten , 1.4937 × 10^-13 , -3.734
1 × 10^-17 Becomes Table 2 shows the values of these coefficients.
Temperature after the rise near the optical axis AX
Distribution T₀ Is considerably larger than in the case of annular lighting
Nevertheless, the coefficient C_Four ~ C_TenThe factor up to is the ring illumination
All are smaller than in the case of formulas and the like. That is, partial polarization
When the σ value is in the range of 0 to 0.75 in the plate method,
Even when irradiating with irradiation energy density P2, annular illumination
Means that there is less variation in higher-order aberrations than
ing.

The present invention is not limited to the stepper type projection exposure apparatus, and the reticle and the wafer are projected onto the projection optical system while a part of the reticle pattern is projected onto the wafer via the projection optical system. The present invention can be similarly applied to a scanning exposure type projection exposure apparatus such as a step-and-scan method in which a reticle pattern is sequentially transferred and exposed to each shot area on a wafer by synchronous scanning.

As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0062]

According to the projection exposure apparatus of the present invention, after the light flux other than the light flux emitted obliquely from the mask or the light flux obliquely incident on the mask is polarized in a predetermined direction by the first polarizing member. Since the polarized light beam is shielded by the second polarizing member, the light beam imaged on the photosensitive substrate is only a light beam emitted obliquely from the mask or a light beam obliquely incident on the mask. There is an advantage that a high resolution almost equivalent to the case of using a pupil filter of the type or using annular illumination or modified illumination can be obtained. Further, between the first polarizing member and the second polarizing member, an effective imaging light beam and a light beam polarized in a predetermined direction by the first polarizing member pass. Therefore, the illuminance distribution of the lens near the pupil plane of the projection optical system disposed between the first polarizing member and the second polarizing member becomes substantially uniform, and higher-order thermal deformation and refraction of the lens in the projection optical system. There is an advantage that a change in the rate is suppressed, and as a result, a higher-order spherical aberration fluctuation of the projection optical system is suppressed.

Further, the first polarizing member sets the polarization direction of the exposure light passing through a region inside the annular region around the optical axis or a region other than a plurality of regions decentered from the optical axis in a predetermined direction. In such a case, the effective imaging light flux passes through an annular zone around the optical axis or a plurality of areas decentered from the optical axis, passes through the second polarizing member, and forms an image on the photosensitive substrate. On the other hand, light beams other than the effective image forming light beam are shielded by the second polarizing member and do not form an image on the photosensitive substrate. Therefore, when the first polarizing member is on a plane conjugate with the pupil plane of the projection optical system, it becomes equivalent to the case where annular illumination or modified illumination is performed. On the other hand, when the first polarizing member is on the pupil plane and allows linearly polarized light to pass through a region inside the annular region around the optical axis, it is equivalent to using a central light blocking pupil filter. .

In the case where drive means for rotating the first polarizing member and the second polarizing member while maintaining a constant relative angular relationship is provided, the first and second polarizing members are rotated during exposure. Accordingly, there is an advantage that occurrence of an abnormal line width in which the line width of the image of the pattern formed on the photosensitive substrate changes depending on the period direction of the pattern is suppressed.

Further, between the second polarizing member and the photosensitive substrate,
Third, which converts the exposure light having passed through the second polarizing member into circularly polarized light.
When the polarizing member is provided, there is an advantage that abnormal line width due to the periodic direction of the pattern can be suppressed without providing a driving unit for rotating the first and second polarizing members.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an embodiment of a projection exposure apparatus of the present invention.

FIG. 2 is a plan view showing various aperture stops provided in the illumination optical system of FIG. 1;

FIG. 3A is a plan view showing the partial polarizing plate 10 of FIG. 1,
(B) is a plan view showing a partial polarizing plate 10A for modified illumination,
(C) is a plan view showing another example of the partial polarizing plate.

FIG. 4 is a perspective view showing a main part of another example of the embodiment of the projection exposure apparatus of the present invention.

FIG. 5 is a diagram for explaining an example of calculating a temperature distribution by irradiation energy in the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 light source 4 fly-eye lens 6A to 6C aperture stop 10, 10A, 10B, 10C partial polarizing plate 12 reticle 13 projection optical system 13A upper lens system 13B lower lens system PS1 pupil plane PS2 illumination system pupil plane 14 polarizing plate 15 wafer 16 wafer Stage 17 Quarter-wave plate 21, 23 Rotation driver 22 Rotation angle control system

Claims (4)

[Claims] 1. A projection optical system for projecting an image of a pattern on a mask onto a photosensitive substrate under exposure light, wherein a light beam emitted from the mask at an angle out of the exposure light, or A projection exposure apparatus that uses a light beam obliquely incident on a mask as an effective imaging light beam, wherein the light beam substantially has a circular shape centered on an optical axis on a plane conjugate with a pupil plane of the projection optical system. An illumination optical system that illuminates the mask using the exposure light from a light source uniformly distributed in a region; and a pupil plane of the projection optical system, or a plane conjugate to the pupil plane, and the effective imaging. A first polarizing member for setting the polarization direction of the exposure light passing through a region other than the region through which the light beam passes in a predetermined direction, and being disposed between the projection optical system and the photosensitive substrate and passing through the projection optical system A second light-shielding part of the exposure light that blocks a light beam polarized in the predetermined direction; Projection exposure apparatus being characterized in that the optical member, the provided. 2. The projection exposure apparatus according to claim 1, wherein the first polarizing member excludes a region inside a ring-shaped region around the optical axis or a plurality of regions decentered from the optical axis. A projection exposure apparatus, wherein a polarization direction of the exposure light passing through a region is set to the predetermined direction. 3. The projection exposure apparatus according to claim 1, further comprising a driving unit that rotates the first polarizing member and the second polarizing member while maintaining a constant relative angular relationship. A projection exposure apparatus characterized by the above-mentioned. 4. The projection exposure apparatus according to claim 1, wherein the exposure light having passed through the second polarizing member is converted into circularly polarized light between the second polarizing member and the photosensitive substrate. A projection exposure apparatus, comprising a third polarizing member.