JP2005018013A - Illumination optical system, and aligner and exposure method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the overall length of an illumination optical system which uniforms an intensity distribution of an illumination light by using an optical integrator. <P>SOLUTION: A diagonal length of an optical element of the optical integrator 20 is made to be 4 mm or less in the illumination optical system that comprises a light source 12 composed of a laser that applies an illumination light 11 to a body 10 to be illuminated such as a two-dimensional SLM, and the optical integrator 20 that is disposed between the light source 12 and the body 10, and uniforms the intensity distribution by letting the illumination light 11 pass through the optical element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an illumination optical system, and more particularly to an illumination optical system in which illumination light emitted from a laser is passed through an optical integrator so that the intensity distribution is uniform.

  The present invention also relates to an exposure apparatus and an exposure method for exposing a photosensitive material by irradiating the photosensitive material with illumination light modulated after being emitted from the illumination optical system as described above.

  Conventionally, a two-dimensional spatial light modulation element such as an LCD (liquid crystal display element) or DMD (digital micromirror device) is illuminated with light from a light source, and a photosensitive material is exposed with light modulated by the spatial light modulation element. There is known an exposure apparatus adapted to do so. In this type of apparatus, it is necessary to uniformly illuminate the spatial light modulator, and therefore an optical integrator is incorporated in the illumination optical system. In this way, the optical integrator that makes the intensity distribution of illumination light uniform is generally used in projectors and the like in addition to the exposure apparatus.

  An optical integrator is one that splits the luminous flux and re-synthesizes it after passing through different paths, thereby eliminating and homogenizing the correlation between the intensity and position (intensity distribution). Therefore, there are roughly two types. One is a fly-eye type that uses a lens array (fly-eye lens) in which a plurality of lenses are two-dimensionally arranged to split the light beam spatially, and the other is a glass rod or inner surface. This is a rod type that splits the light beam angularly by multiple reflections using a hollow rod with a mirror. In addition, by making the lens shape of the fly-eye type optical integrator and the cross-sectional shape of the rod type optical integrator similar to the illumination spatial light modulation element, the shape of the light source and the spatial light modulation element can be different from each other. It is possible to illuminate efficiently.

  Patent Document 1 discloses an example of an illumination optical system using an optical integrator as described above.

Incidentally, in an optical apparatus such as a projector to which an illumination optical system using the optical integrator is applied, a fly-eye lens having an aspect ratio of about 4: 5 and a lens cell size of about 5 to 10 mm is conventionally used. .
JP-A-9-68667

  By the way, in the conventional illumination optical system using the optical integrator described above, an etendue (Etendeu: which will be described in detail later) such as a discharge lamp is used. Then, it is necessary to increase the numerical aperture NA (hereinafter referred to as illumination NA) on the side of the object to be illuminated, and not the magnifying projection apparatus such as a projector, but exposure that exposes the photosensitive material by projecting the spatial light modulation element at equal or reduced magnification. When applied to the apparatus, there is a problem that the image quality is deteriorated due to a small depth of focus. On the other hand, if the illumination NA is reduced in order to increase the depth of focus, the overall length of the optical system tends to be large. Therefore, it is inevitable that the exposure apparatus to which the illumination optical system is applied is increased in size, or the physical layout is increased. Problems such as becoming difficult were recognized.

  In view of the above circumstances, an object of the present invention is to provide an illumination optical system using an optical integrator that can be formed with a short overall length.

  Another object of the present invention is to provide an exposure apparatus that can be formed in a small size by applying the illumination optical system as described above, and an exposure method that uses the illumination optical system.

The illumination optical system according to the present invention includes:
A light source for irradiating illumination light to the spatial light modulation element such as the DMD described above;
In an illumination optical system comprising an optical integrator that is arranged between the light source and the spatial light modulation element and uniformizes the intensity distribution by passing the illumination light through the optical element,
The diagonal length of the optical element of the optical integrator is 4 mm or less.

  Here, the diagonal length of the optical element means a diagonal length of each lens cell in a fly-eye type optical integrator, while it means a diagonal length of a rod section in a rod type optical integrator.

In the illumination optical system of the present invention having the above configuration, it is desirable that the etendue of the light source is 1 mm ² · str (steradian) or less. In the illumination optical system of the present invention, a light source having a configuration in which a plurality of laser beams are incident on one optical fiber and combined, and a plurality of optical fibers are arranged in a bundle shape can be preferably used. That is, this type of light source can be preferably used in the illumination optical system of the present invention because it has a very high output and a small etendue.

  On the other hand, an exposure apparatus according to the present invention modulates the illumination light emitted from the above-described illumination optical system based on a predetermined image signal by the spatial light modulation element, and uses the modulated illumination light to form a photosensitive material. It has a structure to be exposed.

  In the exposure method according to the present invention, the illumination light emitted from the illumination optical system is modulated on the basis of a predetermined image signal by the spatial light modulation element, and the photosensitive material is exposed with a light image by the modulated illumination light. It is characterized by making it.

  FIGS. 1a and 1b show the relationship between the diagonal length of a lens cell and the total length of an optical system in an illumination optical system using a fly-eye type optical integrator, whose basic configuration is shown in FIG. The case of 0.05 is shown. As shown in these figures, when the diagonal length of the lens cell exceeds 4 mm, the total length of the optical system tends to increase suddenly. In the illumination optical system of the present invention, the diagonal length of the optical element of the optical integrator is set to 4 mm or less in view of this new knowledge, thereby making it possible to significantly reduce the total length of the optical system.

  In the above, the illumination optical system using the fly-eye type optical integrator has been described. However, in the illumination optical system using the rod-type optical integrator described above, the diagonal length of the rod cross section of the optical integrator and the total length of the optical system The same can be said about the relationship.

Further, in the illumination optical system of the present invention, when a light source having a particularly small etendue (for example, 1 mm ² · str or less) is used, the illumination NA can be reduced without reducing the illumination efficiency. It is possible to increase the depth of focus of the optical system arranged in the lens or to narrow the beam. In this case, for example, when the illumination optical system is applied to the exposure apparatus, there arises a problem that the focus of the exposure image formed by the imaging optical system arranged at the subsequent stage of the illumination target is shifted. This can be prevented.

  Hereinafter, the relationship between the etendue and the illumination NA will be described in detail. In the exposure apparatus and projector as described above, a discharge lamp such as an ultra-high pressure mercury lamp is often used as a light source. When such a lamp is used, particularly in an exposure apparatus that exposes a photosensitive material, the depth of focus. There is a problem that is very small. The problem of small depth of focus becomes clear when we consider the concept of etendue.

First, details of etendue will be described with reference to FIG. In general, illuminating the spatial light modulation element means that an image of a certain light source is formed on the spatial light modulation element (even if it is devised to have a uniform distribution). Here, if the area of the light source is S ₁ and the optical magnification is β, the area S ₂ of the image is proportional to β ² (S ₂ = β ² S ₁ ), as shown in FIG. The formed angle θ is inversely proportional to the magnification β (θ ₂ = θ ₁ / β). That is, S ₁ θ ₁ ² = S ₂ θ ₂ ² . Here, since the solid angle Ω is substantially proportional to θ ² , Ω ₁ · S ₁ ≈Ω ₂ · S _2, that is, the product of the light source area and the solid angle is constant.

Strictly speaking, the transmission of luminous flux by an ideal lens is
Luminous flux: e = ∫S∫Ωcosθ ・ dS ・ dΩ
It is represented by When θ is sufficiently small (F value of 2.5 or more), cos θ≈1, so
Luminous flux: e = Ω ₁ · S ₁ ≒ Ω ₂ · S ₂
Can be considered. This Ω · S is the etendue. Assuming an ideal optical system with no aberration and 100% transmittance, etendue is preserved. It is known that etendue is preserved even if the optical systems on both sides of the ideal lens are not conjugated. That is, the etendue on the light source side represents the spatial spread of the light beam emitted from the light source, and the etendue on the illuminated side (spatial light modulation element side) represents the spatial spread of the light beam that can be accepted. .

  Here, a calculation example is shown.

<Etendue Es on the light source side>
(1) In the case of a discharge lamp with an arc length of 4 mm If the light source is a cylinder with a diameter of 1 mm and a length of 4 mm, and light is emitted isotropically from the side,
Es = π ・ 1 ・ 4 ・ 2π ≒ 80mm ²・ str (Steradian)
(2) In the case of a fiber light source As an example, consider a light source in which a plurality of optical fibers that propagate laser light are arranged in a bundle. Assuming that the emission part size of the bundle is 0.7 × 0.7 mm and the numerical aperture NA of the optical fiber is 0.2 (≈11.5 deg),
Es = 2π ・ (1-cos11.5) ・ 0.7 ・ 0.7 ≒ 0.06mm ²・ str
In this case, the etendue is very small.

<Light incidence angle (illumination NA) on the spatial light modulation element side obtained from the Etendue Ec on the spatial light modulation element side and the above-mentioned Etendue Es on the light source side>
As an example, the calculation is performed when the number of pixels of the spatial light modulator is 1024 × 768, the pixel pitch is 13.68 μm, and there is no loss.

(1) In the case of the discharge lamp Es = Ec = 2π · (1 -cosθ) · 1024 · 768 · 13.68 2/1000 2 = 80mm 2 · str
Illumination NA = sinθ ≒ 0.4
(2) In the case of the fiber light source Es = Ec = 2π · (1 -cosθ) · 1024 · 768 · 13.68 2/1000 2 = 0.06mm 2 · str
Illumination NA = sinθ ≒ 0.01
As is clear from the above, the illumination NA can be reduced as the etendue Es on the light source side is smaller.

  Considering the etendue, when the etendue Es on the light source side and the etendue Ec on the illuminated spatial light modulation element side are in the relationship of Es <Ec, all light from the light source can be obtained if there is no loss of the optical system on the way. Will be available. However, when the lamp as described above is used as the light source, the etendue of the lamp is large. Therefore, in order to efficiently illuminate, the illumination NA must be very large.

For example, as described above, when a discharge lamp having an arc length of 4 mm is used to illuminate a spatial light modulation element having a pixel number of 1024 × 768 and a pixel pitch of 13.68 μm, the discharge lamp has an etendue of about 80 mm ² · str. In order to illuminate efficiently with the same etendue, the illumination NA must be 0.4. In order to form and expose the image of the spatial light modulator on the photosensitive material with the imaging lens, and to use the light from the spatial light modulator efficiently, the NA of the imaging lens is naturally 0.4 or more (in F value) 1.25), and the focal depth of the imaging lens becomes very small.

  FIG. 3 shows the focal depth of the imaging lens when the light source side Etendue Es is relatively large and the illumination NA is large (a), and when the light source side Etendue Es is relatively small and the illumination NA is small (b). It is shown in comparison. As shown here, from the viewpoint of geometrical optics, the focal depth increases as the NA of the lens decreases.

For example, if the allowable circle of confusion circle is 10 μm, the depth of focus is as follows according to the illumination NA (Table 1). The depth of focus when the illumination optical system is applied to the exposure apparatus depends on the recording beam diameter and resolution, but is preferably ± 100 μm or more in consideration of waviness of the recording material and changes in focus position due to temperature. In view of this, the illumination NA is preferably 0.05 or less, and more preferably 0.02 or less.

  When the light source side Etendue Es is large, if the temperature fluctuation or mechanical fluctuation occurs in the device, or if the photosensitive material thickness varies or warps, the depth of focus is very small, so the exposure image will be out of focus. The problem of end up occurs.

On the other hand, for example, when the fiber light source is used, the etendue Es on the light source side is 0.06 mm ² · str, the illumination NA is extremely small, about 0.01, the focal depth of the imaging lens is increased, and the focus shift is reduced. Problems can be prevented.

  However, even when a light source with a small etendue Es is used, if a fly-eye lens having a general lens cell size used in a projector or the like is applied, the size of each lens is large in order to reduce the illumination NA. Therefore, the size of the entire optical system becomes large. Therefore, in the present invention, as described above, an optical integrator in which the diagonal length of the optical element is 4 mm or less is used.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 4 shows a schematic configuration of an illumination optical system according to an embodiment of the present invention. This illumination optical system converts a light source 12 that irradiates illumination light 11 to a two-dimensional spatial light modulator (SLM) 10 that is an object to be illuminated, and parallel illumination light 11 emitted from the light source 12 in a divergent light state. A collimator lens 13 and an optical integrator 20 disposed between the collimator lens 13 and the two-dimensional SLM 10 for uniformizing the intensity distribution by passing the illumination light 11 through the optical element. is there.

  In the present embodiment, as the light source 12, a fiber light source having a configuration in which a plurality of laser beams are incident on one optical fiber and combined, and a plurality of optical fibers are arranged in a bundle shape is used.

  The optical integrator 20 includes a fly-eye lens ML1, another fly-eye lens ML2 disposed so as to face the fly-eye lens ML1, and a field lens disposed in front of the fly-eye lens ML2, that is, on the two-dimensional SLM 10 side. It consists of FL. The fly-eye lenses ML1 and ML2 are formed by arranging a large number of microlens cells vertically and horizontally, and the illumination light 11 that has passed through each of these microlens cells is incident on the two-dimensional SLM 10 in a state where they overlap each other. The intensity distribution of the illumination light 11 that irradiates the two-dimensional SLM 10 is made uniform.

  On the other hand, as the two-dimensional SLM 10, a DMD (digital micromirror device) is used in the present embodiment. This DMD is formed by two-dimensionally arranging a large number of micromirrors whose reflection surfaces change in response to a control signal on a semiconductor substrate made of silicon or the like, and is irradiated with a wide area. The illumination light 11 is spatially modulated by reflecting the illumination light 11 at different angles for each micromirror according to the image data.

  Here, the light source size, that is, the light emitting part size of the fiber light source 12 is A0, the light source NA is NA0, the focal length of the collimator lens 13 is CL2f, the cell size of the fly-eye lens ML1 is S1, the number of lens cells is N1, The lens size is A1, the focal length is ML1f, the condensing size by each lens cell is Z1, the cell size is S2 for the fly-eye lens ML2, the number of lens cells is N2, the lens size is A2, and the focal length is ML2f. The lens size of the field lens FL is FLD, the focal length is FLf, the illumination size of the two-dimensional SLM 10 is ACS, and the illumination NA is NAC. In this embodiment, S2 = S1, N2 = N1, and A2 = A1, but it is of course not limited to this.

  In this case, the total length of the optical system, that is, the distance from the exit end face of the multimode optical fiber 12 to the two-dimensional SLM 10 is the distance L1 (= CL2f) from the exit end face to the collimator lens 13 as shown in FIG. The distance L2 (= CL2f) from the collimator lens 13 to the fly-eye lens ML1, the distance L3 (= ML1f) from the fly-eye lens ML1 to the fly-eye lens ML2, and the distance from the fly-eye lens ML2 to the two-dimensional SLM10 Summed with L4.

  In this illumination optical system, A0 · NA0 = A1 · NA1 = N1 · S1 · NA1, the imaging characteristics are (1 / L3) + (1 / L4) = 1 / ML2f, and the magnification characteristics are ACS / S1. = L4 / L3, the condensing characteristic is Z1 = 2ML1f · NA1, and the illumination F value (FNo.) Is FNo. = FLf / FLD≈L4 / A2.

Regarding the above specifications and other specifications, specific numerical values in the present embodiment are shown in the left column of Table 2 below. In addition, Table 3 shows three numerical values as comparative examples. In these tables, x and y indicate the horizontal and vertical directions in the plane perpendicular to the optical axis.

As shown in Table 2, in this embodiment, the diagonal lengths of the lens cells of the fly-eye lenses ML1 and ML2 constituting the optical integrator are both (2 ² +0.5 ² ) ^1/2 = 2.1 mm. The aforementioned value is 4 mm or less. Therefore, for the reason described above with reference to FIG. 1, the total length of the optical system is suppressed to about 114 mm.

The right column of Table 2 shows another specification example of the illumination optical system having the same basic configuration as the present embodiment. In this example, the diagonal length of each lens cell of the fly-eye lenses ML1 and ML2 is (3.88 ² +0.97 ² ) ^1/2 = 4.0 mm, which is a value of 4 mm or less. Therefore, also in this example, the total length of the optical system is suppressed to about 524 mm.

On the other hand, in the comparative example shown in Table 3, since the diagonal length of each lens cell is as large as (10 ² +2.5 ² ) ^1/2 = 10.3 mm, the total length of the optical system is about 289 mm, 744 mm, and 1711 mm, respectively. It is relatively large.

In this embodiment, the light source etendue is as small as 0.0086895 mm ² · str of 1 or less, and the illumination NA (NAC) is extremely small as 0.05 and 0.0185014 in the above two examples, respectively. Therefore, when an imaging lens is disposed at the subsequent stage of the two-dimensional SLM 10, the focal depth of the imaging lens becomes large, and the above-described problem of defocusing can be prevented.

On the other hand, in the comparative example shown in the leftmost column of Table 3, the light source etendue is as large as 1.5868265 mm ² · str, and the illumination NA (NAC) is considerably large as 0.25. Therefore, when an imaging lens is disposed in the subsequent stage of the two-dimensional SLM 10, the focal depth of the imaging lens is reduced, and thus the above-described problem of defocusing is likely to occur.

In the comparative example shown in the center column and the rightmost column of Table 3, the light source etendue is 0.0086895 mm ² · str, which is the same as that of the present embodiment, and the illumination NA (NAC) is extremely small, 0.05 and 0.0185185, respectively. . Therefore, in this case as well, the above-described problem of defocusing can be prevented. However, since the cell size is large in these comparative examples, the total length of the optical system becomes extremely large at about 744 mm and 1711 mm as described above. . If the total length of the optical system is as large as the latter example, it becomes even difficult to fit the illumination optical system in a general room.

  Next, an exposure apparatus using the illumination optical system of FIG. 4 will be described with reference to FIG. In FIG. 5, the same elements as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted unless necessary (the same applies hereinafter).

  In this exposure apparatus, an imaging lens 30 is arranged at the subsequent stage of the two-dimensional SLM 10 of the illumination optical system shown in FIG. 4, and an image by the illumination light 11 spatially modulated by the two-dimensional SLM 10 is staged by the imaging lens 30. An image is formed and projected on the photosensitive material 32 on the substrate 31. As a result, the photosensitive material 32 is exposed and an image of the spatially modulated illumination light 11 is recorded on the photosensitive material 32.

  If the illumination optical system shown in FIG. 4 is applied to such an exposure apparatus, the exposure apparatus can be made compact because the overall length of the illumination optical system is short, and the illumination NA (NAC) is small. The depth of focus is increased, thereby making it possible to effectively prevent the exposure image from being out of focus.

  Next, an illumination optical system according to another embodiment of the present invention will be described with reference to FIG. In this embodiment, a substantially rectangular parallelepiped translucent glass rod 40 is used as an optical integrator. Illumination light 11 emitted from the multimode optical fiber 12 constituting the light source is condensed by a condensing lens 41 and guided into the glass rod 40. The light is made uniform. The illumination light 11 emitted from the glass rod 40 in this manner is condensed by the condenser lens 42 and irradiated to the two-dimensional SLM 10.

  Also in the present embodiment in which the glass rod 40 is used as an optical integrator, the overall length of the optical system can be significantly shortened by setting the diagonal length of the cross section of the glass rod 40 to 4 mm or less.

  In the embodiment described above, the fiber light source 12 is used as a light source. However, the present invention is not limited to such a light source, and other ordinary light sources such as a single semiconductor laser or a plurality of light emitting points are used. A multi-cavity semiconductor laser having a plurality of semiconductor lasers or an array laser in which a plurality of semiconductor lasers are arranged in an array can be suitably used.

A graph showing the relationship between the diagonal length of the optical integrator lens cell in the illumination optical system and the total length of the optical system (when illumination NA = 0.019) A graph showing the relationship between the diagonal length of the optical integrator lens cell in the illumination optical system and the total length of the optical system (when illumination NA = 0.05) Explanatory drawing explaining the concept of Etendue Explanatory drawing which shows the relationship between illumination NA and a focal depth in an illumination optical system 1 is a schematic side view showing an illumination optical system according to an embodiment of the present invention. FIG. 4 is a schematic side view showing an exposure apparatus to which the illumination optical system of FIG. 4 is applied. Schematic side view showing an illumination optical system according to another embodiment of the present invention

Explanation of symbols

10 2D SLM
11 Illumination light
12 Fiber light source
13 Collimator lens
20 Optical integrator
30 Imaging lens
31 stages
32 Photosensitive material
40 Glass rod
41, 42 Condensing lens ML1, ML2 Fly's eye lens FL Field lens

Claims (7)

A light source for illuminating the spatial light modulator with illumination light;
In an illumination optical system comprising an optical integrator that is arranged between the light source and the spatial light modulation element and uniformizes the intensity distribution by passing the illumination light through the optical element,
An illumination optical system, wherein the diagonal length of the optical element of the optical integrator is 4 mm or less. The illumination optical system according to claim 1, wherein the etendue of the light source is 1 mm ² · str (steradian) or less.   The illumination optical system according to claim 1 or 2, wherein the light source comprises a laser and an optical fiber that propagates and emits laser light emitted from the laser. The light source enters each laser beam emitted from a plurality of lasers into a single optical fiber, and combines them.
4. The illumination optical system according to claim 3, wherein a plurality of optical fibers are arranged in a bundle to form a bundle.   The illumination optical system according to any one of claims 1 to 4, wherein the spatial light modulation element is a DMD.   The illumination light emitted from the illumination optical system according to any one of claims 1 to 5 is modulated on the basis of a predetermined image signal by the spatial light modulation element, and a photosensitive material is formed by a light image by the modulated illumination light. An exposure apparatus having a configuration for exposing.   The illumination light emitted from the illumination optical system according to any one of claims 1 to 5 is modulated on the basis of a predetermined image signal by the spatial light modulation element, and a photosensitive material is formed by a light image by the modulated illumination light. An exposure method characterized by exposing.

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