JPH09326343A - Method and system for exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the resolution furthermore while satisfying the requirements for the margin of the depth of focus without shortening the wavelength of illumination light for exposure. SOLUTION: Under presence of an illumination light IL from a light source 1, the pattern image of a reticle R is projected through a projection optical system PL onto a wafer W. In order to satisfy the requirements for the margin of the depth of focus that the sum of the focus control accuracy, the level difference of an underlying pattern (level difference of a mark), and a width obtained by multiplying a photoresist by a predetermined coefficient is smaller than the depth of focus, the resolution is enhanced by increasing the numerical aperture of the projection optical system PL when the level difference of mark is low and the photoresist is thin and the numerical aperture is decreased when the level difference of mark is high and the photoresist is thick. A normal illumination method is used when the numerical aperture of the projection optical system PL is large and a modified illumination method is employed in order to enhance the resolution when the numerical aperture is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transfers a mask pattern onto a photosensitive substrate in a photolithography process for manufacturing, for example, a semiconductor element, an image pickup element (CCD or the like), a liquid crystal display element, a thin film magnetic head or the like. The present invention relates to an exposure method and an exposure apparatus for performing.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or the like, a wafer coated with a photoresist as a photosensitive substrate is formed through a projection optical system to form an image of a reticle pattern as a mask under illumination light for exposure. Or, an exposure device for transferring onto a glass plate or the like is used. Conventionally, as the exposure apparatus, a batch exposure type projection exposure apparatus such as a stepper has been mainly used, but recently, in order to transfer a large area pattern without excessively burdening the projection optical system, A scanning exposure type projection exposure apparatus such as a step-and-scan method in which a reticle and a wafer are synchronously scanned with respect to a projection optical system is also receiving attention.

FIG. 13 shows a schematic structure of an example of a conventional projection exposure apparatus. In FIG. 13, the exposure illumination light from the illumination optical system 101 forms a pattern formation area on the pattern formation surface (lower surface) of the reticle R. Lighting up. Under the illumination light, a projection image obtained by reducing the pattern formed on the reticle R at a predetermined magnification via the projection optical system 102 is a wafer W.
The photoresist coated above is exposed. The numerical aperture of the projection optical system 102 is defined by the aperture stop 103. Then, by developing the photoresist, the projected image appears as an uneven resist pattern.

The resolution R and the depth of focus D of the image of the pattern of the reticle R image-projected on the wafer W as described above are respectively expressed by the following equations. R = k ₁ · λ / NA (1) D = k ₂ · λ / NA ² (2) where k ₁ and k ₂ are process coefficients (hereinafter,
“K factor”), λ is the wavelength of the exposure illumination light, N
A is the numerical aperture of the projection optical system 102. As shown in FIG. 13, assuming that the half aperture angle of the image-forming light beam on the wafer side (image side) of the projection optical system 102 is θ _{PL 2} and the surrounding gas is air, the numerical aperture NA is represented by sin θ _PL2 . To be done. Further, the projection magnification of the projection optical system 102 from the reticle R to the wafer W is β (β is ⅕, ¼, etc.), the projection optical system 1
_Letting θ _{PL1 be} the opening half angle on the reticle side (object side) of the image formation light flux by 02, there is the following relationship between the opening half _angles θ _PL2 and θ _PL1 . At this time, among the diffracted light from the reticle R, the diffracted light having a diffraction angle of θ _PL1 or less contributes to the formation of the projected image of the pattern of the reticle R.

Sin θ _PL1 = β · sin θ _PL2 = β · NA (3) Further, the illumination half-angle of the exposure illumination light from the illumination optical system 101 to the reticle R is θ _IL , and the illumination optical system 101
Let σ (σ value) be the coherence factor of, ie, the ratio of the numerical aperture (= sin θ _IL ) on the exit side of the illumination optical system 101 to the numerical aperture (= sin θ _PL1 ) on the incident side of the projection optical system 102. , The aperture half angle θ _IL of the illumination light is expressed as follows using the equation (3). The range of the σ value is 0 ≦ σ <1.
It is.

Sin θ _IL = σ · sin θ _PL1 = σ · β · NA (4) Then, the values of the k factors k ₁ and k ₂ that determine the resolution R and the depth of focus D are the coherence factors. It depends on the σ value. Further, the values of the k factors k ₁ and k ₂ are different from those of the ordinary illumination method in which the shape of the secondary light source is circular in the illumination optical system 101, and the shape of the secondary light source is a plurality of light sources or annular zones decentered from the optical axis. It is also changed by switching to a so-called modified illumination method consisting of the light source of No. 1, and a predetermined optical filter (so-called pupil filter) is arranged on the pupil plane of the projection optical system 102 (optical Fourier transform plane for the pattern formation plane of the reticle R). It also changes depending on what you do. Further, the values of the k factors k ₁ and k ₂ are, as the reticle R, a so-called phase shift reticle that gives a predetermined phase difference in a periodic pattern, or a so-called phase shift reticle that gives a predetermined transmittance distribution in the periodic pattern. It also changes when using a halftone reticle. Due to various conditions as described above,
The values of k factors k ₁ and K ₂ vary in the following ranges.

0.45 ≦ k ₁ ≦ 0.6, 0.7 ≦ k ₂ ≦ 2.0 (5) Therefore, conventionally, by making full use of the above various conditions, the depth of focus D is deep and the resolution is high. The exposure condition with a high R is used properly according to the device to be exposed. Also,
The depth of focus D is expressed by the formula (2). The focus control precision C _F which is the precision when the wafer is focused by the projection exposure apparatus by the auto focus method is C _F , and the step of the underlying pattern on the wafer (hereinafter, alignment). _Assuming that the mark step is representatively referred to as “mark step”) is D _M , the focus control accuracy C _F and the mark step D _{M are} calculated from the depth of focus D.
The width (= D−C _F −D _M ) obtained by subtracting is the width of the substantial depth of focus that can be used on the operator side of this projection exposure apparatus, that is, the usable depth of focus.

In practice, assuming that the thickness of the photoresist on the wafer (resist thickness) is T _R , in order to obtain a good resist pattern after development of the photoresist, the resist thickness T _R is set to a predetermined value. Width obtained by multiplying the following coefficient K _UD (depth of focus width required for photoresist exposure)
However, it only needs to be within the range of the depth of focus that can be used. Therefore, in the following, the width T _R · K _UD obtained by multiplying the resist thickness T _R by the coefficient K _UD is used as the usable depth of focus UD.
Called OF (Usable Depth Of Focus). From the above,
The depth of focus D in the equation (2) is the focus control accuracy C _F , the mark step D _M , and the usable depth of focus U as in the following equation.
It must be wider than the sum of DOF (= T _R · K _UD ). The condition of the following expression (6) is referred to as “condition regarding margin of depth of focus”.

C _F + D _M + T _R · K _UD ≦ D = k ₂ · λ / NA ² (6) As a general example, the illumination light for exposure is i of a mercury lamp.
The line (λ = 365 nm) is used and the k factor k ₁ is 0.
As 55, an image of a line-and-space pattern (L / S pattern) having a line width of 0.4 μm, which corresponds to the pattern of a 64 Mbit DRAM, is projected, that is, a projection for making the resolution R 0.4 μm. Numerical aperture N of optical system
When A is NA ₁ , the numerical aperture NA ₁ is as follows from the equation (1).

0.4 = 0.55 · 0.365 / NA ₁ , NA ₁ ≈0.50 (7) Furthermore, the mark step D _M on the wafer is 0.8 μm, and the resist thickness T _R is 1 μm. When the coefficient K _UD that determines the depth of focus UDOF is 0.7 and the k factor k ₂ is 2.0, the numerical aperture NA of the projection optical system satisfying the condition relating to the margin of the depth of focus in Expression (6) is NA. _{If 2} ,
The numerical aperture NA ₂ is as follows.

0.5 + 0.8 + 1 × 0.7 ≦ 2.0 × 0.365 / NA ₂ ² , NA ₂ ≦ 0.60 (8) From the equations (7) and (8), the i-line of the mercury lamp is obtained. The condition of the numerical aperture NA of the projection optical system for manufacturing the pattern of the 64 Mbit DRAM using is 0.5 ≦ NA ≦ 0.6. Further, in order to set the k factors k ₁ and k ₂ to the above values, it is desirable to set the σ value which is the coherence factor to about 0.7 ≦ σ <0.8. Further, for the conventional periodic pattern, a modified illumination method in which the shape of the secondary light source of the illumination optical system is a plurality of light sources decentered from the optical axis or a ring-shaped light source (ring-shaped illumination method) is applied. It is known that the resolution can be improved without narrowing the depth of focus, and it is also attempted to use the modified illumination method together to further increase the resolution.
Note that the modified illumination method may be limited in a narrow sense to an illumination method in which the shape of a secondary light source is composed of a plurality of light sources that are eccentric from the optical axis. Lighting method shall be included.

[0012]

As described above, the i-line of the mercury lamp is used as the illumination light for exposure, and the numerical aperture NA of the projection optical system is set to about 0.5≤NA≤0.6. Thus, a circuit image corresponding to a 64 Mbit DRAM, that is, an image of a pattern having a resolution R of about 0.4 μm can be transferred onto a wafer with high accuracy. Furthermore, 256 Mbit DRAM, which is a next-generation semiconductor device recently
Is about to be started, and for that purpose, it is necessary to increase the resolution R to about 0.25 μm. In order to increase the resolution R as described above, the wavelength λ of the exposure illumination light may be shortened or the numerical aperture NA of the projection optical system may be increased according to the equation (1).

However, if the wavelength λ is simply shortened,
When the numerical aperture NA is increased, the focal depth D of the equation (2) becomes narrower, and the condition regarding the margin of the focal depth of the equation (6) cannot be satisfied. In particular, as can be seen from the equation (2), the depth of focus D decreases in inverse proportion to the square of the numerical aperture NA, and thus it has not been conventionally considered to increase the numerical aperture NA. Therefore, conventionally, as an exposure light source, a KrF excimer laser light source (exposure wavelength λ = 248n
m) is used to obtain a resolution R of 0.25 μm, and (b) introduction of wafer flattening technology and (b) improvement of focus control technology satisfy the condition concerning the margin of the depth of focus of the equation (6). Was doing.

The wafer flattening technique (a) is a technique for physically or chemically increasing the flatness of the surface of the wafer before exposure in order to reduce the warp of the wafer and the step of the circuit pattern. As a result, the mark step D _M is reduced from the conventional 0.8 μm to about 0.1 μm. Also,
Due to the improvement of the focus control technique (b), the focus control accuracy C _F is improved from the conventional 0.5 μm to about 0.4 μm. Estimating the numerical aperture NA of the projection optical system under these exposure conditions, _first , assuming that the k factor k ₁ is 0.55, the numerical aperture NA ₁ that satisfies (1) is as follows.

0.25 = 0.55 × 0.248 / NA ₁ , NA ₁ ≈0.55 (9) Further, the numerical aperture NA _{2 which} satisfies the condition regarding the depth of focus margin of the equation (6) is as follows. become. The k factor k ₂ is 1.7 because the line width is thin, and the coefficient K _UD that determines the usable depth of focus UDOF remains 0.7.

0.4 + 0.1 + 1 × 0.7 ≦ 1.7 × 0.248 / NA ₂ ² , NA ₂ ≦ 0.59 (10) That is, the numerical aperture NA range is 0.55 under these exposure conditions.
≦ NA ≦ 0.6. Further, in order to further improve the resolution without narrowing the depth of focus, it is also considered to use a modified illumination method and a halftone reticle together.

However, if the exposure light source is changed from a mercury lamp to a KrF excimer laser light source in order to manufacture a semiconductor device equivalent to a 256 Mbit DRAM, the projection exposure apparatus itself becomes expensive, and it is difficult to receive a return commensurate with the investment. There was an inconvenience that cost performance was bad. Further, under the present circumstances, ArF is used as an exposure light source as a projection exposure apparatus for forming a circuit pattern corresponding to the next-generation semiconductor device, 1 Gbit DRAM.
Development of a device using an excimer laser light source (wavelength λ is 193 nm) is planned, and next 4G bit DR
As a projection exposure apparatus for forming a circuit pattern corresponding to AM, at present, there is also a plan to develop an apparatus using exposure light of shorter wavelength, such as X-rays. That is,
Currently, in order to manufacture next-generation semiconductor devices,
The main idea is to shorten the wavelength of the illumination light for exposure to deal with it. However, when the exposure light source is switched to shorten the wavelength of the illumination light for exposure, there is a disadvantage that the manufacturing cost of the projection exposure apparatus increases significantly and the cost performance deteriorates.

In view of the above point, the present invention provides an exposure method capable of improving the resolution without shortening the wavelength of the exposure illumination light and satisfying the condition regarding the depth of focus margin. To aim. In other words, the present invention can form a pattern corresponding to the next-generation 256 Mbit DRAM by using the i-line of a mercury lamp as the illumination light for exposure, and 1 G by using the KrF excimer laser light.
It is an object of the present invention to provide an exposure method capable of forming a pattern corresponding to a bit DRAM and forming a pattern corresponding to a 4G bit DRAM by using ArF excimer laser light.

Another object of the present invention is to provide an exposure apparatus which can carry out such an exposure method.

[0020]

A first exposure method according to the present invention forms a mask (R) with illumination light (IL) for exposure from illumination optical systems (1 to 4, 5A, 10 to 12). In the exposure method, the transferred transfer pattern is illuminated and the image of the pattern of the mask (R) is transferred and exposed on the photosensitive substrate (W) through the projection optical system (PL) under the illumination light. The first area (75A, 75A, where the light amount distribution on the illumination system pupil plane (arrangement plane of 15), which is an optical Fourier transform plane with respect to the pattern plane of the mask (R) in the illumination optical system, includes the optical axis (AX).
75B) and the second region (75) in which the light amount distribution on the illumination system pupil plane does not include the optical axis (AX).
C, 75D) and the modified illumination conditions are freely switchable, and the illumination optical system is switched to either the normal or modified illumination conditions according to the numerical aperture of the projection optical system (PL).

In the present invention, in order to improve the resolution of the transferred image, the wavelength λ of the exposure illumination light is not shortened, but the numerical aperture NA of the projection optical system in the equation (1) is increased. Imagine that. However, simply the numerical aperture NA
When is increased, the depth of focus D becomes narrower in inverse proportion to the square of the formula (2), and the condition regarding the margin of the depth of focus in the formula (6) cannot be satisfied. Therefore, in the present invention, in order to satisfy the condition regarding the margin of the depth of focus,
Thickness T of photosensitive material (photoresist) in equation (6)
_R is thin and usable depth of focus UDOF (= T _R · K _UD ).
And the numerical aperture NA is increased under the exposure condition in which the mark step D _M, which is the step of the underlying pattern, is reduced by using the substrate flattening technique. When the numerical aperture NA is increased in this way, the resolution R can be improved (miniaturized), so that the illumination optical system can have normal illumination conditions, that is, the light amount distribution on the pupil plane of the illumination system can be the optical axis (AX). It suffices if it is in the first region (75A, 75B) including With this, without shortening the wavelength λ of the exposure illumination light,
For example, it becomes possible to transfer a pattern corresponding to a semiconductor device in the first generation with high accuracy.

On the other hand, under an exposure condition in which the thickness T _R of the photosensitive material is large and the mark step D _M is large, the numerical aperture NA is reduced in order to satisfy the condition regarding the margin of the depth of focus. When the numerical aperture NA is reduced in this way, the resolution R may not be sufficient as it is. Therefore, when it is desired to further increase the resolution R, the illumination optical system is set to a modified illumination condition in order to improve the resolution R without making the depth of focus D shallow, that is, the light amount distribution on the pupil plane of the illumination system is set to the optical axis. The second area (75C, 75D) not including (AX) is set. In summary, according to the present invention, the numerical aperture NA of the projection optical system (PL) is set large within a range satisfying the margin of depth of focus condition under various exposure conditions to improve the resolution R, while the numerical aperture NA is increased. When the value cannot be set to a large value, the illumination optical system is used as modified illumination to improve the resolution. By switching the numerical aperture of the projection optical system in this manner, it becomes possible to transfer a pattern corresponding to, for example, two generations of semiconductor devices with one exposure apparatus.

Next, the exposure apparatus according to the present invention includes an illumination optical system (1 to 4, 5A, 10 to 12) for illuminating the transfer pattern formed on the mask (R) with exposure illumination light.
In the exposure apparatus including a projection optical system (PL) that projects an image of the pattern of the mask (R) onto the photosensitive substrate (W) under the illumination light, the numerical aperture of the projection optical system (PL) is set to The projection condition changing means (42, 43) for switching and the illumination conditions of the illumination optical system are such that the light amount distribution on the illumination system pupil plane, which is an optical Fourier transform plane with respect to the pattern plane of the mask (R) in the illumination optical system. The first region (7 including the optical axis (AX)
5A, 75B) and a modified illumination condition in which the light amount distribution on the pupil plane of the illumination system does not include the optical axis (AX) in the second region (75C, 75D). Illumination condition changing means (5A, 5) for switching to illumination conditions
B, 8, 12 to 15, 32), the illumination condition changing means sets the illumination optical system to the normal one when the numerical aperture of the projection optical system (PL) is set to 0.68 or more. The illumination optical system is set to the illumination condition of the deformation when the numerical aperture of the projection optical system (PL) is set to 0.6 or less.

According to such an exposure apparatus of the present invention, the above-mentioned first exposure method of the present invention can be carried out. Further, the projection optical system (under the exposure condition that the mark step D _M can be set to about 0.1 μm or less and the thickness T _R of the photosensitive material can be set to about 0.5 μm or less by flattening the substrate Even if the numerical aperture NA of (PL) is set to be in the range of about 0.8 from 0.68 to 0.8, the condition regarding the margin of the depth of focus in the formula (6) can be almost satisfied. Such numerical aperture NA
Since the resolution R is fine in the range of, the illumination optical system may be in the normal illumination condition. On the other hand, as in the conventional case, the mark step D _M is about 0.8 μm and the thickness T of the photosensitive material is
_{When R} is about 1 μm, the numerical aperture NA of the projection optical system (PL) is set to satisfy the condition regarding the margin of the depth of focus.
Should be set to about 0.6 or less. If the resolution R is rough as it is, the resolution can be improved by setting the illumination optical system to the modified illumination condition.

In this case, an example of the illumination condition changing means is, for example, as shown in FIG. 5, a light beam splitting system (66) for splitting the exposure illumination light into first and second light beams (ILP, ILS). , 67), a first luminous flux expansion system (68) for expanding the cross-sectional shape of the first luminous flux into an annular shape, and a cross section of the second luminous flux with the light amount distributions of the inner and outer molds inverted. A second luminous flux expanding system (71) that expands the shape into an annular shape, and a luminous flux combining system (combining the luminous fluxes from the first and second luminous flux expanding systems (68, 71) before the illumination system pupil plane ( 7
0, 73), and at this time, when the illumination conditions for the deformation are set, the illumination condition changing means sets the light flux (I, I) combined by the light flux combining system (70, 73).
It is desirable to guide L ′) to the pupil plane of the illumination system to perform annular illumination.

At this time, the illuminance distribution of the illumination light on the incident surface of the light beam splitting system (66, 67) monotonously decreases in the radial direction from the optical axis as shown in FIG. 6A (for example, Gaussian distribution). ), The illuminance distribution of the luminous flux emitted from the first luminous flux expanding system (68) becomes a ring-shaped distribution that decreases monotonically in the radial direction as shown in FIG. The illuminance distribution of the luminous flux emitted from the luminous flux expansion system (71) is
As shown in FIG. 6 (c), the distribution is annular and monotonically increases in the radial direction, and the illuminance distribution of the combined light emitted from the light flux combining system (70, 73) is as shown in FIG. 6 (d). It has a flat ring shape. By performing the annular illumination using this combined light, only the portion of the secondary light source in the annular shape is illuminated with a uniform illuminance distribution on the pupil plane of the illumination system, so that the utilization efficiency of the illumination light increases, Moreover, the illuminance distribution on the mask (R) is also uniform.

Next, in the second exposure method according to the present invention, for example, as shown in FIGS. 1 and 11, the alignment optical system (OBL, OBL,
162, 164) to detect the image of the alignment mark (165) on the photosensitive substrate (W), the photosensitive substrate (W) is aligned based on the detection result, and the exposure illumination light ( In the exposure method of transferring and exposing the image of the pattern formed on the mask (R) on the photosensitive substrate (W) through the projection optical system (PL), the photosensitive substrate (IL) in the alignment optical system is used. W), a normal detection condition that allows the imaging light flux to pass uniformly (167A) on the alignment system pupil plane (HF2) which is an optical Fourier transform surface, and the imaging light flux on the alignment system pupil plane (HF2). Are passed through in a predetermined distribution (167B, 167C) and the detection condition for contour enhancement for contour enhancement is switchably provided, and the alignment optical system of the two is provided according to the numerical aperture of the projection optical system (PL). Inspection It is intended to switch to any of the conditions.

According to the present invention, the thickness T of the photosensitive material is
Under the exposure condition that _R is thin and the mark level difference D _M that is the level difference of the underlying pattern is reduced by using the substrate flattening technique, the projection optical system (PL) is controlled within a range in which the condition regarding the depth of focus margin can be satisfied. The numerical aperture NA is increased to increase the resolution R. However, in this way, the mark step D
_{When M} is small, it is difficult to obtain a high-contrast image of the alignment mark on the photosensitive substrate (W) through the alignment optical system under normal detection conditions.
Therefore, when the mark step D _M is small and the numerical aperture NA of the projection optical system is large, the detection condition for contour enhancement is set to enhance the contrast of the image of the alignment mark having the low step, The position of this alignment mark is detected with high accuracy.

Further, thick thick T _R of the photosensitive material, the greater the exposure conditions mark step difference D _M, to reduce the numerical aperture NA of the projection optical system to satisfy about margin of the focal depth (PL), And the alignment optical system is set to the normal detection condition. At this time, since the mark level difference D _M is large, an alignment mark image with sufficiently good contrast can be obtained under the normal detection conditions.

In this case, when the numerical aperture of the projection optical system (PL) is set to 0.68 or more, the alignment optical system is set to the detection condition for contour enhancement, and the aperture of the projection optical system (PL) is set. It is desirable to set the alignment optical system to the normal detection condition when the number is set to 0.6 or less. As described above, the numerical aperture NA of the projection optical system (PL) can be set to 0.68 or more, and the mark step difference D _M to an extent below 0.1 [mu] m, and the thickness T _R of the photosensitive material 0. When the mark step D _M is low as described above, the detection condition for edge enhancement is required to obtain the alignment mark image with good contrast. On the other hand, the numerical aperture of the projection optical system (PL) is set to 0.6 or less because the mark step D _M
Is about 0.8 μm, and the thickness T _{R of the} photosensitive material is 1 μm
However, when the mark step D _M is high as described above, it is possible to obtain a registration mark image with sufficiently good contrast under normal detection conditions.

In the second exposure method, the alignment optical system obtains an image of the alignment mark, but the alignment optical system uses an image pickup method (FIA method) used under normal detection conditions. And a two-beam interference method for detecting the phase of the interference light composed of diffracted light generated in the same direction from the mark by irradiating two light beams to the diffraction grating-shaped alignment mark. An alignment sensor for a low step mark such as (LIA method) may be prepared, and the alignment sensor may be switched according to the mark step.

In the above invention, the projection optical system (P
NA illumination optical system for exposure in accordance with the NA of the L), or it is switched conditions of the optical system for alignment, the numerical aperture NA of the projection optical system, for example, the thickness T _R of the photosensitive material
Is set to be large when T is thin, and is set to be small when the thickness T _R of the photosensitive material is thick. Therefore, the illumination optical system for exposure may be set to either normal or modified illumination conditions depending on the thickness of the photosensitive material.
In addition, the alignment optical system may be set to either normal or contour enhancement detection conditions depending on the thickness of the photosensitive material. Further, depending on the thickness of the photosensitive material, the alignment optical system may be switched to either the alignment sensor for the high step mark or the alignment sensor for the low step mark.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of an exposure method and apparatus according to the present invention will be described below with reference to the drawings. In this example, the present invention is applied to the case where exposure is performed by a step-and-scan type projection exposure apparatus. FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus of this example. In FIG. 1, the illumination light IL consisting of a laser beam having a wavelength of 248 nm pulsed from a KrF excimer laser light source 1 as an exposure light source is reduced. After being dimmed by the optical unit 2 at a predetermined dimming rate, the light is incident on the first-stage fly-eye lens 7 via a beam expander including a first lens 3, a deflection mirror 4 and a second lens 6. The second lens 6 and the fly-eye lens 7 form an input optical system 5A for normal illumination.
A is configured so that it can be exchanged with an input optical system 5B for annular zone illumination, which will be described later, via the exchange device 8.

The illumination light IL whose illuminance distribution is made uniform by the first-stage fly-eye lens 7 is an illuminance distribution correction plate 9 made of parallel flat glass for correcting unevenness of the illuminance distribution depending on the direction of the illumination light, and a relay lens. 10 and deflection mirror 11
Through the fly eye lens 12 for normal lighting in the second stage
Is incident on the incident surface of. The plane of incidence of the first-stage fly-eye lens 7 is conjugate with the plane of incidence of the second-stage fly-eye lens 12, and the planes of incidence of the latter fly-eye lens 12 are the lenses forming the former fly-eye lens 7. A magnified image of the entrance surface of the element is superimposed. In addition, the fly-eye lens 12 is configured to be replaceable with a fly-eye lens 13 for second-stage annular illumination, which will be described later, via an exchange device 14. Hereinafter, an optical axis of the illumination optical system after the second-stage fly-eye lens 12 and the optical axis of the projection optical system PL is the optical axis AX, the Z axis is taken in parallel with the optical axis AX, and is shown in a plane perpendicular to the Z axis. The description will be given by taking the Y axis parallel to the plane of FIG. 1 and the X axis perpendicular to the plane of FIG.

At this time, the second-stage fly-eye lens 12
Is an optical Fourier transform surface (pupil surface) with respect to the pattern formation surface of the reticle R, and a plurality of illumination system aperture stops (hereinafter referred to as “σ stop”) are provided on this exit surface. The σ diaphragm unit 15 is arranged. Figure 7
FIG. 7A shows the σ diaphragm unit 15, which is shown in FIG.
In (a), on the σ diaphragm unit 15 made of a disc rotatable about the drive shaft 15a, a σ diaphragm 75A for a large σ value and a σ diaphragm 75 for a small σ value are arranged at equal angular intervals.
B, a σ diaphragm 75C for the first annular illumination, and a σ diaphragm 75D for the second annular illumination are formed. σ diaphragm 75A
Details of the shapes of ~ 75D will be described later.

Returning to FIG. 1, in response to the main controller 29 that controls the overall operation of the apparatus instructing the illumination system control system 32 about the exposure conditions and the like, the illumination system control system 32 causes the σ diaphragm unit 15 to operate. Is rotated to set a predetermined σ stop on the exit surface of the fly-eye lens 12. At the same time as the operation, the illumination system control system 32 replaces the two input optical systems 5A and 5B via the exchanging device 8 if necessary, and also the two fly-eye lenses 12 and 1 via the exchanging device 14.
Also exchange 3.

Illumination light IL emitted from the fly-eye lens 12 and passing through a predetermined σ diaphragm in the σ diaphragm unit 15.
Enters the fixed field stop (fixed reticle blind) 18 that is sequentially driven in the Z tilt direction and the movable field stop 20 that is driven in the XY directions via the split prism plate 16 and the first relay lens 17. In this example, the movable field stop 2
0 is arranged on a conjugate surface with the pattern forming surface of the reticle R, and the fixed field stop 18 is arranged on a surface slightly defocused from the conjugate surface. And fixed field stop 1
A rectangular fixed aperture for defining a slit-shaped illumination area on the reticle R is formed at 8, and the position and tilt angle (tilt angle) of the fixed field stop 18 in the Z direction are determined by the illumination system control system 32. Can be finely adjusted via the drive unit 19.

On the other hand, the movable field stop 20 is a pair of movable blades 20a and 20b which can move independently in the Y direction.
And a pair of movable blades (not shown) that can be independently driven in the X direction.
The operation such as 0b is performed by the illumination system control system 32 via the drive unit 21.
Controlled by. When scanning exposure is performed on each shot area on the wafer W, the illumination light IL is also applied to the area other than the pattern area on the reticle R immediately after the scanning exposure starts and immediately before the scanning exposure with only the fixed field stop 18. Sometimes. Therefore, the movable field stop 20 plays a role of further limiting the illumination area on the reticle R defined by the fixed field stop 18 immediately after the start of scanning exposure and immediately before the end of scanning exposure.

Fixed field diaphragm 18 and movable field diaphragm 20
The illumination light IL that has passed through the opening of the second relay lens 2
The slit-shaped illumination area 24 on the pattern formation surface (lower surface) of the reticle R is illuminated with a uniform illuminance distribution via the condenser lens 23 and the condenser lens 23. The illumination area 24 in this example is X
This is a rectangular area whose direction is the longitudinal direction, and the scanning direction of the reticle R during scanning exposure is the Y direction parallel to the paper surface of FIG. Under the illumination light IL, the pattern in the illumination area 24 on the reticle R is reduced by the projection optical system PL at the projection magnification β (β is 1/4, 1/5, etc.), and the photoresist is applied. The image is projected onto the slit-shaped exposure area 33 on the surface of the wafer W. A variable aperture stop 42 in the form of, for example, an iris diaphragm is installed on the pupil plane (optical Fourier transform plane for the pattern formation surface of the reticle R) in the projection optical system PL, and the main controller 29 is variable via the drive unit 43. By switching the aperture diameter of the aperture stop 42, the numerical aperture NA of the projection optical system PL can be switched between 0.5 and 0.8, for example.

The reticle R is held on the reticle stage 25 by vacuum suction, and the reticle stage 25 can move at a constant speed in the Y direction on a reticle base 26 provided on a column (not shown), and in the X direction, It is configured so that it can be finely moved in the Y direction and the rotation direction. The movable mirror 27 is fixed to the end of the reticle stage 25,
7 and a laser interferometer 2 arranged so as to face it
The X-coordinate, the Y-coordinate, and the rotation angle of the reticle stage 25 are constantly measured by 8, and the measurement result is supplied to the main controller 29. The operation of the reticle stage 25 is controlled.

On the other hand, the wafer W is held on the Z tilt .theta. XY stage 3
7. In this case, the Z tilt .theta. Z tilt θ stage 35 X
The tilt angle about the axis and the tilt angle about the Y axis can be controlled, and the Z tilt θ stage 35 is configured to be rotatable about the Z axis within a predetermined range. In addition, the XY stage 37 can move the Z tilt θ stage 35 in the Y direction at a constant speed or can move in steps, and
It is configured so that it can be stepped in any direction. Wafer holder 34, Z tilt θ stage 35, fulcrum 36A-
A wafer stage is composed of 36C and the XY stage 37.

A movable mirror 39 is fixed to the end of the Z tilt θ stage 35, and the movable mirror 39 and the laser interferometer 40 arranged opposite thereto move the X tilt of the Z tilt θ stage 35 (wafer W). The coordinates, the Y coordinate, and the rotation angle are constantly measured, the measurement result is supplied to the main controller 29, and the main controller 39 supplies the XY stage 37, and the XY stage 37 via the wafer stage control system 41 based on the supplied measurement value. The operation of the Z tilt θ stage 35 is controlled.

Further, an oblique incidence type multi-point focus position detection system 48 for autofocus and autoleveling is installed on the side surface of the projection optical system PL. In this example, the thickness of the photoresist coated on the wafer W may be thinner than that of the conventional one as described later, and thus higher focus control accuracy than that of the conventional one is required. Therefore, in this example, as disclosed in, for example, Japanese Patent Laid-Open No. 6-283403,
The focus position (position in the Z direction) at a plurality of measurement points on the surface of the wafer W is measured by a method that also uses the pre-reading method. That is,
The focus position detection system 48 of this example includes a plurality of slit-shaped exposure regions 33 on the wafer W, and a plurality of read-ahead regions (for example, about 10) in the pre-reading region preceding the exposure regions 33 in the scanning direction.
Of the irradiation optical system that projects the slit image at the measurement point of, and re-images the slit images by receiving the reflected light from these slit images, and A focusing optical system for generating a focus signal and a plurality of focus signals are supplied to the focus signal processing system 49.

In the focus signal processing system 49, the focus position Z ₁ of the average surface of the exposure area 33 on the surface of the wafer W and the tilt angle θ _Y1 around the Y axis are calculated from the plurality of focus signals as an example. Then, similarly, the average focus position Z _{2 of the} surface in the pre-reading area with respect to the exposure area 33 and the tilt angle θ _Y2 around the Y axis are calculated, and the calculation result is supplied to the main controller 29. In the main controller 29, in consideration of the scanning speed of the wafer W and the response speeds of the auto focus and auto leveling mechanisms, for example, the focus of the controlled object is calculated from the weighted average of the focus positions Z ₁ and Z ₂ of the exposure area 33 and the look-ahead area. The position Z ₃ is calculated. Further, the main controller 29 calculates the tilt angle θ _Y3 around the Y axis of the control target from the weighted average of the tilt angles θ _Y1 and θ _Y2 of the exposure region 33 and the pre-read region, and at the same time, calculates the exposure region 33 and the pre-read region. The tilt angle θ _X3 around the X axis to be controlled is calculated from the difference between the focal positions Z ₁ and Z ₂ .
The focus position Z ₃ and the tilt angles θ _Y3 and θ _{X3 of} these controlled objects
The auto focus and auto leveling control are performed based on.

At the time of scanning exposure, the main controller 29 causes the KrF excimer laser light source 1 via an exposure amount control system 31 described later.
Pulse emission of the reticle stage 25 is started based on the measurement values of the laser interferometers 28 and 40.
The XY stage 37 on the wafer side is scanned in the + Y direction (or −Y direction) at the speed β · VR (β is the projection magnification) in synchronization with the scanning at the constant speed VR in the direction (or the + Y direction). Further, in the main controller 29, based on the plurality of focus signals corresponding to the exposure area 33 and the pre-reading area supplied from the focus signal processing system 49, the focus position Z ₃ of the control target, and Tilt angle θ _Y3 , θ
Sequentially calculated _X3, by driving the fulcrum 36A~36C via wafer stage drive system 41, the auto-focus system to ensure that its focal position Z ₃ is converged to the focal position of the best image plane of the projection optical system PL In addition to controlling the focal position of the wafer W, the inclination angle of the wafer W is controlled by the auto-leveling method so that the inclination angles θ _Y3 and θ _X3 converge on the inclination angle of the best image plane of the exposure region 33. As a result, the reticle R is formed on the transfer target shot area on the wafer W.
Pattern images are successively transferred at high resolution. In addition,
An exposure method for driving the reticle stage 25 and the XY stage 37 on the wafer side in synchronization with the pulsed light emission of the KrF excimer laser light source 1 is disclosed in, for example, Japanese Patent Laid-Open No. 6-1.
It is disclosed in Japanese Patent No. 32191.

Further, since the present example is the step-and-scan method, the width of the exposure region 33 on the wafer W in the scanning direction is narrower than that of the batch exposure method, and the wafer W is continuously exposed during the scanning exposure. Focusing is taking place. Therefore, even if the surface of the wafer W is gently undulating in the scanning direction, the exposure region 33 of the wafer W can be accurately aligned with the best imaging plane at each time point, and the transfer on the wafer W can be performed. The average value of the deviation of the focus position at the time of exposure at each point in the target shot area, that is, the focus control accuracy is higher than that of the collective exposure method (step-and-repeat method) like stepper. However, the wafer W is
If it is known that the surface undulations are small, a sufficiently high focus control accuracy can be obtained even with a projection exposure apparatus of a batch exposure system.

Next, an exposure amount control system in the projection exposure apparatus of this example will be described. First, Z tilt θ stage 3
In the vicinity of the wafer holder 34 on the wafer 5, a dose monitor 38 made of a photoelectric conversion element is installed so that the light receiving surface is at the same height as the surface of the wafer W. When the illuminance of the illumination light IL on the surface of the wafer W is directly detected, the dose monitor 3
The light receiving surface of No. 8 is installed in the exposure area 33, and the detection signal of the irradiation amount monitor 38 is supplied to the exposure amount control system 31 which controls the integrated exposure amount for each shot area of the wafer W.

However, since the exposure amount on the wafer W cannot be directly measured during the actual exposure of the wafer W, it passes through a predetermined σ stop in the σ stop unit 15 of FIG. The exposure amount on the wafer W is indirectly measured by separating a part of the illumination light IL and detecting the light amount. Therefore, the σ diaphragm unit 15 and the first
The split prism plate 16 is arranged between the relay lens 17 and the relay lens 17. That is, the split prism plate 16 is arranged near the pupil plane of the illumination optical system.

2A is a plan view of the split prism plate 16 viewed from the fly-eye lens 12 side, FIG. 2B is a right side view of FIG. 2A, and FIG. It is sectional drawing which follows the AA line when the 2 (a) division | segmentation prism board 16 is divided into two right and left. As shown in FIG. 2A, the split prism plate 16 is made of a glass substrate that transmits the illumination light IL having a predetermined thickness, and the illumination light IL is provided at the central portion and the right end portion thereof, respectively.
Prism type beam splitters 53A and 53B for taking out a part of the are embedded. Each of the beam splitters 53A and 53B has a transmittance of 95% and a reflectance of about 5% with respect to the illumination light IL.

Then, as shown in FIG. 2B, the illumination light ILF reflected by the beam splitter 53B in the illumination light incident from the fly-eye lens 12 side at the end of the split prism plate 16 is relayed. The output signal of the integrator sensor 58B is incident on the integrator sensor 58B composed of a photoelectric conversion element through the lens system 57B and the output signal of FIG.
Is supplied to the integrated exposure amount calculation unit 56. Also, FIG.
In FIG. 2B, the reflected light reflected by the wafer W in the illumination light IL for exposure irradiated on the wafer W via the projection optical system PL in FIG. 2B passes through the projection optical system PL and the reticle R. Returning to the beam splitter 53B, the reflected light ILR reflected by the beam splitter 53B enters the reflectance monitor 55B composed of a photoelectric conversion element via the relay lens system 54B, and the output signal of the reflectance monitor 55B is shown in FIG.
Is supplied to the image formation characteristic variation amount calculation section 59. From the output signal of the reflectance monitor 55B, the imaging characteristic variation amount calculation unit 59 can obtain the reflectance of the illumination light IL on the wafer W.

Further, as shown in FIG. 2A, a portion 1 between the beam splitter 53B and the relay lens systems 57B and 54B is provided at the end of the disc-shaped split prism plate 16.
6a has a rectangular flat plate shape, and the beam splitter 5
The light flux reflected by 3B is efficiently transmitted to the relay lens system 57.
B, 54B is led. Similarly, FIG.
As shown in (c), the illumination light ILF reflected by the beam splitter 53A in the illumination light that has entered the central portion of the split prism plate 16 from the fly-eye lens 12 side.
Enters the integrator sensor 58A via the relay lens system 57A. In addition, the reflected light from the wafer W in FIG.
To the beam splitter 53A of the beam splitter 5
The reflected light ILR reflected by 3A is transmitted to the relay lens system 54.
The light enters the reflectance monitor 55A via A. The output signals of the integrator sensor 58A and the reflectance monitor 55A are supplied to the integrated exposure amount calculation unit 56 and the imaging characteristic variation amount calculation unit 59 of FIG. 1, respectively. Since the split prism plate 16 in FIG. 1 is shown in a side view, only the relay lens systems 54B and 57B, the integrator sensor 58B, and the reflectance monitor 55B appear in FIG.

In this example, the beam splitters 53A,
Since 53B is arranged, for example, the coherence factor (σ
When performing illumination with a small value, the reflected light from the beam splitter 53A at the center is used, and when performing illumination using the illumination light passing through the peripheral annular zone 60B, the beam splitter at the end is used. The reflected light at 53B shall be used. By properly using the beam splitters arranged at two positions in this way, the illumination light can be accurately measured by either the illumination method with a small σ value or the annular illumination method.

Further, for example, in the case of performing modified illumination using a sigma stop composed of four apertures decentered from the optical axis, it is separately provided on the optical path of illumination light from one of the four apertures in the split prism plate 16. The beam splitter may be arranged, and a relay lens system and a photoelectric conversion element for receiving the light beam reflected by the beam splitter may be provided.
This makes it possible to reliably detect the illumination light from the fly-eye lens 12 or 13 and the reflected light from the wafer under all illumination conditions.

Returning to FIG. 1, the split prism plate 16 of this example.
The beam splitters 53A and 53B are arranged in a part, so that it is extremely thin. On the other hand, in the past, for example, immediately after the σ stop, approximately 45 ° with respect to the optical axis.
Since one large beam splitter is arranged at an inclination angle of 1 and the reflected light of this beam splitter is detected, a large space is required to arrange this beam splitter. According to this example, since it is only necessary to dispose the thin split prism plate 16, the illumination optical system can be downsized and the illumination optical system can be easily designed.

In this case, in this example, the dose monitor 3 is previously set.
8 is compared with the output signals of the integrator sensors 58A and 58B to obtain a conversion coefficient for obtaining the exposure amount on the wafer W from the output signals of the integrator sensors 58A and 58B. It is stored in the exposure amount control system 31. When the pulsed emission of the illumination light IL is started during the scanning exposure, the integrated exposure amount calculation unit 56 sets the number of exposure pulses for each point on the wafer W to N, and outputs the output signal from the integrator sensor 58B (or 58A). Is sequentially supplied to the exposure amount control system 31. The exposure amount control system 31 multiplies the integrated signal by the conversion coefficient to obtain an integrated exposure amount at each point on the wafer W, and controls the exposure amount so that the integrated exposure amount converges to a target value. .

In this example, the photoresist layer on the wafer W may be thin, but if the resist thickness is thin in this way, the target value of the integrated exposure amount becomes smaller than in the conventional example. When the target value of the integrated exposure amount is low as described above, in the scanning exposure method, for example, first, the scanning speed of the stage system is increased to shorten the exposure time for each point on the wafer W. However, since the scanning speed of the stage system has an upper limit, it is necessary to reduce the illuminance of the illumination light IL when the scanning speed of the stage system reaches the upper limit. Thus, in order to reduce the illuminance of the illumination light IL, the exposure amount control system 31
Controls the extinction ratio in the extinction unit 2 of FIG. Further, in order to set the number of exposure pulses for each point on the wafer to a predetermined value, or to cope with output fluctuations of the KrF excimer laser light source 1 during exposure to each shot area on the wafer, dimming The unit 2 may control the dimming rate.

FIG. 3 shows a schematic structure of the dimming unit 2 of this example. In FIG. 3, two glass plates 61A and 61B are inclined at a symmetrical inclination angle δ on the optical path of the illumination light IL.
Is installed, and light shielding plates 62A and 62B for respectively shielding the reflected light from the glass plates 61A and 61B are arranged. The glass plates 61A and 61B maintain a symmetrically inclined state by a driving device (not shown), and the inclination angle δ is variable. In this case, when the inclination angle δ changes, the glass plates 61A and 61 with respect to the illumination light IL.
By utilizing the fact that the transmittance (= 1−extinction ratio) at B changes, the illumination light I can be controlled by controlling its inclination angle δ.
The desired extinction ratio for L is obtained. Since the two glass plates 61A and 61B are inclined symmetrically in this way,
Since the optical path of the illumination light IL does not laterally shift between when the light is incident on the light reduction unit 2 and when the light is emitted, it is not necessary to adjust other optical systems even when the light reduction rate is switched. Further, the light shielding plates 62A and 62B prevent the reflected light from the glass plates 61A and 61B from leaking out of the dimming unit 2.

In the dimming unit 2 of FIG. 3, the dimming rate for the illumination light IL can be continuously switched within a predetermined range, but when it is desired to switch the dimming rate for the illumination light IL roughly in a plurality of stages. Before and after the dimming unit 2, for example, an energy rough adjusting unit including a plurality of ND filters having different transmittances arranged on a disc may be arranged. In this case, the dimming rate for the illumination light IL can be roughly switched by rotating the disk, and by combining this energy rough adjustment unit and the dimming unit 2 of FIG. The dimming rate can be continuously switched over a wide range.

Next, a mechanism for correcting the image forming characteristics of the projection optical system PL provided in the projection exposure apparatus of this example will be described. That is, the projection optical system PL is gradually heated by the irradiation of the illumination light IL that is pulsed, and the projection optical system PL is also heated by the light flux that is retransmitted through the projection optical system PL in the return light from the wafer W. As a result, the image forming characteristics such as the projection magnification β and the position of the best image forming surface change. Further, the imaging characteristics of the projection optical system PL also change due to changes in atmospheric pressure and environmental temperature. In order to correct the change in the image forming characteristic, the main controller 29 supplies information such as the illuminance of the illumination light IL and the exposure time so far to the image forming characteristic variation amount calculating section 59 in FIG. To do. Further, as described with reference to FIG. 2, the imaging characteristic variation amount calculation unit 59 has a reflectance monitor 55 which is a signal obtained by photoelectrically converting a part of the reflected light from the wafer W.
The output signals of B and 55A are also provided. Further, measurement values from an atmospheric pressure and temperature sensor (not shown) are also supplied to the image formation characteristic variation amount calculation unit 59.

The image formation characteristic variation calculation section 59 calculates the variation of the projection magnification β of the projection optical system PL based on the integrated value of the output signals of the reflectance monitors 55B and 55A and other information.
The amount of change in the field curvature, the amount of change in the focal position of the best image plane and the amount of change in the tilt angle thereof are predicted, and these prediction results are used as the main controller 29
Let us know. Further, the projection optical system PL is provided with a lens drive mechanism 44 that drives a part of the lens elements in the optical axis AX direction and inclines it with respect to a plane perpendicular to the optical axis AX. Lens drive control system 4
The operation of the lens drive mechanism 44 can be controlled via the control unit 5.

Then, when the predicted value of the change amount of the image formation characteristic is supplied from the image formation characteristic change amount calculation section 59 to the main control unit 29, the main control unit 29 firstly changes the projection magnification β or the image plane. In order to correct the amount of change in the curvature, the lens driving mechanism 44
A part of the lens elements of the projection optical system PL is driven via. Further, main controller 29 drives fulcrums 36A to 36C via wafer stage drive system 41 so as to match the amount of change in the focus position and tilt angle of the best imaging plane, thereby causing Z tilt θ stage 35 ( The height and tilt angle of the wafer W) are corrected. As a result, even if the imaging characteristics of the projection optical system PL change, the state in which the surface of the wafer W matches the best imaging surface of the projection optical system PL is maintained.

Next, the illumination optical system of this example will be described.
The illumination optical system of this example is configured to be able to switch between the normal illumination method in which the σ diaphragm has a circular opening and the annular illumination method which is an example of the modified illumination method. Therefore, the normal fly-eye lens 12 is used as the second-stage fly-eye lens in FIG.
And a fly-eye lens 13 for annular illumination are provided so as to be interchangeable. This fly-eye lens 13 for annular illumination
Is used when the numerical aperture NA of the projection optical system PL is set to 0.6 or less and annular illumination is performed.

FIG. 4 (a) is a side view of the fly-eye lens 13 for annular illumination, and FIG. 4 (b) is a plan view of the fly-eye lens 13, as shown in FIG. 4 (b). The fly-eye lens 13 is formed by bundling lens elements each having a rectangular cross section around a metal member 63 having a cross-shaped cross section. In this case, on the exit surface of the fly-eye lens 13, the annular σ diaphragms 75C, 7C in the σ diaphragm unit 15 of FIG.
Although any of 5D is arranged, if ILC is an annular light flux having a maximum cross-sectional area that passes through the lens element portion of the fly-eye lens 13 in FIG.
The apertures of the diaphragms 75C and 75D are configured to fit within the light flux ILC. Therefore, the fly-eye lens 13
By using the cross-shaped portion as a metal member and reducing the number of lens elements, it is possible to reduce the manufacturing cost and to illuminate the entire surfaces of the apertures of the σ diaphragms 75C and 75D.

When the fly-eye lens 13 for annular illumination is used as described above, the illumination efficiency is better when the distribution of the illumination light IL on the incident surface of the fly-eye lens 13 is annular. Therefore, fly-eye lens 13 for annular illumination
When using, the illumination system control system 32 of FIG. 1 arranges the input optical system 5B for annular illumination between the deflection mirror 4 and the illuminance distribution correction plate 9 via the exchange device 8.

FIG. 5 shows the input optical system 5B,
In FIG. 5, the illumination light I from the deflection mirror 4 in FIG.
Let L be linearly polarized light. The illumination light IL is the lens 6
After it becomes a substantially parallel light flux by 4, the quarter wave plate 65
It is converted into circularly polarized light by and enters the polarization beam splitter 66, and is split into a P polarization component ILP and an S polarization component ILS in the polarization beam splitter 66. FIG.
In the input optical system 5A, a quarter-wave plate (not shown) is also arranged, and the illumination light IL incident on the fly-eye lens 7 is converted into circularly polarized light.

FIGS. 6A to 6D show the illuminance distribution of the cross section of the illumination light in each part of FIG. 5, and FIGS.
Is the optical axis A with reference to the optical axis AX of the illumination optical system.
The position r in the direction perpendicular to X is shown, and the vertical axis shows the illuminance at that position r. First, the illuminance distribution E _IN (r) of the illumination light IL entering the polarization beam splitter 66 of FIG. 5 has a normal distribution centered on the optical axis AX, as shown in FIG. 6A. The illuminance distribution E _IN (r) is also the illuminance distribution of the P-polarized component ILP and the S-polarized component ILS immediately after being separated by the polarization beam splitter 66 except for a predetermined proportional coefficient.

In FIG. 5, the polarization beam splitter 66
The P-polarized component ILP transmitted through the
The optical member 71 having a shape obtained by processing a and 71b into a conical shape is transmitted. With this optical member 71, the P polarization component ILP
Of the P polarization component ILP immediately after being emitted from the optical member 71, because the inside and outside of the illuminance distribution are separated from each other and become parallel light again.
As shown in FIG. 6C, (r) has a distribution obtained by inverting and widening the distribution of FIG. 6A about the optical axis AX.

On the other hand, the S-polarized component ILS reflected by the polarization beam splitter 66 of FIG. 5 is reflected by the mirror 67, the upper portion 68a of the cylinder is cut into a conical shape, and the lower portion 68b is processed into a conical shape. The light passes through the optical member 68 having the above shape. With this optical member 68, the S polarization component IL
Since the illuminance distribution of S is separated at approximately its center and becomes parallel light again, the illuminance distribution E1 (r) of the S-polarized component ILS immediately after being emitted from the optical member 68 is as shown in FIG. 6B. The distribution shown in FIG. 6A is widened around the optical axis AX.

The P-polarized component ILP emitted from the optical member 71 is converted into S-polarized light by the ½ wavelength plate 72, and then reflected by the mirror 73 and incident on the polarization beam splitter 70 and reflected. .. On the other hand, the S-polarized component ILS emitted from the optical member 68 is converted into P-polarized light by the ½ wavelength plate 69, and then the polarization beam splitter 7
After passing 0, the polarization beam splitter 70 outputs a light flux that is a combination of the polarization components emitted from the optical members 68 and 71. This converted illumination light IL ′ is converted into FIG.
It enters the illuminance distribution correction plate 9. The illuminance distribution E _OUT (r) of the illumination light IL ′ thus synthesized has a flat annular shape as shown in FIG. 6 (d). That is, the illuminance distribution is made uniform by the input optical system 5B of the present example as in the case of using the first-stage fly-eye lens 7 in FIG. Furthermore, in this example, since the sectional shape of the illumination light IL 'is shaped like a ring, the utilization efficiency of the illumination light is high when the ring illumination is performed.

Although not shown, a relay lens is arranged on the exit surface of the polarization beam splitter 70 shown in FIG.
With this relay lens and the relay lens 10 in FIG. 1, the exit surface of the polarization beam splitter 70 and the entrance surface of the fly-eye lens 13 for annular illumination in FIG. 4 are substantially conjugated. The cross-sectional shape of the illumination light IL ′ in FIG. 5 on the incident surface of the fly-eye lens 13 in FIG. It has a curved shape. As a result, the loss of illumination light when performing annular illumination is small.

Next, as already described, in FIG.
In this example, the aperture stop (σ stop) of the illumination system is switched by rotating the σ stop unit 15, and the σ stop is selected from the four types of σ stop 75A to 75D shown in FIG. 7A. . In FIG. 7A, the radius of the aperture of the σ stop 75A for large σ values (coherence factors) is rα, and the radius of the aperture of the σ stop 75B for small σ values is rα.
1. The outer radius and inner radius of the ring-shaped aperture of the first σ stop 75C for ring-shaped illumination are rβ and rβ2, respectively.
The outer and inner radii of the ring-shaped opening of the σ diaphragm 75D for ring-shaped illumination are defined as rβ and rβ1, respectively.

In this example, basically, when the numerical aperture NA of the projection optical system PL of FIG. 1 is in the range of 0.5 to 0.6, the σ diaphragms 75C and 75D for annular illumination are used, and the numerical aperture NA is Is in the range of 0.68 to 0.8, the σ diaphragm 75A having a circular aperture,
Use 75B. The σ value of the illumination optical system is usually set to 0.6 to 0.8, and when transferring the contact hole pattern, it is set to a small value of, for example, about 0.3 to 0.4. Therefore, if the projection magnification β of the projection optical system PL is used, the outer radius rβ of the apertures of the σ diaphragms 75C and 75D for annular illumination used when the numerical aperture NA is 0.6 or less is expressed in units of numerical aperture. Is set as follows.

Β · 0.6 × 0.6 ≦ rβ <β · 0.8 × 0.6 (11) Further, the inner radius rβ of the opening of the σ diaphragm 75D (2/3 ring zone)
1 is set to (2/3) rβ, and the σ diaphragm 75C (1/2
The inner radius rβ2 of the opening of the annular zone is set to (1/2) rβ. Regarding the proper use of the ring-shaped σ diaphragms 75C and 75D, for example, test printing is performed in advance using a reticle to be transferred, the resolution of the resist pattern is measured, and the σ diaphragm having a higher resolution is used. You may do it.

On the other hand, the radius rα of the σ diaphragm 75A used when the numerical aperture NA is 0.68 or more is set as follows with the numerical aperture as a unit. An approximate numerical aperture of 0.7 is used instead of the numerical aperture of 0.68. β · 0.6 × 0.7 ≦ rα <β · 0.8 × 0.7 (12) Further, as shown in FIG. 7B, the radius rβ of the aperture for annular illumination has a large σ value. It is set to be smaller than the radius rα of the opening for use, for example, about 0.6 / 0.7. Also, a σ stop 7 for small σ values
The radius rα1 of 5B is set to about ½ of the radius rα, and the σ stop 75B is used when the contact hole pattern is transferred.

Returning to FIG. 1, in the projection exposure apparatus of this example, when the main controller 29 sets the numerical aperture NA of the projection optical system PL to 0.5 to 0.6, the illumination system control system 32 is replaced. Fly-eye lens 13 for annular illumination via device 14
Is selected, the σ diaphragm unit 15 is driven to set either of the σ diaphragms 75C and 75D for annular illumination on the exit surface of the fly-eye lens 13. Further, the illumination system control system 32 selects the input optical system 5B via the exchange device 8.

When the main controller 29 sets the numerical aperture NA of the projection optical system PL to 0.68 to 0.8, the normal fly-eye lens 12 is controlled by the illumination system control system 32.
Is selected, one of the circular σ stops 75A and 75B is set on the exit surface of the fly-eye lens 12, and the input optical system 5A is selected. As a result, the pattern of the reticle R is transferred onto the wafer W always under the optimum σ value and without lowering the utilization efficiency of the illumination light IL.

Next, the resolution and the like obtained when the pattern of the reticle R is transferred and exposed onto the wafer W by the projection exposure apparatus of this example will be described. First, also in this example, the resolution R of the projection image by the projection optical system PL is the illumination light I for exposure.
Using the wavelength λ of L, the k factor k ₁ , and the numerical aperture NA of the projection optical system PL, it is expressed by the following equation similar to the equation (1).

R = k ₁ · λ / NA (13) When the depth of focus of the projected image of the projection optical system PL is D, the depth of focus is expressed by equation (2) using the k factor k ₂ . Furthermore, if the focus control accuracy C _F , the mark step (step of the underlying pattern) D _M , the resist thickness T _R , and the coefficient K _UD for determining the depth of focus UDOF that can be used on the operator side are used, (6 ) It is necessary to satisfy the “condition concerning the margin of the depth of focus”, which is the same as the equation below.

C _F + D _M + T _R · K _UD ≦ D = k ₂ · λ / NA ² (14) Also, in this example, (a) the mark level difference D _M is reduced to 0. 1 μm (further, 0.
The focus control accuracy C _{F is set} to about 0.4 μm by improving the focus control technology (b). Further, in this example, even if the numerical aperture NA of the projection optical system PL is increased and the depth of focus D is narrowed, the resist thickness T _{R is set} to 0.2 μm so that the condition regarding the margin of the depth of focus of the formula (14) can be satisfied. The thickness should be reduced to about 1 μm or more in the conventional example.
Further, the coefficient K _UD for defining the usable depth of focus UDOF is set to 0.7, and the k factor k _{2 is set} to 1.7 in consideration of the narrow line width.

Under these conditions, if the numerical aperture NA satisfying the expression (14) is NA ₂ , the wavelength λ is 248 nm, and the numerical aperture NA ₂ is as follows. 0.4 + 0.1 + 0.2 × 0.7 ≦ 1.7 × 0.248 / NA ₂ ² , NA ₂ ≦ 0.81 (15) That is, the numerical aperture NA of the projection optical system PL is increased to 0.81. However, the condition regarding the margin of the depth of focus is satisfied. Therefore, by taking a margin and setting the numerical aperture NA to 0.78 and substituting this value into the equation (13), the resolution R becomes as follows. However, if the k factor k ₁ is 0.
55.

R = 0.55 × 0.248 / 0.78≈0.18 (μm) (16) This resolution 0.18 μm is the resolution of the circuit pattern corresponding to the 1 Gbit DRAM. However, the resolution R is so small, the value of k factor k ₂ after optimization to become even smaller to about 1.4, by substituting k factor k ₂ to 1.4 (14) , The upper limit of the numerical aperture NA satisfying the condition regarding the depth of focus margin is 0.74.
Becomes Further, by taking into account the margin and substituting 0.7 as the numerical aperture NA of the equation (13), the resolution R is almost 0.
It becomes 19 μm. Therefore, in the projection exposure apparatus of this example, KrF excimer laser light (wavelength 248 nm) is used as the exposure illumination light IL, the thickness of the photoresist on the wafer is set to about 0.2 μm, and the projection optical system P is used.
By setting the numerical aperture NA of L to about 0.7 to 0.74, the circuit pattern of the semiconductor device equivalent to the 1 Gbit DRAM is transferred onto the wafer with high accuracy while satisfying the condition regarding the depth of focus margin. You can do it.

In practice, the resist thickness T _R is 0.5 μm.
In some cases, the upper limit of the numerical aperture NA of the projection optical system satisfying the condition regarding the depth of focus margin of the equation (14) is about 0.7 (k ₂ is 1.7).
However, the numerical aperture NA can be set to about 0.68 with an allowance. Therefore, the resist thickness T _R is 0.5 μ
When set to m or less, numerical aperture NA is approximately 0.68
Even with the above setting, the condition regarding the margin of the depth of focus can be satisfied.

Further, in this example, when the numerical aperture NA of the projection optical system PL is set within the range of 0.5 to 0.6, for example, 0.55, the equations (9) and (10) already shown. As can be seen from the equation), even when the thickness of the photoresist is set to about 1 μm, the circuit pattern of the semiconductor device corresponding to the 256 Mbit DRAM can be transferred while satisfying the condition regarding the margin of the depth of focus. Further, by further performing annular illumination, a resolution equivalent to 256 Mbit DRAM can be obtained more reliably. That is, according to the projection exposure apparatus of this example, the circuit pattern of the second-generation semiconductor device can be formed by switching the numerical aperture of the projection optical system. In other words, according to the projection exposure apparatus of the present example, both the critical layer having a narrow line width and the rough layer having a wide line width can be handled by switching the numerical aperture of the projection optical system.

In this regard, conventionally, when the wafer flattening step is added, the time of the entire exposure step may be doubled. Therefore, a projection exposure apparatus for performing exposure on a critical layer which requires the wafer flattening as described above. And a projection exposure apparatus that performs exposure on other rough layers. Further, since the projection exposure apparatus is selectively used for each layer of the wafer by a so-called mix-and-match method, the process control is complicated. However, in this example, since one projection exposure apparatus can perform exposure on almost all layers of one wafer, the manufacturing line can be simplified and process control becomes easy.

In the above embodiment, the exposure illumination light is used.
The KrF excimer laser light is used as
ArF excimer laser light (wavelength 193 nm) is used
You can also. Therefore, ArF excimer laser light is used
Also try to evaluate the resolution and so on.
The projection optical system PL is newly optimized for a wavelength of 193 nm.
Shall be Even in this case, wafer flattening technology
Therefore, the mark step D_MIs as small as 0.1 μm
And resist thickness T_RTo 0.2 μm and use
Coefficient K for determining the usable depth of focus UDOF_UDTo
Set to 0.7. Further improve focus control technology
Therefore, focus control accuracy C_FTo about 0.2 μm
Shall be raised. Also, considering that the line width becomes narrower
k factor k _TwoIs set to 1.5.

Under these conditions, the numerical aperture NA satisfying the condition regarding the margin of the depth of focus in the equation (14) is set to NA.
Assuming ₂ , the wavelength λ is 193 nm, so the numerical aperture N
A ₂ is as follows. 0.2 + 0.1 + 0.2 × 0.7 ≦ 1.5 × 0.193 / NA ₂ ² , NA ₂ ≦ 0.81 (17) That is, also in this case, the numerical aperture NA of the projection optical system PL is 0.
Even if it is increased to 81, the condition regarding the margin of the depth of focus is satisfied. Therefore, the numerical aperture NA is 0.73 with a margin.
By substituting this value into equation (13),
The resolution R is as follows. However, the k factor k _{1 is set} to 0.45 in consideration of the line width.

R = 0.45 × 0.193 / 0.73≈0.12 (μm) (18) This resolution 0.12 μm is the resolution of the circuit pattern corresponding to the 4 Gbit DRAM. Therefore, in the projection exposure apparatus of this example, ArF excimer laser light (wavelength 193 nm) is used as the exposure illumination light, the thickness of the photoresist on the wafer is set to about 0.2 μm, and the projection optical system PL By setting the numerical aperture NA to about 0.73, while satisfying the conditions regarding the depth of focus margin,
A circuit pattern corresponding to 4 Gbit DRAM can be transferred onto the wafer with high accuracy.

Similarly, when using ArF excimer laser light, the numerical aperture NA of the projection optical system PL is 0.5.
Even if the thickness of the photoresist is set to about 1 μm by setting the thickness within the range of ˜0.6, the condition for the margin of the depth of focus is satisfied and the 1 Gbit DRA is set.
The circuit pattern of a semiconductor device corresponding to M can be transferred.
Also in this case, the resolution equivalent to the 1 Gbit DRAM can be more surely obtained by using the annular illumination together. That is, a single projection exposure apparatus can form a circuit pattern of a second-generation semiconductor device.

Furthermore, in the projection exposure apparatus of this example, the i-line (wavelength 365 nm) of the mercury lamp is used as the illumination light for exposure.
Is used, the numerical aperture NA of the projection optical system PL is set to about 0.7 to 0.8 and the resist thickness is 0.2 μm.
By setting the degree to about, it is possible to transfer the circuit pattern corresponding to the 256 Mbit DRAM with high accuracy while satisfying the condition regarding the depth of focus margin. On the other hand, as described above, when the numerical aperture NA is set to about 0.5 to 0.6, the circuit pattern corresponding to the 64 Mbit DRAM can be transferred with high accuracy. Also at this time, the resolution equivalent to the 64 Mbit DRAM can be more reliably obtained by using the annular illumination together.
As a result, it is possible to form a circuit pattern for a second-generation semiconductor device.

As the exposure illumination light, a metal vapor laser light, a harmonic of a YAG laser, or another bright line may be used. In these cases, too, the photoresist is thinned and the aperture of the projection optical system is used. By increasing the number, it is possible to satisfy the condition regarding the margin of the depth of focus and improve the resolution. Furthermore, if the mark step D _M can be reduced and the resist thickness T _R can be made thinner by the progress of the flattening technology in the future, even if the numerical aperture NA of the projection optical system is made larger than 0.7, the formula (14) is obtained. Since the condition regarding the margin of the depth of focus is easily satisfied, the resolution R can be further increased.

Next, in this example, as one method for satisfying the condition concerning the margin of the depth of focus of the equation (14),
The wafer planarization technique is used as described above. When the wafer is flattened in this manner, the mark step D _M, which is the step of the circuit pattern formed on the wafer W, is reduced to, for example, about 50 nm or less, and the mark step D _M is attached to each shot area on the wafer W. The step of the alignment wafer mark is also reduced. Therefore, in this example, a sensor capable of detecting a low step mark is provided as an alignment sensor for performing alignment of each of the shot areas.

In FIG. 1, an alignment sensor 50 is arranged on the side surface of the projection optical system PL. In addition,
This alignment sensor 50 is disclosed in Japanese Patent Laid-Open No. 5-21783.
The configuration is similar to that of the alignment sensor disclosed in Japanese Patent No. 5 publication. FIG. 8 is a perspective view schematically showing the overall configuration of the alignment sensor 50. In FIG. 8, reflected light from a lattice-shaped wafer mark (not shown) formed on the wafer is reflected by the mirror M1. After being reflected and incident on the objective lens OBL, it is split by the beam splitter BS1. The light flux reflected by the beam splitter BS1 is
The imaging method, that is, the FIA (Field Image), which is reflected by the mirror M2 and is arranged on the upper stage of the alignment sensor 50.
The light enters the detection system (hereinafter referred to as “FIA system”) 51A of the Alignment method. On the other hand, the beam splitter BS1
The light flux that has passed through is a two-beam interference method arranged in the lower part, that is, LIA (Laser Interferometric Alignment)
The light enters a detection system (hereinafter, referred to as “LIA system”) 51B of the method.

FIG. 9 shows the configuration of the FIA system 51A. In FIG. 9, the non-photosensitive broadband (band 270 nm or more) illumination light ALA is emitted from the optical fiber 116A to the photoresist on the wafer. The illumination light ALA illuminates the wafer illumination field diaphragm 121A with a uniform illuminance via the condenser lens 120A. The illumination light limited by the field stop 121A is reflected by the mirror 122A, passes through the lens system 123A, and the illumination system aperture stop plate 16
Incident on 1. A plurality of types of aperture diaphragms (hereinafter referred to as “σ diaphragms”) are arranged on the illumination system aperture diaphragm plate 161, and a desired σ diaphragm can be selected by sliding the illumination system aperture diaphragm plate 161. Is configured.

The illumination light ALA that has passed through a predetermined σ stop in the illumination system aperture stop plate 161 enters the beam splitter BS2 and is reflected by the beam splitter BS2.
LA is reflected by the mirror M2 and is reflected by the beam splitter BS.
Incident on 1. Then, the illumination light ALA illuminates the wafer mark on the wafer along the optical axis AXa via the objective lens OBL and the mirror M1. In this illumination light transmission path for the wafer, the field stop plate 121A is conjugate with the wafer with respect to the combined system of the lens system 123A and the objective lens OBL, and the illumination area for the wafer by the FIA system 51A is
It is uniquely determined by the aperture formed in the field diaphragm 121A.

Reflected light is generated from the wafer irradiated with the illumination light ALA from the optical fiber 116A, and this reflected light is passed through the mirror M1, the objective lens OBL, the beam splitter BS1, and the mirror M2 to the beam splitter BS2. About 1/2 of the reflected light is incident on the detection optical system through the beam splitter BS2. This detection optical system includes an aperture stop plate 163, a lens system 124, a mirror 125, an index plate 126 having index marks, a first relay lens system 127 for imaging, a mirror 128, an interference filter 129, and a second relay lens system. 131 and a beam splitter BS3. Aperture diaphragm plate 1
A plurality of types of aperture diaphragms are also arranged in 63, and the aperture diaphragm plate 1
A desired aperture stop can be selected by sliding 63.

The return light from the wafer, which has passed through a predetermined aperture stop in the aperture stop plate 163, enters the beam splitter BS3 through the lens system 124 and the like, and the beam splitter B
The return light from the wafer divided in S3 is a two-dimensional CCD
Incident on the image sensor 108X for detecting the X direction and the image sensor 108Y for detecting the Y direction,
An image of the wafer mark and an image of the index mark on the wafer surface are formed on the X and 108Y image pickup surfaces.

That is, the objective lens OBL and the lens system 12
For the composite system of No. 4, the wafer surface and the index plate 126 are conjugate, and for the relay lens systems 127 and 131, the index plate 126 and their imaging surfaces are conjugate. Further, a variable power optical system 130 can be inserted in the vicinity of the interference filter 129 so that the magnification of the image of the wafer mark and the index plate can be changed. In addition, the interference filter 1
The numeral 29 also plays a role of blocking strong laser light used in the LIA system 51B described later.

Further, in FIG. 9, an illumination system for independently illuminating the index plate 126 is provided. This illumination system includes an optical fiber 116B and a condenser lens 120.
B, an illumination field diaphragm plate 121B, a mirror 122B, and a lens system 123B. Then, the illumination light ALB emitted from the optical fiber 116B passes through the condenser lens 120B to the lens system 123B, and from the side opposite to the optical path of the illumination light ALA for the wafer, the beam splitter BS.
2 and is reflected by the beam splitter BS2 to illuminate the index plate 126.

Further, the image pickup signals of the image pickup devices 108X and 108Y are supplied to the alignment signal processing system 52 of FIG.
The alignment signal processing system 52 processes the image pickup signals to detect the position of the wafer mark to be detected, and supplies the detection result to the main controller 29.
Main controller 29 aligns wafer W based on the position of each wafer mark.

Next, FIG. 10 shows the configuration of the LIA system 51B. In FIG. 10, the He--Ne laser light source 106 is shown.
The laser beam from is split into two by the beam splitter BS8 via the shutter 140. Beam splitter BS8
The laser beam LB that has passed through is incident on the heterodyne two-beam conversion unit 141X via a plurality of folding mirrors in the LIA system in the X direction. In this heterodyne two-beam conversion unit 141X, a pair of frequency shifters (acousto-optical elements) having different driving frequencies and two frequency-modulated laser beams emitted from the pair of frequency shifters are used as optical axes. And a synthesizing system for synthesizing in parallel with. The two laser beams LB1x and LB2x emitted from the synthesizing system enter the lens system 142X and uniformly illuminate the aperture plate 143X arranged on the rear focal plane of the lens system 142X. Therefore, the two laser beams LB1x and LB are arranged on the aperture plate 143X.
The 2x intersection forms a one-dimensional interference fringe. Moreover, since the drive frequencies of the pair of frequency shifters in the heterodyne two-beam conversion unit 141X are different from each other, the one-dimensional interference fringes flow in the pitch direction at a speed corresponding to the frequency difference.

Now, the two laser beams limited by the aperture plate 143X are beam splitter BS6.
Is partially reflected by, passes through the lens system 144X, the beam splitters BS4 and BS1, and then reaches the wafer through the objective lens OBL and the mirror M1. Since the two laser beams LB1x and LB2x are symmetrically inclined with respect to the X direction, when they are irradiated on the lattice-shaped X-axis wafer mark provided on the wafer, the laser beams LB1x and LB2x are ± 1 perpendicular to the wafer mark.
Next-order diffracted light is generated. The two ± 1st-order diffracted lights have the same polarization direction and thus interfere with each other, and at the same time, the interference intensity periodically changes at the frequency difference between the pair of frequency shifters, that is, the beat frequency.

This interference beat light is incident on the beam splitter BS6 via the mirror M1, the objective lens OBL, the beam splitters BS1 and BS4, and the lens system 144X, and the interference beat light transmitted through this beam splitter BS6 is received by the aperture. Reach plate 145X. The light receiving aperture plate 145X includes a lens system 144X and an objective lens O.
It is arranged at a position conjugate with the wafer with respect to the combined system with BL, and has an opening through which only the interference beat light passes. The interference beat light that has passed through the aperture plate 145X is
It reaches the photoelectric sensor 148X via the mirror 146X and the lens system 147X, and the beat signal is output from the photoelectric sensor 148X.

The laser beam reflected by the beam splitter BS8 is incident on the LIA system for the Y direction via the mirror. This LIA system for Y direction is L for X direction.
Heterodyne 2-beam conversion unit 1 in almost symmetry with the IA system
41Y, lens system 142Y, aperture plate 143Y, beam splitter BS5, lens system 144Y, light receiving aperture plate 145Y, mirror 146Y, lens system 147.
Y and photoelectric sensor 148Y. However, the heterodyne 2-beam conversion unit 141Y
The two laser beams LB1y and LB2y from the heterodyne two-beam forming unit 141Y are arranged so as to be rotated by 90 ° with respect to the beam forming unit 141X so that they intersect the Y-axis wafer mark on the wafer in the Y direction. Is irradiated. Then, the beat signal corresponding to the wafer mark on the Y-axis is output from the photoelectric sensor 148Y.

Further, in order to obtain the reference signal of the beat signal from the photoelectric sensors 148X and 148Y, the laser beam L
The laser beam transmitted through the beam splitter BS4 among B1x and LB2x, and the laser beams LB1y and LB2
The laser beam reflected by the beam splitter BS4 in y is incident on the beam splitter BS7 via the lens system 150 and the mirror 151. Then, the laser beam reflected by the beam splitter BS7 enters the transmission type diffraction grating plate 153X via the mirror 152.
The transmission type diffraction grating plate 153X forms a diffraction grating at a position conjugate with the opening of the X-axis light receiving aperture plate 145X,
Other than that is used as a light-shielding portion, and only the laser beams LB1x and LB2x are incident on the diffraction grating, and interference beat light composed of ± first-order diffracted light generated from the diffraction grating is a lens system 154X for Fourier transform. The incident light enters the photoelectric sensor 155X via the optical sensor 155X, and the reference beat signal for the X axis is output from the photoelectric sensor 155X.

The laser beam transmitted through the beam splitter BS7 is incident on the transmission type diffraction grating plate 153Y. The transmission type diffraction grating plate 153Y forms a diffraction grating at a position conjugate with the opening of the Y-axis aperture plate 145Y for light reception, and forms the other part as a light shielding part. The laser beam LB1y is applied to the diffraction grating. , LB2y is incident, and the interference beat light composed of ± first-order diffracted light generated from the diffraction grating passes through the lens system 154Y and the photoelectric sensor 15
5Y, and the photoelectric sensor 155Y outputs a reference beat signal for the Y axis.

The beat signals from the photoelectric sensors 148X and 148Y and the reference beat signals from the photoelectric sensors 155X and 155Y are respectively the alignment signal processing system 5 of FIG.
2, the alignment signal processing system 52 detects the position of the X-axis and Y-axis wafer marks to be detected from the beat signal and the reference beat signal, and supplies the detection result to the main controller 29. Main controller 29 aligns wafer W based on the position of each wafer mark.

As described above, the alignment sensor 5 of this example
0 includes a FIA system 51A and a LIA system 51B. In this case, the FIA system 51A has 100 nm (0.1 μm)
m) Detection of a wafer mark having a step height higher than SN
In addition, since the image processing method is used, the position detection can be performed with high accuracy even for an asymmetric wafer mark or a wafer mark having a rough surface. On the other hand, the LIA system 51B can detect a low step mark (step 50 nm or less) with high accuracy. Therefore, by using the FIA system 51A for the high step mark and the LIA system 51B for the low step mark, it is possible to deal with any semiconductor device.

Further, in this example, when the mark step D _M is high, the numerical aperture NA of the projection optical system PL is set to 0.6 or less,
When the mark step D _M is low, the numerical aperture NA is 0.6
8 and above. Therefore, in other words, in this example, normally, the FIA system 51A is used when the numerical aperture NA of the projection optical system PL is 0.6 or less, and the LIA system 51B is used when the numerical aperture NA is 0.68 or more. The alignment sensor is switched. However, if the pitch of the wafer marks attached to each shot area on the wafer is, for example, 8 μm, the detection range (capture range) by the LIA system 51B is within ± 2 μm, so that L
Before performing final alignment (fine alignment) using the IA system 51B, it is necessary to perform rough position detection (search alignment) of the wafer mark.
Therefore, in the present example, a mechanism capable of detecting a low step mark is added to the FIA system 51A as described below, and the FIA system 51A switched to detect the low step mark is used, and the wafer having the low step difference is used. Mark search alignment will be performed.

The mechanism for detecting the low step mark by the FIA system 51A will be described in detail below. FIG. 11 (a)
11A and 11B are simplified configuration diagrams in which mirrors and the like are omitted from the FIA system 51A in FIG. 9, and in FIG. 11A, the illumination light ALA emitted from the optical fiber 116A has
A condenser lens 120A and lens system 12
After passing through 3A, the light enters the illumination system aperture stop plate 161. Then, the illumination light that has passed through the predetermined σ stop of the illumination system aperture stop plate 161 enters the beam splitter 162, and the illumination light that has passed through the beam splitter 162 illuminates the wafer mark 165 on the wafer W via the objective lens OBL. To do. Further, the solid line optical path of the illumination light ALA in FIG. 11A shows the conjugate relationship with the wafer mark, and the dotted line optical path shows the pupil conjugate relationship. That is, the illumination system aperture stop plate 161 is arranged on the optical Fourier transform plane (illumination system pupil plane) HF1 with respect to the surface on which the wafer mark 165 is formed.

As shown in FIG. 11B, the illumination system aperture stop plate 161 includes a normal σ stop 166A having a large circular aperture, a ring-shaped σ stop 166B, and four circles decentered from the optical axis. Narrowly defined deformation σ diaphragm consisting of an aperture 166C
Are formed. Then, by sliding the illumination system aperture stop plate 161 in a direction perpendicular to the optical axis AXa, a desired σ stop of the three σ stops is illuminated with the illumination light A.
It is configured so that it can be set on the optical path of LA. In this example, when detecting a high step mark having a mark step D _M of 100 nm or more, a normal σ stop 166A is used, and when detecting a low step mark having a mark step D _M lower than 100 nm, a ring is used. A belt-shaped σ stop 166B or a modified σ stop 166C is used. That is, the ring-shaped σ diaphragm 166B and the modified σ diaphragm 166C are used as a filter for edge enhancement on the illumination system side for enhancing the phase (step) of a phase object having irregularities.

Returning to FIG. 11A, the wafer mark 165
From the image pickup device 108Y through the aperture stop plate 163 and the imaging lens 164 along the optical axis AXb. An image of the wafer mark is formed on the surface. The aperture stop plate 163 is arranged on the optical Fourier transform surface (pupil surface) HF2 with respect to the surface on which the wafer mark 165 is formed.

As shown in FIG. 11C, the aperture stop plate 1
63 is an ordinary aperture stop 16 having a large circular aperture.
7A, a ring-shaped aperture stop 167B, and a modified aperture stop 167C in a narrow sense composed of four circular apertures decentered from the optical axis.
Are formed. Then, the aperture stop plate 163 is moved to the optical axis A.
By sliding in the direction perpendicular to Xb, a desired aperture stop of the three aperture stops can be set on the optical path of the return light. When in this example, when the mark step difference D _M detects a high step mark above 100nm is that using normal aperture stop 167A, the mark step difference D _M is detected less than 100nm low step mark, wheels Band-shaped aperture stop 167B or modified aperture stop 16
Use 7C. That is, the ring-shaped aperture stop 167B and the modified aperture stop 167C are used as a contour enhancement filter for enhancing the phase (step). Thus, in this example, for the low step mark, the σ stop 166B,
Alternatively, since a contour enhancement filter including the modified σ stop 166C and the aperture stop 167B or the modified aperture stop 167C is used, an image of a low step mark can be detected with high contrast.

When the numerical aperture NA of the projection optical system PL is 0.68 or more, the switching between the σ stop and the aperture stop is unconditionally the ring-shaped stop 166B, 167B or the modified stop 166C, 167C. On the other hand, when the numerical aperture NA is 0.6 or less, the mark step D _M is usually high, but even if the mark step D _M is low, the condition regarding the margin of the depth of focus is satisfied, so that the numerical aperture NA is 0 depending on the application. ．
When it is 6 or less, a low step mark may be handled. Therefore, when the numerical aperture NA of the projection optical system PL is set to 0.6 or less and exposure is performed on one lot of wafers, it is possible to determine the level difference of the wafer mark step on the first wafer of the lot as follows. It may be performed.

That is, first, the image pickup signal SY from the image pickup device 108Y is taken in by the first wafer of the lot. As the wafer mark 165, as shown in FIG.
Assume a two-dimensional mark (mark for both X-axis and Y-axis) in which three convex or concave marks are arranged at different intervals in the Y direction and the Y direction. And the imaging device 1
The image pickup signal SY output from 08Y is X-rayed within the rectangular observation field 168 including the wafer mark 165 of FIG.
It is assumed that the wafer mark 165 is discriminated from other marks and the position in the Y direction is detected based on the signal averaged in the direction.

At this time, FIG. 12B shows a large circular shape.
When using σ diaphragm 166A and aperture diaphragm 167A
FIG. 12C shows the obtained image pickup signal SY, and FIG.
σ stop 166B and aperture stop 167B, or modified σ stop
Obtained when using the 166C and modified aperture stop 167C
The captured image signal SY is shown. The image pickup signal SY is observed
It is represented as a function of the Y coordinate within the field of view 168. Soshi
The image pickup signal SY in FIG.
High contrast even when the mark level difference of 5 is 100 nm or more
Signal and the Y of the three marks of the wafer mark 165
Position a₁, B₁, C₁Can be detected with high accuracy. This
On the other hand, the image pickup signal SY in FIG.
Mark 165 has a high mark level even if the mark level difference is 100 nm or less.
Since it becomes a trust signal, the mark step is 100n
Position a in the Y direction of the three marks when m or less_Two,
b_Two, C_TwoCan be detected with high accuracy. In other words, Mar
Step D _MIs reduced from about 100 nm to about 10 nm
12B, the contrast of the image pickup signal SY in FIG.
The lighting conditions are reduced and the unevenness disappears, while the lighting conditions are changed.
The image of FIG. 12C in which the contour of the uneven mark is emphasized
The signal SY should have sufficient contrast to be detected
I have.

When exposing one lot of wafers with the numerical aperture NA of the projection optical system PL being 0.6 or less, the FIA system 51A is first used for the first wafer and a large circular σ diaphragm 166A, Then, the aperture stop 167A is selected and detection is performed to obtain the contrast C1 of the obtained image pickup signal SY in FIG. And this contrast C
When 1 is smaller than a predetermined reference value, the annular σ stop 166B or the modified σ stop 166C is set in the illumination system aperture stop plate 161, and the annular stop aperture 167B or the modified aperture stop 167C is set in the aperture stop plate 163. Is set and detection is performed, and the contrast C2 of the obtained image pickup signal SY in FIG. After that, the first obtained contrast C1 is compared with the second obtained contrast C2, and a detection condition that can obtain a higher contrast is selected. For the second and subsequent wafers of the lot, the FIA system 51A is used.
Is set to the detection condition thus selected to detect the wafer mark. As a result, there is an advantage in that it is possible to detect the wafer mark with high accuracy under a high-contrast detection condition even when it is not known whether the level difference of the wafer mark is higher or lower than 100 nm, or even in the vicinity of 100 nm.

Regarding the proper use of the annular σ stop 166B and the modified σ stop 166C in the illumination system aperture stop plate 161, and the proper use of the annular stop 167B and the modified aperture stop 167C in the aperture stop plate 163. For example, the contrasts of the image pickup signals SY obtained when switching to the apertures 166B and 167B or the apertures 166C and 167C are compared, and the aperture with the higher contrast may be used.
Further, it is not always necessary to combine the annular σ stop 166B and the annular aperture stop 167B, and it is also possible to use a combination in which the obtained image pickup signal SY has a high contrast. Further, in the example of FIG. 11, the aperture stops 167A-16
Although a bright and dark (amplitude distribution) diaphragm is used as 7C, the contour of the low step mark may be emphasized by using a phase filter that changes the phase distribution of the light flux passing through the pupil plane.

Further, when the thickness of the photoresist on the wafer is changed, the type (photosensitive wavelength) of the photoresist may be changed. Specifically, when the type of photoresist is changed to reduce the resist thickness, the photosensitive wavelength of the photoresist on the wafer shifts to a short wavelength range, and the wavelength range not sensitive to the photoresist on the wafer is 55
It may shift from about 0 to 800 nm to about 350 to 600 nm. In such a case, FIG. 11 (a)
In the FIA system 51A, the wavelength range of the illumination light ALA for detecting the wafer mark is changed from about 550 to 800 nm to 3
The wavelength may be shortened to about 50 to 600 nm. By thus shortening the wavelength of the illumination light ALA, the contrast of the image pickup signal obtained by picking up the image of the low step mark is improved, and the detection accuracy of the low step mark can be increased.

Next, in this example, the thickness of the photoresist on the wafer W (resist thickness) may be made thinner than in the conventional example. However, when the photoresist becomes thinner, the target value of the integrated exposure amount for the photoresist is set. Decreases in proportion to its thickness. Specifically, conventionally, the resist thickness is about 1 μm or more, and the variation in the resist thickness is 0.01 to
Since the thickness is 0.02 μm (10 to 20 nm), in the conventional example, the target value of the integrated exposure amount remained substantially constant even if the resist thickness varied. On the other hand, in this example, the resist thickness may be about 0.2 μm as described above, and in this case, it is necessary to correct the target value of the integrated exposure amount according to the variation in the resist thickness. For that purpose, since it is necessary to actually measure the resist thickness on the wafer W, in this example, a resist thickness measuring device 46 is provided on the side surface of the projection optical system PL as shown in FIG. The resist-thickness measuring device 46 is, for example, a device for picking up an image of an equal-thickness interference fringe on a photoresist layer. The thickness of the photoresist is calculated from the signal, and the calculation result is supplied to main controller 29. Then, main controller 29 corrects the target value of the integrated exposure amount according to the thickness of the supplied photoresist. As a result, a proper integrated exposure amount can always be obtained.

In this example, as described above, basically, when the resist thickness T _R is about 1 μm or more, the numerical aperture NA of the projection optical system PL of FIG. The system uses σ diaphragms 75C and 75D for annular illumination and an alignment sensor for high step marks. When the resist thickness T _R is about 0.5 μm or less, the numerical aperture NA of the projection optical system PL is 0.68 to 0.8.
As a degree, the illumination optical system has a circular aperture σ stop 75A,
In addition to using 75B, an alignment sensor for low step marks is used. Therefore, in this example, it is possible to switch the illumination condition and the alignment sensor based on the resist thickness T _R. In this case, when the resist thickness T _R is about 1 μm or more, the illumination optical system uses the σ stops 75C and 75D for annular illumination, and the alignment sensor for high step marks is used. on the other hand,
When the resist thickness T _R is about 0.5 μm or less, the σ stops 75A and 75B having circular openings are used in the illumination optical system, and the alignment sensor for the low step mark is used. This makes it possible to optimize the illumination condition and alignment sensor according to the thickness of the photoresist on the wafer.

Needless to say, the present invention can be applied not only to the case of performing exposure with a step-and-scan type projection exposure apparatus, but also to the case of performing exposure with a collective exposure method such as a stepper. That is, even in the collective exposure method, the resolution can be improved and the alignment mark can be detected with high accuracy by switching the illumination condition and the detection condition of the alignment sensor according to the numerical aperture of the projection optical system.

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

[0123]

According to the first exposure method of the present invention, for example, when the mark step is low and the photosensitive material is thin, the numerical aperture of the projection optical system is increased so that the wavelength of the exposure illumination light is not shortened. There is an advantage that the resolution can be further improved and the condition regarding the margin of the depth of focus can be satisfied. Further, when the numerical aperture of the projection optical system is large, a sufficiently high resolution can be obtained even if the illumination condition is a normal illumination condition.

In other words, according to the present invention, when the i-line of the mercury lamp is used as the illumination light for exposure, it is possible to form a pattern corresponding to the next-generation 256 Mbit DRAM.
1 Gbit D when using rF excimer laser light
A pattern corresponding to RAM can be formed, and a pattern corresponding to 4 Gbit DRAM can be formed when ArF excimer laser light is used, and the cost performance of the exposure apparatus is improved.

On the other hand, when the mark level difference is high and the photosensitive material is thick, the numerical aperture of the projection optical system is reduced to satisfy the margin condition of the depth of focus, and the resolution is increased to some extent by switching to the modified illumination condition. You can As a result, a pattern corresponding to a second-generation semiconductor device can be formed with one exposure apparatus without changing the wavelength of the exposure illumination light. You can manage with just one unit. Therefore, the process control is easy, the process control time is shortened, and the throughput of the exposure process is improved.

In the present invention, it is possible to form a pattern corresponding to, for example, a second-generation semiconductor device by switching the numerical aperture of the projection optical system in two steps. However, depending on the mark step and the thickness of the photosensitive material. The numerical aperture may be switched in three or more steps. As a result, high resolution can be obtained while satisfying the conditions regarding the depth of focus margin according to the thickness of the photosensitive material.

Further, according to the exposure apparatus of the present invention, the first exposure method of the present invention can be carried out. Further, the illumination condition changing means sets the illumination optical system to a normal illumination condition when the numerical aperture of the projection optical system is set to 0.68 or more, and the numerical aperture of the projection optical system is set to 0.6 or less. Although the illumination optical system is set to a modified illumination condition when it is set, for example, when the mark step is about 0.1 μm or less and the thickness of the photosensitive material is about 0.5 μm or less, the numerical aperture is 0. When the mark step is about 0.8 μm and the thickness of the photosensitive material is about 1 μm, the numerical aperture is set to 0.6 or less, so that the margin of the depth of focus can be adjusted according to the thickness of the photosensitive material. The condition can be satisfied and the resolution can be improved.

At this time, the illumination condition changing means includes a light beam splitting system for splitting the exposure illumination light into first and second light beams.
A first light flux expanding system that expands the cross-sectional shape of the first light flux into an annular shape, and a second light flux expansion system that expands the cross-sectional shape into an annular shape with the light amount distribution of the second light flux being inverted between the inner and outer molds. And a light flux combining system for combining the light fluxes from the first and second light flux expanding systems before the illumination system pupil plane.
When the illumination condition changing means sets the modified illumination condition, if the light flux synthesized by the light flux synthesis system is guided to the pupil plane of the illumination system to perform annular illumination, the illumination system pupil Only the part of the secondary light source having a ring-shaped surface is illuminated with a uniform illuminance distribution. Therefore, the utilization efficiency of the illumination light is increased, a high illuminance is obtained on the mask (on the photosensitive substrate), and the illuminance distribution on the mask is also uniform.

Next, according to the second exposure method of the present invention,
For example, when the mark height of the alignment mark is low and the photosensitive material is thin, the numerical aperture of the projection optical system can be increased to improve the resolution without shortening the wavelength of the exposure illumination light and to increase the depth of focus margin. There is an advantage that the condition regarding Further, when the mark step is low, the alignment optical system can switch the detection condition for contour enhancement to detect the alignment mark with high accuracy. On the other hand, when the mark step is high and the photosensitive material is thick, the numerical aperture of the projection optical system is made small so as to satisfy the condition concerning the margin of the depth of focus. Even if set to, the alignment mark can be detected with high accuracy. With this, even if the mark step changes, the position can be detected with high accuracy, and the overlay accuracy can be maintained high.

In this case, the numerical aperture of the projection optical system is 0.
When it is set to 68 or more, the alignment optical system is set to the detection condition for the contour enhancement, and when the numerical aperture of the projection optical system is set to 0.6 or less, the alignment optical system is set to the normal detection. Assuming that the conditions are set, as described above, the numerical aperture of the projection optical system can be set to 0.68 or more when the mark step is about 0.1 μm or less.
In addition, it is a case where the thickness of the photosensitive material is about 0.5 μm or less. When the mark step is low as described above, the detection condition for contour enhancement is necessary to obtain the alignment mark image with good contrast. On the other hand, the numerical aperture of the projection optical system is set to 0.6 or less when the mark step is about 0.8 μm and the thickness of the photosensitive material is about 1 μm. When high,
It is possible to obtain an alignment mark image with sufficiently good contrast under normal detection conditions.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus used in an example of an embodiment of an exposure method and apparatus according to the present invention.

2A is a plan view showing a configuration of a split prism plate 16 and a detection system in FIG. 1, FIG. 2B is a right side view of FIG. 2A, and FIG. 2C is a view of FIG. 2A. It is sectional drawing which follows the AA line.

3 is a schematic configuration diagram showing a configuration of a dimming unit 2 in FIG.

4A is a side view showing a fly-eye lens 13 for annular illumination in FIG. 1, and FIG. 4B is a fly-eye lens 1 thereof.
FIG.

5 is an optical path diagram showing a configuration of an input optical system 5B for annular illumination in FIG.

FIG. 6 is a diagram showing a light amount distribution of illumination light at each point of the input optical system 5B of FIG.

FIG. 7 is a diagram showing a configuration of a σ diaphragm unit 15 in FIG. 1.

8 is a perspective view showing a schematic configuration of an alignment sensor 50 in FIG.

9 is a perspective view showing the FIA system 51A of FIG. 8. FIG.

10 is a perspective view showing the LIA system 51B of FIG. 8. FIG.

11A is a schematic view showing the FIA system 51A of FIG. 9 in a simplified manner, FIG. 11B is a plan view showing an illumination system aperture stop plate 161 arranged in the FIA system 51A, and FIG. It is a plan view showing an aperture stop plate 163 arranged in the FIA system 51A.

12A is an enlarged plan view showing a wafer mark to be detected by the FIA system 51A of FIG. 11A, and FIG. 12B is an image pickup signal obtained by picking up the wafer mark as a high step mark. And (c) is a waveform diagram showing an imaging signal obtained by imaging the wafer mark as a low step mark.

FIG. 13 is a schematic configuration diagram showing a conventional projection exposure apparatus.

[Explanation of symbols]

 R reticle PL projection optical system W wafer 1 KrF excimer laser light source 2 dimming unit 5A, 5B input optical system 7, 12 fly-eye lens 13 fly-eye lens for annular illumination 15 σ diaphragm unit 16 split prism plate 18 fixed field diaphragm 20 Movable Field Stop 25 Reticle Stage 29 Main Controller 31 Exposure Control System 32 Illumination Control System 35 Z Tilt θ Stage 42 Variable Aperture Stop 44 Lens Drive Mechanism 46 Resist Thickness Measuring Device 47 Film Thickness Measurement Calculator 48 Focus Position Detection System 50 Alignment sensor 51A FIA system 51B LIA system 53A, 53B Beam splitter 55A, 55B Reflectance monitor 56 Integrated exposure amount calculation unit 58A, 58B Integrator sensor 59 Imaging characteristic fluctuation amount calculation unit 161 Illumination system aperture diaphragm plate 163 Aperture diaphragm plate

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 21/30 525L 527

Claims (5)

[Claims] 1. A transfer pattern formed on a mask is illuminated with illumination light for exposure from an illumination optical system, and an image of the pattern of the mask is exposed under the illumination light through a projection optical system. In an exposure method of transferring and exposing onto a substrate, a light amount distribution on a pupil plane of an illumination system, which is an optical Fourier transform plane with respect to a pattern surface of the mask in the illumination optical system, is in a first region including an optical axis. The illumination condition and the light amount distribution on the pupil plane of the illumination system that does not include the optical axis,
And a modified illumination condition in the region of (3) are freely switchable, and the illumination optical system is switched to one of the normal and modified illumination conditions according to the numerical aperture of the projection optical system. 2. An illumination optical system that illuminates a transfer pattern formed on a mask with exposure illumination light, and projection optics that projects an image of the mask pattern onto a photosensitive substrate under the illumination light. And a projection condition changing means for switching the numerical aperture of the projection optical system, and an optical Fourier transform surface of the illumination condition of the illumination optical system with respect to the pattern surface of the mask in the illumination optical system. A normal illumination condition in which the light amount distribution on the illumination system pupil plane is in the first region including the optical axis, and a modification in which the light amount distribution on the illumination system pupil plane is in the second region that does not include the optical axis. Lighting conditions changing means for switching to a plurality of lighting conditions including the lighting conditions of the projection optical system having a numerical aperture of 0.
When the illumination optical system is set to 68 or more, the illumination optical system is set to the normal illumination condition, and the numerical aperture of the projection optical system is 0.6.
An exposure apparatus, wherein the illumination optical system is set to the modified illumination condition when set below. 3. The exposure apparatus according to claim 2, wherein the illumination condition changing unit splits the exposure illumination light into first and second light fluxes, and the first light flux. A first luminous flux expansion system that expands the cross-sectional shape of the second luminous flux in an annular shape, and a second luminous flux expansion system that expands the cross-sectional shape in an annular shape with the light amount distribution of the second luminous flux reversed between the inner and outer molds. A light flux combining system that combines the light fluxes from the first and second light flux expanding systems before the illumination system pupil plane, and changes the illumination conditions when setting the illumination conditions for the deformation. An exposure apparatus, wherein the means guides the light fluxes synthesized by the light flux synthesis system to the pupil plane of the illumination system to perform annular illumination. 4. An image of an alignment mark on a photosensitive substrate is detected through an alignment optical system under illumination light for alignment, the photosensitive substrate is aligned based on the detection result, and exposure is performed. In the exposure method of transferring and exposing the image of the pattern formed on the mask on the photosensitive substrate through the projection optical system under the illumination light for use in the optical alignment, the optical Fourier transform is performed on the surface of the photosensitive substrate in the alignment optical system. Normal detection conditions that allow the imaging light flux to uniformly pass on the alignment system pupil plane that is the conversion surface, and contour enhancement for performing contour enhancement by allowing the imaging light flux to pass on the alignment system pupil plane with a predetermined distribution. An exposure method comprising a detection condition and a detection condition, and the alignment optical system is switched to either of the two detection conditions according to a numerical aperture of the projection optical system. 5. The exposure method according to claim 4, wherein when the numerical aperture of the projection optical system is set to 0.68 or more, the alignment optical system is set to the detection condition for the edge enhancement. An exposure method, wherein the alignment optical system is set to the normal detection condition when the numerical aperture of the projection optical system is set to 0.6 or less.