JPH09189520A - Position detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect a position even for a position detection mark with an extremely small amount of recess and projection change (level difference). SOLUTION: A member for limiting the luminous flux of illumination where a plurality of light transmission parts 32A-32J and 33A-33I are formed symmetrically to a light axis is arranged on a lighting system pupil surface (Fourier transform surface for a position detection mark) and a member for limiting the luminous flux for image-forming where a region which is conjugate with the light transmission parts 32A-32J and 33A-33I and a region including the periphery is light-screening parts 34A-34J and 35A-35I is arranged on an image- forming system pupil surface. 0-order diffraction light out of diffraction light due to the position detection mark of illumination light from, for example, one light transmission part 32E is screened by a corresponding light-screening part 34E and other diffraction beams 35A-36C and 37A-37D are transmitted and utilized as luminous flux for image-forming, thus effectively utilizing only the diffraction light and forming the image of the position detection mark.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detection device for detecting the position of a position detection mark formed on a substrate, for example, a semiconductor element, an image pickup element (CCD or the like), a liquid crystal display element, or a thin film magnetic. An alignment for detecting the position of the position detection mark on the photosensitive substrate, which is provided in the exposure device used to transfer the mask pattern onto the photosensitive substrate in the photolithography process for manufacturing the head and the like. It is suitable for use in a sensor.

[0002]

2. Description of the Related Art For example, in a photolithography process for manufacturing a semiconductor device or the like, a transfer pattern formed on a photomask or a reticle (hereinafter, a "reticle" is used as an example) is transferred to a projection optical system. A projection exposure apparatus for transferring onto a wafer or a glass plate or the like (hereinafter, “wafer” is used as an example) coated with a photoresist via a proxy, or a proxy for directly transferring a pattern of a reticle onto a wafer arranged in close proximity. An exposure apparatus such as a Mitty type exposure apparatus is used.

Generally, a semiconductor element or the like is formed by stacking a plurality of layers of circuit patterns on a wafer in a predetermined positional relationship. Therefore, when transferring the circuit patterns of the second and subsequent layers onto the wafer in such an exposure apparatus. Requires highly accurate alignment between the reticle and the wafer prior to exposure. In order to perform this alignment, an alignment mark as a position detection mark is formed on the wafer along with the circuit pattern by the steps up to that point, and the position of the alignment mark is detected by an alignment sensor mounted on the exposure apparatus. This makes it possible to detect the accurate position of the circuit pattern in each shot area on the wafer.

As a conventional alignment sensor, for example, a spot-shaped or sheet-shaped laser beam and an alignment mark are relatively scanned in the measuring direction, scattered light or diffracted light generated is detected, and the mark position is detected based on the intensity change. (Hereinafter, referred to as “laser beam scanning method”) or a pair of diffracted light beams generated from the alignment mark by irradiating a diffraction grating-shaped alignment mark with, for example, a symmetrical coherent laser beam. There is a method of detecting the position by utilizing scattering or diffraction of the laser beam, such as a two-beam interference method of detecting the mark position based on the phase of the interference light. However, when a laser beam is used, its coherence may cause multiple interference between the wafer surface and the photoresist surface coated thereon, which may cause a large error in the mark detection position. .

On the other hand, a halogen lamp or the like is used as a light source to illuminate an area in a predetermined range including the alignment mark with a broadband light beam, an image of the mark is formed by an image forming optical system, and the position is determined based on the image signal. An alignment sensor that performs detection (hereinafter, referred to as "imaging type position detection method") is also used. This imaging type position detection method is sometimes called an FIA (Field Image Alignment) method. In this image formation type position detection method, since a broadband light flux is generally used as an illumination light flux, there is no possibility of causing the above-mentioned multiple interference.

[0006]

In recent years, with the miniaturization of semiconductor integrated circuits and the like, a process of flattening the wafer surface has been introduced after the film forming process and before the photolithography process. In this step, the effect of making the thickness of the generated film, which is the basis of the circuit pattern to be formed, uniform to improve the device characteristics, and the adverse effect such as the line width error that the unevenness of the wafer surface gives to the transfer pattern in the photolithography step are adversely affected. Has the effect of improving.

However, in the method of detecting the position based on the unevenness change or the reflectance change in the alignment mark portion on the wafer surface like the conventional image-forming position detection type alignment sensor, the alignment mark is formed by the flattening process. Since the amount of change in unevenness in the portion is significantly reduced, there is a risk that the alignment mark cannot be detected. Especially,
In the exposure process for an opaque generation film (metal or semiconductor film), the alignment mark part is covered with an opaque film having a uniform reflectance, so position detection depends only on the unevenness of the alignment mark, and thus flattening is required. By doing so, there is an inconvenience that the detection of the alignment mark becomes extremely difficult.

In this regard, a so-called dark field microscope is well known as an optical system for detecting only a stepped portion on a substantially flat object. The dark field microscope first illuminates the test object with illumination light having a large numerical aperture that does not pass through the imaging optical system.
There is a method of forming an image through an imaging optical system using only scattered light from the test object. Further, a circular light-shielding member having an optical axis as a center is provided in a part of an optical Fourier transform plane (image-forming system pupil plane) with respect to the surface to be inspected in the image-forming optical system, and a light-shielding member conjugate with this is provided in the illumination optical system. A diaphragm (σ diaphragm) is provided to limit the distribution of the illumination light in the optical Fourier transform plane (illumination system pupil plane) to the surface to be inspected within the circle forming an image-forming relationship with the circular light shielding member. There is also a method.

The dark-field microscope shields 0th-order diffracted light (regularly reflected light) from diffracted light by illumination light to an object such as an alignment mark on a wafer, and diffracts higher-order diffracted light (and scattered light). ) Has the effect of forming an image only. Of these, the 0th-order diffracted light is the diffracted light that hardly contains information about the unevenness of the test object or the reflectance change, and these information are included in the 1st-order or higher-order diffracted light. In the dark field microscope, the 0th-order diffracted light is blocked and an image is formed only by the high-order diffracted light, so that the step can be visualized more clearly than in a normal bright-field microscope, that is, with high contrast.

However, when the conventional dark-field microscope is used for detecting the position of the alignment mark on the wafer, not only unnecessary 0th-order diffracted light but also relatively low-order useful diffracted light is shielded, and the light intensity of the image is reduced. However, there is a problem that the fidelity of is deteriorated. In view of the above point, the present invention has an object to provide a position detecting device of an image forming type position detecting system capable of surely detecting a position even for a position detecting mark having an extremely small amount of unevenness change (step). And

[0011]

A position detecting apparatus according to the present invention comprises an illuminating optical system (1-5, 8, 8) for illuminating a position detecting mark (11) formed on a substrate (10) to be processed.
9) and an imaging optical system (9, 8, 18, which forms an image of the position detection mark from the illumination light from the position detection mark.
25, 27) and an image pickup element (28) for picking up an image of the position detection mark, and detecting the position of the position detection mark based on the image signal output from the image pickup element. , A plurality of secondary light sources (32A to 32J, 33A to 33I; 38A) which are discretely distributed on the pupil plane of the illumination system, which is an optical Fourier transform surface for the formation surface of the position detection mark in the illumination optical system. ~ 38
G) which forms the illumination light flux limiting member, and is disposed on the pupil plane of the imaging system which is an optical Fourier transform plane with respect to the surface on which the position detection mark is formed in the imaging optical system. A plurality of 2 which are discretely distributed on the pupil plane of the illumination system
A plurality of light shielding regions (34A to 34J, 35A to 35I) including a region having an image forming relationship with the secondary light source and a region in the vicinity thereof.
39A to 39G) which blocks the illumination light and allows the illumination light to pass through in other regions.
6; 16A).

According to the present invention, when an object to be examined is illuminated with illumination light from a large secondary light source as in the conventional dark field microscope, the 0th order diffracted light and the 1st order diffracted light are generated on the pupil plane of the imaging system. Considering that it is difficult to block the 0th-order diffracted light and extract only the 1st-order diffracted light because they partially overlap each other, in view of the fact that the illumination light flux limiting members (6; 6A) are used to emit light from a plurality of small secondary light sources, Position detection mark with illumination light (11)
To illuminate. As a result, considering the diffracted light on the pupil plane of the imaging system from the position detection mark (11) due to the illumination light from one secondary light source, its distribution is as shown in FIG. 5B. The 0th-order diffracted light enters (34E), and the nth-order diffracted light (n = ± 1, ± 2, ...) (36A, 37) on both sides thereof.
The distribution is such that A, 36B, 37B, ... That is, since the 0th-order diffracted light and the 1st-order and higher-order diffracted lights pass through different regions to be easily separated, it is possible to easily shield almost only the 0th-order diffracted light by the imaging light flux limiting member (16; 16A). The useful diffracted light can be efficiently used. As a result, the amount of unevenness change (step)
Even if the position detection mark is extremely small, a high-contrast image can be reliably formed, and the position can be detected with high accuracy based on this image.

In this case, when the position detection mark (11) is a mark having a width in the measurement direction of W and a periodicity of the period P in the measurement direction, a plurality of illumination light flux limiting members (6; 6A) are formed. Secondary light sources (32A to 32J, 33A)
~33I; 38A~38G) of each width D of the direction corresponding to the measurement direction of the position detection mark ₁ the shortest wavelength of the illumination light lambda, the longest wavelength as lambda _2, the following equation a numerical aperture as a unit It is desirable to set the width to be less than or equal to the width d1 determined by When the numerical aperture is used as a unit, the width D
Corresponds to sin θ, the actual width D ′ on the Fourier transform plane (pupil surface) of the optical system is represented by f · D, where f is the focal length of the optical system.

D1 = (λ ₁ / P-2λ ₂ / W) (1) As a result, the 0th-order diffracted light and the 1st-order diffracted light are almost completely separated on the pupil plane of the imaging system. It becomes easier to block light. Further, an image forming light flux limiting member (16; 16A)
A plurality of light blocking regions (34A to 34)
J, 35A-35I; 39A-39G),
The width D1 of the position detection mark (11) in the direction corresponding to the measuring direction has an illumination light flux limiting member (6; 6) in units of numerical aperture.
A) each of a plurality of secondary light sources (32A to 3A)
2J, 33A to 33I; 38A to 38G) is preferably set to a value d2 or more determined by the following equation.

D2 = (D + 2λ ₂ / W) (2) As a result, even if the width W of the position detection mark (11) in the measuring direction is finite and the 0th-order diffracted light spreads in the measuring direction by approximately ± λ ₂ / W. The 0th-order diffracted light can be shielded almost entirely by the imaging light flux limiting member (16; 16A). Further, the width D of each of the plurality of secondary light sources formed by the illumination light flux limiting member (6; 6A) in the direction corresponding to the measurement direction of the position detection mark is 0.06 with the numerical aperture as a unit. It may be set as follows. This is because the wavelengths λ ₁ and λ ₂ are 550 nm and 7
50 nm, the period P of the position detection mark is 6 μm, and the width W of the position detection mark in the measurement direction is 50 μm.
This corresponds to the case where 1 is 0.06. That is, under normal use conditions, by setting the width D to 0.06 or less, the 0th-order diffracted light and the 1st-order diffracted light are almost completely separated on the pupil plane of the imaging system.

Similarly, the imaging light flux limiting member (16; 16)
The width D1 of each of the plurality of light-shielded regions shielded by A) in the direction corresponding to the measurement direction of the position detection mark is formed by the illumination light flux limiting member (6; 6A) with the numerical aperture as a unit. The width D of each of the plurality of secondary light sources may be set to (D + 0.03) or more. This is also because the wavelength λ ₂ is 750 nm in the above formula (2),
This corresponds to the case where the width W of the position detection mark in the measuring direction is 50 μm. That is, under normal use conditions, by setting the width D1 of these light-shielding regions to (D + 0.03) or more, the 0th-order diffracted light can be almost completely shielded on the pupil plane of the imaging system.

Next, in the above-mentioned invention, an example of the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member is, for example, as shown in FIG. It is distributed point-symmetrically with respect to the optical axis of
It has two secondary light sources (38A, 38B) distributed in the same position in the direction corresponding to the non-measurement direction of the position detection mark, and the direction corresponding to the measurement direction of the position detection mark of these two secondary light sources. The center distance D2 of is set such that the center wavelength of the illumination light is λ and is not an integral multiple of λ / P.

In this case, these two secondary light sources (38
A, 38B), the distance in the measurement direction on the pupil plane of the imaging system of the diffracted light of the illumination light is λ / P, so the distance between the secondary light sources (38A, 38B) is from λ / P. By shifting them, the first-order diffracted light from the position detection mark is not shielded by the light-shielding regions (39A, 39B) on the pupil plane of the imaging system corresponding to the second-order light sources (38A, 38B), which ensures that An image of the position detection mark is formed on the. Further, by making the distribution of the secondary light sources point-symmetric with respect to the optical axis, the symmetry of the obtained image is secured.

Further, the distance D2 is a half integer multiple of λ / P,
That is, it is desirable to set to (n + 1/2) λ / P using the integer n. This makes it easier for the first-order diffracted light to pass. Further, in the above-described invention, other examples (32A to 32J, 33A to 3A) of the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member.
3I) is distributed point-symmetrically with respect to the optical axis of the illumination optical system as shown in FIG. 5, and a plurality of secondary light sources are arranged at the same position in the direction corresponding to the non-measurement direction of the position detection mark. It is distributed so that it does not exist.

Thereby, for example, one secondary light source (3
2E) does not block the diffracted light (36A, 37A, 36B, 37B, ...) Of the first order or higher generated from the position detection mark, so that the image of the position detection mark is reliably formed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of a position detecting device according to the present invention will be described below with reference to the drawings.
In this example, the present invention is applied to an alignment sensor of an off-axis type and an image forming type position detection type provided in a projection exposure apparatus. First, FIG. 12 shows an example of a stepper type projection exposure apparatus equipped with the alignment sensor of this example. In FIG. 12, the illumination light for exposure from the illumination optical system 51 (bright line such as i-line of mercury lamp, (Excimer laser light or the like) IL illuminates the pattern on the lower surface (pattern formation surface) of the reticle 52 with a uniform illuminance distribution, and the pattern is reduced by the projection optical system 54 at a projection magnification β (β is, for example, 1/5). Then, it is projected onto each shot area on the semiconductor wafer (hereinafter, simply referred to as “wafer”) 10 coated with the photoresist. In the following, the projection optical system 5
The Z axis is taken parallel to the optical axis AXP of FIG. 4, the X axis is taken parallel to the paper surface of FIG. 12 in the plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the paper surface of FIG.

The reticle 52 is held on a reticle stage 53 which positions the reticle 52 in the X and Y directions and rotates and fixes it by a desired angle. On the other hand, the wafer 10 is held on the wafer stage 12 via a wafer holder (not shown). The wafer stage 12 positions the wafer 10 in the X and Y directions, controls the position (focus position) of the wafer 10 in the Z direction, and corrects the tilt angle of the wafer 10. Further, the surface of the wafer 10 is on the upper surface of the wafer stage 12.
The reference plate 13 is fixed so that it is at the same height as the surface of
Baseline measurement on the surface of the reference plate 13 (projection optical system 54
A reference mark used for measuring the distance between the optical axis AXP and the detection center of the alignment sensor) is formed.

Further, the X-coordinate and Y-coordinate of the wafer stage 12 (wafer 10) are always 0.01 μm by the movable mirror 14 fixed on the wafer stage 12 and the laser interferometer 15 arranged so as to face each other. It is measured with a resolution of the order of magnitude. The coordinate system determined based on the coordinates measured by the laser interferometer 15 in this way is called a stage coordinate system (X, Y). The coordinates measured by the laser interferometer 15 are supplied to a main control system 55 that supervises and controls the operation of the entire apparatus, and an image processing system 29 described later. Based on the supplied coordinates, the main control system 55 uses the wafer stage. Drive system 5
The positioning operation of the wafer stage 12 is controlled via 6. Specifically, when the exposure of a certain shot area on the wafer 10 is completed, the stepping operation of the wafer stage 12 positions the next shot area in the exposure field of the projection optical system 54 to perform the exposure. The exposure is performed by the and repeat method.

Further, the projection exposure apparatus of FIG. 12 uses an off-axis method for detecting the coordinates of an alignment mark (wafer mark) as a position detection mark attached to each shot area on the wafer 10. Image formation type position detection type alignment optical system 57 and image processing system 29
Is provided. The detailed configuration of the alignment optical system 57 of this alignment sensor will be described later.

The image pickup signal DS photoelectrically converted and output by the alignment optical system 57 is supplied to the image processing system 29, and the coordinates of the wafer stage 12 measured by the laser interferometer 15 are also supplied to the image processing system 29. There is. Image processing system 29
Then, by adding the coordinates measured by the laser interferometer 15 to the relative position of the alignment mark obtained by processing the image pickup signal DS with respect to the index mark in the alignment optical system 57, the stage of the alignment mark to be detected is detected. The coordinate value in the coordinate system is detected and this coordinate value is supplied to the main control system 57. In the main control system 57, for example, the so-called enhanced global is obtained from the measured values of the coordinates of the alignment marks attached to a predetermined number of shot areas (sample shots) on the wafer and the designed arrangement coordinates of all the shot areas on the wafer.・ Alignment (EGA)
The array coordinates in the stage coordinate system of all the shot areas are calculated by the method.

The baseline amount, which is the distance from the detection center of the alignment optical system 57 (for example, the center of the index mark) to the optical axis AXP (exposure center) of the projection optical system 54, is obtained in advance using the reference plate 13. It is stored in the storage device in the main control system 55. Therefore, the main control system 55
Drives the wafer stage 12 based on the coordinates obtained by correcting the calculated array coordinates with the baseline amount, and transfers the reticle pattern image to each shot area on the wafer with high overlay accuracy. it can.

Next, the structure of the alignment sensor of the image formation type position detection system of this example will be described in detail. A mechanism for detecting an alignment mark whose measurement direction is the X direction (direction parallel to the X axis) will be described below, but an alignment mark whose measurement direction is the Y direction is also detected by the same mechanism. FIG. 1 shows a schematic configuration of an alignment optical system 57 of this example and an image processing system 29. In the alignment optical system 57 of FIG. 1, a light source 1 such as a halogen lamp is used.
The broadband illumination light flux emitted from the laser beam passes through the condenser lens 2 and the wavelength selection element 3 including a sharp cut filter or an interference filter, and then enters the illumination field stop 4. The wavelength selection element 3 has a wavelength range that is non-photosensitive to the photoresist coated on the wafer 10 (wavelength 5 in this example).
It is an optical filter that transmits only a light flux of 50 nm or more). However, if the alignment sensor of this example is used as a device for detecting an overlay error between the circuit pattern on the wafer after exposure and development and the transferred resist pattern, it is not necessary to prevent the exposure of the photoresist. Since it does not exist, the wavelength selection element 3 may not be provided.

The illumination light flux that has passed through the illumination field stop 4 enters the illumination light flux limiting member 6 via the relay lens system 5. Then, the illumination luminous flux enters the illumination region (observation visual field) including the alignment mark 11 on the surface of the wafer 10 via the beam splitter 8 and the objective lens group 9. In this example, the illumination light flux limiting member 6 has an optical Fourier transform relationship with the surface of the wafer 10 (the surface on which the alignment mark 11 is formed) via the objective lens group 9 and the beam splitter 8. It is arranged on a plane (hereinafter referred to as “illumination system pupil plane”). That is, assuming that the incident angle when the illumination light flux which has passed through the position of the positional deviation amount ΔRI from the illumination system optical axis AXI in the illumination light flux limiting member 6 is incident on the surface of the wafer 10 is θ _in , the positional deviation amount ΔRI. Is its incident angle θ
It is proportional to the sine of the _in.

Further, the light emitting portion of the light source 1 is optically conjugate with the arrangement surface of the illumination light flux limiting member 6, and the wafer 1
The surface of No. 0 is almost Koehler illuminated by the illumination light from the light source 1. However, in this example, since a plurality of light-transmitting portions (secondary light sources), which will be described later, in the illumination light flux limiting member 6 are two-dimensionally distributed, in order to illuminate those light-transmitting portions substantially uniformly, The light flux limiting member 6 may be defocused to some extent from the conjugate plane with the light emitting portion of the light source 1. Further, instead of the illumination light from the light source 1, illumination light guided by an optical fiber bundle having a predetermined cross-sectional shape may be used.

On the other hand, the illumination field stop 4 is conjugate (image formation relationship) with the surface (alignment mark 11) of the wafer 10 via a series of optical systems from the relay lens system 5 to the objective lens group 9. The illumination area on the wafer 10 can be limited according to the shape of the light transmitting portion of the illumination field stop 4. The illumination light flux limiting member 6 is attached to the exchange mechanism 7 so that it can be retracted out of the optical path as needed.

The light flux reflected, diffracted, or scattered in the illumination area including the alignment mark 11 on the wafer 10 reaches the imaging light flux limiting member 16 through the objective lens group 9 and the beam splitter 8. The image formation light flux limiting member 16 is provided on the wafer 10
To the surface (the surface on which the alignment mark 11 is formed)
It is arranged on a surface (hereinafter, referred to as “imaging system pupil surface”) optically in a Fourier transform relationship via the objective lens group 9 and the beam splitter 8. That is, assuming that the light beam emitted from the surface of the wafer 10 at the exit angle θ _out passes through the position of the positional deviation amount ΔRJ from the optical axis AX of the imaging system in the imaging light beam limiting member 16, the positional deviation amount is ΔRJ. ΔRJ is proportional to the sine of the exit angle θ _out .

The relationship of these optical Fourier transforms will be described with reference to FIG. 2. In FIG. 2, the objective lens group 9 of FIG. 1 is represented by one lens for simplicity. In FIG. 2, if the surface of the wafer 10 is arranged on one focal plane (the focal length is f) of the objective lens group 9, the other focal plane becomes an optical Fourier transform plane (pupil plane) FP. . Then, the light flux with the incident angle and the exit angle on the wafer 10 being θ respectively has an optical axis A on the Fourier transform plane (pupil plane) FP.
It will pass a position away from X by f · sin θ.

In FIG. 2, the objective lens group 9 is represented by a single lens, but there is essentially no difference even if this is a lens system composed of a plurality of lenses, and the composite focal plane of the plurality of lenses is shown. If the surface of the wafer 10 is arranged on the other side, the other focal plane becomes the Fourier transform plane (pupil plane). By arranging the beam splitter 8 between the objective lens group 9 and the pupil plane as shown in FIG. 1, the illumination system pupil plane on the light transmitting side and the imaging system pupil plane on the light receiving side are separated. It becomes possible to do. Further, both of the separated pupil planes are Fourier transform planes with respect to the surface of the wafer 10, that is, both pupil planes are conjugate (image formation relationship) via the wafer 10, the objective lens group 9 and the beam splitter 8. ing.

The details of the shapes of the light shielding and transmitting portions of the illumination light flux limiting member 6 and the image formation light flux limiting member 16 will be described later. The light flux (imaging light flux) that has passed through the imaging light flux limiting member 16 passes through the lens system 18 and the beam splitter 19,
An image of the alignment mark 11 is formed on the index plate 24. On the other hand, the index plate 24 is also illuminated by the illumination light emitted from the index plate illumination optical system and reflected by the beam splitter 19. The index plate illumination optical system includes a light source 20 such as a light emitting diode, a condenser lens 21, an index plate illumination field stop 22, and a relay lens system 23. The index plate illumination field stop 22 includes a relay lens system 23,
And conjugate with the index plate 24 via the beam splitter 19,
As a result, it is conjugated with the surface of the wafer 10.

Further, as will be described later, the index plate 24 is formed with an index mark serving as a reference when detecting the position of the alignment mark 11. The index plate illuminating optical system (hereinafter referred to as “20 to 23”) is for illuminating this index mark, and the illumination light from the light source 20 is a monochromatic light unlike the illumination light to the alignment mark 11. But it's okay. Further, since the illumination light from the light source 20 does not irradiate the wafer 10, the wavelength may be the photosensitive wavelength of the photoresist. Therefore, the light source 20 has a wavelength of 5
Using a light emitting diode that emits illumination light of about 00 nm, the reflecting surface of the beam splitter 19 is a dichroic mirror surface that transmits the illumination light selected by the wavelength selection element 3 and reflects the illumination light from the light source 20. By doing so, it is possible to improve the utilization efficiency of the imaging light flux from the wafer 10 and the illumination light of the index mark.

The image on the index plate 24 is the relay lens system 2
5, the aperture stop 26, and the relay lens system 27 for CC
An image is again formed on the image pickup surface of the image pickup device 28 such as D. The image processing system 29, based on the image pickup signal DS from the image pickup device 28, the image of the index mark and the alignment mark 11 described above.
The positional relationship with the image of is calculated. Thereby, the position of the alignment mark 11 can be detected. The aperture stop 2
Reference numeral 6 is arranged on a Fourier transform surface (a surface having an image forming relationship with the arrangement surface of the image forming light beam limiting member 16) with respect to the surface of the wafer 10, and the aperture stop 26 forms an image by the objective lens group 9 to the relay lens system 27. The numerical aperture of the optical system is limited. The imaging light flux limiting member 16 is also attached to the exchange mechanism 17 so that it can be retracted out of the optical path as needed.

Here, the shape of the alignment mark 11 of this example, the shape of the index plate 24, the index plate illumination field stop 22, and the transmission part of the illumination field stop 4, and the light intensity of the image formed on the image sensor 28. An example of the distribution is shown in FIG. 3 and FIG.
This will be described with reference to FIG. First, FIG. 4A shows an enlarged plan view of the alignment mark 11, and FIG. 4B shows FIG.
The cross-sectional view along the measurement direction (X direction) is shown. That is, the alignment mark 11 has three strip-shaped patterns, which are concave portions on the surface of the wafer 10 and are recessed as compared with other portions.
It is composed of periodic marks arranged in a direction with a period (pitch) P. Then, as shown in FIG. 4B, a region having a width W, which is coated with a photoresist 31 on the alignment mark 11 and includes the alignment mark 11 in the measurement direction and is illuminated with illumination light, is called a mark region MA. In this example, the width W is regarded as the width of the alignment mark 11 in the measurement direction.

Further, FIG. 3A is a diagram showing the illumination field diaphragm 4, and FIG. 3C is a diagram showing the index plate 24.
As shown in (A), on the illumination field stop 4, all are shaded parts except for the rectangular transmission part 4M in the center. The transmissive portion 4M is projected onto the surface of the wafer 10, and the bright conjugate image of the transmissive portion 4M becomes the illumination area of the alignment mark 11. This illumination area corresponds to the mark area MA of width W in FIG. 4B, and an image obtained by projecting this illumination area on the index plate 24 shown in FIG. 3C becomes the mark image area MI. There is. That is, an image of the alignment mark 11 is formed in the mark image area MI on the index plate 24.

On the other hand, FIG. 3 (B) shows the indicator plate illumination field stop 2
In FIG. 3B, all the parts except the two rectangular transmission parts 22L and 22R in the index plate illumination field stop 22 are shaded parts shown by hatching. The transmitted light from these transmission parts 22L and 22R illuminates the illumination areas LI and RI on the index plate 24 shown in FIG. 3C, respectively. In the left and right illumination areas LI and RI, the above-mentioned index marks 24L and 24R, which are light shielding portions, are formed.

As a result, the distribution of the light intensity (image intensity) of the image formed on the image pickup device 28 is as shown in FIG. 4 (C). In FIG. 4C, the image intensity is represented by the image pickup signal DS output from the image pickup device 28. In FIG. 4C, centering on the image 11P of the alignment mark 11 illuminated by the illumination light from the light source 1 of FIG. 1, index marks 24L illuminated by the illumination light from the light source 20 on the left and right sides of the image 11P.
Images of 24R (dark images) 24LP and 24RP are formed. In this example, since the illumination of the alignment mark 11 is substantially dark-field illumination, the image 11P of the alignment mark 11 has a double cycle with respect to the alignment mark 11. In addition, in the cross-sectional view of FIG.
Left and right areas LA of the alignment mark 11 in the measuring direction,
Although RA is a flat area, these areas LA,
Since the RA state has no influence on the position detection of the alignment mark 11 (not illuminated by the illumination light), there is no problem even if a circuit pattern or the like exists here.

In the image processing system 29 shown in FIG.
The alignment mark 11 and the index marks 24L, 2 based on the image pickup signal DS shown in FIG.
The positional relationship with 4R is calculated. This process is exactly the same as the process generally performed in the conventional imaging type position detection type alignment sensor. For example, the slice positions L ₂ , L ₁ , M ₁ of the image pickup signal DS at a certain slice level SL
~ M _n , R ₁ , R ₂ can be obtained, and position detection can be performed based on these slice positions. Alternatively, the position detection may be performed based on the correlation between a certain template signal and the image pickup signal DS corresponding to the image 11P of the alignment mark.

Further, prior to these position detections, it is necessary to measure the positional relationship of the index marks 24L and 24R, which are the reference of the detection positions, with respect to the wafer stage 12 (wafer 10), that is, a baseline check. For this reason, in FIG. 12, for example, the wafer stage 12 is driven to move the reference mark on the reference member 13 into the exposure field of the projection optical system 54, and the reference mark and the reticle are aligned by the alignment sensor for the reticle (not shown). The alignment mark on 52 is adjusted to a predetermined relationship, and the coordinate value of the wafer stage 12 at that time (the coordinate value in the stage coordinate system measured by the laser interferometer 15) is stored as the first measured value.

Then, in FIG. 1, the wafer stage 1
2 is driven to move the reference mark formed on the reference member 13 into the observation field of view under the objective lens group 9, and the positional relationship between the reference mark and the index marks 24L and 24R is detected. At the same time, the coordinate value of the wafer stage 12 at this time (coordinate value in the stage coordinate system) is measured, and the sum of this measured value and the detected value for the reference mark is stored as the second measured value. The amount obtained by subtracting the first measured value from the measured value of 2 is stored as the baseline amount. In this case, the alignment mark 11 and the reference indices 24L and 24 obtained from the measurement value of the laser interferometer 15 at the time of measuring the alignment mark 11 and the above-described image pickup signal DS.
A value obtained by subtracting the baseline amount from the sum of the positional relationship with R is the relative position of the alignment mark 11 with respect to the exposure center.

Next, the illumination light flux limiting member 6, the imaging light flux limiting member 16 of this example, and their modifications will be described with reference to FIGS. 5 and 6, respectively. 5A shows the illumination light flux limiting member 6 in FIG. 1, FIG. 5B shows the imaging light flux limiting member 16 in FIG. 1, and the horizontal axis in FIGS. 5A and 5B. U axis corresponds to the X axis of the alignment mark 11 shown in FIG. 4A, and the vertical axis V axis corresponds to the Y axis of the alignment mark 11. Since the illumination light flux limiting member 6 and the imaging light flux limiting member 16 are respectively arranged on the pupil plane with respect to the alignment mark 11, the U axis and the V axis are used according to the convention.

As shown in FIG. 5 (A), the illumination light flux limiting member 6 of this example has a plurality of minute rectangular (square) light-transmitting portions 32A to 32I on a light-shielding portion shown by hatching. , 32
J, 33A to 33I are formed. in this case,
The light transmissive portions 32A to 32I in the upper half area (area where V> 0) of the illumination light flux limiting member 6 and the lower half area are symmetrical with respect to the optical axes (origins of the U axis and the V axis). Light part 33A ~
33I is provided and the light transmitting portion 32J is provided on the optical axis.
Is provided. In addition, the translucent portion 32 is not necessarily located on the optical axis.
It is not necessary to provide J. Further, the number and distribution positions of the light transmitting portions are not limited to those shown in FIG.

By arranging the translucent parts symmetrically with respect to the optical axis in this manner, the translucent parts on the illumination light flux limiting member 6 are arranged such that the barycentric position of the illumination light amount distribution of each translucent part coincides with the optical axis. Match. This ensures the symmetry of the image obtained on the image sensor 28. When it is not necessary to ensure the symmetry of the image due to the shape of the alignment mark to be detected, it is not necessary to arrange the translucent portion on the illumination light flux limiting member 6 symmetrically with respect to the optical axis.

On the other hand, as shown in FIG. 5B, the image forming light beam limiting member 16 includes the light transmitting portions 32 on the illumination light beam limiting member 6.
A to 32I, 32J, 33A to 33I at a conjugate position,
The light-shielding portions 34A to 34I, 3 which are slightly larger than that, respectively
4J and 35A to 35I are formed, and the other region is a light transmitting portion. As such an illumination light flux limiting member 6, one having a transparent opening provided at a specific location on a metal light-shielding plate, or a light-shielding film made of metal or the like on a transparent substrate such as glass and the light-shielding film at a specific location is removed. Things can be used. Also,
As the image forming light flux limiting member 16, a member in which a light shielding portion is formed of a metal thin film or the like at a specific position on a transparent substrate such as glass can be used.

The alignment mark 11 is shown in FIG.
When the periodic pattern is as shown in FIG.
The diffracted light generated from the alignment mark 11 by the illumination light that has passed through one light transmitting portion 32E on the illumination light flux limiting member 6 in (A) is on the imaging light flux limiting member 16 (in the pupil plane of the imaging system). The distribution is as shown in FIG. That is, of the generated diffracted light, the 0th-order diffracted light is blocked by the light-shielding portion 34E that is conjugate with the light-transmitting portion 32E, and the + first-order, + second-order, and + third-order diffracted light 36A, 36B, 36C, and −1st to − The 4th-order diffracted lights 37A to 37D are transmitted through the transmission part, and
And reaches the image sensor 28 and contributes to image formation.

By the way, assuming that the width of each of the light transmitting portions 32A to 32J and 33A to 33I on the illumination light flux limiting member 6 in the U direction (measurement direction) is D, even if the width D is 0,
The 0th-order diffracted light from the alignment mark 11 has a width in the U direction on the imaging light flux limiting member 16. This occurs because the width W of the alignment mark 11 in the measurement direction (X direction) is finite, and its spread is about 2λ / W (the unit is the numerical aperture), where λ is the wavelength of the illumination light. The actual width of spread is about f · 2λ / W in the objective lens group 9 having the focal length f as shown in FIG. That is, the larger the width W of the alignment mark 11 (for example, the larger the line width per mark and the larger the number of marks), the smaller the spread of the image forming light beam on the image forming light beam limiting member 16. . Further, when the illumination light has a predetermined wavelength width, if the longest wavelength is λ ₂ , then 0
The maximum spread width of the _second-order diffracted light is 2λ ₂ / W in numerical aperture unit
Becomes

Therefore, in this example, the image forming light flux limiting member 16 is used.
The width D1 in the U direction of each of the light shielding portions 34A to 34J and 35A to 35I above is set to the light transmitting portion (32E) on the illumination light flux limiting member 6.
Etc.) and the above-mentioned 2λ ₂ / W are set to be equal to or more than the sum of the width D in the U direction (the unit is the numerical aperture, and the unit on the pupil plane is the numerical aperture unless otherwise specified). That is, the following equation is substantially established with the numerical aperture as a unit.

D1 ≧ D + 2λ ₂ / W (3) As a result, the 0th-order diffracted light from the alignment mark 11 can be completely blocked by the imaging light flux limiting member 16. If the width D1 of each light shield on the imaging light flux limiting member 16 in the U direction becomes too large, the diffracted light of the first and higher orders will also be shielded, and, of course, the width D1 of each light shield is It is set to a range not less than (D + 2λ ₂ / W) on the right side of the equation (3) and not blocking the diffracted light of the first order or more.

Diffracted light of another order, for example, m-th order (m is an integer other than 0), is m · λ / P (P is an alignment) on the imaging light beam limiting member 16 in the U direction from the center of the 0th-order diffracted light. It passes through a position separated by the mark 11 period), and its spread width is similar to that of the 0th-order diffracted light. Furthermore, if the illumination light flux is broadband, the respective center positions also change due to the difference in the wavelength λ of each light flux, so that the width of each diffracted light becomes wider. Then, the interval of the diffracted light of each order becomes the smallest at the shortest wavelength λ ₁ , and the spread of the diffracted light of each order at each wavelength becomes the maximum at the longest wavelength λ ₂ .

Focusing on the positional relationship between the 0th-order diffracted light and the 1st-order diffracted light, if the width D of the light transmitting portion 32E on the illumination light flux limiting member 6 in the U direction is too wide, the 0th-order diffracted light is shielded. The width D1 of the portion 34E in the U direction and the spread width of the first-order diffracted light itself increase, and as a result, a part of the ± first-order diffracted light 36A, 37A is also shielded by the light shield portion 34E.

In order to avoid this, the width D of each light transmitting portion on the illumination light flux limiting member 6 in the U direction is set to 0 from the minimum distance λ ₁ / P between the 0th-order diffracted light and the 1st-order diffracted light. In such a case, the maximum value 2λ ₂ / W of the spread width of each diffracted light may be set to a value less than or equal to the value so that the 0th-order diffracted light and the 1st-order diffracted light do not overlap on the imaging light flux limiting member 6. That is, the following equation may be satisfied. The width D may satisfy the equation (4) and may be larger than 0.

D ≦ λ ₁ / P-2λ ₂ / W (4) In the actual alignment mark, the period P is 6 μm.
The width W in the measurement direction of the alignment mark is often about 50 μm. For example, when the illumination light is broadband and the wavelength range is 550 nm (λ ₁ ) to 780 nm (λ ₂ ), the period P is 6 μm (the finest among general marks, that is, the 0th order light and the 1st order light are If you want to detect the most distant alignment mark,
From the formula (4), the width D of each light transmitting portion on the illumination light flux limiting member 6
To 0.06 (≈ 0.55 / 6-2 · 0.78 / 50)
The following should be done. At this time, the spread of the 0th-order diffracted light on the illumination light flux limiting member 6 (D + 2λ ₂ / W)
Is about (D + 0.031), the width D1 of each light-shielding portion of the imaging light flux limiting member 16 is (D + 0.03) according to the equation (3).
It may be 3) or more.

Similarly, for an alignment mark having a period P of 8 μm, the width D of each light transmitting portion of the illumination light flux limiting member 6 is set.
Is 0.038 or less, and the width D of each transparent portion is 0.015 for an alignment mark having a period P of 12 μm.
The following may be performed. Further, as shown in FIG. 5, on the V-coordinate of a certain value, each light-shielding portion (34E or the like) on the imaging light flux limiting member 16 and the corresponding light transmitting portion (on the illumination light flux limiting member 6). 32E, etc.). A group of broken lines parallel to the U-axis in FIG. 5B is an auxiliary line for clarifying this, and the light shielding portion 3 is provided between the broken lines.
There is only one 4A to 34J and 35A to 35I. With such an arrangement, any one transparent part (3
2E and the like), the diffracted light other than the 0th order in the measurement direction (period direction) by the alignment mark of the transmitted light is not blocked at all by the light blocking portion on the imaging light flux limiting member 16. Therefore, an image with extremely high fidelity can be obtained as an image formed on the image pickup device 28.

Next, FIG. 6A shows another example of the illumination light beam limiting member, and FIG. 6B shows another example of the image forming light beam limiting member, which are similar to FIG. U of (A) and (B)
The axis and the V axis respectively correspond to the X axis and the Y axis of the alignment mark 11 shown in FIG. FIG.
As shown in (A), on the illumination light flux limiting member 6A, rectangular light transmitting portions 38A to 38G that are thin in the U direction and long in the V direction are formed in the light shielding portion. Also,
A plurality of (2 to 3) transmissive portions are formed on the same V coordinate, and in this example, the translucent portions 38A to 38G are also arranged symmetrically with respect to the optical axis. Note that although the number of the light-transmitting portions 38A to 38G is six in FIG. 6A, the number of the light-transmitting portions is arbitrary, and the arrangement is not limited to that in FIG. 6A. In this example, the intervals in the measurement direction (U direction) of the plurality of light-transmitting portions (secondary light sources) are the light-transmitting portions 38D and 38 with the central wavelength of the illumination light flux as λ and the numerical aperture as a unit.
The distance D3 from E and the distance D from the translucent portions 38D and 38C
3, the distance D2 between the translucent portions 38A and 38B and the distance D2 between the translucent portions 38F and 38G are set to 3.5 · λ / P.

Further, in the imaging light flux limiting member 16A shown in FIG. 6B, the illumination light flux limiting member 6A shown in FIG.
Similar to the example of FIG. 5, the light-shielding portions 39A to 39G are formed in the region conjugate with the upper transmission portions 38A to 38G and the periphery thereof. At this time, for example, in the diffracted light by the illumination light flux irradiated to the alignment mark 11 from the light transmitting portion 38D, the 0th-order diffracted light is shielded by the light shielding portion 39D on the imaging light flux limiting member 16A of FIG. 6B, + 1st order to + 4th order diffracted light 42A to 42D, and -1st order to -4th order diffracted light 43
A to 43D are transmitted between the light shielding portions. In this example, as described above, the distance between the light transmitting portion 38D and the light transmitting portions 38C and 38E and the distance between the light shielding portion 39D and the light shielding portions 39C and 39E are set to 2.5 · λ / P. Therefore, the diffracted lights 43D to 42D can be transmitted through the imaging light flux limiting member 16 without being shielded by the light shields 39C and 39E.

Further, the -5th-order diffracted light 41D to the + 2nd-order diffracted light 40B generated by the illumination light from the other transparent portion 38B.
For the diffracted light up to, the distance between the light-transmitting portion 38A and the light-transmitting portion 38B and the distance between the light-shielding portion 39A and the light-shielding portion 39B are set to 3.5 · λ / P, respectively. Three
It is possible to pass through the imaging light flux limiting member 16 without being blocked by 9A. In addition, these translucent portions 38A to 38
The distance between G and the light shielding portions 39A to 39G in the measurement direction (U direction) is not limited to the above 2.5 · λ / P and 3.5 · λ / P, and is a half integer of λ / P. Any value may be used as long as it is double.

Further, if the diffracted light may be shielded to some extent, the interval between them may be set so as not to be an integral multiple of λ / P. By the way, the translucent part 3 in FIG.
Regarding the diffracted light generated by the illumination light of 8C and 38E, the −5th order and the + 5th order diffracted light are blocked by the light blocking sections 39E and 39C corresponding to the other light transmitting sections. However, the influence of such higher-order (fifth-order or more) diffracted light on image formation is so small as to be practically negligible, and hardly poses a problem. However, when the wavelength range of the illumination light is wide, in the configuration as shown in FIG.
Of the + 2nd-order diffracted light 42B from the illumination light from, the longest wavelength is diffracted to a greater extent and is shielded by the light shielding portion 39E, and the + 3rd-order diffracted light 42C from the shortest wavelength is also not significantly diffracted. There is a risk of being blocked by 39E. Therefore, the light transmitting portions 38A to 38G and the light shielding portion 3
Each width of 9A to 39G is preferably narrower than that in the example of FIG.

Of course, when the wavelength range of the illumination light is not so wide, the widths of the light transmitting portion and the light shielding portion may be the same as those in the example of FIG. At this time, the total area of the light-transmitting portions can be further increased by the presence of the plurality of light-transmitting portions for the same V coordinate, which has an advantage of increasing the amount of illumination light, that is, brightening the image. Here, for comparison with the above-described embodiment, FIGS. 7A and 7B show light amount distributions on the illumination system pupil plane and the imaging system pupil plane in the conventional dark-field microscope, respectively. Also in FIG. 7, the direction corresponding to the measurement direction is the U axis, and the direction corresponding to the non-measurement direction orthogonal to the measurement direction is the V axis.

In FIG. 7, the light quantity distribution on the pupil plane of the illumination system is limited to the circular area 44 centered on the optical axis AX, and the light-shielding portion on the pupil plane of the imaging system has a circular shape substantially conjugate with the circular area 44. The type of the light-shielding portion 45 is shown. At this time, the diffracted light generated from the alignment mark by the illumination light from the circular area 44 of FIG. 7A is circular + 1st order to + 4th order diffracted light 46A to 46, respectively, as shown in FIG. 7B.
D and −1st to −4th order diffracted lights 47A to 47D. However, for example, ± 1st-order diffracted lights 46A and 47A
Most of the light is blocked by the light blocking portion 45 having a circular shape.
As a result, the obtained image has extremely low fidelity, and naturally, the position detection accuracy using the image also deteriorates. On the other hand, according to the embodiment of the present invention, as shown in FIG. 5 and FIG. 6, almost all the diffracted light of the first order or higher is used as the image forming light flux.
The fidelity of the image obtained is extremely high.

Next, a simulation result by a computer when an image of an alignment mark having an extremely small amount of unevenness change (step) is formed using the alignment sensor of the above-described embodiment will be described. FIG. 8 shows a simulation result of an image intensity distribution of an alignment mark having a step of 5 nm obtained by the alignment sensor of FIG.
In FIG. 8, the horizontal axis indicates the position in the measurement direction (X direction) on the wafer, and the vertical axis indicates the light intensity of the image of the alignment mark. Further, the detailed structure of the alignment mark has a period of 12 μm, the number of concave portions is 5, the width of the concave portions is equal to the width of the convex portions, and the material of the mark surface has a uniform refractive index of 3.55. It is assumed that it is made of a material and a photoresist having a refractive index of 1.68 is applied thereon with a thickness of 1 μm. The wavelength range of the illumination light is set to 550
nm (λ ₁ ) to 750 nm (λ ₂ ), assuming that the light transmitting portions on the illumination light flux limiting member 6 are distributed as shown in FIG. 5, the numerical aperture of the imaging optical system is 0.2. .

At this time, since the width W of the alignment mark in the measuring direction is 60 (= 12 × 5) μm, the width D in the U direction of each transmitting portion of the illumination light flux limiting member 6 is the condition of the expression (4). To 0.02. Further, the image forming light flux limiting member 1
The width D1 of each light-shielding portion on 6 is calculated according to the condition of Expression (3).
It was set to 0.045. The image intensity distribution in FIG. 8 is for one cycle of the alignment mark, the origin of the horizontal axis (position) indicates the center of the concave portion at the center of the alignment mark, and the broken line shown at the position of ± P / 4 is the concave portion of the alignment mark. Shows the edge (boundary between the concave portion and the convex portion). Further, the light intensity on the vertical axis is standardized so that the maximum value of the light intensity of the mark image within one cycle is 1.

On the other hand, FIGS. 9 and 10 show simulation results of images of alignment marks obtained by a normal (bright field) microscope and a dark field microscope, respectively. The σ value, which is the coherence factor of the illumination light of the bright field microscope, was 0.8, and the σ value of the dark field microscope was 0.3. Further, the radius of the light shielding portion on the pupil plane of the imaging system of the dark field microscope was set to 0.33 NA (NA is the numerical aperture), which is slightly larger than the σ value (0.3). Other conditions (alignment mark shape,
The wavelength of the illumination light, the numerical aperture, the position of the horizontal axis, and the standardization of the light intensity of the vertical axis are the same as the simulation conditions in the embodiment of the present invention shown in FIG.

As shown in FIG. 9, it is understood that the image of the bright-field microscope has almost no change in contrast (contrast), and mark position detection from such an image is almost impossible. on the other hand,
As shown in FIG. 10, the contrast in the image of the dark field microscope is large, but as described above, the fidelity of the image is deteriorated because a considerable amount of the first-order diffracted light is shielded, and the contrast is four times the period of the alignment mark. The image of the period is formed. In the actual position detection, the true mark position is unknown before the position detection. Therefore, if position detection is performed on an image with such a quadruple cycle, the mark position is erroneously detected by P / 4. There is a risk that

On the other hand, in the image by the alignment sensor according to the embodiment of the present invention shown in FIG. 8, not only the contrast is sufficient, but also the darkest part thereof coincides with the mark edge. Using this, reliable position detection can be performed. Further, FIG. 11 shows that the σ value of the illumination luminous flux is 0.05 even though the conventional dark field microscope is used.
(The numerical aperture is 0.01), and the radius of the light shielding portion on the pupil plane of the imaging system is 0.12 NA (the numerical aperture is 0.024).
The simulation result of the image in the case of is shown. At this time, the entire widths (0.02 and 0.048) of the transmission part of the illumination system pupil plane and the light shielding part of the imaging system pupil plane satisfy the conditions of the above-described embodiment. Therefore, only the 0th-order diffraction of the diffracted light from the alignment mark is shielded and the 1st-order and higher-order diffracted lights are transmitted, but the image is also close to the quadruple period as shown in FIG. ing. This is because the coherence of the illumination light on the alignment mark becomes too high under the illumination condition (coherent illumination) in which the σ value of the illumination light flux is small as described above, which deteriorates the image quality.

On the other hand, in the embodiment of the present invention, although the size of each secondary light source on the pupil plane of the illumination system is small, a plurality of secondary light sources are arranged, and the entire secondary light source group has σ.
The illumination system has a large value, and there is no fear of image quality deterioration as described above. In the above embodiment of the present invention, the alignment mark that is periodic in the measurement direction is described as the detection target, but it is of course possible to detect an aperiodic mark by the position detection device of the present invention. In this case, the diffracted light generated from the mark to be detected is not discrete as described above, but in the position detecting device of the present invention, the diffracted light blocked in this case is also of a lower order (close to the 0th order). 1), more useful diffracted light can be contributed to the image formation, and more accurate position detection is possible.

As described above, the illumination light flux limiting members 6 and 6A and the imaging light flux limiting members 16 and 16A according to the embodiment of the present invention are extremely effective in detecting marks with small steps. Since the conventional detection optical system has sufficient detection accuracy for a mark having a large step (for example, 100 nm or more), when detecting a mark having a large step, the illumination light flux limiting members 6, 6A are used. Alternatively, the imaging light flux limiting members 16 and 16A may be retracted from the optical path by using the exchange mechanisms 7 and 17 shown in FIG. 1, respectively. The image-forming light flux limiting member 16 made of a glass substrate,
If there is a risk that the aberration state of the optical system will change due to the withdrawal of 16A (or the illumination luminous flux limiting members 6, 6A), insert a transparent member having an equivalent optical thickness when withdrawing these members. There is a need to.

Further, the illumination light flux limiting members 6 and 6A used in the embodiment are designed to transmit only the light flux of a specific portion and shield the other light flux, but the illumination light flux is on the pupil plane of the illumination system. A member that condenses light at a plurality of specific places, for example, an optical system such as a fly-eye lens may be used. Also, FIG.
A laser light source such as a semiconductor laser element may be used as the light source 1 for illuminating. Also in this case, since it is desirable that the illumination light flux has a certain wavelength range, a semiconductor laser element that oscillates at multiple wavelengths (multimode), a dye laser light source, or another laser that oscillates at a plurality of different wavelengths. Use a light source.

In the above embodiment, the present invention is applied to the alignment sensor for detecting the position of the alignment mark on the semiconductor wafer. However, the position detecting device according to the present invention can be applied to optical devices for other purposes. It can also be applied to. For example, if the present invention is applied to a general optical microscope used for visual inspection or observation,
Similar to the above-described embodiment, a high-contrast image can be obtained for a low step pattern. Furthermore, the present invention can be applied to a microscope using transmitted illumination such as a biological microscope.

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.

[0073]

According to the present invention, a plurality of secondary light sources which are discretely distributed are formed on the pupil plane of the illumination system, and the illumination light is emitted by the plurality of light-shielding regions on the pupil plane of the corresponding imaging system. Since the light is shielded, the 0th-order diffracted light from the position detection mark can be shielded and the 1st-order or higher-order diffracted light can be used with high efficiency. Therefore, there is an advantage that an image can be formed with high fidelity even on a position detection mark having an extremely small amount of unevenness change (step), and position detection can be performed reliably. Therefore, for example, it is possible to obtain a mark image with sufficiently high contrast even for an alignment mark whose unevenness (step) is extremely small due to a flattening process, and the light intensity distribution of the mark image is used to determine the mark position. The detection can be performed with high accuracy.

Further, it is possible to realize an optical system capable of detecting various patterns having a small surface level difference or a small change in the phase of a light beam with a higher contrast than the conventional example.
In this case, the position detection mark is a mark having a width of W in the measurement direction and a periodicity of P in the measurement direction, and the position of each of the plurality of secondary light sources formed by the illumination light flux limiting member. The width D of the detection mark in the direction corresponding to the measurement direction is set to (λ ₁ / P-2λ ₂ / W) or less in units of numerical aperture, where λ _{1 is} the shortest wavelength of illumination light and λ ₂ is the longest wavelength. In such a case, since the 0th-order diffracted light and the 1st-order diffracted light are almost completely separated on the pupil plane of the imaging system, it becomes easy to shield only the 0th-order diffracted light.

Further, the width of each of the plurality of light-shielding regions shielded by the imaging light flux limiting member in the direction corresponding to the measuring direction of the position detection mark is formed by the illumination light flux limiting member in units of the numerical aperture. When the width D of each of the plurality of secondary light sources is set to (D + 2λ ₂ / W) or more, even if the zero-order diffracted light has a spread due to the width W of the position detection mark in the measurement direction, The 0th-order diffracted light can be shielded almost completely by the imaging light flux limiting member.

Next, the width D of each of the plurality of secondary light sources formed by the illumination light flux limiting member in the direction corresponding to the measuring direction of the position detection mark is 0.06 or less in units of numerical aperture. When set to, normal operating conditions (illumination light wavelengths λ ₁ and λ ₂ are 550 nm and 75 nm, respectively)
0 nm, the period P of the position detection mark is 6 μm, and the width W of the position detection mark in the measuring direction is about 50 μm), (1)
Since D ≦ d1 holds for the width d1 of the equation, the 0th-order diffracted light and the 1st-order diffracted light are almost completely separated on the pupil plane of the imaging system.

Similarly, the width D1 of each of the plurality of light-shielding regions shielded by the image-forming light flux limiting member in the direction corresponding to the measurement direction of the position detection mark is set to the illumination light-flux limiting member in units of numerical aperture. When (D + 0.03) or more is set for the width D of each of the plurality of secondary light sources formed by, the width d2 of the formula (2) is Since D1 ≧ d2 holds, the 0th-order diffracted light can be shielded almost completely on the pupil plane of the imaging system.

Further, the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member are distributed point-symmetrically with respect to the optical axis of the illumination optical system, and in the non-measurement direction of the position detection mark. It has two secondary light sources distributed in the same position in corresponding directions, and the center interval of the direction detection marks of these two secondary light sources in the direction corresponding to the measurement direction is λ, where λ is the center wavelength of the illumination light. When it is set not to be an integral multiple of / P, the first-order or higher-order diffracted light from the position detection mark is hardly blocked by the light-blocking region on the pupil plane of the imaging system, and the fidelity is high. An image of the position detection mark is formed. Further, by making the distribution of the secondary light sources point-symmetric with respect to the optical axis, the symmetry of the obtained image is secured. Further, since there are a plurality of secondary light sources in the measurement direction, the obtained image becomes bright.

Further, the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member are distributed point-symmetrically with respect to the optical axis of the illumination optical system, and are arranged in the non-measurement direction of the position detection mark. When a plurality of secondary light sources are distributed so as not to exist at the same position in the corresponding direction, the first-order or higher-order diffracted light from the position detection mark is hardly blocked at the pupil plane of the imaging system and is high. An image of the position detection mark is formed with high fidelity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an alignment sensor of an example of an embodiment of a position detecting device according to the present invention.

2 is an explanatory diagram of a pupil plane of an objective lens group 9 in FIG.

3A is a diagram showing a pattern of an illumination field diaphragm 4 in FIG. 1, FIG. 3B is a diagram showing a pattern of an index plate illumination field diaphragm 22 in FIG. 1, and FIG. It is a figure which shows the pattern of the index board 24.

4A is an enlarged plan view showing an example of the alignment mark 11 in FIG. 1, FIG. 4B is a sectional view of FIG.
(C) is a waveform diagram showing an image pickup signal (light intensity distribution) of the image of the alignment mark 11.

5A is a diagram showing an arrangement of a light transmitting portion of the illumination light flux limiting member 6 in FIG. 1, and FIG. 5B is an imaging light flux limiting member 1 in FIG.
It is a figure which shows arrangement | positioning of the light-shielding part of 6.

6A is a diagram showing an arrangement of a light transmitting portion of another example 6A of the illumination light flux limiting member, and FIG. 6B is a diagram showing an arrangement of a light shielding portion of another example 16A of the imaging light flux limiting member. is there.

FIG. 7 is a diagram showing light amount distributions on an illumination system pupil plane and an imaging system pupil plane in a conventional dark field microscope.

FIG. 8 is a diagram showing a simulation result of a light intensity distribution of an alignment mark image obtained in the embodiment of the present invention.

FIG. 9 is a diagram showing a simulation result of a light intensity distribution of an image of an alignment mark obtained by a normal bright-field microscope.

FIG. 10 is a diagram showing a simulation result of a light intensity distribution of an image of an alignment mark obtained by a conventional dark field microscope.

FIG. 11 is a diagram showing a simulation result of a light intensity distribution of an image of an alignment mark obtained when coherent illumination is performed by a conventional dark field microscope.

FIG. 12 is a configuration diagram showing a projection exposure apparatus provided with an alignment sensor according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 4 illumination field stop 6,6A illumination light flux limiting member 7,17 exchange mechanism 9 objective lens group 10 wafer 11 alignment mark 12 wafer stage 16, 16A imaging light flux limiting member 22 index plate illumination field stop 24 index plate 26 aperture stop 28 Image sensor 29 Image processing system 32A-32J, 33A-33I Light transmission part 34A-34J, 35A-35I Light shielding part 38A-38G Light transmission part 39A-39G Light shielding part 57 Alignment optical system

Claims (7)

[Claims] 1. An illumination optical system for illuminating a position detection mark formed on a substrate to be processed; an imaging optical system for forming an image of the position detection mark from illumination light from the position detection mark; An image pickup device for picking up an image of a position detection mark, wherein the position detection device detects the position of the position detection mark based on an image signal output from the image pickup device, the position in the illumination optical system, An illumination light flux limiting member that forms a plurality of secondary light sources that are discretely distributed on an illumination system pupil surface that is an optical Fourier transform surface with respect to a detection mark formation surface, and the position detection in the imaging optical system. A region which is arranged on an image forming system pupil plane which is an optical Fourier transform plane with respect to a mark forming plane and which has an image forming relationship with the plurality of discretely distributed secondary light sources on the illumination system pupil plane and the vicinity thereof. Area of Shields the illumination light at a plurality of light-shielding region, the position detecting device characterized by having, an imaging light beam limiting member allowed to pass through the illumination light in the other regions. 2. The position detection device according to claim 1, wherein the position detection mark has a width W in the measurement direction and is in the measurement direction.
A mark having a periodicity of a period P, wherein the plurality of marks 2 formed by the illumination light flux limiting member
In the measuring direction of the position detection mark of each secondary light source
The width D in the corresponding direction is the shortest wavelength of the illumination light is λ ₁Longest
Wavelength λ_TwoAs a unit of numerical aperture (λ₁/ P-2
λ_Two/ W) Position detection characterized by being set below
apparatus. 3. The position detecting device according to claim 2, wherein the width of each of the plurality of light-shielding regions shielded by the imaging light flux limiting member in a direction corresponding to the measurement direction of the position detection mark. Is set to (D + 2λ ₂ / W) or more with respect to the width D of each of the plurality of secondary light sources formed by the illumination light flux limiting member with a numerical aperture as a unit. 4. The position detecting device according to claim 1, wherein the plurality of 2 formed by the illumination light flux limiting member.
The width D of each of the next light sources in the direction corresponding to the measurement direction of the position detection mark is set to 0.06 or less with a numerical aperture as a unit. 5. The position detecting device according to claim 4, wherein a width of each of the plurality of light-shielding regions shielded by the imaging light flux limiting member in a direction corresponding to a measurement direction of the position detection mark. Is set to (D + 0.03) or more with respect to the width D of each of the plurality of secondary light sources formed by the illumination light flux limiting member with the numerical aperture as a unit. 6. The position detection device according to claim 2, wherein the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member are light of the illumination optical system. It has two secondary light sources which are distributed point-symmetrically with respect to the axis and which are distributed in the same position in a direction corresponding to the non-measurement direction of the position detection mark, and the measurement direction of the position detection mark of the two secondary light sources. The position detection device is characterized in that the center spacing in the direction corresponding to is set so as not to be an integral multiple of λ / P, where λ is the center wavelength of the illumination light. 7. The position detecting device according to claim 1, wherein the plurality of secondary light sources formed on the pupil plane of the illumination system by the illumination light flux limiting member are the plurality of secondary light sources. Position detection which is distributed point-symmetrically with respect to the optical axis of the illumination optical system, and is distributed so that a plurality of secondary light sources are not present at the same position in the direction corresponding to the non-measurement direction of the position detection mark. apparatus.