JPH1027746A - Alignment method and aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the alignment method capable of simultaneously detecting a mask mark and a substrate mark with high precision. SOLUTION: An alignment system 25a simultaneously observing a mask mark formed on a mask 10 and a substrate alignment mark formed on a substrate is provided with the first polarizer 31a irradiating the mask and the substrate with alignment beams 38 as the linear plolarized illumination light, an image pick-up means 37 and the second polarizer 31b entering the polarizing component only in the orthogonal direction to the polarizing direction of the illumination light out of the returning light from the mask 10 and the substrate 14. A 1/4 wavelength plate 32 is arranged in the optical path between the mask 10 and the substrate 14. In such a constitution, the mask mark makes a dark level image while the substrate mark makes a bright level image therby enabling both marks to be observed simultaneously without saturating an image pick-up signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exposure apparatus used for manufacturing a semiconductor memory, a liquid crystal display panel, and the like.

[0002]

2. Description of the Related Art In a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, a CCD imaging device, a thin film magnetic head, and the like, a pattern formed on a photomask or a reticle (hereinafter, referred to as a mask) is formed by a photosensitive agent such as a photoresist. Projection exposure is performed on a photosensitive substrate (hereinafter, simply referred to as a substrate) such as a semiconductor wafer or a glass plate to which is coated. As an exposure apparatus for performing the projection exposure, after exposing a pattern formed on a mask to a predetermined shot area on a substrate, the substrate is stepped by a fixed distance, and the mask pattern is exposed again to the next shot area. An exposure apparatus of a so-called step-and-repeat system that repeats the above-mentioned operations is often used. Further, as another type of exposure apparatus, while scanning the mask and the substrate relatively synchronously with respect to the rectangular or arcuate illumination area,
A scanning exposure apparatus that exposes a mask pattern on a substrate is also known. This scanning type exposure apparatus performs exposure in a shot by a scanning method, and moves between shots in a step-and-scan method.
There is a slit scan type in which the entire surface of the substrate is exposed by one scan.

[0003] In any of the exposure apparatuses, it is required to expose a mask pattern overlaid on a pattern already formed on the substrate. In order to improve the accuracy of the overlay, the mask and the substrate are required to be exposed. Need to be aligned with high accuracy.

Therefore, the exposure apparatus photoelectrically detects a substrate alignment mark (hereinafter, referred to as a substrate mark) formed on a substrate and a mask alignment mark (hereinafter, referred to as a mask mark) formed on a mask. An alignment detection system for aligning the substrate and the substrate is incorporated. As one of the alignment methods, there is an FIA (Field Image Alignment) method in which image data of an alignment mark captured by illuminating with light having a wide wavelength band using a halogen lamp or the like as a light source is processed and measured. . The alignment method uses a TTL (Through The Lens) that measures the position of a substrate via a projection optical system.
Method, a TTM (Through The Mask) method that measures the positional relationship between the mask and the substrate via the projection optical system and the mask, and an off-axis method that directly measures the position of the substrate without using the projection optical system. You.

As an alignment method for detecting a relative position between a mask and a substrate, there is a TTM FIA method in which a substrate mark formed on the substrate and a mask mark formed on the mask are simultaneously measured by an alignment detection system disposed above the mask. In this method, the relative position between the mask and the substrate is detected by simultaneously capturing the substrate mark and the mask mark by the imaging means, performing image processing on the captured mark, and determining the positional relationship between the two marks. The alignment is performed so as to have a predetermined relationship.

[0006]

The conventional TT
The M FIA type alignment detection system has a problem that there is a large difference between the light intensity from the mask mark and the light intensity from the substrate mark incident on the imaging means. That is, even if the reflectance of the substrate mark and the reflectance of the mask mark are equivalent, the amount of light incident on the alignment detection system from the substrate mark is smaller than the amount of light from the mask mark due to reciprocating the projection optical system. Become. Actually, the mask mark is a clear mark formed by chromium etching or the like, whereas the substrate mark is formed by a transparent resist or the edge shape of the mark becomes dull through a process such as development. In general, the amount of light incident on the alignment detection system from the substrate mark is significantly smaller than the amount of light from the mask mark because the state is not uniform due to the influence of the base of the mark and the application of the resist.

Therefore, if the alignment detection system is adjusted so as to be suitable for the detection of the mask mark, the substrate mark cannot be detected. On the contrary, the light amount of the alignment light and the detection of the image pickup means can be detected so that the substrate mark can be detected. If the sensitivity is adjusted, the signal of the mask mark is saturated by the imaging means. In any case, there is a disadvantage that the mask mark and the substrate mark cannot be simultaneously detected with high accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and has as its object to provide an alignment method capable of simultaneously detecting a mask mark and a substrate mark with high accuracy.

[0009]

According to the present invention, the above object is achieved by using linearly polarized light as alignment light, detecting an image with linearly polarized light orthogonal to the linearly polarized light, and observing the mask mark as a dark level image. To achieve.

That is, according to the present invention, the mask alignment mark (mask mark) formed on the mask and the substrate alignment mark (substrate mark) formed on the substrate are simultaneously illuminated by the alignment light, and the image of the mask mark and the substrate mark are illuminated. In a positioning method of positioning a mask and a substrate using position information of an image, linearly polarized light is used as alignment light, and an image of a mask alignment mark and a substrate alignment mark are formed using linearly polarized light orthogonal to the polarization direction of the alignment light. It is characterized by forming.

At this time, the light reflected from the mask mark is not detected, and the image becomes a dark level image. On the other hand, the light returning from the substrate mark has a component that is orthogonal to the polarization direction of the alignment light because the polarization direction is rotated due to edge scattering or the like, and a light level image is generated from the substrate mark by the component light. It is formed. In order to form a high-brightness substrate mark image by making the polarization direction of the light returning from the substrate mark orthogonal to the polarization direction of the alignment light without relying on the rotation of the polarization angle due to edge scattering, etc. It is advantageous to place a quarter-wave plate in the optical path between.

As is apparent from the above description, from another viewpoint, the present invention simultaneously observes a mask alignment mark formed on a mask and a substrate alignment mark formed on a substrate, and obtains a positional relationship between the two. In an alignment method for aligning a mask and a substrate, a mask mark is observed as a dark level image with respect to a background level, and the substrate mark is observed as a light level image with respect to a background level. Is what you do.

Further, the present invention provides a projection optical system for projecting a pattern formed on a mask onto a substrate coated with a photosensitive agent, a mask disposed on the mask, and a mask mark formed on the mask and formed on the substrate. In an exposure apparatus including an alignment system for simultaneously observing the obtained substrate mark, the alignment system includes a light source, a first polarizing unit that irradiates the mask and the substrate with light from the light source as linearly polarized illumination light,
It is characterized by comprising an imaging means and a second polarizing means for making only a polarization component in a direction orthogonal to a polarization direction of the illumination light out of light returned from the mask and the substrate incident on the imaging means.

Also in this case, in order to observe the substrate mark as a high-luminance image, it is advantageous to dispose a quarter-wave plate in the optical path of the alignment system between the mask and the substrate.
According to the present invention, in order to invert the brightness of a detection signal of a mask mark and to detect the mask mark as a dark level signal, light amount adjustment of alignment light and sensitivity adjustment of imaging means are performed in accordance with a substrate mark having a weak signal intensity. However, the detection signal of the mask mark does not saturate. Therefore,
The mask mark and the substrate mark can be simultaneously detected with high accuracy.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an exposure apparatus employing the alignment method of the present invention. Here, a slit-scan type exposure apparatus will be described as an example, but the present invention is not limited to a slit-and-scan type exposure apparatus, but may be a step-and-repeat type exposure apparatus or a step-and-scan type exposure apparatus. The present invention can be generally applied to an exposure apparatus of another type, such as an exposure apparatus, which detects a mask mark and a substrate mark at the same time and aligns the mask and the substrate based on a positional relationship between the two.

A light beam emitted from a light source 1 such as an ultra-high pressure mercury lamp is reflected by an elliptical mirror 2 and then enters a dichroic mirror 3. The dichroic mirror 3 reflects a light beam having a wavelength required for exposure and transmits a light beam having another wavelength. The light beam reflected by the dichroic mirror 3 is allowed or blocked from entering the projection optical system side by a shutter 4 that can be moved forward and backward with respect to the optical axis AX1. By opening the shutter 4, the light beam from the light source 1 enters the wavelength selection filter 5, and the projection optical system 1
2a is suitable for performing the transfer (usually g, h, i
(At least one band of the line).

Further, since the intensity of this light beam has the highest intensity near the optical axis and a Gaussian distribution in which the intensity decreases as approaching the periphery, at least the projection area 13 of the projection optical system 12a is used.
It is necessary to make the intensity distribution uniform within a. Therefore, the fly-eye integrator 6 and the condenser lens 8 make the intensity distribution of the light beam uniform. The mirror 7 is a bending mirror for making the optical system compact. The light flux having a uniform intensity distribution is reflected by a mirror 7 and then applied to a pattern surface of a mask 10 via a field stop 9. The field stop 9 is a photosensitive substrate (hereinafter, referred to as a substrate) 14 such as a glass plate coated with a photosensitive agent such as a photoresist.
It has an opening that limits the upper projection area 13a.

The configuration from the light source 1 to the field stop 9 is an illumination optical system L1 for the projection optical system 12a. In this example, the illumination optical systems L2 to L2 have the same configuration as the illumination optical system L1.
5 is provided to project the light flux from each illumination optical system to the projection optical system 12.
b to 12e. Multiple illumination optical systems L
The luminous flux emitted from each of 1 to L5 is
The different upper partial areas (illumination areas) 11a to 11e are respectively illuminated. A plurality of light beams transmitted through the mask 10 are projected onto the projection optical systems 12a to 12a-1 corresponding to the illumination optical systems L1 to L5.
2e different projection areas 13a-13 on the substrate 14
e, the pattern images of the illumination areas 11a to 11e of the mask 10 are formed. Each of the projection optical systems 12a to 12e is an erect real-size real image (erect erect image) optical system. In FIG.
The optical axis direction of the projection optical systems 12a to 12e is defined as a Z direction, and Z
In the direction perpendicular to the direction, the moving direction of the mask 10 and the substrate 14 is defined as the X direction, and the direction perpendicular to the Z direction and the X direction is defined as the Y direction.

FIG. 2 is a top view of the substrate 14 held on the substrate stage 15. Projection area 13a on substrate 14
As shown in FIG. 2, to 13e, regions adjacent in the Y direction (for example, 13a and 13b, 13b and 13c) are displaced by a predetermined amount in the X direction, and ends of the adjacent regions are indicated by broken lines. As shown by, they are arranged so as to overlap in the Y direction (the positions of the ends in the Y direction of adjacent areas overlap). Therefore, the plurality of projection optical systems 12a to 12e also
The projection areas 13a to 13e are displaced by a predetermined amount in the X direction corresponding to the arrangement of the projection areas 13a to 13e, and are arranged so as to overlap in the Y direction. The plurality of illumination optical systems L1 to L5 are
The upper illumination areas 11a to 11e correspond to the projection areas 13a to 1
It is arranged so as to have the same arrangement as 3e. Accordingly, the entire surface of the pattern region 10a on the mask is transferred to the exposure region 14a on the substrate 14 by scanning the projection optical systems 12a to 12e in the X direction in synchronization with the mask 10 and the substrate 14. Can be. On the substrate 14, substrate alignment marks (substrate marks) 24a to 24f are provided outside the exposure region 14a.

The substrate 14 is mounted on a substrate stage 15, and the substrate stage 15 has a driving device 16 having a long stroke in the scanning direction (X direction) to perform one-dimensional scanning exposure. Furthermore, for the scanning direction, a high-resolution and high-precision position measuring device (eg, a laser interferometer)
Seventeen. The mask 10 is supported by a mask stage (not shown). The mask stage also has a driving device and a position measuring device for detecting the position of the stage in the scanning direction, like the substrate stage 15. Reference marks 22a to 22d are arranged at predetermined positions on the substrate stage 15 outside the range where the substrate 14 is to be mounted, in a plane substantially the same as the surface of the substrate 14 (projection surface of the pattern of the mask). ing.

FIG. 3 is a top view of the mask 10, and the area of the mask 10 to be transferred to the substrate 14 (illumination area, in which a pattern is drawn) is indicated by 10a. A mask alignment mark (mask mark) 21 corresponding to the reference marks 22a to 22d on the substrate stage 15 is provided on the mask 10 outside the transfer range 10a.
a to 21d and mask marks 23a to 23f corresponding to the substrate marks of the substrate 14. The mask marks 21a to 21d and 23a to 23d are light-shielding marks formed by a chrome layer.

As shown in FIG. 1, alignment detection systems 20a and 20b are arranged above the mask 10, and the mask marks 21a to 21d and 23a to 23f on the mask are detected by the alignment detection systems 20a and 20b. In addition, reference marks 22a to 22 provided on substrate stage 15 via projection optical systems 12a to 12e.
d and substrate marks 24a to 24 formed on substrate 14.
Detect f. That is, the alignment detection systems 20a and 20a
b is emitted from the reflection mirror 25
The light is irradiated onto the mask 10 via the projection optical systems a and 25b, and is also irradiated onto the substrate 14 via the projection optical systems 12a and 12e at both ends of the plurality of projection optical systems. A part of the alignment light irradiated on the mask 10 is reflected by the mask mark made of the chrome layer,
a, 25b via the alignment detection systems 20a, 20b
Incident on. The remaining alignment light is transmitted through the mask 10 to form the substrate marks 24 a to 24 formed on the substrate 14.
Illuminate f. The light reflected or scattered by the substrate marks 24a to 24f enters the respective alignment detection systems 20a and 20b via the projection optical systems 12a and 12e and the reflection mirrors 25a and 25b.

FIG. 4 shows the configuration of the alignment detection system. FIG. 4 shows one alignment detection system 20a, but the other alignment detection system 2a.
0b has a similar configuration. The alignment system 20a
Illumination lens 36, first and second polarizing plates 31a, 31
b, half mirror 35, first and second objective lenses 34
a, 34b, and imaging means 37 such as a CCD camera. Here, the surface of the substrate 14, the pattern forming surface of the mask 10, and the imaging surface of the imaging unit 37 have a conjugate relationship with each other. Also, the first polarizing plate 31a and the second polarizing plate 31b
Are orthogonal to each other as shown in FIG.

A light beam 38 from the alignment light source passes through the illumination lens 36 and the first polarizing plate 31a, is converted into linearly polarized light, is reflected by the half mirror 35, and passes through the first objective lens 34a and the reflecting mirror 25a. Thus, a mask mark on the mask 10, for example, a mask mark 23a is irradiated. The light reflected by the mask mark 23a is reflected by the reflection mirror 25a, passes through the first objective lens 34a and the half mirror 35, and enters the second polarizing plate 31b. Here, since the polarization direction of the second polarizing plate 31b is orthogonal to the polarization direction of the first polarizing plate 31a, that is, the polarization direction of the alignment light illuminating the mask mark 23a, it is reflected by the mask mark 23a. Light is applied to the second polarizing plate 31b
Cannot be transmitted, and cannot enter the imaging means 37.

The linearly-polarized alignment light transmitted through the area other than the mask mark 23a of the mask 10 is converted into circularly-polarized light by passing through the quarter-wave plate 32, and then is projected onto the projection optical system 1.
The substrate mark provided on the substrate 14 through 2a is illuminated, for example, a substrate mark 24a. The light scattered or reflected by the substrate mark 24a follows the optical path of the illumination light in the reverse direction, passes through the projection optical system 12a, passes through the quarter-wave plate 32, and has a polarization direction of 90 degrees with respect to the polarization direction of the alignment light. After being converted into the linearly polarized light rotated by °, an image is formed on a pattern surface formed on the lower surface of the mask 10. Then, the mask 10
And is reflected by the reflection mirror 25a and enters the alignment detection system 20a.

The return light from the substrate 14 that has entered the alignment detection system 20a passes through the first objective lens 34a and the half mirror 35 and reaches the second polarizing plate 31b. The return light from the substrate 14 has a polarization direction of the second polarizing plate 31.
Since the polarization direction coincides with the polarization direction b, the light passes through the second polarizing plate 31b and is imaged on the imaging surface of the imaging means 37 via the second objective lens 34b. As shown in FIG. 6, a dark level mask mark image 42 and a light level substrate mark image 43 are formed on the imaging surface of the imaging unit 37 with the light returned from the substrate 14 as a background 41. Mask mark 23a
Is a dark level image because the light reflected by the mask mark 23a cannot pass through the second polarizer 31b, and the return light from the substrate 14 Mask mark 23 formed as a light shielding mark
This is because a cannot be transmitted.

FIG. 7 shows a light intensity profile of the imaging surface of the imaging means 37 on the line AA. Light does not enter the positions 42a and 42b crossing the mask mark image 42, and is at a dark level with respect to the background level 41a. On the other hand, the light intensity is high in a portion 43a crossing the reference mark image 43, which is a light level with respect to the background level 41a. Since the mask mark image 42 is a dark-level image formed by the absence of incident light, even if the intensity of the alignment light 38 is increased, the mask mark image 42 The light intensity does not change. On the other hand, the light intensity of the image 43 of the substrate mark at the background level 41a and the light level increases as the intensity of the alignment light 38 increases, as shown by the imaginary lines 45 and 46 in FIG.

As described above, even if the light amount of the alignment light 38 is increased in accordance with the substrate mark, the dark level of the mask mark does not change, and the image signal of the mask mark does not become saturated as in the related art. Therefore, by appropriately setting the intensity of the alignment light 38 so that the substrate mark 24a can be detected with sufficient sensitivity, the mask mark and the substrate mark can be simultaneously detected. The light amount can be adjusted by controlling the light amount of the alignment light source, or by setting the light amount of the light source to a sufficient light amount in advance.
There are methods for controlling the electronic shutter of the camera and the like, and the present invention is effective for either method.

In the example described here, the insertion position of the quarter-wave plate 32 is set below the mask 10 so that the projection optical system 1
Although the space is above the substrate 2a, the space may be provided below the projection optical system 12a and above the substrate 14, or inside the projection optical system 12a. Further, if the projection optical system 12a has a function of rotating the polarization direction of the transmitted light, a quarter-wave plate need not be provided. Regarding the function of rotating the polarization direction, the polarization direction of the return light from the substrate 14 and the polarization direction of the second polarization plate 31b do not necessarily have to be completely matched like a quarter-wave plate. Second polarizing plate 31b
It is sufficient that the loss of the light amount due to the mismatch between the polarization direction of the light beam and the polarization direction of the return light from the substrate 14 can be covered by the light amount of the alignment light.

A method of forming a bright-level image by utilizing the disorder of the polarization angle when the light is reflected or scattered from the substrate without necessarily providing a means for optically rotating the polarization direction is also conceivable. Further, the first polarizing plate 31a, the second polarizing plate 31b, and the half mirror 35 can be replaced with a polarizing beam splitter.

[0031]

According to the present invention, the mask mark is a dark-level image and the substrate mark is a bright-level image.
It is possible to simultaneously detect the mask mark and the substrate mark with high accuracy by the imaging means. In addition, the alignment accuracy of the exposure apparatus can be improved thereby.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an exposure apparatus according to the present invention.

FIG. 2 is a top view of a substrate placed on a substrate stage.

FIG. 3 is a top view of a mask.

FIG. 4 is a diagram showing a configuration example of an alignment detection system.

FIG. 5 is a diagram illustrating polarization directions of a first polarizing plate and a second polarizing plate.

FIG. 6 is a diagram illustrating an image of a mask mark and an image of a substrate mark formed on an imaging surface of an imaging unit.

FIG. 7 is a diagram illustrating a light intensity profile on an imaging surface of an imaging unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 10 ... Mask, 12a-12e ... Projection optical system, 14 ... Substrate, 15 ... Substrate stage, 16 ... Driver, 20a, 20b ... Alignment detection system, 23a-2
3f: mask mark, 24a to 24f: substrate mark, 2
5a, 25b: reflection mirror, 31a: first polarizing plate, 3
1b: second polarizing plate, 32: quarter-wave plate, 34a ...
A first objective lens, 34b... A second objective lens, 35.
Half mirror, 36: illumination lens, 37: imaging means, 3
8 ... Alignment light, 41 ... Background, 42 ...
Mask mark image, 43 ... substrate mark image

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H01L 21/30 525R 525T

Claims (5)

[Claims] 1. A mask alignment mark formed on a mask and a substrate alignment mark formed on a substrate are simultaneously illuminated by alignment light, and the mask is aligned with the mask using position information of an image of the mask alignment mark and an image of the substrate alignment mark. In the positioning method for positioning the substrate, linearly polarized light is used as the alignment light, and images of the mask alignment mark and the substrate alignment mark are formed using linearly polarized light orthogonal to a polarization direction of the alignment light. And the alignment method. 2. The alignment method according to claim 1, wherein a wave plate is arranged in an optical path between the mask and the substrate. 3. A positioning method for simultaneously observing a mask alignment mark formed on a mask and a substrate alignment mark formed on a substrate, determining a positional relationship between the two, and positioning the mask and the substrate. Wherein the mask alignment mark is observed as a dark level image with respect to a background level, and the substrate alignment mark is observed as a light level image with respect to a background level. . 4. A projection optical system for projecting a pattern formed on a mask onto a substrate coated with a photosensitive agent, and a mask alignment mark disposed on the mask and formed on the substrate and a mask alignment mark formed on the mask. An exposure system including an alignment system for simultaneously observing the obtained substrate alignment mark, wherein the alignment system irradiates the light from the light source to the mask and the substrate as linearly polarized illumination light. A polarization unit, an imaging unit, and a second polarization unit that, of the light returning from the mask and the substrate, only a polarization component in a direction orthogonal to a polarization direction of the illumination light is incident on the imaging unit. Exposure apparatus characterized by the above-mentioned. 5. The exposure apparatus according to claim 4, wherein a wavelength plate is disposed in an optical path of said alignment system between said mask and said substrate.