JPH09162115A - Aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a combined image of a reticle mark and a reference mark well by illuminating an imaginary plane through an alignment mark, reflecting the illumination light through a projection optical system and a reticle mark and illuminating the reference mark, and positioning a light shielding member at a position conjugate to the alignment mark. SOLUTION: Illumination light of an alignment system illuminates an imaginary plane A through a reticle mark RM and passes through a projection optical system 3 and a reference mark SM before entering a plane mirror 22. Illumination light reflected on the plane mirror 22 transmits through the reference mark SM from below. Illumination light passed through the reticle mark RM forms a combined image of the reference mark SM and the reticle mark RM on the image pickup plane of a two-dimensional image pickup element 15 and the positional shift of the reticle mark RM is detected using the reference mark SM as an index. A light shielding plate 20 is arranged optically in conjugate to the reticle mark RM forming plane by means of an illumination relay lens 18 and a first objective lens 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus, and more particularly, it is provided in a projection exposure apparatus used for manufacturing semiconductor elements, liquid crystal display elements, etc. in a lithography process to detect the relative position of a mask to a wafer stage. Alignment device.

[0002]

2. Description of the Related Art A projection exposure apparatus is used in manufacturing semiconductor elements, liquid crystal display elements and the like. In a projection exposure apparatus, a reticle (mask) is illuminated with exposure light, and the pattern is projected onto a wafer (or a glass plate or the like) coated with a photoresist via a projection optical system. As the exposure light, a bright line (g line, i line) of a mercury lamp, an excimer laser, or the like is used.

In a projection exposure apparatus, when performing exposure,
It is necessary to accurately align (align) the reticle and the wafer. Therefore, first, the reticle is positioned at a predetermined position based on the measurement result of the reticle alignment system. Then, after the positioning of the reticle is completed, the relative position of the reticle with respect to the wafer stage on which the wafer is placed is measured. Then, based on this measurement result, the reticle is aligned with respect to the wafer stage and eventually the wafer. Conventionally, a so-called stage emission type reticle alignment system has been used to measure the relative position of the reticle with respect to the wafer stage.

FIG. 7 is a diagram schematically showing a main part of a projection exposure apparatus having a conventional stage emission type reticle alignment system. FIG. 7A is a top view and FIG. 7B is a side view. Shows. In FIG. 7, the reticle 1 is held on the reticle stage 2. Then, based on the exposure light, the pattern on the reticle 1 is projected and exposed onto each shot area on the wafer 4 via the projection optical system 3. Further, cross-shaped reticle marks RM, for example, are formed at both ends of the pattern area of the reticle 1.

The wafer 4 is placed on a wafer stage 6 via a wafer holder 5. A light-transmissive stage substrate 7 is mounted on the wafer stage 6. On the upper surface of the stage substrate 7, two reference marks SM each having a remaining pattern (the index mark portion is reflected) are formed corresponding to the two reticle marks RM. At the time of reticle alignment, the illumination system of the stage emission type alignment system illuminates the reference mark SM from the bottom side. The illumination light transmitted through each reference mark SM illuminates the reticle mark RM formed on the lower surface of the reticle 1 via the projection optical system 3, respectively.

In the illumination system of the stage emission type alignment system, the illumination light guided from the exposure light source (not shown) through the light guide 8 is emitted from the emission end into the wafer stage 6. The illumination light emitted from the exit end of the light guide 8 is reflected vertically upward in the figure by the mirror 9, and then illuminates the reference mark SM by Koehler transmission through the condenser lens 10. Thus, the illumination light that has passed through each reference mark SM and the projection optical system 3 forms an image of each reference mark SM on the lower surface of the reticle 1. Thus, the image of each reference mark SM illuminates the corresponding reticle mark RM.

Illumination light transmitted through the reticle mark RM is
After being reflected by the mirror 11, the two-dimensional C is passed through the first objective lens 12, the mirror 13, and the second objective lens 14.
A composite image of the reference mark SM and the reticle mark RM is formed on the image pickup surface of the two-dimensional image pickup device 15 such as a CD. 2
Based on the two-dimensional image data from the three-dimensional image sensor 15,
The positional deviation of the reticle mark RM with respect to the reference mark SM, that is, the relative position of the reticle 1 with respect to the wafer stage 6 is detected.

FIG. 8 is a diagram schematically showing a main part of a projection exposure apparatus equipped with a conventional epi-illumination type reticle alignment system, in which (a) is a top view and (b) is a side view. Shows. In FIG. 8, elements having the same functions as those of the constituent elements in FIG. 7 are designated by the same reference numerals as those in FIG.

In the epi-illumination type alignment system shown in FIG.
Illumination light guided from an exposure light source (not shown) through the light guide 16 is emitted from its emission end. The illumination light emitted from the exit end of the light guide 16 is condensed through the condenser lens 17, and then the relay lens 1
8, the reticle mark RM is illuminated via the half mirror 19, the first objective lens 12, and the mirror 11. The light passing through the reticle mark RM illuminates the reference mark SM formed on the stage substrate 7 via the projection optical system 3.

The reflected light from each reference mark SM with respect to the illumination light is reflected by the projection optical system 3, the corresponding reticle mark RM,
Mirror 11, first objective lens 12, half mirror 19,
And the two-dimensional image pickup device 1 via the second objective lens 14.
A composite image of the reference mark SM and the reticle mark RM is formed on the imaging surface of No. 5.

[0011]

Generally, in a projection exposure apparatus, the wafer stage is driven at a high speed, and the amount of movement thereof is required to be extremely high precision. Therefore, it is necessary to miniaturize the wafer stage as much as possible and to reduce the load on the wafer stage as much as possible.

However, in the conventional stage emission type alignment apparatus, the illumination light is guided to the inside of the wafer stage 6 via the light guide 8. Then, in order to illuminate the reference mark SM formed on the stage substrate 7 on the wafer stage 6, the mirror 9 and the condenser lens 1
It is necessary to provide a member such as 0 inside the wafer stage 6. As a result, there is an inconvenience that the wafer stage 6 becomes large. In addition, the light guide 8 imposes a load on the free movement of the wafer stage 6.

Further, in the conventional epi-illumination type alignment apparatus, there are two methods for detecting a composite image of the reticle mark RM and the reference mark SM. There are a method in which the reticle mark RM is inevitably left as a pattern (the index mark portion is reflected) and then the reference mark RM is left as a pattern, and a method in which the reference mark RM is a blank pattern (the index mark portion is transparent). .

When the reference mark SM is left as a pattern, the reflected light from both the reticle mark RM and the reference mark SM forms a composite image. Therefore, whether a good image is obtained as a composite image depends on the reflection characteristic of the reticle mark RM. Generally, it is better not to limit the reflectance of the reticle mark RM. Therefore, when the reflectance of the reticle mark RM is set low, a good image of the reticle mark RM cannot be obtained.

On the other hand, in the case where the reference mark is formed as a blank pattern, the image of the reticle mark RM is the image of the reflected light from the reticle mark RM with respect to the epi-illumination light and the epi-illumination light returning from the reflection surface of the reference mark SM. Is a composite image with the image of the reticle mark RM for the transmitted light. Also in this case, whether or not a good image is obtained as an image of the reticle mark RM depends on the reflection characteristic of the reticle mark RM. That is, when the reflected light of the reticle mark RM is equal to the transmitted light, the reticle mark R
The image of M cannot be obtained at all.

The present invention has been made in view of the above problems, and provides an alignment apparatus capable of favorably detecting a composite image of a reticle mark and a reference mark without increasing the size of the wafer stage. The purpose is to

[0017]

In order to solve the above problems, in the present invention, a projection optical system for projecting an image of a pattern formed on a mask onto a photosensitive substrate and the substrate are held. An alignment mark formed on the mask and a reference mark formed on the substrate stage, which is provided in a projection exposure apparatus having a substrate stage movable in a plane perpendicular to the optical axis of the projection optical system. In the alignment apparatus for detecting the relative position of the mask with respect to the substrate stage based on the above, after illuminating a predetermined virtual plane between the alignment mark and the projection optical system via the alignment mark, the projection optical system An illumination system for supplying illumination light toward the reference mark via the projection optical system and the illumination system via the reference mark. A reflection member for reflecting the illumination light passing through the reference mark toward the reference mark so that the illumination light from the system illuminates the reference mark, the reference mark, the projection optical system, and the alignment mark. An image detection system for detecting a composite image of the reference mark and the alignment mark based on the illumination light from the reflection member via, and a position substantially conjugate with the alignment mark, and the predetermined virtual Illumination so that the reflected light from the alignment mark with respect to the illumination light that illuminates the surface and the reflected light from the reference mark with respect to the illumination light that enters the reflecting member do not substantially enter the image plane of the image detection system. An alignment apparatus comprising: a light blocking member for blocking a part of a light flux.

According to a preferred aspect of the present invention, the reflecting member is a plane mirror arranged substantially in parallel with the reference mark and spaced apart by a predetermined distance. Alternatively, the reference mark is formed on a surface of the stage substrate provided on the substrate stage, the surface facing the projection optical system, and the reflecting member is formed on a surface of the stage substrate on the opposite side of the projection optical system. It is preferably a reflective surface.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, an illumination system epi-illuminates a virtual surface below a predetermined distance from an alignment mark (reticle mark) through an alignment mark. This illumination light is incident on the reflecting member arranged below the reference mark via the projection optical system and the reference mark. The reflecting member is arranged at a position where the reflected illumination light illuminates the reference mark. In this way, the reference mark is transmitted and illuminated from below, and the combined image of the reference mark and the alignment mark is detected by the image detection system based on the light that has passed through the projection optical system and the alignment mark.

In the present invention, the light blocking member is arranged at a position substantially conjugate with the alignment mark in the illumination system. Then, due to the action of the light shielding member, a part of the illumination light flux is blocked so that the reflected light from the alignment mark and the reference mark with respect to the epi-illumination light does not enter the image plane of the image detection system. As a result, the reflected light from the alignment mark and the reference mark with respect to the illumination light is not detected by the image detection system, and only the transmitted light of the alignment mark and the reference mark with respect to the illumination light forms a composite image.

That is, in the present invention, although the epi-illumination type illumination system is used, the stage emission type illumination is substantially realized by the cooperation of the light shielding member and the reflecting member. In this case, unlike the conventional epi-illumination type illumination system in which two sets of light guides, mirrors, and condenser lenses have to be placed in the wafer stage, in the illumination system of the present invention, a reflecting member is placed in the wafer stage. Only. Therefore, the composite image can be satisfactorily detected based on the transmitted light of the reticle mark and the reference mark with respect to the illumination light without increasing the size of the wafer stage.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a main part of a projection exposure apparatus provided with an alignment apparatus according to an embodiment of the present invention, in which (a) is a top view and (b) is a side view. . In FIG. 1, the z axis is parallel to the optical axis of the projection optical system 3, the x axis is parallel to the paper surface in a plane perpendicular to the optical axis, and the z axis is perpendicular to the paper surface in a plane perpendicular to the optical axis. The y-axis is set in each direction.

In FIG. 1, a reticle 1 on which a circuit pattern to be transferred is formed is held on a reticle stage 2 parallel to the xy plane. Then, the pattern on the reticle 1 is projected and exposed on each shot area on the wafer 4 through the projection optical system 3 based on the exposure light (for example, the i line and the g line). As shown in an enlarged view in FIG. 2, cross-shaped reticle marks RM (remaining patterns) are formed at both ends of the pattern area PA of the reticle 1 along the x direction.

The wafer 4 is placed on the wafer stage 6 via the wafer holder 5 in parallel with the xy plane. The wafer stage 6 moves the wafer 4 in the xy plane.
The xy stage for positioning the wafer 4, the z stage for positioning the wafer 4 in the z direction, the leveling stage for correcting the tilt angle of the wafer 4, and the like. Then, x of the reticle stage 2 and the wafer stage 6
Laser interferometer (not shown) for coordinates and y-coordinate, respectively
It is always measured by.

Further, a light-transmissive stage substrate 7 is attached near the wafer holder 5 on the wafer stage 6. As shown in FIG. 3, on the upper surface of the stage substrate 7, for example, in two centrally symmetric regions along the x-axis,
A reference mark SM is formed on each. The reference mark SM is, for example, a remaining pattern (the index mark portion is reflected) formed around the rectangular opening. Further, below the stage substrate 7, a plane mirror 22 having a reflecting surface parallel to the xy plane is provided.

The projection exposure apparatus of FIG. 1 is provided with an alignment device for detecting the relative position of the reticle mark RM with respect to the wafer stage 6. The alignment apparatus includes a first alignment system for detecting the relative position of one reticle mark of the pair of reticle marks RM, and a second alignment system for detecting the relative position of the other reticle mark. ing. In addition,
As shown in FIG. 1, the two alignment systems have the same configuration as each other and are arranged symmetrically with respect to the y axis. Hereinafter, the embodiment will be described by focusing on one alignment system.

Each alignment system has a light guide 16 for guiding light from an exposure light source (not shown). The illumination light guided through the light guide 16 is emitted from its emission end and then enters the condenser lens 17. Light that has passed through the condenser lens 17 is blocked by the light blocking plate 20.
And the field relay 21 and then the illumination relay lens 18
Incident on. The illumination light that has passed through the illumination relay lens 18 is
The virtual plane A therebelow is Koehler-illuminated via the half mirror 19, the first objective lens 12, the optical path deflecting mirror 11 and the reticle mark RM.

As shown by the broken line in the figure, the light shield plate 20
Is the lower surface of the reticle 1 (the surface on which the reticle mark RM is formed) due to the illumination relay lens 18 and the first objective lens 12.
And is optically conjugate with. In addition, the field stop 21
Are arranged optically conjugate with the virtual plane A below the reticle mark RM. Further, the light shielding plate 20 is set to a size such that reflected light from the reticle mark RM due to epi-illumination does not enter the image pickup surface of the two-dimensional image pickup device 15 described later.

FIG. 4 is a diagram showing the relationship between the reticle mark RM and the image 20a of the light shielding portion of the light shielding plate 20 formed on the lower surface of the reticle 1. Note that FIG. 4A is a diagram for an illumination light beam focused on the center of the image 21a of the field stop 21 formed on the virtual surface A, and FIG. 4B is a field stop image 21a.
FIG. 6 is a diagram for an illumination light flux that is condensed on the outer periphery of the. As shown in FIG. 4, the two-dimensional image sensor 1 on the lower surface of the reticle 1
The central portion of the cross-shaped reticle mark RM corresponding to the detection field of view 5 (not shown) is the image 20a of the light shielding portion of the light shielding plate 20.
It is completely covered by the shaded area in the figure. As a result, as described above, the reflected light from the reticle mark RM due to the epi-illumination does not enter the image pickup surface of the two-dimensional image pickup device 15.

The light that illuminates the virtual plane A via the reticle mark RM enters the plane mirror 22 via the projection optical system 3 and the reference mark SM on the stage substrate 7. The illumination light reflected by the plane mirror 22 illuminates the reference mark SM from below with Koehler transmission. FIG. 5 is a diagram for explaining the optical path of the illumination light that introduces the reference mark in the mirror image space, that is, the mirror image reference mark SMa, is folded back by the plane mirror 22 and reaches the reference mark SM. The mirror image reference mark SMa is optically conjugate with the virtual surface A below the reticle 1.

Further, the reticle mark RM and the reference mark S
Since M is conjugated, the reference mark SM and the light shielding plate 20 are also conjugated. FIG. 6 shows an image 20b of the light shielding portion of the light shielding plate 20 formed on the upper surface of the stage substrate 7 and the reticle mark R.
It is a figure which shows the relationship between the image RMa of M, and the reference mark SM. That is, FIG. 6 describes the influence of the illumination light flux passing through the light blocking plate 20 and the reticle mark RM.

As shown in FIG. 6, an image RMa of the reticle mark RM is formed on the upper surface of the stage substrate 7 so as to overlap the reference mark SM. The entire reference mark SM and the central portion (the portion corresponding to the detection visual field) of the reticle mark image RMa are covered with the image 20b of the light shielding portion of the light shielding plate 20. Therefore, similarly to the reflected light from the reticle mark RM due to the epi-illumination, the reflected light from the reference mark SM due to the epi-illumination is described later in the two-dimensional image pickup device 15
It does not enter the image pickup surface of.

In this way, the reference mark SM is illuminated by Koehler transmission from the lower plane mirror 22 side. The light transmitted through the reference mark SM formed of the remaining pattern illuminates the reticle mark RM formed on the lower surface of the reticle 1 via the projection optical system 3. At this time, the illumination light has the same wavelength as the exposure light, and the center of the stage substrate 7 and the optical axis AX of the projection optical system 3 coincide with each other. Therefore, the image of the reference mark SM corresponding to each reticle mark RM is formed on the lower surface of the reticle 1. That is, each reference mark S
The image of M illuminates the corresponding reticle mark RM.

Illumination light passing through the reticle mark RM is reflected by a mirror 11 for deflecting an optical path, and then a two-dimensional CCD or the like is passed through a first objective lens 12, a half mirror 19 and a second objective lens 14. A composite image of the reference mark SM and the reticle mark RM is formed on the image pickup surface of the two-dimensional image pickup device 15.

Then, based on the two-dimensional image data from the two-dimensional image pickup device 15, the displacement of the reticle mark RM is detected by visual observation, for example, using the reference mark SM as an index. Further, by performing image processing on the two-dimensional image data, the positional shift of the reticle mark RM is detected as the positional shift amount along the x coordinate and the y coordinate on the wafer stage 6.

As described above, the alignment apparatus of this embodiment has two alignment systems that are symmetrically arranged with respect to the y-axis and have the same configuration as each other. Therefore, one alignment system detects the positional shift of one reticle mark RM, and the other alignment system detects the positional shift amount of the other reticle mark RM. Thus, based on the positional deviation amount of the two reticle marks RM formed on the reticle 1 with respect to the wafer stage 6, the positional relationship of the reticle 1 with respect to the wafer stage 6 (two-dimensional positional deviation amount and rotation around the z-axis). Angle is required.

Next, the reticle stage 2 is driven and the reticle 1 is appropriately moved so that the positional relationship of the reticle 1 with respect to the wafer stage 6 falls within a desired allowable range. Then, the positional relationship between the reticle 1 and the wafer stage 6 is re-measured, and it is confirmed that the measured positional relationship is within a desired allowable range, and the reticle alignment is completed.

As described above, in the present embodiment, the reflected light from the reticle mark RM and the reference mark SM with respect to the epi-illumination light is not detected by the two-dimensional image pickup device 15, but with respect to the illumination light reflected by the plane mirror 22. Only the transmitted light of the reticle mark RM and the reference mark SM forms a composite image.

That is, in this embodiment, the so-called stage emission type illumination is realized by the action of the light shield plate 20 and the plane mirror 22. Then, although it is substantially stage-emission type illumination, a relatively small plane mirror 22 is simply arranged in the wafer stage 6 in parallel with the reference mark SM. Therefore, the composite image can be satisfactorily detected based on the transmitted light of the reticle mark RM and the reference mark SM with respect to the illumination light without increasing the size of the wafer stage 6.

The effect of vignetting (light blocking) of the light beam by the light blocking plate 20 will be considered below with reference to FIG. First, let S be the area of the composite image of the image 20b of the light shielding portion of the light shielding plate 20 formed on the upper surface of the stage substrate 7 and the reticle mark image RMa. In addition, the light blocking plate 20 and the reticle mark RM
Let E0 be the illuminance at the position of the mirror image reference mark SMa when there is no vignetting (light blocking) of the illumination light flux due to a, that is, when S = 0.

At this time, the actual illuminance E when vignetting is present is represented by the following equation (1). E≈E 0 [1-S / {π (2Lθ) ² }] (1) where L: distance between the reference mark SM and the plane mirror 22 (see FIG. 5) θ: numerical aperture NA of illumination light (however, sin θ ≈ θ)

Therefore, if each variable of the equation (1) can be set to such an extent that E≈E0 can be considered, the shading plate 2
The influence of the vignetting of the luminous flux due to 0 on the illuminance can be almost ignored. In other words, for example, (E-E0) is equal to or less than several% of E0, that is, S / {π (2L
If each variable can be set so that θ) ² } is about several percent or less, it is possible to obtain the same illumination performance as that of the stage emission type alignment system in which the reference mark is Koehler illuminated from below in the prior art. become.

In the above-described embodiment, the plane mirror is provided below the stage substrate. However, the reference mark may be formed on the upper surface and the reflective surface may be formed on the lower surface after the thickness of the stage substrate is appropriately adjusted. Further, in the above-described embodiment, an example is shown in which the illumination light of the alignment apparatus and the exposure light are shared, but a light source that supplies light having substantially the same wavelength as the exposure light may be provided separately from the exposure light source.

[0044]

As described above, in the present invention, the epi-illumination type illumination system is used. However, the stage light emission type illumination is substantially realized by the cooperation of the light shielding member and the reflecting member. There is. Therefore, the composite image can be satisfactorily detected based on the transmitted light of the reticle mark and the reference mark with respect to the illumination light without increasing the size of the wafer stage.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a main part of a projection exposure apparatus provided with an alignment apparatus according to an embodiment of the present invention,
(A) is a top view and (b) is a side view.

FIG. 2 is an enlarged view showing a cross-shaped reticle mark RM formed on the lower surface of the reticle 1.

FIG. 3 is an enlarged view showing a reference mark SM formed on the upper surface of a stage substrate 7.

FIG. 4 is a diagram showing a relationship between an image 20a of a light blocking portion of a light blocking plate 20 formed on the lower surface of the reticle 1 and a reticle mark RM.

FIG. 5 is a diagram illustrating an optical path of illumination light that introduces a reference mark in a mirror image space, that is, a mirror image reference mark SMa, is folded back by the plane mirror 22 and reaches the reference mark SM.

FIG. 6 is a light shield plate 20 formed on the upper surface of a stage substrate 7.
FIG. 6 is a diagram showing the relationship between the image 20b of the light shielding part, the image RMa of the reticle mark RM, and the reference mark SM.

FIG. 7 is a diagram schematically showing a main part of a projection exposure apparatus provided with a conventional stage emission type reticle alignment system, in which (a) is a top view and (b) is a side view. .

FIG. 8 is a diagram schematically showing a main part of a projection exposure apparatus provided with a conventional epi-illumination type reticle alignment system,
(A) is a top view and (b) is a side view.

[Explanation of symbols]

 1 reticle 2 reticle stage 3 projection optical system 4 wafer 5 wafer holder 6 wafer stage 7 stage substrate 12 first objective lens 14 second objective lens 15 two-dimensional image sensor 16 light guide 17 condenser lens 18 relay lens 19 half mirror 20 light-shielding plate 21 Field stop 22 Plane mirror RM Reticle mark SM Reference mark

Claims (3)

[Claims] 1. A projection optical system for projecting an image of a pattern formed on a mask onto a photosensitive substrate, and movable in a plane holding the substrate and perpendicular to the optical axis of the projection optical system. An alignment apparatus provided in a projection exposure apparatus having a substrate stage and detecting a relative position of the mask with respect to the substrate stage based on an alignment mark formed on the mask and a reference mark formed on the substrate stage. In the illumination system for illuminating a predetermined virtual plane between the alignment mark and the projection optical system via the alignment mark, and then illuminating the reference mark via the projection optical system. And the reference so that the illumination light from the illumination system via the projection optical system and the reference mark illuminates the reference mark. A reflecting member for reflecting the illumination light passing through the guide toward the reference mark, and the reference based on the illumination light from the reflecting member via the reference mark, the projection optical system and the alignment mark. An image detection system for detecting a composite image of the mark and the alignment mark, and a reflected light from the alignment mark with respect to illumination light that is positioned at a position substantially conjugate with the alignment mark and illuminates the predetermined virtual surface, and the A light blocking member for blocking a part of the illumination light flux so that the reflected light from the reference mark with respect to the illumination light entering the reflecting member does not substantially enter the image plane of the image detection system. An alignment device characterized by the above. 2. The alignment apparatus according to claim 1, wherein the reflection member is a plane mirror that is arranged substantially parallel to the reference mark and spaced apart by a predetermined distance. 3. The reference mark is formed on a surface of a stage substrate provided on the substrate stage, the surface facing the projection optical system, and the reflection member is provided on a surface of the stage substrate opposite to the projection optical system. The alignment device according to claim 1, wherein the alignment surface is formed.