JPH10261576A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection aligner with an alignment system having the advantages of a TTR(through the reticle) on-axis system and those of an off-axis system. SOLUTION: A microscope system 55A of an alignment system 56A is arranged between a reticle 1 and a wafer 3 at the outside of a projection optical system PL. Light is applied to a search alignment mark 54A on the wafer 3 via, for example, a visual field diaphragm 37, a half prism 17, and an objective lens 18 due to a non-photosensitive illumination beam AL1. Reflection light from the mark forms the image of an alignment mark 53A and the search alignment mark 54A on an image pick-up element 29 via, for example, objective lenses 18 and 22, the reticle 1, a relay lens 23, and a mirror 24, thus detecting the amount of position deviation of both marks by processing the image signal of the image pick-up element 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a mask pattern onto a photosensitive substrate in a photolithography process for manufacturing, for example, a semiconductor device, an imaging device (such as a CCD), a liquid crystal display device, or a thin film magnetic head. More specifically, the present invention relates to a projection exposure apparatus having a function of performing alignment between a mask and a photosensitive substrate.

[0002]

2. Description of the Related Art Conventionally, when manufacturing semiconductor devices and the like,
A projection exposure apparatus such as a stepper for transferring a pattern of a reticle (or a photomask or the like) as a mask onto a wafer (or a glass plate or the like) as a photosensitive substrate via a projection optical system is used. In these projection exposure apparatuses, in order to transfer a reticle pattern accurately on a circuit pattern already formed in each shot area on a wafer and to transfer the reticle pattern, the reticle and each shot area on the wafer are aligned. Is provided. This alignment apparatus includes an alignment system for detecting an amount of displacement between an alignment mark (reticle mark) on a reticle and an alignment mark (wafer mark) on a wafer, and a stage system for positioning the reticle and the wafer. It is composed of

As a conventional alignment system, various systems have been proposed and put into practical use. The TTR (through the reticle) on-axis method is a method of observing a reticle mark and simultaneously observing a wafer mark on a wafer via a reticle and a projection optical system. Since this method is a method for directly detecting the amount of displacement between the reticle mark and the wafer mark, the amount of displacement between both marks can be detected with extremely high accuracy. Note that the TTR-on-axis method is usually simply called the TTR method.

Next, an alignment system of a TTL (through-the-lens) system has been put to practical use. In this method, the reticle is not illuminated, but the position of the wafer mark is measured by irradiating the alignment light onto the wafer via the projection optical system. In this TTL system, even if the imaging characteristic of the projection optical system changes due to a change in the irradiation energy of the exposure light, a change in the atmospheric pressure, and the like, and the imaging position of the reticle image shifts, the alignment light also shifts. It is said that it is hard to be affected by such factors. Further, there are advantages that the distance (baseline amount) between the center of the reticle image (exposure center) and the detection center of the alignment system is small, and the fluctuation of the baseline amount is small.

As another method, there is an off-axis method in which a wafer mark is observed through an alignment microscope arranged outside a projection optical system. In this method, since the wavelength of the alignment light can be selected irrespective of the projection optical system, it is possible to use, for example, an alignment light having a wide wavelength which is hardly influenced by various processes or a photoresist on a wafer. Further, recently, the need to detect a wafer mark having a small step has been increasing due to the introduction of a wafer flattening process. For this purpose, a phase contrast microscope, a differential interference microscope, or the like is suitable. In this regard, if the off-axis method is used, as an alignment microscope,
There is also an advantage that any microscope including a phase contrast microscope and a differential interference microscope can be used.

[0006]

Among the conventional alignment systems as described above, the TTR-on-axis method can directly and accurately detect the amount of displacement between a reticle mark and a wafer mark. However, since the chromatic aberration of the projection optical system is corrected only in a very limited range centering on the exposure wavelength, the occurrence of chromatic aberration is inevitable unless an alignment light in the same wavelength range as the exposure light is used. If the chromatic aberration is corrected using any optical system, there is a disadvantage that the alignment system becomes complicated. On the other hand, when using alignment light in the same wavelength range as the exposure light, the light is easily affected by thin film interference of the photoresist, and the amount of light is reduced so as not to expose the photoresist, or the observation time is shortened. There is a need.

Further, the alignment system of the TTL system
Although there are fewer restrictions than the TR method, the TTL method is the same in that the projection optical system is used. Therefore, when the chromatic aberration correcting optical member is not used, only the alignment light in a limited wavelength range is used. There is a disadvantage that it cannot be used. Further, when an alignment light having a wavelength exceeding the range is used without using such an optical member, an alignment error may occur.

On the other hand, in the off-axis method,
The wavelength of the alignment light can be selected irrespective of the projection optical system, and a phase contrast microscope or the like can be used. However, in the conventional off-axis method, only the wafer mark is observed without observing the reticle mark, and the distance between the center of exposure and the center of detection (baseline amount).
Is the longest, there is a disadvantage that a reticle position shift or the like directly causes an alignment error.

In view of the above, the present invention provides a conventional TT capable of directly detecting the amount of displacement between a reticle and a wafer with high accuracy.
It is an object of the present invention to provide a projection exposure apparatus having an alignment system that can take advantage of both the advantages of the R-on-axis system and the advantages of the off-axis system having a high degree of freedom in wavelength selection for alignment light. .

[0010]

A projection exposure apparatus according to the present invention illuminates a mask (1) with predetermined exposure light and projects an image of a pattern formed on the mask (1) under the exposure light. In a projection exposure apparatus for transferring onto a photosensitive substrate (3) via an optical system (PL), a mask (1) is used without using the projection optical system (PL) and using illumination light having a wavelength different from that of the exposure light. ) Formed on the alignment mark (53).
A) and an alignment system (52A; 56A) for simultaneously detecting the positions of the alignment marks (54A) formed on the photosensitive substrate (3).

According to the present invention, the projection optical system (P
L), the alignment mark (53) on the mask is provided by an alignment system including an external microscope and the like.
A) and the position of the alignment mark (54A) on the photosensitive substrate are directly detected substantially coaxially, and the positional deviation between the mask and the photosensitive substrate can be obtained with high accuracy from the detection result. Further, the observation optical system in the alignment system is an optical system independent of the projection optical system (PL), and it is not always necessary to correct aberration for the exposure light. High, for example, a non-photosensitive broadband luminous flux that is less affected by thin film interference on the photosensitive material can be used. In addition, for example, a differential interference function or a phase difference amplification function can be used to support low-level alignment marks on a photosensitive substrate. Can be easily held. In addition, alignment of only the mask (1) can be performed based on the position of the alignment mark (53A) on the mask.

Further, a plurality of the alignment systems are provided,
For example, the plurality of alignment systems measure the amount of misalignment between the plurality of alignment marks (53A, 53B) on the mask and the corresponding alignment marks (54A, 54B) on the photosensitive substrate. Is also good. As a result, the amount of positional deviation including the deviation of the rotation angle and the expansion and contraction of the photosensitive substrate with respect to the mask is obtained. For example, if the layer is a rough layer that does not require such a high overlay accuracy, the amount of positional deviation is corrected and the positioning is performed. (Eg global
The required overlay accuracy can be obtained simply by performing (alignment).

Further, a storage device (41) for storing an interval (baseline amount) from the detection center of the alignment system to the center of the pattern image of the mask, and the detection result of the alignment system and the storage device. An alignment device (2A, 2B, 4Z, 4XY) for performing alignment between the mask and the photosensitive substrate based on the distance between the mask and the photosensitive substrate;
It is desirable to provide. In this case, so-called fine alignment can be performed by detecting the position of an alignment mark provided in a predetermined shot area on the photosensitive substrate with the alignment system and correcting the detection result with the baseline amount. .

In addition to the alignment system, an alignment mark (57A) formed on the mask (1) via a projection optical system (PL) and using illumination light in the same wavelength range as the exposure light. ) And an exposure wavelength alignment system (24 to 36) for detecting the amount of displacement between the alignment mark (58A) formed on the photosensitive substrate (3). The exposure wavelength alignment system uses a normal TTR
An alignment system of an on-axis system, for example, after detecting the positional shift amount of a pair of marks by the exposure wavelength alignment system, detecting the positional shift amount of the pair of marks via the alignment system of the present invention; Thus, calibration of the baseline amount of the alignment system can be performed.

An exposure system (13A; 33A) for exposing an image of a predetermined alignment mark onto the photosensitive substrate (3) without passing through the projection optical system (PL) and through a part of the alignment system. , 37A). With this exposure system, the alignment marks for the alignment system of the present invention can be exposed on the photosensitive substrate in an accurate positional relationship.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of a projection exposure apparatus according to the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a stepper type projection exposure apparatus of this example. In FIG.
Exposure light IL emitted from an unillustrated illumination optical system including a fly-eye lens and a reticle blind (variable field stop) illuminates the pattern area of the reticle 1. Under the exposure light IL, an image of a pattern formed on the reticle 1 is projected onto a projection optical system PL including lens groups PLa and PLb.
Through a predetermined projection magnification β (β is, for example, 1/4, 1/5
Etc.) onto the wafer 3. A photoresist is applied to the surface of the wafer 3. As the exposure light IL,
In addition to an emission line such as an i-line of a mercury lamp, an excimer laser beam such as a KrF excimer laser or an ArF excimer laser can be used, and the projection optical system PL uses an exposure light IL having an extremely narrow wavelength range.
Are corrected with high accuracy. In the following, the Z axis is taken parallel to the optical axis AX of the projection optical system PL, the X axis is taken parallel to the plane of FIG. 1 in a plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the plane of FIG. I do.

First, the reticle 1 is a reticle stage 2A.
The reticle stage 2A is mounted on the reticle base 2B so as to be finely movable in the X direction, the Y direction, and the rotation direction. The position of the reticle stage 2A is the movable mirror 6.
m and the laser interferometer 6, and the measurement result is supplied to a main control system 41 that supervises and controls the operation of the entire apparatus, and the main control system 41 positions the reticle stage 2 A via the reticle stage drive system 7. .

On the other hand, the wafer 3 is held on a Z tilt stage 4Z via a wafer holder (not shown). The Z tilt stage 4Z is moved in the height direction (Z
), Tilt angle correction, and rotation within a predetermined range, and the Z tilt stage 4Z is mounted on an XY stage 4XY that is movable in the X and Y directions. The position of the Z tilt stage 4Z (wafer 3) is measured by the movable mirror 8m and the laser interferometer 8, and the measured value is supplied to the main control system 41. 9 to control the positioning operation of the XY stage 4XY. A wafer stage is composed of the Z tilt stage 4Z, the XY stage 4XY, and the like.

Although not shown, the oblique incidence type focal point including a light transmitting optical system for detecting the position (focus position) of the wafer 3 in the Z direction (focus position) and a light receiving optical system is provided on a side surface of the projection optical system PL. A position detection system is provided. Information on the focus position obtained by the focus position detection system is supplied to the main control system 41, and the main control system 41 controls the height of the Z tilt stage 4Z (wafer 3) by an autofocus method based on the information. At the time of exposure, after exposing one shot area on the wafer 3, the XY stage 4
The pattern image of the reticle 1 is transferred to each shot area on the wafer 3 by a step-and-repeat method in which the next shot area is moved to the exposure field of the projection optical system PL by XY stepping and exposure is repeated.

Next, the alignment system of this embodiment will be described in detail. First, on the Z tilt stage 4Z, a reference mark member 5 on which a plurality of reference marks FM for measuring a baseline amount of an alignment system to be described later is fixed. The reference mark member 5 has a reference mark formed on a chromium film on the surface of low expansion glass such as quartz glass. Then, around the pattern surface of the reticle 1, four alignment marks (two alignment marks 53A and 53B are shown in FIG. 1) for aligning the reticle 1 with the wafer 3 are formed. I have. Further, the four search alignment marks 54A to 54D are arranged on the wafer 3 in the same arrangement as those marks.
(See FIG. 4).

FIG. 4 shows an example of the arrangement of search alignment marks 54A to 54D formed on the wafer 3.
In FIG. 4, coordinates which are parallel to the X axis and the Y axis and have the origin at the optical axis AX of the projection optical system PL are defined as an x axis and a y axis, respectively. At this time, a pair of search alignment marks 54A and 54B are formed at positions substantially symmetric about the origin on the wafer 3 with the center of the wafer 3 substantially coinciding with the optical axis AX. The search alignment marks 54C, 5 are located at positions substantially on the y-axis rotated by 90 °.
4D is formed. Search alignment mark 54
Each of A to 54D is a two-dimensional mark formed of, for example, a cross mark. Search alignment marks 54A-54
Rough positioning (search alignment) is performed based on D and the corresponding alignment mark on reticle 1. Further, in each shot area SA on the wafer 3, an X-axis wafer mark WMX and a Y-axis wafer mark WMY for performing more precise alignment (fine alignment) are also formed.

Returning to FIG. 1, a four-axis alignment system is arranged around the projection optical system PL of this embodiment. FIG. 1 shows only those alignment systems 52A and 52B. The alignment systems 52A, 52B, etc. of this example can be called a TTR (through-the-reticle) off-axis system, but are hereinafter simply referred to as "external alignment systems". The external alignment system may have only one axis in the minimum configuration, but in this example, four axes are arranged in order to increase measurement efficiency and simultaneously measure expansion and contraction of the wafer. In FIG. 1, the center of the reticle 1 and the center of the wafer 3 are respectively positioned near the optical axis AX, and the alignment marks 53A and 53B of the reticle 1 are provided.
Search alignment mark 5 on wafer 3 corresponding to
4A, 54B, etc. are arranged substantially coaxially. In this state, one of the external alignment systems 52A is provided with an alignment mark 53A on the reticle 1.
A microscope 51A arranged between the wafer and a search alignment mark 54A on the wafer 3;
A, and the other external alignment system 52B is also provided with a microscope 51B disposed between the alignment mark 53B and the search alignment mark 54B, and a detection system (not shown) above the alignment mark 53B. (Shown). The other two-axis external alignment systems have the same configuration.

FIG. 2 shows the arrangement of the microscopes of these alignment systems. In FIG. 2, the microscopes 51A and 51B are arranged on the x-axis symmetrical with respect to the origin (optical axis AX). Microscopes 51C and 51D of another two-axis alignment system are arranged on the rotated y-axis. The laser interferometer 8 on the wafer stage side in FIG. 1 is actually a three-axis laser beam that irradiates a corresponding laser beam with one laser beam substantially along the x-axis and two laser beams along the Y-axis. Because it is a laser interferometer, the microscope 51A of FIG.
To 51D are arranged substantially along the optical path of the laser beam from the laser interferometer 8.

However, those external alignment systems,
The microscopes 51A to 51D are then moved to x as shown in FIG.
It may be arranged between the axis and the y axis. Returning to FIG. 1, the configuration of the alignment system 52A will be typically described in detail. In the detection system above the alignment mark 53A of the reticle 1, the wafer 3
Non-photosensitive broadband illumination light AL1 is guided to the upper photoresist. The illumination light AL1 is illumination light selected from a light beam emitted from a white light source such as a halogen lamp (not shown) arranged outside a chamber in which the projection exposure apparatus of the present example is installed. Further, for example, when exposing the image of the alignment mark 53A on the wafer 3, the illumination light AL1 is configured to be switched to the photosensitive light for exposing the photoresist. In order to increase the sensitivity at this time, a part of the exposure light IL may be branched and used as the photosensitive light.

The illumination light AL emitted from the optical fiber 32
1 enters the half prism 27 via the condenser lens 31 and the mirror 30, and the illumination light AL1 reflected by the half prism 27 is reflected by the mirror 24 and the first relay lens 23.
Illuminates the alignment mark 53A on the reticle 1 via the. The illumination light scattered and diffracted by the alignment mark 53A passes through the first relay lens 23, the mirror 24, the half prism 27, and the second relay lens 28, and is transferred onto the two-dimensional imaging device 29 such as a CCD or the like.
An image of 3A is formed. On the other hand, alignment mark 53A
Illumination light AL1 that has passed through the surroundings illuminates the search alignment mark 54A on the wafer 3 via the second objective lens 22 and the first objective lens 18 constituting the microscope 51A, and is scattered and diffracted by the search alignment mark 54A. The illumination light AL1 forms an image of the search alignment mark 54A on the pattern surface of the reticle 1 via the microscope 51A, and this image is transmitted through the first relay lens 23, the mirror 24, the half prism 27, and the second relay lens 28. It is relayed on the image sensor 29. The relay lenses 23 and 28 are corrected for various aberrations with respect to the illumination light AL1 that is not photosensitive to the photoresist.

In this case, it is desirable that the magnification of the relay lenses 23 and 28 be variable as a zoom lens. Then, for example, by setting the magnification to be low at the time of the search alignment and by setting the magnification to be high at the time of the fine alignment, necessary overlay accuracy can be obtained. An image of the alignment mark 53A and an image of the search alignment mark 54A are formed on the image sensor 29 so as to overlap with each other.
9 is supplied to the alignment signal processing system 40, the alignment signal processing system 40 determines the amount of positional deviation between the two mark images from the image signal, and supplies the amount of positional deviation to the main control system 41. Further, the alignment signal processing system 40 can also detect the amount of defocus from the contrast or the like of the mark images.

As described above, with respect to the microscope 51A, the surface of the wafer 3 and the pattern surface of the reticle 1 are set to be conjugate under the non-photosensitive illumination light AL1. Microscope 51
Objectives 18, 2 arranged along the optical axis AX1 of A
Reference numeral 2 denotes a lens system in which various aberrations including chromatic aberration have been corrected in a wide band from a light flux that is photosensitive to a non-photosensitive light to the photoresist, and a working distance between the wafer 3 and the reticle 1 of the microscope 51A ( The working distance is set longer than the working distance of the projection optical system PL. Since the observation field of view of the microscope 51A may be considerably narrower than the field of view of the projection optical system PL, the above optical characteristics can be easily achieved. Due to such a long working distance, even when the reticle 1 and the wafer 3 are moved, a part of the stage or the wafer does not come into contact with the microscope 51A. The magnification of the microscope 51A from the wafer 3 to the reticle 1 (here, determined by the ratio of the focal lengths of the objective lenses 18 and 22) is the projection magnification of the projection optical system PL from the wafer 3 to the reticle 1 (1/1). β), and the objective lenses 18 and 22 are configured to be finely movable in the Z direction for focusing. Thereby, the positional deviation amount between the two marks becomes equal to the positional deviation amount detected via the projection optical system PL, so that the alignment is facilitated. However, it is not always necessary to set the magnification of the microscope 51A equal to the projection magnification of the projection optical system PL. Similarly, the other microscope 51B
Is also composed of objective lenses 18 and 22.

Next, the external alignment system 52 of the present embodiment.
An example of the alignment operation when A or the like is used will be described. First, the XY stage 4XY of FIG. 1 is driven to move a predetermined reference mark in the reference mark FM of the reference mark member 5 into the field of view of the microscope 51A of the alignment system 52A, and this image is observed by the image sensor 29. Thereby, the magnification of the microscope 51A and the relay lenses 23 and 28 is set to a predetermined target value, and focusing is performed based on the contrast of the image and the like. Next, for example, another reference mark in the reference mark FM and the projection optical system PL of the mark on the reticle 1 corresponding thereto.
In a state where the image is combined with the image via the microscope, the predetermined reference mark in the reference mark FM and the alignment mark 53A on the reticle 1 are observed by the image sensor 29 via the microscope 51A.
By processing the image signal by the alignment signal processing system 40, a baseline amount which is an interval between the detection center of the alignment system 52A (the center of the alignment mark 53A in this case) and the center of the pattern image of the reticle 1 is obtained. This baseline amount is stored in the storage unit in the main control system 41. Similarly, magnification adjustment of the other alignment system 52B and the like and measurement of the baseline amount are also performed.

Thereafter, the wafer 3 is moved to the Z tilt stage 4Z.
After being roughly positioned and mounted on the outer shape reference, the alignment mark 53A on the reticle 1 and the search alignment mark 54A on the wafer 3 are observed by an external alignment system 52A, and the alignment signal processing system 40 Detect the displacement amount. Similarly, with respect to the other search alignment marks 54B to 54D shown in FIG. 4, the amount of misalignment with the alignment mark 53B or the like is detected via the corresponding external alignment system 52B or the like. By processing the displacement amount by, for example, the least square method or the like, the displacement amount of the wafer 3 with respect to the pattern of the reticle 1 in the X and Y directions, the rotation error,
And the expansion / contraction rate of the wafer 3 (wafer scaling) is calculated, and the positional shift amount is corrected via the XY stage 4XY.
The rotation error is corrected via the reticle stage 2A.

For example, when exposure is performed on a rough layer that does not require very high overlay accuracy, exposure can be performed as it is based on the result of the search alignment. That is, global alignment is applied, and the array coordinates of each shot area arranged along the sample coordinate system on the wafer 3 are converted to array coordinates on the wafer stage coordinate system based on the result of the search alignment. Each shot area is positioned based on the converted array coordinates, and the pattern image of the reticle 1 is exposed through the projection optical system PL.

When exposing a layer requiring higher overlay accuracy, the coordinates of a wafer mark in a predetermined shot area (sample shot) selected from the wafer 3 via the alignment system 52A are detected. Then, fine alignment is performed by, for example, an enhanced global alignment (EGA) method. When detecting the X coordinate of the wafer mark WMX in the shot area SA in FIG. 4, the XY stage 4XY in FIG. 1 is driven to move the wafer mark WMX into the observation field of the alignment system 52A, and to move the wafer mark WMX with respect to the alignment mark 53A. The amount of displacement may be detected, and the amount of displacement may be added to the coordinates measured by the laser interferometer 8. Then, the coordinates of these sample shots are statistically processed to calculate the array coordinates of each shot area, and the base line amount stored in the storage unit of the main control system 41 is added to the calculation result. The XY stage 4XY is driven and positioned based on the arranged coordinates, and the pattern image of the reticle 1 is exposed through the projection optical system PL.

As a method of forming the search alignment mark 54A on the wafer 3, a reticle on which the alignment mark 53A is formed in the same manner as the reticle 1 at the time of exposing the previous layer is used, and the detection system of the alignment system 52A is used. The alignment mark 53A may be irradiated with photosensitive illumination light instead of the non-photosensitive illumination light AL1, and the image of the alignment mark 53A may be exposed on the wafer 3. In this case, the objective lenses 18 and 2 of the microscope 51A are used.
The reticle 1 and the wafer 3 are conjugated to the photosensitive illumination light by moving 2. Similarly, other search alignment marks 54B to 54B
54D can also be formed.

As described above, according to this embodiment, since the external alignment system 52A and the like are used, the photoresist is not exposed, and the illumination light of a wide band which is less affected by the thin film interference of the photoresist is used. In addition, the amount of displacement between the alignment mark on the reticle 1 and the search alignment mark or wafer mark on the wafer 3 can be directly detected with high accuracy. Therefore, high overlay accuracy can be obtained.
Further, since it is easy to make the microscope 51A between the reticle 1 and the wafer 3 a differential interference microscope, a phase contrast microscope, or the like, the detection target mark on the wafer 3 is a low step mark due to the flattening process. In such a case, the mark can be accurately detected.

Next, a second embodiment of the present invention will be described with reference to FIGS. In this example, the illumination system and the like of the alignment system of the first embodiment are changed, and
An R-on-axis type alignment system is added. In FIG. 5, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 5 shows a main part of the projection exposure apparatus of the present embodiment. In FIG. 5, an external alignment system 56A is arranged on a side surface of the projection optical system PL. Also in this example, the same alignment system as alignment system 56A is arranged on four axes around projection optical system PL. The alignment system 56A of this example also includes a microscope system 55A disposed between the alignment mark 53A of the reticle 1 and the search alignment mark 54A on the wafer 3.
And a detection system above the alignment mark 53A.

First, the broadband illumination light emitted from the white light source 10 such as a halogen lamp outside the chamber in which the projection exposure apparatus of the present embodiment is installed has unnecessary infrared rays removed through the heat absorption filter 11. Thereafter, the light enters the optical fiber 14 via the condenser lens 12 and the wavelength selection filter 13. In the wavelength selection filter 13, the illumination light AL1 that is non-photosensitive to the photoresist on the wafer 3 is selected. For example, when exposing an alignment mark image on the wafer 3, a wavelength selection filter 13 </ b> A for selecting photosensitive illumination light AL <b> 2 on a photoresist is provided instead of the wavelength selection filter 13. Then, the illumination light AL1 via the optical fiber 14 is supplied to the microscope system 55A. Since the white light source 10 is outside the chamber, the adverse thermal effect on the projection exposure apparatus is eliminated. In addition,
When exposing the alignment mark image on the wafer 3, the photosensitive illumination light AL2 is supplied via the optical fiber 14, but if the photosensitive power is not sufficient, or if the exposure light is excimer laser light. In such a case, a light beam obtained by branching a part of the exposure light may be used.

In the microscope system 55A, the optical fiber 14
Illumination light AL1 emitted from the collimator lens 15
Is incident on the field stop 37 through. The arrangement surface of the field stop 37 and the surface of the wafer 3 are conjugate, and the field stop 37 defines an illumination area on the wafer 3. Field stop 37
Can be replaced with a reticle 37A on which an alignment mark pattern is formed.
By exchanging the illumination light AL1 with the photosensitive illumination light AL2, the alignment mark image can be exposed on the wafer 3. The illumination light AL1 that has passed through the field stop 37 enters the first half prism 17 via the relay lens 16 whose aberration has been corrected in a wide band, and the illumination light AL1 reflected downward by the half prism 17 has an aberration in a wide band. The search alignment mark 54A on the wafer 3 is illuminated via the corrected first objective lens 18. The first objective lens 18 and a second objective lens 22, which will be described later, are configured so that the position in the Z direction can be controlled by a main control system 41 via driving units 38 and 39, respectively.

Illumination light scattered and diffracted by the search alignment mark 54A (referred to as BL1) enters the second half prism 19 via the first objective lens 18 and the half prism 17, and is reflected by the half prism 19. The illumination light BL <b> 1 forms an image of the search alignment mark 54 </ b> A on the two-dimensional imaging device 21 such as a CCD via the imaging lens 20 which has been corrected for aberrations in a wide band. An image signal from the image sensor 21 is sent to an alignment signal processing system 40, which processes the image signal to detect a defocus from, for example, the contrast of the mark image, and to detect a defocus from a predetermined reference position. The amount of misregistration of the mark image is detected, and the detection result is transmitted to the main control system 41.
To supply. When the mark image is defocused, the main control system 41 performs focusing through the drive unit 38.

In addition, a normal off-axis alignment can be performed based on the mark image detected via the image sensor 21. In this case, it is desirable that the projection magnification determined by the ratio of the focal lengths of the first objective lens 18 and the imaging lens 20 is variable,
By setting the magnification at a low magnification when performing search alignment and at a high magnification when performing fine alignment via the interface, it is possible to balance work efficiency and measurement accuracy.

On the other hand, the illumination light BL1 transmitted through the half prism 19 is converted to the first objective lens 2 whose aberration has been corrected in a wide band.
An image of the search alignment mark 54A is formed near the alignment mark 53A on the pattern surface of the reticle 1 through the reticle 1, and the alignment mark 53A is illuminated. The illumination light BL1 transmitted through the reticle 1 passes through the first relay lens 23, the mirror 24, the half prism 27, and the second relay lens 28 onto the image sensor 29 on the search alignment mark 54A and the alignment mark 53.
A superimposed image of A is formed. The image signal from the image sensor 29 is sent to the alignment signal processing system 40, where the amount of displacement between the two marks is detected, and the detection result is sent to the main control system 41.
Supplied to The alignment signal processing system 40 detects a defocus from the contrast of the image of the search alignment mark 54A and supplies the detection result to the main control system 41. Perform focusing.

Also in this example, the magnification of the objective lenses 18 and 22 is set equal to the magnification (1 / β) from the wafer to the reticle of the projection optical system PL (however, it may be different), and the relay lens 23 is used. , 28 can be switched between high and low. As described above, in this example, the illumination light AL1 introduced from the half prism 17 illuminates the wafer 3 with incident light and allows the reticle 1 to be transmitted and illuminated. Further, in this example, a wafer mark 58A is formed in a predetermined shot area on the wafer 3, and the reticle mark is placed at a position on the reticle 1 conjugate with the wafer mark 58A in a state where the center of the shot area matches the exposure center. 57A are formed. These wafer mark 58A and reticle mark 57A are marks for alignment system 56A. Similarly, a pair of wafer marks and reticle marks (not shown) correspond to the other three-axis alignment systems.

An illumination system similar to that of the first embodiment is also provided above the reticle 1, so that any illumination system can be selected. That is, the broadband illumination light emitted from the white light source 36 passes through the heat absorption filter 35 and then enters the optical fiber 32 via the condenser lens 34 and the wavelength selection filter 33 or 33A. In the wavelength selection filter 33, the non-photosensitive illumination light AL1 is selected, and in the wavelength selection filter 33A, the illumination light IL2 having the same wavelength as the exposure light is selected, and the illumination light via the optical fiber 32 (the illumination light AL1 in FIG. ) Is supplied to the detection system. The illumination light IL2 having the exposure wavelength is generated by the TTR ·
It is used for illuminating light of an on-axis type alignment system or for exposing an alignment mark image.

The illumination light AL1 enters the mirror 24 via the condenser lens 31, the mirror 30, and the half prism 27,
The illumination light AL1 reflected by the mirror 24 illuminates the alignment mark 53A on the reticle 1 via the first relay lens 23 as in the first embodiment, and is scattered and diffracted by the alignment mark 53A. Hikari AL1 is the first
Relay lens 23, mirror 24, half prism 27,
An image of the alignment mark 53A is formed on the image sensor 29 via the second relay lens. The illumination light AL1 passing around the alignment mark 53A illuminates the search alignment mark 54A on the wafer 3 via the objective lenses 22 and 18, and the illumination light scattered and diffracted by the search alignment mark 54A is imaged. An image of the search alignment mark 54A is formed on each of the elements 21 and 29. In this case, the images of the alignment mark 53A and the search alignment mark 54A are formed on the image sensor 29 so as to be superimposed, and the image signal of the image sensor 29 is processed by the alignment signal processing system 40 to calculate the amount of displacement between the two marks. Then, the positional deviation amount is supplied to the main control system 41. Also in this case, focusing of the objective lenses 18 and 22 is performed.

Further, in this embodiment, the mirror 24 on the reticle 1
Is configured to be retractable with respect to the optical path of the illumination light. When the illumination light IL2 having the exposure wavelength is supplied to the detection system via the optical fiber 32, the mirror 24 is retracted. In this case, the illumination light IL2 having the exposure wavelength reflected by the half prism 27 forms the reticle mark 57A on the pattern surface of the reticle 1 via the first relay lens 25 disposed along the upper surface of the reticle 1 and the mirror 26. Light up. The illumination light I scattered and diffracted by the reticle mark 57A
L2 forms an image of the reticle mark 57A on the image sensor 29 via the mirror 26, the first relay lens 25, the half prism 27, and the second relay lens 28.

On the other hand, the illumination light IL2 of the exposure wavelength transmitted around the reticle mark 57A is applied to the wafer mark 58A on the wafer 3 via the projection optical system PL, and is scattered and diffracted by the wafer mark 58A. IL2 is a projection optical system PL, a reticle 1, a mirror 26, a first relay lens 25, a half prism 27, and a second relay lens 2.
An image of the wafer mark 58 </ b> A is formed on the image sensor 29 through the interface 8. Therefore, the images of the reticle mark 57A and the wafer mark 58A are formed on the image sensor 29 in an overlapping manner.
The alignment signal processing system 40 processes the image signal of the image sensor 29 to detect the amount of displacement between the two marks, and supplies the detection result to the main control system 41. In this case, the detection system including the mirror 26, the first relay lens 25, the half prism 27, the second relay lens 28, and the imaging device 29 is a TTR-on-axis type alignment system using illumination light of an exposure wavelength. Make up.

Similarly, in the TTR-on-axis type alignment system in another external alignment system, the positional deviation amounts of a pair of reticle marks and wafer marks are respectively detected, and the detection results are sent to the main control system 41. Supplied.
The main control system 41 performs high-accuracy overlay by positioning the wafer 3 so that the four positional shift amounts are distributed symmetrically, for example, and then exposing the pattern image of the reticle 1. Further, the microscope system 55 is connected via the TTR-on-axis type alignment system.
A calibration can also be performed. Other configurations of the reference mark member 5, the wafer stage, and the like are the same as those of the first embodiment (FIG. 1).

Next, an example of an exposure sequence of the projection exposure apparatus of this embodiment will be briefly described with reference to FIG. FIG.
6 is a flowchart showing a rough exposure sequence. As shown in FIG. 6, when exposure to the immediately preceding wafer is completed, the wafer is replaced in step 101. In this case, to increase the throughput of the exposure process,
In step 102 in parallel with the wafer exchange, calibration of the baseline amount of the external alignment system 56A and the like is performed as necessary. At the time of calibration, the first reference mark on the reference mark member 5 is moved by driving the XY stage 4XY in FIG.
Is set in the observation field of view of the microscope system 55A, for example, the white light source 10 is turned on, and the image of the reference mark is observed by the imaging devices 21 and 29 under the non-photosensitive illumination light AL1. Magnification adjustment and focusing are performed.

Thereafter, the white light source 10 is turned off, the other white light source 36 is turned on, the mirror 24 is retracted, and the illumination light IL2 having the exposure wavelength is selected. And the reference mark member 5
The upper second reference mark is moved to a position substantially conjugate with the alignment mark 57A on the reticle 1, and the TTR-on-
Axis type alignment system (relay lens 25, 2
8) to detect the positional deviation of both marks, and adjust the position of the wafer stage so that the positional deviation becomes substantially zero. In that state, the illumination light is changed to non-photosensitive illumination light AL.
After returning the mirror 24 to the optical path in place of the reference mark 1, the wafer stage is moved by the initial value of the baseline amount, and the second reference mark and the alignment mark on the reference mark member 5 are transferred via the microscope system 55A. When the amount of misalignment with 53A is detected, the result of adding the amount of misalignment to the initial value of the amount of baseline becomes a new amount of baseline, and the corrected amount of baseline is stored in the storage unit of the main control system 41. It is memorized. In this case, the movement of the reticle 1 is directly reflected on the baseline amount, so that the baseline amount can be obtained more accurately. It is desirable that the operation of measuring the baseline amount be automated. In addition, measurement and correction of the projection magnification of the projection optical system PL are performed using the reference mark member 5.

The correction of the focal position of the projection optical system PL is always performed by moving the reference mark member 5 or the wafer 3 itself up and down based on the measurement value of the focal position detecting system. In this case, the focus position may be shifted. In this case, focusing is performed by the autofocus method by finely moving the objective lenses 18 and 22 in the Z direction via the driving units 38 and 39 based on the contrast of the detected mark image and the like. At this time, the microscope system 55A
Is corrected at the same time so that the magnification does not change.

Next, in step 103, alignment of the wafer 3 is performed. At the time when the wafer 3 is mounted on the wafer holder on the Z tilt stage 4Z, prealignment is performed on the basis of an outer shape such as a notch or an orientation flat. And step 103
First, the amount of misalignment between the search alignment marks 54A to 54D of the wafer 3 in FIG. 4 and the corresponding alignment marks 53A on the reticle 1 is determined by the white light source 1 in FIG.
The microscope system 55 under the non-photosensitive illumination light AL1 from 0
A is detected via A or the like. Then, as in the first embodiment, in a layer where the overlay accuracy may be relatively low, each shot area is positioned based on the result of the search alignment, and the pattern image of the reticle 1 is exposed. In a layer having high overlay accuracy, exposure is performed after detecting the position of a wafer mark in a predetermined shot area via the microscope system 55A and performing fine alignment using, for example, an EGA method. Thereafter, in step 105, the above-described alignment and exposure are repeated until the unexposed wafer runs out.

Further, as described above, the search alignment marks 54A to 54D on the wafer 3 are formed by disposing the reticle 37A instead of the field stop 37 in FIG. It can be easily formed by irradiating the illumination light AL2 or selecting the illumination light IL2 having the exposure wavelength and illuminating a mark similar to the alignment mark 53A. At this time, by forming those marks at the same time via the four-axis alignment system 56A, etc., the marks of the target arrangement can be formed in a very short time and with high accuracy.

As described above, the alignment system 56A of the present embodiment is used.
Is an off-axis method independent of the projection optical system PL.
Moreover, since the mark on the reticle 1 and the mark on the wafer 3 are directly observed coaxially, the projection optical system P
Without being restricted by L, a broadband light beam that is non-photosensitive and less affected by thin film interference can be used. Therefore, the displacement between the two marks can be directly detected with high accuracy. Further, by using various microscopes such as a phase contrast microscope and a differential interference microscope as the microscope system 55A, it is possible to easily cope with a low step mark. Furthermore, a 4-axis alignment system 56A
And so on, particularly, search alignment can be performed in a short time.

It should be noted that, in addition to the stepper type projection exposure apparatus, the present invention applies the reticle and the wafer to the projection optical system while projecting a part of the reticle pattern onto the wafer via the projection optical system. The present invention can be similarly applied to a scanning exposure type projection exposure apparatus such as a step-and-scan method in which a pattern image of a reticle is sequentially transferred to each shot area of a wafer by synchronous scanning. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0053]

According to the projection exposure apparatus of the present invention, an alignment mark formed on a mask and formed on a photosensitive substrate without using a projection optical system and using illumination light having a wavelength different from the exposure light. The conventional TT system has an alignment system for simultaneously detecting the position of the alignment mark thus set.
As in the case of the R-on-axis method, the amount of displacement between two marks can be directly detected with high accuracy. Furthermore, since an alignment system separate from the projection optical system is used, there is an advantage that light beams other than the exposure wavelength can be used freely as in the conventional off-axis system. Therefore, the position of the alignment mark on the photosensitive substrate during various processes can be detected with high accuracy, and alignment can be performed with high accuracy.

Further, a storage device for storing an interval from the detection center of the alignment system to the center of the pattern image of the mask, and a mask and a photosensitive substrate based on the detection result of the alignment system and the interval stored in the storage device. And a positioning device for performing positioning with
For example, fine alignment can be performed with high accuracy.

In addition to the alignment system, an alignment mark formed on the mask and an alignment mark formed on the photosensitive substrate are projected through a projection optical system and using illumination light having the same wavelength range as the exposure light. In the case where an exposure wavelength alignment system for detecting the amount of displacement from the use mark is provided, calibration of the baseline amount of the alignment system of the present invention can be easily performed using the exposure wavelength alignment system.

Further, when an exposure system for exposing an image of a predetermined alignment mark onto a photosensitive substrate through a part of the alignment system without passing through the projection optical system is further provided, the alignment system according to the present invention is provided. There is an advantage that a mark to be detected in the system can be easily formed in an accurate positional relationship.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a main part of a first embodiment of a projection exposure apparatus according to the present invention.

FIG. 2 is a plan view showing an arrangement of a microscope of an external alignment system used in the projection exposure apparatus of FIG.

FIG. 3 is a plan view showing another example of the arrangement of the microscope of the alignment system in FIG. 2;

FIG. 4 is a plan view showing an arrangement of search alignment marks and the like on a wafer to be exposed in the embodiment.

FIG. 5 is a schematic configuration diagram showing an external alignment system used in a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating an example of an exposure sequence according to the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 reticle PL projection optical system 3 wafer 4XY XY stage 5 reference mark member 10, 36 white light source 21, 29 image sensor 40 alignment signal processing system 51A, 51B microscope 52A external alignment system 53A, 53B alignment mark 54A to 54D search alignment Mark 55A Microscope system 56A External alignment system

Claims (4)

[Claims] 1. A projection exposure apparatus which illuminates a mask with predetermined exposure light and transfers an image of a pattern formed on the mask under the exposure light onto a photosensitive substrate via a projection optical system. Detecting the positions of the alignment mark formed on the mask and the alignment mark formed on the photosensitive substrate simultaneously without using a projection optical system and using illumination light having a wavelength different from the exposure light. A projection exposure apparatus having an alignment system. 2. The projection exposure apparatus according to claim 1, wherein a storage device stores an interval from a detection center of the alignment system to a center of a pattern image of the mask, and the detection result of the alignment system and the storage. A projection exposure apparatus, comprising: a positioning device that performs positioning between the mask and the photosensitive substrate based on an interval stored in the device. 3. The projection exposure apparatus according to claim 1, wherein, in addition to the alignment system, via the projection optical system,
And an exposure wavelength alignment system that detects an amount of displacement between an alignment mark formed on the mask and an alignment mark formed on the photosensitive substrate using illumination light having the same wavelength range as the exposure light. A projection exposure apparatus. 4. The projection exposure apparatus according to claim 1, wherein the image of the predetermined alignment mark is exposed through a part of the alignment system without passing through the projection optical system. A projection exposure apparatus further comprising an exposure system for exposing a substrate.