JPH09312251A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alignment system which can detect position deviation with high accuracy and with high speed. SOLUTION: A mark provided on a reticle and a mark provided on reference member are comprised of a V shape mark and an inverted V shape mark respectively and position deviation between the both marks is detected by an image pickup means. A relative position change (ΔLx) of two images 41a and 41b, a position deviation (ΔX) of the X direction and a position deviation (ΔY) of the Y direction are measured according to ΔLy by detecting operation at once. Detecting sensitivities of position deviations of the X direction and the Y direction can be changed by changing combination of opening angles of two V shape marks 36 and 40 and detecting error in the detecting directions set with high sensitivity can be compressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used for exposing a pattern of a semiconductor element, a liquid crystal display element or the like on a photosensitive substrate, a positioning method in the projection exposure apparatus, and an optical system of a projection optical system. The present invention relates to a characteristic measuring method.

[0002]

2. Description of the Related Art In a photolithography process, which is one of the manufacturing processes for semiconductor devices and liquid crystal display devices, a pattern formed on a photomask or reticle (hereinafter referred to as "reticle") is photoresist by using a projection exposure apparatus. Projection exposure is performed on a photosensitive substrate such as a wafer or a glass plate coated with a photosensitive agent such as. At this time, it is necessary to accurately align the reticle and the photosensitive substrate for exposure. Alignment is performed by measuring the position of the reticle with respect to the moving coordinate system of the substrate stage on which the photosensitive substrate is placed and moving, measuring the position of the photosensitive substrate with respect to the moving coordinate system, measuring the relative position of the reticle and the photosensitive substrate, etc. Is done. In addition, by projecting an image of a test reticle provided with a plurality of marks with a projection optical system and measuring the position of the projected mark image, optical characteristics such as distortion of the projection optical system are measured. There is.

[0003]

For example, in the reticle alignment for aligning the reticle with respect to the substrate stage moving coordinate system, the amount of positional deviation between the alignment mark on the reticle and the reference mark provided on the substrate stage is projected. It is measured by an alignment sensor via an optical system. Conventionally, as alignment marks and reference marks on a reticle, a mark for measuring displacement in the X direction and a mark for measuring displacement in the Y direction are individually provided. In order to measure the positional deviation in the two directions, the position detection operation needs to be performed twice. Further, in order to detect the rotation of the reticle and the shift amounts in the X and Y directions, it is necessary to detect the positional deviation amount at two or more measurement points, and (the number of two or more measurement points) × 2 times. Position detection operation is required. Therefore, much time is required for reticle preparation (alignment) before exposure. The present invention has been made in view of such problems of the conventional art, and an object of the present invention is to provide an alignment system capable of detecting a positional deviation with high accuracy and high speed.

[0004]

In the present invention, the mark provided on the reticle and the mark provided on the reference member are made of a light-transmissive V material.
The above-mentioned object is achieved by comprising a V-shaped mark and a light-transmissive inverted V-shaped mark, and detecting the positional deviation of both marks by the imaging means. That is, according to the present invention, an illumination system that illuminates a reticle on which a pattern to be transferred is formed, a projection optical system that forms a pattern image of the reticle on a photosensitive substrate, and a reference member having a reference mark are provided. In a projection exposure apparatus that includes a substrate stage that is placed and movable in two dimensions, a reference mark provided on a reference member is a V-shaped light transmissive mark, and a V-shaped light provided on a reticle is used. It is characterized in that a superimposed image of the transmissive alignment mark and the V-shaped reference mark is captured by the image capturing means.

The V-shaped mark provided on the reticle and the V-shaped reference mark provided on the reference member are superimposed in a V-shaped and inverted V-shaped relationship via the projection optical system, and the image pickup means is V-shaped. An optical image of two quadrangles formed by overlapping the hypotenuses of the V-shaped figure and the inverted V-shaped figure is captured. Taking the case where the symmetry axis of the V-shaped figure is set parallel to the Y-axis as an example, the amount of positional deviation of the two marks in the Y-direction can be obtained from the distance of the two optical images in the X-direction. The amount of positional deviation in the X direction can be obtained from the distance between the two light images in the Y direction. Therefore, it is possible to detect the positional deviation in the two directions of the X direction and the Y direction by a single process, and it is possible to significantly reduce the time required for alignment. The positional deviation detection method using these two V-shaped marks can be used for reticle alignment for aligning the reticle with the moving coordinate system of the substrate stage in the projection exposure apparatus.

Further, a test reticle in which a plurality of marks are formed in a predetermined array is used, images of the plurality of marks are projected on a substrate stage by a projection optical system, and a reference mark provided on a reference member on the substrate stage. By measuring the misalignment with the design position of the mark image by capturing the overlay image with the optical image, the optical characteristics such as distortion of the projection optical system are measured. The V-shaped mark can be used as the mark to be provided.

The opening angle of the V-shaped mark can be set in various ways, and the opening angle of the V-shaped alignment mark provided on the reticle and the opening angle of the V-shaped reference mark provided on the reference member are the same. It may or may not be. Then, by changing the combination of the opening angles of the two V-shaped marks, the positional deviation detection sensitivity in the X direction and the Y direction can be changed, and the detection error can be compressed in the detection direction set to high sensitivity. . Therefore, when the direction in which the accuracy of alignment is severely required in the pattern formation of the liquid crystal element is known in advance, a V-shaped mark whose opening angle is set as the reticle alignment mark is set so that the detection sensitivity in that direction is high. It is convenient to have it. Alternatively, a plurality of V-shaped marks having different opening angles may be provided on the reference member or the reticle, and the V-shaped mark to be used may be selected according to the direction in which highly accurate detection is required.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic view of an exposure apparatus according to the present invention. The exposure apparatus includes an exposure illumination light source 10, a reticle 12 on which a pattern 13 to be exposed is formed on a photosensitive substrate, a projection optical system 15, a substrate stage 16 on which a photosensitive substrate is placed and which can be moved in a two-dimensional direction. Prepare The substrate stage 16 is moved by a driving unit 17 along a substrate stage movement coordinate system (XY coordinate system). Substrate stage 16
A movable mirror 18 is fixed on the substrate, and the two-dimensional position of the substrate stage 16 in the substrate stage moving coordinate system is detected by measuring the distance from the movable mirror 18 with the laser interferometer 19. The substrate stage drive system 20 operates the drive means 17 while monitoring the output of the laser interferometer 19 to step the substrate stage 16 to a predetermined position. Further, the substrate stage 16 is provided with a reference member 21 having a reference mark at the same height position as the surface of the photosensitive substrate placed on the substrate stage 16.

FIG. 2 is a plan view of the reticle and an explanatory view of the alignment marks provided on the reticle. As shown in FIG. 2A, the reticle 12 has a pattern area 13 in which a pattern to be transferred to the photosensitive substrate is formed and alignment mark areas 14a and 14b provided outside thereof. In the alignment mark areas 14a and 14b,
As shown in an enlarged view in FIG. 2B, alignment marks 31a and 31b formed of V-shaped openings having an opening angle θ ₁ formed on the chrome layer 30 deposited on the reticle are formed. The alignment light is V-shaped alignment mark 3
The portions 1a and 31b are transmitted. The illustrated V-shaped alignment mark 31a is arranged with the V-shaped symmetry axis parallel to the Y-axis, but may be arranged with the symmetry axis parallel to the X-axis.

FIG. 3 is a schematic view of the reference mark 36 provided on the reference member 21. The reference mark 36 is also formed by a V-shaped opening having an opening angle θ ₂ formed in the chrome layer 35 on the transparent member, and light is transmitted through the V-shaped reference mark portion. The reference mark 36 in this example is arranged with the V-shaped symmetry axis parallel to the Y-axis. However, when the alignment mark provided on the reticle is a V-shaped mark having a symmetry axis parallel to the X axis, the reference mark 36 is also a V-shaped mark having a symmetry axis parallel to the X axis. Also, the reticle 12
V-shaped alignment marks 31a, 31b provided on the
And the V-shaped reference mark 36 provided on the reference member 21,
The two marks are located at a conjugate position with respect to the projection optical system 15, and are arranged so that the two marks are overlapped with each other through the projection optical system 15 in a V-shape and an inverted V-shape.

Now, with reference to the case where the position of the reticle 12 projected on the substrate stage coordinate system is measured using the alignment marks 31a and 31b formed on the reticle 12 and the reference mark 36 formed on the reference member of the substrate stage 16. Think First, the reticle 1 using the projection optical system 15
The substrate stage 16 is driven so that the reference mark 36 is located at the image forming position of the alignment mark 31a on the position 2, and the amount of displacement of the alignment mark 31a is measured. When the exposure illumination light source 10 is used as a light source for alignment, the illumination light 27 from the exposure illumination light source 10 passes through the illumination optical system 11 and is a V-shaped alignment mark 31 a arranged at a predetermined position on the reticle 12. Is irradiated. As described above, the alignment mark 31a is a light-transmissive mark, and the light flux transmitted through the mark 31a is projected onto the V-shaped reference mark 36 of the reference member 21 arranged on the substrate stage 16 by the projection optical system 15. For example, as shown by the broken line in FIG. 4, images are formed in a relationship of V-shape and inverted V-shape.

The V-shaped reference mark 36 is a light-transmitting mark similar to the alignment mark 31a of the reticle 12, and the light flux passing through the V-shaped reference mark 36 is arranged in the substrate stage 16 by the relay lens 22. C
The image is re-formed on the image pickup surface of the CD image pickup means 23. The image picked up by the CCD image pickup means 23 is image-processed by the image processing means 24 as described later, and the information thereof is signal processing means 2.
5 is input. The output signal from the laser interferometer 19 is also input to the signal processing means 25, and the position coordinate of the alignment mark 31a projected on the substrate stage moving coordinate system is measured.

When the measurement of the alignment mark 31a is completed, the substrate stage 16 is driven by the driving means 17, the reference member 21 is moved to the image forming position of the alignment mark 31b by the projection optical system 15, and the alignment is similarly performed by image processing. The displacement amount of the mark 31b is measured. The rotation and shift of the reticle 12 are calculated from the measurement results of the alignment marks 31a and 31b by a known method, and if the rotation and shift are outside the allowable value, the rotation and shift of the reticle 12 are adjusted so as to be within the allowable value.

Although the case where only one reference mark 36 is provided on the substrate stage 16 has been described here, the two alignment marks 31a, 31a arranged on the reticle 12,
It is also possible to dispose two reference members on the substrate stage 15 at intervals of 31b. In that case, the alignment position of the reticle 12 is measured by measuring the projection position of one alignment mark 31a on the reticle 12 with one reference mark and measuring the projection position of the other alignment mark with the other reference mark. The time required for (alignment) can be significantly reduced.

Next, a method of detecting the amount of positional deviation using the V-shaped alignment mark and the V-shaped reference mark will be described in detail. FIG. 4 is a schematic diagram of an optical image captured by the CCD image capturing means 23. The optical images 41a and 41b are formed on the reticle 12 by the V-shaped alignment marks 31a (31
The position and shape of the portion where the projected image 40 of b) and the V-shaped reference mark 36 formed on the reference member 21 of the substrate stage 16 overlap are reflected. FIG. 4 shows an ideal alignment state in which two optical images 41a and 41b are formed.
The distance in the X direction is Lx = L, and the distance in the Y direction is Ly = 0.

FIG. 5 shows the CCD when the projected image of the reticle 12 is displaced only in the X direction from the ideal alignment state.
Two optical images 41a, 4 picked up by the image pickup means 23
The positional relationship of 1b is shown. FIG. 5A shows a state in which the image 40 of the V-shaped alignment mark of the reticle is displaced by ΔX in the + X direction with respect to the V-shaped reference mark 36, and at this time, the two optical images 41 a and 41 b in the Y direction. Position is optical image 41
The optical image 41a is displaced by + Ly in the + Y direction with respect to b. On the other hand, FIG. 5B shows a state in which the image 40 of the alignment mark of the reticle is displaced by ΔX in the −X direction with respect to the V-shaped reference mark 36.
The positions of 1a and 41b in the Y direction are different from the optical image
1a is displaced by ΔLy in the −Y direction.

FIG. 6 shows the positional relationship between the two optical images 41a and 41b picked up by the CCD image pickup means 23 when the projected image of the reticle 12 is displaced only in the Y direction with respect to the ideal alignment state. Show. FIG. 6A shows a state in which the image 40 of the V-shaped alignment mark of the reticle 12 is displaced by ΔY in the −Y direction with respect to the V-shaped reference mark 36, and FIG. 6B shows the V-shaped reference mark. The projected image 40 of the V-shaped alignment mark of the reticle 12 with respect to 36
Shows a state of being displaced by ΔY in the + Y direction. At this time 2
The distance between the two light images 34a and 34b in the X direction is (Lx + ΔL
x). As is clear from the figure, when ΔY is plus, ΔLx is minus, and when ΔY is minus, ΔLx
x is positive.

Next, a method of detecting the positions of the two optical images 41a and 41b formed on the CCD image pickup means 23 by the image processing means 24 will be described. Figure 7 shows the CCD
An image 50 taken by the image pickup means 23 is shown. In the image processing means 24, images having the same shape as the two square images formed by the overlapping of the V-shaped mark 51 and the inverted V-shaped mark 52 are registered in advance as model images 53 and 54. The image processing means 24 uses the model image 53,
Two optical images 41a and 41b are detected in the image 50 by a well-known pattern matching method using 54, and the relative positions of the two optical images 41a and 41b in the X and Y directions based on the position data of the detected optical images 41a and 41b. The changes ΔX and ΔY are calculated. The relative position of the optical images 41a and 41b can be detected by a method other than image processing. For example, by monitoring the brightness difference of all the elements of the CCD image pickup means 23, the optical image 4
It is also possible to know the address of the element receiving the light 1a, 41b and detect the relative position of the two optical images 41a, 41b from the address.

Next, 2 detected by the CCD image pickup means 23
A method of detecting the positional deviation amount of the reticle 12 from the relative positional changes ΔX and ΔY of the two optical images 41a and 41b will be described. The V-shaped opening angle of the V-shaped alignment marks 31a and 31b provided on the reticle 12 is θ ₁ , and the V-shaped opening angle of the V-shaped reference mark 36 provided on the reference member 21 on the substrate stage 16 is θ. _Set to ₂ . Now, reticle 12
If the image of the alignment mark is shifted from the ideal alignment state by ΔX in the X direction and ΔY in the Y direction, C
Two optical images 41a, 4a formed on the CD imaging means 23
The change ΔLx in the X-direction interval and the change ΔLy in the Y-direction interval of 1b are represented by the following [Equation 1] and [Equation 2], respectively.

[0020]

[Number 1] _{ΔLy = 2ΔX {cos (θ 1} /2) · cos (θ 2/2)}
/ {Sin [(θ ₁ + θ ₂ ) / 2]}

[0021]

[Number 2] _{ΔLx = -2ΔY {sin (θ 1} /2) · cos (θ 2 /
2)} / {sin [(θ ₁ + θ ₂ ) / 2]}

If θ ₁ = θ ₂ = π / 2, then ΔLy
= ΔX, ΔLx = −ΔY. The opening angles θ ₁ and θ ₂ of the V-shaped mark can be set arbitrarily. Further, the reference mark 36 provided on the reference member 21 on the substrate stage 16 may be one kind, or as shown in FIG. 8, a plurality of V-shaped reference marks 37, 38 having different opening angles θ ₂ may be provided. Alternatively, the reference mark to be used may be selected according to the purpose.

According to the present invention, the opening angle θ _{1 of} the V-shaped alignment marks 31a and 31b formed on the reticle 12 is set.
By selecting a combination of the opening angle θ ₂ of the V-shaped reference mark 36 formed on the reference member 21 and the reference member 21, it is possible to expect a magnification effect of compressing the detection error generated when the mark position is detected. In order to measure the position shift amount of the reticle 12 in the X direction with high accuracy, for example, θ ₁ = π / 2, θ ₂ = 2π / 3. In this case, the above [Formula 1] becomes like the following [Formula 3].

[0024]

(3) ΔLy = 1.27ΔX

This [Equation 3] is the X of the mark image of the reticle.
It is shown that the displacement ΔX in the direction appears in the displacement ΔLy magnified by 1.27 times. That is, θ ₁ = π / 2, θ ₂
= 2π / 3, the displacement in the X direction ΔX
A magnification effect is obtained in which is expanded to 1.27 times. vice versa,
To strictly measure the amount of positional deviation of the reticle 12 in the Y direction, for example, θ ₁ = π / 2, θ ₂ = π / 3. At this time, the above [Formula 2] is changed to the following [Formula 4], and the displacement ΔY in the Y direction of the mark image of the reticle can be magnified 1.27 times and measured.

[0026]

[Formula 4] ΔLx = −1.27ΔY

Consider exposure of a superposition pattern of a liquid crystal display element as shown in FIG. 9 (a). Source line 63
It is assumed that the pattern of the gate line 65 is superimposed and exposed on the photosensitive substrate on which the pattern of the pixel element 62 having the signal line 61 and the drain line 64 is formed.
FIG. 9B shows the design positions of the gate 66, the source line 63, and the drain line 64. The relative positions of the gate 66, the source line 63, and the drain line 64 are slightly affected in the Y direction as shown in FIG. 9C, but have little effect on the device performance. If you shift in the X direction as shown,
Since the overlap of the source line 63, the drain line 64, and the gate 66 is changed, the performance of the device is greatly affected. In such a case, alignment of the reticle that exposes the pattern of the gate line requires strict alignment accuracy in the X direction as compared with the Y direction. Therefore, as described above, as the opening angle θ ₁ of the V-shaped alignment mark formed on the reticle and the opening angle θ ₂ of the V-shaped reference mark 36 formed on the reference member 21, for example, θ ₁ = π / 2, θ
This requirement can be met by selecting a combination such as ₂ = 2π / 3.

In the above description, the exposure illumination light source 10 is used as a light source for alignment, and the image pickup means is arranged on the substrate stage side. However, as a light source, you may prepare a dedicated light source for alignment,
The location of the image pickup means is not limited to the stage side. For example, in FIG. 1, a light source is arranged in the substrate stage 16 so as to be located below the reference member 21, or a light beam from an external light source is guided below the reference member 21 by an optical fiber bundle so that the reference member 21 The reference mark may be illuminated from below, and the projection optical system 15 may form an image of the reference mark at the alignment mark position of the reticle 12. In this case, the image pickup means is arranged above the reticle 12, and the image pickup means is used to detect the overlap between the reference mark image and the alignment mark. Further, when the alignment mark of the reticle is imaged on the reference mark to detect the positional deviation, the image pickup means is arranged on the base part so that the light transmitted through the reference mark is made incident on the image pickup means by the optical fiber bundle. May be.

Next, a method of measuring the optical characteristics of the projection optical system according to the present invention will be described. FIG. 10 is a schematic diagram showing an example of a test reticle used for this measurement. This test reticle 70 is provided with a plurality of V-shaped marks 71 to 79 on the entire surface in a predetermined positional relationship. The V-shaped marks 71 to 79 have an opening angle θ ₁ formed on the chrome layer.
Is a light-transmitting mark having a V-shaped opening and transmitting light through a portion of the V-shaped mark.

An image of the test reticle 70 is formed on the substrate stage side by the projection optical system, and the position of each mark image is detected by using the V-shaped mark provided on the reference member of the substrate stage. The V-shaped mark provided on the reference member is also a V-shaped opening having an opening angle θ ₂ formed in the chrome layer, and light is transmitted through the V-shaped mark. The positions of the images of the marks 71 to 79 are detected by moving the substrate stage to sequentially move the reference mark to the design position of each mark image, and are formed by two marks that are superposed in a V-shaped and inverted V-shaped relationship. The same method as described above is performed by capturing two light images. 2 of each mark image detected in this way
Optical characteristics such as distortion of the projection optical system can be measured from the dimensional position data.

According to the measurement using this V-shaped mark,
Since position data in the X direction and position data in the Y direction at one measurement point can be performed by one position detection operation, it is possible to significantly reduce the measurement time of optical characteristics. Further, the measurement accuracy can be improved by selecting the combination of the opening angles θ ₁ and θ ₂ of the V-shaped mark.

[0032]

According to the present invention, by using a V-shaped mark as a mark for position measurement, it is possible to obtain information in two directions by one processing, and it is possible to shorten the measurement time. Further, by changing the combination of the opening angles of the V-shaped marks, it becomes possible to reduce the position measurement error due to the magnification effect.

[Brief description of drawings]

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

FIG. 2 is a plan view of a reticle and an explanatory view of alignment marks.

FIG. 3 is an explanatory view of a reference mark.

FIG. 4 is an explanatory diagram of an optical image formed on an image pickup unit.

FIG. 5 is an explanatory diagram of an optical image formed on the image pickup unit when the reticle is displaced in the X direction.

FIG. 6 is an explanatory diagram of an optical image formed on the image pickup unit when the reticle is displaced in the Y direction.

FIG. 7 is an explanatory diagram of optical image detection by an image processing unit.

FIG. 8 is an explanatory diagram of a reference member provided with a plurality of reference marks.

FIG. 9 is an explanatory diagram of exposure of a superposition pattern.

FIG. 10 is a schematic diagram of an example of a test reticle used to measure the optical characteristics of a projection optical system.

[Explanation of symbols]

10 ... Illumination light source for exposure, 11 ... Illumination optical system, 12 ... Reticle, 13 ... Pattern, 14a, 14b ... Alignment mark area, 15 ... Projection optical system, 16 ... Substrate stage,
Reference numeral 17 ... Driving means, 19 ... Laser interferometer, 21 ... Reference member, 22 ... Relay lens, 23 ... Imaging means, 24 ... Image processing means, 25 ... Signal processing means, 31a, 31b ... V-shaped alignment mark, 36 ... V-shaped reference mark, 40
... Projection image of alignment mark, 41a, 41b ... Optical image, 53, 54 ... Model image, 61 ... Signal line, 62 ... Pixel element, 63 ... Source line, 64 ... Drain line, 65 ...
Gate, 70 ... Test reticle, 71-79 ... V-shaped mark

Claims (6)

[Claims] 1. An illumination system for illuminating a reticle on which a pattern to be transferred is formed, a projection optical system for forming a pattern image of the reticle on a photosensitive substrate, and a reference member having a reference mark are provided. In a projection exposure apparatus including a substrate stage on which a substrate is mounted and movable in a two-dimensional direction, the reference mark provided on the reference member is a V-shaped light transmissive mark, and is provided on the reticle. A projection exposure apparatus comprising: an image pickup means for picking up a superimposed image of a V-shaped light-transmissive alignment mark and the V-shaped reference mark. 2. The projection exposure apparatus according to claim 1, further comprising a positional deviation detecting means for detecting a relative positional deviation amount between the V-shaped alignment mark provided on the reticle and the reference mark. 3. The projection exposure apparatus according to claim 1, wherein the reference member is provided with a plurality of V-shaped marks having different opening angles as reference marks. 4. A position aligning method for aligning a reticle having a pattern to be projected and exposed on a photosensitive substrate with respect to a moving coordinate system of a substrate stage which mounts the photosensitive substrate and is movable in a two-dimensional direction. In, a superposed image of a V-shaped light-transmissive mark provided on the reticle and a V-shaped light-transmissive reference mark provided on the substrate stage is imaged, and a positional deviation amount between them is measured. A positioning method characterized by the above. 5. The opening angle of a V-shaped light transmissive mark provided on the reticle is set so that the sensitivity of the displacement measurement is high in the direction in which high alignment accuracy is required. The alignment method according to claim 4, further comprising: 6. An image of a plurality of V-shaped light-transmitting marks formed on a reticle is projected onto a substrate stage by a projection optical system, and a V-shaped light-transmitting property provided on a reference member on the substrate stage. A method for measuring an optical characteristic of the projection optical system, characterized in that an overlay image with a mark is picked up and a positional deviation from a design position is measured.