JPH07201721A - Focussing device - Google Patents

Abstract

PURPOSE:To avoid the erroneous detection by a method wherein adjacent two out of counter light slit images formed on a photodetecting slit are composed not to be in parallel with one another. CONSTITUTION:When a detected surface 1 is notably slipped out of the focussed surface of a projection optical system 2 so that counter light slit images 5a' and 5b' may be resultantly intersected with adjacent slits 8b and 8c without overlapping with corresponding slits 8a, and 8b, the light quantity of the counter light slit images 5a' and 5b' respectively passing through the slits 8b and 8c is to be extremely small. Furthermore, even if the counter light slit images 5a' and 5b' are shifted in the vertical direction by the actions of a vibrator or the vertical movement of the detecting surface 1, the light quantity to be detected is almost constant resultantly the S curve signal wave form by synchronized detection can not be taken. Through these procedures, any erroneous detection can be avoided without fail.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a focusing device,
In particular, the present invention relates to a substrate focusing device in a projection exposure apparatus used for manufacturing ICs, liquid crystal substrates, thin film magnetic heads, and the like.

[0002]

2. Description of the Related Art In a conventional focusing apparatus applied to a projection exposure apparatus for transferring a circuit pattern on a mask onto a photosensitive substrate such as a wafer through a projection optical system, for example, light from a light sending slit is sent. Through a light optical system, a surface to be detected such as a wafer is obliquely irradiated and a slit image is formed on the surface to be detected. The light from the slit image (reflected light from the surface to be detected) is imaged on the light receiving slit via the light receiving optical system to form a light transmitting slit image on the light receiving slit. The light of the sending slit image that has passed through the light receiving slit is received by the light receiving means. The light receiving means outputs a signal according to the amount of received light. The control system detects the position of the detected surface based on this signal and performs focusing.

The light-sending slit image formed on the light-receiving slit moves in a predetermined direction on the light-receiving slit due to positional displacement (vertical movement) of the wafer surface (detected surface) with respect to the projection optical system. The light receiving slit and the light transmitting slit image formed on the light receiving slit substantially match when the focused surface of the projection optical system and the detected surface substantially match. In this way, the detection target surface is focused on the basis of the amount of light received by the light receiving means via the light receiving slit.

When detecting points are provided at a plurality of points on the surface to be detected, a light transmitting slit and a light receiving slit having a plurality of slits corresponding to slit images formed at the respective detecting points are provided. Each slit of the light receiving slit is
It corresponds to each slit of the light sending slit. Then, when the in-focus surface of the projection optical system and the surface to be detected are substantially coincident with respect to each detection point, each light-transmitting slit image formed on the light-receiving slit and each slit of the light-receiving slit are substantially coincident with each other. It is configured. In this way, the detection target surface is focused based on each light amount (each output signal corresponding to each light amount) received by the light receiving means corresponding to each slit via each slit of the light receiving slit.

[0005]

In the conventional focusing device as described above, as shown in FIG. 5, the two slits 16a and 16b formed in the light receiving slit are formed in parallel with each other, and the two corresponding slits are formed. Transmitting slit image 15
A'and 15b 'were also formed parallel to each other on the light receiving slit. The light-sending slit images 15a 'and 15b' move vertically due to the vertical movement of the surface to be detected, and when the surface to be detected is substantially coincident with the focusing surface of the projection optical system, the light-sending slit image 15a 'is formed. And 15b 'and the slits 16a and 16b are substantially aligned with each other. That is, the slits 16a and 1
The light-sending slit images 15a 'and 15b' are formed at positions parallel to the moving direction of the image 6b.

However, when the position of the surface to be detected is largely displaced from the focusing surface of the projection optical system, the amount of movement of the light-sending slit image on the light-receiving slit also becomes large. Therefore, in FIG.
As shown in FIG. 3, the light-transmitting slit image 15a 'that should originally correspond to the slit 16a may overlap the adjacent slit 16b. In this case, although the position of the detected surface is largely displaced from the focusing surface of the projection optical system,
The light receiving means corresponding to the slit 16b is the light transmitting slit image 1
The same signal as when 5b 'and the slit 16b substantially match is output. Therefore, the light transmission slit image 15a '
Erroneously detects the position of the surface to be detected that coincides with the slit 16b as if it were the in-focus surface of the projection optical system (for example, a signal from the light receiving means corresponding to the slit 16a can be used. If it does not exist, such erroneous detection is possible because focusing is performed based on the signal from the light receiving means corresponding to the slit 16b).

In order to avoid such erroneous detection, it can be considered to increase the distance between adjacent slits.
However, simply increasing the distance between the adjacent slits is nothing but increasing the distance between the detection points. As a result, there is an inconvenience that the detection point cannot be set at a desired position on the surface to be detected. The present invention has been made in view of the above problems, and an object of the present invention is to provide a focusing device capable of avoiding the above-described erroneous detection without widening the interval between detection points.

[0008]

In order to solve the above-mentioned problems, in the present invention, a plurality of slit-shaped images are formed on the surface to be detected by making light obliquely incident on the surface to be detected. Of the light-transmitting means, a light-receiving slit having a plurality of slits, a light-receiving optical system for forming light from the plurality of slit-shaped images on the light-receiving slit, and each of the light-receiving slits. A light receiving element for receiving light, which is formed on the light receiving slit in a focusing device for focusing the detected surface with respect to the objective optical system based on a change in the amount of light received by the light receiving element. The two adjacent images of the plurality of slit-shaped images are not parallel to each other, providing a focusing device.

According to a preferred embodiment, the light transmitting means is
A light source, a light-sending slit having a plurality of slits formed corresponding to the plurality of light-receiving slits, and an image of the light from the light source on the detection surface via the light-sending slit. And a light transmitting optical system. Then, two adjacent images among the plurality of slit-shaped images formed on the light receiving slit are almost in the moving direction of the image on the light receiving slit due to the displacement of the detected surface with respect to the objective optical system. It is preferable to have the same angle and opposite directions.

[0010]

In the focusing device of the present invention, the two adjacent images of the plurality of light-transmitting slit images formed on the light-receiving slit are not parallel to each other. In other words, two adjacent images are formed so as to form an angle with each other. As a result, even if the light-transmitting slit image is largely translated on the light-receiving slit due to the displacement of the surface to be detected, each light-transmitting slit image does not match the slit that should correspond to the adjacent light-transmitting slit image. Instead, they only partially overlap. That is, unless the detected surface is at a predetermined position, for example, the position of the focusing surface of the projection optical system, each light-transmitting slit image does not coincide with the corresponding slit. In this way, it is possible to reliably avoid the conventional erroneous detection due to the fact that each light-transmitting slit image coincides with the slit that should correspond to the adjacent light-transmitting slit image.

Specifically, the vertical movement of the surface to be detected forms an angle of approximately 45 ° with respect to the direction in which the light-sending slit image moves on the light-receiving slit, and the two slit images adjacent to each other face in opposite directions. Therefore, it is preferable that a plurality of light-transmitting slit images are formed in a zigzag shape as a whole. In this case, the plurality of slits formed in the light-receiving slit are also formed in a zigzag shape as a whole, and each light-transmitting slit image coincides with the corresponding slit only when the detected surface coincides with the in-focus surface. On the other hand, when the detected surface is largely displaced from the in-focus surface, each light-transmitting slit image overlaps with the slits that should correspond to the adjacent light-transmitting slit images so as to be orthogonal to each other, and therefore the amount of light passing through each slit. Will be minimal. As a result, the conventional erroneous detection can be reliably avoided.

[0012]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically illustrating the configuration of a focusing device according to an embodiment of the present invention. The focusing device of FIG. 1 comprises a light source 3. The light emitted from the light source 3 is collimated by the condenser lens 4 and is incident on the light transmitting slit surface 5. As shown in FIG. 2, three slits 5a, 5b and 5c are formed on the light transmitting slit surface 5. Each slit is formed in a zigzag shape so as to form a right angle with each other.

Each slit 5a, 5b of the light transmitting slit surface 5
The light having passed 5 and 5c forms an image on, for example, the surface (detection surface) 1 of the wafer W via the light transmission optical system 6. Thus, three zigzag slit images corresponding to the slits 5a, 5b and 5c are formed on the detected surface 1. The center position of each slit image formed on the detected surface 1 corresponds to the detection point. In this way, the light-sending slit surface 5 is positioned in the plane substantially conjugate with the detected surface 1 via the light-sending optical system 6.

The light reflected on the surface to be detected 1 forms an image on the light receiving slit surface 8 via the light receiving optical system 7. In this way, the light receiving slit surface 8 is positioned in the plane substantially conjugate with the detected surface 1 via the light receiving optical system 7. As shown in FIG. 3, the light receiving slit surface 8 is provided with three slits 8a, 8b and 8c corresponding to the three slits 5a, 5b and 5c formed on the light transmitting slit surface 5, respectively. Further, on the light receiving slit surface 8, three light transmitting slit images 5a ', 5b' and 5c 'respectively corresponding to the three slits 5a, 5b and 5c are formed. The shape of the light-transmitting slit image 5a 'and the slit 5a on the light-receiving slit surface 8 are substantially the same. Similarly, the slit images 5b 'and 5c' and the slits 5b and 5c have substantially the same shape. In this way, by making the light-transmitting slit image and the light-receiving slit have substantially the same shape, the inspection accuracy is improved.

The surface 1 to be detected can move along the optical axis of the projection optical system in a direction approaching the projection optical system and a direction away from the projection optical system. Therefore, when the surface to be detected 1 is moved in the optical axis direction of the projection optical system 2 for forming the pattern formed on the mask 16 on the wafer W, the light transmitting slit image 5a ′ formed on the light receiving slit surface 8 is formed. 5b 'and 5c' translate in the vertical direction in FIG. The three slits 8a, 8b and 8 formed on the light receiving slit surface 8
c is an image moving direction L1 indicating the moving direction of the slit image.
Are arranged in a zigzag shape as a whole so as to form an angle θ with each other and to be opposite to each other between two adjacent slits.

Since the light-sending slit image moves up and down in the figure, the angle θ is set substantially equal to θ = 45 ° in this embodiment in consideration of the symmetry in the relative position change between the light-receiving slit and the light-sending slit image. . Another reason for setting the angle θ to about 45 ° will be described below. There may be a pattern having periodicity in two orthogonal directions on the detected surface 1. Therefore, in order to prevent the influence from this pattern,
The longitudinal direction of the slit image is approximately 45 ° with respect to each cycle direction.
It is preferable that the light-transmitting slit image is formed so as to be inclined and the light-receiving slit is determined correspondingly. Therefore, the angle θ is 4
It is preferably 5 degrees.

On the other hand, since the light-transmitting slit image and the light-receiving slit have the same shape as described above, the light-transmitting slit images 5a ', 5b' and 5c 'formed on the light-receiving slit surface 8 have slits 8a, 8b. And 8c in the image movement direction L1
It is almost the same as the shape translated along. Then, when the detected surface 1 substantially coincides with the focusing surface of the projection optical system 2, the light-transmitting slit images 5a ', 5b' and 5c 'substantially coincide with the corresponding slits 8a, 8b and 8c, respectively. The optical system (the focusing device with respect to the in-focus surface) is calibrated by rotating a herbing glass (not shown) of the light receiving optical system. The light receiving optical system 7 is provided with a vibrating mirror 9 having a vibrator. By vibrating the vibrating mirror 9 by the oscillator driving circuit 11, the light-sending slits 5a ′, 5b ′ and 5c ′ are in the same direction as the image moving direction L1 on the light-receiving slit surface 8 and are 1 to 2 times the slit width. Vibrates with a constant amplitude of.

Each slit 8a, 8b of the light-receiving slit surface 8
And the light that has passed through 8c are reflected by the photosensor 10 respectively.
The light is received by a, 10b and 10c, and photoelectrically converted into an electric signal according to the amount of light. Photo sensor 10a, 10b
The signals output from the oscillators 10 and 10c are synchronously detected by the signal processing circuits 12a, 12b, and 12c according to the oscillator drive signals from the oscillator drive circuit 11, respectively. In this way, the light-sending slit image 5 corresponding to the positional deviation of the detected surface 1
A signal (S-curve waveform) corresponding to the fluctuations of a ', 5b', and 5c 'is obtained. A synchronous detection type focusing device is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112. Such a synchronous detection method is more accurate than a method of simply detecting the amount of light. Signal processing circuit 12
The signals respectively generated at a, 12b and 12c are
It is sent to the stage control unit 13. Stage control unit 13
On the basis of the output signals of the signal processing circuits 12a, 12b, and 12c, the stage 14 is appropriately moved along the optical axis of the projection optical system 2 so that the detected surface 1 coincides with the focusing surface of the projection optical system 2. To output to the drive unit 17 such as a motor. The drive unit 17 moves the stage 14 based on the signal from the stage control unit 13.

FIG. 4 is a diagram showing a positional relationship between the slit and the light-transmitting slit image when the detected surface is largely displaced from the focusing surface of the projection optical system. As shown in FIG. 4, the detected surface 1 is largely displaced from the focusing surface of the projection optical system 2, and as a result, the light sending slit images 5a 'and 5b' overlap the corresponding slits 8a and 8b. In the case where the slits 8b and 8c adjacent to each other do not intersect, the light amount of the light-transmitting slit images 5a 'and 5b' passing through the slits 8b and 8c, respectively, is extremely small. Further, even if the light-transmitting slit images 5a 'and 5b' are moved in the vertical direction in the figure due to the action of the vibrator or the vertical movement of the surface to be detected 1, the detected light amount is substantially constant, and as a result, S Since a curve signal waveform cannot be obtained, erroneous detection can be reliably avoided.

In the above-described embodiment, the adjacent light-transmitting slit images are formed so as to form the same angle θ with respect to the image moving direction L1 and opposite directions to each other. If the light slit images are arranged at right angles to each other, that is, θ = 45 °, the amount of received light when the detected surface 1 is largely displaced from the focusing surface of the projection optical system 2 is minimum. become.

Further, in the above-mentioned embodiment, the configuration is such that the adjacent light-transmitting slit images are formed so as to be opposite to each other with the angle of the opposite sign as shown in FIG. It is obvious that the effects of the present invention can be obtained as long as the slit images are arranged so as to form a certain angle with each other, even if they are not opposite to each other. For example, in FIG. 3, the angle formed by the light transmitting slit image 5a 'and the moving direction L1 is 45 °, and the light transmitting slit image 5b' and the moving direction L1.
The angle formed by 1 and 60 may be different from each other, and the angle formed by the light transmission slit image 5c ′ and the moving direction L1 may be 75 °. This makes it possible to avoid erroneous detection even when the surface to be detected 1 is largely displaced and the light-transmitting slit image 5a 'overlaps the light-receiving slit 8c.

As described above, by arranging the adjacent slits so that the slit image moves in the opposite direction to the direction in which the slit image moves due to the displacement of the surface to be detected, the amount of displacement of the surface to be detected is The changes in the electric signal (for example, the slope of the S curve) can be made uniform, and the variation in the sensitivity at each detection point can be substantially eliminated. On the contrary, when the slit angles are not equal to the moving direction, the rate of change of the electric signal with respect to the displacement of the surface to be detected is obtained in advance for each detection point, and the signal processing circuit converts the output of each detection point. Therefore, the drive signal of the stage may be output. Further, when determining the angle at which the slits are arranged, there may be a restriction on the direction of the light-sending slit image on the detected surface in order to make it less susceptible to the pattern formed on the detected surface. . Even in this case, the effect of the present invention can be obtained if the adjacent slits can be arranged on at least two different directions (two different directions having opposite signs as shown in FIG. 3) on the surface to be detected.

Further, in the above-mentioned embodiment, an example is shown in which the light is received by the individual photosensors through the respective slits of the light receiving slits. However, the light receiving slits are not used, and the light receiving regions corresponding to the respective slits are received. Light can be received by an optical element (for example, a CCD camera), and the configuration can be simplified. Further, the present invention is not limited to the synchronous detection type focusing device using the vibrating mirror, and the vibrating mirror is omitted, and the positional deviation of the detected surface is simply obtained based on the light amount from the photosensor or CCD. You may do it. At this time,
, The slit image 5 corresponding to the slit 8a
When a'is displaced so as to overlap the slit 8b, the output signal from the photosensor 10b becomes extremely small, and it can be seen that the detected surface is largely displaced from the in-focus surface.

[0024]

As described above, in the focusing device of the present invention, the adjacent light-transmitting slit images are arranged so as not to be parallel to each other but to form a certain angle, so that the detected surface is located at a large position from the predetermined position. Even when they are deviated, each light-transmitting slit image does not coincide with the slit that should correspond to the adjacent light-transmitting slit image. Therefore, the conventional erroneous detection can be reliably avoided. In addition, since the amount of light passing through the slits that should correspond to the adjacent slit images of each slit is almost constant and does not depend much on the displacement of the surface to be detected, even if the detection points are close to each other Detection can be reliably avoided.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a configuration of a focusing device according to an embodiment of the present invention.

FIG. 2 is a diagram showing slits formed on a light transmitting slit surface in the embodiment of FIG.

FIG. 3 is a diagram showing a positional relationship between a slit on a light receiving slit surface and a formed light transmitting slit image in the embodiment of FIG.

FIG. 4 is a diagram showing a positional relationship between a slit on a light-receiving slit surface and a light-transmitting slit image when a detected surface is largely displaced from a predetermined position in the embodiment of FIG.

FIG. 5 is a diagram showing a positional relationship between a slit on a light receiving slit surface and a formed light transmitting slit image in a conventional focusing device.

[Explanation of symbols]

 1 Surface to be detected 2 Projection optical system 3 Light source 4 Condenser lens 5 Light-transmitting slit surface 6 Light-transmitting optical system 7 Light-receiving optical system 8 Light-receiving slit surface 9 Vibrating mirror 10 Photosensor 11 Transducer drive circuit 12 Signal processing circuit 13 Stage control section 14 stage 17 drive unit

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display area G03F 7/207 H

Claims (5)

[Claims] 1. A light transmitting means for obliquely entering light on a surface to be detected to form a plurality of slit-shaped images on the surface to be detected, and a light receiving slit having a plurality of slits.
A light receiving optical system for forming light from the plurality of slit-shaped images on the light receiving slit, and a light receiving element for receiving light passing through each slit of the light receiving slit, the light receiving element In a focusing device that focuses the detection target surface with respect to the objective optical system based on a change in the amount of light received by, two adjacent images of a plurality of slit-shaped images formed on the light receiving slit are: Focusing device characterized in that they are not parallel to each other. 2. The light transmitting means includes a light source, a light transmitting slit having a plurality of slits formed corresponding to a plurality of slits of the light receiving slit, and light from the light source via the light transmitting slit. And a light-transmitting optical system for forming an image on the surface to be detected, and two adjacent images of a plurality of slit-shaped images formed on the light-receiving slit are the objects to be detected by the objective optical system. 2. An angle substantially the same as the moving direction of the image on the light receiving slit due to the displacement of the detection surface and opposite directions to each other.
Focusing device according to. 3. The focusing device according to claim 2, wherein two adjacent images of the plurality of slit-shaped images formed on the light receiving slit are substantially perpendicular to each other. 4. The plurality of slit-shaped images formed on the light-receiving slit are substantially different from each other in the moving direction of the image on the light-receiving slit due to the displacement of the surface to be detected with respect to the objective optical system. The focusing device according to claim 1, wherein the focusing device is angled. 5. The shape of the plurality of slits of the light-receiving slit is substantially the same as the shape of the plurality of slit-shaped images formed in the light-receiving slit.
The focusing device according to claim 1.