JPH06130678A - Position detecting device - Google Patents

Abstract

PURPOSE:To provide the position detecting device which can accurately detect the position and tilt of a partial area on a surface to be inspected in the optical axis direction of an objective optical system and can be arranged compactly in a limited space. CONSTITUTION:Projection lights from light sources 11a1 and 11a2 are passed through a condenser lens 12 and a projection slit 13 and are bent by a mirror 14, and further passed through an optical transmission side objective 15 and split by a half-prism 16. The split lights form images of the slit 13 at mutually different detection positions a1-a4 on the surface to be inspected. Reflected lights from respective detection positions are passed through a mirror 14a and a photodetection side objective 15 and photodetected by photodetecting elements 17a1-17a4. Shifts in the detection positions from a reference surfaces are detected on the basis of the output signals of the photodetecting elements 17a1-17a4 and the tilt of the mean plane of the partial area containing the detection positions is found.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device used for accurately setting a partial area of a surface to be inspected such as a wafer surface in a vertical position with respect to an optical axis of an objective lens of a projection exposure apparatus.

[0002]

2. Description of the Related Art Generally, a projection type exposure apparatus for manufacturing an integrated circuit uses a projection objective lens having a large numerical aperture, so that an allowable focus range is very small. For this reason,
Unless the exposure area of the wafer is kept at a position perpendicular to the optical axis of the projection objective lens, a clear pattern cannot be exposed over the entire exposure area.

The entire wafer can be aligned almost perpendicularly to the optical axis of the objective lens by detection on the wafer surface by a separately provided autofocus mechanism, but the size of the wafer is increased and gallium arsenide, etc. which is replaced by silicon, etc. With the new material, the flatness of the wafer itself becomes unstable, so it is necessary to partially detect the vertical position of the wafer. Similarly, a projection exposure apparatus is also used when manufacturing a liquid crystal display element or the like. In recent years, however, the flatness of the substrate itself needs to be detected because the size of a glass substrate or the like increases as the size of the liquid crystal display element increases. Further, since the deformation of the wafer, glass substrate, etc. (hereinafter collectively referred to simply as "substrate") is further increased by each exposure and chemical treatment, accurate horizontal detection of the exposure area has become indispensable.

For this reason, it is necessary to detect the inclination state of the plane in each area so that the optimum state can be maintained for each area to be exposed. A light flux is applied to collect the reflected light at this time on the light receiving element, or multiple detection positions are set in the exposure area, and the tilt of the substrate surface is corrected based on the amount of deviation from the reference plane at each detection position. Was there.

FIG. 4 is a schematic optical path diagram showing a configuration in which a conventional position detecting device is adopted in a reduction projection type exposure device. In the figure, a reticle or mask (collectively referred to as a mask hereinafter) 2 and a substrate 3 are arranged in a conjugate manner with respect to a projection objective lens 1, and a pattern on the mask 2 illuminated by an illumination optical system (not shown) is reduced on the substrate 3. , Projected in the same size or enlarged. Such baking exposure of the substrate 3 is repeated by moving the substrate 3 by a predetermined amount, which is called step-and-repeat, and the same operation is repeated every time a mask having a different pattern is exchanged.

The projection optical system 50 comprises a light source 61, a condenser lens 62, a diaphragm 63 having a minute circular aperture, and a projection objective lens 64. The condenser lens 62 is the light source 6.
The image of No. 1 is formed on the diaphragm 63, and the parallel light flux is supplied onto the substrate 3 by the projection objective lens 64 having a focus on the diaphragm 63. The light supplied from the projection optical system 50 has a wavelength different from that of the exposure light because the resist on the substrate 3 is not exposed.

The light receiving optical system 50a is a light receiving objective lens 6
The light beam, which is composed of five and four split light receiving elements 66, is supplied from the projection optical system 50 and reflected by the substrate 3 is a light receiving objective lens 6
4 provided at the focal position of the light receiving objective lens 65 by
The light is received on the divided light receiving element 66. Here, with respect to the optical axis 1a of the projection objective lens 1, the optical axis of the projection optical system 50 and the optical axis of the light receiving optical system 50a are symmetrical. Therefore, if the exposure area of the substrate 3 is kept perpendicular to the optical axis 1a of the projection objective lens 1, the light flux from the projection optical system 50 is received at the center position of the four-division light receiving element 66. If the exposure area of the substrate 3 is tilted by θ from the vertical, the parallel light flux from the projection optical system 50 reflected by the substrate 3 is received by the light receiving optical system 5.
Since it is inclined by 2θ with respect to the optical axis of 0a, the 4-division light receiving element 66
The light is received at a position off the center above. The tilt direction of the exposure area of the substrate 3 is detected from the position of the light receiving point on the four-division light receiving element 66, and the control means generates a control signal corresponding to the displacement direction and the displacement amount of the light receiving point on the four-division light receiving element 66. Then
The supporting device 3b is moved by the driving means, and the stage 3a on which the substrate 3 is placed is moved so as to correct the inclination of the exposure area surface of the substrate 3.

According to such a configuration, the projection optical system 50
The tilt of the substrate surface in the range projected by is detected, and the projection area on the substrate 3 is made substantially the same size as the exposure area by the projection objective lens 1, so that the exposure area is the light of the projection objective lens 1. The position can be automatically set to an accurate vertical position on average with respect to the axis 1a (see Japanese Patent Laid-Open Publication No. 46606/1988).

On the other hand, a system in which a large number of grazing incidence type position detection devices are installed has also been proposed (for example, Japanese Patent Laid-Open Publication No. 50418 of 1990). This method will be described with reference to FIGS. In the figure, projection optical systems 51 to
Light beams 51a to 54a having a predetermined shape are projected from 54 at different positions in the exposure area on the substrate 3, and reflected lights 51a 'to 54a' from the respective detection positions are received by the light receivers 51 'to 5'.
It is received at 4 '. Then, a virtual plane of the exposure area is obtained based on the output signals of the light receivers 51 ′ to 54 ′, and the stage 3a tilts the exposure area surface of the substrate 3 so that the virtual plane and the focal plane of the projection objective lens 1 are parallel to each other. Is corrected.

[0010]

In the prior art as described above, in order to maintain the best condition for each area to be exposed, the inclination state of the plane in each area is maintained. It is necessary to detect, but it is necessary to provide not only the tilt but also a focus detection device for accurately adjusting the position of the objective lens on the optical axis. However, it was extremely difficult to insert an optical device for various measurements in the limited space between the objective lens and the substrate.

Particularly, in the method of correcting the inclination by setting a plurality of detection positions in one exposure area and detecting the reflected light from each detection position (FIGS. 5 and 6),
The number of members increases and the arrangement of the optical system becomes more difficult. In addition, if the intensity of the light source of the projection optical system corresponding to each detection position is not constant or close to that, the variation will cause an error. There's a problem.

On the other hand, as a recent tendency of semiconductor elements, the chip size of the elements is increasing more and more due to the demand for high integration despite the miniaturization of patterns. In particular, the size of 20 mm square or more for VLSIs of 4 Mbit DRAM or more and 100 mm square or more for liquid crystal display devices is the mainstream. It is very difficult to make a parallel light beam incident over the entire large exposure area as large as 100 mm square or more, and even if it can be realized, it will be a very complicated configuration. Therefore, the method of making the parallel light flux incident on the entire exposure region to correct the inclination of the exposure region (FIG. 4) cannot cope with the tendency of the exposure region to expand.

The present invention has been made in view of the above point, and the position of the exposure area (partial area of the surface to be inspected) in the optical axis direction of the objective optical system and the inclination with respect to the optical axis can be accurately and easily. It is an object of the present invention to provide a position detection device that can detect a position and can cope with an expansion tendency of an exposure area.

[0014]

A position detecting device according to the present invention tilts with respect to an optical axis of the objective optical system at a predetermined detection position on a surface to be inspected which is arranged on a substantially image plane of the objective optical system. A projection optical system that projects light from a direction having, and a light receiving optical system that has a light receiving surface that is substantially in a conjugate relationship with the test surface, and that receives reflected light from the test surface, In order to achieve the above object, in the position detecting device that detects the position of the surface to be inspected in the optical axis direction of the objective optical system and the tilt with respect to the optical axis based on the signal from the light receiving optical system, The first and second projection optical systems that project the light at different detection positions on the inspection surface, and the optical paths of the projection light from the first and second projection optical systems are divided respectively to obtain the first and second projection optical systems. The projection light from the first projection optical system is moved to the first and second detection positions from the second projection optical system. Dividing means for guiding the emitted light to the third and fourth detection positions, respectively, and first and second receiving means for independently receiving the reflected light from the first, second and third detection positions on the surface to be detected. The second, third and fourth light receiving optical systems are provided.

[0015]

In the apparatus of the present invention, the light from the first and second projection optical systems is split by the splitting means and guided to different detection positions (first to fourth detection positions).
Then, the reflected light from each detection position is independent of the first
~ Received by the fourth light receiving optical system. That is, in the present invention,
Increase the number of light beams projected on the substrate by dividing the optical path,
The structure is such that the reflected light from different detection positions is detected by dedicated light receiving optical systems, respectively. By providing two sets of projection optical systems, at least four arbitrary detection positions can be set, and at least four detection positions can be set. The reflected light from the detection position can be detected at the same time. Therefore, according to the present invention, it is possible to detect the average inclination of the objective optical system with respect to the optical axis in a wide area on the surface to be inspected, and to perform the optimum angle correction of the area exposed for each exposure. It can be done efficiently.

Since the apparatus of the present invention also serves as the projection optical system for different detection positions as described above, the number of projection optical systems is smaller than the number of detection positions, and the structure is simple. In a reduction projection type exposure apparatus for manufacturing an integrated circuit, a plurality of microscopes for the overall alignment of the substrate and the like, and an automatic transport mechanism for the substrate and the like are provided around the projection objective lens. Although subject to great restrictions, the position detecting device of the present invention can be compactly arranged in a limited space.

Furthermore, since the apparatus of the present invention has a small number of optical systems, it is easy to assemble and adjust, and erroneous detection due to variations in light source intensity can be reduced. That is, in the present invention, the light from the same light source is split, projected onto different detection positions, and detected by different light receiving optical systems, so the intensity of reflected light from a certain detection position is extremely low (or high). In this case, by comparing with the reflected light intensity of another detection position where the light from the same light source is projected, it can be judged that there is a problem in the light source intensity when both have similar anomalies, and only one detection position If there is an abnormality, it is determined that there is a problem in the coating state of the resist in that portion. As described above, according to the present invention, it is possible to accurately detect variations in the characteristics of the optical system and abnormalities in the substrate surface state, which is advantageous in preventing erroneous detection.

Incidentally, in terms of detecting reflected light from a large number of detection positions with a small number of optical systems, as proposed in Japanese Patent Application No. 4-32949 filed by the same applicant as the present application,
A configuration in which the light receiving optical system is also used for different detection positions is also conceivable. However, in this case, a synthesizing means (half prism or the like) for synthesizing the optical paths of the reflected light from different detection positions and guiding it to the dual-purpose light-receiving optical system is required. The reflected light from the detection position is detected in time series. In contrast,
INDUSTRIAL APPLICABILITY The present invention requires no synthesizing means and is capable of simultaneous multipoint detection, which is advantageous in terms of throughput.

[0019]

1 is a perspective view showing a schematic configuration of an optical system of a position detecting device according to a first embodiment of the present invention. 2 is a view showing the arrangement when FIG. 1 is viewed from above. Figure 1,
In FIG. 2, light sources 11a ₁ and 11a ₂ such as light emitting diodes (LEDs) and halogen lamps (an optical system including the light source 11a ₁ is a first projection optical system, and an optical system including the light source 11a ₂ is a second projection optical system). The projection light from (1) illuminates the projection slit 13 via the condenser lens 12. The light projecting slit 13 has a rectangular elongated slit opening, and the projection light projected through this slit opening is bent by a mirror 14 so as to be substantially parallel to the surface 3 to be inspected such as a wafer or a glass substrate. Next, the projection light is transmitted to the light-transmitting side objective lens 1.
5 enters the half prism 16 (splitting means),
Here, the light is divided into two directions, the projection light from the first projection optical system is at detection positions a ₁ and a ₂ on the surface to be inspected 3, and the projection light from the second projection optical system is at the detection positions a ₃ and a _4. Light projection slit 13
Connect the slit images of.

Each detection position a ₁ , a ₂ , a ₃ , on the surface 3 to be inspected,
The reflected light reflected on the surface of a ₄ is reflected by the mirror 14a.
Is bent upward by the light receiving elements 17a ₁ and 17a.
₂ , 17a ₃ , 17a ₄ (light receiving elements 17a ₁ , 17a
_An optical system including ₂ , 17a ₃ and 17a ₄ is first,
The slit image is re-formed on the light receiving surfaces of the second, third, and fourth light receiving optical systems).

Light receiving elements 17a _{1 to} 17 in this embodiment
Reference numeral a ₄ is a position sensor that measures the position of incident light, and detects the image formation position of the slit image on the light receiving surface that is substantially conjugate with the surface to be inspected. The deviation of the slit image from the reference position on the light receiving surface is the reference plane of each of the detection positions a _{1 to} a ₄ (the exposure apparatus is not shown in the figure, but the projection objective for projecting the pattern image on the surface to be inspected. It corresponds to the deviation from the image plane of the lens).

[0022] Then, on the basis of the shift amount at each detection position a ₁ ~a ₄ which is detected as described above, the angle correction as a plane including the respective detection positions a ₁ ~a ₄ is parallel to the reference plane Then, the average surface of the partial area (exposure area) on the surface 3 to be inspected can be matched with the reference surface. Even if the exposure area is large, the average surface inclination of the exposure area can be detected by setting the detection points so that they are located substantially evenly within the exposure area by adjusting the position and angle of the optical system.

In the above embodiment, the reflected light from the _four detection positions a _{1 to} a _{4 is} converted into the four light receiving elements 17a ₁ to 1a.
7a ₄ is used to detect simultaneously, but it is not always necessary to detect the reflected light from all the detection positions at the same time, and in some cases, turning on / off the power of the light sources 11a ₁ and 11a ₂ or using a shutter or the like. The reflected light from each detection position may be detected in time series by using this.

Next, FIG. 3 is a perspective view showing a schematic structure of a position detecting device according to a second embodiment of the present invention. In this embodiment, position sensors 17a _{1 to} 17a are used as light receiving elements.
Instead of ₄ , light receiving elements 27a _{1 to} 27a ₄ made of photoelectric conversion elements such as a photoelectric microscope are used, and in combination with the oscillating mirror 24a, the optical axis direction from the reference plane (image plane of the objective lens) at each detection position is measured. It is configured to detect the amount of displacement. The configuration other than this is the same as that of the apparatus of FIGS.

In the figure, the projection light from the light sources 11a ₁ and 11a ₂ illuminates the light projecting slit 13, and the image of the slit 13 passes through the light-transmitting-side objective lens 15 and the half prism 16 on each surface 3 to be examined. An image is formed at the detection positions a _{1 to} a ₄ . The lights reflected at the detection positions a _{1 to} a ₄ are reflected by the vibrating mirror 24.
It is reflected by a and is re-imaged on the light receiving slit 20 by the light receiving side objective lens 15a. The light passing through the slit opening provided in the light receiving slit 20 is condensed by the condenser lens 21 and received by the light receiving elements 27a _{1 to} 27a ₄ , respectively. That is, by vibrating the vibrating mirror 24a, the image of the light-transmitting side slit 13 is scanned by the opening of the light-receiving side slit 20, and the opening of the slit 20 when the detection signals of the light-receiving elements 27a _{1 to} 27a ₄ become maximum. The displacement of the surface 3 to be detected from the reference surface is detected from the amount of displacement from the reference position. Of course, even without the condenser lens 21, the light receiving element 27a
It is possible to receive light at _{1 to} 27a ₄ .

The detection of the displacement of the detection position from the reference plane in this embodiment will be described more specifically below. Figure 3
When the detection position coincides with the reference plane (that is, the in-focus state), the center of the image of the light-transmitting side slit 13 and the opening center of the light-receiving side slit 20 coincide with each other. The amount of light emitted is maximum. When the oscillating mirror 24a is simply oscillated with a constant angular frequency and a constant amplitude in this state, the slit image reciprocates on the light-receiving side slit 20, and the light amount decreases as the center of the slit image moves away from the center of the slit opening. , When the center of the slit image and the slit aperture center again, the amount of light becomes maximum.

That is, the detection signals of the light receiving elements 27a _{1 to} 27a ₄ draw a sine curve having a half cycle of the vibration cycle of the vibrating mirror 24a. At this time, if the detection position deviates from the reference plane, the vibration center of the slit image is displaced from the center of the opening of the light-receiving side slit 20 accordingly, and the light receiving element 27
sine curve of a ₁ through 27a ₄ detection signal is lost, the deviation of the detection position is detected. The direction of displacement of the slit image with respect to the slit aperture corresponds to whether the detection position is above the reference plane (front pinned state) or below the reference plane (rear pinned state).

In this way, in this embodiment, the position of the projection objective lens (not shown) in the optical axis direction at each detection position on the surface 3 to be detected is detected. When performing the angle correction, move the substrate so that the sum of the deviation amounts at each detection position becomes the smallest, in other words, the matching area between the virtual plane including each detection position and the reference plane becomes maximum. Good. This makes it possible to match the average surface of a wide area having irregularities with the image plane of the projection objective lens, and to minimize the area of defocus.

Although the polarization is not particularly limited in the above-mentioned first and second embodiments, a polarizing member may be used as the dividing means in the present invention. At this time, the means for controlling the polarization state is not limited to the wave plate, and a Faraday element that controls the magnetic field to rotate and adjust the polarization plane or another optical element having an optical rotatory property may be used.

The present invention is not limited to the above-described embodiments, but can be modified in various ways without departing from the scope of the present invention, and the device can be incorporated therein, depending on the space. It is the one that is selected. For example, the light from one light source may be divided into three or more. Further, it goes without saying that the position detecting device of the present invention can be applied not only to an exposure device for manufacturing a semiconductor integrated circuit, but also to a microscope or the like.

[0031]

As described above, according to the present invention, with respect to the partial area of the surface to be inspected, which is arranged substantially on the image plane of the objective optical system,
The position of the objective optical system in the optical axis direction and the inclination with respect to the optical axis can be easily detected without contact. In the present invention,
The projection optical system is also used for different detection positions,
Simultaneous multi-point detection is realized by detecting the reflected light from each detection position with a dedicated light receiving optical system, so the configuration is simple and it can be compactly arranged in a limited space. Is easy to adjust. With the use of the device of the present invention, even if the target partial region is wide and the surface has irregularities, the average plane of the partial region can be set to be perpendicular to the optical axis of the objective optical system. The best image can be obtained over the entire partial area even if the allowable focus range of the objective optical system is very narrow.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an optical system of a position detecting device according to a first embodiment of the present invention.

2 is a plan view of an optical system of the apparatus of FIG.

FIG. 3 is a perspective view showing a schematic configuration of an optical system of a position detecting device according to a second embodiment of the present invention.

FIG. 4 is a schematic optical path diagram for explaining a conventional device.

FIG. 5 is a schematic optical path diagram for explaining a conventional device.

FIG. 6 is a schematic optical path diagram for explaining a conventional device.

[Explanation of symbols]

1 projection objective 1a projection optical axis 2 mask 3 test surface 11a ₁ of the objective lens 1, 11a ₂ the light source 12 a condenser lens 13 light projecting slit 14 mirror 14a mirrors _{17a 1 ~17a 4, 27a 1 ~27a} 4 light receiving element 15, 15a the objective lens 16 half prism 20 receiving slit 21 a condenser lens 24a oscillating mirror a ₁ ~a ₄ detection position

Claims (1)

[Claims] 1. A projection optical system for projecting light from a direction having an inclination with respect to an optical axis of the objective optical system to a predetermined detection position on a surface to be inspected arranged on a substantially image forming plane of the objective optical system. And a light receiving optical system that has a light receiving surface that is substantially in a conjugate relationship with the surface to be inspected and that receives reflected light from the surface to be inspected, and the object to be detected based on a signal from the light receiving optical system. A position detecting device for detecting a position of an inspection surface in an optical axis direction of the objective optical system and an inclination with respect to the optical axis, wherein first and second projections of the light are performed at different detection positions on the inspection surface. The projection optical system and the optical paths of the projection light from the first and second projection optical systems are respectively divided so that the projection light from the first projection optical system is located at the first and second detection positions and at the first detection position. Splitting means for guiding the projection light from the two projection optical systems to the third and fourth detection positions, respectively, and the surface to be inspected. The first, second, third and fourth detection positions are independently received, and the first, second, third and fourth light receiving optical systems are provided. Detection device.