JPH11264800A - Inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct simply a dislocation of the image forming position on a photographing means generated at each selected wavelength without moving an image forming optical system or the photographing means. SOLUTION: An inspecting device is composed of a light source 1 to emit illumination light, an illumination optical system 2 to illuminate an object to be observed 3 using the illumination light, an image forming optical system 4 to form an image of the object 3 upon condensing the beams of light from the object 3 illuminated, a photographing means 5 to photograph the image of the object 3, a wavelength selecting means 8 which can be installed in the optical path leading from the light source 1 to the photographing means 5 and selects any desired wavelength among the wavelengths of the illumination light, and an image forming position correcting means 9 whereby the position of the image shifting according to the selected wavelength is image formed on the photographing surface of the photographing means 5. This device does not require moving the image forming optical system or photographing means which should lead to a complication in structure, and it is possible to correct simply the dislocation of the image forming position on the photographing means generated at each selected wavelength any arbitrary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for obtaining information on the shape, dimensions, defects, and the like of an observed object by capturing an image of the observed object illuminated at an arbitrary wavelength.

[0002]

2. Description of the Related Art Conventionally, in order to measure information on defects such as scratches on the surface of an object to be observed such as a wafer, dust, unevenness in film thickness, and measurement of minute dimensions, an image of the object to be observed is illuminated. Inspection has been carried out by taking in the image and further performing image processing and the like. Further, if information from the object to be observed can be selected and observed at an arbitrary wavelength at that time, more information on the object to be observed can be obtained. In particular, when inspecting the film thickness unevenness of the resist applied on the wafer, the wavelength that is easy to observe may change depending on the state of the thickness of the coated resist film. Also, the diffraction angle of the diffracted light from the pattern formed on the wafer changes depending on the pitch and wavelength of the pattern. As described above, information obtained from an observation object changes depending on a difference in wavelength.

[0003]

Normally, an image pickup means such as a CCD is arranged at the image forming position of the observation object. However, the position of the image of the observation object formed by the image forming optical system differs depending on the wavelength. It changes due to the influence of chromatic aberration on the optical axis, which causes an inconvenience that an image is formed on a CCD at a certain wavelength but shifted to a different position from that on the CCD at another wavelength.

In order to solve this inconvenience, it is considered that the position of the imaging lens is moved along the optical axis in accordance with each wavelength so that the imaging position of the observation object is adjusted on the CCD as the imaging means. Can be However, if the diameter or the total length of the moving imaging lens is large, the moving means of the imaging lens becomes large, which is not preferable. In some cases, the lens moving means may not physically enter.

[0005] It is conceivable to move the CCD itself, which is the image pickup means, along the optical axis. However, even in this case, the moving means becomes large, which is not preferable. Accordingly, it is an object of the present invention to easily correct a shift of an image forming position on an image pickup unit which occurs at each selected wavelength without moving an image forming optical system or an image pickup unit.

[0006]

In order to achieve the above object, the present invention provides a light source for emitting illumination light, an illumination optical system for illuminating an object to be observed based on the illumination light, and an illuminated optical system. An imaging optical system that condenses light from the observed object to form an image of the observed object; an imaging unit configured to capture an image of the observed object; and a light source and the imaging unit. Wavelength selecting means for selecting an arbitrary wavelength from the wavelength of the illumination light that can be arranged in the optical path between, and the position of the image to be imaged at a different position depending on the selected wavelength,
An image forming position correcting means for forming an image on an image pickup surface of the image pickup means.

Here, according to an embodiment, the wavelength selecting means is arranged on the light source side of the object to be observed. According to another aspect, the wavelength selection means is arranged on the imaging means side of the observed object. Further, it is preferable that the imaging position correcting means has an optical member which is provided between the object to be observed and the imaging means so as to be insertable and removable.

According to a preferred aspect of the present invention, the wavelength selecting means and the imaging position correcting means are integrally formed. In this preferred aspect, the wavelength selection unit and the imaging position correction unit are configured to determine a first member having a first wavelength selection characteristic and a first center thickness, and a second member having a second wavelength selection characteristic and a second center thickness. A second member having at least the first center thickness, the first center thickness is set to a thickness that allows an image formation position by the light of the first wavelength to coincide with the imaging surface; It is further preferable that the center thickness is set to a thickness that allows an image forming position by the light of the second wavelength to coincide with the imaging surface.

Preferably, the imaging position correcting means comprises an optical member having a predetermined center thickness, and the center thickness of the optical member represents an imaging position at a wavelength selected by the wavelength selecting means. It is preferable that the thickness be set to a value that can be matched on the imaging surface. Further, it is preferable that the imaging position correcting means is formed of a plane parallel plate.

Further, it is preferable that the wavelength selecting means comprises an interference filter. Further, it is preferable that at least the observation object side of the imaging optical system is configured to be telecentric. Preferably, the inspection apparatus further includes an image output unit for observing an image obtained from the imaging unit.

It is preferable that the inspection apparatus automatically detects a defect of the observed object by performing image processing on an image obtained from the imaging unit. Further, it is preferable that the object to be observed is a substrate, and that unevenness in the thickness of a resist applied to the substrate can be observed. Preferably, the object to be observed is a substrate, and an image based on at least one of diffracted light and scattered light from the substrate can be observed.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a first embodiment according to the present invention. In FIG.
The light beam from the light source 1 is selected to have an arbitrary wavelength by passing through a wavelength selection unit 8 composed of, for example, an interference filter, and is radiated to the observation target object 3 via the illumination optical system 2.
The position of the light source 1 or the light source image substantially coincides with the front focal position of the illumination optical system 2, and the object to be observed is almost uniformly illuminated under Koehler illumination.

In the example of FIG. 1, in order to receive the diffracted light and the scattered light from the observed object 3 illuminated by the illumination optical system 2, the optical axis tilted with respect to the optical axis of the illumination optical system 2 is used. The imaging optical system 4 is provided. This imaging optical system 4
Forms an image of the observed object 3 on an imaging surface (a light receiving surface of the CCD) of the imaging means 5 composed of, for example, a CCD, based on the diffracted light / scattered light from the observed object 3. It is preferable that at least the observation object side of the imaging optical system 4 is configured to be telecentric.

FIG. 2 is a diagram showing an example of the wavelength selection means 8. In FIG. 2, interference filters 8a, 8b,...
Is arranged. Here, by rotating the turret-shaped component 12, an arbitrary wavelength can be selected, and the object to be observed 3 can be illuminated under an arbitrary wavelength. In this embodiment, the wavelength selection characteristics of the filters 8a, 8b,...
Each wavelength width is ± 5 nm with respect to the center wavelength. However, the wavelength selection characteristics are not limited to those described above.
Any center wavelength and wavelength width can be set. Further, the wavelength selecting means is not limited to the interference filter, and any device can be used as long as light in a predetermined wavelength range can be selected.

If the wavelengths selected by the wavelength selection means 8 are different, an image of the observed object 3 may be formed at a position off the imaging surface of the imaging means. Hereinafter, description will be made with reference to FIGS. FIG. 3 is a diagram illustrating chromatic aberration on the optical axis generated by a lens having a positive refractive power.
In general, the refractive index of optical glass increases as the wavelength decreases. Therefore, as shown in FIG. 3, the focal length of a lens having a positive refractive power is shorter for a lens having the same wavelength (λ2) than for a longer wavelength (λ1), even if the lens has the same wavelength. Aberrations generated from this characteristic include axial chromatic aberration. This can be corrected by using a plurality of lens members so that the focal position is almost the same within a certain range of wavelengths. It becomes difficult to correct the displacement.

FIG. 4 is a view showing a state in which an image forming position is moved by an optical member having a predetermined thickness. The amount by which the paraxial image point moves on the optical axis when a light ray passes through an optical member having no refractive power in air, for example, a parallel plane plate, can be obtained by the following equation (1).

[0017]

ΔX = d (1-1 / n) (1) where ΔX: the amount of movement of the paraxial image point on the optical axis d: the thickness of the optical member on the optical axis n: the optical member Is the refractive index.

By calculating the axial chromatic aberration due to the wavelength as ΔX according to the above equation (1), the center thickness of the optical member serving as the image position correcting means can be obtained. As shown in FIG.
In the present embodiment, a plurality of parallel plane plates (a plurality of imaging position correcting means) having a center thickness determined by the above equation (1)
Is arranged on the turret-shaped part 13. As a result, an arbitrary image position correcting means 9 can be selected. At this time, it is preferable that the switching between the wavelength selecting means 8 and the image forming position correcting means 9 be operated in conjunction with each other so that the image forming position correcting means 9 corresponding to the selected wavelength is selected.

In the above example, parallel plane plates having different center thicknesses are used as the imaging position correcting means, but parallel plane plates having different refractive indices may be used instead. A lens having a thickness and a curvature may be applied. It is needless to say that the number of optical members arranged in FIGS. 2 and 5 is determined as needed. With this configuration, even when the object to be observed 3 is illuminated with an arbitrary wavelength selected by the wavelength selection unit 8, the imaging surface of the imaging unit 5 is always substantially unaffected by the chromatic aberration of the imaging optical system 4. An image of the observed object 3 can be formed thereon.

Returning to FIG. 1, the imaging means 5 outputs a signal to the image processing means 6 based on the image formed thereon,
The image processing means 6 causes the image output means (monitor) to display an image of the observed object based on the output signal from the imaging means 5. Based on this image, it is possible to observe the unevenness of the film thickness of the resist applied on the substrate, which is the object 3 to be observed, and to observe an image due to diffracted light or scattered light from this substrate.

Next, a second embodiment will be described with reference to FIG. The inspection apparatus shown in FIG. 6 captures an image of the observed object based on the directly reflected light from the observed object 3. In FIG. 6, members having the same functions as those in the example shown in FIG. 1 are denoted by the same reference numerals.
In FIG. 6, a light beam from a light source 1 is selected to an arbitrary wavelength by a wavelength selection unit 8, and is radiated to an observed object 3 via an illumination optical system including optical members 2 and 10. Then, the observed object 3 is input to the imaging unit 5 by the imaging optical system including the optical members 10 and 4. In the present embodiment, the half mirror 1 is placed in the optical path between the optical member 2 and the optical member 10 (in the optical path between the optical member 10 and the optical member 4).
The optical member 10 is shared by the illumination optical system and the imaging optical system. The optical member 2 in the illumination optical system forms an image of the light source 1 in the vicinity of the front focal position of the optical member 10. Thereby, the observed object 3 is Koehler-illuminated.

In this embodiment, an image position correcting means 9 is provided between the image forming optical systems 4 and 10 and the image pickup means 5. In the present embodiment, the configurations and operations of the wavelength selection unit 8 and the imaging position correction unit 9 are the same as those in the above-described example of FIG.
Also in the present embodiment, even when the object 3 to be observed is illuminated with an arbitrary wavelength selected by the wavelength selection unit 8, the imaging unit 5 is always substantially unaffected by the chromatic aberration of the imaging optical system 4. An image of the observed object 3 can be formed on the imaging surface. It should be noted that the output from the imaging means 5 is
Is output by the image output means (monitor) 7 through

In the above example, the image forming position correcting means 9 is used.
Is arranged between the imaging optical system and the imaging means, but may be arranged in the optical path between the imaging optical system and the surface to be observed instead. May be arranged in an optical path that does not become a parallel light beam. By the way, in the above-described example, the wavelength selecting unit 8 and the imaging position correcting unit 9 are separately provided, but these may be provided on one optical member.

FIG. 7 is a diagram showing a third embodiment in which one optical member 11 has the functions of the wavelength selecting means and the imaging position correcting means. Note that, in FIG. 7, members that perform the same functions as in FIG. 1 are denoted by the same reference numerals. The optical member 11 is composed of a turret-shaped component as shown in FIG. 2 or 5 provided with a plurality of optical members having different center thicknesses. Each of the plurality of optical members has a predetermined transmittance. A thin film having characteristics is provided.
That is, in the example of FIG. 7, a plurality of interference filters having different center thicknesses respectively function as a wavelength selection member and an imaging position correction member. Note that the center thickness of these interference filters is set to a thickness such that the imaging position of the observed object 3 under an arbitrary wavelength selected by the interference filters is located on the imaging surface of the imaging unit 5. .

In the fourth embodiment shown in FIG. 8, in the inspection apparatus shown in FIG. 6, the functions of the wavelength selecting means and the imaging position correcting means are provided in one optical member 11. The functions and operations of the optical member 11 are the same as those in the third embodiment, and thus the description thereof is omitted here. When an interference filter is used as the wavelength selection means as in each of the above embodiments, it is preferable to configure the interference filter as in the example of FIG.

FIG. 9 is a diagram showing a method of selecting a specific wavelength when an interference filter is used as a wavelength selecting means for selecting an arbitrary wavelength. In FIG. 9, the horizontal axis represents the wavelength λ, and the vertical axis represents the transmittance T of the filter. FIG. 9A is a diagram showing the transmittance characteristics of the interference filter A. As is clear from FIG. 9A, when a light beam having many wavelength components passes through the interference filter A, a different wavelength other than the specific wavelength to be selected is selected. Components may also be transmitted.

FIG. 9B is a diagram showing the transmittance characteristics of the second interference filter B. This second interference filter B
It has a characteristic of cutting unnecessary wavelength components and has a characteristic of transmitting necessary wavelength components, though having a wider wavelength width than the interference filter A. As a result, as shown in FIG. 9C, any desired wavelength can be selected. When two filters are used as described above, one filter is disposed in the wavelength selection means of the present invention, the other filter is disposed at the position of the image position correction means, and the image position correction means is provided. It is sufficient to have a center thickness according to each wavelength selected to fulfill the role of.

[0028]

As described above, according to the present invention, without moving the imaging optical system or the image pickup means having a complicated structure,
It is possible to easily correct the shift of the imaging position on the imaging means, which occurs for each selected wavelength. Furthermore, by providing the optical member used in the wavelength selecting means with the function of the image position correcting means, the number of moving parts can be reduced and the number of parts can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an inspection device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a wavelength selection unit.

FIG. 3 is a diagram showing axial chromatic aberration caused by a lens.

FIG. 4 is a diagram showing a state in which an imaging position is moved by an optical member.

FIG. 5 is a diagram illustrating an example of an imaging position correcting unit.

FIG. 6 is a diagram showing an inspection device according to a second embodiment of the present invention.

FIG. 7 is a diagram showing an inspection device according to a third embodiment of the present invention.

FIG. 8 is a diagram showing an inspection device according to a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a wavelength selection method performed when a specific wavelength component is selected.

[Explanation of symbols]

 1: light source 2 (10): illumination optical system 3: observed object 4 (10): imaging optical system 5: imaging means

Claims (7)

[Claims] A light source that emits illumination light; an illumination optical system for illuminating an object to be observed based on the illumination light; and a light source that collects light from the illuminated object to be observed. An imaging optical system that forms an image of the object, imaging means for capturing an image of the object to be observed, and a light source that can be arranged in an optical path between the light source and the imaging means, Wavelength selecting means for selecting an arbitrary wavelength, and an image position correcting means for forming a position of the image to be formed at a different position by the selected wavelength on an imaging surface of the imaging means. An inspection device, comprising: 2. An inspection apparatus according to claim 1, wherein said wavelength selecting means is arranged on said light source side of said object to be observed. 3. The inspection apparatus according to claim 1, wherein said wavelength selection means is arranged on said imaging means side of said object to be observed. 4. The image forming apparatus according to claim 1, wherein said image forming position correcting means has an optical member which is inserted and removed between said object to be observed and said image pickup means. Inspection equipment. 5. An inspection apparatus according to claim 3, wherein said wavelength selecting means and said imaging position correcting means are integrally formed. 6. The wavelength selection means and the imaging position correction means, wherein a first member having a first wavelength selection characteristic and a first center thickness and a second member having a second wavelength selection characteristic and a second center thickness are determined. The first center thickness is set to a thickness that allows an image formation position by light of the first wavelength to coincide with the imaging surface; The inspection apparatus according to claim 5, wherein the center thickness is set to a thickness that allows an image formation position by the light of the second wavelength to coincide with the imaging surface. 7. The imaging position correcting means comprises an optical member having a predetermined center thickness, wherein the center thickness of the optical member indicates an imaging position at a wavelength selected by the wavelength selecting means, and The inspection apparatus according to claim 1, 2, 3, 4, or 5, wherein the thickness is set to a thickness that can be matched with the above.