JPH04336415A - Color aberration double focus device - Google Patents

Abstract

PURPOSE:To lighten the manufacturing cost of a pattern barrier filter by using a filter for illumination having the function of the pattern barrier filter, using the filter for illumination which takes out only lights of two wavelengths of an illumination system. CONSTITUTION:An illumination system makes an illumination light of wavelength alpha and an illumination light of wavelength beta from the luminous fluxes emitted out of two light source 1 and 2 through a filter 3 for illumination and a filter 4 for illumination. The luminous fluxes of wavelengths alpha and beta are put together with a dichroic mirror 5 through collimator lenses 18 and 19, and it is let fall to irradiate an X-ray mask face 8 and a wafer face 9, respectively, through a half mirror 6 and an objective 7. The images of a mask mark 14 and wafer mask 15 are formed in the same position by an color aberration objective 7 on the axis. These image are picked up with a CCD camera 13 through a pattern barrier filter 12. Thereby, the manufacturing cost of the pattern barrier filter an be lightened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a bifocal device that utilizes axial chromatic aberration to detect the relative position of a first object and a second object separated by a minute distance.

0002

[Prior Art] The inventor of the present invention filed a patent application for a device for detecting the relative position of an X-ray mask and a wafer in close exposure as a “device for detecting the position of two objects separated by a minute distance.”
We have applied for No. 4 and are already implementing it. This prior art will be briefly explained below.

FIG. 11 is a diagram showing the image formation state in the paraxial region of the objective lens. It is assumed that a wafer W is placed at the position. Here, if the amount of axial chromatic aberration of the objective lens L for light of two different wavelengths α and β is equal to the gap δ between the X-ray mask M and the wafer W, then points B and C on the optical axis O Images of the wafer W and the X-ray mask M are generated at points C and D, respectively. Here, at the central point C, an image of the X-ray mask M by light of wavelength α and an image of wafer W by light of wavelength β are formed at the same time, and two object points and one image are formed on the same optical axis O. An optical system with an imaging point is realized.

On the other hand, the light beams formed at points B and D on the optical axis O are superimposed on the image formed at point C, reducing the resolution of the image formed at point C. Also, at point C on the optical axis O, the wavelength α
, β are formed on the same plane, so the image contrast decreases due to interference. Therefore, in order to remove the light beams that are focused on points B and D,
A pattern barrier filter 20, which combines a filter a that transmits only light of wavelength α at the center and a filter b that transmits only light of wavelength β on both sides, as shown in FIG. 2, is installed in front to form an image at point C. This is to remove unnecessary light flux.

[0005]

Table 1 shows the specifications of the longitudinal chromatic aberration bifocal device based on the above principle.

[0006]

[Table 1]

FIG. 13 shows an optical path diagram of this longitudinal chromatic aberration bifocal device. Wafer mark 1 consisting of an X-ray mask 8 having a tantalum (Ta) mask mark 14 and a step mark
The wafers 9 having the wafers 5 and 5 are placed horizontally on their respective stages in parallel with a minute interval δ. The objective lens 7 of the bifocal detection device having axial chromatic aberration has the above-mentioned wavelength α.
This lens system is designed so that the light of wavelength β and the light of wavelength β have an axial chromatic aberration equal to the minute distance δ between the X-ray mask 8 and the wafer 9. Therefore, for example, the illumination filter 1 collimates the luminous flux emitted from the light source 17 of an ultra-high pressure mercury lamp.
Wavelength α [α=546 nm (e-line)] by 6a and 16b
, the illumination light of wavelength β [β=573 nm (d-line)] is taken out and introduced into the detection optical system via the half mirror 6, and is passed through the axial chromatic aberration objective lens 7 to the mask mark 14 on the X-ray mask 8 and The wafer marks 15 on the wafer 9 are each illuminated.

The mask mark 14 of the X-ray mask 8 illuminated by the illumination light of wavelength α and the wafer mark 15 of the wafer 9 illuminated by the illumination light of wavelength β are imaged at the same position by the axial chromatic aberration objective lens 7. Form an image. A pattern barrier filter 20 shown in FIG. 12 is arranged near this, and this image is formed on the imaging plane of the CCD camera 13 by the relay lens 11.

The patterned barrier filter 20 is a filter whose central region a transmits only light of wavelength α,
Areas b on both sides are formed by bonding filters that transmit only light of wavelength β at interface c, and the image of mask mark 14 is formed in area a in the center, and the image of wafer mark 15 is formed in area b. By transmitting each, unnecessary light that can cause blurring is removed.

Next, the outer diameter dimensions and spectral characteristics of such a patterned barrier filter 20 are shown in FIGS. 14 and 15. In addition, the actual pattern barrier filter 2
0 is shown in an enlarged perspective view in FIG. The specifications required for the interference filter that constitutes this patterned barrier filter are that the half width for both e-line and d-line is 1.2 nm, and a
Strict conditions are imposed, such as an overlap margin of 0.1 nm or less at the boundary between the region and the b region. In order to satisfy these requirements, the final product could not be created without adopting a complicated configuration in which five sheets of interference filters and anti-reflection films 21 to 25 were stacked on top of each other, as shown in the perspective view of FIG. It's gone. As shown in FIG. 15, its spectral characteristics had a half-width of 2.2 nm, which required a very high level filter for an interference filter that could clearly cut short and long wavelengths.

Next, the reason for this will be explained in more detail. As described above, by using two single-wavelength lights, the wavelength of the light is selected for observing the X-ray mask 8 and the wafer 9, which are separated by a minute distance, only by the pattern barrier filter 20 placed near the image point thereof. Although there is no problem in principle, it has become clear that there are extremely severe technical difficulties and cost difficulties in manufacturing patterned barrier filters. That is, let us consider a case in which the X-ray mask 8 is illuminated with monochromatic light (e-ray) and the wafer 9 is illuminated with band light (630 nm to 750 nm) in the chromatic aberration bifocal device as described above. Note that the reason why band light is used for this wafer 9 is that, as shown in Japanese Patent Laid-Open No. 2-816, a resist film, a transparent film, etc. are formed on the wafer, and standing waves are generated due to light interference caused by this. This is because the reflection intensity of the alignment mark on the wafer changes sinusoidally as a result of this effect, and the relative intensity of the signal light for detecting the mark varies greatly.

FIG. 2 shows the spectral transmission characteristics of the wafer imaging area (area b) of a patterned barrier filter that satisfies the above specifications.
Figure 2 shows the spectral transmission characteristics of the mask imaging area (area a).
Shown in 3.

Assume that an ultra-high pressure mercury lamp having high luminance in the e-line is used as a light source for monochromatic light, and a halogen lamp with extremely low coherence is used as a light source for band light. The relative spectral characteristics of these light sources are as shown in FIGS. 24 and 25. It can be seen that both light sources emit light in a wide visible range.

Next, in the chromatic aberration bifocal device shown in FIG. 13, it is assumed that a highly responsive line sensor is used as the light receiving element of the CCD camera 13. As shown in FIG. 26, the spectral sensitivity characteristics of this line sensor have a wide sensitivity characteristic over a short wavelength region of 200 nm or less to a long wavelength region of 1100 nm.

From FIGS. 24 and 25, it can be seen that the line sensor for receiving the image formed by the light beam having a wide wavelength range transmitted through the patterned barrier filter 20 has wide spectral sensitivity characteristics, so the pattern of the chromatic aberration bifocal device is The starting point wavelength λ1 and ending point wavelength λ2 in the spectral transmission characteristics required for the barrier filter 20 are λ1 = 200 nm (2
Light of 00 nm or less is absorbed by the lens. ), and λ2 = 1100 nm (the line sensor has no sensitivity above 1100 nm). From this, it can be seen that the pattern barrier filter 20 must be an interference filter that takes into consideration transmission characteristics in a wide wavelength range.

Next, the interference filter will be explained. Generally, an interference filter is formed by coating a glass substrate with a multilayer film so that only light of a required wavelength is transmitted by utilizing the phenomenon of light interference in a thin film. There are three main factors that determine the degree of difficulty in designing and manufacturing this thin film: (1) full width at half maximum of the transmitted light beam, (2) target wavelength range, and (3) transmittance.

The narrower the full width at half maximum in (1) above, the more layers are required, the wider the wavelength range in (2), the more layers are needed, and the transmittance in (3) decreases as the number of layers increases. This will result in Along with these three items, (
4) Reproducibility of optical properties, (5) Changes in thin film properties over time, (
6) Quality deterioration, (7) Processability, (8) Handleability, (9
) manufacturing cost, (10) optical performance, etc. are added.

Now, for example, if the central part (X-ray mask imaging area) of the pattern barrier filter 20 of the chromatic aberration dual focus detection device shown in FIG. 13 is designed as a thin film, the transmittance is 546 nm±5 nm. (Full width at half maximum = 10
Even if only the thickness (nm) is taken into consideration, a super multilayer film of 60 or more layers is generally required.

Furthermore, if this is done alone, a so-called ripple region q will occur, as shown in FIG. 27, in which light passes through a region where it is not desired to pass light due to the thin film design. In order to eliminate this ripple component q, the number of films must be further increased. This increase in the number of membranes further lowers the transmittance, and the conditions (1) to (10) described above deteriorate.

Therefore, in general, the spectral transmission characteristics of the central portion of a patterned barrier filter are at least as narrow as the full width at half maximum of around 10 nm, as shown in FIG. This can be achieved by bonding two or more interference filters together. This also applies to the wafer imaging areas on both sides of the patterned barrier filter. The spectral characteristics of this band light are shown in FIG.

Specifically, the patterned barrier filter prototyped by the inventor of the present invention has a five-layer structure as shown in FIG. That is, 21 and 22 are short wavelength component cut filters, 23 and 24 are transmission filters for a light beam of 546 nm±5 nm, and 25 is a long wavelength component cut filter.

Problems with the performance characteristics of such filters are the above (5) change in thin film characteristics over time, (6) processability, (7) quality deterioration, (8) ease of handling, and (9) manufacturing. It covers six items: cost and (10) optical performance.

From the above explanation, it can be seen that it is extremely difficult to achieve the function of a pattern barrier filter only with a pattern barrier filter in a chromatic aberration bifocal device due to the current manufacturing technology of pattern barrier filters. .

[0024] Therefore, in order to reduce the technical burden on manufacturing this patterned barrier filter and make it a practical technology, the inventor of the present invention believes that it is best to have a lighting filter share a part of the function of the patterned barrier filter. We found it to be a simple and practical means.

Next, the pattern of the mask mark and wafer mark imaged on the image receiving surface of the CCD camera 13 by the detection optical system configured as described above will be explained. In this case, an example will be explained in which the d-line shown in Table 1 is used instead of the band light.

As schematically shown in FIG.
The area is an e-ray imaging area, and an image 14' of the mask mark 14 of the vertical X-ray mask 8 is imaged in the center of this area. An image c' of a boundary surface c, which is a filter bonding surface of the patterned barrier filter 20, is formed on both sides of this. Then, there are regions b, which are d-line imaging regions, on both outer sides, and images 15' of wafer marks 15 on the wafer 9 are formed in the centers of these regions.

[0027] When the focus center of the monitor formed on the image-receiving surface of the CCD camera 13 is used in this manner, the overall view is obtained when focusing on the X-ray mask imaging area, which is the central part of the pattern barrier filter. (
Fig. 18 shows a line diagram of the photo). The magnification at this time is 140 times. FIG. 19 is a diagram showing an enlarged close-up photograph of this center image formation. In addition, FIG. 20 is a line diagram showing the panoramic view (photograph) when observation was performed by moving the focus of the monitor by 51 μm in the optical axis direction to correspond to the wafer mark of the pattern barrier filter.
FIG. 21 shows a line diagram of a close-up photograph of this side image formation enlarged.

The following is clear from these FIGS. 18 to 21.

(1) The proportion of the area occupied by the image c' of the boundary surface c of the patterned barrier filter 20 is relatively large.

(2) Within the pattern barrier filter 20, the imaging light beams of e-line and d-line cause multiple reflection interference,
This causes a speckle pattern.

(3) The imaging light beam is diffused within the patterned barrier filter 20, resulting in a decrease in both resolution and contrast.

The reasons for (1), (2), and (3) above are that the pattern barrier filter 20 is constructed by stacking five filters as shown in FIG.
This is due to the large number of sheets to be bonded together, which increases the bonding allowance for the filter. Furthermore, more adhesive is used on the bonding surface of the patterned barrier filter 20, which is formed by bonding five interference filters, which causes problems. Moreover, the flatness and surface roughness of each interference filter will be affected by the large number of interference filters, and these must be created with sufficient precision. Another possible cause is that the anti-reflection coating for e-line and d-line was insufficient.

As described above, the quality of the pattern barrier filter is an important point that greatly affects the resolution and contrast of this axial chromatic aberration bifocal device, and the specifications required for its production are extremely strict. .

The present invention has been made in view of the above points, and an object of the present invention is to provide an improved longitudinal chromatic aberration bifocal device that can significantly reduce the burden of manufacturing pattern barrier filters.

[0035]

[Means for Solving the Problems] The present invention provides an optical device using a lens system having axial chromatic aberration for simultaneously observing a first object and a second object separated by a minute distance in the optical axis direction. A pattern barrier filter consisting of a color filter is arranged in the detection optical system, and a first and second illumination filter that transmits light of different wavelengths is arranged in the detection optical system.
The blurring of longitudinal chromatic aberration on the imaging plane based on the image of the second object due to the light of the wavelength and the blurring of the longitudinal chromatic aberration on the imaging plane based on the first object image due to the light of the second wavelength This is an axial chromatic aberration bifocal device that is characterized in that each of these aberrations is efficiently removed.

[0036]

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is an optical path diagram showing the configuration of an axial chromatic aberration bifocal device. The illumination system passes the light beams emitted from two light sources 1 and 2 through an illumination filter 3 and an illumination filter 4, respectively, to a wavelength α [α=436 nm (g-line)].
Illumination light and wavelength β [β = 540 to 650 nm (band light)
] and collimate lens 1.
The X-ray mask surface 8 and the wafer surface 9 are epi-illuminated through the dichroic mirror 5 and the half mirror 6 and the objective lens 7 through the beams 8 and 19, respectively.

Mask mark 14 on X-ray mask 8 illuminated with light of wavelength α and wafer 9 illuminated with light of wavelength β
The upper wafer mark 15 is imaged at the same position 10 by the axial chromatic aberration objective lens 7. This image is relay lens 11
and the CCD after passing through the pattern barrier filter 12.
An image is formed on the image receiving surface of the camera 13 and converted into an electrical signal.

In this example, illumination filters 3 and 4
By combining the pattern barrier filter 12 with the pattern barrier filter 12, it is possible to block the light flux that is focused on points B and D that prevents the image formation of point C at the same position in FIG. 11 described above. That is, the illumination color filters 3 and 4 select two light fluxes of wavelengths α and β that are incident on the detection optical system.

The characteristics of the pattern barrier filter 12 are as follows:
Assuming a wavelength γ such that α<γ<β for two light fluxes of wavelengths α and β, the filters in the region b on both sides in FIG. The filter is a color filter that transmits light having a wavelength of γ or less. As shown in FIG. 6, these two types of color filters constitute one pattern barrier filter 12 by bonding three filters b, a, and b together at a boundary c.

FIG. 7 shows the spectral wavelength characteristics of the patterned barrier filter 12 formed in this manner. This is because the filters in areas a and b that make up the pattern barrier filter 12 are color filters with the most common spectral characteristics, and instead of being constructed by overlapping multiple interference filters as in the past, they are made up of one filter each. It is possible to create it without any problem using the filter.

Next, referring back to FIG. 1 and based on the above, it will be explained in detail how the mask mark and the wafer mark are each illuminated by two light beams of different wavelengths and are imaged well. The light beam emitted from the light source 1 is collimated, and only the light of wavelength α is transmitted and selected by the illumination filter 3. The light is then collimated by the collimating lens 18, transmitted through the dichroic mirror 5, and taken into the detection optical system by the half mirror 6. On the other hand, the light beam emitted from the light source 2 passes through the illumination filter 4, so that only the light of wavelength β is transmitted and selected, collimated by the collimating lens 19, and reflected by the dichroic mirror 5 to be the light of the wavelength α. It is incorporated into the detection optical system by the combined half mirror 6.

These two beams of wavelength α and β are focused by the axial chromatic aberration objective lens 7 at a point separated by the axial chromatic aberration. That is, in FIG. 1, the illumination light with wavelength α is focused on the X-ray mask surface 8, and the illumination light with wavelength β is focused on the wafer surface 9.

These X-ray mask surface 8 and wafer surface 9
The distance δ between them is set to, for example, 40 μm, assuming the positional state of the X-ray mask and wafer in close exposure.

FIG. 2 shows mask marks 14 on the X-ray mask 8.
An enlarged view is shown. This is formed by providing, for example, tantalum (Ta) in a straight line on an X-ray mask 8 consisting of a self-supporting film (emblem).

FIG. 3 shows an enlarged view of the wafer mark 15 on the wafer 9. This is formed by forming two vertically parallel step marks on the wafer 9.

Wavelength α is applied to the X-ray mask surface 8 and wafer surface 9.
, β are respectively focused and illuminated by the axial chromatic aberration objective lens 7, images of the mask mark 14 and the wafer mark 15 are formed by the axial chromatic aberration objective lens 7 so as to overlap at the same position 10. . This image is multiplied by an intermediate magnification by a relay lens 11, unnecessary light is blocked by a pattern barrier filter 12, and then formed on an image receiving surface of a CCD camera 13.

FIG. 4 is a front view showing the structure of the pattern barrier filter 12. That is, the central region a is a color filter that transmits light including the light of wavelength α that is transmitted through the mask mark 14 of the X-ray mask 8, and the b regions on both sides of the boundary surface c are wafer marks on the wafer 9. This is a color filter that transmits light including light with a wavelength β that transmits light. These are pasted together at the boundary surface c to form a single sheet.

FIG. 5 shows the state of the pattern imaged on the image receiving surface of the CCD camera 13. An image c' of the boundary c of the pattern barrier filter 12 is formed on both sides of the image 14' of the central mask mark 14, and an image 15' of the wafer mark 15 is formed in parallel on both sides thereof. The image 14' is formed by the light of the wavelength α of the mask mark 14, and the image 15
' is an image of the wafer mark 15 formed by light of wavelength β.

Next, Table 2 shows the specifications of the axial chromatic aberration bifocal device that was actually manufactured.

[0050]

[Table 2]

FIG. 9 shows the appearance of an axial chromatic aberration bifocal device having this specification. That is, the two light beams selected by the illumination filter are guided by an optical fiber and enter the fiber illumination section 26. This light flux illuminates two object points, namely the mask mark 14 of the X-ray mask 8 and the wafer mark 15 on the wafer 9, respectively, by the axial chromatic aberration objective lens 7, and these marks are illuminated by the axial chromatic aberration objective lens 7.
The image is formed on the image receiving surface of the CCD camera 13.

FIG. 8 shows actual measured values of the spectral characteristics of the patterned barrier filter 12 that was actually used. Both areas a and b are formed of a single color filter having these characteristics, and are constructed by bonding these together.

Next, the results of actually observing mask marks and wafer marks using the axial chromatic aberration bifocal device shown in FIG. 1 will be explained.

FIG. 10 shows a photograph of the monitor observed with a CCD camera as a line diagram. The state of each mark shown in FIG. 5 is well reproduced. What you see in the center of the monitor is g.
An image 14' of the mask mark 14 formed by the line light, an image c' of the boundary surface c of the pattern barrier filter on both sides thereof, and an image 15' of the wafer mark 15 illuminated by the band light on both sides thereof. The image is clearly formed, and no phenomenon that would reduce the speckle pattern, contrast, or resolution shown in FIGS. 19 and 21 occurs.

As explained above, in the present invention, by sharing the function of the pattern barrier filter with the illumination filter, a chromatic aberration bifocal device is obtained which overcomes the technical difficulties in manufacturing the pattern barrier filter.

Next, problems in the manufacturing technology of the improved patterned barrier filter will be summarized and explained.

(1) In order to maintain the transmission center wavelength at a constant value, it is necessary to precisely control the film thickness, and as the film becomes more multilayered, it becomes more difficult, and the reproducibility of optical properties decreases. Ta. By assigning this to the illumination filter, the number of films constituting the patterned barrier filter can be reduced and the reproducibility during film production can be increased. Particularly when the absorption filter shown in the above embodiment is used, this problem is completely solved.

(2) By sharing the function of the patterned barrier filter with the illumination filter, the number of films can be reduced, and changes in thin film characteristics over time can be reduced. This problem is also completely solved when an absorption filter is used as in the embodiment.

(3) By sharing the function of the pattern barrier filter with the illumination filter, the number of films and the number of sheets to be bonded are reduced, so the processability of the pattern barrier filter is greatly improved. In particular, when a single sheet structure is used as shown in the embodiment, the workability reaches a level where there is no problem at all.

(4) Since the number of films in a patterned barrier filter can be reduced, the residual stress in the thin film is reduced, making it easier to suppress film peeling and film cracking, and reduce quality deterioration. can.

(5) Handling efficiency is improved because the number of layers in the patterned barrier filter is reduced.

(6) Since the number of films is reduced and workability is improved, the manufacturing cost is significantly reduced.

(7) In order to achieve the function of a patterned barrier filter only with a patterned barrier filter, there are still many problems as mentioned above, but by sharing these with the illumination filter, the optical performance can be improved. It has become possible to suppress deterioration to a level that does not affect final performance.

In the case of a chromatic aberration bifocal device, its image performance is greatly influenced by the correction of chromatic aberration. This is Figure 22
In the spectral characteristics shown in FIG. 23, this means that the steepness of the rise and fall of the transmission curve greatly influences the imaging performance. In other words, the gentler the transmission curve, the more chromatic aberration remains, resulting in a decrease in resolution at the image point. The fact that patterned barrier filters require this steepness makes their manufacturing technology even more difficult.

[0065]

As explained above, according to the axial chromatic aberration bifocal device of the present invention, an illumination filter that extracts only two wavelengths of light is used in the illumination system, and the effect of the conventional pattern barrier filter is improved. By assigning this function to the axial chromatic aberration bifocal filter, various problems encountered in the production of patterned barrier filters can be solved at once, and the performance of the axial chromatic aberration bifocal device can be dramatically improved.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram showing the configuration of an axial chromatic aberration bifocal device according to an embodiment of the present invention;

[Fig. 2] Front view showing an enlarged mask mark of an X-ray mask.

[Fig. 3] Front view showing an enlarged view of the wafer mark;

[Figure 4]
Front view showing enlarged pattern barrier filter,

FIG. 5 is a diagram showing the state of a pattern formed on the image receiving surface of a CCD camera;

FIG. 6 is a perspective view showing the configuration of a pattern barrier filter;

FIG. 7 is a graph showing the spectral transmittance of a patterned barrier filter.

FIG. 8 is a graph showing the spectral transmittance curve of the patterned barrier filter that was actually manufactured.

FIG. 9 is a perspective view of an actually manufactured axial chromatic aberration bifocal device;

FIG. 10 is an explanatory diagram illustrating a photograph of a pattern received by a CCD camera as a diagram;

FIG. 11 is a diagram for explaining the imaging state in the paraxial region of the axial chromatic aberration objective lens;

FIG. 12 is an enlarged front view of a prior art patterned barrier filter;

FIG. 13 is an optical path diagram showing the configuration of a prior art axial chromatic aberration bifocal device;

FIG. 14 is a front view showing the configuration of a patterned barrier filter of the prior art;

FIG. 15 is a spectral wavelength characteristic diagram of a patterned barrier filter of the prior art;

FIG. 16 is a perspective view showing the configuration of a patterned barrier filter of the prior art;

FIG. 17 is a schematic diagram of a pattern imaged by a CCD camera,

FIG. 18 is a diagram showing a photograph in the center image formation of the monitor;

FIG. 19 is a diagram showing an enlarged view of the photograph in FIG. 18;

[Figure 20
] Line diagram showing a photograph in the side imaging of the monitor,

FIG. 21 is a diagram showing an enlarged view of the photograph in FIG. 20;

[Figure 22
] A graph showing the spectral transmission characteristics of the wafer imaging area of the patterned barrier filter.

FIG. 23 is a graph showing the spectral transmission characteristics of the mask imaging area of the patterned barrier filter;

FIG. 24 is a graph showing the relative spectral distribution of an ultra-high pressure mercury lamp.

FIG. 25 is a graph showing the relative spectral distribution of a halogen lamp.

FIG. 26 is a graph showing the spectral sensitivity characteristics of the line sensor.

FIG. 27 is a graph for explaining ripples of an interference filter.

[Explanation of symbols]

1, 2 Light source 3,4　Lighting filter 5 Dichroic mirror 6 Half mirror 7 Axial chromatic aberration objective lens 8. X-ray mask surface 9 Wafer surface 10 Imaging plane 11 Relay lens 12 Pattern barrier filter 13 CCD camera

Claims (1)

[Claims] Claim 1: In an optical device using a lens system having axial chromatic aberration for simultaneously observing a first object and a second object separated by a small distance in the optical axis direction, the illumination system includes a first object and a second object.
A pattern barrier filter consisting of a color filter is arranged in the detection optical system, and an illumination filter that transmits light of different wavelengths is arranged on the axis of the imaging plane based on the image of the second object by the light of the first wavelength. Chromatic aberration blur and second
An axial chromatic aberration bifocal device characterized in that it is configured to efficiently remove axial chromatic aberration blurring on an imaging plane based on a first object image caused by light having a wavelength of .