JP2811127B2 - Chromatic aberration double focus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a double focus apparatus utilizing axial chromatic aberration for detecting a relative position between a first object and a second object separated by a small distance.

[0002]

2. Description of the Related Art The inventor of the present invention has proposed a device for detecting a relative position between an X-ray mask and a wafer in proximity exposure as a "position detecting device for two objects separated by a minute distance" in Japanese Patent Application No. 62-19617.
No. 4 has been filed and is being implemented. Hereinafter, this prior art will be briefly described.

FIG. 11 is a view showing an image forming state in a paraxial region of an objective lens. In front of an objective lens L, an X-ray mask M is further separated by δ at a position on an optical axis O separated by S. It is assumed that a wafer W is placed at the position. Here, assuming that 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, points B and C on the optical axis O Then, images of the wafer W and the X-ray mask M are generated at points C and D, respectively.
Here, at the center point C, an image of the X-ray mask M by light of the wavelength α and an image of the wafer W by light of the wavelength β are formed at the same time, and two object points and one An optical system having an imaging point is realized.

[0004] On the other hand, the light flux formed at points B and D on the optical axis O is superimposed on the image formed at point C, and the resolution of the image formed at point C is reduced. Further, at point C on the optical axis O, since the images formed by the light beams having the wavelengths α and β can be formed on the same plane, the image contrast is reduced due to interference.
Therefore, in order to remove a light beam which forms an image at points B and D, FIG.
As shown in FIG. 2, a pattern barrier filter 20 in which a filter a that transmits only light of wavelength α and a filter b that transmits only light of wavelength β is installed on the both sides in front of the filter a to form an image at point C It removes unnecessary light flux.

[0005]

Table 1 shows the specifications of the axial chromatic aberration double focus apparatus based on the above principle.

[0006]

[Table 1]

FIG. 13 shows an optical path diagram of the axial chromatic aberration double focus apparatus. An X-ray mask 8 having a mask mark 14 of tantalum (Ta) and a wafer mark 1 composed of a step mark
The wafers 9 having the wafers 5 are horizontally mounted on the respective stages in parallel with a small interval δ. The objective lens 7 of the dual focus detection device having axial chromatic aberration has the wavelength α described above.
Is a lens system designed so that the light of wavelength .beta. And the light of wavelength .beta. Therefore, for example, the light beam emitted from the light source 17 of the ultra-high pressure mercury lamp is collimated to form the illumination filter 1.
The wavelength α [α = 546 nm (e
Line)], an illumination light having a wavelength β [β = 573 nm (d-line)] is introduced into a detection optical system via a half mirror 6, and a mask on an X-ray mask 8 via an axial chromatic aberration objective lens 7. Mark 14 and wafer mark 15 on wafer 9
Are respectively illuminated.

The mask mark 14 of the X-ray mask 8 illuminated by the illumination light of the wavelength α and the wafer mark 15 of the wafer 9 illuminated by the illumination light of the 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 in the vicinity of this, and this image is formed on the image forming surface of the CCD camera 13 by the relay lens 11.

The pattern barrier filter 20 is a filter in which the central region a transmits only light having a wavelength α.
The b regions on both sides are formed by bonding a filter that transmits only light of the wavelength β at the boundary surface c. The image of the mask mark 14 is in the central a region, and the image of the wafer mark 15 is in the b region. Unnecessary light that causes bleeding is removed by transmitting each light.

Next, the outer diameter of such a pattern barrier filter 20 and its spectral characteristics are shown in FIGS. Also, the actual pattern barrier filter 2
0 is enlarged and shown in the perspective view of FIG. The specification required for the interference filter constituting this pattern barrier filter is that the half width of both the e-line and the d-line is 1.2 nm and a
Strict conditions are imposed such that the overlap between the boundary between the region and the region b is 0.1 nm or less. In order to satisfy such a demand, it can be finally produced unless a complicated configuration in which five interference filters and antireflection films 21 to 25 are superposed as shown in the perspective view of FIG. Is gone. As shown in FIG. 15, the spectral characteristics of the interference filter require a very high level as an interference filter whose half width is 2.2 nm and whose short and long wavelengths are cut cleanly.

Next, the reason will be described in more detail.
As described above, the wavelength of light for observing the X-ray mask 8 and the wafer 9 separated by a small distance by using the two single-wavelength lights only by the pattern barrier filter 20 arranged near the image point thereof is selected. Although there is no problem in principle, it has been found that there are extremely severe technical difficulties and cost difficulties in manufacturing a pattern barrier filter. That is, in the chromatic aberration double focus apparatus as described above, the X-ray mask 8 is irradiated with the monochromatic light (e
Line), and the case where the wafer 9 is illuminated with the band light (630 nm to 750 nm). Note that this wafer 9
As described in JP-A-2-816, a resist film, a transparent film, or the like is formed on a wafer, and a standing wave effect based on light interference caused by the light is used on the wafer. This is because the reflection intensity of the alignment mark changes sinusoidally, and the relative intensity of the signal light for detecting the mark greatly changes.

FIG. 2 shows the spectral transmission characteristics of the wafer image forming region (region b) of the pattern barrier filter satisfying the above specifications.
FIG. 2 shows the spectral transmission characteristics of the mask image formation area (area a) in FIG.
3 is shown.

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

Next, it is assumed that a line sensor having a high response is used for the light receiving element of the CCD camera 13 in the chromatic aberration double focus apparatus shown in FIG. As shown in FIG. 26, the spectral sensitivity characteristics of this line sensor have wide sensitivity characteristics from a short wavelength of 200 nm or less to a long wavelength region of 1100 nm.

FIGS. 24 and 25 show that a line sensor for receiving an image formed by transmitting a light beam having a wide wavelength range through the pattern barrier filter 20 has a wide spectral sensitivity characteristic. The start wavelength λ ₁ and the end wavelength λ ₂ in the spectral transmission characteristics required for the barrier filter 20 are λ ₁ = 200 nm (200
Light below nm is absorbed by the lens. ), And λ
₂ = 1100 nm (the line sensor has no sensitivity above 1100 nm). From this, it is understood that the pattern barrier filter 20 must be an interference filter in consideration of transmission characteristics in a wide wavelength range.

Next, the interference filter will be described.
In general, an interference filter is formed by coating a glass substrate with a multilayer film so as to transmit only light having a required wavelength by utilizing the interference phenomenon of light in a thin film. Factors that determine the degree of difficulty in designing and manufacturing the thin film mainly include three items: (1) full width at half maximum of transmitted light flux, (2) target wavelength region, and (3) transmittance.

The narrower the full width at half maximum of (1), the more multilayers are required, the wider the wavelength range of (2), the more multilayers are required, and the transmittance of (3) decreases as the number of layers increases. Would be. Accompanying these three items,
(4) Reproducibility of optical characteristics, (5) Temporal change of thin film characteristics,
(6) quality deterioration, (7) workability, (8) handleability,
(9) Manufacturing cost, (10) Optical performance, etc. are added.

Now, for example, assuming that the central portion (X-ray mask image forming area) of the pattern barrier filter 20 of the chromatic aberration double focus detecting device shown in FIG. 13 is designed as a thin film, the transmittance of 546 nm ± 5 nm is obtained. (Full width at half maximum = 10
nm), an ultra-multilayer film of 60 layers or more is generally required.

Further, only by this, as shown in FIG. 27, a so-called ripple region q in which light is transmitted from a thin film design to a region where light is not to be transmitted occurs. In order to eliminate the ripple component q, the number of films must be further increased. Due to the increase in the number of films, the transmittance is further reduced, and the conditions (1) to (10) are reduced.

Therefore, in general, the spectral transmission characteristic of the central portion of the pattern barrier filter is at least because the full width at half maximum is as narrow as about 10 nm as shown in FIG. 23 and the target wavelength region is as wide as 200 nm to 1100 nm. This can be realized by laminating two or more interference filters. This also applies to the wafer imaging regions on both sides of the pattern barrier filter. FIG. 22 shows the spectral characteristics of this band light.

More specifically, the pattern barrier filter prototyped by the inventor of the present invention has a five-sheet configuration 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.

The problems with the performance characteristics of such a filter are as follows: (5) Temporal change in thin film characteristics, (6) Workability, (7) Quality deterioration, (8) Handling, (9) Manufacturing It covers six items of cost and (10) optical performance.

From the above description, it can be seen that it is extremely difficult to achieve the function of the pattern barrier filter only with the pattern barrier filter in the chromatic aberration double focus apparatus from the viewpoint of the manufacturing technology of the pattern barrier filter at present. .

Therefore, in order to reduce the burden on the manufacturing technology of the pattern barrier filter and make it practical, the present inventor most preferably shares a part of the function of the pattern barrier filter with the illumination filter. It was found to be a simple and practical means.

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

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

The state of the whole view when focusing is performed on the focus center of the monitor formed on the image receiving surface of the CCD camera 13 in this way, that is, when the X-ray mask image forming area which is the central part of the pattern barrier filter is focused. FIG. 18 shows (photo) as a diagram. The magnification at this time is 140 times. FIG. 19 shows, as a diagram, a photograph when the center image is magnified and taken in close-up. FIG. 20 shows a diagram (photograph) of the whole view (photograph) when observation is performed by shifting the focus of the monitor by 51 μm in the optical axis direction so as to correspond to the wafer mark of the pattern barrier filter. FIG. 21 is a diagram showing a photograph of the side image formed by enlarging and taking a close-up image.

The following can be understood from FIGS.

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

(2) In the pattern barrier filter 20, the image-forming light beams due to the e-line and the d-line cause multiple reflection interference,
This produces a speckle pattern.

(3) The imaging light flux is diffused in the pattern barrier filter 20, and both the resolution and the contrast are reduced.

As a cause of the above (1), (2) and (3), the pattern barrier filter 20 is constituted by superposing five filters as shown in FIG.
This is because the joining margin of the filter is increased by the large number of sheets to be bonded. Further, the amount of adhesive used on the bonding surface of the pattern barrier filter 20 formed by joining the five interference filters increases, which causes a problem.
Then, the flatness and the surface roughness of each interference filter are affected by the large number, and these must be made sufficiently precisely. Another cause is that the antireflection film for e-line and d-line is insufficient.

As described above, the quality of the pattern barrier filter is an important point that greatly affects the resolution and contrast of the axial chromatic aberration double focus device, and the specifications required for its manufacture have been 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 axial chromatic aberration double focus apparatus which greatly reduces the manufacturing load of a pattern barrier filter.

[0035]

SUMMARY OF THE INVENTION The present invention relates to an optical apparatus using a lens system having an axial chromatic aberration for simultaneously observing a first object and a second object separated by a small distance in the optical axis direction. And a pattern barrier filter composed of a color filter in the detection optical system, and an illumination filter that transmits light of the first and second different wavelengths.
Of the axial chromatic aberration on the image plane based on the image of the second object due to the light of the wavelength and the chromatic aberration of axial chromatic aberration on the image plane based on the first object image due to the light of the second wavelength. An axial chromatic aberration bifocal device characterized in that each is efficiently removed.

[0036]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an optical path diagram showing a configuration of an axial chromatic aberration double focus device. The illumination system emits the light fluxes from the two light sources 1 and 2 through an illumination filter 3 and an illumination filter 4, respectively, at a wavelength α [α = 436 nm (g-line)].
And illumination light having a wavelength β [β = 540-650 nm (band light)], and these light fluxes are combined by a dichroic mirror 5 through collimating lenses 18 and 19, and X is passed through a half mirror 6 and an objective lens 7. The line mask surface 8 and the wafer surface 9 are configured to be illuminated by incident light.

The mask mark 14 on the X-ray mask 8 illuminated with light of wavelength α and the 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 a relay lens 11
And CCD through the pattern barrier filter 12
An image is formed on the image receiving surface of the camera 13 and converted into an electric signal.

In this example, the illumination filters 3 and 4
In combination with the pattern barrier filter 12, the luminous fluxes formed at the points B and D which prevent the image formation at the point C at the same position in FIG. 11 are blocked. That is, two light beams having wavelengths α and β incident on the detection optical system are selected by the illumination color filters 3 and 4.

The characteristics of the pattern barrier filter 12 are as follows:
Assuming that the wavelength γ satisfies α <γ <β for two light fluxes of wavelengths α and β, the filters in the b region on both sides in FIG. 4 are color filters that transmit light of wavelength γ or more, and the filters in the central a region 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 form a single pattern barrier filter 12 by bonding three filters b, a, and b at a boundary c.

FIG. 7 shows the spectral wavelength characteristics of the pattern barrier filter 12 formed as described above. This is because the filters in the regions a and b constituting the pattern barrier filter 12 are color filters having the most general spectral characteristics, and each of the filters a and b does not need to be configured by overlapping a plurality of interference filters. Filter can be created without any problem.

Returning to FIG. 1, the fact that the mask mark and the wafer mark are respectively illuminated by two light beams having different wavelengths based on the above and are well formed will be described in detail. The light beam emitted from the light source 1 is collimated, and only the light having the wavelength α is transmitted and selected by the illumination filter 3. Then, the light is collimated by the collimating lens 18, passes through the dichroic mirror 5, and is taken into the detection optical system by the half mirror 6. On the other hand, the luminous flux emitted from the light source 2 is transmitted through the illumination filter 4 so that only the light having the wavelength β is transmitted and selected. The combined half mirror 6 takes in the detection optical system.

The two light beams having the wavelengths 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 having the wavelength α is illuminated on the X-ray mask surface 8 and the illumination light having the wavelength β is illuminated on the wafer surface 9.

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

FIG. 2 shows a mask mark 14 on the X-ray mask 8.
The enlarged view of FIG. This is formed by providing, for example, tantalum (Ta) linearly on an X-ray mask 8 made of a self-supporting film (emblem).

FIG. 3 is an enlarged view of the wafer mark 15 on the wafer 9. This is one in which two vertically parallel step marks are formed on the wafer 9.

When illumination light of wavelengths α and β is focused on the X-ray mask surface 8 and the wafer surface 9 by the axial chromatic aberration objective lens 7, respectively, and illuminated, the images of the mask mark 14 and the wafer mark 15 become axial. The chromatic aberration objective lens 7 overlaps and forms an image at the same position 10. This image is multiplied by the intermediate magnification by the relay lens 11 and unnecessary light is blocked by the pattern barrier filter 12 before the CCD
An image is formed on the image receiving surface of the camera 13.

FIG. 4 is a front view showing the structure of the pattern barrier filter 12. That is, the region a in the center is a color filter that transmits light including the light having the wavelength α that transmits the mask mark 14 of the X-ray mask 8, and the regions b on both sides of the boundary c are the wafer marks on the wafer 9. 15 is a color filter that transmits light including light having a wavelength β that transmits the light. These are bonded together at the boundary surface c to constitute one sheet.

FIG. 5 shows the state of the pattern formed on the image receiving surface of the CCD camera 13. The 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 the image 15 'of the wafer mark 15 is formed on both sides thereof in parallel. The image 14 'is an image formed by the light of the wavelength α of the mask mark 14, and the image 1'
5 'is an image formed on the wafer mark 15 by light having a wavelength β.

Next, Table 2 shows the specifications of the axial chromatic aberration double focus apparatus actually manufactured.

[0050]

[Table 2]

FIG. 9 shows the appearance of an axial chromatic aberration double focus apparatus having the above specifications. That is, the two light beams selected by the illumination filter are guided by the optical fiber, and enter the fiber illumination unit 26. This light beam illuminates two object points, that is, a mask mark 14 of the X-ray mask 8 and a wafer mark 15 on the wafer 9 by the axial chromatic aberration objective lens 7, and illuminates these marks with the axial chromatic aberration objective lens 7.
To form an image on the image receiving surface of the CCD camera 13.

FIG. 8 shows actually measured spectral characteristics of the pattern barrier filter 12 actually used. Each of the regions a and b is formed by a single color filter having these characteristics, and is configured by laminating these.

Next, the result of actually observing the mask mark and the wafer mark using the axial chromatic aberration double focus apparatus shown in FIG. 1 will be described.

FIG. 10 is a diagram showing a photograph of a monitor observed with a CCD camera. The state of each mark shown in FIG. 5 is well reproduced. G in the center of the monitor
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 sharply formed, and the speckle pattern shown in FIGS. 19 and 21 and the phenomenon that lowers the contrast and the resolution do not occur at all.

As described above, according to the present invention, the function of the pattern barrier filter is shared with the illumination filter, thereby providing a chromatic aberration double focus apparatus which overcomes the difficulty in manufacturing the pattern barrier filter.

Next, the problems in the manufacturing technology of the improved pattern barrier filter will be explained together.

(1) In order to keep the transmission center wavelength at a constant value, it is necessary to precisely control the film thickness, and it becomes stricter for a multilayer film, and the reproducibility of optical characteristics is reduced. Was. By sharing this with the illumination filter, the number of films constituting the pattern barrier filter is reduced, and the reproducibility at the time of film generation is improved. In particular, when the absorption filter shown in the above embodiment is used, this problem is completely solved.

(2) By sharing the function of the pattern barrier filter with the illumination filter, the number of films can be reduced, and the temporal change in thin film characteristics can be reduced. This problem is 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 that the workability of the pattern barrier filter is remarkably improved. In particular, when a single-sheet structure is used as shown in the examples, the workability reaches a level at which there is no problem.

(4) Since the number of films of the pattern barrier filter can be reduced, the residual stress in the thin film is reduced, so that peeling of the film and cracking of the film can be easily suppressed, and quality deterioration can be reduced. it can.

(5) Since the number of films of the pattern barrier filter is reduced, handleability is improved.

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

(7) In order to achieve the function of the pattern barrier filter only by the pattern barrier filter, the problems remain piled up as described above, but by sharing this with the illumination filter,
Deterioration of optical performance can be suppressed to a level that does not affect final performance.

In the case of a chromatic aberration double focus apparatus, the image performance of the apparatus largely depends on the correction of chromatic aberration. This is shown in FIG.
In the spectral characteristics shown in FIG. 23 and FIG. 23, the steepness of the rise and fall of the transmission curve significantly affects the imaging performance. That is, since the chromatic aberration remains as the transmission curve becomes gentler, the resolution at the image point decreases. The requirement of the pattern barrier filter for this steepness further complicates the manufacturing technology.

[0065]

As described above, according to the axial chromatic aberration double focus apparatus of the present invention, the illumination system uses an illumination filter for extracting only light of two wavelengths, thereby illuminating the function of the conventional pattern barrier filter. The problems associated with the production of the pattern barrier filter can be solved all at once, and the performance of the axial chromatic aberration double focus device can be dramatically improved.

[Brief description of the drawings]

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

FIG. 2 is an enlarged front view showing a mask mark of the X-ray mask;

FIG. 3 is an enlarged front view showing a wafer mark;

FIG. 4 is an enlarged front view showing a pattern barrier filter.

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

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

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

FIG. 8 is a graph showing a spectral transmittance curve of an actually manufactured pattern barrier filter;

FIG. 9 is a perspective view of an actually manufactured axial chromatic aberration double focus apparatus,

FIG. 10 is an explanatory diagram showing a photograph obtained by monitoring a pattern received by a CCD camera in a diagrammatic manner;

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

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

FIG. 13 is an optical path diagram showing a configuration of a prior art axial chromatic aberration double focus apparatus;

FIG. 14 is a front view showing a configuration of a prior art pattern barrier filter.

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

FIG. 16 is a perspective view showing a configuration of a prior art pattern barrier filter.

FIG. 17 is a schematic diagram of a pattern received by a CCD camera;

FIG. 18 is a diagram showing a photograph at the center image formation of the monitor,

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

FIG. 20 is a diagram showing a photograph in side imaging of a monitor;

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

FIG. 22 is a graph showing a spectral transmission characteristic of a wafer imaging region of the pattern barrier filter;

FIG. 23 is a graph showing a spectral transmission characteristic of a mask image forming area of the pattern 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 a relative spectral distribution of a halogen lamp.

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

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

[Explanation of symbols]

 1, 2 light source 3, 4 illumination filter 5 dichroic mirror 6 half mirror 7 on-axis chromatic aberration objective lens 8 X-ray mask surface 9 wafer surface 10 imaging surface 11 relay lens 12 pattern barrier filter 13 CCD camera

Claims (1)

(57) [Claims] 1. An optical apparatus 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, wherein an illumination system has first and second different illumination systems. An illumination filter that transmits light of a wavelength and a pattern barrier filter composed of a color filter are arranged in the detection optical system, and an axial chromatic aberration on an image plane based on an image of a second object by light of the first wavelength is arranged. An axial chromatic aberration double focus apparatus, wherein blur of axial chromatic aberration on an image forming surface based on a first object image due to light of a second wavelength is efficiently removed.