JPS6217705A - Telecentric optical system lighting device - Google Patents

Abstract

PURPOSE:To prevent ununiform light quantity on a pupil surface of an illuminating light by dividing the incident luminous flux which is made incident on one end face of a random fiber bundle for leading the luminous flux which has condensed light from a light source, to an object side, into plural fluxes, and distributing them uniformly in the other end face. CONSTITUTION:The illuminating light from a light source 1 is focused to an incident end face 20a of a random fiber bundle 20 by a condensing lens 2 and a concave mirror 3, and emitted from an emitting and face 20b. Its light travels to a lighting system lens 5 through an aperture diaphragm 4, condensed and becomes a parallel luminous flux, reflected along an objective lens optical axis by a half-transmission flux, reflected along an objective lens optical axis by a half-transmission prism 6, focused at a pupil position of the first objective lens 8 through the second objective lens 7, and an image of the aperture diaphragm 4 is formed at its pupil position together with an image of the emitting end face 20b. The light becomes a parallel luminous flux again and projected to an object to be inspected 10 from the first objective lens 8, and illuminates vertically the object to be inspected 10, along the optical axis. The random fiber bundle 20 is formed by bundling plural optical fibers, making a line of fibers of one end face different from a line of fibers of the other end face, and twisting them together so that they become an irregular arrangement each other.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a telecentric optical system for an optical device.

In particular, the present invention relates to an illumination device for effectively functioning the telecentric optical system.

[Background of the invention]

In optical devices such as optical measurement devices and optical position detection devices, a focal shift in the direction of the optical axis on the surface of the object to be measured results in a positional shift in the direction perpendicular to the optical axis on the observation surface or light receiving surface of a sensor, etc. This will cause the measurement to go awry.

In order to prevent this, it has traditionally been common practice to configure the optical system as a telecentric optical system, and to set the objective lens on the test object side in a telecentric arrangement so that the principal ray is parallel to the optical axis. There is. In this case, a light beam whose principal ray is parallel to the optical axis is used as the illumination light that illuminates the object to be examined, and the configuration is such that a light source image of the illumination light is formed on the pupil plane of the objective lens. However, in this case, if the light source image is placed offset from the optical axis, the center of gravity of the illumination light amount will be offset from the optical axis at the pupil plane of the objective lens. This had the disadvantage that the tilt telecentricity was lost and the measurement was disturbed.

In order to eliminate this drawback, in conventional devices, a test lens is inserted into the illumination optical system to form a light source image on the observation surface, etc., and then the light source image is positioned at the center of the observation surface (center of the optical axis). When it is necessary to adjust the position of the light source, and when replacing the light source or when the use of the optical device has been interrupted for a long time, the position of the light source must be verified each time before use. Adjustments were needed. If the verification work was neglected, there was a drawback that the measurement results would be unreliable.

[Purpose of the invention]

The present invention solves the above-mentioned drawbacks of the conventional device and provides an illumination device for a telecentric optical system that does not cause deviation in measurement accuracy even if the position of the light source is biased or the light source has uneven brightness. With the goal.

(Summary of the invention) In order to achieve the above object, the present invention.

The random fiber bundle includes a light source, a condensing means for collecting light from the light source, and a random fiber bundle that guides the light beam condensed by the condensing means to the object side.
Bundle many fibers together.

It is formed by gluing the fibers so that the arrangement of the fibers on one end face is irregularly distributed with respect to the arrangement on the other end face, and the incident light beam incident on one end face is divided into multiple parts, and the fibers on the other end face are The technical point is to configure it so that it is distributed uniformly.

〔Example〕

Next, one embodiment of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is an optical system layout diagram of an epi-illumination type optical measuring device showing a first embodiment of the present invention. In FIG. 1, illumination light from a light source 1 is focused by a condensing lens 2 and a concave mirror 3 onto an incident end face 20a of a random fiber bundle 20, which forms the main part of the present invention and will be described in detail later. Incidence end surface 2
The light beam incident from 0a is guided to the random fiber bundle 20 and exits from the exit end face 20b. The light emitted from the exit end surface 20b passes through the aperture diaphragm 4 provided close to the exit end surface 20b, and is directed to the illumination system lens 5, where it is condensed by the illumination system lens 5 and becomes a parallel beam of light. . The parallel light flux is reflected along the optical axis of the objective lens by the semi-transparent prism 6, passes through the second objective lens 7, and then passes through the pupil position of the first objective lens 8 (in this example, the first
The light is focused at the position of the aperture stop 9 within the objective lens 8, and an image of the aperture stop 4 is formed at the pupil position together with an image of the exit end surface 20b. Furthermore, the light becomes a parallel light beam again and is projected from the first objective lens 8 onto the object to be inspected IO, illuminating the object to be inspected 10 perpendicularly along the optical axis. The illumination range is determined by a field stop 11 provided near the illumination system lens 5.

The above-mentioned random fiber bundle 20 is formed by bundling a plurality of optical fibers and twisting them together in an irregular arrangement with the fibers arranged at one end face different from the arrangement of the fibers at the other end face. An example of this is shown in Figure 2. The random fiber bundle 20 shown in FIG.
m to about 10 Tsuru, fibers A and B on both end faces
.

C... are glued together in an irregular arrangement as shown in FIG. 2, and both ends are crimped and bound with a binding tube 21 made of metal or the like. The way the fibers are glued is good, and the fibers A and B on the input end surface 20a are
The cut end of each fiber is on the injection end surface 20b side with respect to the arrangement of C....

If the light is distributed uniformly over the entire surface of the exit end surface 20b, even if the incident light shows a biased light intensity distribution at the entrance end surface, it will have an extremely uniform light intensity distribution when it exits from the exit end surface. It becomes a luminous flux.

FIG. 3 is a diagram showing an example of the light amount distribution on both end faces of the random fiber bundle 20. The incident light beam A, which exhibits maximum light intensity at the center 0 of the end face of the undamped fiber bundle 20 and decreases toward the periphery, becomes a flat exit light flux A′ and is emitted from the exit end face 20b. Also,
Even if the maximum light intensity portion enters the incident end face 20a unevenly as shown by the broken line vAB, it is averaged by passing through the random fiber bundle 20 and becomes almost flat as shown by the broken line B''. This allows for uniform illumination.

Note that the fibers A and B are separated by binding tubes 21 provided at both ends of the random fiber bundle 20.

C... does not fall apart and is firmly maintained in a random state. Therefore, it is easy to handle and is extremely convenient to install in a telecentric optical system. In addition, when the total length of the random fiber bundle 20 is relatively short and the diameter of the fiber itself is relatively thick, a plurality of thin optical fibers of about several tens of microns may be bundled together to provide flexibility. As shown in the figure, diameter δ=
A unit fiber bundle of approximately 0.2 m to 0.3 fi may be made, and a large number of these bundles may be collected to form a random fiber similar to the random fiber 20 shown in FIG.

Now, in FIG. 1, the entrance end surface 2 of the fiber bundle 20
Curve A in FIG. 3 represents the illumination flux at 0a.

Even if there is extreme unevenness in the amount of light as shown in B.

At the exit end surface 20b, the emitted light beams A' and B' have a uniform light quantity distribution, so the chief ray of the illumination light beam emitted from the aperture stop 4 always passes through the center of the pupil of the first objective lens 8, It becomes parallel to the optical axis on the test object 10 side.

Therefore, even if the illumination luminous flux of light source 1 has unevenness in the amount of light as shown by curve A in FIG. Correct telecentric illumination can always be performed even when the light intensity distribution is biased.

The reflected light from the test object 10 illuminated by this illumination light passes through the pupil position of the first objective lens 8 (the position of the diaphragm 9), and passes through the second objective lens 7 onto the test object 12. Like forming an image.

First objective lens8. A second objective lens 7 and a screen 12 are arranged to constitute a telecentric optical system. Therefore, the chief ray of the light beam forming the image of the object to be measured 10 passes through the center of the pupil of the first objective lens 8 and becomes parallel to the optical axis on the object side, so that focusing errors do not affect measurement accuracy.

The device can be fully telecentric.

In the measurement device of the first implementation side, even if the illumination light at the input end face of the random fiber bundle 20 has unevenness or bias in the light amount, the illumination light can be made to have a uniform light amount distribution at the exit end face. So.

The principal ray of the illumination light beam is not substantially tilted with respect to the principal axis of the objective lens depending on the position of the light source 1, so that telecentricity cannot be maintained. Therefore, there is no need to repeatedly verify the light source position prior to measurement work.

FIG. 5 is an optical system layout diagram showing a second embodiment of the present invention used in an illumination optical system for alignment of a reduction projection type exposure apparatus for semiconductor manufacturing. The light emitted from the ultra-high pressure mercury lamp 101 is focused by the elliptical reflector 102 onto the reflecting surface of the rotary mirror shutter 103, and after passing through the aperture provided in the rotary mirror shutter 103, it passes through the meter lens. 104. A reticle 107 on a projection original plate is illuminated through an optical integrator 105 and a condenser lens 106 configured with a fly's eye lens, and the pattern image on the illuminated reticle 107 is reduced to a projection lens 1.
It is configured to be formed on the wafer 109 using 0B and subjected to printing exposure.

On the other hand, the light beam reflected by the rotary mirror shutter 103 and incident on the first condensing lens 110 of the alignment optical system is condensed onto the incident end surface 2Oa of the random fiber bundle 20. The illumination light beam focused on the incident end surface 20a is canted in the central part by one electrode of the ultra-high pressure mercury lamp 101, so that when the light source image is not in the best focus state, the illumination light beam is as shown in FIG. 6(A). As shown in FIG. 3, the light amount distribution shows a curve (2) with a portion where the light amount is extremely reduced at the center. However, random fiber bundle 20
At the exit end surface 20b, the light is averaged and emitted with a flat light amount distribution as shown by curve 1. The illumination light emitted from the exit end surface 20b is transmitted through the second condensing lens 111.
．． Field diaphragm 112, semi-transparent mirror 113. Second alignment objective lens 115. First alignment objective lens 114
゜The alignment mark P on the reticle 107 is illuminated via the moving mirror 116, and the reduction projection lens 108
The alignment mark Q on the wafer 109 is illuminated through the wafer 109. Further, both alignment marks P and Q on the reticle 107 and the wafer 109 are superimposed on each other and are imaged by the alignment objective lenses 114 and 115 onto the ITV image pickup tube 117 disposed behind the semi-transmissive mirror 113, The correct positioning of the alignment mark Q on the wafer with respect to the alignment mark P on the reticle 107 is confirmed through the ITV image pickup tube 117.

In the illumination optical system that illuminates both alignment marks P and Q, each lens 111, 114, 115 is set so that the image of the exit end surface 20b of the random fiber bundle 20 is formed at the position of the pupil 108a of the reduction projection lens 108.
are arranged so that so-called Koehler illumination is applied to the reticle 107, and telecentric illumination is applied to the wafer 109. Also, the reticle 107 is replaced with one of a different size.

The first alignment objective lens 114 and the movable mirror 116 provide alignment light parallel to the surface of the reticle 107 so that alignment is possible even when the position of the alignment mark on the reticle is changed from the position of point P to the position of point P''. As shown by the broken line along the axis Y, the first alignment objective lens 114 and the second
The light flux between the alignment objective lens 115 and the alignment objective lens 115 is a parallel light flux.

This first alignment objective lens 114 and the moving mirror 1
By moving the reticle 10, the alignment mark on the two points P° and the alignment mark on the point Q′ on the wafer 109 can be observed in a superimposed manner.
Points P and P' on 7 and the pupil 108 of the projection lens 108
The angle of the chief ray passing through the center of a with respect to the projection optical axis X is θ
From θ.

Changes to Therefore, the light flux passing through the pupil 108a to illuminate different points Q and Q' on the wafer 109 is
The random fiber bundle 2o passes through different positions R and R' at the exit end face 20b.

Now, the projection of the pupil 108a on the exit end surface 20b is expressed as the sixth
As shown in figure (B), let it be L'.

Point Q on wafer 109 is illuminated by light passing through a range L, and point Q' is illuminated by light passing through a range L.

Therefore, if the fibers constituting the random fiber bundle 20 are arranged randomly as shown in FIG. 2, even if the light intensity at the input end surface 20a is Even if the distribution is not uniform, it is almost uniformly flat at the exit end surface 20b as shown by the curve H, so the light intensity distribution of the light flux passing through the pupil 108a of the projection lens 108 is similar to that of the first objective lens 114. Even if the movable mirror 116 is moved together, it will not become biased.

Therefore, the principal ray of the illumination light beam is always parallel to the projection optical axis on the wafer 109 side, and correct telecentric illumination is performed.

However, due to manufacturing defects in the random fiber bundle 20, the fibers on both end faces are not arranged randomly, and the light intensity distribution of the incident light and the light intensity distribution of the emitted light may show little difference or a large deviation. Thus, a light beam having a mountain-shaped light intensity distribution is emitted, which is high in the center and low in the periphery. In this case, the light intensity distribution of the light beam that passes through the range of the exit end face 20b to illuminate point Q on the wafer 109 and the light intensity distribution of the light beam that passes through the range L'' and illuminates the point Q'' on the wafer 109 are as follows. As shown in Figure 6 (A) (
different. For example, within the range L''.

The amount of light is distributed asymmetrically with respect to the center R′ of the range L′,
The position of the center of gravity of the light amount is the center R of the 5 range L°.

It will be biased from Therefore, even at the position of the pupil 108a of the projection lens 108, the center of gravity of the light quantity of the light beam illuminating point Q'' is shifted from the center of the pupil 108a.
The substantial chief ray passing through the pupil 108a of the projection lens 108 does not pass through the center of the pupil 108a and is not parallel to the projection optical axis X on the wafer 109 side. That is, telecentric illumination is not performed, and if there is a focusing error between the wafer 109 and the projection lens 108, the alignment accuracy will be disrupted. Therefore, in order to always perform correct telecentric illumination, when replacing a reticle with a reticle with a different alignment mark position, move the exit end face of the fiber bundle 20 or change the positions of the light source 101 and the elliptical mirror 102 each time. Adjustments must be made frequently so that the light intensity distribution of the illumination light flux passing through the pupil 108a is symmetrical with respect to the pupil center.

However, a random fiber bundle 2 as shown in FIG.
0, the optical fibers are arranged irregularly at both ends so that there is no unevenness in the light intensity distribution at the exit end surface, and when replacing the reticle 107 or light source 101, the position of the light source or fiber bundle can be adjusted. This makes it possible to perform telecentric lighting stably and correctly without any problems.

The above embodiments are all related to the illumination optical system of an epi-illumination type telecentric optical system that illuminates the object to be examined through the pupil center of the objective lens. It goes without saying that the illumination light source device of the present invention can also be applied to an illumination optical system for a transmitted illumination type telecentric optical system that illuminates a test object by forming a light source image at the position or a position conjugate thereto. In this case, the exit end surface (20b) of the random fiber bundle or its conjugate surface may be imaged on the front focal plane of the condenser lens.

〔Effect of the invention〕

As described above, when the present invention is incorporated into an optical measuring device or the like, it is possible to eliminate unevenness in the amount of illumination light over the entire surface of the pupil that is illuminated perpendicularly to the object to be measured, with a simple configuration.
In addition, the loss of light intensity that occurs when using a diffuser plate is extremely small, and the illumination light can be guided to any position like a conventional fiber bundle, so it is possible to achieve correct telecentricity without having to repeatedly verify the position of the light source. It enables illumination and maintains high measurement accuracy.

[Brief explanation of the drawing]

Fig. 1 is an optical position diagram of a telecentric illumination optical system of a measuring instrument showing a first embodiment of the present invention, Fig. 2 is an enlarged perspective view of a random fiber bundle that forms the main part of the present invention, and Fig. 3 is , a diagram for explaining the light intensity distribution of the incident light and the emitted light on both end faces of the random fiber bundle shown in FIG. 2,
FIG. 4 is a perspective view showing an example of a unit fiber bundle used in the random fiber bundle shown in FIG. 2, and FIG. 5 is a perspective view showing an example of a unit fiber bundle used in the random fiber bundle shown in FIG. FIG. 6 is an optical system layout diagram showing a second embodiment of the present invention used in a reduction projection type exposure apparatus for semiconductor manufacturing equipment. In the explanatory diagrams showing the light amount distribution, (A) is a line diagram showing the state of the light amount distribution, and (B) is a plan view showing the viewing range at the exit end face of the random fiber bundle. [Explanation of symbols of main parts]

Claims (2)

[Claims] (1) Includes a light source, a condensing means for collecting light from the light source, and a random fiber bundle consisting of a large number of optical fibers that guide the light flux from the light source condensed by the condensing means to the object side. , the random fiber bundle is formed by bundling a large number of fibers and twisting them together so that the arrangement of the fibers on one end face is irregularly distributed compared to the arrangement on the other end face, and 1. An illumination device for a telecentric optical system, characterized in that the incident light beam is divided into a plurality of parts and distributed uniformly on the other end face. (2) The illumination light beam emitted from the other end surface (20b) of the random fiber bundle (20) passes through the pupil center of the objective lens (8) in the telecentric optical system, and the principal ray is parallel to the optical axis of the objective lens. 2. The illumination device for a telecentric optical system according to claim 1, wherein the illumination device is arranged so as to illuminate an object.