JPS6217630A - Apparatus for inspecting fiber bundle for illumination - Google Patents

Abstract

PURPOSE:To perform inspection generating no illumination irregularity, by scanning the emitting end surface of an illumination fiber bundle by an aperture stop having a predetermined aperture and measuring the quantity of light passing through the aperture to measure the quantity-of-light distribution of emitted luminous flux at the emitting end surface. CONSTITUTION:The light of a light source 2 lighting by the current supplied from a power source 1 is incident on one end 20a of a random fiber bundle 20 by a condensing lens 3 and emitted from the emitting end 20b thereof. The emitting end part 20c of the fiber bundle 20 is held by a fixed holding jig 4. One end of a rotary mirror cylinder 5 is supported in a rotatable manner by the jig 4 and an iris plate 6 having a fan-shaped aperture 6a, a condensing lens 7 and a light receiving element 8 are provided in the mirror cylinder 5. The output of the element 8 is amplified by an amplifier 9 and subsequently displayed by a digital voltmeter 10. The change in the quantity of light during measurement is detected by a light receiving element 11 and the measured value of the meter 10 is corrected on the basis of detected output. By this method, inspection generating no illumination irregularity can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an inspection device for a fiber bundle used in an illumination optical system, and particularly to an inspection device for an illumination fiber bundle suitable for a telecentric illumination optical system.

[Background of the invention]

In optical measurement devices, optical position detection devices, etc., in order to avoid defocusing in the optical axis direction on the surface of the object to be measured, the optical system is configured as a telecentric optical system, and the objective lens is placed on the object side to be measured. It has been common practice in the past to set telecentricity so that the chief ray is parallel to the optical axis. 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 illumination light is configured to form a light source image on the pupil plane of the objective lens. However, if there is partial brightness unevenness in the light source image at that time, the center of gravity of the illumination light amount will be shifted from the optical axis on the pupil plane of the objective lens, and the effective chief ray on the object side of the objective lens will be tilted from the optical axis. This has the disadvantage that it may cause the measurement to go awry.

On the other hand, an illumination optical system is also known that is configured to guide light from the illumination light source to the test object via a fiber bundle in order to install the illumination light source at a suitable position optically separated from the test object. It is. However, the fiber bundle used for this has conventionally been necessary and sufficient to simply guide the light beam from the light source image formed at one end to the exit surface, and the fiber bundle on the entrance surface There was virtually no consideration given to the relationship with that at the exit surface. Therefore, when this fiber bundle is used in the above-mentioned telecentric illumination optical system, there may be uneven brightness in the illumination light source or the illuminance of the light entering one end face of the fiber bundle may be substantially reduced on the object side of the objective lens. This had the disadvantage that the chief ray was tilted from the optical axis and the telecentric effect was lost.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an extremely convenient inspection apparatus for a fiber bundle for special illumination, which is used to solve the drawbacks of the conventional telecentric illumination optical system and is capable of eliminating illumination unevenness.

[Summary of the invention]

In order to achieve the above object, the present invention provides a light source device that makes a light beam having a predetermined light intensity distribution enter one end face of an illumination fiber bundle formed by randomly bundling a plurality of optical fibers; a diaphragm means having an aperture that scans the other exit end face through which the light flux that has passed through the bundle exits and allows a part of the light flux that is emitted from the exit end face to pass through; The technical point is that the photometric means outputs a signal corresponding to the light intensity distribution of the emitted light flux at the exit end surface in accordance with the scanning of the diaphragm means. be.

〔Example〕

FIG. 1 is a sectional view of the embodiment device of the present invention showing the measurement state;
FIG. 2 is a plan view of the aperture stop provided in the embodiment of FIG. 1, and FIG. 3 is a diagram showing the unevenness in light amount measured by the embodiment of FIG. 1.

In FIG. 1, light from a light source 2 turned on by a current supplied from a power source 1 is incident on one end 20a of a random fiber bundle 20, which will be described in detail later, through a condensing lens 3, and the light is transmitted to the other exit end 20a. It is ejected from 20b. The injection end 20c of the random fiber bundle 20 is held by a fixed holding fitting 4. One end of the rotating lens barrel 5 is rotatably supported by the holding fitting 4, and a fan-shaped opening 6a is provided inside the rotating lens barrel 5 as shown in FIG.
A diaphragm plate 6 having a diaphragm plate 6, a condensing lens 7, and a first light receiving element 8 made of a silicon photodiode (SPD) are provided. Incidentally, all the light beams passing through the aperture 6a of the diaphragm plate 6 are focused onto the first light receiving element 8 by the condensing lens 7, and the output of the light receiving element 8 is amplified by the amplifier 9 and then amplified by the digital voltmeter 10. Is displayed.

Furthermore, if the amount of illumination light changes during measurement, the measured value will fluctuate, so the change in the amount of light is detected by the second light receiving element 11, and the measured value shown on the digital voltmeter 10 is determined based on the detection output. It is configured so that it can be corrected. Further, a light shielding plate 12 having an opening that can be eccentrically moved in a direction perpendicular to the optical axis is provided in the vicinity of the random fiber bundle 200 Å emission end face 20a, and is configured to block part of the illumination light. There is.

Since the embodiment shown in FIG. 1 is constructed as described above,
When the light source 2 is turned on, the illumination light is directed to the incident end surface 2 of the random fiber bundle needle (test object) 20 by the condenser lens 3.
The light is focused on 0a. At this time, part of the illumination light is cut by the diaphragm plate 12, and the light amount distribution on the incident end surface 20a becomes biased. Next, the injection end 20C of the random fiber bundle 20 is attached to the holding fitting 4, and the rotating lens barrel 5 is rotated. This rotation of the rotating lens barrel 5 causes the aperture diaphragm 6 to rotate, and if there is unevenness in the random surface distribution, the aperture 6a will change as shown in the solid line in FIG. The output change as shown by the curve is shown on the digital voltmeter 10. Furthermore, if there is little unevenness in the amount of light on the exit end surface 20b, the measured value will be shown as a substantially flat curve as shown by the broken line in FIG. Therefore, if an optical fiber bundle is used in a telecentric optical system, the light intensity distribution at the exit end surface 20b becomes almost flat even if the light intensity distribution of the illumination light incident on the input end surface 20a is biased. , illumination light source 1
Complete telecentric illumination can be achieved even if the luminance of the fiber is not uniform and the light intensity distribution is biased and enters the random fiber bundle 20.

The random fiber bundle 20 shown in FIG. 1 is made by bundling a plurality of optical fibers and arranging them so that the fibers are arranged irregularly on one end surface and the fibers on the other end surface are different. The random fiber bundle 20 in FIG. 4, an example of which is shown in FIG. 4, has a diameter δ = 0.1 m to 0.
．． Collect a large number of optical fibers of about 31 and make the diameter Φ=
About 5m~1Oam, fiber A on both end faces
, B, C, . . . are formed by gluing so that the arrangement is random as shown in FIG. 4, and both ends are crimped and bound with a binding tube 21 made of metal or the like.

The fibers A, B, C... are badly glued,
If the alignment of the fibers at both end faces is substantially the same, or if there is deviation, the output of the light receiving element 8 (see FIG. 1) will vary greatly, as shown by the solid line in FIG. However, the way the fibers were glued was good, and as shown in Fig. 4, the fibers A, B, C, etc. were lined up on the input end face 2Oa side, while the fibers were cut on the exit end face 20b side. If the light is uniformly distributed so as to be distributed on the inclined surface of the exit end face, the light amount distribution at the exit end face 20b will be almost flat as shown by the dotted line in FIG. 3, and will be uniform. It can be converted into illumination light.

Note that fibers A, B, C, etc. are connected to each other by binding tubes 21 provided at both ends of the random fiber bundle 20.
Since it does not fall apart and is firmly maintained in a random state, it is easy to handle and is extremely convenient to install in the above-mentioned inspection equipment or a telecentric optical system that will be explained in detail later. Furthermore, when the total length of the random fiber bundle 20 is relatively short and the diameter of the fibers themselves is relatively thick, a plurality of thin optical fibers of about several tens of microns are bundled together to provide flexibility. As shown in Figure 5, diameter δ = 0.2 va ~ 0.3
It is also possible to create a unit fiber bundle the size of a chicken and collect a large number of unit fiber bundles to form a random fiber bundle 20 as shown in FIG.

FIG. 6 is a cross-sectional view showing a second embodiment of the present invention for inspecting a random fiber bundle 30 whose injection end side is branched into two. There is a distinction. Other members having the same functions as those in FIG. 1 are designated by the same reference numerals as those in FIG. 1, and detailed explanations thereof will be omitted.

Two sets of inspection device main bodies 4-8. 4'-8' light receiving elements 8.
The 8° outputs are each amplified by an amplifier 9.9°, and then the difference between the true outputs is extracted by a differential amplifier 12, and the measured value is displayed by a digital voltmeter 10. In this case, two sets of inspection device bodies 4-8 and 4°
One of the two branched exit end surfaces is fixed, and the other is rotated to measure the light amount distribution state of the other exit end surface on the side to be rotated and measured based on the light amount of one of the two branched exit end surfaces. Therefore, even if the amount of light from the lamp 2 changes over time during measurement, a correct measurement value can be obtained because the difference in output between the amounts of light at both ends 30A and 30B of the fiber east branch is taken. This makes it possible to measure light intensity unevenness with high precision.

7 and 9 show an optical measuring machine equipped with a telecentric illumination optical system having a random fiber bundle (test object) 20 inspected by the embodiment apparatus of FIG. 1, and a projection exposure apparatus for semiconductor manufacturing. FIG. 2 is an optical system layout diagram.

In the optical system layout diagram of the epi-illumination type optical measuring instrument shown in FIG. 7, light from a light source 101 is focused onto an incident end face 20a of a random fiber bundle 20 by a condensing lens 102 and a concave mirror 103. In this case, when the light source 101 is placed at a position that coincides with the optical axis of the condenser lens 102, the general entrance end surface 20
The light intensity distribution shows a light intensity distribution in which the maximum light intensity is at the center of point a and the light intensity decreases toward the periphery. However, if the light source 101 is mounted off-center from the optical axis of the condenser lens 102, for example, as indicated by the broken line B in FIG. As shown, the light intensity distribution is biased. However, at the exit end face 20b of the random fiber bundle 20, the light amount distribution is equalized, and the actual iA
The incident light distribution at the exit end surface 20b is as shown by A'', and the incident light distribution at the broken line B is flat as shown by B'' at the exit end surface 20b.

The light emitted through the aperture stop 104 close to the exit end surface 20b of the random fiber bundle 20 is condensed by the illumination system lens 105 to become a parallel beam of light, and is reflected by the semi-transparent prism 106 along the optical axis of the objective lens. ,
After passing through the second objective lens 107, the first objective lens 1
The light is condensed at the position of the aperture 109 (the position of the pupil of the first objective lens 108) in 08, and an image of the exit end surface 20b is formed at the pupil position. Furthermore, the light becomes a parallel light beam again and is projected onto the object to be examined 110 from the first objective lens 108.

Therefore, the object to be inspected 110 is illuminated from above in FIG. 7 with extremely uniform illumination light with no bias in the light amount distribution. Its illumination range is defined by a field stop 111.

Further, the reflected light from the test object 110 illuminated by the illumination light is reflected at the pupil position of the first objective lens 108 (aperture 10
The chief ray of the light beam that passes through the aperture 109 and forms an image of the object 110 passes through the center of the pupil and becomes parallel to the optical axis on the object side. Therefore, it is possible to obtain a measuring device that performs a complete telecentric function and has no measurement errors.

FIG. 9 shows an example in which a random fiber bundle is used in the illumination optical system for alignment of a reduction projection type exposure device, in which light emitted from an ultra-high pressure mercury lamp 201 is passed through an elliptical reflector 202 onto the reflecting surface of a rotary mirror shutter 203. After passing through the aperture provided in the rotary mirror shutter 203, the light passes through a remeter lens 204, an optical integrator 205 composed of a fly's eye lens, and a condenser lens 206, and is then directed to a reticle 207 on a projection original plate.
The pattern image on the illuminated reticle 207 is formed on the wafer 209 by the reduction projection lens 208 to perform printing exposure.

On the other hand, the light beam reflected by the rotary mirror shutter 203 and incident on the first condensing lens 210 of the alignment optical system is condensed onto the incident end surface 20a of the random fiber bundle 20. Since the illumination light beam focused on the incident end surface 20a has its center beam cut by one electrode of the ultra-high pressure mercury lamp 201, the illumination light beam focused on the incident end face 20a is as shown in FIG. 10(A) when the light source image is not in the best focus state. 2 shows a light amount distribution as shown by curve 2, which has a portion where the light amount is extremely reduced at the center. However, random fiber bundle 2
At the exit end surface 20b of 0, the light is averaged and emitted with a flat light amount distribution as shown by the curve (2). The illumination light emitted from the exit end surface 2Qb passes through the second condensing lens 211
, field stop 212, semi-transmissive mirror 213, second alignment objective lens 215, first alignment objective lens 214
, the alignment mark P on the reticle 207 is illuminated via the moving mirror 216, and the reduction projection lens 208
The alignment mark Q on the wafer 209 is illuminated through the wafer 209. Further, alignment marks P and Q on both the reticle 207 and the wafer 209 are superimposed on each other to form an alignment pair, and the alignment mark P on the reticle 207 is confirmed.

In the illumination optical system that illuminates both alignment marks P and Q, each lens 211, 214, 215 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 208a of the reduction projection lens 2O8.
are arranged so that so-called Koehler illumination is applied to the reticle 207, and telecentric illumination is applied to the wafer 209. Also, the reticle 207 is replaced with one of a different size, and the position of the alignment mark on the reticle changes from point P to point P.
The first alignment objective lens 214 and the movable mirror 21 are arranged so that alignment is possible even when the position is changed to
6 is configured to be movable along an alignment optical axis Y parallel to the surface of the reticle 207 as shown by a broken line. In this case, the light beam between the first alignment objective lens 214 and the second alignment objective lens 215 is a parallel light beam.

This first alignment objective lens 214 and the moving mirror 2
16, the alignment mark on point P'' and the alignment mark on point Q'' on wafer 209 can be observed in a superimposed manner.
P point and P on 7.

The angle of the principal ray passing through the point and the center of the pupil 208a of the projection lens 208 with respect to the projection optical axis X is from θ to θ.

Changes to Therefore, the light beams passing through 1i 208a to illuminate different points Q and Q' on the wafer 209 pass through different positions R and R' at the exit end face 20b of the random fiber bundle 20.

Now, if the projection of l1208a on the exit end surface 20b is as shown in FIG. 10(B) and is L'', then the wafer 2
Point Q on 09 is illuminated by light passing through the range L, and point Q' is illuminated by light passing through the range L'.

Therefore, if the fibers constituting the random fiber bundle 20 are arranged randomly as shown in FIG.
Even if the light intensity distribution is not uniform as shown by the curve I in the middle, it becomes almost uniformly flat at the exit end face 20b as shown by the curve ■, so that the pupil 208a of the projection lens 20B
The light intensity distribution of the light flux passing through the lens does not become biased even if the movable mirror 216 is moved together with the first objective lens 214. Therefore, the principal ray of the illumination light beam is always parallel to the projection optical axis on the wafer 209 side, and correct telecentric illumination is performed.

However, when the random fiber bundle 20 is not randomly arranged on both end faces due to poor manufacturing or the like, and the light intensity distribution of the incident light and the light intensity distribution of the emitted light are not much different or have a large deviation. From the exit end face 20b of the random fiber bundle 20, a light beam is emitted with a mountain-shaped light intensity distribution that is high in the center and low in the periphery, as shown by curve 1 in FIG. 10(A), for example. It turns out. In this case, the light intensity distribution on the pupil plane of the light beam that passes through the range of the exit end face 20b and illuminates the Q point on the wafer 209, and the light intensity of the light flux that passes through the range L' and illuminates the Q° point on the wafer 209. The distribution is different as shown in FIG. 10(A). For example, within the range L'', the light quantity is distributed asymmetrically with respect to the center R' of the range L°, and the position of the center of gravity of the light quantity is deviated from the center R' of the range L'. Therefore, the projection lens 208 Q also at the l1208a position of
The center of gravity of the light quantity of the light beam illuminating the point is shifted from the center of the pupil 208a. Therefore, the pupil 208 of the projection lens 208
The substantial chief ray passing through a does not pass through the center of the pupil 208a and is not parallel to the projection optical axis X on the wafer 209 side. That is, telecentric illumination will not be performed, and if there is a focusing error between the wafer 209 and the projection lens 208, the alignment accuracy will be disrupted. Therefore, in order to always perform correct telecentric illumination, it is necessary to use a reticle 207 with different alignment marks.
When replacing the fiber bundle 20, the exit end face of the fiber bundle 20 is moved each time, or the positions of the light source 201 and the elliptical mirror 202 are changed, so that the light intensity distribution of the illumination light flux passing through the pupil 208a becomes symmetrical with respect to the pupil center. must be adjusted accordingly.

However, the light intensity distribution on the exit end face side of the fiber bundle is measured and inspected using the inspection device shown in the embodiment of the present invention, and the light intensity distribution is evenly distributed in the illumination optical system of the above-mentioned projection exposure apparatus. If used, telecentric illumination can be performed correctly without adjusting the position of the light source or fiber bundle when replacing the reticle or light source.

In the embodiment shown in FIG. 1 above, the diaphragm 6, the condenser lens 7, and the light receiving element 8 are configured to rotate together, and the relative position between the aperture 6a of the diaphragm 6 and the substantial light receiving surface of the light receiving element 8 remains unchanged even if the lens barrel 5 is rotated. Therefore,
Since there is no photometry error caused by rotation of the lens barrel, accurate light intensity distribution can be measured. Note that although the aperture 6a of the diaphragm 6 is formed in a fan shape, it may also be configured to be circular and to freely slide along the exit end surface 20b of the random fiber bundle 20 together with the lens barrel 5. Good, also light source 2
Or, by decentering the condensing lens 3 with respect to the lighting customer axis,
If the light shielding plate 12 is configured to bias the light intensity distribution at the incident end face 20a of the random fiber bundle 20, the light shielding plate 12 may not be provided.

〔Effect of the invention〕

As described above, according to the present invention, the exit end face of a random fiber bundle is scanned by an aperture diaphragm (diaphragm means) having a predetermined aperture, the amount of light passing through the aperture is measured by a light receiving element, and the exit end surface is measured by a light receiving element. Since the light intensity distribution of the emitted light beam at the end face can be measured, the degree of irregularity in the arrangement of optical fibers at both ends of a random fiber bundle can be inspected with a simple operation.
Furthermore, if a random fiber bundle with a uniform light intensity distribution of the emitted light flux inspected by this inspection device is used in the telecentric illumination optical system of an optical device, it will be possible to easily perform correct telecentric illumination. There are advantages.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention showing a state in which a random fiber bundle to be tested is attached, FIG. The figure shows a light intensity distribution output diagram measured by the example device shown in FIG.
FIG. 4 is a perspective view of a random fiber bundle inspected by the embodiment apparatus shown in FIG. 1, FIG. 5 is a perspective view of a unit fiber bundle constituting the random fiber bundle shown in FIG. 4, and FIG. 7 is a cross-sectional view showing the second embodiment of the present invention in which a branched fiber bundle is attached, and FIG.
An optical system layout diagram of an optical measuring machine having a telecentric illumination optical system in which a random fiber bundle inspected by the example device shown in the figure is arranged. FIG. 9 is an explanatory diagram showing the light intensity distribution at the exit end face.
FIG. 10 is an optical system layout diagram of a projection exposure apparatus equipped with a telecentric illumination optical system for alignment in which a fiber bundle is arranged. FIG. 10 shows the light intensity distribution at the input end face and exit end face of the random fiber bundle shown in FIG. In the explanatory diagram (
A) is a light amount distribution diagram thereof, and (B) is a plan view showing the range of the luminous flux actually used. [Explanation of symbols of main parts] 20.30---Random fiber bundle (lighting fiber bundle)

Claims (1)

[Claims] A light source device that makes a light beam having a predetermined light intensity distribution enter one end face of an illumination fiber bundle formed by bundling a plurality of optical fibers; The aperture means has an aperture that allows a part of the light to pass through and scans the exit end surface, and a photometric means that receives the light beam that has passed through the aperture and outputs a detection signal according to the light intensity, and the aperture means An apparatus for inspecting a fiber bundle for illumination, characterized in that the photometric means is configured to output a signal according to the light intensity distribution of the emitted light beam at the exit end surface in accordance with the scanning.