JP2002006223A - Illuminating optical system for microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illuminating optical system for a microscope capable of obtaining a bright image by suppressing the intensity reduction of illuminating light and scattered light. SOLUTION: The illuminating light is emitted from a light source. The illuminating light emitted from the light source is reflected by a reflection mirror. The illuminating light reflected by the reflection mirror is transmitted through an objective lens so that an object to be observed may be illuminated, and also, the scattered light from the object to be observed is converged by the objective lens. The luminous flux scattered by the object to be observed and then converged by the objective lens reaches a light receiving surface through a through-hole formed in the reflection mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope illumination optical system, and more particularly to a microscope illumination optical system suitable for obtaining a bright image of an object to be observed.

[0002]

2. Description of the Related Art A conventional illumination optical system will be described with reference to FIG.

FIG. 6 is a schematic diagram of a position detecting device used in the oblique position detecting method disclosed in Japanese Patent Application Laid-Open No. 9-27449. The position detecting device includes a wafer / mask holding unit 110 and an optical system 120.

The wafer / mask holder 110 comprises a wafer holder 115 and a mask holder 116. At the time of alignment, the wafer 111 is held on the upper surface of the wafer holder 115 and the mask 112 is held on the lower surface of the mask holder 116. The wafer 111 and the mask 112 are arranged such that a certain gap is formed between the exposure surface of the wafer 111 and the mask 112. A wafer mark 113 for positioning is formed on the exposure surface of the wafer 111, and a mask mark 114 for positioning is formed on the lower surface (mask surface) of the mask 112.

[0005] Wafer mark 113 and mask mark 11
4 has edges that scatter incident light. When light enters these marks, the incident light that strikes the edges is scattered, and the incident light that strikes other areas is specularly reflected.

The optical system 120 includes an image detecting device 121, a lens 122, a half mirror 123, and a light source 124. The optical system 120 is arranged so that its optical axis 125 is oblique to the exposure surface. Illumination light emitted from the light source 124 is reflected by the half mirror 123 to be a light beam along the optical axis 125,
Obliquely incident on the exposure surface through the

[0007] Wafer mark 113 and mask mark 11
The light incident on the entrance pupil of the lens 122 among the scattered light scattered by the edge of No. 4 is converged by the lens 122 and forms an image on the light receiving surface of the image detection device 121. As described above, since the optical axis of the illumination light and the optical axis of the observation optical system are arranged obliquely with respect to the exposure surface, it is not necessary to arrange each optical system on the exposure area of the exposure surface. Therefore, exposure can be performed without retreating the optical system from the exposure area. Further, the alignment mark can be observed even during the exposure.

[0008]

In the position detecting device shown in FIG. 6, when the illumination light emitted from the light source 124 is reflected by the half mirror 123, the intensity is reduced to about 1/2. Further, when the light beam scattered by the wafer mark 113 and the mask mark 114 and incident on the lens 122 passes through the half mirror 123, the intensity thereof is reduced to about 1 /
Drops to 2. Therefore, an image formed on the light receiving surface of the image detection device 121 becomes dark.

An object of the present invention is to provide an illumination optical system for a microscope capable of suppressing a decrease in intensity of illumination light and scattered light and obtaining a bright image.

[0010]

According to one aspect of the present invention, a light source for emitting illumination light, a reflector for reflecting illumination light emitted from the light source, and an illumination light reflected by the reflector are provided. While illuminating the observation target through transmission,
An objective lens that converges scattered light from the observation target, and penetrates through the reflection mirror so that a light beam scattered by the observation target and converged by the objective lens passes through the reflection mirror. An illumination optical system for a microscope provided with a hole is provided.

The light beam scattered by the object to be observed and converged by the objective lens passes through the through-hole provided in the reflecting mirror, and reaches the light receiving surface with almost no attenuation. Further, since the illumination light is reflected by the reflecting mirror, the amount of attenuation can be reduced as compared with the case where the illumination light is reflected by the half mirror.

[0012]

FIG. 1 is a schematic sectional view of a position detecting apparatus employing an illumination optical system according to an embodiment of the present invention.
The position detecting device includes a wafer / mask holding unit 10, an optical system 20, and a control device 30.

The wafer / mask holder 10 includes a wafer holder 15, a mask holder 16, and driving mechanisms 17 and 18. At the time of alignment, the wafer 11 is held on the upper surface of the wafer holder 15 and the mask 12 is held on the lower surface of the mask holder 16. Wafer 11 and mask 12
Is arranged substantially parallel so that a constant gap is formed between the exposure surface of the wafer 11 and the surface of the mask 12 on the wafer side (mask surface). A wafer mark for alignment is formed on the exposure surface of the wafer 11, and a mask mark for alignment is formed on the mask surface of the mask 12.

The driving mechanism 17 includes the wafer 11 and the mask 12
The wafer holding table 15 or the mask holding table 16 can be moved so that the relative position of the wafer holding table 15 with respect to the exposure plane changes. The drive mechanism 18 can move the wafer holder 15 so that the distance between the exposure surface of the wafer 11 and the mask surface of the mask 12 changes. X-axis from left to right in the figure, Y from front to back in a direction perpendicular to the paper surface
When the Z axis is set in the axis and the normal direction of the exposure surface, the driving mechanism 17
Are the X-axis direction and Y-axis direction of the wafer 11 and the mask 12,
The driving mechanism 18 adjusts the relative position with respect to the rotation direction (θ _Z direction) about the axis, and the relative position in the rotation (tilt) direction (θ _X and θ _Y direction) about the Z axis direction, X axis and Y axis. Adjust the position.

The optical system 20 illuminates the wafer mark formed on the wafer 11 and the mask mark formed on the mask 12 with illumination light, and obtains an image by the scattered light scattered by these marks. Hereinafter, the configuration of the optical system 20 will be described with reference to FIG.

FIG. 2 shows a schematic diagram of the optical system 20. The light source 23 emits the illumination light L1. The light source 23 is, for example, an emission end face of an optical fiber. After the illumination light L1 emitted from the light source 23 is converged by the converging lens 24, the reflecting mirror 26
Reflected by The illumination light L2 reflected by the reflecting mirror 26 propagates along the optical axis 25 of the objective lens 22,
Incident on. The converging lens 24 forms an image of the light source 23 at a focal point BF on the image space side of the objective lens 22. For this reason, the illumination light L2 is collimated by the objective lens 22, and becomes a parallel light beam L3. The parallel light beam L3 illuminates the wafer mark and the mask mark formed on the wafer 11 and the mask 12.

The converging lens 24 and the objective lens 22 may be used as critical illumination in which an image of the light source 23 is formed on the observation target.

The scattered light L4 scattered by the wafer mark and the mask mark enters the objective lens 22. Objective lens 2
2 converges the scattered light L4 into a converged light beam L5, and forms an image on the light receiving surface 29 of the image detection device 21. Reflector 26
Has a through hole 26a centered on a point intersecting the optical axis 25. The convergent light beam L5 passes through the through hole 26a and reaches the light receiving surface 29.

The reflecting mirror 26 is arranged near the light receiving surface 29. Therefore, at the position where the through-hole 26a is arranged, the convergent light beam L5 is thin. Through hole 26a
Should be large enough to allow the narrowed convergent light beam L5 to pass without vignetting. The cross section S2 of the light beam of the illumination light L2 at the position where the through hole 26a is arranged is:
It is sufficiently larger than the cross section S5 of the convergent light beam L5. Therefore, most of the illumination light is reflected by the reflecting mirror 26.

When the optical system 20 shown in FIG. 2 is used, the illumination light L1 emitted from the light source 23 can efficiently reach a wafer mark or a mask mark which is an object to be observed. The scattered light L4 incident on the objective lens 22
Can be made to reach the light receiving surface 29 without being attenuated.

The convergent light beam L5 becomes thicker as it approaches the objective lens 22. Therefore, when the position where the reflecting mirror 26 is disposed moves toward the objective lens 22, the through hole 26a must be enlarged. The larger the through hole 26a, the greater the loss of illumination light. In order to sufficiently obtain the effect of using the reflecting mirror 26 having the through hole 26a, the area of the cross section S5 of the convergent light beam L5 at the position where the through hole 26a is arranged is one of the area of the cross section S2 of the illumination light L2. / 10
It is preferable to arrange the reflecting mirror 26 at a position below.

FIG. 2 shows a case where the reflecting mirror 26 is provided with a through hole 26a, but a light transmitting area may be provided instead of the through hole. For example, by depositing a metal film on a region other than the light transmission region on the surface of the transparent substrate,
Such a reflecting mirror is obtained.

Returning to FIG. 1, the description will be continued. Image detection device 2
Reference numeral 1 denotes a wafer 11 and a mask 1 imaged on a light receiving surface 29.
An image is obtained by photoelectrically converting an image caused by the scattered light from Step 2.
These image signals are input to the control device 30.

The control device 30 processes the image signal input from the image detection device 21 to detect the relative position between the wafer 11 and the mask 12. Further, the wafer 11 and the mask 1
Control signals are sent to the drive mechanisms 17 and 18 so that 2 has a predetermined relative positional relationship. The driving mechanism 17
Based on this control signal, the mask holder 16 is translated in the XY plane and rotated around the Z axis. Drive mechanism 18
Moves the wafer holder 15 in the Z-axis direction based on this control signal, and slightly rotates it around the X-axis and the Y-axis.

FIG. 3A shows a wafer mark 13 for alignment formed on the wafer 11 and the mask 12 shown in FIG.
FIG. 3 is a plan view illustrating an example of a relative positional relationship between A, 13B, and a mask mark 14. 3 rectangular patterns in Y-axis direction
Wafer marks 13A and 13B are arranged in rows and columns in the X-axis direction. One mask mark 14 is formed by arranging three similar rectangular patterns in the Y-axis direction and five in the X-axis direction in a matrix. In the state where the alignment has been completed, the mask mark 14 is disposed substantially at the center between the wafer marks 13A and 13B in the Y-axis direction.

The long sides of the rectangular patterns of the wafer marks 13A and 13B and the mask mark 14 are parallel to the X axis, and the short sides are parallel to the Y axis. The length of the long side of each rectangular pattern is, for example, 2 μm, and the length of the short side is, for example, 1 μm.
m, and the arrangement pitch in the X-axis and Y-axis directions of the rectangular pattern in each mark is 4 μm. The center-to-center distance between wafer marks 13A and 13B is 56 μm.

FIG. 3B is a dashed line B3 of FIG.
The sectional view in -B3 is shown. The wafer marks 13A and 13B are formed by patterning, for example, a SiN film, a polysilicon film, and the like formed on the exposed surface. The mask mark 14 is formed by patterning a Ta ₄ B film formed on the mask surface of the membrane 12 made of, for example, SiC or the like.

FIG. 3C is a dashed line C3 of FIG.
The sectional view in -C3 is shown. Wafer mark 13A, 1
3B and the illumination light incident on the mask mark 14 are shown in FIG.
The light is scattered at the short edge of each rectangular pattern in FIG. The light applied to the area other than the edge is specularly reflected, and FIG.
Does not enter the objective lens 22. Therefore, only the scattered light from the alignment mark can be detected by the image detection device 21.

In the object space of the objective lens 22 shown in FIG. 1, scattered light from a plurality of points on one plane perpendicular to the optical axis 25 simultaneously forms an image on the light receiving surface 29 of the image detecting device 21.
A plane in which object points in the object space formed on the light receiving surface 29 are collectively called an "object surface".

In FIG. 3C, the wafer mark 13
Of the edges of A, 13B and the mask mark 14, scattered light from the edge on the object surface 27 is focused on the light receiving surface, but scattered light from the edge not on the object surface is not focused, As the edge moves away from the object surface, the image becomes out of focus due to scattered light from the edge. Therefore, among the edges of each mark, the image due to the scattered light from the edge closest to the object surface is the sharpest, and the image due to the scattered light from the edge distant from the object surface is blurred.

FIG. 4 is a diagram in which an image on the light receiving surface due to scattered light from the edges of the wafer marks 13A and 13B and the mask mark 14 is sketched. The u-axis in FIG. 4 is shown in FIG.
, The v-axis corresponds to the Y-axis in FIG. 3C. Wafer mark 1
Images 40A and 40B due to scattered light from 3A and 13B
Appear apart in the v-axis direction, during which the mask mark 14
The image 41 due to the scattered light from appears.

Since scattered light due to the front edge and the rear edge of each rectangular pattern is observed, two dot images appear for one rectangular pattern. In each image, an image due to the scattered light from the edge near the object surface 27 in FIG. 3C clearly appears, and then becomes more blurred as the distance from the edge in the u-axis direction increases. Further, as shown in FIG. 3 (C), since the observation optical axis 25 is inclined with respect to the exposure surface, the position u _{0 where the} images 40A and 40B are most focused by the scattered light from the wafer mark and the mask. the position u ₁ that matches the most focused image 41 by scattered light from the mark, does not coincide with respect to the u-axis direction.

Image 41 due to scattered light from mask mark
Is positioned at the center between the images 40A and 40B in the v-axis direction so that the wafer holder 15 and the mask holder 1 in FIG.
6, the wafer 11 and the mask 12 can be aligned with respect to the Y-axis direction, that is, the direction of the line of intersection between the object surface and the exposure surface.

FIG. 5 shows a case where the wafer mark is formed of SiN and the mask mark is formed of Ta ₄ B.
An example of an image signal obtained by the image detection device 21 is shown.
The horizontal axis corresponds to the v-axis in FIG. 4, and the vertical axis represents the light intensity. Note that this image signal is the most in-focus scanning line of the image 41 and the scanning line at the position where the images 40A and 40B are most in-focused among the image signals obtained by scanning the light receiving surface shown in FIG. The image signal corresponding to the scanning line at the position is synthesized. Three peaks corresponding to the mask mark appear at substantially the center, and three peaks corresponding to the wafer mark appear on both sides thereof.

Hereinafter, an example of a method of detecting the relative position between the mask mark and the wafer mark from the waveform shown in FIG. 5 will be briefly described. First, the correlation coefficient with the peak waveform corresponding to each of the two wafer marks is calculated while shifting the peak waveform corresponding to the mask mark in the v-axis direction. The shift amount giving the maximum correlation coefficient corresponds to the center-to-center distance between the wafer mark and the mask mark.

By moving the wafer and the mask so that the interval between the peak waveform corresponding to the mask mark and the peak waveform corresponding to each of the wafer marks on both sides thereof becomes equal, the position in the Y-axis direction in FIG. Matching can be performed.

The two-dimensional image signal shown in FIG.
The relative position between the wafer and the mask may be obtained by performing parallel pattern movement in the axial direction and the v-axis direction and performing similarity pattern matching between the image of the mask mark and the image of the wafer mark. By performing pattern matching of a two-dimensional image, a distance between images in the u-axis direction and the v-axis direction can be obtained.

In order to detect the in-focus position on the u-axis from the image shown in FIG. 4, it is necessary to obtain a bright image having a certain reference value or more. By using the optical system according to the embodiment shown in FIG. 2, a bright image can be obtained. Further, comparing the optical system of the conventional position detecting device shown in FIG. 6 with the optical system according to the embodiment shown in FIG.
By using the optical system according to the embodiment, it becomes possible to employ a darker light source.

The present invention has been described in connection with the preferred embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0040]

As described above, according to the present invention,
The illumination light is reflected by a reflecting mirror having a through hole to illuminate the observation target. The scattered light from the observation object is converged, and an image is formed through the through hole. Since the half mirror is not used, attenuation of the illumination light and the scattered light can be prevented by the half mirror. This makes it possible to obtain a relatively bright image using a dark light source.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a position detecting device using an illumination optical system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an illumination optical system according to an embodiment.

FIG. 3 is a plan view and a sectional view of a wafer mark and a mask mark.

FIG. 4 is a diagram in which an image due to scattered light from a wafer mark and a mask mark is sketched.

FIG. 5 is a graph showing an image signal according to a comparative example for explaining the embodiment.

FIG. 6 is a schematic front view of a conventional oblique detection device.

[Explanation of symbols]

 Reference Signs List 10 Wafer / mask holder 11 Wafer 12 Mask 13A, 13B Wafer mark 14 Mask mark 15 Wafer holder 16 Mask holder 17, 18 Drive mechanism 20 Optical system 21 Image detector 22 Objective lens 23 Light source 24 Convergent lens 25 Optical axis 26 Reflector 26a Through hole 27 Object surface 29 Light receiving surface 30 Controller 40A, 40B Image due to scattered light from wafer mark 41 Image due to scattered light from mask mark

Claims (5)

[Claims] A light source that emits illumination light; a reflector that reflects the illumination light emitted from the light source; and an illumination device that illuminates the observation target by transmitting the illumination light reflected by the reflector. An objective lens that converges the scattered light from the observation target; and a transmission area formed on the reflection mirror so that a light beam scattered by the observation target and converged by the objective lens passes through the reflection mirror. An illumination optical system for a microscope provided with. 2. The illumination optical system for a microscope according to claim 1, wherein the transmission area of the reflection mirror is a through hole formed in the reflection mirror. 3. The optical axis of the illumination light reflected by the reflecting mirror coincides with the optical axis of the objective lens.
2. The illumination optical system for a microscope according to 1. 4. The illumination optical system for a microscope according to claim 1, further comprising a converging lens that converges illumination light emitted from the light source and makes the light incident on the reflecting mirror. 5. A cross-sectional area of a light beam scattered by the observation object and converged by the objective lens at a position where a through hole of the reflecting mirror is arranged is 1/10 or less of that of the illumination light. The illumination optical system for a microscope according to claim 4, wherein the reflecting mirror is disposed at a position that becomes: