JPS6235653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lighting device having an ellipsoidal reflecting mirror, and particularly to an optical system for detecting the position of a light source thereof.

In general, in an illumination optical system that uses a parabolic mirror or a condensing lens with a small F number, and places a light source such as an ultra-high pressure mercury lamp near the focal point,
Correct predetermined positioning of the light source is necessary for high performance. Therefore, each time the light source is replaced, its position must be adjusted in each three-dimensional direction. Conventionally, in order to detect that the light source position is correct, the illuminance and its location unevenness on the lighting surface were measured, and the light source position was adjusted based on this information, but this required a great deal of effort and time. did.
It is known that illumination devices using ellipsoidal mirrors include a screen that forms a light source image at the second focal point of the ellipsoidal mirror or its conjugate point, but since the screen is on the optical axis of the illumination system, Three-dimensional information about the light source position cannot be clearly obtained, and it is difficult and inefficient to judge in which direction and by how much the light source should be moved in order to adjust the light source to the correct position.

For this reason, the patent application filed in 1983 by the same applicant as the present application is
No. 162343 discloses a light source position detection optical system for detecting the light source position, in which a part of the light flux from the light source is taken out from outside the optical axis of the illumination optical system, and a light source image is formed by this part of the light flux. .

According to this configuration, a clear image can be formed over a relatively wide range of light source positions, so basically it is possible to accurately position the light source on the optical axis. However, when the light source is relatively large compared to the radius of curvature of the vertex of the ellipsoidal mirror, (1) the partial magnification of the light source image is different, so the distortion of the light source image is large;

(2) When the light source is an ultra-high pressure mercury lamp or the like, there is an opening in the center of the ellipsoidal mirror, which may cause vignetting in the light source image.

This problem exists, and it has been found that it is difficult to accurately align the light source.

The purpose of the present invention is to eliminate the above-mentioned drawbacks,
An object of the present invention is to provide an illumination device that can accurately detect the position of a light source even when the light source is large relative to the radius of curvature of the apex of an ellipsoidal mirror.

The present invention includes an illumination optical system having an ellipsoidal mirror and a light source arranged in a predetermined positional relationship with respect to a first focal position of the ellipsoidal surface, and a light source position detection optical system for detecting the position of the light source. In the illumination device, a field lens is provided on or near the second focal point of the ellipsoidal surface, and the light source position detection optical system detects a part of the luminous flux emitted from the light source and reflected by the ellipsoidal mirror after exiting the field lens. a condensing element arranged so as to have an optical axis tilted at a predetermined angle with respect to the optical axis outside the optical axis of the illumination optical system, in order to extract from the position of the illumination optical system and form an image of the light source; The principal rays reaching each position of the light source image by the condensing element are configured to be substantially parallel to each other between the ellipsoidal mirror and the field lens due to the action of the field lens, and the optical axis of the condensing element is configured to be substantially orthogonal to the optical axis of the illumination optical system through reflection by the ellipsoidal mirror.

Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a perspective view showing a schematic optical system of an embodiment according to the present invention. This embodiment is applied to a reduction projection type exposure apparatus for VLSI manufacturing using an ellipsoidal reflecting mirror.

The ultra-high pressure mercury lamp 11 as a light source is provided on the first focus F 1 of the ellipsoidal reflector ₁₂ , and the light flux emitted from the first focus F ₁ is focused on the second focus F ₂ of the ellipsoidal reflector 12 . , it is well known that a light source image is formed here. The light beam reflected by the dichroic mirror 17 installed obliquely between the ellipsoidal reflector 12 and the second focal point _F2 passes through an optical member 18 including an interference filter and an integrator, and is reflected by the reflector 19. condenser lens 20
guided by. The light flux emitted from the condenser lens 20 uniformly illuminates the mask 21, and the pattern image on the mask is reduced and projected onto a wafer (not shown) by a reduction projection lens (not shown) for printing exposure.
For such an illumination optical system, a field lens 30 is provided as a light source position detection optical system at the second focal point _F2 behind the dichroic mirror 17, and a field lens 30 is further provided outside the optical axis _A0 of the illumination optical system. positive lens 13a, reflecting mirror 14a, signboard 15a
and a positive lens 13b similarly provided outside the optical axis _A0 .
A second light source position detection optical system consisting of a reflecting mirror 14b and a signboard 15b is provided. The optical axis of the field lens 30 is the optical axis A ₀ of the ellipsoidal mirror 12.
, and its focal length is approximately equal to the distance to each positive lens 13a, 13b. The optical axis A ₁ of the first detection optical system and the optical axis A ₂ of the second detection optical system are respectively bent by the ellipsoidal reflecting mirror 12 to form the optical axis A ₀ of the illumination optical system.
Furthermore, since both optical axes A ₁ and A ₂ are orthogonal to each other at the first focal point F ₁ where the light source should be located, by detecting the image of the light source on the signboards 15a and 15b, It is possible to grasp the position of the light source 11 three-dimensionally and to accurately position it at the optimal position.

The light beam used for light source position detection is transmitted through a positive lens 13.
This partial luminous flux is determined by the apertures of a and 13b, and is reflected by the partial areas S ₁ and S ₂ of the ellipsoidal reflecting mirror 12. The positive lenses 13a and 13b have the function of extracting a light beam contributing to the formation of a light source image and the second focal point.
The secondary image of the light source image formed on F ₂ is displayed on the signboard 15.
a, 15b.
The reflecting mirrors 14a and 14b each have positive lenses 13a and 13.
This is simply to change the traveling direction of the luminous flux from b, and by combining it with other reflecting mirrors, relay lens systems, etc., the signboards 15a and 15b can be placed at positions where they can be most easily observed.

Here, the first and second detection optical systems are substantially equivalent optical systems, and the operation of the first detection optical system will be explained below with reference to the drawings. FIG. 2 is a schematic optical path diagram from the light source to the light source image formed by the first detection optical system.
In an ellipsoidal reflector, its first focus F ₁ and second focus
The focal point _F2 is conjugate, and the image of the object point on the first focal point _F1 is formed on the second focal point _F2 . However, the image on the second focal point _F2 of an object having a size on the first focal point _F1 becomes complicated, and for this reason, it is shown only conceptually by arrows in the figure. As shown in the figure, the field lens 3 overlaps the image on the second focal point _F2 .
0 is placed, and the image on the second focal point _F2 is the positive lens 1
3a and the reflecting mirror 14a, the image is re-imaged onto the signboard 15a. For the sake of explanation, based on the reversibility law of the light source, the center point of the target plate 15a in the detection optical system is
Let's trace back the chief ray that reaches P', point Q' at one end, and point R' at the other end. First, the light ray _l1 from the center point P' is reflected by the reflecting mirror 14a, and then, as shown in the figure, the light ray l1 is emitted from the positive lens 13a, which is arranged at a predetermined angle with respect to the optical axis _A0 of the ellipsoidal mirror 12. Along the axis _A1 , it passes through the center of the positive lens 13a and the field lens ₃₀ , that is, the second focal point F2, and reaches the ellipsoidal mirror 12, where it is reflected in a direction approximately perpendicular to the optical axis _A0 of the ellipsoidal mirror 12. and reaches the first focus _F1 . On the other hand, the ray l ₂ from one end Q' of the signboard 15a and the ray l ₃ from the other end R' each pass through the center of the positive lens 13a, reach outside the center of the field lens 30, and are combined by the field lens 30. Positive lens 1
It is almost parallel to the optical axis _A1 of 3a. Then, they are each reflected by the ellipsoidal mirror 12 and reach points Q and R in the vicinity away from the first focus _F1 .

In this way, the chief rays corresponding to each position of the light source image reach the ellipsoidal mirror in parallel with each other, so the partial area _S1 of the ellipsoidal mirror 12 as an aspheric surface becomes a small range, and the part of the light source image The difference in magnification is small and the distortion is also small. At the same time, since the partial region _S1 does not include the opening 12a of the ellipsoidal mirror 12, the possibility of vignetting is also reduced.

FIG. 3 is a comparative optical path diagram showing the effect of the detection optical system according to the present invention shown in FIG. 2. In the figure, members with the same symbols as in FIG. 2 have the same functions. In the configuration shown in FIG. 3, the field lens above the second focal point _F2 is removed, so the signboard 15a
The partial area S' ₁ for which the light rays reaching the area are reflected by the ellipsoidal mirror 12 occupies a fairly large area. That is, when the principal ray reaching the signboard 15a is traced back in the same way as above, the principal ray _l1 from the center point P' of the signboard 15a is reflected by the reflecting mirror 14a as in the case of FIG. , passes through the second focal point F ₁ at the center of the positive lens 13a, is reflected by the ellipsoidal mirror 12 in a direction perpendicular to its optical axis A ₀ , and reaches the first focal point F ₁ . The principal rays l ₂ and l ₃ from one end and the other end of the signboard 15a are reflected by the reflecting mirror 14a, pass through the center of the positive lens 13a, directly reach the ellipsoidal mirror 12, and are reflected there. Neighboring points Q″ and R″ are reached which are away from the first focus F ₁ . Both principal rays l ₂ and l ₃ reach the ellipsoidal mirror 12 in a diverging state while maintaining the angle at which they intersect at the positive lens 14a, so the partial area S′ ₁ on the ellipsoidal mirror necessary for their reflection is the second Partial area S ₁ when both chief rays shown in the figure become parallel due to the field lens 30
considerably larger than Therefore, as shown by the arrows in the diagram, the difference in imaging magnification between Q', Q'' and R', R'' in Figure 3 is the same as the difference in imaging magnification between Q', Q and R', R'' in Figure 2.
It is clear that the difference in image magnification is greater than the difference in the respective imaging magnifications, and the distortion of the image becomes large. In addition, the reflection area _S1 necessary for the light source position detection system on the ellipsoidal mirror is the third
As shown in the partial area S' ₁ in the figure, there is a possibility that the light source approaches the center opening 12a of the ellipsoidal mirror 12 and causes vignetting in the light source image.

As described above, it is clear from the comparison between FIG. 2 and FIG. 3 that the effect of the field lens 30 according to the present invention is very large. Note that since the field lens 30 is placed overlapping the light source image on the second focal point _F1 , the conjugate relationship between the first focal point _F1 and the signboard 15a remains unchanged; But that's fine. Furthermore, since the optical axis of the field lens 30 coincides with the optical axis of the ellipsoidal mirror, the effects of the field lens 30 on the first light source position detection optical system and the second light source position detection optical system are equivalent. Needless to say.

Furthermore, in FIG. 1, the positive lens 13a,
13b has the function of extracting the light beam for forming a light source image for detecting the light source position, and substantially limits the light beam contributing to the formation of the light source image. However, in the vicinity of these positive lenses, It is also possible to provide a diaphragm in the diaphragm and limit the light flux extracted by this diaphragm.

As described above, according to the illumination device of the present invention, even when the light source is large relative to the radius of curvature of the apex of the ellipsoidal mirror, the distortion of the light source image is reduced due to the action of the field lens, and there is also a possibility that vignetting may occur. Therefore, the light source position can be detected accurately, and more accurate light source positioning is possible.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment according to the invention;
3 and 3 are comparative optical path diagrams for explaining the effects of the present invention. Explanation of symbols of main parts, 12...Ellipsoidal mirror,
F ₁ ...First focus, _F2 ...Second focus, 30...Field lens, {13a, 13b...Positive lens, 14a, 14b...Reflector, 15a, 15b
...Character} Light source position detection optical system.

Claims (1)

[Scope of Claims] 1. An illumination optical system having an ellipsoidal mirror and a light source arranged in a predetermined positional relationship with respect to the first focal position of the ellipsoidal mirror, and a light source position detection for detecting the position of the light source. In the lighting device having an optical system, a field lens is provided on or near the second focal point of the ellipsoidal mirror, and the light source position detection optical system detects part of the light beam emitted from the light source and reflected by the ellipsoidal mirror. The illumination optical system is arranged so as to have an optical axis inclined at a predetermined angle with respect to the optical axis outside the optical axis of the illumination optical system in order to extract the light source from a position after exiting the field lens and form an image of the light source. It has a condensing element 13a, and is configured such that principal rays reaching each position of the light source image by the condensing element 13a are substantially parallel to each other between the ellipsoidal mirror and the field lens due to the action of the field lens. An illumination device characterized in that the optical axis of the condensing element 13a is substantially perpendicular to the optical axis of the illumination optical system through reflection by the ellipsoidal mirror.