JPH0415924B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alignment optical system for a projection exposure apparatus, and more particularly to an alignment optical system for two objects to be made mutually conjugate by a projection objective.

In a reduction projection type exposure apparatus used for manufacturing LSI, VLSI, etc., an alignment optical system for observing or detecting the positional relationship between a reticle as a projection original and a wafer through a projection objective lens is a patent application filed by the same applicant as the present application. This was proposed in 1987-142612. According to this alignment optical system, it is possible to accurately observe the alignment mark on the wafer and the reference mark on the reticle without adversely affecting the exposure area of the wafer, and in addition, it is possible to change the printed size, that is, to change the reticle size. Even when the position of the reference mark on the reticle changes, the reticle and wafer can be aligned by moving some of the members. However, if some parts are moved in response to changes in reticle size, the state in which the illumination light coaxially supplied by the alignment optical system illuminates the alignment marks on the wafer will also change, so it will always remain constant. It was not possible to form an alignment mark image under these conditions. For this reason, it has been difficult to perform stable and highly accurate alignment even when the reticle size changes.

An object of the present invention is to provide an alignment optical system that can always align a reticle and a wafer with a constant high accuracy even when the reticle size changes.

The present invention provides a projection exposure apparatus for aligning a reticle and a wafer through a projection objective lens for projecting a pattern on a reticle onto a wafer. a first positive lens group for converting into a parallel light beam; a second positive lens group for condensing the light beam from the first positive lens group onto a predetermined image plane; the first positive lens group and the second positive lens group; and an optical correction member disposed between the first positive lens group and the first positive lens group, the first positive lens group being movable in order to convert a light beam from a second object point different from the first object point into a parallel light beam. The optical correction member is movable on the optical path between the first positive lens group and the second positive lens group in a predetermined relationship with respect to the amount of movement of the first positive lens group, and By moving the first positive lens group and the optical correction member, an image of the second object is formed on the predetermined image plane in the same manner as the image of the first object, and an image of the first object is formed on the predetermined image plane. an optical system including the first positive lens group, the second positive lens group, and the optical correction member when forming an image of the second object on the predetermined image plane and when forming an image of the second object on the predetermined image plane; An illumination means is provided that maintains the positions of the entrance pupil and the exit pupil constant and supplies illumination light to the object surface through the optical system, and a rectangular aperture arranged at a position conjugate with the entrance pupil of the optical system. The longitudinal direction of the rectangular aperture optically coincides with the moving direction of the first positive lens group. The alignment optical system basically employs the double conjugate maintaining optical system proposed in Japanese Patent Application No. 57-34366 by the same applicant as the present application, and in this configuration, a rectangular aperture diaphragm is further combined with the light source means. It is something that In other words, in the alignment optical system of a projection exposure apparatus that aligns a reticle and a wafer through a projection objective lens for projecting a pattern on a reticle onto a wafer, an afocal system consisting of a plurality of lens groups and an afocal system are used. Two positive lens groups coaxially arranged on both sides of the afocal system, and a light source means for supplying illumination light to the object plane via the afocal system and the two positive lens groups, The reticle-side positive lens group of the positive lens group and the afocal system are configured to be movable with respect to the light source means, and
The light source means is provided with a rectangular opening, and the longitudinal direction of the rectangular opening corresponds to the direction in which the reticle-side focal point of the reticle-side positive lens group can move on the reticle.

The present invention will be explained below based on the drawings.

FIG. 1 is a basic configuration diagram of an alignment optical system according to the present invention. The wafer W and the reticle R are arranged at a conjugate position with a predetermined magnification with respect to the projection objective lens _L50 , and the reticle R is uniformly illuminated by a main illumination optical system (not shown), so that the pattern on the reticle R is aligned with the wafer W. The projection is printed on top. The projection objective L ₅₀ equivalently consists of two positive lens groups L ₅₁ and L ₅₂
and a diaphragm _S50 provided between the two. The projection objective L ₅₀ is usually designed to be telecentric on the wafer W side.
For this purpose, the diaphragm _S50 is arranged on the focal point of the wafer-side positive lens group _L51 . The alignment optical system according to the present invention observes or measures the state of alignment between the positions of the wafer W and the reticle R through such a projection objective lens _L50 . This alignment optical system includes a first positive lens group L ₁₀ , an afocal system L ₂₀ consisting of a negative lens L ₂₁ and a positive lens L ₂₂ , a second positive lens group L ₄₀ , a third positive lens group L ₆₀ , and a rectangular aperture 7
It consists of a rectangular opening 70a formed by 0. Here, the longitudinal direction of the rectangular aperture 70a is within a plane containing the optical axis A×1 of the projection objective lens _L50 , that is, within the meridian plane of the optical axis A×1, and the reticle R
is arranged to match the front focal position of the first positive lens group _L10 . Furthermore, the second positive lens group _L40 is telecentric on the image side. The third positive lens group _L60 is for supplying the light beam from the rectangular aperture 70 as a parallel light beam. Since the alignment mark Wm on the wafer W and the reference mark Rm on the reticle R are provided at the periphery of a predetermined exposure pattern, the optical axis A× of the alignment optical system
2 is disposed offset from the optical axis A×1 of the projection objective lens L ₅₀ by the distance from the center of the reticle R of the reference mark Rm, as shown. FIG. 1A shows light rays representing a conjugate relationship with respect to the pupil of the alignment optical system, and the position of the pupil on the reticle R side of the alignment optical system matches the entrance pupil position of the projection objective L ₅₀ . That is, the third positive lens group
L ₆₀ , second positive lens group L ₁₂ , afocal system L ₂₀ ,
Through the first positive lens group _L10 , an image E' of the light source E on the rectangular aperture 70a is formed at the entrance pupil position of the projection objective _L50 , and a light source image E'' at the position of the aperture _S50 of the projection objective _L50 . is formed, resulting in so-called Koehler illumination.Since the projection objective lens _L50 and the alignment optical system are decentered, the light source E is also placed decentered from the optical axis A×2 of the alignment optical system. On the image side of the positive lens group L ₄₀ , it is not strictly telecentric, but is a parallel beam system having a slight angle with respect to the optical axis.
Figure B shows a light ray representing a conjugate relationship with respect to the object for the alignment optical system, that is, the reference mark Rm on the reticle R, and the reference mark Rm on the reticle R and the rear focal position of the second positive lens group L ₄₀ . It can be seen how the formed reference mark forms an image with the image R′m. The focal point of the third positive lens group L ₆₀ coincides with the position of the reference mark image R'm, and the rectangular aperture 70 side of the third positive lens group L ₆₀ is a parallel system.
An image of the alignment mark Wm on the wafer W is projected at the position of the reference mark Rm by a projection objective lens _L50 , and an image of the alignment mark Wm on the wafer W is projected at the position of the reference mark image R′m. Subsequent images are also formed, and the state of alignment between the wafer W and the reticle R is observed and measured from these images.

In this alignment optical system, when the reticle R, projection objective lens L ₅₀ and wafer W move relative to the alignment optical system,
By moving the first positive lens group _L10 by the same amount and aligning the front focus of the first positive lens group _L10 with the reticle R, and by interlocking the afocal system _L20 , the reticle image R' m can be formed at a fixed position, and a pupil image, that is, a light source image E' can be formed at a fixed position from the reticle R.

Here, the focal lengths of the negative lens L ₃₁ and the positive lens L ₂₂ forming the afocal system L ₂₀ are respectively f ₂ ,
f ₃ , the amount of movement of the first positive lens group L ₁₀ in the optical axis direction is △dt, and the amount of movement of the afocal system L ₂₀ in the optical axis direction is △d ₃ , then △dt = (1 - f ² / ₂ / ^f2 / ₃ )△ _d3 ...(1) Regarding the interlocking of the first positive lens group _L10 and the afocal system _L20 ,
This is as explained in the previous patent application No. 57-34366. As mentioned above, the same applies to the case where the afocal system L ₂₀ is composed of two positive lenses. In addition, in FIG. 1, when the distance of the optical axis (A x 1) of the projection objective lens L ₅₀ changes with respect to the optical axis (A x 2) of the alignment light, the longitudinal direction of the rectangular aperture 70a changes. Since it coincides with the meridian plane of the optical axis (A×1) of the projection objective lens, an illumination state with a constant aperture width can be maintained at all times. Therefore, with the above configuration, even if the positions of the reticle R, wafer W, and projection objective lens change relative to the alignment system, the state of alignment between the reticle and wafer can always be observed and maintained at a constant position. It is possible to maintain Koehler illumination at all times while being able to perform measurements. Here, the image R′m of the reference mark Rm on the reticle R and the image of the alignment mark Wm on the wafer W are in the parallel light beam shown in FIG. 1B, that is, the first positive lens group L ₁₀ and the afocal system L ₂₀ A semi-transmissive mirror can be inserted and taken out between the afocal system _L20 and the second positive lens group _L12 , or on the image side of the second positive lens group _L12 .

2 and 3 are schematic configuration diagrams of an embodiment of the alignment optical system for a projection exposure apparatus according to the present invention, and FIGS. 2A and 3A show the same embodiment, with the size of the reticle R ( Fig. 2B and Fig. 3B show cases where the exposure area size) is different.
is an explanatory diagram of the entrance pupil of the projection objective lens, and FIGS. 2C and 3C are explanatory diagrams of the aperture plane of the light source section. In the figure, members having the same functions as those in FIG. 1 are given the same reference numerals. In this embodiment, the first positive lens group L ₁₀ and the reflecting mirror M ₁₀ are integrally provided by the objective lens barrel 10.
is provided so as to be movable along the optical axis parallel to the reticle R. The afocal lens barrel 20, which integrally has an afocal system _L20 constituted by two lens groups _L21 and _L22 , is movable along the optical axis in conjunction with the objective lens barrel 10. be. The wafer W and the reticle R are arranged conjugately with respect to the projection objective lens L ₅₀ , and the reticle R is illuminated by illumination light 50 supplied from a main illumination device (not shown).
The upper pattern is projected onto the wafer W. The images of the alignment mark Wm on the wafer W and the reference mark Rm on the reticle R are captured by the reflecting mirror M ₁₀ , the first positive lens group L ₁₀ , the afocal system L ₂₀ , and the second positive lens group
It is formed on the imaging surface 6a of the imaging tube 6 via L ₄₀ and the semi-transmissive mirror M ₂₀ . On the other hand, the light beam from the light source on the rectangular aperture 70a passes through the third positive lens group _L60 , is reflected by the reflecting mirror _M30 and the semi-transparent mirror _M20 , reaches the reticle R and the wafer W, and is transferred to the second positive lens group _L40. , the afocal system L ₂₀ , the first positive lens group L ₁₀ , and the reflecting mirror M ₁₀ project an image E'' of the light source E onto the position of the aperture S ₅₀ of the projection objective lens L ₅₀ to perform Köhler illumination.

In such a configuration, when the reticle R is replaced with another larger reticle R' and the position of the alignment reference mark Rm changes, the objective lens barrel 10 is moved as shown in FIG. 3A. Place the reference mark at the front focus of the first positive lens group _L10.
Rm, and by interlocking the afocal lens barrel 20 so as to satisfy the above formula (1), the standard can be placed on the imaging surface 6a of the imaging tube 6 without moving any other members. Image R′m of mark Rm and alignment mark Wm on wafer W
can form an image of the rectangular aperture 70.
An image E'' of the light source E on a can be formed at the aperture position of the projection objective L ₅₀ , and the Köhler illumination can be completely maintained.

Here, the rectangular opening 70a formed by the slit-shaped rectangular diaphragm 70 provided in the light source section is
It is arranged so that its longitudinal direction corresponds to the movement direction of the focal position of the first positive lens group _L10 , that is, the radial direction of the reticle R in this case, so that the image of the rectangular aperture 70a is Lens L ₅₀
It is formed so that its longitudinal direction coincides with the meridian direction at the entrance pupil position. Figures 2B and 3B respectively show the entrance pupil plane of the projection objective _L50 , and the image of the aperture plane of the light source overlaps the entrance pupil _IE .
I _F ' and an image 70a' of the rectangular opening 70a is formed.

Further, FIG. 2C and FIG. 3C each show the aperture plane of the light source section, and a rectangular aperture 70a exists in the aperture plane I _F , and the projection objective lens L ₅₀ is incident on the rectangular aperture 70a. A pupil image I _E ' is formed. In each figure, the area where illumination light is present is indicated by diagonal lines.

The configuration in FIG. 2 is for a case where the reticle R is small, and the configuration in FIG. 3 is for a case where the reticle R' is larger than the reticle R in FIG. As shown in each figure, as the reticle size changes,
When the objective lens barrel 10 and the afocal lens barrel 20 in the alignment system move, the projection objective lens
In the entrance pupil plane of L ₅₀ , the rectangular aperture image 70a' of the light source moves in its longitudinal direction with respect to the entrance pupil _IE , while in the aperture plane of the light source, the entrance pupil of the projection objective L ₅₀ The image I _E ' moves over the rectangular opening 70a in the longitudinal direction of the rectangular opening 70a. Therefore, both in the entrance pupil plane of the projection objective _L50 and in the aperture plane of the alignment system, the rectangular aperture 70a or its image 70a' and the entrance pupil _IE of the projection objective or its image _IE ' are rectangular. It only moves relatively in the longitudinal direction of the aperture 70a, and therefore there is almost no change in the state of illuminating the alignment mark Wm on the wafer W through the projection objective lens _L50 . This is because, as shown in FIGS. 2B and 3B, the diameter φ _E of the entrance pupil I _E and the rectangular aperture image 70
The ratio of a' to the width D, D/φ _E , is always kept constant, which means that the sigma value in the width direction of the rectangular aperture (the N of the illumination system relative to the NA of the projection objective).
This is because the ratio of A.:σ) is constant. Note that in the longitudinal direction of the rectangular aperture, the sigma value is always much larger than 1, and the illumination state in this direction hardly changes even when the alignment optical system is moved. In such a configuration, by changing the width of the slit-like rectangular opening 70a formed by the rectangular diaphragm 70, it is possible to change the sigma value in the width direction.

FIG. 4 is a perspective view showing a schematic configuration of the light source section used in FIGS. 2A and 3A, in which a light beam from a light source 71 becomes a substantially parallel beam by a condensing lens 72, and a second condensing lens The light is focused onto the rectangular diaphragm 70, and an enlarged image of the light source is formed on the rectangular diaphragm 70. As shown in FIG.
After the light is focused by the optical fiber bundle 7
4, the exit side portion 74a of the optical fiber 74 may be rectangular, and the exit end 70a' may form a substantially rectangular opening.

According to the configuration of the alignment optical system according to the present invention as described above, the longitudinal direction of the rectangular aperture is provided corresponding to the radial direction of the reticle, that is, the meridional plane, and the sigma value in the sagittal direction perpendicular to the radial direction is Since the images are kept constant, if the reference marks on the reticle and the alignment marks on the wafer are placed in a radial straight line, that is, radially along the meridian line, these images will always be kept constant. can be formed with a resolution of Fig. 6 is a plan view of a reticle in which three radial reference marks Rx, Ry, and Rθ are provided in mutually orthogonal directions, and Fig. 7 is a plan view of a reticle in which three radial alignment marks Wx, Wy, and Wθ are provided in directions perpendicular to each other. FIG. The relative positioning of these reticles and the wafer is determined by the three reference marks on the reticle R, as shown in the plan view of Figure 8.
This is achieved by three alignment optical systems installed perpendicularly to the optical axes of Rx, Ry, and Rθ. That is, by aligning the three reference marks with each alignment mark on the wafer through the projection objective lens, the reticle and the wafer can be arranged in a predetermined relationship. If the reticle is replaced with one with a smaller effective area and the reference marks Rx', Ry', and Rθ' on the reticle move to the center as shown by the dotted lines in FIG. In each system, as described above, the objective lens barrel 10 and the afocal lens barrel 20 move in the radial direction of the reticle R to maintain the same illumination state as before the reticle was replaced. That is, in each alignment system, the rectangular opening 70a formed by the rectangular diaphragm 70 is
In the figure, the direction perpendicular to the plane of the paper) coincides with the radial direction of the reticle R, that is, the meridian plane of the projection objective L ₅₀ , so the sigma value in the sagittal direction of the projection objective L ₅₀ is constant, and the radius The image of each mark in the direction is always formed with a constant resolution. In this way, the reticle and wafer are perfectly aligned in the x, y, and rotational directions.
In addition, three alignment systems were provided for the x direction, y direction, and rotation;
If the amount of rotation is also detected in one of the directions, the wafer and reticle can be aligned with only two alignment systems.

According to the alignment optical system configured as described above, even when the reticle size changes, images of both the reticle reference mark and the wafer alignment mark can be maintained at a fixed position by simply moving some of the members. It is possible to form a rectangular aperture stop, maintain a Kohler illumination state at all times, and keep the sigma value constant in the width direction of the rectangular aperture stop. Therefore, for example, images of both the radial reference mark on the reticle and the radial alignment mark on the wafer can be formed with constant high resolution, and alignment with high precision is always possible.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an alignment optical system according to the present invention, FIGS. 2A and 3A are schematic configuration diagrams of an embodiment of the present invention, and FIGS. 2B and 3B are projection objective lenses. FIGS. 2C and 3C are explanatory diagrams of the aperture of the light source section, FIGS. 4 and 5 are perspective views showing examples of the light source section, and FIGS. 6 and 7 The figures are plan views of a reticle and a wafer used in Examples, respectively, and FIG. 8 is a schematic plan view of a projection exposure apparatus using an alignment optical system according to the present invention. Explanation of symbols of main parts, R...Reticle, W...
...Wafer, L ₅₀ ...Projection objective, L ₁₀ ...First
Positive lens group, L ₂₀ ... Affocal system, L ₄₀ ... Second positive lens group, 70 ... Rectangular aperture diaphragm, 70a...
...Rectangular opening.

Claims (1)

[Claims] 1. In a projection exposure apparatus for aligning a reticle and a wafer through a projection objective lens for projecting a pattern on a reticle onto a wafer, from a first object point on the reticle; a first positive lens group for converting the light beam into a parallel light beam, and a second positive lens group for condensing the light beam from the first positive lens group onto a predetermined image plane.
a positive lens group; and an optical correction member disposed between the first positive lens group and the second positive lens group, and the first positive lens group has a second object point different from the first object point. The optical correction member is movable in order to convert the light beam from the object point into a parallel light beam, and the optical correction member
is movable on an optical path between the first positive lens group and the second positive lens group in a predetermined relationship with respect to the amount of movement of the positive lens group, and the first positive lens group and the optical correction member , the image of the second object is formed on the predetermined image plane in the same manner as the image of the first object, and the image of the first object is formed on the predetermined image plane and the image of the second object is formed on the predetermined image plane. Maintaining constant positions of an entrance pupil and an exit pupil of an optical system including the first positive lens group, the second positive lens group, and the optical correction member when forming images of two objects on the predetermined image plane. An illumination means for supplying illumination light to the object plane through the optical system is provided, and a rectangular aperture is provided at a position conjugate with the entrance pupil of the optical system, and the longitudinal direction of the rectangular aperture is aligned with the An alignment optical system for a projection exposure apparatus, characterized in that the direction optically matches the moving direction of a first positive lens group. 2. The optical correction member has two optical elements that are integrally movable in order to guide the parallel light beam from the first positive lens group toward the second positive lens group as a parallel light beam. An alignment optical system for a projection exposure apparatus according to claim 1. 3. The projection exposure apparatus according to claim 2, wherein the two optical elements of the optical correction member are an afocal system consisting of lenses arranged apart by a difference in focal length from each other. Alignment optics.