JP2017003783A - Exposure apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make use of advantages of an exposure apparatus employing an Offner optical system, and make practical use possible in wider applications.SOLUTION: In an Offner optical system 1 in which a first spherical mirror 11 being a convex surface and a second spherical mirror 12 being a convex surface which is smaller than the first spherical mirror 11 are provided on Offner central axis C in a coaxially facing manner, at least one lens 5 is arranged so as to position on an optical path from an object point to the first spherical mirror 11 and on an optical path from the first spherical mirror 11 to an image point. The lens 5 is symmetric with respect to Offner central axis C, and makes deviation between a focal point on a tangential plane and a focal point on a sagittal plane smaller regarding light emitted from the object point at a remote position from an optical axis A.SELECTED DRAWING: Figure 1

Description

  The invention of this application relates to an exposure apparatus using an Offner optical system.

  Photolithography technology is employed in various semiconductor integrated circuit manufacturing processes and various FPD (Flat Panel Display) manufacturing processes. One of the main apparatuses used for photolithography is an exposure apparatus. An exposure apparatus broadly means an apparatus that exposes an object with a mask pattern and transfers an image of the pattern onto the object. Therefore, the important indexes indicating the performance of the exposure apparatus are the resolution and the overlay accuracy.

  As is well known, with the miniaturization of circuits, the requirements for resolving power and overlay accuracy are becoming stricter. Of these, the major factor that determines the resolving power is, of course, the performance of the optical system. In order to obtain a finer circuit, a high-resolution optical system in which aberrations are sufficiently suppressed is required. An exposure apparatus employing a lens system such as a stepper in order to obtain submicron resolution is composed of several tens of lenses to form an optical system and has a very complicated structure.

On the other hand, in addition to an exposure apparatus using such a lens system, an exposure apparatus using an Offner optical system is conventionally known as an exposure apparatus having an optical system composed of only a mirror system. 10 and 11 are schematic views of a conventional exposure apparatus using an Offner optical system. FIG. 10 is a schematic perspective view, and FIG. 11 is a schematic front sectional view.
The Offner optical system is an optical system that projects an image of a mask at an equal magnification using two spherical mirrors. As shown in FIGS. 10 and 11, the two spherical mirrors 11 and 12 are arranged coaxially, that is, in a state where the centers of the spherical surfaces are located on the same straight line. Hereinafter, this straight line is referred to as the Offner central axis and is indicated by C in the figure. One of the two spherical mirrors 11 and 12 is large and the other is small. Hereinafter, the larger one 11 is called a first spherical mirror, and the smaller one 12 is called a second spherical mirror.

The first spherical mirror 11 is a concave mirror, and the second spherical mirror 12 is a convex mirror. The mask M is arranged on one side with respect to the Offner center axis C, and the workpiece W which is an object to be exposed is arranged on the other side. For convenience of explanation, a virtual plane including the Offner center axis C is referred to as a reference plane and is indicated by S in FIG.
As shown in FIG. 10, the mask M is arranged in a posture perpendicular to the reference surface S, and the workpiece W is also arranged in a posture perpendicular to the reference surface S on the opposite side. The reference point on the arrangement surface of the mask M and the reference point on the arrangement surface of the workpiece W are on the same straight line perpendicular to the Offner center axis C and are located at the same distance from the Offner center axis C. . Hereinafter, a reference point on the placement surface of the mask M called the object side reference point, indicated by M ₀ in FIG. 10. A reference point on the arrangement surface of the workpiece W is called an image-side reference point, and is indicated by W ₀ in FIG. The object side reference point M ₀ and the image side reference point W ₀ are on the reference plane S.

In the optical system 1 shown in FIGS. 10 and 11, the optical axis A is set as an axis from the object side reference point M ₀ to the image side reference point W ₀ and is included in the reference plane S. That is, the object side reference point M ₀ is the object origin on the optical axis A, and the image side reference point W ₀ is the image origin on the optical axis A.
A trapezoidal mirror body 4 is disposed behind the second spherical mirror 12. The trapezoidal mirror body 4 is a member having a trapezoidal cross section, and each surface corresponding to the hypotenuse of the trapezoid is a reflecting surface. For convenience of explanation, one reflecting surface 41 of the trapezoidal mirror body 4 is called a first plane mirror, and the other reflecting surface 42 is called a second plane mirror. The angle of each flat mirror 41, 42 is 45 ° with respect to the optical axis A.

As shown in FIG. 11, the optical axis A exits from the object side reference point M ₀ , reaches the first plane mirror 41, is bent at a right angle by the first plane mirror 41, and reaches the first spherical mirror 11. Then, the optical axis A is folded back by the first spherical mirror 11 and reaches the second spherical mirror 12, and is folded by the second spherical mirror 12 and reaches the first spherical mirror 11 again. Thereafter, the optical axis A is turned back by the first spherical mirror 11, bent at a right angle by the second plane mirror 42, and reaches the image side reference point W ₀ .

In the exposure apparatus shown in FIGS. 10 and 11, the light emitted from the mask M is coupled onto the workpiece W by the action of the first and second spherical mirrors 11 and 12, and an image of the mask M is projected onto the workpiece W. At this time, since no lens is used, aberrations caused by the lens such as chromatic aberration do not occur. In the Offner optical system 1, the aberration is automatically corrected by the two spherical mirrors 11 and 12, and a high-quality image is obtained at a certain image height. A region where a good quality image is obtained is an arc-shaped region centered on the Offner central axis C.
For this reason, as shown in FIG. 10, the exposure apparatus using the Offner optical system 1 irradiates the mask M with the arc-shaped pattern light L, and the workpiece W with the arc-shaped pattern image I at the same magnification. Form with. A mechanism for moving (scanning) the mask M and the workpiece W integrally with the stationary optical system 1 is provided. By moving the mask M and the workpiece W together, exposure is performed so that an image of the entire mask M is transferred to the workpiece W.

JP 59-144127 A JP 7-235486 A JP-A-8-306618

  As described above, since the Offner optical system can perform high-quality image projection without aberration, application to an exposure apparatus has been tried for a long time, and some of them have been put into practical use. However, since the Offner optical system basically projects an image at an equal magnification, it has not been put to practical use for manufacturing a semiconductor integrated circuit that has been miniaturized to the nano order. Nevertheless, an exposure apparatus that employs an Offner optical system has been put into practical use in a process with a relatively low degree of integration, such as a post-process in a semiconductor integrated circuit manufacturing process or a liquid crystal display manufacturing process, and is still in use.

  One of the reasons that the practical use of the exposure apparatus adopting the Offner optical system is limited is the problem of productivity. As described above, in an exposure apparatus that employs an Offner optical system, an area where an image can be projected without aberration is limited to an arc-shaped area centered on the Offner center axis. At this time, if an image is projected with a sufficiently high resolution, the width of the arc-shaped region becomes very narrow (for example, about 1 mm), and the region can be called a linear shape. This is related to the problem of astigmatism.

Since an area where an image can be projected without astigmatism is very narrow, an exposure apparatus using an Offner optical system has a drawback that the time required for one exposure becomes long. Since the arc-shaped pattern projected onto the work is narrow, it is necessary to perform the synchronous movement of the mask and the work at a slow speed in order to obtain the required integrated exposure amount. For this reason, productivity cannot be increased. If this drawback is eliminated, it is considered that the advantage of the Offner optical system that there is no aberration will be utilized more and this type of exposure apparatus will be put into practical use more widely.
The invention of this application has been made in consideration of the above-described problems, and aims to enable practical use in a wider range of applications by taking advantage of the exposure apparatus employing the Offner optical system. It is said.

In order to solve the above-mentioned problem, in the invention according to claim 1 of this application, a first spherical mirror that is a concave mirror and a second spherical mirror that is a convex mirror smaller than the first spherical mirror face each other. An exposure apparatus provided with an Offner optical system provided, wherein the center of curvature of each spherical mirror is located on the Offner center axis,
There is at least one lens on the optical path from the object point to the first spherical mirror or on the optical path from the first spherical mirror to the image point, and the lens is compared to the case without the lens. Thus, the astigmatism at a position away from the optical axis in the radial direction around the Offner central axis is reduced.
In order to solve the above problem, the invention according to claim 2 is provided such that a first spherical mirror that is a concave mirror and a second spherical mirror that is a convex mirror smaller than the first spherical mirror are provided facing each other. An exposure apparatus having an Offner optical system in which the center of curvature of each spherical mirror is located on the Offner center axis,
There is at least one lens on the optical path from the object point to the first spherical mirror and on the optical path from the first spherical mirror to the image point, and the curved surface of the lens is in relation to the Offner central axis. Arranged symmetrically, the lens is configured to reduce astigmatism at a position away from the optical axis in the radial direction around the central axis of the optical system Offner as compared to the case without the lens. Have
In order to solve the above problem, the invention according to claim 3 is the configuration according to claim 2, wherein the lens is a first lens located on an optical path from the object point to the first spherical mirror. And a second lens arranged on the optical path from the first spherical mirror to the image point, and these lenses are arranged symmetrically with respect to the Offner central axis.
In order to solve the above-mentioned problem, in the invention according to claim 4, in the configuration of claim 3, the first and second lenses are provided with a moving mechanism, and the moving mechanism is It has a configuration in which the position of the lens in the direction along the optical axis can be adjusted.
In order to solve the above problem, the invention according to claim 5 has a configuration in which the lens is two lenses constituting an achromatic lens in the configuration of claim 1 or 2.
In order to solve the above problem, the invention according to claim 6 is that in the configuration of claim 3 or 4, the first and second lenses are two lenses constituting an achromatic lens. It has a configuration.

As described below, according to the invention of claim 1 of this application, the exposure area in which astigmatism is suppressed to be small by the lens is enlarged in the radial direction about the Offner central axis. Even if the width of the arc-shaped pattern to be irradiated is increased, the resolving power does not decrease. For this reason, productivity can be drastically improved by exposure with a wide pattern while maintaining resolution.
According to the second aspect of the present invention, the exposure region in which the astigmatism is suppressed to be small by the lens having the curved surface arranged symmetrically with respect to the Offner center axis is a radial direction centered on the Offner center axis. Therefore, even if the width of the arc-shaped pattern irradiated to the mask is widened, the resolving power does not decrease. For this reason, productivity can be drastically improved by exposure with a wide pattern while maintaining resolution. For this reason, productivity can be improved while increasing exposure accuracy.
According to the invention described in claim 3, in addition to the above effect, the lenses are first and second lenses provided on the incident side and the emission side of the first spherical mirror. Fine adjustment when ensuring accuracy can be easily performed.
According to the invention described in claim 4, in addition to the above effect, the magnification of the projected image can be adjusted with a simple configuration.
According to the fifth aspect of the present invention, it is possible to eliminate the defects (occurrence of chromatic aberration) caused by the use of the lens, and to obtain the above-mentioned effects without impairing the advantages of the Offner optical system.
According to the sixth aspect of the present invention, it is possible to eliminate the drawbacks (occurrence of chromatic aberration) caused by the use of the lens, and to obtain the above-mentioned effects without impairing the advantages of the Offner optical system.

1 is a schematic front sectional view of an exposure apparatus according to a first embodiment. It is a figure which shows the result of having simulated by calculation how much the area | region where astigmatism is suppressed in 1st embodiment is expanded by an area expansion lens. It is a figure which shows the result of the simulation evaluated about the effect of the reduction of astigmatism by a field expansion lens. It is a figure which shows the result of the simulation evaluated about the effect of the reduction of astigmatism by a field expansion lens. It is a figure for description of each simulation result of Drawing 3 (1) (2) and Drawing 4. It is front sectional schematic of the exposure apparatus of 2nd embodiment. It is a front cross-sectional schematic of the exposure apparatus of 3rd embodiment. FIG. 8 is a schematic side view showing the shapes of the area enlarging lenses 53 and 54 in the embodiment shown in FIG. 7. It is the side schematic diagram which showed the modification of the area expansion lenses 53 and 54 in 3rd embodiment. FIG. 10 is a schematic perspective view of a conventional exposure apparatus using an Offner optical system. It is a front cross-sectional schematic diagram of the conventional exposure apparatus which uses an Offner optical system.

Next, modes for carrying out the invention of the present application (hereinafter referred to as embodiments) will be described.
FIG. 1 is a schematic front sectional view of the exposure apparatus of the first embodiment. The exposure apparatus according to the embodiment is an exposure apparatus including an Offner optical system 1. Specifically, the exposure apparatus includes an Offner optical system 1, a mask holder (not shown in FIG. 1) that holds a mask M on a plane including the position of the object focus of the Offner optical system 1, and the Offner optical system 1. And a work stage (not shown in FIG. 1) for holding the work W on a plane including the position of the image focus. In FIG. 1, a trapezoidal mirror body is omitted for simplification of illustration. Actually, a trapezoidal mirror body similar to that shown in FIG. 10 is provided, and the optical axes A are each bent by 90 °.

The mask holder holds the mask M so that the mask M is positioned at a correct position in relation to the projection position of the image on the workpiece W (image superposition position). A pattern to be transferred to the workpiece W is formed in advance on the mask M.
Similarly, the work stage holds the work W so that the work W is positioned at a correct position in relation to the image projection position by the Offner optical system 1. The mask holder and the work stage are provided with a moving mechanism (not shown) as in the prior art.

A light source and illumination optical system (not shown) are provided on the incident side of the mask holder. As the light source, an ultraviolet lamp such as an ultra high pressure mercury lamp is used. The illumination optical system includes an integrator lens and a collimator lens, and is configured to irradiate the mask M uniformly.
The illumination optical system includes an aperture (not shown) for making the light applied to the mask M a predetermined arc-shaped pattern. The projection position of the arc-shaped pattern on the mask M by the aperture is a position where the center of the arc-shaped pattern coincides with the object side reference point M ₀ .

  A major feature of the exposure apparatus of such an embodiment is that a special optical element capable of increasing the width of the arc-shaped pattern by the aperture is provided. “It is possible to increase the width of the arc-shaped pattern” means that even if the width is increased, the resolving power of the exposure does not decrease. In other words, the width of the region where the image can be projected with a high resolving power is increased. That is. Hereinafter, this point will be described.

  As shown in FIG. 1, the exposure apparatus of the first embodiment includes a single lens 5 whose curved surface is arranged symmetrically with respect to the Offner central axis C. The lens 5 is a spherical lens. The lens surface 501 on the first spherical mirror 11 side is convex, and the lens surface 502 on the opposite side is concave. As shown in FIG. 1, the center axis of the lens 5 coincides with the Offner center axis C. Therefore, the centers of curvature of the lens surfaces 501 and 502 are on the Offner center axis C. However, the center of the lens surface 501 on the first spherical mirror 11 side and the center of the lens surface 502 on the opposite side may be at the same position (concentric) on the Offner center axis C, or on the Offner center axis C. There may be different positions. In any case, the lens 5 has an action of expanding a region where an image can be projected while maintaining a high resolving power. Hereinafter, this lens 5 is referred to as a region magnification lens.

As is well known, when a transparent parallel plate is inserted perpendicularly to the optical axis in the projection optical system, the focal length becomes slightly longer. At this time, if the parallel plate is inserted obliquely with respect to the optical axis, the light emitted from the object point on the optical axis of the eyelid that does not naturally generate astigmatism is also other than the plane along the axis of inclination. Causes astigmatism.
The area enlarging lens 5 of the embodiment uses this action in reverse. In other words, the astigmatism is suppressed to be small by arranging a light transmitting member on the optical path. At this time, the curvature of the lens 5 is selected so that the aberration is reduced in a wide range in the radial (tangential) direction. The ray diagram of FIG. 1 shows rays on the tangential plane.

  The curved surface of the lens 5 is symmetric with respect to the Offner central axis C in order to extend the region free of astigmatism expanded in the radial direction in the circumferential (sagittal) direction. The radial direction and the circumferential direction are a radial direction and a circumferential direction around the Offner central axis C.

Next, an actual design example (example) for enlarging a region where astigmatism is suppressed to a small extent by the above technical idea will be described.
First, specific optical conditions of this design example will be described. The curvature radius R (hereinafter simply referred to as curvature) of the first spherical mirror 11 is -750.7 mm, and the curvature of the second spherical mirror 12 is -361.3 mm. The separation distance (indicated by D in FIG. 1) between the first spherical mirror 11 and the second spherical mirror 12 viewed on the Offner central axis C is 389.8 mm, and the first spherical mirror 11 side of the area expanding lens 5 The lens surface 501 has a curvature of −260.5 mm, and the opposite lens surface 502 has a curvature of −239.1 mm. The distance between the Offner center axis C and the optical axis A (indicated by r in FIG. 1) is called the Offner distance, but in this example, r is 115 mm.

In such an embodiment, the extent to which the region where astigmatism is suppressed to be small is expanded by the region expansion lens 5 was simulated by calculation. FIG. 2 is a diagram showing the results of this simulation. For the simulation, OSLO PREMIUM EDITION REVISION 6.4.1 or 6.2 manufactured by Lambda Research, which is optical calculation software, was used.
FIG. 2A shows a simulation result when the area magnifying lens is not arranged, and FIG. 2B shows a simulation result when the area magnifying lens is arranged. 2A and 2B, the vertical axis indicates the focal position, that is, the position in the focal depth direction (optical axis A direction), and the horizontal axis indicates the width direction of the image pattern on the image plane (the surface of the workpiece W). The position (indicated by d in FIG. 1) is shown. The origin is the center position (image side reference point W ₀ ) in the width direction. That is, the horizontal axis in FIGS. 2A and 2B indicates how far from the optical axis A in the radial direction centered on the Offner central axis. In FIGS. 2A and 2B, the horizontal axis is different in scale.

As shown in FIG. 2A, when there is no area magnifying lens, the image side reference point W _{0, that} is, a point on the optical axis A in the image plane (position on the horizontal axis 0 in FIG. 2A) is tangential. surface and there is no deviation of the focal point in the sagittal plane, but the deviation of the focal point (astigmatism) occurs deviates even slightly from the image side reference point W ₀ in the pattern width direction. For example, according to FIG. 2 (A), the focal position of the tangential surface and the focal point of the sagittal surface deviate by about 8 μm only by being separated from the point on the optical axis A by 0.5 mm.
On the other hand, when the area enlarging lens is provided, the focal position of the tangential surface and the sagittal surface at a point on the optical axis A (position of the horizontal axis 0 in FIG. 2B) is about 5 μm apart due to the effect of the lens. However, as the distance from the point on the optical axis A increases, the difference between the focal positions of both decreases, and only a maximum difference of about 3 μm occurs within a range 10 mm (20 mm in total) away. In other words, if an area where the difference in position between the focal position of the tangential surface and the focal point of the sagittal surface is less than 8 μm is defined as an “area in which astigmatism is minimized, It can be seen that the “region where the is suppressed small” expands from 1 mm to at least 20 mm.

  The effect of the improvement (reduction) of astigmatism as described above in relation to the necessary resolving power and productivity will be described with reference to FIGS. 3 and 4 are diagrams showing the results of a simulation for evaluating the effect of reducing astigmatism by the area enlarging lens 5. FIG. 5 is a diagram for explaining the simulation results of FIGS. 3 (1), (2), and FIG. The horizontal axis represents spatial frequency, and the vertical axis represents MTF (contrast).

  3 (1) and 3 (2) show the simulation results when there is no area expansion lens 5 (conventional example), and FIG. 4 shows the simulation results when there is an area expansion lens (embodiment). 3A, 3B, and 4, each horizontal axis represents a spatial frequency, and each vertical axis represents a calculated MTF value. In the case of FIG. 4, as in the case of FIG. 2B, the lens surface 501 on the first spherical mirror 11 side of the region magnifying lens 5 is R = −260.5 mm, and the lens surface 502 on the opposite side is R = −239. .1 mm. In addition, OSLO PREMIUM EDITION REVISION 6.4.1 or 6.2 made by Lambda Research was also used for the simulation.

  FIGS. 3A, 3B, and 4 show graphs of MTFs at respective positions in the width direction of the arc-shaped pattern image. Each graph is data at each point of the width d of the image I of the arc-shaped pattern shown in FIG. In other words, the MTF is calculated at each point shifted in the direction of the width d up to a distance half the width d, with the point on the optical axis A of the image plane being ± 0. In FIG. 3 (1), since the total length of the width is 1 mm, the data is at the positions of ± 0.125 mm, ± 0.25 mm, ± 0.375 mm, and ± 0.5 mm. In FIG. 3 (2), since the total length of the width d is 20 mm, the data is at positions of ± 2.5 mm, ± 5 mm, ± 7.5 mm, and ± 10 mm. In addition, + is a direction away from the Offner center axis C in FIG. 1, and a-direction is a direction approaching the Offner center axis C. In FIGS. 3A and 4, the MTFs do not differ greatly at each position, so the graphs overlap. However, in FIG. 3B, the MTFs differ greatly at each position. The correspondence between each graph and the position in the width direction is shown in FIG.

The wavelength condition was premised on exposure with light having a wavelength of 355 nm to 380 nm. At this time, since the refractive indexes are different, the wavelength of 365 nm is basically used, and the other wavelengths are weighted. It is assumed that the wavelength expanding lens 5 is made of quartz glass.
FIG. 3A shows the case where there is no area magnifying lens and the width d of the arc-shaped pattern is 1 mm as described above. The MTF (resolution) decreases as the spatial frequency increases, which is a general tendency. In the case of FIG. 3 (1), each graph almost overlaps one line, and the resolving power is almost constant over the entire width d (range of ± 0.5 mm from the optical axis A). That is, it is shown that high-quality exposure with substantially no aberration can be performed within a width of 1 mm.

  FIG. 3 (2) shows a simulation result when the width d of the arc-shaped pattern is enlarged to 20 mm under the same optical conditions as in FIG. 3 (1). In order to make it easy to confirm the variation of the MTF in the width direction, the scale of the spatial frequency on the horizontal axis is set to 0 to 100 unlike FIG. As shown in FIG. 3 (2), when the pattern is as wide as 20 mm, the MTF is a good value of about 0.8 to 1 on the optical axis A, but the MTF greatly decreases with the deviation from the optical axis A. I know that That is, the influence of aberration is large at a position off the optical axis A, and exposure with sufficient pattern accuracy cannot be performed.

  On the other hand, as shown in FIG. 4, when the area enlarging lens 5 is employed, the graphs are almost overlapped, indicating that image projection can be performed without aberration in a range of 20 mm in width. In the case of an exposure apparatus, the MTF of the projection optical system is required to be at least 0.3 to 0.4. In the case of the embodiment whose simulation results are shown in FIG. 4, an MTF of about 0.4 is obtained at a spatial frequency of about 300 lines / mm. 333 lines / mm corresponds to exposure of a circuit having a line width of 1.5 μm, and the above result shows that the apparatus of the embodiment can be used for exposure up to about 1.5 μm.

Thus, according to the exposure apparatus of the embodiment, since the area magnifying lens 5 is provided, the resolution does not decrease even if the width of the arc-shaped pattern irradiated to the mask M is widened. For this reason, productivity can be drastically improved by exposure with a wide pattern while maintaining resolution.
That is, the exposure apparatus shapes the light from the light source with the aperture and irradiates the mask M with the arc-shaped pattern light, and the illuminance at each point on the workpiece W is the same even when a wide image is projected. . Therefore, when the width is increased, scanning can be performed at a higher speed by performing exposure with a necessary dose. In the above example, since the conventional 1 mm width is expanded to 20 mm, the productivity is 20 times in terms of calculation. Of course, since it is also necessary to improve the accuracy (alignment accuracy) of the mechanical system such as feed accuracy and stop accuracy, it is not simply 20 times, but even if it is estimated to be small, improvement of several times or more can be expected.

  Next, a second embodiment will be described. FIG. 6 is a schematic front sectional view of the exposure apparatus of the second embodiment. In the second embodiment, two lenses 51 and 52 whose curved surfaces are arranged symmetrically with respect to the Offner central axis are provided as the area enlarging lenses. The two area enlarging lenses 51 and 52 are spherical lenses arranged coaxially with the Offner central axis C. Of the two area magnifying lenses 51 and 52, the lens 51 located far from the first spherical mirror 11 is referred to as a first area magnifying lens, and the lens 52 located closer is referred to as a second area magnifying lens. In the first area enlargement lens 51, as in the first embodiment, the surface 511 closer to the first spherical mirror 11 is a convex lens surface, and the opposite surface 512 is a concave lens surface. The second region enlargement lens 5 also has a large curvature. Similarly, the surface 521 closer to the first spherical mirror 11 is a convex lens surface, and the opposite surface 522 is a concave lens surface.

  In the second embodiment, the first and second area enlarging lenses 51 and 52 have a so-called achromatic lens configuration and perform chromatic aberration correction. As described above, the advantage of the Offner optical system is that it is unrelated to chromatic aberration because no lens is used. In this respect, if the lens is used as in the embodiment, it is considered that the advantages of the Offner optical system are damaged. Nevertheless, in the narrow wavelength range of about 355 nm to 380 nm as described above, there is little problem in exposure with a line width of up to about 1.5 μm.

However, when exposure with higher resolution than this is performed, or when exposure is performed with light in a wider wavelength range, an optical system that also corrects chromatic aberration is preferable. The second embodiment takes this point into consideration. As an example of the curvature, the curvature of the lens surface 511 on the first spherical mirror 11 side of the first region enlargement lens 51 is about −230.2 mm, and the curvature of the lens surface 512 on the opposite side is about −211.2 mm. is there. Further, the curvature of the lens surface 521 on the first spherical mirror 11 side of the second region magnification lens 52 is about −1235 mm, and the curvature of the lens surface 522 on the opposite side is about −8564 mm.
According to the second embodiment, the disadvantages of using a lens are eliminated, exposure with higher resolution becomes possible, and even when exposure is performed with light in a wide wavelength range, high resolution and high productivity are achieved. The exposure process can be performed.

Next, a third embodiment will be described. FIG. 7 is a schematic front sectional view of the exposure apparatus of the third embodiment. In the third embodiment shown in FIG. 7, two lenses 53 and 54 obtained by dividing a lens whose curved surface is arranged symmetrically with respect to the Offner central axis are provided as a region enlarging lens. FIG. 8 is a schematic side view showing the shapes of the area enlarging lenses 53 and 54 in the third embodiment shown in FIG.
In the third embodiment, the area enlarging lenses 53 and 54 have a semicircular shape as shown in FIG. The two area enlarging lenses 53 and 54 have the same shape and size, and their curved surfaces are arranged symmetrically with respect to the Offner center axis C. That is, the center of the semi-circular contour of each of the area enlarging lenses 53 and 54 is on the Offner center axis C.

  In the two area enlarging lenses 53 and 54, the centers of curvature of the lens surfaces 531 and 541 on the first spherical mirror 11 side are at the same position on the Offner center axis C. The centers of the opposite lens surfaces 532 and 542 are also on the Offner center axis C. Similarly, the center of curvature of the lens surfaces 531 and 541 on the first spherical mirror 11 side and the center of curvature of the lens surfaces 532 and 542 on the opposite side may be at the same position on the Offner center axis C. However, the position may be shifted on the Offner center axis C. In addition, although the angle of the circular arc in the semi-annular shape of each of the area magnifying lenses 53 and 54 is less than 180 °, the angle is larger than the angle of the arc of the arc-shaped pattern to be projected.

  In this way, configuring the area enlarging lens with the two lenses 53 and 54 has several advantages. First, as compared with the case where one lens is arranged coaxially with the Offner center axis C, the lenses 53 and 54 can be reduced in size, so that the lens can be easily held and adjusted. Further, in the exposure apparatus as in the embodiment, after mounting components such as the spherical mirrors 11 and 12 and the mask holder, the position and posture of each component are finely adjusted in order to make the accuracy of the entire optical system required. Work is required. At this time, if the area enlargement lens is composed of the two lenses 53 and 54, fine adjustment can be made finely and balance can be easily obtained.

Further, in this embodiment, as shown in FIG. 7, moving mechanisms 61 and 62 are attached to the respective area enlarging lenses 53 and 54. Each of the moving mechanisms 61 and 62 is a mechanism that independently moves the area enlarging lenses 53 and 54 in the direction along the optical axis A. “Independently” means that one area magnifying lens is moved independently of the other area magnifying lens.
Each moving mechanism 61 and 62 has the significance of facilitating fine adjustment when ensuring the accuracy of the entire optical system described above. In addition, each of the moving mechanisms 61 and 62 has a meaning that enables fine adjustment of the magnification of the image projected onto the workpiece W. If the other region magnifying lenses 53 and 54 are moved in a state where one position is fixed, or moved in different directions or distances, the magnification changes. The change of magnification here is a very small change of about several tens of PPM (for example, 20 PPM). The moving distance is, for example, about 0.05 to 0.2 mm.

  There are several factors that require such fine adjustment of the magnification. For example, magnification adjustment may be performed as fine adjustment for ensuring the accuracy of the entire optical system described above. At this time, the moving mechanisms 61 and 62 are preferably used. Also, each moving mechanism can be suitably used when ensuring alignment accuracy. In an exposure apparatus, the requirement for alignment accuracy is stricter than the resolution, and is generally about 1/4 of the resolution. For example, when performing exposure with a line width of 1.5 μm, an alignment accuracy of about 0.3 μm is required. In this case, the final fine adjustment may be performed by changing the magnification of the image after being realized by the performance of the alignment mechanism close to the required accuracy. In such a case, the moving mechanisms 61 and 62 are preferably used. The fine adjustment of the magnification may be performed, for example, by controlling the temperature of the workpiece W. However, compared to this, the configuration of this embodiment is easy to adjust and easy to ensure accuracy. As the moving mechanisms 61 and 62, for example, a mechanism (piezo linear motion mechanism) combined with a piezo element and a linear guide can be employed.

  In the third embodiment, the chromatic aberration can be removed as in the second embodiment. In other words, each of the area enlarging lenses 53 and 54 can be two lenses constituting an achromatic lens. In this case, two sets of two lenses (achromatic lens) are provided. The moving mechanisms 61 and 62 are mechanisms for moving one pair of two lenses integrally with each other independently of the other pair of two lenses.

  FIG. 9 is a schematic side view showing a modification of the area enlarging lenses 53 and 54 in the third embodiment. In the third embodiment, the two area magnifying lenses 53 and 54 are semicircular, but it is sufficient that the curved surfaces are arranged symmetrically with respect to the Offner central axis C, and they are not necessarily semicircular. . An example of a symmetrical arrangement that is not semi-annular is shown in FIG.

In addition to the embodiments described above, a configuration in which an area expansion lens is disposed only on one side with respect to the first spherical mirror 11 may be employed. That is, even when an area magnifying lens is arranged only on the incident side of the first spherical mirror 11 or an area magnifying lens is arranged only on the emission side of the first spherical mirror 11, image projection without astigmatism is achieved. It is possible to enlarge the area where In the third embodiment, a configuration in which any one of the two region magnifying lenses 53 and 54 is eliminated corresponds to this. In this case, in order to balance the image on the side closer to the Offner center axis C as viewed from the optical axis A and the image on the far side, the area enlargement lens is not uniform in thickness (is unevenly distributed). Is done. However, even in such a case, the distortion of the image is larger than in the above embodiments. Compared with this, the configuration of each of the above embodiments is preferable in that the distortion of the image can also be suppressed to be small.
In addition, as an application of the exposure apparatus of each embodiment, it can be used for a photolithography in a manufacturing process of a liquid crystal display manufacturing process, a printed circuit board manufacturing process, and various MEMS in addition to a use in a post process of a semiconductor integrated circuit manufacturing process.

DESCRIPTION OF SYMBOLS 1 Offner optical system 11 1st spherical mirror 12 2nd spherical mirror 2 Mask holder 3 Work stage 4 Trapezoid mirror body 5 Area expansion lens 51 Area expansion lens 52 Area expansion lens 53 Area expansion lens 54 Area expansion lens 61 Movement mechanism 62 Movement mechanism C Offner center axis A Optical axis d Width of arc-shaped pattern

Claims (6)

A first spherical mirror that is a concave mirror and a second spherical mirror that is a convex mirror smaller than the first spherical mirror are provided facing each other, and the center of curvature of each spherical mirror is located on the Offner center axis. An exposure apparatus having an Offner optical system,
There is at least one lens on the optical path from the object point to the first spherical mirror or on the optical path from the first spherical mirror to the image point, and the lens is compared to the case without the lens. An astigmatism at a position away from the optical axis in the radial direction about the Offner central axis is reduced. A first spherical mirror that is a concave mirror and a second spherical mirror that is a convex mirror smaller than the first spherical mirror are provided facing each other, and the center of curvature of each spherical mirror is located on the Offner center axis. An exposure apparatus having an Offner optical system,
There is at least one lens on the optical path from the object point to the first spherical mirror and on the optical path from the first spherical mirror to the image point, and the curved surface of the lens is in relation to the Offner central axis. It is arranged symmetrically, and the lens reduces astigmatism at a position away from the optical axis in the radial direction around the central axis of the optical system Offner as compared to the case without the lens. A featured exposure apparatus.   The lens is a first lens located on the optical path from the object point to the first spherical mirror, and a second lens disposed on the optical path from the first spherical mirror to the image point, 3. An exposure apparatus according to claim 2, wherein these lenses are arranged symmetrically with respect to the Offner central axis.   The at least one of the first and second lenses is provided with a moving mechanism, and the moving mechanism is capable of adjusting the position of the lens in the direction along the optical axis. An exposure apparatus according to claim 3.   The exposure apparatus according to claim 1, wherein the lenses are two lenses constituting an achromatic lens. 5. The exposure apparatus according to claim 3, wherein the first and second lenses are two lenses constituting an achromatic lens.

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