JPH1010430A - Double image-formation optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an optical system while maintaining image-formation performance, to excellently correct distortion aberration and to easily absorb a production error by forming a reflection surface in a non-planar surface and an aspherical surface. SOLUTION: This projection optical system is provided with a 1st image- formation optical system A forming the intermediate image of a pattern drawn on a reticle R, the reflection surface M2 arranged in the vicinity of the intermediate image, and a 2nd image-formation optical system B forming the reformed image of the intermediate image on a wafer W. The optical system A comprises four dioptric lenses and one concave mirror M1 , and light from the reticle R passes forward and backward. The reflection surface M2 is arranged to guide the light passing through the optical system A on a return path to the optical system B. The reflection surface M2 is formed as the aspherical surface. The optical system B comprises 17 dioptric lenses and an aperture diaphragm S is arranged in the optical system B. Thus, the distortion aberration is compensated without affecting the distortion aberration, coma aberration and astigmatism occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of a reduction exposure apparatus such as a stepper mainly used for manufacturing a semiconductor, and more particularly, to a submicron unit in an ultraviolet wavelength region by using a catadioptric optical system for the optical system. The present invention relates to a 1 / 4x to 1 / 5x scanning catadioptric reduction optical system having resolution.

[0002]

2. Description of the Related Art In recent years, semiconductor circuit patterns have become increasingly finer, and an exposure apparatus for printing such patterns has been required to have a higher resolution. In order to satisfy this requirement, the wavelength of the light source is shortened and N
A (numerical aperture of the optical system) must be increased. However, as the wavelength becomes shorter, optical glass that can withstand practical use is limited due to light absorption. When the wavelength is less than 300 nm, the only practically usable glass materials are synthetic quartz and fluorite. However, the Abbe numbers of synthetic quartz and fluorite are not far enough apart to correct for chromatic aberration. Therefore, when the wavelength is 300 nm or less, it is extremely difficult to correct the chromatic aberration if the projection optical system is constituted only by the refractive optical system.
Fluorite cannot be used in many parts because fluorite has poor refractive index change due to temperature change, so-called temperature characteristic, and has many problems in lens polishing. Therefore, it is very difficult to configure a projection optical system having a required resolution only by a refraction system.

On the other hand, attempts have been made to construct a projection optical system using only a reflection system. However, in this case, the projection optical system must be large and the reflection surface must be aspheric. However, high-precision aspherical surfaces are extremely difficult to manufacture.
Therefore, various techniques have been proposed for forming a reduction projection optical system by a so-called catadioptric system combining a reflection system and a refraction system made of optical glass that can be used for a used wavelength. Among them, various types that perform one or more intermediate image formations in the middle of the optical system have been proposed.
If the intermediate image is limited to one that forms only once,
-25170, JP-A-63-163319, JP-A-4-
234722, USP-4,779,966.

Among the above prior arts, those using only one concave mirror are disclosed in Japanese Patent Application Laid-Open No. 4-234722 and US Pat.
P-4, 779, 966. In these optical systems, a reciprocating optical system constituted by a concave mirror employs only a concave lens, and does not use an optical system having a convex power. As a result, the light beam spreads and enters the concave mirror, so that the diameter of the concave mirror tends to increase. In particular, the reciprocating optical system disclosed in Japanese Patent Application Laid-Open No. Hei 4-234722 is a completely symmetrical type. Since an optical system is employed, a working distance in the vicinity of the first surface is difficult to be obtained, and a half prism must be used. In the optical system disclosed in US Pat. No. 4,779,966, a mirror is used in a secondary imaging optical system behind the intermediate image. Therefore, in order to ensure the required brightness of the optical system, the light beam spreads and enters the concave mirror, making it difficult to reduce the size of the mirror.

In the case of using a plurality of mirrors, there is a possibility that the number of lenses in the refractive optical system can be reduced. However, these types have the following problems. That is, recently, a phase shift method for shifting the phase of a selected portion of a mask has been devised in order to increase the resolution while increasing the depth of focus.
The ratio σ between A and the NA of the imaging optical system is made variable. At this time, an aperture stop can be installed in the illumination optical system. However, when the above-described catadioptric optical system is used as an objective lens, an effective stop installation portion cannot be taken anywhere.

Further, in a catadioptric optical system of the type employing the reciprocating optical system having such an arrangement on the second surface side on the reduction side,
Since the distance to the wafer after reflection by the reflection mirror cannot be taken long due to the reduction magnification, the number of objective lenses inserted into this optical path cannot be so large, and the brightness of the obtained optical system is limited. It had to be something. Even if an optical system with a high NA can be realized, since many optical members are inserted into a limited length, the optical system cannot take a long distance between the wafer and the end surface of the objective lens, that is, a so-called working distance WD. I was Further, in such a conventional catadioptric optical system, it is necessary to decenter the optical axis of the optical path in the middle, and it is difficult to adjust the eccentric part of the so-called eccentric optical system, thereby realizing a highly accurate system. I couldn't do that.

Therefore, the present applicant forms an intermediate image on the first surface by the first image forming optical system, forms a re-image of the intermediate image on the second surface by the second image forming optical system, A reflecting surface for guiding a light beam from the imaging optical system to the second imaging optical system, and a lens group through which the first imaging optical system transmits a concave mirror and both incident light and reflected light to the concave mirror A two-time imaging optical system formed to have a reciprocating optical system consisting of This 2
According to the rotational imaging optical system, the diameter of the concave mirror can be reduced, and the ratio σ of the NA of the illumination optical system and the NA of the imaging optical system for the phase shift method can be made variable. It is possible to realize an optical system that can take an effective diaphragm installation part and can take a long working distance WD, that is, the distance between the wafer and the end surface of the objective lens, while sufficiently maintaining the brightness of the optical system. it can. Further, the adjustment work of the eccentric part of the so-called eccentric optical system is easy, and a highly accurate optical system is realized.

[0008]

As described above, the two-time imaging optical system has many excellent points. However, if it is attempted to reduce the size of the optical system while maintaining the imaging performance, distortion is inevitable. Aberrations occur. That is, since the arrangement of the optical system is out of symmetry, even if other aberrations are well corrected, only distortion may remain. In particular, high-order distortion cannot be corrected only by the curvature or the surface spacing of the refractive lens, and the system may have to be enlarged. In addition, with the correction of distortion, astigmatism occurs in return, and correcting both aberrations simultaneously is
It is usually the most difficult technique. In such a case, there is a case where it is desired to correct distortion and astigmatism, particularly high-order distortion, while leaving other well-corrected aberrations as they are.

In addition to the above-described pure aberration correction, when manufacturing such a high-precision optical system, there will inevitably occur product variations due to manufacturing errors. This variation has different aberrations for each product, and is usually corrected by partial adjustment of the optical system. However, if asymmetrical aberrations with different amounts of aberration occur throughout the image plane due to manufacturing errors, or if the amount of occurrence itself is too large, it is often not possible to correct it only by adjusting with optical components.
In such a case, correction may be performed by inserting an aberration correction plate made of an aspherical surface near the image. However, such a correction plate is effective for correcting aberrations related to the angle of view when it is as close as possible to the image plane. However, in reality, various correction mechanisms and measurement devices near the image plane are required to correct the image. It must usually be placed farther from the surface than the object. In that case, even if it is originally desired to correct only the aberration related to the angle of view, the aberration related to other apertures is affected, and complicated correction must be performed. Therefore, according to the present invention, it is possible to reduce the size of the optical system while maintaining the imaging performance. In particular, the present invention can favorably correct distortion and can easily absorb manufacturing errors. It is an object to provide an image optical system.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. That is, an intermediate image on a first surface is formed by a first image forming optical system, and a second image forming optical system is formed. In the two-time imaging optical system in which a re-imaging of the intermediate image is formed on the second surface and a reflecting surface is provided so as to guide the light beam from the first imaging optical system to the second imaging optical system, A double imaging optical system characterized in that the surface is formed as a non-planar and aspherical surface. In that case, it is preferable to arrange the reflection surface near the intermediate image. The shape of the aspheric lens surface can be a rotationally symmetric aspheric surface, a toric aspheric surface, or a completely asymmetric aspheric surface. With this configuration, at least distortion can be corrected, at least spherical aberration of the pupil can be corrected, and at least a manufacturing error of the optical system can be corrected.

In order to correct distortion and astigmatism, correct manufacturing errors, and not affect other aberrations, a correction optical system may be provided near the intermediate image. In particular, in order to correct only high-order distortion and astigmatism, it is effective means to provide an aspherical correction optical system. On the other hand, since a reflecting surface is arranged near the intermediate image, it is effective means to make the reflecting surface aspherical to form a correction optical system. Since this reflecting surface can be placed very close to the vicinity of the intermediate image, making the reflecting surface aspherical can directly bring distortion and astigmatism to desired values, and furthermore, other aberrations Has little effect.

The aspherical surface is usually symmetrical about the center, but may have a shape that changes only in the longitudinal direction of the reflecting surface in accordance with a rectangular reflecting surface, or may be similar. From the effect of the above, a toric surface may be used. In other words, the effect of the shape of the aspherical surface on the distortion is largely influenced by the change in the inclination of the aspherical surface in the longitudinal direction, and the change in the inclination in the lateral direction is not so large because the change in the image height is not large. It is because it does not give. However, from the viewpoint of the processing of the aspherical surface, it is better that the surface is easy to produce, and from that point, it is preferable that the surface is symmetrical with respect to the center or that the surface changes in the longitudinal direction. If the former is centrally symmetrical, the aspherical surface processing is carried out symmetrically with respect to the optical axis as a circular reflecting surface, and it can later be cut into a rectangular shape. In the latter case, a unidirectional aspherical surface processing machine is used.

If aberrations due to different manufacturing errors occur everywhere on the image surface, a completely asymmetric aberration-correcting aspheric surface can be obtained according to the amount of the aberrations. Of course, at this time, since it can be placed near the intermediate image, depending on the case, only the correction related to the angle of view can be performed with priority. By taking the above measures,
As the size of the optical system is reduced, distortion that tends to occur and tends to cause higher-order aberrations that are difficult to correct and aberrations that occur due to manufacturing errors, etc. The correction can be made almost completely according to the shape curve of the generated high-order distortion while freely avoiding the influence on the aberration, the sine condition, the axial chromatic aberration and the like as much as possible.

[0014]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. In this embodiment, the present invention is applied to a projection optical system for reducing and transferring a circuit pattern on a reticle R onto a semiconductor wafer W. The projection optical system includes a first imaging optical system A for forming an intermediate image of the pattern drawn on the reticle R, a reflecting surface M ₂ which is disposed near the intermediate image, the re-imaging the intermediate image on the wafer W And a second imaging optical system B formed at the same time. The first imaging optical system A, composed refractive lens four and one concave mirror M ₁ Tokyo,
Light from the reticle R reciprocates. The reflecting surface M ₂ transmits the light passing through the first imaging optical system A on the return path to the second imaging optical system B.
Are arranged to direct, this reflective surface M ₂ is formed aspherical. The second imaging optical system B is a refracting lens 17
An aperture stop S is disposed in the second imaging optical system B. This projection optical system has a magnification of 1/4, a numerical aperture NA on the image side of 0.6, a maximum object height of 72, a length of 16 to 40 in length 24, and a width of 120 in length. Is a lens system having an opening a. The refractive lens uses fused silica (SiO ₂ ) and fluorite (CaF ₂ ), and is ± 0.2 at a wavelength of 193 nm of an ultraviolet excimer laser.
On-axis and lateral chromatic aberrations are corrected for a 1 nm wavelength width.

FIG. 2 is a schematic structural view of a second embodiment. FIG. 3 shows a developed optical path diagram of the embodiment, that is, in order to avoid the complexity of reflected light on the drawing, the concave mirror M _{1 is used.}
And by placing a virtual plane reflecting mirror immediately after the reflecting surface M _2, in which light is always displayed toward the same direction. In the second embodiment, the second imaging optical system B
By placing a reflective surface M ₃ in, it is a traveling direction of light for exposing the traveling direction and the wafer W of the light that illuminates the reticle R that is matched. Other configurations are the same as those of the first embodiment, and therefore have the same imaging performance as the first embodiment.

Table 1 below shows data of the numerical embodiment shown in FIG. Here, the optical path arrangement shown in FIG. 2 is adopted. In the table, the first column is the number of the lens surface from the reticle R,
The second column r is the radius of curvature of each lens surface, the third column d is the distance between each lens surface, the fourth column is the material of each lens, the fifth column
The column indicates the group number of each optical member. Surface marked with first column in asterisk indicates the reflection surfaces M ₂ aspherical. The shape of the aspheric surface is y: height in the direction perpendicular to the optical axis S (y): displacement amount in the optical axis direction at height y r: radius of curvature on the optical axis κ: conical coefficient C _n : n-th aspherical coefficient And the cone coefficient κ in [Aspherical data]
And the aspheric coefficient C _n are shown. In the fifth column, an asterisk indicates a return route. In addition, fused quartz (SiO ₂ ) and fluorite (Ca
F ₂ ) Refractive index n with respect to reference wavelength for use (193 nm)
And the Abbe number ν at ± 0.1 nm of the reference wavelength is as follows. SiO ₂ : n = 1.56019 ν = 1780 CaF ₂ : n = 1.50138 ν = 2550 FIG. 4 shows the lateral aberration of this embodiment. In the figure, Y indicates the image height.
As is clear from this aberration diagram, it is understood that the optical system has excellent performance in which the lateral aberration is satisfactorily corrected to a state close to almost no aberration. FIG. 5 shows distortion. As is clear from this aberration curve, it is understood that the distortion is corrected very well.

[0017]

[Table 1]

[0018]

As described above, according to the present invention, since the aspherical reflecting optical system is arranged near the intermediate image, the distortion, coma, astigmatism, etc. generated in the optical system are affected. Without giving, distortion can be corrected. Therefore, this is a two-time imaging optical system that can simultaneously improve the imaging performance of the optical system and reduce the size.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment.

FIG. 2 is a schematic view showing a second embodiment.

FIG. 3 is a developed optical path diagram of a numerical example.

FIG. 4 is a lateral aberration diagram of a numerical example.

FIG. 5 is a distortion diagram of a numerical example.

[Explanation of symbols]

A: first imaging optical system M ₁ : concave mirror M ₂ , M ₃ : reflecting surface B: second imaging optical system S: aperture stop a: aperture

Claims (5)

[Claims] An image formed on a first surface is formed by a first image forming optical system, and a re-image of the intermediate image is formed on a second surface by a second image forming optical system. A double imaging optical system provided with a reflecting surface (M ₂ ) so as to guide a light beam from the first imaging optical system (A) to the second imaging optical system (B); ₂ ) A two-time imaging optical system characterized in that ( ₂ ) is formed as a non-planar and aspherical surface. 2. The optical system according to claim 1, wherein said first imaging optical system (A) is a concave mirror (M).
₁₎ and having a reciprocating optical system which both consist of a lens group that transmits the incident light and the reflected light to the concave mirror (M _1), according to claim 1 2 Kaiyuizo optical system according. 3. The double imaging optical system according to claim 1, wherein said reflection surface (M ₂ ) is arranged near said intermediate image. 4. The reflecting surface (M ₂ ) is a rotationally symmetric aspherical surface,
4. The double imaging optical system according to claim 1, wherein the optical system is a toric aspherical surface or a completely asymmetrical aspherical surface. 5. An image forming apparatus according to claim 1, wherein at least one of the image forming magnifications of said first image forming optical system (A) and said second image forming optical system (B) is a reduction magnification. Or a catadioptric optical system according to 4.