JP2000098227A - Reflecting reduction projection optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid a shortcoming that power gets so strong that aberration easily occurs by arranging an aperture diaphragm at a position satisfying a specified arrangement condition between a concave reflection mirror near to a 2nd surface and a convex reflection mirror near to the 2nd surface. SOLUTION: The basic constitution of this optical system is constituted of four mirrors, that is, the concave reflection mirror M1, the convex reflection mirror M2, the convex reflection mirror M3 and the concave reflection mirror M4 in order from a 1st surface R side. Namely, the mirror M1 is provided at the rear of the 1st surface R, and the aperture diaphragm S is provided through two opposed mirrors M2 and M3, so that an image is formed on the 2nd surface W by the mirror M4. In such a case the diaphragm S is arranged at the position satisfying the arrangement condition of 0.1<=x/L<=0.9. In the expression, L shows a distance on an optical axis from the mirror M4 near the 2nd surface W to the mirror M3 near to the 2nd surface W, and (x) shows the distance on the optical axis from the mirror M3 near to the 2nd surface W to the diaphragm S.

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 projection exposure apparatus such as a stepper used for manufacturing a semiconductor. In particular, the present invention relates to an optical system of a scanning-type reduction projection exposure apparatus having a resolution of a submicron unit in a wavelength range from ultraviolet rays to X-rays by using a reflection optical system as an optical system.

[0002]

2. Description of the Related Art In recent years, in the manufacture of semiconductors and semiconductor chip mounting substrates, miniaturization has been further advanced, and a projection exposure apparatus for printing these patterns has been required to have a higher resolution. In order to satisfy this requirement, the wavelength of the light source must be shortened and the NA (number of ports of the projection optical system) must be increased. However, as the wavelength becomes shorter, the optical glass that can withstand practical use due to light absorption is limited. When the wavelength goes below 180nm,
The only glass material that can be used practically is fluorite. Furthermore, when ultraviolet rays or X-rays having a short wavelength are used, there is no optical glass that can be used. In such a case, it is impossible at all to configure the reduction projection optical system using only the refractive optical system or the catadioptric optical system.

For this reason, various reflection reduction optical systems have been proposed in which a projection optical system is constituted only by a reflection system. Among them, as a reflection reduction optical system proposed so far, JP-A-52-5544, Japanese Patent No. 2603225, US
P-5,063,586, USP-5,153,898, USP-5,220,590, USP-
5,353,322, USP-5,410,434, JP-A-9-211332 and the like.

[0004] Among the techniques proposed above, the first one disclosed in Japanese Patent Application Laid-Open No. 52-5544 is basically a famous one-fold aberration-free optical system constituted by concentric mirrors. , Which was developed from Offner's catadioptric optical system. This optical system has a radius of curvature of 2: 1
The first spherical mirror and the second spherical mirror are configured as follows, and the centers of curvature of the respective spherical mirrors coincide with each other. Then, the light beam emitted from an object point on the optical axis perpendicular plane passing through the center of curvature enters the concave first spherical mirror parallel to the optical axis, is reflected, enters the convex second reflecting mirror, and is further reflected. And the third
The light enters a spherical mirror, is reflected there, and forms an image with no aberration at an opposite point symmetrical to the optical axis.

[0005] In this case, the image magnification is the same, but if the object point is moved farther away from the mirror than the mirror perpendicular to the optical axis, the image point will move from the mirror perpendicular to the optical axis. To a reduced projection system. However, since the system changes from the same magnification system to the reduction system, the position of the stop is shifted, and the concave first spherical mirror used as a reflecting surface twice is appropriately separated and used in accordance with the reflection, and the magnification is increased. Must match. Naturally, the aberration-free optical system collapses, and to compensate for this, the reflecting surface is made aspherical, and of course, the use of only the annular zone is restricted.

Although the above configuration is fundamental, in this case, the object and the image are on the same side as it is.
If an object and an image are to be arranged on opposite sides, the number of reflecting mirrors must be an even number. Therefore, a plane reflecting mirror is inserted inside one surface to reverse the optical path, or a convex surface is formed on the enlarged side. Some have been added to increase the degree of freedom. The one disclosed in Japanese Patent Application Laid-Open No. Hei 9-211332, which is the last of the conventional example, is basically the above-mentioned concave surface, convex surface, and a reduction projection system composed of a reflective surface having a concave surface configuration in which two reduction projection systems are arranged in series. In some cases, an intermediate image is formed on the way.

[0007]

As described above, these optical systems are basically based on a three-component reflecting optical system consisting of a concave surface, a convex surface, and a concave surface. I have. However, when it is desired to further improve the performance of the optical system, the disadvantage is the convex mirror existing at the center.

The convex mirror diverges the light beams from the concave mirrors on both sides of the convex mirror. However, in order to cope with the concave mirrors on both sides, the power is too strong (the refractive power is too large), so that aberrations are easily generated. ing. It is an object of the present invention to avoid this drawback.

[0009]

According to the present invention, there is provided a reflection / reduction projection optical system for reducing and imaging an object on a first surface on a second surface. , Inside the two opposing concave reflecting mirrors,
At least one set of two convex reflecting mirrors, and an aperture stop, wherein the aperture stop is a concave reflecting mirror near the second surface of the two opposing concave reflecting mirrors, and the two opposite convex reflecting mirrors. A reflection reduction projection optical system is provided which is arranged between a mirror and a convex reflecting mirror close to the second surface and at a position satisfying the following arrangement condition.

0.1 ≦ x / L ≦ 0.9 (1) where L is a distance on the optical axis from the concave reflecting mirror near the second surface to the convex reflecting mirror near the second surface. And x
Is the distance on the optical axis from the convex reflecting mirror near the second surface to the aperture stop.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, in order to avoid the above-mentioned drawbacks, the basic structure is changed from a first surface side to a concave mirror,
This is a four-mirror configuration including a convex mirror, a convex mirror, and a concave mirror. With such a configuration, the power (refractive power) of one convex mirror at the center is distributed to the two convex mirrors,
The aberration generated here can be suppressed as much as possible. Two convex mirrors are provided in place of one convex mirror to reduce the occurrence of meridional coma and sagittal coma which are likely to occur with the convex mirror.

However, usually, when such a configuration is adopted,
Although the light beam is extremely off-axis reflected by the two convex mirrors, in the present invention, the light beam is received by the concave mirror while being relaxed by the power and the selection of the arrangement.
The generation of off-axis aberration is suppressed as much as possible, and the distortion is corrected. With such a configuration, a high-performance reflection reduction projection optical system can be obtained. Of course, this completely departs from the shape of the Offner-type stigmatic lens of the initial configuration, and is a completely different kind of optical system. In other words, the Offner-type aberration-free lens is characterized in that the centers of curvature of the spherical mirrors are aligned with each other, and that the image magnification is equal, so that the aberration generated on each reflecting surface is a perfectly symmetrical surface. The structure is offset. Further, in the optical system of the reduction magnification shown in the above-mentioned known example derived from this, the center of curvature of each reflecting mirror is basically configured to be on the same side with respect to each reflecting mirror, and the image magnification is In consideration of the fact that the magnification is not an equal magnification but a reduction magnification, the aberration generated in each reflecting mirror is also offset at an appropriate ratio.

However, according to the present invention, since two opposed convex mirrors are included, the centers of curvature of the two reflecting mirrors are located completely opposite to the reflecting mirror. On the other hand, in the Offner-type astigmatic lens described in the above conventional example and the known example derived therefrom, the centers of curvature are made to coincide or exist on the same side, and such a configuration itself is impossible in the first place. It has a simple configuration.

For this reason, the aberration generation structure of the optical system is completely different from that of the conventional one, so that it is necessary to find a new correction method. The present invention has been able to obtain a high-performance optical system by applying the new method. One is that the power of the two opposing convex mirrors is reduced.
By dividing the power of the convex mirror, which has become too strong, between the two convex mirrors, aberrations occurring in each of them can be suppressed as much as possible.

Here, in the present invention, the position of the aperture stop is defined as described above. That is, the condition between the concave reflecting mirror near the second surface and the convex reflecting mirror near the second surface and the condition (1)
To satisfy. By arranging the aperture stop in this way, the optical path can be made reasonably easy, and the degree of freedom in optical design increases, so that off-axis aberration can be corrected well. When the value falls outside the range of the condition (1), the aperture stop becomes too close to the reflecting mirror, which is not preferable in design. In particular, it becomes difficult to correct off-axis aberrations, and mechanical interference occurs when an aperture stop is actually arranged. Note that the upper limit is 0.7 and the lower limit is 0.1
A value of 5 will give better results.

Further, it is preferable that the aperture stop is arranged at a position where all the effective light beams are circular. Considering the case where the present invention is applied to a projection exposure apparatus, it is necessary to make the line width equal in the meridional direction and the sagittal direction on the second surface. For this purpose, the pupil of the projection optical system is required to be a perfect circle. Therefore, it is preferable that all effective light beams passing through the aperture stop are not vignetted.

The second is control of the image plane. Even in an optical system with an annular aperture, it is better to make the image plane as flat as possible, so it is first necessary to keep the Betzval value generated by the concave mirror as small as possible. When the Petzval values of the two concave reflecting mirrors are P1 and P4, respectively, it is preferable that -0.005 <(P1 + P4) <0.000 (2). If the lower limit is deviated, the image plane will be excessively curved concavely, and will exceed the range that can be corrected by the convex mirror. If the value exceeds the upper limit, the shape of the optical system is different from that of the present invention, so that a high-performance optical system cannot be obtained.

Next, the Betzval value generated by the convex mirror is:
It should be close to the Betzval value generated by the concave mirror, but with the opposite sign. Also, as described above, since the power of the two convex mirrors must be weakened, the Petzval values of the two convex reflective mirrors facing each other are P2 and P3, respectively.
In this case, it is preferable that 0.000 <(P2 + P3) <0.005 (3). If the upper limit is deviated, the image surface will be excessively curved, and will exceed the range in which the amount generated by the concave mirror can be corrected. If the lower limit is deviated, the shape of the optical system differs from that of the present invention, so that it is impossible to obtain a high-performance optical system.

Further, the Betzval value generated by the two concave mirrors must be canceled by the two convex mirrors. Therefore, it is preferable to satisfy the following conditions. -0.005 <(P1 + P4) + (P2 + P3) <0.005 (4) If the lower limit is deviated, the image surface will be too concavely curved, exceeding the range that can be corrected by a convex mirror. If the upper limit is deviated, the rear surface will be excessively convexly curved, exceeding the range in which the amount generated by the concave mirror can be corrected.

In the present invention, the curvature of field on the second surface can be corrected as much as possible by arranging the configuration so as not to deviate from this relationship. The values in each example are shown in Table 1 below. Here, r1, r2, r3, and r4 represent the radii of curvature of the first concave mirror, the first convex mirror, the second convex mirror, and the second concave mirror, respectively, and K1, K2, K3, and K4 are the first concave mirrors, respectively. , The first convex mirror, the second convex mirror, and the second concave mirror.

[0021]

Table 1 Example 1 Example 2 Example 3 Example r1 -872 -811 -853.5 r2 -1894 -1473 -1704.4 r3 487.5 520.5 520.3 r4 687 708.6 713.9 K1 -0.00115 -0.00123 -0.001172 K2 -0.000528 -0.000679 -0.000587 K3 0.00205 0.00192 0.00192 K4 0.00146 0.00141 0.00140 (P1 + P4) -0.00261 -0.00264 -0.002572 (P2 + P3) 0.002578 0.002599 0.002507 (P1 + P4) + (P2 + P3) -0.000024 -0.000041 -0.000065 In each of the examples, it can be seen that each of the examples satisfies the conditional expression and has a good image plane.

Further, a third point is that since the reflecting mirrors are all constituted by rotationally symmetric aspherical surfaces, the optical system has excellent image forming performance. The expression of the aspheric surface is: Z = cy ² / [1+ {1− (1 + κ) c ² y ² } ^1/2 ]
+ Ay ⁴ + By ⁶ + Cy ⁸ + Dy ¹⁰ ..., Where Z is the distance from the center tangent plane to the aspheric surface, c is the center curvature, y is the distance from the optical axis, κ is the conic constant, and A is 4 The next aspheric coefficient, B is a sixth-order aspheric coefficient, C is an eighth-order aspheric coefficient, and D is a tenth-order aspheric coefficient.

By employing the above-mentioned rotationally symmetric high-order aspherical surfaces, high-order aberrations occurring on each surface can be corrected, and a high-performance optical system can be obtained. .

[0024]

With the above arrangement, in the reflection-reduction projection optical system of each embodiment according to the present invention, the power of one convex mirror at the center is borne by two convex mirrors.
The generated aberration can be suppressed.
Further, since the reflecting mirrors are all constituted by rotationally symmetric aspherical surfaces, the optical system has an excellent imaging performance.

Furthermore, since it is better to make the image plane as flat as possible, the configuration is such that the Betzval sum is close to zero. With the above configuration, the present invention provides an excellent reflection reduction projection optical system. Hereinafter, examples of the present invention will be described. First Embodiment As shown in FIG. 1, the first embodiment is a projection optical system having a reduction magnification. A first concave mirror M1 is provided after a first surface R, and two opposed convex mirrors M2 are provided. An aperture stop S is provided through the first and second mirrors M3 and M3, and is configured to form an image on the second surface W by the second concave mirror M4.

In the present embodiment, the reduction magnification is 1/4, the number of gates NA on the second surface W side is 0.1, the maximum object height is 60.5 mm, the exposure size is 60 mm in radius, and the orifice opening is 1 mm in width. The exposure is performed by scanning the entire exposure area to 26 × 33 mm. First
The distance D between the surface R and the second surface W is 150 mm, and the maximum effective diameter of the used mirror is 335 mm.

As shown in FIG. 2, at a single wavelength of 13.4 nm for extreme ultraviolet lithography (hereinafter referred to as EUVL), spherical aberration and coma are well corrected to a state in which almost no aberration is present. An optical system with excellent performance in which distortion in the band is also corrected well is provided. The reflecting mirrors are all composed of rotationally symmetric aspherical surfaces. Table 2 shows the specifications of the present embodiment.

[0028]

Table 2 Surface number Curvature radius r Surface spacing d 0 1474.688780 R 1 -871.84140 -159.812984 M1 2 -1894.01300 128.062415 M2 3 487.47890 -169.000000 M3 4 ∞ -342.106767 S5 687.16284 568.178834 M4 (non-spherical) 5 κ -0.457980 40.021760 -2.882965 0.211737 A -0.164768 * 10 -10 0.103412 * 10 -8 0.541764 * 10 -8 -0.284804 * 10 -10 B -0.334226 * 10 -15 -0.496949 * 10 -15 0.557637 * 10 -14 - ^{0.433530 * 10 -16 C 0.363279 * 10} -20 0.217517 * 10 -18 0.255260 * 10 -17 -0.243275 * 10 -21 D -0.270219 * 10 -25 -0.380199 * 10 -23 -0.210921 * 10 -21 0.422095 * 10 - ²⁶ (Condition) x / L = 169 / 511.106767 = 0.33 [Second Embodiment] As shown in FIG.
A projection optical system having a magnification of 2.times., A first concave mirror M1 is provided after the first surface R, and two opposed convex mirrors M2 are provided.
And M3, an aperture stop S is provided, and the second concave mirror M
4 so as to form an image on the second surface W.

In the present embodiment, the reduction magnification is 1/4, the numerical aperture NA on the second surface W side is 0.13, the maximum object height is 90.5 mm, the exposure size is 90 mm in radius, and the orifice is 1 mm in width. The exposure is performed by scanning the entire exposure area to 26 × 33 mm. First
The distance D between the surface R and the second surface W is 1489 mm, and the maximum effective diameter of the used reflector is 444 mm.

As shown in FIG. 4, at a single wavelength of EUVL of 13.4 nm, spherical aberration and coma were corrected satisfactorily to almost no aberration, and distortion in the used orbital zone was also corrected satisfactorily. We offer optical systems with excellent performance. The reflecting mirrors are all composed of rotationally symmetric aspherical surfaces. Table 3 shows the specifications of the present embodiment.

[0031]

Table 3 Surface number Curvature radius r Surface distance d 0 1446.494640 R 1 -811.30103 -137.292540 M1 2 -1473.54944 109.320020 M2 3 520.49317 -169.000000 M3 4 ∞ -351.076040 S5 708.60536 590.712854 M4 (non-spherical) 5 κ -0.378940 22.243233 -4.178595 0.204072 A -0.660040 * 10 ^-10 0.605528 * 10 ^-9 0.490911 * 10 ^-8 -0.271175 * 10 ^-10 B -0.245853 * 10 ^-15 0.514066 * 10 ^-14 0.207057 * 10 ^-14 -0.456580 * 10 ^-16 C -0.608272 * 10 ^-21 0.153342 * 10 ^-19 0.112104 * 10 ^-18 -0.109405 * 10 ^-21 D 0.167051 * 10 ^-26 0.638335 * 10 ^-24 0.811872 * 10 ^-23 -0.705656 * 10 ^-28 ( Condition) x / L = 169 / 520.076040 = 0.32 [Third Embodiment] In the third embodiment, as shown in FIG.
A projection optical system having a magnification of 2.times., A first concave mirror M1 is provided after the first surface R, and two opposed convex mirrors M2 are provided.
And M3, an aperture stop S is provided, and the second concave mirror M
4, so as to form an image on the second surface W.

In this embodiment, the reduction magnification is 1/4, the numerical aperture NA on the second surface W side is 0.16, the maximum object height is 112.5 mm,
The exposure is performed by scanning with a radius of 111 mm and a 1 mm wide annular opening with a total exposure area of 26 × 33 mm. The distance D between the first surface R and the second surface W is 1456 mm, and the maximum effective diameter of the used reflecting mirror is 553 mm.

As shown in FIG. 6, at a single wavelength of EUVL of 13.4 nm, both spherical aberration and coma were well corrected to almost no aberration, and the distortion in the orbital zone used was also well corrected. We offer optical systems with excellent performance. The reflecting mirrors are all composed of rotationally symmetric aspherical surfaces. Table 4 shows the specifications of the present embodiment.

[0034]

Table 4 Surface number Curvature radius r Surface distance d 0 ∞ 1374.280233 R 1 -853.46550 -128.101268 M1 2 -1704.44202 125.101268 M2 3 520.28809 -169.000000 M3 4 ∞ -352.123814 S5 713.85066 606.097744 M4 (1 aspherical shape) 5 κ -0.255188 14.534013 -4.401675 0.181804 A -0.983673 * 10 -10 -0.178114 * 10 -9 0.500211 * 10 -8 -0.207371 * 10 -10 B -0.267713 * 10 -15 0.247201 * 10 -14 0.156649 * 10 -14 - ^{0.286238 * 10 -16 C -0.178682 * 10} -21 -0.103591 * 10 -19 0.105717 * 10 -18 -0.102662 * 10 -21 D -0.238078 * 10 -26 0.668065 * 10 -25 0.332409 * 10 -23 0.184894 * 10 - ²⁷ (Conditions) x / L = 169 / 521.123814 = 0.32 When using the above three embodiments in a reduction projection exposure apparatus such as a stepper used in the manufacture of semiconductors using a light source for EUVL, a multilayer film reflecting mirror should be used. To The multilayer mirror is a mirror formed by stacking a large number of thin films, and has an increased reflectance in the X-ray region.

As described above, in each embodiment according to the present invention, a so-called Offner-type reflective imaging optical system constituted by one convex mirror between two concave mirrors is used. Two convex mirrors are provided in place of the convex mirror to reduce the occurrence of meridional coma and sagittal coma which are likely to occur with the convex mirror. In the normal case, the light beam is extremely off-axis reflected by the two convex mirrors, but while reducing it by selecting the power and the arrangement, the off-axis aberration is generated by receiving the light east with the concave mirror. Minimizing distortion and correcting distortion

[0036]

According to the construction described above, a high-performance reflection reduction projection optical system can be obtained.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of a cross section of a projection optical system according to a first embodiment. However, the width of the luminous flux represents only the cross section.

FIG. 2 is a lateral aberration diagram of the first embodiment.

FIG. 3 is an actual optical path diagram of a projection optical system according to a second embodiment. However, the width of the luminous flux represents only the cross section.

FIG. 4 is a lateral aberration diagram of the second embodiment.

FIG. 5 is an actual optical path diagram of a projection optical system according to a third embodiment. However, the width of the luminous flux represents only the cross section.

FIG. 6 is a lateral aberration diagram of the third embodiment.

[Explanation of symbols]

 R 1st surface M1 1st concave mirror M2 1st convex mirror M3 2nd convex mirror S diaphragm M4 2nd concave mirror W 2nd surface

Claims (4)

[Claims] 1. A reflection reduction projection optical system for reducing and imaging an object on a first surface on a second surface, comprising: two opposing concave reflecting mirrors; and an inner side of the two opposing concave reflecting mirrors. At least one pair of two opposing convex reflecting mirrors and an aperture stop, the aperture stop being a concave reflecting mirror near the second surface of the two opposing concave reflecting mirrors, Between a convex reflector close to the second surface of the two convex reflectors,
The reflection reduction projection optical system is arranged at a position satisfying the following arrangement condition. 0.1 ≦ x / L ≦ 0.9 where L is the distance on the optical axis from the concave reflecting mirror near the second surface to the convex reflecting mirror near the second surface, and x
Is the distance on the optical axis from the convex reflecting mirror near the second surface to the aperture stop. 2. The reflection reduction projection optical system according to claim 1, wherein said aperture stop is arranged at a position where all effective light beams are circular. 3. The reflection reduction projection optical system according to claim 1, wherein the second surface side of the reflection reduction projection optical system is telecentric. 4. When the Petzval values of the two opposing concave reflecting mirrors are P1 and P4, respectively, and the Petzval values of the two opposing convex reflecting mirrors are P2 and P3, the following expression is satisfied. 4. The reflection reduction projection optical system according to claim 1, wherein: -0.005 <(P1 + P4) <0.000 0.000 <(P2 + P3) <0.005 -0.005 <(P1 + P4) + (P2 + P3) <0.005