JPS61212815A - Reflection optical system - Google Patents

Abstract

PURPOSE:To compensate various aberrations excellently by providing four mirror systems which form an object image, making the optical axis of at least one of them eccentric from those of other optical systems, and providing the whole system with reduction image formation power. CONSTITUTION:Luminous flux from an object point P1 in a specific area on an optical axis is reflected by reflecting mirrors M1, M2, and M3 of the 1st mirror system S1 in the order of a concave, a convex, and a concave mirror, to form an image at the 1st image point P'1. This image point P'1 is aligned to the image point of the 2nd mirror system S2, and the luminous flux is reflected by reflecting mirrors M4, M5, and M6 similarly and then reflected by the 3rd and the 4th mirror systems S3 and S4 to form an image at the 4th image point P'4. The optical axis L12 in which optical axes of the 1st and the 2nd mirror systems S1 and S2 are aligned and the optical axis L34 of the 3rd and the 4th mirror systems S3 and S4 are made parallel and eccentric to prevent mechanical interference among respective mirror systems and reduce the eclipse of the luminous flux, thereby compensating comatic aberration, distortion aberra tion, etc., excellently although this system is a reduction system on the whole.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a reflective optical system, and more particularly to a reflective optical system used in a projection exposure apparatus for manufacturing semiconductors such as ICs and LSIs.

(Prior Art) Conventionally, a reflective optical system for printing patterns of integrated circuits such as ICs and LSIs using a projection exposure apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 48-1203948-120.
39 No. 5 and Japanese Patent Application Laid-Open No. 52-5544, the centers of curvature of two reflecting mirrors, a concave mirror and a convex mirror, are concentric or non-concentric. The reflective optical system is configured such that the imaging magnification is equal to Kfi. Further, in Japanese Patent Application Laid-open No. 1002:10, a meniscus-shaped lens with negative refractive power is used in addition to a concave mirror and a convex mirror to improve optical performance.

In this way, since the conventional reflective optical system has the same imaging magnification, the optical system can be arranged symmetrically, and various aberrations (including commis aberration and distortion aberration) are eliminated. Relatively high optical performance could be easily obtained despite the small number of reflecting mirrors.

On the other hand, in R-near IC manufacturing, a so-called stepper-type projection exposure apparatus that reduces the pattern on the mask IIi onto the wafer surface and exposes it by projection is used to produce the mask. It is being used and used in various fields because it improves the overall throughput.
, :・1・[However, in general, reflection optics is transmitted to projection exposure equipment; if you try to configure the system as an imaging magnification reduction system, the optical system Do not compose it asymmetrically (it must not be 1, and as a result of B, it should be a same-size system;
There are many cases of convulsions and distortion convergence (occurrence 1,
It is difficult to maintain good overall optical performance.

Particularly, book 1 in which the imaging magnification is 'A-'. ``It is very difficult to perform good aberration correction. - In addition, various proposals have been made to configure the projection system of a projection exposure apparatus using a refractive optical system instead of a reflective optical system. However, L
The 4*mm optical system is used to obtain high resolution; however, since it uses light at shorter wavelengths, the transmittance decreases, and because the types of glass that can be used are limited, chromatic aberration occurs. It is difficult to satisfactorily correct f′.1゛(Objective of the present invention)′1 The present invention provides a projection exposure apparatus (suitable for use with a high reduction system, 1) only a reflective system capable of The object is to provide a nine-reflection optical system using a refractive system and a refractive system. , 1' (Main features for achieving the object of the present invention).

After reflection in the order of concave mirror, convex mirror, and concave mirror, the object II2 is imaged at a predetermined position. So, a, b = i 'y -' system s, ', s'2
．． Place s3' and s4 in sequence, and (+ 42 above)
Memi 9□-system 511s2, 531sj radiation optical system with the four mirror systems ζ 8':';
・Oi Tanabata ・Constructed so that the image formation is repeated repeatedly. The optical axis of at least one of S and S4 is decentered with respect to the optical axis of the other 1-system, and
This is because only a predetermined area on the optical axis is used for imaging, and the imaging magnification of the entire system is reduced to 1.
:'Furthermore, features and features for achieving the objectives of the present invention even better are detailed in the Examples.
,゛(Example),′ ・・
\11., ,; Figure '1 is a schematic diagram of an optical system according to an embodiment of the present invention. The reflective optical system in the same figure has curvature in the same direction;
A four-mirror arrangement with three reflections of a concave mirror
-1 The overall imaging magnification is reduced.

In the figure, the first mirror system S is made up of reflecting mirrors M□ to M3, the second mirror system S2 is made up of reflecting mirrors M4 to M6, the third mirror system S is made up of reflecting mirrors M7 to M9, and the fourth mirror system is made up of reflecting mirrors M0° to M12. They each constitute a color system S4. The light flux from the object point P within a predetermined area on the optical axis is reflected by the reflecting mirror M□9M of the first mirror system S0.
It is reflected in the order of 22M3 and is imaged at the first image point P0'.

The first image point P' becomes the object point P2 of the second mirror system S2, and the light flux from the object point P2 becomes the reflecting mirror M4 of the second mirror system S2.
It is reflected in the order of Ms and M6 and is imaged at the second image point P2'. Similarly, the second image point P2', that is, the object point P3, is imaged to the third image point P' by the third mirror system S3, and the object point P4 is imaged to the fourth image point P4' by the fourth mirror system S4. It is configured.

In this example, each mirror system has a basic configuration of a concave mirror, a convex mirror, and a concave mirror with so-called positive, negative, and positive refractive powers, and by using four of these mirror systems, each While reducing aberrations generated by the mirror system, various aberrations such as coma and distortion are well corrected overall.

Furthermore, in this embodiment, the optical axis of at least one of the mirror threads of the four mirror systems is decentered with respect to the optical axis of the other mirror systems. A reduced-reflection optical system has been achieved while maintaining good quality.

In particular, in this embodiment, the first mirror system S and the second mirror system S2
The optical axis L12 and the third mirror system S whose optical axes are aligned with each other
and the optical axis L3 of the fourth mirror system S4 are made to coincide with each other.
It has two optical axes of 4. By making the optical axis L12 and the optical axis L34'tl parallel and eccentric, K prevents mechanical interference between each mirror system, further reduces vignetting of the light beam, and efficiently directs the light beam to the final image plane P, l/. It constitutes a reflective optical system that is a reduced system as a whole while guiding all light.

In this case, it is preferable to set the amount of parallel eccentricity ΔX based on the height of the principal ray incident on the third mirror system in order to correct aberrations and to reduce curvature of the light beam.

In this embodiment, when the height of the object point P from the optical axis L1° is h, the height h' of the image point p2', that is, the object point P3 from the optical axis "12" is the first mirror system and the second mirror system. The imaging magnification of each system is 0.
．． 42, 0.8, so h/=0.336.

Here, the height of the object point P3 on the optical axis with respect to the optical axis L34 is b
3, parallel eccentricity Δx'xΔx = 0.336h
+h3 −・・・・・・−・(a). Note that from the viewpoint of correcting aberrations and preventing currant light beams, it is not necessary to limit the equation to formula (A), and 0.7 (β, ・β 2 h + h 3 ) < Δx (1, 3 (β 1 ・
β2h+h3) (b) The object of the present invention can be achieved by making the parallel eccentricity within the range.

For example, as in this embodiment, the optical axis of the third mirror system is
If the mirror system is not eccentrically parallel to the optical axis, the light beam reflected from the reflecting mirror M7 of the third mirror system will be eclipsed by the reflecting mirror M5 of the second mirror system. In order to avoid this, for example, a prism must be placed between the reflecting mirrors M6 and M7. For this reason, when used in a projection exposure device, the scanning directions of the object point P and the final image point P4' must match, which requires the installation of an additional plane mirror or total reflection prism, which complicates the entire device. So I don't like it. If decentered optical system sound is used as in this embodiment, the scanning directions of the object point P and the image point pj can be made the same.

In this embodiment, by configuring at least one of the four mirror systems as a fully equal magnification or magnification system, various aberrations occurring in the other mirror systems, especially spherical aberration, coma aberration, field curvature, etc., can be canceled out. I have to.

For example, if all four mirror systems are configured as reduction systems, it will be efficient in terms of imaging magnification, but the effect of canceling out various aberrations generated by each mirror system will be small, resulting in better overall aberration correction. This is because it becomes difficult.

In this example, the imaging magnifications of the first, second, third, and fourth mirror systems are 0.42, 0.8, 0.65, and 1.1, respectively.
The overall imaging magnification is 0.24.

The fourth mirror system is used as an enlargement system to correct aberrations generated in the first, second, and third mirror systems.

□In the present invention, in order to maintain particularly good formation and imaging performance within an arcuate range on the optical axis, the radius of curvature of the first reflecting mirror counting from the object point must be adjusted. R1, 1st and i-1-1
If the th air interval is Dl, then 1RII) 1R2
1...--(1) 1D11 > ID21
,, (2) It is preferable to satisfy all conditions 1.

Conditional expression 111, +21 is the reflecting mirror M1 of the first mirror system.
The conditional expression (xl) is related to the configuration of M2 and air spacing, and the conditional expression (xl) (if 21k deviates, the radius of curvature of reflector M2 becomes larger than the radius of curvature of reflector town) or the distance between reflector M2 and Mj becomes larger than that of reflector Mj. If the distance is larger than the distance between M0 and M2, the meridional flare increases and the astigmatism difference increases, making it difficult to maintain good arc-shaped imaging performance.

Further, in the present invention, it is more preferable that the distance between each reflecting mirror and the air in the second, third, and 41st Ra systems is |R1 /R21
>lR4/R61・・・・・・・・・(3)lR7/R
81) |R1O/R11l ・・・・・・・・・(
4) lR9/R81) 1R12/R11l...
・・・・・・(5)+0101) IDII+
It is preferable to set as shown in (6).

Conditional expression (3) is intended to satisfactorily correct the coma aberration of the entire screen by limiting the radius of curvature of the first mirror system M, , , M2 and the second mirror system M, , M6060. If conditional expression (3) is violated, the coma flare of the entire screen increases. - Conditional expression (4) applies to the reflecting mirror M7 of the third mirror system. Regarding the radius of curvature of M8 and the fourth mirror system M1G'``110'', 1) If the conditional expression +41' is not satisfied, it will not be possible.
□Flare increases and astigmatism difference also increases.

Conditional expressions (5) and (6) apply to the reflecting mirror M8jM of the eighth mirror system.
9 and the fourth mirror system reflector M□□9M12 and the fourth
This is related to the air spacing between each reflector in the Milani system, and the purpose is to effectively use the magnifying system to perform good aberration correction.If conditional expressions (5) and (6) are violated, the screen Flare occurs throughout, and astigmatism also increases.1. It becomes difficult to obtain good optical performance.
- Fig. 3 is a schematic diagram of an optical system according to another embodiment of the present invention. The embodiment shown in FIG. 1 is the same as the embodiment shown in FIG.
Lens groups □...Q* are placed between the lens and 4 to enlarge the aperture ratio by 10), and chromatic aberration is well corrected.
・□ □Especially in this example, the lens group Q1 is
A meniscus-shaped lens with a positive refractive power with the convex surface facing the image surface side of the mirror system S1, and a meniscus-shaped lens with a positive refractive power with the concave tube facing the image surface side of the lens group Qit a-th mirror system S3. The lens groups Q1, q2'ta are composed of lenses that correct off-axis spherical aberrations, correct chromatic aberrations well, and expand the aperture ratio. ,,. Gaka□ Air Ah, 17 Ah 1
．． 1 is also good. ,,4.1□・→・
′ Between the □ system Dentsu system and the reduced system Mira, - system Ω-4
, : positioning them in the respective parts makes it easy to correct aberrations.
It is preferable because it can be done.

In this embodiment, when the lens group Q1 is considered as the first lens system S□, and the lens group Q2'ft is considered as the third mirror system or part of the mirror system, the imaging and magnification are α42° and 0.8°, respectively. 0.
6971 LO4; t" exists. 5.Next, numerical examples of the embodiments shown in FIGS. 1 and 3 will be shown.R
1 is the radius of curvature of the reflector at □ counting from the object point P □ Di is the 1st and 1st counting from the object point P □
+1st air interval, StO.

is quartz glass.6 Air spacing is positive when measured from left to right in the direction of light travel, and negative when measured from the opposite direction, ・(1
And then you're on the water. 1 Numerical implementation 1lI R[) N 1 -700 -275.25 -12
-11L5 230 13 -417.1
1 -1390 -14 602.5
335 15 154.8 -292
-16 495.925 707.25 17
-434.83 -240 -18 -
234.69 259.03 19 -416
．． 88 -114L5 -11]20α33
-280 -112 451.72
1Fe-3,75 Slit width 1.5m+n Magnification A Parallel eccentricity jx=140 Numerical example 2 RD N 1 -700 -275.25 -12
-16SL5 230
14 207.97 -1115
-8in25 203.82 -107&66
-16 607+5 335 18
495.925 707.07 110
-218.34 259.04 111 -4
30.52 -345 -112 -82
&65 -35 -810213 -10
00.66 -781.43 -115 2
09.79 -280 -116 45L
72 1Fe-&5 Slit width 1.51m Magnification A Amount of parallel eccentricity ΔX-140 (Effects of the present invention) According to the present invention, a four-mirror system having positive, negative, and positive refractive power reflecting mirrors is arranged, The optical axis of at least one of the mirror systems is decentered from the optical axis of the other mirror systems, and only a region within a certain range on the optical axis is used, resulting in an overall reduced system. It is possible to achieve a full reflective optical system that provides excellent imaging performance.

Further, by arranging a lens group in a part of the mirror system, it is possible to satisfactorily correct off-axis spherical aberration and chromatic aberration, and to achieve a reflective optical system with a fully enlarged aperture ratio.

[Brief explanation of drawings]

FIGS. 1 and 3 are optical cross-sectional views of numerical embodiment 1.2 of the present invention, and FIGS. 2 and 4 are optical cross-sectional views of numerical embodiment 1.2 of the present invention, respectively.
This is a diagram of the lateral aberration of No. 2. In the aberration diagrams, (8) shows aberrations on the meridional plane and (8) on the sagittal plane. Yoii, M to M12 are each reflecting mirrors.

Claims (8)

[Claims] (1) Four mirror systems S_1, S_2, S_3, and S_4 are sequentially arranged to form an object image at a predetermined position after being reflected in the order of a concave mirror, a convex mirror, and a concave mirror, and the four mirror systems S_1, A reflective optical system configured to repeatedly form images in S_2, S_3, and S_4, and the four mirror systems S_1, S_2, S_3, and
_4 The optical axis of at least one mirror system is decentered from the optical axis of the other mirror system, and only a predetermined area on the optical axis is used for imaging, and the imaging magnification of the entire system is reduced. A reflective optical system characterized by being configured so that. (2) The reflective optical system according to claim 1, wherein the reflective optical system has at least one reduction system and at least one equal-magnification or magnification mirror system. (3) The reflective optical system according to claim 1, wherein the mirror system S_1 is configured as a reduction system. (4) Optical axis L_1 of the two mirror systems S_1 and S_2
The optical axis L_1_2 and the optical axis L are coaxial with the optical axis L_3_4 of the two mirror systems S_3 and S_4.
3. The reflective optical system according to claim 1, characterized in that _3_4 are eccentrically arranged relative to each other. (5) The radius of curvature of the i-th reflecting mirror counting from the object point is R
i, the i-th and the i+1-th air interval is Di, |Ri|>|R2| |Di|>|D2| Reflective optics. (6) In the reflective optical system according to claim 5 |R1/R2|>|R4/R6| |R7/R8|>|R10/R11| |R9/R8|>|R12/R11| |D10|>|D11| A reflective optical system characterized by satisfying the following conditions. (7) A lens group Q is provided between the mirror systems S_1 and S_2.
_1 is connected to the lens group Q between the mirror systems S_3 and S_4.
2. The reflective optical system according to claim 1, wherein the reflective optical system is characterized in that _2 are arranged respectively. (8) The lens group Q_1 is a meniscus-shaped lens with a convex surface facing the image plane of the mirror system S_1, and the lens group Q_2 is a meniscus-shaped lens with a concave surface facing the image plane of the mirror system S_3. 8. A reflective optical system according to claim 7, characterized in that the reflective optical system has the following configurations.