JPS6147916A - Reflecting optical system - Google Patents

Abstract

PURPOSE:To obtain a reflecting optical system having high resolution, which is suitable for a projecting exposure device, by combining appropriately four mirror systems and one relay system, and constituting them so that the overall image forming magnification is reduced. CONSTITUTION:The first mirror system S1, the second mirror system S2, a relay system F, and the third mirror system S3 and the fourth mirror system S4 are constituted of relecting mirrors M1-M3, reflecting mirrors M4-M6, a reflecting mirror M7, and reflecting mirrors M8-M10, and reflecting mirrors M11-M13, respectively, and an object point P1 is made to form an image at an image point P'5 (P6) in the end so that the image forming magnification becomes about 1/4. In this way, by using plural mirror systems consisting of a concave mirror, a convex mirror, and a concave mirror, various aberrations generated from one mirror system are reduced and a good image forming performance is obtained as a whole. Especially, by using the mirror systems S2, S3 as a magnifying system, a comatic aberration, a curvature of image, distortion, etc. generated in the mirror systems S1, S4 and the relay system F are corrected satisfactorily, and also vignetting of a luminous flux generated in case of constituting a reflecting optical system by plural mirror systems is prevented by placing total reflecting mirrors H1-H4.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 integrated circuits such as ICs and LSIs.

Conventionally, reflective optical systems for printing integrated circuit patterns such as IC, L, SI, etc. onto silicon wafers using a projection exposure apparatus have been proposed, for example, in Japanese Patent Laid-Open Nos. 48-12039 and 1988-53. This method has been proposed in Japanese Patent No. 100230 and the like.

The reflective optical systems used in these projection exposure apparatuses have extremely high resolving power.

Generally, the shorter the wavelength used, the better the resolution of the projection image. For this purpose, a light source that emits as short a wavelength as possible is used. Optical systems that are almost completely corrected for aberrations are being praised so that high resolution can be obtained not only in the center of the screen but over a wide screen.

Generally, an imaging optical system using a lens is constructed using a plurality of glass materials in order to correct chromatic aberration. Light on the short wavelength side is advantageous for obtaining high resolution, but chromatic dispersion is large on the short wavelength side, so it is difficult to properly correct chromatic aberration due to the design.

For this reason, optical systems using reflective mirrors are often used as imaging optical systems for printing IC patterns and the like that require high resolution.

This is because reflective optical systems have features such as no chromatic aberration, can use light of any wavelength, and can increase the transmittance of the entire optical system compared to when using a lens system. be.

An object of the present invention is to provide a reflective optical system that can obtain high resolution and is suitable for a projection exposure apparatus that takes advantage of the characteristics of a reflective optical system.

The main feature of the reflective optical system for achieving the purpose of the present invention is that when a plurality of single mirror systems are arranged in a chain so that a four-sided mirror, a convex mirror, and then a concave mirror are reflected in this order,
A relay system having a concave mirror for relaying an object image is disposed at at least one location between the mirror systems, so that the overall imaging magnification is reduced.

As described above, in the present invention, the four mirror systems and the relay system are configured to function like a field system, and among these, the mirror system s5 following the relay system. By reducing the outer diameter of s4, overall good aberration correction is achieved.

Next, embodiments of the present invention will be described with reference to each drawing.

FIG. 1 is a schematic diagram of a reflective optical system according to an embodiment of the present invention. The reflective optical system in the same figure consists of three reflective mirrors M shown in FIG.
Six mirror systems S consisting of 1t M2+ MS and a third
The figure shows one mirror system S' consisting of three reflecting mirrors [1', M2', ) (3') and a relay system F consisting of a concave mirror.
are arranged so that they are located substantially on the same optical axis and the overall imaging magnification is reduced, thereby achieving a high-resolution reflective optical system.

In the embodiment shown in FIG. 1, the first mirror system S1 is formed by reflecting mirrors M1 to M3, the second mirror system S2 is formed by reflecting mirrors M4 to M6, the relay JF is formed by reflecting mirror M7, and the third mirror system is formed by reflecting mirrors 11M5 to M10. S3 and reflecting mirrors M11 to M13 constitute a fourth mirror system S4.

The mirror system S1+S2+S4 is constructed from the mirror system S shown in FIG. 82, and the mirror system S3 is constructed from the mirror system S' shown in FIG.

Then, the object point P1 is sequentially moved to the mirror system S1. Repeat imaging with S2, relay system F, and mirror system S5+84, and f
! 1. The image is finally formed at an image point Ps' (P+s) at an imaging magnification of 1/4.

Next, the image forming state of the mirror system constituting the reflective optical system shown in FIG. 1 will be explained.

In FIG. 2, six reflecting mirrors 4+M2*M3 are arranged so that the light beam L1 from the object point P1 is reflected in the order of concave mirror M1+convex mirror M2 and concave mirror M3, and then focused on image point P1'.

The mirror system S shown in FIG. 2 has a concave mirror M3 located between the convex mirror M2 and the concave mirror M1, and the mirror system S' shown in FIG.
/ is located between.

In this embodiment, the effective surface of the object is an arcuate portion Q1 as shown in FIG. For this purpose, five reflectors M1* x2. The outer shape of KM does not necessarily have to be circular, and unnecessary parts may be deleted, for example, as shown in FIG. 3, the lower part of concave mirror M1 may be deleted and the shape shown in the same figure may be obtained. As a result, it is possible to adopt a configuration in which the concave mirror M3 is placed to the right of the concave mirror M1.

In this way, in this embodiment, the light flux from the object point P is
Consisting of a convex mirror and a concave mirror, i.e. positive.

By using multiple mirror systems consisting of reflecting mirrors with negative and positive refractive powers, various aberrations generated by a single mirror system, especially coma aberration and field curvature, are reduced, resulting in good overall focusing performance. .

In this embodiment, as shown in FIG. 1, the mirror system S1 moves the object point P1 to the image point P1', that is, the mirror system S2 moves the object point P2 to the image point P2', and the mirror system S2 moves the object point P2 to the image point P2'.
In other words, to object point P3 of relay system F, relay system 1
i', mirror system S3+mirror system S4 sequentially repeat imaging, and finally object point P1 is reduced to tsukudani P5' and imaged.

In this embodiment, the mirror system S1+84+ and the relay system F are reduced systems, and the mirror system S2. S3 is configured as an expansion system. Specifically, the imaging magnification of each mirror system and relay system is shown in Table 1.

Table-1 Imaging magnification of each mirror system In this example, in order to achieve an overall imaging magnification of 1A, four mirror systems and a relay system are configured to have the imaging magnification shown in Table-1. As a result, aberration correction is performed in a well-balanced manner overall.

In particular, by using the mirror system 82zS5 as an enlarging system, comatic aberration, field curvature, distortion, etc. caused by the mirror thread S1+84 and the relay system are effectively corrected.

In addition, in this embodiment, the relay system F is optically disposed between the second mirror system S2 and the mirror system S3 of @3, and the diameter of the light beam to the third mirror system S3 is changed by applying a field effect. is made smaller.

In this embodiment, total reflection mirrors H1 to H4 are arranged between the respective mirror systems to prevent the curvature of the light beam that occurs when a reflective optical system is configured with a plurality of mirror systems.

In this embodiment, in order to particularly reduce the curvature of the luminous flux and obtain good overall optical performance, the mirror system 51y
Concave mirror 4 + convex mirror M2 and concave mirror M3 that constitute S4
When the radius of curvature of is R1t R2+R5, R
It is preferable to satisfy the following conditions: 1/R2≧2...0(1) R1/R3>1...(2).

Conditional expressions (1) and (2) are used to reduce the size of the entire mirror system while suppressing the occurrence of off-axis aberrations when the effective screen of the object is a portion of a circular arc as shown in Figure 4. This is to allow the light beam from to form an image at a predetermined position without blurring.

If conditional expression (1) is not satisfied, coma flare will increase and the light beam will have more currant. Moreover, if conditional expression (2) is not satisfied, the radius of curvature of the concave mirror M3 becomes t11. This becomes too large compared to M1, making it difficult to obtain a predetermined refractive power while downsizing the mirror system as a whole.

Particularly in this embodiment, in order to reduce field curvature and obtain a high-contrast object image, the radius of curvature R1+R2p R
3 is further set as 1R11''>lRx1>lR21 (3).

If this condition is violated, the f&111in curve becomes large and the beam angle becomes large, and it becomes difficult to perform good aberration correction in a reflective optical system that combines a plurality of mirror systems.

Furthermore, in this embodiment, in order to reduce the curvature of the light beam and reduce the amount of J-to aberrations generated from each mirror system to achieve a reflective optical system that performs good aberration correction, the concave mirror M1. When the radius of curvature of convex mirror M2 and concave mirror M3 is R4t R5, R6, respectively, and the radius of curvature of convex mirror M1 of mirror system S5 is R8y, R9r, R10, respectively, R4/Rs
> 1 ... (4) R4/ Rs > 1 ・
...(5) RB / 'ELq≧2・l...(6)
R1G/R9) 1 @11@@・(Satisfies the condition ``C''.

Conditional expressions (4) and (5) are intended to satisfactorily correct comatic aberration and field curvature; if conditional expression (4) is not satisfied, comatic aberration increases and the tilt of the meridional image plane increases. , and if conditional expression (5) is not satisfied, the sagittal image plane will become more tilted.

Conditional expressions (6) and (7) are based on comatic aberration and sagittal image plane.
This is to reduce the flare. If conditional expression (6) is not satisfied, comatic aberration will increase and it will be difficult to obtain a high-contrast projected image, and if conditional expression (7) is not satisfied, there will be more flare on the sagittal image plane. I don't like it because it comes.

In this embodiment, when the radius of curvature of the concave mirror of the relay system F is R7, it is preferable to set it as follows.

Is this the relay system F used as the field system? −
, 1% This is to efficiently converge the luminous flux from s2 and form an image on the object point of the third mirror system S3.If this condition (8) is violated, the field system will not function sufficiently and the mirror It becomes difficult to downsize the system S3.

In the present invention, the image formation adjustment of the object image is performed using mirror systems 81 to 81.
It is preferable for aberration correction and magnification adjustment to be performed by moving at least one mirror system of S4 or the relay system.

Next, the index values of the example shown in FIG. 1 are shown. R( is the radius of curvature of the th reflecting mirror counting from the object point P1, and Dt is the distance between each reflecting mirror when measured from left to right along the direction of light propagation, and vice versa. Shown as negative.

The effective screen of the object has a slit width of 3 fins, and the effective F-number is 3.0 (NA-0,165). The effective screen width of the object point P1 is within a height range of 197-200 mm from the optical axis.

As described above, according to the present invention, a reflective optical system with high resolution can be achieved by appropriately combining five mirror systems.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG.
FIG. 3 is an explanatory diagram of a portion of FIG. In the figure, Y indicates a storeroom, 81 to $4 each indicate a mirror system, F indicates a relay system, and M1 to M15 each indicate a reflecting mirror.

Claims (4)

[Claims] (1) When a plurality of single mirror systems configured to reflect in the order of a concave mirror, a convex mirror, and a concave mirror are arranged in a chain, a concave mirror is provided at least at one point between the mirror systems to relay an object image. A reflective optical system characterized by having a relay system arranged so that the overall imaging magnification is reduced. (2) The reflective optical system is connected in order from the object side to the first mirror system, the second mirror system S_1, S_2, the relay system, and the third and fourth mirror systems.
The reflective optical system according to claim 1, characterized in that it is constituted by mirror systems S_3 and S_4. (3) The radius of curvature of the concave mirror M_1, convex mirror M_2, and concave mirror M_3 of the mirror systems S_1 and S_4 is R_
1, R_2, and R_3, the reflective optical system according to claim 2 satisfies the following conditions: R_1/R_2≧2 R_1/R_3>1. (4) Concave mirror M_1 and convex mirror M_ of the mirror system S_2
2, and the radius of curvature of concave mirror M_3 is R_4 and R_5, respectively.
, R_6, and the radius of curvature of the concave mirror M_1, convex mirror M_2, and concave mirror M_3 of the mirror system S_3 is R_8, respectively.
The reflective optical system according to claim 3, characterized in that, when R_9 and R_1_0, the following conditions are satisfied: R_4/R_5>1 R_4/R_6>1 R_8/R_9≧2 R_1_0/R_9>1.