JPS6147915A - 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 three 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 are constituted of reflecting mirrors M1-M3, reflecting mirrors M4-M6, reflecting mirrors M7-M8, and reflecting mirrors M9-M11, respectively, and an object point P1 is made to form an image at an image point P'4 (P5) in the end so that the image forming magnification becomes about 1/4.5. In this way, by constituting the mirror systems S1, S2 and S3 of a concave mirror, a convex mirror, and a concave mirror, respectively, 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 system S2 as a magnifying system, a comatic aberration, a curvature of image, distortion, etc. generated in the mirror systems S1, S3 and the relay system F are corrected satisfatorily, and also vignetting of a luminous flux generated in case of constituting a reflecting optical system of plural mirror systems is prevented by placing total reflecting mirrors H1, H2.

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, a reflective optical system used in projection exposure equipment &11 for printing patterns of integrated circuits such as ICs and LSIs onto silicon wafers has been proposed in, for example, Japanese Patent Application Laid-Open Nos. 48-12039 and 1982-100230. has been done. The reflective optical systems used in these projection exposure apparatuses have extremely high resolving power.

The shorter the wavelength used, the better the resolution of the projected image becomes. For this purpose, a light source that emits short wavelengths is used.

In order to obtain high resolution not only in the center of the screen but also over a wide screen, an optical system is used that is almost completely corrected for aberrations.

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 on the long wavelength side, chromatic dispersion is large, so it is difficult to properly correct chromatic aberration due to the design ◇For this reason, high resolution is required. As an imaging optical system for printing IC patterns, etc., a secondary optical system using a reflecting mirror is often used.

This is because the reflective optical system has 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. Ru.

The purpose of the present invention is to provide a reflective optical system that can obtain high resolution and is suitable for a nine-projection exposure apparatus by taking advantage of the characteristics of a reflective optical system.〇The main feature of the reflective optical system to achieve the object of the present invention is a concave mirror. When a plurality of mirror systems are arranged in a chain so as to be reflected in the order of a convex mirror and then a concave mirror, a plurality of concave surfaces gIA for relaying an object image are provided at at least one place between the mirror systems. The relay system is arranged so that the overall imaging magnification is reduced.

In this way, the present invention is composed of three mirror systems and one relay system, and the relay system is configured to function like a field system.
Achieving a reflective optical system.

Next, the implementation sequence of the present invention will be explained with reference to each figure.

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 figure consists of three reflective 6Ails shown in Figure 2.
i□, M2. The mirror system S1 consisting of M3 is
and the two reflections shown in Figure 3! 3! M3□.

Relay system Ft consisting of M3□ is arranged so as to be located substantially on the same optical axis and the overall imaging magnification is reduced. I have achieved this.

In the actual M row in Fig. 1, the first mirror system S1 is made up of reflecting mirrors M□-M3, the second mirror system S2 is made up of reflecting mirrors M4-M6, the relay system F is made up of reflecting mirrors M7-M8, and the reflection @M9-M1. , respectively constitute the third mirror system 83.

Then, the object point P is sequentially transferred to the mirror system S1.82 and the relay system F.
Then, each image is formed repeatedly by the mirror system S3, and finally an image point P' (P5) is formed at an imaging magnification of 17, . It is visualized as 5.

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

In Fig. 2, there are three reflecting mirrors M1. M2°M3 are arranged so that the light beam L from the object point P is reflected by the concave surface mM1, the convex mirror M2, and the concave mirror M3 in this order, and after t, is imaged at the image point P'.

The concave mirror M3 of the mirror system S shown in FIG. 2 is located between the convex mirror M2 and the concave mirror section.

The two concave mirrors of the relay system F shown in Fig. 3 convert the light beam from the object point P into the image point P□' by the two concave mirrors M3□2M3□.
It is arranged so that the image is formed on the

In this embodiment, the IJ v-system Ffr: Optically, the second mirror system S and the third mirror system S3 are arranged in an open field, and the diameter of the light beam to the third mirror system S3 is made smaller without causing a field effect. The aim is to downsize the reflective optical system.

In this embodiment, the object has a more circular arc-shaped portion Q□ shown in FIG. 4 as an effective surface. For this reason, the external shape of each reflecting mirror in the mirror system does not necessarily have to be circular, and by removing unnecessary portions, the overall reflecting optical system can be made smaller.

In this implementation, mirror systems s, s2. By configuring s3 with a concave mirror, a convex mirror, and a concave mirror, that is, a reflecting mirror with positive, negative, and positive refractive powers, various aberrations generated from one mirror system, especially coma aberration and field curvature, can be reduced and the overall effect can be improved. It has achieved good imaging performance.

In this embodiment, as shown in FIG.
to the object point pt - image point P', that is, the mirror system S
from the mirror system SK to the object point P2 of the image point P2.
In other words, the object point P3 of the relay system F is successively imaged by the relay system F and the mirror system 83, and finally the object point Plt is reduced to an image point P4'.

In this embodiment, the mirror systems S, S4 and the relay system Pi are reduced, and the mirror system 52t is configured as an enlarged 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 implementation, three mirror systems and one relay system have the imaging magnification shown in Table-1 to achieve an overall imaging magnification of 4.5. With this configuration, aberration correction is performed in a better balanced manner overall.

In particular, by making the mirror system S2 an enlarged system, the mirror system 8
184 and the relay system F, the order comatic aberration, field curvature, distortion, etc. are well corrected.

In this implementation, a total reflection mirror is used between the second mirror system S2 and the relay system F and behind the third mirror system S3 to eliminate the vignetting V of the light flux that occurs when a reflective optical system is configured with a plurality of mirror systems. )
(,, H2t- is placed and prevented.

In this implementation, in order to reduce the clamping of the luminous flux by % and obtain good overall optical performance, the mirror systems S, S
When the radii of curvature of the concave mirror M, convex /a, M2, and concave mirror M3 constituting 3 are R, R2, and R3, respectively, R□/R2≧2... (1)
R□/R3〉l ・・・・・・・・・(2
) It is preferable to satisfy the following conditions.

Conditional expressions 111 and +21 are such that when the effective screen of the object is a part of a circular arc as shown in FIG. This is to allow the image to be formed at a predetermined position without having to be moved.

If conditional expression (11t) is off, the coma flare will increase and the number of clans in the luminous flux will increase.Also, if conditional expression (21t) is off, the radius of curvature of concave mirror M3 will be too large compared to concave mirror M, making the mirror system as a whole smaller. It becomes difficult to obtain a predetermined refractive power while trying to achieve the desired refractive power.

In particular, in this embodiment, K to reduce field curvature and obtain a high-contrast object image is the radius of curvature R□ of the three reflecting mirrors in the mirror system S and S3.

Change R2 and R3 K IR, I > lR31 > lR21・・・・・・・・・
- (3).

If the condition is not met, the curvature of field becomes large, the clump of the light beam becomes large, and it becomes difficult to perform good aberration correction in a nine-reflection optical system by combining a plurality of mirror systems.

In addition, in this embodiment, in order to reduce the clamping of the luminous flux and to downsize the mirror system, it is preferable that the radius of curvature of the concave mirror M, the convex mirror M2, and the concave mirror M of the mirror system S2 is set to R.
It is necessary to satisfy the following conditions when R2', R2', and a3' are set.

If this condition is not met, it will be difficult to focus the object image formed by the mirror system S□ on the object point of the relay system F without the clamp of the light beam.

Then, the light flux from the relay system F1 mirror system S2 used as a field system is efficiently converged and transferred to the third mirror system S3.
In order to form a sharp image of the object, the concave mirror 1v of the relay system F is
When the radii of curvature of ll and M are R and R, respectively, it is preferable to satisfy the condition IR3□7R3□l (1°-curvature (5)).

If this condition is exceeded, the action as a field system will not be sufficient, and it is necessary to downsize the 9-mirror system S3 and move at least one mirror system of the relay system to correct aberrations and adjust magnification. preferable.

Next, the i) & numerical values of the implementation column shown in FIG. 1 are shown.

Ri is the radius of curvature of the first reflecting mirror counting from the object point P□, and D is the distance between each reflecting mirror, which is the positive value when it reaches from the left to the right along the direction of light travel, and vice versa. is shown as negative.

The effective screen of the object is 2 mNmN effective number 3 (NA-α15) in slit width. The effective screen width of the object point P0 is within the height range of 218 to 220w0 from the optical axis.

R(D) 2-14α5 270 3 -385. -1010 5 439.67 -280 6 44&68 580? -42L3B -292,58101L5
625 1G-167,58310 11-449,79 As described above, according to the present invention, a reflective optical system with high resolution can be achieved by appropriately combining four 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.
3 is an explanatory diagram of a part of FIG. 1, FIG. 4 is an explanatory diagram of an effective screen of an object according to the present invention, and FIG. 5 is a diagram of various aberrations of the optical system of FIG. 1. In the figure, Y indicates a storeroom, S-83 indicates a mirror system, F indicates a relay system, and M□ to M□□ each indicate a reflecting mirror.

Claims (5)

[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 plurality of concave mirrors are used to relay an object image to at least one location between the mirror systems. 1. A reflective optical system characterized in that a relay system having a relay system is arranged so that the overall imaging magnification is reduced. (2) The reflective optical system is arranged in order from the object side: the first mirror system, the second mirror system S_1, S_2, the relay system F_1, and the third mirror system.
The reflective optical system according to claim 1, characterized in that it is constituted by a mirror system S_3. (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, respectively.
, 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_1' and R_
2', R_3', the reflective optical system according to claim 3, which satisfies the following conditions: R_1'/R_2'>1 R_1'/R_3'>1. (5) The relay system F has two concave mirrors M_3_1, M_
3_2, and the concave mirrors M_3_1, M_3_
5. The reflective optical system according to claim 4, wherein the reflective optical system satisfies the following condition: |R_3_1/R_3_2|<1, where the radii of curvature of R_3_1 and R_3_2 are R_3_1 and R_3_2, respectively.