JPH10301058A - Reflection refraction type projecting optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection/refraction type projecting optical system attaining a large numerical aperture in the wavelength region of a ultraviolet ray. SOLUTION: In a reflection/refraction type projecting optical system projecting all images of patterns of a first plane R on a second plane W by forming the image in an exposing area A from among the patterns of the first plane R on the second plane W with a reduced magnification and synchronously scanning the first plane R and the second plane W with a velocity ratio mutually corresponding to the reduced magnification, this optical system is composed, in order of the passage of light ray from the first plane R, of a first optical system G1 , a half mirror HM, a second optical system G2 arranged on at least either optical path among the transmitting path or the reflecting path of the half mirror and a third optical system G3 arranged on the optical path on the opposite side to the reflecting optical path of the half mirror, the exposing area A is located in one half-circle area bisected by a diameter L orthogonal to the scanning direction, the second optical system G2 has a concave mirror and, by representing the image forming magnification by βm , the conditional relation: 0.7<|βm |<1.3 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system used for manufacturing, for example, a semiconductor device or a liquid crystal display device by a photolithography process, and more particularly to a reflection system in addition to a refraction system as an optical system element. The present invention relates to a catadioptric projection optical system having a resolution of a quarter micron unit in the ultraviolet wavelength region.

[0002]

2. Description of the Related Art In a photolithography process for manufacturing a semiconductor device or the like, a photoresist or the like is applied via a projection optical system to a pattern image of a photomask or a reticle (hereinafter collectively referred to as a "reticle"). A projection exposure apparatus for exposing a wafer (or a glass plate or the like) is used. As the degree of integration of semiconductor elements and the like increases, the resolution required for a projection optical system used in a projection exposure apparatus has been increasing. In order to satisfy this requirement, it has been necessary to shorten the wavelength of the illumination light and increase the numerical aperture (NA) of the projection optical system. However, when the wavelength of the illumination light is shortened, the types of glass materials that can withstand practical use by absorbing light are limited, and when the wavelength is 300 nm or less, only synthetic quartz and fluorite are practically usable. Since the Abbe numbers of both are not far enough apart to correct the chromatic aberration, if the wavelength becomes 300 nm or less, if the projection optical system is constituted only by the refraction system, various aberrations including the chromatic aberration Correction becomes difficult.

On the other hand, since the reflection system has no chromatic aberration,
Various techniques have been proposed in which a projection optical system is configured by a so-called catadioptric system combining a reflection system and a refraction system. A catadioptric reduction optical system having an optical path changing beam splitter for inputting / outputting a light beam to / from a reflecting system is disclosed in Japanese Patent Publication No. Hei.
No. 300973, JP-A-5-88089, JP-A-3-282527 and PCT / EP95 / 0
1719 and the like.

[0004]

The prior art as described above requires the use of a beam splitter having a transmission / reflection surface for splitting an optical path. In order to prevent the generation of stray light such as light amount loss and flare, as disclosed in Japanese Patent Application Laid-Open No. 3-282527, it is conceivable to employ a polarizing beam splitter. A transmission / reflection film having a multilayer structure that transmits when the incident light is P-polarized light and reflects when the incident light is S-polarized light is required. In addition, a quarter-wave plate for changing polarization is indispensable. These optical elements are very difficult to manufacture and the manufacturing costs are very high in order to achieve quarter-micron resolution. On the other hand, when the optical path is separated by a half mirror without using polarized light, the amount of light reaching the wafer is one of the amount of illumination light.
/ 2 to ４, but a laser is used as a light source of illumination light used for recent projection exposure, and the conventional g
Since the amount of light is much larger than the case where the emission line spectrum of a high-pressure mercury lamp such as a line or an i-line is used for the illumination light, a half mirror can be employed. However, when a half mirror is employed, ２〜 to 光線 of the light rays that do not reach the wafer become stray light, causing flares, ghosts, and the like, thereby deteriorating the imaging performance.

In view of the foregoing, the present invention achieves a large numerical aperture in the ultraviolet wavelength range, has a practical size optical system, has a sufficient working distance on the image side, and has a half mirror for separating the optical path. It is an object of the present invention to provide a catadioptric projection optical system having a resolution of a quarter-micron unit without deteriorating the imaging performance and generating stray light such as flare and ghost even if is used.

[0006]

In order to achieve the above object, a projection optical system according to the present invention includes a lens and a concave mirror, and forms an image of an exposure area in a pattern on a first surface at a reduced magnification. All images of the pattern on the first surface are projected onto the second surface by forming an image on the second surface and scanning the first and second surfaces in synchronization with each other at a speed ratio corresponding to the reduction magnification. In the catadioptric projection optical system, the first optical system, the half mirror, and the second mirror disposed in at least one of the transmission optical path and the reflection optical path of the half mirror in the order in which light rays pass from the first surface. An optical system, and a third optical system disposed in an optical path opposite to the reflected optical path of the half mirror,
The exposure area is in one semicircular area of the effective area of the projection optical system divided into two by a diameter perpendicular to the scanning direction, the second optical system has a concave mirror, and the imaging magnification of the concave mirror is β
_{When m} , 0.7 <| β _m | <1.3 (1) It is configured to satisfy the following conditional expression.

In the present invention as described above, the first aspect
The light beam emitted from the surface passes through the first optical system, is reflected or transmitted by the half mirror, is reflected by the second optical system, is transmitted or reflected by the half mirror, passes through the third optical system, and passes through the third optical system. Leads to. However, the exposure area A of the present invention is, as shown in FIG. 1, an effective area centered on the optical axis z of the projection optical system.
It is provided in one of the semicircular regions divided by the diameter L perpendicular to the scanning direction. That is, the exposure area A is not formed so as to extend over both semicircular areas divided into two by the diameter L. Further, the imaging magnification of the concave mirror of the second optical system is formed at approximately the same magnification as shown in equation (1).

As a result, as shown by the dotted line in FIG. 2, of the light beam emitted from the first surface R, it passes through the first optical system G ₁ , is reflected or transmitted by the half mirror HM, and is transmitted to the second optical system G _2. The light flux reflected by the half mirror HM and reflected or transmitted by the half mirror HM in the same way as on the outward path returns to the first surface R again, but returns to a position symmetrical with respect to the optical axis z. In the case of using a high sensitive material reflectance such as a wafer on a second surface W, the light beam is reflected by the second surface W, of the reflected light beam passes through the third optical system G _3, half Reflected or transmitted by the mirror HM,
Second reflected by the optical system G _2, the light beam which has also reflected or transmitted the forward half mirror HM, although returns again on the second surface W, its position also returns to the symmetrical positions with respect to the optical axis z . That is, the stray light returning to the first surface R or the second surface W returns to the outside of the exposure area A on the first surface or the second surface to be actually used, thereby preventing the deterioration of the imaging performance of the projection exposure. be able to.

The conditional expression (1) is a conditional expression relating to the imaging magnification of the concave mirror. If this expression is not satisfied, the first surface or the second surface
Light rays returning to the surface return to the exposure area A on the first surface or the second surface to be actually used, thereby deteriorating the imaging performance of projection exposure. More preferably, conditional expression (1)
Is preferably set to 1.2 and the lower limit to 0.8. Further, in order to prevent the generation of stray light due to the light returning to the second surface described above and to prevent exposure of an area other than the exposure area A on the second surface, the last lens surface of the third optical system and the second surface must be it is desirable to provide a field stop S _W between. To prevent the occurrence of stray light due to light returning to the first surface in the same manner, it is desirable to provide a field stop S _R between the first lens surface and the first surface of the first optical system.

On the other hand, in order to prevent the light quantity loss, the first optical system has a positive refractive power, and the light beam guided to the half mirror by the first optical system is divided into transmitted light and reflected light on the half mirror surface. In this case, it is desirable to employ two sets of second optical systems having approximately the same magnification as the optical path of the transmitted light and the optical path of the reflected light. On the other hand,
In the case where the light amount of the light source is sufficiently large and the light amount loss due to the optical system is not a problem, when the light flux guided to the half mirror by the first optical system is divided into transmitted light and reflected light on the half mirror surface, the transmitted light By disposing the second optical system having an imaging magnification of approximately the same magnification only on one of the optical paths of the reflected light and the reflected light, and disposing the light absorbing member on the other optical path, Occurrence can be prevented.

As the second optical system, at least one lens having a negative refracting power is used in addition to one concave mirror, so that each aberration can be satisfactorily corrected. You will be able to get closer. Also the third
Since the optical system has a positive refractive power and has a variable aperture stop AS between the third optical system side exit surface of the half mirror and the third optical system or inside the third optical system, the exposure can be performed. The resolution and depth of focus can be adjusted to be optimal for the pattern. The wavelength of light used for projection exposure is 300n
When the laser beam is less than m, the present invention is particularly effective, and can achieve a resolution of a quarter micron unit.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows a first embodiment of a catadioptric projection optical system according to the present invention. This projection optical system forms an image of an exposure area A of a pattern on a reticle R on a wafer W at a reduced magnification. The optical system projects all images of the pattern on the reticle R onto the wafer W by scanning the reticle R and the wafer W in synchronization with each other at a speed ratio corresponding to the reduction magnification. This optical system includes, in order from the reticle R side, a first optical system G ₁ , a half mirror HM, and second optical systems G ₂ and G ₂ arranged on both a transmission optical path and a reflection optical path of the half mirror HM. and a third optical system G ₃ Metropolitan disposed on the opposite side the optical path of the reflected light path of the half mirror HM. The two second optical systems G ₂ and G ₂ are formed identically, and each is composed of one negative lens and one concave mirror. A reticle-side field stop S _R is disposed between the reticle R and the first optical system G _1, and a plane mirror M is disposed between the first optical system G ₁ and the half mirror HM. A variable aperture stop AS is disposed between the half mirror HM and the third optical system G _3, and a wafer-side field stop _SW is disposed between the third optical system G ₃ and the wafer W. I have.

FIG. 5 shows a second embodiment of the catadioptric projection optical system according to the present invention. This second embodiment is provided only on the reflection optical path side of the light beam incident on the half mirror HM from the plane mirror M.
Place the optical system G _2, the transmitted light path side is obtained by disposing the light-absorbing member B. In this embodiment, the light absorbing member B is disposed in the optical path after transmitting through the half mirror HM, but a light absorbing material may be applied to the emission surface of the half mirror.

The exposure area A of each of the above embodiments is defined by a diameter of the effective area of the projection optical system which is orthogonal to the scanning direction.
As shown in FIG. 1, the exposure area A in one of the divided semicircular areas has a rectangular slit shape that is short in the scanning direction and long in the direction perpendicular to the scanning direction. However, an arc-shaped slit obtained by translating the arc in the scanning direction may be used. Further, in both of the above embodiments, the half mirror HM is provided on the bonding surface of the pair of right-angled triangular prisms.
However, as the half mirror, a flat mirror that spreads in the direction of the split surface can also be used.

Tables 1 and 2 show the specifications of the first embodiment and the second embodiment, respectively. In [Main Specifications] of each table, the exposure area indicates a value on the reticle R. In [Optical member specifications],
The first column No is the number of each optical surface from the reticle R side,
Column r indicates the radius of curvature of each optical surface, third column d indicates the distance between the optical surfaces, column 4 indicates the glass material of each optical member, and column 5 indicates the group number to which each optical member or optical surface belongs. The radius of curvature r is positive when the center of curvature is on the side of the light beam traveling direction, and is negative when the center of curvature is on the side opposite to the traveling direction of the light beam. However, each time a light ray is reflected by the reflection surface, the sign is inverted and displayed. The distance d between the optical surfaces is also shown by inverting the sign each time a light ray is reflected by the reflection surface.

In the first embodiment, both the optical path first reflected and then transmitted by the half mirror HM and the optical path first transmitted and then reflected are used. The positive and negative of the radius of curvature r and the surface distance d are displayed along the former optical path. When the curvature radius r and the surface distance d are displayed along the latter optical path, only the sign is switched.

[0017]

[Table 1] [Main specifications] Exposure wavelength 193.3nm ± 5pm Image side numerical aperture 0.6 Exposure area a = 4 mm b = 6 mm c = 25 mm β _m = 1.0000 [Optical member specifications] Nord Glass material 0 (reticle) 52.464 1 -191.3364 20.000 Quartz G ₁ 2 -267.9167 1.597 3 416.5071 27.633 Quartz G ₁ 4 -271.1370 5.104 5 213.6204 20.000 quartz G ₁ 6 649.0929 34.235 7 -355.9542 20.000 quartz _{G 1 8 168.1397 24.328 9 -257.5430 20.000} CaF 2 G 1 10 1278.9250 22.156 11 -153.5848 20.512 quartz G ₁ 12 -741.0107 24.612 13 -276.5159 20.000 Quartz G ₁ 14 -212.8862 0.693 15 762.0099 40.317 Quartz G ₁ 16 -308.2859 0.500 17 -874.5016 22.304 Quartz G ₁ 18 -334.1368 10.126 19 -248.9104 20.000 Quartz G ₁ 20 -361.0763 0.500 21 -936.6808 20.000 Quartz G ₁ 22- 120.000 23 ∞ -160.000 Flat mirror M 24 ∞ -110.000 Quartz 25 ∞ 110.000 Quartz HM (reflection) 26 ∞ 38.672 27 -196.5742 20.000 Quartz G ₂ 28 -337.5700 0.500 29 -566.5796 -0.500 Concave Mirror G ₂ 30 -337.5700 -20.000 quartz G ₂ 31 -196.5742 -38.672 32 mm -110.000 quartz 33 mm -110.000 quartz HM (transmission) 34 mm -10.000 35 (aperture stop) 9.935 36 -191.0256 -25.649 quartz G ₃ 37- 923.9232 -8.514 38 1051.4400 -35.000 Quartz G ₃ 39 -212.1568 -34.703 40 -400.0000 -35.000 CaF ₂ G ₃ 41 474.2273 -0.500 42 -209.3909 -35.000 CaF ₂ G ₃ 43 3195.0126 -0.919 44 -123.9664 -26.860 CaF ₂ G ₃ 45 -1236.0228 -6.958 46 548.8242 -24.655 Quartz G ₃ 47 1164.8700 -0.500 48 -1996.7884 -44.782 Quartz G ₃ 49 863.3677 -0.500 50 -408.0838 -20.000 Quartz G ₃ 51 -3000.0000 -17.000 52 (wafer)

[0018]

[Table 2] [Main specifications] Exposure wavelength 193.3nm ± 5pm Image side numerical aperture 0.65 Exposure area a = 3 mm b = 5 mm c = 23 mm β _m = 1.0000 [Optical member specifications] Nor d 0 (reticle) 50.000 1 -175.3321 20.000 Quartz G ₁ 2 -264.8469 0.500 3 391.3145 25.076 Quartz G ₁ 4 -251.5778 2.746 5 230.8678 20.000 quartz G ₁ 6 1051.2622 35.045 7 -297.6821 20.000 quartz _{G 1 8 164.4810 24.873 9 -182.0039 21.198} CaF 2 G 1 10 -2240.2794 19.815 11 -166.3163 21.114 quartz G ₁ 12 -793.3420 25.882 13 -269.4889 20.013 Quartz G ₁ 14 -205.8559 2.869 15 770.1003 41.200 Quartz G ₁ 16 -297.2918 0.500 17 -651.6010 21.357 Quartz G ₁ 18 -310.0752 9.236 19 -242.1483 20.000 Quartz G ₁ 20 -364.5125 0.500 21 -1496.2990 20.142 Quartz G ₁ 2247 7.4 120.000 23 ∞ -180.000 Flat mirror M 24 115 -115.000 Quartz 25 ∞ 115.000 Quartz HM (reflection) 26 ∞ 42.202 27 -198.3038 20.000 Quartz G ₂ 28 -343.4520 0.500 29 -578.7272 -0.500 Concave mirror G ₂ 30 -343.4520 -20.000 quartz G ₂ 31 -198.3038 -42.202 32 ∞ -115.000 quartz 33 ∞ -115.000 quartz HM (transmission) 34 ∞ -10.000 35 (aperture stop) -5.000 36 -185.1517 -28.828 quartz G ₃ 37- 937.6323 -9.903 38 1037.6213 -35.000 Quartz G ₃ 39 -202.0440 -18.592 40 -488.3867 -35.000 CaF ₂ G ₃ 41 455.1024 -0.500 42 -189.2867 -35.000 CaF ₂ G ₃ 43 3380.7853 -5.446 44 -116.0852 -27.956 CaF ₂ G ₃ 45 -791.6593 -7.717 46 580.0609 -20.000 Quartz G ₃ 47 4355.3792 -0.500 48 -631.5761 -39.351 Quartz G ₃ 49 1048.4735 -0.500 50 -463.6847 -20.000 Quartz G ₃ 51 -3000.0000 -17.000 52 (Wafer)

FIGS. 4 and 6 show lateral aberrations of the first embodiment and the second embodiment, respectively. In the lateral aberration diagram, Y represents the image height. As shown in the aberration diagrams, it can be seen that both examples have excellent imaging performance.

[0020]

As described above, according to the present invention, a large numerical aperture is achieved in the ultraviolet wavelength range, the optical system is of a practical size, the working distance on the image side is sufficiently ensured, and the optical path separation is improved. Therefore, even if a half mirror is used, a catadioptric projection optical system having a resolution of a quarter-micron unit was obtained without deteriorating the imaging performance and generating stray light such as flare and ghost.

[Brief description of the drawings]

FIG. 1 is a plan view showing an exposure area of the present invention.

FIG. 2 is an explanatory view showing the principle of stray light prevention according to the present invention.

FIG. 3 is a configuration diagram showing a first embodiment.

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

FIG. 5 is a configuration diagram showing a second embodiment.

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

[Explanation of symbols]

G ₁ : first optical system G ₂ : second optical system G ₃ : third optical system AS: aperture stop M: plane mirror HM: half mirror R: reticle W: wafer S _R : reticle side field stop _SW : wafer side Field stop A: Exposure area B: Light absorbing member

Claims (9)

[Claims] An image of an exposure area of a pattern on a first surface is formed on a second surface at a reduction magnification, and the first surface and the second surface are mutually reduced. By scanning synchronously at a speed ratio corresponding to the magnification, the first
In a catadioptric projection optical system for projecting all images of a surface pattern onto a second surface, a first optical system, a half mirror, a transmission optical path and a reflection optical path of the half mirror in the order in which light rays pass from the first surface. A second optical system disposed on at least one of the optical paths, and a third optical system disposed on an optical path opposite to the reflected optical path of the half mirror, wherein the exposure area is a projection optical system. Of the effective area, one of which is divided into two semicircular areas by a diameter perpendicular to the scanning direction, wherein the second optical system has a concave mirror, and the imaging magnification of the concave mirror is β _m 0.7 <| β _m | <1.3. A catadioptric projection optical system, characterized by satisfying the following conditional expression: 0.7 <| β _m | <1.3. 2. A catadioptric projection optical system according to claim 1, wherein a plane mirror is arranged between the last lens surface of said first optical system and said half mirror. 3. The catadioptric projection optical system according to claim 1, wherein the half mirror is formed on a bonding surface of a pair of right-angled triangular prisms. 4. A catadioptric projection optical system according to claim 1, further comprising a field stop between the last lens surface of said third optical system and said second surface. 5. The catadioptric projection optical system according to claim 1, further comprising a field stop between the first lens surface of said first optical system and said first surface. 6. The optical system according to claim 1, wherein said first optical system has a positive refracting power, and said second optical system is disposed in each of a transmission optical path and a reflection optical path of said half mirror. 6. The catadioptric projection optical system according to 1, 2, 3, 4 or 5. 7. The first optical system has a positive refracting power, and the second optical system is arranged in one of a transmission optical path and a reflection optical path of the half mirror, and one of the other optical systems. 6. The catadioptric projection optical system according to claim 1, wherein a light absorbing member is disposed in the optical path. 8. The second optical system has at least one negative lens in addition to the concave mirror, the third optical system has a positive refractive power, and the half mirror and the third optical system The catadioptric projection optical system according to any one of claims 1 to 7, further comprising a variable aperture stop during or inside the third optical system. 9. The catadioptric projection optical system according to claim 1, wherein the wavelength of light used for projection exposure is 300 nm or less.