JPS6341042B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an illumination optical system, particularly to an improvement of a mirror condensing type illumination optical system used in a projection exposure apparatus or the like. In an illumination optical system using a discharge type light source such as an ultra-high pressure mercury lamp, it is most efficient to focus the light using a concave reflector such as an elliptical reflector, but the light flux does not exist near the optical axis. This results in an illumination light beam that is not centered. Regarding this drawback, patent application No. 141677 of 1982 filed by the same inventor as the present application,
This problem can be solved by the invention filed as No. 043416, that is, by arranging a refractive member consisting of a conical convex surface and a conical concave surface in a parallel light beam. On the other hand, conventionally, with respect to the diameter φe of the entrance pupil of the projection objective lens, let φa be the diameter of the image of the aperture stop in the illumination system at the entrance pupil position of the projection objective lens.
φa/φe=σ is called the σ (sigma) value.
In general, the σ value is often selected to be smaller than 1 and between 0.5 and 0.7, and the larger this value is, the worse the resolution and the shallower the depth of focus will be in fine patterns, but image deformation due to interference between fine patterns is less likely to occur. Conversely, as the value of σ becomes smaller, both resolution and depth of focus improve, but image deformation becomes more likely. From the perspective of the exposure efficiency of the projection objective lens, if the illuminance at the entrance pupil is constant, it is advantageous to increase the σ value. In other words, as shown in Table 1, it is known that they have contradictory properties.

[Table] As a mechanism for simply changing the σ value, a turret-type variable aperture diameter mechanism has been proposed, for example, as disclosed in Japanese Utility Model Application Publication No. 56-119646, but when the σ value is decreased, light is blocked. As the amount of light emitted increases, the exposure efficiency inevitably decreases. The present invention provides a mirror condensing illumination optical system in which σ
The purpose of this invention is to obtain an illumination optical system that can always maintain the maximum amount of light without causing any loss of light amount even if the aperture diaphragm in the illumination optical system is changed when making the value variable. The present invention provides a mirror condensing illumination optical system comprising a reflecting mirror having at least a quadratic curved surface, a collector lens for converting a light beam collected by the reflecting mirror into a parallel light beam, and an aperture stop, the collector lens having the following features: A conical refractive member having a conical convex surface and a conical concave surface is disposed between the aperture stop and the aperture stop so that the apex of the cone substantially coincides with the optical axis, and between the aperture stop and the refractive member. The light beam width is changed by the afocal variable magnification system according to the change in the aperture diameter of the aperture stop. Hereinafter, the present invention will be explained based on examples. FIGS. 1 and 2 are schematic configuration diagrams in which an illumination optical system according to the present invention is used in a projection exposure apparatus. In FIG. 1, a light beam from a light source S is condensed by an elliptical reflector 1, and converted into a substantially parallel light beam by a collector lens 2. This parallel light flux passes through a refracting member 3 having a conical convex surface 3a and a conical concave surface 3b, and reaches an optical integrator 4 consisting of a group of fly's eye lenses. In the figure, the light flux from the light source S to the optical integrator 4 is indicated by diagonal lines, but as can be seen from the figure, the light flux exiting the collector lens 2 is in a hollow state with almost no light rays in the center near the optical axis. The light beam is rotationally symmetrically shifted toward the optical axis by the conical refraction member 3, and becomes a substantially uniform light beam that fills the hollow near the optical axis. As shown in FIGS. 1 and 2, this conical refraction member 3 is configured to have a conical convex surface 3a and a conical concave surface 3b having approximately the same apex angle as the conical convex surface. Each conical surface is arranged with its convex surface 3a facing toward the collector lens 2 so that the axis of rotational symmetry of each conical surface substantially coincides with the optical axis of the illumination optical system.
For example, optical integrators are
This is for forming a plurality of secondary light sources, as disclosed in Japanese Patent No. -81813. An aperture stop 5 is provided near the exit surface of the optical integrator, and the light beam passing through the aperture stop 5 passes through a condenser lens 6 and illuminates a reticle R as an original to be projected. The reticle R is set on the wafer W at a predetermined magnification by the projection objective lens 10.
projected on top. Here, the aperture stop 5 and the entrance pupil 11 of the projection objective lens 10 are conjugate with respect to the condenser lens 6, and so-called Koehler illumination is performed. When the aperture of the entrance pupil of the projection objective lens 10 is φe, and the size of the image of the aperture stop 5 formed here is φa, the σ (sigma) value is φa/φe, as described above. By changing the size of the aperture stop 5 by means not shown, σ
The value can be changed, and the optimum σ value can be obtained by changing the reticle pattern. FIG. 2 shows the aperture stop 5 in the configuration shown in FIG.
The figure shows a state in which an afocal system 20 consisting of a positive lens L ₁ and a negative lens L ₂ is inserted between the refractive member 3 and the optical integrator 4 when the aperture of the lens is reduced from D to β·D. The σ value in this case is β times that in the state shown in FIG. Here, the magnification of the afocal system 20 is the reduction magnification β of the aperture stop 5.
Since almost all of the uniform light beam emitted from the refracting member 3 passes through the aperture stop 5, there is no loss in the amount of light and extremely high efficiency can be obtained.
Here, it is important that the afocal system 20 is placed behind the refractive member 3 (on the exit light side). If the order is reversed, the hollow state of the medium-sized light beam from the collector lens 2 will change depending on the magnification of the afocal system, so unless the amount of shift of the light beam toward the center by the refracting member is changed, the illumination light will not be efficiently used. cannot be supplied. In Fig. 2, when reducing the aperture diameter of the aperture stop 5, an afocal system is inserted to reduce the beam diameter. When increasing the aperture diameter to increase the σ value to about 1, it is also possible to insert an afocal system that expands the beam diameter. Furthermore, an afocal system that can change the magnification is placed between the refractive member 3 and the optical integrator without inserting or removing the afocal system, and the magnification of the afocal system can be changed in conjunction with changes in the diameter of the aperture stop 5. It's okay. It goes without saying that in this case as well, the ratio of the aperture diameters of the aperture stop is approximately equal to the magnification of the afocal system. The afocal system is not limited to the Galilean type consisting of positive and negative lenses, but may also be the Keplerian type consisting of two positive lenses. Note that the shape of the aperture diaphragm is not limited to a circle, but may be an ellipse or a rectangle depending on the pattern of the original to be projected.Afocal systems use a Tory lens system to make the cross-sectional shape of the light beam anisotropic. It is also possible to do so. For example, in a Torritz lens system, a Galileo-type afocal system is constructed in one meridional plane and a Keplerian-type afocal system is configured in a meridional plane perpendicular to this, and the shape of the light flux is made to approximately match the aperture stop with an anisotropic shape. Bye. As described above, according to the present invention, the σ value can be made variable without loss of light quantity, and whereas conventionally the σ value could only be selected based on the relationship shown in Table 1, the exposure efficiency can always be maintained at the best condition. Make it.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of an embodiment in which the present invention is applied to a projection exposure apparatus. Explanation of symbols of main parts, 1...Elliptical reflector, 2
...Corrector lens, 3...Conical refractive member,
4... Optical integrator, 5... Aperture stop, 6... Condenser lens, 10... Projection objective lens, 11... Entrance pupil, 20... Affocal system.

Claims (1)

[Scope of Claims] 1. A reflecting mirror having at least a quadratic curved surface, a collector lens for converting the light beam focused by the reflecting mirror into a parallel light beam, and a plurality of light source images disposed in the parallel light beam. In a mirror condensing illumination optical system having an optical integrator for forming an optical integrator and an aperture stop disposed at an image position of a plurality of light sources by the optical integrator, , a refractive member having a conical convex surface and a conical concave surface having approximately the same apex angle as the conical convex surface, with the conical convex surface facing the collector lens side so that the rotational symmetry axis of each conical surface is aligned with the optical axis. An illumination optical system characterized in that the refracting member and the optical integrator are arranged so as to substantially coincide with each other, and the beam width can be changed in accordance with a change in the diameter of the aperture stop by an afocal variable magnification system arranged between the refractive member and the optical integrator. system.