JPH08162402A - Lighting optics - Google Patents

Abstract

(57) [Summary] [Object] To provide an illumination optical device capable of maintaining desired illuminance uniformity even if the energy distribution of a light flux changes due to, for example, the movement of a bright spot of a lamp. According to the present invention, in an illumination optical device for uniformly illuminating an object, light source means for supplying illumination light and illumination light from the light source means are condensed and positioned at spatially separated positions. An image forming unit that forms a light source image, a collector lens that collects illumination light from the light source image, an optical integrator that forms a plurality of light source images based on the light flux from the collector lens, and an optical integrator. A condenser lens that condenses the light fluxes from the plurality of light source images and illuminates the object in a superimposed manner, and diffuses the energy distribution of the light fluxes in the optical path on the light source means side of the optical integrator. A light diffusing means is provided for uniforming by action.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminating optical device, and illuminates a mask, a reticle or the like having a transfer pattern formed therein with a uniform illuminance in an exposure apparatus for manufacturing a semiconductor element, a liquid crystal display element or the like. The present invention relates to an illumination optical device.

[0002]

2. Description of the Related Art An illumination optical apparatus of this type used in an exposure apparatus for manufacturing highly integrated semiconductor elements or the like is required to have excellent illuminance uniformity on the object surface to be illuminated. Therefore, a conventional illumination optical device of this type employs a device that illuminates in a superimposed manner via an optical integrator such as a fly-eye lens. That is, the light beam incident on the fly-eye lens is two-dimensionally divided by a plurality of lens elements forming the fly-eye lens, and these divided light beams are superposed on the illuminated object plane. In this way, it is possible to suppress the uniformity of the illuminance distribution on the illuminated object surface to within a few percent.

In recent years, with the miniaturization of patterns, variations in line widths of fine patterns have become apparent due to nonuniformity of illuminance with respect to a mask (hereinafter, reticle), and higher illuminance uniformity is required. ing. Further, it has been pointed out that the illuminance uniformity varies with the use time of the light source lamp. Then, as a cause of the variation in the illuminance uniformity, it is considered that the bright spots move with the increase in the brightness of the lamp.

Due to the demand for higher throughput of the exposure apparatus, the illuminance required on the illuminated object surface continues to increase year by year. However, according to Straubel's theorem, the opening degree of the light flux reaching the surface to be exposed (wafer or the like), that is, the product of the solid angle and the area of the surface to be exposed is more than the product of the area of the light source and the solid angle of the light flux from the light source. It is known that if it is small, it is not possible to capture all of the light flux from the light source in the intervening optical system.

Therefore, in order to increase the illuminance of the surface to be exposed in the exposure apparatus, the light is emitted from the bright spot of the lamp without increasing the size of the bright spot of the lamp and without widening the spread angle of the light beam from the light source lamp. The amount of energy consumed per hour must be increased. In other words, in order to increase the illuminance of the exposed surface, it is necessary to increase the brightness of the lamp.

An ultra-high pressure mercury lamp is often used as the light source of this type of exposure apparatus. By the way, in the ultra-high pressure mercury lamp, the divergence angle of the light ray from the bright spot is almost defined based on the lamp shape. Therefore, in order to increase the brightness of the ultra-high pressure mercury lamp, it is necessary to increase the input power to the lamp without changing the size of the bright spot. However, it is necessary to increase the input power while maintaining the bright line width of the exposure wavelength capable of correcting the chromatic aberration of the projection optical system. However, when the potential difference per distance between the poles of the ultra-high pressure mercury lamp is increased, the bright line width of the exposure wavelength is widened.

Therefore, for example, a method of simply increasing the amount of current can be considered. However, according to this method,
The electrodes are likely to be damaged, and the movement of the bright spots increases with the lapse of the lamp usage time. Further, by increasing the distance between the electrodes, the potential difference between the electrodes is increased without increasing the potential difference per distance between the electrodes, and by reducing the area of the tip of the cathode, the current density is increased to increase the current between the electrodes. There is also a method of controlling the expansion of bright spots associated with increasing the distance. However, with this method, the damage due to the Joule heat generation of the cathode increases. As a result, the electrodes are easily worn, and the movement of bright spots increases with the lapse of the lamp usage time.

[0008]

As described above, in the above-mentioned conventional illumination optical device, the bright spot largely moves with the lapse of the usage time of the light source lamp, so that the incident path of the light ray to the fly-eye lens changes. However, the intensity distribution of the light beam incident on the fly-eye lens changes. As a result, there is a disadvantage that desired illuminance uniformity cannot be maintained within the life of the lamp.

As a measure to reduce the influence of the movement of the bright spot of the lamp, a method of increasing the integral effect of the fly-eye lens by increasing the number of lens elements constituting the fly-eye lens several times can be considered. However, not only does each lens element become smaller (smaller) and difficult to manufacture, but also the manufacturing cost increases due to the increase in the number of elements.

The present invention has been made in view of the above-mentioned problems, and can maintain desired illuminance uniformity even if the energy distribution of the light flux changes due to the influence of the movement of the bright spot of the lamp, for example. An object is to provide an illumination optical device.

[0011]

In order to solve the above problems, in the present invention, in an illumination optical device for uniformly illuminating an object, a light source means for supplying illumination light,
Image forming means for collecting illumination light from the light source means to form a light source image at spatially separated positions, a collector lens for collecting illumination light from the light source image, and light flux from the collector lens An optical integrator that forms a plurality of light source images based on, and a condenser lens that condenses the light flux from the plurality of light source images formed by the optical integrator to illuminate the object in a superimposed manner, the optical Provided is an illumination optical device characterized in that a light diffusing means for equalizing the energy distribution of a light flux by a light diffusing action is provided in an optical path of the integrator on the side of the light source means.

According to a preferred embodiment of the present invention, the light diffusing means is positioned adjacent to the light source means side of the optical integrator. Further, it is preferable that tilting means for tilting the light diffusing means with respect to the optical axis of the optical integrator is provided according to the illuminance distribution of the illumination light on the object.

[0013]

In the illuminating optical device using the fly-eye lens, the light flux from the light source is two-dimensionally divided into a rectangular shape by the fly-eye lens. Then, the respective luminous fluxes divided into the rectangular shape are superposed on the illuminated object surface by the condenser lens, so that the illuminated object surface is efficiently and uniformly illuminated. FIG. 2 is a diagram for explaining the action of the fly-eye lens and the variation of the illuminance uniformity when the energy distribution of the light flux changes. In order to clearly show the action of the fly-eye lens in FIG.
The structure is simple in layers.

As shown in FIG. 2, the light beam incident on the fly-eye lens generally has a strong Gaussian energy distribution at the center. Such energy distribution is based on the characteristics of the elliptical mirror for forming the light source image by collecting the light flux from the light source. When a light flux having an energy distribution as shown in FIG. 2A enters the fly-eye lens 6, light source images are formed at the exit ends of the lens elements 6a to 6c, respectively. The lights from the respective light source images are superimposed on the illuminated object plane 10 via the condenser lens 9.

That is, the lights from the light source images of the lens elements 6a to 6c exhibit illuminance distributions A to C on the illuminated object plane 10, respectively. So overall,
The illuminance distribution D on the illuminated object surface 10 becomes substantially uniform. In other words, for the light flux having the energy distribution as shown in FIG. 2A, other optics are used so that the illuminance distribution on the illuminated object surface 10 via the lens elements 6a to 6c becomes substantially uniform. Parts are adjusted.

However, when the luminous spot moves as the lamp is used for a long time and the energy distribution of the light beam incident on the fly-eye lens 6 changes as shown in FIG. The illuminance distributions A ′ to C ′ due to the light from the light source image 6c also change. As a result, the illuminance distribution D ′ on the illuminated object surface 10 cannot maintain uniformity as a whole.

Here, if each of the lens elements forming the fly-eye lens is infinitely small, that is, if the fly-eye lens is formed of an infinite number of lens elements, what kind of energy distribution of light beam will enter. That is, no matter how the energy distribution changes, perfect illumination uniformity should be obtained and maintained at the illuminated object plane.

However, due to the manufacturing cost and the like,
An actual fly-eye lens is usually constructed by arranging about 100 lens elements vertically and horizontally. For this reason,
When the energy distribution of the light flux incident on the fly-eye lens changes, the illuminance distribution on the illuminated object surface also changes.
That is, it becomes impossible to maintain the illuminance uniformity under the influence of the movement of the bright spots of the lamp. Therefore, in the present invention, the energy distribution of the light flux incident on the fly-eye lens does not substantially change even if the energy distribution of the light flux from the light source changes significantly due to the movement of the bright spot of the light source. Has been adopted.

FIG. 3 is a diagram for explaining the operating principle of the present invention. In FIG. 3, only the point that the light diffusion plate 11 is provided on the light source side of the fly-eye lens is structurally different from FIG. 2. In the present invention, the direction of the incident light beam is randomly bent by the light diffusing plate 11 for each minute area,
The energy distribution of the light flux incident on the fly-eye lens 6 is made uniform to some extent. The light diffusion plate 11 may be a surface scattering type or an internal diffusion type. However, in order to prevent the loss of the amount of light, it is preferable that the angle of the light beam emitted from the light diffusion plate 11 is equal to or smaller than the numerical aperture of the fly-eye lens.

As described above, in the present invention, the light flux from the light source having a strong energy distribution at the center is converted into a light flux having a somewhat uniform energy distribution by the action of the light diffusion plate 11. That is, as shown in FIG. 3A, a light flux having a strong center energy distribution 12 is converted into a light flux having a somewhat uniform energy distribution 14 through the light diffusion plate 11. The light flux having a somewhat uniform energy distribution 14 illuminates the illuminated object surface 10 with a substantially uniform illuminance via the fly-eye lens 6.

Then, even if the luminous spot moves with the lapse of the use time of the lamp and the energy distribution of the light beam incident on the light diffusing plate 11 changes as shown by the reference numeral 13 in FIG. 3B. The energy distribution 15 of the light beam incident on the fly-eye lens 6 is uniform to some extent, like the energy distribution 14 of FIG. Therefore, the illuminance distribution on the illuminated object surface 10 can be maintained substantially uniform.

That is, according to the present invention, even if the energy distribution of the light flux changes greatly due to the movement of the bright spots of the light source, the energy distribution of the light flux entering the fly-eye lens is uniform to some extent and has little fluctuation due to the light diffusion effect. . Therefore,
It is possible to maintain the uniformity of the illuminance distribution without being substantially affected by the movement of the bright spot of the light source.

Further, in the case where the illuminance distribution on the illuminated object surface 10 has uneven inclination due to the eccentricity of the optical components,
It is possible to correct the unevenness of inclination by appropriately inclining the light diffusion plate 11 with respect to the optical axis. FIG. 4 is a diagram for explaining the operation principle for correcting the unevenness of inclination of the illuminance distribution. As shown in FIG. 4, even when the light flux from the light source has a symmetrical energy distribution 12 with respect to the optical axis, the light diffusing plate 11 is rotated clockwise in FIG. As described above, it is possible to obtain the energy distribution 16 which is asymmetric with respect to the optical axis such that the energy of the light beam incident on the lens element 6a is large and the energy of the light beam incident on the lens element 6c is small.

In this way, by making the light flux having the asymmetrical energy distribution 16 incident on the fly-eye lens 6, an illuminance distribution D ″ asymmetrical with respect to the optical axis can be obtained even on the illuminated object plane 10. In other words, it is possible to correct the unevenness of inclination by appropriately inclining the light diffusion plate 11 with respect to the optical axis. It is also possible to attach a plane-parallel plate between the light source and the fly-eye lens and correct the plane-parallel plate or the plane-parallel plate and the light diffusion plate appropriately with respect to the optical axis to correct the unevenness of inclination. It is possible.

[0025]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically illustrating the configuration of an illumination optical device according to an embodiment of the present invention. The illumination optical device of FIG. 1 includes a light source 1 such as a mercury lamp.
The light source 1 outputs a luminous flux having bright lines such as g-line, h-line, and i-line. The bright spot 21 of the light source 1 is positioned at the first focal position of the elliptical mirror 2 described later.

The light beam emitted from the light source 1 is condensed by the elliptic mirror 2 via the mirror 3 to form a light source image 22 at the second focal position of the elliptic mirror 2. The light flux diverging from the light source image 22 enters the bandpass filter 5 after passing through the collector lens 4. In the bandpass filter 5, for example, as the exposure light from the incident light flux, the mercury emission line 436 nm (g
Line), 365 nm (i-line), etc. The light flux passing through the bandpass filter 5 has a strong center energy distribution due to the characteristics of the elliptical mirror 2.

The light beam of the specific wavelength selected by the bandpass filter 5 is converted into a light beam having a somewhat uniform energy distribution through the light scattering plate 11. In this way, the light flux whose energy distribution is converted to a certain degree is incident on the fly-eye lens 6 configured by arranging a large number of lens elements vertically and horizontally. Then, the light flux incident on the fly-eye lens 6 is condensed, and a large number of secondary light source images of the light source image 22 are formed on the exit side surface thereof.

The light fluxes from the plurality of secondary light source images formed on the exit side surface of the fly-eye lens 6 are shaped by the aperture stop 7 arranged immediately after that. Light fluxes from a plurality of shaped light source images are reflected by a mirror 8 and condensed by a condenser lens 9, and then uniformly illuminate an illuminated object surface 10 such as a mask in a superimposed manner. The light scattering plate 11
If the angle of the light beam emitted from the light source is less than or equal to the numerical aperture of the fly-eye lens 6, all the light beams can be guided to the optical system after the light scattering plate 11. Therefore, the structure of the present embodiment does not reduce the efficiency of light transmission.

In this embodiment, the fly-eye lens is used as the optical integrator. However, for example, JP-A-2-
The internal reflection type optical integrator disclosed in Japanese Patent No. 48627 can be used instead of the fly-eye lens.

[0030]

As described above, in the illumination optical apparatus of the present invention, a light beam whose energy distribution is made uniform to some extent by a light diffusing plate is incident on an optical integrator such as a fly's eye lens. Even if the energy distribution of the light flux from the light source changes significantly due to this, the uniformity of the illuminance distribution on the illuminated object surface can be substantially maintained.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a configuration of an illumination optical device according to an example of the present invention.

FIG. 2 is a diagram for explaining the action of the fly-eye lens and the variation in illuminance uniformity when the energy distribution of the light flux changes.

FIG. 3 is a diagram illustrating the operating principle of the present invention.

FIG. 4 is a diagram illustrating an operation principle for correcting unevenness in inclination of the illuminance distribution according to the present invention.

[Explanation of symbols]

 1 Light Source 2 Elliptical Mirror 3, 8 Mirror 4 Collector Lens 5 Bandpass Filter 6 Fly's Eye Lens 7 Aperture Stop 9 Condenser Lens 10 Illuminated Object Surface 11 Light Diffusing Plate

Claims (3)

[Claims] 1. An illumination optical device for uniformly illuminating an object, comprising: light source means for supplying illumination light; and illumination light from said light source means to be condensed to form a light source image at a spatially separated position. Image forming means for forming, a collector lens for converging illumination light from the light source image, an optical integrator for forming a plurality of light source images based on the light flux from the collector lens, and a plurality of optical integrators formed by the optical integrator And a condenser lens for converging the light flux from the light source image to illuminate the object in a superimposed manner, and in the optical path on the light source means side of the optical integrator, the energy distribution of the light flux is made uniform by a light diffusion action. An illuminating optical device, characterized in that a light diffusing means for converting the illuminating light is provided. 2. The illumination optical apparatus according to claim 1, wherein the light diffusing means is positioned adjacent to the light source means side of the optical integrator. 3. The tilting means for tilting the light diffusing means with respect to the optical axis of the optical integrator according to the illuminance distribution of the illumination light on the object. Or the illumination optical device according to 2.