JPH0721584B2 - Illumination optics - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an illumination optical system of an apparatus for projecting and exposing patterns of IC, LSI and the like.

(Background of the Invention) Conventionally, as an illumination optical system of this type, there is, for example, a structure as shown in FIG.

That is, in the conventional illumination optical system shown in the figure, a collimation lens 2 collimates a light flux emitted from a light source image 1, and a large number of secondary light sources are provided on the exit side surface of a fly-eye lens 3 arranged in the parallel light flux. The entire irradiation surface 5 is superposed and illuminated by the large number of secondary light sources through the condenser lens 4 so that the illuminance on the irradiation surface 5 is averaged and smoothed.

However, in such a conventional illumination optical system, the fly-eye lens 3 is formed by assembling element lenses having the same focal length, and the fly-eye lens incident side end surface and the irradiation surface 5 have all magnification relationships. Since the element lenses of the fly's eye are constant, if the intensity distribution of the light flux entering the fly's eye lens 3 (correctly, the light flux density distribution) is symmetrical as shown in FIG. Illumination with a uniform illuminance distribution is obtained on the surface 5, but when a light flux having an asymmetric light flux density distribution enters as shown in FIG. 6 (b), each element lens of the fly-eye lens 3 The inclination components of the luminous flux density distribution cannot be canceled out, and the illuminance distribution on the irradiation surface 5 has an inclination.
However, there is a problem in that it is not possible to obtain illumination with a uniform illuminance distribution.

In particular, the asymmetrical luminous flux density distribution as shown in FIG. 6 (b) is a phenomenon that is often found in light sources such as excimer lasers which have been spotlighted in recent years.

(Object of the Invention) The present invention has been made by paying attention to such conventional problems. Even if the incident light flux to the fly-eye lens has an asymmetrical light flux density distribution, It is an object of the present invention to provide an illumination optical system that can illuminate with a uniform illuminance distribution.

(Summary of the Invention) The gist of the present invention for achieving such an object is to arrange a fly-eye lens in a parallel light flux and illuminate an object plane through a condenser lens with a large number of light fluxes from the fly-eye lens. In the illumination optical system, a small lens group is formed by an aggregate in which a first element lens of an afocal system having a magnification of minus 1 times and a second element lens of an afocal system having a magnification of 1 time are mixed. The illumination optical system is characterized in that it is arranged closer to the light source than the fly-eye lens.

In the illumination optical system of the present invention as described above, the light flux that has passed through the first element lens of the afocal system of the small lens group having an angular magnification of −1 is the first element by the first element lens. The light rays are switched upside down and inverted with respect to the optical axis of the lens, and are incident on the corresponding element lenses of the fly-eye lens. On the other hand, the light flux passing through the second element lens of the afocal system having an angular magnification of +1 in the lens group, the upper and lower rays are switched with respect to the optical axis of the second element lens by the second element lens. Without incident on the corresponding element lens of the fly-eye lens. As a result, the illuminance distribution on the object plane is inverted between the light flux that has passed through the first element lens and the light flux that has passed through the second element lens. Therefore, even if the incident light flux is asymmetrical, that is, has an inclination, the inclination of the illuminance distribution by each element lens is reversed, and illumination with uniform illuminance as a whole on the object plane can be obtained.

(Embodiment) Each embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an illumination optical system according to the first embodiment of the present invention, and the illumination optical system is used in an exposure apparatus for semiconductor manufacturing.

The illumination optical system 10 shown in FIG. 1 has a fly-eye lens 30 arranged in a parallel light flux 20 that has passed through a collimation lens (not shown), and a light source side of the fly-eye lens 30. A small lens group 40 provided corresponding to each element lens 31, 31, ... Of the fly-eye lens 30 and a condenser lens 50 for condensing multiple luminous fluxes from the fly-eye lens 30 on an irradiation surface (object surface) 60. And consists of.

The fly-eye lens 30 is formed of a plurality of element lenses 31, 31, ... Aggregates having the same focal length. Only four element lenses 31, 31, ... Can be seen in the figure, but the fly-eye lens 30 is formed by a large number of element lenses 31, 31, ... . The cross-sectional shape in the plane perpendicular to the optical axis of each element lens 31, 31, ... Is quadrangular or hexagonal.

In the small lens group 40, the afocal first element lenses 41, 41, ... Having an angular magnification of minus 1 and the afocal second element lenses 42, 42 ,. It is made up of aggregates arranged in. Here, the angular magnification is
It is a value corresponding to the ratio between the width of the light flux on the incident side and the width of the light flux on the exit side.

Also for the small lens group 40, the first and second element lenses 41, 42
Although only four lenses are visible in the figure, the small lens group 40 is composed of a large number of first and second element lenses 41, 42 arranged corresponding to the fly-eye lens 30 so as to spread around the optical axis. Has been formed. The cross-sectional shape of each of the first and second element lenses 41 and 42 in the plane perpendicular to the optical axis is the same as that of each element lens 31, 31, ... Of the fly-eye lens 30.

The first element lenses 41, 41, ... Are each formed of a biconvex lens, and a convex surface on the incident side and a convex surface on the exit side form a so-called Kepler-type afocal system of equal magnification. Further, the second element lenses 42, 42, ... Are respectively formed as parallel plane prisms having flat surfaces on both sides.

In the illumination optical system 10 having the above configuration, the parallel light flux 20 enters the small lens group 40, and the first element lens 4 of the small lens group 40.
The light fluxes transmitted through the first lens elements 41, 41, ... And the second lens elements 42, 42 ,.
The light fluxes that are respectively incident on 1, ... And have passed through the respective element lenses 31, 31 ,.
Then, almost the same area from the point A to the point B on the irradiation surface 60 is superposedly irradiated by the respective luminous fluxes.

In FIG. 1, the behavior of the light flux passing through the first element lenses 41, 41, ... Is shown by a broken line, and the behavior of the light flux passing through the second element lenses 42, 42 ,.

Now, when the parallel light flux 20 having the light flux density distribution shown as 20a in FIG. 1 enters the small lens group 40, each of the first element lenses 41, 41, 41 of the small lens group 40, The illuminance distribution on the irradiation surface 60 of each light flux that has passed through is as shown by the broken line in FIG. 2, and each second element lens of the small lens group 40.
The illuminance distribution on the irradiation surface 60 of each light flux passing through 42, 42, ... Is as shown by the solid line in FIG. In FIG. 2, the horizontal axis represents the distance of the irradiation surface 60 in the in-plane direction, and the vertical axis represents the illuminance.

That is, each portion of the parallel light flux 20 incident on each first element lens 41, 41, ... Of the small lens group 40 is
Inverted once inside 1, 41, ... And incident on each corresponding element lens 31, 31, ... Of the fly-eye lens 30 as a parallel light beam, and each surface on the exit side of each element lens 31, 31 ,. A secondary light source is formed on each of the light sources, and each light flux emitted from the secondary light source is applied to the same area from point A to point B on the irradiation surface 60 by the condenser lens 50.

Therefore, the illuminance distribution on the irradiation surface 60 of each light flux passing through each of the first element lenses 41, 41, ... Is downwardly inclined from the point A to the point B as shown by the broken line in FIG. , The inclination and direction of the luminous flux density distribution on the incident surface side of each of the first element lenses 41, 41 ,.

On the other hand, each part of the parallel light flux 20 incident on each second element lens 42, 42, ... Of the small lens group 40 is
Inside of the fly-eye lens 30, the parallel light flux is not inverted but is emitted and enters the corresponding element lenses 31, 31 ,. Secondary light sources are formed, and the respective luminous fluxes emitted from the respective secondary light sources are respectively irradiated onto the same area from point A to point B on the irradiation surface 60 by the condenser lens 50.

Therefore, the illuminance distribution on the irradiation surface 60 of each light flux that has passed through each second element lens 42, 42, ... Is an upward slope from point A to point B as shown by the solid line in FIG. The inclination and direction of the luminous flux density distribution on the incident surface side of each of the second element lenses 42, 42, ... Are opposite.

In this way, the respective light fluxes passing through the respective first element lenses 41, 41, ... And the respective light fluxes passing through the respective second element lenses 42, 42 ,.
Since the illuminance distributions on the irradiation surface 60 have different inclinations,
By providing substantially the same number of element lenses and second element lenses, it is possible to obtain illumination with a uniform illuminance distribution as a whole on the irradiation surface 60.

Next, a second embodiment of the present invention will be illuminated based on FIG.

In the first embodiment, when the small lens group 40 is tilted, the light flux is reflected by the inner side surface of each second element lens 42, 42, ...
There is a possibility that this reflected light may hinder the uniform illumination, and the second embodiment shown in FIG. 3 has improved this point.

In the second embodiment, each second element lens of the small lens group 40 is
42, 42, ... Are respectively formed by two meniscus lenses 42a, 42b.

According to the illumination optical system of the second embodiment, the parallel light flux incident on the respective second element lenses 42, 42, ...
The width of the luminous flux is reduced by a, and the reduced luminous flux is returned to the original width by each meniscus lens 42b. Therefore, even if the small lens group 40 is tilted, each second element lens
The light flux passing through 42, 42, ... Is not likely to be reflected on the inner surface as in the first embodiment. Where the second element lens
The two meniscus lenses constituting 42 are equal to each other and are arranged to face each other, and each meniscus lens has a convex surface and a concave surface, which constitute a so-called Galilean afocal system.

Next, a third embodiment of the present invention will be described with reference to FIG.

In the above-mentioned first and second examples, each first element lens 41, 4
Since there is a condensing point inside 1, ..., When a high-output light source is used, there is a risk that the first element lenses 41, 41 ,. This is the third embodiment shown in FIG.

In the third embodiment, each first element lens of the small lens group 40
Two plano-convex positive lenses 41a, 41, 41, ...
41b, and each second element lens 42,
42 are formed by two afocal meniscus lenses 42a, 42b having the same shape.

According to the illumination optical system of the third embodiment, in each of the first element lenses 41, 41, ..., The converging point is two positive lenses 41a, 41b.
Since it is located between them, there is no fear that the first element lenses 41, 41, ... Will be destroyed by heat generation as in the first and second embodiments. It goes without saying that the two positive lenses constituting the first element lens 41 are not limited to the plano-convex shape, and the lenses 41a and 41b do not necessarily have the same shape. The same applies to the second element lens 42.
Particularly, in the second element lens 42, it is important that the entire 42 is afocal, and it is not essential that each of 42a and 42b is afocal.

In each of the above embodiments, the small lens group 40 includes the afocal first element lenses 41, 41, ...
And an afocal second element lens 42, 42, ... Having an angular magnification of 1 × are formed alternately. However, the present invention is not limited to the above embodiments, and the small lens Even if the small lens group 40 is formed by an assembly in which the first element lenses 41, 41, ... And the second element lenses 42, 42, ... Are mixed according to the luminous flux density distribution of the luminous fluxes incident on the group 40. Good. Further, in the above embodiment, the first element lens and the second element lens of the small lens group 40 are provided so as to correspond to the respective element lenses of the fly-eye lens in a one-to-one relationship, but the present invention is not limited to this. It goes without saying that one element lens in the small lens group 40 may correspond to a plurality of element lenses of the fly-eye lens.

Furthermore, the present invention is applicable not only to the illumination optical system of the exposure apparatus for semiconductor manufacturing, but also to the illumination optical system of a laser annealing apparatus, a photo CVD apparatus, or the like.

(Effect of the Invention) According to the illumination optical system of the present invention, the illuminance distribution on the object plane is determined by each light flux that has passed through the first element lens and each light flux that has passed through the second element lens of the small lens group. Since the direction of is reversed, even when the light flux incident on the fly-eye lens has an asymmetric light flux density distribution, the object plane can be illuminated with a uniform illuminance distribution.

Therefore, it is effective when an excimer laser or the like whose luminous flux density distribution tends to be asymmetric is used as the light source of the illumination optical system of the exposure apparatus for semiconductor manufacturing.

[Brief description of drawings]

1 and 2 show a first embodiment of the present invention, and FIG. 1 is a schematic optical system layout diagram showing an illumination optical system.
FIG. 2 is an explanatory view showing the illuminance distribution on the object surface, FIG. 3 is a side view showing the main part of the second embodiment of the present invention, and FIG. 4 is a main part of the third embodiment of the present invention. FIG. 5 is a side view, FIG. 5 is a schematic optical system layout diagram showing a conventional illumination optical system, and FIG. 6 is an explanatory diagram showing a luminous flux density distribution of luminous flux incident on a fly-eye lens. FIG. 6 is an explanatory diagram when the luminous flux density distribution is symmetric, and FIG. 6B is an explanatory diagram when the luminous flux density distribution is asymmetric. 10 …… Illumination optical system, 20 …… Parallel light flux 30 …… Fly eye lens 31 …… Element lens, 40 …… Small lens 41 …… First element lens, 42 …… Second element lens 50 …… Condenser lens ( Condensing lens) 60 ... Irradiation surface (object surface)

Claims (1)

[Claims] 1. An illumination optical system in which a fly-eye lens is arranged in a parallel light flux, and a large number of light fluxes from the fly-eye lens illuminate an object plane through a condenser lens. A small lens group formed by an assembly in which a first element lens of a focal system and a second element lens of an afocal system having an angular magnification of +1 are mixed is arranged on the light source side of the fly-eye lens. Illumination optical system.