GB2040431A

GB2040431A - Illumination system for photo-copying devices

Info

Publication number: GB2040431A
Application number: GB7943915A
Authority: GB
Original assignee: Carl Zeiss Jena GmbH
Current assignee: Jenoptik AG
Priority date: 1978-12-20
Filing date: 1979-12-20
Publication date: 1980-08-28
Also published as: DE2949708A1; DD143323A1

Abstract

An illumination system for photo-copying devices, particularly photo-lithographic devices, comprising a reflector (2) whose whole reflective surface is illuminated by a single light source (1) and divided up into areas (3) each of which produces an image of the light source separated from an adjacent image so that the reflector can cover the widest possible image area, the reflector being constructed to mix light from the light source images in such a manner that an even illumination is obtained over a definite range in a preselected plane (E). Preferably, the reflective surface comprises individual reflectors having an envelope face in common. For instance, the individual reflectors may be plane or parts of an ellipsoid, paraboloid, or hyperboloid. <IMAGE>

Description

SPECIFICATION Illumination system for photo-copying devices The'invention relates to an illumination system for photographic copying devices, particularly for photolithographic devices, and can be used with advantage where an overall even illumination is required in addition to a high illumination power.

Previousiy reflectors have been used to have a high exploitation of the light source. Said reflectors which either are sphericai segments or ellipsoids with respect to geometry direct light into a predetermined direction at a definite space angle.

The light source is reflected in itself when a spheric reflector is used.

Due to the condition D, x sin a = dF x sin aO (where d, = diameter of the light spot, a, = half angle of aperture, dF = field diameter in the object plane, a0 = half angle of aperture of the object side objective), of the radiation characteristic of the light source and of the constructive possibilities the maximum exploitable angle of aperture a, and the maximum light spot diameter d,, respectively, are limited and, hence, the exploitation ofthe light energy.

Additional losses occur due to absorption in the glass bulb of the light source at the repeated passage of the light reflected at the reflector.

Said absorption losses are remarkable particularly after long lighting periods.

An efficiency increase can be obtained when using an ellipsoidal reflector.

The light source which is located in the first focus is imaged into the second focus of the reflector. Thus the enhanced absorption in the spheric reflectors due to the lamp bulb is eliminated.

Furthermore, a considerably wide space angle can be covered when an ellipsoidal reflector of respective size and shape is used.

The ellipsoidal reflectors have the disadvantage that the light source is imaged by each reflector element into the second focal point at different imaging scales.

Here the light source images are superimposed with different sizes and apertures.

The maximum aperture is defined through the smallest angle of radiation which is still captured by the reflector.

The maximum radiation angle of the light source image is defined by the maximum angle of radiation captured by the reflector.

The useful maximum size of the light source image and the maximum aperture are also in this case limited by the sine condition.

Under definite conditions (small objective aperture, small object field, small desired coherance parameter) either the entire aperture or the entire second light spot cannot be exploited.

This involves, however, that either the minimum radiation angle or the maximum radiation angle cannot be exploited. Light losses as they occur with spherical reflectors result from the fact that the entire angle of aperture given by the radiation characteristic of the light source is not exploited. An improvement is disclosed in the US-Patent 3 241 440. Here only a portion of the space angle is covered from the ellipsoidal reflector and thus the maximum aperture of the secondary light spot is reduced.

To completely exploit the space angle a spheric reflector is located in opposition to the eliipsoidal reflector, the former images the lamp in itself.

The additional absorption losses in the lamp bulb are again disadvantageous.

To obtain an even illumination of the object plane very often fly's eye condenser lenses are used in the illumination path of rays.

In this event the aperture angles are subdivided into individual ranges and a plurality of light source images is produced in a defined plane by means of a fly's eye plate. The subsequently described optical arrangement is such that the light derived from the individual light sources is superimposed in the object plane and that the images of the light sources are imaged into the pupil of the subsequent objective.

When the planes corresponding to the object plane are the individual fly's eyes of the fly's eyes plate, it is necessary that a second fly's eyes plate has to be inserted into the plane of the light source images. Otherwise, the corresponding plane is located at infinity (US-Patent 3 241 440).

however, considerable light losses occur at the fly's eyes plates due to a) absorption losses in the glass of the individual fly's eyes, b) reflection losses at the boundary faces, c) absorption losses at the faces between the individual fly's eyes.

Particularly the light losses under c) are considerable with annular individual fly's eyes.

The arrangement disclosed in the US-Patent specification No. 3 225 188 uses individual annular reflectors which produce an even superimposition of the light in a given plane. The exploitation of the space angle illuminated by the light source is considerably limited due to the arrangement of the reflector circles.

It is an object of the present invention to obviate the above disadvantages.

It is a further object of the invention to provide a system which ensures a comparatively high exploitation of the light source energy so that the exposure times in photo-lithographic copying devices can be reduced, and, hence, an increase of the output of such devices.

The invention relates to an illumination system for photocopying devices, particularly for photolithographic devices, characterised in that the entire space angle illuminated from the light source is divided in different ranges by a reflector, each of said ranges of the reflector produces an image of the light source and the individual light sources are separated from each other in order to cover a considerably wide space angle by the reflector and to mix the light from the light source images in such a manner that in a preselected plane an even illumination is obtained over a definite range.

The illumination system does not include a fly's eye plate. In order that the invention will be more readily understood reference is made to the accompanying drawings which illustrate diagrammatically and by way of example 16 embodiments thereof and where Figs. 1 to 16 schematically show respective reflector types where like components are designated by iike numerals.

The following geometries are concerned having envelope curves 2 and a light source 1: ellipsoid (curve of rotation is an ellipse) hyperboloid (curve of rotation is a hyperbola) paraboloid (curve of rotation is a parabola).

Said envelope curves 2 form reflecting faces which definitely image the light sources when they are arranged in a focus of said faces.

They, however, do not divide the space angle illuminated from the light source to produce a greater number of light source images. This can only be achieved by a portion-wise variation of the enveloping face. The reflector portions 3 are therefore portions of ellipsoids, hyperboloids, paraboloids or of plane reflectors, where the reflecting face and the envelope curve tangentially contact each other in one point.

Each reflector portion images the light source in a definite plane E utilizing the light of a definite space angle range. Thus a plurality of light source images is produced.

The following optical arrangement performs a mixing of the light originating from the individual light sources.

The geometry of the envelope and of the optical arrangement following the reflector defines the location of the plane in which the light derived from the individual light sources is mixed.

An embodiment using a fly's eye plate 4 and two lenses 5,6 is shown in Fig. 2.

To obtain rotation symmetry of the arrangement the variation is performed at the rotation curve producing the envelope (hereinafter referred to as envelope curve). The envelope curve is divided into i-portions.

Each portion is substituted by a differently shaped curve, one point of the new curve portion (hereinafter referred to as imaging curve) is located on the envelope curve and both curves tangentially contacting each other in said point. Straight lines, hyperbola, parabola, and ellipses are suitable as imaging curves. Therefrom 11 different possibilities of combination of envelope curves and imaging curves result. The combination parabola-parabola can be omitted since in this event the curves are identical one. The imaging curves define the positions of the light source images and the envelope curve defines the place of superposition of the light originating from the light source images.

The Figures 3 to 13 show the different feasible combinations, where 7 designates the envelope curve, 8 the imaging curve, 9 the axis of rotation = optical axis, and 1 the light source.

envelope imaging ellipse hyperbola straight parabola place of curve curve line super position ellipsa Fig. 3 Fig. 6 Fig. 9 Fig. 12 in the real hyperbola Fig.4 Fig.7 Fig. 10 Fig. 13 inthe virtual parabola Fig. 5 Fig. 8 Fig. 11 - in infinite C,) m Co, OiE Co Co o Co Co Co z z r C n C C C v, Due to the rotation symmetry of the reflector i-concentric rings are obtained as light source images. Said rings are a superposition of an infinite number of light source images. Considerable intensity variations over the space angle can be compensated for in direction or rotation. The feasibility of compensation in a direction at right angles to the rotation direction is given through the number of diverse imaging curves. The optical system following the reflector has to be so constructed that the plane E, where the light source images are located, is imaged into the pupil of the objective, and that the face F, where the light rays originating from the light source images are superimposed, are imaged into the object plane. To this purpose a particular imaging system is arranged in the plane of the light source images similar to a fly'y eye condenser lens.

A different solution is shown in Fig. 14. The imag ing system comprises two annular lens systems 10 and two lenses 11, 12 operating as condenser lenses.

9 is the axis ofthe rotation. The ring lens system effects that planes in the infinity are imaged into the object plane O.

The plane of the light source images E has to be in the real. Light source images in the virtual have to be transformed into the real by a corresponding optical arrangement. The plane E is imaged into the plane of the pupil P by a respective optical arrangement.

All mentioned reflector arrangements have the advantagethat considerably wide space angle ranges are covered and that - in contrast to a fly's eye condenser-a fly's eye plate is substituted by a reflector thus reducing light losses.

The size and the maximum aperture angle of the secondary light source depend on the parameters of the envelope curve and of the imaging curve. With respect to small values of d, x sin aL required, the use of a parabola as an envelope curve and a hyperbola as an imaging curve is favorable. Due to the light source images being located in the virtual the aper ture angle can be considerably reduced without the necessity of increasing the construction length of the illumination system.

A reduction of the value d, x sin a, can be obtained through a spheric reflector 14 (Fig. 16) which is arranged in opposition to the new reflector system 13 so that a part of the illuminated space angle range is covered through the spheric reflector.

By a respective silvering the reflector-system can be rendered selective towards wavelengths so that a thermic stress of the following optical system is eliminated.

Claims

1. An illumination system for photo-copying devices, particularly for photo-lithographic devices, characterised in that the entire space angle illumi nated from the light source is divided in different ranges by a reflector, each of said ranges of the reflector produces an image of the light source and the individual light sources are separated from each other in orderto cover a considerably wide space angle by the reflector and to mix the light from the light source images in such a manner that in a pre selected plane an even illumination is obtained over a definite range.

2. An illumination system as claimed in claim 1, characterised in that the reflector surface is com posed of individual reflectors having an envelope face in common.

3. An arrangement according to claim 2, wherein the individual reflectors are parts of an ellipsoid.

4. An arrangement according to claim 2, wherein the individual reflectors are parts of a paraboloid.

5. An arrangement according to claim 2, wherein the individual reflectors are parts of a hyperboloid.

6. An arrangement according to claim 2, wherein the individual reflectors are plane reflectors.

7. An arrangement according to claim 2, wherein the envelope face is an ellipsoid.

8. An arrangement according to claim 2, wherein the envelope face is a paraboloid.

9. An arrangement according to claim 2, wherein the envelope face is a hyperboloid.

10. An illumination system including a reflector according to claim 2, wherein in the plane of the light source images an arrangement of lenses is provided in such a manner that in each lens an image of the light source is projected and that the lens system has the task individually or in combination with a subsequent optical system to image defined planes in the finite into the object plane.

11. An arrangement as claimed in claim 1, wherein the reflector face is a face of rotation the axis of rotation of which coincides with the optical axis and the producing curve being composed of at least two arc portions with a common envelope face, the arc portions contacting the envelope curve in a tangential point.

12. An illumination system including a reflector according to claim 11, wherein an arrangement of ring lenses is provided in the plane of the light source images in such a manner that a light source image blurred to exactly one concentric ring is projected into each ring lens and that the ring lens system has the task to image individually or in combination with a subsequent optical system defined planes in the finite into the object plane to be illuminated.

13. An arrangement according to claim 11, wherein the envelope curve is an ellipse the major semi-axis of which lies on the optical axis.

14. An arrangement according to claim 11, wherein the envelope curve is a parabola, the axis of which lies on the optical axis.

15. An arrangement according to claim 11, wherein the envelope curve is a hyperbola the real axis of which lies on the optical axis.

16. An arrangement according to claim 11, wherein the arc portions are ellipse portions.

17. An arrangement according to claim 11, wherein the arc portions are parabola portions.

18. An arrangement according to claim 11, wherein the arc portions are hyperbola portions.

19. An arrangement as claimed in claim 11, wherein the arc portions are straight lines.

20. An illumination system including a reflector as claimed in claim 2, or including a reflector as claimed in claim 1, wherein the reflector is opposed by a spheric reflector which covers a portion of the space angle illuminated from the light source and which images the light source in itself, in order to reduce the product out of illumination aperture and light spot diameter and to increase the illumination intensity.

21. An arrangement as claimed in claim 2 or an arrangement as claimed in claim 1, wherein the reflecting face is covered with a layer in such a manner that only the light of at least one wavelength range is reflected.

22. An illumination system substantially as herein described and illustrated in anyone of Figures 1 to 16 of the accompanying drawings.