FLY EYE LENS UNIT FOR ILLUMINATION

Abstract: An illumination system includes a light source (LS), an ellipsoidal mirror (EM) for converging light emitted from the light source, a fly eye lens unit (FU) disposed at a converging point of the ellipsoidal mirror, a collimation lens (CS) for collimating light rays exited from the fly eye lens unit, and an object (PM) disposed along the optical path of the illumination system. The fly eye lens unit includes a first and a second frame defining an incident aperture and an exit one, a plurality of element lenses aligned in a matrix of rows closely in contact with each other, side walls disposed between the first and second frames for housing the element lenses therein, and biasing element for applying a biasing force to the element lenses sideward with respect to the rows of matrix. The respective element lenses are fixedly held without any intermedium therebetween.

Description: The present invention relates to an illumination system according to the first part of claim 1 as known from DE-A-2 939 204 and a fly eye lens unit according to the first part of claim 16, resp., as known from FR-A-2 526 962. DE-A-2 939 204 discloses an illumination system with a fly eye lens unit, the construction of which is not shown. In the eye lens construction of FR-A-2 256 962 there is only one plane of element lenses extending transverse to the optical path. It is the object of the present invention to provide an illumination system and a fly eye lens unit for such system, resp., which illuminates an object with an uniform irradiance distribution. This object is accomplished by the features of the second part of claim 1 and claim 16, resp. Subject matter of sub claims 2 to 15 are preferred embodiments of the illumination system according to claim 1. Other novel features and advantages of the present invention will become apparent in the course of the following detailed description taken together with the accompanying drawings, which are directed only to the understanding of the present invention and not to the restriction of the scope off the invention. Figure 1 is a schematic view of an illumination system embodying the present invention; Figure 2 is a perspective cross-sectional view showing a fly eye lens unit, in its halved state, embodying the present invention; Figure 3 is a perspective analytical view of a first embodiment of the fly eye lens unit shown in Figure 2; Figures 4-A and 4-B are a perspective view and a plane view of an element lens, respectively; Figure 5 is a perspective analytical view of a second embodiment of the fly eye lens unit according to the present invention; and Figures 6 through 8 are illustrative views for showing assembling operations of the fly eye lens unit. Referring to Figure 1, which shows an illumination system embodying the present invention, the illumination system generally comprises a light source LS, an ellipsoidal mirror EM disposed with respect to the light source, a first folding mirror M₁, a fly eye lens unit FU, a second folding mirror M₂, a collimation system CS, a mask film MF bearing desired circuit patterns thereon and a photosensitive material PM, respectively disposed along the optical path in order. The light source LS is positioned at or adjacent to the first focal point off the ellipsoidal mirror EM, so that light emitted from the light source is condensed and directed to the fly eye lens unit FU through the folding mirror M₁. The folding mirror M₁ comprises so-called a cold mirror which allows most of infrared radiation to pass therethrough and reflects most of ultraviolet radiation. The fly eye lens unit FU is positioned at a point adjacent to the second focal point of the ellipsoidal mirror EM, which is preferred in order to form the secondary light source thereby, since light emitted from the light source is most condensed at this point. However, it is sufficient if the fly eye lens unit FU is disposed at a position optically nearer to the light source LS than that as mentioned above, as long as the light directed toward the fly eye lens unit FU is received within the effective area thereof. Light condensed by the ellipsoidal mirror EM enters the fly eye lens unit FU to impinge upon the incident surface of the collimation system CS. The characteristics of the fly eye lens unit FU as an optical system is designed so that the following equation is substantially established: h = K tan ϑ where h is an entrance height of a light beam, k is a proportional constant and ϑ is an exit angle from the fly eye lens unit. On such an optical system having the aforementioned characteristics, the detailed description is shown in the European Patent Application No. 87101235.7 (Publication No. 0 231 029). Accordingly, the detailed discussion thereon is omitted here. The fly eye lens structure is very useful for resolving the irradiance non-uniformity at the entrance pupil of such optical system, which enables the incident surface of the collimation system CS to be illuminated uniformly independent of the irradiance distribution at the entrance pupil. Moreover, respective element lenses of the fly eye lens unit provides uniform irradiance through the entire area of the incident surface of the collimation system, thus the irradiance distribution on the incident surface of the collimation system will become uniform. The illumination system shown in Figure 1 is designed so that the entrance pupil of the fly eye lens unit FU is conjugated with the incident surface of the collimation system CS, accordingly light passing through a predetermined common point in the entrance pupil will impinge upon a predetermined common point on the incident surface of the collimation system, and consequently light emitted from the light source and received in the entrance pupil will illuminate the predetermined area of the incident surface of the collimation system, without any loss of light. The collimation system CM comprises a single Fresnel lens, which is advantageous to reduce the optical path between the light source LC and an object to be illuminated. The photosensitive material PM is positioned immediately under the mask film MF, and exposure of a desired circuit pattern is made accurately and effectively on the photosensitive material. Referring to Figures 2 and 3, which show a structural outline of a first embodiment of a fly eye lens unit FU according to the present invention, the fly eye lens unit generally comprises a base frame 11 defining a square opening 12, side walls 13, 16, 22 and 27, spacer plates 14, 23 and 26, a multiple structure of element lenses 31 to 34, and a lid plate 24 defining a circular opening 25 thereon. The base frame 11 is made of aluminum alloy, and the square opening 12 defined thereon is adapted to pass light rays from a light source. The square opening 12 defines an exit aperture of the fly eye lens uuit FU, which has a large inner diameter not to block the light beam exited from the fly eye lens unit. The respective side walls 13, 16, 22 and 27 is also made of aluminum alloy, and is secured upright on the respective peripheral edges of the base frame 11. On the side wall 16, there defined are small bores suitable for allowing the insertion of screws 15 therethrough. Each of the bores 17 has a threaded section 17 s and a non-threaded cylindrical section 17 c therein. The threads provided in the threaded section 17 s is designed to be engageable with those of the screw. The non-threaded section 17 c has a larger diameter than that of the threaded section 17 s . The non-threaded section 17 c accomodates a biasing means comprising a first metal disk 18, a coil spring 19, a second metal disk 20 of the same shape as that of the first disk 18, and a contact element 21 made of fluorine-contained polymers, in order. The respective bores 17 on the side wall 16 are positioned at positions corresponding to respective rows of the element lenses aligned in respect of the corresponding screws 15. The respective spacer plates 14, 23 and 26 is made of fluorine-contained polymers, and is closely disposed between the respective side walls 13, 22 and 27 and the assembly of the element lenses 31 to 34, respectively. It is preferable to chose fluorine-contained polymers as the spacer plates because of its elasticity and heat insulating characteristics. However, it may be also applicable to use any materials having appropriate elasticity for absorbing the thermal expansion either of the element lenses or metallic base frame and side walls, and having appropriate heat insulating characteristics for blocking the heat transmission from the metallic base frame and side walls to the element lenses, or vice versa. On the inner surface of the spacer means there provided are a plurality of grooves 35 extending in the vertical direction. Positions of the grooves 35 are determined so as to correspond to respective adjacent element lenses on the matrices. Air existing between respective matrices of the element lenses can freely communicate with the outside thereof. Respective element lenses 31 e to 34 e constitute four units of matrices 31 to 34, and each of these matrices includes 5 X 5 pieces of element lenses EM. Each matrix of the element lenses is assembled only by the biasing forces of the coil springs 19, without any adhesive agent or the like. The biasing force to be applied to each row of element lenses in respect of the Corresponding screw 15 is adjusted by the screw, and according to experimental demonstrations it was preferable to apply the biasing force in the range of 1.0 to 1.5 kg to respective rows of the element lenses. The element lenses in each of the matrices have substantially the same optical characteristics. Each of the element lenses EL has an incident surface and an exit surface having a predetermined curvature, respectively, and four plane side surfaces, as best shown in Figures 4-A and 4-B It is especially preferable to form a precise square by the side surfaces in the plane view. The adjacent element lenses in each matrix are closely in contact with each other, without any intermedium. The adjacent matrices disposed along the optical axis are spaced from each other by a predetermined distance, where respective optical axes of the element lenses EL in each matrix are precisely coincident with each other. The distance between the adjacent matrices is determined on the basis of the optical characteristics on an object to be illuminated. The lid plate 24 is also made of aluminum alloy, and defines an circular opening 25 thereon. The circular opening 25 defines an incident aperture of the fly eye lens unit FU, where the inner diameter of the opening 25 is designed so that the light beam converging on the fly eye lens unit should not be blocked by the lid plate. In the aforementioned embodiment, assemblage of the respective element lenses is accomplished only by the biasing forces of the biasing coil springs 19, which are applied to the rows aligned in respect of the screws from a longitudinal direction and are appropriately adjusted only by manipulating respective screws. Referring to Figure 5, which shows a second embodiment of a fly eye lens unit FU according to the present invention, the same reference numerals as in Figure 3 denote the same elements. In this embodiment, a side wall 27' is comprised substantially in the same manner as the side wall 16, and the spacer plate 26 in Figure 3 is replaced by assemblies of biasing means as those in Figure 3, each of which includes screw 15', a first disk plate 18', a coil spring 19', a second disk plate 20' and a contact element 21'. The biasing force applied to the respective rows in respect of the screws 15' is adjusted to be smaller by approximately 500g than that applied to the respective rows of the screws 15. Referring to Figures 6 through 8, when assembling the fly eye lens unit, first both the side walls 13 and 22 are fixed to the base frame 11, and the spacer plates 14 and 23 are mounted along these side walls. Then, an appropriate square plate 51 corresponding to the square opening 12 is placed within the opening. The fourth (i.e. lowermost) matrix 31 of element lenses are aligned, on the square plate 51, along the side walls 13 and 22. After that, the side wall 16 is mounted to the base frame 11, where the respective bores 17 accomodates a biasing means comprising the contact element 21, the coil spring 19 and a pair of the metal disks 18 and 19. Then, Screws 15 are set to the bores 17, applying the biasing forces to the rows aligned in respect of the screws. Thus, the respective rows of the element lenses is fixedly held by the biasing forces. Next, as shown in Figure 7, an adjusting plate 71 is placed on the fourth (i.e. lowermost) matrix 31 of the element lenses, where the adjusting plate 71 has a thickness precisely corresponding to the distance between the fourth matrix 31 of the element lenses and the third matrix 32 thereof. The element lenses of the third matrix 32 are aligned in the same manner as those of the fourth matrix. In such a manner as above, four matrices of element lenses are superposed in order. Respective rows of the element lenses in the each matrix are fixedly held by the biasing forces. Then, as shown in Figure 8, the respective adjusting plates 71 interposed between the matrices are drawn in the direction of an arrow A, and are removed from the fly eye lens unit. Then, the spacer plate 26 and the side wall 27 are fixedly mounted on the base frame 11, in the case of the first embodiment shown in Figure 3, or the side wall 27' having substantially the same structure as the side wall 16 is fixedly mounted on the base frame 11, in the case of the second embodiment shown in Figure 5. After that, the lid plate 24 is mounted on the side walls, whereby assembling of the fly eye lens unit is accomplished. As mentioned above, since the fly eye lens unit FU is positioned at a point adjacent to the second focal point of the ellipsoidal mirror EM, the fly eye lens unit FU will be heated considerably, in spite of interposition of the cold mirror M₁. However, since the spacer plates having heat insulating characteristics are interposed between the element lenses and a housing comprising the base frame, side walls and lid plate of aluminum alloy, the thermal transmission from the housing to the element lenses, or vice virsa, is efficiently blocked. Even if the thermal expansion may occur in the fly eye lens unit, it is efficiently absorbed by the spacer plates 14, 23 and 26 and the biasing means, and accordingly the optical characteristics of the fly eye lens unit is kept substantially constant. Since there is no intermediate between respective element lenses of the fly eye lens unit, light entering the fly eye lens unit is not blocked and passes therethrough without any loss of light.

Claims: An illumination system for illuminating an object including a light source (LS), converging means (EM) disposed with respect to said light source (LS) for converging light emitted from said light source (LS), a fly eye lens unit (FU) disposed at a converging point of said converging means (EM); collimation means (CS) for collimating light rays exited from said fly eye lens unit (FU) and an object disposed along the optical path of said illumination system, characterized in that said fly eye lens unit (FU) comprises: a first frame (24) defining an incident aperture thereon; a second frame (11) defining an exit aperture thereon; a plurality of element lenses orderly aligned in a plane, said element lenses being closely in contact with each other; side walls (13, 16, 22, 27) disposed between said first and second frames (24, 11) for housing said element lenses therein; wherein said element lenses form a plurality of rows lying in a plane extending transverse to the optical path; said fly eye lens unit (FU) comprises a plurality of such planes, each plane comprising a plurality of rows of element lenses, said planes being parallel to each other, and said fly eye lens unit (FU) further comprises biasing means (18, 19, 20, 21) each assigned to one of the rows for applying an adjustable biasing force to each row of the element lenses in a direction transverse to the optical path. An illumination system as set forth in claim 1, wherein a plurality of bores (17) are provided on at least one of said side walls (13, 16, 22, 27), said bores (17) being defined at positions corresponding to the respective rows of the element lenses, and said biasing means (18, 19, 20, 21) are accommodated in the respective bores (17). An illumination system as set forth in claim 1 or 2, wherein said biasing means (18, 19, 20, 21) comprises a contact member (21) for contacting with an element lens aligned in a corresponding row of the element lenses, a biasing coil spring (19) for applying a biasing force to a corresponding row of the element lenses and adjusting means (15) for adjusting the biasing force. An illumination system as set forth in claim 3, wherein said rows of the element lenses are formed in a matrix. An illumination system as set forth in claim 4, wherein said element lenses are formed in a plurality of matrices. An illumination system as set forth in claim 3, wherein said adjusting means comprises a screw (15), and said respective bores (17) includes a threaded section (17s) engageable with said screw (15). An illumination system as set forth in claim 3, wherein said contact member (21) comprises a material having heat insulating characteristics. An illumination system as set forth in claim 3, wherein said contact member (21) comprises a material having elasticity adaptable for absorbing the thermal expansion of elements. An illumination system as set forth in claim 1, further comprising spacer means (14, 23, 26) disposed closely between said respective side walls (13, 16, 22, 27) and said element lenses. An illumination system as set forth in claim 9, wherein said spacer means (14, 23, 26) comprises a resin plate made of fluorine-contained polymers. An illumination system as set forth in claim 9, said spacer means (14, 23, 26) comprises a material having heat insulating characteristics. An illumination system as set forth in claim 9, said spacer means (14, 23, 26) comprises a material having elasticity adaptable for absorbing the thermal expansion of elements. An illumination system as set forth in either one of claims 9 through 12, wherein said spacer means (14, 23, 26) comprises a plurality of grooves (35) extending along the optical axes of the respective element lenses, respective grooves (35) corresponding to borders of respective adjacent element lenses. An illumination system as set forth in claim 1, wherein said incident aperture provided on the first frame (24) has an enough inner diameter to receive light rays directed toward the fly eye lens unit. An illumination system as set forth in claim 1, wherein said exit aperture provided on the second frame has an enough inner diameter to pass light rays received in the fly eye lens unit. A fly eye lens unit, comprising: a first frame (24) defining an incident aperture (25) of the fly eye lens thereon; a second frame (11) defining an exit aperture (12) of the fly eye lens thereon; a plurality of element lenses orderly aligned in a plane, said element lenses being closely in contact with each other; side walls (13, 16, 22, 27) disposed between said first and second frames (24, 11) for housing said element lenses therein; said element lenses forming a plurality of rows lying in the plane, said plane extending transverse to the optical path; characterized in that the fly eye lens unit (FU) comprises a plurality of such planes, each plane comprising a plurality of rows of element lenses, said planes being parallel to each other, and in that said fly eye lens unit (FU) further comprises biasing means (18, 19, 20, 21) each assigned to one of the rows for applying an adjustable biasing force to each row of the element lenses in a direction transverse to the optical path.

Inventors: UEMURA, HARUO
Applicants: DAINIPPON SCREEN MFG. CO., LTD.
Application year: 1987
Main classification: G02B3
IPC codes: G03F7, G02B19, G02B3