Illuminating apparatus and device manufacturing method

Abstract: A laser beam from an excimer laser is split into three beams along a first plane by a pair of prisms and the three beams are caused to intersect each other at the position of the object side focal point of a first cylindrical lens and be incident upon the first cylindrical lens. The three beams are respectively focused independently from each other by the first cylindrical lens. The above focused three beams are then focused along a second plane perpendicular to the first plane by a second cylindrical lens; then, the three beams are caused to superimpose each other on a mask and at the same time are brought to a defocus along said first plane and into focus again along said second plane by an anamorphic optical system containing a third cylindrical lens and a lens having a rotation symmetry, thereby a line-like illumination area extended in the first direction is formed on the mask. The linear illumination area and an area containing a pattern of a series of openings arranged in said first direction or a rectangular pattern extended in said first direction are caused to coincide on the mask to efficiently illuminate the pattern. An image of the illuminated pattern is projected onto a workpiece for an orifice plate by a projection lens system to process the workpiece in accordance with the pattern.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to illuminating apparatus and device manufacturing methods and, more particularly relates to an illuminating apparatus and a device manufacturing method suitable in processing a nozzle hole or a groove of an ink reservoir of an orifice plate for an ink-jet printer. Description of the related art Recently, it is increasingly common to fabricate a precision part by a mask projection method, see e.g. EP-A- 660 158 which is an Art. 54(3) EPC prior art document for the parts of this application to which the priority date of 27.12.94 can be accorded. Lasers are used as the light source and a pattern on a mask illuminated by a laser beam is projected by a projection lens onto a surface to be processed so that the precision processing is effected by an optical energy of the laser beam which has passed through the pattern. This method is particularly excellent in its high productivity and in that the processing may be effected stably at a high precision. One of the types of part processing suitably using the mask projection method is the processing of an orifice plate for an ink-jet printer or bubble jet printer (hereinafter referred to as ink-jet printer). In general, an ink-jet printer refers to the type of printer in which characters or graphics are printed by intermittently ejecting an ink onto a surface of a sheet from a large number of small holes having a diameter of 20 to 50 µm which are arranged in a row. An orifice plate refers to a member having the large number of small holes (nozzle) for ejecting the ink. In order to improve the quality of characters to be printed, it is important, in addition to an accurate control on timing of the ink ejection, that the large number of small holes on the orifice plate are provided at a high precision. Further, in order to lower the cost per unit of the orifice plate, i.e., the cost per unit of printer, it is necessary to improve the productivity in mass production of the orifice plate. If the orifice plate is manufactured by using the mask projection method, it is important to efficiently illuminate the pattern of a mask. SUMMARY OF THE INVENTION It is an object of the present invention to provide an illuminating apparatus and a device manufacturing method in which a linear area may be efficiently illuminated. An illuminating apparatus according to the present invention includes: a first anamorphic optical system for focusing an illuminating beam with respect to a first direction; a second anamorphic optical system for focusing said focused illuminating beam with respect to a second direction substantially perpendicular to said first direction; and a third optical system for bringing the illuminating beam focused with respect to said two directions into focus again with respect to said second direction and at the same time into a defocus with respect to said first direction to form a linear illumination area extended in said first direction on an illuminated surface. Further, a device manufacturing method according to the present invention includes the steps of: forming said linear illumination area of said illuminating apparatus on a mask; and exposing a workpiece through a pattern within said linear illumination area on said mask. In an embodiment of the present invention to be described later, said illuminating apparatus includes a beam splitter having a pair of prisms for forming a plurality of beams serving as said illuminating beam by splitting the light from a light source, and the third optical system is so constructed as to cause said plurality of beams to superimpose each other on said illuminated surface and at the same time to bring each of said plurality of beams into focus with respect to said second direction and to a defocus with respect to said first direction on said illuminated surface. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a plan view schematically showing certain portions of a first embodiment of the present invention. Fig.2 is a side view schematically showing certain portions of the first embodiment of the present invention. Fig.3 shows in detail the portion from y-direction beam splitting means 4 to second cylindrical lens 7. Fig.4 is a front view of a mask. Fig.5 illustrates the illumination range of a mask pattern. Fig.6 shows a nozzle and groove of an ink reservoir. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig.1 is a plan view schematically showing certain portions of a first embodiment of the present invention; and Fig.2 is a side view of certain portions of the first embodiment of the present invention. For the convenience of explanation, an optical axis of an optical system is defined as an x-axis and x-y-z coordinates are set as having an x-y plane corresponding to the plan view and an x-z plane corresponding to the side view. Here, the y-axis and z-axis are determined as a first direction and a second direction, respectively, and the x-y plane and x-z plane are determined as a first plane and a second plane, respectively. In the figures, what is denoted by numeral 1 is a light source for which a laser such as KrF excimer laser is used. Numerals 2 and 3 are bending mirrors, respectively, and an y-direction beam splitting means 4 splits the laser beam into a plurality of beams that are different in direction from each other within the x-y plane. Denoted by numeral 5 is a shield mask and 6 is a first cylindrical lens (first anamorphic optical system) which has a light converging effect only in the y-direction. Denoted by SL2 is a cylindrical lens unit consisting of a second cylindrical lens (second anamorphic optical system) 7 having a light converging effect only in the z-direction and a third cylindrical lens (cylindrical lens unit) 8 having a light converging effect only in the z-direction. Denoted by numeral 9 is an ordinary convex lens (condenser) shaped in a rotation symmetry having a light converging effect in both the y- and z-directions. Numeral 10 is a mask which is disposed on a surface to be illuminated. The position of the mask 10 and the image focal point F 9 ' of the convex lens 9 coincide. Numeral 12 is a projection lens and 11 is an entrance pupil of the projection lens 12 (in some case, an aperture stop serving as the entrance pupil). Numeral 13 is a workpiece which, in the case of the present embodiment, is a plate consisting of a plastic material to be processed into the orifice plate of an ink-jet printer. The projection lens 12 projects an image of a pattern on the mask 10 (referred to as mask pattern or projection pattern) onto a surface of the workpiece 13. The orifice plate has an array of nozzle holes 61 as shown in Fig.6. Further, an ink groove 62 for keeping an ink is provided corresponding to each nozzle hole. Accordingly, a pattern arranging small circular openings in a row or a pattern of a slender rectangular opening is provided on the mask 10 so as to be used in the processing of an array of nozzle holes 61 and/or an ink groove 62. Fig.3 shows in detail the portion of the y-direction beam splitting means 4, shield mask 5, first cylindrical lens 6 and second cylindrical lens 7. Fig.3A is a plan view and Fig.3B is a side view. Fig.4 is a front view of the mask 10 of the present embodiment. The pattern of the mask 10 is in the form regularly disposing transparent small holes having a diameter L z0 along a straight line in the y-direction on an opaque background portion, the total length in the y-direction being L y0 and the width in the z-direction being L z0 . The mask 10 is obtained such that a metal film (background portion) such as a chrome film is formed on a transparent substrate and a pattern (array of small holes) is formed by a patterning. In the present embodiment, the pattern of the mask 10 is projected onto the workpiece (plate member) 13 to form a large number of small holes having a diameter of 20 to 50 µm within a length of about 10 mm on the workpiece. Supposing the projecting magnification of the projection lens 12 as 1/5, the size of the mask pattern is a pattern where transparent small holes having a diameter of L z0 = 0.1 ∼ 0.25 mm are arranged in a distance of L y0 = 50 mm. The direction of length of the mask pattern (y-direction), the beam splitting direction of the y-direction beam splitting means 4, the direction of generating lines of the second cylindrical lens 7 and third cylindrical lens 8 all coincide, and the mask 10 is disposed so that the center of the mask pattern and the x-axis coincide. The operation of the present embodiment will now be described. The optical operation of the present embodiment will be described in two steps, since the operation in the x-y plane and the operation in the x-z plane are different from each other. The operation in the x-y plane (first plane) will be first described by way of Fig.1 and 3A. A substantially collimated laser beam emitted in the direction of optical axis from the light source 1 is a beam having a cross section of which the width in the y-direction is larger than the width in the z-direction. This beam is reflected at the mirrors 2, 3 and is then incident upon the y-direction beam splitting means 4. As shown in Fig.3A, the y-direction beam splitting means 4 has two prisms 4a, 4b arranged in the y-direction with a separation from each other and splits the incident beam into three beams that are different in travelling direction from each other within the x-y plane. These beams are not converged nor diverged in the z-direction by the splitting means 4. The respective central rays (principal rays) of the three split beams intersect at a point F 6y on the optical axis, and the shield mask 5 having an opening at the center thereof is disposed at the position F 6y . The shield mask 5 equalizes the y-direction width of the three split beams to each other and at the same time eliminates stray light occurred prior to the y-direction beam splitting means 4. The shield mask 5 is disposed at the position of an object focal point F 6y (the subscript letters y,z indicating the elements of y-direction and z-direction, respectively) of the first cylindrical lens 6, thereby the center ray of each beam emitted from the first cylindrical lens 6 becomes parallel to the optic axis. That is, the mask 5 and lens 6 constitute a so-called telecentric optical system. Thus, three images (intermediate images in the x-y plane) I 6y+ , I 6y0 , I 6y- are formed at the focal point position F 6y ' on the image side of the first cylindrical lens 6. In this image formation within the plane, the second cylindrical lens 7 acts simply as a parallel flat plate. It should be noted that these images within the x-z plane are straight line-like images parallel to the z-axis, since each beam is spread in a direction parallel to the z-axis. Next, the third cylindrical lens 8 also acts simply as a parallel flat plate, and the convex lens 9 forms the above line image I 6y+ , I 6y0 , I 6y- into image I 9y- , I 9y0 , I 9y+ on the entrance pupil plane 11 of the projection lens 12. Here, since the position of the mask 10 is the image side focal point of the convex lens 9, all the three beams thereat superimpose each other within the x-y plane at the same time of being defocused. The length of this overlapped portion is defined as L y . The extent L y is so designed as to sufficiently cover an extent L Y0 in the y-direction of the mask pattern as shown in Fig.5. The projection lens 12 forms an image of the pattern of the mask 10 illuminated by the three beams on the workpiece 13. As described, according to the present embodiment, the beam from the laser 1 within the x-y plane is split into three beams and they are respectively formed into an image as a linear light source I 6y+ , I 6y0 , I 6y- , and its image I 9y- , I 9y0 , I 9y+ is formed again within the entrance pupil 11 of the projection lens 12 to achieve a Köhler illumination on the mask 10 and workpiece 13. The mask 10 and workpiece 13 are thus illuminated by a light having a uniform illuminance with respect to the y-direction. It should be noted that the focal distance f 6y of the first cylindrical lens 6 is determined based on the diameter (width) a 6y in the y-direction of the beam incident upon the first cylindrical lens 6, the focal distance f 9y of the convex lens 9 and the length L y of the illuminated area on the mask 10. That is, supposing m 9y as an image forming magnification by which the convex lens 9 forms an image of the light source image I 6y+ , I 6y0 , I 6y- having formed by the first cylindrical lens 6 on the entrance pupil (aperture of stop) 11, and b 9y as the distance from the image side principal plane of the convex lens 9 to the entrance pupil 11 of the projection lens 12, the focal distance f 6y of the first cylindrical lens 6 is obtained as: f 6y = a 6y * {(b 9y - f 9 )/L y } * 1/m 9y where "*" indicates a multiplication. It is desirable that the illumination area L y of the mask 10 has about the same as or is increased by as much as 20 % from the length L y0 in the y-direction of the pattern of the mask, i.e.: L y0 ≤ L y ≤ 1.2 * L y0 To achieve this, it suffices that the focal distance f 6y of the first cylindrical lens 6 is determined by setting the incident width a 6y of the beam upon the first cylindrical lens 6 as a 6y ∼ (a 6y /1.2), while, in effect, a beam having a width of a 6y is caused to be incident thereupon. In other words, the focal distance f 6y may be determined by the following equation: f 6y = k * a 6y * {(b 9y - f 9 )/L y0 } * l/m 9y where k = 1 ∼ 1/1.2 and "*" indicates a multiplication. Next, based on this result, the apex angle (wedge angle) of the two prisms 4a, 4b that constitute the y-direction beam splitting means 4 are calculated. The emitting angle for the y-direction beam splitting means 4 is determined by the focal distance f 6y of the first cylindrical lens 6, the diameter A 11 of the entrance pupil 11 of the projection lens 12, and the image forming magnification m 9y in the y-direction of the convex lens 9. That is, in order that an image of the above three light sources I 6+ , I 60 , I 6- be formed within the entrance pupil 11, the following conditions of: tan(q 6y-max ) ≤ (A 11 /2)/(f 6y * m 9y ) must be met, where  6y-max is an angle between the optical axis and the beam emitted from the y-direction beam splitting means 4 (see Fig.3) and "*" indicates a multiplication. The two prisms 4a, 4b may be constituted by prisms having an angle of deviation of  6y-max as obtained by equation (4). It should be noted that, in determining their optical disposition, the optical effects of the second cylindrical lens 7 and third cylindrical lens 8 must be considered. The optical operation of the present embodiment within the x-y plane is as described above. The operation within the x-z plane (second plane) will now be described by way of Figs. 2 and 3B. In this plane, the y-direction beam splitting means 4 and the first cylindrical lens 6 act only as a parallel flat plate with respect to the incident beam. The incident beam is subjected to a converging effect respectively at the second cylindrical lens 7 and third cylindrical lens 8. Within this plane, the beam from the light source 1 is incident upon the second cylindrical lens 7 as a beam consisting of a bundle of rays that are substantially parallel to each other. A light source image (intermediate image within the x-z plane) I 7z is then formed at a focal point position F 7z ' (second converging point) of the second cylindrical lens 7. Since this light source image is spread into three beams in the y-direction, it is formed as three linear images I 7z+ , I 7z0 , I 7z- (see Fig.1). Next, these images are subjected to a converging effect by the third cylindrical lens 8 and is furthermore subjected to a converging effect by the convex lens 9 to be focused again at the position of the mask 10. That is, the three line images I 7z+ , I 7z0 , I 7z- , are formed into an image again at the position of the mask 10 as one line image I 9z by the third cylindrical lens 8 and convex lens 9. The image forming magnification at this time is m 8∼9,z . The projection lens 12 forms an image of the pattern of the mask 10 illuminated by a beam having a size close to a point in the z-direction on the workpiece 13. It should be noted that, supposing w as a divergence angle of the laser and f 7z as the focal distance of the second cylindrical lens 7, the size in z-direction s 7z of the image I 7z formed by the second cylindrical lens 7 is obtained as: S 7z = w * f 7z and the size in z-direction L z of the image I 9z formed on the mask 10 is obtained as: L z = s 7z * m 8∼9,z L z = w * f 7z * m 8∼9,z According to the experiments, a suitable range of the size L z is: 3 * L z0 ≤ L z ≤ 30 * L z0 where "*" indicates a multiplication. That is, with respect to the z-direction, the focal distance f 7z of the second cylindrical lens 7 and the image forming magnification m 8∼9,z of the second cylindrical lens 8 and convex lens 9 satisfying equation (6) are determined from the laser divergence angle w and a desired dimension L z , and, then, the focal distance f 8z of the second cylindrical lens 8 and the position thereof may be determined. Thereby, the width of a line-like illumination area may now be varied at a greater degree of freedom by suitably arranging the two cylindrical lenses, i.e., the second and third cylindrical lenses. It is however preferable that the focal distances f 7z , f 8z of the second cylindrical lens 7 and third cylindrical lens 8 and the positions of the two satisfy the following conditions. I. The distance from the first cylindrical lens 6 to the convex lens 9 is already determined from the relation of the image formation within the x-y plane. Accordingly, the second cylindrical lens 7 is preferably disposed within this distance. However, the third cylindrical lens 8 may be disposed either the light source 1 side or the mask 10 side from the convex lens 9. II. The incident beam is preferably incident upon the entrance pupil 11 of the projection lens 12 without causing a vignetting of lens. To achieve this, it is preferable to satisfy the following conditions. (d 10∼11 /m 8∼9,z ) * (a 7z /f 7z ) ≤ A 11 where: a 7z is the width in z-direction of the beam incident upon the second cylindrical lens 7; d 10∼11 is a distance from the mask 10 to the entrance pupil 11; and A 11 is a diameter of the entrance pupil. It should be noted that, since the line-like images I 9y- , I 9y0 , I 9y+ are formed within the entrance pupil 11 and the shape of these images as a whole is rectangular, it is preferable to consider this fact when suitably determining the size or shape of the entrance pupil 11. ("*" indicates a multiplication.) Based on the above construction, in the present embodiment, the laser beam within the x-z plane is formed into a linear image on the mask 10 as shown in Fig.5 to achieve a critical illumination with sufficiently covering the dimension L z0 in z-direction of the pattern. Thereby, an illumination having a very high density may be achieved when a pattern is projected on the workpiece. As described, according to the present embodiment, a Köhler illumination for uniformly illuminating the pattern to be projected is achieved within the x-y plane with sufficiently covering the length in the y-direction thereof, while, in the x-z plane, a Critical illumination is achieved for covering the dimension in the z-direction of the pattern to be projected for a suitable range to form (an image in that range with) the beam from the light source into. Thereby, a projection apparatus is achieved, which is far superior to a conventional laser processing optical system in the efficiency of energy consumption. The constructing procedure for the projection apparatus will now be described. First, from the processing dimension on a workpiece and the processing precision thereof, a suitable projection lens and its projecting magnification for processing are determined. Upon the determination of the projection lens, the position and diameter of its entrance pupil are also determined. Then, the pattern of the mask is thereby determined. Next, upon the determination of the illuminating dimensions L y , L z on the mask, of the optical elements of the illuminating system, the basic numerical values for the optical elements of the y-direction beam splitting means 4, shield mask 5, first cylindrical lens 6 and convex lens 9 are determined from the equations (3), (4). By satisfying these relations, a laser processing optical system may be achieved, which is capable of providing a uniform illumination in the y-direction. Next, based on equation (6), the respective focal distance and disposition of the second cylindrical lens 7 and third cylindrical lens 8 for securely illuminating the z-direction of the mask are determined. Thereby, the pattern to be projected may be securely illuminated also with respect to the z-direction. The constructing procedure is as described above. It should be noted that, while, in the present embodiment, the cylindrical lenses are each constructed by a single cylindrical lens, they may be respectively constituted by a plurality of cylindrical lenses. If the projection apparatus of the present embodiment is applied to the manufacturing of an orifice plate, i.e., an ink-jet printer, the orifice plate may be manufactured at a high productivity. It is thereby possible to reduce the cost of the orifice plate, i.e., of the ink-jet printer. If, in the above described embodiment, the light source is constructed by something other than a laser, rays of light emitted from the light source are brought into parallel to each other and then may be caused to be incident upon the y-direction beam splitting means 4. Any size larger than the effective portion of the y-direction beam splitting means 4 suffices as the size of a beam to be incident upon the y-direction beam splitting means 4. Further, if no ununiformity occurs in the intensity distribution of the beam in the y-direction, a system may be constructed without using a y-direction beam splitting means. It should be noted that, while, in the present embodiment, no beam expanding means or no beam reducing means is provided between the light source 1 and the y-direction beam splitting means 4, the disposition of such means causes no problem if the beam sufficiently covers the effective portion of the y-direction beam splitting means 4. Further, it is also possible to project a mask pattern on the workpiece 13 without an intermediary of a projection lens. Based on the construction as described above, the present embodiment achieves a projection apparatus suitable for a laser processing optical system which is capable of illuminating a unidimensional line-like mask pattern at a very high efficiency of energy utilization (light utilization efficiency). Also, an optimal projection apparatus for performing a laser processing of a line-like pattern is achieved, in which, by suitably setting the respective elements of the illumination means, the lengthwise dimension and widthwise dimension of a line-like illumination area may be varied at a high degree of freedom and the respective changes in the first and second directions of the illumination area on the illuminated surface may be made independently while securing a high energy density. A projection apparatus is achieved, which is capable of laser processing at a high accuracy by a simple construction by using a beam splitting element for example of a prism group, without using a fly-eye lens. A manufacturing method of an orifice plate is achieved in which the productivity is improved and a lower cost is achieved as a part processing. A low-cost ink jet printer using a low-cost orifice is achieved. A laser beam from an excimer laser is split into three beams along a first plane by a pair of prisms and the three beams are caused to intersect each other at the position of the object side focal point of a first cylindrical lens and be incident upon the first cylindrical lens. The three beams are respectively focused independently from each other by the first cylindrical lens. The above focused three beams are then focused along a second plane perpendicular to the first plane by a second cylindrical lens; then, the three beams are caused to superimpose each other on a mask and at the same time are brought to a defocus along said first plane and into focus again along said second plane by an anamorphic optical system containing a third cylindrical lens and a lens having a rotation symmetry, thereby a line-like illumination area extended in the first direction is formed on the mask. The linear illumination area and an area containing a pattern of a series of openings arranged in said first direction or a rectangular pattern extended in said first direction are caused to coincide on the mask to efficiently illuminate the pattern. An image of the illuminated pattern is projected onto a workpiece for an orifice plate by a projection lens system to process the workpiece in accordance with the pattern.

Claims: An illuminating apparatus for forming a linear illumination area on a plane to be illuminated, said apparatus comprising: a first anamorphic optical system (6) for bringing an illumination beam into focus with respect to a first direction; a second anamorphic optical system (7) for bringing said focused illumination beam into focus with respect to a second direction substantially perpendicular to said first direction; and a third optical system (8,9) for forming a linear illumination area extended in said first direction on said plane by bringing said illumination beam focused with respect to said two directions into focus again with respect to said second direction and into a defocus with respect to said first direction. An apparatus according to claim 1, further comprising a beam splitter (4) for forming a plurality of beams serving as said illumination beam by splitting light from a light source, and wherein said third optical system (8,9) causing said plurality of beams to overlap each other on said illuminated surface and bringing each of said plurality of beams into focus with respect to said second direction and at the same time to a defocus with respect to said first direction on said illuminated surface. An apparatus according to claim 2, wherein said beam splitter (4) directs said plurality of beams to different directions from each other along a first plane containing said first direction and the optical axis such that said plurality of beams intersect each other at a point on the optical axis along said first plane. An apparatus according to claim 3, wherein said intersecting position and the position of an object side focal point of said first anamorphic optical system (6) along said first plane substantially coincide. An apparatus according to claim 4, wherein said beam splitter (4) includes a plurality of prisms. An apparatus according to any one of claims 1 to 5, wherein said first anamorphic optical system (6) is constituted by a single cylindrical lens. An apparatus according to any one of claims 1 to 5, wherein said first anamorphic optical system is constituted by a plurality of cylindrical lenses. An apparatus according to any one of claims 1 to 7, wherein said second anamorphic optical system (7) is constituted by a single cylindrical lens. An apparatus according to any one of claims 1 to 7, wherein said second anamorphic optical system is constituted by a plurality of cylindrical lenses. An apparatus according to any one of claims 1 to 9, wherein said third optical system (8,9) is an anamorphic optical system. An apparatus according to claim 10, wherein said third optical system (8,9) includes a cylindrical lens (8) having a refracting power with respect to said first direction and a lens (9) having the same refracting power with respect to said first and second directions. An exposure system having an apparatus according to one of claims 1 to 11, said exposure system forming said linear illumination area on a mask (10) and exposing a substrate (13) through a pattern within said linear illumination area on said mask (10). An exposure system according to claim 12, further comprising a projection optical system for projecting an image of the pattern of said mask (10) onto said substrate (13). An exposure system according to claim 13, wherein the focus position of said illumination beam by said first anamorphic optical system (6) and a pupil position of said projection optical system occupy optically conjugate positions. A device manufacturing method comprising the steps of: forming said linear illumination area on a mask by the apparatus of one of claims 1 to 11 or the system of claims 12-14; and exposing a workpiece through a pattern within said linear illumination area on said mask. A method according to claim 15, wherein said pattern on said mask includes a plurality of small openings arranged along said first direction. A method according to claim 15, wherein said pattern on said mask includes a rectangular opening having its length direction along said first direction.

Inventors: NISHIWAKI MASAYUKI, NISHIWAKI, MASAYUKI, NISHIWAKI, MASAYUKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: B41J2
IPC codes: B41J2, G02B27, G02B13, B23K26, G03F7