Illuminating apparatus and device manufacturing method

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 the first plane and into focus again along the 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 the first direction or a rectangular pattern extended in the 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.

BACKGROUND OF THE INVENTION 
1. 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. 
2. Description of the Related Art 
Recently, it is increasingly common to fabricate a precision part by a mask 
projection method. 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 a 
bubble jet printer (hereinafter referred to as an 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 ink onto a 
surface of a sheet from a large number of small holes having a diameter of 
20 to 50 .mu.m which are arranged in a row. An orifice plate refers to a 
member having the large number of small holes (nozzles) for ejecting the 
ink. In order to improve the quality of characters to be printed, it is 
important, in addition to an accurate control of timing of the ink 
ejection, that the large number of small holes on the orifice plate be 
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.

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 to be a first direction 
and a second direction, respectively, and the x-y plane and x-z plane are 
determined to be 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 a KrF excimer laser is used. Numerals 2 and 3 are bending 
mirrors, respectively, and an a 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.sub.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 cases, 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 a 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 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. 
FIGS. 3(A) and 3(B) show 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(A) is a front view of the mask 10 of the present embodiment. The 
pattern of the mask 10 is in the form of regularly disposing transparent 
small holes having a diameter L.sub.z0 (FIG. 4(B)) along a straight line 
in the y-direction on an opaque background portion, the total length in 
the y-direction being L.sub.y0 and the width in the z-direction being 
L.sub.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 .mu.m 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.sub.z0 =0.1.about.0.25 mm are arranged in a 
distance of L.sub.y0 =50 mm. 
The direction of the 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 FIGS. 1 and 3(A). A substantially collimated laser beam emitted in the 
direction of an 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. 3(A), 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.sub.6y on the optical axis, and the shield mask 5 
having an opening at the center thereof is disposed at the position 
F.sub.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 
occurring prior to the y-direction beam splitting means 4. 
The shield mask 5 is disposed at the position of an object focal point 
F.sub.6y (the subscript letters .sub.y,z indicating the elements of the 
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 optical 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.sub.6y+, I.sub.6y0, I.sub.6y- 
are formed at the focal point position F.sub.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.sub.6y+, 
I.sub.6y0, I.sub.6y- into an image I.sub.9y-, I.sub.9y0, I.sub.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.sub.y. The extent L.sub.y is so designed as to 
sufficiently cover an extent L.sub.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.sub.6y+, I.sub.6y0, 
I.sub.6y-, and its image I.sub.9y-, I.sub.9y0, I.sub.9y+ is formed again 
within the entrance pupil 11 of the projection lens 12 to achieve a Kohler 
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.sub.6y of the first 
cylindrical lens 6 is determined based on the diameter (width) a.sub.6y in 
the y-direction of the beam incident upon the first cylindrical lens 6, 
the focal distance f.sub.9y of the convex lens 9 and the length L.sub.y of 
the illuminated area on the mask 10. That is, supposing m.sub.9y as an 
image forming magnification by which the convex lens 9 forms an image of 
the light source image I.sub.6y+, I.sub.6y0, I.sub.6y- having been formed 
by the first cylindrical lens 6 on the entrance pupil (aperture of stop) 
11, and b.sub.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.sub.6y of the first cylindrical lens 6 is obtained as: 
EQU f.sub.6y =a.sub.6y *{(b.sub.9y -f.sub.9)/L.sub.y }* .vertline.1/m.sub.9y 
.vertline. (1) 
where "*" indicates a multiplication. 
It is desirable that the illumination area L.sub.y of the mask 10 has about 
the same as or is increased by as much as 20% from the length L.sub.y0 in 
the y-direction of the pattern of the mask, i.e.: 
EQU L.sub.y0 .ltoreq.L.sub.y .ltoreq.1.2*L.sub.y0. (2) 
To achieve this, it suffices that the focal distance f.sub.6y of the first 
cylindrical lens 6 is determined by setting the incident width a.sub.6y of 
the beam upon the first cylindrical lens 6 as a.sub.6y .about.(a.sub.6y 
/1.2), while, in effect, a beam having a width of a.sub.6y is caused to be 
incident thereupon. In other words, the focal distance f.sub.6y may be 
determined by the following equation: 
EQU f.sub.6y =k*a.sub.6y *{(b.sub.9y -f.sub.9)/L.sub.y0 }*.vertline.1/m.sub.9y 
.vertline. (3) 
where k=1.about.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 is 
calculated. The emitting angle for the y-direction beam splitting means 4 
is determined by the focal distance f.sub.6y of the first cylindrical lens 
6, the diameter A.sub.11 of the entrance pupil 11 of the projection lens 
12, and the image forming magnification m.sub.9y in the y-direction of the 
convex lens 9. 
That is, in order that an image of the above three light sources I.sub.6+, 
I.sub.60, I.sub.6- be formed within the entrance pupil 11, the following 
conditions of: 
EQU tan (q.sub.6y-max).ltoreq.(A.sub.11 /2)/(f.sub.6y *m.sub.9y) (4) 
must be met, where .theta..sub.6y-max is an angle between the optical axis 
and the beam emitted from the y-direction beam splitting means 4 (see 
FIGS. 3(A) and 3(B)) and "*" indicates a multiplication. 
The two prisms 4a, 4b may be constituted by prisms having an angle of 
deviation of .theta..sub.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 3(B). 
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.sub.7z is then formed at a 
focal point position F.sub.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.sub.7z+, 
I.sub.7z0 , I.sub.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.sub.7z+, I.sub.7z0, I.sub.7z- are formed 
into an image again at the position of the mask 10 as one line image 
I.sub.9z by the third cylindrical lens 8 and convex lens 9. The image 
forming magnification at this time is m.sub.8.about.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.sub.7z as the focal distance of the second cylindrical lens 7, the size 
in the z-direction s.sub.7z of the image I.sub.7z formed by the second 
cylindrical lens 7 is obtained as: 
EQU S.sub.7z =w*f.sub.7z (5) 
and the size in the z-direction L.sub.z of the image I.sub.9z formed on the 
mask 10 is obtained as: 
EQU L.sub.z =S.sub.7z *m.sub.8.about.9,z 
EQU L.sub.z =w*f.sub.7z *m.sub.8.about.9,z (6) 
According to the experiments, a suitable range of the size L.sub.z is: 
EQU 3*L.sub.z0 .ltoreq.L.sub.z .ltoreq.30*L.sub.z0 (7) 
where "*" indicates a multiplication. 
That is, with respect to the z-direction, the focal distance f.sub.7z of 
the second cylindrical lens 7 and the image forming magnification 
m.sub.8.about.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.sub.z, and, then, the focal distance f.sub.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.sub.7z, f.sub.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 on 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 the lens. To 
achieve this, it is preferable to satisfy the following conditions. 
EQU (d.sub.10.about.11 /m.sub.8.about.9,z)*(a.sub.7z /f.sub.7z).ltoreq.A.sub.11 
(8) 
where: a.sub.7z is the width in the z-direction of the beam incident upon 
the second cylindrical lens 7; d.sub.10.about.11 is a distance from the 
mask 10 to the entrance pupil 11; and A.sub.11 is a diameter of the 
entrance pupil. 
It should be noted that, since the line-like images I.sub.9y-, I.sub.9y0, 
I.sub.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 while sufficiently covering 
the dimension L.sub.z0 in the 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 Kohler illumination 
for uniformly illuminating the pattern to be projected is achieved within 
the x-y plane while 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 a desired image. 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.sub.y, 
L.sub.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 
accurately illuminating the z-direction of the mask are determined. 
Thereby, the pattern to be projected may be accurately 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 nonuniformity 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 assuring 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.