Projection exposure apparatus including a condenser optical system for imaging a secondary light source at positions different in an optical axis direction with respect to two crossing planes

A projection exposure apparatus includes a projection optical system for projecting a pattern of a first object onto a second object; a laser source; an optical integrator for forming a secondary light source from the laser source; and a condenser optical system for imaging the secondary light source behind the first object at positions different in a direction of an optical axis with respect to two different directions to illuminate the first object therewith.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to a projection exposure apparatus and a 
device manufacturing method for manufacturing various devices using the 
projection exposure apparatus, usable for manufacturing a semiconductor 
device such as an IC or LSI, a display device such as a liquid crystal 
panel, a magnetic head or the like. 
Recently, the density of a semiconductor device such as an IC or LSI is 
acceleratedly increased, and the resultant development for the fine 
processing for a semiconductor wafer is also remarkable. The projection 
exposure technique, which is the key part of the fine processing, is under 
development for an increase of the resolution to form an image of a 
dimension not more than 0.5 .mu.m. The increase of the resolution is 
directed, in the projection exposure optical system, to an increase of the 
NA (numerical aperture) or a decrease of the wavelength of the exposure 
beam. 
With the decrease of the wavelength of the exposure light, the 
transmissivity of the glass material decreases, and therefore, the kinds 
of the glass, materials usable for the projection optical system decreases 
in number. When the number of kinds of the glass materials decreases, the 
correction of the chromatic aberration becomes difficult, and therefore, 
it is desired to reduce the wavelength band width of the light source to 
such an extent that the resultant chromatic aberration is negligibly 
small. For example, in the projection optical system using light having a 
wavelength of 300 nm or less, the usable glass materials are quartz and 
fluorite, and the light source provides a narrow band laser beam. When a 
laser is used as a light source, a plurality of spots are formed on a 
pupil of the projection optical system from a single spot to which the 
laser beam is condensed, since the laser beam has high directivity. The 
energy density is very high in the spot, and when an optical element is 
disposed at this position, the glass material or coating thereof is 
deteriorated by the laser spot, or damaged by long term illumination. If 
this occurs, the transmissivity of the glass material decreases, and the 
property of the coating is changed. In order to avoid this problem, it 
would be considered that the lens or a concave mirror is not disposed 
adjacent the pupil plane of the projection optical system. 
However, when the NA of the optical system is increased for the purpose of 
increasing the resolution, or when the size of the field of the image is 
increased, with the result of an increase of the number of lenses 
constituting the optical system, it is difficult to provide a space 
without an optical element in the neighborhood of the pupil plane. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide a 
projection exposure apparatus and a device manufacturing method using the 
same in which the density of the energy of the laser beam condensed in the 
optical system can be reduced. 
According to a first aspect of the present invention, there is provided a 
projection exposure apparatus and a device manufacturing method including 
a projection optical system for projecting a pattern of a first object 
onto a second object, and an illumination system for illuminating the 
pattern on the first object, wherein the illumination optical system 
includes a laser beam source and an illumination optical system for 
illuminating the surface of the first object with the beam from the laser 
source and for condensing the light beam from the laser source at 
different plural positions in the optical axis direction of the projection 
optical system, behind the first object plane. Thus, the surface of the 
first object is illuminated with the laser beam, and the laser beam is 
condensed at the positions different in the optical axis direction of the 
projection optical system, and therefore, the laser beam does not form a 
spot adjacent the pupil plane, thus reducing the energy density of the 
laser beam so that the durability of the apparatus is improved. 
According to a second aspect of the present invention, there is provided a 
projection exposure apparatus comprising: a projection optical system for 
projecting a pattern of a first object onto a second object; a laser 
source; an optical integrator for forming a secondary light source from 
the laser source; and a condenser optical system for imaging the secondary 
light source behind the first object at positions different in a direction 
of an optical axis with respect to two different directions to illuminate 
the first object therewith. 
The surface of the first object is illuminated by the beam from the 
secondary light source, and the beam from the secondary light source is 
focused at positions different in the optical axis direction in two 
different directions, behind the first object surface, by the condenser 
optical system. Since the surface of the first object is illuminated by 
the beam from the secondary light source of the optical integrator, the 
first object surface can be illuminated with a uniform illumination 
intensity. In addition, the laser beam is prevented from forming a spot 
adjacent the pupil plane. Thus, the energy density of the laser beam is 
reduced, and therefore, the durability of the apparatus is improved. 
According to a third aspect of the present invention, there is provided a 
projection exposure apparatus comprising: a projection optical system for 
projecting a pattern of a first object onto a second object; a laser 
source; an optical integrator for forming a secondary light source from 
rays of the laser source; a condenser lens for illuminating the first 
object with rays from the secondary light source; wherein the optical 
integrator comprises a plurality of lenses disposed such that rear focus 
positions are a predetermined distance away from each other in two 
orthogonal directions, wherein the rays are condensed behind the first 
object at positions different in a direction of an optical axis in the two 
directions through the condenser optical system. 
According to this feature, the surface of the first object is illuminated 
by the beam from the secondary light source of the optical integrator, and 
therefore, the surface of the object can be illuminated with a uniform 
illumination intensity. By preventing spot formation of the laser beam 
adjacent the pupil plane, the energy density of the laser beam is reduced, 
so that the durability of the apparatus is increased. Additionally, since 
the plural light sources for providing the secondary light source have a 
linear configuration, it is effective to form an illumination area in the 
form of a slit. 
According to a fourth aspect of the present invention, there is provided a 
projection exposure apparatus and a device manufacturing method, including 
a projection optical system for projecting a pattern of a first object 
onto a second object, and an illumination system for illuminating the 
pattern on the first object, and the illumination system includes a laser 
light source as a light source, and an illumination optical system or 
condensing the beam from the laser source at positions different in the 
optical axis direction of the projection optical system to illuminate the 
first object surface, wherein a beam condensing position in a direction 
perpendicular to the scanning direction is on the pupil plane of the 
projection optical system, whereas the condensing position in a plane 
including the scanning direction is deviated from the pupil position of 
the projection optical system. In the plane including the scanning 
direction, the condensing position of the laser beam is deviated from the 
pupil plane of the projection optical system. The illumination beam (image 
formation beam) will be deviated (tilted) depending on the image height, 
but adjacent the optical axis of the projection optical system (in front 
of and at the back of the optical axis in the scanning direction), the 
scanning exposure is effected, by which the deviation of the illumination 
beam in the scanning direction is made even, so that the exposure can be 
effected without deviation of the beam. 
According to a fifth aspect of the present invention, the third aspect is 
improved in that a rear focus position in a direction perpendicular to the 
scanning direction of the optical integrator constituted by a plurality of 
lenses disposed such that the rear focus positions are deviated through a 
predetermined distance in the optical axis direction, in two orthogonal 
directions, is optically conjugate with the pupil plane of the projection 
optical system, and the rear focus position in the scanning direction is 
not in optical conjugation with the pupil plane of the projection optical 
system. In the plane including the scanning direction, the image position 
of the secondary light source provided by the optical integrator is 
deviated from the pupil plane of the projection optical system. Therefore, 
the illumination beam (imaging beam) is deviated (tilted) depending on the 
image height. The deviation can be made even in the scanning direction by 
effecting the scanning exposure adjacent the optical axis of the 
projection optical system (in front of and at the back of the optical axis 
in the scanning direction), by which the exposure is possible with the 
beam without the deviation. 
According to a sixth aspect of the present invention, there is provided a 
projection exposure apparatus, and a device manufacturing method, which 
includes a projection optical system for projecting the pattern on the 
first object onto the second object and an illumination system for 
illuminating the pattern of the first object, and the illumination system 
includes a laser source, and an illumination optical system for condensing 
the light beam from the laser source at positions different in the 
direction of the optical axis of the projection optical system behind the 
first object to illuminate the first object surface with the laser beam 
from the laser source, and the illumination optical system is effective to 
condense the beam from the laser source at a position of the pupil plane 
of the projection optical system and a position deviated therefrom. By 
doing so, the energy density of the laser beam can be increased by 
avoiding the spot formation adjacent the pupil plane, thus improving the 
durability of the apparatus. Additionally, the reduction of the imaging 
performance is avoided by placing one condensing position at the pupil 
plane. 
According to a seventh aspect of the present invention, there is provided a 
projection exposure apparatus, and a device manufacturing method, which 
comprises a projection optical system for projecting a pattern of a first 
object onto a second object and an illumination system for illuminating 
the pattern of the first object, and the illumination system includes a 
laser source and an illumination optical system for condensing the light 
beam from the laser source at positions different in the direction of the 
optical axis of the projection optical system, behind the first object 
surface to illuminate the surface of the first object with the beam from 
the laser source. By doing so, the spot formation of the laser beam is 
prevented adjacent the pupil plane, thus decreasing the energy density of 
the laser beam, by which the durability of the apparatus is improved, and 
by using an illumination optical system producing astigmatism, by which 
the beam from the light source is condensed into a linear shape at 
different positions, thus further reducing the energy density. 
According to an eighth aspect of the present invention, the sixth and the 
seventh aspect are further improved in that the first and the second 
objects are scanned by the laser beam from the laser source so that each 
part of the pattern of the first object is sequentially projected onto the 
second object, and an illumination optical system condenses the light from 
the laser source at a position of the pupil plane in a plane including the 
optical axis and a direction perpendicular to the scanning direction, and 
condenses the light from the laser source at a position away from the 
pupil plane in a plane containing the optical axis and the scanning 
direction. By doing so, the energy density of the laser beam can be 
reduced without reduction of the imaging performance. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 schematically show a projection exposure apparatus usable for 
manufacturing a semiconductor device such as an IC or LSI, an image pickup 
device such as a CCD, a display device such as a liquid crystal panel, a 
magnetic head or the like, according to a first embodiment of the present 
invention. In FIGS. 1 and 2, the direction of the optical axis is 
represented by "X", and FIG. 1 is a view in an XY plane, and FIG. 2 shows 
the same in a ZX plane. 
In FIG. 1, a substantially collimated laser beam emitted from the laser 
source 1 is incident on a device 2 for making the beam incoherent. In the 
device 2, the shape of the laser beam emitted from the laser source 1 is 
reformed to match the shape of the optical integrator 3, and divide or 
scan the laser beam so that no speckle pattern or other interference 
fringes, are formed on the wafer 8. The light passing through the device 2 
is incident on the optical integrator 3 and is divided into a number of 
light beams thereby, into a number of scattering beams. In other words, 
the light emitting surface of the optical integrator 3 functions as a 
secondary light source, and a number of scanning beams from the secondary 
light source is incident on a condenser lens 4, which in turn are overlaid 
on the reticle 5 to effect uniform illumination. 
The condenser lens 4 comprises a cylindrical lens 4a and 4b. In the XY 
plane, the lens 4a has a refraction power, but the lens 4b has no 
refraction power in this plane. The light rays from the secondary light 
source are overlaid on the surface, to be illuminated, of the reticle 5 by 
the condenser lens 4a. At this time, if the projection optical system 6 is 
a telecentric optical system, the principal ray of the illumination is 
incident on the reticle 5 in the form of afocal light, and forms an image 
of the secondary light source in the XY plane on a pupil plane 7 of the 
projection optical system 6. The reticle 5 has a circuit pattern of a 
semiconductor device to be transferred onto the wafer 8, so that the 
projection optical system 6 forms an image of the circuit pattern on the 
wafer 8, and therefore, the pattern image is transferred thereonto. 
FIG. 2 is a view in a ZX plane (as seen perpendicular to the sheet of the 
drawing of FIG. 1), and the lens 4a of the condenser lens 4 is a 
cylindrical lens not having a refraction power in the XY plane, but it has 
a refraction power in the ZX plane. The light rays from the secondary 
light source in the emitting side surface of the optical integrator 3 are 
overlaid on the reticle 5 by the condenser lens 4b. The condenser lens 
forms an image of the secondary light source in the ZX plane at a position 
B away from the pupil plane 7 of the projection optical system 6 by a 
predetermined distance. Each principal ray of the illumination light 
incident on each point on the reticle 5, is parallel in the XY plane of 
FIG. 1, but is inclined at a predetermined angle toward the optical axis 
in the ZX plane of FIG. 2, so that the light is converged as shown in the 
Figure. 
FIGS. 3A and 3B show images of the light source in a plane perpendicular to 
the optical axis at a position A at the pupil plane 7 (aperture position) 
of the projection optical system 6 and at a position B away from the 
position A. In FIG. 3A, the light from the optical integrator 3 is 
converged in the Y direction, but is diverged in the Z direction to a 
predetermined degree. On the other hand, in FIG. 3B, it is converged in 
the Z direction but is diverged in the Y direction, contrary to FIG. 3A. 
The shapes of the secondary light sources formed in the projection optical 
system 6 shown in FIGS. 3A and 3B, are dependent on the structure of the 
shape of the optical integrator 7 and the structure of the device 2. 
As described, the projection exposure apparatus of this embodiment uses an 
anamorphic illumination optical system having a different focal length in 
two orthogonal directions so that the astigmatism is provided for the 
formation of images of the secondary light source within the projection 
optical system, by which linear spots are formed at positions A and B. 
Thus, no spot is formed at any position in the projection optical system 6 
by the light from the laser source, thus avoiding an occurrence of high 
energy density projection. Therefore, the durability of the optical system 
6 and therefore, the apparatus, is increased. This advantageous effect is 
provided in the other embodiments of the present invention. 
FIGS. 4 and 5 illustrate a projection exposure apparatus usable for 
manufacturing devices such as a semiconductor device such as an IC or LSI, 
an image pickup device such as a CCD, a display device such as a liquid 
crystal device, a magnetic head or the like, according to a second 
embodiment of the present invention. In this embodiment, the scanning 
operation is effected in the direction indicated by an arrow in FIG. 5 in 
synchronism with the reticle 5 and the wafer 8, so that the wafer 8 is 
exposed through the pattern of the reticle 5. Therefore, the present 
invention is applied to a scanning type exposure apparatus. 
In the scanning type exposure apparatus, the shape of the illumination area 
on the wafer and on the reticle 5, is slit-like. The optical integrator 3 
is constructed by a cylindrical lens or the like having a different 
refraction power in the two orthogonal directions perpendicular to the 
optical axis, by which a plurality of slit-like light sources are formed 
on the secondary light source surface. The longitudinal directions of the 
slit light source and the illumination area are made the same, by which 
the illumination area can be illuminated efficiently by the slit-like 
light. 
In this embodiment, the optical integrator 3 is constituted by cylindrical 
lenses 3a and 3b. The cylindrical lens 3a has a refraction power in an XY 
plane, and the light is collimated by a condenser lens 4a to illuminate in 
the longitudinal direction the slit like illumination area of the reticle 
5. On the other hand, a cylindrical lens 4b has a refraction power in a ZX 
plane, and the condenser lens 4b is effective to illuminate the slit-like 
illumination area in a width (scanning direction). 
In FIG. 4, the secondary light source formed on the emitting surface of the 
optical integrator 3 is formed on a pupil plane of the projection optical 
system 6 by the condenser lens 4a in the XY plane. 
In FIG. 5, there is shown a positional relationship between the secondary 
light source and the pupil plane of the projection optical system 6 in the 
ZX plane, including the scanning direction. In the ZX plane, the emitting 
surface of the optical integrator 3 is imaged at a position C which is a 
predetermined distance away from the pupil plane 7 in the optical axis 
direction, by the condenser lens 4b. The image of the secondary light 
source on the pupil plane 7 in FIG. 4 has the same distribution as shown 
in FIG. 3A, and the image of the secondary light source at a position C in 
FIG. 5, has the same distribution as in FIG. 3B, in embodiment 1, so that 
there is no high energy density position resulting from a converged spot 
image. 
In FIG. 5, if it is assumed that the projection optical system 6 is 
telecentric at a light emitting side (wafer 8 side), the principal ray is 
incident with an angle relative to the optical axis at positions D and E 
on the wafer. Generally, when the principal ray is incident with 
inclination, the size of the image changes if the wafer 8 is exposed with 
defocusing. However, in the embodiment of FIG. 5, the sequential exposure 
is carried out while scanning in the direction of the arrow, and 
therefore, the inclination of the principal ray is made uniform by the 
scanning exposure from a position D to a position E, and therefore, the 
size of the image remains the same despite the defocusing. 
Accordingly, when the present invention is used in the scanning type 
exposure apparatus, it is desirable that the secondary light source is 
imaged on the pupil plane of the projection optical system in a plane 
including the optical axis direction and a longitudinal direction of the 
slit (perpendicular to the scanning direction), and the image of the 
secondary light source is formed at a position a predetermined distance 
away from the pupil plane of the projection optical system in a plane 
including the scanning direction and the optical axis direction. 
FIGS. 6 and 7 show a projection exposure apparatus usable for manufacturing 
devices such as a semiconductor device such as an IC or LSI, an image 
pickup device such as a CCD, a display device such as a liquid crystal 
panel, a magnetic head or the like. The structures of the exposure 
apparatus are substantially the same as in the first and second 
embodiments, and therefore, only the optical system downstream of the 
optical integrator 3 is shown. In this embodiment, the condenser lens 4 in 
the illumination system comprises a rotation symmetry lens having a 
uniform refraction power. The optical integrator 3 comprises a plurality 
of cylindrical lenses 3a and 3b so that the rear focus positions are 
deviated from each other in the direction of the optical axis by a 
predetermined distance, in two orthogonal directions. 
FIG. 6 is a view as seen in the XY plane of the apparatus according to the 
third embodiment of the present invention. In FIG. 6, the optical 
integrator 3A is in the form of a group of cylindrical lenses having 
refraction powers in the XY plane to converge the laser beam from the 
laser source 1 at a rear focus position F. The optical integrator 3b does 
not have a refraction power in the XY plane, and is constituted by 
cylindrical lenses overlaid in the direction perpendicular to the sheet of 
the drawing. The condenser lens 4 has a focal length fc, and the 
projection optical system 6 is telecentric relative to the object 
(reticle) side. In this case, the rear focus position F is a distance fc 
away from the condenser lens 4. In this case, the secondary light source 
formed at the position F is formed on the pupil plane 7 of the projection 
optical system in the XY plane. 
FIG. 7 is a view as seen in the ZX plane of the apparatus of the third 
embodiment. The optical integrator 3b has a refraction power in the ZX 
plane, and the laser beam is condensed at a position of the rear focus 
position F' to form a secondary light source there. The rear focus 
position F' is (fc+X) away from the condenser lens. Therefore, the 
secondary light source in the ZX plane is imaged at a position a 
predetermined distance (xp) away from the pupil plane 7 of the projection 
optical system 6. Here, the following is satisfied: 
EQU xp=(fi/fc).sup.2 .times.X 
where fi is a focal length of the lens group 6a in front of the projection 
optical system 6. 
Similar to the first and second embodiments, the image of the secondary 
light source in the pupil plane 7 of the projection optical system 6 in 
FIG. 6 is slit-like in the third embodiment, too. Additionally, the 
secondary light source image at the image position adjacent the pupil 
plane 7 in he ZX plane in FIG. 7, is slit-like, as shown in FIG. 3B. 
Therefore, the laser beam is not condensed into a spot in the projection 
optical system 6. 
When the third embodiment is used for a scanning type projection exposure 
apparatus in which the wafer 8 is scanned and exposed to the circuit 
pattern on the reticle 5 in synchronism therewith, the scanning direction 
is selected to be in accord with the Z direction, by which the 
illumination light is made uniform with the result that the exposure can 
be effected with uniform light. 
FIG. 8 shows an example of a projection optical system used in the first, 
second and third embodiments. In this example, nine lenses 61-71 are used, 
and the pupil plane (aperture) 7 is in proximity with the lens 66. 
FIG. 9 shows another example of a projection optical system 6 usable with 
the first, second and third embodiments. The optical system shown in FIG. 
10 comprises lens groups 101 and 104, a concave mirror 103, and a beam 
splitter 102, which constitute a reflection and refraction optical system. 
The light from the reticle 5 passes through the lens group 101 and the 
beam splitter 102 and is then reflected by the concave mirror 103. The 
light reflected by the concave mirror 103 is further reflected by the beam 
splitter 102 and is condensed on a wafer 8 by the lens group 104, so that 
the pattern of the reticle 5 is imaged on the wafer 8, in this optical 
system, the pupil plane (aperture plane) 7 is substantially in accord with 
the position of the concave mirror. In the projection optical system, the 
optical path is not folded by a mirror or the like, but it is possible to 
fold the optical path using a mirror or mirrors. 
According to the foregoing embodiments, the spot-like condensation of the 
laser beam can be avoided in a projection optical system in an exposure 
apparatus using a high directivity such as a laser, and therefore, the 
durability of the optical elements at or adjacent the pupil plane, for 
example, against the laser beam can be improved. 
The description will now be made as to an embodiment of a device 
manufacturing method using the scanning exposure apparatus. FIG. 10 is a 
flow chart of manufacturing semiconductor devices such as ICs, LSIs or the 
like, or devices such as liquid crystal panels or CCDs or the like. At 
step 1, (circuit design), the circuits of the semiconductor device are 
designed. At step 2 (mask manufacturing), the mask (reticle 304) having 
the designed circuit pattern is manufactured. On the other hand, at step 
3, a wafer (306) is manufactured using the proper material such as 
silicon. Step 4 (wafer processing) is called a pre-step, in which an 
actual circuit pattern is formed on a wafer through lithographic 
techniques using the prepared mask and wafer. At step 5 (post-step), a 
semiconductor chip is manufactured from the wafer subjected to the 
operations of step 4. The step 5 includes assembling steps (dicing, 
bonding), a packaging step (chip sealing) or the like. At step 6 
(inspection), the operation of the semiconductor device manufactured by 
the step 5 is inspected, and a durability test thereof is carried out. In 
this manner, the semiconductor device is manufactured and delivered at 
step 7. 
FIG. 11 is a flow chart of detailed wafer processing. At step 11 
(oxidation), the surface of the wafer is oxidized. At step 12 (CVD), an 
insulating film is formed on a surface of the wafer. At step 13 (electrode 
formation), an electrode is formed on the wafer by evaporation. At step 14 
(ion injection), the ions are implemented into the wafer. At step 15 
(resist processing), a photosensitive material is applied on the wafer. At 
step 16 (exposure), the circuit pattern of the mask (reticle 304) is 
projected onto the wafer by the above-described exposure apparatus. At 
step 17 (development), the exposed wafer is developed. At step 18 
(etching), the portion outside the resist image are removed. At step 19 
(resist removal), the resist is removed after the etching. By repeating 
the above-described steps, overlaid circuit patterns are formed on the 
wafer. 
According to the manufacturing method according to the embodiments of the 
present invention, the integration density can be improved. 
While the invention has been described with reference to the structures 
disclosed herein, it is not confined to the details set forth and this 
application is intended to cover such modifications or changes as may come 
within the purposes of the improvements or the scope of the following 
claims.