Light source device and illumination system

An illumination system includes a light source device including a light source and a reflection mirror for reflecting light from the light source, and an optical system, including a plurality of lenses, for illuminating a surface with light from the light source device. A shadow of the light source is projected from the light source device in a direction inclined with respect to an optical axis of the optical system such that the shadow of the light source is not substantially projected on the surface through the optical system.

FIELD OF THE INVENTION AND RELATED ART 
This invention relates to a light source device and/or an illumination 
system. More particularly, the invention is concerned with a light source 
device and/or an illumination system usable in an optical microscope, an 
exposure system or an alignment system of an exposure apparatus for the 
manufacture of microdevices such as semiconductor memories, CCDs, display 
devices or magnetic heads, for example. 
As regards illumination methods used in an optical microscope, there are 
critical illumination wherein an image of a light source is placed at a 
position optically conjugate with an object, to be observed, with respect 
to an illumination optical system, or Koehler illumination wherein an 
image of a light source (or the light source itself) is placed at a pupil 
plane position of an illumination optical system. Practically, rather than 
the critical illumination which easily causes non-uniformness of 
illumination (because an image of a filament is formed on the object to be 
observed), Koehler illumination is used in many cases (because 
non-uniformness of the light source does not appear on the object). 
In optical microscopes, in many cases, a halogen lamp unit which provides 
white light arid which is easy to handle is used as an illumination light 
source. FIG. 8 shows an example of such a halogen lamp unit, wherein a 
lamp and a reflection mirror are formed into an integral structure. 
FIG. 7 is a schematic view of a general structure of a reflection type 
microscope, which is an example of an optical microscope using a halogen 
lamp unit as an illumination source. This halogen lamp unit is a light 
source device of the type in which a halogen electrode 3 providing a 
luminous point of the halogen lamp 1 is disposed at a first focal point 
position of an elliptical reflection mirror 2 such that an image of the 
halogen electrode 3 is formed at a second focal point position 4 of the 
reflection mirror 2. The light converged at that position 4 is directed by 
a lens 5 to a field stop 6, and, by this stop 6, it is shaped into light 
having a sectional shape and size necessary for illuminating an 
illumination region. Then, through refraction by a lens 7 and reflection 
by a half mirror 8, the light is refracted by a lens 9 and it illuminates 
an object 10 which is the subject to be observed. The light is reflected 
and diffracted (or scattered) by the object 10, and it is projected onto a 
CCD 12 via the lens 9, the half mirror 8 and a lens 11, whereby an 
enlarged image of the object 10 is formed on the CCD 12. 
FIG. 8 illustrates the structure of a halogen lamp unit usable as an 
illumination source. Halogen lamp 1 has a filament 40 of a coiled 
structure which is formed as a unit with a mirror 42 of revolving cup-like 
shape. Formed at the inside face of the mirror 42 is a mirror reflection 
surface 43 of a rotational paraboloidal surface shape or an elliptical 
surface shape, for example. Luminous point 3 of the halogen lamp 1 is 
formed in coincidence with a focal point position 45 of the reflection 
surface 43, and the central axis passing the focal point coincides with 
the axis of the halogen lamp 1. Also, the optical axis of the halogen lamp 
unit is the optical axis (central axis) of the reflection surface 43. 
Light emitted by the filament 40 of the halogen lamp 1 is reflected by the 
reflection surface 43, and it is projected through an illumination opening 
of the mirror 42. When the reflection surface 43 comprises an elliptical 
surface and the luminous point 3 of the halogen lamp 1 is disposed at the 
first focal point position of the elliptical surface 43, the light as 
reflected by the elliptical surface 43 is collected at a second focal 
point position of the elliptical surface 43. 
In a halogen lamp unit of the type, as described above, in which a luminous 
point 44 of a halogen lamp 41 is imaged by a reflection surface 43 of an 
elliptical surface shape, there is a problem that, at the second focal 
point position where the light from the luminous point 3 is collected, the 
convergent light from the reflection surface 43 is blocked by the halogen 
electrode 3. As a result, shade light (low intensity component) is 
produced in the central portion of the light flux which is being 
converged. As illustrated in FIG. 7, the halogen electrode 3 blocks the 
reflection light from the reflection mirror 2, and this causes shade light 
13 as depicted by hatching. In the case of Koehler illumination, this 
shade light 13 corresponds to light rays which illuminate a central 
portion of the observation region of the object 10. Thus, it results in a 
decrease of illuminance in the vicinity of the center of the observation 
region and causes insufficiency of the illumination light quantity or 
non-uniformness of illuminance. 
Also, in the case of a paraboloidal surface mirror wherein reflection light 
from a reflector is parallel light, a similar problem arises. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a light source device 
and/or an illumination system which assures that no shadow of a light 
source is projected onto a surface to be illuminated or, even if a shadow 
is projected, the effect of it is suppressed sufficiently. 
In accordance with an aspect ot the present invention, there is provided a 
light source device, comprising: a light source; and a reflection mirror 
for reflecting light from said light source, wherein a shadow of said 
light source is projected in a direction inclined with respect to an 
optical axis of said reflection mirror. 
In accordance with another aspect of the present invention, there is 
provided a light source device, comprising: a light source: and a concave 
mirror for reflecting light from said light source; wherein said light 
source is eccentric with respect to an optical axis of said concave mirror 
such that a shadow of said light source is projected in a direction 
inclined with respect to an optical axis of said concave mirror. 
In accordance with a further aspect of the present invention, there is 
provided an illumination system, comprising: a light source device 
including a light source and a reflection mirror for reflecting light from 
said light source; and an optical system for illuminating a surface with 
light from said light source device; wherein a shadow of said light source 
is projected from said light source device in a direction inclined with 
respect to an optical axis of said optical system such that the shadow of 
said light source is not substantially projected on the surface through 
said optical system. 
In accordance with a yet further aspect of the present invention, there is 
provided an illumination system for illuminating a surface, comprising: a 
light source device including a light source and a concave mirror for 
reflecting light from said light source; and an optical system for 
illuminating the surface with light from said light source device; wherein 
said light source device is arranged to project a shadow of said light 
source in a direction inclined with respect to an optical axis of said 
optical system such that the shadow of said light source is not 
substantially projected on the surface through said optical system. 
A light source device or an illumination system according to the present 
invention is suitably usable in an optical microscope, or an exposure 
optical system or an alignment optical system in an exposure apparatus for 
the manufacture of microdevices such as semiconductor memories, CCDs, 
display devices or magnetic heads, for example. 
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 
FIG. 1 is a schematic view of an optical microscope according to a first 
embodiment of the present invention. The elements corresponding to those 
of the FIG. 7 example are denoted by like numerals. An important feature 
of the present embodiment is that a halogen lamp unit is rotationally 
tilted by an angle .theta. about a rotational center at a second focal 
point 4 (light convergence position) of an elliptical reflection mirror 2. 
The convergence position 4 may be considered as an input position of 
illumination light to an illumination optical system, following it. The 
convergence position 4 is located on an optical axis of the illumination 
optical system (5-7). Also, the angle .theta. is such an angle with which 
a shade light 13 of a halogen electrode 3 within the convergent light flux 
from the elliptical reflection mirror 2 is positioned outside a light flux 
15, for illuminating an observation region upon an object 10 to be 
observed, such that it is eclipsed by a field stop 6. 
FIG. 2 is a graph for explaining a light intensity distribution, with the 
angle, of convergent light at the convergence position 4. The reference 
for the angle in this graph is taken on the optical axis of the halogen 
lamp unit. It is seen in this graph that the light intensity is slowed 
down in a portion about an angle of zero deg. where the shade light 13 of 
the halogen electrode is influential. It is to be noted that, although in 
FIGS. 1 and 7, the shade light 13 of the halogen electrode 3 is depicted 
as being clearly separated from other regions not eclipsed, actually the 
intensity profile does not vary interruptedly but there is produced an 
uninterrupted light intensity profile such as depicted in FIG. 2. This 
applies to any other embodiment to be described later. 
Conventionally, the optical axis of a halogen lamp unit is aligned with the 
optical axis of an illumination optical system and, as a result, light 
rays about an angle of zero deg. are mainly used for Koehler illumination. 
In this embodiment, as compared therewith, a high light-intensity region 
about an angle of -10 deg. shown in the graph of FIG. 2 is used for 
Koehler illumination. This enables illumination and observation of the 
object 10, to be observed, with higher illuminance. To this end, in this 
embodiment, the tilt angle of the optical axis of the halogen lamp unit 
with respect to the optical axis of the illumination optical system is set 
to about 10 deg., such that a brighter light portion from the halogen lamp 
unit is used for the illumination. Since the tilt angle of the optical 
axis of the halogen lamp unit is determined on the basis of the 
characteristic as depicted in FIG. 2, practically an angular distribution 
of light intensity may be predetected in accordance with the type of the 
halogen lamp unit to be used, and an optimum angle may then be determined. 
An adjusting member for adjusting the tilt angle of the halogen lamp unit 
may bc provided, and an optimum angle may be determined by using it. 
In FIG. 1, the halogen lamp unit is displaced downwardly. However, the 
direction is not important. Any direction is acceptable provided that the 
optical axis of the halogen lamp unit deviates by .theta. from the optical 
axis of the illumination optical system. Tilting the axis enables use ot a 
high intensity portion of convergent light flux at the convergence 
position 4 and also makes it possible to utilize the performance of the 
halogen lamp unit sufficiently. As a result, the non-uniformness of 
illuminance within the illumination region upon the object 10 to be 
observed is improved. 
FIG. 3 shows a second embodiment of the present invention, which is an 
example wherein light from a halogen lamp unit is directed to an 
illumination optical system by means of an optical fiber bundle 14. Since 
a light source portion is a heat source, if the system is used in a 
step-and-repeat exposure apparatus (stepper), for example, wherein strict 
temperature control is required, the light source portion and the other 
main portion of the optical microscope may preferably be disposed 
separately with an adequate distance maintained therebetween. Also in this 
embodiment, the halogen lamp unit is tilted, and this enables use of a 
light intensity portion of the light flux therefrom for illumination of an 
illumination region upon an object 10 to be observed. Higher uniformness 
of illuminance is assured. 
In the FIG. 3 arrangement, a light entrance end of the optical fiber bundle 
14 is disposed at a second focal point position 4 of the halogen lamp 
unit, and the other end (light exit end) of the fiber bundle is disposed 
at a pupil plane of an illumination optical system of the optical 
microscope. The optical fiber bundle has a characteristic that an input 
light is transmitted while preserving the angular characteristic of the 
input light and, for this reason, the halogen lamp unit and the optical 
fiber bundle 14 are disposed opposed to each other. More specifically, 
they are disposed so that a normal to the center of the light entrance end 
face of the optical fiber bundle 14 is aligned with the optical axis of 
the halogen lamp unit 1. This causes a shade light of the halogen 
electrode 3 to provide light rays which illuminated a portion around the 
center of the observation region upon the object 10 to be illuminated. As 
a result, the illuminance in the portion around the center of the 
observation region decreases due to the effect of the shade light 13. 
In consideration of this, in the FIG. 3 embodiment, the optical axis of the 
halogen lamp unit is disposed inclined by an angle .theta. with respect to 
a normal to the center on the light entrance end face of the optical fiber 
bundle 14. With this arrangement, the shade light 13 exits the light exit 
end of the fiber bundle 14, with inclination, such that within the 
illumination optical system there are produced expansions of light as 
depicted by hatchings 13' and 13". These shade lights 13' and 13" are then 
eclipsed by a field stop 6 having an opening corresponding to the 
observation region and, therefore, they do not illuminate the object 10. 
Thus, the light which illuminates the observation region is the light 15 
of a high illuminance region shown in FIG. 3, not having been eclipsed by 
the halogen electrode 3. As a result, illumination and observation with 
higher illuminance and less non-uniformness are assured. 
Also, like the first embodiment, what is important is the relative tilt 
.theta. between the optical axis of the halogen lamp unit and the end face 
of the optical fiber bundle. There is a latitude in the direction of tilt, 
provided that such a relative angular relation is maintained. 
While the foregoing embodiments have been described with reference to 
examples wherein a commercially available halogen lamp unit is used and 
the effect of shade light is removed by the structure of an optical 
system, similar advantages are attainable by modifying the structure of 
the halogen lamp itself. FIG. 4 shows a third embodiment of the present 
invention, which is an example wherein the structure of a halogen lamp 
unit is modified. In the halogen lamp unit of this embodiment, a halogen 
lamp 21 (light source) is provided with a reflector which comprises an 
elliptical reflection mirror 22 mounted to the lamp into an integral 
structure. The arrangement is such that a luminous point 23 of the halogen 
lamp 21 is disposed at a position shifted from a first focal point 
position 24 of the elliptical reflection mirror 22. 
The halogen lamp 21 is made of quartz or silica glass and, within this 
glass cylinder, an inertia gas and a small amount of halogenide are 
contained together with a filament 25 and sealed by means of a sealing 26. 
The filament 25 is of a longitudinal yoke type and it is wound into a coil 
around the axial center of the halogen lamp 21. The elliptical reflection 
mirror 22 has a projection opening 22a of approximately circular shape, 
formed at its forward end. Also, a neck 27 of approximately cylindrical 
shape is formed at the back of the reflector 22. The axis of the 
cylindrical portion of the neck 27 is disposed in alignment with the 
longitudinal direction of the halogen lamp 21, and the seal 26 of the 
halogen lamp 21 is fixed to this neck 27. The longitudinal direction ot 
the halogen lamp 21 is set so as to be substantially in alignment with the 
direction connecting the second focal point position 28 of the elliptical 
reflector 22 and the luminous point of the halogen lamp 21. 
In the system of FIG. 4, the luminous point 23 of the halogen lamp 21 is 
disposed at a position which is deviated from the first focal point 
position 24 of the elliptical reflection mirror 22, in a direction 
perpendicular to the optical axis of the elliptical reflection mirror 22. 
The light from the halogen lamp 21 is collected at a position 29 which is 
deviated, by an amount corresponding to the amount of that deviation, from 
the second focal point position 28 of the elliptical reflection mirror 22 
in a direction perpendicular to the optical axis. Here, shade light 13 of 
the luminous point 23 of the halogen electrode is inclined by an angle 
.theta. with respect to the optical axis 32 of the illumination optical 
system, as depicted by hatching. Since the shade light 31 is not included 
in the illumination region (light), to be used, of the illumination 
optical system as denoted by a reference numeral 33, combined use of a 
lamp unit according to this embodiment and an illumination optical system 
accomplishes illumination of higher illuminance and less non-uniformness. 
FIG. 5 shows a halogen lamp unit according to a fourth embodiment of the 
present invention. Like numerals as those of the third embodiments are 
assigned to corresponding elements. A distinction to the third embodiment 
resides in that the longitudinal direction of a halogen lamp 21 is placed 
substantially in alignment with the direction which connects the luminous 
point 23 of tile halogen lamp and a convergent point 29 where the luminous 
point 23 is imaged by the elliptical reflection mirror 22. The structure 
of the remaining portion and the operation thereof are similar to those 
having been described with reference to FIG. 4. As depicted by hatching, 
shade light 31 is tilted by an angle .theta. with respect to the optical 
axis of the illumination optical system, and it is not included in the 
illumination region (light), to be used, of the illumination optical 
system as denoted by reference numeral 33. Thus, illumination of higher 
illuminance and less non-uniformness is achieved. 
FIG. 6 shows an example wherein a halogen lamp unit according to the FIG. 4 
or 5 embodiment is incorporated into an optical microscope. Also in this 
example, like numerals as those of the foregoing embodiments are assigned 
to corresponding elements. As has been described with reference to FIG. 4 
or 5, the halogen lamp unit of this embodiment is arranged so that the 
luminous point 23 of the halogen lamp 21 is deviated from the first focal 
point position 24 of the elliptical reflector 22. The amount of deviation 
is so set that shade light 31 of a halogen electrode within the convergent 
light from the elliptical reflector 22 toward the second focal point 29 is 
eclipsed by a field stop 6, to assure that it is not included in the light 
used for the illumination. 
Practical advantages of the halogen lamp unit of this embodiment may be 
explained similarly to the first embodiment. In the graph of FIG. 2, the 
angle of a conventional halogen lamp unit along the optimal axis is zero, 
whereas, in the halogen lamp unit of this embodiment, this zero position 
corresponds to the tilt angle .theta. as described. Thus, the light to be 
projected to the illumination optical system and used as effective light 
is light in a region about -.theta.. In this embodiment, the shade light 
among output light from the halogen lamp unit is inclined by about an 
angle .theta.=10 deg. with respect to the optical axis of the illumination 
system. As a result, with an illumination optical system for an optical 
microscope for performing Koehler illumination, it is possible to use 
brighter light of about -.theta.=-10 deg. That is, with the use of the 
halogen lamp unit, it becomes possible to use a high light-intensity 
region for Koehler illumination. Illumination and observation of the 
object 10 with brighter illuminance is thus assured. 
Since the tilt angle is determined in accordance with the characteristic as 
shown in FIG. 2, the angular light-intensity distribution may be 
determined in accordance with the type of a halogen lamp unit to be used, 
and an optimum angle may then be determined. Also, while in FIG. 6 the 
halogen lamp unit is displaced downwardly, the direction of displacement 
is not important and tilt may be in any direction. Further, an optical 
fiber bundle may be used in the FIG. 6 embodiment, like the FIG. 3 
embodiment. 
Tilting the shade light provides an additional advantage, in addition to 
usability of a higher intensity portion (light) of convergent light at the 
convergence paint 29. Since in Koehler illumination the angular 
light-intensity distribution is reflected to the uniformness of 
illuminance upon the region being illuminated, the uniformness of 
illuminance in that region is enhanced such that it becomes possible to 
utilize the performance of the halogen lamp unit sufficiently. 
Further, in the structure of FIG. 6, if the mount of the halogen lamp unit 
is modified like a conventional one, then by simply changing the halogen 
lamp unit of the FIG. 4 or 5 example by a conventional unit while keeping 
the optical axis of the halogen lamp unit in alignment with the optical 
axis of the illumination optical system, observation of observation region 
upon the object with higher illuminance is accomplished. 
The present invention is applicable not only to an illumination system 
using a halogen lamp unit but also to an illumination system which uses 
any other lamp unit. For such a lamp unit, there may be one that uses a 
light collecting mirror such as paraboloidal surface mirror, for example. 
Another example of a lamp unit may be one that uses a lamp comprising a 
xenon lamp, a high pressure Hg lamp or a metal haloide lamp, for example. 
Further, the fiber bundle 14 may be replaced by a single optical fiber of 
an appropriate diameter or a glass rod of a suitable diameter. 
FIG. 9 shows a projection exposure apparatus for the manufacture of 
semiconductor devices. 
Denoted in FIG. 9 at M is a reticle having a circuit pattern formed 
thereon. Denoted at w is a wafer which is coated with a resist. Denoted at 
10 is an optical axis of the apparatus, and denoted at 20 is a light 
source (primary light source). Denoted at 30 is an illumination optical 
system for directing light from the light source 20 to the reticle M. 
Denoted at 30A is an aperture stop of the illumination optical system 30. 
The stop 30A is disposed in the vicinity of a light exit face of an 
optical integrator (fly's eye lens), not shown, of the illumination 
optical system 30, and it cooperates with the optical integrator to define 
a ring-like secondary light source at the opening thereof. Denoted at 40 
is a reticle stage for holding the reticle M, and denoted at 50 is a 
projection lens system for projecting a reduced image of the circuit 
pattern of the reticle M, as it is illuminated uniformly with light from 
the ring-like secondary light source of the illumination optical system 
30. Denoted at 50A is an aperture stop of the projection lens system 50, 
and it serves to define a pupil of the projection lens system 50. The 
following description will be made while taking the position of the 
opening of the stop 50A as a pupil position. Denoted at 60 is a wafer 
stage for holding the wafer W, and it serves to hold the wafer W so that 
the surface of the wafer W coincides with the imaging plane ot the circuit 
pattern of the reticle M provided by the projection lens system 50. 
Denoted at 70 is an optical system for an alignment operation, and it 
comprises a microscope shown in FIGS. 1, 3 or 6 as a main component 
thereof. 
With the structure described above and when the reticle M is illuminated by 
means of the light source 20 and the illumination optical system 30, 
diffraction light caused by the circuit pattern (which mainly comprises a 
combination of longitudinal and lateral patterns) of the reticle M is 
caught by the opening of the stop 50A of the projection lens system 50, 
and, by using this diffraction light, the projection lens system 50 
projects an image of the circuit pattern of the reticle M onto the wafer 
W. By this, the circuit pattern image is transferred to the resist of the 
wafer W. Through such an exposure-transfer process, semiconductor chips 
are produced from the wafer W. 
In the apparatus of FIG. 9, before projecting the image of the circuit 
pattern onto the wafer W, alignment marks formed on the wafer W are 
detected by using the optical system 70 and, on the basis of it, the 
position of the wafer W with respect to the lens system 50 is detected. 
Then, the position of the wafer W with respect to the lens system 50 (or 
reticle M) is adjusted. 
Next, an embodiment of a microdevice manufacturing method according to the 
present invention, which uses an exposure apparatus such as described 
above, will be explained. 
FIG. 10 is a flow chart of a procedure for the manufacture of microdevices 
such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels, 
CCDs, thin film magnetic heads or micro-machines, for example. Step 1 is a 
design process for designing a circuit of a semiconductor device. Step 2 
is a process for making a mask on the basis of the circuit pattern design. 
Step 3 is a process for preparing a wafer by using a material such as 
silicon. Step 4 is a wafer process which is called a pre-process wherein, 
by using the so prepared mask and wafer, circuits are practically formed 
on the wafer through lithography. Step 5 subsequent to this is an 
assembling step which is called a post-process wherein the wafer having 
been processed by step 4 is formed into semiconductor chips. This step 
includes an assembling (dicing and bonding) process and a packaging (chip 
sealing) process. Step 6 is an inspection step wherein an operation check, 
a durability check and so on for the semiconductor devices provided by 
step 5, are carried out. With these processes, semiconductor devices are 
completed and they are shipped (step 7). 
FIG. 11 is a flow chart showing details of the wafer process. Step 11 is an 
oxidation process for oxidizing the surface of a wafer. Step 12 is a CVD 
process for forming an insulating film on the wafer surface. Stop 13 is an 
electrode forming process for forming electrodes upon the wafer by vapor 
deposition. Step 14 is an ion implanting process for implanting ions to 
the wafer. Step 15 is a resist process for applying a resist 
(photosensitive material) to the wafer. Step 16 is an exposure process for 
printing, by exposure, the circuit pattern of the mask on the wafer 
through the exposure apparatus described above. Step 17 is a developing 
process for developing the exposed wafer. Step 18 is an etching process 
for removing portions other than the developed resist image. Step 19 is a 
resist separation process for separating the resist material remaining on 
the wafer after being subjected to the etching process. By repeating these 
processes, circuit patterns are superposedly formed on the wafer. 
With these processes, high density microdevices can be manufactured. 
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.