CA1170234A - Illumination system - Google Patents
Illumination systemInfo
- Publication number
- CA1170234A CA1170234A CA000396460A CA396460A CA1170234A CA 1170234 A CA1170234 A CA 1170234A CA 000396460 A CA000396460 A CA 000396460A CA 396460 A CA396460 A CA 396460A CA 1170234 A CA1170234 A CA 1170234A
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- Canada
- Prior art keywords
- illumination system
- light
- source
- central axis
- lens
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
An illumination system having a light source disposed along a central axis of the system is provided with a conical reflector coaxially disposed about the light source for forming an annular virtual image of an arc of the light source. A toroidal lens is coaxially disposed about the central axis for forming a cir-cular real image of the annular virtual image of the arc at the input port of a utilization device.
An illumination system having a light source disposed along a central axis of the system is provided with a conical reflector coaxially disposed about the light source for forming an annular virtual image of an arc of the light source. A toroidal lens is coaxially disposed about the central axis for forming a cir-cular real image of the annular virtual image of the arc at the input port of a utilization device.
Description
'7(~3'~
IMPROVED ILLUMINATION S~STEM
Background and Summary of the Invention This invention relates to illumination systems of the type employing a light source and a reflector coaxially mounted along a central axis of the illumination system for 5 reflecting light, which emanates radially outward from an arc of the light source, generally along the central axis to a utilization device.
Prior art illumination systems of the foregoing type employing light sources, such as mercury or xenon lamps of the short arc type, and elliptical reflectors are commonly used in the semiconductor industry to illu-minate light integrators used with such illumination systems or other such utilization devices. However, these illumination systems are not capable of efficiently imaging reflected light from the elliptical reflector at the utilization device because the magnification o the arc of the light sources varies significantly in the azi-muthal direction across the curved surface of the ellip-tical reflector so that the field size of the lmage of the arc also varies significantly at the utili ation de~ice.
It is an object of an aspect of thls invention to provide an improved illumination system of the same general type for more efficiently imaging the reflected light at the utilization device.
According to one aspect`of this invention there is provided an illumination system comprising: a source of light dlsposed along a central axis of the illumina-tion system for radiating llght outwardly from the .
:~ ~7(:~;Z3~
central axis; a conical reflector coaxially disposed about the source of light for forming an annular virtual image of the source of light; and a lens co-axially disposed about the central axis of the illu-mination system for providing a circular real imageof the annular virtual image of the source of light.
By way of added explanationt the foregoing object is accomplished in accordance with the illus-trated preferred embodiment of the present invention by employing a light sourcet such as a mercury or xenon lamp of the short arc or capillary typet mount-ed along a central axis of the illumination system ~ J
to emit light radially outward from an arc disposed on the -la---\
~ .~'7(~2~4 central axis, and by further employing a conical reflector and a toroidal lens coaxially mounted abou~ the central axis to direct light, which emanates radially outward from the arc of the light source, symmetrically about the central axis to a utilization device. The conical reflector and the toroidal lens provide a substantially constant magnification of the arc of the light source and concomitantly a substantially constant field size of the image of the arc that may be matched to the i.nput port of the utiliza-tion device.
Brief Description of the Drawinqs Other ob~ects and features of the invention will become apparent from the following detalled description taken in combina-tion with the accompanying drawings in which:
Figuxe 1 is a cross-sectional view of an:improved illumina-tion system employing a conical reflector and a toroidal lens in accordance with the preferred embodiment of the invention;
Figure 2 is a cross-sectional view of the toroidal lens employed in the illumination system of Figure 1 with dimensional information illustrating how such a toroidal lens may be constructed;
Figure 3 is a diagrammatic view of an improved illumination system like that of Figure 1 illustrating the imaging of the light radially emanating from the light source and reflected gen-erally along the central axis of the illumination system by the conical reflector;
Figure 4 is a diagrammatic view of a prior art illumination system employing an elliptical reflector and illustrating the imaging o~ the light radially emanating from the light source and reflected along the central axis of the illumination system by the elliptical reflector;
7(~3~
Figure 5 is a plot of the percent of maximum intensity of imaged light as a function of radius in a solid line for a prior art illumination system utilizing an elliptical reflector as shown in Figure 4 and in a dashed line for an illumination system utilizing a conical reflector and a toroidal lens in accordance with the preferred embodiment of the invention as shown in Figures 1 and 3; and Figure 6 is a plot of the percent of total energy of imaged light as a function of radius in a solid line for a prior art illumination system utilizing an elliptical reflector as shown in Figure 4 and in a dashed line for an illumination system utilizing a conical reflector and a:toroidal lens in accordance with the preferred embodiment of the inventîon as shown in Figures 1 and 3.
Description of the Preferred Embodiment Referring to Figure 1, there is shown an improved illumination syst m 10 accordi.ng to the preferred embodiment sf the invention.
This illumination system 10 employs a light source 12 comprising a mercury or xenon lamp of the short arc type coaxially and fixedly mounted along a central axis 14 of the illumination system to emit light 16 radially outward from an arc 18 dispo~ed in a central region o~ the lamp along the central axis. Illumination system 10 further employs a conical reflector 20 and a toroidal lens 22 both also coaxially~and fixedly:mounted along the central axis 14 for directing:light 16, which emanates:radially outward from the arc 18 of light ource 12 and the central axis, along the central axis to an input ~ort of a utilization device 24 via a pair of mirrors 26 and 28 each fixedly mounted at an angle.of forty-five degrees with respect to the central axis~ Utilization device 24 may comprise, for example, a light integrator that is 7(~3~
utilized with illumination systems in some applications, as shown and describedr for example~ in Canadian Patent Application Serial No. 3~9,215 entitled IMPROVED STEP-AND-REPEAT PROJECTION ALIGNMENT AND EXPOSURE SYSTEM, filed on April 3, 1980. Conical reflector 20 may be formed as an integral part of a reflector and mounting member including nonconical portions for peripherally engaging and holding toroidal lens 22 in place between the conical reflector and utilization device 24. The conical reflector 20 lor the reflector and mounting member of which it is a part) and the toroidal lens 22 may each lnclude a central opening through which opposite ends of light source 12 protrude to facilitate mounting and making electrical connections to the light source.
Toroidal lens 22 may be fabricated as shown in Figure 2 where Rl is a dependent variable representing .
t~e radius of every point on the upper surface of the toroidal lens as measured from an R = O reference line coaxially passing through the toroidal lens, and where Zl is a dependent variable representing the distance of every point on the upper surface of the toroidal lens with the same value of Rl from a Z = O reference plane orthogonally intersecting the R = O reference line.
The dependent variables Rl and Zl are defined by the foliowing equations7 where gl is an independent variable representing the orthogonal distance between every point on the upper surface of the toroidal lens and a reference cone cc~xially disposed about the R = O
4--. . .
7(b~23~
reference line and def.ning an angle of 3.5 with respect to that reference line:
(1) R = 0 57795 + 0 99813p 0jO2 99~ + 0 0000948p 4 ,-:
:: : :
~:
-4a-, :
~.~ 7(~;~3~
0 40B53p
IMPROVED ILLUMINATION S~STEM
Background and Summary of the Invention This invention relates to illumination systems of the type employing a light source and a reflector coaxially mounted along a central axis of the illumination system for 5 reflecting light, which emanates radially outward from an arc of the light source, generally along the central axis to a utilization device.
Prior art illumination systems of the foregoing type employing light sources, such as mercury or xenon lamps of the short arc type, and elliptical reflectors are commonly used in the semiconductor industry to illu-minate light integrators used with such illumination systems or other such utilization devices. However, these illumination systems are not capable of efficiently imaging reflected light from the elliptical reflector at the utilization device because the magnification o the arc of the light sources varies significantly in the azi-muthal direction across the curved surface of the ellip-tical reflector so that the field size of the lmage of the arc also varies significantly at the utili ation de~ice.
It is an object of an aspect of thls invention to provide an improved illumination system of the same general type for more efficiently imaging the reflected light at the utilization device.
According to one aspect`of this invention there is provided an illumination system comprising: a source of light dlsposed along a central axis of the illumina-tion system for radiating llght outwardly from the .
:~ ~7(:~;Z3~
central axis; a conical reflector coaxially disposed about the source of light for forming an annular virtual image of the source of light; and a lens co-axially disposed about the central axis of the illu-mination system for providing a circular real imageof the annular virtual image of the source of light.
By way of added explanationt the foregoing object is accomplished in accordance with the illus-trated preferred embodiment of the present invention by employing a light sourcet such as a mercury or xenon lamp of the short arc or capillary typet mount-ed along a central axis of the illumination system ~ J
to emit light radially outward from an arc disposed on the -la---\
~ .~'7(~2~4 central axis, and by further employing a conical reflector and a toroidal lens coaxially mounted abou~ the central axis to direct light, which emanates radially outward from the arc of the light source, symmetrically about the central axis to a utilization device. The conical reflector and the toroidal lens provide a substantially constant magnification of the arc of the light source and concomitantly a substantially constant field size of the image of the arc that may be matched to the i.nput port of the utiliza-tion device.
Brief Description of the Drawinqs Other ob~ects and features of the invention will become apparent from the following detalled description taken in combina-tion with the accompanying drawings in which:
Figuxe 1 is a cross-sectional view of an:improved illumina-tion system employing a conical reflector and a toroidal lens in accordance with the preferred embodiment of the invention;
Figure 2 is a cross-sectional view of the toroidal lens employed in the illumination system of Figure 1 with dimensional information illustrating how such a toroidal lens may be constructed;
Figure 3 is a diagrammatic view of an improved illumination system like that of Figure 1 illustrating the imaging of the light radially emanating from the light source and reflected gen-erally along the central axis of the illumination system by the conical reflector;
Figure 4 is a diagrammatic view of a prior art illumination system employing an elliptical reflector and illustrating the imaging o~ the light radially emanating from the light source and reflected along the central axis of the illumination system by the elliptical reflector;
7(~3~
Figure 5 is a plot of the percent of maximum intensity of imaged light as a function of radius in a solid line for a prior art illumination system utilizing an elliptical reflector as shown in Figure 4 and in a dashed line for an illumination system utilizing a conical reflector and a toroidal lens in accordance with the preferred embodiment of the invention as shown in Figures 1 and 3; and Figure 6 is a plot of the percent of total energy of imaged light as a function of radius in a solid line for a prior art illumination system utilizing an elliptical reflector as shown in Figure 4 and in a dashed line for an illumination system utilizing a conical reflector and a:toroidal lens in accordance with the preferred embodiment of the inventîon as shown in Figures 1 and 3.
Description of the Preferred Embodiment Referring to Figure 1, there is shown an improved illumination syst m 10 accordi.ng to the preferred embodiment sf the invention.
This illumination system 10 employs a light source 12 comprising a mercury or xenon lamp of the short arc type coaxially and fixedly mounted along a central axis 14 of the illumination system to emit light 16 radially outward from an arc 18 dispo~ed in a central region o~ the lamp along the central axis. Illumination system 10 further employs a conical reflector 20 and a toroidal lens 22 both also coaxially~and fixedly:mounted along the central axis 14 for directing:light 16, which emanates:radially outward from the arc 18 of light ource 12 and the central axis, along the central axis to an input ~ort of a utilization device 24 via a pair of mirrors 26 and 28 each fixedly mounted at an angle.of forty-five degrees with respect to the central axis~ Utilization device 24 may comprise, for example, a light integrator that is 7(~3~
utilized with illumination systems in some applications, as shown and describedr for example~ in Canadian Patent Application Serial No. 3~9,215 entitled IMPROVED STEP-AND-REPEAT PROJECTION ALIGNMENT AND EXPOSURE SYSTEM, filed on April 3, 1980. Conical reflector 20 may be formed as an integral part of a reflector and mounting member including nonconical portions for peripherally engaging and holding toroidal lens 22 in place between the conical reflector and utilization device 24. The conical reflector 20 lor the reflector and mounting member of which it is a part) and the toroidal lens 22 may each lnclude a central opening through which opposite ends of light source 12 protrude to facilitate mounting and making electrical connections to the light source.
Toroidal lens 22 may be fabricated as shown in Figure 2 where Rl is a dependent variable representing .
t~e radius of every point on the upper surface of the toroidal lens as measured from an R = O reference line coaxially passing through the toroidal lens, and where Zl is a dependent variable representing the distance of every point on the upper surface of the toroidal lens with the same value of Rl from a Z = O reference plane orthogonally intersecting the R = O reference line.
The dependent variables Rl and Zl are defined by the foliowing equations7 where gl is an independent variable representing the orthogonal distance between every point on the upper surface of the toroidal lens and a reference cone cc~xially disposed about the R = O
4--. . .
7(b~23~
reference line and def.ning an angle of 3.5 with respect to that reference line:
(1) R = 0 57795 + 0 99813p 0jO2 99~ + 0 0000948p 4 ,-:
:: : :
~:
-4a-, :
~.~ 7(~;~3~
0 40B53p
(2) Z = 0.03535 + 0.06~05~1 + 1 + /1 + 0.7223pl~
Similarly, R2 is a dependent variable representing the radius of every point on the lower surface of the toroidal lens as measured from the R = 0 reference line, and Z2 i~ a dependent variable representing the distance of every point on the lo~er surface of the toroidal lens with the same value of R2 from the Z = O reference plane. The dependent variables R2 and Z2 are defined by the fol-lowing equations, where ~2 is an inde~endent variable representing the orthogonal distance between every point on the lower surface of the toroidal lens and the reference cone:
0 04271~
Similarly, R2 is a dependent variable representing the radius of every point on the lower surface of the toroidal lens as measured from the R = 0 reference line, and Z2 i~ a dependent variable representing the distance of every point on the lo~er surface of the toroidal lens with the same value of R2 from the Z = O reference plane. The dependent variables R2 and Z2 are defined by the fol-lowing equations, where ~2 is an inde~endent variable representing the orthogonal distance between every point on the lower surface of the toroidal lens and the reference cone:
0 04271~
(3) R2 = 0.51385 + 0.9981,~2 + ~2 _ + 0.0002098p2 1 + ~/1 + 0.09118p22 0.69829 2
(4) Z2 = 1.08339 ~ 0.06105p2 - ~ 0 09118 - 0.003431p2 As further shown in Figure 2, toroidal lens Z2 may have a thickness of 1.050 inches, an outer diameter of 3.800 inches, and an inner diameter (i.e., the diameter of the central opening therein) of 0.60 of an inch~ For these dimensions the upper and lower surace of the toroidal lens 22 may be defined by employing values of the independent variables Pl and ~2 ranging between -0.30 and ~1.40.
. Referring now to Figure 3j there is shown a diagrammatic view of an illumination system 10 like that of Figure 1 (without the mirrors 26 and 28). From this diagrammatic view it may be seen that conical reflector 20 ref}ects light 16, which emanates radially outward from the arc 18 disposed on the central axis 14 of the illumination system, downward rom a virtual light source or im~ge 18'of the arc in the form of an annulus symmetrically dis-posed about the central axis, Toroidal lens 22 in turn directs :~ ~L7(~;~34 the reflected light from conical reflector 20 downward and inwardsymmetrically about the central axis 14 to form real images of all portions of the annular virtual light source 18' overlaid at an image plane to form a circular field of light that may be posi-tioned coincident with the input of the utilization device. Each of these real images has the same magnification as determlned by the distance from toroidal lens 22 to the real image plane divided by the distance from the toroidal lens to the annular virtual light sour~e 18'. Thus, the circular field of light may be pro- -vided with a single size f and a numerical aperture (i.e., the sine of the angle ~ ) optimally matched to the size and required numerical aperture of the input port of the utilization device.
It has not been possible to achieve such optimum imaging with prior art illumination systems of the same general type which typically employ an elliptical reflector. As may be seen from the diagrammatic view of such an illumination system 30 shown in Figure 4, light emanating radially outward from an arc 18 disposed on a central axis 32 of the illumination system is reflected downwardly from the elliptical reflector 34 to form real images of the a~rc as viewed by different azimuthal annuli of the elliptical reflector at an image plane. Each of these real images has a different magnification as determined by the distance between the corresponding azimuthaI annulus of elliptical reflector 34 and the real image plane divided by the distance between that azimuthal annulus of the elliptical reflector and arc 18. Thus, the real images formed by the light reflected from elliptical reflector 34 range in size between f' and f'' and in numerical aperture from the sine of the angle ~' to the sine of the angle ~'' thereby maXing it impossible to optimally match the illumination system 30 to an input port of a fixed size and ~7()234 a required numerical aperture.
Assuming that it is desired to employ an improved illumina-tion system lQ such as that shown in Figure 1 with a utilization device 24 having an input port with a radius of 0.225 inch, it may be seen from Figure 5 (as shown by the dashed line) that the light provided by the illumination system is concentrated within a radius substantially equal to that of the input port of the desired utilization device. In contrast it may also be seen from Figure 5 (as shown by the solid line) that a large portion of the light provided by a prior axt illumination system 30 such as that shown in Figure 4 falls at radii greater than the radius of the input port of the desired utilization device. Thus, the intensity of the light provided within the input port of the desired utilization device by the prior art illumination system 30 is much lower than the intensity of the light provided by the lmproved illumination system 10.
5imilarly, with reference to Figure 6 (as shown by the dashed line) it may be seen that substantialLy alL of the~energy of~the light provided by an improved illumlnatlon system 10 such as that shown ln Figure 1 falls within a~radLus substantially equal to the radius of the input port of the desired utllization device.
In contrast~it may also be seen from Figure 6 (as shown by the solid line) that a large~portion~of the energy of; the~light pro-vided by a prior art illumina~ion~system 30 such as that shown in Figure 4 falls at radii greater~than~the radius of the input port of the desired utilization device~. Thus, the energy of the light provided within the i~put port of the desired utilization device by the prior art illumination sy~tem 30 is much lower than the energy of the light provided by the improved illumination system 10,
. Referring now to Figure 3j there is shown a diagrammatic view of an illumination system 10 like that of Figure 1 (without the mirrors 26 and 28). From this diagrammatic view it may be seen that conical reflector 20 ref}ects light 16, which emanates radially outward from the arc 18 disposed on the central axis 14 of the illumination system, downward rom a virtual light source or im~ge 18'of the arc in the form of an annulus symmetrically dis-posed about the central axis, Toroidal lens 22 in turn directs :~ ~L7(~;~34 the reflected light from conical reflector 20 downward and inwardsymmetrically about the central axis 14 to form real images of all portions of the annular virtual light source 18' overlaid at an image plane to form a circular field of light that may be posi-tioned coincident with the input of the utilization device. Each of these real images has the same magnification as determlned by the distance from toroidal lens 22 to the real image plane divided by the distance from the toroidal lens to the annular virtual light sour~e 18'. Thus, the circular field of light may be pro- -vided with a single size f and a numerical aperture (i.e., the sine of the angle ~ ) optimally matched to the size and required numerical aperture of the input port of the utilization device.
It has not been possible to achieve such optimum imaging with prior art illumination systems of the same general type which typically employ an elliptical reflector. As may be seen from the diagrammatic view of such an illumination system 30 shown in Figure 4, light emanating radially outward from an arc 18 disposed on a central axis 32 of the illumination system is reflected downwardly from the elliptical reflector 34 to form real images of the a~rc as viewed by different azimuthal annuli of the elliptical reflector at an image plane. Each of these real images has a different magnification as determined by the distance between the corresponding azimuthaI annulus of elliptical reflector 34 and the real image plane divided by the distance between that azimuthal annulus of the elliptical reflector and arc 18. Thus, the real images formed by the light reflected from elliptical reflector 34 range in size between f' and f'' and in numerical aperture from the sine of the angle ~' to the sine of the angle ~'' thereby maXing it impossible to optimally match the illumination system 30 to an input port of a fixed size and ~7()234 a required numerical aperture.
Assuming that it is desired to employ an improved illumina-tion system lQ such as that shown in Figure 1 with a utilization device 24 having an input port with a radius of 0.225 inch, it may be seen from Figure 5 (as shown by the dashed line) that the light provided by the illumination system is concentrated within a radius substantially equal to that of the input port of the desired utilization device. In contrast it may also be seen from Figure 5 (as shown by the solid line) that a large portion of the light provided by a prior axt illumination system 30 such as that shown in Figure 4 falls at radii greater than the radius of the input port of the desired utilization device. Thus, the intensity of the light provided within the input port of the desired utilization device by the prior art illumination system 30 is much lower than the intensity of the light provided by the lmproved illumination system 10.
5imilarly, with reference to Figure 6 (as shown by the dashed line) it may be seen that substantialLy alL of the~energy of~the light provided by an improved illumlnatlon system 10 such as that shown ln Figure 1 falls within a~radLus substantially equal to the radius of the input port of the desired utllization device.
In contrast~it may also be seen from Figure 6 (as shown by the solid line) that a large~portion~of the energy of; the~light pro-vided by a prior art illumina~ion~system 30 such as that shown in Figure 4 falls at radii greater~than~the radius of the input port of the desired utilization device~. Thus, the energy of the light provided within the i~put port of the desired utilization device by the prior art illumination sy~tem 30 is much lower than the energy of the light provided by the improved illumination system 10,
Claims (14)
1. An illumination system comprising:
a source of light disposed along a central axis of the illumination system for radiating light outwardly from the central axis;
a conical reflector coaxially disposed about the source of light for forming an annular virtual image of the source of light; and a lens coaxially disposed about the central axis of the illumination system for providing a circular real image of the annular virtual image of the source of light.
a source of light disposed along a central axis of the illumination system for radiating light outwardly from the central axis;
a conical reflector coaxially disposed about the source of light for forming an annular virtual image of the source of light; and a lens coaxially disposed about the central axis of the illumination system for providing a circular real image of the annular virtual image of the source of light.
2. An illumination system as in claim 1 wherein the lens is generated by revolving an aspheric lens section about the central axis of the illumination system.
3. An illumination system as in claim 2 wherein the lens is a toroidal lens.
4. An illumination system as in claim 1 wherein the lens is generated by revolving a lens section about the central axis of the illumination system.
5. An illumination system as in claim 4 wherein the lens is a toridal lens.
6. An illumination system as in claim 1, 2 or 3 wherein the source of light is of a mercury or xenon type.
7. An illumination system as in claim 1, 2 or 3 wherein all portions of the real image have the same magnification with respect to the source of light.
8. An illumination system as in claim 1, 2 or 3 wherein the real image is provided at the input port of a light integrator.
9. An illumination system as in claim 4 wherein all portions of the real image have the same magnification with respect to the source of light.
10. An illumination system as in claim 9 wherein the source of light is of a mercury or xenon type.
11. An illumination system as in claim 5 wherein all portions of the real image have the same magnification with respect to the source of light.
12. An illumination system as in claim 11 wherein the source of light is of a mercury or xenon type.
13. An illumination system as in claim 4 or 5 wherein the real image is provided at the input port of a light integrator.
14. An illumination system as in claim 4 or 5 wherein the source of light is of a mercury or xenon type.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000396460A CA1170234A (en) | 1982-02-17 | 1982-02-17 | Illumination system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000396460A CA1170234A (en) | 1982-02-17 | 1982-02-17 | Illumination system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1170234A true CA1170234A (en) | 1984-07-03 |
Family
ID=4122083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000396460A Expired CA1170234A (en) | 1982-02-17 | 1982-02-17 | Illumination system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1170234A (en) |
-
1982
- 1982-02-17 CA CA000396460A patent/CA1170234A/en not_active Expired
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| MKEX | Expiry |