Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2000-11-02
2004-05-25
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S626000, C359S625000, C359S628000
Reexamination Certificate
active
06741394
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavefront dividing type optical integrator; an illumination optical apparatus comprising this optical integrator; and an illumination optical apparatus suitable for exposure apparatus, observation apparatus (microscopes), and the like using this illumination optical apparatus.
2. Related Background Art
In a typical exposure apparatus for making micro devices such as semiconductor device, imaging picking device, liquid crystal display device, and thin film magnetic head, a beam emitted from a light source is incident on a micro fly's eye lens, and a secondary light source composed of a number of light sources is formed on the image-side focal plane thereof. Beams from the secondary light source are made incident on a condenser lens after being restricted by an aperture stop disposed near the image-side focal plane of the micro fly's eye lens.
The Beams collected by the condenser lens illuminate, in a superimposing manner, a mask formed with a predetermined pattern. The light transmitted through the pattern of mask forms an image on a photosensitive substrate by way of a projection optical system. Thus, a mask pattern is projected (transferred) onto the photosensitive substrate. The pattern formed in the mask is highly integrated. As a consequence, for accurately transferring this fine pattern onto a photosensitive substrate, it is indispensable that a uniform illuminance distribution be obtained on the photosensitive substrate.
The micro fly's eye lens is a wavefront dividing type optical integrator composed of a number of micro lenses densely arranged in a matrix. In general, the micro fly's eye lens is constructed by etching a plane-parallel glass sheet, for example, so as to form a micro lens group. Here, each micro lens constituting the micro fly's eye lens is smaller than each lens element constituting a fly's eve lens.
SUMMARY OF THE INVENTION
As mentioned above, it is indispensable for a photolithgrahic exposure apparatus for transferring a fine pattern onto a photosensitive substrate to yield a uniform illuminance distribution on the mask and/or on the photosensitive substrate. Reducing the unevenness in illuminance, it has been desired to increase the number of micro lenses micro optical elements constituting the micro fly's eye lens (micro fly's eye optical member), i.e., to increase the number of divisions of wavefront.
On the other hand, when making a micro fly's eye lens by etching and the like, the glass sheet is harder to etch deeply, and the making will be easier if the size of each micro lens is made smaller. However, simply reducing the size of each micro lens is disadvantageous in that illuminance decreases by the amount of diffraction limit with respect to the entrance surface of each micro lens in marginal areas of an illumination field formed on a surface to be irradiated which is optically conjugate with the entrance surface.
It is an object of the present invention to provide a wavefront dividing type optical integrator which can yield a uniform illuminance distribution substantially over the whole illumination field formed thereby even when the size of each micro lens is made smaller so as to set a large number of wavefront divisions; an illumination optical apparatus comprising this optical integrator; and a photolithgrahic exposure apparatus and-observation apparatus comprising this illumination optical apparatus.
The optical integrator in accordance with a first aspect of the present invention is a wavefront dividing type optical integrator, having a number of micro lenses (micro optical elements) arranged two-dimensionally, for forming a number of light sources by dividing a wavefront of an incident beam; each micro lens having a rectangular entrance surface and a rectangular exit surface, and satisfying at least one of the following conditions:
(
d
1
/2)(
D
1
/2)/(&lgr;·
f
)≧3.05
(
d
2
/2)(
D
2
/2)/(&lgr;·
f
)≧3.05
where f is the focal length of each micro lens, d
1
is the length of one side of the entrance surface of each micro lens, d
2
is the length of the other side of the entrance surface of each micro lens, D
1
is the length of the side of exit surface in each micro lens corresponding to the one side of entrance surface, D
2
is the length of the side of exit surface in each micro lens corresponding to the other side of entrance surface, and ë is the wavelength of the incident beam.
The optical integrator may be characterized in that the length d
1
of the one side of entrance surface is longer than the length d
2
of the other side of entrance surface, and the condition of
(
d
1
/2)(
D
1
/2)/(&lgr;·
f
)≧3.05
is satisfied.
The optical integrator in accordance with a second aspect of the present invention is a wavefront dividing type optical integrator, having a number of micro lenses (micro optical elements) arranged two-dimensionally, for forming a number of light sources by dividing a wavefront of an incident beam; each micro lens having a rectangular entrance surface and a circular or regular hexagonal exit surface, and satisfying at least one of the following conditions:
(
d
1
/2)(
D
/2)/(&lgr;·
f
)≧3.05
(
d
2
/2)(
D
/2)/(&lgr;·
f
)≧3.05
where f is the focal length of each micro lens, d
1
is the length of one side of the entrance surface of each micro lens, d
2
is the length of the other side of the entrance surface of each micro lens, D is the diameter of the circular exit surface or the diameter of a circle circumscribing the regular hexagonal exit surface of each micro lens, and ë is the wavelength of the incident beam.
The optical integrator may be characterized in that the length d
1
of the one side of entrance surface is longer than the length d
2
of the other side of entrance surface, and the condition of
(
d
1
/2)(
D
1
/2)/(&lgr;·
f
)≧3.05
is satisfied.
The optical integrator in accordance with a third aspect of the present invention is a wavefront dividing type optical integrator, having a number of micro lenses (micro optical elements) arranged two-dimensionally, for forming a number of light sources by dividing a wavefront of an incident beam; each micro lens having a circular entrance surface with a diameter of d or a regular hexagonal entrance surface inscribed in a circle having a diameter of d, and satisfying the following condition:
(
d
1
/2)2/(&lgr;·
f
)≧3.05
where f is the focal length of each micro lens, and ë is the wavelength of the incident beam.
The illumination optical apparatus in accordance with a fourth aspect of the present invention is an illumination optical apparatus for illuminating a surface to be irradiated according to a beam from a light source, the illumination optical apparatus comprising the optical integrator, disposed in an optical path between the light source and the surface to be irradiated, for forming a number of light sources according to a luminous beam the light source; and a light-guiding optical system, disposed in an optical path between the optical integrator and the surface to be irradiated, for guiding beams from a number of light sources formed by the optical intergrator to the surface to be irradiated.
In the illumination optical apparatus, the light-guiding optical system may comprise a condenser optical system, disposed in the optical path between the optical integrator and the surface to be irradiated, for condensing beams from a number of light sources formed by the optical integrator so as to form an illumination field in a superimposing manner; an image forming optical system, disposed in an optical path between the condenser optical system and the surface to be irradiated, for forming an image of the illumination field near the surface to be irradiated according to a beam from the illumination field; and an aperture stop, disposed in an optical path of the image forming optical system at a position substantially optically conjugate with a position where the light sources are formed, for blocking an unnecessary beam.
Kudo Yuji
Shibuya Masato
Tanitsu Osamu
Toyoda Mitsunori
Mack Ricky
Nikon Corporation
Oliff & Berridg,e PLC
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