Illumination – Light source and modifier – Including reflector
Reexamination Certificate
1999-07-22
2001-08-28
Husar, Stephen (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S296040, C362S347000
Reexamination Certificate
active
06280062
ABSTRACT:
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 and 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 of 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.
REFERENCES:
patent: 3669524 (1972-06-01), Shio
patent: 4497013 (1985-01-01), Ohta
patent: 4530578 (1985-07-01), Kato
patent: 4682885 (1987-07-01), Torigoe
patent: 4734829 (1988-03-01), Wu et al.
patent
Mori Tetsuya
Shima Shinichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Husar Stephen
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