Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-05-08
2002-01-01
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S066000, C355S071000, C362S298000, C359S850000, C359S864000
Reexamination Certificate
active
06335786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus for use in transferring a pattern formed on a mask onto a substrate in a lithography process for manufacturing semiconductor elements, image pickup elements (CCDs, etc.), liquid crystal display elements, thin-film magnetic heads, and the like. The exposure apparatus is particularly appropriate for use as an exposure apparatus for perform a so-called modified illumination.
2. Description of the Related Art
Hitherto, projection exposure apparatuses (steppers) of a batch exposure type have been extensively used which are designed to illuminate a reticle as a mask with an exposing illumination light from an illumination optical system and to project the mask pattern formed on the reticle as a reduced image onto each of shot regions on a wafer (or a glass plate, etc.) as a substrate, with a photoresist coated thereon, through a projection optical system. In recent years, attention has also been drawn to a projection exposure apparatus of a scanning exposure type (a scanning exposure apparatus), such as an exposure apparatus of a step-and-scan system that is capable of executing exposure by transferring a reticle and a wafer in synchronism with each other at a projection magnification that is set as a speed ratio, in order to transfer a pattern having a large area onto each shot region on the wafer with high precision without making a projection optical system larger in size.
For those conventional exposure apparatuses, a higher uniformity of the distribution of illumination is required so that line widths of a pattern image of the reticle to be transferred onto the wafer is made uniform in an illumination area of the projection optical system. In conventional techniques, an optical integrator including a fly-eye lens or a rod lens, etc. is disposed in an illumination optical system, in order to make the distribution of illumination uniform. When the fly-eye lens is adopted as an optical integrator, the plane of the fly-eye lens from which light leaves is typically set so as to form a plane that has a Fourier transform relationship with respect to the pattern plane of the reticle on which the pattern is formed (that is, a so-called “pupil plane”).
Moreover, recently, higher resolution has been demanded. A simple increase in a numerical aperture of a projection optical system in an attempt to meet the requirement has the drawback that the depth of focus becomes shallower in inverse proportion to the second power of the numerical aperture. In order to overcome this problem, illumination optical system have been developed which utilize modified illumination techniques with a view to improving resolution and providing an increase in the depth of focus. Such systems are disclosed, for example, in Japanese Patent Application Laid-open No. 4-225,514 and a European counterpart, i.e., European Patent Application Publication No. (EP) 0 486 316 A2 (1992). This technique involves limiting a scope of an angle of incidence of an illumination light irradiated onto a reticle to a predetermined value. More specifically, the limitation is realized by locating a stop on a pupil plane, to thereby restrict a shape in section of an illumination flux. As the pupil plane is an optical Fourier transform plane for a pattern plane of the reticle, a scope of the angle of incidence of the illumination light on the pattern plane can be restricted by limiting the position of the illumination light passing through the pattern plane.
In the conventional modified illumination technique as described above, the illumination light flux is partially shaded on the pupil plane and the sectional shape thereof is restricted. Therefore, as a matter of course, this technique suffers from the disadvantage that illuminance of the illumination light decreases by an amount corresponding to the quantity of light cast in shade. This naturally leads to a decrease in the amount of light energy reaching a wafer. Consequently, a long exposure time is required to gain an appropriate quantity of exposure that is defined in accordance with a resist sensitivity. As a result, a throughput of the exposure apparatus involved is decreased.
SUMMARY OF THE INVENTION
The present invention has been completed to overcome the problems inherent in the conventional exposure apparatuses, and it has as its the object the provision of an exposure apparatus that is capable of attaining a high level of uniformity in a distribution of illuminance upon carrying out modified illumination or the like, and that can suppress a decrease in illumination of an illumination light.
The present invention has another objects to provide a method for manufacturing of the exposure apparatus and a method for device such as semiconductor elements and so on by using the exposure apparatus.
A first exposure apparatus in a first embodiment of the present invention is directed to an exposure apparatus that transfers a pattern formed on a mask R onto a substrate via a projection optical system PL under an exposing illumination light from an illumination optical system. The exposure apparatus comprises an illuminance-uniformity optical system
3
A which includes a first reflecting member
34
having an outer plane consisting of two reflecting planes
34
a
and
34
b
in a planar form on the outer side of a columnar body, and a second reflecting member
33
having an inner plane facing the outer plane of the first reflecting member, which constitutes a reflecting plane
33
a
in a planar form on the inner side of a cylindrical body, and which is located within the illumination optical system. The illumination light passes through a clearance provided between the reflecting planes of the two reflecting members.
The exposure apparatus according to the present invention provides a uniform distribution of illumination light upon passage of the illumination light through a clearance provided between the reflecting planes of the two reflecting members
33
and
34
, by way of multiple reflections or the like. After passage of the illumination light between the two reflecting members, substantially modified illumination is carried out by irradiating the illumination light onto the mask, the shape of which in section is in the form of a ring or in a form having plural apertures, or the like. Upon irradiation, the illumination light is not subject to any shading thus preventing any decreases in illuminance on the mask or substrate.
It is preferable for the two reflecting members
33
and
34
to be disposed in series with an optical integrator containing either a fly-eye lens
35
or a rod lens
45
being provided. This configuration enables increased uniformity of distribution of illuminance.
Furthermore, it is preferred that a plurality of illuminance-uniformity optical systems
3
A and
3
B are disposed so as to be shifted to enable shapes of the reflecting planes
34
a
and
34
b
of the first reflecting member
34
or a reflecting plane
38
a
of a first reflecting member
38
to be made to differ from one another. The shifting of the illuminance-uniformity optical systems
3
A and
3
B enables the use of illumination, such as a ring form illumination or illumination by means of a plurality of secondary light sources, in accordance with the type of patterns on a mask.
Moreover, it is preferred that the optical integrator
3
C containing either the fly-eye lens or the rod lens be disposed in a row with the illuminance-uniformity optical systems so as to enable shifting relative to each other. This configuration can also to be used to carry out ordinary illumination.
By way of example, the first reflecting member
34
may have the reflecting plane in the form of a conical plane
34
b
on its light-entering plane side and in the form of a columnar plane
34
a
on the plane side extending therefrom. In this case, it is preferable that transparent spacers
51
and
52
each in a ring form be disposed between the first and second reflecting members
34
and
33
. The light-entering
Adams Russell
Fuller Rodney
Nikon Corporation
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