Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-02-23
2004-10-12
Rutledge, D. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S068000, C355S069000
Reexamination Certificate
active
06803991
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an exposure amount control method, a device manufacturing method, and/or an exposure apparatus, suitably applicable to a projection exposure apparatus, for example, to be used in a lithographic process for the manufacture of semiconductor devices, liquid display devices, image pickup devices (e.g., CCDs), or thin film magnetic heads, for example. The present invention is particularly suitably applicable to a scanning exposure type projection exposure apparatus of a step-and-scan method wherein a mask and a substrate are scanningly moved in synchronism with each other and relative to a projection optical system while a portion of the mask pattern is being projected onto the substrate, by which the mask pattern is sequentially transferred to shot regions on the substrate.
FIG. 1
shows a conventional scan type projection exposure apparatus having an illumination unit for uniformly illuminating a pattern by use of light from an exposure light source, and a projection optical system for projecting the thus illuminated pattern onto a substrate. While the following description will be made on an example wherein a divergent light source such as a Hg lamp, for example, is used, the same applies to an example wherein a light source has a directionality such as a laser, for example. Denoted in
FIG. 1
at
1
is a light source, and denoted at
2
is a condensing mirror for collecting light emitted from the light source
1
. The light divergently emitted from the light source
1
is collected by the mirror
2
, and the light then passes through an optical system
3
. Then, it goes through a light attenuating unit
18
and enters an internal reflection member
4
.
The internal reflection member
4
has a structure that the light incident thereon is reflected plural times at the side face thereof, whereby the light intensity distribution being non-uniform at the light entrance surface is made uniform at the light exit surface thereof. The internal reflection member
4
may be mirrors disposed opposed to each other, or it may be simply a rod-like glass material. In the latter case, it should be designed so that, when the light impinges on the side face of the rod-like glass material, the light is totally reflected due to the difference in refractive index between the glass material and the air, and that the side face should be polished.
Denoted at
5
is an optical system for projecting a uniform intensity distribution, produced at the light exit surface of the internal reflection member
4
, onto a light entrance surface of a fly's eye lens
6
. The fly's eye lens
6
comprises a bundle of rod lenses each having a light entrance surface and a light exit surface being mutually placed at their focal points. Light rays incident on the rod lenses at the same angle are collected at the light exit surfaces of the rod lenses, such that, in total, a number of light convergence points are defined at the light exit surface of the fly's eye lens
6
.
Denoted at
7
is an optical system for uniformly illuminating an illumination region by using, as secondary light sources, the light convergence points produced at the light exit surface of the fly's eye lens
6
. In projection exposure apparatuses, it is necessary to control the illumination region and, for this reason, the illumination region is not directly illuminated but a uniform light intensity distribution is provided once at a position optically conjugate with the mask surface. Denoted at
8
is a stop for controlling the illumination region, and the position thereof is placed optically conjugate with the mask surface. A uniform light intensity distribution produced there is projected by a relay optical system
9
to illuminate a mask
10
(illumination region).
The stop
8
for controlling the illumination region is made movable, and it can be moved in accordance with the illumination region on the mask
10
. Only a set of stop components is illustrated in the drawing, but actually it comprises at least two sets of stop components. One set of them is used to restrict the exposure region on a substrate, and it moves in synchronism with the substrate at the start and the end of the exposure region. Another set is used to control the illumination region of the illumination light, and it is held fixed during the exposure. This stop is driven so as to change the width of the illumination region in the scan direction to control the exposure amount, or to change the width at each position so as to remove exposure non-uniformness in the direction perpendicular to the scan direction.
Denoted at
11
is a projection optical system for imaging a pattern, formed on the mask
10
, onto a substrate
12
. It serves to print the pattern of the mask
10
, as illuminated with uniform illumination light provided by the above-described illumination system, on a photosensitive material applied to the substrate
12
thereby to transfer the mask pattern to the substrate. The projection optical system
11
is a telecentric system such that, even with a shift of the mask
10
position or substrate
12
position in the optical axis direction, the projection magnification is unchanged. The exposure apparatus is a scan type projection exposure apparatus and, thus, the mask
10
and the substrate
12
are scanningly moved in synchronism with each other. Also, because the mask
10
moves, the illumination region changes accordingly and, therefore, the stop
8
for controlling the illumination region is also made movable.
Denoted at
13
is a movable stage on which an illuminance sensor
14
is mounted. This stage is arranged to provide scan motion for scan exposure of the substrate
12
, and stepwise motion for exposures of plural shots on the substrate. Further, it is operable to move the illuminance sensor
14
to the same position where the substrate
12
is present during the exposure process, to ensure that the sensor measures the illuminance at the same position as the substrate.
In projection exposure apparatuses for use in the manufacture of semiconductor devices, for satisfactory transfer of the pattern of the mask
10
onto the substrate
12
, it is necessary to expose the substrate
12
with a proper exposure amount which is dependent upon the photosensitive material applied to the substrate
12
and the pattern of the mask
10
. For example, when a positive pattern and a negative resist are used, an exposure with an amount less than a proper exposure amount causes insufficient printing, which leads to thinning of pattern lines or disconnection of the lines. On the other hand, an exposure amount with an amount larger than the proper exposure amount causes excessive printing, which leads to thickening of pattern lines or connection of adjacent lines. When a negative pattern and a positive resist are used, an exposure with an amount less than a proper exposure amount causes insufficient exposure, which leads to thickening of pattern lines or connection of adjacent lines. On the other hand, an exposure with an amount larger than the proper exposure amount causes excessive printing, which leads to thinning pattern lines or disconnection of lines. Anyway, an exposure with an improper exposure amount results in failure of formation of an adequate pattern on the substrate, which directly leads to a decrease of the yield.
The exposure amount in such a scan type projection exposure apparatus is “s×I/v” where s is the length of the illumination region in the scan direction, I is the illuminance on the substrate
12
, and v is the scan speed. Thus, for the control of the exposure amount in the scan type projection exposure apparatus, at least one of the length s of the illumination region in the scan direction, the illuminance I on the substrate, and the scan speed v should be controlled. The length s of the illumination region in the scan direction can be changed by moving the stop
8
for controlling the illumination region. The scan speed v can be changed by changing the scan spe
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