Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-03-11
2002-05-14
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C355S071000
Reexamination Certificate
active
06388733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus for printing a pattern formed on a mask onto a photosensitized substrate such a photoresist-coated wafer, and particularly suitable for use with such an exposure apparatus having an illumination optical system including a vibration source.
2. Description of the Related Art
There have been used various exposure apparatuses (including steppers) for a photolithographic process in the fabrication of semiconductor devices, liquid crystal displays or the like, in which a pattern on a reticle (or mask) is transferred by exposure onto each shot area on a photoresist-coated wafer (or glass plate). In a one-shot exposure type of exposure apparatus such as a stepper, in order to print a pattern formed on a reticle onto each shot area on a wafer, the reticle and the wafer have to be held almost completely stationary. For this purpose, such an exposure apparatus has its platen (or its surface block) mounted on a floor through vibration isolators so as to substantially prevent any harmful vibrations from transmitting from the floor to the platen and to the portion of the exposure apparatus on the platen (i.e, the main portion of the exposure apparatus).
Recently, exposure apparatuses using the scanning projection exposure technique (such as the step-and-scan type of exposure apparatus) have drawn engineers' attention because they enable transferring a significantly larger pattern formed on a reticle onto a wafer, without the need for a larger size of projection optical system. In the scanning projection exposure apparatus, the reticle is moved in a direction perpendicular to the optical axis of the projection optical system for scanning, while the wafer is moved in synchronism with the reticle and in a direction corresponding to the direction of the movement of the reticle for scanning, with the ratio between the velocities of the reticle and the wafer being equal to the demagnification ratio of the projection optical system, so that the pattern on the reticle is serially transferred by exposure onto the wafer. In the scanning projection exposure apparatus with such arrangement, vibration isolators have to be used to reject any harmful vibrations which would otherwise transmitted from the floor, in order to ensure that the reticle and the wafer may be moved for scanning at constant velocities with stability during the scanning exposure operation.
FIG. 5
is a schematic representation, partially cutaway, showing a typical stepper type of exposure apparatus. As shown in
FIG. 5
, the exposure apparatus has an illumination optical system
37
comprising an illumination system lens barrel
42
and other components mounted on the illumination system lens barrel
42
, the components including a light source
39
such as a mercury-vapor lamp, a relay lens
40
A, a reticle blind (field stop)
41
, condenser lens
40
B, and a cooling fan
43
with a casing
43
A covering the cooling fan
43
for introducing cooled air through a cooling-air duct
38
into the illumination system lens barrel
42
. The illumination optical system
37
comprises further components including an optical integrator, but they are not shown in the figure for simplicity. Below the illumination optical system
37
, there are disposed, from upper to lower positions in the following order, a reticle stage
27
for carrying a reticle, a projection optical system
25
, and a wafer stage
20
for carrying a wafer
22
.
The projection optical system
25
is directly mounted on a first column
124
, the reticle stage
27
is mounted to the first column
124
through a second column
126
, and the illumination system lens barrel
42
confining the components of the illumination optical system is mounted to the first column
124
through a third column
136
. The first column
124
, in turn, is fixedly mounted on a platen
106
(or a surface block
106
). The wafer stage
20
carrying the wafer
22
is also mounted on the platen
106
. The platen
106
, the wafer stage
20
, the first column
124
, the projection optical system
25
, the second column
126
and the reticle stage
27
together compose the main portion of the exposure apparatus. Accordingly, the illumination optical system
25
is mounted to the main portion of the exposure apparatus through the third column
136
.
There are disposed on the floor
1
three or four base plates (of which
FIG. 5
shows only two base plates
102
A and
102
B), on which three or four vibration isolators (of which
FIG. 5
shows only two vibration isolators
111
A and
111
B) are mounted one on each base plate, for supporting the platen
106
. The exposure apparatus further includes various alignment systems for establishing the alignment between the reticle
28
and the wafer
9
, which alignment systems are, however, not shown in the figure.
In this conventional arrangement, the illumination optical system
37
is directly connected to the main portion of the exposure apparatus, that is, an integral structure is used. This arrangement, however, generates various sorts of vibrations, one of which is the vibration produced by the cooling fan
43
for removing the heat generated by the light source
39
and transmitted to the illumination optical system
37
, and the others of which are the vibrations produced by a fan in an air conditioning system and/or by a pump for a water-cooling system. Therefore, this arrangement suffers from a drawback that such vibrations will be transferred to the stage system such as the wafer stage
20
, so that the alignment accuracy of the exposure apparatus and the positioning accuracy for positioning the stage are deteriorated thereby.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an exposure apparatus capable of positioning a wafer with precision and without being influenced by any vibrations produced for example by a cooling fan for cooling an exposure light source of an illumination optical system, by virtue of an arrangement wherein the vibrations are transferred to an independent column separate from the main portion of the exposure apparatus, and thereby the vibrations are prevented from being transferred to an alignment system and a stage system provided on the main portion of the exposure apparatus.
It is another object of the present invention to provide an exposure apparatus capable of positioning a wafer with further precision, by virtue of an arrangement wherein a misalignment detection mechanism is provided between the illumination optical system and the exposure machine main portion (which are separated from each other) for detecting any misalignment between them, and the misalignment detection mechanism is used to detect not only the vibrations produced for example by the cooling fan but also any misalignment which may be caused by the vibrations as produced by the movement of a reticle stage and/or a wafer stage, and to cancel out any of such vibrations by correction.
In order to achieve the above and other objects, according to the present invention, as shown in
FIG. 1
, there is provided an exposure apparatus for transferring a pattern formed on a mask (
28
) onto a photosensitized substrate (
22
), comprising: an illumination optical system (
37
) for illuminating the mask (
28
) with an exposure illumination beam (IL); an exposure machine main portion (
29
) serving to hold the mask (
28
) and the photosensitized substrate (
22
); and first and second support structures on which the illumination optical system (
37
) and the exposure machine main portion (
29
) are mounted, respectively, the first and second support structures being separate from each other.
In this arrangement, it may be preferable that: the second support structure on which the exposure machine main portion (
29
) is mounted comprises a vibration isolation structure (
3
A,
3
B,
4
A,
4
B,
5
A,
5
B,
6
,
7
A,
7
B,
31
A,
31
B,
32
A,
32
B,
35
A,
35
B) capable of six-degree-of-freedom position and orientation control; th
Armstrong Westerman & Hattori, LLP
Mathews Alan A.
Nikon Corporation
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