Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2000-07-05
2002-08-20
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C355S052000, C355S053000, C355S055000, C356S399000, C356S400000, C356S401000
Reexamination Certificate
active
06437354
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 10-13431 filed Jan. 7, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure method and a scanning-type exposure apparatus utilized in a photolithography process implemented to manufacture semiconductor devices, liquid crystal display devices, thin-film magnetic heads or the like, and more specifically, it relates to an exposure method and a scanning-type exposure apparatus that are ideal in application for exposing a substrate that has become deformed during the manufacturing process.
2. Related Art
The use of liquid crystal display devices as display elements in personal computers, television sets and the like has become increasingly extensive in recent years. Such a liquid crystal display device is manufactured by laminating a plurality of pattern layers constituting transparent electrode layers and switching elements on a glass substrate. These pattern layers are patterned through photolithography. During the photolithography process implemented to manufacture a liquid crystal display device, a projection exposure apparatus that projects an image of an original pattern formed on a mask onto the glass substrate via a projection optical system and transfers the pattern onto the glass substrate by photosensitizing a photoresist layer applied on the glass substrate, for instance, is utilized.
An example of such a projection exposure apparatus is now explained in reference to
FIGS. 12 and 13
, which illustrate a scanning-type exposure apparatus that performs exposure processing on a glass substrate (plate).
FIG. 12
is a perspective illustrating a schematic structure of a scanning-type exposure apparatus in the prior art.
FIG. 13
illustrates an alignment operation performed to align the mask and the plate in the scanning-type exposure apparatus in the prior art shown in FIG.
12
.
In
FIG. 12
, a plate
22
is held at one sidewall of a carriage
21
having its cross section formed in a U shape and a mask
23
is held at the other sidewall. The pattern in a partial area of the mask
23
held by the carriage
21
is illuminated by exposing light irradiated from an illumination system
24
and as the exposing light having been transmitted through the mask
23
is transmitted through a projection optical system
25
, the pattern at the partial area of the mask
23
is transferred onto an area on the plate
22
. During such an operation, the carriage
21
is caused to travel over a guide
20
in a specific direction A (the scanning direction) so that the pattern in the entire area on the mask
23
is transferred onto the plate
22
.
During the exposure operation described above, the projected image of the pattern formed at the mask
23
and the pattern layer that is already formed on the plate
22
must be accurately aligned with each other. Accordingly, an alignment operation is performed to align the mask
23
and the plate
22
.
In order to implement this alignment operation, alignment marks formed on the mask
23
and alignment marks formed on the plate
22
are observed with alignment microscopes
26
and
27
to correct the positional relationship between the mask
23
and the plate
22
by detecting any positional misalignment between them. The plate
22
and the mask
23
are each provided with a plurality of alignment marks formed at the two ends along direction Y, which are formed to extend along direction X, and one or a plurality of these alignment marks are observed through the alignment microscope
26
or
27
. Based upon the results of detections performed by using the alignment microscopes
26
and
27
, the position of the plate
22
relative to the mask
23
, the size of the plate
22
relative to the mask
23
and the like are ascertained, and using such information, the position of the mask
23
is adjusted or the magnification power of the projection optical system
25
is corrected.
For instance, if it is detected through the alignment microscopes
26
and
27
mentioned above that the plate
22
and the mask
23
are offset from each other in parallel along direction X and direction Y, as illustrated in FIG.
13
(
a
), the mask
23
is caused to move in parallel over a specific distance by driving an actuator
28
that moves a mask table
32
holding the mask
23
along direction X and driving two actuators
29
and
30
that move the mask table
32
along direction Y (shift correction).
In addition, if there is a rotational misalignment between the plate
22
and the mask
23
around the Z axis, as illustrated in FIG.
13
(
b
), the mask
23
is caused to rotate by a specific quantity by varying the degrees to which the actuators
29
and
30
are driven (rotation correction). If the sizes of the mask
23
and the plate
22
do not match relative to each other, as illustrated in FIG.
13
(
c
), the magnification power of the projection optical system
25
is corrected along direction Y and the magnification power along direction X is corrected by driving the actuator
28
along direction X to move the mask
23
indirection X while the carriage
21
is engaged in a scanning movement and change the relative scanning speed of the mask
23
and the plate
22
by a specific degree (scaling correction).
In more specific terms, if the plate
22
extends along direction X by 4 ppm, for instance, the actuator
28
must be driven to move the mask
23
by 4 ppm in the opposite direction from the scanning direction as the carriage
21
engages in a scanning operation.
It is to be noted that the alignment marks at the mask
23
are formed in advance when the mask is formed, whereas the alignment marks at the plate
22
are normally formed during the initial exposure processing.
A plate that is delivered to a projection exposure apparatus to be exposed usually undergoes a plurality of heat treatments during the process and undergoes repeated exposure of the original pattern over a plurality of layers. Expansion or contraction of the plate mainly attributable to the heat treatments implemented in the process may result in deformation of the plate. For instance, after the plate undergoes various process, a plate having a rectangular planar shape with individual sides each extending almost linearly, as illustrated in FIG.
14
(
a
), may become warped with a curvature along direction Y as illustrated in FIG.
14
(
b
) or become deformed into a parallelogram shape, as illustrated in FIG.
14
(
c
).
When exposing a plate that has become deformed, as illustrated in FIG.
14
(
b
) or FIG.
14
(
c
), the degree of deformation along direction Y successively changes as it travels along direction X for scanning during an exposure operation, and this poses a problem in that full alignment correction cannot be achieved through the shift correction, the rotation correction or the scaling correction in the prior art. A pattern that is exposed without an accurate alignment manifests a significant alignment overlay error relative to the base pattern, which results in a problem in that the characteristics of numerous elements formed on the plate become inconsistent among the individual areas of the plate.
An object of the present invention is to provide an exposure method and a scanning-type exposure apparatus that achieve accurate alignment for a deformed substrate.
SUMMARY OF THE INVENTION
The object described above is achieved with an exposure method for exposing a substrate with a pattern formed on a mask by synchronously moving the mask and the substrate, comprising a step in which any change in the shape of the substrate is detected and a step in which the relative positions of the mask and the substrate are corrected during the synchronous movements based upon the results of the detection results.
In addition, in the exposure method according to the present invention, the pattern on the mask may be projected onto the substrate by a projection optical system. Also, in the correction s
Kato Hirokazu
Nara Kei
Ho Allen C.
Nikon Corporation
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