Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1998-11-05
2003-03-11
Nguyen, Hung Henry (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C355S077000
Reexamination Certificate
active
06532056
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an alignment system and a projection exposure apparatus with the same. The present invention is suitably usable in a lithographic process for the manufacture of semiconductor devices or other devices such as CCD's or liquid crystal displays, for example, for lithographically transferring or imagewise projecting a pattern of a reticle or mask onto a substrate directly or through a projection optical system in a step-and-repeat or step-and-scan method.
In projection exposure apparatuses for the manufacture of semiconductor devices, for example, increases in density of an integrated circuit have necessitated that a circuit pattern formed on a reticle be projected and printed on a wafer (substrate) with higher resolution.
At the same time, due to miniaturization of a circuit pattern, it is required that a wafer and a reticle having an electronic circuit pattern formed thereon be aligned with each other very precisely. Generally, as an alignment method for the reticle and the wafer, there is a baseline method wherein positional information about an alignment mark provided on a wafer is detected (observed) through an alignment microscope (alignment scope).
This method contains a factor for an error of reticle-to-wafer alignment, called a baseline error, which is an error related to baseline measurement.
FIG. 1A
is a schematic view of a main portion of a conventional projection exposure apparatus, and
FIG. 1B
is a schematic view of a portion of FIG.
1
A. The baseline measurement will be described briefly, with reference to these drawings.
In
FIGS. 1A and 1B
, a reticle
1
is held on a reticle stage
6
by attraction. The projection exposure apparatus is equipped with a reticle reference mark
19
which is positioned exactly with respect to a projection optical system
7
and which is to be used for aligning the reticle
1
with respect to a predetermined position. Second mark detecting means
18
has a detection region at a predetermined position within the projection field of the projection optical system
7
, and it serves to optically detect, within this detection region, the positional relation between the reticle
1
and the reticle reference mark
19
as well as the relative positional relation between a second reticle mark
5
, provided on the reticle
1
, and a second reference mark
14
formed on a substrate stage
11
. The second mark detecting means
18
includes moving means. By use of this second mark detecting means
18
and with reference to the reticle reference mark
19
, a first reticle mark
4
provided on the reticle
1
is moved into registration with the reticle reference mark
19
, and registration is measured. This is called a first measurement. On the basis of the result of this measurement, a deviation between the reticle
1
and the reticle reference mark
19
is detected.
A reference mark plate
12
is provided in a portion of the reticle stage
11
, and it has formed thereon a first reference mark
13
which can be detected through first mark detecting means
17
and a second reference mark
14
which can be detected through the second mark detecting means
18
. These first and second reference marks
13
and
14
are disposed with a certain interval corresponding to positions of the detecting regions of the first and second mark detecting means
17
and
18
. The substrate stage
11
is moved and positioned so that the second reticle mark
5
on the reticle
1
and the second reference mark
14
on the reference mark plate
12
can be detected through the second mark detecting means
18
. After such positioning, a relative positional deviation between the second reference mark
14
and the detection center of the second reticle mark
5
is measured, and the deviation is memorized as a deviation of a relative position of the reticle
1
and the substrate stage
11
. This is called a second measurement.
Then, a deviation between the detection center of the first mark detecting means
17
and the first reference mark
13
on the reference plate
12
is measured. This is called a third measurement.
From the results of the first to third measurements, the relative distance between the reticle reference mark
19
and the detection center of the first mark detecting means
17
is taken as a baseline, and a relative positional deviation detected by measurement is determined as a baseline correction value.
As described, in conventional projection exposure apparatuses, first the relative position between a first reticle mark
4
of a reticle
1
and a reticle reference mark
19
, positioned accurately with respect to a projection optical system
7
for alignment of the reticle
1
with respect to a predetermined position, is detected (first measurement). Second, the relative position between a second reticle mark
5
of the reticle
1
and a second reference mark
14
formed on a reference mark plate
12
, provided in a portion of a substrate stage
11
, is detected (second measurement). Third, the relative position between a first reference mark
13
, having predetected positional relation with the first reference mark
14
on the reference mark plate
12
, and the detection center of first mark detecting means
17
capable of optically detecting a mark on the substrate stage
11
and having its detection center positioned at a predetermined distance from the optical axis of the projection optical system
7
, is detected (third measurement). From the results of these three detections, the distance between the detection center of the first mark detecting means
17
and the reticle reference mark
19
, for alignment of the reticle with a predetermined position, is detected as a baseline, and it is memorized into a storing medium.
The baseline measurement in conventional projection exposure apparatuses is performed with the intervention of a reticle. This creates a possibility that an error of reticle patterning causes a baseline error. It necessitates preparation of reticles to be used exclusively with a particular projection exposure apparatus. This is very inconvenient. In other words, performing baseline measurement through a peculiar reticle to be used with a particular projection exposure apparatus, necessitates that the baseline measurement and stage correction measurement are executed after that reticle is loaded at a predetermined position in the exposure apparatus. This requires complicated operations for exposure apparatus control and for reticle control, and numerous operations have to be involved in the exposure apparatus operation.
Further, the relative distance between the reticle reference mark
19
and the detection center of the first mark detecting means
17
is detected as a baseline length, on the basis of the three measurements made to (i) the reticle
1
and the reticle reference mark
19
, (ii) the reticle
1
and the substrate stage
11
, and (iii) the substrate stage
11
and the detection center of the first mark detecting means
17
. Each of these three measurements may contain a measurement error. Therefore, there is a certain limitation to precision improvement in the baseline measurement. Further, the necessity of three measurements produces a certain limitation to improvement of the baseline measurement speed.
Baseline measurement using a reticle peculiar to a particular exposure apparatus means that the baseline measurement is unattainable if a reticle loaded is different or when no reticle is loaded in the exposure apparatus. This provides a certain limitation to the reduction of operation time for baseline measurement or to baseline measurement control.
Furthermore, baseline measurement or stage running correction measurement cannot be performed if a reticle is placed at a predetermined position within the exposure apparatus. This applies an adverse effect to throughput of the whole exposure apparatus.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved alignment system and/or an improved projection exposure apparatus b
Kodachi Nobuhiro
Osakabe Yuichi
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