Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2001-08-07
2004-09-07
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C250S205000
Reexamination Certificate
active
06788390
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light receiving apparatus which is an image capturing apparatus which uses pulse light such as a pulsed laser as illumination light, mark detecting apparatus using the light receiving apparatus, exposing apparatus, maintenance method of exposing apparatus, manufacturing method of semiconductor device using exposing apparatus and semiconductor manufacturing plant.
BACKGROUND OF THE INVENTION
In a semiconductor manufacturing apparatus (such as an exposing apparatus) which manufactures a memory with high density or a CPU with high specification, required exposure resolution is not more than 0.20 [&mgr;m]. Thus, in order to transfer a finer pattern, a KrF laser (248 [nm]), an ArF laser (193 [nm]) and further an F
2
laser (157 [nm]) are used as exposure light sources.
As part of a positioning method of the semiconductor manufacturing apparatus, there is a need for accurately measuring a positional relationship between a reticle which is an original plate or a reticle stage (original plate stage) on which the reticle is set and a wafer stage (substrate stage). The most advantageous measuring method thereof is TTR measurement for simultaneously measuring the reticle and stage. The TTR measurement is measurement carried out via a projection lens located between the reticle and stage. For an illumination light source used in the TTR measurement, exposure light is the most suitable. The reason is that aberration of the projection lens (such as chromatic aberration) is adjusted to the exposure light, which allows the reticle and stage to be simultaneously measured.
Presently, a main illumination apparatus which can emit light with high energy and short wavelength is an apparatus with an excimer laser or the like as a light source. Such a laser is a pulse light emitting laser (pulse light emitting apparatus).
An image capturing apparatus of a pulsed laser is disclosed in Japanese Patent Laid-Open Nos. 3-226187 and 5-190421, and the apparatuses disclosed in the specifications use the following four methods to generate images with reduced illumination non-uniformity.
(1) The illumination non-uniformity of the laser is restrained by oscillating means in an illumination apparatus.
(2) The laser is synchronized with a picture synchronizing signal input in the image capturing apparatus and is controlled to have the same number of pulses during light storage.
(3) In order to reduce the illumination non-uniformity, captured electrical signals are integrated.
(4) A cycle of the oscillating means is synchronized with the cycle of image capture.
FIG. 11
is a schematic view of a configuration of a light receiving apparatus according to a conventional example. Light of a pulse laser (Laser)
14
which is a pulse light emitting apparatus is leveled (uniformed) by oscillating means
7
such as a wedge, and after passing through mirrors
4
,
5
and a half mirror
6
, illuminates a mark of a wafer
3
on a substrate stage via a projection lens
2
. After passing through the mirror
5
and half mirror
6
via the projection lens
2
, the reflected light from the mark an image is imaged by a CCD camera (cam)
8
which is a storage-type position sensor. A synchronizing signal of the CCD camera
8
is generated by a synchronizing signal generator (Sync)
15
. At the same time, the synchronizing signal is sent to the oscillating means
7
and laser (Laser)
14
to synchronize the CCD camera
8
, oscillating means
7
and laser
14
.
In
FIG. 11
, reference numeral
1
denotes a reticle;
9
, driving means (motor);
10
, an interferometer (inter);
11
, a stage control apparatus (SF); and
12
, an exposure control apparatus (com). Further, reference numeral
13
denotes a oscillating control apparatus (IS Cont);
16
, an A/D converter; and
18
, a control section for an image processing apparatus.
The CCD camera
8
, which is of an NTSC system, stores light divided between even/odd timing, and as shown in
FIG. 12
, an oscillating cycle is adjusted to a cycle corresponding to an integral multiple of even/odd fields.
FIG. 12
is an explanatory view of timing of the oscillating means, laser light emitting and image storing according to the conventional example.
In the conventional example, stored image data are added by an adder (sum)
17
shown in
FIG. 11
, and in
FIG. 12
, images of three or six frames are combined to generate images for measurement.
However, scan exposure has come to be carried out, which has caused the need for synchronizing the oscillating means with a scanning speed. That is, in the scan exposure, a resist on the wafer is irradiated with the light of the pulse laser as if a slit scanned over the wafer (substrate). In order to carry out exposure without illumination non-uniformity within a scanning area, exposure must be carried out in such a manner that a certain point on the wafer is irradiated with pulse light for one cycle or n cycles (n: natural number) of the oscillating means in a time period during which the point moves across the width of the slit. Thus, an increased scanning speed requires increased oscillation frequency of the oscillating means. The scanning speed is inversely proportional to energy for exposing the resist on the wafer, and an increased amount of exposure requires increased number of laser pulses (energy). Oscillation frequency of the laser is fixed (generally largest), so that a reduced scanning speed controls the oscillation frequency of the laser. In this way, for accommodating the scan exposure, the oscillating means must change an oscillation amount (oscillation frequency) in accordance with the scanning speed (exposure amount).
In case of storing the pulse light by the CCD camera of the NTSC system, the exposure time is limited to {fraction (1/60)} second. When the storage time is limited, oscillation by the oscillating means must be adjusted to an integral multiple of {fraction (
1
/
60
)} second in order not to produce illumination non-uniformity and not to cause even/odd difference at any time in imaging by an interlace system with even/odd time division specific to the NTSC system.
There is an optimum oscillation frequency requested in according with terms of the scanning speed, while the oscillation frequency must be adjusted separately in accordance with terms of the measurement, and each measurement requires control of the oscillating means. Generally, for changing in a short time an operation speed of an object moving at a high speed, control time for about a few second is required under the influence of inertia. In order to reduce the time to a few milliseconds, control means with high performance must be used. For this purpose, there is also a configuration which has oscillating means dedicated to measurement separately from the oscillating means for scanning.
However, the problem of the configuration is that the size of the illumination apparatus is increased and that double optical members for forming each oscillating means are required. Further, part of the light emitted from the light source must be directed to an optical system dedicated to measurement, which reduces illumination intensity for pattern exposure. Accordingly, the optimum configuration is such that part of an illumination system of a scan exposure system is utilized without making a dedicated optical system.
The TTR measurement is a measuring system which is used in calibration of a stage position and reticle position, calibration of a projection lens, or the like, and the measurement is carried out using wafer replacement time or the like. However, a recent exposing apparatus has the shortest wafer replacement time to increase throughput (wafer processing capacity per unit of time). In the measurement carried out in the wafer replacement, dead time of the apparatus is used until the oscillating means is stabilized.
The conventional system has a problem that the oscillating means must be controlled for image capture for measurement, which has influence on the throughput of the
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mathews Alan
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