Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2001-11-20
2004-03-16
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C356S399000
Reexamination Certificate
active
06707533
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a detection apparatus capable of detecting the position of an object or the like at high precision, an exposure apparatus having the detection apparatus, and a device manufacturing method using the detection and exposure apparatuses. The present invention is preferable when the position of an object such as a wafer is detected at high precision by observing an image on the object, and the object is aligned based on the detection information in an exposure apparatus for manufacturing various devices such as a semiconductor IC, LSI, CCD, liquid crystal panel, and magnetic head.
BACKGROUND OF THE INVENTION
Along with the recent remarkable development of semiconductor element manufacturing techniques, the progress of micropatterning techniques is also prominent. As an optical processing technique, reduction projection exposure apparatuses generally called steppers having submicron resolutions are mainstream. For higher resolutions, a larger numerical aperture (NA) of an optical system and a shorter exposure wavelength are being realized.
As the exposure wavelength decreases, the exposure light source is shifting from high-pressure mercury lamps of g-line and i-line to KrF and ArF excimer lasers.
As the resolution of a projection pattern increases, high precision is also demanded for relative alignment between a wafer and a mask (reticle) in a projection exposure apparatus. The projection exposure apparatus needs to function not only as a high-resolution exposure apparatus but also as a high-precision position detection apparatus.
For this purpose, high performance is required for a position detection apparatus, also called an alignment scope, for detecting an alignment mark on a substrate such as a wafer.
As the form of the alignment scope, there are roughly proposed two methods. One form of an alignment scope is a so-called off-axis alignment detection system (Off-Axis AA; to be simply referred to as an “OA” hereinafter), which is separately disposed without the mediacy of a projection exposure optical system and optically detects an alignment mark.
The other one of the conventional methods is a method of detecting an alignment mark on a wafer by using the alignment wavelength of non-exposure light via a projection optical system called a TTL-AA (Through The Lens Automatic Adjustment).
In either alignment scope, the aberration of the alignment scope generates a position detection error. This aberration must be minimized, or the generated aberration must be corrected.
A projection exposure optical system having a conventional OA detection system will be described with reference to the schematic view of FIG.
3
.
Light IL emitted by an exposure illumination optical system
1
including an exposure light source (as the light source, a mercury lamp, a KrF excimer laser, an ArF excimer laser, or the like may be used) illuminates a mask (reticle)
2
having a pattern. At this time, the reticle
2
is aligned in advance by reticle holders
12
and
12
′ such that an alignment detection system
11
above (or below) the reticle
2
makes the center of the reticle pattern coincide with an optical axis AX of a projection exposure optical system
3
.
The light having passed through the reticle pattern transfers the image of the reticle pattern onto a wafer
6
held on a wafer stage
8
at a predetermined magnification via the projection exposure optical system
3
. Note that an exposure apparatus for irradiating the reticle
2
with irradiation light from above the reticle
2
and sequentially exposing the wafer
6
to reticle pattens at a fixed position is called a stepper. An exposure apparatus for relatively moving the reticle
2
and wafer
6
(the moving amount of the reticle
2
is the product of the moving amount of the wafer
6
by a projection magnification) is called a scanner (scanning exposure apparatus).
A kind of wafer
6
is called a second wafer already bearing a pattern. To form the next pattern on this wafer, the position of the formed pattern must be detected. This position detection method includes the TTL-AA method and OA detection method described above.
An alignment scheme having an OA detection system will be explained based on FIG.
3
. As shown in
FIG. 3
, an OA detection system
4
is arranged separately from the projection exposure optical system
3
. The wafer stage
8
is driven based on an output from an interferometer
9
capable of measuring a lateral distance. The wafer
6
is aligned in the observation region of the OA detection system
4
. The OA detection system
4
detects the position of an alignment mark AM formed on the wafer
6
aligned based on the output from the interferometer
9
, thereby obtaining layout information of chips (elements) formed on the wafer
6
.
The wafer stage
8
is driven to the exposure region of the projection exposure optical system
3
(transfer region of the reticle) on the basis of the chip (element) layout information. Then, the wafer
6
is sequentially exposed.
A focus detection system
5
for measuring the focus direction of the projection exposure optical system
3
is generally located in the exposure region of the projection exposure optical system
3
. In the focus detection system
5
, a slit pattern
503
is illuminated via an illumination lens
502
with light emitted by an illumination light source
501
. The light having passed through the slit pattern
503
forms the slit pattern on the wafer
6
via an illumination optical system
504
and mirror
505
.
The slit pattern projected on the wafer
6
is reflected by the surface of the wafer
6
, and enters a mirror
506
and detection optical system
507
arranged on a side opposite to the illumination system. The detection optical system
507
forms the slit image of the wafer
6
on a photoelectric conversion element
508
again. As the wafer
6
vertically moves, the slit image on the photoelectric conversion element
508
moves. From this moving amount, the distance of the wafer
6
in the focus direction can be measured. A plurality of such slits (points on the wafer
6
) are prepared, and used one by one to detect focus positions at a plurality of positions on the wafer
6
. As a result, the inclination of the wafer
6
with respect to the image plane of the reticle image of the projection exposure optical system
3
can be measured.
The OA detection system will be described with reference to the schematic view of FIG.
4
.
In
FIG. 4
, light emitted by an illumination light source
401
(fiber or the like) is guided to a polarization beam splitter
403
via an illumination optical system
402
. S-polarized light reflected by the polarization beam splitter
403
in a direction perpendicular to the sheet surface of
FIG. 4
passes through a relay lens
404
and &lgr;/4 (quarter-wave plate)
409
. Then, the S-polarized light is converted into circularly polarized light to Köhler-illuminate the alignment mark AM on the wafer
6
via an objective lens
405
.
Reflected light, diffracted light, and scattered light from the alignment mark AM return to the object lens
405
and &lgr;/4 plate
409
, and are converted into P-polarized light parallel to the sheet surface of FIG.
4
. The P-polarized light passes through the polarization beam splitter
403
and forms the image of the alignment mark AM on a photoelectric conversion element
411
(e.g., a CCD camera) via an imaging optical system
407
a
(
407
b
). The position of the wafer
6
is detected based on the position of the photoelectrically converted alignment mark image.
To detect the alignment mark AM on the wafer
6
at a high precision, the image of the alignment mark AM must be clearly detected. In other words, the alignment mark AM must be adjusted to the focus surface of the OA detection system
4
.
For this purpose, an AF detection system (not shown) is generally adopted. The alignment mark is detected by being driven to the best focus plane of the OA detection system on the basis of the detection result of the AF detection system.
Alth
Adams Russell
Esplin D. Ben
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