Optics: measuring and testing – By alignment in lateral direction – With light detector
Reexamination Certificate
1999-03-25
2002-08-13
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With light detector
C355S053000
Reexamination Certificate
active
06433872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus designed to transfer a pattern formed on a mask or reticle onto a photosensitive substrate and used in a photolithographic process for manufacturing a semiconductor element, a liquid crystal display element, a thin-film magnetic head, or the like and, more particularly, to a method and apparatus for positioning a photosensitive substrate with respect to a predetermined reference plane (e.g., the imaging plane of a projection optical system).
2. Related Background Art
Conventionally, an exposure apparatus incorporates a plane position detection unit for performing proximity gap setting, focusing, leveling, and the like. Especially in a projection exposure apparatus, when a reticle pattern is to be projected/exposed on a photosensitive substrate (a wafer or glass plate on which a photoresist is coated) via a projection optical system having a high resolving power, a surface of the photosensitive substrate must be accurately aligned with the imaging plane (the projection imaging plane for the reticle pattern) of the projection optical system, that is, focusing must be performed, as disclosed in U.S. Pat. No. 4,650,983.
In order to achieve proper focusing throughout the projection field of view of the projection optical system, some consideration needs to be given to the inclination of a partial area, on the projection optical system, which enters the projection field of view, i.e., one projection/exposure area (shot area). As a technique of performing a focusing operation in consideration of the inclination of the surface of one shot area on a photosensitive substrate, a technique disclosed in U.S. Pat. No. 4,558,949 and the like is known. Especially in U.S. Pat. No. 4,383,757, there is disclosed a technique of projecting the spots of light beams on four points on a photosensitive substrate via a projection optical system, and photoelectrically detecting spot images formed by the reflected light beams, thus performing focusing and inclination correction (leveling) with respect to the photosensitive substrate.
A multi-point oblique incident type focus detection system like the one disclosed in, e.g., U.S. Pat. No. 5,118,957 is also known as a system developed from the oblique incident type focus detection system disclosed in U.S. Pat. No. 4,558,949. In this system, pin hole images are projected on a plurality of points (e.g., five points) in a shot area on a projection optical system by an oblique incident scheme without the mediacy of a projection optical system, and the respective reflected images are received by a two-dimensional position detection element (CCD) at once. The system is generally called an oblique incident type multi-point AF system, which can execute focus detection and inclination detection with high precision.
As a conventional projection exposure apparatus, a reduction projection exposure apparatus of a step-and-repeat scheme, a so-called stepper, is widely used. This apparatus is designed to sequentially move shot areas on a photosensitive substrate into the projection field of view (exposure field) of a projection optical system to position them and expose a reticle pattern image on each shot area.
FIG. 27
shows the main part of a conventional stepper. Referring to
FIG. 27
, a pattern image on a reticle
51
is projected/exposed on each shot area on a wafer
53
, on which a photoresist is coated, via a projection optical system
52
with exposure light EL from an illumination optical system (not shown). The wafer
53
is held on a Z leveling stage
54
. The Z leveling stage
54
is mounted on a wafer-side X-Y stage
55
. The wafer-side X-Y stage
55
performs positioning of the wafer
53
within a plane (X-Y plane) perpendicular to an optical axis AX
1
of the projection optical system
52
. The Z leveling stage
54
sets the focus position (the position in a direction parallel to the optical axis AX
1
) of an exposure surface (e.g., an upper surface) of the wafer
53
and the inclination angle of the exposure surface in designated states.
A movable mirror
56
is fixed on the Z leveling stage
54
. A laser beam from an external laser interferometer
57
is reflected by the movable mirror
56
so that the X- and Y-coordinates of the wafer-side X-Y stage
55
are constantly detected by the laser interferometer
57
. These X- and Y-coordinates are supplied to a main control system
58
. The main control system
58
controls the operations of the wafer-side X-Y stage
55
and the Z leveling stage
54
through a driving unit
59
so as to sequentially expose pattern images of the reticle
51
on the respective shot areas on the wafer
53
by the step-and-repeat scheme.
In this case, the pattern formation surface (reticle surface) on the reticle
51
and the exposure surface of the wafer
53
need to be conjugate to each other with respect to the projection optical system
52
. However, the reticle surface does not vary much because of the high projection magnification and the large depth of focus. In general, therefore, an oblique incident type multi-point AF system is used to only detect whether the exposure surface of the wafer
53
coincides with the imaging plane of the projection optical system
52
within the range of the depth of focus (i.e., whether an in-focus state is achieved), thus controlling the focus position and inclination angle of the exposure surface of the wafer
53
.
In the conventional multi-point AF system, illumination light with which the photoresist on the wafer
53
is not sensitized, unlike the exposure light EL, is guided from an illumination light source (not shown) via an optical fiber bundle
60
. The illumination light emerging from the optical fiber bundle
60
is radiated on a pattern formation plate
62
via a condenser lens
61
. The illumination light transmitted through the pattern formation plate
62
is projected on the exposure surface of the wafer
53
via a radiation objective lens
65
. As a result, a pattern image on the pattern formation plate
62
is projected/formed on the exposure surface of the wafer
53
obliquely with respect to the optical axis AX
1
. The illumination light reflected by the wafer
53
is re-projected on the light-receiving surface of a light-receiving unit
69
via a focusing objective lens
66
, a vibration plate
67
, and an imaging lens
68
. As a result, the pattern image on the pattern formation plate
62
is formed again on the light-receiving surface of the light-receiving unit
69
. In this case, the main control system
58
vibrates the vibration plate
67
through a vibrating unit
70
, and detection signals from a large number of light-receiving elements of the light-receiving unit
69
are supplied to a signal processing unit
71
. The signal processing unit
71
supplies, to the main control system
58
, a large number of focus signals obtained by performing synchronous detection of the detection signals in response to a driving signal from the vibrating unit
70
.
FIG. 28B
shows opening patterns formed on the pattern formation plate
62
. As shown in
FIG. 28B
, nine slit-like opening patterns
72
-
1
to
72
-
9
are arranged on the pattern formation plate
62
in a crisscross form. Since these opening patterns
72
-
1
to
72
-
9
are radiated on the exposure surface of the wafer
53
from a direction crossing the X- and Y-axes at 45°, projection images AF
1
to AF
9
of the opening patterns
71
-
1
to
72
-
9
are arranged in the exposure field, of the projection optical system
52
, formed on the exposure surface of the wafer
53
in the manner shown in FIG.
28
A. Referring to
FIG. 28A
, a maximum exposure field
74
is formed to be inscribed to the circular illumination field of view of the projection optical system
52
, and the projection images of the slit-like opening patterns are respectively projected on measurement points AF
1
to AF
9
on the central portion and the two diagonal lines in the maximum exposure field
74
.
FIG. 28C
shows a state of the
Murakami Seiro
Nishi Kenji
Tanaka Yasuaki
Font Frank G.
Miles & Stockbridge P.C.
Natividad Phil
Nikon Corporation
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