Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
2001-04-16
2002-11-26
Dunn, Drew A. (Department: 2882)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
C356S500000, C356S511000
Reexamination Certificate
active
06486955
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reflecting surface shape measuring method, a reflecting surface shape measuring unit, a position control method, a stage unit, an exposure apparatus, a method of making the exposure apparatus, a device, and a method of manufacturing the device and, more particularly, to a shape measuring method and shape measuring unit for the reflecting surface of a reflecting mirror provided for a moving object such as a stage, a position control method using the shape information of the reflecting surface measured by the shape measuring method, a stage unit for controlling the position of a sample mounted thereon by the position control method, an exposure apparatus which controls the position of a mask or substrate by the position control method, a method of making the exposure apparatus, a microdevice manufactured by using the exposure apparatus, and a method of manufacturing the microdevice.
BACKGROUND ART
In a lithography process for manufacturing a semiconductor element, liquid crystal display element, or the like, an exposure apparatus has been used. In such an exposure apparatus, patterns formed on a mask or reticle (to be generically referred to as a “reticle” hereinafter) are transferred through a projection optical system onto a substrate such as a wafer or glass plate (to be referred to as a “substrate or wafer” hereinafter, as needed) coated with a resist or the like. As apparatuses of this type, a static exposure type projection exposure apparatus, e.g., a so-called stepper, and a scanning exposure type projection exposure apparatus, e.g., a so-called scanning stepper are mainly used. In these types of projection exposure apparatuses, a wafer stage capable of moving two-dimensionally while holding a wafer is provided to sequentially transfer patterns formed on a reticle onto a plurality of shot areas on the wafer. In a scanning exposure type projection exposure apparatus, a reticle stage for holding a reticle can also move in the scanning direction.
In such a projection exposure apparatus, since a circuit pattern having a very minute structure is transferred onto a wafer, position control on the wafer and reticle must be accurately performed. For this accurate position control, a reflecting mirror arranged on the wafer stage or reticle stage is irradiated with a measurement beam, and the two-dimensional position of the wafer stage or reticle stage is accurately detected on the basis of the fringe pattern of interference light between the reflected light and reference light or the phase difference therebetween.
In the above two-dimensional position detection, the height position of a detection point is preferably matched with the height position of a wafer surface coated with a resist or the like, or the pattern formation surface of the reticle. However, for example, in the case of a wafer stage, as the distance (so-called working distance) between the projection optical system and the wafer stage decreases with an increase in the N.A. of the projection optical system, it is becoming difficult to arrange a reflecting mirror on the upper surface of the wafer stage. For this reason, there is proposed a technique of arranging a reflecting mirror on a side surface of a wafer stage and correcting a so-called Abbe error caused when the height position of the detection point does not coincide with the height position of a wafer surface coated with a resist or the like.
A conventional technique of correcting such an Abbe error will be described below with reference to
FIGS. 23A
to
23
C by exemplifying the case where an Abbe error in the X direction of the wafer stage moving along the X-Y plane is corrected.
In the conventional technique, as shown in
FIG. 23A
, a tilt interferometer (heterodyne differential interferometer)
103
is used to detect the tilt state of a substrate table
101
, i.e., the rotation amount of a reflecting surface
102
S of a reflecting mirror (plane-parallel plate mirror)
102
around the Y-axis, which is arranged on one side surface of the substrate table
101
and extends along the Y-axis direction.
In the tilt interferometer
103
, two light beams which are emitted from a light source unit (not shown), slightly differ in their wavelengths, and are polarized in orthogonal directions are incident on a polarizing beam splitter
105
to be split into two light beams in accordance with each polarizing direction. A light beam LU that is deflected by the polarizing beam splitter
105
and propagates in the +Z direction is reflected by a reflecting prism
106
. This light beam is then incident on the reflecting surface
102
S (the Z position of the incident point=Z
A
) and reflected. Note that the tilt interferometer
103
shown in
FIGS. 23A
to
23
C uses the double-pass scheme. The light beam LU reflected by the reflecting prism
106
is reflected twice by the reflecting surface
102
S via a polarizing beam splitter
107
U for double-pass branching and a quarter-wave plate
108
U. The light beam LU reflected in this manner propagates toward a light-receiving unit (not shown) via the quarter-wave plate
108
U, polarizing beam splitter
107
U, reflecting prism
106
, and polarizing beam splitter
105
.
In the mean time, a light beam LL that is transmitted through the polarizing beam splitter
105
and propagates in the +X direction passes through a half-wave plate
109
, and then strikes a polarizing beam splitter
107
L for double-pass branching. Subsequently, like the light beam LU, the light beam LL strikes two points (each having Z position=Z
B
(=Z
A
−D)) on the reflecting surface of the reflecting mirror
102
via the polarizing beam splitter
107
L, a &lgr;/4 plate
108
L, and the like. Thereafter, the light beam sequentially passes through the &lgr;/4 plate
108
L, polarizing beam splitter
107
L, half-wave plate
109
, and polarizing beam splitter
105
and propagates toward the light-receiving unit (not shown) along almost the same optical path as that of the light beam LU.
The light input to the light-receiving unit is therefore the composite light of the light beams LU and LL. In the light-receiving unit, the light beams LU and LL are made to interfere with each other, with their polarizing directions being matched with each other, to generate interference light reflecting the optical path length difference between the light beams LU and LL, thereby measuring the interference light. Therefore, the tilt interferometer
103
can be used to monitor the rotation state of the reflecting surface of the reflecting mirror
102
around the Y-axis with reference to the reset state of the tilt interferometer
103
, i.e., the rotation state of the substrate table
101
around the Y-axis.
Consider a case where the rotational angle of the reflecting surface
102
S of the reflecting mirror
102
around the Y-axis direction is 0° while the tilt interferometer
103
is in the reset state, and a wafer W has a taper angle &thgr; in the X direction, as shown in FIG.
23
B. In this case, in an exposure apparatus having an autofocus system for detecting the Z position of the surface of the wafer W and its rotations around the X- and Y-axes and matching an exposure area on the surface of the wafer W with the image plane of a projection optical system, the substrate table
101
is rotated through the taper angle &thgr; around the Y-axis in accordance with the observation result obtained by the autofocus system. With this operation, the surface of the wafer W is matched with the image plane of the projection optical system. As shown in
FIG. 23C
, however, there is an offset between the actual X position of each point on the surface of the wafer W and the X position of the corresponding point on the surface of the wafer W which is obtained from the corresponding X position on the substrate table
101
which is obtained by an X position detection interferometer using the reflecting mirror
102
. This positional offset (Abbe error) &Dgr;X
A
is given by
&Dgr;
X
A
=L·&thgr;
&emsp
Dunn Drew A.
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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