Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
1999-11-18
2003-03-25
Hilten, John S. (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
C355S030000, C355S043000, C382S151000, C250S548000
Reexamination Certificate
active
06539326
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates generally to a position detecting method or position detecting system, and a projection exposure method and apparatus, and a device manufacturing method using the same. The present invention is particularly suitably usable in a projection exposure apparatus called a stepper, for the maintenance of semiconductor devices, having a function of automatic focus adjustment (i.e., autofocusing function) in a reduction projection exposure process wherein a circuit pattern of a reticle is repeatedly printed on the surface of a semiconductor wafer.
Further miniaturization in size and further enlargement in density of a pattern for a semiconductor device such as an LSI or a VLSI have required a projection exposure apparatus having an image (projection) optical system with a very high resolving power. This necessitates enlargement of the numerical aperture (NA) of an imaging optical system, which leads to shortness of the depth of focus of the imaging optical system.
As regards wafers, because of the flatness machining technique, they have dispersion in thickness and warp. Generally, as regards the wafer warp correction, a wafer is placed on a wafer chuck having its surface flatness finished at a submicron order, and then the bottom face of the wafer is vacuum-attracted to thereby perform the flatness correction. However, because of irregularity in thickness inside a single wafer or of an attraction method used, or as a result of execution of processes, deformation may be produced in the wafer. On that occasion, the wafer may have a surface irregularity within an exposure region where a reticle pattern is to be projected and printed in a reduced scale, and the effective depth of focus of the optical system will be reduced more.
In consideration of the above, an automatic focus adjusting method effective to bring a wafer surface in registration with a focal plane (image plane of a projection optical system) is a very important factor in a projection exposure apparatus.
Examples of a wafer surface position detecting method in a projection exposure apparatus are a method using an air micro-sensor, a method (optical method) wherein light is projected on a wafer surface long an oblique direction thereto without going through a projection optical system and a positional deviation of reflected light therefrom is detected, and a method called “Through The Lens Autofocus (TTLAF)” wherein a focal plane is detected through a projection optical system.
FIG. 15
is a schematic view of a projection exposure apparatus having an autofocusing function, such as disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 286418/1989. Denoted in
FIG. 15
at
107
is a reticle which is held by a reticle stage
170
. A circuit pattern formed on the reticle
107
is imaged upon a wafer
109
, placed on an X-Y-Z stage
110
, by a reduction projection lens
108
in a reduced scale of 1/5, whereby wafer exposure is performed.
In
FIG. 15
, disposed adjacent to the wafer
109
is a reference flat mirror
117
which has a mirror surface placed substantially coplanar with the top face of the wafer
109
. This reference flat mirror
117
is used for focusing and alignment operations. The X-Y-Z stage
110
is movable in an optical axis direction (Z) of the projection lens
108
and along a plane (X-Y) orthogonal to this direction. Also, it can be rotationally moved about the optical axis. As regards the reticle
107
, a picture field region thereof through which the circuit pattern transfer is to be performed can be illuminated with an illumination optical system having components
101
-
106
shown in the drawing.
A light source for exposure comprises a Hg lamp
101
having its light emitting portion placed at the position of a first focal point of an elliptical mirror
102
. Thus, the light emitted by the Hg lamp
101
is collected at a second focal point position of the elliptical mirror
102
. An optical integrator
103
has its light entrance surface placed at the second focal point position of the elliptical mirror
102
, such that secondary light sources are produced at a light exit surface of the optical integrator
103
. The light from the optical integrator
103
, defining the secondary light sources, goes through a condenser lens
104
and, by means of a mirror
105
, the optical axis (light path) is deflected by 90 degrees. The exposure light thus reflected by the mirror
105
goes through a field lens
106
and it illuminates the picture field region on the reticle
107
through which the circuit pattern transfer is to be performed.
The mirror
105
has a structure for partially (e.g., 5-10%) transmitting the exposure light therethrough. The light passed through the mirror
105
goes through a filter
151
effective to transmit an exposure wavelength but to intercept light unnecessary for photoelectric detection, and then it impinges on a photodetector
150
which is provided to monitor fluctuation in quantity of the light from the light source, for example.
Those components shown at
111
-
112
in the drawing constitute an off-axis autofocus optical system of a known type. Denoted at
111
is a light projecting optical system which produces non-exposure light (non-sensitizing light). The light from the light projecting optical system is collected at a point on the reference flat mirror
117
(or upon the top face of the wafer
109
) which intersects the optical axis of the reduction projection lens
108
, and the light is reflected thereby. The light reflected by the reference flat mirror
117
enters a detection optical system
112
. While not shown in the drawing, there is a position detecting light receiving element disposed inside the detection optical system
112
. The light reflection point on the reference flat mirror
117
and the unshown position detecting light receiving element are disposed in an optically conjugate relation with each other, such that any positional deviation of the reference flat mirror
117
with respect to the optical axis direction of the reduction projection lens
108
can be measured as a positional shift of the incident light upon the light receiving element inside the detection optical system
112
.
The positional deviation of the reference flat mirror
118
from a predetermined reference plane, as measured by the detection optical system
112
, is transmitted to an autofocus control system
119
. The autofocus control system
119
applies a signal, for movement in the Z direction, to a driving system
120
for driving the X-Y-Z stage
110
on which the reference flat mirror
117
is fixedly mounted. Also, when the focus position is detected in accordance with the TTL method, the autofocus control system
119
operates to move the reference flat mirror
117
upwardly or downwardly, in the neighborhood of the predetermined reference position, along the optical axis direction (Z direction) of the projection lens
108
. Further, the autofocus control system
119
functions to perform position control for the wafer
109
, in a practical exposure operation (to place the wafer
109
at the position of the reference flat mirror
117
shown in FIG.
15
).
Next, a focus position detecting optical system for the reduction projection lens
108
will be described. In
FIGS. 13 and 14
, denoted at
107
is a reticle, and denoted at
121
are pattern portions formed on the reticle
107
and having a light blocking property. Denoted at
122
is a transmissive portion defined between the pattern portions
121
. Here, for detection of the focus position (image plane position) of the reduction projection lens
108
, the X-Y-Z stage
110
is moved along the optical axis direction of the reduction projection lens
108
. Also, the reference flat mirror
117
is placed on the optical axis of the reduction projection lens
108
, and the reticle
107
is illuminated with the illumination optical system (
101
-
106
) shown in FIG.
15
.
First, a case where the reference flat mirror
117
is just positioned upon the focal plane
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hilten John S.
Le John
LandOfFree
Position detecting system for projection exposure apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Position detecting system for projection exposure apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Position detecting system for projection exposure apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3061815