Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
2001-11-01
2004-10-12
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S053000, C355S055000
Reexamination Certificate
active
06803990
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an exposure apparatus and a method of correcting for air pressure. More particularly, the invention is suited to a projection exposure apparatus in which a correction is made for a fluctuation component of an image-formation characteristic that accompanies a fluctuation in atmospheric air pressure or ambient air pressure within the apparatus, thereby making it possible to achieve highly precise projection exposure.
BACKGROUND OF THE INVENTION
In a projection exposure apparatus used to manufacture a semiconductor device, a circuit pattern that has been formed on a mask or reticle is transferred to a photoresist layer on a wafer or glass plate, which serves as a photosensitive substrate, with a high degree of overlay precision. In order to accomplish this, it is required that the reticle and wafer be positioned (aligned) highly precisely.
Focus calibration is well known as a technique for making the focal point of the wafer agree with that of the reticle.
FIG. 1
is a schematic view illustrating the projection exposure apparatus having a focus calibration function based upon the TTL (Through The Lens) method. The apparatus shown in
FIG. 1
includes a light source
1
for exposure. When a circuit pattern on a reticle
2
is transferred to a wafer
8
by exposing the wafer to the pattern, an exposure-apparatus control system
70
transmits a command to a light-source control system
30
, and the operation of the light source
1
is controlled by a command from the light-source control system
30
.
The reticle
2
is held on a reticle stage
4
. A reticle reference plate
3
is held on the reticle stage
4
, though there are instances where the plate
3
is secured at a position that is optically equivalent to that of the reticle
2
.
In a scanning-type exposure apparatus, the reticle stage
4
is capable of being moved along the optic axis (z) of projection optics
5
, and along axes (x, y) perpendicular to this axis, and is also capable of being rotated about the optic axis.
Control to drive the reticle stage
4
is carried out by sending a command from the exposure-apparatus control system
70
to a reticle-stage control system
40
and implementing control in accordance with a command from the reticle-stage control system
40
.
Though not shown, several types of reference marks are provided on the reticle reference plate
3
.
The projection optical system
5
is constituted by a plurality of lenses. When exposure is carried out, the image of the circuit pattern on the reticle
2
is formed on the wafer
8
at a magnification that corresponds to the reduction magnification of the projection optics
5
. A projection optics control system
50
will be described later.
A projection optical system
6
and a detection optical system
7
form an off-axis autofocus optical system. The projection optical system
6
emits a non-exposure light beam that is condensed on a point on a stage reference plate
9
(or on the top of the wafer
8
) and is reflected from this point. The reflected light impinges upon the detection optical system
7
. Though not shown, a photoreceptor element for position detection is placed within the detection optical system
7
and the arrangement is such that the photoreceptor element and the light reflection point on the stage reference plate
9
will be conjugate points. Accordingly, a deviation in position along the optical axis of the projection optics
5
on the stage reference plate
9
is measured as a deviation in the position of the incident light beam on the position-detection photoreceptor element in the detection optical system
7
.
A deviation in position from a predetermined reference plane of the stage reference plate
9
measured by the detection optical system
7
is transmitted to a wafer-stage control system
60
. When focus calibration (described below) is measured, the wafer-stage control system
60
performs control to drive the stage reference plate
9
up or down along the optic axis (z direction) of the projection optics
5
in the vicinity of a predetermined reference position. The wafer-stage control system
60
also controls the position of the wafer
8
at the time of exposure.
Described next will be components for sensing the state of focus on the wafer
8
and driving a wafer stage
10
to detect the optimum focal point of the wafer
8
with respect to the reticle
2
.
An image detection optical system
20
for focus calibration has elements
21
,
22
,
23
,
24
,
25
, described later. Illuminating light emitted from a fiber
21
passes through a half-mirror
22
and is condensed in the vicinity of the reticle reference plate
3
(or reticle
2
) via an objective lens
23
and mirror
24
.
The illuminating light that has been condensed in the vicinity of the reticle reference plate
3
is condensed on the stage reference plate
9
via the projection optics
5
. The top of the stage reference plate
9
is provided with reference marks (not shown) of several types. Light reflected from the stage reference plate
9
returns along the original optical path, traverses the projection optics
5
, reticle reference plate
3
, mirror
24
and objective lens
23
in the order mentioned, is reflected by the half-mirror
22
and impinges upon a position sensor
25
.
The stage reference plate
9
is placed on the wafer stage
10
in a manner similar to that of the wafer
8
. The stage reference plate
9
is fixed in a focal plane equivalent to that of the wafer
8
.
The exposure-apparatus control system
70
manages the focal-point positions on the top surfaces of the wafer
8
and the stage reference plate
9
with respect to the projection optics
5
, or the amount of focus offset between both surfaces and the projection optics
5
.
The operation of a TTL-based focus calibration will now be described in detail.
FIG. 7
is a flowchart illustrating the sequence of focus calibration. With reference to
FIGS. 1 and 7
, the detection optical system
20
is focused coarsely on a reference mark on the reticle reference plate
3
(or on a mark on the reticle
2
) (step S
701
). The purpose of step S
701
is to focus the image detection optical system
20
on the mark of the reticle reference plate
3
(or reticle
2
).
This will be described taking as an example a case in which the stage reference mark is measured while shifting the focal-point position of the stage reference mark at 100-nm intervals over a range of from −1439 nm to +361 nm.
First, the stage reference plate
9
is moved to a position at which the reference mark on the stage reference plate
9
can be observed by the image detection optical system
20
(step S
702
). The focal point of the stage reference mark is −1439 nm at step S
702
.
The procedure represented by steps (1) to (3) below (the loop of steps S
703
to S
705
) is repeated until the focal-point position of the stage reference mark becomes +361 nm. In the repetition process, the value of the quantity of light or the contrast value that prevails when the focal point of the stage reference plate
9
is varied with respect to the projection optics
5
is measured. The measured value of the quantity of light or the measured contrast value is stored in association with the focal point of the stage reference plate
9
prevailing at the time of measurement.
(1) The reference mark is measured by the image detection optical system
20
(step S
703
).
(2) The focal point on the top surface of the stage reference plate
9
with respect to the projection optics
5
is measured by the autofocus detection system (the projection optical system
6
and detection optical system
7
) (step S
704
). (It should be noted that the order of steps S
703
and S
704
may be reversed.)
(3) The focal point of the stage reference plate
9
with respect to the projection optics
5
is changed (step S
705
). More specifically, the stage reference plate is driven +100 nm from its present position.
On the basis of the value of the quantity of light or contrast value thus obtai
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Fuller Rodney
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