Photocopying – Projection printing and copying cameras – Focus or magnification control
Reexamination Certificate
2000-03-08
2004-03-30
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Focus or magnification control
C355S053000, C250S548000
Reexamination Certificate
active
06714281
ABSTRACT:
BACKGROUND OF A INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus of a projection type or the like for a semiconductor circuit apparatus such as an IC, LSI, and VLSI, and a device manufacturing method capable of using this apparatus. More particularly, the present invention relates to an exposure apparatus of a projection type having an auto-focusing control function a time of repetitively reducing and projection-exposing a circuit pattern of a reticle onto a semiconductor wafer surface, a so-called auto-focusing function and a device manufacturing method using the apparatus, preferably in the field of manufacturing a semiconductor device.
2. Description of the Related Art
In a projection exposure apparatus employed in the manufacture of a semiconductor device, the alignment of a reticle and a wafer at a high precision is required so as to transfer a circuit pattern as a mask, formed on the reticle, onto a photoresist layer on a wafer, glass plate, etc., as a photo-substrate at a high precision of alignment. There has been known a technique such that in a projection exposure apparatus such as a stepper, the alignment of a reticle and a wafer is executed by both reticle alignment to align a reticle with a projection exposure optical system and wafer alignment to align a wafer with the projection exposure optical system. As for a reticle alignment method, there are methods, e.g., an FRA (Fine Reticle Alignment) method, which have been disclosed by the present applicant. As for a wafer alignment method, there has been known a TTL (Through-The-Lens) method of directly aligning the wafer with the projection optical system, an off-axis method of aligning the wafer with an observation optical system having another optical axis different from that of the projection optical system, and the like.
FIG. 1
is a schematic diagram of a projection exposure apparatus having an auto-focusing function by the TTL method, which has been disclosed in Japanese Patent Application Laid-Open No. 9-260269. Referring to
FIG. 1
, reference numeral
6
denotes a reticle which is held to a reticle stage
7
. A projection lens (exposure lens)
9
allows a circuit pattern on the reticle
6
to be reduced to ⅕ or {fraction (1/10)} in size onto a wafer
12
on an xyz stage (a wafer stage)
11
, thereby forming an image and exposing it. In
FIG. 1
, a reference flat mirror
13
, in which a surface of the mirror
13
is almost aligned with an upper surface of the wafer
12
, is arranged at a position adjacent to the wafer
12
. A stage reference mark
13
a
(mark for detecting focus) in
FIG. 2
is formed onto the reference flat mirror
13
. The xyz stage
11
can move in an optical axis (z) direction of the projection lens
9
and in a surface (x, y) perpendicular thereto and, of course, be rotated around the optical axis. An illumination optical system shown by component elements
1
to
5
in
FIG. 1
illuminates an area in a picture plane of the reticle
6
where a circuit pattern is transferred.
A light-emitting portion of a light source
1
for exposure is positioned at a first focus of an elliptical mirror
2
. Light emitted from the light source
1
is made incident to an optical integrator (fly eye lens)
3
where the light incident surface is positioned to a second focus position of the elliptical mirror
2
and a light emitting surface of the optical integrator
3
forms a secondary light source. The light emitted from the optical integrator
3
as a secondary light source illuminates the reticle
6
via a lens for illumination
4
and a field lens
5
.
Component elements
10
,
13
, and
14
form an auto-focusing optical system of an off-axis type. Reference numeral
10
denotes a projection optical system (auto-focusing incident system). Light beams as non-exposing light emitted from the projection optical system
10
are converged and reflected to a point on the reference flat mirror
13
(or an upper surface of the wafer
12
). The light beams reflected by the reference flat mirror
13
are made incident to a detection optical system (auto-focusing light-receiving system)
14
. A light receiving device for position detection (not shown) is arranged in the detection optical system
14
, and constructed so that an incident light point of the light receiving device for position detection is made conjugate to a reflecting point of light beams on the reference flat mirror
13
. A positional offset in the optical axis direction of the reduction projection lens
9
of the reference flat mirror
13
is measured as a position offset of incident light beams on the light receiving device for position detection in the detection optical system
14
.
Transmitted to an auto-focusing control system
32
is the positional offset from a predetermined reference surface of the reference flat mirror
13
, which the detection optical system
14
has measured. The auto-focusing control system
32
instructs a driving system
33
for driving the xyz stage
11
, to which the reference flat mirror
13
is fixed, to move toward the z-direction. When a detection optical system
27
, as will be explained hereinafter, detects a TTL defocus position, the auto-focusing control system
32
drives the reference flat mirror
13
to move up and down in the optical axis direction (z direction) of the projection lens
9
near a predetermined reference position. The auto-focusing control system
32
also controls a position of the wafer
12
during exposure.
Next, the description turns to component elements for detecting a focusing state on the surface of the wafer
12
, driving the wafer stage
11
on the basis of the detected signal, and detecting an in-focus position of the projection lens
9
. Reference numeral
27
denotes a TTLAF (Through The Lens Auto-Focusing) detection optical system having component elements
23
,
24
,
26
,
40
, and
41
, which will be mentioned hereinafter. Illuminating light beams emitted from a fiber
40
pass through a half mirror
41
and are converged near the reticle
6
via an objective lens
24
and a mirror
23
. A translucent portion (opening window portion) (not shown) having a predetermined size is set at a position in an area other than an actual device area on the reticle
6
. The illuminating light beams pass through the opening window portion and, thereafter, are converged on the reference flat mirror
13
via the projection lens
9
. As discussed above, a stage reference mark (mark for focus detection)
13
a
is marked onto the reference flat mirror
13
, as shown in FIG.
2
. Reflecting light from the reference flat mirror
13
is returned through an original light path, reflected to the half mirror
41
through the projection lens
9
, opening window portion, mirror
23
, and objective lens
24
according to this order and is made incident onto a position sensor
26
.
The reference flat mirror
13
is arranged onto the wafer stage
11
similar to the wafer
12
, and is fixed to the focusing surface, almost matching the wafer
12
. The auto-focusing control system
32
controls focus positions of the wafer surface
12
a
and the stage reference surface
13
a
of the flat mirror
13
or focus offset amounts between both of these surfaces. As a result, in accordance with a successive sequence, the reference flat mirror
13
is focused and only the supply of a predetermined offset amount results in automatically focusing the actual wafer thereon.
As shown in
FIG. 2
, the stage reference mark
13
a
is composed of lines and spaces in the vertical direction, which have a predetermined line width. Light beams emitted from the stage reference mark
13
a
on the reference flat mirror
13
return in the passed path (in the pass-back path) and reach the objective lens
24
. The light beams passing through the objective lens
24
are reflected to the half mirror
41
at a next time, and an image is formed onto a sensor surface
26
a
of the position sensor
26
. The position sensor
26
may be a one-dimensional array sensor or two-dimensional array
Amano Toshitaka
Morimoto Osamu
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