Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-10-18
2001-01-09
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C356S401000, C355S053000
Reexamination Certificate
active
06172373
ABSTRACT:
This application claims the benefit of Application Nos.: 8-247162, filed in Japan on Aug. 29, 1996 and 8-225474, filed in Japan on Aug. 27, 1996, which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an exposure apparatus used in photolithography processes in the manufacture of semiconductor devices, liquid crystal display devices, etc., and in particular concerns an exposure apparatus provided with a levelling device for matching the surface of the photosensitive substrate with the image formation plane of the projection optical system.
The present invention also concerns a stage apparatus, more specifically, a stage apparatus which is provided with a No. 1 stage which is able to move in a specified direction along a guidance plane over an antivibration stage which is held horizontally via antivibration pads, and a No. 2 stage which is mounted on this No. 1 stage and can be tilt-driven. The stage apparatus of the present invention can be used effectively as a stage for the positioning of photosensitive substrates in exposure devices, etc.
2. Discussion of the Related Art
In the past, in the manufacture of semiconductor devices, liquid crystal display elements, etc., using photolithographic techniques, an exposure apparatus has been used in which a pattern formed on a photomask (hereinafter referred to as mask) or reticle is projected and exposed on each shot area of a photosensitive substrate such as a semiconductor wafer or glass plate, etc., which has been coated with a photosensitive agent such as photoresist via a projection optical system. As an exposure apparatus, a so-called step-and-repeat type exposure apparatus, wherein the photosensitive substrate is mounted on a substrate stage which is moveable in two dimensions, and the operation of exposing the pattern image of the mask on each shot area of the photosensitive substrate is repeated by stepping the photosensitive substrate using this substrate stage, and, in particular, reductive projection type exposure apparatuses have often been used. Also, step-and-scan type exposure apparatuses have been used in which pattern exposure is performed on each shot area of the photosensitive substrate by reductive projection and, by means of a scanning exposure system, movement is performed between the shot areas in a stepping mode.
In general, since a projection optical system which has a large numerical aperture and a shallow focal depth is used in the exposure apparatus, in order to transcribe a fine pattern with high resolution, levelling control, whereby the angle of inclination of the photosensitive substrate surface is matched so as to be parallel with the angle of inclination of the image formation plane of the projection optical system, and autofocus control, whereby the height (focal point position) of the surface of the photosensitive substrate is matched with the position of the image formation plane of the projection optical system are necessary.
In order to perform levelling control, it is necessary to measure accurately the average inclination amount of local parts of or the entire photosensitive substrate surface. In the past, various such measurement methods have been proposed, for example, in Japanese Examined Patent No. [Kokoku] Hei 3-5652, Tokko Hei 4-42601, U.S. Pat. Nos. 4,084,903, 4,383,757, etc. For example, the height position in the optical axis direction (Z direction) is measured on at least 3 points on the photosensitive substrate using a gap sensor such as an air micrometer, an approximate plane formula of the photosensitive substrate surface is specified based on the measurement values thereof, and a levelling mechanism provided on the substrate stage is driven so that the approximate plane matches the image formation plane of the projection optical system.
Also, in the past, in shot areas existing on the peripheral area of the photosensitive substrate, which are shot areas for which autofocus control is difficult due to the scattering of the focal point position detection light, etc., exposure is performed in the focal point position of the shot area which is adjacent to this shot.
The sensor which measures the height position of the photosensitive substrate in the Z direction is fixed on the apparatus main body and is unable to move. Accordingly, in order to measure the Z direction positions of several points on the photosensitive substrate surface, the photosensitive substrate is moved by means of the substrate stage, and the multiple points on the photosensitive substrate are taken to the measurement point of the sensor in sequence. For this reason, when the running of the substrate stage itself carries a displacement amount in the Z direction, the Z direction displacement of the photosensitive substrate surface caused by the running of the substrate stage and the Z direction displacement within the plane of the photosensitive substrate cannot be separated, so that even if the surface of the photosensitive substrate itself is perpendicular to the Z direction, it may be judged that the photosensitive substrate surface is inclined, creating the problem that the levelling operation will be performed in error.
Problems in conventional levelling control are explained referring to FIG.
13
. Here, the action of performing levelling control based on sensor measurement values having measurement points in the positions indicated by the broken line are explained making the running direction of the substrate stage the X direction and the direction parallel to the optical axis the Z direction. FIGS.
13
(
a
) through (
c
) consists of diagrams explaining the concept of levelling control in the case where there is no displacement of the substrate stage running in the Z direction and FIGS.
13
(
d
) through (
f
) consists of diagrams explaining the concept of levelling control when the running of the substrate stage has displacement in the Z direction.
Assuming that the surface SF
1
of the photosensitive substrate
80
is inclined as shown in FIG.
13
(
a
). First, the photosensitive substrate is positioned in the position indicated by the solid line by means of the movement of the substrate stage (
85
) and the height position of point P
1
of the photosensitive substrate surface SF
1
is measured. The X coordinate of point P
1
is X
1
, and the height measurement position at this time is made Z
1
. Next, the photosensitive substrate (
80
) is moved to a different position on an imaginary line as indicated by the arrow by the movement of the substrate stage and the height position of another point P
2
on the photosensitive substrate surface SF
1
is measured. The X coordinate of point P
2
is made X
2
, and the height measurement value is made Z
2
.
From the coordinate values (X
1
, Z
1
) of point P
1
and the coordinate values (X
2
, Z
2
) of point P
2
at this time, the exposure apparatus recognizes that the surface SF
1
of the photosensitive substrate is inclined as shown in FIG.
13
(
b
). Accordingly, as shown in FIG.
13
(
c
), levelling control is performed so that the mounting object table
81
upon which the photosensitive substrate
80
is mounted is inclined by operating the levelling mechanisms
82
a,
82
b
of the substrate stage, and the surface SF
1
of the photosensitive substrate
80
becomes horizontal. In this way, if the running of the substrate stage
85
becomes displaced in the Z direction, a conventional exposure apparatus can perform suitable levelling control based on the height measurement values.
On the other hand, when, as indicated by the wavy imaginary line in FIG.
13
(
d
), the running of the substrate stage
85
has displacement in the Z direction, a conventional exposure apparatus cannot perform levelling control. It is assumed, as shown in FIG.
13
(
d
), that the photosensitive substrate
87
has no inclination within the plane. Initially, the photosensitive substrate
87
will be positioned as indicated by the solid line by the movement of the substrate stage
85
, and the height posi
Hara Hideaki
Imai Yuji
Murayama Masayuki
Allen Stephone B.
Morgan & Lewis & Bockius, LLP
Nikon Corporation
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