Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1998-03-24
2001-07-17
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S072000, C355S075000
Reexamination Certificate
active
06262794
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
This invention relates to an exposure apparatus for use in a process of semiconductor device manufacture and, more particularly, to a projection exposure apparatus for projecting and transferring a pattern of a reticle onto a silicon wafer. Specifically, the invention is concerned with a scanning exposure apparatus for projecting and printing a pattern of a reticle onto a silicon wafer while scanningly moving the reticle and the wafer in synchronism with each other, relative to a projection exposure system.
In simultaneous-exposure type exposure apparatuses (called a stepper), if the projection optical system is provided by lenses, the imaging region thereof has a circular shape. Generally, however, a semiconductor integrated circuit has a rectangular shape and, therefore, the transfer region defined in the simultaneous exposure process has to be a rectangular region inscribed within the circular imaging region of the projection optical system. Thus, even a largest transfer region has a size of a square with each side corresponding to 1/{square root over (2)} of the diameter of the circle.
On the other hand, a scanning exposure method (step-and-scan exposure method) has been proposed, in accordance with which a slit-like exposure region having a size approximately equal to the diameter of the circular imaging region of a projection optical system is used and in which a reticle and a wafer are scanningly moved in synchronism with each other, thereby to expand the transfer region. In this method, if a projection optical system with an imaging region of the same size is used, use of a projection lens system enables simultaneous exposure to individual transfer regions of a larger size as compared with that defined in the case of steppers. More specifically, with regard to the scan direction, there is no restriction by the optical system and, therefore, a size corresponding to the stroke of the scanning stage is assured. With regard to a direction perpendicular to the scan direction, a transfer region of a size approximately equal to {square root over (2)} times is assured.
For exposure apparatuses for the manufacture of the semiconductor integrated circuits, enlargement of the transfer region and improvement of the resolving power have been desired from the viewpoint of manufacture of higher density chips. The usability of a smaller projection optical system is advantageous in the point of optical performance and, also, in the point of cost. Thus, the step-and-scan exposure method will be the most effective in future exposure apparatuses.
Such a step-and-scan exposure method, however, involves some problems.
FIG. 14
is a schematic view of a step-and-scan exposure apparatus as described above. In this exposure apparatus, a portion of a pattern of a reticle substrate
102
mounted on a reticle stage
101
is projected onto a wafer
6
, mounted on a wafer stage
7
, through a projection optical system
12
, while the reticle substrate
102
and the wafer
6
are moved in the Y direction, relative to the projection optical system
12
, in synchronism with each other, whereby the pattern of the reticle substrate
102
is transferred to the wafer
6
held by the wafer stage
7
. Stepwise motion is added to repeat the scan exposure to different transfer regions (shot areas) on the wafer
6
, whereby step-and-scan exposures are performed.
The reticle stage
101
is moved in the Y direction, as shown in
FIG. 16A
, by means of a linear motor (
103
A,
103
B,
103
C and
103
D) having a symmetrical structure on the opposite sides of the stage. Denoted at
103
A and
103
B are coils for actuating the reticle stage
101
, and denoted at
103
C and
103
D are yokes of a magnetic circuit, comprising magnets, for applying a magnetic field to the coils
103
A and
103
B.
During the exposure process with this exposure apparatus, the reticle stage
101
scanningly moves in the Y direction (
FIGS. 16A and 16B
, and FIGS.
17
A-
17
E). Prior to a start of a scanning motion of the reticle stage
101
(FIG.
17
B), the weight or load gravity center position of the reticle stage
101
is in the distance C from the end face of the reticle stage with respect to the Y direction. Just after the scan exposure and at the moment the reticle stage
101
has just moved in the Y direction (FIG.
17
C), the load gravity center of the reticle stage
101
displaces, with the stage movement, to the position in the distance D from the stage end face with respect to the Y direction. Further, after completion of the scan exposure, the reticle stage
101
moves back to the position shown in
FIG. 17D
, for preparation of the subsequent exposure operation. Thus, as the scan exposure proceeds, and before and after the scan exposure, the load gravity center position of the reticle stage
101
displaces in the Y direction, between the ranges of distance C to the distance D in synchronism with the movement of the reticle stage
101
. As a result, as shown in
FIG. 17E
, at the positions C and D, loads W
C
and W
D
are applied from the reticle stage
101
to the structural member
113
which supports the stage
101
. In response, the top plate displaces in the Z direction to produce flexure deformation Z. In this manner, the scan exposure is performed with deformation of the structural member
113
produced. Such deformation of the structural member
113
then causes tilt of the reticle stage
101
or distortion within the supporting system of the reduction exposure system or in the whole exposure optical system. It causes degradation of exposure precision.
Further, with the scanning motion of the reticle stage
101
, thrust and a reaction force thereto are produced in the linear motor coil
103
B and yoke
103
D for moving the reticle stage
101
(FIGS.
18
A-
18
C). At the start of scanning motion of the reticle stage
101
(FIG.
18
A), a thrust F
f
is produced in the linear motor coil
103
B (
103
A) and, in response, a reaction force F
f
′ is produced in the fixed side yoke
103
D (
103
C). The reaction force F
f
′ produced in the yoke
103
D (
103
C) directly acts on the structural member
113
on which the yoke
103
D (
103
C) is fixed. Thus, a reaction force is produced in the direction for moving the structure
113
in the -Y direction. As a result, a small shift and vibration are produced in the structural member
113
as well as in a barrel base table
11
.
Such a small shift and vibration serve as a disturbance to the scanning exposure system and, during the synchronous scan of the reticle stage
101
and the wafer stage
7
in the scanning exposure operation, it is an unstable control factor for an exposure control system that should function to assure exposure precision stability.
Japanese Laid-Open Patent Application, Laid-Open No. 21894/1991 or No. 107639/1991 shows an exposure apparatus wherein, in relation to a wafer (not a reticle), a balancer which is movable in a vector direction opposite to the movement direction of a wafer stage is provided to reduce vibration of the wafer stage with acceleration and deceleration.
However, this arrangement requires completely separate drive sources for the stage and for the balancer. Further, the drive source uses a feed-screw mechanism. This necessitates enlargement of size and weight of the structure. Additionally, since the movement axis of gravity center of the stage is not registered with the movement axis of gravity center of the balancer, operational axes of reaction forces of the stage and the balancer do not match with each other. This causes a moment force between them during the motion and, as a result, complete balancing is not attainable. This problem is particularly serious in the case of a reticle stage whose gravity center position is generally higher than that of the wafer stage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an arrangement suitable for use in an exposure apparatus, by which, when used in an exposure apparatus, deformation of a structure due to a shift o
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mathews Alan A.
Nguyen Hung Henry
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