Photocopying – Projection printing and copying cameras – Detailed holder for original
Reexamination Certificate
2000-10-18
2002-07-09
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for original
C355S072000, C355S053000, C310S012060
Reexamination Certificate
active
06417914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stage device and an exposure apparatus. More particularly, the present invention relates to a stage device including two stages, which hold two objects, and an exposure apparatus, which includes the stage device.
2. Description of the Related Art
Conventionally, in a lithographic process to manufacture devices such as semiconductors and liquid crystal displays, various types of exposure apparatus have been used to transfer patterns formed on a mask or a reticle (to be generically referred to as a “reticle” hereinafter) onto a substrate such as a wafer or a glass plate (to be generically referred to as a “wafer” hereinafter) coated with a resist or the like. In recent years, a projection exposure apparatus based on a step-and-repeat method (a so-called stepper) and a scanning type projection exposure apparatus based on a step-and-scan method (a so-called scanning stepper) have been mainly used.
With an exposure apparatus such as the stepper, since the wafer must be accurately positioned to a projection position of a reticle pattern, the wafer is held on a wafer holder by vacuum chucking, and the wafer holder is fixed on a wafer table.
In the process performed by the exposure apparatus such as the stepper, after the wafer loading process to load a wafer onto the wafer stage by using the wafer loader, the alignment process to measure the position of each shot area on the wafer is performed. This alignment process, in general, includes: the search alignment process which is performed based on the outer shape of a wafer or by detecting search alignment marks on the wafer; and the fine alignment process which is performed following the search alignment process to accurately obtain the position of each shot area on the wafer. For this fine alignment process, the EGA (Enhanced Global Alignment) method disclosed in, for example, U.S. Pat. Nos. 4,780,617 and 4,962,318 is used. With this method, a plurality of sample shots within a wafer are selected in advance, and the position of alignment marks (wafer marks) with respect to the sample shots are sequentially measured. The array data of all the shots on the wafer are then obtained by performing statistical calculation based on a so-called least-squares method based on the measurement results and the shot array designed values. According to this method, the coordinate position of each shot area can be obtained relatively accurately with a high throughput.
Next, the respective shot areas on the wafer are sequentially positioned based on the coordinate positions of the respective shot areas obtained by the EGA method or the like and a baseline amount measured in advance. Then, the exposure process is performed to transfer the reticle pattern image onto the wafer through the projection optical system. After the exposure process, the wafer unloading process to unload the wafer having completed exposure from the wafer stage by using the wafer unloader is performed. The wafer unloading process constitutes the wafer exchanging process, along with the wafer loading process in which the wafer is exposed. The exposure apparatus, when focusing on each wafer, sequentially repeats three main operations, i.e., wafer exchange, alignment, and exposure. In the case the exposure apparatus performs these process by using one wafer table, T
T
is the processing time per wafer, T
1
is the wafer exchange time, T
2
is the alignment time, and T
3
is exposure time, therefore:
T
T
=T
1
+T
2
+T
3
(1)
The wafer exchange time T
1
is shorter than the alignment time T
2
and exposure time T
3
. Most of the processing time T
T
per wafer is taken up by the alignment T
2
and exposure time T
3
.
Exposure apparatus such as steppers are apparatus that mass-produce semiconductor devices and the like, therefore inevitably require an improvement in productivity (throughput). In order to meet such a requirement, an exposure apparatus which concurrently performs the alignment and exposure process by using two substrate tables, while incorporating resources to independently drive the tables, has been proposed in, for example, Japan Patent Laid Open No. 10-214783 (to be referred to as a “prior art” hereinafter). with this apparatus, the processing time T
T
′ is as follows:
T
T
′=MAX[T
1
+T
2
, T
3
] (2)
That is, the throughput greatly improves compared with the case in which only one substrate table is used.
Recently, when producing semiconductor devices, in order to improve the productivity, the size of the wafer tends to gradually increase from 6 inches to 8 and 12 inches. And the wafer stage, which has also increased in size, requires to be driven with a higher speed. That is, as the wafer stage increases in weight, the driving force of the wafer stage needs to be further increased. An increase in the weight of the wafer stage causes the center of gravity to move more frequently in a stage device including the wafer stage, along with the movement of the wafer stage. This causes the exposure apparatus including the stage device to lose its stability, and will lead to deformation of the exposure apparatus. Also, for example, when the wafer stage performs reciprocal movements, vibration is caused in the overall exposure apparatus.
And, if the wafer stage is driven with a large force, the reaction force causes the overall exposure apparatus to deform or to vibrate.
Further, the above conventional technique is an excellent technique to improve the throughput. However, when considering the increase in the size and weight of each wafer stage, and the two wafer stages being independently driven with large driving forces corresponding to the respective stages, the exposure apparatus may further deform and vibrate compared to the exposure apparatus with one wafer stage.
As the degree of integration of semiconductor devices increases, the device rule (practical minimum line width) decreases every year, and an improvement in pattern transfer precision is thus required. In spite of such a requirement for an improvement in pattern transfer precision, the above deformation and vibration of the exposure apparatus act as factors that cause a deterioration in pattern transfer precision. In other words, it is becoming difficult to satisfy both the requirements for an improvement in pattern transfer precision and an improvement in throughput.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of this situation, and has as its first object to provide a new stage device which independently drives two stages, while reducing the influence of the center of gravity shifting caused by the stages being driven and vibration caused by the reaction force.
It is the second object of the present invention to provide an exposure apparatus that can improve the throughput while improving the precision of pattern transfer.
According to the first aspect of the present invention, there is provided a stage device comprising: a first and second stage movably supported on a base; and a moving member which is movably supported on the base and moves to cancel out a shift in a center of gravity of the stage device when at least one of the first and second stages move. The term “canceling out a shift in a center of gravity” includes completely canceling out a shift in the center of gravity as well as partially canceling out a shift in the center of gravity, i.e., reducing the amount of the center of gravity position moving.
According to this arrangement, the center of the gravity of the stage device moves when at least one of the first and second stage moves. However, this is canceled out by moving the moving member. That is, the shift in the center of gravity of the stage device when at least one of the first and second stage moves can be prevented. This makes it possible to prevent the external members from losing stability when compared with the initial state of the stage device.
The stage device of the present invention can
Adams Russell
Nguyen Hung Henry
Nikon Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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