Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Reexamination Certificate
1999-12-23
2001-08-28
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
C318S592000, C318S575000, C318S568170, C074S47100R
Reexamination Certificate
active
06281655
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a stage for an exposure apparatus. More specifically, the present invention is directed to a low mass, high performance stage for an exposure apparatus.
BACKGROUND
Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage retaining a reticle, a lens assembly and a wafer stage retaining a semiconductor wafer. The reticle stage and the wafer stage are supported above a ground with an apparatus frame. Typically, one or more motors precisely position the wafer stage and one or more motors precisely position the reticle stage. The images transferred onto the wafer from the reticle are extremely small. Accordingly, the precise relative positioning of the wafer and the reticle is critical to the manufacturing of high density, semiconductor wafers.
A typical reticle stage includes a coarse stage and a fine stage. The coarse stage is used for relatively large movements of the reticle and the fine stage is used for relatively small, precise movements of the reticle. Existing reticle stages typically utilize a pair of spaced apart fine Y motors to move the fine stage along a Y axis and a pair of spaced apart coarse Y motors to move the coarse stage along the Y axis.
Unfortunately, existing reticle stages that utilize both a coarse stage and a fine stage have a relatively large total mass. As a result of the large mass, large motors are needed to move and position the fine stage and the coarse stage. These motors occupy valuable space near the stage, consume large amounts of electric current and generate a significant amount of heat. The heat is subsequently transferred to the surrounding environment, including the air surrounding the motors and the other components positioned near the motors. The heat changes the index of refraction of the surrounding air. This reduces the accuracy of any metrology system used to monitor the positions of the stages and degrades machine positioning accuracy. Additionally, the heat causes expansion of the other components of the device. This further degrades the accuracy of the device.
Moreover, a large mass, reticle stage has a relatively low resonant frequency and a low servo bandwidth. As a result of the low resonant frequency and low servo bandwidth, external forces and/or small reaction forces can easily vibrate and distort the reticle stage. This will influence the position of the reticle stage and the performance of the exposure apparatus.
Additionally, the multiple motors required for both the coarse stage and the fine stage complicates the layout of the reticle stage and the system required to control both the coarse stage and the fine stage.
In light of the above, it is an object of the present invention to provide a stage assembly that has a relatively low mass, a relatively high resonance frequency and a relatively high servo bandwidth. Another object is to provide a stage assembly that is relatively simple to control, allows space for service access, and allows space for a measurement system. Still another object is to provide a stage assembly that utilizes efficient motors to move the components of the stage assembly. Yet another object is to provide a low mass stage assembly that can simultaneously carry two reticles. Another object is to provide a stage assembly that offsets the mass of a fine stage to minimize distortion to a stage base and a lens assembly. Another object is to provide a stage that utilizes reaction force cancellation to minimize the forces transferred to a mounting frame. Still another object is to provide an exposure apparatus capable of manufacturing high density, semiconductor wafers. Yet another object is to provide a stage assembly having a guideless fine stage and a guideless coarse stage.
SUMMARY
The present invention is directed to a stage assembly for moving an object that satisfies these needs. The stage assembly includes a fine stage and a coarse stage. The fine stage includes a holder that retains the object. As provided herein, the stage assembly can be used to precisely position one or more objects during a manufacturing and/or an inspection process.
The stage assembly includes a fine Y mover and a fine X mover that precisely move the fine stage relative to the coarse stage. Additionally, the stage assembly can also include a coarse Y mover and a coarse X mover that move the coarse stage relative to a reaction assembly. Uniquely, the fine movers and the coarse movers are positioned on only one side of the holder. With this design, the fine stage has a relatively low mass and a relatively high servo bandwidth. Because of the low mass, smaller movers can be used to move the fine stage. Because of the high servo bandwidth, external forces and small reaction forces are less likely to influence the position of the fine stage. This allows for more accurate positioning of the object by the stages and the production of higher quality wafers. Further, with this design, the stage assembly is easily accessible for service and the measurement system can be easily positioned near the fine stage.
Moreover, both the fine stage and the coarse stage are guideless along the X axis, along the Y axis and about the Z axis. More specifically, both the fine stage and the coarse stage are not constrained along the Y axis, the X axis and about the Z axis. Stated another way, each stage can be moved with at least three degrees of freedom. With this design, the movers control the position of the stages along the X axis, along the Y axis and about the Z axis. This allows for more accurate positioning of the stages and better performance of the stage assembly.
Further, the stage assembly can also include an anti-gravity mechanism that urges the fine stage upwards towards the coarse stage. This minimizes distortion to a stage base that supports the fine stage as the fine stage moves above the stage base.
Additionally, the stage assembly can include a mounting frame that supports the reaction assembly and allows the reaction assembly to move relative to the mounting frame. With this design, the reaction assembly reduces the amount of reaction forces from the coarse movers that is transferred to the ground.
The present invention is also directed to a method for moving an object, a method for manufacturing a stage assembly, a method for manufacturing an exposure apparatus and a method for manufacturing a wafer and a device.
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Poon Alex Ka Tim
Watson Douglas
Leypkin Rita
Nikon Corporation
Ro Bentsu
Roeder Steven G.
Rose Jim
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