Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-05-17
2003-02-18
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S072000, C355S075000, C248S550000, C073S662000
Reexamination Certificate
active
06522388
ABSTRACT:
This application is a continuation of PCT International Application No. PCT/JP98/05173 filed Nov. 18, 1998.
The disclosures of the following priority applications are herein incorporated by reference: Japanese Patent Application No. 9-316955 filed Nov. 18, 1997 and, Japanese Patent Application No. 10-006117 filed January 14, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration eliminator and an exposure apparatus, and more specifically, it relates to a vibration eliminator capable of reducing vibrations occurring within a structure supported by a vibration eliminating base, an exposure apparatus that employs the vibration eliminator and a projection exposure method achieved by employing the exposure apparatus.
2. Related Art
As a higher degree of accuracy is achieved in high precision apparatuses such as step-and-repeat type exposure apparatuses, i.e., so-called steppers, it has become necessary to block very slight vibrations imparted from the installation floor to the fundamental base (a vibration eliminating base) at a micro-G level. The various types of vibration eliminating pads including a mechanical damper achieved by placing a compressible coil spring in a damping fluid and a pneumatic damper are employed to support the vibration eliminating base of the vibration eliminator, and such a vibration eliminating pad itself has a certain degree of centering function. In particular, a pneumatic spring vibration eliminator provided with a pneumatic damper, which allows the spring constant to be set at a small value and is capable of blocking vibrations of approximately 10 Hz or more is utilized in a wide range of applications for supporting high precision apparatuses. In addition, active vibration eliminators have been proposed in recent years as a means for overcoming the limitations of passive vibration eliminators in the prior art (refer to Japanese Laid-Open Patent Publication No. H8-166043 submitted by the applicant of the present application, for instance). The vibration eliminator disclosed in the publication achieves vibration control by detecting vibrations of the vibration eliminating base with sensors and driving actuators in conformance with the outputs from the sensors and realizes ideal vibration insulation with no resonance peak in the low frequency control range.
In the vibration eliminator described above, the vibration eliminating base control loop is constituted by combining a velocity loop employed mainly for vibration elimination and a position loop implemented for positioning of the main unit. Six vibration sensors and six position sensors are mounted at the vibration eliminating base, and displacement and vibration along six degree of freedom directions detected by these sensors are converted to motion in six degree of freedom directions in the orthogonal coordinate system (coordinate system in mechanical design) which is set as appropriate during the vibration eliminator design stage and, based upon the results of the conversion, damping feedback control is implemented.
In addition, in order to prevent the vibration eliminating base from becoming excited by the reactive force generated as a stage repeats acceleration and deceleration on the vibration eliminating base, a force along the opposite direction achieving the same level as that of the reactive force (counter force) is input through feed-forward so that vibrations caused by stage acceleration and decelerations are reduced while maintaining good blockage of floor vibrations since it is not necessary to increase the position loop gain within the control loop.
The vibration eliminating base described above is designed on the premise that the apparatus mounted on the vibration eliminating base, which constitutes the source of vibration, vibrates together with the vibration eliminating base. In other words, by eliminating vibrations of the vibration eliminating base, which would try to vibrate together with the apparatus constituting the source of vibration, with the active vibration eliminator mentioned earlier, vibration damping is achieved for both the vibration eliminating base and the apparatus mounted at the vibration eliminating base.
The vibration eliminating base is controlled on the premise that the entire vibration eliminating base, i.e., the vibration eliminating base and the apparatus mounted on the vibration eliminating base, vibrates uniformly in a rigid mode without undergoing elastic deformation.
However, as the need for higher performance to be achieved by the vibration eliminating base increases, vibrations occurring on the vibration eliminating base in a local elastic mode can no longer be disregarded. The following is an explanation on vibrations occurring in the local elastic mode. Vibrations occurring in the local elastic mode refer to relative vibrations occurring between an apparatus or a structure mounted on the vibration eliminating base or the like and the vibration eliminating base itself and also local vibrations occurring as a result of elastic deformation of the vibration eliminating base.
If a vibration in the local elastic mode occurs, the vibration detected by a sensor mounted on the vibration eliminating base does not always match the vibration actually occurring on the vibration-eliminating base and, as a result, the effect of active vibration elimination is reduced.
In order to address the problem described above, it is necessary to reduce local vibrations occurring as a result of an elastic deformation of a member constituting the vibration eliminating base (hereafter referred to simply as the “member”). Vibrations occurring at the member is reduced by increasing the rigidity of the member or by constituting the member with a material achieving a high Young's modulus and a large damping coefficient such as a high attenuation cast iron, a typical example of which is FCD, in the prior art.
As further miniaturization of semiconductors is achieved necessitating an increase in the semiconductor exposure area, the overall size of exposure apparatuses has become larger. At the same time, the installation conditions under which an exposure apparatus is installed usually do not allow the exposure apparatus to become heavier. Thus, many exposure apparatuses in recent years adopt an open rib structure. There is a problem with such a rib structure, however, in that while the resonance frequency is high, a sufficient degree of rigidity is not achieved and, as a result, vibrations cannot be suppressed.
When a vibration occurs under such circumstances, this vibration in the local elastic mode becomes superimposed on the vibration detected by a sensor of the active vibration eliminator. This poses a concern that the vibration control system of the active vibration eliminator may be caused to vibrate, resulting in the active vibration eliminator exciting the vibration-eliminating base.
This is a problem that may occur at other various apparatuses in which vibrations must be eliminated, as well as at exposure apparatuses.
SUMMARY OF THE INVENTION
An object of the present invention, which has been completed to address the problem discussed above, is to provide a vibration eliminator achieving outstanding vibration-eliminating performance by reducing vibrations occurring in the local elastic mode at an apparatus or a structure mounted at the vibration eliminating base or at the vibration eliminating base itself, an exposure apparatus provided with the vibration eliminator and a projection exposure method achieved by employing the vibration eliminator.
In order to achieve the object described above, the vibration eliminator according to the present invention comprises a supporting member; a supported member that is supported by the supporting member; a drive device provided between the supporting member and the supported member, that generates a driving force along the support direction, in which the supporting member supports the supported member; a first vibration detector provided at the supporting member to detect a vibra
Ono Kazuya
Takahashi Masato
Nguyen Henry Hung
Nikon Corporation
Oliff & Berridg,e PLC
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