Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
2001-11-30
2004-09-21
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S441110
Reexamination Certificate
active
06794657
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to exposure apparatuses. More specifically, the present invention is directed to a magnetic shunt assembly for an exposure apparatus.
BACKGROUND
Motors are used in a variety of electrical devices. For example, lithography systems and other semiconductor processing equipment typically utilize one or more linear motors to precisely position a reticle stage holding a reticle and a wafer stage holding a wafer. Alternately, motors are used in other devices, including machine tools, metal cutting machines, measurement machines, and inspection machines.
A typical electric motor includes a magnet component and an electrical conductor component. The magnet component includes a plurality of permanent magnets positioned adjacently. Each of the magnets generates a surrounding magnetic field. The conductor component includes one or more coils. When electric current flows in the coils, a Lorentz type force is created in a direction mutually perpendicular to the direction of the current in the coils and the magnetic field of the magnets. The force can be used to move one of the components relative to the other component of the motor. Also the electrical current in the coils typically generates additional surrounding magnetic fields.
Unfortunately, stray magnetic fields from the motors can influence a number of manufacturing, measurement, and/or inspection processes. For example, electron beams are influenced by time dependent magnetic fields of sufficient magnitude. As a result thereof, the electric motors must be positioned a relatively large distance away from the electron beam. More specifically, for an electron beam projection lithography system, the motors used to position the reticle stage and the wafer stage must be positioned a relatively large distance away from the electron beam. Similar design considerations apply to other charged particle lithography systems, including ion beam systems, as well as charged particle inspection or metrology systems.
In order to increase the performance of electron beam lithography systems, it may be necessary to improve the performance of reticle and/or wafer stages. This may require integrating the electric motors directly into the reticle stage and the wafer stage. This means the motors must be positioned relatively close to the electron beam. As a result thereof, the surrounding, or stray, time dependent magnetic fields from the motors present a problem.
In light of the above, there is a need for an assembly that reduces the magnitude of the stray magnetic fields from the motors near the beam, without significantly degrading the dynamic performance of the stage assembly. Further, there is a need for an improved stage assembly for an exposure apparatus that utilizes a charged particle beam. Moreover, there is a need for a stage assembly for precisely positioning a device during a manufacturing, measurement and/or an inspection process. Additionally, there is a need for an exposure apparatus capable of manufacturing precision devices, such as high density, semiconductor wafers.
SUMMARY
The present invention is directed to a magnetic field shielding system consisting of a magnetic shunt assembly for an exposure apparatus. The exposure apparatus includes an optical assembly, a gap within the optical assembly, and a stage assembly having a stage and a mover assembly that moves the stage in the gap. The mover assembly is a source of magnetic fields which surround it. The magnetic shunt assembly includes a first magnetic shunt positioned near the optical assembly approximately between the optical assembly and at least a portion of the mover assembly. The first magnetic shunt is made of a magnetically permeable material. With this design, the first magnetic shunt provides a low magnetic reluctance path that redirects at least a portion of the magnetic field from the mover assembly away from the gap in the optical assembly.
A number of alternate embodiments of the magnetic shunt assembly are provided herein. In some of the embodiments, the magnetic shunt assembly also includes a second magnetic shunt. In this design, the first magnetic shunt can be positioned above the stage near the gap and the second magnetic shunt can be positioned below the stage near the gap. Alternately, for example, the first magnetic shunt can be positioned below the stage near the gap and the second magnetic shunt can be positioned above the stage near the gap. Further, in some embodiments, the stage assembly includes a container that encircles the stage and provides a controlled environment around the stage. In these embodiments, the magnetic shunt assembly can be secured and coupled to the container. The container may be made of magnetically permeable material which can enhance the performance of the magnetic shunt.
In some embodiments, the first magnetic shunt can be substantially flat plate shaped. Alternately, for example, in other embodiments, the first magnetic shunt can be tubular shaped.
In one or more of the embodiments, the first magnetic shunt is maintained spaced apart from the optical assembly and/or maintained spaced apart from the stage. With this design, the magnetic flux is redirected with the first magnetic shunt away from a housing of the optical assembly back to the mover assembly and the first magnetic shunt does not inhibit the movement of the stage.
The present invention is also directed to a stage assembly, an exposure apparatus, a device and a semiconductor wafer. Further, the present invention is also directed to a method for reducing stray magnetic fields, a method for manufacturing a stage assembly, and an exposure apparatus and a method for making a device and semiconductor wafer utilizing the exposure apparatus.
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Gurzo Paul M.
Lee John R.
Nikon Corporation
Roeder Steven G.
Rose Jim
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