Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-08-13
2004-09-21
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S442110, C250S453110, C378S034000, C378S035000, C378S208000
Reexamination Certificate
active
06794660
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a stage assembly for moving a device. More specifically, the present invention is directed to a long stroke mover for moving a stage of the stage assembly.
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 assembly that retains a reticle, a lens assembly and a wafer stage assembly that retains a semiconductor wafer. The reticle stage assembly and the wafer stage assembly are supported above a ground with an apparatus frame.
Typically, the wafer stage assembly includes a wafer stage base, a wafer stage that retains the wafer, a wafer vacuum preload type air bearing that supports the wafer stage, and a wafer mover assembly that precisely positions the wafer stage and the wafer. Somewhat similarly, the reticle stage assembly includes a reticle stage base, a reticle stage that retains the reticle, a reticle vacuum preload type air bearing that supports the reticle stage and a reticle mover assembly that precisely positions the reticle stage and the reticle. Typically, the wafer vacuum preload type air bearing is created by releasing air from outlets in a bottom of the wafer stage towards the wafer stage base and pulling a vacuum in inlets in the bottom of the wafer stage. Similarly, the reticle vacuum preload type air bearing is created by releasing air from outlets in a bottom of the reticle stage towards the reticle stage base and pulling a vacuum in inlets in the bottom of the reticle stage.
The size of the images and features within the images transferred onto the wafer from the reticle are extremely small. Accordingly, the precise positioning of the wafer and the reticle relative to the lens assembly is critical to the manufacture of high density, semiconductor wafers.
Depending upon the type of energy beam generated by the illumination source, the type of fluid surrounding the reticle and the wafer can influence the performance of the exposure apparatus. For example, some types of beams, e.g. electron beams and very short wavelengths of ultraviolet light, are absorbed by oxygen and other gases. As is well known, air is a gaseous mixture that is approximately twenty-one percent oxygen. Thus, air surrounding the reticle and wafer can influence the performance of the exposure apparatus and the quality of the integrated circuits formed on the wafer can be compromised. As a result thereof, the performance of the exposure apparatus and the quality of the integrated circuits formed on the wafer can be enhanced by controlling the environment around one or both stages.
One way to control the environment around a stage is to position a chamber around the stage. Subsequently, the desired environment can be created within the chamber around the stage. For example, the chamber may be filled with an inert fluid. Alternately, some processes require that the controlled environment is a vacuum.
Historically, stage assemblies used in a vacuum environment have utilized mechanical type bearings to support the stage. Typical mechanical type bearings include ball bearings, roller bearings or sliding contact. However, limitations on the use of lubricants in a vacuum, rolling or sliding noise or vibration, particle generation, and friction also limit the accuracy and velocity of such stages.
Another solution is to use an air bearing in the vacuum to support the stage. However, air bearings typically require substantial preload forces to have high stiffness, which is desirable for precision stages. Unfortunately, it is not possible to create a vacuum preload type air bearing if the stage is surrounded by a vacuum.
Alternately, a lower air bearings and an opposed upper air bearing can be used to support the stage in the vacuum environment. In this embodiment, the upper air bearing preloads the lower air bearing to create a relatively stiff bearing. However, this design requires an increase in stage mass and/or complexity and an increase in the number of air bearings required by the stage assembly. In addition, the opposed air bearings can deform the stage. Further, the air released to create the air bearing that supports the stage is also released into the chamber. This can compromise the vacuum that is created within the chamber. Thus, the use of air bearings to support the stage can make it difficult to control the environment around the stage.
Additionally, depending upon the type of energy beam generated by the illumination source, the motors used to move the stages can influence the performance of the exposure apparatus. For example, a typical brushless electric motor includes one or more magnets and one or more coils. Unfortunately, the magnetic fields from the motor can influence a number of manufacturing, measurement and/or inspection processes. More specifically, for example, electron beams are influenced by magnetic fields of sufficient magnitude. As a result thereof, the electric motors 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 light of the above, there is a need for a bearing assembly and method for supporting a stage that does not compromise the desired environment around the stage. Additionally, there is a need for a relatively stiff bearing assembly for supporting a stage in a vacuum. Moreover, there is a need for a bearing assembly for an exposure apparatus that utilizes an electron beam. Further, there is a need for a mover that can be positioned relatively close to a stage while reducing the influence of the motor on the energy beam. Also, there is a need for an exposure apparatus capable of manufacturing precision objects, such as high density, semiconductor wafers.
SUMMARY
The present invention is directed to a stage assembly that moves a device. The stage assembly includes a guide base, a stage that retains the device, and a stage bearing assembly that supports the stage spaced apart from the guide base. Uniquely, the stage bearing assembly generates an electrostatic force that urges the stage towards the guide base. Typically, an opposing force is required to balance the electrostatic force. The opposing force can be provided by a number of alternate ways. Further, the electrostatic force can be modulated based on position feedback to provide stiffness and damping relative to a reference. As a result of this design, the stage bearing assembly can be relatively stiff without gas leakage or mechanical contact. Thus, the stage bearing assembly is particularly useful in manufacturing, measurement and/or inspection processes that are operated in a controlled environment such as a vacuum.
As provided herein, the stage bearing assembly includes a base conductive section and a stage conductive assembly that cooperate to generate the electrostatic force that urges the stage towards the guide base. Further, the stage conductive assembly includes a first stage conductive section, a second conductive section and a third conductive section. Moreover, each of the stage conductive sections is electrically isolated from the other stage conductive sections.
The stage assembly also includes a control system that controls the voltage to each of the conductive sections. As provided herein, the control system controls the voltage to the stage conductive sections to actively adjust the force generated by the stage bearing assembly. Preferably, the control system individually controls the voltage to each of the stage conductive sections to adjust the position of the stage relative to the guide base along a Z axis, about an X axis and about a Y axis.
As an overview, the electrostatic attractive pressure between two conductive surfaces is proportional to the voltage difference squared divided by the gap squared. The electrostatic repulsive forces caused by common voltag
Gurzo Paul M
Lee John R.
Nikon Corporation
Roeder Steven G.
Rose Jim
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