Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
2002-12-12
2004-08-03
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S440110, C250S491100, C250S492200, C310S012060, C318S038000, C318S687000
Reexamination Certificate
active
06770890
ABSTRACT:
FIELD
This disclosure pertains to stage devices used for moving and positioning an object with extremely high accuracy and precision. Such stage devices are especially suitable for use in microlithography systems that perform transfer-exposure of a pattern, defined on a “master plate” (mask, reticle, or the like, generally termed “reticle” herein) onto an exposure-sensitive substrate (e.g., semiconductor wafer or the like). More specifically, the disclosure pertains to stage devices actuated by a linear motor and that perform highly accurate and precise movements and positionings while generating very low magnetic turbulence, and to microlithography systems including at least one such stage device.
BACKGROUND
Microlithography is a key technique used in the fabrication of microelectronic devices such as displays and semiconductor integrated circuits. Most current microlithography techniques utilize, as a pattern-transfer energy beam, a beam of deep ultraviolet (UV) light propagating through air at normal atmospheric pressure. These deep-UV techniques collectively are termed “optical microlithography.”
Other microlithography techniques currently under active development utilize any of various other types of energy beams such as “extreme UV” (“EUV”) radiation, X-radiation, and charged particle beams such as an electron beam or ion beam. Microlithography systems utilizing these alternative types of energy beams are being actively developed mainly because they offer prospects of substantially greater pattern-transfer resolution than obtainable with optical microlithography.
In any microlithography system, accurate and precise positioning of the reticle and substrate is extremely important for obtaining maximal pattern-transfer accuracy. Hence, the reticle and substrate are mounted to respective “chucks” on respective “stages.” The reticle stage and substrate stage generally are configured to move the reticle chuck and substrate chuck, respectively, in a respective X-Y plane relative to an optical axis extending in the Z-direction. For achieving such motions, the reticle and substrate stages include respective motors or analogous actuators.
Currently, most stage devices used in optical microlithography systems are so-called “H-type” or “I-type” X-Y stages. In both types of stages a movable guide extends in one of the X- and Y-directions between two parallel fixed guides that extend in the other of the X- and Y-directions. The respective chuck is mounted on a platform attached to a slider that moves along and relative to the movable guide. These types of stage devices are so-named because of the overall profile of the two fixed guides and the movable guide in the form of the letter “H” or the letter “I”.
Most recently, linear motors have become the actuators of choice for achieving stage motions in the X- and Y-directions. Use of linear motors desirably facilitates reducing the mass and size of each stage, and increases the operational efficiency of the stages. H-type stages are used mainly for substrate stages, which desirably have long respective movements (“strokes”) in both of the X- and Y-directions. I-type stages are used mainly for reticle stages, which usually require a long stroke in only one of the X- and Y-directions, and thus have a relatively short stroke in the other of the X- and Y-directions.
For optical microlithography systems, since the energy beam can propagate readily through air at normal atmospheric pressure, the reticle and substrate chucks can be of the “vacuum-suction” type. Also, the respective stages can be supported relative to a guide plate and on their guides by non-contacting “single-sided” fluid bearings (typically air bearings) that provide a high degree of freedom of motion when used with linear motors as actuators.
In contrast, charged-particle-beam (CPB) and extreme ultraviolet (EUV) microlithography must be performed in a vacuum environment because the beam is attenuated greatly in air at normal atmospheric pressure. As a result, reticle and substrate stages that utilize only single-sided fluid bearings (even if the bearings include vacuum-scavenging of bearing fluid) are not feasible, and movements along each guide must be supported by respective fluid bearings on all sides of the guide. The need to provide a respective fluid bearing on each side of the guide greatly complicates use of actuators such as linear motors for moving the stage platform relative to the guides.
As is well known, a linear motor has a “stationary” portion, termed a “stator,” and a moving portion, termed a “mover.” In an H-type or I-type stage device, as described above, used as a reticle stage or substrate stage in a CPB microlithography system, both the stator and mover of at least one linear motor move along a movement guide. This motion of the entire linear motor causes problematic magnetic-field fluctuations (“magnetic turbulence”) in the vicinity of the motor during operation of the stage device. Magnetic turbulence can perturb the trajectory of the beam and thus degrade the quality of microlithographic exposure.
The generation of magnetic turbulence from a conventional linear motor is shown schematically in
FIG. 6
, which is an elevational depiction. Two opposing permanent magnets
101
,
102
of the stator are shown, situated laterally adjacent the trajectory of an electron beam EB. The trajectory is from top to bottom in the figure, and the permanent magnets
101
,
102
of the stator are shown vertically aligned with each other beside the electron beam EB. The magnet
101
is disposed so that its S pole faces upward, and the magnet
102
is disposed so that its N pole faces upward. As a result, the respective N poles of each permanent magnet
101
,
102
, face each other. With such a disposition of the magnets
101
,
102
, the magnetic flux (dashed line) extending downward from the magnet
101
and the magnetic flux (dashed line) extending upward from the magnet
102
mutually repel and are diverted strongly to the left and right in the figure. Such strong lateral diversion of the magnetic flux causes the flux to reach the beam EB and cause distortion of the beam trajectory, which reduces the accuracy and precision of exposures performed with the beam.
In an actual CPB microlithography apparatus, the charged particle beam is contained in a “beam tube” evacuated to a suitable vacuum, and the beam is deliberately deflected by magnetic fields produced by electromagnetic coils. The beam tube can be configured to provide some protection of the beam from stray magnetic fields from the external environment. Nevertheless, control and reduction of environmental and other stray magnetic fields around the beam tube is especially important in CPB microlithography. As evident in
FIG. 6
, an important source of stray magnetic fields is a nearby linear motor including permanent magnets arranged as shown in the figure. Whereas it is possible, using magnetic shields, to block stray magnetic fields produced by linear motors, this approach undesirably tends to add substantial complexity to the structure of the overall system.
SUMMARY
In view of the shortcomings of conventional systems as summarized above, the present invention provides, inter alia, a stage device that can position an object (mounted to the stage) with high accuracy and precision, without causing magnetic-field turbulence.
A first aspect of the invention is set forth in the context of a stage device including a guide bar extending along a longitudinal axis, a slider slidably attached to the guide bar in a manner allowing the slider to slide relative to the guide bar along the longitudinal axis, and a stage platform connected to the slider. According to the first aspect, and in such context, actuators are provided for moving the stage platform in a direction parallel to the axis. An embodiment of such an actuator comprises a first linear motor situated on a first side of the guide bar and a second linear motor situated on a second side of the guide bar such that the first and second linear motors are situated in
Klarquist & Sparkman, LLP
Nikon Corporation
Wells Nikita
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