Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
2001-10-04
2004-02-17
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S492200, C356S401000
Reexamination Certificate
active
06693284
ABSTRACT:
FIELD
This disclosure pertains to microlithography (pattern transfer) performed using a charged particle beam (e.g., electron beam or ion beam). Microlithography is a key technique used in the manufacture of microelectronic devices such as integrated circuits, displays, thin-film magnetic heads, and micromachines. More specifically, this disclosure pertains to stage apparatus that provide highly accurate and precise movement and positioning of, e.g., a reticle or substrate as used in a charged-particle-beam (CPB) microlithography apparatus. The stage apparatus also provide multiple degrees of freedom of stage movement with substantially reduced disturbance of the charged particle beam caused by magnetic fields generated by the stage apparatus.
BACKGROUND
In many types of industrial processes, it is important that the workpiece be held and moved in an accurate and precise manner. This need is especially acute in microlithography, in which pattern transfer must be performed under extremely high demands of positioning accuracy and precision.
In microlithography, the pattern-defining reticle and a substrate usually are mounted on respective stages that achieve positioning of the substrate and reticle relative to each other sufficient to permit the pattern defined on the reticle to be transferred to the substrate. To ensure maximal flexibility in positioning measurement and control, many degrees of freedom of movement of the stage are desirable. In photolithography, for example, stages have been devised that include a table provided with three degrees of freedom of movement (&thgr;
X
, &thgr;
Y
, and Z directions), wherein the table is mounted on a stage that is movable in the X, Y, and &thgr;
Z
directions.
Photolithography systems do not include optical systems that dynamically correct the projected beam position. Hence, in photolithography systems, stage apparatus must be extremely accurate in their positioning ability and in their ability to synchronize motion with a second stage. To achieve such ends, a conventional stage apparatus for a photolithography system has a stacked two-level configuration as summarized above. Movements of the stage are performed by VCM (Lorentz-type “voice-coil motor”) or EI core (electromagnetic) devices that utilize inexpensive electromagnetic power. These types of stage apparatus consume relatively low electrical power and have long service lives. Also, due to their simple configuration in which drive elements extend in respective linear directions, these types of stage apparatus are widely used in photolithography because they are relatively easy to control.
Stage apparatus conventionally used in photolithography, however, are not suitable for use in charged-particle-beam (CPB) microlithography systems. I.e, whenever a stage apparatus configured for use in photolithography is used in a CPB microlithography system, the following problems arise: (1) Since VCMs or electromagnets are used as drive means, as the stage is moved corresponding magnetic-field fluctuations are generated. These fluctuations cause minute deflections of the charged particle beam, which can have an adverse effect on the accuracy and precision of pattern transfer as achieved with the CPB microlithography system. (2) Use of magnetic and/or electrically conductive components in the stage and its drive mechanisms causes magnetic-field fluctuations as the stage is moved, which can have an adverse effect on the charged particle beam.
A conventional stage apparatus employs a biaxial air bearing for moving the stage in the X and Y directions. Such a stage apparatus is disclosed in Japan Kôkai Patent Publication No. Sho 62-182692, in which the stage apparatus includes multiple box-shaped air bearings. An oblique view of such a stage apparatus
140
is shown in FIG.
8
. The stage apparatus
140
includes a base
141
to which two box-shaped base guides
142
are mounted. Each base guide
142
includes respective permanent-magnet plates mounted to the inner surfaces of the base guide
142
, thereby forming a respective motor yoke
142
a
. Respective box-shaped coil bobbins
143
engage the respective “upper” (in the figure) portions of the base guides
142
. Each combination of a motor yoke
142
a
and a coil bobbin
143
constitutes a respective linear motor that can be moved in the X-direction.
A box-shaped movable guide
144
extends between the two coil bobbins
143
. A permanent magnet plate (not detailed) is mounted to the inner surface of the movable guide
144
to form a motor yoke
144
a
. A box-shaped coil bobbin
145
is engaged with the “upper” portion of the movable guide
144
. The motor yoke
144
a
and coil bobbin
145
collectively constitute a linear motor providing movement in the Y-direction. A stage
146
is mounted to the coil bobbin
145
. A substrate or reticle can be mounted to the stage
146
.
Each coil bobbin
143
,
145
includes air jets (not shown) defined in the respective inner surfaces thereof, facing the respective motor yokes
142
a
,
144
a
, thereby forming respective air bearings.
Whenever a stage apparatus as shown in
FIG. 8
is used in a CPB microlithography system, the following problems may arise: (1) Since VCMs or electromagnets are used for actuating movement of the stage, moving the stage generates corresponding fluctuations in the magnetic field in the vicinity of the charged particle beam. These fluctuations adversely affect the charged particle beam, which decreases pattern-transfer accuracy and precision. (2) The stage apparatus
140
is configured such that X-Y movements involve respective movements along respective guides (coil bobbins
143
on base guides
142
for X-direction motion, and coil bobbin
145
on movable guide
144
for Y-direction motion) that are stacked relative to each other. Hence, to provide movement along the lower of these axes (in this instance the X-axis) a large and heavy movement mechanism must be employed.
Another conventional stage apparatus that provides motion in the X- and Y-directions comprises two uni-axial drives each configured in a respective “H” configuration. More specifically, the two uni-axial drives are arranged at 90° relative to each other. Such a configuration eliminates the need for respective permanent magnets on the “inner” surfaces of the movable guide
144
. Also, in this configuration, the stage is freely movable in the Y-direction on the movable guide
144
instead of on the coil bobbin
145
. But, two stages
145
′ must be provided, wherein one stage is rigidly mounted on top of the other. By placing the drive actuators at respective ends of the movable guide, the effects of magnetic fluctuations on the charged particle beam are minimized, with a corresponding improvement of pattern-transfer accuracy and precision. However, because the two stages are rigidly fixed to each other, their relative movements are too restricted. I.e., the operation of one stage is affected whenever the other stage is being actuated, which decreases the positioning-control accuracy of the stage apparatus. In addition, whenever two stages are rigidly fixed to each other in this manner, extremely high accuracy and precision must be applied during assembly of the stage apparatus.
SUMMARY
In view of the shortcomings of the prior art as summarized above, an object of the invention is to provide stage apparatus, for use in charged-particle-beam (CPB) microlithography apparatus, in which the stage table can be driven in multiple degrees of freedom with minimal magnetic disturbance to the charged particle beam, thereby improving the accuracy with which stage position can be controlled.
To such end, and according to a first aspect of the invention, stage apparatus are provided. An exemplary embodiment of a stage apparatus includes an XY stage that is movable and positionable within an XY plane defined by mutually perpendicular X- and Y-axes that are perpendicular to a Z-axis. The stage apparatus also includes a first table that is mounted to the XY stage and that is configured to be driven in a &thgr;
Z
drive
El-Shammaa Mary
Klarquist & Sparkman, LLP
Lee John R.
Nikon Corporation
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