Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
2001-08-09
2004-07-20
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S075000, C355S030000
Reexamination Certificate
active
06765650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to semiconductor processing equipment. More particularly, the present invention relates to a scanning stage apparatus which may be efficiently implemented for use in an electron beam projection system.
2. Description of the Related Art
Lithography processes, e.g., photo-lithography processes, are integral to the fabrication of wafers and, hence, semiconductor chips. Conventional systems used for lithography include optical lithography systems and electron beam projection systems. Many optical lithography systems and electron beam projection systems may use a direct writing process to “write” on wafers. However, direct writing processes are often relatively slow, as will be appreciated by those skilled in the art.
In order to increase the speed at which wafers may be written to, electron beam projection systems, as well as optical lithography systems, may project beams of finite area through patterns. The patterns are generally resident on a reticle, which effectively serves as a mask or a negative for a wafer. For an electron beam projection system, a relatively broad beam of electrons may be collimated and provided to a reticle, which may be a silicon wafer, e.g., a wafer that is suitable for scattering with angular limitation projection electron beam lithography or a stencil-type wafer. Typically, rather than absorbing the beam, the pattern deflects portions of the beam in order to prevent electrons from being ultimately focused onto a wafer.
FIG. 1
a
is a diagrammatic representation of one standard configuration of a lens system of an electron beam projection system. In general, a lens system
104
includes an illumination lens
108
and a projection lens
124
. An electron beam is arranged to pass through illumination lens
108
, to a reticle
112
that is held by a reticle stage
116
in a vacuum chamber
120
. As an electron beam passes through reticle
112
, portions of the electron beam are allowed to pass through reticle
112
, while other portions of the electron beam may be scattered to prevent those portions from being focused onto a wafer
128
that is held, e.g., by a stage (not shown), in a wafer chamber
130
, i.e., a vacuum chamber. In other words, reticle
112
acts as a mask to effectively mask out part of an electron beam. Projection lens
124
is arranged to project the pattern of electrons, i.e., the pattern of electrons which are not masked out by reticle
112
, onto wafer
128
.
Stages, such as reticle stage
116
or a wafer stage, are often used to facilitate a lithography process. The use of reticle stage
116
, for example, enables reticle
112
to be readily scanned over a surface of wafer
128
to enable a pattern of electrons to be projected onto different portions of wafer
128
. The design of a stage such as reticle stage
116
for use in an electron beam projection system may be complicated, as an electron beam projection system generally must not include moving magnets or metals which alter the magnetic field associated with the electron beam projection system and, hence, the electron beam.
Although separate vacuum chambers may be used to house a reticle and a wafer, an entire lens system may generally be housed in a single vacuum chamber.
FIG. 1
b
is a diagrammatic representation of a standard lens system of an electron beam projection system which is contained within a vacuum chamber. Like lens system
104
of
FIG. 1
a
, a lens system
154
includes an illumination lens
158
and a projection lens
174
. An electron beam is arranged to pass through illumination lens
158
. The electron beam then passes from illumination lens
158
to a reticle
162
that masks out part of the electron beam. Reticle
162
is generally positioned on a reticle stage
170
that allows reticle
162
to be scanned. After passing through reticle
162
, portions of the electron beam which are not masked out by the reticle then pass through projection lens
174
and onto wafer
178
. As shown, illumination lens
158
, reticle
162
, reticle stage
170
, projection lens
174
, and wafer
178
are all contained within a vacuum chamber
180
.
Electron beam projection systems are often used in lieu of optical systems because a lens system associated with an electron beam projection system may dynamically move a projection image to follow a stage, which is generally not possible with an optical system, as will be appreciated by those skilled in the art. In addition, electron beam lens systems typically correct for relatively small errors in relative stage positions, whereas optical systems generally do not. However, electron beam projection systems often have specific requirements which are not requirements for typical optical lithography systems. By way of example, an electron beam projection system generally must operate in a high vacuum environment. Maintaining a high vacuum environment may be expensive, as any gas leakage into the vacuum environment must be corrected as the gas leakage typically compromises the vacuum level.
It is often desirable to have moving parts associated with an electron beam projection system. For example, a wafer may be placed on a wafer stage which enables the wafer to be positioned beneath a projection column as appropriate. Similarly, a reticle placed on a reticle stage enables the position of the reticle with respect to a wafer to be readily adjusted. However, moving parts within a vacuum may cause problems with electron beams as linear motors and magnetic elements may interfere with magnetic fields. An electron beam projection system may not include moving magnets, as moving magnets cause the magnetic field associated with the electron beam projection system to change. Further, an electron beam projection system also may not having moving iron structures, due to the fact that moving iron dynamically alters the static magnetic fields around an electron beam lens, as will be appreciated by those skilled in the art.
Many scanning stage devices which are suitable for use in a high vacuum environment are relatively large, e.g., have a relatively large moving mass. The size of the scanning stage devices is due, at least in part to, arranging the stage device such that linear motors or magnetic elements do not significantly affect an electron beam. As will be appreciated by those skilled in the art, the larger a mass is, the larger the power requirements are for moving the mass. Many conventional stage devices also leak a significant amount of gas into a vacuum chamber, as air bearings are often used to support and guide portions of stages within a vacuum, and many standard air bearings leak. Maintaining the vacuum level in a vacuum chamber to accommodate gas leakage is often difficult or impractical.
Therefore, what is needed is a method and an apparatus for enabling reticles to be scanned efficiently within an electron beam projection system. That is, what is desired is a vacuum compatible stage which is relatively compact, efficient, and suitable for use in a relatively high vacuum environment.
SUMMARY OF THE INVENTION
The present invention relates to an air bearing stage device for use in a vacuum environment which maintains linear motors and magnetic elements outside of a vacuum chamber. According to one aspect of the present invention, a scanning stage apparatus includes a table that is positioned in a system vacuum chamber and a first rod that carries the table. The apparatus also includes first and second plates that support the first rod. The first plate includes an air bearing surface that is arranged to be held against the first side of a first wall by a first vacuum force. A first drive mechanism drives the first plate to move the first rod in a first direction, and also drives the second plate to move the first rod in the first direction, while a second drive mechanism which includes a second rod and a first linear motor causes the second rod to move the first rod in a second direction. In one embodiment, the first wall is an exterior wal
Esplin D. Ben
Nikon Corporation
Ritter Lang & Kaplan LLP
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