Radiant energy – Irradiation of objects or material
Reexamination Certificate
2001-03-19
2003-09-09
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
C250S492200, C250S492210, C250S492220, C250S492300, C250S491100
Reexamination Certificate
active
06617592
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-094573, filed Mar. 30, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a charged particle beam system such as an electron beam lithography system used in pattern writing or pattern transfer to a substrate and, more particularly, to a chamber of this charged particle beam system.
As the integration degree of LSI devices increases, demands for the writing accuracy and throughput of a lithography system used in the fabrication of LSIs are becoming more and more strict. At present, a charged particle beam system such as an electron beam lithography system used as a lithography system employs lithography schemes such as a VSB (Variable Shaped Beam) scheme, CP (Character Projection) scheme, or pattern transfer scheme, in order to ensure sufficient throughput.
FIG. 1
is a schematic view of a VSB electron beam lithography system. This system will be described below in order. An electron beam emitted from an electron gun
51
enters into an electron optics system
50
. More specifically, the electron beam passes through a condenser lens
52
and illuminates a first shaping aperture
53
. This first shaping aperture
53
is, e.g., a rectangle 100 &mgr;m square. Hence, the electron beam passing through this first shaping aperture
53
is shaped into a square of 100 &mgr;m side.
The shaped electron beam is projected onto a second shaping aperture
56
through a projection lens
54
. This second shaping aperture
56
is a square aperture of, e.g., 100 &mgr;m side. A beam shaping deflector
55
is disposed upstream of the second shaping aperture
56
. The propagating direction of the electron beam can be changed by applying an appropriate voltage to this beam shaping apparatus
55
. Consequently, the position of the first shaping aperture image projected onto the second shaping aperture
56
can be changed.
By thus changing the projection position, the overlap of the first shaping aperture image and the second shaping aperture changes, so square beams differing in size can be shaped. The beam shaped into a square is reduced by a reduction lens (not shown) and positioned by a sub deflector
57
and a main deflector
59
. Furthermore, the focusing position of the beam is determined by an objective lens, and the beam arrives at a predetermined position of a specimen
60
.
The specimen
60
can move by moving mechanisms called an X stage and Y stage. By these moving mechanisms, writing is performed by a step-and-repeat scheme or a continuous stage moving scheme. The continuous stage moving scheme will be described below. In this continuous stage moving scheme, a pattern to be written is divided into stripes, and each stripe is written. During the writing of each stripe, a stage (e.g., the X stage) is continuously moved. When one stripe is completely written, a stage (this time the Y stage perpendicular to the X stage) is moved one step by the width of a stripe to write the next stripe. In this way, an LSI pattern having a large writing area can be written efficiently at a high speed.
In this continuous stage moving scheme, the position of a specimen changes every moment, so this movement of each stage must be added to information about a position at which the beam should arrive. To this end, the position of each stage at each time must be accurately known. A laser interferometer is commonly used to measure this stage position.
FIG. 2
is a schematic view for explaining the principle of a laser interferometer. A laser beam emitted from a laser oscillator
61
is split into two directions by a beam splitter
63
and incident on a movable mirror
64
and a fixed mirror
62
via a reflective mirror
67
. The laser beam reflected by the fixed mirror
62
and further by the reflective mirror
67
and the laser beam reflected by the movable mirror
64
merge on the beam splitter
63
to generate interference fringes. This interference component is detected by a detector
65
and analyzed by an analyzer
66
to find the position of the movable mirror
64
.
This movable mirror
64
is set on a specimen stage. The fixed mirror
62
is fixed to, e.g., the ceiling of a chamber.
The position of this fixed mirror must always be fixed in the entire laser interferometer system. Otherwise, changes in the position of the movable mirror cannot be accurately detected any longer.
On the other hand, the walls of the chamber thermally expand or contract owing to temperature changes. Therefore, if the temperature of the environment in which the chamber is set changes, the position of the fixed mirror fixed to an inner wall of the chamber also changes.
This chamber is usually made of stainless steel. A coefficient &agr; of linear expansion of stainless steel is 15×10
−6
/° C. near a room temperature. This means that the linear expansion of 1-m long stainless steel is 15 &mgr;m/° C.
Assume that the temperature of the installation environment of the charged particle beam system is controlled within the range of ±0.1° C. In this state, a positional change of about ±0.225 &mgr;m occurs in a position apart by 150 mm from the center of the stainless steel chamber. Accordingly, the position of the fixed mirror fixed to this position also changes by 0.225 &mgr;m. As described above, the landing position of the electron beam is determined by referring to the stage position information. Consequently, an error corresponding to the positional change of the fixed mirror is produced, and this significantly degrades the writing accuracy. This is a fatal drawback for writing required to have a nanometer-level dimensional accuracy.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to reduce positional changes of a fixed mirror of a laser interferometer, which is fixed to an inner wall of a chamber, in accordance with temperature changes of a charged particle beam system.
To achieve the above object, a charged particle beam system according to the first aspect of the present invention comprises
a chamber having a space to accommodate a specimen therein and a first opening to communicate with the space in an upper surface,
a table placed, immediately below the first opening, on a bottom surface of the chamber, the table being movable in at least one direction,
a laser interferometer set in the chamber, the laser interferometer comprising
a laser oscillator placed along the one moving direction of the table,
a movable mirror placed on that side surface of the table, which opposes the laser oscillator,
a beam splitter placed on a line connecting the laser oscillator and the movable mirror, and
a fixed mirror perpendicular to the line connecting the laser oscillator and the movable mirror and fixed, immediately above the beam splitter, on the upper surface of the chamber,
an optical lens barrel having a second opening communicating with the first opening of the chamber, and coupled with the chamber so as to match the first and second openings, and
a beam gun set on an inner upper surface of the optical lens barrel to irradiate the specimen placed on the table set on the bottom surface of the chamber with a charged particle beam through the first and second openings,
wherein at least an upper wall portion from the opening to a fixed portion of the fixed mirror of the chamber is made of an invar alloy.
A charged particle beam system according to the second aspect of the present invention is characterized in that the chamber is made of an invar alloy in the arrangement of a charged particle beam system according to the first aspect.
A chamber of a charged particle beam system according to the third aspect of the present invention comprises
a housing having a space to accommodate a specimen therein and an opening to communicate with the space in an upper surface,
a table placed, immediately below the first opening, on a bottom surface of the housing, the t
Akeno Kiminobu
Hattori Kiyoshi
Ogasawara Munehiro
Shimomura Naoharu
Sunaoshi Hitoshi
Kabushiki Kaisha Toshiba
Lee John R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Vanore Dail A.
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