Electron beam lithography apparatus

Details Electron beam lithography apparatus Electron beam lithography apparatus

2000-10-19

2004-05-04

Berman, Jack (Department: 2881)

Radiant energy

Inspection of solids or liquids by charged particles

Analyte supports

C250S492200, C310S013000

Reexamination Certificate

active

06730916

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an electron beam lithography apparatus and, more particularly, to an electron beam lithography apparatus in which a leakage magnetic field from a stage driving mechanism that uses a permanent magnet is shielded to realize accurate lithography.
BACKGROUND OF THE INVENTION
In recent years, along with an increase in degree of integration of semiconductor elements, demand for a finer design rule has arisen. An electron beam lithography apparatus directly draws a fine pattern on a sample surface by converging an electron beam by an electron lens and deflecting it by a deflector.
The stage of the electron beam lithography apparatus is required to be able to operate under high-vacuum environment and be made of a non-magnetic material that does not change the electron beam position on the sample.
A factor that degrades the beam position accuracy due to a laser measurement system used for stage position control is Abbe error. This Abbe error is given by (change amount of stage posture)×(offset amount between the position to be drawn and laser measurement optical axis). For example, to suppress the Abbe error to 5 nm when the offset amount of the laser measurement optical axis is 1 mm, the allowable value of the stage posture change amount is 1 sec (=5 &mgr;rad). Conventionally, a rolling guide made of a non-magnetic cemented carbide alloy (to be referred to as a cemented carbide material hereinafter) as described in Japanese Patent Laid-Open No. 05-198469 is used as a stage guide. However, since the stage posture changes due to straightness errors of the guide, it is very difficult to suppress pitch/yaw/roll to 1 arc-sec or less.
In addition, since a ceramic table is softer than a rolling element formed from cemented carbide, the table slightly deforms as the rolling element moves. As a result, the distance between the sample and a measurement mirror changes on the nanometer order, and measurement errors occur. As described above, the position accuracy of a lithography pattern degrades due to Abbe errors or small deformation of the stage.
Such degradation in position accuracy is caused by a change in stage posture and the deformation amount of the stage. In consideration of this problem, when an air bearing guide for vacuum environment is used as a stage guide, a stage posture change of 1 sec or less can be achieved as long as the surface accuracy of the guide surface plate is on the submicron order. Additionally, since this stage guide is a non-contact moving mechanism, the deformation amount of the table is small. An air bearing guide for polygon mirror working machine, which is disclosed in Japanese Patent Laid-Open No. 10-217053 sometimes uses a permanent magnet in the stage as a pre-load applying means for preventing a change in stage posture. This permanent magnet attracts the stage main body to the guide surface plate side. A non-contact constraint means using the repelling force between permanent magnets in vacuum, which is disclosed in Japanese Patent Laid-Open No. 10-281110, is also effective to prevent the table from deforming as the stage moves. However, if the external leakage magnetic field from the permanent magnet is not shielded, the static magnetic field distribution of the permanent magnet moves as the stage moves, resulting in positional shift of the electron beam on the sample.
The allowable magnetic field change amount will be estimated from the viewpoint of electron beam position accuracy with reference to FIG.
4
. Any variation in magnetic field present in the space between an electron lens
5
and a sample
7
changes the position illuminated by an electron beam
4
. Let H be the distance from the lower surface of the electron lens
5
to the sample
7
, and &Dgr;B(T) be the variation amount of the magnetic field in this space. Electrons that have passed through the electron lens
5
are affected by the variation in magnetic field, deflected by a deflection angle &thgr; along an orbit with a Bohr radius R, and reach a point separated from the target irradiation position by &Dgr;X.
Where the deflection angle &thgr; is sufficiently small, &Dgr;X can be approximated by
&Dgr;
X=H
2
/(2
R
)  (1)
The Bohr radius R is given by
R=mv
/(
e&Dgr;B
)  (2)
where m: the mass of electrons m=9.1×10
−3
(kg)
e: the charge of electrons e=1.6×10
−8
(C)
v: the velocity of electrons
Substitution of the Bohr radius into equation (1) yields
&Dgr;
X/&Dgr;B=eH
2
/(2
mv
)  (3)
On the other hand, the energy of electrons is given by
E=mv
2
/2  (4)
Elimination of v from equations (3) and (4) yields
&Dgr;
X/&Dgr;B=eH
2
/(2{square root over ( )}(2
mE
))  (5)
FIG. 5
is a graph showing the relationship (calculation values) between the beam position shift and the magnetic field when the acceleration voltage is used as a parameter assuming &Dgr;X=10 nm and H=25 mm. When a change in magnetic field is 2×10
−8
T or less, and the acceleration voltage is 30 kV or more, the positional shift of the beam is 10 nm or less. Hence, the leakage magnetic field from the permanent magnet must be shielded such that it becomes 2×10
−8
T or less.
On the other hand, the leakage magnetic field from the electron lens is always present in the space under the electron lens. A shield member formed from a ferromagnetic material moves in the leakage magnetic field of the electron lens. This disturbs the magnetic field in the space from the lower surface of the electron lens to the sample and causes a positional shift of electron beam on the sample. To reduce this positional shift amount, the leakage magnetic field from the electron lens must also be made small.
For accurate lithography, both the leakage magnetic field from the permanent magnet and that from the electron lens must be shielded, and the magnetic field change amount at the sample position must be reduced to 2×10
−8
T or less.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electron beam lithography apparatus suitable for accurate lithography and to provide an apparatus structure capable of reducing the magnetic field change amount at the sample position to 2×10
−8
T or less.
In order to achieve the above object, according to the present invention, a leakage magnetic field from a permanent magnet in a stage main body is reduced by shielding all surfaces of the permanent magnet except the attracting surface by a ferromagnetic material.
A leakage magnetic field generated when a shield moves in a leakage magnetic field from an electron lens is reduced by providing a shield for reducing the
A leakage magnetic field from the electron lens on the lower surface of an electron optical lens-barrel.
With the above-described two shield means, even when the stage moves, the external leakage magnetic field from the permanent magnet or electron lens does not affect the electron beam irradiation position, and accurate lithography can be realized.


REFERENCES:
patent: 4607167 (1986-08-01), Petric
patent: 6072251 (2000-06-01), Markle
patent: 53-94176 (1978-08-01), None
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patent: 61-59825 (1986-03-01), None
patent: 1-125932 (1989-05-01), None
patent: 5-198469 (1993-08-01), None
patent: 6-44093 (1994-11-01), None
patent: 6-334381 (1994-12-01), None
patent: 7-201726 (1995-08-01), None
patent: 7-263300 (1995-10-01), None
patent: 10-217053 (1998-08-01), None
patent: 10-281110 (1998-10-01), None
patent: 10-302696 (1998-11-01), None
patent: 11-317353 (1999-11-01), None

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