Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-12-16
2003-12-30
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S398000, C250S42300F, C250S42300F, C313S336000, C313S34600R, C315S003000, C315S500000
Reexamination Certificate
active
06670620
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electron gun, an illumination apparatus using the electron gun, and an electron beam exposure apparatus using the electron gun, which are used for lithography in the manufacture of semiconductor devices.
In the mass production process of the manufacture of semiconductor memory devices, an optical stepper with high productivity is used. 1 G or 4 G DRAMs and memory devices having larger capacities than 1 G or 4 G DRAMS have a line width of 0.2 &mgr;m or less. To produce them, electron beam exposure methods with high resolution and productivity are expected as one of exposure techniques replacing the optical exposure schemes.
The mainstreams of conventional electron beam exposure schemes are the Gaussian scheme and variable shaping scheme using a single beam. These electron beam exposure schemes are poor in productivity and are used for limited applications such as mask drawing, research and development of VLSI or ULSI, or production of a small quantity of ASIC devices. To apply electron beam exposure to mass production, how to improve the productivity is important. As one solution to this problem, an electron beam exposure apparatus of full-plate transfer type as shown in
FIG. 4A
has been proposed recently. In this scheme, a repeated portion of a memory circuit pattern is divided into several-&mgr;m cell regions to decrease the number of exposure shots. This improves the productivity.
In an exposure apparatus, the exposure line accuracy is important as is productivity. To ensure performance, the uniformity of the irradiation intensity in exposure regions is required to be 1% or less in all exposure regions. The full-plate exposure area of the above full-plate exposure scheme is about 5 &mgr;m
2
. The focus half-angle of the projecting lens is set at several m rad in consideration of the resolution condition of lens aberration. Let &egr; be the emittance defined by the product of the cross-over diameter of the electron gun and the irradiation beam extraction half-angle. At this time, the condition required for uniform illumination is represented by &egr;> exposure region x focus half-angle of lens ≈10 &mgr;m rad.
The energy of the exposure electron beam is about 50 keV. An electron gun having a triode electron gun structure as shown in
FIG. 4A
is used. To obtain uniform irradiation electron beam components from an electron beam emitted from the electron gun, beam components within the range of several m rad with satisfactory characteristics are selected from the electron beam emitted at several tens of m rad and used as the irridiation beam, as shown in FIG.
4
B.
In recent years, to further widen the exposure area to improve the productivity, for example, the SCALPEL scheme (S. D. Berger et al. “Projection electron beam lithography: A new approach.” J. Vac. Sci. Technology B9, 2996 (1991)) has been proposed as an electron beam transfer/exposure scheme using an electron beam scattering mask. This scheme can increase the exposure area by 2,500 times or more as compared to the conventional variable shaping scheme or full-plate transfer/exposure scheme. Since the influence of interaction between electrons due to the Coulomb effect can be reduced, the beam current can be increased by one or more orders of magnitudes, so high productivity can be expected. For an exposure area of 250 &mgr;m
2
and an electron beam focus half-angle of 2 m rad, the emittance condition required for the electron gun of the SCALPEL exposure scheme is emittance &egr;>700 &mgr;m•m rad. An electron gun having an emittance higher than that of the conventional electron gun by about 100 times is necessary.
To further increase the exposure area to improve the productivity, an EB mask transfer/exposure apparatus (Japanese Patent Laid-Open No. 10-135102) using an arcuated beam has been proposed. As the characteristic feature of this exposure scheme, an arcuated beam sandwiched by two arcs centered on the optical axis is used to reduce the curvature of field of the projecting lens, thereby increasing the exposure area. When an arcuated beam having an arc length of 3 mm, width of 0.1 mm, and a focus half-angle of 1 to 2 m rad is extracted from a circularly emitted electron beam as an exposure region, the electron gun of this scheme requires an emittance higher than that of the above-described SCALPEL scheme by 5 times or more.
When arcuated beam components are extracted from the planar electron beam emitted from the electron gun to form an arcuated beam, the utilization efficiency of the electron beam emitted from the electron gun is as low as about 1/1000. Hence, it is very difficult to obtain a stable electron beam because of the problems of heat and load of the power supply of the electron gun.
FIG. 5
is a view showing the relationship between the brightness and emittance of the electron guns required for each electron beam exposure apparatus. A brightness B represents a value determined by a current density J (A/cm
2
) and a focus half-angle &agr; (radian) of the exposure region determined by each exposure scheme (B=J/&pgr;&agr;
2
(A/cm
2
sr)). Although a conventional full-plate transfer apparatus has an exposure region area of 5 &mgr;m
2
, a planar beam transfer apparatus has a rectangular exposure region of several hundred &mgr;m
2
. This scheme is called a planar beam scheme in contrast to the arcuated beam scheme. This includes the above-described SCALPEL scheme.
All the exposure apparatuses for which the relationship between the brightness and emittance of the electron gun shown in
FIG. 5
is required increase the exposure area to improve the productivity. However, an electron gun capable of uniformly irradiating the irradiation region is hard to obtain. The difficulty increases as the emittance becomes high.
An electron beam exposure scheme with high productivity requires not only a high emittance but also an electron gun capable of selecting the brightness and emittance condition in accordance with a condition that the size of the arcuated beam to be used is 1 to 3 mm, and the focus half-angle is 1 to 2 m rad, as in the arcuated beam transfer apparatus shown in FIG.
5
.
In an electron beam transfer/exposure scheme using a scattering EB mask, the electron beam energy must be increased to about 100 keV or more to reduce the influence of electron scattering of an electron beam passing through the EB mask substrate. In the conventional electron gun having the triode structure, it is difficult to suppress high-voltage discharge and obtain a stable electron beam. As a measure against discharge of this electron gun, a multi-stage acceleration electron gun is used in general. Assume that the second acceleration electrode for forming an electric field for the second cross-over following the first cross-over is disposed on the rear side of the first acceleration electrode. According to the arrangement and voltage setting method of a conventional acceleration electrode, when the voltage of the first acceleration electrode is adjusted, the characteristics of the first and second cross-over simultaneously change. For this reason, an electron gun requiring high emittance characteristics or an illumination apparatus using such an electron gun has poor controllability and is difficult to adjust.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a practical electron gun which stably operates against a high voltage and has high emittance characteristics and also a large exposure area, large irradiation current, high uniformity of the irradiation current, and excellent controllability, which are required for a high-throughput electron beam exposure apparatus, and an illumination apparatus and electron beam exposure apparatus using the electron gun. In order to achieve the above object, an electron gun according to the present invention, an illumination apparatus using the electron gun, or an electron beam exposure apparatus using the electron gun has the following arrangement.
More specifically, there is pr
Hashmi Zia R.
Lee John R.
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